Relative fracture toughness of bis-acryl interim resin materials

Abstract

Fracture of the interim partial denture may cause patient discomfort and result in unplanned appointments and expense. At present, limited information is available concerning the fracture toughness of bis-acryl interim resins, especially immediately following fabrication. The purpose of this investigation was to evaluate the relative fracture toughness and Weibull parameters of 4 commercial chemically polymerized (Protemp Garant 3, Perfectemp II, Integrity, Temphase) and 1 dual polymerizing (Luxatemp Solar) bis-acryl interim resin materials with various filler loading after 1 hour and 24 hours. Disk-shaped, mini-compact test specimens (8.20 × 1.85 mm thick, n=18) with introduced pre-cracks were prepared in a pre-heated split-mold and maintained at 37°C for 5 minutes during polymerization to simulate clinical conditions. Polymerization temperature was measured using an infrared digital thermometer. Specimens were stored in distilled water at 37°C after which the peak load to fracture was recorded at 1 and 24 hours and the fracture toughness (K(1c)) was calculated. An overall Weibull analysis of the fracture toughness was performed incorporating the fracture toughness data with factors polymerization method, time of testing and filler load of the resin. Weibull analysis was performed at (α =.05). Fracture surfaces of representative specimens were examined using scanning electron microscopy. The overall Weibull analysis results showed significant differences (P<.001) in fracture toughness between the times of testing (1 and 24 hours), polymerization method, and as a function of filler loading. The results of the individual Weibull survival analyses showed a significant increase in Weibull Characteristic Strength (σo) values between 1 and 24 hours for all materials. The Weibull moduli (m) for the interim resins ranged between 5.8 and 10.3. SEM analysis of fractured surfaces revealed that crack propagation occurred primarily through the resin matrix between filler particles. Post-gelation polymerization has an important role in determining the fracture properties of both chemical and dual-polymerized bis-acryl interim materials within the first 24 hours. For the materials tested, the higher the filler load, the lower the fracture toughness.