Incidence of C-shaped root canal systems in mandibular second molars in the native Chinese population by analysis of clinical methods

The aims of the study were to investigate the incidence of C-shaped root canal systems in mandibular second molars in a native Chinese population using radiography and clinical examination under microscope and to compare the relative efficacies of these methods. For the recognition of C-shaped root canal system, 1 146 mandibular second molars were selected and examined. Teeth with C-shaped canal systems were categorized by using the radiographic classification criteria and the modified Melton＇s method. C-shaped canals were identified in 397 （34.64%） mandibular second molars by radiography （type I, 31.23%; type II, 38.29%; type III, 30.48%）. Clinical examination showed that 449 （39.18%） cases exhibited C-shaped canal systems （C1, 22.94%; C2, 48.11%; C3a, 15.59%; C3b, 13.36%）. As for the result of the radiographic and clinical combined examination, C-shaped root canals were found in 473 （41.27%） mandibular second molars （C1, 21.78%; C2, 45.67%; C3a, 16.70%; C3b, 15.86%）. The incidence of C-shaped root canal diagnosed by radiographic method was statistically different from that by clinical examination and the combined examination （P〈O.05）. The study indicated a high incidence of C-shaped canal system in a Chinese population. The combination of microscopic and radiographic examination is an effective method in identifying the C-shaped root canal system.

Three-dimensional analysis of the physiological foramen geometry of maxillary and mandibular molars by means of micro-CT

The aim of this study was to investigate the physiological foramen diameter, shape and distance between physiological and anatomical apex of maxillary and mandibular first and second molars. Accurate knowledge of the physiological foramina morphology; thus, inherent mechanical shaping technical hindrances, is decisive when taking the corresponding root canal final preparation decision. The morphological dimensions of a total of 1 727 physiological foramina were investigated by means of micro-computed tomography. Mean narrow and wide （to a high number, oval） diameters of the physiological foramen were 0.24, 0.22 and 0.33 mm and 0.33, 0.31 and 0.42 mm in mesiobuccal （MB）, distobuccal （DB） and palatal （P） roots in maxillary first molars; 0.24, 0.22 and 0.33 mm and 0.41, 0.33 and 0.44 in MB, DB, and P roots in maxillary second molars. Mandibular first molars showed mean narrow and wide diameters of 0.24 and 0.30 mm and of 0.39 and 0.46 mm in mesial （M） and distal （D） roots; second mandibular molars showed 0.25 and 0.31 mm and 0.47 mm in M and D roots. The mean distance between the physiological foramina and anatomical apex was 0.82, 0.81 and 1.02 mm and 0.54, 0.43 and 0.63 mm in MB, DB and P roots of the maxillary first and second molars, respectively. A mean distance of 0.95 mm （M） and 1.05 mm （D） in the first and 0.78 mm （M） and 0.81 mm （D） in the second mandibular molars was observed. Based on the results obtained, assumable recommendations for final preparation size of the physiological foramen were calculated. However, when taking into consideration, the resulting standard deviations of marginal errors must be cautiously considered when taking a final decision in clinical endodontic treatment.

Two-stage extraction by partial grinding of impacted mandibular third molar in close proximity to the inferior alveolar nerve

BACKGROUND Extraction of impacted third molars often leads to severe complications caused by damage to the inferior alveolar nerve(IAN).AIM To proposes a method for the partial grinding of an impacted mandibular third molar(IMM3)near the IAN to prevent IAN injury during IMM3 extraction.METHODS Between January 1996 and March 2022,25 patients with IMM3 roots near the IAN were enrolled.The first stage of the operation consisted of grinding a major part of the IMM3 crown with a high-speed turbine dental drill to achieve sufficient space between the mandibular second molar and IMM3.After 6 months,when the root tips were observed to be away from the IAN on X-ray examination,the remaining part of the IMM3 was completely removed.RESULTS All IMM3s were extracted easily without symptoms of IAN injury after extraction.CONCLUSION Partial IMM3 grinding may be a good alternative treatment option to avoid IAN injury in high-risk cases.

