Abstract : In this study, dentin surfaces of ten extracted human teeth were irradiated by 1,064 nm Neodymium : Yttrium-Aluminum-Garnet (Nd : YAG), 10,600 nm carbon dioxide (CO₂) and 488.0 nm Argon lasers. The morphological changes of dentin were observed by light and scanning electron microscope (SEM). The specimens were lased as follows : with no cooling, air-cooling and water-cooling. Under the condition of low powers, the effects of laser irradiation with water cooling spray, on dentin surface, could not be well observed. The results indicated that less cracks formation on dentin surfaces were observed when cooling system was used during lasing.

Abstract : The purpose of this study was to examine the correlation ship between clinical findings and apical morpholgy, using 150 human teeth indicated for extraction. After routine clinical and radiographic examinations, specimens were extracted and fixed by 10% formalin solution. 97 out of them were removed of soft tissues by 5% NaOCl to observe root apices with a light and scanning electron microscopes, and remaining 53 specimens were split longitudinally to observe intracanal contents of the apical canal under the same microscopes.

 1. The cement-dentine junctions were located 0.5 mm from the apex in only 52% of vital roots (15/29 roots). In the apical canals of non-vital roots, dentine chips, necrosed pulp tissue, filling materials and bacteria were found, while the vital roots showed vessels, nerves and odontoblatsts.

 2. Of endodontically treated 106 roots (85 teeth), 80 roots (62 teeth) were under-filled. Periapical radiolucencies were found in 34 roots (28 teeth : 43%), and the apical foramina of 16 roots (16 teeth : 20%) were completely colsed by cementum. Of properly-filled 24 roots (21 teeth : 23%), periapical radiolucencies were found in 9 roots (9 teeth : 38%), and the apical foramina were competely closed in 4 roots (4 teeth : 19%). Over-filled 2 roots (2 teeth) showed no periapical radiolucencies and no apical closure with cementum.

 3. Coincidence of root apex and apical foramen was observed in 48% (64/134 roots ; 97 teeth). In other roots, apical foramina were evenly devitated to all directions. Incidence of lateral canals was 26% (35/134 roots, 97 teeth), mostly locating 500～1500 μm from the apex evenly on all root surfaces. The shapes of main apical foramina of 112 roots investigated were classified into oval type (47%), circular type (44%) and others (9%).

 Although the morphology of root apecies was found complicated, it was concluded that the closure of apical foramen with cementum could be induced, even of infected root canal, when the canal was filled 0.5 mm radiographically under from the apex with no remaining debris in the apical canal.

Abstract : We verified the exactitude of the Dentin Sensor which can measure the thickness of dentin between prepared surface and pulpal wall with an electrical resistance.

 To examine the accuracy of this apparatus we compared the results of dentin thickness measurements by X-ray pictures and by “Dentin Sensor”.

 Dentin Sensor had a good enough exatitude of measurement ability.