lNTRODUCTlON

Crown-root fracture originates from the crown and extends apically in an oblique direction[1]. It is usually caused by fall, fight, traffic accident, or foreign bodies[2]. It is reported that the incidences of crown-root fractures are 2% in the deciduous teeth and 5% in the permanent dentition[3]. According to the International Association of Dental Traumatology (IADT) guidelines for the management of traumatic dental injuries, the options for the treatment of complicated crown-root fractures with pulpal exposure include partial pulpotomy, root canal therapy, gingivectomy, orthodontic extrusion, surgical extrusion, root submergence, and extraction with immediate or delayed implant-retained crown restoration or a conventional bridge[4]. Due to the complexity of crown-root fracture, its treatment is not always the same and different dentists may choose different treatments.

在預(yù)試驗中，筆者比較了不同體積分?jǐn)?shù)的甲醇（60%、70%、80%、90%）作為提取溶劑時的提取效率。結(jié)果，采用70%甲醇作為提取溶劑時，色譜峰數(shù)量較多，峰面積響應(yīng)好，故選擇70%甲醇作為提取溶劑。因丹皮酚為易揮發(fā)性物質(zhì)，故提取方法選擇超聲提取。筆者考察了不同超聲提取時間（15、30、45、60 min）對提取效率的影響，結(jié)果30 min的提取效率優(yōu)于15 min，而再延長提取時間后提取效率無明顯差別，因此選擇30 min作為提取時間。

Due to the bacterial invasion from the gingival sulcus, the reported incidence of tooth survival for root fractures in the cervical third is only 30%[18]. In these two cases, the fracture was closer to gingival sulcus than most root fractures, and the labial fracture lines were located in the gingival sulcus. Thus, it is intriguing how and why the pulp survived in these two cases. Based on the age of the patients, it is possible that the initial injuries occurred during the later phase of the maxillary central incisors eruption when the tooth roots were still immature. At that moment, the cervical region of the enamel was still covered by the junctional epithelium, which seals the fracture from the oral cavity. The junctional epithelium and the pulp also contain immune cells (, neutrophils, lymphocytes, macrophages, and mast cells) that can protect the pulp against the microbes near the gingival sulcus[16,19]. Moreover,pulpal vitality after injury might be maintained by the stability of the oblique fracture line, which is in consistent with our clinical finding that there is no severe displacement of coronal fragment after injury.Finally, the immature teeth have more sufficient blood supply with a large amount of stem cells that can promote and accelerate healing. All these favorable factors provided an ideal circumstance to maintain the vitality of the pulp. The vital pulp and the intact periodontal ligament contain large number of odontoblasts and cementoblasts[19], which might contribute to the deposition of hard tissue matrix between the fragments and the healing of the fractures.

In this report, we present two clinical cases with spontaneous healing of complicated crown-root fractures of permanent central incisors in children. In both of these two cases, the fractured fragments healed spontaneously with hard tissue deposition around the fracture lines, which suggested that dentists may have more treatment options when dealing with crown-root fracture.

CASE PRESENTATlON

Chief complaints

A 12-year-old boy was referred to our department complaining of pain at his maxillary right central incisor following an accidental fall 1 d ago.

A 10-year-old girl visited our department with her parents after she fell 1 d ago, complaining of pain at her maxillary left central incisor.

History of present illness

The patient recalled that this tooth once struck the floor when he fell approximately 1 year ago,and he did not seek any treatment then due to the absence of symptoms.

According to the patient’s dental history, tooth 11 was fractured 1 year ago and was treated with injectable Root Canal Paste (Vitapex, Morita, Japan) for apexification and composite resin being placed in chamber by a local general dentist. During the examination after that injury, the general dentist did not find any responsive sign and symptoms of injury for tooth 21.

可以設(shè)想，在不斷地完善的醫(yī)院的內(nèi)部控制中，未來還與其他系統(tǒng)集成，延伸到成果管理，完善科研資金的績效評估。加強對科研成果中專利權(quán)等無形資產(chǎn)的管理，確保其產(chǎn)權(quán)歸屬清晰，保障國有資產(chǎn)完整。

History of past illness

The patient was medically healthy without taking any medications.