A Case Report of Kissing Molars Class II

Kissing molars (KMs) is a condition of occlusal molar surfaces in a single follicular space with roots extending in opposite directions. Here, we have reported a case of KMs in a 58-year-old woman. The patient complained of pain in the right mandibular molar region and was diagnosed with KMs consisting of the right mandibular second and third molars. Because of the patient’s pain having subsided at the time of the visit and her unwillingness to undergo tooth extraction, the patient was followed up. KMs is classified into three classes (I-III) and is either true-KMs or pseudo-KMs and presents with or without cystic variants of dental follicles. The presents as true-KMs class II without a cystic variant. With reference to the literature and based on our analysis, the mean age of patients affected by this specific case of KMs is 31.7 years and unilateral KMs is relatively more common (85.7%). Histopathological findings of dentigerous cysts are more often indicated (42.9%). The treatment policy for KMs should therefore be based on the classification of KMs. Importantly, the focus should be on preserving the first and second molars as much as possible. The treatment approach, such as the employment of surgical removal or orthodontics, should be determined by considering the associated factors such as the crowns, tissues, and age of the patient.

The Buccal Lid Approach for Removal of Impacted Mandibular Molars—When, How and Why?

Background: The surgical removal of impacted mandibular molars represents one of the most prevalent procedures carried out by the oral and maxillofacial surgeon. Despite its prevalence, unusual impaction location of mandibular molars necessitates alternative extraction approaches. One of the methods described for extraction of deeply impacted molars is the bony lid approach which was first presented for surgical endodontic treatment of mandibular molars. The aim of this study was to evaluate the outcome of the bony lid approach in extracting mandibular molars. In addition, critical clinical key points, new aspects while performing this procedure, indications and contraindications are discussed. Materials and Methods: 9 patients were treated with the bony lid technique. A retrospective analysis of medical charts was conducted to evaluate the results of surgery. Results: The operative technique described in the article was successfully carried out in 12 cases of impacted mandibular molars. No incidence of permanent sensory deficit was recorded. In one patient, an infection mandated the removal of the bony lids. In all other cases the healing process was uneventful. Conclusion: The bony lid technique has many advantages over alternative extraction methods and should be considered as a treatment option in cases of critical proximity between an impacted tooth and the inferior alveolar nerve.

Ultrasonic piezotome surgery: is it a benefit for our patients and does it extend surgery time? A retrospective comparative study on the removal of 100 impacted mandibular 3rd molars

Aim of the study was to evaluate if there is a constant and significant reduction in traumaticity when mas- sively traumatic oral surgical procedures such as the removal of third molars are conducted with only ul- trasonic surgical devices (Piezotomes) expressed in a reduction of postsurgical pain and swelling on the patient’s side since such clinical experiences by the authors suggested this. Since oral surgeons criticize a higher time consumption for surgeries with Piezoto- mes also the objective time consumption was evalu- ated and compared to the traditional methods. Mate- rial and Methods: 56 female and male patients were selected that already underwent a removal of an im- pacted third mandibular molar on one side with rota- ry instruments by bone destructive burring with a still persisting comparable third mandibular molar on the contralateral side complaining about recur- rent pain episodes and were already documented for pain and swelling before. The ultrasonic surgical re- moval with the Piezotome was conducted with a buc- cal osteotomy of the compacta lateral to the impacted third molar, preservation of the resected compacta in saline solution, removal of the third molar by single or multiple dentotomy and full anatomical restitution of the surgical site with the preserved buccal com- pacta. The swelling was documented by kephalome- try 24/48/72 hours and 1 week post surgery, the pain index by the total consumption of ibuprofen-400 mg—tablets. Lesions of the mandible nerve were documented. Netto surgery time was taken from the first incision to the last suture of the procedure. Re-sults: 6 patients had to be excluded from evaluation due to incomplete post surgical follow up. A signify-cant (***, p > 0.999) decrease in pain and swelling of 50% was detected both for the parameters swelling and pain with Piezotome-surgery. No lesions of the mandible nerve were detected with Piezotome sur- gery whereas surgery with rotary instruments re- sulted in 16% hypesthesia at least up to one week. Although netto surgery time was approximately 50% longer when done with the Piezotome at the begin-ning the time consumption normalized with the growing experience of the surgeons back to the time schedule when surgery was performed with rotary instruments revealing no significant differences (-, p < 0.73). Conclusions: The results of this retrospective study suggest that Piezotome-surgery is superior in atraumaticity and soft-tissue safety compared to tra- ditional procedures with burs and grants the patients significantly less post surgical pain and swelling. Al- though—as it is with all new surgical tools and pro- tocols—surgery time is longer at the beginning when purely working with ultrasonic surgical devices time consumption reduces to normal values after a learn- ing curve.

