Misfit of suprastructures on implants processed by electrical discharge machining or the Cresco method.

OBJECTIVE: To assess the accuracy of fit of frameworks on implants processed with electrical discharge machining (EDM) or the Cresco technique (Astra Tech). METHOD AND MATERIALS: On 12 identical master casts with implants at positions 9(21), 11(23), and 13(25), high-gold alloy frameworks were produced by standard casting procedure. Six frameworks were used for the Cresco technique (group CRE) by employing specific fixed partial denture supports. The remaining 6 frameworks were cast with prefabricated gold copings and served as control. The finished frameworks were screwed onto implant 25 of the corresponding master cast. Dimensions of the marginal gaps were measured at 4 locations on each implant under the scanning electron microscope, applying the replica technique. Subsequently, the control group was processed by EDM (SAE EDM 2000) (group EDM) and analyzed alike. Statistical analysis of the results was performed with Kruskal-Wallis and Mann-Whitney U tests. RESULTS: The mean marginal gaps were measured as follows (CRE/EDM/control): position 25: 0.0 microm/1.0 +/- 1.6 microm/1.5 +/- 2.1 microm; position 23: 5.2 +/- 5.6 microm/18.7 +/- 29.3 microm/23.6 +/- 30.7 microm; and position 21: 36.0 +/- 21.6 microm/40.7 +/- 31.0 microm/46.0 +/- 41.1 microm. The only statistically significant difference was found at location 23 between group CRE on one side and both group EDM and control on the other side. The strong increase of misfit for group CRE from location 23 to location 21 indicates that laser welding is the crucial parameter in this technique. CONCLUSION: The Cresco technique has a potential to reduce the marginal gap between implants and suprastructures.

The effect of all-ceramic and porcelain-fused-to-metal restorations on marginal peri-implant soft tissue color: a randomized controlled clinical trial.

The aim of this study was to test the color-change effect of all-ceramic restorations compared with porcelain-fused-to-metal (PFM) restorations on marginal peri-implant soft tissue. Thirty patients were randomly divided into 2 groups of 15 subjects each. The all-ceramic group received all-ceramic crowns on aluminum oxide-based abutments, while the PFM group received crowns on titanium or gold abutments. A reflectance spectrophotometer was used to measure the color difference (deltaE(Implant)) between the midfacial peri-implant mucosa before and after restoration insertion. The color difference (deltaE(Tooth-implant)) between the midfacial peri-implant mucosa and the gingival margin of the corresponding neighboring tooth was tested. The mucosal thickness was measured midfacially around the implant (MT(Implant)) and neighboring tooth (MT(Tooth)). deltaE(Implant) values were similar for the all-ceramic (7.4 +/- 2.7) and PFM groups (7.6 +/- 2.8). The all-ceramic group induced significantly less visible mucosal color change (3.4 +/- 1.4) compared to the PFM group (5.2 +/- 2.3). The MT(Implant) value of the all-ceramic group was 3.4 +/- 0.8 mm, while that of the PFM group was 2.9 +/- 0.9 mm, which was not significantly different. Significant differences were found when comparing MT(Implant) (3.1 +/- 0.9) and MT(Tooth) (1.2 +/- 0.3) values for test and control groups. All-ceramic restorations revealed a better color match to the neighboring teeth than PFM restorations.

Clinical study of the color stability of veneering ceramics for zirconia frameworks.

PURPOSE: The purpose of this study was to compare 3 veneering ceramics for zirconia frameworks regarding color stability and predictability of the esthetic result. MATERIALS AND METHODS: Six patients with 1 maxillary central incisor to be restored were enrolled in the study. The contralateral incisor had to be nonrestored and vital to serve as a reference tooth. For each patient, 4 single crowns with zirconia frameworks were fabricated. Three veneering ceramics were assessed and masked to eliminate bias. Choice of the veneering ceramics was done at random. The veneering was performed by 4 dental technicians. Three veneering ceramics were compared: ceramic A (Initial, GC), ceramic B (Triceram, Esprident), and ceramic C (Cercon Ceram S, DeguDent). The color of the crowns and reference teeth was captured using spectrophotometric analysis (SpectroShade, MHT), and the color difference (deltaE) was calculated (objective method). In addition, the crowns and reference teeth were compared subjectively by 11 observers blind to the ceramic used for veneering. Statistical analysis was performed with analysis of variance (ANOVA). RESULTS: Regardless of the veneering ceramic used, all crowns showed a high color deviation from the reference teeth when applying the objective analysis (deltaE(A) 6.8 +/- 2.5, deltaE(B) 5.6 +/- 1.2, deltaE(C) 5.7 +/- 2.1). In addition, no significant differences were found between the deltaE of crowns and teeth for the 3 ceramics. In the framework-supported area, ceramic B showed a significantly lower difference in value (deltaL) compared to the reference teeth than the other 2 ceramics (deltaL(A) 4.9 +/- 2.3, deltaL(B) 1.1 +/- 2.1, deltaL(C) 4.1 +/- 1.5; P < .01 ANOVA). When performing the subjective analysis, ceramic B was chosen as the best match by a majority of observers (> 60%) in 4 of 6 patients. CONCLUSIONS: All 3 ceramics met the esthetic demands only to a limited extent. Ceramic B allowed for the most predictable result in terms of color stability.