Medical history of this patient was noncontributory.

2.報表填報不規(guī)范問題。一是建議加強教育主管部門與財政部門、財政業(yè)務(wù)部門與預(yù)算編審部門之間溝通，以便在預(yù)算下達(dá)時就能保持口徑一致，避免高校財務(wù)人員憑職業(yè)判斷來填報。二是建議主管部門每年編制完決算報表后，組織編報者進(jìn)行學(xué)習(xí)總結(jié)，指出不規(guī)范的地方及其原因，防止在下一年度會計核算中重復(fù)出錯。三是建議建立決算報表員交流平臺，就如何提高決算報表質(zhì)量、報表數(shù)據(jù)分析應(yīng)用等相關(guān)情況展開經(jīng)驗討論，有利于統(tǒng)一和提升業(yè)務(wù)能力、操作技能。

Personal and family history

There were no specific family health histories.

五年來，全省上下以習(xí)近平新時代中國特色社會主義思想為指導(dǎo)，全面貫徹落實中央和省委的決策部署與工作要求，把綠色發(fā)展理念貫徹于經(jīng)濟社會發(fā)展全過程，全力推進(jìn)生態(tài)文明先行示范區(qū)建設(shè)和國家生態(tài)文明試驗區(qū)建設(shè)，創(chuàng)新制度建設(shè)，厚植生態(tài)優(yōu)勢，發(fā)展綠色經(jīng)濟，做活山水文章，打響“綠色生態(tài)”品牌，促進(jìn)經(jīng)濟與生態(tài)協(xié)調(diào)發(fā)展，邁出了打造美麗中國“江西樣板”的堅實步伐。

Physical examination

Clinical examination showed that tooth 11 was responsive to palpation and had bleeding from the gingival crevice (Figure 1A) but showed no displacement and no increased mobility. Using a dental probe without any pressure, a crack line was detected on the crown of tooth 11, which was slightly below the gingival margin. Cold test showed no response.

Extra-oral examinations were normal. Intra-oral examination showed that there was a complicated crown fracture in tooth 11 with discolored crown and pulp chamber being filled by resin from the lingual surface. Tooth 21 exhibited class I mobility and a facial fracture line below the gingival margin was detected by a probe without any pressure. Tooth 21 was responsive to cold test and palpation (Figure 1B).

Imaging examinations

Cone beam computed tomography (CBCT) images showed an oblique crown-root fracture line extending from the labial surface of the tooth 11 to the palatal alveolar ridge, which is approximately 3.8 mm below the palatal gingival margin. Surprisingly, the images also showed signs of hard tissue deposition between the fractured fragments (Figure 2).

CBCT images of tooth 21 showed an oblique crown-root fracture line starting from the labial surface and extending palatally below the alveolar ridge for approximately 3.5 mm beneath the palatal gingival margin (Figure 3), which resulted in the abnormal mobility of the coronal fragment.Interestingly, it also showed signs of hard tissue deposition at the pulpal side between the fractured fragments, indicating a healing process for the pre-existing fracture in tooth 21. Upon reviewing the radiographs taken 1 year ago after the first injury, the fracture line on tooth 21 was noticed (Figure 4).Since the patient never complained of any symptoms on tooth 21, and the periapical radiograph showed no signs of abnormality, the fracture was overlooked by the general dentist.

FlNAL DlAGNOSlS

Case 1

Based on the history and findings of the imaging examinations, tooth 11 was diagnosed as complicated crown-root fractures (old fracture spontaneous healing).

At this point, since there were no other signs and clinical symptoms, and the coronal fragment was not loose, the patient was recommended to wear a mandible occlusal pad for 2 wk with periodical revisit and special attention of not re-injuring the tooth (Figure 5A).

Case 2

In this case report, we observed hard tissue healing without any intervention in two pediatric cases of crown-root fracture, suggesting that spontaneous healing with hard tissue deposition may occur in pediatric patients with complicated crown-root fractures and minimal displacement. It should be emphasized that conservative treatments with regular follow-up should be preferred for cases of children after trauma.

