In vitro study of fracture load and fracture pattern of ceramic crowns: a finite element and fractography analysis.

PURPOSE: This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses. MATERIALS AND METHODS: Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resin cores. Crowns were fabricated using the ceramics listed, cemented with dual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests, and fractured specimens were visually inspected under a stereomicroscope (20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography. RESULTS: Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction. CONCLUSIONS: Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluated before clinical use due to the high incidence of failure with tooth involvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.

Flexural modulus, flexural strength, and stiffness of fiber-reinforced posts.

BACKGROUND: The radiopacity degree of posts is not enough for adequate visualization during radiographic analyses. Glass fiber post with stainless steel reinforcement has been fabricated in an attempt to overcome this limitation. AIM: This study was designed to determine the influence of this metal reinforcement on the post mechanical properties. MATERIALS AND METHODS: This study evaluated flexural modulus (E), flexural strength (sigma), and stiffness (S) of five different fiber post systems (n = 5): RfX (Reforpost Glass Fiber RX; Angelus, Londrina, PR, Brazil); RG (Reforpost Glass Fiber, Angelus); RC (Reforpost Carbon Fiber, Angelus); FP (Fibrekor Post; Jeneric Pentron Inc., Wallingford, CT, USA); and CP (C-Post; Bisco Dental Products, Schaumburg, IL, USA), testing the hypothesis that the insertion of a metal reinforcement (RfX) jeopardizes the mechanical properties of a glass fiber post. Posts were loaded in three-point bending using a testing machine with a crosshead speed of 0.5 mm/min. RESULTS: The results were statistically analyzed using one-way ANOVA and Tukey's multiple range tests (a = 0.05). Mean and standard deviation values of E (GPa), s (MPa), and S (N/mm) were as follows: RfX: 10.8 +/- 1.6, 598.0 +/- 52.0, 132.0 +/- 21.9; RG: 10.6 +/- 1.0, 562.0 +/- 24.9, 137.8 +/- 5.5; RC: 15.9 +/- 2.4, 680.5 +/- 34.8, 190.9 +/- 12.9; FP: 10.9 +/- 1.4, 586.8 +/- 21.9, 122.4 +/- 17.3; CP: 6.3 +/- 1.7, 678.1 +/- 54.2, 246.0 +/- 41.7. Carbon fiber posts showed the highest mean s values (P < 0.05). In addition, RC showed the highest mean E value and CP showed the highest mean S value (P < 0.05). CONCLUSION: The hypothesis was rejected since the metal reinforcement in the glass fiber post (RfX) does not decrease the mechanical property values. Posts reinforced with carbon fibers have a higher flexural strength than glass fiber posts, although all posts showed similar mechanical property values with dentin.

Comparison of different wear burs after cavity preparation and sterilization methods / Comparação do desgaste de diferentes pontas após preparo cavitário e diferentes métodos de esterilização

Objetivo: Avaliar a perda estrutural e alteração morfológica da superfície de diferentes instrumentos de corte após preparo cavitário e diferentes métodos de esterilização. Material e Método: Cavidades padronizadas na superfície vestibular de incisivos bovinos foram realizadas na região do limite cemento-esmalte usando cinco diferentes tipos de instrumentos de corte (n= 4): Ca- broca cilíndrica Carbide #56 (KG Sorensen), Kg- ponta diamantada cilíndrica #1093 (KG Sorensen), Mi- ponta diamantada cilíndrica #1093 (Microdont), Fa- ponta diamantada cilíndrica #1093 (Fava) e Cv- ponta diamantada cilíndrica artificial #8,2137 (CVDentUS). Cada ponta foi submetida a um ciclo que envolveu a realização de microscopia eletrônica de varredura (MEV) inicial, preparo cavitário (PC), limpeza com ultrassom (US), três métodos de esterilização: glutaraldeído a 2% (Gl), estufa - calor seco (DH) ou autoclave - calor úmido (WH), e MEV final. Resultados: Foram encontradas diferenças significativas para a interação entre os fatores. Conclusão: O método de esterilização modifica estruturalmente os instrumentos de corte de modo diferente entre os tipos de instrumentos testados. O glutaraldeído foi o método que apresentou pior resultado para as brocas carbides. As pontas diamantadas apresentaram grande variabilidade de resultados para a interação dos fatores desgaste de instrumentos de corte e processos de esterilização.

