Cementation of Prosthetic Restorations: From Conventional Cementation to Dental Bonding Concept

The cementation procedure of metal-free fixed partial dentures exhibits special characteristics about the porcelains and cementation agents, which turns the correct association between these materials necessary. Our purpose in this literature review was to point the main groups of cements associated to metal-free restoration and discuss about the advantages, disadvantages, and recommendations of each one. Our search was confined to the electronic databases PubMed and SciELO and to books about this matter. There are essentially 3 types of hard cement: conventional, resin, or a hybrid of the two. The metal-free restorations can be fixed with conventional or resin cements. The right choice of luting material is of vital importance to the longevity of dental restorative materials. Conventional cements are advantageous when good compressive straight, good film thickness, and water dissolution resistance are necessary. However, they need an ideal preparation, and they are not acid dissolution resistant. Conventional cements are indicated to porcelains that cannot be acid etched. Resin cements represent the choice to metal-free restoration cementation because they present better physical properties and aesthetic than conventional agents

Three-Dimensional Finite Element Analysis of Vertical and Angular Misfit in Implant-Supported Fixed Prostheses

Purpose: Three-dimensional finite element analysis was used to evaluate the effect of vertical and angular misfit in three-piece implant-supported screw-retained fixed prostheses on the biomechanical response in the peri-implant bone, implants, and prosthetic components. Materials and Methods: Four three-dimensional models were fabricated to represent a right posterior mandibular section with one implant in the region of the second premolar (2PM) and another in the region of the second molar (2M). The implants were splinted by a three-piece implant-supported metal-ceramic prosthesis and differed according to the type of misfit, as represented by four different models: Control = prosthesis with complete fit to the implants; UAM (unilateral angular misfit) = prosthesis presenting unilateral angular misfit of 100 pm in the mesial region of the 2M; UVM (unilateral vertical misfit) = prosthesis presenting unilateral vertical misfit of 100 pm in the mesial region of the 2M; and TVM (total vertical misfit) = prosthesis presenting total vertical misfit of 100 pm in the platform of the framework in the 2M. A vertical load of 400 N was distributed and applied on 12 centric points by the software Ansys, ie, a vertical load of 150 N was applied to each molar in the prosthesis and a vertical load of 100 N was applied at the 2PM. Results: The stress values and distribution in peri-implant bone tissue were similar for all groups. The models with misfit exhibited different distribution patterns and increased stress magnitude in comparison to the control. The highest stress values in group UAM were observed in the implant body and retention screw. The groups UVM and TVM exhibited high stress values in the platform of the framework and the implant hexagon, respectively. Conclusions: The three types of misfit influenced the magnitude and distribution of stresses. The influence of misfit on peri-implant bone tissue was modest. Each type of misfit increased the stress values in different regions of the system. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:788-79

A comparison of profilometer and AutoCAD software techniques in evaluation of implant angulation in vitro

Purpose: The aim of this study was to compare 2 different methods of assessment of implants at different inclinations (90 degrees and 65 degrees)-with a profilometer and AutoCAD software. Materials and Methods: Impressions (n = 5) of a metal matrix containing 2 implants, 1 at 90 degrees to the surface and 1 at 65 degrees to the surface, were obtained with square impression copings joined together with dental floss splinting covered with autopolymerizing acrylic resin, an open custom tray, and vinyl polysiloxane impression material. Measurement of the angles (in degrees) of the implant analogs were assessed by the same blinded operator with a profilometer and through analysis of digitized images by AutoCAD software. For each implant analog, 3 readings were performed with each method. The results were subjected to a nonparametric Kruskal-Wallis test, with P <= .05 considered significant. Results: For implants perpendicular to the horizontal surface of the specimen (90 degrees), there were no significant differences between the mean measurements obtained with the profilometer (90.04 degrees) and AutoCAD (89.95 degrees; P=.9142). In the analyses of the angled implants at 65 degrees in relation to the horizontal surface of the specimen, significant differences were observed (P=.0472) between the mean readings with the profilometer (65.73 degrees) and AutoCAD (66.25 degrees). Conclusions: The degrees of accuracy of implant angulation recording vary among the techniques available and may vary depending on the angle of the implant. Further investigation is needed to determine the best test conditions and the best measuring technique for determination of the angle of the implant in vitro

Platform Switching: Biomechanical Evaluation Using Three-Dimensional Finite Element Analysis

