The influence of DLC-coating deposition method on the mechanical properties and reliability of abutment's screws

Orientador: Altair Antoninha Del Bel CuryTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de PiracicabaResumo: As complicações protéticas em reabilitações unitárias implantossuportadas envolvem o comprometimento da integridade do sistema de parafuso-pilar onde o afrouxamento e/ou fratura do parafuso do pilar é a falha protética mais frequente. Dessa forma, a utilização de tratamentos de superfície que melhorem o desempenho mecânico dos parafusos pode contribuir para o aumento do sucesso das reabilitações em longo prazo. O objetivo desse estudo foi avaliar a influência do método de deposição do DLC (Diamond-like carbon) em parafusos de pilares quanto ao desempenho mecânico de restaurações unitárias implantossuportadas. Para isso, setenta e cinco parafusos de geometria idêntica foram randomizados em três grupos de acordo com o método de aplicação do DLC: CTRL: controle (sem nenhum tratamento); RFPA (DLC aplicado pelo método de radio frequence plasma-activated) (grupo experimental); UMS- DLC aplicado pelo método de unbalanced magnetrom sputtering (grupo experimental). Inicialmente foi realizada a mensuração das propriedades mecânicas das superfícies tratadas ou não, avaliando a nanodureza e o módulo de elasticidade (ME) de doze parafusos (n=4/grupo). As diferenças entre os grupos foram avaliadas por meio do modelo linear misto. Os dados obtidos no teste de nanodureza foram utilizados como parâmetros para alimentar uma análise de elementos finitos (in silico) e avaliar a tensão gerada diretamente sobre o DLC e na interface com o titânio. Para isso, foi modelado um bloco (5 x 5 x 10mm) considerado como substrato de titânio. Sobre ele, foi modelada uma camada representativa de tratamento de superfície de 4µm de espessura e uma contraparte representando uma secção de rosca para aplicação de carga. Foram obtidos três modelos virtuais totais, simulando a presença dos tratamentos de superfície: Ctrl, UMS e RFPA (n=1/grupo). Sobre a contraparte foi aplicada uma carga de 30 N para simular um torque de apertamento de parafusos. As variáveis respostas foram a tensão de cisalhamento (MPa) e deformação (µm) em duas superfícies: em contato com a contraparte e na interface com o substrato. Para o teste de fadiga progressiva acelerada (in vitro), os vinte e um parafusos remanescentes de cada grupo foram conectados à pilares personalizados e esses conectados à implantes de conexão hexagonal externa (4,0 x 10mm). Todos os parafusos receberam o mesmo torque de apertamento (30 Ncm) de acordo com as recomendações do fabricante e verificado por meio de torquímetro digital. Três espécimes de cada grupo foram submetidos ao teste uniaxial de compressão até a falha. Os valores médios de falha foram utilizados para a obtenção de três perfis de carga necessários para o teste de fadiga progressiva acelerada. Os perfis nomeados de leve (n=9/grupo), moderado (n=6/grupo) e agressivo (n=3/grupo) se referiram ao aumento progressivo da carga. A curva de probabilidade de Weibull (resistência característica vs. módulo de Weibull) e a probabilidade de sobrevivência foram calculadas considerando a simulação das missões de 50.000 e 100.000 ciclos e cargas de 100, 150 e 200 N. As amostras fraturadas, mais representativas, de cada grupo foram avaliadas em microscopia eletrônica de varredura (MEV) para caracterização fractográfica. De acordo com os resultados obtidos no teste de nanoindentação, ambos grupos recobertos com DLC demonstraram nanodureza superiores ao controle (p,05). A análise in silico demonstrou que quanto maior o módulo de elasticidade do DLC, maior a tensão de cisalhamento, especialmente na região de interface entre DLC e substrato de titânio. Em relação ao teste mecânico de fadiga, os grupos CTRL e RFPA demonstraram valores de Beta (ß) .05). The in silico analysis showed that, the higher the Young¿s modulus the greater the shear stress at interface between substrate and coating. Regarding the fatigue testing, the CTRL and RFPA showed ß<1, (ß =0.68 and ß=0.62, respectively), indicating that failures were attributed to materials strength (egregious flaws) associated to early failures. Nevertheless, the UMS showed ß =1.14 indicating that fatigue contributed to accelerate failure (damage accumulation) and tends to behave as late failures. All groups showed high reliability at 100 N-mission (99%). However, a decreased reliability was observed at 200 N for all groups at 50,000 cycles (Ctrl: 51.46%; UMS: 66.53%; RFPA: 54.75%) and 100,000 cycles (Ctrl: 41.14%; UMS: 40.66%; RFPA: 39.56%). There was no difference between experimental and control group regardless the number of cycles and loads simulated (missions). The screw fracture was the chief failure mode for all groups. According to the results, it can be concluded that both DLC-coatings increase the hardness but did not influence the probability of survival of abutment¿s screwsDoutoradoProtese DentalDoutor em Clínica Odontológica6780/2015-06CAPE

Influence of abutment collar height and implant length on stress distribution in single crowns

