Maximal bite force in young adults with temporomandibular disorders and bruxism.

Braz Oral Res. 2007 Jul-Sep;21(3):278-83

Authors: Pizolato RA, Gavião MB, Berretin-Felix G, Sampaio AC, Trindade Junior AS

Parafunctional habits, such as bruxism, are contributory factors for temporomandibular disorders (TMD). The aim of this study was to evaluate the maximal bite force (MBF) in the presence of TMD and bruxism (TMDB) in young adults. Twelve women (mean age 21.5 years) and 7 men (mean age 22.4 years), composed the TMDB group. Ten healthy women and 9 men (mean age 21.4 and 22.4 years, respectively) formed the control group. TMD symptoms were evaluated by a structured questionnaire and clinical signs/symptoms were evaluated during clinical examination. A visual analogical scale (VAS) was applied for stress assessment. MBF was measured with a gnatodynamometer. The subjects were asked to bite 2 times with maximal effort, during 5 seconds, with a rest interval of about one minute. The highest values were considered. The data were analyzed with Shapiro-Wilks W-test, descriptive statistics, paired or unpaired t tests or Mann-Whitney tests when indicated, and Fisher's exact test (p < 0.05). TMDB women presented lower values of MBF as compared to those presented by TMDB men and by the control group. MBF for TMDB men was similar to that of the control group. The proportion of TMDB women with muscle pain and facial/teeth/head pain upon waking up was significantly higher than that of men. Control women presented significantly lower stress scores than the others. It was concluded that MBF was reduced in TMDB women, as they presented more signs and symptoms. Men presented higher MBF values than women, but TMD and bruxism did not significantly decrease MBF. Stress was not an influencing factor for TMD and bruxism in men.

PMID: 17710296 [PubMed - in process]

Complete denture impression techniques: evidence-based or philosophical.

Indian J Dent Res. 2007 Jul-Sep;18(3):124-7

Authors: Singla S

Code of practice is dangerous and ever-changing in today's world. Relating this to complete denture impression technique, we have been provided with a set of philosophies--"no pressure, minimal pressure, definite pressure and selective pressure". The objectives and principles of impression-making have been clearly defined. Do you think any philosophy can satisfy any operator to work on these principles and achieve these objectives? These philosophies take into consideration only the tissue part and not the complete basal seat, which comprises the periphery, the tissues and the bone structure. Under such circumstances, should we consider a code of practice dangerous or should we develop an evidence-based approach having a scientific background following certain principles, providing the flexibility to adapt to clinical procedures and to normal biological variations in patients rather than the rigidity imposed by strict laws?

PMID: 17687175 [PubMed - indexed for MEDLINE]

Maximal bite force and its association with temporomandibular disorders.

Braz Dent J. 2007;18(1):65-8

Authors: Pereira-Cenci T, Pereira LJ, Cenci MS, Bonachela WC, Del Bel Cury AA

Individuals with temporomandibular disorders (TMD) are expected to have decreased maximum bite forces (MBF). This way, this study compared the MBF in subjects with TMD to a control group and also evaluated its association with age, gender, height and weight. Forty healthy adults with complete natural dentition divided into four groups according to gender and presence or absence of TMD signs/symptoms (based on the Research Diagnostic Criteria RDC) underwent a MBF test with a gnathodynamometer in molar and incisal areas. Statistical analysis was performed by ANOVA and Student-Newman-Keuls test (p=0.05), and the relationship between age, gender, weight, height and MBF was verified by Pearson's correlation test. There were no differences in MBF results between TMD and control groups (p>0.05). Female subjects exhibited lower MBF than male and MBF for the anterior area was lower than that for posterior area (p<0.05). Significant correlation was found between MBF and weight in TMD subjects (p<0.05), except for the anterior area in female subjects. There was a positive correlation between MBF and height in TMD male subjects (p<0.05). Within the limitations of this study, it is possible to conclude that bite force was not affected by TMD. Correlation between MBF and weight in TMD subjects and between MBF and height in TMD male subjects was observed.

PMID: 17639204 [PubMed - indexed for MEDLINE]

Masticatory performance and bite force in children with primary dentition.

Braz Oral Res. 2007 Apr-Jun;21(2):146-52

Authors: Gavi&#xE3;o MB, Raymundo VG, Rentes AM

The aim of this study was to evaluate the relationship between masticatory performance and maximum bite force in the primary dentition. The sample comprised 15 children of both genders, aged 3 to 5.5 years, with good systemic and oral health, presence of all primary teeth without large caries, no structural anomalies, without severe malocclusion, and no history of orthodontic treatment. They chewed one standardized silicone tablet for 20 strokes and the median areas of the chewed particles were measured by an optical digital system. Enhanced performance was measured by a decrease in the chewed particle areas and an increase in the amount of chewed particles. The bite force was determined using a transmitter pressurized tube connected to an analog/digital electronic circuit. Weight, height and body mass index (kg/m(2)) were determined. The data were analyzed by descriptive statistics and Pearson or Spearman's correlations, after assessment of the normality of the distribution by Shapiro-Wilks' W-test. There was no correlation between bite force and particle area and amount (p > 0.05), neither were the body variables correlated with the masticatory variables (p > 0.05). It was concluded that the bite force was not a primary determinant of masticatory performance, and both variables were not dependent on body variables in the studied sample.

PMID: 17589650 [PubMed - in process]

Pressure from the lips and the tongue in children with class III malocclusion.

J Zhejiang Univ Sci B. 2007 May;8(5):296-301

Authors: Ruan WH, Su JM, Ye XW

OBJECTIVE: To discuss possible relationships between class III malocclusion and perioral forces by measuring the pressure from the lips and the tongue of children with class III malocclusion. METHODS: Thirty-one children with class III malocclusion were investigated and their perioral forces were measured at rest and during swallowing under natural head position by a custom-made miniperioral force computer measuring system. RESULTS: The resting pressures exerted on the labial side and palatine side of the upper left incisor, as well as the labial side and lingual side of the lower left incisor, were 0 g/cm(2), 0 g/cm(2), 0.57 g/cm(2) and 0.23 g/cm(2), respectively. Correspondingly, the swallowing forces were 2.87 g/cm(2), 5.97 g/cm(2), 4.09 g/cm(2) and 7.89 g/cm(2), respectively. No statistical difference between muscular pressure and gender existed. During swallowing, the lingual forces were significantly higher than the labial forces (P<0.01), however, at rest there was no significantly different force between these two sides. Compared to the normal occlusion patients, children with class III malocclusion had lower perioral forces. The upper labial resting forces (P<0.01), the lower labial resting forces (P<0.05) and all the swallowing pressures from the lips and the tongue (P<0.01) showed statistical differences between the two different occlusion conditions. Meanwhile, no significant difference was found for the resting pressure from the tongue between class III malocclusion and normal occlusion. CONCLUSION: Patients with class III malocclusion have lower perioral forces and this muscle hypofunction may be secondary to the spatial relations of the jaws. The findings support the spatial matrix hypothesis.

PMID: 17542055 [PubMed - indexed for MEDLINE]

Fight versus flight: physiological basis for temperature-dependent behavioral shifts in lizards.

J Exp Biol. 2007 May;210(Pt 10):1762-7

Authors: Herrel A, James RS, Van Damme R

Previous studies have demonstrated that a behavioral shift from flight to aggressive behavior occurs at low temperatures in some lizards. Our data for the agamid lizard Trapelus pallida demonstrate how the effect of temperature on whole organism performance traits such as sprint speed (much lower performance at lower temperature) and bite force (largely independent of temperature) may explain the shift from flight to fight behavior with decreasing temperature. Moreover, our data hint at the physiological basis for this effect as isolated muscle power output, twitch and tetanus time traits, relevant to sprinting, appear to be strongly temperature-dependent muscle properties. Maximal muscle force production, on the other hand, appears largely independent of temperature. Unexpectedly, differences in the physiological properties of jaw versus limb muscle were observed that enhance the ability of the jaw muscle to generate maximal force at all temperatures tested. Thus our data show how behavioral responses may be determined by the limitations set by temperature on physiological processes.

PMID: 17488939 [PubMed - in process]

Modulation of mandibular loading and bite force in mammals during mastication.

