[Long-term observation of 920 porcelain fused to metal prostheses]

Shanghai Kou Qiang Yi Xue. 2006 Oct;15(5):490-2

Authors: Jiang YL, Sun J, Weng WM, Zhang FQ

PURPOSE: To evaluate the long-term clinical results of porcelain fused to metal prostheses. METHODS: Since January 1995, 920 porcelain fused to metal prostheses were fabricated. The long-term outcome were evaluated according to the condition of the prosthese, abutment and the periodontal tissue in the respects of successful rate and causes of failure. RESULTS: 74 patients were found to be during the follow up period, including 36 anterior crowns (46 units), 18 posterior crowns (22 units), 12 percentage of anterior bridges and 8 posterior bridges. The overall failure rate was 8.04%, 4.84% for crown, 8.77% for bridge. The failed prostheses was 5.39%. CONCLUSIONS: Porcelain fused to metal prostheses is an ideal method for restoration. The standard process both for the clinician and the technician must be obeyed to improve the success rate.

PMID: 17348221 [PubMed - in process]

[Clinical use of glassfiber-reinforced composites post and core]

Shanghai Kou Qiang Yi Xue. 2006 Feb;15(1):101-3

Authors: Han YM, Dong Y, Xu XJ

PURPOSE: To evaluate the usefulness of glassfiber-reinforced composites post and core in restoration of serious dentine defects. METHODS: 59 cases, 87 teeth with serious dentine defects were selected. Glassfiber was used as the reinforcement frame and glassfiber-reinforced composites post and core were fabricated. Then the defected teeth were restored with porcelain-fused-metal crown. All patients were asked to re-visit 3 months, 6 months and 12 months after treatments. RESULTS: 2 cases (3 teeth) were out of visit 12 months after treatments. The restorations of other 57 cases (84 teeth) were firm and the occlusion was rebuilt satisfactorily during 12 months' clinical observations. Only one crown restoration was found to be loose. But the post and core was found to be still firm after the crown was taken off. Satisfactory results were achieved after being restored again. No dentine fracture was found in all restored teeth. The clinical results were satisfactory. CONCLUSION: Glassfiber-reinforced composite can be considered as a good material to fabricate post and core due to its high-strength, aesthetics and convenient operation.

PMID: 16525622 [PubMed - in process]

[Application of Bränemark system's multi-unit abutment: report of 37 consecutive cases]

Shanghai Kou Qiang Yi Xue. 2005 Apr;14(2):120-2

Authors: Yu YC, Gu ZY, Wang Q, Gong YM, Bi W, Ruan H

PURPOSE: To evaluate the short-term clinical effect and advantages of Bränemark system's multi-unit abutment used for standard or MK III implants supported fixed prosthodontics. METHODS: Routine clinical examinations and preparations, including panoramic tomography, periapical radiograph and surgical guide plate, were performed in 37 cases with multiple lost teeth. A total of 117 Bränemark system's implants were placed using a two-stage surgical approach. Multi-unit abutment connection was performed 3-6 months after implant installation. All superstructure prosthetic appliances were porcelain-fused-to-golden metal bridges. RESULTS: The follow-up period for the implants was 12 to 24 months. The total survival rate was 95.7%. Two implants were lost at second-stage surgery (the survival rate was 98.29% for first-stage), and 3 implants were lost after loading (the survival rate was 97.43% for second-stage). The other 112 implants function uneventfully. There were no bone loss around implants, no abutment and gold cylinder screw loosen. CONCLUSIONS: The multi-unit abutment, on basis of collecting all the merits of the traditional abutment, was further designed in a simplified way, which not only expands its clinical application, operate easily, but also enhance its whole superstructure. It is more suitable for implant supported fixed prosthodontics with high success rate and more advantages than the traditional abutment.

