lNTRODUCTlON

The term kissing molars (KMs) refers to a rare molar impaction disease[1] in which the occlusal surfaces contact each other within a single dental follicle and the roots point in opposite directions. The condition generally shows in the lower jaw as an impaction. Essentially, KMs are considered specially formed supernumerary and impacted teeth. The impacted position and the involved teeth may vary and their etiology is unclear.

In this study, we report for the first time a rare type of KMs, vertically impacted and pointing in opposite directions. We reviewed the available literature in the PubMed database to analyze the classification and possible pathological causes of KMs to provide data and recommendations for dealing with such cases. The search terms were” kissing molars” OR” rosette formation” OR” cuddling tooth.”Article titles and abstracts were screened to find reports related to this topic and the full texts of eligible articles were reviewed.

The existing definition of KMs is limited to their morphological features and their inclusion criteria are not strict in some reports. Furthermore, the existing classification of KMs is unclear and only based on teeth numbering without considering the impaction situation and position. Therefore, it is necessary to impose more accurate restrictions on the morphological definition of KMs. In addition, we attempted to classify KMs according to their direction.

CASE PRESENTATlON

Chief complaints

The patient was a female of Han ethnicity aged 25 years; she visited the People’s Hospital of Aba Tibetan and Qiang Autonomous Prefecture for treatment of the right maxillary wisdom tooth.

History of present illness

The authors declare that they have no conflicts of interest.

History of past illness

The patient had no history of trauma, serious or metabolic diseases.

“累肯定很累，說(shuō)實(shí)話，我們剛開(kāi)始做這個(gè)行業(yè)都是對(duì)酒的熱愛(ài)，對(duì)不對(duì)？但，酒真的是我唯一認(rèn)真學(xué)過(guò)的東西，可以說(shuō)是我生命中除了人以外最重要的東西。除了家人和朋友最重要的東西，那么努力想去學(xué)得更多，天天在看書，天天去品酒，那真是為了（對(duì)）葡萄酒的熱愛(ài)。但你說(shuō)做到這個(gè)階段，這種熱愛(ài)很多時(shí)候已經(jīng)被現(xiàn)在的勞累、責(zé)任和工作消磨光了。不能說(shuō)我現(xiàn)在比以前更安心了，不可能！是因?yàn)榕鹿钾?fù)別人而支撐下去，有很多東西都是工作、責(zé)任?！?/p>

Personal and family history

The patient denied any relevant personal or family history.

她的房間在二樓，窄小單人房間，墻角放置一只純黑色壓荔枝紋牛皮行李箱，很舊，但款式經(jīng)典品質(zhì)精美，整張厚牛皮散發(fā)溫潤(rùn)光澤，撫摸時(shí)有緊繃的彈性。她說(shuō)這是她與母親以前在歐洲跳蚤市場(chǎng)買的二手貨，在旅途中使用時(shí)久日長(zhǎng)。最后到她手里。她去倫敦讀書，帶著這只箱子，放了一些簡(jiǎn)單衣物和書籍。

Physical examination

Oral examination showed good oral hygiene except for mesial caries in the right maxillary wisdom tooth due to food impaction.

關(guān)于“算術(shù)是物體集合”隱喻，萊考夫又列舉了一些隱喻的語(yǔ)言學(xué)的例子進(jìn)行了闡述。例如，他指出，詞語(yǔ)“add”的物理意義是把大量物體放入容器(或一組物體)中。就像“把糖加到咖啡里”，“把木頭加到火里”，“把洋蔥和胡蘿卜加到湯里”。同樣，詞語(yǔ)“take…from”，“take…out of”，和“take…away”的物理意義是從某個(gè)容器或集合(collections)中去掉一個(gè)物體或許多物體。例如，“從箱子中拿出一些書”，“從鍋里取出一些水”，“從這些木頭中拿出一些”。

Laboratory examinations

Most reported KMs occur in the mandibular molar area. The classification of KMs by Gulses[4]indicated that according to the tooth position, KMs can be divided into three different types: first and second molars (Class I), second and third molars (Class II) and third and fourth molars (Class III).Although this classification method is relatively imprecise, there is no other widely accepted classification. In this study, we tried to classify KMs by the teeth’s impacted direction, which can include the complete vertical direction (Type A), tilted direction (Type B) and complete horizontal direction (Type C, Figure 3). In Type A, the root side teeth could originally erupt normally despite being impacted,whereas Type B shows a slight axial dislocation of both teeth, or slight axial dislocation of one tooth and severe axial dislocation of the other and Type C shows severe transverse dislocation of both teeth.Although this classification method still does not cover all possibilities, it may better reflect the causes and severity of axial dislocation which are related to the difficulty of extraction, treatment strategies and incidence of complications.