Prevalence of Distolingual Roots in the Permanent Mandibular Molars in a Chinese Population

Objective: The purpose of this study was to detect the prevalence of distolingual(DL) roots in the permanent mandibular molars in a Chinese population by using cone-beam computed tomography(CBCT).Methods : A total of 500Chinese patients'CBCT images were examined.The incidences and bilateral concurrence rates of DL roots were determined for the permanent mandibular first,second and third molars.The differences between sexes and sides were tested by using Chi-square tests.The antimeric correlations for occurrence of the trait were analyzed with the Spearman's rank order correlation test.Results : The prevalence of 3-rooted mandibular first molars was 31.98%(134 / 419individuals) calculated by individuals,and 25.89%(217 / 838teeth) calculated by teeth.The bilateral concurrence rate was 61.94%.A significant right-side predilection was found in the female group(P=0.025) as well as for both sexes combined(P=0.009).The Spearman's correlations coefficient between antimeres was 0.77(P=0.000).The prevalence of DL roots in the mandibular second and third molars were 2.02%(8 / 396individuals) and 12.10%(19 / 157individuals),respectively.The corresponding bilateral concurrence rate was 12.50% and 35.83%,and the bilateral correlation coefficient was 0.22(P=0.000) and 0.50(P=0.000),respectively.Conclusion : Clinicians should be aware of the high prevalence of the DL roots in the Chinese population.Understanding the pattern of occurrence would be useful for dental treatment.

The influence of the eruption of mandibular third molars on the craniofacial morphology in Han youth of North China

Teeth affect not only oral problems but also facial morphology.In China,there are few reports about the influence of the third molars on the craniofacial morphology of Han youths.Using in vivo imaging software,3D reconstruction of craniofacial CTs were performed on 32 Chinese Han youths without mandibular third molars and 25 Chinese Han youth with full mandibular third molars.The morphology of their mandible and mandibular tissue was measured to identify differences.Among the morphological characteristics of hard tissues,except for∠ANB,people with a full eruption of the mandibular third molars had statistically significantly larger angle indicators than people without the eruption of the third molars.The soft tissue indicators also showed statistically significant discrepancies in terms of morphological facial height,mouth to gnathion distance,lip height,and mouth breadth.The most influential index for mandibular third molars was length of symphysis,followed by the four indicators of soft tissue and mandible length and height.Morphology facial height,mouth to gnathion distance,lip height,and height of symphysis were moderately correlated.The experimental results show that among Han youth in North China,the third molar eruption has a widespread influence on mandibular morphology,especially in angle,length,and height indicators.It also has a certain influence on maxillofacial soft tissue morphology.These results can be applied to future clinical risk assessment of the wisdom teeth and forensic personal identification of the cranial and maxillofacial region.

