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1.
Journal of Dental School-Shahid Beheshti University of Medical Sciences. 2012; 29 (Special issue): 299-305
in Persian | IMEMR | ID: emr-138795

ABSTRACT

One of the problems involved in the restoration of extensive cavities is loss of the fracture resistance of the remaining tooth structure to withstand masticatory forces. But possible reinforcement of remaining tooth structure has been increased by the use of adhesive restorative materials. Tooth reinforcement may be affected by the different physical properties of direct and indirect composite resin restorations. So, theaim of this study was tocompare direct and indirect composite resin restorations effect on the fracture resistance of maxillary premolars with mesio-occluso distal [MOD] cavities. In this experimental [in vitro] study, 24 human maxillary premolars free of any caries, restoration or crack, which had been extracted in a 6 month period, were selected and MOD cavities with the bucco- lingual extension equal to two third of intercuspal distance were prepared on them all. The teeth were divided randomly in 3 groups including A [8 teeth and direct restoration group], B [8 teeth and indirect restoration group] and C [8 teeth and preparation without restoration group] and were undergone fracture test with universal testing machine. Variance and Tukey tests were used for analysis of results; the level of significance was set at 0.05. The mean fracture resistance was!314.75 +/- 332.26, 1192.25 +/- 352.45 and 382.45 +/- 142.51 for direct restoration, indirect restoration and preparation withoutrestoration groups,respectively. There was no significant difference between A and B groups [P=0.60], whereas the differences were significant between A and C groups [P=0.00] and also B and C groups [P=0.00]. According to the present study, both direct and indirect composite restorations cause increase in the fracture resistance of teeth and so can have an important role in extensive cavities

2.
Journal of Islamic Dental Association of Iran [The]-JIDA. 2012; 24 (4): 336-342
in Persian | IMEMR | ID: emr-153142

ABSTRACT

Composite resins can play an important role in dentin support and enamel strength via bonding to tooth structure. The purpose of this study was to compare the effects of hybrid and microfilled composite restorations on the fracture resistance of extensively weakened teeth. In this case control study 40 intact maxillary premolars were mounted in transparent acrylic resin blocks. The samples were divided into 4 groups [n=10 each]. Group PC comprised of intact teeth, without preparation and restoration. In other three groups MOD preparations with constant depths and converged walls toward occlusal surfaces were prepared. Group NC composed of teeth with preparations but without any restoration. Group HR included prepared and restored teeth using a hybrid composite and Group MR contained prepared and restored samples with a microfilled composite. Samples were thermocycled [500 cycles in 5-55°C], then were placed under compressive loads in a universal testing machine, and the curves were drawn with a software called Test Xpert. Mean fracture resistance in HR, MR, PC, and NC groups were 48.1010, 59.1773, 83.1420, and 21.9220, respectively. There was a statistically significant difference among the groups [P<0.05]. The increasing effect of microfilled group on the fracture resistance of restored teeth is significantly more than that of hybrid group

3.
Journal of Dental School-Shahid Beheshti University of Medical Sciences. 2012; 29 (4): 268-273
in Persian | IMEMR | ID: emr-122574

ABSTRACT

Extensive caries restoration has always been considered as one of dental issues. To resolve this problem different methods have been suggested such as dentinal pins.Previous clinical studies revealed that the use of retentive pins, faces numerous risks [pulp exposure, dentin cracks, root perforations, etc]. Introducing of bonding and composite systems, resulted in minimized mechanical retention for cavity preparation. Advantages of amalgam restorations such as simplicity of use, better mechanical properties, suitable clinical longevity and being less costly sustained its use in practice. On the other hand, caries removal usually results in a cavity form with small undercuts. So if we fill these small undercuts with [Bonding and Composite], then insertion of pins in this base, could be considered as a safe way for obtaining retention. The purpose of this study was comparing the retention of creative pin placement [using composite] to the retention of traditional method. In this experimental study thirty sound human mandibular molar teeth free from decay and restoration were selected. The occlusal surface of samples was removed up to 3mm above CEJ. Teeth were divided in 2 groups: Group A: [N=15] T.M.S Minim pin inserted in dentin at 2mm depth. Group B: [N=15] One layer of composite [1mm] bond to flat occlusal surface of teeth and then the pin was inserted in it at 2mm depth so only 1mm of pin placed into dentin. Group C: [N=15] cylinders of composite were prepared [height=5mm, dimension= 8mm] and pin was inserted in them at 2mm depth. The retention of pins was determined under tensile force with Zwick universal testing machine and data was charted by Test Xpert. 10-11 program. Data were analyzed by variance analysis [ANOVA] and L.S.D test. The ANOVA showed: a statistically significant difference between all groups. [p< 0.05] The L.S.D test showed: - No significant difference between A and B. [p> 0.05] - Significant difference between A, B and C. [p< 0.05]. The highest tensile strength belonged to group A. there was no significant difference between group A and B. So by using this technique 1mm depth of pin in dentin can result as same retention as 2mm depth. The lowest tensile strength belonged to group C


Subject(s)
Humans , Composite Resins , Dental Bonding , Mandible , Molar , Tensile Strength
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