Fracture resistance of fibre-reinforced composite crown restorations

Purpose: To evaluate the laboratory fracture resistance of teeth restored with crowns constructed in one of these materials (BelleGlass HP with and without fiber reinforcement. Methods: 40 sound maxillary premolar teeth were chosen and were allocated to four groups of 10 teeth, with the mean size of any group varying by less than 2.5% from other test groups. The teeth were stored in water. Each tooth was fixed in a steel mold and subjected to a standardized crown preparation. Crowns were constructed in belleGlass HP. Group A contained no fiber reinforcement. In Group B, Construct polyethylene braided fibers were applied from the mesial margin over the coronal aspect of the die down to the distal margin, and circumferentially around the preparation, prior to crown construction as in Group A. In Group C, a bundle of experimental S-glass fiber of 9 pm diameter was applied circumferentially prior to crown construction as in Group A. In Group D, two layers of Stick net pre-impregnated woven glass fibers were adapted over the whole surface of the initial thin coping, prior to constructing crowns as in Group A. Crowns were luted with a dual cure resin cement (Nexus), with the dentin surface of the specimens having first been treated with a dentin bonding system. Each specimen was stored under water at 37degreesC for 24 hours prior to testing, and were then subjected to compressive loading at a cross-head speed of 1 mm/minute in a Universal Testing Machine by way of a 4 mm diameter steel bar placed along the midline fissure of the upper premolar crown. Results: The mean force required (kN) to cause fracture was as follows: Group A 2.0kN, Group B 2.4kN, Group C 2.7kN, Group D 2.3kN. ANOVA showed that there was no statistically significant difference between the groups.