Tabriz University of Medical Sciences Medical Journal of Tabriz University of Medical Sciences 2783-2031 29 1 2007 03 22 The Effect of Horizontal Pin on Fracture Resistance of Composite Restored Endodontcally Treated Teeth 59 64 EN SAVADI OSKUEE S ALIZADEH OSKUEE P JAFARI NAVIMIPUR E MOHAMMADI N Journal Article 2010 05 23 Backgraund and objectives: Restoration of endodontically treated teeth by a simple method, with low cost in a short time is one of the major problems in dentistry. The purpose of this study was to evaluate the effect of horizontal pins in fracture resistance of endodontically treated maxillary premolars restored with composite. Materials and Methods: In this study, 48 sound, closed apex, maxillary human premolars, without crack, extracted for orthodontic reasons, were randomly divided into 3 groups of 16 as follows: Group 1: intact (unprepared) teeth Group 2: composite restoration without horizontal pin Group 3:composite restoration with 2 horizontal pins in buccal cusp. In groups 2,3 after preparation of the standard access cavity and endodontic treatment, the palatal cusp was reduced to 1.5 mm coronal to the CEJ, leaving the remaining buccal cusp 3mm in buccolingual thickness at the height of contour. After thermocycling , each tooth was loaded in compression until fracture occured. Data were analyzed with one-way ANOVA and Tukey test. The pattern of fracture was analyzed by Chi-Square test. Results: The mean fracture resistance in groups 1-3 were 689.59  179, 632.86  119 and 533.49  168 (in N) respectively. The differences between group 1 and group 3 were statistically significant (p<0.05). Among patterns of fracture, the maximum number of favourable fractures occured in group 1 and the minimum number was in group 3. Conclusion: 1) Composite restoration with dentin bonding agents in endodontically treated maxillary premolars increased resistance to fracture. 2) Horizontal pins caused statistically significant reduction in fracture resistance of teeth. 3) The use of horizontal pins did not result in favorable fracture pattern.