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Statement of problem The mechanical behavior of the conical connection implant with different torque levels requires evaluation. Purpose The purpose of the finite element analysis study was to investigate the impact of abutment screw torque on the formation of microgaps at the implant-to-abutment interface of a conical connection under oblique loading. This is important because it is thought that bacteria can invade the internal implant space through the abutment-implant microgaps, causing peri-implantitis. Material and methods Three-dimensional finite element analyses of the conical implant-abutment connection were performed by using screw torques of 20 Ncm and 30 Ncm. Oblique loads from 10 N to 280 N were applied to the prosthesis placed on the implant. The maximum von Mises stress in the abutment screw, the microgap formation process, and the critical load for bridging the internal implant space were evaluated. Results The stresses in the abutment screw under oblique loading had limited sensitivity to the screw torque. However, the residual stress in the screw with a 30-Ncm torque was 35% higher than that with a 20-Ncm torque in the absence of an external load. The area in contact at the implant-to-abutment interface decreased with increasing load for both torque values. The critical load for bridging the internal implant space was 160 N for a screw torque of 20 Ncm and 220 N for a screw torque of 30 Ncm. The maximum gap size was approximately 470 μm with all the loads. Conclusions Increasing the screw torque can reduce the formation of microgaps at the implant-to-abutment interface. However, this will result in higher mean stress in the abutment screw, which may reduce its fatigue life and consequently that of the prosthesis. Further research is needed to evaluate the relationship between the abutment screw torque and microleakage in implant-supported restorations.

Objetivo. El objetivo de este estudio fue evaluar la adaptación marginal de coronas de disilicato de litio obtenidas mediante técnicas de escaneo (CAD/CAM), antes y después de la cristalización, a través de análisis in vitro con microscopía confocal (MC). Métodos. Fueron confeccionadas 16 réplicas en poliuretano a partir de la pieza 1.4, de modelo typodont, tallada para corona total. Las réplicas fueron divididas en dos grupos, de acuerdo a la técnica de escaneo: Técnica Indirecta (Grupo IND, n=08), donde modelos de yeso fueron escaneados con escáner de laboratorio (inEos X5, Sirona Dental Systems) y Técnica Directa (Grupo DIR, n=08), donde modelos typodont fueron escaneados con escáner intraoral (CEREC BlueCam, Sirona Dental Systems). A seguir, se fresaron (inLab MC XL, Sirona Dental Systems) coronas en disilicato de litio (IPS e.max CAD, Ivoclar Vivadent) y se adaptaron a las réplicas. Se evaluó la adaptación marginal con análisis de MC en dos momentos, antes y después de la cristalización del disilicato de litio. Los datos fueron analizados con la prueba de Mann-Whitney, t de Student y Wilcoxon (α= 0,05). Resultados. Hubo una diferencia estadísticamente significativa en la adaptación marginal horizontal entre los grupos IND y DIR después de la cristalización (p=0,05). En el grupo IND, la comparación de la adaptación marginal vertical antes y después de la cristalización mostró una diferencia estadísticamente significativa (p=0,038). Conclusiones. Las coronas de disilicato de litio obtenidas mediante escaneo directo (CAD/CAM) presentaron menor desajuste marginal vertical. La etapa de cristalización afectó la adaptación marginal de las coronas.

