[Fatigue resistance and failure mode of endodontically restored premolars with indirect composite resin restoration-in vitro]

The present study aimed at determination of the fatigue resistance and failure mode of cusp-replacing onlays in endodontically treated premolars using indirect composite resin restorations. In this experimental study, 84 human premolars were randomly divided into 7 groups of 12. These groups were prepared as follows: Intact teeth used in group1 as control, the second group covers the endodontically treated teeth, restored with indirect onlays using Z-250 composite resin, the next two groups [i.e. 3, 4] were similar to the second group, but subjected to 1 and 2 million fatigue load cycles, respectively. Groups 5, 6, 7 were similar to groups 2, 3, 4, respectively, however, in these groups Tetric Ceram used as the restorative material. All specimens were loaded using a Universal Testing Machine until fracture occurred and the mode of failure observed with naked eye. Kruskal-Wallis and Chi-Square tests were used to analyze the data [alpha=.05]. All specimens withstood the masticating simulation. The mean fracture strength for groups 1 to 7 were: 1276.92, 1269.05, 1217.80, 1188.13, 1228.97, 1127.86, 1105.58, respectively. No statistically significant differences were found between the groups in fracture strength and failure mode. There was no statistically significant difference between two types of resin composite [P=0.203] and load cycles [P=0.298] after zero, 4 and 8 years aging. Within the limitation of this study, restored premolars with indirect composite onlays show fatigue resistance equal to natural tooth up to 8 years after restoration. Furthermore, no statistically significant differences were found between 4 and 8 years of load cycles. Tetric Ceram Z-250 restoration agent showed no effect on the tooth fracture resistance with the most observed fractures to be occur under CEJ with no capability to be restored

[ effect ofpost type on stress distribution in endodontically treated maxillary central incisors: a finiie element study]

Following endodontic therapy, teeth need to be protected from fracture. The likelihood of fracture depends on the type of restoration. This simulated study was designed to compare the effect of two different restorations on stress transmission to dental tissue. Four 3-dimentional models of maxillary central incisor were created as following by finite element analysis: [I] Restored with prefabricated stainless steel post, composite core and full ceramic crown [IPS lmpress2], [2] restored with prefabricated Fiber glass post, composite core and full ceramic crown [IFS lmpress2], [3] restored with Accessory Fiber glass post, composite core and full ceramic crown [[PS Impress 2] and [4] without restoration. Each of the models received 100 loads to incisal edge at an angle of 45 degrees to tooth long axis Von Mises Stress analysis was performed for each model, comparing maximum stress intensity observed. In all groups the greatest stress was observed in the cervical region. The stress increased steadily from apex to C.E.J and decreased from C.E.J to incisal edge. The Von Misses Stress in CEJ was highest in Accessory pin group to compared the other groups. Prefabricated stainless steel post, Fiber Glass post and vital tooth groups showed slight differences in CEJ stress. In all groups the greatest stress was observed in the cervical region. It seems the use of Fiber glass posts in weakened anterior teeth acts better than accessory fiber glass post

Effect of HEMA on shear bond strength of enamel bonding to dentin after 1 year

Adhesion to dentin is the major problem in using tooth color composite resins. The way proposed is the use of hydrophile resins, of which, HEMA is the most important one. Because of the importance of the subject, this study was conducted to evaluate the effect of HEMA on shear bond strength of enamel bonding agent to dentin after 1 year water storage. This invitro study carried out experimentally on 36 extracted premolar teeth. The teeth randomly assigned to 4 groups, each group containing 6 samples. In group 1, the solution of%35 HEMA and Acetone and in group 2, the solution of%35 HEMA and Water was used. Multipurpose Scotchbond primer was used in group 4. In group 1 and 2, enamel bonding and in group 4 the adhesive was used. In group 3, teeth were dried and enamel bonded after etching. Composite cylinders were bonded on the areas with the same dimensions. The prepared samples were thermocycled 1000 times at 55°C and 5°C after keeping in distilled water for 1 year. Shear bond strength of the samples were tested by Instron machine. Results showed that the [HEMA and Acetone] group had the highest strength [25.12 +/- 3.52], and then, [Scotchbond] group [23.55 +/- 1.6]. [HEMA and Water] group [14.3H5.6] and [enamel bonding] group [4.25 +/- 2.61] had the next ranks respectively. Analysis of variance test showed that the overall difference between them was statistically significant [P<0.0001]. Difference in strength of HEMA and Scotchbond was not significant but was significantly different from other groups. Shear bond strength of [HEMA and Acetone] and [HEMA and Scotchbond] became acceptable after thermocycling and storage in distilled water for one year but not in enamel bonding group