Objectives: This study was to compare the fracture resistance and failure mode of natural teeth with endodontically treated teeth, with and without post systems that have different shapes and components.

Materials & Methods: Total 45 human mandibular incisors were divided into 9 groups; natural teeth (A), root canal treated teeth without post (B), and teeth with their crowns removed and restored with seven kinds of post systems. Each post was cemented with dual-cured resin cement, DUOLINK^TM (Bisco) and core build-up was done with light-cured composite, LIGHT-CORE^TM (Bisco), except cast posts. Each specimen was embedded in acrylic resin with periodontal ligament simulation and shear load was applied using universal testing machine (Z020, Zwick) at a crosshead speed of 5 mm/min. After test, the fracture aspects were evaluated by naked eye and SEM.

Results: The followings are the data of fracture resistance and they were analyzed by Kruskal-Wallis test and Duncan's multiple range test at P=0.01 (unit: N). Standard deviations are in parenthesis.

A	B	Cast post	Parapost (Whaledent)	Parapost fiber white (Whaledent)	Filpost (Filhol Dental)	C-post (Bisco)	FRC Postec (Ivoclar)	Cosmo post (Ivoclar)
		46% Au alloy (parallel)	S-S (parallel)	Glass fiber (parallel)	Titanium (taper)	Carbon fiber (taper)	Glass fiber (taper)	Zirconia (taper)
974.0a (80.0)	838.6b (80.9)	642.4c (102.3)	639.8c (44.8)	542.4d (40.0)	551.8d (58.2)	556.4d (31.3)	508.8d (59.4)	501.6d (39.8)

The highest fracture resistance was recorded for Cast post and Para post (P<0.01). In failure mode, C-post and FRC Postec showed favorable aspects with few cracks around apical third.

Conclusions: The carbon and glass fiber posts with tapered shape resulted in good failure mode, in spite of their lower strength than metal post, meaning the possibility of re-treatment when post fails.

Supported by grant No. R04-2003-000-10167-0 from the Basic Research Program of the Korea Science & Engineering Foundation.