J Exp Biol. 2007 Mar;210(Pt 6):1046-63

Authors: Ross CF, Dharia R, Herring SW, Hylander WL, Liu ZJ, Rafferty KL, Ravosa MJ, Williams SH

Modulation of force during mammalian mastication provides insight into force modulation in rhythmic, cyclic behaviors. This study uses in vivo bone strain data from the mandibular corpus to test two hypotheses regarding bite force modulation during rhythmic mastication in mammals: (1) that bite force is modulated by varying the duration of force production, or (2) that bite force is modulated by varying the rate at which force is produced. The data sample consists of rosette strain data from 40 experiments on 11 species of mammals, including six primate genera and four nonprimate species: goats, pigs, horses and alpacas. Bivariate correlation and multiple regression methods are used to assess relationships between maximum (epsilon(1)) and minimum (epsilon(2)) principal strain magnitudes and the following variables: loading time and mean loading rate from 5% of peak to peak strain, unloading time and mean unloading rate from peak to 5% of peak strain, chew cycle duration, and chew duty factor. Bivariate correlations reveal that in the majority of experiments strain magnitudes are significantly (P<0.001) correlated with strain loading and unloading rates and not with strain loading and unloading times. In those cases when strain magnitudes are also correlated with loading times, strain magnitudes are more highly correlated with loading rate than loading time. Multiple regression analyses reveal that variation in strain magnitude is best explained by variation in loading rate. Loading time and related temporal variables (such as overall chew cycle time and chew duty factor) do not explain significant amounts of additional variance. Few and only weak correlations were found between strain magnitude and chew cycle time and chew duty factor. These data suggest that bite force modulation during rhythmic mastication in mammals is mainly achieved by modulating the rate at which force is generated within a chew cycle, and less so by varying temporal parameters. Rate modulation rather than time modulation may allow rhythmic mastication to proceed at a relatively constant frequency, simplifying motor control computation.

PMID: 17337717 [PubMed - indexed for MEDLINE]

Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints.

J Exp Biol. 2007 Feb;210(Pt 4):628-41

Authors: Ravosa MJ, Kunwar R, Stock SR, Stack MS

Excessive, repetitive and altered loading have been implicated in the initiation of a series of soft- and hard-tissue responses or ;functional adaptations' of masticatory and locomotor elements. Such adaptive plasticity in tissue types appears designed to maintain a sufficient safety factor, and thus the integrity of given element or system, for a predominant loading environment(s). Employing a mammalian species for which considerable in vivo data on masticatory behaviors are available, genetically similar domestic white rabbits were raised on diets of different mechanical properties so as to develop an experimental model of joint function in a normal range of physiological loads. These integrative experiments are used to unravel the dynamic inter-relationships among mechanical loading, tissue adaptive plasticity, norms of reaction and performance in two cranial joint systems: the mandibular symphysis and temporomandibular joint (TMJ). Here, we argue that a critical component of current and future research on adaptive plasticity in the skull, and especially cranial joints, should employ a multifaceted characterization of a functional system, one that incorporates data on myriad tissues so as to evaluate the role of altered load versus differential tissue response on the anatomical, cellular and molecular processes that contribute to the strength of such composite structures. Our study also suggests that the short-term duration of earlier analyses of cranial joint tissues may offer a limited notion of the complex process of developmental plasticity, especially as it relates to the effects of long-term variation in mechanical loads, when a joint is increasingly characterized by adaptive and degradative changes in tissue structure and composition. Indeed, it is likely that a component of the adaptive increases in rabbit TMJ and symphyseal proportions and biomineralization represent a compensatory mechanism to cartilage degradation that serves to maintain the overall functional integrity of each joint system. Therefore, while variation in cranial joint anatomy and performance among sister taxa is, in part, an epiphenomenon of interspecific differences in diet-induced masticatory stresses characterizing the individual ontogenies of the members of a species, this behavioral signal may be increasingly mitigated in over-loaded and perhaps older organisms by the interplay between adaptive and degradative tissue responses.

PMID: 17267649 [PubMed - indexed for MEDLINE]

No trade-off between biting and suction feeding performance in clariid catfishes.

J Exp Biol. 2007 Jan;210(Pt 1):27-36

Authors: Van Wassenbergh S, Herrel A, Adriaens D, Aerts P

It is generally assumed that biting performance trades off with suction performance in fish because both feeding types may place conflicting demands on the cranial musculo-skeletal system. However, the functional consequences of morphological adaptations enhancing biting on the mechanics and performance of suction feeding in fish remain obscure. In this study, suction feeding performance was compared between three clariid catfish species differing considerably in their biting capacity, by measuring the velocity of a standardized prey being sucked into the buccal cavity using high-speed cineradiography. In addition, buccal volume changes during prey capture were quantified by ellipse modelling. As all species were able to accelerate the prey to similar peak velocities, our results demonstrate the possibility for catfishes to increase bite performance considerably without compromising suction performance. The amount of buccal expansion in the ventral direction is approximately equal for all species. Consequently, the system generating expansion through ventral rotation of the lower jaw, hyoid and pectoral girdle is apparently not constrained (mechanically or architectonically) by the hypertrophy of the jaw adductors. As the effect of a reduced magnitude of lateral expansion (suspensorium abduction) on suction performance in Clariidae appears to be negligible (for example in Gymnallabes typus), these data demonstrate the dominant role of ventral expansion for producing suction in these fish.

PMID: 17170145 [PubMed - indexed for MEDLINE]

Influence of alveolar support on stress in periodontal structures.

J Dent Res. 2006 Dec;85(12):1087-91

Authors: Ona M, Wakabayashi N

The influence of alveolar bone support on the functional capability of a tooth remains unclear. It was hypothesized that a reduction in alveolar support causes an increase of maximum stress in the periodontal structures. Mathematical models of the maxillary incisor to simulate in vivo tooth movement were constructed with periodontium of normal or reduced bone height, and normal or widened periodontal ligament (PDL) space. Under simulated bite force, the maximum tensile stress at the lingual cervical region in the PDL increased with bone height reduction, but decreased with PDL widening. The compressive stress at the cervical region in the cortical bone was no more than 22% of the yield strength of bone, and did not increase by the height reduction with widened PDL. The result suggests that the height reduction potentially causes mechanical damage to the PDL, but, of itself, is not likely to have a negative effect on the bone.

PMID: 17122159 [PubMed - indexed for MEDLINE]

Is there an association between occlusion and periodontal destruction?: Only in limited circumstances does occlusal force contribute to periodontal disease progression.

J Am Dent Assoc. 2006 Oct;137(10):1381, 1383, 1385 passim

Authors: Deas DE, Mealey BL

PMID: 17012717 [PubMed - indexed for MEDLINE]

Is there an association between occlusion and periodontal destruction?: Yes--occlusal forces can contribute to periodontal destruction.

J Am Dent Assoc. 2006 Oct;137(10):1380, 1382, 1384 passim

Authors: Harrel SK, Nunn ME, Hallmon WW

PMID: 17012716 [PubMed - indexed for MEDLINE]

Dietary consistency and plasticity of masseter fiber architecture in postweaning rabbits.

Anat Rec A Discov Mol Cell Evol Biol. 2006 Oct;288(10):1105-11

Authors: Taylor AB, Jones KE, Kunwar R, Ravosa MJ

Dietary consistency has been shown to influence cross-sectional area and fiber type composition of the masticatory muscles. However, little is known about the effects of dietary consistency on masticatory muscle fiber architecture. In this study, we explore the effects of dietary consistency on the internal architecture of rabbit masseter muscle. Because activity patterns of the rabbit chewing muscles show inter- and intramuscular heterogeneity, we evaluate if alterations in fiber architecture are homogeneous across various portions of the superficial masseter muscle. We compared masseter muscle fiber architecture between two groups of weanling rabbits raised on different diets for 105 days. One group was raised on a diet of ground rabbit pellets to model underuse of the masticatory complex, while the other group was fed a diet of intact pellets and hay blocks to model an overuse diet. In all portions of the superficial masseter, physiological cross-sectional areas (PCSAs) are greater in the overuse compared to underuse diet rabbits. Thus, the mechanical demands for larger muscle and bite forces associated with early and prolonged exposure to a tough diet are met by an increase in PCSA of the superficial masseter. The larger PCSA is due entirely to increased muscle mass, as the two rabbit groups show no differences in either fiber length or angle of pinnation. Thus, increasing pinnation angle is not a necessary biomechanical solution to improving muscle and bite force during growth. The change in PCSA but not fiber length suggests that variation in dietary consistency has an impact on maximum force production but not necessarily on excursion or contraction velocity.

PMID: 16952171 [PubMed - indexed for MEDLINE]

Toward understanding human masticatory control: serendipity and a scientific journey.

