Restoring function and esthetics in a patient with amelogenesis imperfecta: a case report.

J Contemp Dent Pract. 2007;8(4):95-101

Authors: Gokce K, Canpolat C, Ozel E

AIM: The purpose of this case report is to present the esthetic and functional rehabilitation of the teeth in a 22-year-old patient with Amelogenesis imperfecta (AI). BACKGROUND: AI is a group of hereditary defects of enamel, unassociated with any other generalized defects. It is a rare developmental abnormality of the enamel, with a variable occurrence of approximately 1:4000 to 1:14000 in Western populations. Al results in poor development or complete absence of the enamel of the teeth caused by improper differentiation of the ameloblasts. REPORT: This report describes the diagnosis and treatment of a young male patient with AI and missing molar teeth using contemporary restorative strategies. Initially, the tooth surfaces were treated with a professional cleaning along with conservative restorative treatment. Later, metal-ceramic crowns for posterior teeth and full-ceramic crowns for anterior teeth were utilized for final restorations. SUMMARY: The complexity of the management of patients with AI supports the suggestion the dental profession should have appropriate methods for the rehabilitation of rare dental disorders. The treatment of patients with AI should start with early diagnosis and intervention to prevent later restorative problems.

PMID: 17486193 [PubMed - indexed for MEDLINE]

The influence of commercially pure titanium and titanium-aluminum-vanadium alloy on the final shade of low-fusing porcelain.

J Contemp Dent Pract. 2007;8(2):97-104

Authors: Al Wazzan KA, Al Hussaini IS

AIMS: The aims of this study were to investigate the influence of commercially pure titanium (PTi) and titanium-aluminum-vanadium (Ti-6Al-4V) alloys (TiA) on the final shade of low-fusing porcelain bonded to them and to compare the shade changes with those of three conventional metal-ceramic systems. METHODS AND MATERIALS: A titanium casting unit was used to cast PTi and Ti-6Al-4V alloy specimens followed by A3 shade low-fusing porcelain (Noritake) being bonded to them. Gold-based (AuA), palladium-based (PdA), and nickel-chromium (Ni-Cr) alloys were cast with an automatic centrifugal casting machine, then A3 shade conventional porcelain material (Vita, VMK 95) was applied to them. Ten specimens of each metal were then fabricated. The CIE L* a* b* color coordinates of the specimens were measured with a spectrophotometer. RESULTS: All alloys had significant color changes when compared with A3 shade tabs. The color differences from the shade tabs were 5.79 for the Ti-6Al-4V group, 6.46 for PdA alloy, 8.12 for AuA alloy, 8.15 for Ni-Cr alloy, and 12.58 for PTi. The specimens differed from the shade tabs primarily because of the differences in a* and b* coordinate values. CONCLUSIONS: Predictable shade reproduction of metal-ceramic restorations (MCRs) may be impaired by the underlying metal. The PTi had the greatest color differences among all the tested metal when compared with the shade tabs, whereas the Ti-6Al-4V alloy had the lowest. PTi is more likely to affect the final shade of low-fusing porcelain than Ti-6Al-4V alloy.

PMID: 17277832 [PubMed - indexed for MEDLINE]

Surface roughness of a dental ceramic after polishing with different vehicles and diamond pastes.

Braz Dent J. 2006;17(3):191-4

Authors: Camacho GB, Vinha D, Panzeri H, Nonaka T, Gonçalves M

During fabrication of bonded ceramic restorations, cervical adaptation, occlusal adjustment and final finishing/polishing are procedures to be performed at the dental office after adhesive cementation. Final adjustments may result in loss of ceramic glaze, which requires new polishing of the ceramic surface, with special attention for selection of adequate materials and instruments. The purpose of this study was to evaluate the efficiency of different vehicles associated with diamond pastes indicated for dental ceramic polishing. Two polishing pastes (Crystar Paste and Diamond Excell) associated with four vehicles (rubber cup, Robinson bristle brush, felt wheel and buff disc) were evaluated. Disc-shaped specimens were fabricated from Ceramco II dental ceramic. Surface roughness means (Ra) of the ceramic specimens were determined with a rugosimeter. Data were analyzed statistically by two-way ANOVA and Tukey's test at 5% significance level. There was no statistically significant difference (p>0.01) between the polishing pastes. However, there were statistically significant differences (p<0.01) among the tested vehicles. Vehicle-paste interaction showed statistically significant difference (p<0.05) as well. It may be concluded that: 1) Robinson bristle brush, felt wheel and buff disc were efficient vehicles to be used in association with a diamond polishing paste; 2) The use of rubber cup as a vehicle showed poor efficiency for mechanical polishing of the ceramic surfaces; 3) Both pastes provided similar and efficient polishing and may be recommended for use with an appropriated vehicle.

PMID: 17262123 [PubMed - indexed for MEDLINE]

Porcelain laminate veneer restorations bonded with a three-liquid silane bonding agent and a dual-activated luting composite.

J Oral Sci. 2006 Dec;48(4):261-6

Authors: Matsumura H, Aida Y, Ishikawa Y, Tanoue N

This clinical report describes the fabrication and bonding of porcelain laminate veneer restorations in a patient with anterior open spaces. Laminate veneer restorations made of feldspathic porcelain were etched with 5% hydrofluoric acid, rinsed under tap water, ultrasonically cleaned with methanol, and primed with a chemically activated three-liquid silane bonding agent (Clearfil Porcelain Bond). The enamel surfaces were etched with 40% phosphoric acid, rinsed with water, and primed with a two-liquid bonding agent (Clearfil New Bond) that contained a hydrophobic phosphate (10-methacryloyloxydecyl dihydrogen phosphate; MDP). The restorations were bonded with a dual-activated luting composite (Clapearl DC). The veneers have been functioning satisfactorily for an observation period of one year. Combined use of the Clearfil bonding agents and Clapearl DC luting composite is an alternative to conventional materials for seating porcelain laminate veneer restorations, although the system is inapplicable to dentin bonding.

PMID: 17220627 [PubMed - indexed for MEDLINE]

Antagonist enamel wears more than ceramic inlays.

J Dent Res. 2006 Dec;85(12):1097-100

Authors: Kr&#xE4;mer N, Kunzelmann KH, Taschner M, Mehl A, Garcia-Godoy F, Frankenberger R

Wear phenomena of ceramic inlays are not fully understood. The aim of the present study was to evaluate ceramic wear, antagonist enamel wear, and luting cement wear over 8 years. The two-fold null hypothesis was that there would be (1) no difference in wear behavior between ceramic and enamel, and (2) no influence of filler content of luting composites on composite wear. From 96 restorations, 36 Class II inlays from 16 participants were selected. For inlays with opposing enamel cusps (n=17), replicas of inlays and enamel were scanned with a 3-D laser scanner. Luting gaps of inlays (n=36) were analyzed with a profilometer, including 3-D data analysis. Ceramic and enamel wear increased between 4 and 8 years, with significantly higher values for enamel after 6 years (p<0.05). Luting gap wear increased continuously up to 8 years (p<0.05), with no influence of luting composites (p>0.05) and location of teeth (p>0.05).

PMID: 17122161 [PubMed - indexed for MEDLINE]

Influence of different post core materials on the color of Empress 2 full ceramic crowns.