Successful individualized endodontic treatment of severely curved root canals in a mandibular second molar:A case report

BACKGROUND The incidence rate of severely curved root canals in mandibular molars is low,and the root canal treatment of mandibular molars with this aberrant canal anatomy may be technically challenging.CASE SUMMARY A 26-year-old Chinese female patient presented with intermittent and occlusal pain in the left mandibular second molar.The patient had undergone filling restoration for caries before endodontic consultation.With the aid of cone beam computed tomography(CBCT),a large periapical radiolucency was observed,and curved root canals in a mandibular second molar were confirmed,depicting a severe and curved distolingual root.Nonsurgical treatments,including novel individualized preparation skills and techniques and the use of bioceramic materials as an apical barrier,were performed,and complete healing of the periapical lesion and a satisfactory effect were achieved.CONCLUSION A case of severely curved root canals in a mandibular second molar was successfully treated and are reported herein.The complex anatomy of the tooth and the postoperative effect were also evaluated via the three-dimensional reconstruction of CBCT images,which accurately identified the aberrant canal morphology.New devices and biomaterial applications combined with novel synthesis techniques can increase the success rate of intractable endodontic treatment.

Clinical Effect of Resistance-free Removal of the Bone Embedded Mandibular Third Molar

[Objectives] To shorten the time of removal of the bone embedded mandibular third molar,reduce the complications of tooth extraction,and explore a surgery method of resistance-free removal of the mandibular third molar. [Methods] A total of 50 patients with bone embedded mandibular third molar needing to be removed were selected. A 45° elevation turbine and a long tungsten steel drill were used to remove the mesial,buccal,and distal resistances. When necessary,tongue side and root resistance was removed,and the third molar was removed when there was basically no resistance around it. The removal time was recorded,followed up for 10 d,and the postoperative reaction was observed. [Results] The bone embedded mandibular third molars were removed for all patients within 15 min,and there was no serious postoperative reaction,all patients showed high satisfaction. [Conclusions]The method of resistance-free removal of the bone embedded mandibular third molar can significantly shorten the removal time,reduce the fear of patients,and ease pain of patients.

A Case Report of Kissing Molars Class III

Kissing molars (KMs), first reported by Van Hoof in 1973, refer to molars with occlusal surfaces that contact each other in a single follicular space while their roots extend in opposite directions. This is a case of a 20-year-old male who presented with complaints of right mandibular molar pain with cold water contact and occlusion. Panoramic and cone-beam computed tomography (CBCT) images revealed impaction of the right mandibular third and fourth molars, with the occlusal surfaces contacting each other while the roots extended in opposite directions. KMs are classified according to the impaction of the mandibular first and second molars (Class I), second and third molars (Class II), and third and fourth molars (Class III). Our patient was considered Class III. Given the patient’s preference for surgical treatment, successful teeth extraction and extirpation were performed under intravenous sedation. The patient’s postoperative course was unremarkable. We describe a case of KMs Class III with a cystic variant assessed by panoramic and CBCT images. We additionally review all KMs Class III reported in the literature.

Comparison of an alveolar expansion technique and buccal guttering technique in the extraction of mandibular third molar. A Pilot Study

Background: The over-ambitious use of surgical drills for almost every case of third molar impaction is on the increase in most established oral surgery centers. The purpose of this study was to assess and compare the severity of post operative symptoms of swelling and pain that accompany the use of surgical drill in the buccal guttering technique and the non application of drill in an alveolar expansion technique. Methods: Consecutive patients with bilateral impacted lower third molars not associated with pericoronitis were included in the study, a total of 10 patients were included in the study. Extraction of both impacted third molars was done consecutively on the same day under local anaesthesia. Post operative morbidities that were assessed clinically are swelling and pain. Results: A total of 10 patients, 70% were females and males were 30%. Age range was 27 - 35 yrs.Out of the eight patients that had the two different techniques, 7 preferred the use of the alveolar expansion technique in which drill was not used. There were statistically significant differences in swellings between these two techniques, (p 0.01). Conclusions: To avoid excessive swelling and pain from over-ambitious cut-ting of soft tissues and drilling of bone, alveolar expansion technique should be considered first in pa-tients with less dense bone.

