الفهرس 
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Abstract
This study was carried out to evaluate the effect load cycling on fracture resistance of a new bioactive restorative material (Activa) and compared with Nano resin composite material.
A total of 60 teeth were used in the study. Sixty upper premolars was divided into two groups of 30 specimens each according to type of restorative materials. The first group was restored by bioactive restorative material (Activa), the second group was restored by Nanohyperid composite restorative material, and each tested restorative material was applied and cured in the prepared cavities according to manufacturer’s instructions.
Each group was subdivided into 2 subgroups of 15 specimens each according to the number of received cycles that represent 24 hours and 3 months the first subgroup (T1) represented 24 hours load cycling and the second subgroup (T2) 3 months load cycling.
Mesio-Occluso-Distal (MOD) cavities were prepared in all the specimens using high speed hand piece with a long straight bur No.245. Dimensions of the MOD cavities were standardized using standard diameter size of fissure diamond point and graduated periodontal probe so preparing cavities with a 2 ± 0.2 mm pulpal depth, 1.5 ± 0.2 mm gingival width, 2 ± 0.2 mm axial height. All specimens were prepared by the same operator to eliminate inter-operator differences.
Etching gel was applied to the prepared enamel with 37% phosphoric acid for 15 seconds then the etchant was rinsed off with water for 10 s and then air dried for 5 s. Tofflemire matrix system was used to give bioactive composite its shape during its packing. Syring that containing Activa restorative material was inserted into ACTIVA-SPENSER and snap into place using firm pressure. Material was dispensed using gentle pressure to obtain an even mix of base and catalyst (1-2mm) in the cavity. Syringe firstly applied in the proximal part of cavity (mesial or distal) and keep tip of the syring at the gingival margin until proximal surfaces filed then light cured for 20 seconds using light curing device(lead light 1,470 mW/cm2 intensity). Also, Keep tip submerged in the material at all times to avoid air bubbles. Maintain contact with the floor. ACTIVA then was applied in the cavity of 2mm depth (according to manufacturer’s instructions), then light curing for 20 second was done.
Nano-hybrid resin composite (Filtek Z250 XT) was used for restoration buildup. Tofflemire matrix system was used to give the restoration its shape during resin composite packing The first layer of composite of 1.5 millimeters was applied to the one of proximal surfaces of the cavity using gold plated composite applicator, and light cured for 20 seconds. The second layer of composite was added to restore the other proximal surface of the cavity and light cured for 20 seconds. The last layer of two millimeters is applied to pulpal floor to fill the remaining of the cavity with slightly overfilled mesially, distally, and occlusally for developing proper mesiodistal and occlusal contour, inclines and ridges of occlusal anatomy, and then light cured for 20 seconds according to manufacturer’s instructions.
In order to mimic the intra-oral conditions. The specimens were subjected to mechanical fatigue in a pneumatic fatigue device. Mechanical aging test was conducted using the newly developed four stations multi-modal ROBOTA chewing simulator which has four chambers simulating the vertical and horizontal movements simultaneously in the thermodynamic condition. Each of the chambers consists of an upper hardened steel stylus holder that can be tightened with a screw for use as antagonistic materials and a lower plastic sample holder in which the specimen can be embedded. The dental specimens were embedded in acrylic resin in the lower sample holder. The samples were positioned to maintain the occlusal surface perpendicular to the loading axis. After cavity preparation and restoratrion fracture resistance test were done using the universal testing machine (Instron model 3345 Ingland)
The analysis of variance ANOVA test revealed that:
1- There was no statistical significant difference between both groups as indicated by two-way ANOVA test regardless to mechanical loading.
2- Irrespective of group totally it was found that fracture resistance means values significantly influenced by mechanical loading. (p=<0.0001<0.05) where (24h > 3m cyclic loading).
3- There was a statistical significant difference between groups load cycled equivalent to 24 hours and that load cycled equivalent to 3 months. Decrease in mean value of fracture resistance was shown in all groups load cycled for 3 months.
Under the limitation of the current study the following conclusions could be derived:
1. Chewing simulation that subjects the restorations to mechanical fatigue has an influence on their fracture resistance.
2. Application of cycling loading for longer periods negatively affects the fracture resistance of tested restoratives.
3. The use of Activa bioactive material and nanohybrid resin composite in MOD cavities prepared in premolar teeth are able to restore the weakened tooth structure.
4. The lack of bonding agent under active restoration may be related to its behavior under load.
5. Chewing simulator is a valuable research tool for simulation of the oral environmental condition and help in evaluating the longevity and success of any tested material.