Failure probability, stress distribution and fracture analysis of experimental screw for micro conical abutment

Abstract The aim of this study was to evaluate the failure probability of two types of abutment screws after compressive load and to analyze the stress distribution with finite element method. Sixty (60) single-tooth implant restorations were assembled on titanium implants (e-fix, A.S. Technology - Titanium Fix). The groups were divided into Conventional screw (Screw neck 1.5 ø mm) and Experimental screw (Screw neck constricted with 1.2 ø mm). Specimens were subjected to single load to failure with compressive test according ISO 14801. The fractured specimens were subjected to stereomicroscopy for measurement of remaining screws inside the implant and characterization of fracture origin. Representative specimens were analyzed by scanning electronic microscopy. For finite element method (FEM), an identical 3D model of the two in vitro test groups were used with similar conditions (30º, 100 N load). The stress in the abutment screw was analyzed by von-Mises criteria. The results of strength means were 4132.5 ± 76 MPa and 4528.2 ± 127.2 for conventional and experimental groups, respectively. During microscopy, the mean (mm) of the remaining screw piece inside the implants were 0.97 ± 0.23 and 1.32 ± 0.12 for conventional and experimental groups, respectively. In FEM, the conventional group showed stress concentered in an unfavorable region (peak of 39.23 MPa), while the experimental group showed more stress areas but less concentration than the conventional group (36.6 MPa). In using the tested experimental geometry, the abutment screw can have its strength improved, and the origin of failure can be more favorable to clinical resolution.

Resumo O objetivo deste estudo foi avaliar a probabilidade de falha de dois tipos de parafusos para pilar protético após a compressão e analisar a distribuição da tensão com o método dos elementos finitos. Sessenta (60) restaurações unitárias foram montadas em implantes de titânio (e-fix, A.S. Technology - Titanium Fix). Os grupos foram divididos em parafusos convencionais (parafuso de pescoço 1,5 ø mm) e parafuso experimental (parafuso de pescoço estreitado com 1,2 ø mm). As amostras foram sujeitas ao teste de compressão de acordo com ISO 14801. Os espécimes fraturados foram submetidos a estereomicroscopia para a mensuração dos parafusos restantes dentro do implante e caracterização da origem da fratura. Os espécimes representativos foram analisados ​​por microscopia eletrônica de varredura. Para o método de elementos finitos (FEM), utilizou-se um modelo 3D idêntico dos dois grupos de teste in vitro com condições semelhantes (30º, 100 N). A tensão no parafuso do pilar foi analisada pelo critério de von-Mises. Os resultados de resistência a compressão foram 4132,5 ± 76 MPa e 4528,2 ± 127,2 para grupos convencionais e experimentais, respectivamente. Durante a microscopia, a média do remanescente do parafuso restante dentro dos implantes foi de 0,97 ± 0,23 e 1,32 ± 0,12 mm para os grupos convencionais e experimentais, respectivamente. Em FEM, o grupo convencional mostrou tensão concentrada em uma região desfavorável (pico de 39,23 MPa), enquanto o grupo experimental apresentou mais áreas de tensão, porém menor concentração do que o grupo convencional (36,6 MPa). Ao usar a geometria experimental testada, o parafuso do pilar pode ter sua resistência melhorada e a origem da falha pode ser mais favorável à resolução clínica.

Finite element analysis of the effect of novel Lock Screw system preventing abutment screw loosening

PURPOSE: The purpose of this finite element analysis study is to introduce the novel Lock screw system and analyze its mechanical property to see if it can prevent abutment screw loosening. MATERIALS AND METHODS: The Lock screw is a component tightened on the inside of the implant abutment which applies compressive force to the abutment screw head. To investigate the effect, modeling was done using CAD program and it was analyzed by finite element analysis under various load conditions. First, the preload was measured according to the tightening torque of the abutment screw then it was compared with the theoretical value to verify the analytical model. The validated analytical model was then divided into those with no external load and those with 178 N, and the tightening torque of the lock screw was changed to 10, 20, 30 Ncm respectively to examine the property of stress distribution on the implant components. RESULTS: Using Lock screw under various loading conditions did not produce equivalent stresses beyond the yield strength of the implant components. In addition, the axial load was increased at the abutment-abutment screw interface. CONCLUSION: The use of Lock screw does not exert excessive stress on the implant components and may increase the frictional force between the abutment-abutment screw interface, thus it is considered to prevent loosening of the abutment screw.

A study of the effect of an anti-rotational inner post screw systems on abutment screw loosening for single implant : Part 1 / 대한치과보철학회지

STATEMENT OF PROBLEM: Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. PURPOSE: Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. MATERIAL AND METHODS: 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 10(6) cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. RESULTS: In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. CONCLUSION: Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.