PMID: 15886831 [PubMed - in process]

[Effect of staining method and sintering temperature on the color of porcelain-fused-to-metal restorations]

Shanghai Kou Qiang Yi Xue. 2004 Dec;13(6):553-6

Authors: Wang Y, Yan WH, Zhang XC, Huang Y, Shen LH

PURPOSE: To investigate the effect of staining method and sintering temperature on the color of porcelain-fused-metal restorations. METHODS: 40 cylindrical stained porcelain-metal specimens of 15 mm in diameter and 6 mm in height were fabricated with customized mould, consisting of 2 mm Ni-Cr metal, 1 mm opaque porcelain, 2 mm dentine porcelain and 1 mm enamel porcelain. The specimens were prepared by 5 techniques, 8 for each group. Group A: internal staining, Group B: external staining, 900 degrees centigrade sintering temperature was used in both A and B group; Group C to E: external staining, with the sintering temperature of 880 degrees centigrade, 900 degrees centigrade and 920 degrees centigrade respectively. Sofu A2 porcelain and Sofu 44 stain system were used for the study. Using standard white plate as a reference, colors (L*,a*,b* coordinates) of the specimens were measured with a computerized colorimeter. Student's t test and one way ANOVA were used to analyze the data. RESULTS: DeltaE, b* and Delta C(ab)* of Group B (external staining) and group A (internal staining) were 43.72 +/- 2.99/26.51 +/- 1.64/31.31 +/- 2.48 and 39.71 +/- 1.78/23.69 +/- 0.36/26.55 +/- 2.16, respectively. The values of the former group were significantly higher than that of the latter (P < 0.05); For Group C to E, there were no significant differences in all the color parameters. CONCLUSIONS: Staining method has a significant effect on the color parameters of porcelain-fused-to-metal restorations; For external staining, within the clinically-used range, changing the sintering temperature does not have an obvious effect on the color.

PMID: 15619704 [PubMed - in process]

[The test of metal-ceramic bonding strength among three ceramic alloies]

Shanghai Kou Qiang Yi Xue. 2004 Jun;13(3):186-8

Authors: Ding WS, Wang D, Lan J, Du ZX, Liu WX

PURPOSE: To compare the metal-ceramic bonding strength of different ceramic alloies. METHODS: 30 wax sheets were divided into 6 groups at random.Each group included 5 sheets.After being invested conventionally with Bellaves SH,the samples were casted and fused with porcelain.The metal-ceramic bonding strength was evaluated. RESULTS: The highest bonding strength was found in Bio Herador N alloy, and then in TILITE alloy and Heraenium S alloy respectively. Bio Herador N alloy and TILITE alloy all had significant differences of the bonding strength before and after treatment (P<0.05). There was no significant differences in the bonding strength of the Heraenium S alloy after treatment (P>0.05). CONCLUSION: The bonding strength of precious metal-ceramic was higher than that of non-precious metal-ceramic.Pre-oxygen treatment can improve the metal-ceramic bonding strength of Bio Herador N alloy and TILITE alloy,but it had no effect on the metal-ceramic bonding strength of the Heraenium S alloy.

PMID: 15269855 [PubMed - indexed for MEDLINE]

[The use of computer-aided colorimeter in porcelain-fused-to-metal (PFM) crowns among patients with special colored teeth]

Shanghai Kou Qiang Yi Xue. 2004 Feb;13(1):76-7

Authors: Fu YF, Weng WM

PURPOSE: To evaluate the roll of ShadeEye-NCC, a computer-aided colorimeter, in Porcelain-Fused-to-Metal crowns among patients with special colored Teeth. METHODS: The first step was to choose the proper patients. The next was to use the colorimeter to measure the base shade of tooth and fabricate the PFM crowns according to the recipe given by the colorimeter. At last, the effects of the PFM crowns were evaluated subjectively by patients and doctor. RESULTS: The satisfaction rates of patients and doctor were 83.7% and 81.4% respectively, there was no significant difference between the two rates. CONCLUSIONS: The computer-aided colorimeter can offer good base shade recipe for fabricating PFM crowns of patients with special colored teeth.

PMID: 15007490 [PubMed - indexed for MEDLINE]

[A study on the colour of natural tooth and porcelain fused to metal crown]

Shanghai Kou Qiang Yi Xue. 2001 Mar;10(1):83-4

Authors: Yang H, Zhang SX, Xie YB, Wu ZP, Zhu XF, Xu YB

PMID: 14994094 [PubMed]

[Causes and prevention of "black line" in porcelain-fused-to-metal crown margins]

Shanghai Kou Qiang Yi Xue. 2003 Dec;12(6):460-2

Authors: Dong ZJ, Xu K

PMID: 14966592 [PubMed - indexed for MEDLINE]

Repairing fractured porcelain-fused-to-metal bridge pontics.