Root Canal System Variation in Mandibular Second Molar: Middle-Mesial Canal

Middle-mesial canals in mandibular molars are present in the population depending on age, sex and ethnicity. However, limited literature alludes to its prevalence. Troughing procedures may enhance identification, cleaning and shaping. This case report expresses the recognition and management of middle-mesial canal in a mandibular second molar of 24 years old Hispanic-Latino male.

Root Canal Treatment of Mandibular First Molar with Radix Entomolaris

Aim: To confirm the effect of root canal treatment on radix entomolaris. Case: Radix entomolaris was an additional root that located on the distolingual of mandibular first molars. In this case, the radix entomolaris was detected clinically and radiographically with root canal configuration such as curves. An awareness and understanding of this unusual root and root canal morphology could contribute to the successful outcome of endodontic treatment. Conclusion: Root canal treatment on this case shows the lack of symptoms and normal radiographic presentation for two months follow-up.

Transfer learning-based super-resolution in panoramic models for predicting mandibular third molar extraction difficulty: a multi-center study

Background:This study aims to predict the extraction difficulty of mandibular third molars based on panoramic images using transfer learning while employing super-resolution(SR)technology to enhance the feasibility and validity of the prediction.Methods:We reviewed a total of 608 preoperative mandibular third molar panoramic radiographs from two medical facilities:the First Affiliated Hospital of Zhengzhou University(n=509;456 in the training set and 53 in the test set)and the Henan Provincial Dental Hospital(n=99 in the validation set).We conducted a deep-transfer learning network on high-resolution(HR)panoramic radiographs to improve the longitudinal resolution of the images and obtained the SR images.Subsequently,we constructed models named Model-HR and Model-SR using high-dimensional quantitative features extracted through the Least Absolute Shrinkage and Selection Operator method.The models’performances were evaluated using the receiver operating characteristic curve(ROC).To assess the reliability of the model,we compared the results from the test set with those of three dentists.Results:Model-SR outperformed Model-HR(area under the curve(AUC):0.779,sensitivity:85.5%,specificity:60.9%,and accuracy:79.8%vs.AUC:0.753,sensitivity:73.7%,specificity:73.9%,and accuracy:73.7%)in predicting the difficulty of extracting mandibular third molars.Both Model-HR(AUC=0.821,95%CI 0.687–0.956)and Model-SR(AUC=0.963,95%CI 0.921–0.999)demonstrated superior performance compared to expert dentists(highest AUC=0.799,95%CI 0.671–0.927).Conclusions:Model-SR yielded superior predictive performance in determining the difficulty of extracting mandibular third molars when compared with Model-HR and expert dentists’visual assessments.

罹患重度牙周炎下颌磨牙拔牙微翻瓣牙槽嵴保存效果评价

目的:通过临床及影像学评价罹患重度牙周炎下颌磨牙拔牙同期微翻瓣牙槽嵴保存的效果,探讨该术式的适应证。方法:选择2013年9月至2021年6月于北京大学口腔医院牙周科因重度牙周炎拔除下颌磨牙患者的临床资料进行回顾性分析,根据微创拔牙后进行同期微翻瓣牙槽嵴保存术(micro crestal flap-alveolar ridge preservation,MCF-ARP)或仅清创处理后自然愈合分为微翻瓣牙槽嵴保存组(MCF-ARP组)和自然愈合组。通过对拔牙前或拔牙即刻(作为基线)及种植前(拔牙愈合后)拍摄的锥形束计算机断层扫描配准后分析骨高度、宽度和体积及其变化,并比较两组种植时同期引导骨再生(guided bone regeneration,GBR)的比例。结果:共纳入87例患者96颗下颌磨牙,MCF-ARP组愈合后拔牙窝底中心处距离下颌管骨皮质最冠方的高度(中心骨高度)平均增加了(8.34±2.81)mm,自然愈合组平均增加了(3.82±3.58)mm,两组间差异有统计学意义(P<0.001)。MCF-ARP组高骨壁骨嵴顶下1 mm处的牙槽骨宽度平均增加了(3.50±4.88)mm,自然愈合组牙槽嵴宽度减少了(0.16±5.70)mm,两组间差异有统计学意义(P=0.019)。MCF-ARP组愈合后的牙槽骨中心骨高度均大于8 mm,其中97.1%的牙槽骨中心骨高度>10 mm;自然愈合组愈合后有23.1%的牙槽骨中心骨高度<8 mm,仅61.5%的牙槽骨中心骨高度>10 mm。愈合后MCF-ARP组牙槽窝总体积、颊侧体积和舌侧体积增加量及增加比例均大于自然愈合组,两组间差异有统计学意义(P<0.001)。MCF-ARP组68颗种植体有5颗(8.3%)种植同期进行GBR,自然愈合组26颗种植体有8颗(30.8%)种植同期进行GBR,两组间差异有统计学意义(P=0.003)。结论:对于罹患重度牙周炎的下颌磨牙,如果拔牙前拔牙窝底中心处距下颌管骨皮质最冠方距离较小(<7 mm)时,临床医生可考虑进行拔牙同期微翻瓣牙槽嵴保存术,为未来种植治疗时提供充足的骨量,减少种植同期进行引导骨再生的比例,降低种植治疗的难度与风险,提高种植治疗的安全性。

