The influence of screw type, alloy and cylinder position on the marginal fit of implant frameworks before and after laser welding

Abstract

Misfit at the abutment-prosthetic cylinder interface can cause loss of preload, leading to loosening or fracture of gold and titanium screws. Objectives: To evaluate the influence of screw type, alloy, and cylinder position on marginal fit of implant frameworks before and after laser welding. Methods: After Estheticone-like abutments were screwed to the implants, thirty plastic prosthetic cylinders were mounted and waxed-up to fifteen cylindrical bars. Each specimen had three interconnected prosthetic components. Five specimens were one-piece cast in titanium and five in cobalt-chromium alloy. On each specimen, tests were conducted with hexagonal titanium and slotted gold screws separately, performing a total of thirty tested screws. Measurements at the interfaces were performed using an optical microscope with 5 μm accuracy. After sectioning, specimens were laser welded and new measurements were obtained. Data were submitted to a four-way ANOVA and Tukey's multiple comparisons test (α =0.05). Results: Slotted and hexagonal screws did not present significant differences regarding to the fit of cylinders cast in titanium, either in one-piece casting framework or after laser welding. When slotted and hexagonal screws were tested on the cobalt-chromium specimens, statistically significant differences were found for the one-piece casting condition, with the slotted screws presenting better fit (24.13μm) than the hexagonal screws (27.93 μm). Besides, no statistically significant differences were found after laser welding. Conclusions: 1) The use of different metal alloys do exert influence on the marginal fit, 2) The slotted and hexagonal screws play the exclusive role of fixing the prosthesis, and did not improve the fit of cylinders, and 3) cylinder position did not affect marginal fit values.

A Comparison of Two Soldering Techniques on the Misfit of Bar‐Retained Implant‐Supported Overdentures

“…Therefore, although it is widely recognized that soldering is a valid method for improving the passive fit, our results suggest just the opposite. This could possibly be explained by an error made along the method pathway, most likely during the linear shortening caused by soldering shrinkage not compensated for by investment expansion, an error on the microscope reading at the cross‐section of the bar, since the diagonal section showed a lower misfit, the excessive separation of the sectioned parts or another, unknown, cause. Also, the misfit values obtained in our study may be higher because they were measured opposite the tightened side, and previous studies have shown that the misfit is higher on the side opposite the tightened screw .…”

“…This could possibly be explained by an error made along the method pathway, most likely during the linear shortening caused by soldering shrinkage not compensated for by investment expansion, an error on the microscope reading at the cross‐section of the bar, since the diagonal section showed a lower misfit, the excessive separation of the sectioned parts or another, unknown, cause. Also, the misfit values obtained in our study may be higher because they were measured opposite the tightened side, and previous studies have shown that the misfit is higher on the side opposite the tightened screw . On the other hand, the different misfit values in our data on the left and right sides after tightening the screw at the opposite side, both before and after soldering, might be caused by differences located at the point where the bars were cut, the section area, or solder volume, or differences at the joint between the bars and gold cylinders.…”

“…This misfit value, although not exactly comparable to the values obtained in other studies due to the different variables involved in each of them (frameworks, alloys, tightening torque, whether all the screws are tightened) and regardless of whether the framework is going to be soldered, occupies an intermediate position between studies that found a higher misfit in a range between 62 and 450 µm 12,32,39 and others that found a lower misfit in a range between 11.18 and 43.04 µm. 6,30,31,34,38,40,41 In any case, the misfit obtained before the soldering procedure may be within a clinically acceptable range, although there is no unanimous agreement regarding the maximum level of clinically or biologically acceptable misfit in frameworks for implant-supported prostheses. Some authors maintain that this level should not exceed 30 µm 42 or 38 µm, 26 while others argue that misfit levels might be acceptable up to 150 µm.…”

Adaptação de infraestruturas metálicas de próteses fixas sobre implantes instalados na maxila por meio da cirurgia virtual guiada

“…As estruturas metálicas fundidas em monobloco, em virtude da contração de fundição inerente aos metais e ligas metálicas, parecem ter os níveis de desadaptação finais mais críticos (Castilio et al, 2006;Tiossi et al, 2010). Observando esses resultados, é interessante notar que, com a aplicação do torque de 10 Ncm, no método Todos houve redução considerável dos espaços existentes entre a infraestrutura metálica e os pilares de suporte, em relação aos valores encontrados nos métodos de Passividade A e D.…”

“…Esses achados reforçam os relatos da literatura (Goll, 1991;Tan, 1995;Torres et al, 2011) Esses desajustes das peças protéticas, assim como os desvios lineares e angulares dos implantes na cirurgia virtual guiada, podem estar relacionados às diferentes etapas envolvidas no processo de fabricação, incluindo desde a aquisição e manipulação das imagens da TC até o acabamento e polimento da prótese final (Tan, 1995;Castilio et al, 2006).…”