Cement fixation and screw retention: parameters of passive fit

Abstract

It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation--i.e. cement and screw retention--provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development.

Strain Gauge Analysis of the Effect of Porcelain Firing Simulation on the Prosthetic Misfit of Implant-Supported Frameworks

“…These results corroborate previous studies 8,12,13,16,27,28,29 which demonstrated that no metallic framework presents perfect fit. Despite the advanced technology, the material and techniques performed for fabrication of prostheses are not dimensionally accurate and require further research and development 6,15 .…”

“…The accomplishment of five measurements per sample, for both groups, at the three moments, aimed to minimize errors. High standard deviation values were recorded, similar to previous reports 28 , probably due to the high sensitivity of strain gauges when compared to the forces yielded in the system. It should be noted that despite the search for standardization, each metallic framework was a unique structure which implies unpredictable three-dimensional alterations.…”

“…The strain gauges were positioned on the upper aspect of the experimental block to record the micro-strain on the cervical region of the implants, since this area is subjected to the highest stress concentrations yielded by misfit 1,14,33 . Selection of this location was based on the methodology described in other studies 28,31,33,34 .…”

Estudo comparativo das microdeformações resultantes de cargas estáticas axiais e não axiais em próteses de três elementos implantossuportadas

“…Quanto ao posicionamento linear dos extensômetros, este trabalho está de acordo com Heckmann et al 19 , que estudaram deformações ao redor de implantes com estruturas metálicas A qualidade óssea é um fator de importância na eficácia do tratamento com implantes. O osso que os circunda não constitui um substrato homogêneo, de modo que suas propriedades físicas variam conforme a idade, o estado funcional e os fatores sistêmicos do paciente 7 .…”

Microdeformation of Infrastructure for Implant-Supported fixed Dental Prosthesis by Strain-Gauge Method: Influence of Technique and Material Impression

“…Electrical strain gauges are used to determine stress and deformation measurements in relation to the forces exerted on implants, and their transfer to the supporting structures [21][22][23][24][25]. The method is based on the use of electrical strain gauges, small electrical resistances that change the resistance to low intensity current, which detects the slightest deformation in the structure evaluated.…”