J Dent Res. 2006 Sep;85(9):801-3

Authors: Miles TS

PMID: 16931860 [PubMed - indexed for MEDLINE]

Seed husking time and maximal bite force in finches.

J Exp Biol. 2006 Sep;209(Pt 17):3329-35

Authors: van der Meij MA, Bout RG

Many studies on the efficiency of feeding in finches concentrate on husking time in relation to average seed size and bird size. Large species are capable of eating larger seeds and are able to husk large seeds faster than smaller species. It is generally assumed that husking time is related to bite force. However, there are very few studies that investigate the relationship between husking time, seed hardness and bite force directly. In our experiments we measured the seed husking time and the maximal bite force of two taxa of seed cracking birds. Husking time is related to maximal bite force in a highly non-linear way and differs between estrildids and fringillids. Fringillids with the same bite force as estrildids take less time to crack seeds, but only when the strength of the seed coat is close to their maximal bite force. For seeds that are relatively soft the difference in husking time becomes very small. A preliminary jaw motion analysis provides evidence that this difference in husking time between estrildids and fringillids is paralleled by a difference in husking technique. This difference in technique does not affect bite force as such, but decreases the chance of failed cracking attempts. The selective advantage of a small increase in maximal bite force may be related more to the decrease in husking time for seeds with hardness below the maximal bite force, than to the increase in range of seed hardness that the bird is able to crack.

PMID: 16916969 [PubMed - indexed for MEDLINE]

Percentile curves for food acceptance response scores in assessing chewing functions in adults.

Bull Tokyo Dent Coll. 2005 Nov;46(4):123-34

Authors: Sakurai M, Tada A, Suzuki K, Yoshino K, Sugihara N, Matsukubo T

The purpose of this study was to evaluate whether percentile curves for food acceptance response scores were useful in assessing oral and occlusal conditions. We used data obtained from Chiba City Patient Surveys (males: 1,276, females: 1,381, aged 20 to 64), which were conducted in 1998 and 1999. Subjects were assigned scores of between 1 and 4 for 31 different kinds of food based on their food acceptance responses. Occlusal conditions were measured with pressure-sensitive sheets. We calculated the percentile values from 5 to 95 at intervals of five years. We divided the subjects into two groups at the twenty-fifth percentile and statistically analyzed various oral conditions in the two groups. Significant differences were found between them in the mean numbers of present, sound, and missing teeth for almost all age groups. Moreover, there were significant differences in tooth-contact area and occlusal force between the two groups. The results of multiple regression analysis revealed that the scores had a stronger correlation with occlusal conditions than number of teeth in 55-year-olds, although the effect teeth-factors had on scores was more significant in 45- to 50-year-old males. Females' scores had a stronger correlation with occlusal conditions than number of teeth in all age groups. These results indicate that the questionnaire on the acceptance of 31 different kinds of food is useful in providing a basis for oral health instruction and dental treatment aimed at improving chewing ability in adults.

PMID: 16829711 [PubMed - indexed for MEDLINE]

The effect of periodontal surgery on bite force, occlusal contact area and bite pressure.

J Am Dent Assoc. 2006 Jul;137(7):978-83; quiz 1028

Authors: Alkan A, Keskiner I, Arici S, Sato S

BACKGROUND: Tooth mobility resulting from the loss of periodontal support or trauma induced by periodontal surgery may change the amount of bite force (BF) and bite pressure (BP) and number of occlusal contact areas (OCAs). The aim of the authors' study was to compare BF, BP and OCA of teeth with periodontal disease before and after periodontal surgery with similar values of healthy teeth. METHODS: The authors performed quantitative analysis of BF, BP and OCA using a pressure measurement film. Ten patients with periodontitis who needed periodontal surgery served as the test group. The authors took measurements of BF, BP, OCA and mobility (using Miller's Mobility Index) just before surgery and at one, four and 12 weeks after surgery. They also measured clinical attachment levels (CAL) before surgery and 12 weeks after surgery. Ten subjects without periodontitis served as the control group. RESULTS: Although BF and OCA increased the first week after periodontal surgery, analysis of variance (ANOVA) showed no statistically significant differences at a 95 percent confidence interval. There were statistically significant differences between first-week mobility and that at four and 12 weeks (P = .001). A factorial ANOVA showed significant interaction between BF and mobility (P < .05). CONCLUSIONS: The authors' findings suggest that changes in BF, BP and OCA were not affected by periodontal surgery. However, mean mobility values and BF are correlated. Further investigations of this measurement method involving larger study populations and a longer follow-up period are needed. CLINICAL IMPLICATIONS: It seems to be helpful to follow occlusal changes after periodontal surgery using a pressure measurement film. It also may be suggested that this measurement method could be used to evaluate the treatment prognosis.

PMID: 16803824 [PubMed - indexed for MEDLINE]

Mandibular biomechanics and development of the human chin.

J Dent Res. 2006 Jul;85(7):638-42

Authors: Ichim I, Swain M, Kieser JA

The development of the chin, a feature unique to humans, suggests a close functional linkage between jaw biomechanics and symphyseal architecture. The present study tests the hypothesis that the presence of a chin changes strain patterns in the loaded mandible. Using an anatomically correct 3-D model of a dentate mandible derived from a CT scan image, we analyzed strain patterns during incisal and molar biting. We then constructed a second mandible, without a chin, by 'defeaturing' the first model. Strain patterns of the second model were then compared and contrasted to the first. Our main finding was that chinned and non-chinned mandibles follow closely concordant patterns of strain distribution. The results suggest that the development of the human chin is unrelated to the demands placed on the mandible during function.

PMID: 16798865 [PubMed - indexed for MEDLINE]

Effect of texture of plastic and elastic model foods on the parameters of mastication.

J Neurophysiol. 2006 Jun;95(6):3469-79

Authors: Foster KD, Woda A, Peyron MA

Mastication is continually modified throughout the chewing sequence in response to the texture of the food. The aim of this work was to compare the effects of an increase in hardness of two model food types, presenting either elastic or plastic rheological properties, on mastication. Each model food type consisted of four products of different hardness. Sensory testing experiments conducted with one group of 14 subjects showed significant perceived differences between products in terms of their increasing hardness. Fifteen other volunteers were asked to chew three replicates of each elastic and plastic product during two sessions. EMGs of masseter and temporalis muscles were recorded simultaneously with jaw movement during chewing. Numerous variables were analyzed from these masticatory recordings. Multiple linear regression analyses were used to assess the respective effects of food hardness and rheological properties on variables characterizing either the whole masticatory sequence or different stages of the sequence. Muscle activities were significantly affected by an increase in hardness regardless of the food type, whereas the shape of the cycles depended on the rheological properties. The masticatory frequency was affected by hardness at the initial stage of the sequence but overall frequency adaptation was better explained by a change in rheological behavior, with plastic products being chewed at a slower frequency. A dual hypothesis was proposed, implicating first a cortical-brain stem preprogrammed mechanism to adapt the shape of the jaw movements to the rheological properties of the food, and second, a brain stem mechanism with mainly sensory feedback from the mouth to adapt muscle force to the food hardness.

PMID: 16709719 [PubMed - indexed for MEDLINE]

The change of stress distribution on the condyle after mandibular setback surgery.

Eur J Orthod. 2006 Oct;28(5):433-9

Authors: Ueki K, Nakagawa K, Takatsuka S, Yamamoto E

The rigid-body spring model (RBSM) theory was incorporated into a model as a discrete method for analysing problems of limit, such as the stress distribution on the condyle. The purpose of this study was to evaluate the two-dimensional RBSM for determining stress on the temporomandibular joint (TMJ) in patients after orthognathic surgery. Thirty-two patients (five males and 27 females, mean age 21.4 +/- 4.9 years) with mandibular prognathism underwent bilateral sagittal split ramus osteotomy (SSRO) and setback; 48 subjects were recruited as controls. Anatomical landmarks were traced from pre- and post-operative lateral cephalograms and the information was processed using the Fortran analysis program. The force vector on the condyle, its degree, its direction, and the displacement co-ordinates (x, y) and rotation (theta) at the gonial angle were calculated. When muscular power was assumed to be 1, the post-operative degree of the force vector was higher than the pre-operative value (P < 0.05). The X co-ordinate, x, and rotation, theta, of the displacement vector in the pre-operative patients with mandibular prognathism were significantly higher than those in the control subjects (P < 0.05). There were still significant differences between the displacement values post-operatively between the patients and controls (P < 0.05). The results suggest that the degree and direction of the force vector and the resulting displacement co-ordinates can be used as parameters in a surgical model. The RBSM may also be useful in evaluating the pre- and post-operative skeletal morphology of jaw deformities.

