Magnetic resonance imaging for jawbone assessment: a systematic review.

PURPOSE: To evaluate the accuracy of magnetic resonance imaging (MRI) for jawbone assessment compared to reference-standard measurements in the literature. MATERIALS AND METHODS: An electronic database search was conducted in PubMed, EMBASE, Scopus, Web of Science, and the Cochrane Library in June 2022, and updated in August 2023. Studies evaluating the accuracy of MRI for jawbone assessment compared with reference-standard measurements (histology, physical measurements, or computed tomography) were included. The outcome measures included bone histomorphometry and linear measurements. The risk of bias was assessed by the Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS-2). The review was registered in the PROSPERO database (CRD42022342697). RESULTS: From 63 studies selected for full-text analysis, nine manuscripts were considered eligible for this review. The studies included assessments of 54 participants, 35 cadavers, and one phantom. A linear measurement error ranging from 0.03 to 3.11 mm was shown. The accuracy of bone histomorphometry varies among studies. Limitations of the evidence included heterogeneity of MRI protocols and the methodology of the included studies. CONCLUSION: Few studies have suggested the feasibility of MRI for jawbone assessment, as MRI provides comparable results to those of standard reference tests. However, further advancements and optimizations are needed to increase the applicability, validate the efficacy, and establish clinical utility of these methods.

Application of polyetheretherketone (PEEK) posts: evaluation of fracture resistance and stress distribution in the root: in vitro and finite element analyses.

To evaluate the feasibility of using a milled polyetheretherketone (PEEK) post and core in endodontically treated teeth with or without a ferrule. Sixty bovine tooth roots were endodontically treated followed by cementation of intraradicular retainers (IR), according to each experimental group: a) non-ferrule glass fiber post (f0FP); b) 2-mm-ferrule glass fiber post (f2FP); c) non-ferrule resized glass fiber post (f0PR); d) 2-mm-ferrule resized glass fiber post (f2PR); e) non-ferrule PEEK post and core (f0PPC); and f) 2-mm-ferrule PEEK post and core (f2PPC). Metal crowns were made and cemented. A periodontal ligament was simulated using polyether. A force was applied to the palatine portion of each sample at 45°, until fracture. Fracture resistance data were submitted to two-way ANOVA and Tukey's test (α = 0.05). Three-dimensional digital models were developed to calculate the tensions formed in the root using finite element analysis. Models of glass fiber posts and PEEK posts and cores were evaluated with or without a ferrule. The results were analyzed by the Mohr-Coulomb criterion. The type of IR was not influenced by fracture strength (p = 0.243). There were significant statistical differences among the remaining factors. Ferrule groups had greater fracture resistance, and the failure mode of teeth with a ferrule was more catastrophic than the non-ferrule group. A ferrule increases fracture resistance and influences failure mode; the PEEK post and core did not modify the biomechanics of endodontically treated teeth, and resembled the glass fiber post results. The crack initiation point differed between the ferrule and non-ferrule groups.

Influence of alveolar bone height on the biomechanical behavior of roots restored with custom-made posts-and-cores.

OBJETIVE: This study evaluated the influence of alveolar bone height and post type on compressive force resistance, fracture pattern, and stress distribution in endodontically treated teeth. MATERIALS AND METHODS: Bovine roots were endodontically treated and divided into eight groups (n = 10) according to alveolar bone height (normal alveolar bone and alveolar bone loss - 2 and 5 mm from the margin of the crown, respectively) and post type (prefabricated glass fiber post, anatomic glass fiber post, customized milled glass fiber post-and-core and customized milled polyetheretherketone (PEEK) post-and-core). Mechanical fatigue was simulated (300.000 cycles/50 N/1.2 Hz). Compression force resistance (N) was analyzed by two-way ANOVA and Tukey test (α = 0.05). Fracture patterns were described as percentages. Stress distribution was analyzed by finite element analysis. RESULTS: Significant diferences were found for alveolar bone height (P < 0.0001): normal alveolar bone groups showed higher mean values of compression force resistance compared to alveolar bone loss groups, while no significant differences were found for post type (P = 0.4551), and there was no double interaction between them (P = 0.5837). Reparable fractures were more predominant in normal alveolar bone groups, especially in the milled glass fiber and PEEK post-and-core groups. Stress distribution was similar in groups with prefabricated glass fiber posts and milled PEEK posts-and-cores, and the alveolar bone loss condition significantly increased stress concentration and strain values, mainly on apical dentin. CONCLUSIONS: Alveolar bone loss due to physiological aging and/or periodontal disease may lead to increased risk of restored tooth failure, although milled glass fiber and PEEK posts-and-cores provide more reparable fractures. CLINICAL SIGNIFICANCE: Custom-made glass fiber and PEEK post-and-cores are interesting options, since they enable clinicians to work with a single-body post-and-core system that avoid several materials interfaces and fits well in the root canal provided promising results to improve the failure behavior of restored roots, as they offer more reparable fractures even in situations of alveolar bone loss.

