Influence of tooth removal on mandibular bone response to mastication

The quantification of biomechanical response of mandibular bone to mastication is an integral component for a key in understanding the biological consequence of masticatory functions. Understanding the response of mandibular bone to external loading may also well explain the mechanisms of bone turnover. In this study, three finite element (FE) models simulating the lower second premolar, first and second molars along with their supporting structures were developed to determine stress/strain levels and distribution under different occlusal loading. The changes in stress/strain values and profiles have been investigated in three scenarios: pre-extraction of the lower first molar, post-extraction and after full healing of the extracted socket. The mastication induced equivalent strains within the supporting mandibular bone at each of these three scenarios were quantified and compared against the Frost's mechanostat theory. The results of stress/strain profiles show considerably lower magnitudes in the post-extracted and healed scenarios compared with the pre-extraction case. Following the Frost's MES hypothesis, the initial equivalent strains are related to local bone remodelling. It is found that in the extracted case the bone near the tooth socket undergoes resorption from lingual respect whilst filling the cavity, whereas in the healed case bone turnover reaches equilibrium. The results provide important data for clinical assessment of constructing dentures or other restorative devices.     

Characteristics of iatrogenic mandibular fractures associated with tooth removal: review and analysis of 189 cases

Fracture of the mandible during exodontia is fortunately rare, but is under-reported. A review identified 189 documented cases of iatrogenic fractures of the mandible (IFM) associated with the removal of teeth. The reasons for its occurrence are thought to be multifactorial and include age, sex, degree of tooth impaction, relative volume of the tooth in the jaw, pre-existing infection or bony lesions, failure to maintain a soft diet in the early postoperative period, and the surgical technique. The clinical experience of the surgeon does not seem to have an important role. We review the aetiology of iatrogenic mandibular fracture and summarise the ways of minimising this complication.     

Growth hormone receptor gene variant and three-dimensional mandibular morphology

Objective:To examine the relationship between three-dimensional mandibular morphology and growth hormone receptor (GHR) gene variants in a healthy Japanese population.Materials and Methods:The subjects, who were unrelated Japanese orthodontic patients, consisted of 64 men and 114 women. Using the Taqman genotyping assay, GHR gene rs6184 and rs6180 variants were detected in genomic DNA extracted from saliva. Mandibular volume and length were measured from cone-beam computed tomography images that were analyzed using Analyze image-processing software. The relationship between GHR gene variants and three-dimensional mandibular morphology was statistically examined.Results:Statistical significance for the relationship between the distance between the left and right coronoid processes and rs6180 was noted (P < .05).Conclusion:Our results indicate that the GHR variant rs6180 is associated with the distance between the left and right coronoid process in the Japanese subjects.     

下颌骨牵引成骨区即刻牙移动的实验研究

目的：研究下颌骨牵引成骨后在新骨区即刻牙移动时牙周组织的改建行为及牙移动规律。方法：选择4只牙列完整的Beagle犬,其中2只犬建立双侧下颌骨牵引成骨动物模型,牵引完成后,即刻以30g力远中移动下颌第三前磨牙进入牵引成骨区;另外2只犬拔除双侧下颌第四前磨牙后3个月,以30g力远中移动下颌第三前磨牙。实验中,每周加力1次拍摄X线片,并记录牙移动速率。牙移动8周后,观察实验牙及其牙周组织特点。测量数据采用SPSS12.0软件包进行t检验。结果：实验牙借助自制的持续加力装置移动进入牵引成骨区,实验牙未产生倾斜,牙无明显松动,牙根未见明显吸收。实验组牙移动速度显著快于对照组,P〈0.01。组组织学观察发现,牙槽骨和牙周膜未出现不可逆性损伤。结论：牵引成骨区的新生骨质中,牙可以快速而平稳地移动。     

Relationship between masticatory rhythm,body mass and mandibular morphology in primates

Objective

It has been proposed that rhythmic movements such as locomotion and respiration have a period proportional to body mass^1/4. Mastication basically consists of rhythmic alternation of jaw-closing and jaw-opening movements. We studied the relation between masticatory rhythm and body mass in primates, and masticatory rhythm and mandible morphology.

