Search

Objectives: The purpose of this randomized clinical study was to evaluate the clinical performance of posterior, metal-free polymer crowns after follow-up for up to six years, and to compare it with the performance of metal-ceramic crowns., Methods: Eighty single crowns, manufactured from a polymer composite resin, were set on posterior teeth. Half of these received a glass-fibre framework (group 1) whereas half were prepared without framework stabilization (group 2). As the control group, 40 conventional metal-ceramic crowns were inserted. Primary endpoints were incidence of complications, investigated on a time-to-event basis, plaque status, and aesthetic performance., Results: Thirty clinically relevant complications occurred after a median time of 2.3 years. Median follow-up time was four years. The most frequent complications were delamination (n=24) and root-canal treatment (n=4) of the crowns; the incidence of complications was not significantly different among crown materials (p=0.60). Twenty crowns had to be replaced (six polymer crowns in group 1, nine polymer crowns in group 2, four crowns in the control group, and one tooth (in group 1) had to be extracted). Mean plaque and gingival indexes for the test groups did not differ from those for the control group., Conclusions: Within a median follow-up period of four years, the clinical performance of posterior polymer crowns with and without a glass-fibre framework was not significantly different from that of metal-ceramic crowns, although the number of catastrophic failures of composite crowns was higher than that of the metal-ceramic crowns., Clinical Significance: On the basis of the study results, posterior polymer crowns may be an alternative to metal-ceramic crowns, although additional research is needed before they can be recommended, without reservation, as permanent restorations., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

To compare differences between the wear behavior of two types of metal-free resin composite crown with a control after three years in clinical service. Sixty-six participants needing one to three posterior single crowns were fitted with 120 crowns. Abutment teeth were randomly assigned to three groups: 40 resin composite crowns with fiber-reinforced framework, 40 resin composite crowns without fiber-reinforced framework, and 40 metal-ceramic crowns. To assess wear, gypsum replicas of the crowns were fabricated and scanned with a 3D laser scanner at baseline and after three years. Differences between the groups were analyzed by use of mixed-effects regression models. Wear of resin composite crowns with fiber-reinforced framework (p=0.0043) and resin composite crowns without framework (p=0.0246) was significantly greater than in the metal-ceramic group. Wear of metal-free resin composite crowns after three years was significantly greater than that of metal-ceramic crowns, but the wear was still clinically acceptable.

The purpose of this study is to compare success rates of dual-viscosity impressions for two types of mixing techniques of the polyether elastomeric impression material. Additionally, influencing parameters on the success rates should be evaluated. The expectation was that there would be no difference between the success rates for the two mixing techniques. Two centres enrolled 290 subjects (727 teeth) into the trial. Patients were randomized for the two types of mixing techniques. One step, dual-viscosity impressions were made with either statically mixed Impregum Soft tray material (SAM) or dynamically mixed Impregum Penta H DuoSoft (DMM). Low viscosity Impregum Garant L DuoSoft was used for both groups. Gingival displacement involved the use of two braided cords. Full-arch trays were used exclusively. Both critical defects and operator errors were assessed for the first impression taken by trained dentists. The primary outcome was impression success. For comparison of the two mixing techniques, the odds ratio for success and the corresponding one-sided 95% confidence interval was calculated by a logistic regression model. To account for the dependence between several teeth within one patient, the method of general estimating equations was used. The overall impression success rate was 35.4%. Both mixing techniques showed equal success rates indicated by an OR of 1.0 and a lower limit of the one-sided 95% confidence interval of 0.71. Using this result to develop the corresponding interval for the difference, it could be shown that the success rate using SAM was at most 8.2% lower than that when using DMM with a probability of 95%. Multivariate logistic regression analysis of other potential influencing factors showed position of finish line (p = 0.008, supra compared to mixed), blood coagulation disorder (p = 0.021) and the level of training of the clinician (student vs dentist, p=0.008) to have an independent influence on the success rate. Dynamic mechanical mixing and the new static mixing of polyether tray material showed nearly equal success rates in the study even though success rates were comparatively low (DMM, 35.3%; SAM, 35.4%).

Statement of Problem: Although composite resin materials are used for posterior crown restorations, the influence of preparation design, material thickness, convergence angle, and method of cementation on fracture resistance remains unclear., Purpose: The purpose of this in vitro study was to test the hypothesis that minimal preparation designs provide an acceptable level of fracture resistance for posterior composite resin crowns., Material and Methods: Nonreinforced Artglass composite resin crowns (n=128) were fabricated on human molars in 16 test groups (n=8). Axial tooth preparation included a 1-mm-deep shoulder or a 0.5-mm chamfer preparation, whereas occlusal reduction was either 0.5 mm or 1.3 mm. The total angle of convergence was 4 or 11 degrees and the crowns were cemented either with glass ionomer cement (Ketac Cem) or resin cement (2bond2). After 10,000 thermal cycles, crowns were vertically loaded until failure occurred; load was measured in newtons. Statistical analysis was performed by a 4-way ANOVA (alpha=.05)., Results: Statistical analysis revealed significant effects of occlusal thickness (P<.001), cement (P<.001), preparation design (P=.011), and convergence angle (P=.001) on the fracture resistance of the composite crowns. For composite resin crowns with an occlusal thickness of 0.5 mm, the resistance to fracture was lower than for crowns with a 1.3-mm thickness. Fracture resistance was greater when resin cement was used, and greater for the chamfer finish line than for the shoulder finish line. Use of a greater total convergence angle reduced fracture resistance., Conclusions: Fracture resistance of composite resin crowns was significantly improved by increasing the occlusal thickness of the crowns, by using resin cement, and by reducing the total convergence angle.