Application of polyetheretherketone (PEEK) posts: evaluation of fracture resistance and stress distribution in the root: in vitro and finite element analyses

Abstract To evaluate the feasibility of using a milled polyetheretherketone (PEEK) post and core in endodontically treated teeth with or without a ferrule. Sixty bovine tooth roots were endodontically treated followed by cementation of intraradicular retainers (IR), according to each experimental group: a) non-ferrule glass fiber post (f0FP); b) 2-mm-ferrule glass fiber post (f2FP); c) non-ferrule resized glass fiber post (f0PR); d) 2-mm-ferrule resized glass fiber post (f2PR); e) non-ferrule PEEK post and core (f0PPC); and f) 2-mm-ferrule PEEK post and core (f2PPC). Metal crowns were made and cemented. A periodontal ligament was simulated using polyether. A force was applied to the palatine portion of each sample at 45°, until fracture. Fracture resistance data were submitted to two-way ANOVA and Tukey's test (α = 0.05). Three-dimensional digital models were developed to calculate the tensions formed in the root using finite element analysis. Models of glass fiber posts and PEEK posts and cores were evaluated with or without a ferrule. The results were analyzed by the Mohr-Coulomb criterion. The type of IR was not influenced by fracture strength (p = 0.243). There were significant statistical differences among the remaining factors. Ferrule groups had greater fracture resistance, and the failure mode of teeth with a ferrule was more catastrophic than the non-ferrule group. A ferrule increases fracture resistance and influences failure mode; the PEEK post and core did not modify the biomechanics of endodontically treated teeth, and resembled the glass fiber post results. The crack initiation point differed between the ferrule and non-ferrule groups.

Stress distribution in restorations with glass fiber and polyetheretherketone intraradicular posts: An in silico analysis.

This study evaluated stresses generated at maxillary central incisor (21) root restored with lithium disilicate crown (LDC), and glass fiber (GFP) or polyetheretherketone (PEEK) post. 3D models created by computed tomographic image (i-CAT Cone Beam 3D Dental Imaging System) reproduced maxillary central incisor. Each model had prosthetic LDCs (2.0 mm thick) cemented to GFP or PEEK posts with dual resin cement. Different loads were applied to each model (cervical, incisal, axial, middle). At maximum principal stress, PEEK showed higher stress than GFP in all loads, but with qualitative similarity. At minimum principal stress, PEEK and GFP showed qualitative and quantitative similarities, except axial load. Maxillary central incisor restored with GFP or PEEK and LDC presented, in general, similar stress intensity and distribution for main occlusal loads. Only two of sixteen occlusal loads tested (cervical for maximum principal; axial for minimum principal) showed significant quantitative difference.

Dental displacement in complete dentures influenced by different flask types and polymerization cycles.

This study evaluated the dental displacement in dentures included in different flasks and processed by the Australian cycle modified or by microwave. Metal pins were placed on the teeth as reference for measurements: a) Incisal edge of maxillary and mandibular central incisors, buccal cusp of maxillary and mandibular vestibular first premolars, and mesiobuccal maxillary and mandibular cusps of second molars; b) Incisor to incisor, premolar to premolar and molar to molar; c) Left incisor to left molar and right incisor to right molar, and d) Vertical. Dentures were divided according to flasks (n=10): G1- Metal; G2- HH bimaxillary metal; G3-Microwaves; G4- HH bimaxillary microwaves. For G1 and G2, polymerization at 65ºC/30 min, flame quenched for 30 min, heating at 65ºC/30 min, boiling water for 1 h. For G3 and G4, microwave (20 min/140 W and 5 min/560 W). Comparator microscope with digital camera and analytical unit assessed the measurements before and after denture polymerization. The final distance was made subtracting the distance before the denture processing from the distance of the dental displacement after processing. The value of the difference was submitted to 2-way ANOVA, considering the flask type and denture type. Maxillary denture showed greater displacement when compared to mandibular denture. Flask types and interaction with denture types showed similar difference between before and after polymerization. In conclusion, displacement promoted by flask types in dentures cured by polymerization cycles promoted similar effect on the distance between teeth. Greater value for distance between teeth occurred for maxillary denture.