Purpose: The objective of this study was to evaluate, using three-dimensional finite element analysis (3D FEA), the stress distribution in peri-implant bone tissue, implants, and prosthetic components of implant-supported single crowns with the use of the platform-switching concept. Materials and Methods: Three 3D finite element models were created to replicate an external-hexagonal implant system with peri-implant bone tissue in which three different implant-abutment configurations were represented. In the regular platform (RP) group, a regular 4.1-mm-diameter abutment (UCLA) was connected to regular 4.1-mm-diameter implant. The platform-switching (PS) group was simulated by the connection of a wide implant (5.0 mm diameter) to a regular 4.1-mm-diameter UCLA abutment. In the wide-platform (WP) group, a 5.0-mm-diameter UCLA abutment was connected to a 5.0-mm-diameter implant. An occlusal load of 100 N was applied either axially or obliquely on the models using ANSYS software. Results: Both the increase in implant diameter and the use of platform switching played roles in stress reduction. The PS group presented lower stress values than the RP and WP groups for bone and implant. In the peri-implant area, cortical bone exhibited a higher stress concentration than the trabecular bone in all models and both loading situations. Under oblique loading, higher intensity and greater distribution of stress were observed than under axial loading. Platform switching reduced von Mises (17.5% and 9.3% for axial and oblique loads, respectively), minimum (compressive) (19.4% for axial load and 21.9% for oblique load), and maximum (tensile) principal stress values (46.6% for axial load and 26.7% for oblique load) in the peri-implant bone tissue. Conclusion: Platform switching led to improved biomechanical stress distribution in peri-implant bone tissue. Oblique loads resulted in higher stress concentrations than axial loads for all models. Wide-diameter implants had a large influence in reducing stress values in the implant system. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:482-49

Evaluation of the Effect of Retightening and Mechanical Cycling on Preload Maintenance of Retention Screws

Purpose: The aim of this study was to evaluate the effect of retightening and mechanical cycling on the maintenance of preload in the retention screws of implant-supported crowns. Materials and Methods: Five groups (n = 12 in each group) of implant-crown assemblies were created according to different abutments and veneering materials: Gold UCLA abutments cast in gold alloy veneered with ceramic (group 1) and light-curing resin (group 2), UCLA abutments cast in titanium veneered with ceramic (group 3) and light-curing resin (group 4), and zirconia abutments with ceramic veneering (group 5). The crowns were attached to implants by gold retention screws. The assemblies were submitted to mechanical cycling for a total of 1 million cycles. Removal torque measurements were performed initially and after each period of 100,000 cycles; this was followed by screw retightening with 35 Ncm of torque. Data were evaluated with analysis of variance, the paired t test, and the Student t test. Results: All groups exhibited reduced removal torque values in comparison to insertion torque initially and after all periods of mechanical cycling. Analysis of variance revealed statistically significant differences among the groups, but there were no differences among the periods of mechanical cycling or for the interaction between groups and cycling. Group I was the only group that did not show a difference between removal torque values of different cycling periods. The Student t test did not reveal statistically significant differences between mean removal torque values obtained before and after mechanical cycling, except for group 4. Conclusions: Torque maintenance allowed screw joint stability in the present study Mechanical cycling associated with the retightening of abutment screws did not influence the maintenance of insertion torque. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:251-256Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Effect of polymerization methods and thermal cycling on color stability of acrylic resin denture teeth

Statement of problem: Acrylic resin denture teeth are widely used due to the chemical bond to the acrylic resin of the denture base. However, discoloration of acrylic resin denture teeth can be a problem. Purpose: The purpose of this study was to investigate the effect of polymerization methods and thermal cycling on the color change of acrylic resin denture teeth. Material and methods: Ten different brands of acrylic resin denture teeth were evaluated: Art Plus (AP), Biolux (BX), Biotone IPN (BI), Magister (MG), Mondial 6 (MD), Premium 6 (PR), SR Vivodent PE (SR), Trilux (TR), Trubyte Biotone (TB), and Vipi Dent Plus (VP). Each brand was divided into 2 groups (n=12); each group was subjected to 1 of 2 polymerization methods (microwave, 500 W for 3 minutes, or water bath, 74°C for 9 hours). After polymerization, all of the specimens were thermal cycled between 5°C and 55°C with 30-second dwell times for 5000 cycles. The specimen colors were measured with a spectrophotometer, using the CIE L*a*b* system, at baseline (B), after polymerization (P), and after thermal cycling (T). Color differences (ΔE) were calculated for periods between P and B (PB), T and B (TB), and T and P (TP). A ΔE of ≤3.3 was considered clinically acceptable. The data were evaluated by 3-way repeated-measures ANOVA and the Tukey HSD test (α=.05). Results: The highest ΔE values were obtained for BI and SR teeth; these were significantly higher than the values obtained for the other brands (P<.05). There was no significant difference between the 2 polymerization methods. There was no significant difference between TB and PB for either polymerization method. Conclusions: The ΔE values are within acceptable clinical limits for all brands, for both polymerization methods and different measurement periods. © 2009 The Editorial Council of the Journal of Prosthetic Dentistry.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Comparing the efficacy of mandibular implant-retained overdentures and conventional dentures among elderly edentulous patients: satisfaction and quality of life