Methods

We measured the chewing cycle duration (CCD), mandibular length, mandible height, mandible width and distance from the condylar process of mandible to the centre of gravity of the mandible. Body mass was quoted from the literature.

Results

The CCD is related to mandible morphology and was found to be proportional to body mass^1/6.

Conclusion

These findings suggest that masticatory rhythm is correlated with body mass and mandibular morphology, and that scaling rate of masticatory rhythm to body mass is slower than for the other rhythms.     

Growth hormone receptor gene is related to root length and tooth length in human teeth

Objectives:To examine the relationship between tooth length and growth hormone receptor (GHR) gene variants in a healthy Japanese population.Materials and Methods:The subjects consisted of 193 Japanese adults (69 men, 124 women), aged 13 to 56 years. Genomic DNA was extracted from saliva and genotyped GHR rs6184 and rs6180 variants using the Taqman genotyping. Computed tomography (CT) images were acquired using a dental cone-beam CT scanner and reconstructed using open-source OsiriX medical image processing software. The maxillary (upper; U) and mandibular (lower, L) central incisors (1), lateral incisors (2), canines (3), first premolars (4), second premolars (5), first molars (6), and second premolars (7) were evaluated. Teeth were assessed for crown height (CH), root length (RL), overall tooth length (C+R), and crown to root ratio (C/R). The relationships between GHR variants and CH, RL, C+R, and C/R were statistically examined.Results:The GHR variant rs6184 was associated with the root lengths and tooth length for the upper and lower lateral incisors and upper canines (U2 RL; U3 RL, C+R; L2 RL [P < .05]).Conclusions:The results indicate that the GHR rs6184 variant is associated with tooth length and ratio dimensions in a Japanese cohort. Further studies utilizing a larger sample size are needed to confirm this finding.     

Construction of three-dimensional tooth model by micro-computed tomography and application for data sharing

The study of dental morphology is essential in terms of phylogeny. Advances in three-dimensional (3D) measurement devices have enabled us to make 3D images of teeth without destruction of samples. However, raw fundamental data on tooth shape requires complex equipment and techniques. An online database of 3D teeth models is therefore indispensable. We aimed to explore the basic methodology for constructing 3D teeth models, with application for data sharing. Geometric information on the human permanent upper left incisor was obtained using micro-computed tomography (micro-CT). Enamel, dentine, and pulp were segmented by thresholding of different gray-scale intensities. Segmented data were separately exported in STereo-Lithography Interface Format (STL). STL data were converted to Wavefront OBJ (OBJect), as many 3D computer graphics programs support the Wavefront OBJ format. Data were also applied to Quick Time Virtual Reality (QTVR) format, which allows the image to be viewed from any direction. In addition to Wavefront OBJ and QTVR data, the original CT series were provided as 16-bit Tag Image File Format (TIFF) images on the website. In conclusion, 3D teeth models were constructed in general-purpose data formats, using micro-CT and commercially available programs. Teeth models that can be used widely would benefit all those who study dental morphology.     

A novel method for volumetric assessment of tooth wear using three-dimensional reverse-engineering technology: A preliminary report

Objective:To describe a newly developed three-dimensional (3D) digital superimposition method for quantitative evaluation of tooth wear that occurs during orthodontic treatment.Materials and Methods:The sample consisted of dental casts obtained from 56 patients (23 male patients and 33 female patients; mean ± standard deviation age  =  21.8 ± 5.1 years) who received orthodontic treatment with extraction of four premolars. The maxillary and mandibular dental casts taken before (T1) and after (T2) orthodontic treatments were scanned, and 3D images of the canines were constructed. The canines at T1 were superimposed with those at T2 with the best-fit method using the middle third of the labial and lingual surface as the reference area. To measure the volume of the canines, four boundary planes were constructed, and the differences in volume before and after orthodontic treatment were calculated.Results:The mean volume of tooth wear of the 224 canines was 2.0 mm³ after 35.5 months of orthodontic treatment. The volume of canine tooth wear was 2.3 ± 1.5 mm³ in male subjects and 1.9 ± 1.2 mm³ in female subjects. The mean wear of the upper right canines (2.4 ± 2.0 mm³) was significantly greater than that of the lower right canines (1.9 ± 2.6 mm³).Conclusions:Regional registration of teeth in 3D digital models is useful for quantitative evaluation of tooth wear in orthodontic patients. This method may also be used to assess treatment results in restorative dentistry.     

