RESUMEN
Objective: The recycling of heat pressed lithium disilicate glass-ceramic leftover material has been reported to be done by dental laboratories. The effect of this procedure on the fracture resistance of single crowns is unknown, especially when it is functioning inside the oral cavity with subsequent exposure to temperature changes and cycles of mastication. Material and Methods: A total of 28 lithium disilicate glass-ceramic crowns (IPS emax Press) were constructed and randomly assigned into two groups (n = 14); Group (P): Included crowns fabricated from new e.max ingots. Group (R): Included crowns fabricated from repressed e.max buttons. Specimens of each group were divided into two equal subgroups (n = 7) according to whether the aging of specimens will be performed or not before fracture resistance testing. Subgroup (N), samples were subjected to fracture resistance without thermo-mechanical aging, while subgroup (A), samples were subjected to thermo-cycling and cyclic loading before being subjected to fracture strength testing. Different methods; SEM, XRD, EDAX were used to characterize the properties of lithium disilicate glass-ceramics before and after repressing. Results: The highest statistically significant fracture resistance value was recorded for the subgroup (RN) repressed/non-aged, followed by the subgroup repressed/aged (RA), while the lowest statistically significant mean value was recorded for the subgroup pressed/aged (PA). There was no significant difference between pressed/non-aged (PN) and repressed/aged (RA) subgroups. Conclusion: Repressing of leftover buttons may increase the fracture resistance of IPS emax Press crowns. Thermo-mechanical aging may negatively affect the fracture resistance of IPS emax Press crowns, yet Repressing may decrease this effect. Clinical implications:This is a novel approach that targets a point of research that has not been investigated before. It elaborates how repressing may decrease the effect of aging and increase the fracture resistance of lithium disilicate crowns. Thus, recycling of lithium disilicate glass ceramics might decrease its failure and prolong their serviceability (AU)
Objetivo: A reutilização de material residual de vitrocerâmicas de dissilicato de lítio prensadas a quente tem sido realizada pelos laboratórios de prótese. O efeito deste procedimento na resistência à fratura de coroas unitárias é desconhecido, especialmente quando estão em função na cavidade oral com subsequente exposição às variações de temperatura e ciclos mastigatórios. Material e Métodos: Vinte e oito coroas de dissilicato de lítio (IPS e.max Press) foram confeccionadas e divididas aleatoriamente em dois grupos (n = 14); Grupo (P): Incluiu coroas fabricadas de pastilhas novas de e.max; Grupo (R): Incluiu coroas fabricadas de e.max reprensado. As amostras de cada grupo foram divididas em dois subgrupos iguais (n = 7) de acordo com a realização de envelhecimento dos espécimes antes do teste de resistência à fratura. As amostras do subgrupo (N) foram submetidas ao teste de resistência à fratura sem envelhecimento termomecânico, enquanto as amostras do subgrupo (A) foram submetidas ao envelhecimento termomecânico antes do teste de resistência à fratura. Diferentes métodos (MEV, DRX e EDS) foram usados para caracterizar as propriedades da cerâmica de dissilicato de lítio antes e depois da reprensagem. Resultados: O maior valor de resistência à fratura estatisticamente significativo foi do subgrupo (RN) reprensado/não envelhecido, seguido pelo subgrupo reprensado/envelhecido (RA), enquanto o menor valor médio estatisticamente significativo foi do subgrupo prensado/envelhecido (PA). Não houve diferença estatística entre os subgrupos prensado/não envelhecido (PN) e reprensado/envelhecido (RA). Conclusão: A reprensagem de material residual pode aumentar a resistência à fratura de coroas de IPS e.max Press. O envelhecimento termomecânico pode afetar negativamente na resistência à fratura deste material, enquanto a reprensagem pode diminuir este efeito. Relevância clínica: Esta é uma nova abordagem que busca estudar um tema que não havia sido investigado anteriormente. Este estudo demonstrou como a reprensagem pode diminuir o efeito do envelhecimento e aumentar a resistência à fratura de coroas de dissilicato de lítio. Assim, a reutilização de vitrocerâmicas de dissilicato de lítio pode diminuir o risco à falha e aumentar o tempo de vida útil (AU)
Asunto(s)
Coronas , Reciclaje , Resistencia Flexional , BocaRESUMEN
OBJECTIVES: To determine and compare the fracture resistance of endodontically treated maxillary central incisors restored with different posts and cores. MATERIALS AND METHODS: Forty-eight upper central incisors were randomly divided into four groups: cast post and core (group 1), fiber-reinforced composite (FRC) post and composite core (group 2), composite post and core (group 3), and controls (group 4). Mesio-distal and bucco-lingual dimensions at 7 and 14 mm from the apex were compared to ensure standardization among the groups. Twelve teeth were prepared for crown restoration (group 4). Teeth in other groups were endodontically treated, decoronated at 14 mm from the apex, and prepared for posts and cores. Resin-based materials were used for cementation in groups 1 and 2. In group 3, composite was used directly to fill the post space and for core build-up. All samples were restored by standard metal crowns using glass ionomer cement, mounted at 135degrees vertical angle, subjected to thermomechanical aging, and then fractured using a universal testing machine. Kruskal-Wallis and Mann-Whitney U tests were used to analyze the data. RESULTS: Fracture resistance of the groups was as follows: Control (group 4) > cast post and core (group 1) > fiber post and composite core (group 2) > composite post and core (group 3). All samples in groups 2 and 3 fractured in restorable patterns, whereas most (58%) in group 1 were non-restorable. CONCLUSIONS: Within the limitations of this study, FRC posts showed acceptable fracture resistance with favorable fracture patterns for reconstruction of upper central incisors.