Mitsuyoshi Tsumita

Clinical marginal and internal gaps of zirconia all-ceramic crowns

PURPOSE Marginal and internal gaps of NobelProcera crown zirconia were clinically evaluated using silicone materials. MATERIALS AND METHODS Ninety-one crowns were examined before final cementation, and white and black silicone materials were used to record the marginal and internal fit. The silicone materials were sectioned bucco-lingually and mesio-distally, and the thickness of the silicone layers was measured using a microscope. Sixteen reference points were measured on each specimen, and mean marginal and internal gaps were obtained. Mean marginal gaps among anterior, premolar, and molar tooth groups, in addition to mean gaps at the reference points within the groups, were compared using two-way ANOVA and Games-Howell analysis. RESULTS The marginal mean values were the smallest among all tooth groups, and the largest were at the rounded shoulders. There were no significant differences in the mean marginal gaps among the three tooth groups, while there were significant differences in the mean marginal and internal gaps of each tooth group. CONCLUSIONS The mean marginal gap of the NobelProcera crown zirconia was 44.2 μm, which is within clinically accepted standards.

Clinical evaluation of posterior all-ceramic FPDs (Cercon): A prospective clinical pilot study

PURPOSE This study prospectively evaluated the clinical performance of posterior zirconium-oxide-based all-ceramic fixed partial dentures (FPDs). METHODS Forty-two abutments of 21 Cercon FPDs were fitted in 20 patients at the Tsurumi University Dental Hospital from August 2005 to August 2006. The performance of these FPDs was evaluated using the California Dental Association (CDA) quality assessment system at baseline and at all follow-up examinations. RESULTS All FPDs were examined after a mean observation period of 28.1 (+/-3.4) months. During the observation period, no fracturing of FPDs was seen. All of the FPDs examined were rated as satisfactory with regard to all factors at the follow-up examinations based on the CDA quality assessment criteria. CONCLUSION Within the limitations of this short-term clinical study, no core framework fractures were seen. According to the CDA criteria, 100% of the FPDs were rated as satisfactory during this observation period.

Effect of framework shape on the fracture strength of implant-supported all-ceramic fixed partial dentures in the molar region

PURPOSE The aim of the present study was to clarify the effects of the shape of the zirconium framework of implant-supported, all-ceramic fixed partial dentures (FPDs) on the fracture strength and fracture mode. MATERIALS AND METHODS This study consisted of mechanical strength testing and 3D finite element analysis (FEA). The three framework shapes used in this study were: (1) conventional shape (control); (2) convex shape: 1.0-mm curve in the direction of the occlusal surface; and (3) concave shape: 1.0-mm curve in the direction of the gingival surface. Five frameworks were made for each condition (total: 15). A load (N) was applied until the FPD fractured. For FEA, a 3D model consisting of cortical bone, cancellous bone, implant bodies, and superstructure was constructed. RESULTS The results of the mechanical strength test showed that fracture load was 916.0 +/- 150.1 N for the conventional shape, 1690.5 +/- 205.3 N for the convex shape, and 1515.5 +/- 137.0 N for the concave shape. The mean final fracture load for the FPDs with frameworks was the highest for the convex shape; however, a critical crack in the veneer porcelain (736.5 +/- 145.2 N) was confirmed during loading for the convex shape. Stress distribution maps for all conditions showed that tensile stress was generated at the veneer porcelain on the gingival side of the mesial and distal connectors of the pontic; however, there were differences in the maximum value and stress distribution within the framework. CONCLUSION The shape of the framework, particularly the shape of the pontic-connector interface, affects the stress distribution, fracture strength, and fracture mode of all-ceramic FPDs, and stress concentration inside a framework may induce cracking of layering porcelain.

Clinical evaluation of Procera AllCeram crowns in Japanese patients: results after 5 years

Procera AllCeram crowns were prospectively evaluated clinically in both anterior and posterior regions in Japanese. One-hundred and one crowns were fabricated for 57 patients at the Tsurumi University Dental Hospital from August 2001 to October 2002 and evaluated according to the California Dental Association (CDA) quality evaluation system at baseline and annually at all follow-up examinations for 5 years. The plaque index (PI) and gingival index (GI) were recorded, and chipping and fracture were checked at the same time as well. A total of 75 Procera AllCeram crowns were evaluated, and the cumulative survival rate was 90.2% over the 5-year clinical trial. Six crowns experienced fractures within the veneering porcelain and from aluminium oxide coping, all of which occurred on the premolar and molar regions, and they had to be removed. Small chipping was observed on three crowns. According to the CDA criteria, 98% of Procera AllCeram crowns were rated as satisfactory, and PI and GI were comparable to those of control teeth during the observation period.

Five-year clinical evaluation of In-Ceram crowns fabricated using GN-I (CAD/CAM) system.

This study prospectively evaluated the clinical performance of computer-assisted design and computer-assisted manufacturing (CAD/CAM)-generated In-Ceram Alumina core crowns in Japanese patients for up to 5 years. A total of 101 In-Ceram crowns with aluminium copings fabricated using the GN-I system were placed in Japanese patients. The crowns were evaluated using a California Dental Association (CDA) quality assessment system at baseline and at all follow-up examinations. Gingival condition was assessed using plaque and bleeding scores. The survival of anterior and posterior crowns was analysed according to the Kaplan-Meier method. The scores of gingival condition were compared between restored crowns and contralateral teeth using a t-test. During the observation period, six crowns were lost to follow-up. Five crowns were fractured from the copings and removed, and four crowns were removed for other reasons. Chipping within the porcelain was detected in three crowns, which were then polished. The cumulative survival rates after 60 months were 96·9% for anterior crowns and 87·7% for posterior ones, and there were no significant differences between anterior and posterior crowns. According to the CDA criteria, most of the crowns were rated as satisfactory during the observation period. There were significant differences in soft tissue conditions between In-Ceram crowns and control teeth at 2- and 5-year examinations. Despite the five fractures from copings, In-Ceram Alumina crowns with copings fabricated using the CAD/CAM (GN-I system) for replacing both anterior and posterior teeth showed predictable results during a 5-year observation period.

The effect of fatigue loading on the screw joint stability of zirconium abutment

PURPOSE This study evaluated the effect of fatigue loading on the screw joint stability of a zirconium abutment connected to an external hexagon implant in vitro. MATERIALS AND METHODS Fifteen titanium and 15 zirconia abutments of 3 different heights (5, 8, and 11 mm) were connected to external titanium implants with titanium screws. A torque gauge was used to measure the reverse torque values before and after loading. An air cylindrical loading device was used to simulate mastication at a 45-degree angle to the longitudinal axis of the implant. RESULTS There were significant differences (P<0.05) before and after the loading of titanium (5mm) and zirconia (5, 8, and 11 mm) abutments. CONCLUSION Zirconia abutments for external hexagon implants had durability rates similar to those of titanium abutments after repeating load on the reverse torque of the abutment screw, indicating that the zirconia abutment could be reliably used instead of the titanium abutment.