Chin Med J (Engl). 2006 Oct 20;119(20):1715-20

Authors: Ge J, Wang XZ, Feng HL

BACKGROUND: For esthetic consideration, dentin color post core materials were normally used for all-ceramic crown restorations. However, in some cases, clinicians have to consider combining a full ceramic crown with a metal post core. Therefore, this experiment was conducted to test the esthetical possibility of applying cast metal post core in a full ceramic crown restoration. METHODS: The color of full ceramic crowns on gold and Nickel-Chrome post cores was compared with the color of the same crowns on tooth colored post cores. Different try-in pastes were used to imitate the influence of a composite cementation on the color of different restorative combinations. The majority of patients could not detect any color difference less than DeltaE 1.8 between the two ceramic samples. So, DeltaE 1.8 was taken as the objective evaluative criterion for the evaluation of color matching and patients' satisfaction. RESULTS: When the Empress 2 crown was combined with the gold alloy post core, the color of the resulting material was similar to that of a glass fiber reinforced resin post core (DeltaE = 0.3). The gold alloy post core and the try-in paste did not show a perceptible color change in the full ceramic crowns, which indicated that the color of the crowns might not be susceptible to change between lab and clinic as well as during the process of composite cementation. Without an opaque covering the Ni-Cr post core would cause an unacceptable color effect on the crown (DeltaE = 2.0), but with opaque covering, the color effect became more clinically satisfactory (DeltaE = 1.8). CONCLUSIONS: It may be possible to apply a gold alloy post core in the Empress 2 full ceramic crown restoration when necessary. If a non-extractible Ni-Cr post core exists in the root canal, it might be possible to restore the tooth with an Empress 2 crown after covering the labial surface of the core with one layer of opaque resin cement.

PMID: 17097019 [PubMed - indexed for MEDLINE]

[The use of CAD/CAM system with zirconia in modern prosthodontics]

Shanghai Kou Qiang Yi Xue. 2006 Aug;15(4):337-44

Authors: Sun F, Zhang GR, Zhang F, Liu F, Mao H, Huang L, Wang PF

Computer assisted design/computer assisted machining (CAD/CAM) technology has received considerable clinical and research interest from modern dental practices as a means of delivering all-ceramic restorations. Up to now the CAD/CAM system with zirconia has the highest fracture strength in all all-ceramic materials, and consistently enabled the most esthetic, lifelike reproduction of natural dentition. They have been widely received by both dentists and patients. The CAD/CAM system with zirconia is indicated for crowns and bridges in natural teeth or implants and telescope dentures, the CAD/CAM with zirconia can be placed anywhere in the mouth, and can replace the porcelain crowns and bridges for single crown and bridges less than 6 units. This paper described the techniques of CAD/CAM system with zirconia in fabrication of crowns, bridges, telescope dentures and implant dentures with colored illustrations.

PMID: 16955153 [PubMed - in process]

Making informed decisions about incorporating a CAD/CAM system into dental practice.

J Am Dent Assoc. 2006 Sep;137 Suppl:32S-36S

Authors: Trost L, Stines S, Burt L

BACKGROUND: The authors drew from their clinical application and practice management experience to present a guide to incorporating into the dental practice computer-aided design/computer-aided manufacturing (CAD/CAM) technology for creating dental restorations. METHODS: The authors examine various factors in the purchase of CAD/CAM technology: clinical considerations and implications, practice and patient impact, and practical aspects of financial return. They also offer guidelines to and provide questions for dentists who may be considering a purchase of such technology. CONCLUSIONS: CAD/CAM technology is a key component for a technologically current dental office. CLINICAL IMPLICATIONS: Today's dental care consumer is more aware of his or her treatment options, and CAD/CAM technology may help the dentist meet such a patient's needs. With software improvement, attention to user-friendliness and positive clinical performance history, CAD/CAM systems are a significant stride forward into one-appointment esthetic dentistry.

PMID: 16950935 [PubMed - indexed for MEDLINE]

Clinical performance of chairside CAD/CAM restorations.

J Am Dent Assoc. 2006 Sep;137 Suppl:22S-31S

Authors: Fasbinder DJ

BACKGROUND: The CEREC system (Sirona Dental Systems GmbH, Bensheim, Germany) is marking its 20th year of clinical service. The author reviews the literature on the effectiveness of this chairside CAD/CAM system. TYPES OF STUDIES REVIEWED: The author identified and reviewed clinical studies from 1985 through 2006 that included CEREC-generated inlays, onlays or crowns. These studies were conducted in both private practice and university settings. The author summarized the findings as they relate to postoperative sensitivity, restoration fracture, color match, margin adaptation and clinical longevity. RESULTS: Although postoperative sensitivity was reported, it was due to mainly occlusal interferences. Long-term postoperative sensitivity was not a reported problem. Similar to other ceramic restorations, restoration fracture is the primary mode of failure for CEREC-generated restorations. Although margin wear is detected consistently, consequences of the wear leading to restoration failure were reported rarely. The survival probability of CEREC-generated restorations was reported to be approximately 97 percent for five years and 90 percent for 10 years. CLINICAL IMPLICATIONS: The low rate of restoration fracture and long-term clinical survivability document the effectiveness of the CEREC system as a dependable, esthetic restorative option for patients.

PMID: 16950934 [PubMed - indexed for MEDLINE]

Materials for chairside CAD/CAM-produced restorations.

J Am Dent Assoc. 2006 Sep;137 Suppl:14S-21S

Authors: Giordano R

BACKGROUND: and Overview. Although the use of computer-aided design/computer-aided manufacturing (CAD/CAM) seems to be a recent addition to the dental restorative armamentarium, this concept was first investigated more than 35 years ago. CEREC (Sirona Dental Systems GmbH, Bensheim, Germany) was the first and is the only available chairside system, and it has more than 20 years of use in the dental office. The initial concept had three tenets: esthetic ceramic reconstruction, a single patient visit and minimal tooth reduction (inlays and onlays instead of crowns). The author reviews the materials used for CAD/CAM-fabricated restorations. The structure, properties and clinical success of the materials for full-contour chairside restorations, as well as laboratory-based high-strength all-ceramic restorations are presented. RESULTS: CAD/CAM restorations have demonstrated clinical success owing to a combination of improvements in materials with advances in CAD/CAM systems. Full-contour ceramic restorations fabricated chair-side may reinforce the tooth, providing good long-term clinical success. High-strength milled restorations allow for the use of all-ceramic restorations for multiple-unit posterior and anterior bridges. CLINICAL IMPLICATIONS: Examination of the structure, properties and clinical results of CAD/CAM materials supports their use in routine dental practice.

PMID: 16950933 [PubMed - indexed for MEDLINE]

The evolution of the CEREC system.

J Am Dent Assoc. 2006 Sep;137 Suppl:7S-13S

Authors: M&#xF6;rmann WH

BACKGROUND AND OVERVIEW: Early in 1980, the author anticipated the attraction of restoring posterior teeth with tooth-colored material. He conducted studies and developed the clinical concept of bonded ceramic inlays, at the same time raising the issue of the fast fabrication of the ceramic restorations. The author developed plans for in-office computer-aided design/computer-aided manufacturing (CAD/CAM) fabrication of ceramic restorations specifically to enable the dentist to complete one or multiple ceramic restorations chairside, in a single appointment. The initial concept comprised a small mobile CAD/CAM unit integrating a computer, keyboard, trackball, foot pedal and optoelectronic mouth camera as input devices, a monitor and a machining compartment. CEREC 3 (Sirona Dental Systems GmbH, Bensheim, Germany) divided the system into an acquisition/design unit and a separate machining unit. Three-dimensional software makes the handling illustrative and easy both in the office and in the laboratory. CONCLUSIONS: It appears that the CEREC CAD/CAM concept is becoming a significant part of dentistry. CLINICAL IMPLICATIONS: Sound knowledge of adhesive bonding and diligent planning are essential for the successful integration of CAD/CAM into clinical dental offices.

PMID: 16950932 [PubMed - indexed for MEDLINE]

Effects of surface conditioning on bond strength of metal brackets to all-ceramic surfaces.

