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.

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.

Influence of one- or two-stage methods for polymerizing complete dentures on adaptation and teeth movements / Influência dos métodos de um ou dois estágios para polimerização de próteses totais na adaptação e movimentação de dentes

Introduction: The quality of complete dentures might be influenced by the method of confection. Objective: To evaluate the influence of two different methods of processing muco-supported complete dentures on their adaptation and teeth movements. Material and method: Denture confection was assigned in two groups (n=10) for upper and lower arches according to polymerization method: 1) conventional one-stage - a wax trial base was made, teeth were arranged and polymerized; 2) two-stage method - the base was waxed and first polymerized. With the denture base polymerized, the teeth were arranged and then, performed the final polymerization. Teeth movements were evaluated in the distances between incisive (I-I), pre-molars (P-P), molars (M-M), left incisor to left molar (LI-LM) and right incisor to right molar (RI-RM). For the adaptation analysis, dentures were cut in three different positions: (A) distal face of canines, (B) mesial face of the first molars, and (C) distal face of second molars. Result: Denture bases have shown a significant better adaptation when polymerized in the one-stage procedure for both the upper (p=0.000) and the lower (p=0.000) arches, with region A presenting significant better adaptation than region C. In the upper arch, significant reduction in the distance between I-I was observed in the one-stage technique, while the two-stage technique promoted significant reduction in the RI-RM distance. In the lower arch, one-stage technique promoted significant reduction in the distance for RI-RM and two-stage promoted significant reduction in the LI-LM distance. Conclusion: Conventional one-stage method presented the better results for denture adaptation. Both fabrication methods presented some alteration in teeth movements.

Introdução: A qualidade das próteses totais pode ser influenciada pelo método de confecção. Objetivo: Avaliar a influência de diferentes métodos de confecção de próteses totais na adaptação e movimentação de dentes. Material e método: A confecção das próteses foi dividida em dois grupos (n=10) para arcadas superior e inferior de acordo com o método: 1) convencional de uma etapa - realizada uma base de prova em cera onde foram montados os dentes e levada para a termopolimerização; 2) Método de duas etapas - a base foi encerada e termopolimerizada. Com a base da prótese polimerizada, os dentes foram montados e em seguida realizou a polimerização da outra porção. Para movimentação de dentes foram avaliadas as distâncias entre incisivos (I-I), pré-molares (PM-PM), molares (M-M), incisivo esquerdo a molar esquerdo (IE-ME) e incisivo direito a molar direito (ID-MD) antes e após polimerização final. As próteses foram seccionadas em três posições para análise de adaptação: (A) face distal de caninos, (B) face mesial de primeiros molares, e (C) face distal de segundos molares. Resultado: As bases das próteses demonstraram melhor adaptação quando polimerizadas no processo de uma etapa, tanto superiores (p< 0,05) quanto inferiores (p< 0,05), com a região A apresentando melhor adaptação que a região C. Na arcada superior uma redução na distância entre I-I foi observada na técnica de uma etapa, enquanto que na técnica de duas etapas houve redução na distância ID-MD. Na arcada inferior, na técnica de uma etapa houve redução na distância ID-MD e houve redução significativa na distância IE-M pelo método de duas etapas. Conclusão: O método de uma etapa apresentou melhores resultados para a adaptação da prótese. Ambos os métodos de confecção apresentaram alteração na movimentação de dentes.

Overdenture retaining bar stress distribution: a finite-element analysis.