牙动度与牙周膜宽度关第的实验性研究

目的：提取牙动度信号中与牙周膜宽度的有关的参数,为临床应用提供依据,方法：以离体上颌中切牙为实验牙,硅橡胶模拟牙,募在丙烯酸甲酯模仿槽骨,用FX－1型牙动度测量系统采集,处理不同牙周膜宽度时的牙动度信号。结果：牙动度信号中的幅值R、斜率K及时间参数值t2随牙周膜宽度增加而减小;时间参数值t1随机周膜宽度增加而增大;R,t2与牙周膜宽度呈显著负相关。结论：牙动度信号中的R值,t2值可作为反映牙周膜宽度变化的特异性指标。     

Idiopathic osteosclerosis in the mandible associated with abnormal tooth root formation

Idiopathic osteosclerosis (IO) is a localized, well-defined, intrabony radiopaque lesion within cancellous bone. The causes of IO are still unknown and most lesions are nonexpansile and asymptomatic, so they are often detected incidentally on radiographic examination for other purposes. In the case of jaw lesions, IO is considered to be of no clinical significance and usually requires no treatment. This paper describes two clinical cases about the long-term treatments and observations of mandibular IO in adolescents. The lesions were associated with abnormal tooth root formation and tooth malposition. In these cases, the orthodontic treatments finished successfully without any complication despite the lesions. IO in the jaw needs regular follow-up to ensure normal orofacial development during adolescence.     

Characterizing mandibular growth using three-dimensional imaging techniques and anatomic landmarks

ObjectiveTo provide quantitative data on the multi-planar growth of the mandible, this study derived accurate linear and angular mandible measurements using landmarks on three dimensional (3D) mandible models. This novel method was used to quantify 3D mandibular growth and characterize the emergence of sexual dimorphism.DesignCross-sectional and longitudinal imaging data were obtained from a retrospective computed tomography (CT) database for 51 typically developing individuals between the ages of one and nineteen years. The software Analyze was used to generate 104 3DCT mandible models. Eleven landmarks placed on the models defined six linear measurements (lateral condyle, gonion, and endomolare width, ramus and mental depth, and mandible length) and three angular measurements (gonion, gnathion, and lingual). A fourth degree polynomial fit quantified growth trends, its derivative quantified growth rates, and a composite growth model determined growth types (neural/cranial and somatic/skeletal). Sex differences were assessed in four age cohorts, each spanning five years, to determine the ontogenetic pattern producing sexual dimorphism of the adult mandible.ResultsMandibular growth trends and growth rates were non-uniform. In general, structures in the horizontal plane displayed predominantly neural/cranial growth types, whereas structures in the vertical plane had somatic/skeletal growth types. Significant prepubertal sex differences in the inferior aspect of the mandible dissipated when growth in males began to outpace that of females at eight to ten years of age, but sexual dimorphism re-emerged during and after puberty.ConclusionsThis 3D analysis of mandibular growth provides preliminary normative developmental data for clinical assessment and craniofacial growth studies.     

Relationship between maximal bite force and tooth wear in bruxist and non-bruxist individuals

Objective

(i) To compare individuals with self-reported bruxism and non-bruxist individuals in terms of maximal bite force (MBF) and temporomandibular joint (TMJ) primary assessment parameters and (ii) to examine the relationship between MBF and tooth wear in these subjects.

Materials and methods

Twenty-nine bruxist subjects and 29 healthy controls were enrolled. MBF measurements were carried out by the use of bite force recorder. Tooth wear indices, maximal mouth opening, maximal lateral excursions and maximal protrusions were measured for every subject.

Results

MBF and tooth wear index scores were significantly higher in bruxists (p values <0.05) compared to non-bruxists. MBF and tooth wear index scores were found to be significantly correlated in the bruxist group (r = 0.79, p = 0.00). Less significant correlation was observed in the non-bruxist group (r = 0.38, p = 0.04). No differences in masticatory clinical examination parameters were identified between the groups.