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone. Resumo Neste estudo foi avaliado desajuste vertical, a passividade e a distribuição de tensões após o aperto dos parafusos de diferentes próteses. Dois implantes foram usados para simular a reabilitação do espaço edêntulo da mandíbula do segundo pré-molar ao segundo molar. Quarenta próteses dentárias fixas parafusadas de três elementos com cantilever distal foram confeccionadas e separadas em quatro grupos de acordo com o método de obtenção da infraestrutura (n = 10): G1 = fundição convencional estrutura monobloco, G2 = fundição convencional seccionada e soldagem a laser, G3 = fundição convencional seccionada e soldagem com gás inerte de tungstênio (TIG) e G4 = infraestrutura obtida pelo sistema CAD / CAM (computer-aided design/computer-aided manufacturing). Os desajustes verticais com ambos os parafusos apertados e os desajustes relativos à avaliação de passividade com um parafuso apertado foram medidos com microscópio comparador óptico. Os dados foram submetidos ao teste de Shapiro-Wilk para comparação com ANOVA seguida de ajuste de Tukey com Bonferroni (α = 0,05). A análise qualitativa da distribuição de tensões foi realizada pelo método fotoelástico. G2 (24 μm) e G3 (27 μm) apresentaram valores significativamente maiores que G4 (10 μm) (p = 0,006) de desajuste vertical (ambos os parafusos apertados). Os valores de desajustes nos G1 (64 μm) e G3 (61 μm), do lado não apertado, foram significativamente maiores que no G4 (32 μm) (p = 0,009). G1 apresentou maior tensão entre os implantes na análise fotoelástica e G4 apresentou menor tensão. O método CAD/CAM resultou em menor desajuste, maior passividade e melhor distribuição de tensões no osso.

Objective Evaluate the effects of the scanning techniques and the crystallization in the internal and marginal adaptation of milled lithium disilicate crowns by two techniques computer microtomography analysis. Materials and methods Sixteen polyurethane teeth prepared for a complete crown were divided into two groups according to the scanner method (n = 8): indirect (IND), dental stone models were scanned with laser-surface scanner, and direct (DIR), digital typodont creates with an intraoral scanner. Internal and marginal gap were evaluated by micro-computed tomography (microCT). The replica technique (RT) was applied for analysis of total volume (TV) and marginal volume (MV) gap in microCT. The data showed normal distribution (Shapiro-Wilk test). One-way ANOVA (scanner techniques) with repeated measures (crystallization) was performed. Multiple comparisons were performed with Bonferroni adjustment (α = .05). Results The axial gap showed a significant difference between the times (P = .017) for lower values after crystallization. The vertical marginal gap presented a significant difference in times for higher value after crystallization (P = .001). The marginal horizontal gap IND was greater than DIR after crystallization (P = .001) and IND before lower than after crystallization. For TV was not significant difference and MV in DIR was reduction (P = .002) after crystallization. Conclusion Crystallization changes the relationship between the crown and tooth, reducing internal gap and preventing the adequate fit in indirect and direct scanning. Clinical significance The measure gap under technological methodology is useful for adjust clinical parameters prosthetic in the CAD/CAM and the applicability of the new possibilities of analysis.

O comportamento biomecânico de próteses parafusadas sobre implantes tem sido estudado para que haja melhor distribuição de stress, menor incidência de infiltração bacteriana e menor perda de torque no conjunto prótese-implante. Este estudo teve como objetivo analisar a interação do desajuste na interface implante-componente com a perda de torque, correlacionando com resultados obtidos na análise de comportamento biomecânico por meio do método de elementos finitos. Foram utilizados implantes de conexão interna cônica repondo o primeiro molar inferior. O presente estudo foi separado em dois grupos (n=10) para analisar dois diferentes componentes (micro pilar e UCLA) parafusados sobre o mesmo tipo de implante. Após a confecção da prótese metalo-cerâmica do tipo parafusada feita sobre cada tipo