Resistenza alla fatica di restauri indiretti CAD-CAM con diversi margini di preparazione: uno studio in vitro

OBJECTIVE The purpose of this in vitro study was to evaluate and compare the biomechanical behavior of indirect composite resin and lithium disilicate restorations, performed on endodontically treated molars with different preparation design. METHODS This study was designed in 6 study groups (n=14), randomly allocated, considering the tooth preparations design in three level: adhesive crown, table-top and butt-joint overlay and “CAD-CAM blocks” in two levels: a nanohybrid composite resin (PINC) and a lithium disilicate ceramic(LiDis). Specimens, non-carious molars with mature apices, extracted for periodontal reasons, were submitted to endodontic treatment. A single and trained operator prepared the standardized MOD cavities setting residual wall thickness of buccal and oral cusps at the height of the contour to 1.5 ± 0.2 mm and placing mesial and distal cervical margins 1 mm coronally to the CEJ. Subsequently the MOD cavity was horizontally incrementally restored with a bulk fill material. All specimens were then divided in 3 groups: table top preparation, adhesive overlay preparation and adhesive crown preparation. Then, prepared specimens were scanned with an intraoral optical camera and indirect adhesive restorations were digitally designed with a similar occlusal anatomy and a standardized thickness of 2 mm. Specimens were then divided in 2 subgroups: lithium disilicate and polimer infliltrated network composite. Each overlay was then luted, subjected to cyclic intermittent loading, submitted to static fracture resistance test and examined under a scanning electron microscope. Lastly, a fractographyc analysis was performed. RESULTS: Fracture resistance was not significantly related to the CAD-CAM material employed (p>0.05) but to the preparation design (p=0.03), with table top and adhesive crown restorations showing higher resistance than adhesive overlay. Different proportion of restorable and non-restorable fractures was observed through the subgroups. CONCLUSIONS : The study shows that there is not significant difference in fracture strength between PINC and LiDis used for indirect adhesive restorations. The study shows that there is a significant difference between the three types of preparations with table tops and adhesive crowns demonstrating highest resistance to the fracture regardless of the material.