Finite Element Analysis of Stress in Anterior Prosthetic Rehabilitation with Zirconia Implants with and without Cantilever.

OBJECTIVES: The aim of this study was to evaluate using finite element analysis (FEA), the stress distribution in prostheses (lithium disilicate crowns) on monotype zirconia implants with and without cantilever in the anterior region of the maxilla. MATERIALS AND METHODS: From a virtual reconstruction of bone model of the toothed maxilla from a computed tomography, three models (groups) were created: Zr (11-21)-implants placed in the area of 11 and 21 with cantilever; Zr (12-22)-implants placed in the area of 12 and 22 without cantilever; and Zr (11-22)-implants intercalated placed in the area of 11 and 22. In all models, monotype zirconia implant (4.1 × 12.0 mm) was used in single-body configuration. Lithium disilicate crowns were designed on the implants and pontics for all groups. A 150-N load was applied to the prostheses. The materials used were considered isotropic, homogeneous, and linearly elastic. FEA was performed to evaluate the maximum (tensile) and minimum (compressive) principal stresses in the implant, crowns, and bone tissue. Data were analyzed qualitatively and quantitatively. RESULTS: For all groups, the highest maximum principal stress occurred in the palatal cervical area of the implant, with the high values for the Zr (12-22) group and the low values for the Zr (11-21) group. The maximum principal stress was concentrated in the cervical palatal area of the crown, with the Zr (11-21) group presented the highest values and the Zr (12-22) group showed the lowest values. In the bone tissue all the groups presented similar values of maximum and minimal principal stress, with the palatal (maximum principal) and vestibular (minimum principal) close to the cervical of the implants the area with the highest concentration of stresses. CONCLUSIONS: The position of monotype zirconia implant did not interfere in the bone tissue stress, and the implants placed in the 11-21 present lower stress in implants and higher in the crown. The cantilever does not increase the stress in the implants, crown, and bone tissue.

Dental displacement in complete dentures influenced by different flask types and polymerization cycles

Abstract This study evaluated the dental displacement in dentures included in different flasks and processed by the Australian cycle modified or by microwave. Metal pins were placed on the teeth as reference for measurements: a) Incisal edge of maxillary and mandibular central incisors, buccal cusp of maxillary and mandibular vestibular first premolars, and mesiobuccal maxillary and mandibular cusps of second molars; b) Incisor to incisor, premolar to premolar and molar to molar; c) Left incisor to left molar and right incisor to right molar, and d) Vertical. Dentures were divided according to flasks (n=10): G1- Metal; G2- HH bimaxillary metal; G3-Microwaves; G4- HH bimaxillary microwaves. For G1 and G2, polymerization at 65ºC/30 min, flame quenched for 30 min, heating at 65ºC/30 min, boiling water for 1 h. For G3 and G4, microwave (20 min/140 W and 5 min/560 W). Comparator microscope with digital camera and analytical unit assessed the measurements before and after denture polymerization. The final distance was made subtracting the distance before the denture processing from the distance of the dental displacement after processing. The value of the difference was submitted to 2-way ANOVA, considering the flask type and denture type. Maxillary denture showed greater displacement when compared to mandibular denture. Flask types and interaction with denture types showed similar difference between before and after polymerization. In conclusion, displacement promoted by flask types in dentures cured by polymerization cycles promoted similar effect on the distance between teeth. Greater value for distance between teeth occurred for maxillary denture.

Resumo O objetivo neste estudo foi avaliar o deslocamento dental em próteses totais incluídas em diferentes tipos de muflas e polimerizadas pelo ciclo australiano ou por micro ondas. Pinos metálicos foram colocados nos dentes como pontos de referência para as medidas: a) Borda incisal dos incisivos centrais maxilares e mandibulares, cúspide vestibular dos primeiros pré molares maxilares e mandibulares e cúspides mésiovestibulares dos segundos molares maxilares e mandibulares; b) Distâncias látero-laterais incisivo a incisivo, pré-molar a pré-molar e molar a molar; c) Distâncias horizontais anteroposterior incisivo esquerdo a molar esquerdo e incisivo direito a molar direito, e d) Vertical. As próteses foram separadas de acordo com o tipo de mufla (n=20): G1- Metálica; G2-HH bi-maxilar metálica; G3- Micro-ondas; G4- HH bi-maxilar micro ondas. Ciclo de polimerização para G1 e G2, água a 65ºC por 30 minutos, aquecimento interrompido por 30 minutos, reaquecimento a 65ºC por 30 minutos, seguido de água fervente por 1 hora. Para G3 e G4, micro ondas (20 minutos a 140 W e 5 minutos a 560 W). As medidas foram avaliadas com microscópio comparador linear. A distância final entre os dentes foi obtida subtraindo o valor da distância antes do processamento da prótese do valor da distância resultante do deslocamento dentário após o processamento. A diferença obtida entre essas distâncias foi submetida à ANOVA de 2 fatores, considerando como variáveis tipo de mufla e tipo de prótese. A prótese maxilar apresentou maior deslocamento dental quando comparada à mandibular. Os tipos de muflas e a interação com os tipos de próteses mostraram movimentos dentais similares antes e depois da polimerização. Em conclusão, o deslocamento dental promovido por diferentes tipos de frascos em próteses curadas por diferentes ciclos de polimerização promoveu efeito semelhante na alteração da distância entre os dentes. Maior valor para a mudança de distância entre os dentes ocorreu na prótese maxilar.

