Influência de diferentes pilares e materiais de recobrimento estético na manutenção da pré-carga do parafuso de retenção de coroas implantosuportadas

A longevidade das próteses e implantes é dependente da adequada adaptação entre os componentes bem como da distribuição favorável de forças às estruturas de suporte. O afrouxamento do parafuso de retenção é uma falha mecânica comumente observada devido à redução da pré-carga gerada no parafuso de retenção, responsável pela manutenção da estabilidade da união parafusada e resistência às forças que tendem a separar os componentes. O objetivo do estudo foi avaliar a influência de diferentes pilares e materiais de recobrimento estético na manutenção da pré-carga do parafuso de retenção de coroas implantosuportadas, submetidos a sucessivos reapertos e ciclagem mecânica. Foram confeccionadas 60 coroas de acordo com os grupos de estudo (n=12): Grupo I - pilares Gold UCLA fundidos em liga de ouro para obtenção de coroas metalocerâmicas, Grupo II - pilares Gold UCLA fundidos em liga de ouro para obtenção de coroas metaloplásticas, Grupo III – pilares do tipo UCLA fundidos em liga de titânio para obtenção de coroas metalocerâmicas, Grupo IV – pilares do tipo UCLA fundidos em liga de titânio para obtenção de coroas metaloplásticas, Grupo IV - pilares de zircônia obtidos pelo sistema CAD/CAM (computer-aided design/computer-aided manufacturing) para obtenção de coroas cerâmicas. As coroas foram unidas a implantes de hexágono externo por meio de parafuso de retenção quadrado de ouro com torque de inserção de 35 Ncm e submetidas à ciclagem mecânica com aplicação de carregamento vertical dinâmico de 50N a uma freqüência de 2Hz. Valores de destorque foram mensurados antes da ciclagem mecânica e após cada período de 1x105 ciclos seguido de reaperto com 35 Ncm de modo a completar 1x106 ciclos. Mensurações da desadaptação vertical na interface pilar-implante foram realizadas através de estereomicroscopia inicialmente e ao final da...The longevity of prostheses and implants depends on fit betweenn components as well as adequate forces distribution to supporting structures. Retaining screw loosening is a commom mechanical complication due to preload reduction that provides joint stability and resistance to separating forces. The aim of this study was to evaluate the influence of different abutments and veneering materials on preload maintenance of retaining screw of implant-supported crowns submitted to repeated tightening and mechanical cycling. Sixty crowns were obtained according to the groups (n=12): Group I – Gold UCLA abutment cast in gold allow with ceramic vennering, Group II – Gold UCLA abutment cast in gold alloy with resin veneering, Group III – UCLA abutment cast in titanium with ceramic veneering, Group IV – UCLA abutment cast in titanium with resin veneering, and Group V – zirconia abutment obtained by CAD/CAM (computer-aided desing/computer-aided manufacturing) system with ceramic veneering. The crowns were attached to external hexagon implants by gold retaining screws with insertion torque of 35Ncm. The replicas were submitted to mechanical cycling with vertical dinamic loading of 50N at 2Hz. Detorque measurements were performed initially and after each period of 1x105 cycles followed by retightening of retaining screw with 35Ncm until 1x106 cycles. Measurements of vertical misfit on abutment-implant interface were performed through estereomicroscopy initially and after mechanical cycling. Data were submitted to analysis of variance, Fisher’s exact test, paired t test, Student’s t-test and Pearson correlation (P<.05). All detorque measurements were lower than insertion torque of 35Ncm. There was statistically significant difference among the 5 groups (P<.05) for detorque values obtained initially and after mechanical cycling. However, there was no statistically significant difference... (Complete abstract click electronic access below

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

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

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

Retention Systems to Implant-Supported Craniofacial Prostheses

Osseointegrated implants in craniofacial reconstructions improve prostheses retention and stability and comfort and safety for a patient. According to biomechanical principles, the treatment success regarding osseointegration maintenance depends on an adequate surgical technique associated to a retention system that provides favorable tension distribution to implants. Furthermore, patient expectation, esthetics, function, and anatomic limitations must be evaluated during treatment planning. Therefore, the aims of this study were to present available retention systems to implant-supported craniofacial prosthesis and to highlight the advantages, indications, and limitations. A literature review was conducted through a MEDLINE search. Sixteen articles and 2 textbooks met the inclusion criteria and were included in the review. It was concluded that the success of craniofacial rehabilitation with implants depends on an adequate surgical technique and an adequate selection of a retention system

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