Karla Zancopé

Placement of a distal implant to convert a mandibular removable Kennedy class I to an implant-supported partial removable Class III dental prosthesis: A systematic review

STATEMENT OF PROBLEM A number of authors have reported the placement of a distal implant associated with a partial removable dental prosthesis (PRDP) to make this rehabilitation more stable. This strategy may represent an option for resolving the problem of the intrusive movements of the PRDP and for reducing treatment costs. PURPOSE The purpose of this systematic review was to evaluate the current evidence about the placement of a distal implant associated with a mandibular PRDP to improve patient satisfaction and the clinical performance of the abutment tooth and distal implant. MATERIAL AND METHODS Two independent prosthetic specialist reviewers conducted this systematic review. The search was performed using selected clinical studies with PRDP associated with distal implants published in English up to May 2014 from the PubMed and Cochrane Library databases. A data extraction form was developed to collect general information: authors, title, year of publication, aim of study, level of evidence, number of participants, number of implants used, implant system, implant length and diameter, abutment type, masticatory performance, patient satisfaction, implant mean bone loss, abutment tooth mean bone loss, prosthetic complications, follow-up period, and implant survival rate. The quality of the selected studies and the risk of bias were also reported. RESULTS The initial electronic search identified 231 studies, and the manual process identified 15 studies (total of 246 studies). After the title and abstract reading and the removal of duplicates, the full texts of 43 studies were obtained. The articles that did not meet the inclusion criteria were excluded (28 studies), and the data from 15 studies were extracted. Seven were retrospective studies, 1 a crossover pilot study, 2 case series, 2 paired clinical studies, and 3 case reports, demonstrating that a high number of the selected studies were of low methodological quality. Nevertheless, the high survival rates for PRDP associated with dental implants have been described. CONCLUSIONS The use of a PRDP associated with dental implants to convert a Kennedy class I to class III dental prosthesis benefits patients by improving their satisfaction and masticatory abilities without decreasing implant survival rates. Considering the abutment tooth survival rate, clinical studies with comparable methodology are still lacking to define protocols regarding the use of distal implants associated with PRDP. Long-term, prospective clinical trials are still needed to understand which implant abutments increase abutment tooth survival rate.

Micrometric precision of prosthetic dental crowns obtained by optical scanning and computer-aided designing/computer-aided manufacturing system

Abstract. The current study evaluated prosthetic dental crowns obtained by optical scanning and a computer-aided designing/computer-aided manufacturing system using micro-computed tomography to compare the marginal fit. The virtual models were obtained with four different scanning surfaces: typodont (T), regular impressions (RI), master casts (MC), and powdered master casts (PMC). Five virtual models were obtained for each group. For each model, a crown was designed on the software and milled from feldspathic ceramic blocks. Micro-CT images were obtained for marginal gap measurements and the data were statistically analyzed by one-way analysis of variance followed by Tukey’s test. The mean vertical misfit was T=62.6±65.2  μm; MC=60.4±38.4  μm; PMC=58.1±38.0  μm, and RI=89.8±62.8  μm. Considering a percentage of vertical marginal gap of up to 75 μm, the results were T=71.5%, RI=49.2%, MC=69.6%, and PMC=71.2%. The percentages of horizontal overextension were T=8.5%, RI=0%, MC=0.8%, and PMC=3.8%. Based on the results, virtual model acquisition by scanning the typodont (simulated mouth) or MC, with or without powder, showed acceptable values for the marginal gap. The higher result of marginal gap of the RI group suggests that it is preferable to scan this directly from the mouth or from MC.

Influence of scanner, powder application, and adjustments on CAD-CAM crown misfit

Statement of problem. The manufacturers of computer‐aided design and computer‐aided manufacturing (CAD‐CAM) systems emphasize that new technologies can improve the marginal fit of dental crowns. However, data supporting this claim are limited. Purpose. The purpose of this in vitro study was to investigate the differences among the following fabrication methods on the marginal discrepancy of dental crowns: intraoral optical scanners, powder application, and adjustments of intaglio surface. Material and methods. A single human premolar was fixed on a typodont and prepared to receive crowns prepared by the CEREC CAD‐CAM system. Three fabrication techniques were used: digital scans using the CEREC Bluecam scanner with titanium dioxide powder (TDP), digital scans using the CEREC Omnicam scanner without TDP, and digital scans using the Omnicam scanner with TDP. Five experimental groups (n=10) were designated: Bluecam (group B), Bluecam with adjustments (group BA), Omnicam (group O), Omnicam with adjustments (group OA), and Omnicam with TDP (group OP). The specimens were scanned using microcomputed tomography to measure the vertical, horizontal, and internal fit and volumetric 3‐dimensional (3D) internal fit values of each luting space. The paired t test was used to evaluate mean marginal fit change after adjustments within the same group. One‐way analysis of variance and post hoc tests were used to compare groups B, O, and OP (&agr;=.05). Results. Mean vertical fit values ±standard deviations of group B=29.5 ±13.2 &mgr;m; BA=26.9 ±7.7 &mgr;m; O=149.4 ±64.4 &mgr;m; OA=49.4 ±12.7 &mgr;m; and OP=33.0 ±8.3 &mgr;m. Adjustments in the intaglio surface and TDP application statistically influenced the vertical fit of group O (P<.001). The percentage of vertical fit values <75 &mgr;m in group B=89.3%, BA=92.7%, O=31.0%, OA=73.5%, and OP=92.0%. Mean horizontal fit values for group B=56.2 ±21.5 &mgr;m; 85.8 ±44.4 &mgr;m for group BA; 77.5 ±11.8 &mgr;m for group O; 102.5 ±16.2 &mgr;m for group OA; and 91.4 ±19.4 &mgr;m for group OP. Results from group B were significantly different from those of the other test groups (P<.05). The percentages of horizontal misfit were 61.2% in group B; 73.5% in group BA; 88.1% in group O; 92.4% in group OA; and 85.0% in group OP. Volumetric 3D internal fit values in group B were 9.4 ±1.3 mm3; 10.7 ±1.0 mm3 in group BA; 11.8 ±2.1 mm3 in group O; 11.0 ±1.3 mm3 in group OA; and 9.6 ±0.9 mm3 in group OP. The overall results from groups B and OP were better than those of group O, with regard to vertical misfit and volumetric 3D internal fit. Conclusions. Different intraoral optical scanners, powder application, and internal adjustments influenced the marginal discrepancy of crowns. Crowns fabricated using the Omnicam system had significantly higher vertical discrepancy and volumetric 3D internal fit than those fabricated using the Bluecam scanner with TDP. Adjustments of the intaglio surface improved the vertical fit of crowns made using the Omnicam scanner; however, TDP application before Omnicam scanning improved the vertical fit as well as the volumetric 3D internal fit value of the luting space of crowns.