Objective: Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic., Material and Methods: Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay-crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated., Results: The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown., Conclusions: Inlay-inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay-crown and crown-crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.

Purpose: To evaluate the fracture resistance of teeth restored using an adhesive core material placed under artificial crowns without pins or posts and to assess the effect of different preparation designs and cementation techniques (glass ionomer compared with adhesive cementation) used for the crowns., Materials and Methods: Eighty-three intact molars were collected. Sixty-seven teeth were decoronated (test groups and one control group), a 2-mm circular ferrule design was prepared, and four different preparation designs (2-mm- or 1-mm-deep cavities and 2-mm- or 1-mm-thick walls) were used. Three control groups were also established. Cores were built up using an adhesive material. After preparation, standardized artificial crowns (cobalt-chromium alloy) were fabricated. Half of the crowns in the test group (n = 32) were cemented using Panavia (P group); glass-ionomer cement was used for the other half (KC group). All teeth were exposed to 10,000 thermal cycles and loaded until fracture. Statistical analysis was performed, including nonparametric tests (Mann-Whitney U-test) and ANOVA., Results: In the P group, the fracture strength was significantly (p = 0.004) higher (591.75 +/- 177.95 N) than in the KC group (430.18 +/- 193.67 N). The effect of the preparation design was more pronounced in the KC group. In all groups simulating the most moderate type of tooth decay (2-mm-deep cavity and a 2-mm-thick wall), the fracture strength was comparable with that of intact teeth. Results from ANOVA showed that the type of cementation of the crowns affected fracture strength., Conclusion: Fracture strengths of adhesive core/crown complexes are greater when an adequate cavity for retention (at least 2 mm deep) is prepared and the crown is luted.

Objectives: The purpose of this randomized clinical trial was to evaluate the clinical wear behavior of posterior, metal-free polymer crowns, with and without a glass-fiber framework, and to compare it with that of metal-ceramic crowns., Methods: Eighty single crowns manufactured from a newly designed polymer composite were set in posterior teeth. Half of these received a glass-fiber framework (group 1) whereas half were prepared without framework stabilization (group 2). All polymer crowns were adhesively luted with resin cement. As the control group, 40 conventional metal-ceramic crowns were inserted with hybrid cement. Wear was measured, by use of gypsum replicas, at baseline and after 12 months, by use of a 3D laser scanner. Statistical analysis was performed using mixed-effects regression model analyses., Results: The mean total wear of posterior single crowns was -8.1 microm (+/-9.7 microm) in group 1, -7.0 microm (+/-9.1 microm) in group 2, and -3.4 microm (+/-6.3 microm) in the control group. Statistical analysis revealed wear behavior was significantly different from the control group for group 1 (p=0.014) and group 2 (p<0.01). No significant difference was detected between groups 1 and 2. Age, gender, and opposing teeth had no significant effect on wear behavior., Conclusions: Within a 12-month observation period mean total wear of posterior polymer crowns with and without a glass-fiber framework was significantly greater than for metal-ceramic crowns. The selection of restorative materials should be based on knowledge of clinical wear in order to preserve occlusal stability.

Objectives: The aim of this study was to evaluate the clinical performance of posterior, metal-free polymer crowns with and without a glass-fiber framework, in comparison to metal-ceramic crowns., Methods: After randomisation, 80 single crowns, manufactured from a newly designed polymer composite, were set in posterior teeth. Half of these received a glass-fiber framework, while half were prepared without any framework stabilisation. All polymer crowns were adhesively luted with resin cement. As the control group, 40 conventional metal-ceramic crowns were inserted with hybrid cement. Documentation included failures and other complications, as well as gingival/plaque status and aesthetic performance., Results: During the 12-month observation period, eight polymer crowns and three metal-ceramic crowns showed clinically relevant complications. The most frequent complications were root canal treatments (n=4) and decementation (n=4) of the crowns. A total of two crowns (one polymer crown with fiber network and one crown of the control group) had to be replaced. After 12 months, polymer crowns with glass-fiber framework exhibited significantly higher plaque accumulation (p=0.005) and gingival index (p=0.04) than metal-ceramic crowns, while no significant differences could be demonstrated for polymer crowns without fiber reinforcement. Postoperative sensibility and aesthetic performance did not differ significantly between the groups., Conclusions: Within a 12-month observation period, posterior polymer crowns with and without glass-fiber framework demonstrated acceptable stability and aesthetic performance. Polymer crowns with fiber framework showed significant higher plaque accumulation and gingival index than metal-ceramic crowns.