锥形术CT测量分析下颌第一磨牙拟种植区剩余牙槽嵴的骨量

背景:随着口腔领域的发展与进步,口腔种植技术逐渐成为替代传统义齿的主流选择。近年来,多种骨增量技术的成熟以及口腔数字化领域的不断发展,使种植适应证不断扩大,种植手术的成功率也越来越高。但是种植手术前使用锥形术CT对剩余牙槽嵴骨量进行准确测量并且个性化制定合适的种植方案,成为一部分临床医师的难题。目的:采用锥形束CT对下颌第一磨牙拟种植区剩余牙槽嵴骨量进行测量分析,为优化下颌第一磨牙区种植方案的设计提供参考。方法:采用回顾性研究设计,纳入205例下颌第一磨牙缺失患者的锥形术CT影像,测量下颌第一磨牙拟种植区剩余牙槽嵴高度及宽度,并将剩余牙槽嵴形态分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4类(Ⅱ、Ⅲ、Ⅳ类剩余牙槽嵴为骨量不足),统计分析下颌第一磨牙剩余牙槽嵴高度、宽度、形态频数分布,不同性别患者下颌第一磨牙剩余牙槽嵴高度和牙槽嵴顶宽度的差异,剩余牙槽嵴高度与剩余牙槽嵴顶宽度、剩余牙槽嵴底宽度的相关性,年龄与剩余牙槽嵴顶宽度、高度的相关性。结果与结论:①下颌第一磨牙拟种植区剩余牙槽嵴高度平均为(12.14±2.96)mm,其中<12 mm者占43.41%(89/205),下颌第一磨牙拟种植区牙槽嵴顶宽度平均为(6.80±1.65)mm,其中<6 mm者占26.34%(54/205);②男性下颌第一磨牙剩余牙槽嵴高度高于女性,但差异无显著性意义(P>0.05),男性下颌第一磨牙剩余牙槽嵴顶宽度宽于女性,差异有显著性意义(P<0.01);③剩余牙槽嵴高度与剩余牙槽嵴顶宽度和剩余牙槽嵴底宽度呈负相关(P<0.05);年龄与剩余牙槽嵴顶宽度呈正相关(P<0.05),与剩余牙槽嵴高度无明显相关性(P>0.05);④剩余牙槽嵴形态Ⅰ类占58.05%(119/205),Ⅱ类占9.27%(19/205),Ⅲ类占20.49%(42/205),Ⅳ类占12.19%(25/205),其中多数为Ⅲ类剩余牙槽嵴骨量不足,临床医生需要根据剩余牙槽嵴类型个性化设计最佳的种植方案。

Clinical relevance of distolingual roots and periodontal status in mandibular first molars: a cross-sectional study employing CBCT analysis

