Fracture Strength Of Teeth With Different Post And Core Designs

Objectives: The purpose of this study was to investigate the influence of different post and core designs on fracture strength and fracture patterns of endodontically treated premolars and maxillary central incisors.
Methods: 30 extracted premolars and 30 extracted upper central incisors underwent removal of their clinical crowns and endodontic treatment. Premolars and incisors were divided into three groups (n=10) each to receive either cast base metal post-cores (ParaPost XP), titanium (Ti) posts (ParaPost XH) or fiber reinforced composite (FRC) posts (ParaPost Fiber Lux) the latter both with composite cores. All teeth received chamfer preparation with 1.5 mm ferrule design. Impressions were taken and base metal crowns were cemented. After artificial aging (10.000 thermo-cycles, 5°C/55°C) all teeth were loaded in a universal testing machine (135° angulation) until failure. Fracture patterns were rated as catastrophic failure (root fracture) or non-catastrophic failure (post or core failure). Statistical analysis used the U-Test (p=0.05).
Results: Overall mean failure loads for premolars (457N) and incisors (412N) did not differ significantly (p=0.23). Mean failure loads in teeth with cast post-cores (500N) compared to Ti posts (409N) or FRC posts (395N) differed significantly (p<0.03). Failure loads in teeth with Ti or FRC posts did not differ significantly (p=0.73). Catastrophic failure was 100% in teeth with cast post-cores, 80% in premolars with Ti posts and 90% in premolars with FRC posts. Incisors showed 60% catastrophic failures in both Ti and FRC posts.
Conclusions: Within the limits of this study it is concluded that teeth with cast post and cores exhibit superior fracture resistance but probably fail catastrophically when overloaded. The inferior strength of Ti and FRC posts with composite cores might provide a certain level protection in maxillary central incisors. In the event of accidents these teeth have the highest risk of trauma.