Objectives: the aim of this study was to compare the satisfaction and the quality of life in an elderly population using either mandibular conventional dentures or implant-retained overdentures.Materials and methods: A total of 34 patients were divided into two groups: group I-complete dentures users; group II - users of upper complete dentures opposed by implant-retained overdentures. The subjects were submitted to a questionnaire based on Oral Health impact Profile and oral health related quality of life to evaluate their satisfaction levels and quality of life with their prostheses. Data were evaluated using a non-parametric statistical analysis (Fischer test) with significant difference at alpha = 0.05.Results: There were no significant differences between the groups in relation to comfort, aesthetics, chewing ability, overall satisfaction, pain, functional, phonetic, social, and psychological limitations (p > 0.05). Comparing the stability of mandibular dentures, group II presented the better results (p < 0.05).Conclusion: Although the stability of the mandibular implant-retained overdenture was enhanced compared to a conventional denture, the quality of life and satisfaction levels were similar for both the groups

The Role of Implant/Abutment System on Torque Maintenance of Retention Screws and Vertical Misfit of Implant-Supported Crowns Before and After Mechanical Cycling

Purpose: This study aimed to evaluate the role of the implant/abutment system on torque maintenance of titanium retention screws and the vertical misfit of screw-retained implant-supported crowns before and after mechanical cycling. Materials and Methods: Three groups were studied: morse taper implants with conical abutments (MTC group), external-hexagon implants with conical abutments (EHC group), and external-hexagon implants with UCLA abutments (EHU group). Metallic crowns casted in cobalt-chromium alloy were used (n = 10). Retention screws received insertion torque and, after 3 minutes, initial detorque was measured. Crowns were retightened and submitted to cyclic loading testing under oblique loading (30 degrees) of 130 +/- 10 N at 2 Hz of frequency, totaling 1 x 10(6) cycles. After cycling, final detorque was measured. Vertical misfit was measured using a stereomicroscope. Data were analyzed by analysis of variance, Tukey test, and Pearson correlation test (P < .05). Results: All detorque values were lower than the insertion torque both before and after mechanical cycling. No statistically significant difference was observed among groups before mechanical cycling. After mechanical cycling, a statistically significantly lower loss of detorque was verified in the MTC group in comparison to the EHC group. Significantly lower vertical misfit values were noted after mechanical cycling but there was no difference among groups. There was no significant correlation between detorque values and vertical misfit. Conclusions: All groups presented a significant decrease of torque before and after mechanical cycling. The morse taper connection promoted the highest torque maintenance. Mechanical cycling reduced the vertical misfit of all groups, although no significant correlation between vertical misfit and torque loss was found

Influence of Abutment Type and Esthetic Veneering on Preload Maintenance of Abutment Screw of Implant-Supported Crowns

Purpose: The effect of veneering materials on screw joint stability remains inconclusive. Thus, this study evaluated the preload maintenance of abutment screws of single crowns fabricated with different abutments and veneering materials. Materials and Methods: Sixty crowns were divided into five groups (n = 12): UCLA abutment in gold alloy with ceramic (group GC) and resin (group GR) veneering, UCLA abutment in titanium with ceramic (group TiC) and resin (group TiR) veneering, and zirconia abutment with ceramic veneering (group ZiC). Abutment screws made of gold were used with a 35 Ncm insertion torque. Detorque measurements were obtained initially and after mechanical cycling. Data were analyzed by ANOVA and Fisher's exact test at a significance level of 5%. Results: For the initial detorque means (in Ncm), group TiC (21.4 ± 1.78) exhibited statistically lower torque maintenance than groups GC (23.9 ± 0.91), GR (24.1 ± 1.34), and TiR (23.2 ± 1.33) (p < 0.05, Fisher's exact test). Group ZiC (21.9 ± 2.68) exhibited significantly lower torque maintenance than groups GC, GR, and TiR (p < 0.05, Fisher's exact test). After mechanical cycling, there was a statistically significant difference between groups TiC (22.1 ± 1.86) and GR (23.8 ± 1.56); between groups ZiC (21.7 ± 2.02) and GR; and also between groups ZiC and TiR (23.6 ± 1.30) (p < 0.05, Fisher's exact test). Conclusions: Detorque reduction occurred regardless of abutment type and veneering material. More irregular surfaces in the hexagon area of the castable abutments were observed. The superiority of any veneering material concerning preload maintenance was not established. © 2013 by the American College of Prosthodontists.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP