Retention System and Splinting on Morse Taper Implants in the Posterior Maxilla by 3D Finite Element Analysis

Abstract The purpose of this study was to evaluate different retention systems (cement- or screw-retained) and crown designs (non-splinted or splinted) of fixed implant-supported restorations, in terms of stress distributions in implants/components and bone tissue, by 3-dimensional (3D) finite element analysis. Four 3D models were simulated with the InVesalius, Rhinoceros 3D, and SolidWorks programs. Models were made of type III bone from the posterior maxillary area. Models included three 4.0-mm-diameter Morse taper (MT) implants with different lengths, which supported metal-ceramic crowns. Models were processed by the Femap and NeiNastran programs, using an axial force of 400 N and oblique force of 200 N. Results were visualized as the von Mises stress and maximum principal stress (σmax). Under axial loading, there was no difference in the distribution of stress in implants/components between retention systems and splinted crowns; however, in oblique loading, cemented prostheses showed better stress distribution than screwed prostheses, whereas splinted crowns tended to reduce stress in the implant of the first molar. In the bone tissue cemented prostheses showed better stress distribution in bone tissue than screwed prostheses under axial and oblique loading. The splinted design only had an effect in the screwed prosthesis, with no influence in the cemented prosthesis. Cemented prostheses on MT implants showed more favorable stress distributions in implants/components and bone tissue. Splinting was favorable for stress distribution only for screwed prostheses under oblique loading.

Resumo O objetivo deste estudo foi avaliar diferentes sistemas de retenção (cimentada x parafusada) e configuração da coroas (unitárias x esplintadas) de próteses fixas implantossuportadas em relação a distribuição de tensões nos implantes/componentes e tecido ósseo pela análise de elementos finitos 3D. Quatro modelos 3D foram simulados com auxílio dos programas Invesalius, e Rhinoceros 3D, e SolidWorks. Os modelos foram confeccionados simulando bloco ósseo de região posterior da maxila (tipo ósseo III), com 3 implantes cone Morse com 4,0 mm de diâmetro e diferentes comprimentos, suportando prótese metalocerâmica de 3 elementos. Os modelos foram processados pelos programas FEMAP e NEiNastran sob força axial de 400 N e oblíqua de 200N. Os resultados foram plotados através de mapas de tensão de von Mises (vM) (implantes e componentes) e tensão máxima principal (TMP) (tecido ósseo). Sobre o carregamento axial, não foi observada diferenças entre os diferentes sistemas de retenção e tipo de prótese na distribuição das tensões nos implantes/componentes, porém, sobre o carregamento oblíquo as próteses cimentadas apresentaram melhor distribuição de tensões em comparação com as próteses parafusadas, enquanto que as próteses esplintadas apresentou uma tendência de redução das tensões no implante do primeiro molar. No tecido ósseo as próteses cimentadas apresentaram melhor distribuição das tensões em comparação com as próteses parafusadas, independente do carregamento. A esplintagem foi favorável somente para as próteses parafusadas, não havendo influência sobre as próteses cimentadas. As próteses cimentadas sobre implantes cone Morse apresentam melhor comportamento biomecânico nos implantes/componentes e tecido ósseo. A esplintagem foi efetiva somente nas próteses parafusadas sob carregamento oblíquo.

The prognosis of splinted restoration of the most-distal implants in the posterior region

PURPOSE: The aim of this study was to compare the efficacies of two-implant splinting (2-IS) and single-implant restoration (1-IR) in the first and second molar regions over a mean functional loading period (FLP) of 40 months, and to propose the appropriate clinical considerations for the splinting technique. MATERIALS AND METHODS: The following clinical factors were examined in the 1-IR and 2-IS groups based on the total hospital records of the patients: sex, mean age, implant location, FLP, bone grafting, clinical crown-implant ratio, crown height space, and horizontal distance. The mechanical complications [i.e., screw loosening (SL), screw fracture, crown fracture, and repeated SL] and biological complications [i.e., peri-implant mucositis (PM) and peri-implantitis (PI)] were also evaluated for each patient. In analysis of two groups, the chi-square test and Student's t-test were used to identify the relationship between clinical factors and complication rates. The optimal cutoff value for the FLP based on complications was evaluated using receiver operating characteristics analysis. RESULTS: In total, 234 patients with 408 implants that had been placed during 2005 - 2014 were investigated. The incident rates of SL (P<.001), PM (P=.002), and PI (P=.046) differed significantly between the 1-IR and 2-IS groups. The FLP was the only meaningful clinical factor for mechanical and biological complication rates in 2-IS. CONCLUSION: The mechanical complication rates were lower for 2-IS than for 1-IR, while the biological complication rates were higher for 2-IS. FLP of 39.80 and 46.57 months were the reference follow-up periods for preventing biological and mechanical complications, respectively.