PMID: 16679326 [PubMed - indexed for MEDLINE]

Cyclical tensile force on periodontal ligament cells inhibits osteoclastogenesis through OPG induction.

J Dent Res. 2006 May;85(5):457-62

Authors: Kanzaki H, Chiba M, Sato A, Miyagawa A, Arai K, Nukatsuka S, Mitani H

The periodontal ligament (PDL) maintains homeostasis of periodontal tissue under mechanical tensile-loading caused by mastication. Occlusal load inhibits atrophic alveolar bone resorption. Previously, we discovered that continuous compressive force on PDL cells induced osteoclastogenesis-supporting activity, with up-regulation of RANKL. We hypothesized that, unlike compression, cyclical tensile force up-regulates OPG expression in PDL cells via TGF-beta up-regulation, and does not induce osteoclastogenesis-supporting activity. PDL cells were mechanically stimulated by cyclical tensile force in vitro. The conditioned media of PDL cells that had been subjected to cyclical tensile force inhibited osteoclastogenesis. Cyclical tensile force up-regulated not only RANKL mRNA expression, but also OPG mRNA expression in PDL cells. Tensile force up-regulated TGF-beta expression in PDL cells as well. Administration of neutralizing antibodies to TGF-beta inhibited OPG up-regulation under cyclical tensile-force stimulation in a dose-dependent manner. Additionally, the osteoclastogenesis-inhibitory effect of the conditioned media of PDL cells under cyclical tensile force was partially rescued by the administration of TGF-beta neutralizing antibodies. In conclusion, tensile force inhibited the osteoclastogenesis-supporting activity of PDL cells by inducing the up-regulation of OPG via TGF-beta stimulation.

PMID: 16632761 [PubMed - indexed for MEDLINE]

Mandibular mechanics following osteotomy and appliance placement II: Bone strain on the body and condylar neck.

J Oral Maxillofac Surg. 2006 Apr;64(4):620-7

Authors: Rafferty KL, Sun Z, Egbert MA, Baird EE, Herring SW

PURPOSE: The purpose of this investigation was to determine if the mechanical environment of the mandible is changed by osteotomy and fixation, as assessed by the measurement of bone strain on the condylar neck and mandibular corpus. MATERIALS AND METHODS: Immediately following unilateral mandibular osteotomy and distractor placement, strain gauges were attached directly to the corpus and condylar neck in a sample of domestic pigs. Bone strains were recorded during mastication and muscle stimulation. Comparisons of principal strain magnitudes and orientations were made between sides and between the osteotomy sample and a control database. RESULTS: The animals preferred to chew on the non-osteotomy side. Corpus strains were higher for osteotomy-side chewing but were comparable to the control database, regardless of chewing side. For the condyle, compared with the control database and the non-osteotomy side, the osteotomy side was underloaded in compression. Furthermore, the orientation of compressive strain was highly variable and more horizontally oriented than that of control and non-osteotomy condyles. Stimulation of the masseter and medial pterygoid loaded the mandible to normal levels. CONCLUSION: Masticatory behavior was altered, probably as a combined result of disruption of the occlusion, changes in muscle recruitment, and probable loss of sensory feedback. However, neither these changes nor damage to the muscles explain the decrease and reorientation of compressive strain on the condylar neck. Alternatively, the modified strain pattern could have arisen from positional instability of the proximal bone fragment.

PMID: 16546641 [PubMed - indexed for MEDLINE]

Mandibular mechanics after osteotomy and distraction appliance placement I: Postoperative mobility of the osteotomy site.

J Oral Maxillofac Surg. 2006 Apr;64(4):610-9

Authors: Sun Z, Rafferty KL, Egbert MA, Herring SW

PURPOSE: Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation. MATERIALS AND METHODS: Twenty-eight domestic pigs, 6 to 8 weeks old, underwent osteotomy of the right mandible and placement of a distractor appliance. Immediately after surgery, displacement at 3 different locations (superior-lateral, inferior-lateral, and inferior-medial) of the osteotomy site was assessed using ultrasound piezoelectric crystals or differential variable reluctance transducers (DVRTs). The amount of lengthening or shortening at each location was measured during mastication and muscle stimulation. Displacement was also measured for bilateral osteotomy during muscle stimulation from a subgroup of 12 pigs. RESULTS: The osteotomy site demonstrated significant mobility during power strokes of mastication with an average magnitude of 0.3 to 0.4 mm. Distinct patterns of displacement were associated with different locations, and the patterns varied between chewing sides. The most common pattern was lengthening at the superior-lateral and shortening at both inferior sites. Similar amounts of displacement were observed during the stimulation of jaw-closers (masseter and medial pterygoid), but the patterns produced by these muscles did not completely explain the masticatory pattern. Opening the osteotomy to 1.5 mm did not alter the displacements observed during muscle stimulation. Bilateral osteotomy tended to decrease displacement. CONCLUSIONS: The study demonstrates that during mastication and masticatory muscle stimulation, an acute mandibular osteotomy site is mobile despite fixation by a distractor appliance.

PMID: 16546640 [PubMed - indexed for MEDLINE]

[Effect of bite force lost on the expression of iNOS in the rat periodontium]

Shanghai Kou Qiang Yi Xue. 2005 Dec;14(6):617-20

Authors: Li J, Sun W, Zhong M, Ai HJ

PURPOSE: To investigate the molecular mechanism of the effect of bite force loss on periodontium remodeling. METHODS: For establishing a rat model of different bite forces for the study, the left maxillary molars of Wistar rats were extracted and the left mandibular molar area was used as the model of the bite force lost. The animals were sacrificed after 6 hours,1,2,3 days and 1,2,3,4weeks. The prepared tissue specimens were processed for the study of the change in the histologic morphology and the expression of iNOS protein in PDLC and osteoblasts with HE staining, immunohistochemistry and RT-PCR techniques, and the results were analyzed by one-way ANOVA,Dunnet t test and paired samples test. RESULTS: In the group of lost biting force, the derangement of periodontal ligament and resorption of alveolar bone were observed in histologic study: the structure of periodontal ligament deranged ,fibers and cells arrayed abnormally, there were many holes in the alveolar bone, even osteoclasts were present; the expression of iNOS was observed dramatically changed: the expression of iNOS in periodontal ligament fibroblasts and osteoblasts was higher than normal, especially at 2 days and 3 weeks,so as the results of RT-PCR.There was a significant correlation between bite force lost and the increased expression of iNOSmRNA. CONCLUSIONS: Bite force lost significantly increased the expression of iNOSmRNA in PDLC and osteoblasts, which suggests that iNOS may play an important role in the process of periodontium remodeling.

PMID: 16400492 [PubMed - in process]

[Stress analysis of the post and core system under loading]

Shanghai Kou Qiang Yi Xue. 2005 Dec;14(6):613-6

Authors: Weng WM, Zhu ZY, Zhang BW, Weng DX

PURPOSE: To analyze the stress of the post and core system by using finite element analysis and study the influence of the "crown materials" on the analytic results. METHODS: Three groups of 3D finite element models of maxillary incisors were established according to the fabricating standard of the post and core system by using I-DEAS finite element analysis software. Group A was consisted of the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group B was composed of the PFM, the cast metal post and core, the tooth structure after preparation and the periodontal structure. Group C was composed of the resin crown, the cast metal post and core, the tooth structure after preparation and the periodontal structure. The three groups were loaded and analyzed under the same loading according to the mean value of the bite force of incisors. RESULTS: (1)The maximum stress of dentin in group A was twice higher than that in group B. The maximum primary stress, minimum primary stress and maximum shear stress of group A were respectively 236.35, 228.83 and 218.05 percent of those in group B. The difference of maximum stress values of group B and group C was neglectable. (2) The maximum stress distribution of dentin in group A and group B was quite different (the stress was concentrated in labial and lingual side of the cervical dentin in group A, otherwise in group B it was concentrated in the area around the alveolar and the labial and lingual side of the dentin which was opposite to the tip of the cast metal post and core). The maximum stress distribution of dentin in group A and group B was almost the same. CONCLUSIONS: Different materials of the crown did not influence the result of 3D finite element stress analysis of the post and core system. Supported by Shanghai Leading Academic Discipline Project (T0202).