Eur J Orthod. 2006 Oct;28(5):450-6

Authors: T&#xFC;rk T, Saraç D, Saraç YS, Elekdağ-Türk S

The aim of this study was to determine the effectiveness of bonding brackets to ceramic restorations. Sixty feldspathic and 60 lithium disilicate ceramic specimens were randomly divided into six groups. Shear bond strength (SBS) and bond failure types were examined with six surface-conditioning methods: silane application to glazed surface, air particle abrasion (APA) with 25- and 50-microm aluminium trioxide (Al(2)O(3)), etching with 9.6 per cent hydrofluoric acid (HFA), and roughening with 40- and 63-microm diamond burs. Silane was applied to all roughened surfaces. Metal brackets were bonded with light cure composite, then stored in distilled water for 1 week and thermocycled (x500 at 5-55 degrees C for 30 seconds). The ceramic surfaces were examined with a stereomicroscope at a magnification of x10 to determine the amount of composite resin remaining using the adhesive remnant index. The lowest SBS values were obtained with HFA for feldspathic (5.39 MPa) and lithium disilicate (11.11 MPa) ceramics; these values were significantly different from those of the other groups. The highest SBS values were found with 63-microm diamond burs for feldspathic (26.38 MPa) and lithium disilicate (28.20 MPa) ceramics, and were not significantly different from 40-microm diamond burs for feldspathic and lithium disilicate ceramics (26.04 and 24.26 MPa, respectively). Roughening with 25- and 50-microm Al(2)O(3) particles showed modest SBS for lithium disilicate (22.60 and 26.15 MPa, respectively) and for feldspathic ceramics (17.90 and 14.66 MPa, respectively). Adhesive failures between the ceramic and composite resin were noted in all groups. Damage to the porcelain surfaces was not observed. The SBS values were above the optimal range, except for feldspathic ceramic treated with HFA and silane. With all surface-conditioning methods, lithium disilicate ceramic displayed higher SBS than feldspathic ceramic.

PMID: 16772317 [PubMed - indexed for MEDLINE]

Facing the challenges of ceramic veneers.

J Am Dent Assoc. 2006 May;137(5):661-4

Authors: Christensen GJ

Ceramic veneers are extremely popular and have been used for many years. In spite of their phenomenal success, they offer numerous challenges during service. In this column, I have identified and discussed several degenerative situations commonly observed, and I have described methods of preventing or reducing the problems. When properly placed, ceramic veneers are among the most beautiful and long-lasting of all dental restorations.

PMID: 16739547 [PubMed - indexed for MEDLINE]

Fracture resistance of different partial-coverage ceramic molar restorations: An in vitro investigation.

J Am Dent Assoc. 2006 Apr;137(4):514-22

Authors: Stappert CF, Att W, Gerds T, Strub JR

BACKGROUND: The authors conducted a study to evaluate the influence of preparation design on reliability and fracture resistance of press-ceramic posterior partial-coverage restorations (PCRs) under fatigue. They compared the results for PCRs fabricated of a new press ceramic (IPS e.max Press-VP 1989/4, Ivoclar-Vivadent, Schaan, Liechtenstein) with results for ceramic inlays and unprepared molars. METHODS: The authors randomly divided 96 human upper molars into six equal groups. Control group NP specimens remained unprepared. Control group IN specimens received a mesio-occlusal-distal (MOD) inlay preparation. The test groups received PCR preparation designs based on group IN's inlay design, with additional cuspal reduction that increased from group to group. The authors fabricated 16 ceramic inlays and 64 PCRs of IPS e.max Press and luted them adhesively. All specimens underwent masticatory fatigue loading (1.2 million cycles, 1.6 hertz, 98 newtons), 5,300 thermal cycles and observation for fracture patterns. Afterward, the authors loaded all surviving specimens until fracture. RESULTS: No fractures occurred during the exposure to the masticatory simulation. After undergoing loading in a universal testing machine, the groups showed no significant differences in fracture strength values (P = .6026). Thus, the different preparation designs of the PCRs demonstrated no significant influence on the restorations' fracture resistance. The median failure loads ranged from 1,567 to 1,960 newtons. CONCLUSION: All-ceramic PCRs for molars made of IPS e.max Press were shown to be fracture-resistant, results comparable with those of natural unprepared teeth. CLINICAL IMPLICATIONS: When a posterior ceramic PCR is indicated, the clinician should perform a defect-oriented preparation that preserves tooth structure. Further clinical investigations are recommended to verify the authors' in vitro results.

PMID: 16637481 [PubMed - indexed for MEDLINE]

Is now the time to purchase an in-office CAD/CAM device?

J Am Dent Assoc. 2006 Feb;137(2):235-6, 238

Authors: Christensen GJ

In-office CAD/CAM is a reality. It allows fabrication of tooth-colored inlays and onlays, crowns and veneers in one appointment. It is especially well-suited to dentists who accomplish many single-tooth or single-quadrant restorations. As with any new technology, its cost is high, but using it can be financially feasible. Clinical and basic science investigations have resulted in positive findings on the concept. There are some significant advantages and several disadvantages. In-office CAD/CAM works well for many dentists, but practitioners should evaluate it carefully before accepting it, as it is not for everybody.

PMID: 16521390 [PubMed - indexed for MEDLINE]

Failures related to crowns and fixed partial dentures fabricated in a Nigerian dental school.

J Contemp Dent Pract. 2005 Nov 15;6(4):136-43

Authors: Oginni AO

The purpose of this investigation was to document the failure rate and length of service of crowns and fixed partial dentures (FPDs) fabricated in a Nigerian dental school. The reasons for failure of the initial restorations and their length of service were also ascertained. Also, the numbers of retainers, pontics, and the types of restoration were recorded. Poor esthetics was the most frequent cause of failure, 66 units (40.5%); followed by fracture, 58 units (35.6%); and dental caries, 25 units (15.4%). These outcomes were contrary to findings previously reported in studies from western countries where dental caries was principally responsible for failures (22.0% to 38.0% of cases). The resin-retained FPDs had the shortest mean years of service at 2.7 years, while the three-unit metal-ceramic FPDs had the greatest longevity at 8.6 years. The overall mean years of service for replaced restorations were 5.6 years. The study found a decrease in the mean years of service as the number of units in the fixed-fixed partial dentures increased. This is in sharp contrast to previous reports where no relationship existed between length of service and the number of units in a FPD.

PMID: 16299615 [PubMed - indexed for MEDLINE]

Immediate loading of two single tooth implants in the maxilla: preliminary results after one year.

J Contemp Dent Pract. 2005 Aug 15;6(3):148-57

Authors: Nuzzolese E

This clinical report describes the traumatic avulsion of the left maxillary central and lateral incisors with minimal tissue trauma, followed by placement of provisional restorations of two root-form implants in a 14-year old female patient. Ten days following the avulsion, implant therapy was performed with Summers osteotomes and flapless technique using a root-form 3i osseotite NT. Angulated abutments and acrylic provisional crowns were placed. No occlusal contact was detected. An impression was made 30 days after implant insertion and ceramic restorations were placed 3 months later. No significant soft tissue contraction was observed during the provisional period. The patient exhibited no clinical or radiologic complications for 8 months after loading. In carefully selected under-aged patients implant therapy and immediate loading in the anterior maxilla for traumatic tooth avulsion may prove to be valuable to avoid soft tissue contraction, alveolar bone resorption, and positive esthetic/psychological response.

PMID: 16127484 [PubMed - indexed for MEDLINE]

A review of the management of endodontically treated teeth. Post, core and the final restoration.

J Am Dent Assoc. 2005 May;136(5):611-9

Authors: Cheung W

BACKGROUND: The clinical decision as to whether an endodontically treated (ET) tooth requires a post and a crown poses a challenge to dental practitioners. The author conducted a review of the principles for the use of post and core and the newer materials such as ceramic and fiber-reinforced posts. TYPES of STUDIES REVIEWED: Using a MEDLINE search and resulting cross-references, the author selected original research articles and previous review articles on the topic of ET teeth, as well as that of post and core. RESULTS: The author reviewed the principles for the use of posts in terms of when it is necessary to use a post, different types of posts, various post materials and designs. He also reviewed the criteria and technique for post space preparation and post cementation. Finally, he discussed the principles of core buildup, as well as options for the final restorations. CLINICAL IMPLICATIONS: The author provides a review of the principles for the use of post and core, crowns and the different materials available today to help clinicians make a clinical decision based on sound evidence.

