Purpose: With the increase in number of remaining teeth per capita, the incidence of noncariogenic diseases other than dental caries and periodontal disease is also increasing. Among the noncariogenic diseases, microcracks in enamel (enamel cracks) may be a cause of hypersensitivity with no substance defect. The incidence of enamel cracks in healthy teeth is reported to exceed 95% in subjects aged 40 years or older. Considering sealing of enamel cracks with dentin desensitizers (desensitizers) based on their fast-acting property and convenience, we measured the permeation inhibition rate using a dentin hypersensitivity model. At the same time, the influence of the storage condition on the permeation inhibition rate was also investigated by storing specimens in either distilled water or remineralization solution.

 Methods: Enamel crack specimens were prepared using healthy bovine teeth with no dental caries. A device was prepared following the method reported by Pashley et al., each specimen was connected to the device and the inner pressure was set at 25 mmHg. The desensitizers used in the experiment were SUPER SEAL (SS), MS Coat F (MS), Nano Seal (NS), Teethmate Desensitizer (TD), and G-Premio BOND (GP). After the application of each desensitizer, the enamel crack permeation inhibition rate was measured. After measurement, the specimens were stored in distilled water (DW group) or remineralization solution (RS group), and the enamel crack permeation inhibition rate was measured after one week, after one month and after three months.

 Results: The permeation inhibition rates at one month and at three months were significantly higher than that immediately after application in the SS-, TD-, and NS-applied DW groups. In the SS- and NS-applied RS groups, the permeation inhibition rates at one month and at three months were significantly higher than that immediately after application. In the TD-applied RS group, the permeation inhibition rate at three months was significantly higher than that immediately after application. In the MS-applied DW and RS groups, the permeation inhibition rates at one week, at one month and at three months were significantly higher than that immediately after application. In the GP-applied DW and RS groups, high sealability was noted from immediately after application, but the differences were not significant.

 Conclusion: It is suggested that although the timing of the demonstrated effect differs among the desensitizers, the effect is demonstrated by repeated application.

 Purpose: For endodontic re-treatment, the removal of root canal-filled material and patency of root apex are essential. In the present study, we examined the removability of a newly developed bioactive glass based sealer (BG based sealer) from a root canal, and analyzed the dentin surface of the root canal after re-preparation and irrigation.

 Methods: Four weeks after filling human extracted teeth with each sealer (eugenol based, non-eugenol based, bioceramic based, and BG based sealers), each root canal-filled material was removed by a gutta-percha removal instrument. The ability to regain the working length (WL), patency of root foramen, and time for removal were examined. Additionally, the dentin surface of the re-prepared root canal was analyzed by FE-SEM.

 Results: In the removability test, WL gain and patency of root foramen to the root canal filled by BG-based sealer were possible as seen in other sealer groups. FE-SEM analysis showed that dentin tubules in the coronal and middle third of root canals were opened, whereas the number of opened dentinal tubules was low in the apical third as seen in other sealer groups.

 Conclusion: BG based sealer showing suitable properties as a sealer was able to be removed from the root canal, suggesting that root canals filled with BG based sealer can be retreated.

 Purpose: Clinically, resin composite repair for dentin hypersensitivity with substantial defects such as wedge-shaped defects is commonly performed a few days after applying the densensitizer to dentin. In this study, we investigated the influence of pre-treatment of dentin densensitizers on bond strength.

 Materials and Methods: We applied three desensitizers (MS coat ONE, F Varnish, and Nanoseal) on an artificial model of hypersensitive dentin using human premolars, and observed the surface structure by scanning electron microscope (SEM). Then, the specimens to which the three desensitizers had been applied were treated with Clearfil Mega Bond FA. We morphologically observed by SEM the surface of dentin which had been treated with the primer. Furthermore, the micro-tensile bond strength (μTBS) for the specimens which were incrementally built up by resin composites was measured in a universal testing machine. The interface between resin and dentin of specimens was observed by SEM and confocal laser scanning microscope (CLSM).