This in silico study evaluated the influence of the abutment collar height and implants length on the biomechanical behavior of morse taper single dental implants with different crown-to-implant ratio. Six virtual models were constructed (S11, M11, L11, S13, M13 and L13) by combining short (S: 2.5 mm), medium (M: 3.5 mm) or long (L: 4.5 mm) abutment collar heights with different implant lengths (11 or 13-mm). An upper central incisor of 11-mm height was constructed on top of each abutment. Each set was positioned in a virtual bone model and exported to analyze mathematically. A 0.60-mm mesh was created after convergence analysis and a 49 N load was applied to the cingulum of the crown at an angle of 45°. Load-generated stress distribution was analyzed in the prosthetic components according to von Mises stress criteria (σvM) and in the cortical and cancellous bone by means of shear stress (εmax). The use of longer collar abutments (L11) increased the stress on the abutment by 250% and resulted in 40% higher stresses on the screw and 92% higher cortical shear stresses compared to short collared abutments (S11). Increasing the implant length produced a slight stress reduction on cortical bone. Cancellous bone was not affected by the crown-to-implant ratio. Longer abutment collars concentrate stresses at the implant level and cortical bone by increasing the crown-to-implant ratio303238243COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES33003033008P

Residual stress estimated by nanoindentation in pontics and abutments of veneered zirconia fixed dental prostheses

Glass ceramics’ fractures in zirconia fixed dental prosthesis (FDP) remains a clinical challenge since it has higher fracture rates than the gold standard, metal ceramic FDP. Nanoindentation has been shown a reliable tool to determine residual stress of ceramic systems, which can ultimately correlate to failure-proneness. Objectives: To assess residual tensile stress using nanoindentation in veneered three-unit zirconia FDPs at different surfaces of pontics and abutments. Methodology: Three composite resin replicas of the maxillary first premolar and crown-prepared abutment first molar were made to obtain three-unit FDPs. The FDPs were veneered with glass ceramic containing fluorapatite crystals and resin cemented on the replicas, embedded in epoxy resin, sectioned, and polished. Each specimen was subjected to nanoindentation in the following regions of interest: 1) Mesial premolar abutment (MPMa); 2) Distal premolar abutment (DPMa); 3) Buccal premolar abutment (BPMa); 4) Lingual premolar abutment (LPMa); 5) Mesial premolar pontic (MPMp); 6) Distal premolar pontic (DPMp); 7) Buccal premolar pontic (BPMp); 8) Lingual premolar pontic (LPMp); 9) Mesial molar abutment (MMa); 10) Distal molar abutment (DMa); 11) Buccal molar abutment (BMa); and 12) Lingual molar abutment (LMa). Data were assessed using Linear Mixed Model and Least Significant Difference (95%) tests. Results: Pontics had significantly higher hardness values than premolar (p=0.001) and molar (p=0.007) abutments, suggesting lower residual stress levels. Marginal ridges yielded higher hardness values for connectors (DPMa, MMa, MPMp and DPMp) than for outer proximal surfaces of abutments (MPMa and DMa). The mesial marginal ridge of the premolar abutment (MPMa) had the lowest hardness values, suggesting higher residual stress concentration. Conclusions: Residual stress in three-unit FDPs was lower in pontics than in abutments. The outer proximal surfaces of the abutments had the highest residual stress concentration

Influence of cantilever position and implant connection in a zirconia custom implant-supported fixed partial prosthesis: in silico analysis

Abstract Introduction A better tension distribution on implants and abutments in implant-supported fixed partial prosthesis is essential in the rehabilitation of posterior mandible area. Objective: To evaluate the influence of cantilever position and implant connection in a zircônia custom implant-supported fixed partial prosthesis using the 3-D finite element method. Material and method: Four models were made based on tomographic slices of the posterior mandible with a zirconia custom three-fixed screw-retained partial prosthesis. The investigated factors of the in silico study were: cantilever position (mesial or distal) and implant connection (external hexagon or morse taper). 100 N vertical load to premolar and 300 N to molar were used to simulate the occlusal force in each model to evaluate the distribution of stresses in implants, abutments, screws and cortical and cancellous bone. Result: The external hexagon (EH) connection showed higher cortical compression stress when compared to the morse taper (MT). For both connections, the molar cantilever position had the highest cortical compression. The maximum stress peak concentration was located at the cervical bone in contact with the threads of the first implant. The prosthetic and abutment screws associated with the molar cantilevers showed the highest stress concentration, especially with the EH connection. Conclusion: Morse taper implant connetions associated with a mesial cantilever showed a more favorable treatment option for posterior mandible rehabilitation

