Fast Fracture Strength and Fracture Toughness of Provisional Materials

Objectives: This study was to evaluate and compare the fast fracture strength and fracture toughness of several commercially available materials for provisional applications. 

Methods: An anatomically-correct three-unit posterior bridge design, with 5X5mm connectors, was selected for fast fracture strength testing. The force required to fracture the bridge was measured by applying a load with an Instron on a steel ball, which was balanced between the buccal and lingual cusps of the 1^st molar pontic.  To determine the effect of thermocycling on fast fracture, specimens with 4X5mm connectors were prepared, where the half of samples were thermocycled and fractured, and the other half was tested as control.  Thermocycled specimens underwent 1,500 cycles between 5°C and 55°C water baths.  To determine K_max, notched fracture toughness specimens (4mmx8mmx40mm) were prepared and tested according to ISO20795-2, where a pre-notched specimen was loaded in a 3-point bend.  All materials were prepared according to manufacturers' instructions. Mechanical properties of each material were statistically compared by ANOVA (a = 0.05). 

Results: Statistically analysis (ANOVA a = 0.05) shows that the fast fracture strength and fracture toughness of Radica™ were superior to those of Jet acrylic, and Integrity™.  There was no significant difference in the fast fracture strengths of Radica™ specimens prior to (800±150N) and after thermocycled (760±220N).

Fast Fracture Strength and Fracture Toughness of Various Materials (5X5mm)

Material	Fast Fracture Strength (N)	Fracture Toughness Kmax (MPa*M1/2)
Radica™ Dentin (Dentsply)	1,450±135	1.75±0.24
Jet Acrylic (Lang)	720±85	1.43±0.15
Integrity™ (Dentsply)	740±110	1.33±0.24

Conclusion: The fast fracture strength and fracture toughness of Radica™ are higher than those established commercial provisional materials Jet acrylic and Integrity™.  Thermocycling of the Radica™ specimens was shown to have no affect on their fracture strengths.