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

Abstract 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.

Marginal misfit of heat-pressed milled wax-pattern and CAD/CAM crowns and its effect on stress distribution in implant-supported rehabilitations

Aim: To compare the marginal fit of lithium disilicate CAD/CAM crowns and heat-pressed crowns fabricated using milled wax patterns, and evaluate its effect on stress distribution in implantsupported rehabilitation. Methods: A CAD model of a mandibular first molar was designed, and 16 lithium disilicate crowns (8/group) were obtained. The crown-prosthetic abutment set was evaluated in a scanning electron microscopy. The mean misfit for each group was recorded and evaluated using Student's t-test. For in silico analysis, a virtual cement thickness was designed for the two misfit values found previously, and the CAD model was assembled on an implant-abutment set. A load of 100 N was applied at 30° on the central fossa, and the equivalent stress was calculated for the crown, titanium components, bone, and resin cement layer. Results: The CAD/CAM group presented a significantly (p=0.0068) higher misfit (64.99±18.73 µm) than the heat-pressed group (37.64±15.66 µm). In silico results showed that the heat-pressed group presented a decrease in stress concentration of 61% in the crown and 21% in the cement. In addition, a decrease of 14.5% and an increase of 7.8% in the stress for the prosthetic abutment and implant, respectively, was recorded. For the cortical and cancellous bone, a slight increase in stress occurred with an increase in the cement layer thickness of 5.9% and 5.7%, respectively. Conclusion: The milling of wax patterns for subsequent inclusion and obtaining heat-pressed crowns is an option to obtain restorations with an excellent marginal fit and better stress distribution throughout the implant-abutment set

Three-dimensional misfit between Ti-Base abutments and implants evaluated by replica technique

Abstract An important factor affecting the biomechanical behavior of implant-supported reconstructions is the implant-abutment misfit. Objective: This study evaluated the misfit between Ti-Base abutments and implants by means of polyvinyl siloxane replica technique using microcomputed tomography (μCT). Methodology: Volumetric and linear (central and marginal) gaps of four Ti-base abutments (n=10/group): (i) Odontofix LTDA (OD), (ii) Singular Implants (SING), (iii) EFF Dental Components (EFF), and (iv) Control Group (S.I.N implants) compatible with an implant system (Strong SW, S.I.N Implants) were measured using μCT reconstructed polyvinyl siloxane replicas. Results: The results showed significantly lower volume gap for Control S.I.N (0.67±0.29 mm3) and SING (0.69±0.28 mm3) Ti-base abutments relative to OD (1.42±0.28 mm3) and EFF groups (1.04±0.28 mm3) (p<0.033), without significant difference between them (p=0.936). While gap values were homogenous in the central region, EFF presented a significantly higher marginal gap. Accordingly, the Control S.I.N and Singular Ti-base abutments showed improved volumetric and marginal fit relative to Odontofix and EFF. Conclusion: The method of manufacturing abutments influenced the misfit at the implant-abutment interface.

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

Abstract 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 (p<0.001) and AMD (p=0.003) values were greater in ZLS than in LDS crowns. TMA did not affect the fracture load of either material. However, fracture loads of ZLS crowns were lower than those of LDS crowns (p<0.001). Fracture load was moderately correlated with MG (r=-0.553) and AMD (r=-0.497). ZLS with TMA was least reliable, according to Weibull probability. Conclusion Within the limitations of this study, ZLS crowns had lower fracture load values and greater marginal misfit than did LDS crowns, although these values were within acceptable limits.

Transferência precisa da morfologia do tecido mole peri-implantar em prótese anterior: relato de caso / Accurate transposition of peri-implant soft tissue morphology in anterior prosthesis: case report

O perfil de emergência em próteses implantossuportadas é a porção da restauração que emerge coronalmente do implante até a gengiva marginal livre, visando conferir suporte e estabilidade ao tecido mole peri-implantar, mimetizando o dente natural. As restaurações com contornos apropriados têm um efeito significativo na higiene bucal, saúde do tecido peri-implantar e estética. O maior desafio para a confecção de próteses implantossuportadas definitivas está na duplicação do perfil de emergência obtido com a prótese provisória para o modelo de trabalho, sendo que há várias técnicas publicadas, porém não há um consenso na literatura sobre qual método é mais preciso. O objetivo do presente estudo é apresentar, por meio do relato de um caso clínico, uma técnica de moldagem do perfil de emergência e tecido peri-implantar...

The emergence profile for implant-supported prostheses is the portion of the restoration that emerges coronally from the implant to the free gingival margin, giving support and stability to peri-implant soft tissues and mimicking the natural tooth. Restorations with appropriate contour have a significant effect on oral hygiene, health and esthetics of peri-implant tissues. The greatest challenge involved in manufacturing permanent prosthesis is the duplication of the emergence profile obtained with the provisional restoration secured to the cast. Several techniques have been published, but no consensus has been reached on the literature regarding which method is the most accurate. The objective of this study is to present a technique for molding the emergency profile and peri-implant tissues by presenting a clinical case...

