Evaluation of the Effect of Air Polishing With Different Abrasive Powders on the Roughness of Implant Abutment Surface: An In Vitro Study.

The aim of this in vitro study was to evaluate the effect of air polishing on the implant abutment surface using different abrasive powders: sodium bicarbonate and amino acid glycine. Fifteen grade III machined surface titanium disks with 8-mm diameter and 2-mm thickness were divided in 3 groups of 5 samples each and subjected to air polishing for 20 seconds with an Ultrajet Flex air-abrasive device and a distinct prophylaxis protocol: air and water (G1); air, water, and sodium bicarbonate (G2); and air, water; and amino acid glycine (G3). After the air polishing, the average roughness (Ra) of the samples was measured using an optical profilometer, and the obtained data were statistically analyzed. We found that G1 and G3 had similar Ra, while Ra values for G2 were significantly higher. This study demonstrated that air-polishing powders containing glycine had less of an effect on the roughness of the surface of titanium disks compared with sodium bicarbonate powders. Future in vivo studies will be conducted to investigate the clinical relevance of the present results.

A microstrain comparison of passively fitting screw-retained and cemented titanium frameworks.

STATEMENT OF PROBLEM: An imprecise fit between frameworks and supporting dental implants in loaded protocols increases the strain transferred to the periimplant bone, which may impair healing or generate microgaps. PURPOSE: The purpose of this study was to investigate the microstrain between premachined 1-piece screw-retained frameworks (group STF) and screw-retained frameworks fabricated by cementing titanium cylinders to the prefabricated framework (group CTF). This procedure was developed to correct the misfit between frameworks and loaded implants. MATERIAL AND METHODS: Four internal hexagon cylindrical implants were placed 10 mm apart in a polyurethane block by using the surgical guides of the corresponding implant system. Previously fabricated titanium frameworks (n=10) were divided into 2 groups. In group STF, prefabricated machined frameworks were used (n=5), and, in group CTF, the frameworks were fabricated by using a passive fit procedure, which was developed to correct the misfit between the cast titanium frameworks and supporting dental implants (n=5). Both groups were screw-retained under torque control (10 Ncm). Six strain gauges were placed on the upper surface of the polyurethane block, and 3 strain measurements were recorded for each framework. Data were analyzed with the Student t test (α=.05). RESULTS: The mean microstrain values between the framework and the implants were significantly higher for group STF (2517 mε) than for group CTF (844 mε) (P<.05). CONCLUSIONS: Complete-arch implant frameworks designed for load application and fabricated by using the passive fit procedure decreased the strain between the frameworks and implants more than 1 piece prefabricated machined frameworks.

Influence of different maintenance times of torque application on the removal torque values to loosen the prosthetic abutment screws of external hexagon implants.

PURPOSE: To analyze the torque application on prosthetic abutment screws using different maintenance times, to determine an influence on the removal torque values. MATERIALS AND METHODS: A total of 40 external hexagon implants, 40 titanium screws, and 40 customized abutments were used. In group 1, the screws received a torque of 30 N·cm by instant torque application; in groups 2, 3, and 4, torque of 30 N·cm was applied and maintained for 10, 20, and 30 seconds, respectively. Removal torque was performed 10 minutes after torque application. Data were statistically analyzed using 1-way ANOVA and Tukey HSD test (α = 0.05). RESULTS: The mean and standard deviation (±SD) of removal torque values found were 11.61 ± 1.43 N·cm for group 1; 18.64 ± 1.71 N·cm for group 2; 21.62 ± 0.97 N·cm for group 3; and 21.48 ± 1.55 N·cm for group 4. Groups 3 and 4 exhibited statistically higher values than group 2, which demonstrated significantly higher values than group 1 (P < 0.05). CONCLUSIONS: A torque of 30 N·cm applied for 20 seconds seemed to be the best option when considering the removal torque values of external hexagon implants.

Strain gauge analysis of the effect of porcelain firing simulation on the prosthetic misfit of implant-supported frameworks.