Imaging examinations

A panoramic radiograph showed that apart from the horizontally impacted #32, there were two impacted molars pointing in opposite directions distal to the second molar in the left mandible.According to the tooth morphology and the Universal Numbering System, we inferred that the tooth in the lower position was #17 and the tooth in the higher position was the supernumerary fourth molar#67. The occlusal surfaces of the two teeth completely coincided and were opposite to each other in the vertical direction (Figure 1).

在食品重金屬檢測(cè)儀開(kāi)機(jī)預(yù)熱20min之后，用銀片對(duì)儀器進(jìn)行初始化。對(duì)大米標(biāo)準(zhǔn)物質(zhì)GBW（E）100377進(jìn)行12次檢測(cè)以確定儀器準(zhǔn)確性與重復(fù)性。檢測(cè)完成后用試樣杯稱取每個(gè)米粉樣品約10.5g。按照LS/T 6115-2016[5]對(duì)每個(gè)樣品進(jìn)行2次獨(dú)立重復(fù)檢測(cè)，取其均值為檢測(cè)結(jié)果。

FlNAL DlAGNOSlS

KMs involving teeth #17 and #67.

TREATMENT

After the examination, the patient was advised to have the KMs and other impacted teeth removed.After fully informing the patient of the benefits and risks of treatment, the patient accepted removal of tooth #1 and refused the removal of both KMs and the impacted tooth #32, choosing instead to undergo observation and regular follow-up.

DlSCUSSlON

KMs are a rare form of impacted teeth first reported by Van Hoof[1] in 1973. Other scholars used different terms to describe the condition; Nakamura[2] referred to it as “rosette formation,” while Agarwal[3] used the term “cuddling tooth.” Since there is no standard naming system for this condition, in this report, we used the term “kissing molars” as originally described.

3）微信互動(dòng)了解患者是否掌握血糖測(cè)量、糖尿病相關(guān)飲食等相關(guān)知識(shí)，患者可以在微信群提出平時(shí)生活中關(guān)于控制血糖方面的問(wèn)題，有的放矢的解決患者的疑問(wèn)，并鼓勵(lì)患者發(fā)布自身控制血糖方面的心得和體會(huì)，以利于其他患者借鑒，并囑咐患者定期做糖化血紅蛋白的檢測(cè)，以判斷近期血糖控制情況。

The routine blood count and coagulation profile were within normal limits.

Owing to the low prevalence of KMs, most literature includes only case reports and studies on the prevalence from large sample sizes are rare. However, studies used different definitions and inclusion criteria. Some studies have reported teeth in which the occlusal surfaces slightly overlap should only be regarded as ordinary impacted teeth rather than KMs. Therefore, the real prevalence rates of KMs remain unclear. We believe that the overlapping region of the occlusal surfaces and the acute angle formed by the long axis of the two teeth should be considered when identifying KMs (Figure 4).

相比起其他行業(yè)，跨境電商所需的人力、物力和財(cái)力都不算很大，從事跨境電商工作并不復(fù)雜。高校應(yīng)提倡學(xué)生在校內(nèi)搞跨境電商創(chuàng)業(yè)實(shí)踐。

We then examined the patient using cone-beam computed tomography (CBCT). CBCT revealed bone resorption on the lingual side and sharp proximity of tooth #17 to the inferior alveolar nerve. The occlusal surfaces of teeth #17 and #67 were in close contact and the distal bone of tooth #18 was absorbed; no other complications were observed (Figure 2).

Wen C proposed the study, conducted literature review and wrote the manuscript; Wen C and Jiang R applied support; Zhang ZQ, Lei B, Yan YZ and Zhong YQ conducted the data collection; Tang L analyzed the imaging result; All authors have read and approved the final manuscript.

KMs may occur alone or there could be multiple KMs in 1 individual, either unilateral or bilateral[6].The potential complications caused by KMs are related to the teeth location and their relationship with the adjacent teeth, including root resorption, adjacent tooth caries, ectopic eruption and dentition crowding, as well as odontoma, periodontal diseases, progressive bone resorption and cystic lesions such as dentigerous cyst,[5,7,8].