Is one dental mini-implant biomechanically appropriate for the retention of a mandibular overdenture? A comparison with Morse taper and external hexagon platforms.

STATEMENT OF PROBLEM: Limited information is available to clinicians on the use of dental mini-implants (MI) as opposed to standard-diameter implants (SDIs) for the stabilization of implant-retained mandibular overdentures (MOs). PURPOSE: The purpose of this in vitro and finite element analysis study was to analyze and compare the biomechanical behavior of MOs with either 1 or 2 implants with external hexagon (EH), Morse taper (MT) SDIs, and MIs. MATERIAL AND METHODS: Thirty photoelastic models (n=30) of each group (n=5) of SDIs (EH-1, EH-2, MT-1, MT-2) and MI (MI-1, MI-2) were fabricated for posterior, peri-implant, and total maximum shear stress evaluation by quantitative photoelastic analysis. One specimen of each group was further used to create the 6 computational models to be analyzed by finite element analysis. The maximum von Mises values and stress maps were plotted for each ductile component. Two types of load were applied to the overdenture: a150-N load bilaterally and simultaneously on the first molar and a 100-N load on the incisal edge of the central incisors at a 30-degree angle. The data were subjected to the 2-way ANOVA test and the Tukey honestly significant difference test (α=.05). RESULTS: The EH-2 and MT-2 showed the lowest posterior (P<.001) and total (P<.05) mean shear stress values. For peri-implant shear stress, no difference was found among all groups (P>.05). Regardless of the loading area, the MI-1 and MI-2 groups showed the lowest von Mises stress values. However, for implant housing, the MI-1 group, under incisor loading, presented greater stress, followed by MT-1, EH-1, EH-2, MI-2, and MT-2. The attachment was the most overloaded structure, with high values under incisor loading, especially for the groups with 2 implants (MT-2, EH-2) as compared with the other models. CONCLUSIONS: Biomechanically, regardless of the implant number, MI is a promising rehabilitation method with similar peri-implant shear stress and lower von Mises stress on the implant when compared with SDIs for MOs.

Fracture of upper incisors: a three-year follow-up of a multidisciplinary approach / Fratura em incisivos centrais superiores: tratamento multidisciplinar com acompanhamento clínico de três anos

ABSTRACT Multiple clinical specialties are usually needed for a successful long-term treatment in buccal cavity. The aim of this article is to report a clinical case of multi-disciplinary rehabilitation of fracture upper incisors without pulp exposure, concerning about endodontics, periodontics and restorative dentistry comments or procedures. A case of a patient reporting trauma that resulted in fracture and substantial loss of hard tissue, in mesial angle of both upper central incisors (11 and 21). In palatal side, fracture extended beyond cingulum up to subgingival region. Periodontal surgery was performed in order to reestablish biological space. Clinical and radiographic assessments demonstrated no need for endodontic treatment, since pulp was vital and non-altered. Preparations for restorative procedures were minimally invasive, followed by composite direct. A three-year follow-up was performed, consisting in re-assessment of clinical and radiographic aspects, re-polishing of the restorations and photographic documentation. No pulp tissue alteration was observed after the follow-up period. Restorative procedures, adjacent tissues and pulp vitality were considered adequate, and the patient was satisfied with the treatment.