J Am Dent Assoc. 2003 Aug;134(8):1097-100

Authors: Quarnstrom FC, Aw TC

PMID: 12956351 [PubMed - indexed for MEDLINE]

Long-term water-aging of whisker-reinforced polymer-matrix composites.

J Dent Res. 2003 Jan;82(1):48-52

Authors: Xu HH

Long-term water exposure may degrade polymer-matrix composites. This study investigated the water-aging of whisker composites. It was hypothesized that whiskers would provide stable and substantial reinforcement, and that whisker type would affect water-aging resistance. Silica-fused Si(3)N(4) and SiC whiskers were incorporated into a resin. The specimens were tested by three-point flexure and nano-indentation vs. water-aging for 1 to 730 days. After 730 days, SiC composite had a strength (mean +/- SD; n = 6) of 185 +/- 33 MPa, similar to 146 +/- 44 MPa for Si(3)N(4) composite (p = 0.064); both were significantly higher than 67 +/- 23 MPa for an inlay/onlay control (p < 0.001). Compared with 1 day, the strength of the SiC composite showed no decrease, while that of the Si(3)N(4) composite decreased. The decrease was due to whisker weakening rather than to resin degradation or interface breakdown. Whisker composites also had higher moduli than the controls. In conclusion, silica-fused whiskers bonded to polymer matrix and resisted long-term water attack, resulting in much stronger composites than the controls after water-aging.

PMID: 12508045 [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]

Fusing of dental ceramics to titanium.

J Dent Res. 2001 Mar;80(3):848-54

Authors: K&#xF6;n&#xF6;nen M, Kivilahti J

Titanium is known as a useful biometal because of its good biocompatibility and mechanical performance. However, titanium is chemically an exceptional metal, reacting strongly with gaseous elements like oxygen, hydrogen, and nitrogen and also dissolving them extensively. This high reactivity causes problems, for example, when dental ceramics are fused to titanium. Commercial ceramic-titanium systems are increasingly used in prosthetic dentistry, but little is known about the microstructure and composition of the system. Better understanding of chemical reactions between ceramics and titanium is necessary if mechanically more compatible ceramic-titanium bonds are to be developed. This review deals with titanium as a metal, titanium's affinity for nonmetallic elements (especially oxygen), and reactions with other elements. Different aspects are discussed relative to the fusing of dental ceramics to titanium.

PMID: 11379883 [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]

Immediate placement of implants in extraction sites of maxillary impacted canines.

J Am Dent Assoc. 1999 Dec;130(12):1767-70

Authors: Mazor Z, Peleg M, Redlich M

BACKGROUND: Treatment of asymptomatic impacted maxillary canines in adults is inevitable when primary canine becomes lost through extraction or exfoliation or when the impacted tooth becomes symptomatic. Treatment alternatives include an orthodontic procedure to bring the unerupted tooth to the dental arch or prosthetic replacement of the missing tooth. The authors describe an alternative treatment that involves immediate placement of implants into extraction sockets of the teeth. CASE DESCRIPTION: A patient with bilateral palatally impacted upper canines chose to have the unerupted teeth removed and replaced with implants and crowns. Two hydroxyapatite cylindrical implants were inserted through the alveolar ridge into the extraction sites. The unfilled areas in the extraction sites, around the dental implants, were packed and covered with demineralized freeze-dried bone allograft in conjunction with a collagen membrane barrier. Six months after implantation, computed tomography revealed complete osseous fill of the extraction defects and no bone loss around the implants. The implants were uncovered, and porcelain-fused-to-metal restorations were fabricated and placed. CLINICAL IMPLICATIONS: This treatment modality avoids the need for conventional preparation of teeth as part of prosthetic reconstruction or prolonged orthodontic treatment aimed at bringing the impacted canine to the dental arch. Combining the implantation with bone augmentation preserved the alveolar bone and shortened the treatment period.

PMID: 10599180 [PubMed - indexed for MEDLINE]

Porcelain-fused-to-metal vs. nonmetal crowns.

J Am Dent Assoc. 1999 Mar;130(3):409-11

Authors: Christensen GJ

PMID: 10085664 [PubMed - indexed for MEDLINE]

Cementing porcelain-fused-to-metal crowns.