Biofilm And Saliva Affect The Biomechanical Behavior Of Dental Implants

Friction coefficient (FC) was quantified between titanium-titanium (Ti-Ti) and titanium-zirconia (Ti-Zr), materials commonly used as abutment and implants, in the presence of a multispecies biofilm (Bt) or salivary pellicle (Pel). Furthermore, FC was used as a parameter to evaluate the biomechanical behavior of a single implant-supported restoration. Interface between Ti-Ti and Ti-Zr without Pel or Bf was used as control (ad). FC was recorded using tribometer and analyzed by two-way Anova and Tukey test (p < 0.05). Data were transposed to a finite element model of a dental implant-supported restoration. Models were obtained varying abutment material (Ti and Zr) and FCs recorded (Bf, Pel, and Ctrl). Maximum and shear stress were calculated for bone and equivalent von Misses for prosthetic components. Data were analyzed using two-way ANOVA (p < 0.05) and percentage of contribution for each condition (material and FC) was calculated. PC significant differences were observed between Ti-Ti and Ti-Zr for Ctrl and Bf groups, with lower values for Ti-Zr (p < 0.05). Within each material group, Ti-Ti differed between all treatments (p < 0.05) and for Ti-Zr, only Pel showed higher values compared with Ctrl and Bf (p < 0.05). PC contributed to 89.83% (p < 0.05) of the stress in the screw, decreasing the stress when the FC was lower. FC resulted in an increase of 59.78% of maximum stress in cortical bone (p = 0.05). It can be concluded that the shift of the FC due to the presence of Pel or Bf is able to jeopardize the biomechanical behavior of a single implant-supported restoration. (C) 2015 Elsevier Ltd. All rights reserved.486997100

The role of prosthetic abutment material on the stress distribution in a maxillary single implant-supported fixed prosthesis

Evaluate the influence of abutment's material and geometry on stress distribution in a single implant-supported prosthesis. Materials and Methods Three-dimensional models were made based on tomographic slices of the upper middle incisor area, in which a morse taper implant was positioned and a titanium (Ti) or zirconia (ZrN) universal abutments was installed. The commercially available geometry of titanium (T) and zirconia (Z) abutments were used to draw two models, TM1 and ZM1 respectively, which served as control groups. These models were compared with 2 experimental groups were the mechanical properties of Z were applied to the titanium abutment (TM2) and vice versa for the zirconia abutment (ZM2). Subsequently, loading was simulated in two steps, starting with a preload phase, calculated with the respective friction coefficients of each materials, followed by a combined preload and chewing force. The maximum von Mises stress was described. Data were analyzed by two-way ANOVA that considered material composition, geometry and loading (p 0.05). Conclusion The screw was the piece most intensely affected, mainly through the preload force, independent of the abutment's material65909

Candida albicans biofilms and MMA surface treatment influence the adhesion of soft denture liners to PMMA resin

The effect of Candida albicans biofilms and methyl methacrylate (MMA) pretreatment on the bond strength between soft denture liners and polymethyl methacrylate (PMMA) resin was analyzed. Specimens were prepared and randomly divided with respect to PMMA pretreatment, soft liner type (silicone-based or PMMA-based), and presence or absence of a C. albicans biofilm. Samples were composed of a soft denture liner bonded between two PMMA bars. Specimens (n = 10) were incubated to produce a C. albicans biofilm or stored in sterile PBS for 12 days. The tensile bond strength test was performed and failure type was determined using a stereomicroscope. Surface roughness (SR) and scanning electron microscopy (SEM) analysis were performed on denture liners (n = 8). Highest bond strength was observed in samples containing a silicone-based soft liner and stored in PBS, regardless of pretreatment (p &lt; 0.01). Silicone-based specimens mostly underwent adhesive failures, while samples containing PMMA-based liners predominantly underwent cohesive failures. The silicone-based specimens SR decreased after 12 days of biofilm accumulation or PBS storage, while the SR of PMMA-based soft liners increased (p &lt; 0.01). The PMMA-based soft liners surfaces presented sharp valleys and depressions, while silicone-based specimens surfaces exhibited more gentle features. In vitro exposure to C. albicans biofilms reduced the adhesion of denture liners to PMMA resin, and MMA pretreatment is recommended during relining procedures.616

Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate

Zirconia-reinforced lithium silicate (ZLS) is a ceramic that promises to have better mechanical properties than other materials with the same indications as well as improved adaptation and fracture strength. Objective In this study, marginal and internal misfit and fracture load with and without thermal-mechanical aging (TMA) of monolithic ZLS and lithium disilicate (LDS) crowns were evaluated. Material and methods Crowns were milled using a computer-aided design/computer-aided manufacturing system. Marginal gaps (MGs), absolute marginal discrepancy (AMD), axial gaps, and occlusal gaps were measured by X-ray microtomography (n=8). For fracture load testing, crowns were cemented in a universal abutment, and divided into four groups: ZLS without TMA, ZLS with TMA, LDS without TMA, and LDS with TMA (n=10). TMA groups were subjected to 10,000 thermal cycles (5-55°C) and 1,000,000 mechanical cycles (200 N, 3.8 Hz). All groups were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 1 mm/min until failure. Student’s t-test was used to examine misfit, two-way analysis of variance was used to analyze fracture load, and Pearson’s correlation coefficients for misfit and fracture load were calculated (α=0.05). The materials were analyzed according to Weibull distribution, with 95% confidence intervals. Results Average MG (