RESUMO O objetivo deste artigo é relatar um caso clínico de reabilitação de incisivos superiores fraturados sem exposição pulpar, com considerações na área de endodontia, periodontia e dentística restauradora. O caso relata um trauma que resultou em perda substancial de tecido dentário em ângulo mesial de ambos os incisivos centrais superiores. Na parede palatina, a fratura se estendeu além do cíngulo até a região subgengival. A cirurgia periodontal foi realizada para restabelecer o espaço biológico. As avaliações clínicas e radiográficas não demonstraram necessidade de tratamento endodôntico, pois a polpa se apresentava vital e sem alterações. Os procedimentos restauradores foram minimamente invasivos através da realização de restauração direta com resina composta. Foi realizado acompanhamento de três anos, consistindo em reavaliação dos aspectos clínicos e radiográficos, polimento das restaurações e documentação fotográfica. Nenhuma alteração do tecido pulpar foi observada após o período de acompanhamento. Os procedimentos restauradores, tecidos adjacentes e vitalidade pulpar foram considerados adequados e a paciente demonstrou satisfação com o tratamento.

Implant Volume Loss, Misfit, Screw Loosening, and Stress In Custom Titanium and Zirconia Abutments.

The aim of this study was to verify the effect of the implant volume loss, vertical misfit between abutment and prosthetic platform, prosthetic screw loosening torque, and screw stress distribution in titanium and zirconia abutments. Ten CAD/CAM system custom abutments of each material were milled and attached to the titanium implants. The implant volume loss was evaluated by microtomography, the vertical misfit with optical microscopy, and digital torque wrench measured the prosthetic screw loosening. All experimental analyses were performed before and after mechanical cycle (1,000,000 cycles, 100 N/2 Hz). Virtual models of the structures were created for finite element analysis, and the stress on the screw obtained with von Mises procedure. Data were analyzed using an independent t-test, two-way ANOVA for repeated measures, and Tukey's HSD test (a=0.05). There was no significant difference in the implant volume loss for the two abutment materials (p=0.662). Titanium abutments provided higher loosening torque values after mechanical cycling (p<0.001). Lesser marginal misfit was obtained with titanium abutments before and after mechanical cycling (p<0.001). The stress distribution on the screw was similar between abutment materials. In conclusion, CAD/CAM custom titanium abutment reduced the marginal misfit and increased the torque maintenance of prosthetic screws when compared to CAD/CAM custom zirconia abutment.

Implant volume loss, misfit, screw loosening, and stress in custom titanium and zirconia abutments

Abstract The aim of this study was to verify the effect of the implant volume loss, vertical misfit between abutment and prosthetic platform, prosthetic screw loosening torque, and screw stress distribution in titanium and zirconia abutments. Ten CAD/CAM system custom abutments of each material were milled and attached to the titanium implants. The implant volume loss was evaluated by microtomography, the vertical misfit with optical microscopy, and digital torque wrench measured the prosthetic screw loosening. All experimental analyses were performed before and after mechanical cycle (1,000,000 cycles, 100 N/2 Hz). Virtual models of the structures were created for finite element analysis, and the stress on the screw obtained with von Mises procedure. Data were analyzed using an independent t-test, two-way ANOVA for repeated measures, and Tukey's HSD test (a=0.05). There was no significant difference in the implant volume loss for the two abutment materials (p=0.662). Titanium abutments provided higher loosening torque values after mechanical cycling (p<0.001). Lesser marginal misfit was obtained with titanium abutments before and after mechanical cycling (p<0.001). The stress distribution on the screw was similar between abutment materials. In conclusion, CAD/CAM custom titanium abutment reduced the marginal misfit and increased the torque maintenance of prosthetic screws when compared to CAD/CAM custom zirconia abutment.

Resumo O objetivo neste estudo foi verificar o efeito da diminuição de volume do implante, desajuste vertical entre o pilar e plataforma protética, torque de afrouxamento do parafuso protético e distribuição da tensão no parafuso em pilares de titânio e zircônia. Dez pilares personalizados de cada material foram fresados e conectados aos implantes de titânio. A diminuição de volume do implante foi avaliada com microtomografia, o desajuste vertical com microscopia óptica e o torque de afrouxamento do parafuso protético com chave de torque digital. Todas as análises experimentais foram realizadas antes e após aplicação do ciclo mecânico (1.000.000 ciclos, 100 N/2 Hz). Modelos virtuais das estruturas foram criados para análise por elementos finitos e a tensão no parafuso obtida com valores de von Mises. Os dados foram analisados usando teste t independente, análise de varância dois fatores para medidas repetidas e teste de Tukey HSD (a=0,05). Não houve diferença significativa na diminuição de volume do implante para os dois materiais do pilar (p= 0,662). Os pilares de titânio proporcionaram maiores valores de torque de afrouxamento após o ciclo mecânico (p<0,001). O menor desajuste marginal foi obtido com os pilares de titânio antes e após o ciclo mecânico (p<0,001). A distribuição da tensão no parafuso foi similar entre os materiais. Em conclusão, os pilares personalizados de titânio reduziram o desajuste marginal e aumentaram a manutenção do torque dos parafusos protéticos quando comparados aos pilares de zircônia.