TREATMENT

Case 1

如果它的形式適合于它的動作目的，它的本質(zhì)就可以被人們清楚了解和認(rèn)識。一件東西必須在各個方面都同它的目的性吻合，即它能夠從實際方面完全達(dá)到自身的功能目的，這樣才是可以運用的，可以信賴的，并且是造價低廉的。

At 1-year follow up visit, tooth 21 remained stable and was responsive to pulp test. The periapical radiograph of tooth 21 revealed no signs of periapical abnormality and no significant change of the fracture line (Figure 7A). The patient was not followed until 4 years later. Clinical examination on tooth 21 revealed no sign of abnormality. The coronal fragment was not loose, and the CBCT image of tooth 21 showed signs of healing (Figure 7B-D).

Case 2

During the current visit, tooth 21 was stabilized with a flexible fiber splint (RTD Quartz Splint?,France, Figure 5B) and a mandible occlusal pad was placed for 2 wk. Three months later, the splint was removed and the root canal of tooth 11 was completed after obturation with gutta-percha and sealer(Figure 5C and D). Tooth 11 was then restored with resin composite 1 wk later (Figure 5E). Tooth 21 showed normal mobility and normal response in the pulp sensibility test. There were no discoloration or radiographic signs of periapical lesions at this point and no further treatment was applied.

由于小學(xué)生正處于比較敏感、感性的階段，無論在生活上還是在學(xué)習(xí)上，容易受到情感的熏陶。因此，在語文教學(xué)中，創(chuàng)造良好的學(xué)習(xí)氛圍是非常重要的。例如在學(xué)習(xí)古詩《憶江南·江南好》時，教師可利用多媒體展示相關(guān)圖片，讓學(xué)生通過觀賞江南春景，并伴隨背景音樂朗誦古詩，表達(dá)出自己的感觸感想。這種教學(xué)方式不僅讓課堂氛圍變得活躍，同時也有利于學(xué)生想象力的培養(yǎng)，進(jìn)而加深學(xué)生對閱讀的理解。在閱讀文章時，不能只注重學(xué)生閱讀的次數(shù)，應(yīng)引導(dǎo)學(xué)生找出文章中優(yōu)美的語句，并提出相關(guān)問題，讓學(xué)生帶著問題去閱讀，可達(dá)到良好的閱讀效果。

OUTCOME AND FOLLOW-UP

Case 1

During the periodical monitoring of the pulp condition every 3 mo for 1 year, the tooth showed normal color and mobility and became responsive to pulp sensibility test (Figure 1C). Radiographic examination revealed that the fracture line became blurred gradually (Figure 6A). The patient was followed annually for 3 years, and there were no signs of abnormality on tooth 11. The periapical radiographs also appeared to be normal (Figure 6B-D).

Case 2

釋智林，高昌人。初出家為亮公弟子。幼而崇理好學(xué)，負(fù)笈長安，振錫江豫，博采群典，特善雜心。及亮公被擯（453-459），弟子十二人皆隨之嶺外。林乃憩踵番禺，化清海曲……至宋明之初（465），勅在所資給，發(fā)遣下京，止靈基寺……林形長八尺，天姿瓌雅，登座震吼，談吐若流。后辭還高昌。齊永明五年（487年）卒。春秋七十有九①〔梁〕釋慧皎：《高僧傳》卷8《智林傳》，中華書局，1992年，第309-311頁。。

DlSCUSSlON

National Natural Science Foundation of China, No. 81771095; Shaanxi Provincial Key R&D Program,China, No. 2021KWZ-26; and State Key Laboratory of Military Stomatology, No. 2020ZA01.

Inorganic compound accounts for 95% of the enamel[16], and fracture on the enamel is unlikely to heal. That is the reason why the enamel fragments were still separated by a narrow radiolucent line in the CBCT images, and we can still detect a fracture on the labial surface of the enamel clinically. To some extent, the two cases are analogous to root fractures in the cervical third except for the fracture on the enamel. Healing of crown-root fractures is the healing of the dentine and cementum, which is similar to the healing of root fractures. According to Andreasen and Hjorting-Hensen, healing of root fractures can be classified into four types[17]: (1) Calcified tissue wound healing; (2) Healing by interposition of connective tissue; (3) Healing by interposition of bone and connective tissue; and (4)Healing by interposition of granulation tissue. The most desirable outcome is the calcified tissue wound healing. In these two cases, it is likely that calcified tissue wound healing occurred since CBCT showed deposition of radiopaque tissues between the separated fragments. In addition, both teeth exhibited response in the pulp test during the follow-up examination, which can demonstrate the reparative dentin formation and calcified tissue wound healing.

