Reliability, failure probability, and strength of resin-based materials for CAD/CAM restorations

ABSTRACT Objective: This study investigated the Weibull parameters and 5% fracture probability of direct, indirect composites, and CAD/CAM composites. Material and Methods: Discshaped (12 mm diameter x 1 mm thick) specimens were prepared for a direct composite [Z100 (ZO), 3M-ESPE], an indirect laboratory composite [Ceramage (CM), Shofu], and two CAD/CAM composites [Lava Ultimate (LU), 3M ESPE; Vita Enamic (VE), Vita Zahnfabrik] restorations (n=30 for each group). The specimens were polished, stored in distilled water for 24 hours at 37°C. Weibull parameters (m= modulus of Weibull, σ0= characteristic strength) and flexural strength for 5% fracture probability (σ5%) were determined using a piston-on-three-balls device at 1 MPa/s in distilled water. Statistical analysis for biaxial flexural strength analysis were performed either by both one-way ANOVA and Tukey's post hoc (α=0.05) or by Pearson's correlation test. Results: Ranking of m was: VE (19.5), LU (14.5), CM (11.7), and ZO (9.6). Ranking of σ0 (MPa) was: LU (218.1), ZO (210.4), CM (209.0), and VE (126.5). σ5% (MPa) was 177.9 for LU, 163.2 for CM, 154.7 for Z0, and 108.7 for VE. There was no significant difference in the m for ZO, CM, and LU. VE presented the highest m value and significantly higher than ZO. For σ0 and σ5%, ZO, CM, and LU were similar but higher than VE. Conclusion: The strength characteristics of CAD/ CAM composites vary according to their composition and microstructure. VE presented the lowest strength and highest Weibull modulus among the materials.

Stability evaluation of tocopheryl acetate and ascorbyl tetraisopalmitate in isolation and incorporated in cosmetic formulations using thermal analysis / Estabilidade de avaliação de acetato de tocoferol e ascorbil tetraisopalmitato isoladamente e incorporados em formulações de cosméticos por meio de análise térmica

In view of the increase in the number of cosmetic preparations containing antioxidant vitamins, chiefly, due to their action in preventing the process of skin aging, there is a need to develop pre-formulation studies and to validate analytical methods in order to obtain high quality products. Thus, the objective of this research was to evaluate and compare the thermal behavior of tocopheryl acetate and ascorbyl tetraisopalmitate as raw materials, and incorporated into a base cream. Thermogravimetry (TG / DTG) and differential scanning calorimetry (DSC) were used for this purpose. Both vitamins were found to be stable up to 250ºC. The base cream (placebo) and the sample (base cream containing the vitamins) presented different weight loss. Thermal analysis has shown itself to be an excellent tool for the characterization of these vitamins and can be used in routine analysis for quality control of this type of cosmetic formulation.

Considerando o potencial antioxidante das vitaminas utilizadas em produtos cosméticos, seu uso na prevenção do processo de envelhecimento da pele e a necessidade de estudos de pré-formulação que garantam o desenvolvimento de cosméticos de qualidade, foi objetivo deste trabalho avaliar e comparar o comportamento térmico dos ativos acetato de tocoferila e tetraisopalmitato de ascorbila, matérias-primas, isoladamente e incorporados em creme base. As técnicas termogravimetria/termogravimetria derivada (TG/DTG) e calorimetria exploratória diferencial (DSC) foram utilizadas para tal finalidade. Verificou-se que as vitaminas mantiveram-se estáveis até a temperatura de, aproximadamente, 250 ºC, observando-se diferença na perda de massa entre o creme base e o creme base associado às vitaminas. Assim sendo, a análise térmica mostrou-se como excelente ferramenta para caracterização das vitaminas e do creme base, podendo ser empregada em análises de rotina no controle de qualidade deste tipo de formulação cosmética.