J Am Dent Assoc. 1997 Aug;128(8):1165-7

Authors: Christensen GJ

PMID: 9260430 [PubMed - indexed for MEDLINE]

[Three dimensional finite element analysis of margin configurations and stresses of porcelain fused to metal crowns]

Shanghai Kou Qiang Yi Xue. 1997 Mar;6(1):14-6

Authors: Chen LP, Zhang FQ, Xiong HG

As to using the method of three dimensional finite element,this study has analyzed the stress distribution of the porcelain fused to metal crowns with three different labial margin configurations under the forces from diverse direction.The results showed that the chamber margins exhibited fewer tensile stresses than the shoulder or shoulder with a bevel margins.The labial margin exhibited more tensil stresses when the incisal edge of the crown was loaded with labial forces.so,we provide the mechanical basis for the conclusions as follows: (1)The labial chamber margin is preferable to shoulder or shoulder with a bevel margin. (2)The porcelain may fracture when the incisal edge of porcelain fused to metal crown is loaded with labial forces.

PMID: 15159958 [PubMed - as supplied by publisher]

Microcracks in dental porcelain and their behavior during multiple firing.

J Dent Res. 1996 Jul;75(7):1484-90

Authors: Mackert JR, Williams AL

Dental porcelains rely on the high-thermal-expansion mineral leucite to elevate their bulk thermal expansion to levels compatible with dental PFM alloys. The microcracks that form around these leucite particles when cooled during porcelain manufacture are a potential source of change in bulk porcelain thermal expansion during fabrication of porcelain-fused-to-metal crowns and bridges. The purpose of the present study was to determine whether multiple firings of commercial dental porcelains could produce changes in microcrack density. Specimens of six commercial porcelains and the "Component No. 1" of the Weinstein patent were fabricated and subjected to 1, 2, 4, 8, and 16 firings. The microcrack densities were determined by quantitative stereology, whereby intersections of microcracks were counted with a test grid. The microcrack data were subjected to linear regression analysis and analysis of variance. The microcrack densities of four of the six porcelains and the Component No. 1 frit were not significantly affected by the number of firings (p > 0.05). One porcelain exhibited a weak but highly significant positive correlation between microcrack density and multiple firings (r2 = 0.24, p = 0.0003), while the remaining porcelain exhibited a weak but statistically significant negative correlation between microcrack density and multiple firings (r2 = 0.15, p = 0.006). The results of this study indicate that even for porcelains that exhibit a measurable change in microcrack density as a function of multiple firings, the magnitude of the increase or decrease in microcrack density after several firings is sufficiently small to cause only negligible shifts in porcelain bulk thermal expansion.

PMID: 8876600 [PubMed - indexed for MEDLINE]

Clinical evaluation of restored maxillary incisors: veneers vs. PFM crowns.

J Am Dent Assoc. 1995 Nov;126(11):1523-9

Authors: Pippin DJ, Mixson JM, Soldan-Els AP

This cross-sectional study compared the periodontal health and clinical acceptability of maxillary incisors restored with porcelain veneers vs. porcelain-fused-to-metal crowns. The authors evaluated 60 patients, a total of 120 restorations, in groups according to the age of the restorations (zero to 60 months). Margins of veneers were generally more supragingival with less gingival inflammation. All veneers were clinically acceptable, while 5 percent of PFMs failed because of secondary caries.

PMID: 7499649 [PubMed - indexed for MEDLINE]

Early bond strength of luting cements to a precious alloy.

J Dent Res. 1992 Sep;71(9):1633-9

Authors: Mojon P, Hawbolt EB, MacEntee MI, Ma PH

Previous studies have reported that glass-ionomer and adhesive resin cements can bond to various alloys, while zinc phosphate cements lack this adhesive property. This study evaluated the bonding properties of three luting cements during the first seven days after cementation. Thirty cylinders were cast with a high-noble porcelain-fused-to-metal (PFM) alloy and luted in pairs with one of the cements. The joints were stored in water at 37 degrees C for one, two, or seven days before being fractured in shear. The cylinders were re-used to provide 40 joints within each test group. The data were subjected to a Weibull analysis, a curve-fitting method shown to be appropriate for comparing the bond strengths of dental materials. The results showed that the zinc phosphate cement was the weakest material, whereas the adhesive resin produced the strongest joints. Microscopic observations of the fractured samples did not reveal any specific differences between the samples in terms of their mechanism of fracture. The glass-ionomer cement reached its maximum bond strength after two days, whereas storage time had no influence on the zinc phosphate cement. The adhesive resin cement was slightly, but not significantly, weaker after one week in water. We suggest that excessive loading of restorations cemented with glass ionomer should be avoided for the first two days after the placement. The use of an adhesive resin cement can be recommended on endodontically treated teeth, but further studies are needed to evaluate its biocompatibility and adhesion to dentin.