OBJECTIVES: This study investigated the effect of porcelain firing on the misfit of implant-supported frameworks and analyzed the influence of preheat treatment on the dimensional alterations. MATERIALS AND METHODS: Four external-hex cylindrical implants were placed in polyurethane block. Ten frameworks of screw-retained implant-supported prostheses were cast in Pd-Ag using 2 procedures: (1) control group (CG, n = 5): cast in segments and laser welded; and test group (TG, n = 5): cast in segments, preheated, and laser welded. All samples were subjected to firing to simulate porcelain veneering firing. Strain gauges were bonded around the implants, and microstrain values (µÎµ = 10⁻6ε) were recorded after welding (M1), oxidation cycle (M2), and glaze firing (M3). Data were statistically analyzed (2-way analysis of variance, Bonferroni, α = 0.05). RESULTS: The microstrain value in the CG at M3 (475.2 µÎµ) was significantly different from the values observed at M1 (355.6 µÎµ) and M2 (413.9 µÎµ). The values at M2 and M3 in the CG were not statistically different. Microstrain values recorded at different moments (M1: 361.6 µÎµ/M2: 335.3 µÎµ/M3: 307.2 µÎµ) did not show significant difference. CONCLUSIONS: The framework misfit deteriorates during firing cycles of porcelain veneering. Metal distortion after porcelain veneering could be controlled by preheat treatment.

Effect of cast rectifiers on the marginal fit of UCLA abutments.

OBJECTIVES: This study assessed the effect of cast rectifiers on the marginal misfit of cast UCLA abutments compared to premachined UCLA abutments. The influence of casting and porcelain baking on the marginal misfit of these components was also investigated. METHODS: Two groups were analyzed: test group - 10 cast UCLA abutments, finished with cast rectifier and submitted to ceramic application; control group - 10 premachined UCLA abutments, cast with noble metal alloy and submitted to ceramic application. Vertical misfit measurements were performed under light microscopy. In the test group, measurements were performed before and after the use of cast rectifiers, and after ceramic application. In the control group, measurements were performed before and after casting, and after ceramic application. Data were submitted to statistical analysis by ANOVA and Tukey's test (a= 5%). RESULTS: The use of cast rectifiers significantly reduced the marginal misfit of cast UCLA abutments (from 25.68mm to 14.83mm; p<0.05). After ceramic application, the rectified cylinders presented misfit values (16.18mm) similar to those of premachined components (14.3 mm). Casting of the premachined UCLA abutments altered the marginal misfit of these components (from 9.63 mm to 14.6 mm; p<0.05). There were no significant changes after porcelain baking, in both groups. CONCLUSION: The use of cast rectifiers reduced the vertical misfit of cast UCLA abutments. Even with carefully performed laboratory steps, changes at the implant interface of premachined UCLA abutments occurred. Ceramic application did not alter the marginal misfit values of UCLA abutments.

In vitro evaluation of the precision of working casts for implant-supported restoration with multiple abutments.

OBJECTIVE: The purpose of this study was to compare the accuracy of two working cast fabrication techniques using strain-gauge analysis. METHODS: Two working cast fabrication methods were evaluated. Based on a master model, 20 working casts were fabricated by means of an indirect impression technique using polyether after splinting the square transfer copings with acrylic resin. Specimens were assigned to 2 groups (n=10): Group A (GA): type IV dental stone was poured around the abutment analogs in the conventional way; Group B (GB), the dental stone was poured in two stages. Spacers were used over the abutment analogs (rubber tubes) and type IV dental stone was poured around the abutment analogs in the conventional way. After the stone had hardened completely, the spacers were removed and more stone was inserted in the spaces created. Six strain-gauges (Excel Ltd.), positioned in a cast bar, which was dimensionally accurate (perfect fit) to the master model, recorded the microstrains generated by each specimen. Data were analyzed statistically by the variance analysis (ANOVA) and Tukey's test (I+/-= 5%). RESULTS: The microstrain values (microepsilon) were (mean+/-SD): GA: 263.7+/-109.07microepsilon, and GB: 193.73+/-78.83microepsilon. CONCLUSION: There was no statistical difference between the two methods studied.