PMID: 15966648 [PubMed - indexed for MEDLINE]

Longevity of posterior tooth dental restorations.

J Am Dent Assoc. 2005 Feb;136(2):201-3

Authors: Christensen GJ

Several forms of restorative techniques are used for posterior teeth. They vary significantly in cost and longevity. The following restorative concepts are the most commonly used: amalgam, resin-based composite, PFM, cast gold alloy restorations and all-ceramic restorations. I suggest that patients be informed about the potential longevity of restorative treatment for posterior teeth as they make decisions about treatment for their oral restorative needs.

PMID: 15782524 [PubMed - indexed for MEDLINE]

[Short-term observation of gold-plating unprecious metal ceramic crown in restoring anterior tooth]

Shanghai Kou Qiang Yi Xue. 2005 Feb;14(1):11-3

Authors: Shi YL, Mu YZ, Zhao N, Ge SH

PURPOSE: To evaluate the short-term effect of gold-plating technique used in Ni-Cr metal ceramic crown in restoring anterior teeth. METHODS: 64 teeth from 38 cases were divided into two groups. Each group consisted of 32 teeth. All the teeth were restored with Ni-Cr metal ceramic crown. The restorations in group 1 had no treatment while those in group 2 were treated with gold-plating technique in the base metal alloy.Gingiva discoloration, bleeding on probing (BOP), plaque index (PLI) and sulcular bleeding index (SBI) were examined 1 and 12 months after restoration. Chi-square test and Wilcoxon rank sum test were used for statistical analysis. RESULTS: Gingiva discoloration was found in both groups after bonding. According to the percentage of gingival discoloration, there was no significant difference between group 1 and group 2 (12.5% vs 28.1%) (P>0.05). However, 12 months later, significant difference was found between the two groups (15.6% vs 37.5%)(P<0.05). According to PLI, BOP and SBI, there was no statistical difference between two groups (P>0.05). CONCLUSION: Gold-plating was a good method in solving the problem of gingival discoloration in unprecious metal ceramic crown.

PMID: 15747005 [PubMed - in process]

Threshold intensity factors as lower boundaries for crack propagation in ceramics.

Biomed Eng Online. 2004 Nov 17;3(1):41

Authors: Marx R, Jungwirth F, Walter PO

BACKGROUND: Slow crack growth can be described in a v (crack velocity) versus KI (stress intensity factor) diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip) induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. METHODS: We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly) disappeared. RESULTS: We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. CONCLUSION: The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness), which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials that have larger critical stress intensity factors.

PMID: 15548323 [PubMed - indexed for MEDLINE]

[Treatment of gingival recessions of teeth with ceramic full crown by autogenous connective tissue graft]

Shanghai Kou Qiang Yi Xue. 2004 Aug;13(4):343-5

Authors: Liu P

PURPOSE: The aim of this clinical study was to evaluate gingival recession of teeth with ceramic full crown treated with subepithelial connective tissue grafts. METHODS: In 20 systemically healthy, whose ages ranging from 31 to 58 years, 32 teeth with ceramic full crown developed gingival recession. Selection of gingival recession defects was based upon the following criteria: A minimum of 2 mm of root surface exposure in coronal-apical height. Miller class I and II recession. Interproximal and labial probing depth </=4 mm. No active caries or restorations on the tooth surfaces. Gingival recession were treated with subepithelial connective tissue grafts technique. RESULTS: The results indicated that subepithelial connective tissue grafts increased the height of gingival recession (GR) and gingival thickness (GT), the mean percentage of root coverage (RC) was 85.1%. CONCLUSION: These results suggest that subepithelial connective tissue grafts were able to successfully treat gingival recession defects. Moreover, the results has significant clinical benefit for aesthetics and treatment outcomes.

PMID: 15349685 [PubMed - indexed for MEDLINE]

Clinical performance of large, all-ceramic CAD/CAM-generated restorations after three years: a pilot study.

J Am Dent Assoc. 2004 May;135(5):605-12

Authors: Reich SM, Wichmann M, Rinne H, Shortall A

BACKGROUND: Adhesively luted all-ceramic restorations preserve and stabilize weakened tooth structure, but there is little published information about the clinical performance of large, all-ceramic restorations. METHODS: In this pilot study, the authors placed 58 large, single-tooth, all-ceramic restorations in 26 patients using a computer-aided design/computer-aided manufacturing, or CAD/CAM, system (CEREC 2, Sirona Dental Systems GmbH, Bensheim, Germany). They documented the maximum height of the restoration and remaining cementoenamel junction, or CEJ. In 21 cases, rubber dam isolation was not possible during adhesive luting. They re-evaluated the restorations after three years according to the U.S. Public Health Service criteria. RESULTS: After three years, the authors rated 56 (97 percent) of the 58 restorations as Bravo or better in regard to marginal integrity, secondary caries (four could not be rated), discoloration and anatomical form. One restoration was rated as Charlie because of poor marginal integrity, and one restoration had to be replaced owing to a bulk fracture. The authors rated the adequacy of proximal contact and occlusal relationships as acceptable-to-good for all restorations. Neither the extent of the remaining enamel at the cavity margin nor application of a rubber dam had any statistically significant influence (chi2 test, P > .05) on the clinical performance of the restorations after three years. CONCLUSIONS: At the three-year recall appointment, the authors found that the adhesively luted all-ceramic restorations had successfully repaired large coronal defects, irrespective of the cavity margin location (that is, coronal or apical to the CEJ). CLINICAL IMPLICATIONS: Tooth-colored, all-ceramic CAD/CAM-generated restorations are an alternative to conventional restorations if large coronal defects need to be treated.

PMID: 15202752 [PubMed - indexed for MEDLINE]

Informatics challenges in tissue engineering and biomaterials.

Adv Dent Res. 2003 Dec;17:49-54

Authors: Rekow D

Both tissue engineering and biomaterials have made tremendous strides recently, yet major questions remain unanswered. Tissue-engineered products have come to the market; others are in development. A fundamental issue that informatics could address for tissue engineering is to describe and to predict the cascade of biochemical and cellular reactions that occur as a function of time and implant material: surface texture, microporosity; pore size, density, and connectivity; and three-dimensional configuration. Behavior of ceramics, a subset of tissue-engineering scaffold materials and a mainstay of dental restorations, has been studied extensively for very thin layers and for thicknesses greater than 2 mm. Until recently, little has been known about dentally relevant thickness of 1-2 mm. Results have been surprising and are continuing to develop. Still, at least one fundamental question remains that could be addressed by informatics techniques: Where, along the spectrum of flat-polished material to 10-year clinical in vivo study, can we test to predict clinical performance of all-ceramic crowns accurately?

PMID: 15126207 [PubMed - indexed for MEDLINE]

Effect of surface roughness on flexural strength of veneer ceramics.

J Dent Res. 2003 Dec;82(12):972-5

Authors: Fischer H, Sch&#xE4;fer M, Marx R

The strength of ceramic restorations depends on the occlusal surface roughness of the veneering porcelain, which is influenced by the final preparation. The hypothesis of the study was that roughnesses below a critical microscopic defect size--based only on fracture mechanics considerations--also affect flexural strength. The bending failure stress was evaluated on standard specimens of 4 veneer ceramics with 4 different surfaces of defined roughnesses, respectively. A linear correlation was found between roughness and failure stress. A "roughness-free" failure stress value was predicted for each tested material. This theoretical value can represent the "true" strength of the respective ceramic material. We conclude from our results that the final preparation of a ceramic restoration is critical to the strength of the material, and that ceramic veneering materials can be compared more objectively with respect to their strength by means of roughness-free strength values.

PMID: 14630897 [PubMed - indexed for MEDLINE]

The confusing array of tooth-colored crowns.