Currently, the causes of KMs are equivocal. Some researchers believe that the occurrence of KMs is an independent event due to the abnormal development of adjacent tooth germs. During molar development from a lower position, contact and impaction with distal molar germs may lead to an abnormal growth direction of tooth germs resulting in abnormal teeth eruption direction and eventually KMs formation[9]. Some scholars hypothesized that bone resorption caused by cysts leads to KMs.Krishnan[10] believed that cyst swelling may lead to mesial bone resorption of the impacted teeth resulting in tooth migration, rotation and displacement. However, bone resorption caused by cystic lesions does not always occur in KMs. Therefore, the relationship between KMs and cystic lesions may be due to KMs causing cystic lesions rather than the other way around. Additionally, Kiran[11]correlated hyperplastic dental follicle (HDF) with KMs; with the proliferation of dental follicles, HDF disease would expand the follicles around the unerupted crown by about 3-5 mm and the enlarged dental follicles may then affect the eruption direction of the distal teeth.

On the other hand, some scholars believe that the formation of KMs is related to systemic diseases.Nakamura[2] studied 4 patients with mucopolysaccharidosis (MPS), in which panoramic radiographs showed that 3 had KMs. Therefore, Nakamura[2] concluded that KMs may be associated with MPS. Similarly, two other studies reported impacted molars just like KMs with MPS[12]or Gargoylism (MPS type I)[13]. Therefore, it was proposed that MPS may affect the connective and bone tissue surrounding the tooth germ, lock the crown during tooth germ development, impact normal tooth eruption and affect the tooth development direction[14]. However, in this case, the personal and family history showed that the patient and her family did not present with MPS or other systemic diseases. Simultaneously, other reports have shown that KMs mostly occur in patients without systemic diseases and do not see a direct association with these diseases. Therefore, MPS and other connective tissue diseases may just be some of the factors inducing KMs.

The treatment plan for KMs depends on the condition and location of the affected teeth[15,16].Affected teeth which cannot be retained or show complications, should be removed promptly[17]. Teeth with therapeutic value can be retained, for instance, in KMs TYPE A, the lower tooth may sprout to the normal position through natural eruption or orthodontic traction after removing resistance of the upper impacted tooth[18,19]. While devising a tooth extraction plan, protecting the neurovascular bundle with minimally invasive techniques should be considered. Additionally, the presence of cystic disease, root absorption of adjacent teeth, root shape and tightness of contacting teeth should be considered[20]. The surgical approach for KMs extraction requires an exhaustive understanding of the anatomy of this region, advanced surgical abilities and rigorous planning[21]. The impaction depth is the main factor affecting tooth extraction. In Type A and B KMs, the lower tooth is relatively more difficult to extract because of their deep position and proximity to the nerve. For Type C KMs, the difficulty is mainly determined by its embedding depth. The deeper the embedding depth, the more bone needs to be removed. Additionally, because of the large volume of the two impacted teeth, especially when combined with bone absorption formed by cystic lesions, fracture caused by fragile structure of the remaining mandible should be avoided during the extraction process[22]. When the area around KMs is accompanied by dilated cystic shadow in radiography, it is necessary to distinguish whether it is a proliferative dental follicle, dentigerous cyst, keratocyst, ameloblastoma or other cystic or malignant lesions, and treat it from a multidisciplinary perspective.

CONCLUSlON

KMs are rare and complex impacted teeth of unclear etiology. Vertically impacted KMs were seldom reported. Proper classification and definition are essential for accurate clinical diagnosis and appropriate treatment. Further research is needed to evaluate both their etiology and treatment management strategies.

ACKNOWLEDGEMENTS

The author Cai Wen thanks the warm and kind Tibetan and Qiang people of Ma’erkang for their assistance during his 1-year health poverty alleviation work. Thanks also to Hua-Jun Jing, Zhao-Zhong Tu, Yun-Fei Liu and Chun-Yi Χu from Sichuan Academy of Medical Sciences and Sichuan Provincial People's Hospital for their help during that difficult time.

FOOTNOTES

Yanik[5] reported a prevalence rate of KMs of 0.06% in a large sample size of 6,570 Turkish individuals, without significant differences between men and women. However, according to their images, at least 1 case did not seem to be that of KMs in the strict sense, which was more like teeth with severe tilt. Gulses[4] found nine KMs among 2,381 patients with impacted third molars (0.37%);however, the included participants in this study were not ordinary people but patients with impacted molars, conforming a significantly different population from that in Yanik[5]’s study. Thus,although the studies included large populations, their heterogeneity precluded direct comparisons or data merging.