Objectives:Distolingual root of the permanent mandibular first molar(PMFM-DLR)has been frequently reported,which may complicate the treatment of periodontitis.This study aimed to assess the morphological features of PMFM-DLR and investigate the correlation between the morphological features of PMFM-DLR and periodontal status in patients with Eastern Chinese ethnic background.Materials and methods:A total of 836 cone beam computed tomography(CBCT)images with 1497 mandibular first molars were analyzed to observe the prevalence of PMFM-DLR at the patients and tooth levels in Eastern China.Among them,complete periodontal charts were available for 69 Chinese patients with 103 teeth.Correlation and regression analyses were used to evaluate the correlation between the morphological features of DLR,bone loss,and periodontal clinical parameters,including clinical attachment loss(CAL),probing pocket depth(PPD),gingival recession(GR),and furcation involvement(FI).Results:The patient-level prevalence and tooth-level prevalence of DLR in mandibular first molars were 29.4%and 26.3%,respectively.Multiple linear regression analysis suggested that bone loss at the lingual site and CAL were negatively affected by the angle of separation between distolingual and mesial roots in the transverse section,while they were significantly influenced by age and the angle of separation between distobuccal and mesial roots in the coronal section.Conclusions:The prevalence of PMFM-DLR in Eastern China was relatively high in our cohort.The morphological features of DLR were correlated with the periodontal status of mandibular first molars.This study provides critical information on the morphological features of DLR for improved diagnosis and treatment options of mandibular molars with DLR.

Loss of Masticatory Function Affects Growth and Development of the Mandibular Condyle in Rats

The effects of childhood masticatory function loss and soft foods on the mandibular condyle have been the subject of much research. However, the corresponding bone turnover is not fully understood. The purpose of the present study was to clarify the effects of a lack of teeth and a soft food diet during the growth period on bone turnover in the mandibular condyle. We divided 3-week-old Wistar rats into the following three groups: 1) Extraction group: The maxillary molars were extracted at the age of 4 weeks, and animals were fed powdered standard feed. 2) Powder group: Animals were fed powdered standard feed without tooth extraction. 3) Control group: Animals were fed solid standard feed without tooth extraction. Non-decalcified thin-slice specimens of sagittal sections of the mandibular condyle were obtained at the age of 20 weeks for histological analysis. We used micro-CT analysis and bone histomorphometry to measure bone volume (BV), bone mineral content (BMC), bone mineral density (BMD), bone microstructure, bone resorption, and osteogenesis in the mandibular condyle, and we compared the results among groups. In the extraction and the powder groups, we found deformation and disruption of the arrangement of chondrocytes, coagulation of chondrocytes, and duplication of the tidemark in the cartilage. We also found an increase in multinuclear osteoclasts in the cancellous bone. We found a reduction in BV, BMC, and BMD in the extraction and powder groups compared to the control group, as well as a reduction of bone volume, a lowering of osteogenesis parameters, and an increase in bone resorption parameters in the secondary cancellous bone. These results suggest that a lack of teeth and a soft food diet during the growth period cause a decline in bone microstructure, a decrease in osteogenesis, and an increase in bone resorption.

Research on the Related Factors of the Second Molar Dislocation and Orthodontic Erect Method

The second molar dislocation is more common clinically.To investigate the related factors of the second permanent molar dislocation,and provide reference for the clinical diagnosis and treatment of orthodontics.From the current clinical research,the clinical methods of orthodontic erect secondary molars are also diverse and clinical.The narrower first molar alveolar arch width,smaller ANB angle,and crowded maxillary posterior segment arch are the factors that cause the maxillary second permanent molar dislocation.The narrow alveolar arch width,the smaller SNB angle,the larger ANB angle,and the crowded lower mandibular arch are the factors leading to the dislocation of the mandibular second permanent molar.In addition,for the second mandibular molar malposition,it is particularly important to select the corrective treatment plan.It is especially important to improve the treatment.