J Am Dent Assoc. 2003 Sep;134(9):1253-5

Authors: Christensen GJ

The venerable PFM crown or fixed prosthesis still dominates the tooth-colored restoration market. However, use of PFMs is declining slightly, as the many new all-ceramic and resin-based composite crowns and fixed-prosthesis products flood the market. Several situations may indicate the use of materials other than PFM. They include patients requiring a high level of esthetic acceptability, patients with proven or perceived allergies to the metals used in dentistry and bruxing or clenching patients with metal allergies or desire to eliminate metal from their mouths. PFM restorations have been proven during 40 years of successful use. They provide acceptable esthetics for most situations, minimal fracture during service, proven ability to serve in multiple-unit situations and excellent fit, and the profession has detailed knowledge of these restorations' advantages, disadvantages and physical characteristics. PFM restorations have only a few well-known negative characteristics. Be cautious as you elect to move from the reliability and positive history of PFM to relatively unknown types of restorations.

PMID: 14528998 [PubMed - indexed for MEDLINE]

Direct and indirect restorative materials.

J Am Dent Assoc. 2003 Apr;134(4):463-72

Authors:

BACKGROUND: In recent years, dentistry has benefited from a marked increase in the development of esthetic materials, including ceramic and plastic compounds. But the advent of these new materials has not eliminated the usefulness of more traditional restorative materials such as gold, base metal alloys and dental amalgam. OVERVIEW: This report outlines important features of direct and indirect restoratives, with an emphasis on the safety and efficacy of each material. CONCLUSIONS AND PRACTICE IMPLICATIONS: This article was developed to help dentists explain to their patients the relative pros and cons of various materials used in dental restorations, which include fillings, crowns, bridges and inlays. The weight of the scientific evidence indicates that all of these materials are safe and effective for their intended use. Patients, in consultation with their dentists, are free to choose the most appropriate among them for their particular needs.

PMID: 12733780 [PubMed - indexed for MEDLINE]

Clinical application and effective assessment of cerinate porcelain laminate veneers.

Chin Med J (Engl). 2002 Nov;115(11):1739-40

Authors: Shang X, Mu Y

OBJECTIVE: To study the esthetic and long-term effectiveness of cerinate porcelain laminate veneers. METHODS: A total of 736 front teeth were restored with cerinate porcelain laminate veneers, which were then tested at different time points by clinical tracking observation and appraisal. RESULTS: The short and long term rates of effectiveness were 96.6% and 96.2%, respectively. There was no relationship between clinical effectiveness and the length of restoration time. The failure rate was higher in 18 - 30 years old patients and those with discolored teeth. The major clinical performance was fold fissure and deciduous of porcelain laminate veneers. CONCLUSIONS: Cerinate porcelain laminate veneers are an ideal choice for dental esthetic restorations because they are unnoticeable, stable, strong and require no excessive dental preparation.

PMID: 12609099 [PubMed - indexed for MEDLINE]

Shade-match perception of porcelain-fused-to-metal restorations: a comparison between dentist and patient.

J Am Dent Assoc. 2002 Sep;133(9):1220-5; quiz 1260-1

Authors: Al-Wahadni A, Ajlouni R, Al-Omari Q, Cobb D, Dawson D

BACKGROUND: Patient satisfaction with the shade match of restorations has not been appraised carefully in the dental literature. This study compared patients' and a prosthodontist's satisfaction with the shade o f existing porcelain-fused-to-metal, or PFM, restorations. METHODS: The authors selected a convenience sample of 212 patients for this study. Patients and a prosthodontist were asked independently, under standardized conditions, to express their satisfaction with the shade match of the patient's restoration. Kendall's tau-b statistic was used to measure the strength of the association between the shade satisfaction rating of the patient and that of the prosthodontist. The authors also examined patient satisfaction with respect to sex, treatment location and clinician. RESULTS: The prosthodontist was less satisfied than the patient with the shade match in a significant number of cases. The authors found no difference in patient satisfaction with respect to sex. They did find that patients were more satisfied with the shade match of restorations placed by a prosthodontist or placed under the supervision of a prosthodontist than they were with restorations placed by general practitioners. CONCLUSIONS: Patients were more satisfied with the shade match of their PFM restorations than was the prosthodontist. Patients also were more satisfied with restorations placed by a prosthodontist or placed under the supervision of a prosthodontist in a hospital or academic setting. Clinical Implications. Patient satisfaction with shade match is important when constructing or replacing a restoration, and the level of satisfaction might be different from that of the clinician. When selecting restoration shades, clinicians should take into consideration the opinions of their patients.

PMID: 12356253 [PubMed - indexed for MEDLINE]

Crowns and other extra-coronal restorations: porcelain laminate veneers.

Br Dent J. 2002 Jul 27;193(2):73-6, 79-82

Authors: Walls AW, Steele JG, Wassell RW

Porcelain veneers are resin-bonded to the underlying tooth and provide a conservative method of improving appearance or modifying contour, without resorting to a full coverage crown. The porcelain laminate veneer is now a frequently prescribed restoration for anterior teeth. The sums spent by the Dental Practice Board on this type of treatment increased from quarter of a million pounds in 1988/89 to over seven million in 1994/95, representing some 113,582 treatments. Since that time the number has stabilised at over 100,000 veneers prescribed each year. The objective of this paper is to give a practical guide on providing these restorations.

PMID: 12199127 [PubMed - indexed for MEDLINE]

Reliability and properties of ground Y-TZP-zirconia ceramics.

J Dent Res. 2002 Jul;81(7):487-91

Authors: Luthardt RG, Holzh&#xFC;ter M, Sandkuhl O, Herold V, Schnapp JD, Kuhlisch E, Walter M

Yttria-stabilized zirconia ceramics is a high-performance material with excellent biocompatibility and mechanical properties, which suggest its suitability for posterior fixed partial dentures. The hypothesis under examination is that the strength and reliability of Y-TZP zirconia ceramics are affected by the inner surface grinding of crowns, and vary with the grinding parameter. Flexural strength, surface roughness, and fracture toughness were determined on samples machined by face and peripheral grinding with varied feed velocities and cutting depths. Results have been compared with those on lapped samples. Analysis of variance and Weibull parameter were used for statistical analysis. It was found that inner surface grinding significantly reduces the strength and reliability of Y-TZP zirconia compared with the lapped control sample. Co-analysis of flexural strength, Weibull parameter, and fracture toughness showed counteracting effects of surface compressive stress and grinding-introduced surface flaws. In conclusion, grinding of Y-TZP needs to be optimized to achieve the CAD/CAM manufacture of all-ceramic restorations with improved strength and reliability.

PMID: 12161462 [PubMed - indexed for MEDLINE]

Has tooth structure been replaced?

J Am Dent Assoc. 2002 Jan;133(1):103-5

Authors: Christensen GJ

In my opinion, there is an obvious trend in the dental literature and in continuing education courses to promote overcutting teeth when preparing them for restorations. There are many reasons for overcutting. Some feel that there is a more optimum esthetic potential when the teeth are prepared more deeply, which is a debatable view. Others are using all-ceramic crowns or polymer crowns when other types of less radical crowns could be used. There also is a significant tendency to prepare teeth for crowns instead of for onlays or inlays, thereby removing more tooth structure than is necessary. High-speed dental air rotor or electric handpieces can cause inadvertent removal of more tooth structure than is necessary. Using large burs can overcut tooth structure, and teeth should be reversed.

PMID: 11811729 [PubMed - indexed for MEDLINE]

Fatigue of restorative materials.

Crit Rev Oral Biol Med. 2001;12(4):350-60

Authors: Baran G, Boberick K, McCool J

Failure due to fatigue manifests itself in dental prostheses and restorations as wear, fractured margins, delaminated coatings, and bulk fracture. Mechanisms responsible for fatigue-induced failure depend on material ductility: Brittle materials are susceptible to catastrophic failure, while ductile materials utilize their plasticity to reduce stress concentrations at the crack tip. Because of the expense associated with the replacement of failed restorations, there is a strong desire on the part of basic scientists and clinicians to evaluate the resistance of materials to fatigue in laboratory tests. Test variables include fatigue-loading mode and test environment, such as soaking in water. The outcome variable is typically fracture strength, and these data typically fit the Weibull distribution. Analysis of fatigue data permits predictive inferences to be made concerning the survival of structures fabricated from restorative materials under specified loading conditions. Although many dental-restorative materials are routinely evaluated, only limited use has been made of fatigue data collected in vitro: Wear of materials and the survival of porcelain restorations has been modeled by both fracture mechanics and probabilistic approaches. A need still exists for a clinical failure database and for the development of valid test methods for the evaluation of composite materials.