Conclusion

This study is the first to show that MBF can increase in bruxist individuals and that the increase in MBF are correlated with tooth wear in bruxist subjects. Further studies regarding the possible role of MBF in bruxism are to be done.     

Relationship between tooth loss and carotid intima-media thickness in Korean adults

PURPOSE

The aim of this study was to examine the relationship between tooth loss and sub-clinical atherosclerosis in Korean adults.

MATERIALS AND METHODS

The subjects were part of a cohort study conducted in Ansan city by the Korea University medical school as part of the Korean Genome project. 749 subjects over than 40 years old were evaluated. After taking panoramic radiography, the amount of tooth loss was calculated. The intima-media thickness (IMT) was assessed by using ultrasonography at the common carotid artery. Traditional cardiovascular risk factors for atherosclerosis were also evaluated. The relationship between tooth loss and the IMT was evaluated using ANOVA with Scheffe''s multiple comparison method in univariate analysis. Multiple regression analysis was also performed to determine the significance between the IMT and tooth loss.

RESULTS

With age, tooth loss increased, but there was no significant increase in other traditional cardiovascular risk factors. Univariate analysis revealed the IMT to be positively related with the amount of tooth loss. Regression analysis of the IMT in the anterior and posterior tooth loss revealed that only the posterior tooth loss was significantly related with the IMT at all sites of the common carotid artery (right far wall, P = .015; left far wall, P = .008; right near wall, P < .001; left near wall, P = .001).

CONCLUSION

This study verified the positive relationship between the increased tooth loss at the posterior area and the accumulation of atheroma in arteries.     

下颌牵张成骨速度对大鼠下颌骨形态的影响

目的研究大鼠下颌牵张成骨过程中牵张速度对大鼠下颌骨形态的影响。方法对139只雄性SD 大鼠施以单侧乙状切迹至下颌骨下缘的纵向骨切开,放置口外牵张器。3天的潜伏期后随机分成17组,分别以0mm/天、0.2mm/天、0.4mm/天、0.6mm/天的牵张速度连续加力5天,并在术后第3、6、10、24、38天处死。拍摄双侧下颌骨8×10 inch诊断领片,利用NIH Image Software测量及分析下颌骨长度及牵张间隙面积的变化。结果①快速牵张组的下颌骨长度大于中、慢速组,但低于预期伸长量。②中、慢速组的下颌骨伸长量近乎一致。③牵张间隙的面积随牵张量的增加而增加。结论牵张速度对下颌骨形态有很大影响。快速骨牵张可能导致下颌骨预期长度的减少,而这一变化为该治疗的风险所在。     

男性2型糖尿病患者失牙与吸烟相关关系的研究

目的 探讨吸烟对2型糖尿病男性患者失牙是否产生影响.方法 354例男性2型糖尿病患者依据吸烟与否分为2组,吸烟组151人,非吸烟组203人.问卷调查吸烟状况,口腔检查牙缺失数及其分布.应用SAS软件包及回归分析法统计分析失牙与吸烟的关系.结果 吸烟组与非吸烟组的失牙均数分别为:8.7、6.0,吸烟组显著高于非失牙组(P＜0.05);吸烟组平均失牙数与吸烟指数显著相关.结论 吸烟会加重2型糖尿病男性患者牙齿的丧失.     

下颌阻生第三磨牙与下颌管位置的曲面体层X线片和锥形束CT观察

目的 观察分析在曲面体层x线片上人群中下颌阻生第三磨牙(impacted mandibular third molar,IMTM)与下颌管位置关系的类型,并对二者关系密切的病例行锥形柬CT(conc beam computed tomography,CBCT)检查,了解二者实际位置关系.为临床制定IMTM拔除手术方案提供参考.方法 观察390例(645侧)曲面体层X线片,将IMTM与下颌管的位置关系的影像分为3种类型:①无接触类,二者影像无任何重叠或接触;②点状接触类,二者之间影像仅为点状接触;③部分重叠类,二者影像部分重叠或有较大范围接触.统计3种类型的构成比.曲面体层X线片显示IMTM与下颌管影像呈部分重叠或较大范围接触的部分病例行CBCT检查,观察曲面体层X线片IMTM与下颌管关系密切者中,IMTM实际突破下颌管壁所占的比例.结果 390例(645侧)IMTM的曲面体层X线片影像中,无接触类441侧(68.4%);点状接触类149侧(23.1%);部分重叠类55侧(8.5%).对31例(50侧)曲面体层X线片上显示IMTM与下颌管呈部分重叠或较大范围接触的CBCT检查发现,25侧(50%)IMTM突破下颌管壁.结论 ①曲面体层X线片可以排除90%以上IMTM与下颌管关系不密切的病例;②曲面体层X线片IMTM与下颌管影像呈部分重叠或较大范围接触表现的病例有必要行CBCT进一步检查.     

