Abstract : We experienced two clinical cases who had long been suspected of having root fractures.

 In the first case, the mesial root of the mandibular right first molar was finally extracted and restored with a bridge. It took many years from the first manifestation of clinical symptoms to the extraction, because the patient did not agreed to extraction.

 In the second case, the mesial root of the mandibular left first molar was strongly suspected of having a root fracture by dental X-ray. The tooth was re-treated with usual endodontic procedures. After the re-treatment, the tooth exhibited clear improvement of the symptoms.

 The necessity and methods for early diagnosis of root fracture are discussed.

Abstract : To assess pathological changes during endodontic treatment, dental radiographs are very important. Particularly in clinical cases with a transparent round area at the apex of a tooth on a dental radiograph, such a radiograph is very useful for evaluation of changes in bone recalcification. In previous studies, many interesting results have been reported leading to much discussion on the absorption of artificial bone by dry bone. We considered that attention should be paid to the difference between normal bone and dry bone on radiographic images. Pathological bone lesions are generally filled with pus or organic tissue. The aim of this study was to analyze the reflecting effect of pus or organic tissue on radiolucent images in dental radiography. We created five types of bone defect in the cancellous bone of a cow. These defects were filled with saline or soft tissue. On radiolucent radiographs, the image of an unfilled defect was clear. In contrast it was difficult to identify the edge and outline of a filled defect. Usually a clinical apical lesion is filled with pus or granulation tissue. As a result it is necessary to pay careful attention to real images of apical lesions.

Abstract : For the removal of broken instruments, the application of ultrasonic vibration is the most common technique. This study attempted to analyze and consider the degree of difficulty associated with different broken portions and conditions. Eighteen patients treated with an ultrasonic device were selected from among patients who were referred to our university hospital from general practitioners to remove broken instruments during the 10 years from 2001 to 2011. The treatment records were analyzed to identify the teeth involved, the affected area, the types of files, and the treatment time for their removal using ultrasonic waves and microscopy. Finally, the reasons for any difficulty encountered during treatment were analyzed. The greatest number of broken files was found in molar cases. The accident site and types of files were related to the difficulty of removal, and the ability to directly observe the site decreased the difficulty. More time was needed for removal of a partially pushed out file compared to a completely broken file in the canal because contact pain occurred when the ultrasonic tip reached the fragment. The expansion or reversal of blades was observed in the separated files. These results show that use of the ultrasonic removal technique combined with microscopy is useful and effective for the removal of broken files, while the position and condition of the break contributes to the difficulty of removal.

Abstract : In the present study, we examined the effect of heat stimulation on a rat clonal odontoblast-like cell line (KN-3) under the under-nutrition condition. KN-3 was cultured with medium containing 10% (for normal condition) or 1% (for under-nutrition condition) fetal bovine serum, and exposed to heat stimulation at 43°C for 45 minutes. Cell proliferation was assessed by MTS assay and cell apoptosis was determined by TUNEL staining. We also evaluated the alkalinephosphatase (ALP) activity and expression of dentin sialoprotein (DSP) and dentin matrix protein-1 (DMP-1). Increase of apoptotic cells and decrease of total cell number were observed after heat stimulation, and these phenomena were markedly enhanced under the under-nutrition condition. By day 3 after heat stimulation, the expression of DSP and DMP-1 was maintained even under the under-nutrition condition. On the other hand, the ALP activity tended to decrease under the under-nutrition condition by day 7 after heat stimulation. These results indicate that cell damage including apoptosis by heat was severe under the under-nutrition condition, and some odontoblast functions such as ALP activity were depressed under the under-nutrition condition. However, their odontoblast properties were resistant to heat stimulation under the under-nutrition condition.