Esther Gonzalo

A comparison of the marginal vertical discrepancies of zirconium and metal ceramic posterior fixed dental prostheses before and after cementation

STATEMENT OF PROBLEM Marginal discrepancies of zirconia posterior fixed dental prostheses (FDPs) fabricated using various systems have been assessed to determine the quality of the restorations and facilitate clinical use; however, studies are limited and results are ambiguous because of the sample sizes and measurement methods. PURPOSE The purpose of this in vitro study was to compare changes in marginal fit of posterior fixed dental prostheses of 3 zirconia systems manufactured using CAD/CAM technology and metal ceramic posterior fixed dental protheses fabricated with the conventional lost-wax technique, before and after cementation. MATERIAL AND METHODS Forty standardized master steel dies with 2 abutments simulating first mandibular premolars were fabricated to receive a posterior 3-unit FDP (from first molar to first premolar) and divided into 4 groups (n=10): Lava All-Ceramic System, Procera Bridge Zirconia, VITA In-Ceram 2000 YZ, and metal ceramic (control group). All FDPs were prepared for an internal space of 50 microm. The external marginal gap of the restorations was investigated by measuring 30 points in the middle of the buccal and lingual surfaces; therefore, 60 measurements per abutment were recorded. Measurements were made with an image analysis program on the master steel model before and after conventional cementation with a glass ionomer agent (Ketac Cem Easymix). The data obtained were statistically analyzed using 1-way ANOVA, Duncans multiple range post hoc test, and Students paired t test (alpha=.05). RESULTS No significant differences in the vertical marginal fit before and after cementation were recorded for the analyzed groups. The marginal discrepancy of Procera abutments before and after cementation (9 +/-10 microm and 12 +/-9 microm, respectively) was less than that of the other groups. Significant differences (P=.001) were observed in marginal adaptation between Procera Bridge Zirconia and the other groups. CONCLUSIONS The results of this study showed that cementation did not cause a significant increase in the vertical marginal discrepancies of the FDPs and that an internal space of 50 mum provided a high precision of fit of the restorations. The accuracy of fit achieved for the 3 zirconium oxide groups analyzed was within the range of clinical acceptance, and the discrepancies were lower than in the metal ceramic group. Procera Bridge Zirconia showed the lowest vertical discrepancies.

Marginal Vertical Discrepancies of Monolithic and Veneered Zirconia and Metal-Ceramic Three-Unit Posterior Fixed Dental Prostheses.

PURPOSE The aim of this study was to investigate and compare the marginal fit of posterior fixed dental prostheses (FDPs) made of monolithic and veneered computer-aided design/computer-assisted manufacture (CAD/CAM) zirconia ceramic with metal-ceramic posterior FDPs. MATERIALS AND METHODS Thirty standardized steel dies were prepared to receive posterior three-unit FDPs. Specimens were randomly divided into three groups (n = 10): (1) metal-ceramic (control group), (2) veneered zirconia, and (3) monolithic zirconia. All FDPs were cemented using a glass-ionomer cement. The specimens were subjected to thermal cycling (5°C to 55°C). A scanning electron microscope (SEM) with a magnification of ×500 was used for measurements. The data were statistically analyzed using one-way analysis of variance and paired t test. RESULTS Both zirconia groups showed similar vertical marginal discrepancies, and no significant differences (P = .661) in marginal adaptation were observed among the groups. No differences were observed in either group in marginal discrepancies between surfaces or abutments. CONCLUSION Monolithic zirconia posterior FDPs exhibit similar vertical marginal discrepancies to veneered zirconia posterior FDPs. No influence of localization measurements was observed.

Fracture Load Before and After Veneering Zirconia Posterior Fixed Dental Prostheses.

PURPOSE To evaluate the fracture load of 3-unit zirconia-based posterior fixed dental prostheses (FDPs) before and after veneering the frameworks. MATERIALS AND METHODS Forty standardized stainless-steel master dies were fabricated (height: 5 mm, convergence: 6º, chamfer: 1 mm) and randomly screwed in pairs onto metal bases. The bases were randomly divided into two groups (n = 20 each) according to the zirconia CAD/CAM system used for constructing 3-unit structures for FDPs: group 1 (L): Lava All-ceramic, group 2 (Z): IPS e.max ZirCAD. Half of the zirconia structures per group were randomly selected and veneered, while the remaining half was left unveneered. The specimens were luted in standard fashion onto the stainless steel master dies using conventional glass ionomer cement. All specimens were tested for fracture load (FL). Specimens were subjected to a three-point bending test until fracture by applying an axial compressive load at the central fossa of the pontics with a universal testing machine at a 0.5 mm/min crosshead speed. Wilcoxons rank-sum test and Weibull statistics were used for statistical analysis (α = 0.05). RESULTS L structures recorded significantly higher values of load to fracture than the Z group both before and after veneering. Within each ceramic group, no differences were found between unveneered and veneered frameworks. CONCLUSIONS Although further studies are necessary to corroborate these findings, both zirconia systems could be recommended for restoring posterior teeth on the basis of the fracture load values recorded in this experiment (>1000 N). The veneering procedure did not affect the overall load to fracture in any group.

Marginal and Internal Discrepancies of Posterior Zirconia-Based Crowns Fabricated with Three Different CAD/CAM Systems Versus Metal-Ceramic.