Propriedades mecânicas e ópticas das cerâmicas feldspáticas e dissilicato de lítio: Revisão de literatura / Mechanical and optical properties of feldspathic ceramics and lithium disilicate: literature review

Objetivo: o objetivo dessa revisão de literatura é apresentar os dados existentes sobre capacidade estética e resistência à fratura das cerâmicas feldspáticas e dissilicato de lítio confeccionadas para o uso em CAD/CAM. Material e Métodos: para realizar o estudo foram levantados artigos originais sobre as cerâmicas feldspáticas e dissilicato de lítio em periódicos na base de dados PubMed e ScienceDirect, desde 2015 até 2020 utilizando como termos de busca "lithium disilicate AND esthetic AND CAD/CAM", "lithium disilicate AND fadigue AND CAD/CAM", "lithium disilicate AND fracture AND CAD/CAM", "feldspathic AND esthetic AND CAD/CAM", "feldspathic AND fadigue AND CAD/CAM", "feldspathic AND fracture AND CAD/CAM". Ainda, foram selecionados artigos de relevância publicados em datas anteriores selecionados pelos autores. Constam trabalhos longitudinais, de revisão de literatura, casos clínicos e pesquisas in vitro. Resultados: no total, 209 artigos foram encontrados e somente 16 foram incluídos para comparação. Os dados apresentaram boa capacidade estética para ambos materiais, sendo o dissilicato com maior resistência à fratura. Conclusão: concluiu-se que cerâmicas feldspáticas e dissilicato de lítio para CAD/CAM apresentam capacidade ópticas satisfatórias para restaurações estéticas quando utilizado os blocos multicores, devendo-se optar pelo dissilicato de lítio em situações de maior esforço mastigatório ou menor espessura da peça protética

Objective: this literature review presents the existing data on the esthetic capacity and fracture resistance of feldspathic and lithium disilicate ceramics made for CAD/CAM. Material and Methods: original articles on feldspathic ceramics and lithium disilicate were collected in journals in the PubMed and ScienceDirect databases from 2015 to 2020 using the search terms "lithium disilicate AND esthetic AND CAD/CAM," "lithium disilicate AND fatigue AND CAD/CAM," "lithium disilicate AND fracture AND CAD/CAM," "feldspathic AND esthetic AND CAD/CAM," "feldspathic AND fatigue AND CAD/CAM," "feldspathic AND fracture AND CAD/CAM." relevant articles published previously to 2015 were also selected by the authors. Longitudinal studies, literature reviews, clinical cases and in vitro studies were included. Results: in total, 209 articles were selected and 16 included for comparison. Data presented good esthetic capability for both materials, disilicate presented higher fracture strength. Conclusion: the study concluded that feldspathic ceramics and lithium disilicate for CAD/CAM have satisfactory optical capacity for esthetics restorations when multicolor blocks are used. Lithium disilicate should be chosen in situations of greater masticatory effort or thinness of the prosthetic piece

How many implants are needed for mandibular full-arch rehabilitation?

Aim: To analyze the stress distribution at the peri-implant bone tissue of mandible in full-arch implant-supported rehabilitation using a different number of implants as support. Methods: Three-dimensional finite element models of full-arch prosthesis with 3, 4 and 5 implants and those respective mandibular bone, screws and structure were built. ANSYS Workbench software was used to analyze the maximum and minimum principal stresses (quantitative analysis) and modified von Mises stress (qualitative analysis) in peri-implant bone tissue after vertical and oblique forces (100N) applied to the structure at the cantilever site (region of the first molars). Results: The peak of tensile stress values were at the bone tissue around to the distal implant in all models. The model with 3 implants presented the maximum principal stress, in the surrounding bone tissue, higher (~14%) than the other models. The difference of maximum principal stress for model with 4 and 5 implants was not relevant (~1%). The first medial implant of the model with 5 implants presented the lower (17%) stress values in bone than model with 3 implants. It was also not different from model with 4 implants. Conclusion: Three regular implants might present a slight higher chance of failure than rehabilitations with four or five implants. The use of four implants showed to be an adequate alternative to the use of classical five implants

Comparison of endocrowns made of lithium disilicate glass-ceramic or polymer-infiltrated ceramic networks and direct composite resin restorations: fatigue performance and stress distribution.