PMID: 1522298 [PubMed - indexed for MEDLINE]

Influence of tempering method on residual stress in dental porcelain.

J Dent Res. 1992 Sep;71(9):1623-7

Authors: Asaoka K, Kuwayama N, Tesk JA

The porcelain component of a porcelain-fused-to-metal restoration is strengthened by residual (tempering) stresses which are induced by cooling procedures followed in dental laboratories. The thermophysical properties of materials and cooling rate are the main factors which determine the residual stress. In this paper, the temperatures in the midplane of body-porcelain disks were measured from a heat-soak temperature (1000 degrees C) to room temperature during two different cooling procedures: slow cooling in air and forced-air cooling. Experimental results approximated exponential cooling wherein the cooling rates could be represented by a linear equation of temperature. Residual stresses, as affected by the tempering method and thickness of a porcelain disk, were calculated by computer simulation for regions away from the edges. The following temperature-dependent factors were incorporated into the simulation: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling rate dependencies of the glass transition temperature and the temperature distribution during cooling were also included. The cooling rates used in this simulation were derived from the tempering data. The agreement between development of transient and residual stresses--calculated by computer simulation for various cooling methods, and the tendency toward failures of porcelain disks subjected to the tempering processes--was examined. Simulated residual stresses were also in good agreement with those measured by the indentation fracture method of Marshall and Lawn (1977) and Anusavice et al. (1989).

PMID: 1522297 [PubMed - indexed for MEDLINE]

Casting alloys: side-effects.

Adv Dent Res. 1992 Sep;6:38-43

Authors: Hensten-Pettersen A

Side-effects from dental materials are a minor problem, but should be recognized. In recent questionnaire surveys about side-effects, the incidence was estimated to be 1:300 in periodontics and 1:2600 in pedodontics. None of these reactions was related to dental casting alloys. In prosthodontics, the incidence was calculated to be about 1:400, and about 27% were related to base-metal alloys for removable partial dentures (cobalt, chromium, nickel) and to noble/gold-based alloys for porcelain-fused-to-metal restorations. The complaints consisted of intra-oral reactions (such as redness, swelling, and pain of the oral mucosa and lips), oral/gingival lichenoid reactions, and a few instances of systemic reactions. In orthodontics, the incidence was 1:100, and most reactions (85%) were related to metal parts of the extra-oral anchorage devices. Even though the extensive use of base-metal alloys has been of major concern to the dental profession, relatively few case reports substantiate this concern. Allergy to gold-based dental restorations has been more commonly reported. Palladium-based alloys have been associated with several cases of stomatitis and oral lichenoid reactions. Palladium allergy seems to occur mainly in patients who are very sensitive to nickel. All casting alloys, except titanium, seem to have a potential for eliciting adverse reactions in individual hypersensitive patients. Tolerance induction may be a possible benefit of the use of intra-orally placed alloys. In non-sensitized individuals, oral antigenic contacts to nickel and chromium may induce tolerance rather than sensitization. A variety of systemic diseases and reactions has been claimed to be caused by dental materials. The claims are generally poorly documented.

PMID: 1292460 [PubMed - indexed for MEDLINE]

Cytotoxicity of experimental casting alloys evaluated by cell culture tests.

J Dent Res. 1990 Aug;69(8):1539-42

Authors: Craig RG, Hanks CT

The cytotoxicity of a series of 29 experimental alloys and six pure metals was determined with cell culture techniques and succinic dehydrogenase histochemistry. The width of any ring of inhibition, optical density of the histochemically stained cells, and a visual ranking of the intensity of the blue color of the stained cells were compared for determination of cytotoxicity. Twenty-four of the 35 metals and alloys (approximately 70%) had the same rankings by the three methods. Of the pure metals, Au, Pd, and Ti were the least cytotoxic, followed by Ag, then Ni, and finally, Cu. Single-phase alloys with moderately high Cu and without high Pd and Au concentrations had high cytotoxicity, as did multiphase alloys, even when they were high in Au and Ag. High Pd was more effective in maintaining the biocompatibility of alloys containing Cu than was Au. Single-phase alloys with compositions typical of those to be used for porcelain-fused-to-metal restorations showed good biocompatibility, as did those base metal alloys that formed adherent oxide surface layers.