PMID: 16400491 [PubMed - in process]

Mastication effort estimated by electromyography for cooked rice of differing water content.

Biosci Biotechnol Biochem. 2005 Sep;69(9):1669-76

Authors: Kohyama K, Yamaguchi M, Kobori C, Nakayama Y, Hayakawa F, Sasaki T

The objective of this study was to quantify the mastication effort for cooked rice. We analyzed mastication patterns while normal subjects ate a spoonful of cooked rice that had been prepared by cooking with different amounts of water (1.5, 2.0, 3.0, and 4.0 times the water to rice weight). The rice samples were served with the same weight, same volume and same solid content, and electromyography (EMG) of the masticatory muscles was measured. The texture of the four cooked rice samples was instrumentally analyzed by the two-bite method. The number of chews, masticatory time, and jaw-closing muscle activities per chew evaluated by EMG were higher in the rice sample cooked with least water, which exhibited a high firmness value in the instrumental test. Rice cooked with 4.0 times the amount of water exhibited the longest jaw-opening duration, which was related to the adhesiveness value in the instrumental test. The ratio of jaw-opening muscle activity to the preceding jaw-closing muscle activity was lower for the rice containing least water, this corresponding to the area ratio (balance degree) in the instrumental test. Softer rice containing more water reduced the total mastication effort until swallowing because it required a shorter mastication time. It was not difficult for the softer rice with high density to be ingested in greater weight, decreasing the mastication effort for a certain amount.

PMID: 16195583 [PubMed - indexed for MEDLINE]

Analysis of the bite force and mechanical design of the feeding mechanism of the durophagous horn shark Heterodontus francisci.

J Exp Biol. 2005 Sep;208(Pt 18):3553-71

Authors: Huber DR, Eason TG, Hueter RE, Motta PJ

Three-dimensional static equilibrium analysis of the forces generated by the jaw musculature of the horn shark Heterodontus francisci was used to theoretically estimate the maximum force distributions and loadings on its jaws and suspensorium during biting. Theoretical maximum bite force was then compared with bite forces measured (1) voluntarily in situ, (2) in restrained animals and (3) during electrical stimulation of the jaw adductor musculature of anesthetized sharks. Maximum theoretical bite force ranged from 128 N at the anteriormost cuspidate teeth to 338 N at the posteriormost molariform teeth. The hyomandibula, which connects the posterior margin of the jaws to the base of the chondrocranium, is loaded in tension during biting. Conversely, the ethmoidal articulation between the palatal region of the upper jaw and the chondrocranium is loaded in compression, even during upper jaw protrusion, because H. francisci's upper jaw does not disarticulate from the chondrocranium during prey capture. Maximum in situ bite force averaged 95 N for free-swimming H. francisci, with a maximum of 133 N. Time to maximum force averaged 322 ms and was significantly longer than time away from maximum force (212 ms). Bite force measurements from restrained individuals (187 N) were significantly greater than those from free-swimming individuals (95 N) but were equivalent to those from both theoretical (128 N) and electrically stimulated measurements (132 N). The mean mass-specific bite of H. francisci was greater than that of many other vertebrates and second highest of the cartilaginous fishes that have been studied. Measuring bite force on restrained sharks appears to be the best indicator of maximum bite force. The large bite forces and robust molariform dentition of H. francisci correspond to its consumption of hard prey.

PMID: 16155227 [PubMed - indexed for MEDLINE]

Fracture resistance of premolar teeth restored with different filling techniques.

J Contemp Dent Pract. 2005 Aug 15;6(3):62-9

Authors: Fran&#xE7;a FM, Worschech CC, Paulillo LA, Martins LR, Lovadino JR

The aim of this study is to verify the fracture resistance of premolars with large mesiocclusodistal (MOD) preparations with composite resin using different incremental techniques when subjected to an occlusal load. Forty maxillary premolar teeth were randomly divided into four groups (n=10). Class II MOD cavities were prepared in all specimens with parallel walls and no approximal boxes. The resulting isthmus width was 1/3 the distance between the cusp tips and (3/4) the height of the crown. Teeth in group I, the control group, were not restored. Specimens in group II were restored in three incremental vertical layers. Group III specimens were restored in three horizontal layers, and finally, specimens in group IV were restored in oblique layers. With exception of the placement technique, specimens in groups II, III and IV were restored using the Single Bond adhesive system and P60 composite resin following manufacturer's recommendations. A 4 mm diameter steel sphere contacted the buccal and lingual cusps of the tested teeth at a crosshead speed of 0.5 mm/min until fracture occurred. The values obtained in this study were subjected to Analysis of Variance (ANOVA) and a Tukey-Kramer test. Only group I (non-restored) obtained a minor means of fracture resistance. No significant differences among groups II, III, and IV were found. This study shows on large MOD cavities the incremental filling techniques do not influence the fracture resistance of premolar teeth restored with composite resin.

PMID: 16127473 [PubMed - indexed for MEDLINE]

Fiber-type composition of the human jaw muscles--(part 2) role of hybrid fibers and factors responsible for inter-individual variation.

J Dent Res. 2005 Sep;84(9):784-93

Authors: Korfage JA, Koolstra JH, Langenbach GE, van Eijden TM

This is the second of two articles about fiber-type composition of the human jaw muscles. It reviews the functional relationship of hybrid fibers and the adaptive properties of jaw-muscle fibers. In addition, to explain inter-individual variation in fiber-type composition, we discuss these adaptive properties in relation to environmental stimuli or perturbations. The fiber-type composition of the human jaw muscles is very different from that of limb and trunk muscles. Apart from the presence of the usual type I, IIA, and IIX myosin heavy-chains (MyHC), human jaw-muscle fibers contain MyHCs that are typical for developing or cardiac muscle. In addition, much more frequently than in limb and trunk muscles, jaw-muscle fibers are hybrid, i.e., they contain more than one type of MyHC isoform. Since these fibers have contractile properties that differ from those of pure fibers, this relatively large quantity of hybrid fibers provides a mechanism that produces a very fine gradation of force and movement. The presence of hybrid fibers might also reflect the adaptive capacity of jaw-muscle fibers. The capacity for adaptation also explains the observed large inter-individual variability in fiber-type composition. Besides local influences, like the amount of muscle activation and/or stretch, more general influences, like aging and gender, also play a role in the composition of fiber types.

PMID: 16109985 [PubMed - indexed for MEDLINE]

Effect of occlusal interference on habitual activity of human masseter.

J Dent Res. 2005 Jul;84(7):644-8

Authors: Michelotti A, Farella M, Gallo LM, Veltri A, Palla S, Martina R

It has been suggested that occlusal interference may increase habitual activity in the jaw muscles and may lead to temporomandibular disorders (TMD). We tested these hypotheses by means of a double-blind randomized crossover experiment carried out on 11 young healthy females. Strips of gold foil were glued either on a selected occlusal contact area (active interference) or on the vestibular surface of the same tooth (dummy interference) and left for 8 days each. Electromyographic masseter activity was recorded in the natural environment by portable recorders under interference-free, dummy-interference, and active-interference conditions. The active occlusal interference caused a significant reduction in the number of activity periods per hour and in their mean amplitude. The EMG activity did not change significantly during the dummy-interference condition. None of the subjects developed signs and/or symptoms of TMD throughout the whole study, and most of them adapted fairly well to the occlusal disturbance.

PMID: 15972594 [PubMed - indexed for MEDLINE]

A functional morphological approach to the scaling of the feeding system in the African catfish, Clarias gariepinus.

J Exp Biol. 2005 Jun;208(Pt 11):2091-102

Authors: Herrel A, Van Wassenbergh S, Wouters S, Adriaens D, Aerts P

Effects of size are pervasive and affect nearly all aspects of the biology of animals and plants. Theoretical scaling models have been developed to predict the effects of size on the functioning of musculo-skeletal systems. Although numerous experimental studies have investigated the effects of size on the movements of skeletal elements during locomotion and feeding in vertebrates, relatively little is known about the scaling of the muscles and bones responsible for the actual movements. Here, we examine the scaling of external morphology, skeletal elements of the feeding system, and a number of cranial muscles to understand how this may affect the movements observed during suction feeding in the African catfish, Clarias gariepinus. The results show that neither the head nor the cranial elements themselves scale according to geometric similarity models. Relative to head size, distinct changes in the mass and configuration of the feeding structures takes place. Unexpectedly, different cranial muscles show different scaling patterns that ultimately all lead to a positive allometry of muscle cross-sectional area relative to fish head size. This suggests that (1) the scaling of the cranial elements cannot be predicted a priori based on the scaling of external head dimensions and (2) the scaling of the feeding system is optimised towards high force output in the larger animals. An analysis of the consequences of the observed changes in morphology with size on performance traits, including bite force and jaw closing velocity, suggests a tight link between the scaling of the feeding system and the natural diet of these fish. Whereas for smaller size classes the system is tuned towards high bite forces, for animals with cranial lengths greater than 65 mm the scaling of the feeding system appears to be dictated by the hydrodynamic constraints on suction feeding.