de componente, os conjuntos foram escaneados usando micro-CT, submetidos à ciclagem termomecânica (1 x 106 ciclos, sob carga de 100 N) e a perda de torque dos parafusos foi calculada antes e depois do carregamento oclusal simulado. A análise por elementos finitos (EF) também foi conduzida para avaliar a distribuição de tensão nos elementos. Desajustes de 30 µm foram detectados nas interfaces implantecomponente UCLA e este grupo apresentou também altos valores de perda de torque antes (28,78%) e após (32.75%) o ensaio termomecânico. O micro pilar exibiu a menor perda de torque antes (6.79%) e depois (4.11%) do carregamento cíclico oclusal. Já o parafuso protético apresentou 23.82% de perda de torque antes do ensaio e 27.85% após o ensaio. Os mais altos percentuais de perda de torque coincidiram com os valores mais altos de concentração de tensões nos parafusos, conforme analisados em EF. Dentro das limitações deste estudo, o design dos componentes, o desajuste na interface implante-componente e altas tensões nos parafusos foram associados a maior taxa de perda do torque. The biomechanical behavior of the prosthesis-implant-bone complex have been evaluated in order to propose improvements about the stress, less microleakage, and less torque loss in the implant assembly. This study aimed to evaluate the interaction of microgap and torque loss, correlating with the results of biomechanical behavior from finite element analysis (FEA). The conical internal connection implants replacing the first inferior molar were used in this study. The present study used two groups (n=10) with different abutments (micro-pilar and UCLA) screw-retained on the same type of implant. After the metal-ceramic prosthesis made on the abutments, the assemblies were subjected to cyclic loadings (n=10). Then, one specimen from each group were scanned using micro-CT. To the torque loss analysis, a digital torque gauge was used to evaluate the screw loosening before and after the thermo-mechanical cyclic load in each sample. Three-dimensional finite element (FEA) of the models were conducted to enable the stress distribution analysis among the components. A microgap of 30 µm was detected at UCLA abutment-implant interface. The samples with UCLA abutment presented the higher values of torque loss ratio before (28.78%) and after (32.75%) the cyclic load. The pilar abutment exhibited the lowest torque loss ratio before (6.79%) and after (4.11%). The prosthetic screw presented 23.82% of torque loss before loading and 27.85% after loading. The greater screw loosening agreed with the highest values of stress concentration assessed in FEA. The microgap and the design of the abutment has influence on screw loosening. The high stress concentration evaluated in FEA agreed with the torque loss in the screw.

This study used digital image correlation (DIC) to evaluate the strain transferred by splinted and non-splinted screw-retained fixed partial dentures (FPDs) supported by short and conventional implants.Four polyurethane models were fabricated to simulate half of the mandibular arch with acrylic resin replicas of the first premolar. Short (5 mm) and/or conventional (11 mm) implants replaced the second premolar and the first and second molars. Groups were: G1, two conventional (second premolar and first molar) and one short (second molar) implant; G2, one conventional (second premolar) and two short (first and second molar) implants; G3, three short implants; and G4, three conventional implants. Splinted (S) and non-splinted (NS) FPDs were screwed to the implant abutments. Occlusal load and a single point load on the second premolar, both of 250 N, were applied. Strain in the horizontal direction (ƐSplinted crowns presented the highest strain magnitudes of all tested groups (p 0.05). The strain was concentrated near the short implants and presented a higher magnitude compared to conventional implants, especially in G2S (-560.13 μS), G3S (-372.97 μS), and G4S (-356.67 μS).Splinted crowns presented a higher strain concentration around the implants, particularly near the implant replacing the first molar. A combination of short and conventional implants seems to be a viable alternative for the rehabilitation of the posterior edentulous mandible with reduced bone height.

