Purpose: This study aimed to determine the reasons for the extraction of permanent teeth in the Kami-Ina Area, Nagano Prefecture, Japan.

 Methods: Dentists belonging to the Kami-Ina Dental Association were asked to fill in a questionnaire when they extracted one or more permanent teeth during the 41-day period between June 27, 2016 and August 6, 2016. Items in the questionnaire on tooth extraction included gender, age, location of extracted tooth, main reasons for extraction structures in the oral cavity (attrition, wedge shaped defect (WSD), palatal torus and mandibular torus), oral hygiene condition, snacking habit, preference for sweets, dental check-up and pulp vitality. Logistic regression was used to compare the frequency distributions. Data analyses were performed using SPSS version 22 (IBM).

 Results: Information on 1,010 extracted teeth from 804 patients was obtained; 549 teeth were removed from males, 457 teeth from females and 4 teeth from unknown gender. The largest number of teeth extracted was in patients aged over 75 years. A total of 265 teeth were extracted due to periodontal disease, 239 teeth due to third molar problems, 208 teeth due to apical periodontitis, 201 teeth due to fracture, and 84 teeth due to caries. The results of logistic regression analysis showed that tooth loss due to caries and periodontal disease had significantly lower odds for persons with good hygiene and that tooth loss due to caries and apical periodontitis had significantly lower odds for persons receiving regular dental check-ups. There was a significant association between structures in the oral cavity (attrition and WSD) and tooth loss due to fracture.

 Conclusions: In this study, periodontal disease was the most frequent cause of tooth extraction, followed in order by third molar problems, apical periodontitis, tooth fracture, and caries. The results suggest that:

 1. The risk of tooth extraction due to caries and periodontal disease is low when the periodontal condition is good.

 2. The risk of tooth extraction due to caries and apical periodontitis is low with regular dental check-ups.

 3. The risk of tooth extraction due to fracture increases with attrition and WSD.

 Purpose: The decision to perform a root canal filling is influenced by many factors including subjective symptoms and clinical signs. Sterility of the root canal before filling is usually confirmed using the bacterial culture method. However, the outcome of this method is not known for about 24 to 48 hours, and it is associated with a risk of technical contamination, which may affect the results. Therefore, we investigated the possibility of evaluating sterility inside the root canal using blue light of wavelength of approximately 405 nm.

 Materials and Methods: A total of 31 root canals were investigated. After checking subjective symptoms and clinical signs, one drop of sterile water was introduced into the root canal. The water was absorbed 30 seconds later by inserting two sterilized paper points into the root canal. One paper point was used for the bacterial culture test and the outcome was evaluated after 48 hours. The other was analyzed with the high-sensitivity fluorescence-induced test using 406-nm wavelength excitation light and the resulting waveform of the fluorescence spectrum obtained using the microscope multi-photometry system was recorded.

 Results: Clinical signs indicated that performing a root canal filling was not appropriate in 10 cases. These 10 cases had positive results with both the bacterial culture test and the fluorescence test. Of the remaining 21 cases, 16 had negative results for both tests, while the bacterial culture test was positive in the other 5 cases. Three of these 5 cases had negative fluorescence test results, indicating technical contamination; the other 2 cases had positive fluorescence test results, indicating bacterial infection.

 Conclusion: Light-induced fluorescence analysis may be able to evaluate the bacterial state in the root canal, and could replace the simple bacterial culture test in the analysis of root canal bacteria.

 Purpose: We studied the early bond strengths of various resin cements to the following: 1) CAD/CAM resin block (C-RC), 2) Dentin (D-RC), and 3) Both CAD/CAM resin block and dentin (D-RC-C). The effects of applying one-step self-etch adhesives to dentin surfaces prior to luting were also investigated.

 Methods: Flat dentin surfaces (#800 finished) of bovine teeth and flat surfaces [#800 finished/sandblasting/silanization (Ceramic Primer Plus, Kuraray Noritake Dental)] of the CAD/CAM resin blocks (Cerasmart, GC) were prepared. As for the C-RC specimens, only the resin cement paste [RelyX Unicem2 Automix (UN, 3M ESPE), RelyX Ultimate Resin Cement (UL, 3M ESPE), SA luting plus (SA, Kuraray Noritake Dental)] was applied to the pretreated resin blocks. As for the D-RC specimens, UN, UL or SA paste was also applied to the dentin substrates both with and without the adhesive, Scotchbond Universal Adhesive (SBU, 3M ESPE) or Clearfil Universalbond Quick (CUQ, Kuraray Noritake Dental) [SBU−/UN (UN group), SBU+/UL (UL group), CUQ−/SA (SA− group), CUQ+/SA (SA+ group)]. As for the D-RC-C specimens, the substrates of the dentin and resin block were butted together with and without the adhesive. The micro-tensile bond strengths (μ-TBS) and fractomorphology were evaluated (Tukey’s test, α=0.05).

 Results: The μ-TBSs of the C-RC in the UN or UL group were approximately 66 or 68 MPa respectively, showing excellent bonding of the resin cements to the resin blocks. The D-RC or D-RC-C in the UN group was approximately 5 or 10 MPa respectively with adhesive failure, while the same groups when using SBU (UL group) demonstrated values of approximately 31 or 33 MPa respectively accompanied by cohesive failure in SBU, UL or dentin, leading to significant adhesion-promoting effects to dentin substrates (p<0.05). The C-RC in the SA group was around 41 MPa with adhesive failure. The μ-TBSs of D-RC or D-RC-C were 27 or 14 MPa respectively in the SA+ group, demonstrating the efficacy of the adhesive, however the level could not be quantified in the SA− group.

 Conclusion: This study revealed that the promotion of adhesion of the resin cement to dentin substrates by using the one-step self-etch system might be indispensable for securely bonding resin blocks and dentin substrates. The findings also indicated the need for a butt bonding test of various adherents from a clinical point of view.

 Purpose: The purpose of this study was to evaluate the adhesive interface of both the cavity surface and glass ionomer cement after removing carious dentin by hand instrument by applying a chemo-mechanical caries removal agent and filling the site using several types of glass ionomer cement.

 Methods: Twenty-five extracted human permanent teeth with cervical dental caries were used in this study. The chemo-mechanical caries removal agent was applied to the carious dentin surface that had been prepared using a prototype agent containing 10% bromelain and 20% limonene, then carious dentin was removed using a spoon excavator. After observing the cavity surface by stereomicroscopy, all specimens were divided into five groups of five teeth each. Each cavity was filled with Fuji IXGP EXTRA as a conventional glass ionomer cement, HY-BOND RESIGLASS as a resin-modified glass ionomer cement, and G-CEM, Adshield RM, IONOTITE-F as resin-type glass ionomer cements in each group. After 10,000 cycles of thermal cycling, a micro-leak test was performed. Finally, all specimens were bisected using a diamond saw disk, and observed by a scanning electron microscope (SEM).

 Results: The micro-leakage test showed no specimens with no leakage. The highest leakage was observed in the Fuji IXGP EXTRA group. The specimens of the other four groups that were filled using resin-type glass ionomer cements showed similar good conditions with slight leakage. In the SEM observation, many specimens of the Fuji IXGP EXTRA group showed the formation of a gap between the cavity surface and glass ionomer cement, whereas the other four groups using resin-type glass ionomer cements showed almost no such gap formation.

 Conclusion: Based on these results, resin-type glass ionomer cements are recommended as a better filling material than conventional glass ionomer cements for cavities in which chemo-mechanical caries removal agents and hand instruments have been used.