PMID: 15914653 [PubMed - indexed for MEDLINE]

Functional activity of superior head of human lateral pterygoid muscle during isometric force.

J Dent Res. 2005 Jun;84(6):548-53

Authors: Ruangsri S, Whittle T, Wanigaratne K, Murray GM

There is controversy as to the jaw tasks for which the superior head of the human lateral pterygoid muscle (SHLP) becomes active. The aim was to describe the functional activities of SHLP single motor units (SMUs) during horizontal isometric force tasks. In 11 subjects, 48 SMUs were recorded from computer-tomography-verified SHLP sites during generation of horizontal isometric force in the contralateral (CL), protrusive (P), and ipsilateral (IL) directions and intermediate directions (CL-P, IL-P). In eight subjects, SHLP SMUs were active in CL, CL-P, and P. Qualitatively, SHLP EMG activity increased with increased isometric force. Forty-two SMUs were active in directions other than IL; 6 exhibited activity at IL and other directions. The similarity of these data to previous human lateral pterygoid (IHLP) data supports the notion that SHLP and IHLP should be regarded as a single muscle, with activities shaded according to the biomechanical demands of the task.

PMID: 15914593 [PubMed - indexed for MEDLINE]

Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa.

Proc Biol Sci. 2005 Mar 22;272(1563):619-25

Authors: Wroe S, McHenry C, Thomason J

We provide the first predictions of bite force (BS) in a wide sample of living and fossil mammalian predators. To compare between taxa, we calculated an estimated bite force quotient (BFQ) as the residual of BS regressed on body mass. Estimated BS adjusted for body mass was higher for marsupials than placentals and the Tasmanian devil (Sarcophilus harrisii) had the highest relative BS among extant taxa. The highest overall BS was in two extinct marsupial lions. BFQ in hyaenas were similar to those of related, non-osteophagous taxa challenging the common assumption that osteophagy necessitates extreme jaw muscle forces. High BFQ in living carnivores was associated with greater maximal prey size and hypercarnivory. For fossil taxa anatomically similar to living relatives, BFQ can be directly compared, and high values in the dire wolf (Canis dirus) and thylacine (Thylacinus cynocephalus) suggest that they took relatively large prey. Direct inference may not be appropriate where morphologies depart widely from biomechanical models evident in living predators and must be considered together with evidence from other morphological indicators. Relatively low BFQ values in two extinct carnivores with morphologies not represented among extant species, the sabrecat, Smilodon fatalis, and marsupial sabretooth, Thylacosmilus atrox, support arguments that their killing techniques also differed from extant species and are consistent with 'canine-shear bite' and 'stabbing' models, respectively. Extremely high BFQ in the marsupial lion, Thylacoleo carnifex, indicates that it filled a large-prey hunting niche.

PMID: 15817436 [PubMed - indexed for MEDLINE]

Modeling masticatory muscle force in finite element analysis: sensitivity analysis using principal coordinates analysis.

Anat Rec A Discov Mol Cell Evol Biol. 2005 Apr;283(2):288-99

Authors: Ross CF, Patel BA, Slice DE, Strait DS, Dechow PC, Richmond BG, Spencer MA

Our work on a finite element model of the skull of Macaca aims to investigate the functional significance of specific features of primate skulls and to determine to which of the input variables (elastic properties, muscle forces) the model behavior is most sensitive. Estimates of muscle forces acting on the model are derived from estimates of physiological cross-sectional areas (PCSAs) of the jaw muscles scaled by relative electromyographic (EMG) amplitudes recorded in vivo. In this study, the behavior of the model was measured under different assumptions regarding the PCSAs of the jaw muscles and the latency between EMG activity in those muscles and the resulting force production. Thirty-six different loading regimes were applied to the model using four different PCSA sets and nine different PCSA scaling parameters. The four PCSA sets were derived from three different macaque species and one genus average, and the scaling parameters were either EMGs from 10, 20, 30, 40, 50 and 60 msec prior to peak bite force, or simply 100%, 50%, or 25% of peak muscle force. Principal coordinates analysis was used to compare the deformations of the model produced by the 36 loading regimes. Strain data from selected sites on the model were also compared with in vivo bone strain data. The results revealed that when varying the external muscle forces within these boundaries, the majority of the variation in model behavior is attributable to variation in the overall magnitude rather than the relative amount of muscle force generated by each muscle. Once this magnitude-related variation in model deformation was accounted for, significant variation was attributable to differences in relative muscle recruitment between working and balancing sides. Strain orientations at selected sites showed little variation across loading experiments compared with variation documented in vivo. These data suggest that in order to create an accurate and valid finite element model of the behavior of the primate skull at a particular instant during feeding, it is important to include estimates of the relative recruitment levels of the masticatory muscles. However, a lot can be learned about patterns of skull deformation, in fossil species for example, by applying external forces proportional to the estimated relative PCSAs of the jaw adductors.

PMID: 15747351 [PubMed - indexed for MEDLINE]

Finite-element analysis of biting behavior and bone stress in the facial skeletons of bats.

Anat Rec A Discov Mol Cell Evol Biol. 2005 Apr;283(2):319-30

Authors: Dumont ER, Piccirillo J, Grosse IR

The wide range of dietary niches filled by modern mammals is reflected in morphological diversity of the feeding apparatus. Despite volumes of data on the biomechanics of feeding, the extent to which the shape of mammal skulls reflects stresses generated by feeding is still unknown. In addition to the feeding apparatus, the skull accommodates the structural needs of the sensory systems and brain. We turned to bats as a model system for separating optimization for masticatory loads from optimization for other functions. Because the energetic cost of flight increases with body mass, it is reasonable to suggest that bats have experienced selective pressure over evolutionary time to minimize mass. Therefore, the skulls of bats are likely to be optimized to meet functional demands. We investigate the hypothesis that there is a biomechanical link between biting style and craniofacial morphology by combining biting behavior and bite force data gathered in the field with finite-element (FE) analysis. Our FE experiments compared patterns of stress in the craniofacial skeletons within and between two species of bats (Artibeus jamaicensis and Cynopterus brachyotis) under routine and atypical loading conditions. For both species, routine loading produced low stresses in most of the skull. However, the skull of Artibeus was most resistant to loads applied via its typical biting style, suggesting a mechanical link between routine loading and skull form. The same was not true of Cynopterus, where factors other than feeding appear to have had a more significant impact on craniofacial morphology.

PMID: 15747350 [PubMed - indexed for MEDLINE]

Comparison of beam theory and finite-element analysis with in vivo bone strain data from the alligator cranium.

Anat Rec A Discov Mol Cell Evol Biol. 2005 Apr;283(2):331-48

Authors: Metzger KA, Daniel WJ, Ross CF

The mechanical behavior of the vertebrate skull is often modeled using free-body analysis of simple geometric structures and, more recently, finite-element (FE) analysis. In this study, we compare experimentally collected in vivo bone strain orientations and magnitudes from the cranium of the American alligator with those extrapolated from a beam model and extracted from an FE model. The strain magnitudes predicted from beam and FE skull models bear little similarity to relative and absolute strain magnitudes recorded during in vivo biting experiments. However, quantitative differences between principal strain orientations extracted from the FE skull model and recorded during the in vivo experiments were smaller, and both generally matched expectations from the beam model. The differences in strain magnitude between the data sets may be attributable to the level of resolution of the models, the material properties used in the FE model, and the loading conditions (i.e., external forces and constraints). This study indicates that FE models and modeling of skulls as simple engineering structures may give a preliminary idea of how these structures are loaded, but whenever possible, modeling results should be verified with either in vitro or preferably in vivo testing, especially if precise knowledge of strain magnitudes is desired.

PMID: 15747347 [PubMed - indexed for MEDLINE]

Molar bite force in relation to occlusion, craniofacial dimensions, and head posture in pre-orthodontic children.

