Abstract : To solve the problem of mechanical instrumentation, we developed a cone-shaped laser irradiation tip (top angle=84 degree). This tip delivers 80% of the energy of the laser laterally, and 20% of the energy forward. This tip was equipped with a water nozzle. We used this tip to enlarge the root canal of beagle dogs’ teeth, and root canal was filled with gutta-percha point and sealer using the lateral condensation method. At 1 day, 1 week, 2 weeks, and 4 weeks after laser irradiation, we sacrificed 6 dogs, using over-anesthesia by pentobarbital-sodium. Under ordinal histopathological technique and light microscopic-observation, the surface of canal dentin was stained with hematoxylin. So this tip could abrade and vaporize pulp tissue, predentin and canal dentin.

 We think our new developed laser enlarging method is useful for human root canal treatment, and that this technique may have an advantage of low preparation time and stress.

Abstract : In this study, we examined the smear layer of root canal dentin after using hand instruments : stainless steel K-file and H-file, and rotary instruments : a nickel-titanium ProFile and Quantec, by SEM. After application of 10% polyacrylic acid to those smear layer, root canal dentin was observed by SEM. After application of 10% polyacrylic acid to those smear layer for 20 s, dentinal plugs were not observed by SEM, except using K-file. Therefore, it is considered that H-file, the ProFile, and Quantec hardly created dentinal plugs in root canal shaping. It is suggest that 2 min application of EDTA is necessary to remove the smear layer and dentinal plug in K-file using ; however, 20 s application of 10% polyacrylic acid is enough to remove the smear layer created by using an H-file, a ProFile, and Quantec.

Abstract : Twenty-eight years ago, I treated a case of root intrusion by “the trial and error” method. Recently the opportunity arose to observe the case again.

 In 1973, an 18 year old male fell down stairs causing the maxillary central incisors to become intruded. Twelve hours after the injury, he consulted my clinic. Radiographs showed these teeth were intruded about 3 mm from the original position.

 Both teeth were surgically repositioned and stabilized with an acrylic resin splint. Later, root canal therapy was performed on these teeth followed by restoration with porcelain fused to metal bridge.

 Twelve years later, the gingiva appeared healthy but radiograph demonstrated cervical root resorption and the periodontal ligament space was not well defined. Twenty-two years later, the bridge was still functioning well and not mobile. The gingiva showed slight marginal inflammation. The cervical root resorption appeared larger than it had on the previous consultation and the periodontal ligament space was less well defined.

 Now, 28 years later, the bridge was still functioning well and not mobile. The gingival showed slight marginal involution as before. However the cervical root resorption appeared even larger, and the periodontal ligament space was progressively less defined.

Abstract : Mineral Trioxide Aggregate (MTA) was developed in 1993. Many clinicians have been used MTA to perforation part, root-end filling, root canal filling, etc. Previously, amalgam, glassionomer cement, or super EBA cement were used to perforation part for healing of patient part. In this case report, the patient feels the pain after infected root canal treatment, because the patient tooth has perforation. Then, patient tooth was treated by laser irradiation or Ca(OH)₂ agent ; however, spontaneous pain did not disappear. The patient visited us for the treatment of the patient tooth. We checked the patient tooth, and MTA was applied to the perforation part, after obtaining the patient’s consent. The patient tooth healed, and the prognosis is good. It is suggested that MTA is good material for repair of a perforation of the pulp floor.