Evaluation of Implant Body Diameter, Platform Diameter, and the Use of a Transepithelial Component on Implant-Abutment Connection Microgap: An In Vitro Study with In Situ Hard X-Ray Radiography.

PURPOSE: To evaluate the effect of implant body diameter, platform diameter, and the use of transepithelial components on implant-abutment connection (IAC) microgap width. MATERIALS AND METHODS: In total, 16 tests were performed on four commercial dental restoration models (BTI Biotechnology Institute). Different static loads were applied to the embedded implants according to the International Organization for Standardization (ISO) 14801, using a customized loading device. Measurements of the microgap were taken by means of highly magnified x-ray projection in situ in a micro-CT scanner. Regression models were obtained and compared through an analysis of covariance (ANCOVA). To quantify the effect of each variable, t tests (α = .05) of experimental results were performed. RESULTS: Under 400 N, using a transepithelial component for the dental restoration, the microgap width was reduced by 20% (P = .044). Meanwhile, a 22% microgap reduction was observed when the implant body diameter was increased by 1 mm (P = .024). Finally, increasing the platform diameter by 1.4 mm led to a microgap reduction of 54% (P = .001). CONCLUSION: The use of a transepithelial component in dental restorations reduces the microgap width in IACs. Furthermore, given sufficient space for the implantation, larger implant bodies and platform diameters can also be used for this purpose. Int J Oral Maxillofac Implants 2023;38:489-495. doi: 10.11607/jomi.9855.

Effect of the geometry of butt-joint implant-supported restorations on the fatigue life of prosthetic screws.

STATEMENT OF PROBLEM: Dental implant geometry affects the mechanical performance and fatigue behavior of butt-joint implant-supported restorations. However, failure of the implant component has been generally studied by ignoring the prosthetic screw, which is frequently the critical restoration component. PURPOSE: The purpose of this in vitro study was to evaluate the effect of 3 main implant geometric parameters: the implant body diameter, the platform diameter, and the implant-abutment connection type (external versus internal butt-joint) on the fatigue life of the prosthetic screw. The experimental values were further compared with the theoretical ones obtained by using a previously published methodology. MATERIAL AND METHODS: Four different designs of direct-to-implant dental restorations from the manufacturer BTI were tested. Forty-eight fatigue tests were performed in an axial fatigue testing machine according to the International Organization for Standardization (ISO) 14801. Linear regression models, 95% interval confidence bands for the linear regression, and 95% prediction intervals of the fatigue load-life (F-N) results were obtained and compared through an analysis of covariance (ANCOVA) to determine the influence of the 3 parameters under study on the fatigue behavior (α=.05). RESULTS: Linear regression models showed a statistical difference (P<.001) when the implant body diameter was increased by 1 mm; an average 3.5-fold increase in fatigue life was observed. Increasing the implant abutment connection diameter by 1.4 mm also showed a significant difference (P<.001), leading to 7-fold longer fatigue life on average. No significant statistical evidence was found to demonstrate a difference in fatigue life between internal and external implant-abutment connection types. CONCLUSIONS: Increasing the implant platform and body diameter significantly improved (P<.001) the fatigue life of the prosthetic screw, whereas external and internal connections provided similar results. In addition, experimental results proved the accuracy of the fatigue life prediction methodology.

Fatigue performance of prosthetic screws used in dental implant restorations: Rolled versus cut threads.

STATEMENT OF PROBLEM: Cold rolling is widely used for screw thread manufacturing in industry but is less common in implant dentistry, where cutting is the preferred manufacturing method. PURPOSE: The purpose of this in vitro study was to compare the surface finish and mechanical performance of a specific model of prosthetic screw used for direct restorations manufactured by thread rolling and cutting. MATERIAL AND METHODS: The thread profiles were measured in an optical measuring machine, the residual stresses in an X-ray diffractometer, the surface finish in a scanning electron microscope, and then fatigue and static load tests were carried out in a direct stress test bench according to the International Organization for Standardization (ISO) 14801. Finally, linear regression models and 95% interval confidence bands were calculated and compared through ANCOVA for fatigue tests while the t test was used for statistical comparisons (α=.05). RESULTS: The surface finish was smoother, and compressive residual stresses were higher for the roll-threaded screws. Linear regression models showed a fatigue life 9 times higher for roll-threaded screws (P=1) without affecting static behavior, which showed statistically similar static strengths (P=.54). However, the thread profile in the roll-threaded screws was not accurately reproduced, but this should be easily corrected in future prototypes. CONCLUSIONS: Rolling was demonstrated to be a better thread-manufacturing process for prosthetic screws, producing improved surface quality and fatigue behavior.

Influence of vertical misfit in screw fatigue behavior in dental implants: A three-dimensional finite element approach.

Misfit is unavoidable in dental implant-supported prostheses due to machining process or inappropriate assembling, and the definition of an admissible misfit is still a controversial issue. This work aims to understand the behavior of the screws in dental implant-supported prostheses to estimate an admissible vertical misfit value in terms of screw fatigue failure. For that purpose, a finite element model of a dental implant-supported prosthesis was created and analyzed. Vertical misfits were introduced in different positions, the lower and upper screws were tightened to the bolting force values recommended by the manufacturer, and two different occlusal loads were analyzed. In addition, two different prosthesis materials were studied. Screw load variations were reported and a fatigue analysis was performed. As a result, it was observed that the screw tightening sequence closed small vertical misfits (equal to or less than 40 µm), whereas larger misfits (more than 40 µm) remained open. If the vertical misfit is closed by the end of the tightening sequence, it may be considered equivalent to the ideal fit situation in regard to screw fatigue failure. The prosthesis material had no significant influence on the fatigue behavior.