PMID: 11603506 [PubMed - indexed for MEDLINE]

Cast gold restorations. Has the esthetic dentistry pendulum swung too far?

J Am Dent Assoc. 2001 Jun;132(6):809-11

Authors: Christensen GJ

PMID: 11433863 [PubMed - indexed for MEDLINE]

The suitability of packable resin-based composites for posterior restorations.

J Am Dent Assoc. 2001 May;132(5):639-45

Authors: Manhart J, Chen HY, Hickel R

BACKGROUND: Packable composites, promoted for the restoration of stress-bearing posterior teeth, have captured clinicians' interest. METHODS: The authors tested three packable composites (Alert, Jeneric/Pentron; Solitaire, Heraeus Kulzer, Wehrheim, Germany; SureFil, Dentsply De Trey, Konstanz, Germany); a new packable organically modified ceramic, or ormocer (Definite, Degussa AG, Hanau, Germany); a hybrid composite (Tetric Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) and an ion-releasing composite (Ariston pHc, Ivoclar Vivadent, Schaan, Liechtenstein). They determined modulus of elasticity according to EN 24049:1993 of the European Committee for Standardization. They measured Vickers hardness using a 200-gram load for 40 seconds. To determine the materials' depth of cure, they used both a scraping method (International Standards Organization standard CD 4049:1997) and a hardness profiling method. RESULTS: The authors calculated means and standard deviations from 10 replications of each test and used one-way analysis of variance and post hoc Tukey tests (alpha = .05). The materials had significant differences (P < .001) in all characteristics. Solitaire had the significantly lowest elastic modulus and microhardness; Alert had the highest values for these characteristics. Ariston pHc exhibited the significantly lowest depth of cure. There was a significant correlation between the two methods of measuring depth of cure (r2 = 0.9945; P = .021). CONCLUSIONS: The material group of packable composites is rather inhomogeneous in terms of mechanical and physical data. Our data suggest that bulk curing of packable composites in deep cavities still is not recommendable. CLINICAL IMPLICATIONS: The clinician needs to select packable composites carefully, as it seems that not all of these materials quality for stress-loaded posterior restorations.

PMID: 11367968 [PubMed - indexed for MEDLINE]

Improvement of strength parameters of a leucite-reinforced glass ceramic by dual-ion exchange.

J Dent Res. 2001 Jan;80(1):336-9

Authors: Fischer H, Marx R

An innovative dual ion-exchange process can improve the limited strength and the scatter-in-strength of technical glasses. The objective of this study was to prove whether such a two-stage ion-exchange process can also improve the limited strength and the problematic scatter-in-strength of dental ceramic materials. The first exchange was done in KNO3 on a leucite-reinforced glass-ceramic material, the second exchange in 70 mol% KNO3, 30 mol% Na NO3 at different treatment times and temperatures. The dual-exchange process approximately doubled the Weibull strength. Moreover, the Weibull modulus showed a four-fold increase, i.e., the coefficients of variation were reduced from 18.3 to 4.7%. We conclude that the dual-exchange process may help significantly to increase the clinical reliability of glass-ceramic dental restorations, because the strength and the scatter-in-strength will be substantially improved by this treatment.

PMID: 11269725 [PubMed - indexed for MEDLINE]

Ask the expert. Will ceramic restorations be challenged in the future?

J Am Dent Assoc. 2001 Jan;132(1):46-7

Authors: Leinfelder KF

PMID: 11194398 [PubMed - indexed for MEDLINE]

Effects of whisker-to-silica ratio on the reinforcement of dental resin composites with silica-fused whiskers.

J Dent Res. 2000 Nov;79(11):1844-9

Authors: Xu HH, Quinn JB, Giuseppetti AA, Eichmiller FC

Resin composites need to be strengthened to improve their performance in large stress-bearing restorations. This study aimed to reinforce composites with whiskers and to investigate the effects of the whisker:silica ratio. It was hypothesized that changing the whisker-silica ratio would affect the whisker-matrix bonding and the filler's distribution, and hence alter the composite properties. Silica particles and whiskers were mixed at various whisker:silica mass ratios, thermally fused, and combined with a dental resin at filler mass fractions of 0-65%. Whisker:silica ratio and filler level had significant effects on composite properties. At 60% filler level, the silica composite (whisker:silica = 0:1) had a flexural strength (mean +/- SD; n = 6) of 104 +/- 21 MPa; that at a whisker:silica ratio of 1:0 was 74 +/- 36 MPa. However, that of the silica-fused whisker composite (whisker:silica = 5:1) was 210 +/- 14 MPa, compared with 109 +/- 23 MPa and 114 +/- 18 MPa of two prosthetic controls. Mixing silica with whiskers minimized whisker entanglement, improved filler distribution in the matrix, and facilitated whisker silanization and bonding to the matrix, thus resulting in substantially stronger composites.

PMID: 11145353 [PubMed - indexed for MEDLINE]

High-temperature X-ray diffraction measurement of sanidine thermal expansion.

J Dent Res. 2000 Aug;79(8):1590-5

Authors: Mackert JR, Twiggs SW, Williams AL

Dental porcelains that are designed to be fused to PFM (porcelain-fused-to-metal) alloys are formulated by their manufacturers to be closely matched in thermal expansion to these alloys. The high thermal expansion of the mineral leucite has been exploited to regulate porcelain expansion. Leucite, however, has been observed to convert to the sanidine polymorph of feldspar during certain heat treatments within the normal firing range of dental porcelain. The effects of this conversion on porcelain thermal expansion and porcelain-metal thermal compatibility have been uncertain, due to the paucity of published data on the thermal expansion of sanidine. The purpose of this study was to measure the thermal expansion of sanidine by high-temperature X-ray diffraction over the temperature range in which thermal mismatch stresses can develop in porcelain-fused-to-metal restorations, i.e., from room temperature to 700 degrees C. The lattice parameters a, b, c, and beta were determined from the d-spacings and hkl values of multiple reflections by means of a least-squares iteration. The dependence of each lattice parameter on temperature was determined via analysis of variance, and the coefficient of thermal expansion, alpha, was obtained from this analysis. The lattice parameters of sanidine at room temperature were determined to be: a = 0.8524 +/- 0.0015 nm, b = 1.3020 +/- 0.0004 nm, c = 0.7165 +/- 0.0002 nm, and beta = 116.02 degrees +/- 0.01 degree (mean +/- 95% confidence interval). The linear thermal expansion coefficient, a, over the range from room temperature to 700 degrees C was determined to be 4.1 x 10(-6) K(-1) +/- 0.6 x 10(6) K(-1) (mean +/- 95% confidence interval). Because the coefficient of thermal expansion for sanidine is substantially lower than that of leucite (the effective linear thermal coefficient of thermal expansion of leucite over the range of 25 degrees to 700 degrees C is 28 x 10(-6) K(-1)), the conversion of leucite to sanidine during porcelain heat treatments would produce a detrimental lowering of the porcelain thermal expansion.

PMID: 11023280 [PubMed - indexed for MEDLINE]

Using a modified subopaquing technique to treat highly discolored dentition.

