Does the Misfit Volume of Prosthetic Crowns Differ Before and After Ceramic Application? An In Vitro Radiographic Microtomography Analysis.

PURPOSE: To estimate the misfit volume of zirconia vs metal-ceramic crowns. MATERIALS AND METHODS: Five specimens were fabricated from zirconia and five from nichrome (metal-ceramic). Microcomputed tomography techniques were used to obtain volumetric reconstructions of misfit volume before and after ceramic application. RESULTS: The mean misfit volume for metal-ceramic crowns was 8.80 mm3, and for zirconia crowns was 6.76 mm3 (P = .003, 95% confidence interval [CI] 0.714 to 3.358). Misfit volume also did not differ significantly before and after ceramic application (metal-ceramic, P = .375, 95% CI 0.513 to 1.363; zirconia, P = .253, 95% CI 0.257 to 0.977). CONCLUSION: Zirconia crowns had a smaller mean misfit volume than metal-ceramic crowns. The change in misfit volume after ceramic application was minimal and unlikely to be of clinical relevance.

Clinical and Radiographic Assessment of Three-Implant-Supported Fixed-Prosthesis Rehabilitation of the Edentulous Mandible: Immediate Versus Delayed Loading.

PURPOSE: To evaluate and compare the clinical and radiographic outcomes of mandibular rehabilitation with fixed prostheses on three implants with immediate versus delayed loading. MATERIALS AND METHODS: The sample comprised 21 patients who underwent treatment with immediate loading and 23 who received delayed loading. All had worn their prostheses for at least 18 months. Radiographic evaluation of bone loss was carried out in Adobe Photoshop CS5 by a single calibrated examiner using digitized panoramic radiographs. Clinical examination of the technical conditions of the prosthetic device assessed the condition of the acrylic resin base, dental occlusion, metal framework, presence of cover screws, screw fixation of the prosthesis and abutments, length of cantilever (effort) and resistance arms, presence of plaque on prosthetic abutments, and hygiene of the prosthesis. RESULTS: One implant failed in each group, resulting in a 95.23% treatment success rate with immediate loading and 95.65% with delayed loading (no statistically significant between-group difference). In the immediate-loading group, the mean bone loss was 1.96 ± 0.73 mm around central implants and 1.64 ± 0.84 mm at distal implants. In the delayed-loading group, the mean bone loss was 1.85 ± 0.67 mm around central implants and 1.70 ± 0.77 mm at distal implants. According to Student t test, there was no significant within-group difference in bone loss and no difference between the immediate-loading and delayed-loading groups. The only prosthesis-related complications that differed significantly between groups were "condition of the acrylic base," "occlusion," and "presence of right cover screw." There was no statistically significant association of lever arm ratio with peri-implant bone loss or bone loss on the mesial surfaces compared to the distal surfaces of the distal implants. CONCLUSION: The three-implant-supported fixed prosthesis protocol tested in this study proved to be a viable therapeutic strategy for mandibular edentulous patients with maxillary complete dentures, regardless of whether loading was immediate or delayed, with no difference in peri-implant bone loss.

Wear Potential of Dental Ceramics and its Relationship with Microhardness and Coefficient of Friction.

PURPOSE: To evaluate, by means of pin-on-disk testing, the wear potential of different dental ceramic systems as it relates to friction parameters, surface finish, and microhardness. MATERIALS AND METHODS: Three groups of different ceramic systems (Noritake EX3, Eris, Empress II) with 20 disks each (10 glazed, 10 polished) were used. Vickers microhardness (Hv) was determined with a 200-g load for 30 seconds. Friction coefficients (µ) were determined by pin-on-disk testing (5 N load, 600 seconds, and 120 rpm). Wear patterns were assessed by scanning electron microscopy (SEM). The results were analyzed using one-way ANOVA and Tukey's test, with the significance level set at α = 0.05. RESULTS: The coefficients of friction were as follows: Noritake EX3 0.28 ± 0.12 (polished), 0.33 ± 0.08 (glazed); Empress II 0.38 ± 0.08 (polished), 0.45 ± 0.05 (glazed); Eris 0.49 ± 0.05 (polished), 0.49 ± 0.06 (glazed). Microhardness measurements were as follows: Noritake EX3 530.7 ± 8.7 (polished), 525.9 ± 6.2 (glazed); Empress II 534.1 ± 8 (polished), 534.7 ± 4.5 (glazed); Eris, 511.7 ± 6.5 (polished), 519.5 ± 4.1 (glazed). The polished and glazed Noritake EX3 and polished and glazed Eris specimens showed statistically different friction coefficients. SEM image analysis revealed more surface changes, such as small cracks and grains peeling off, in glazed ceramics. CONCLUSIONS: Wear potential may be related to the coefficient of friction in Noritake ceramics, which had a lower coefficient than Eris ceramics. Within-group analysis showed no differences in polished or glazed specimens. The differences observed were not associated with microhardness.

Evaluation of retention forces and resistance to fatigue of attachment systems for overdentures: plastic and metal components.

PURPOSE: To compare retention forces of 3 overdenture attachment systems with metal and plastic components. MATERIALS AND METHODS: Four samples of each system evaluated (Ball-Attachment [metal]; O-Ring, and ERA [plastic]) were prepared and underwent fatigue and retention force in a universal testing machine. Maximum retention force (N) was measured at 6 time points (from 0 to 36 months-0.5 mm/min). Two-way analysis of variance and the Tukey test were used (α = 0.05). RESULTS: The Ball-Attachment group showed the highest retention values, statistically greater than the other systems, without differences during the trial (42.75-44.75). The ERA group had intermediate values and a statistically significant decrease during the trial (20.75-14). The lowest retention forces were found for the O-Ring group (13.75-11.75), with no statistical differences during the trial. CONCLUSION: Retention forces are significantly affected by abutment type because the metal retainer was more retentive than plastics, possibly providing better fixation of the prosthesis in position, and more difficult to remove. After 6 months of simulation, retentiveness of both plastic components was similar. There was no fracture of any component.

Assessment of rehabilitation in edentulous patients treated with an immediately loaded complete fixed mandibular prosthesis supported by three implants.

PURPOSE: Conventionally, in patients with completely edentulous mandibles, fixed prostheses have been supported by four or more implants. However, an alternative protocol employing three implants and immediate loading has been developed. The objective of the present study was to assess the rehabilitation of edentulous patients treated with a complete fixed mandibular prosthesis with immediate loading and supported by three implants. MATERIALS AND METHODS: In this observational study, a total of 99 implants placed in 33 patients was evaluated after 18 months in use. Panoramic radiographs were digitized to measure bone loss at the mesial and distal surfaces of each implant. RESULTS: Mean peri-implant bone loss was 0.66 ± 0.51 mm for the left implant, 0.92 ± 0.61 mm for the central implant, and 0.82 ± 0.53 mm for the right implant. The bone loss observed around the distal implants was similar to that seen around the central implant, and there were no statistically significant differences in peri-implant bone loss between the three implant locations. There was no significant correlation between implant length and bone loss. The results were compatible with the peri-implant bone loss that has been described for prostheses of the same type supported by larger numbers of implants. CONCLUSIONS: The use of a complete fixed mandibular prosthesis with immediate loading supported by three implants proved to be an adequate option for the rehabilitation of edentulous patients. The protocol allowed simplification of treatment while maintaining similar bone loss to that reported for the same type of treatment supported by a larger number of implants.