抄 録：歯科用コーンビームCTは，対象の構造を三次元的に観察できるというメリットがあるが，実際は任意の断面画像を平面のディスプレイに出力して表示する方法が現時点で主流となっており，厳密な意味では三次元的な観察ができているとはいえない．近年，Extended Realityと呼ばれる技術が発展しており，三次元の情報をそのまま三次元の構造物として観察することが可能になった．歯根・根管形態の三次元的形態を理解することは適切な歯内治療を行ううえで不可欠である．Extended Realityのメリットならびに本技術を歯内治療領域で活用する際の課題点について概説した．

抄 録：根管内にはさまざまな微生物が生息している．これらの微生物，主に細菌種は口腔内の常在菌であることが多く，一般的に病原性が低い．このため，感染根管を無菌化することは難しいが，微生物と生体防御機構の間でバランスが保たれている場合は臨床的に無症状となる．ところが，生体の防御機構が破綻し，易感染状態になると，病原性が低いとされる細菌種が重篤な全身感染症を引き起こす場合がある．Enterococcus faecalis，あるいはviridans group streptococciは全身感染症を引き起こす細菌としてよく知られている．これらの細菌種に加えて，近年Rothia種による全身感染症の報告が増加している．Rothiaは口腔内常在菌だが，歯科医師にとってもあまり馴染みのない細菌種かもしれない．われわれが調べた結果では比較的高頻度に根管内に分布しており，本菌種が根尖性歯周炎の病態と関連している可能性がある．Rothiaを含めて，根管内には全身感染症を引き起こすポテンシャルをもった細菌種が多く存在する．しかしながら，感染根管（根尖性歯周炎）と全身疾患の関連性はいまだ十分に解明されていない．感染根管の全身的リスクをより詳細に評価したうえで，歯内治療の重要性を社会に提示する必要がある．

Abstract : Purpose : In 2003, a study was conducted in Japan on the use of a rubber dam during endodontic treatment. As a result, 25.4% of the Japan Endodontic Association (JEA) member group and 5.4% of the general dentists group (JEA non-member group) answered that they routinely use it. On the other hand, with the increasing interest in preserving teeth among Japanese people in recent years, interest in endodontic treatment has increased too, and the equipment and materials used have also made great progress. Therefore, we hypothesized that the frequency of use of a rubber dam might have changed, and examined it in this study.

 Materials and Methods : The study period was from October 2019 to November 2020, and questionnaires were conducted through workshops and seminars, etc. held by the JEA, and the Internet. The recovery rate of questionnaires was 97.5%, and responses were received from a total of 986, including 463 in the JEA member group, 100 in the endodontist/dental clinical instructor group of the Japan Endodontic Association (JEA endodontist group), and 523 in the JEA non-member group.

 Results and Discussion : As a result of the questionnaire, 51.5% of the JEA member group, 60.0% of the JEA endodontist group, and 14.1% of the JEA non-member group answered that they would routinely use a rubber dam. The percentages who use it on a daily basis were : 74.0%, 81.1%, and 28.6%, respectively. In addition, 65.3%, 61.1%, and 34.8% of these three groups answered that they would perform pre-endodontic build-up when necessary for root canal treatment. The JEA member group and the JEA endodontist group were aware of the necessity of the rubber dam isolation technique and pre-endodontic build-up, but the JEA non-member group seemed to have a low usage rate due to complexity and economic reasons.

 Conclusion : Compared to the 2003 study, it was revealed that the frequency of rubber dam use had increased significantly in both the JEA member group including the JEA endodontist group, and the non-JEA member group. In addition, more than half of the JEA member group and JEA endodontist group routinely perform pre-endodontic build-up, and one third in the non-JEA member group also perform it, suggesting increasing awareness of the importance of using a rubber dam in endodontic treatment.

Abstract : Purpose : The aim of this study was to assess the root anatomy and canal morphology of mandibular third molars as well as these molars’ positional relationships with the mandibular canal in a Japanese population using dental cone-beam computed tomography (CBCT).

 Materials and Methods : We analyzed the CBCT images of 155 mandibular third molars from 105 patients. The following parameters were observed on CBCT : (1) number of roots and root canals ; (2) Vertucci classifications of the root canal configurations ; (3) frequency of C-shaped roots ; (4) classifications of axial canal images of C-shaped canals ; and (5) the positional relationship between mandibular third molars and the mandibular canals.

 Results : Most mandibular third molars had two roots with two root canals (62.6%), in which most of the mesial root canals (90.7%) of the two-rooted molars were Type I. The C-shaped root prevalence was 14.2%, with a bilateral incidence of 2.0%. Additionally, most canals with continuous C-shapes appeared to fuse into one or divide into two canals toward the canal terminus. Regarding the positional relationship between the mandibular third molar and mandibular canal in the non-bone-mediated type, the frequency of the inferior type was 21.3% and that of the lingual type was 7.1% ; mandibular canal flattening was often seen in the former.