J Am Dent Assoc. 2000 Jul;131(7):945-50

Authors: Okuda WH

BACKGROUND: The objective of esthetic dentistry is to treat diverse problems and achieve natural-appearing results. The author reviews the issues involved in the discoloration of human dentition and the concerns associated with current treatment for this problem. Understanding the proper use of materials in esthetic dentistry can result in a conservative, natural-appearing restoration. OVERVIEW: Dentition discoloration due to intrinsic staining can be a severe esthetic problem. Current treatment using crowns and highly opaque porcelain veneers has inherent disadvantages in regard to the final restorations. The author explores a subopaquing technique that allows for progressive lightening of highly stained teeth to create natural color depth in a conservative porcelain veneer procedure. CLINICAL IMPLICATIONS: In treating dental problems, the clinical practitioner looks for solutions that conserve tooth structure. To achieve natural-appearing esthetic results, it is important for the practitioner to be aware of technological advances in materials science as well as the proper use of esthetic dental techniques. Understanding the problems associated with dental discoloration and ways of correcting them will allow the practitioner to solve these moderate-to-severe esthetic problems on a consistent basis.

PMID: 10916333 [PubMed - indexed for MEDLINE]

Whisker-reinforced heat-cured dental resin composites: effects of filler level and heat-cure temperature and time.

J Dent Res. 2000 Jun;79(6):1392-7

Authors: Xu HH

Currently available dental resin composites are inadequate for use in large stress-bearing crown and multiple-unit restorations. The aim of this study was to reinforce heat-cured composites with ceramic whiskers. It was hypothesized that whiskers substantially strengthen heat-cured composites. It was further hypothesized that whisker filler level and heat-cure temperature and time significantly influence composite properties. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whiskers for improved retention in the matrix. The whisker filler mass fraction was varied from 0% to 79%, the heat-cure temperature from 80 degrees C to 180 degrees C, and cure time from 10 min to 24 hrs. Flexural strength, work-of-fracture, and fracture toughness of the composites were measured, and specimen fracture surfaces were examined with scanning electron microscopy. Filler level had a significant effect on composite properties. The whisker composite with 70% filler level had a flexural strength in MPa (mean +/- SD; n = 6) of 248 +/- 23, significantly higher than 120 +/- 16 of an inlay/onlay composite control and 123 +/- 21 of a prosthetic composite control (Tukey's multiple comparison test; family confidence coefficient = 0.95). Heat-cure time also played a significant role. At 120 degrees C, the strength of composite cured for 10 min was 178 +/- 17, lower than 236 +/- 14 of composite cured for 3 hrs. The strength of whisker composite did not degrade after water-aging for 100 d. In conclusion, heat-cured composites were substantially reinforced with whiskers. The reinforcement mechanisms appeared to be whiskers bridging and resisting cracks. The strength and fracture toughness of whisker composite were nearly twice those of currently available inlay/onlay and prosthetic composites.

PMID: 10890718 [PubMed - indexed for MEDLINE]

Lifetime-limiting strength degradation from contact fatigue in dental ceramics.

J Dent Res. 2000 Feb;79(2):722-31

Authors: Jung YG, Peterson IM, Kim DK, Lawn BR

The hypothesis under examination in this paper is that the lifetimes of dental restorations are limited by the accumulation of contact damage during oral function; and, moreover, that strengths of dental ceramics are significantly lower after multi-cycle loading than after single-cycle loading. Accordingly, indentation damage and associated strength degradation from multi-cycle contacts with spherical indenters in water are evaluated in four dental ceramics: "aesthetic" ceramics-porcelain and micaceous glass-ceramic (MGC), and "structural" ceramics-glass-infiltrated alumina and yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). At large numbers of contact cycles, all materials show an abrupt transition in damage mode, consisting of strongly enhanced damage inside the contact area and attendant initiation of radial cracks outside. This transition in damage mode is not observed in comparative static loading tests, attesting to a strong mechanical component in the fatigue mechanism. Radial cracks, once formed, lead to rapid degradation in strength properties, signaling the end of the useful lifetime of the material. Strength degradation from multi-cycle contacts is examined in the test materials, after indentation at loads from 200 to 3000 N up to 10(6) cycles. Degradation occurs in the porcelain and MGC after approximately 10(4) cycles at loads as low as 200 N; comparable degradation in the alumina and Y-TZP requires loads higher than 500 N, well above the clinically significant range.

PMID: 10728973 [PubMed - indexed for MEDLINE]

In vitro wear device for determining posterior composite wear.

J Am Dent Assoc. 1999 Sep;130(9):1347-53

Authors: Leinfelder KF, Suzuki S

BACKGROUND: An in vitro device has been developed to predict the long-term clinical performance of posterior composite resins. In contrast to most systems, it is based on three-bodied wear--the type of wear generated by food bolus during mastication. METHODS: The authors wear-tested two groups of materials that included posterior composite resins, a castable ceramic, an amalgam and an unsalinated composite resin. After the wear-testing device concluded 400,000 cycles, the authors evaluated replicas of restoration surfaces for material loss. They used scanning electron microscopy to determine the mechanism of wear. RESULTS: The authors detected considerable differences in wear among the various materials included in the study. All of the differences, however, fell within the range of results obtained from the positive and negative controls (unsilanated composite resin and ceramic, respectively). A comparison of the in vitro wear values with the wear values obtained from a series of ongoing clinical studies at the same institution revealed a high level of agreement. Furthermore, replicas of the laboratory-tested composite resin samples revealed the same wear patterns as those generated from clinical restorations. The variation coefficients for the in vitro data generally did not exceed 5 percent, whereas those for the clinical data commonly averaged 20 percent. CONCLUSIONS: Based on the results of this study, the authors conclude that the in vitro testing device is reliably capable of predicting long-term clinical wear values. The results obtained after 92 hours of wear testing correlated closely with those obtained after three years of clinical testing. CLINICAL IMPLICATIONS: Long-term clinical studies are both time-consuming and expensive. Reliable in vitro wear-testing techniques allow manufacturers to develop or modify composite resin systems in considerably shorter periods.

PMID: 10492543 [PubMed - indexed for MEDLINE]

Dental composite resins containing silica-fused ceramic single-crystalline whiskers with various filler levels.

J Dent Res. 1999 Jul;78(7):1304-11

Authors: Xu HH

Currently available direct-filling composite resins are susceptible to fracture and hence are not recommended for use in large stress-bearing posterior restorations involving cusps. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to use ceramic single-crystalline whiskers as fillers to reinforce composites, and to investigate the effect of whisker filler level on composite properties. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whiskers, thereby improving retention in the matrix. The composite flexural strength, elastic modulus, hardness, and degree of polymerization conversion were measured as a function of whisker filler mass fraction, which ranged from 0% to 70%. Selected composites were polished simulating clinical procedures, and the surface roughness was measured with profilometry. The whisker composite with a filler mass fraction of 55% had a flexural strength (mean +/- SD; n = 6) of 196+/-10 MPa, significantly higher than 83+/-14 MPa of a microfill and 120+/-16 MPa of a hybrid composite control (family confidence coefficient = 0.95; Tukey's multiple comparison). The composite modulus and hardness increased monotonically with filler level. The flexural strength first increased, then plateaued with increasing filler level. The degree of conversion decreased with increasing filler level. The whisker composite had a polished surface roughness similar to that of a conventional hybrid composite (p>0.1; Student's t). To conclude, ceramic whisker reinforcement can significantly improve the mechanical properties of composite resins; the whisker filler level plays a key role in determining composite properties; and the reinforcement mechanisms appear to be crack pinning by whiskers and friction from whisker pullout resisting crack propagation.

PMID: 10403457 [PubMed - indexed for MEDLINE]

Damage modes in dental layer structures.