A passividade da prótese parcial fixa (PPF) sobre implante e a distribuição de tensões ao osso pela infraestrutura, contribuem não só com a osseointegração como também para a sua manutenção. A análise de tensões por fotoelasticidade permite visualizar as magnitudes de tensões e deformações em um modelo confeccionado em resina fotoelástica que possui padrão de concentração e distribuição de tensões semelhantes ao tecido ósseo. Assim, este estudo teve como objetivos comparar a distribuição de tensões de PPFs associadas à cantilever com diferentes materiais de infraestrutura (Co-Cr e Zircônia [Zr]) e métodos de obtenção (CAD/CAM e fundição convencional [monobloco, soldagem a laser e soldagem com TIG]), quando submetidos a diferentes carregamentos oclusais (puntiforme e oclusal distribuído). A partir de um modelo mestre, foram confeccionados 3 modelos fotoelásticos simulando extremidade livre mandibular,com o dente 44 em resina e 2 implantes substituindo os dentes 45 e 46. Os grupos deste estudo incluíram PPFs com infraestruturas obtidas por meio de fundição convencional em monobloco (G1), seccionadas e soldadas a laser (G2) e com TIG (G3) e obtidas por meio do sistema CAD/CAM em Co-Cr (G4) e Zr (G5). As PPFs foram parafusadas sobre os mini pilares e submetidas a carregamento oclusal puntiforme e distribuído (150 N) para avaliação qualitativa das franjas e quantitativa em seis diferentes pontos: apical (P1) e distal (P2) do dente 44, apical (P3) e distal (P4) do implante substituindo o dente 45, apical (P5) e distal (P6) do implante substituindo o dente 46. A análise fotoelástica mostrou maior concentração de tensões na PPF com infraestrutura em monobloco (G1) e menor concentração nas próteses obtidas pelo método CAD/CAM (G4 e G5). Quando submetidos ao carregamento oclusal distribuído, a PPF com infraestrutura em Zr (G5) apresentou um aumento considerável na concentração de tensões, seguida por monobloco (G1) e as que foram soldadas a laser (G2) e TIG (G3). No carregamento pontual sobre o cantilever, a infraestrutura em Co-Cr soldada a TIG (G3) mostrou a maior concentração de tensões. Dentro das limitações deste estudo, concluiu-se que PPFs com infraestruturas obtidas por meio do sistema CAD/CAM foram associadas com menor concentração de tensões e que a secção de infraestruturas metálicas para posterior soldagem pode também ser uma alternativa viável, de acordo com a distribuição de tensões peri-implantes. The passivity of fixed partial denture (FPD) on implant and the stress distribution to the bone by the infrastructure, contribute not only to osseointegration but also to its maintenance. The stress analysis by photoelasticity allows visualizing the stresses and deformations magnitudes in a model fabricated in photoelastic resin that has a concentration pattern and stress distribution similar to the bone tissue. The aim of this study was to compare the stress distribution of cantilever FDPs with different infrastructure materials (Co-Cr and Zirconia [Zr]) and methods of manufacture (CAD/CAM and conventional casting [one piece, laser welding and welding with TIG]), when submitted to different occlusal loads (punctiform and distributed occlusal). From a master model, 3 photoelastic models were fabricated to simulate the mandibular free end, with the tooth 44 in resin and 2 implants replacing the teeth 45 and 46. The groups of this study included FPDs with infrastructures obtained by conventional casting in one piece (G1), sectioned and laser welded (G2) and TIG (G3) and obtained by the CAD/CAM system in Co-Cr (G4) and Zr (G5). The FDPs were screwed onto the abutments and subjected to punctate and distributed occlusal loading (150 N) for qualitative evaluation of the fringes and quantitative at six different points: apical (P1) and distal (P2) of the tooth 44, apical (P3) and distal (P4) of the implant replacing the tooth 45, apical (P5) and distal (P6) of the implant replacing the tooth 46. The photoelastic analysis showed a higher concentration of stresses in the FPD with one piece infrastructure (G1) and a lower concentration in the prosthesis obtained by CAD/CAM method (G4 and G5). When submitted to distributed occlusal loading, the FPD with Zr infrastructure (G5) showed a considerable increase in stress concentration, followed by one piece (G1) and those that were laser (G2) and TIG (G3) welded. In the cantilever load, the TIG welded Co-Cr infrastructure (G3) showed the highest stress concentration. Within the limitations of this study, it was concluded that FPDs with infrastructures obtained by the CAD/CAM system were associated with lower stress concentrations and that the section of metal infrastructures for later welding may also be a viable alternative, according to the peri-implant stress distribution.