Estudo do comportamento do sulfatode cálcio: bioatividade e solubilidade em fluido corpóreo simulado / Studying the behavior of calcium sulfate: bioactivity and solubility in simulated body fluid

Com a finalidade de correção de defeitos ósseos, diversos materiais sintéticos têm sido utilizados, entre os quais está o sulfato de cálcio. Objetivo: o objetivo do presente estudo foi avaliar, in vitro, a bioatividade do sulfato de cálcio em fluido corpóreo simulado (SBF). Métodos: quatro corpos de prova foram preparados em matrizes de policloreto de vinila (PVC) circulares, misturando-se o sulfato de cálcio nas proporções de líquido/pó recomendadas pelo fabricante, com água destilada. As amostras ficaram imersas em 50ml de SBF, a 36,5ºC, por até 21 dias, sendo que a solução foi renovada a cada três dias. A bioatividade foi verificada por meio de Espectroscopia no Infravermelho por Transformada de Fourier (FTIR). Resultados: no teste de bioatividade in vitro, a análise por FTIR detectou a presença de apatita sobre o substrato de sulfato de cálcio, demonstrando tratar-se de um material bioativo. Além disso, foi observada uma redução expressiva do tamanho da amostra vinculada ao processo de reabsorção. Conclusão: dentro das limitações do estudo, pode-se concluir que o sulfato de cálcio é um material bioativo e rapidamente reabsorvido...

Several types of synthetic material have been used to correct bone defects, among which is calcium sulfate. Objective: the present in vitro study aimed at assessing the bioactivityof calcium sulfate in simulated body fluid (SBF). Methods: four specimens were prepared in polyvinyl chloride (PVC) circle matrices by mixing calcium sulfate with distilled water, as recommended by the manufacturer. Samples were immersed in 50 ml of SBF, at 36.5 ºC, for no longer than 21 days. The solutionwas renewed every three days. Bioactivity was assessed by means of Fourier transform infrared spectroscopy (FTIR). Results: The in vitro bioactivity test, carried out by means of FTIR analysis, revealed the presence of apatite formation over calcium sulfate substrate, thereby proving it to be a bioactive material. In addition, there was significant reduction in the size of the sample, which was associated with the process of resorption. Conclusion: within the limitations of the present study, it is reasonable to conclude that calcium sulfate is a bioactive material which is quickly absorbed...

Fluoride concentrations in the water of Maringá, Brazil, considering the benefit/risk balance of caries and fluorosis

Current Brazilian law regarding water fluoridation classification is dichotomous with respect to the risks of and benefits for oral diseases, and fluoride (F) concentrations less than 0.6 or above 0.8 mg F/L are considered outside the normal limits. Thus, the law does not consider that both caries and fluorosis are dependent on the dosage and duration of fluoride exposure because they are both chronic diseases. Therefore, this study evaluated the quality of water fluoridation in Maringá, PR, Brazil, considering a new classification for the concentration of F in water the supply, based on the anticaries benefit and risk of fluorosis (CECOL/USP, 2011). Water samples (n = 325) were collected monthly over one year from 28 distribution water networks: 20 from treatment plants and 8 from artesian wells. F concentrations were determined using a specific ion electrode. The average F concentration was 0.77 mg F/L (ppm F), ranging from 0.44 to 1.22 mg F/L. Considering all of the water samples analyzed, 83.7% of them presented from 0.55 to 0.84 mg F/L, and according to the new classification used, they would provide maximum anticaries benefit with a low risk of fluorosis. This percentage was lower (75.4%) in the water samples supplied from artesian wells than from those distributed by the treatment plant (86%). In conclusion, based on the new classification of water F concentrations, the quality of water fluoridation in Maringá is adequate and is within the range of the best balance between risk and benefit.

Reabilitação de maxila edêntula com prótese fixa implantossuportada: relato de caso / Rehabilitation of edentulous maxilla with implant-supported fixed prosthesis: a case report

Introdução: os problemas funcionais, estéticos e psicológicos decorrentes do edentulismo têm levado a uma busca crescente por reabilitação bucal com próteses sobre implantes. Esse tipo de reabilitação necessita de um planejamento meticuloso, especialmente para os casos de maxila edêntula com prótese fixa sobre implantes, em decorrência da anatomia dessa região. Objetivo: o objetivo do presente caso clínico é descrever a reabilitação de uma maxila edêntula com prótese total fixa implantossuportada, cuja infraestrutura recebeu elementos metalocerâmicos cimentados individualmente.

Introduction: Functional, aesthetic and psychological issues arising from edentulism have led to a growing search for oral rehabilitation with implant-supported prostheses. This type of rehabilitation requires detailed planning, especially for treating edentulous maxilla with implantsupported fixed prostheses due to the anatomy of this region. Objective: The aim of this case report is to describe the rehabilitation of an edentulous maxilla with implantsupported full fixed prosthesis of which framework received metal-ceramic elements individually cemented.