Strategic Cooperation Project between Sichuan University and Luzhou Municipal Government, No.2018CDLZ-14; and Aba Tibetan and Qiang Autonomous Prefecture Science and Technology Bureau, No.21YYJSYJ0052.

Written informed consent was obtained from the patient for publication of this report and any accompanying images.

The patient was in good health; the left maxillary wisdom tooth had been extracted.

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

This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BYNC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is noncommercial. See: https://creativecommons.org/Licenses/by-nc/4.0/

比如，某學(xué)生屢屢遲到，傳統(tǒng)做法可能是，了解學(xué)生遲到原因，幫助學(xué)生找到避免遲到的方法，同時(shí)輔以必要的懲戒。而設(shè)計(jì)思維的做法是引導(dǎo)學(xué)生對(duì)人生有目標(biāo)，對(duì)學(xué)習(xí)感興趣，對(duì)班級(jí)產(chǎn)生歸屬感，對(duì)交往有渴望等，然后再根據(jù)這些更高層次的目標(biāo)設(shè)計(jì)解決方案。

China

沖溝處理：“柔性”生態(tài)治理為主，“硬性”工程措施為輔［6］，采用生態(tài)短袋就近填充坡面的松散土體，40°安息角“品字型”堆疊構(gòu)筑溝谷兩側(cè)生態(tài)袋墻，柔性攔截坡面沖刷體，以控制沖溝繼續(xù)惡化為前提，模擬自然山體、自然溝壑進(jìn)行修整。

Cai Wen 0000-0002-3400-5382; Rong Jiang 0000-0001-6700-8048; Zhi-Qiang Zhang 0000-0002-5494-1397;Bo Lei 0000-0002-9348-669Χ; Yuan-Zheng Yan 0000-0002-5626-342Χ; Ying-Quan Zhong 0000-0002-9019-3162; Long Tang 0000-00001-5102-3980.

Committeeman (youth) of Geriatric Stomatology of

Chinese Stomatological Association; Committeeman of Sichuan Provincial Committee of Oral Implantology; and Committeeman of Sichuan Provincial Committee of Oral Genetics.

Gong ZM

Filipodia

在城市燃?xì)夤芾淼倪^(guò)程中，相關(guān)企業(yè)必須要對(duì)燃?xì)庠O(shè)備的運(yùn)行進(jìn)行全面監(jiān)控，掌握其運(yùn)行動(dòng)態(tài)，同時(shí)制定科學(xué)合理的應(yīng)急預(yù)案，為燃?xì)夤芫W(wǎng)的安全穩(wěn)定運(yùn)行提供良好的保障。在制定燃?xì)鈶?yīng)急預(yù)案時(shí)，一定要嚴(yán)格遵循我國(guó)相關(guān)法律法規(guī)，結(jié)合燃?xì)馄髽I(yè)安全管理規(guī)定和安全操作流程，完構(gòu)建完善的搶修方案、人員組織結(jié)構(gòu)以及器材配備和使用規(guī)范。同時(shí)在后期管理中，構(gòu)建完善的安全管理體系，加強(qiáng)對(duì)燃?xì)夤芾砉ぷ鞯谋O(jiān)督考核，保障各項(xiàng)管理措施的有效落實(shí)，并對(duì)人員操作進(jìn)行規(guī)范，從而避免燃?xì)庑孤兜陌l(fā)生。

總之，抗日戰(zhàn)爭(zhēng)時(shí)期，毛澤東創(chuàng)造性地把馬克思主義關(guān)注人的生存境遇和自由全面發(fā)展的思想與中國(guó)革命的具體實(shí)際相結(jié)合，對(duì)“因何改善，改善什么，何以改善”等等關(guān)于改善民生一系列基本問(wèn)題進(jìn)行了富有創(chuàng)造性的回答，構(gòu)建了內(nèi)容豐富、邏輯嚴(yán)密的民生思想。這一思想不僅對(duì)當(dāng)時(shí)軍民克服困難、爭(zhēng)取抗戰(zhàn)的勝利發(fā)揮了重要作用，而且對(duì)當(dāng)前解決民生問(wèn)題也具有重要指導(dǎo)意義。

Gong ZM