 Results: The surfaces of specimens to which each desensitizer had been applied showed morphological characters having the effects of suppressing hypersensitivity. Regarding μTBS, there were no significant differences among all groups. In the group of MS coat ONE, MS coat ONE was not completely removed by the application of Mega Bond FA primer. Although the penetrations of the primer into dentin tubules were small, the thickness of the bond layer was greater. The specimens of F Varnish showed the functions of self-etching adhesive systems, because the varnishes had been partially removed by Mega Bond FA primer. In the group of Nanoseal, Mega Bond FA primer was almost removed by Nanoseal, and penetrated deeply into the dentinal tubules.

 Conclusion: The three desensitizers used in this study had no effect on the bond strength of self-etching adhesive systems to the artificial model of hypersensitive dentin.

 Purpose: Instrumented root canal walls are covered with a smear layer, which can harbor bacteria, provide an avenue for leakage and limit the disinfection of intratubular bacteria by preventing the penetration of intracanal irrigants and medicaments. Although ethylenediaminetetraacetic acid (EDTA) is most widely used for smear layer removal, high concentrations of EDTA can induce hyper-demineralization (erosion) of intraradicular dentin. This study aimed to evaluate the smear layer removal effect of a pH-modified low-concentration EDTA irrigant, and examine whether it induces dentin hyper-demineralization.

 Methods: Dentin slices prepared from extracted human teeth were ground with #600 SiC paper to create an experimental smear layer. Each specimen was treated with one of the following solutions: 3% EDTA solution (Smear Clean, Nippon Shika Yakuhin, pH=9.5: SC), 14.3% EDTA solution (Morhonine, Showa Yakuhin Kako, pH=7.2: MH), or 20% citric acid solution (Ultradent citric acid, Ultradent Japan, pH=1.4: CA). Smear layer removal and dentinal erosion were examined by scanning electron microscopy (SEM). Dentin slices treated with SC or MH for up to 30 min were examined with Ca and P mapping with energy dispersive X-ray spectrometry (EDX). Root canals of single-rooted human teeth instrumented with Ni-Ti rotary instruments (EndoWave, Morita) were also examined with SEM to evaluate the effect of SC irrigation on smear layer removal.

 Results: SC, MH and CA effectively removed the smear layer created on dentin slices. Dentinal erosion was hardly seen on SC- and MH-treated specimens, while it was frequently detected on CA-treated specimens. Thirty-minute treatment by MH caused severer dentinal decalcification compared with that by SC. Following intracanal irrigation with SC, the smear layer generated by Ni-Ti rotary instrumentation was almost completely removed in the middle portion of tooth roots, although a small amount of the smear layer remained in the apical portion.

 Conclusions: The 3% EDTA solution (SC) showed a smear layer removal effect comparable to that of the 14.3% EDTA solution (MH) and 20% citric acid solution (CA), and effectively removed the intracanal smear layer generated by Ni-Ti rotary instrumentation. Among the three irrigants, SC induced the mildest dentinal erosive changes.

 Purpose: Diagnosis and treatment plan are important to preserve teeth. However, it is difficult to diagnose correctly from symptoms and findings. In this report, we present two cases of periodontal-endodontic lesions in which endodontic treatment was effective to preserve teeth that had formed deep pockets and that had severely resorbed bone.

 Case 1: A 54-year-old woman who complained about repeat gingival swelling in the left molar region. Probing pocket depth (PD) of over 7 mm was found in the left second premolar. Radiographic examination showed that marginal bone resorption was more severe than in the periapical region. The pulp condition could not be examined because of a fixed metal bridge in the left second premolar. However, because the pulp was not vital when a small hole was drilled through the crown and into the dentin, root canal treatment was performed. At 3 weeks after the treatment began, the reduction of PD and improvement of bone around the tooth were observed.

 Case 2: A 33-year-old woman who complained about swelling and bleeding in the right molar region. PD of over 7 mm was widely observed. Radiographic examination showed severe bone resorption around the distal root and furcation region, however, furcation involvement was not detected by furcation probe. Although the canal filling did not seem to be bad, periapical bone loss was observed. We considered that the endodontic problem had induced the bone loss although the canal filling did not seem to be bad, therefore, canal treatment was performed. Bone resorption in the periapical region and furcation area improved after the treatment. Scaling, root planing and flap operation led to improvement of the bone condition in the distal area of the distal root.

 Conclusion: The condition of bone destruction was so severe that tooth extraction or hemisection of distal root was considered. However, bone resorption was improved and teeth could be preserved by endodontic treatment.