Search

Objective: This study evaluated the effect of different ferrule heights and varying degrees of substance loss on the fracture resistance of endodontically treated premolars. Methods: Eighty extracted and endodontically treated lower premolars were used and divided into 5 test groups (n =16) depending on the ferrule height: A (0.0mm), B (0.5mm), C (1.0mm), D (1.5mm) and E (2.0mm) respectively. Teeth in subgroups were either with 1 or 2 residual coronal dentin walls which were 3mm in height and 1mm in thickness. Teeth were restored with glass fiber posts and cast crowns. All specimens were then subjected to dynamic loading in a masticatory simulator for 1,200,000 loading cycles with a nominal load of 5kg at 1.2Hz combined with thermal cycling (5–55°C, dwell time 30s). Then specimens were quasi-statically loaded at 30° in a universal testing machine until fractured. Data were analyzed with 2-way ANOVA, followed by multiple comparisons using Tukey HSD test (α =.05). Results: Mean (SD) failure loads for groups ranged from 679.5±164.9N to 1084.5±269.9N. Two-way ANOVA revealed that both the ferrule height and the number of residual coronal walls had a significant influence on the fracture resistance (P <.001 and P =.006, respectively). Significant increases were produced in the final fracture resistance, when the ferrule height was increased, which was reduced to approximately 37% when teeth with 2mm ferrule height were compared with teeth without a ferrule. Significance: Under the conditions of this in vitro study, increasing the number of residual coronal walls and ferrule height had a significant effect on the fracture resistance of endodontically treated premolars restored with prefabricated posts. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The aim of this study was to evaluate the linear and volumetric dimensional changes of six denture base resins processed by their corresponding injection-molding systems at 3 time intervals of water storage. Materials and methods: Two heat-curing (SR Ivocap Hi Impact and Lucitone 199) and four auto-curing (IvoBase Hybrid, IvoBase Hi Impact, PalaXpress, and Futura Gen) acrylic resins were used with their specific injection-molding technique to fabricate 6 specimens of each material. Linear and volumetric dimensional changes were determined by means of a digital caliper and an electronic hydrostatic balance, respectively, after water storage of 1, 30, or 90 days. Means and standard deviations of linear and volumetric dimensional changes were calculated in percentage (%). Statistical analysis was done using Student's and Welch's t tests with Bonferroni–Holm correction for multiple comparisons (α =0.05). Results: Statistically significant differences in linear dimensional changes between resins were demonstrated at all three time intervals of water immersion (p ≤0.05), with exception of the following comparisons which showed no significant difference: IvoBase Hi Impact/SR Ivocap Hi Impact and PalaXpress/Lucitone 199 after 1 day, Futura Gen/PalaXpress and PalaXpress/Lucitone 199 after 30 days, and IvoBase Hybrid/IvoBase Hi Impact after 90 days. Also, statistically significant differences in volumetric dimensional changes between resins were found at all three time intervals of water immersion (p ≤0.05), with exception of the comparison between PalaXpress and Futura Gen. Significance: Denture base resins (IvoBase Hybrid and IvoBase Hi Impact) processed by the new injection-molding system (IvoBase), revealed superior dimensional precision. [Copyright &y& Elsevier]