The effect of screw tightening techniques on the detorque value in internal connection implant superstructure / 대한치과보철학회지

PURPOSE: This study evaluated the effect of different screw tightening sequences and methods on detorque values in a well-fitting implant superstructure. MATERIAL AND METHODS: A fully edentulous mandibular master model and a metal framework directly connected to four parallel implants (Astra Tech) with a passive fit to each other were fabricated. Six stone casts were made with a splinted impression technique to represent a 'well-fitting' situation with the metal framework. Detorque values were measured twice after screw tightening using 20 Ncm. Detorque values and minimum detorque values for three screw tightening sequences (1-2-3-4, 2-4-3-1, and 2-3-1-4) and for two tightening methods (two-step and one-step) were analyzed using multi-way analysis of variance and two-way analysis of variance, respectively, at a .05 level of significance. RESULTS: The mean detorque values for screw tightening sequences ranged from 12.8 Ncm (2-4-3-1) to 13.1 Ncm (2-3-1-4), and for screw tightening methods were 13.1 Ncm (two-step) and 11.8 Ncm (one-step). The mean of mimimum detorque values for screw tightening sequences were 11.1 Ncm (1-2-3-4) and 11.2 Ncm (2-4-3-1 and 2-3-1-4), and for screw tightening methods were 11.2 Ncm (two-step) and 9.9 Ncm (one-step). No statistically significant differences among three screw tightening sequences were found for detorque values and for mimimum detorque values. But, statistically significant differences between two screw tightening methods were found for two values. Two-step screw tightening method showed higher detorque value (P = .0003) and higher minimum detorque value (P = .0035) than one-step method. CONCLUSION: Within the limitations of this study, the screw tightening sequence was not a critical factor for the detorque values in a well-fitting implant superstructure by the splinted impression technique. But, two-step screw tightening method showed greater detorque values than one-step method.

Evaluation of the accuracy of fixture-level impression technique for internal connection implant using clinical methods / 대한치과보철학회지

Statement of problem: Accurate impression is essential to success of implant prostheses. But there have been few studies about the accuracy of fixture-level impression technique in internal connection implant system. Purpose: This study evaluated the accuracy of splinted fixture-level impression technique using clinical methods and the effect of internal hex on fit of superstructure in internal connection implant system (Astra Tech). Material and method: Two metal master frameworks made from two abutments (Cast-to Abutment ST) each for parallel and divergent conditions and a corresponding, passively fitting, dental stone master cast with four fixture replicas (Fixture Replica ST) were fabricated. Ten dental stone casts were made with vinyl polysiloxane impressions from the master cast by acrylic resin splinted fixture-level impression technique. To evaluate the accuracy of impression technique, the fit of master frameworks for test models was evaluated using screw resistance test (SRT) and onescrew test. The results of SRT were recorded as SRT values from grade 1 to grade 5 by 1/4 turn. And to evaluate the effect of hex on fit of superstructure, the same tests were performed after removing hexes of master frameworks. Results: 1. There was only one case (2.5%) showing SRT value of test model below grade 2 in total before and after removing hexes of master frameworks. And, by removing hexes, SRT values decreased in only one test model (5%) and did not change in 17 test models (85%). 2. SRT values of the 1st screws were grade 2 in 80% of cases before, and grade 1 in 80% of cases after removing hexes. And, by removing hexes, SRT values decreased in 72.5% of cases. 3. SRT values of the 2nd screws were grade 3 in 85% of cases before, and grade 3 in 95% of cases after removing hexes. And, by removing hexes, SRT values did not change in 85% of cases. 4. There were only 2 cases regarded as acceptable fit by one-screw test, and SRT values of 2nd screws of both cases were grade 2. Conclusion: Within the limitations of this study, fixture-level impression of internal connection implant system is considered to obtain inaccurate working cast, even using acrylic resin splinted impression technique. And, it is considered to be unable to improve the fit to remove the hexes of implant restoration.