OBJECTIVE: Evaluate the stress distribution on the peri-implant bone tissue and prosthetic components of bar-clip retaining systems for overdentures presenting different implant inclinations, vertical misfit and framework material. MATERIALS AND METHODS: Three-dimensional models of a jaw and an overdenture retained by two implants and a bar-clip attachment were modeled using specific software (SolidWorks 2010). The studied variables were: latero-lateral inclination of one implant (-10°, -5°, 0°, +5°, +10°); vertical misfit on the other implant (50, 100, 200 µm); and framework material (Au type IV, Ag-Pd, Ti cp, Co-Cr). Solid models were imported into mechanical simulation software (ANSYS Workbench 11). All nodes on the bone's external surface were constrained and a displacement was applied to simulate the settling of the framework on the ill-fitted component. Von Mises stress for the prosthetic components and maximum principal stress to the bone tissue were evaluated. RESULTS: The +10° inclination presented the worst biomechanical behavior, promoting the highest stress values on the bar framework and peri-implant bone tissue. The -5° group presented the lowest stress values on the prosthetic components and the lowest stress value on peri-implant bone tissue was observed in -10°. Increased vertical misfit caused an increase on the stress values in all evaluated structures. Stiffer framework materials caused a considerable stress increase in the framework itself, prosthetic screw of the fitted component and peri-implant bone tissue. CONCLUSIONS: Inclination of one implant associated with vertical misfit caused a relevant effect on the stress distribution in bar-clip retained overdentures. Different framework materials promoted increased levels of stress in all the evaluated structures.

Influence of different flask systems on tooth displacement and framework misfit in mandibular fixed implant-supported complete dentures.

PURPOSE: To evaluate the influence of different metallic flask systems for acrylic resin denture processing on tooth displacement and framework misfit of mandibular fixed implant-supported complete dentures. METHODS: Standard mandibular implant-supported complete dentures in five implants were waxed and randomly assigned to three groups: G1 - conventional flask, G2 - double flask, and G3 - occlusion flask. Framework misfit in all the implants and the linear distances between teeth (I-I - incisor-to-incisor; P-P - premolar-to-premolar; M-M - molar-to-molar; RI-RM - right-incisor-to-right-molar; and LI-LM - left-incisor-to-left-molar) were measured before and after denture processing using an optical microscope. Dentures were processed by hot water curing cycle (9h/74°C). Collected data were analyzed by paired Student's t-test and one-way ANOVA (α=0.05). RESULTS: All the measured distances presented changes in tooth displacement after denture processing. However, the M-M distance for G1 (p=0.003) and the P-P (p=0.042) and LI-LM (p=0.044) distances for G3 showed statistically significant differences. Differences between the flask systems were not statistically significant. Statistically significant differences in the framework misfit due to denture processing were found for all the implants and groups, with the exception of right median implant for G2 and right distal implant for G3. A comparison of the flask systems found statistically significant differences in which G1 presented an increase in the misfit values and G2 and G3 a decrease. CONCLUSIONS: Different flask systems did not cause significant changes in tooth displacement. Frameworks misfit values were influenced by the different flask systems. The conventional flask presented an increase in the framework misfit, while the experimental flasks showed a decrease.

Influence of post-thickness and material on the fracture strength of teeth with reduced coronal structure.

PURPOSE: To evaluate the fracture strength of endodontically treated teeth with reduced coronal structure reinforced with glass-fiber posts and cast posts and core (nickel-chromium alloy) with different thickness. MATERIALS AND METHODS: Forty maxillary central incisors were sectioned at 1 mm of the cementoenamel junction and endodontically treated. The teeth were divided into four groups (n = 10) and restored with cast post and core and glass-fiber posts with diameters of 1.5 mm and 1.1 mm. The fracture strength was evaluated using a Universal Testing Machine (Instron 1144) at 45° of angulation. The results were submitted to analysis of variance two-way and Tukey's test (P < 0.05). The failure mode was also evaluated. RESULTS: Cast post and core were statistically superior to the glass-fiber posts with the self-post diameter (P = 0.001). When the self-post material was considered, no significant difference was observed between the two post-diameters (P = 0.749). The glass-fiber post-groups presented more fractures in the cervical third than the cast post and core groups. CONCLUSION: Teeth restored with cast post and cores present higher fracture strength than those reinforced with glass-fiber posts. An increased post-thickness does not increase the fracture strength. Glass-fiber posts lead to less severe fractures.