Abstract : In 1905, Albert Einstein suggested that the new energy would be produced by stimulating atoms following up with the formula of E=MV², After 55 years, Maiman succeeded in making ruby-laser based on the Einstein's theory, Nowadays, lasers are applied for many objects including telecommunication, light―measurement, mechanical engineering and medicine. unfortunately, in dentistry, there are not so many indications of lasers. We have been researching in not only operative dentistry but also endodontic applications. As a result, we could put these laser treatments into practice in clinic. So, among of them were presented at the 16 JEA Meeting including pulp diagnosis, the treatment of dentine hypersensitivity, surgical treatment of dental pulp and root canal treatment. The following paper is the summary of my presentation at that time.

Abstract : Sodium hypochlorite (NaOCl) and formalin guaiacol (FG) are frequently used in endodontic treatment. Their efficiency in vitro has been evaluated by many investigators. however, their efficiency in vivo has never been investigated.

 The purpose of this study is to evaluate in vivo the efficiency of NaOCl and FG in root canals using a culture test.

 35 necrotic teeth with single root canal were chosen and divided in 4 different groups. The following treatments were carried out according to the groups.

 Group #1 Mechanical root canal preparation and FG dressing were carried out in 10 teeth.

 Group #2 Mechanical root canal preparation and NaOCl irrigation were carried out in 10 teeth.

 Group #3 Mechanical root canal preparation, NaOCl irrigation and FG dressing were carried out in 10 teeth.

 Group #4 Mechanical root canal preparation without using any disinfectant was carried out in 5 teeth.

 the results were followed :

  1. The average of treatment times (visiting times) needed to obtain a negative culture were : 1.7 times for group #1,1.4 times for group #2, and 1.1 times for group #3.

  2. In 4 teeth of group #4 (80%), a negative culture was not obtained after 5 treatment times.

  3. No side effect and flare up were recognized in all cases.

Abstract : The objects of this study were to examine the pH change of calcium hydroxide paste mixed with ten kinds of solution in vitro and vivo, and the stability of calcium hydroxide powder exposed in air. As the solution mixed with calcium hydroxide powder, sterilized water, physiological saline, weak acid water, strong acid water, alkali water, propylene glycol, 2% lidocaine, glycerin, 70% alcohol and 100% alcohol were used. The measurement of the pH change of calcium hydroxide paste was carried out by the pH meter (Horiba Co., type D-12, Japan and Unique Medical Co., type FL-7D, U. S. A.). The duration of the measurement time was 3 days to 2 months. As a result, the pH of the calcium hydroxide paste mixed with 10 kinds of solution showed almost constant values in the two cases exposed the calcium hydroxide powder in air or not during about two months. In clinic, the pH in root canals did not change also during about two weeks.

Abstract : Our therapeutic experience of 6 cases of molar presumably involving vertical incomplete fractures is reported.

 Two of these 6 cases had extracted their teeth as a result of vertical complete fractures because of undetection of their vertical incomplete fractures, 3 had preserved their teeth because of detection of vertical incomplete fractures as such a stage as fractures come short of periodontium and of tooth canal treatment and 1 had conserved pulp in vital condition because of comparatively early detection of vertical incomplete fractures and of appropriate treatments.

 Early vertical incomplete fracture is difficult of macroscopic detection and diagnosis.

 However, vertical incomplete fracture is to be suspected in case the patient complains of cold-water pain and occlusal pain and no other doubtful lesion is detectable.

 Early detection of vertical incomplete fracture will lead to dental conservation in better condition.

Abstract : Reamers and files are essential and indispensable hand instruments for Modern Endodontic Practice. However ; generally speaking, today, art and science of the manipulation of these vitally important instruments are rather prone to be neglected because of their so frequent routine daily use.

 Under the title of this series, attempts to pursuit logical, fundamental, radical, systematic and effective methods of manipulation of reamers and files would be carried out and the results would be introduced in the following papers.

 In this first paper of this series, important problems existing mainly between these hand instruments and the operators (endodontists) were pointed out and discussed for the future consideration and improvements.

Abstract : The purpose of this study was to measure the temperature changes in the tooth structures when Er-YAG laser was irradiated on the extracted human teeth.

 Four extracted human permanent teeth which were clinically intact were used for this research. The changes of temperature were measured with Thermovision 870 (AGEMA, Sweden). On the sectioned tooth with water, it was no change. On the sectioned tooth without water, it was 11.3 ℃ after 3 sec. After cavity preparation with water, it was 1 ℃ after 10 sec. After cavity preparation without water, it was 4.7 ℃ after 10 sec.

 From the above results, it could be concluded that Er-YAG laser was useful and safety for human teeth if it was irradiated with water.

Abstract : We have developed and already reported on a new cordless engine driven root canal preparation system which electronically monitors the location of the file tip during instrumentation procedures.

 The load, torque, rotation speed, and current flowing through the motor were measured when this system was used with nickel-titanium files for the preparation of human extracted tooth canals.

 The maximum load applied to the tooth was approximately 800 gram. The maximum torque observed in this system was approximately 450 g-cm. There was a linear relation between the magnitude of the torque and the current flowing through the motor. It was assumed that the Auto-torque-reverse mechanism should start at 40-80 g-cm when the ProFile or McXIM file was used. This torque range corresponded to the motor current of 100-200 mA. The rotation speed of the motor decreased as the load or torque increased, although this change was in a small range (240-280 rpm).

 This Auto-torque-reverse mechanism promises to prevent file breakage.

Abstract : Five cases which needed for extraction or any other surgery at the first examinations were saved from surgical operation and retained by conservative treatment. One case diagnosed as extraction clinically and radiographically was retained for 16 years after traditional endodontic treatment.

 Two cases which needed for apicotomy because of radiographical diagnosis as a radicular cyst and an apical alveolar abscess were retained due to successful endodontic therapy. After 9 months, the dental X-ray photograph revealed the recovery of the radiolucent apical lesion. Another two cases which complicated with dental fistula after endodontic and periodontic flare-ups were retained by fistula irrigation with antimicrobial agents (metronidazole, minocycline, ciprofloxacin mixed in powder form) in 3% H₂O₂ solution. These outcomes indicated the importance of the conservative ideas as the first thinking without preconceptions.

Abstract : Recently, I developed a twist contra-angle of repeated motion with 30° based on a technique of original super file, a kind of k-file, used by installing in a twist contra-angle which I had developed about ten years ago under manufacturer's aid.

 The angle of ordinary twist contra-angle is too wide for preparation of root canal, and furthermore, in some cases, it is inadequate. After trial and error, I found that the change of angle of twist motion (repeated motion) from 90° to 30° and use of the super file resulted in easy preparation of root canal, and this was well accepted by lots of dentists. This report shows its details.