J Dent Res. 1999 Apr;78(4):887-97

Authors: Jung YG, Wuttiphan S, Peterson IM, Lawn BR

Natural teeth (enamel/dentin) and most restorations are essentially layered structures. This study examines the hypothesis that coating thickness and coating/substrate mismatch are key factors in the determination of contact-induced damage in clinically relevant bilayer composites. Accordingly, we study crack patterns in two model "coating/substrate" bilayer systems conceived to simulate crown and tooth structures, at opposite extremes of elastic/plastic mismatch: porcelain on glass-infiltrated alumina ("soft/hard"); and glass-ceramic on resin composite ("hard/soft"). Hertzian contacts are used to investigate the evolution of fracture damage in the coating layers, as functions of contact load and coating thickness. The crack patterns differ radically in the two bilayer systems: In the porcelain coatings, cone cracks initiate at the coating top surface; in the glass-ceramic coatings, cone cracks again initiate at the top surface, but additional, upward-extending transverse cracks initiate at the internal coating/substrate interface, with the latter dominant. The substrate is thereby shown to have a profound influence on the damage evolution to ultimate failure in the bilayer systems. However, the cracks are highly stabilized in both systems, with wide ranges between the loads to initiate first cracking and to cause final failure, implying damage-tolerant structures. Finite element modeling is used to evaluate the tensile stresses responsible for the different crack types. The clinical relevance of these observations is considered.

PMID: 10326733 [PubMed - indexed for MEDLINE]

Intracoronal and extracoronal tooth restorations 1999.

J Am Dent Assoc. 1999 Apr;130(4):557-60

Authors: Christensen GJ

PMID: 10203907 [PubMed - indexed for MEDLINE]

Ceramic whisker reinforcement of dental resin composites.

J Dent Res. 1999 Feb;78(2):706-12

Authors: Xu HH, Martin TA, Antonucci JM, Eichmiller FC

Resin composites currently available are not suitable for use as large stress-bearing posterior restorations involving cusps due to their tendencies toward excessive fracture and wear. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to reinforce dental resins with ceramic single-crystalline whiskers of elongated shapes that possess extremely high strength. A novel method was developed that consisted of fusing silicate glass particles onto the surfaces of individual whiskers for a two-fold benefit: (1) to facilitate silanization regardless of whisker composition; and (2) to enhance whisker retention in the matrix by providing rougher whisker surfaces. Silicon nitride whiskers, with an average diameter of 0.4 microm and length of 5 microm, were coated by the fusion of silica particles 0.04 microm in size to the whisker surface at temperatures ranging from 650 degrees C to 1000 degrees C. The coated whiskers were silanized and manually blended with resins by spatulation. Flexural, fracture toughness, and indentation tests were carried out for evaluation of the properties of the whisker-reinforced composites in comparison with conventional composites. A two-fold increase in strength and toughness was achieved in the whisker-reinforced composite, together with a substantially enhanced resistance to contact damage and microcracking. The highest flexural strength (195+/-8 MPa) and fracture toughness (2.1+/-0.3 MPa x m(1/2)) occurred in a composite reinforced with a whisker-silica mixture at whisker:silica mass ratio of 2:1 fused at 800 degrees C. To conclude, the strength, toughness, and contact damage resistance of dental resin composites can be substantially improved by reinforcement with fillers of ceramic whiskers fused with silica glass particles.

PMID: 10029470 [PubMed - indexed for MEDLINE]

Replacing posterior teeth with freestanding implants: four-year prosthodontic results of a prospective study.

J Am Dent Assoc. 1998 Aug;129(8):1097-102

Authors: Muftu A, Chapman RJ

This article presents prospective four-year prosthetic results of the placement of 432 posterior freestanding, conventionally cemented prosthetic tooth implants in posterior edentulous spaces using the Bicon Dental Implants system (Bicon Dental Implants). Over four years, 0.74 percent of the abutments loosened, 0.5 percent of the abutments fractured, and 2.47 percent of the crowns experienced porcelain fracture, (all porcelain fractures occurred at time of placement). This low rate of problems appears to make free-standing single-tooth implant restorations a reliable solution to treating posterior edentulism.

PMID: 9715010 [PubMed - indexed for MEDLINE]

Mechanical characterization of dental ceramics by hertzian contacts.

J Dent Res. 1998 Apr;77(4):589-602

Authors: Peterson IM, Pajares A, Lawn BR, Thompson VP, Rekow ED

Hertzian indentation testing is proposed as a protocol for evaluating the role of microstructure in the mechanical response of dental ceramics. A major advantage of Hertzian indentation over more traditional fracture-testing methodologies is that it emulates the loading conditions experienced by dental restorations: Clinical variables (masticatory force and cuspal curvature) identify closely with Hertzian variables (contact load and sphere radius). In this paper, Hertzian responses on four generic dental ceramics systems-micaceous glass-ceramics, glass-infiltrated alumina, feldspathic porcelain, and transformable zirconiaare presented as case studies. Ceramographic sectioning by means of a "bonded-interface" technique provides new information on the contact damage modes. Two distinct modes are observed: "brittle" mode, classic macroscopic fracture outside the contact (ring, or cone cracks), driven by tensile stresses; and "quasi-plastic" mode, a relatively new kind of deformation below the contact (diffuse microdamage), driven by shear stresses. A progressive transition from the first to the second mode with increasing microstructural heterogeneity is observed. The degree of quasi-plasticity is readily apparent as deviations from ideal linear elastic responses on indentation stress-strain curves. Plots of threshold loads for the initiation of both fracture and deformation modes as a function of indenter radius constitute "damage maps" for the evaluation of prospective restoration damage under typical masticatory conditions. The degree of damage in both modes evolves progressively with load above the thresholds. Strength tests on indented specimens quantify sustainable stress levels on restoration materials after damage. The most brittle responses are observed in the fine glass-ceramics and porcelain; conversely, the most quasi-plastic responses are observed in the coarse glass-ceramics and zirconia; the medium glass-ceramics and alumina exhibit intermediate responses. Implications of the results in relation to future materials characterization, selection, and design are considered in the clinical context.

PMID: 9539462 [PubMed - indexed for MEDLINE]

Effect of ion exchange on the microstructure, strength, and thermal expansion behavior of a leucite-reinforced porcelain.

J Dent Res. 1998 Apr;77(4):583-8

Authors: Denry IL, Holloway JA, Rosenstiel SF

Leucite (KAlSi2O6) is used as a reinforcing agent in some porcelains for all-ceramic restorations; however, it increases their coefficients of thermal expansion, imposing constraints on the processing of the material. The potassium ions in leucite are exchangeable for rubidium or cesium ions, leading to rubidium leucite or cesium leucite (pollucite). Both rubidium leucite and pollucite exhibit a lower coefficient of thermal expansion and inversion temperature than leucite. The purpose of this study was to evaluate the effects of rubidium and cesium leucites on thermal expansion, microstructure, crack deflection patterns, and flexural strength of a leucite-reinforced porcelain. A dental porcelain powder was mixed with rubidium or cesium nitrate and heat-treated. Porcelain bars (n = 3) and discs (n = 15) were made with the exchanged powders. X-ray diffraction analyses were performed before and after bars were fired. Controls were made of untreated Optec HSP porcelain powder, formed into bars and disks, and baked following manufacturer's recommendations. The density of all specimens was determined by Archimedes' method. The thermal expansion behavior of the materials was measured by dilatometry. The microstructure and Vickers indentation crack patterns were investigated by scanning electron microscopy. X-ray diffraction showed that after ion-exchange and firing, leucite transformed into either tetragonal rubidium leucite or cubic cesium leucite. The mean coefficient of thermal contraction (550 to 50 degrees C) was significantly (p < 0.003) greater for the control material, followed by the rubidium-exchanged material, and lowest for the cesium-exchanged material. Crack pattern analyses revealed that the cesium-exchanged material exhibited a significantly lower number of crack deflections compared with those in the two other materials (p < 0.001). The microstructure of the two exchanged porcelain materials was dense, with well-dispersed small crystals as well as larger rubidium or cesium leucite crystals. The mean flexural strength of the rubidium-exchanged material was significantly higher than those of the other materials, which were not significantly different. It was concluded that the thermal expansion of leucite-reinforced porcelain can be lowered by ion-exchange, which also modifies the microstructure, crack deflection patterns, and flexural strength of the material.

PMID: 9539461 [PubMed - indexed for MEDLINE]