PMID: 2384632 [PubMed - indexed for MEDLINE]

Transient and residual stress in a porcelain-metal strip.

J Dent Res. 1990 Feb;69(2):463-9

Authors: Asaoka K, Tesk JA

Porcelain-fused-to-metal (PFM) restorations may develop cracks during processing or in-mouth service if the relative physico-mechanical properties of the porcelain and metal are highly mismatched. Precise conditions when this might occur are not known. Many processing and property variations can affect the stresses developed throughout a porcelain-metal system. To understand this, we conducted a computer simulation of stress developed in a PFM beam. The simulation considers cooling from temperatures higher than the porcelain sagpoint. The following temperature-dependent factors were incorporated: the elastic modulus, shear viscosity (porcelain), and coefficients of thermal expansion. The cooling rate dependencies of the glass transition temperature, (Tg), and the temperature distribution during cooling were also included. The results suggest that transient tensile stress at the porcelain alloy interface may result in cracks in the porcelain during cooling. Occlusal forces may set up stresses to cause cracking at the surface of the porcelain if the compressive residual stress is not high enough. PFM restorations with an alloy of high thermal expansion coefficient require rapid cooling; on the contrary, PFM restorations with the alloys of lower coefficients require slow cooling. A high cooling rate can make up for thermal expansion mismatches between the alloy and the porcelain up to 2 x 10(-6)/degrees C. Finally, the results indicated that curvature was not a sensitive indication of stress for a multimaterial beam when visco-elastic relaxation and high cooling rates are involved. For the case modeled here, curvature varied inversely with a 1/2 to 1/7th power of the stress.

PMID: 2307748 [PubMed - indexed for MEDLINE]

The effect of thermal history on porcelain expansion behavior.

J Dent Res. 1989 Sep;68(9):1313-5

Authors: Fairhurst CW, Hashinger DT, Twiggs SW

Porcelain-fused-to-metal restorations are fixed several hundred degrees above the glass-transition temperature and cooled rapidly through the glass-transition temperature range. Thermal expansion data from room temperature to above the glass-transition temperature range are important for the thermal expansion of the porcelain to be matched to the alloy. The effect of heating rate during measurement of thermal expansion was determined for NBS SRM 710 glass and four commercial opaque and body porcelain products. Thermal expansion data were obtained at heating rates of from 3 to 30 degrees C/min after the porcelain was cooled at the same rate. By use of the Moynihan equation (where Tg systematically increases in temperature with an increase in cooling/heating rate), the glass-transition temperatures (Tg) derived from these data were shown to be related to the heating rate.

PMID: 2778174 [PubMed - indexed for MEDLINE]

Interactive effect of stress and temperature on creep of PFM alloys.

J Dent Res. 1985 Aug;64(8):1094-9

Authors: Anusavice KJ, Shen C, Hashinger D, Twiggs SW

The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the glass transition temperature of dental porcelains. In comparison, a Ni-Cr alloy and a Pd-Co alloy demonstrated superior creep resistance at high-stress, low-temperature conditions. This indicates a relatively low potential for deformation due to stresses which may result from a thermal contraction differential between these two alloys and incompatible dental porcelains.

PMID: 3894455 [PubMed - indexed for MEDLINE]

An x-ray spectrometric technique for measuring porcelain-metal adherence.

J Dent Res. 1983 Aug;62(8):933-6

Authors: Ringle RD, Mackert JR, Fairhurst CW

This study demonstrated a correlation between silicon x-ray counts and area fractions of adherent porcelain as determined by point-counting. This correlation has allowed a method to be devised for measuring area fractions of porcelain adherent to porcelain-fused-to-metal (PFM) fracture surfaces. The described method, after controlled destruction of the porcelain mass, uses silicon x-rays excited by the electron beam in a scanning electron microscope. Under the conditions employed in these studies, the x-ray technique has shown that this gold alloy retains more porcelain than does either of two particular nickel-chromium alloys.