而現(xiàn)實中的很多人卻跟他周圍的同學(xué)一般，對自己喜歡什么全然不知，從來不去積極改變。當(dāng)看到別人與自己不同的行為時，又感到不可理喻。

There are still some limitations in this study. The use of the mandibular pad in treatments was not based on the IADT guidelines. Instead, the treatment was based on a previous study[20]. Further research is needed to compare different treatments.

CONCLUSlON

Based on the history and findings of the imaging examinations, tooth 11 was diagnosed as complicated crown fractures and tooth 21 was diagnosed as complicated crown-root fractures (old fracture spontaneous healing).

FOOTNOTES

Zhou ZL, Gao L and Wu LA performed the dental treatment; Zhou ZL, Sun SK, Zhang CD and Kou WW reviewed the literature, and contributed to the drafting of the manuscript; Xu Z, Li HS and Wu LA were responsible for the revision of the manuscript for important intellectual content; all authors issued final approval for the version to be submitted.

Crown-root fracture is a severe dental trauma involving the enamel, dentin, cementum, and periodontal ligament[5,6]. According to the classifications of Andreasen, it can be classified as complicated crownroot fracture if there is pulpal involvement and non-complicated crown-root fracture if there is no pulpal involvement[7]. In the case of complicated crown-root fracture, complications,, pulp necrosis,apical periodontitis, and root resorption, may occur if the pulp is left untreated[8,9]. The mobile coronal fragment usually needs to be removed or reattached with bonding agent depending on the extent of the injury. Multidisciplinary care is usually required for the treatment of crown-root fracture. While relatively common in root fractures, spontaneous healing with hard tissues has been rarely reported in crown-root fracture so far[10-12]. This is probably due to the severe pulp injury and the connections of the fracture in the coronal portion with the oral cavity, leading to inevitable microbial contamination in the pulp and subsequent pulpal necrosis[13-15].

轉(zhuǎn)變經(jīng)濟發(fā)展方式、提升發(fā)展質(zhì)量的主要途徑，就是調(diào)整經(jīng)濟結(jié)構(gòu)。抓住經(jīng)濟結(jié)構(gòu)問題，就抓住了經(jīng)濟發(fā)展的主線，調(diào)整經(jīng)濟結(jié)構(gòu)就真正推進(jìn)了經(jīng)濟發(fā)展方式的轉(zhuǎn)變。

Informed written consent was obtained from the patients’ parents for publication of this report and any accompanying images.

天然氣燃燒分為完全燃燒和不完成燃燒，完全燃燒生成CO2和H2O，不完全燃燒則生成CO和H2O。SCR4500生產(chǎn)線的燃燒系統(tǒng)則是通過調(diào)節(jié)空氣和燃?xì)獗壤龑?dǎo)致燃?xì)獠煌耆紵龔亩a(chǎn)生 CO，CO 與氧結(jié)合生成 CO2(CO+O→CO2)，使氧從流銅液中擴散析出，從而達(dá)到控制銅液中氧的含量。

The authors declare that they have no conflict of interest to report.

The authors have read the CARE Checklist (2016), and the manuscript was prepared and revised according to the CARE Checklist (2016).

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China

Zi-Ling Zhou 0000-0002-9739-766X; Lei Gao 0000-0001-9828-8994; Shu-Kai Sun 0000-0002-2123-977X;Hong-Shi Li 0000-0003-3331-4957; Cai-Di Zhang 0000-0001-8395-2231; Wen-Wen Kou 0000-0002-2693-0965; Zheng Xu 0000-0002-9028-7935; Li-An Wu 0000-0001-8909-328X.

Gao CC

Wang TQ

Gao CC