Strain analysis of different diameter Morse taper implants under overloading compressive conditions

The aim of this study was to evaluate the amount of deformation from compression caused by different diameters of Morse taper implants and the residual deformation after load removal. Thirty Morse taper implants lacking external threads were divided into 3 groups (n = 10) according to their diameter as follows: 3.5 mm, 4.0 mm and 5.0 mm. Two-piece abutments were fixed into the implants, and the samples were subjected to compressive axial loading up to 1500 N of force. During the test, one strain gauge remained fixed to the cervical portion of each implant to measure the strain variation. The strain values were recorded at two different time points: at the maximum load (1500 N) and 60 seconds after load removal. To calculate the strain at the implant/abutment interface, a mathematical formula was applied. Data were analyzed using a one-way Anova and Tukeys test (α = 0.05). The 5.0 mm diameter implant showed a significantly lower strain (650.5 μS ± 170.0) than the 4.0 mm group (1170.2 μS ± 374.7) and the 3.5 mm group (1388.1 μS ± 326.6) (p < 0.001), regardless of the load presence. The strain values decreased by approximately 50% after removal of the load, regardless of the implant diameter. The 5.0 mm implant showed a significantly lower strain at the implant/abutment interface (943.4 μS ± 504.5) than the 4.0 mm group (1057.4 μS ± 681.3) and the 3.5 mm group (1159.6 μS ± 425.9) (p < 0.001). According to the results of this study, the diameter influenced the strain around the internal and external walls of the cervical region of Morse taper implants; all diameters demonstrated clinically acceptable values of strain.

Micro-CT analysis of in-office computer-aided designed/computer-aided manufactured dental restorations

Abstract Purpose: The current study evaluated two different materials, using micro-CT to compare the marginal gap of feldspathic ceramic (V) and resin nano-ceramic (L) crowns obtained by two different computer-aided design/computer-aided manufacturing (CAD/CAM) systems, CEREC CAD/CAM system and E4D Technologies. Methods: A human lower left first premolar was mounted on a typodont model and prepared for an all-ceramic crown. Two groups (n = 5) were divided based on the system for obtaining the crowns and the material used for it (V and L). Micro-CT images were obtained for marginal gap measurements of each crown, and the data were statistically analysed by one-way analysis of variance followed by Tukey’s post hoc test for pairwise comparisons (α¼ 0.05). Results: There were no statistically significant differences between marginal gap of groups V and L (p = 0.473). The mean and standard deviation for the vertical misfit was V = 62.6 (65.2) and L = 66.5 (59.0). For the horizontal misfit, the values were divided into three groups: underextension (L = 20.8%) and (V = 54.6%), equally extended (L = 16.9%) and (V = 36.9%) and overextension (L = 62.3%) and (V = 8.5%). Conclusion: The results revealed no difference in the marginal fit of crowns produced by different materials and different chairside CAD/CAM systems. Both are considered clinically acceptable according to all cited classifications.

Influence of the Prosthetic Index on Fracture Resistance of Morse Taper Dental Implants

PURPOSE Manufacturers have inserted a prosthetic index, an internal hexagon to guide prosthetic components inside Morse taper implants. However, it is still unclear if this mechanism could decrease the mechanical strength of Morse taper implants. The aim of this study was to evaluate the influence of the prosthetic index inside Morse taper implants on fracture resistance compared with nonindexed implants. MATERIALS AND METHODS Fifty-seven Morse taper implants, with 11.5-degree angulation of the internal conical portion, were divided into three groups: implants without the prosthetic index and solid Morse taper universal post (group 1), implants with the prosthetic index and solid Morse taper universal post (group 2), and implants and abutments with the prosthetic index (group 3). All groups were modeled for finite element stress analysis (FEA), simulating force application of a perpendicular load to the abutments. Fracture resistance (n = 10) was determined under the same condition. Dynamic loading (n = 9) was also performed. The statistical analysis was performed using one-way analysis of variance (ANOVA), and the Tukey test was applied (α = .05). The metallographic analysis was used to identify the fracture distribution and the microstructure of the titanium alloy. RESULTS There was no statistically significant difference between the values of all tested groups. According to the FEA, the prosthetic index region was out of stress. The mean fracture resistances and loading test were 353.7 N and 200 N for group 1, 397.3 N and 170 N for group 2, and 372.0 N and 160 N for group 3, respectively. Metallographic analysis showed a macroscopic failure pattern just as demonstrated by FEA. CONCLUSION The presence of the prosthetic index on Morse taper implants did not decrease its resistance to fracture for the tested implants.