PURPOSE The aim of this study was to analyze the marginal and internal fit of metalceramic and zirconia-based crowns. MATERIALS AND METHODS Forty standardized steel specimens were prepared to receive posterior crowns and randomly divided into four groups (n = 10): (1) metal-ceramic, (2) NobelProcera Zirconia, (3) Lava Zirconia, and (4) VITA In-Ceram YZ. All crowns were cemented with glass-ionomer agent and sectioned buccolingually. A scanning electron microscope was used for measurements. Kruskal-Wallis and Wilcoxon signed rank test (α = .05) statistical analyses were conducted. RESULTS Significant differences (P < .0001) in marginal discrepancies were observed between metal-ceramic and zirconia groups. No differences were found for the axial wall fit (P = .057). Significant differences were shown among the groups in discrepancies at the occlusal cusp (P = .0012) and at the fossa (P = .0062). No differences were observed between surfaces. CONCLUSIONS All zirconia groups showed better values of marginal discrepancies than the metal-ceramic group. Procera Zirconia showed the lowest gaps.

SEM evaluation of the precision of fit of CAD/CAM zirconia and metal-ceramic posterior crowns

The purpose of this study is to evaluate the precision of fit of posterior crowns made from three commercial CAD/CAM zirconia ceramics and conventional metal-ceramic technique. The external and internal marginal fit of the crowns was evaluated using direct SEM-based measurements. The data were subjected to Kruskal-Wallis, multicomparison post hoc analysis and Wilcoxon rank sum tests (α=0.05). Significant differences were observed for the external (p<0.002) and the internal (p<0.0001) marginal evaluation among the groups. No differences were observed between the buccal and lingual surfaces for the external (p=0.34) and internal (p=0.55) evaluations. No differences were showed between the external and internal measurements (p=0.37). The accuracy of fit was within the range of clinical acceptance. The lowest discrepancies corresponded to the NobelProcera group for external (39.3±11.81 μm) and internal (41.09±7.54 µm) marginal fit. The results confirmed that destructive methods are not required to assess the marginal fit of dental prosthetic crowns.

The Marginal Fit of CAD/CAM Monolithic Ceramic and Metal-Ceramic Crowns

PURPOSE Studies on the marginal fit of monolithic restorations are limited. This study aimed to evaluate the marginal fit among monolithic zirconia, monolithic lithium disilicate, and conventional metal-ceramic crowns and to compare the buccal and lingual surfaces. MATERIALS AND METHODS Thirty standardized stainless steel master dies were fabricated (height: 5 mm; convergence: 6°; chamfer: 1 mm). The dies were randomly divided into three groups (n = 10 each) according to the material used to construct the crowns: group 1 (LM): Lava Plus; group 2 (DM): IPS e.max CAD; and group 3 (MC): Metal-ceramic. The crowns were luted in a standard manner onto the stainless steel master dies using conventional glass ionomer cement. The vertical marginal gap of the restorations was evaluated under a scanning electron microscope (SEM) at 500x magnification. One-way ANOVA, Tukey´s HSD test, and Students paired t test were used to assess the marginal discrepancy among the groups. The cutoff value for statistical significance was set at α = 0.05. RESULTS Significant differences among the three groups (p = 0.0001) were recorded. DM group showed the lowest discrepancies (27.95 ± 9.37 μm). Significant differences were observed for the buccal (p = 0.007) and lingual (p = 0.0001) surfaces between the DM group and the other groups. CONCLUSIONS The accuracy of fit achieved for the three groups was within the range of clinical acceptance. IPS e.max CAD showed the lowest discrepancies.

Fracture resistance and failure mode of posterior fixed dental prostheses fabricated with two zirconia CAD/CAM systems.

Background In recent years there has been an improvement of zirconia ceramic materials to replace posterior missing teeth. To date little in vitro studies has been carried out on the fracture resistance of zirconia veneered posterior fixed dental prostheses. This study investigated the fracture resistance and the failure mode of 3-unit zirconia-based posterior fixed dental prostheses fabricated with two CAD/CAM systems. Material and Methods Twenty posterior fixed dental prostheses were studied. Samples were randomly divided into two groups (n=10 each) according to the zirconia ceramic analyzed: Lava and Procera. Specimens were loaded until fracture under static load. Data were analyzed using Wilcoxon´s rank sum test and Wilcoxon´s signed-rank test (P<0.05). Results Partial fracture of the veneering porcelain occurred in 100% of the samples. Within each group, significant differences were shown between the veneering and the framework fracture resistance (P=0.002). The failure occurred in the connector cervical area in 80% of the cases. Conclusions All fracture load values of the zirconia frameworks could be considered clinically acceptable. The connector area is the weak point of the restorations. Key words:Fixed dental prostheses, zirconium-dioxide, zirconia, fracture resistance, failure mode.

A Randomized Clinical Trial Comparing Zirconia and Metal-Ceramic Three-Unit Posterior Fixed Partial Dentures: A 5-Year Follow-Up: Survival of Zirconia Posterior FPDs

PURPOSE To compare the survival, success rates, and biological/technical complications of posterior metal-ceramic (MC) and zirconia fixed partial dentures (FPDs). MATERIALS AND METHODS A total of 40 patients requiring 40 posterior FPDs were randomly assigned to receive 20 zirconia and 20 MC restorations. The restorations were examined 1 week (baseline) and 1, 3, and 5 years after the end of treatment. Technical and biological outcomes were compared. Data were statistically analyzed using the Wilcoxon signed-rank and Mann-Whitney U tests. RESULTS The survival rates of both groups were 100%, and the success rates were 80% (zirconia) and 100% (MC). No biological complications were observed. Minor chipping was found in 20% of the zirconia restorations. No differences in periodontal parameters were observed between groups. CONCLUSIONS Zirconia FPDs exhibited the same survival rate (100%) as MC FPDs after 5 years; however, the success rate was 80%, because an increased rate of chipping was observed in zirconia restorations.