The effect of framework fabrication technique on the fit accuracy of full arch screw retained implant supported prostheses.

Purpose: The purpose of this study was to compare the accuracy of fit of Co-Cr full arch screw-retained implant-supported fixed dental prosthesis fabricated among three different methods: conventional casting, milling, and additive manufacturing technology. Materials and methods: A master model of a completely edentulous mandible with five internal connection implants was utilized. Thirty full arch Co-Cr screw-retained implant-supported frameworks were fabricated by three different methods: conventional casting, milling, and additive manufacturing (AM) technology. The marginal fit was measured using a coordinate measuring machine in x-, y-, and z-axes, as well as the three-dimensional discrepancy. The casting group were measured twice: before the adaptation procedure and again after the adaptation procedure (sectioning and laser welding). For comparisons of marginal fit of frameworks between different groups one-way analysis of variance and Games Howell test was used. Paired t-test was used to compare cast frameworks before and after adaption. Results: There were statistically significant differences in marginal fit and width distortion between groups (P <.05). The mean of total distortion of each group was 94.6 µm (SD 50.5 µm) for casting group before adaptation, 92.44 µm (SD 49.6 µm) for casting group after adaptation, 71.4 µm (SD 37.2 µm) for additive manufacturing group, while for the milling group the total distortion was 50.1 µm (SD 27.5 µm). Conclusion: Full arch screw-retained implant-supported frameworks fabricated with any of the three fabrication techniques using cobalt-chromium material exhibited acceptable marginal fit. Milling fabrication technique showed the most accurate marginal fit. Adaptation procedure for the cast group has significantly improved the marginal fit.

Convergence angles of clinical tooth preparations achieved by dental students at King Saud University, Saudi Arabia.

The appropriate convergence angle (CA) for adequate retention and resistance of cast crowns has always been a matter of research and discussion. The purpose of this study was to measure the CA of tooth preparation for single crown (SC) or as abutments for fixed partial denture (FPD) carried out by final-year undergraduate dental students at the College of Dentistry, King Saud University and to compare them with the recommended CA. The convergence angles of 355 tooth preparations were evaluated and grouped into SC preparations and FPD abutment preparations. Dies were scanned using the computer-assisted design (CAD) system (Cercon, Degudent), and snapshots were then taken from buccal and mesial views. CA was calculated from a colored printout for each snapshot using a protractor. The overall mean CA was 18.56°. Only 32.7 percent of the preparations were within the recommended CA (<12°). The mean CA of SC (17.7°) was less than the mean CA for FPD abutment preparations (19.58°). The mean CA for anterior tooth preparations (15.8°) was significantly less than the mean CA for posterior tooth preparations (20.3°). The mean CA for mesio-distal axial wall preparations (16.66°) was less than the mean CA for the buccolingual axial wall preparations (20.45°). A wide range was found for the convergence of the axial walls among dental students. The recommended CA (<12°) was difficult to achieve clinically by these students.

Effect of three endodontic sealers on the bond strength of prefabricated fiber posts luted with three resin cements.

STATEMENT OF PROBLEM: There is limited information in the literature regarding the effect of eugenol-based sealers on the bond strength of resin-bonded endodontic posts. PURPOSE: The purpose of this study was to evaluate the effect of 1 resin-based and 2 different eugenol-based endodontic sealers on the bond strength of prefabricated fiber posts luted with 3 different resin cements. MATERIAL AND METHODS: One hundred thirty-five prefabricated fiber posts were luted into extracted single-rooted teeth with 1 of 3 composite resin cements (Rely X Unicem, Paracore, and Variolink II). Specimens were divided into 3 groups with 45 teeth each. The first 2 groups were obturated with gutta percha and 1 of 2 eugenol-based endodontic sealers (Endofil, Tubli-Seal). The third group was obturated with a resin-based root canal sealer (AH26). The forces required for dislodgment of posts from their prepared post spaces were recorded by using a universal testing machine. Data were collected and a 2-way ANOVA was applied to the mean retentive strengths of various combinations of sealer and cement. A Tukey multiple comparison test was performed to determine which groups were significantly different (α=.05). RESULTS: Endofil and Tubli-Seal (eugenol-based sealers) groups had significantly lower bond strengths for the posts than the AH26 group (P<.001). There was no significant difference between the means of post bond strength for the Endofil and Tubli-Seal groups. There was significant difference among the means of post bond strength for all 3 cement groups (P<.05). CONCLUSIONS: Endofil and Tubli-Seal (eugenol-based) sealers demonstrated significantly reduced mean bond strength for prefabricated fiber posts luted with resin cement. Rely X Unicem resin cement exhibited higher mean bond strength than with Paracore and Variolink II resin cements when a eugenol sealer was used.