PMID: 6345620 [PubMed - indexed for MEDLINE]

Calculation of interfacial stress in porcelain-fused-to-metal systems.

J Dent Res. 1980 Nov;59(11):1972-7

Authors: Bertolotti RL

A method is given for calculating interfacial shear stress in porcelain-fused-to-metal restorative materials. Thermal history of the porcelain and dynamic stress relief relations are utilized to predict interfacial stress as a function of temperature. Calculations are in agreement with experimental results based on the deflection of bimaterial strips and are consistent with previously reported data.

PMID: 7000868 [PubMed - indexed for MEDLINE]

Castability of low gold content alloys.

J Dent Res. 1980 May;59(5):824-30

Authors: Howard WS, Newman SM, Nunez LJ

A test pattern composed of 14 gauge sprue wax and various gauges of nylon lines was constructed, and used to differentiate the castability of several alloys. The castability of seven commercial low gold content alloys for porcelain fused to metal restorations was compared. Five commercial low gold content yellow alloys for full cast restorations were compared to each other and to a Type III certified control.

PMID: 6988479 [PubMed - indexed for MEDLINE]

Comparative evaluation of ceramic-metal bond tests using finite element stress analysis.

J Dent Res. 1980 Mar;59(3):608-13

Authors: Anusavice KJ, Dehoff PH, Fairhurst CW

Eleven porcelain-fused-to-metal bond tests were analyzed for interfacial shear stress distribution using finite-element stress analysis. Stress concentration effects are significant in ten of the 11 tests. A high probability of tensile failure within porcelain or the interfacial region was found in eight of the 11 tests analyzed.

PMID: 7009667 [PubMed - indexed for MEDLINE]

Fit of porcelain fused-to-metal crown and bridge castings.

J Dent Res. 1979 Dec;58(12):2360-8

Authors: Eden GT, Franklin OM, Powell JM, Ohta Y, Dickson G

The dimensional accuracy of porcelain fused to metal crown and bridge castings was determined on truncated cone-shaped steel dies. Ni-Cr castings produced in manufacturers' laboratories were consistently undersize, while precious metal castings were consistently oversize. Ni-Cr castings, produced in NBS laboratories using a modified investing technique, were routinely oversize.

PMID: 389980 [PubMed - indexed for MEDLINE]

Topography and distribution of trace surface metals (Sn, In) on alloys for porcelain-metal restoration: influence of surface treatment.

J Dent Res. 1978 Feb;57(2):237-43

Authors: Stewart GP, Maroso D, Schmidt JR

Gold alloys were given five different conditioning treatments prior to porcelain firing. The alloys were examined with a scanning electron microscope and energy dispersive X-ray analyzer. Only two of the alloys had tin and indium present; these were concentrated in particles partially fused to the alloy's surface.

PMID: 355281 [PubMed - indexed for MEDLINE]

Distribution of stresses in porcelain-fused-to-metal and porcelain jacket crowns.

J Dent Res. 1975 Mar-Apr;54(2):255-61

Authors: Farah JW, Craig RG

An idealized porcelain jacket and porcelain-fused-to-metal crown model was prepared, loaded, and analyzed to establish the trends and distributions of the internal and external stresses. Loads at 30 degrees to the vertical axis created adverse tensile stresses at the level of the gingiva and specifically at the gold-dentin-cement interface.

PMID: 1054335 [PubMed - indexed for MEDLINE]

Stress distribution in photoelastic models of transverse sections of porcelain-fused-to-gold crowns and preparations.

J Dent Res. 1973 Sep-Oct;52(5):1060-4

Authors: Craig RG, el-Ebrashi MK, Farah JW

PMID: 4582466 [PubMed - indexed for MEDLINE]

Stress distribution in porcelain-fused-to-gold crowns and preparations constructed with photoelastic plastics.

J Dent Res. 1971 Sep-Oct;50(5):1278-83

Authors: Craig RG, el-Ebrashi MK, Peyton FA

PMID: 4937466 [PubMed - indexed for MEDLINE]

Study of bond strength of dental porcelain fused to metal.

J Dent Res. 1966 Jul-Aug;45(4):1047-51

Authors: Knap FJ, Ryge G

PMID: 5332429 [PubMed - indexed for MEDLINE]