MECHANISMS OF FORMATION OF WEDGE SHAPED DEFECT BY ABFRACTION AND ITS RESTORATIVE MRTHIDS.

The aims of this examination are to identify the relationships between the biomechanic factor and stress-induced cervical lesion by abfraction，and investigate more effective restorative methods at these regions.Artificial formation of cervical lesion by fatigue loadingAn extracted human upper premolar was fixed in die at an angle of 45°to the long axis of the tooth。Repeated stress(10.0Kgf/2.5Kgf)at 4 Hz was applied the buccal cusp of the tooth up to 6x10^6 cycles in 37℃DW using a servo-hydraulic machine.Morphological changes were observed using precision replica under SEM.The development of a crack network about1.2 mm in width was observed on the cementum along the CEJ.As the number of cycles increased，the number of crack networks increased.On the other hand，a falling off a smear layer and opening of dentinal tubules were recognized on the gingival dentin under the DEJ at 4x10^6cycles。Furthermore，growth of cleavage-type cracks was observed at the coronal dentin.These findings may support。Stress-induced theory.The micro-cracks on the cementum and dentin resulting from the accumulation of fatigue stress may act as the initial contributor to the formation of cervical lesion.Treatment of cervical lesion by abfractionIn order to obtain long-term success for cervical restoration，restorative materials themselves should be required biomechanically acceptable characteristics；higher fracture toughness(K_1c)that exhibits high acture biomechanically acceptable characteristics；higher fracture toughness(K_1c)that exhibits high fracture biomechanically acceptable characteristics；higher fracture toughness。Furthermore，the formation of adhesive interface with superior fatigue resistance should be desired.On dentin adhesive system，an increase of width of hybrid layer，sufficient monomer penetration up to the front of demineralized dentin and an increase of conversion rate of monomer might contribute to the improvement in fatigue limit of the adhesive interface。

The aims of this examination are to identify the relationships between the biomechanic factor and stress-induced cervical lesion by abfraction, and investigate more effective restorative methods at these regions.Artificial formation of cervical lesion by fatigue loadingAn extracted human upper premolar was fixed in die at an angle of 45゜ to the long axis of the tooth. Repeated stress (10.0Kgf/2.5Kgf) at 4Hz was applied the buccal cusp of the tooth up to 6 x 10^6 cycles in 37℃ DW using a servo-hydraulic machine. Morphological changes were observed using precision replica under SEM.The development of a crack network about 1.2 mm in width was observed on the cementum along the CEJ.As the number of cycles increased, the number of crack networks increased. On the other hand, a falling off a smear layer and opening of dentinal tubules were recognized on the gingival dentin under the DEJ at 4 x 10^6 cycles. Furthermore, growth of cleavage-type cracks was observed at the coronal dentin. These findings may support. stress-induced theory. The micro-cracks on the cementum and dentin resulting from the accumulation of fatigue stress may act as the initial contributor to the formation of cervical lesion.Treatment of cervical lesion by abfractionIn order to obtain long-term success for cervical restoration, restorative materials themselves should be required biomechanically acceptable characteristics ; higher fracture toughness (K_1c) that exhibits high fracture resistance and lower modulus of elasticity that can compensate for shear stress at adhesive interface. Furthermore, the formation of adhesive interface with superior fatigue resistance should be desired.On dentin adhesive system, an increase of width of hybrid layer, sufficient monomer penetration up to the front of demineralized dentin and an increase of conversion rate of monomer might contribute to the improvement in fatigue limit of the adhesive interface.