This study compared the fatigue performance and the stress distribution of endodontically treated molars restored with endocrowns obtained with lithium disilicate glass-ceramic or a polymer-infiltrated ceramic network, both processed by CAD-CAM, and direct composite restorations. Forty-eight human mandibular molars were randomly assigned into 03 groups (n = 16) and restored with endocrowns (LD - lithium disilicate glass-ceramic or PICN - polymer-infiltrated ceramic network) or with direct composite restorations. Fatigue testing followed a step-stress approach (initial maximum load of 200 N and 5000 cycles, incremental step load of 200N and 10,000 cycles/step, being the specimens loaded until failure or to a maximum of 135,000 cycles at 2800 N). The fatigue failure load and number of cycles until failure were recorded and statistically analyzed. Fractographic and finite element (FEA) analyzes were conducted as well. There were no differences in fatigue failure load, number of cycles until fracture and mean survival probabilities among groups. However, indirect endocrowns had higher mechanical structural reliability, and LD restorations lasted more time before start to failing. FEA showed that the stress concentration in tooth tissues was higher for the resin composite, followed by PICN and LD in a decreasing order. Almost all fractures were restricted to the restorative material (without tooth involvement), and origins were identified at occlusal surface. The type of restoration did not influence the fatigue failure load, number of cycles until fracture and mean survival probabilities of the restorative strategies. Despite that, the mechanical structural reliability of endocrowns, especially those made of lithium disilicate, was higher and lasted more time before start to failing.

Comparative evaluation of different fixation techniques for sagittal split ramus osteotomy in 10 mm advancements. Part two: Finite element analysis.

PURPOSE: To evaluate three rigid, stable fixation methods for sagittal split ramus osteotomy (SSRO), using finite element analysis. The hypothesis is that a customized miniplate presents better stress concentration and distribution. MATERIALS AND METHODS: A 3D model of a hemimandible was created, and a 10-mm-advancement SSRO was simulated and fixed as follows: 3-DCP group - one custom miniplate fixed by eight screws; 4-H2P group - two miniplates of four holes each, fixed by eight screws; and 6-H2P group - two miniplates of six holes each fixed by 12 screws. After a vertical loading of 100 N, the values for von Mises stress, modified von Mises stress, and maximum and minimum principal stresses were measured. RESULTS: The area of maximum principal stress was similar for the three groups - located in the upper miniplate, in the screw near the proximal segment osteotomy. The maximum von Mises stresses were 1580.4 MPa, 1005 MPa, and 977.56 MPa for the 3DCP, 4-H2P, and 6-H2P groups, respectively, showing an allowable displacement of 2.57 mm, 1.62 mm, and 1.52 mm for the 3DCP, 4-H2P, and 6-H2P groups, respectively. CONCLUSION: The customized miniplate did not present better stress distribution than two commonly used types of fixation. Fixation with two straight miniplates, either with four or six holes, offers adequate resistance for 10 mm linear advancements.

Fracture Strength and Stress Distribution in Premolars Restored with Cast Post-and-Cores or Glass-Fiber Posts Considering the Influence of Ferule.

OBJECTIVES: The aim of this study was to evaluate the influence of ferule and the post type on the fracture strength and stress distribution in premolars. MATERIALS AND METHODS: Forty human mandibular premolars were decoronated, allocated in four groups, and restored as follows: CPC-NF: cast post-and-core and absence of ferule; CPC-F: cast post-and-core and presence of ferule; FPC-NF: glass-fiber posts and absence of ferule; FPC-F: glass-fiber posts and presence of ferule. The fracture strength (FS) and failure patterns were evaluated. Finite element analysis (FEA) evaluated the stress distribution. RESULTS: FS did not differ between CPCs and FPC either in presence or in absence of ferule. The presence of ferule increased FS with both post types. Mean values of FS for ferule groups were higher than functional or parafunctional loads reported in literature, which was not the case for FPC-NF when compared to parafunctional loads. FEA with a functional load showed slightly higher compressive stresses in dentin in the group CPC-NF, which was much lower than the compressive strength of dentin. Lower percentage of catastrophic failures was observed in nonferule groups irrespective of post type, which was explained by the stress concentration in the cervical root region when FEA with the FS load was simulated. CONCLUSION: Ferule effect was shown to be more important than post type in the analysis. Both posts showed potential to withstand functional loads irrespective of presence of ferule. However, the mean FS was lower than parafunctional loads for FPC in the absence of ferule.

