Naohiko Iwasaki1, Hidekazu Takahashi2, Natthavoot Koottathape3, Masafumi Kanehira4, Werner J Finger5, Keiichi Sasaki6. 1. Assistant Professor, Oral Biomaterials Engineering, Course for Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan. 2. Professor and Chair, Oral Biomaterials Engineering, Course for Oral Health Engineering, School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan. 3. Lecturer Department of Prosthodontics, Faculty of Dentistry Chulalongkorn University, Pathumwan, Bangkok, Thailand. 4. Assistant Professor, Department of Restorative Dentistry, Division of Operative Dentistry, Tohoku University Graduate School of Dentistry Sendai, Japan. 5. Professor and Guest Researcher, Liaison Center for Innovative Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan. 6. Professor and Chair, Department of Oral Function and Morphology, Tohoku University Graduate School of Dentistry, Sendai, Japan.
Abstract
PURPOSE: To analyze on scanning electron microscopy (SEM) pictures from eight composite resins, taken in the centers of the initial, the middle and the terminal thirds of in vitro produced wear tracks morphological features to explain causative mechanisms for the material wear observed under two- and three-body wear. MATERIALS AND METHODS: In vitro wear behavior of eight composite resins, three conventional and five nanofiller containing marketed products was evaluated using a custom-made Zr-ball-on-disk sliding device. The composite specimens were subjected to 50,000 one-way sliding cycles (1.2 Hz, 50 N load), either simulating two-body wear with water as the intermediate medium or three-body wear using aqueous suspensions of polymethyl methacrylate (PMMA) beads and poppy seeds, respectively. Volume loss of the materials was determined in previous study. Representative specimens were selected for inspection by scanning electron microscopy at 500-fold magnification. From each of the 24 wear tracks microphotographs were taken in the central deepest parts of the initial, middle and terminal thirds of the tracks. RESULTS: For most materials morphological differences were detected depending on the location within the wear track. As a rule, the surface deterioration found increased toward the final part of the wear scar. According to common classification in tribology abrasive wear and fatigue wear, or a combination of both mechanisms were found for all materials tested. Wear was dependent both on the testing mode and on the composition of the individual composite resin material. CONCLUSION: The morphological assessment of wear tracks refects the nature of the abrasive and reveals insight into the mechanism generating wear patterns. Morphological details confirmed abrasive and fatigue-related wear as main failure mechanisms. Selection of food-like slurries as third-body media, such as poppy seed suspension is mandatory to simulate wear of composite restorations in occlusal cavities where three-body wear is the dominating determinant of loss of substance and surface deterioration.
PURPOSE: To analyze on scanning electron microscopy (SEM) pictures from eight composite resins, taken in the centers of the initial, the middle and the terminal thirds of in vitro produced wear tracks morphological features to explain causative mechanisms for the material wear observed under two- and three-body wear. MATERIALS AND METHODS: In vitro wear behavior of eight composite resins, three conventional and five nanofiller containing marketed products was evaluated using a custom-made Zr-ball-on-disk sliding device. The composite specimens were subjected to 50,000 one-way sliding cycles (1.2 Hz, 50 N load), either simulating two-body wear with water as the intermediate medium or three-body wear using aqueous suspensions of polymethyl methacrylate (PMMA) beads and poppy seeds, respectively. Volume loss of the materials was determined in previous study. Representative specimens were selected for inspection by scanning electron microscopy at 500-fold magnification. From each of the 24 wear tracks microphotographs were taken in the central deepest parts of the initial, middle and terminal thirds of the tracks. RESULTS: For most materials morphological differences were detected depending on the location within the wear track. As a rule, the surface deterioration found increased toward the final part of the wear scar. According to common classification in tribology abrasive wear and fatigue wear, or a combination of both mechanisms were found for all materials tested. Wear was dependent both on the testing mode and on the composition of the individual composite resin material. CONCLUSION: The morphological assessment of wear tracks refects the nature of the abrasive and reveals insight into the mechanism generating wear patterns. Morphological details confirmed abrasive and fatigue-related wear as main failure mechanisms. Selection of food-like slurries as third-body media, such as poppy seed suspension is mandatory to simulate wear of composite restorations in occlusal cavities where three-body wear is the dominating determinant of loss of substance and surface deterioration.