 Conclusion : This study provided detailed information regarding the root anatomy and root canal morphology of mandibular third molars and these molars’ positional relationships with the mandibular canal in a Japanese population.

Abstract : Purpose : This study was designed to understand the effect of iodine potassium iodide (IKI) on the surface texture and mechanical strength of set white mineral trioxide aggregate (WMTA).

 Materials and Methods : WMTA powder (ProRoot MTA) was mixed with distilled water (DW) at the ratio of 1 : 3. It was cured in the molds for 3 or 24 hours at 37°C and 100% humidity to form WMTA discs and cylinders. The set discs and cylinders were immersed in DW (D-WMTA) or 2% IKI (I-WMTA) for 24 hours. The surface texture of WMTA discs without immersion (Cont-WMTA), D-WMTA and I-WMTA was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX). The compressive strength of the WMTA cylinders and the amount of calcium ion release from the WMTA discs were also investigated.

 Results and Discussion : IKI induced discoloration of the WMTA discs and cylinders from yellowish-white to brown and the formation of white precipitate on the bottom of the tubes. The main crystal structure of I-WMTA was the same as that of Cont-WMTA and D-WMTA. The particle morphology and elemental distribution on the surface of I-WMTA were almost the same as those of Cont-WMTA and D-WMTA. I-WMTA significantly increased the amount of calcium ions released into the medium and decreased the compressive strength compared with D-WMTA.

 Conclusion : IKI induces no change in the surface texture of set WMTA, but causes its discoloration, decrease of mechanical strength and disruption. IKI-treated WMTA may induce esthetic problems and increase the risk of micro leakage.

Abstract : Purpose : We describe a case of perforating internal resorption in the root of the mandibular left central incisor. We performed nonsurgical endodontic treatment and achieved a successful outcome.

 Case : A 73-year-old male patient complained of occlusal pain in the mandibular left central incisor. Chronic apical periodontitis was diagnosed by clinical examination (oral symptoms, electric pulp test) and intraoral radiography. Cone-beam computed tomography (CBCT) images revealed internal resorption with perforation on the lingual side of the root and resorption of the cortical bone surrounding the involved tooth.

 Discussion : Infected root canal treatment was performed under microscopy. After the sinus tracts resolved, the root canal was obturated in the apical area and the resorption space separately. The internal resorption space was filled using a vertical condensation technique. Postoperative periapical radiography showed that the resorption space was well obturated with no extrusion of obturating materials from the perforation site.

 Conclusion : Nonsurgical endodontic treatment was performed for a case with perforating internal root resorption by using CBCT to acquire accurate 3-dimensional information, such as the existence, size, and location of the perforation and the extent of bone resorption. Additionally, obturation of the perforated site, resorption space, and apical area was precisely achieved without material extrusion by using an electric heat root canal plugger and an electric heating injector.

Abstract : Purpose : Dens invaginatus is a morphologically abnormal tooth in which enamel and dentin are deeply invaginated into the pulp cavity due to developmental abnormalities during tooth formation. Difficulties may arise if we encounter dens invaginatus clinically and root canal treatment is required. We report a case in which the condition of dens invaginatus was accurately grasped by using cone beam computed tomography (CBCT) and root canal treatment was performed.

 Case : The maxillary left lateral incisor had undergone restoration treatment about 10 years ago, but recently the symptoms had gradually become stronger, so the patient visited our clinic. The maxillary left lateral incisor had a negative reaction in the electrical pulp test and thermal test, and severe percussion pain was observed. Upon X-ray examination, an X-ray transmission image was found at the apex of the maxillary left lateral incisor. In addition, an unusual pulp cavity structure was observed. The pulp cavity branched from near the center of the root to the crown side. A structure suspected of invagination was confirmed in the center. The findings of CBCT showed that the dental pulp cavity expanded in a dome shape from the center of the root to the crown side, and lesion-like transmission images were confirmed on the apical and palatal sides. The affected tooth was the left maxillary incisor, the pulp was diagnosed as necrotic, and the apical periodontal tissue was diagnosed as acute apical periodontitis. It was decided to perform root canal treatment first, and if there was no healing tendency, to consider surgical endodontic treatment. The symptoms disappeared after root canal treatment, and a postoperative evaluation was performed by CBCT imaging at follow-up 12 months after treatment, which confirmed that the lesion-like X-ray transmission images on the apical and palatal sides had disappeared.

 Discussion : AAE and AAOMR have expressed the view that CBCT imaging to clarify the anatomical morphology is the optimal diagnostic imaging method before operating on teeth with suspected complex morphology. It was confirmed by CBCT images that this case was classified as Oehlers type 2. In addition, by sufficiently grasping the morphology by CBCT imaging, it was relatively easy to remove the invaginated part by file attached to the ultrasonic transmitter.

 Conclusion : By accurately grasping the pathophysiology of dens invaginatus using CBCT, root canal treatment could be performed safely. CBCT imaging is considered to be useful for dens invaginatus.