Materials and methods
fracture, incisors, orthodontic
STERILE, ROOT CARIES
This study was in-vitro, parallel controlled in which fracture resistance and failure mode of four parallel groups were examined. It was held at the Conservative Dentistry Department laboratory at the Faculty of Dentistry, Alexandria University, Egypt. A sample size was calculated using a sample size calculation program(G*Power version 3.1.9.2, Department of Biomedical Informatics and Medical Statistics, Medical Research Institute, University of Alexandria, Egypt.) [For this study, 20 freshly extracted, for orthodontic or diabetic purpose, maxillary central incisors were collected and preserved in normal sterile saline until the onset of use. For teeth standardization, teeth selected for this study had nearly same size and shape with intact coronal and apical structure as well as root canal diameters that aided in drilling of post spaces. Periapical radiographs were taken for each specimen to verify the straight pathway of the root canals. Each specimen was measured using a Digital Caliper (Sedradent, TDV Co. Pomerode, Santa Catarina, Brazil) to insure size range at the cervical line area of 6 ± 1 mm bucco-lingually and 5 ± 1 mm mesio-distally and root length from cemento-enamel junction to the root apex of 13 ± 0.5 mm. The specimens with similar root length and diameters were selected and stored in sterile saline solution until use.Teeth with extensive root caries, fracture, and internal/external cracks/resorption were excluded from this study. Also, teeth with previous endodontic treatment or severe apical curvature were excluded.