Lithium disilicate glass-ceramic vs translucent zirconia polycrystals bonded to distinct substrates: Fatigue failure load, number of cycles for failure, survival rates, and stress distribution.

The present study evaluated the fatigue behavior of monolithic translucent zirconia polycrystals (TZ) and lithium disilicate glass-ceramic (LD) bonded to different substrates. Disc-shaped specimens of ceramic materials TZ and LD were bonded to three substrates with different elastic modulus (E) (fiber-reinforced composite (FRC) - softest material, E = 14.9 GPa; titanium alloy (Ti) - intermediary properties, E = 115 GPa; and zirconia (Yz) - stiffest material, E = 210 GPa). The surfaces were treated and bonded with resin cement (disc-disc set-up). Fatigue testing followed a step-stress approach (initial maximum load = 200 N for 5000 cycles, incremental step load = 200 N for 10,000 cycles/step). The fatigue failure load and number of cycles until failure were recorded and statistically analyzed. Fractographic and finite element (FEA) analyzes were conducted as well. TZ ceramic depicted higher fatigue failure load, number of cycles until failure, and survival probabilities than LD, irrespective of the substrate. Moreover, TZ and LD presented better fatigue behaviors when bonded to substrates Ti and Yz in comparison to FRC. FEA revealed lower tensile stresses at restorative material when bonded to stiffer substrates. Fractography showed that the fracture origin started at bottom surface of restorative material (except for TZ bonded to Yz, in which crack initiated at load contact point). Translucent zirconia polycrystals present superior mechanical behavior than lithium disilicate glass-ceramic. The substrate type influences the mechanical performance of monolithic dental ceramics (stiffer substrates lead to better fatigue behavior).

Optical properties and colorimetric evaluation of resin cements formulated with thio-urethane oligomers.

OBJECTIVE: The aim of this study was to evaluate the color parameters and optical properties of resin cements (RCs) formulated with thio-urethanes (TUs). MATERIALS AND METHODS: Six TUs were synthesized by combining thiols (pentaerythritol tetra-3-mercaptopropionate [PETMP] or trimethylol-tris-3-mercaptopropionate [TMP]) with di-functional isocyanates (1,6-Hexanediol-diissocyante [HDDI] [aliphatic-AL] or 1,3-bis(1-isocyanato-1-methylethyl) benzene [BDI] [aromatic-AR] or Dicyclohexylmethane 4,4'-Diisocyanate [HMDI] [cyclic-CC]). TUs (20 wt%) were added to a BisGMA/UDMA/TEGDMA matrix. Filler was introduced at 60 wt%. Fluorescence was evaluated through an UV-light emitting equipment. Coordinates L*, a*, and b* were obtained in the black and white reflectance to evaluate the contrast ratio (CR) and translucency parameter (TP00 ). The coordinates obtained from transmittance were used to evaluate lightness (L*), chroma (C*), color difference (ΔE00 ) after 6 month, and whiteness index for Dentistry (WID ). RESULTS: RCs formulated with TUs presented significantly higher CR, and fluorescence (with T_AR). Significantly lower C*, L*, and TP00 (except for P_AR and T_AL) were also observed in RCs containing TUs. ΔE00 were not significant among the materials. WID was not influenced. CONCLUSION: RCs composed by TU oligomers present higher CR and lower translucency. The material also present higher fluorescence depending on the oligomer used. CLINICAL SIGNIFICANCE: The use of thio-urethanes to formulate resin cements can ensure a luting material with improved potential to mask colored substrates due to the higher contrast ratio and lower translucency obtained. A final higher fluorescence of restoration is also expected with the use of specific oligomer.

The Influence of Post System Design and Material on the Biomechanical Behavior of Teeth with Little Remaining Coronal Structure.

PURPOSE: To evaluate the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. MATERIALS AND METHODS: Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Finite element models evaluated the stress distribution after the application of 100 N. RESULTS: All specimens survived TC. Similar FS was observed among post-containing groups. Groups P-FP and CC presented 100% repairable fractures. The von Mises analysis showed the maximum stresses into the root canal in groups restored with metallic posts. Glass-fiber posts and CC presented the maximum stresses at the load contact point. Glass-fiber groups showed lower stresses in the analysis of maximal contact pressure; CPC led to the highest values of contact pressure. The modified von Mises (mvM) stress in dentin did not show differences among groups. Moreover, mvM values did not reach the dentin fracture limit for any group. CONCLUSIONS: The type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure.