抄 録：職業的血液曝露によって感染症を引き起こす重要なウイルスとして，ヒト免疫不全ウイルス（Human immunodeficiency virus，HIV），B型肝炎ウイルス（Hepatitis B virus，HBV）およびC型肝炎ウイルス（Hepatitis C virus，HCV）があり，歯科医療従事者は，これら3つのウイルスの曝露後の対応に関する基礎知識を習得する必要がある．

 HIVの血液曝露による感染率は低く，未治療者からの針刺し切創による感染率はわずか0.23%である．治療中の患者で血中にHIVが検出されない場合には，理論上感染はないと考えてよい．また未治療者からの血液曝露があっても，できるだけ早く1回目の曝露後予防内服を開始することで感染を防ぐことができる．HBVの感染予防対策はワクチン接種であるが，ワクチン抗体価が低い，あるいはHBs抗体ができていない者もいる．その場合，血液曝露後すみやかにHBV免疫グロブリンを注射したうえで，採血を行い，HBs抗体価を確認後，該当者（HBs抗体価が低い者，HBs抗体がない者）に，HBVワクチンを追加接種する．HCVには曝露後予防のための薬やワクチンはないが，感染した場合には，直接作用型抗ウイルス薬 Direct Acting Anti-viralsで根治できるうえ，早期にこの治療を開始すれば肝癌発生リスクもほとんどない．

 歯科医療行為を行うかぎり，針刺し切創などの血液曝露は起こりうる．歯科診療中に血液曝露が生じた場合には，血液曝露した歯科医療従事者のプライバシーに配慮し，迅速かつ正確に対応しなければならない．

抄 録：新型コロナウイルス禍における歯科医療は，今までになく院内感染予防対策が大変注目を浴びた時期にある．歯科医院のホームページを見れば，どこも器具の滅菌をアピールする時代になった．今回は，院内感染予防対策を実施する際の自医院での対処方法を，分野ごとに具体的に述べていく．

抄 録：歯髄炎を生じた歯髄および根尖性歯周炎の根管や根尖病変には，ヒトヘルペスウイルス（HHV）が高頻度に感染している．HHVはヒトに感染した後症状を引き起こすが，その後は潜伏感染し，抗ウイルス薬を服用しても体内から排除することができない．刺激が加わると再活性化し，HHV感染細胞から炎症性サイトカインや細胞遊走因子（ケモカイン）が発現されるため，歯髄や根尖歯周組織に炎症を生じる可能性が示唆されている．すなわち，一度HHVが感染すると，潜伏感染したHHVが生涯にわたって歯髄炎や根尖性歯周炎を生じさせる可能性がある．これまで，歯髄炎や根尖性歯周炎は細菌感染が病因とされていたが，HHVもこれらの炎症に関与することが示唆されるため，HHVの特徴や根尖性歯周炎への関与について理解することは重要である．

Abstract : Purpose : Many of the instruments used in dental treatment are minute and complex in shape, and may not be sufficiently cleaned, but there have been few studies on the effectiveness of such cleaning. Therefore, we cleaned actual files after root canal treatment using the cleaning method most commonly used in dental clinics, and examined its cleaning effectiveness.

 Methods : In order to understand the instrument reprocessing methods practiced in dental clinics, 188 dental clinics in the main city of Gunma Prefecture were surveyed.

 The two most commonly used methods in the survey were cleaning with an ultrasonic cleaner for 10 minutes (US10) and brushing for 10 seconds followed by US10 (B＋US10). The files used during the root canal formation procedure (formation files) (n=33) and the files used after root intracanal medication paste treatment (paste files) (n=27) were cleaned and compared in terms of RLU values of ATP (Log RLU (mean±standard deviation)). Comparisons were also made with unused files (n=5).

 Results : Seventy-eight clinics responded (response rate : 42.2%). Of these, 97% reused files. The Log RLU values of the formation files before cleaning were 3.7±0.8 versus 1.6±0.5 (＜0.01) after US10 and 1.3±0.3 (＜0.01) after B＋US10, and for the pasted files, 2.7±0.4 before cleaning versus 1.8±0.5 (＜0.01) after US10 and 1.6±0.3 (＜0.01) for B＋US10. The Log RLU values of both files were significantly reduced after cleaning. Furthermore, a comparison of the unused file and both files after cleaning showed that the unused file had approximately 1 Log lower value.

 Conclusions : Both types of post-treatment files actually used in dental clinics were significantly decontaminated in a before-and-after comparison of the two types of files. On the other hand, it was clear that the files after cleaning were not equivalent to new files and that the residual debris could not be completely removed.

Abstract : Purpose : To achieve satisfactory results after root canal treatment, bacteria and debris present in root canals should be removed. Sometimes, infectious or necrotic pulp tissue present in a lateral root canal causes pain after root canal treatment. Although thorough cleaning of the lateral root canal is required, it is difficult to do. Moreover, it is very difficult for dentists to detect and locate lateral root canals, except in cases where detected incidentally on dental radiographs. We have developed an improved model of electric root canal meter, Justy Ⅲ (m-EMR), which can detect lateral root canals thanks to an improved calculation system. The purpose of this study was to investigate the ability of this prototype to detect lateral root canals by clinical evaluations using dental cone-beam CT (CBCT) as a standard.

 Materials and Methods : With the approval of the Tohoku University Hospital Ethics Committee, we examined 15 patients (2 males, 13 females) who had chronic dental pain after root canal treatment at Tohoku University Hospital. After detecting a lateral root canal using m-EMR, the same tooth was imaged using CBCT. This CBCT image was used to measure the length from the entrance of the lateral root canal to the coronal top of this tooth. Data gathered were statistically analyzed using paired t-tests.

 Results and Conclusion : The mean length using m-EMR was 15.36±3.28 mm, while that using CBCT was 15.65±3.31 mm, showing no significant difference between the two measuring apparatuses. By using m-EMR to detect the presence and location of lateral root canals, it may be possible to determine the location with clinical accuracy comparable to CBCT.

Abstract : Purpose : In Japan, the number of elderly people with many teeth has increased through the 8020 campaign. As a result, there is a growing number of dental diseases that are difficult to treat. Their causative diseases include apical root fracture and cemental tear, but external root resorption is also considered a disease that must be differentiated from other diseases. In this study, external resorption showing a characteristic morphology was observed in the root apex of a mobile molar, and is reported from the viewpoint of its microstructure.

 Case : A 69-year-old male presented to our clinic with a chief complaint of a mobile mandibular right first molar. Treatment consisted of tooth extraction, and observation of the extracted tooth using micro X-ray CT and scanning electron microscopy revealed external root resorption in the mesial root.

 Results and Discussion : In the distal root, there was tartar deposition all the way to the root apex, and a variety of bacteria had formed a biofilm. The shape of the root apical foramen remained and was circular, with a diameter of 0.42 mm. The mesial root had lost surrounding dentin, leaving a root canal, and microstructural observation revealed a shell-shaped resorption fossa and external root resorption of dentin. The structure of the root apical foramen was flat, at 0.12×2.13 mm, and the edges were sharp.

 Conclusion : In teeth in which external resorption of the root apex has occurred, the morphology of the root apical foramen may be altered by the progression of the lesion, making treatment more difficult. Proper treatment and explanation to the patient should be carefully considered.

Abstract : Purpose : Chemokines are a family of signaling proteins secreted by cells to induce directional movement of leukocytes. CX3CL1 (fractalkine) is the only chemokine that displays both migratory and adhesion functions, and plays a key role in the immune response in pulpitis. We examined the expression of C-X3-C motif chemokine receptor 1 (CX3CR1) and whether fractalkine/CX3CR1 is expressed in cultured human dental pulp cells following inflammatory stimulation.

 Materials and Methods : Expression of fractalkine and CX3CR1 in inflamed human dental pulp tissue was analyzed by immunohistochemical staining. The expression of fractalkine mRNA and protein in cultured human dental pulp cells was examined by Real-time PCR, Western blotting, and immunofluorescence. The expression of fractalkine/CX3CR1 was examined by cell staining. Additionally, the production of fractalkine-stimulated prostaglandin E₂ (PGE₂) was measured using an ELISA kit.

 Results and Discussion : Fractalkine and CX3CR1 signals were detected in dental pulp cells at sites of strong pulp tissue inflammation, accompanied by neutrophil infiltration. The CX3CR1 signal was enhanced by IL-1β, and the production of PGE₂ by fractalkine was increased. It is possible that fractalkine acts in an autocrine and paracrine manner and promotes inflammatory reactions and hard tissue formation.

 Conclusion : Fractalkine/CX3CR1 is involved in promoting the inflammatory response and forming hard tissue in pulpitis.

Abstract : Conventionally, the apexification method for immature teeth with periapical lesions has been root canal treatment. In this method, only the apical area is restored. In addition, long-term use of calcium hydroxide preparations reduces the strength of root dentin, making long-term tooth preservation difficult with this method. In recent years, the AAE has requested clinical dentists around the world to use regenerative endodontic therapy. This case study, I reports pulp regeneration using regenerative endodontic therapy for an immature tooth with a periapical lesion.