Abstract : The purpose of this study was to evaluate the decision of the first file size that fits the apical portion (FFFA). One hundred and thirteen extracted intact human mandibular premolars with single canals were used. The reason for extraction and age of the patients were unknown. After coronal flaring, FFFA was decided with the stepback technique (n=55, group 1) or crown-down technique (n=58, group 2). The mean size of FFFA was 0.25 mm and 0.29 mm for group 1 and group 2, respectively. The stepback technique showed a significantly smaller FFFA size than the crown-down technique.

Abstract : The purpose of this study was to evaluate the use of Er:YAG laser in root canal preparation in vitro. Six human extracted lower incisors were used. The root canals were enlarged mechanically up to a size of #35 and then were irradiated by Er:YAG laser (Erwin Adverl, Morita) using two kinds of cone-shaped fiber tips (R200T and R300T). The tip was moved 20 times from the apex to the orifice, at a speed of 1 mm/s, with water spray (8.5 mL/min). The output energy was 30 mJ with a pulse frequency of 25 pps. Before and after laser irradiation, the teeth were scanned by micro computed tomography (μ-CT). Thereafter, three-dimensional images of the teeth were reconstructed and the volume of root canals was calculated. Subsequently, the teeth were split longitudinally and observed under a scanning electron microscope (SEM). It was confirmed that the root canals were enlarged after laser irradiation. The mean rates of increase of root canal spaces were 112.97±3.75% after R200T application, and 148.99±11.15% after R300T application. SEM observation showed that irradiated areas had an undulating wave-like appearance and showed no smear layer. These results show that the Er:YAG laser is an effective tool for root canal preparation.

Abstract : This study diagnosed root perforation using cone-beam CT image, and investigated the procedure using apex locator.

 We were verified this procedure using a root perforation experimental model for porcine mandible molars.

 We present a clinical diagnosis of cases of mandible perforation. The results suggested that the combination of dental CT and apex locator is useful for diagnosis of root perforation.

Abstract : The purpose of this study was to observe the healing that takes place after apexification of immature monkey teeth. Maxilla and mandibular second molars of two crab-eating monkeys were used. After extirpating the coronal pulp, the remaining pulp was coagulated with a high frequency current. The teeth were divided into two groups : an infected group and a non-infected group. One month after apexification, infected root canal treatment was initiated and calcium hydroxide or FR-Ca was applied in the canal finally. Twelve months later, the animals were sacrificed and evaluated histologically.

 In the non-infected group, continuous root development with normal tubular dentin very similar to apexogenesis or with severe osteo-like tissue that filled up the canal space were observed at apical areas. The deposited osteo-like tissue changed to tubular dentin with rare dentinal tubules, and apical foramens were formed. In the infected group, although osteo-like tissue became deposited on the apical foramen, the complete closure and root development were not seen.

 The results indicated the healing after apexification consisted of the deposition of osteo-like tissue or fibrous scar tissue in most cases. The apical closure and continuous root development depended on the conditions of the periapical tissue and in particular on the presence of infection.

Abstract : The characteristic changes of gutta-percha point following ethylene oxide gas (EOG) sterilization and electrolyzed acid water disinfection were investigated in this study.

 Two kinds of gutta-percha point (#40 GP and #40 SGP) were immersed in 20 mL of electrolyzed acid water (pH 2.3-2.7, over ORP>1100 mV, residual chlorine concentration>10 ppm) or 20 mL of distilled water for 1 or 30 min. On the other hand, both kinds of gutta-percha point were sterilized by EOG.

 Five specimens of each group were fixed to a dynamic viscoelasticity measurement apparatus to measure the storage modulus (E’) and loss modulus (E”).

 The surfaces of GP were observed with a scanning electron microscope (SEM) and underwent qualitative analysis with an electric probe microanalyzer (EPMA). The results were as follows. E’ of GP following EOG sterilization increased. SEM observation showed that particle-like structures did not remain on the GP following 30 min of immersion in electrolyzed acid water, but there was little change in the qualitative analysis.

 These results suggested that electrolyzed acid water could be used to disinfect gutta-percha point. However, the soaking time and constituent materials of gutta-percha must be considered carefully.

Abstract : This case report describes the root development following apexification of an immature tooth. The patient was a 9-year-old girl. The upper right central incisor suffered apical periodontitis with gingival abscess after rapid orthodontic treatment with a removable appliance. The root canal was cleaned by both biomechanical preparation and biochemical preparation with 6% sodium hypochlorite and 3% hydrogen peroxide. After disinfection of the root canal, calcium hydroxide paste was applied. The medicaments were replaced several times during the follow-up term. After five years and six months, radiographic images showed disappearance of the apical lesion and continuous root development. The shape of the root-end was an irregular, sharp-pointed outline with narrow canal. Following confirmation of the calcified apical barrier at the root end by palpation with a K-file, the lateral condensation procedure with a custom cone and canal sealer was done.

 This report suggests that root development after apexification occurs because of the existence of apical vital tissue even if the tooth is a non-vital tooth with open apex.