Objective: evaluate the loss of mass and the morphologic surface alteration of different cutting instruments after cavity preparation from dental structure and different methods of sterilization. Material and Method: standardized cavities in the buccal surface of bovine incisors had been carried through in the region of the limit enamel-cementum using five different types of cut instruments (n=4): Ca- cylinder carbide bur #56 (KG Sorensen), Kg- cylindrical diamond bur #1093 (KG Sorensen), Mi- cylindrical diamond bur #1093 (Microdont), Fa- cylindrical diamond bur #1093 (Fava) and Cv- cylindrical artificial diamond bur #8.2137 (CVDentUS). Each tip was submittes to a cycle that involved: Initial Scanning Electron Microscopy (SEM), cavity preparation (PC), clean-up ultrasonic (US), three methods of sterilization: glutaraldehyde 2% (Gl), dry heat (DH) or wet heat (WH) and final SEM. Results: significant difference for the interaction between factors was found. Conclusion: the sterilization method modifies structurally the cut instruments in different way among types of the instruments tested. Glutaraldehyde proved to be the worst method for sterilizing carbide bur. The diamond instruments showed great variability of results for the interaction of wear of cutting instruments and sterilization processes.

Reabilitação conservadora com prótese adesiva reforçada por fibra de vidro: princípios, técnicas e resultados / Conservative oral rehabilitation with glass fiber reinforced composite fixed partial dentures: principles, technique and results

O objetivo deste trabalho é apresentar os princípios, técnicas (laboratorial e clinica) e resultados da reabilitação por prótese adesiva em resina composta reforçada com fibra de vidro. Paciente do gênero feminino, 23 anos, com ausência do 36, 35 íntegro e 37 com restauração em amálgama classe I, compareceu à universidade para tratamento. Preparos expulsivos OD e MO foram executados nos dentes 35 e 37, respectivamente,sendo que no 37 aproveitou-se a cavidade deixada após remoção do amálgama. A moldagem final, em passo único, foi realizada e o provisório confeccionado com resina acrílica. Na fase laboratorial, utilizou-se o sistema de fibra de vidro Fibrex-Lab (Angelus) e a resina microhíbrida Natural Look (DFL), nas cores A3 e A2, de esmalte e dentina. A prótese foi jateada internamente com óxido de alumínio, silanizada e após acabamento e polimento, foi cimentada adesivamente com Single Bond 2 e Rely-X (3M-ESPE). Após, foi feito ajuste oclusal e repolimento com pastas diamantadas. O caso resultou em uma solução conservadora, pois houve economia de desgaste no dente 35, que era hígido, e do 37 que aproveitou o preparo prévio da restauração existente. Os materiais empregados possibilitaram a recuperação da função mastigatória e estética, e o ajuste da oclusão garantiu conforto e possibilidade de maior longevidade ao tratamento. A obediência aos princípios de preparo, concepção e critério para inclusão de fibras, planejamento protético, princípios adesivos e correta seleção dos materiais garantiram excelente resultado estético e funcional.

This case report presents the principles, techniques (laboratory and clinical) and the results of an oral rehabilitation with a glass berreinforced composite fxed partial denture (GFCPD). A 23-year-old female patient with absence of tooth 36, intact 35 and 37 with class I amalgam restoration came to dental school. Expulsive OD and MO conservative cavity preparations were executed on teeth 35 and 37, respectively. Defnitive impressions were taken with a condensation silicone and provisional restorations made with acrylic resin. The glass-fiber system plus the microhybrid composite resin, in colors A3 e A2 (enamel and dentin), were employed. After finishing and polishing the prosthesis, intaglio surfaces were aluminum oxide sandblasted, silanized and adhesively fxed with Adper Single Bond 2 and Rely-X ARC. Then, a rigorous occlusal adjustment and new polishment were performed with diamond pastes. This conservative treatment option enabled tooth 35 to receive minor cavity preparations and also tooth 37, which had already been prepared in the past to receive an amalgam restoration. The employed materials restored occlusal function and esthetical appearance, and occlusal adjustment rises the chances for greater longevity. The knowledgement about GFCPD cavity preparation principles, fibers issues, prosthodontics planning and adhesive principles are the principal reason for successful treatments.