Eur J Orthod. 2005 Feb;27(1):58-63

Authors: Sonnesen L, Bakke M

The present study examined bite force in relation to occlusion, craniofacial dimensions, and head posture. The sample comprised 88 children (48 girls, 40 boys) aged 7-13 years, sequentially admitted for orthodontic treatment of malocclusions entiling health risks. Bite force was measured in the molar region by means of a pressure transducer. Angle classification, number of teeth and contact in the intercuspal position (ICP) were recorded and dental arch widths were measured on plaster casts. Craniofacial dimensions and head posture were recorded from lateral cephalometric radiographs taken with the subject standing with their head in a standardized posture (mirror position). Associations were assessed by Spearman correlations and multiple stepwise regression analyses.The maximum bite force increased significantly with age in girls, with teeth in occlusal contact in boys, and with increasing number of erupted teeth in both genders. Bite force did not vary significantly between the Angle malocclusion types. Only in boys was there a clear correlation between bite force and craniofacial morphology: cranial base length (n-ba, n-ar), posterior face height (s-tgo, ar-tgo), vertical jaw relationship (NL-ML), mandibular inclination (NSL-ML), form (ML-RL) and length (pg-tgo), and inclination of the lower incisors (Ili-ML). Multiple regression analysis showed that the vertical jaw relationship (P < 0.001) and the number of teeth present (P < 0.01) were the most important factors for the magnitude of bite force in boys. In girls, the most important factor was the number of teeth present (P < 0.001). No correlations between bite force and head posture were found.

PMID: 15743864 [PubMed - indexed for MEDLINE]

A determination of bite force in northern Japanese children.

Eur J Orthod. 2005 Feb;27(1):53-7

Authors: Kamegai T, Tatsuki T, Nagano H, Mitsuhashi H, Kumeta J, Tatsuki Y, Kamegai T, Inaba D

The bite force of 2594 school children (1248 males and 1346 females) living in northern Japan was investigated during oral health examinations in May and June 2001, using a new type of occlusal force gauge. The subjects were recruited from a variety of educational institutes and comprised: 73 nursery (3-5 years old), 1019 primary (6-11 years old), 902 junior high (12-14 years old) and 600 high (15-17 years old) school children. The measuring apparatus consisted of a hydraulic pressure gauge, with a bite element encased in a plastic tube. The bite force was measured at the first molar or second primary molar in the children presenting in the permanent and primary dentitions, respectively.The findings revealed significant variations in bite force between children of different ages. The average bite force was 186.2 N in males and 203.4 N in females of nursery school children; 374.4 N in males and 330.5 N in females of primary school children; 514.9 N in males and 448.7 N in females of junior high school children; and 545.3 N in males and 395.2 N in females of high school children. The prevalence of malocclusion in the nursery school children was found to be less than 30 per cent, which contrasted with almost 70 per cent in the high school children.

PMID: 15743863 [PubMed - indexed for MEDLINE]

Effect of direct relining on stresses at the denture base and the metal frame of removable partial dentures.

J Contemp Dent Pract. 2005 Feb 15;6(1):37-47

Authors: Al-Ghannam NA, Fahmi FM

The Kennedy Class I removable partial denture (RPD) can cause stress to supporting hard and soft tissues and may lead to harmful effects. The purpose of this study is to investigate the pattern of these stresses in three different positions before and following a relining procedure. Ten patients, five males and five females, with a lower distal extension RPD and an opposing upper class III type RPD were selected for this study. Strain gauges together with a strain gauge indicator were used to study the pattern of stresses in three selected positions. Some changes were significantly different at the site of the denture base and at the metal frame near the direct retainer. After relining, the stresses were shared partially by the abutments and partially by the tissues. Maximum stresses were reported during swallowing. No significant difference was noticed between males and females.

PMID: 15719075 [PubMed - indexed for MEDLINE]

Occlusal force and condylar motion in patients with anterior open bite.

J Dent Res. 2005 Feb;84(2):133-7

Authors: Miyawaki S, Araki Y, Tanimoto Y, Katayama A, Fujii A, Imai M, Takano-Yamamoto T

Patients with open bite often show a weak occlusal force and temporomandibular disorders (TMDs). If these are the main cause of open bite, it may be hypothesized that both pre-pubertal and adult open-bite patients would show a weak occlusal force and abnormal condylar motion. The purpose of this study was to test this hypothesis. Test group subjects consisted of 13 consecutive pre-pubertal and 13 adult patients with anterior open bite. They were compared with age-matched normal subjects. The adult open-bite group showed a weaker occlusal force and a shorter range of condylar motion compared with the control subjects. In the pre-pubertal subjects, however, there were no significant differences in the occlusal force and range of condylar motion between the open-bite and control groups. Therefore, these results suggest that a weak occlusal force or TMDs may not be the main cause of open bite.

PMID: 15668329 [PubMed - indexed for MEDLINE]

Application of "prescale" as an aid to clinical diagnosis in orthodontics.

Bull Tokyo Dent Coll. 2004 May;45(2):99-108

Authors: Kitafusa Y

We examined the feasibility of applying the Dental Prescale Occluzer System to the evaluation of occlusion in orthodontic patients. The patients were classified according to the type of malocclusion or facial pattern. The values of occlusal contact area and occlusal force obtained from these individuals differed depending on the type of occlusion or facial pattern. These values were higher in individuals with normal occlusion than in patients with malocclusion and higher in patients with the Brachyo facial pattern than in those with the Dolico facial pattern. Because this system can very easily analyze the occlusal contact area, the mean pressure on each occlusal contact point, and the occlusal force during the process of orthodontic treatments, it can be useful as an aid for the initial diagnosis of occlusal problems, the observation of the changes in occlusion during treatment, and the establishment of the final goal of orthodontic treatments.

PMID: 15536861 [PubMed - indexed for MEDLINE]

Effects of cross-sectional area on human bite studied with raw carrot and surimi gel.

Biosci Biotechnol Biochem. 2004 Oct;68(10):2104-10

Authors: Kohyama K, Sasaki T, Hayakawa F, Hatakeyama E

The effects of the cross-sectional area of food samples on bite force with molar teeth were investigated using raw carrots and surimi gels. We evaluated human bite force for food samples with different sizes between the upper and lower molars using a multiple-point sheet sensor and electromyography (EMG). The bite force curve and EMG clearly showed textural characteristics of the carrot and gel. In particular, the first peak in the bite curves corresponded to breaking point in the compression test. With increasing cross-sectional area of both foodstuffs, the bite force and contact area increased and the average stress to which the specimen was subjected (mean stress) tended to decrease, while the stress produced between the teeth and the specimen (active stress) did not change. Chewing rhythm and EMG activities were not greatly influenced by sample size. These findings suggest that higher bite force might cause difficulty in biting food with a larger cross-sectional area.

PMID: 15502356 [PubMed - indexed for MEDLINE]

Attrition, abrasion, corrosion and abfraction revisited: a new perspective on tooth surface lesions.

J Am Dent Assoc. 2004 Aug;135(8):1109-18; quiz 1163-5

Authors: Grippo JO, Simring M, Schreiner S

OVERVIEW: The authors propose updated and revised nomenclature, definitions and classification for tooth surface lesions. Their objective is standardization, clarity and clinical utility for the dental practitioner. The article presents a schema of the pathodynamic mechanisms in the formation of tooth surface lesions--three basic physical and chemical mechanisms, their interactions and their dental manifestations. CONCLUSIONS AND CLINICAL IMPLICATIONS: The use of precise definitions will assist the practitioner in determining the etiology of various tooth surface lesions. Understanding the pathodynamic mechanisms and their many possible interactions, as set forth in the schema, will enable the practitioner to make an accurate differential diagnosis and to provide effective prevention and treatment. It also will assist dentists in communicating more effectively with their colleagues as well as with their patients. In addition, the schema helps identify areas in which future research is indicated.

PMID: 15387049 [PubMed - indexed for MEDLINE]

Scaling of jaw muscle size and maximal bite force in finches.

J Exp Biol. 2004 Jul;207(Pt 16):2745-53

Authors: van der Meij MA, Bout RG

Fringillids and estrildids differ in their husking performance on hard closed-shelled seeds, which are cracked before they are eaten. The time required to husk a seed is directly related to seed hardness, and husking time is therefore expected to be related to bite force as well. We investigated whether there is a significant difference in jaw muscle mass and maximal bite force between fringillids and estrildids. The analysis shows that fringillids have relatively larger jaw muscles than estrildids and are able to produce higher bite forces than estrildids of the same body size. This difference in jaw muscle mass mainly results from a difference in jaw closing muscles. Compared with other birds, the jaw muscles of both fringillids and estrildids scale strongly positively allometric with body size. Muscle fibre length scales negatively allometric with body size, which results in relatively high muscle and bite forces. Comparison with the scarce data available for other trophic groups suggests that the scaling of jaw muscle size depends on diet and that jaw muscle size in finches is an adaptation to their feeding behaviour.

PMID: 15235003 [PubMed - indexed for MEDLINE]

Effects of increased muscle mass on mouse sagittal suture morphology and mechanics.

Anat Rec A Discov Mol Cell Evol Biol. 2004 Jul;279(1):676-84

Authors: Byron CD, Borke J, Yu J, Pashley D, Wingard CJ, Hamrick M

The purpose of this study is to test predicted form-function relationships between cranial suture complexity and masticatory muscle mass and biomechanics in a mouse model. Specifically, to test the hypothesis that increased masticatory muscle mass increases sagittal suture complexity, we measured the fractal dimension (FD), temporalis mass, and temporalis bite force in myostatin-deficient (GDF8(-/-)) mice and wild-type CD-1 mice (all male, 6 months old). Myostatin is a negative regulator of muscle mass, and myostatin-deficient mice show a marked increase in muscle mass compared to normal mice. We predicted that increased sagittal suture complexity would decrease suture stiffness. The data presented here demonstrate that increased suture complexity (measured as FD) was observed in a hypermuscular mouse model (GDF8(-/-)) with significantly increased temporalis muscle mass and bite forces. Hypermuscular mice were also found to possess suture connective tissue that was less stiff (i.e., underwent more displacement before failure occurred) when loaded in tension. By decreasing stiffness, suture complexity apparently helps to dissipate mechanical loads within the cranium that are related to chewing. These results suggest that cranial suture connective tissue locally adapts to functional demands of the biomechanical suture environment. As such, cranial sutures provide a novel model for studies in connective tissue mechanotransduction.

PMID: 15224409 [PubMed - indexed for MEDLINE]

Effect of nitric oxide on the recovery of the hypofunctional periodontal ligament.

J Dent Res. 2004 Apr;83(4):338-42

Authors: Watarai H, Warita H, Soma K

The relationship between occlusal stimuli and a hypofunctional periodontal ligament (PDL) structure has been reported, though changes in occlusal recovery conditions were still unclear. Nitric oxide (NO) produced by NO synthase (NOS) is considered a factor for vascular and immune system control, and it increases according to mechanical stimuli. The objective of this study was to examine the relationship between NOS and occlusal stimuli in PDL by comparing hypofunction with occlusal recovery. The study focused on the expression of endothelial NOS (eNOS) and inducible NOS (iNOS). Their expression significantly decreased in occlusal hypofunction compared with the control group and increased close to normal in an occlusal recovery group. The change in the immunopositive area was more dramatic than the immunopositive cell number. Moreover, the rate of iNOS increase was higher than that of eNOS. This study suggests that NO plays an important role in the recovery of the hypofunctional PDL.

PMID: 15044510 [PubMed - indexed for MEDLINE]

Effect of decreased loading on the metabolic activity of the mandibular condylar cartilage in the rat.

Eur J Orthod. 2004 Feb;26(1):1-5

Authors: Pirttiniemi P, Kantomaa T, Sorsa T

The aim of this study was to measure the effect of decreased temporomandibular loading on the proliferative activity and the level of matrix production of the condylar cartilage. The effect of reduced joint loading on the activity of stromelysin-1 (MMP-3), which has been associated with conditions of articular cartilage matrix breakdown, was also examined. Eighty 14-day-old female rats were assigned to two groups. Following weaning at 20 days, the experimental group was fed a soft diet and the incisors were shortened regularly to keep them out of occlusion. The controls were fed a hard diet. The activity of tritiated thymidine incorporation and the incorporation of radiolabelled sulphur were measured 2, 6, 12, 24 and 48 hours after initiation of the experiment. The radiolabelled sulphur intake was significantly lower in the condylar cartilage of the experimental group 6-24 hours after initiation of the experiment, and tritiated thymidine activity was lower after 12-24 hours, indicating lower proliferation and matrix production. The cartilage in the experimental group showed marked immunostaining against MMP-3 in all cartilage layers 9 days after initiation of the experiment. In the control group, the staining was clearly seen only in the superficial fibrous layer and in the erosion front. A marked reduction in proliferative activity and proteoglycan synthesis in mandibular condylar cartilage was found after a continuous soft diet and suppressed incisal mastication in the rat. The results show that sufficient loading is important for condylar cartilage growth, to maintain both ideal proliferation and matrix chondrocyte production.

PMID: 14994876 [PubMed - indexed for MEDLINE]

Marginal peri-implantitis due to occlusal overload. A case report.

Med Oral. 2004 Mar-Apr;9(2):160-2, 159-60

Authors: Uribe R, Pe&#xF1;arrocha M, Sanchis JM, García O

The etiology of marginal peri-implantitis describes an infectious factor and a biomechanical factor resulting from occlusal overload. Clinical and experimental articles oriented to the biomechanical factor are scarce, so as the studies about the histology associated to periimplantitis. We present a case of marginal peri-implantitis on an implant in the mandibular molar zone caused by occlusal overload, which led to an osseous defect on the marginal crest. The treatment was composed of occlusal adjustment, removal of contaminated surgical tissue, and autogenous bone graft, which varies from the common treatment of infectious peri-implantitis. Histologic analysis of peri-implantitis tissue reveals a juxtaepithelial lympho-plasmocytorious infiltrate and a central zone of dense fibro-connective tissue with scanty inflammatory cells, which differs from the chronic inflammatory tissue associated with infectious peri-implantitis. Clinical and radiographic followup control after 12 months evidenced the remission of the symptoms and bone regeneration on the marginal crest. We consider that in the treatment of marginal peri-implantitis, it is necessary to continue the studies on the histological differences between the infectious types and those that are caused by occlusal overload.

PMID: 14990883 [PubMed - indexed for MEDLINE]

Photoelastic study of the effects of occlusal surface morphology on tooth apical stress from vertical bite forces.

J Contemp Dent Pract. 2004 Feb 15;5(1):74-93

Authors: Wang MQ, Zhang M, Zhang JH

The aim of the study was to determine how the morphology of occlusal surfaces might affect occlusal loading that is transferred to the tooth apex. Photoelastic methods were used to assess apical stress generated by seven variations of occlusions. A test assembly with a 2 kg weight was applied to teeth to create a vertical load. By analyzing the direction and magnitude of the apical principle stress under the polar light that was measured at the apexes of mandibular teeth, the occlusal loading position of each tooth and its direction was obtained based on general mechanical principles. It was found distal incline planes (or slopes) of cusps and lingual incline planes (or slope) of buccal cusps of mandibular posterior teeth carried the greatest occlusal load in normal occlusion. In the other six variations of occlusion presented in this study, the principle apical stresses changed more or less as a result of the different occlusal contact relationships. The magnitude of principle apical stress increased considerably in the flat surface occlusion because of the lack of distribution of occlusion loading by the smooth dentition surface. It is concluded the occlusal surface morphology has a significant effect on the direction and magnitude of apical stress. To establish a suitable relationship of occlusion that can conduct favorable occlusal loading physiologically is very important.

PMID: 14973562 [PubMed - indexed for MEDLINE]

Asymmetry in the condylar long axis and first molar rotation.

J Dent Res. 2004 Feb;83(2):109-14

Authors: Kanomi R, Hidaka O, Yamada C, Takada K

Asymmetric growth occurs frequently in the mandibulofacial region, but little attention has been given to asymmetry in the temporomandibular joint. The purpose of this study was to clarify the feature of asymmetry in the condylar long axis and its relation to upper first molar rotation. Records of 148 pre-orthodontic patients were used. The angle of the condylar long axis and that of the molar rotation were both larger on the left side than on the right side. Positive correlations were found between the corresponding bilateral measurements of condylar long axes and also between those of molar rotations, whereas no correlation was found between the condylar long axis and molar rotation. These findings were found in most subgroups classified by dental age, skeletal pattern, bite force balance, or gender. These results suggest that consistent left-right differences in the condylar long axis and first molar rotation are common.

PMID: 14742646 [PubMed - indexed for MEDLINE]