Relationship between pterygomaxillary fissure morphology and maxillary/mandibular position

The aim of this study was to investigate the possible correlation between maxillary and mandibular positioning via cephalometric analysis with pterygomaxillary fissure (PMF) morphology using cone...     

Cranial base,maxillary and mandibular morphology in Down syndrome

Objective:To test the null hypothesis that there is no difference between craniofacial measurements of individuals with Down syndrome (DS) and normal controls.Materials and Methods:A cephalometric analysis including additional landmarks and measurements to study specific craniofacial features was undertaken on pretreatment cephalograms of 25 patients with DS (12 male, 13 female; mean age 15.1 years) treated at The Hospital for Sick Children, Toronto. Measurements were compared with those from cephalograms of racial groups age and gender matched, normal, Class I children, available from the Burlington Growth Center. Data were analyzed using paired t-tests.Results:Large reductions were measured in the size and spatial relationships of craniofacial structures in the DS group. The greatest differences included a larger cranial base angle; reduced elevation of sella from FHP; reduced anterior and posterior cranial base lengths; reduced anterior and posterior face heights; smaller maxilla with reduced anterior basal and apical dimensions; and smaller mandibular ramus, body and symphyseal dimensions and proclined symphysis. Maxillary incisors were severely proclined and undererupted, while mandibular incisors were undererupted. Alveolar heights were reduced. Anterior open bite was frequently noted. Maxillary and mandibular planes exhibited forward rotation patterns, promoting overclosure. Mandibular hypoplasia was less severe than cranial base and maxillary hypoplasia. Hypodontia of one or more permanent teeth was found in 92% of the sample.Conclusions:The null hypothesis was rejected. Significant hypoplasia in endochondral, mesodermal, and ectomesenchymal derived structures of the cranium and face in subjects with DS was clearly evident. More severe platybasia than previously reported was found.     

Relationship between the tooth eruption and regional blood flow in angiotensin II-induced hypertensive rats

OBJECTIVE: The mechanism of action of vasoactive drugs on tooth movement is unknown. The purpose of the present study was to measure simultaneously the axial movement of the mandibular incisor, regional blood flow at the base of the incisor, and systemic arterial blood pressure in angiotensin II-induced hypertensive rats to determine the possible cause of tooth displacement. DESIGN: The measurements were made under artificial respiration with halothane anaesthesia. In the experimental animals, 2.5 microg of angiotensin II in 1 ml of Ringer's solution was infused at 0.83 ml/h for 12 h from the femoral vein. In the control animals, only Ringer's solution was infused. RESULTS: Angiotensin II caused an increase of the mean arterial blood pressure from 86 to 119 mm Hg, and decreases of the eruption rate from 667 to 494 microm/24 h and the regional blood flow from 262 to 214 mV. There was a positive correlation between the eruption rate and regional blood flow, and a negative correlation between the blood pressure and regional blood flow. CONCLUSION: These results suggest that angiotensin II caused constriction of the peripheral vascular smooth muscle resulting in an increase of arterial blood pressure and a decrease of regional blood flow, followed by a decrease of fluid volume and then a reduction of either the pressure within the socket or of the eruptive force. We assume that the regional vascular pressure within the socket plays an important role in determining the position of the rat incisor.     

Notch1蛋白在小鼠下颌切牙发育中的表达

目的探讨Notch1在小鼠下颌切牙牙胚发育过程中的组织学分布。方法制作ICR小鼠下颌切牙不同发育阶段的冰冻组织切片,对小鼠下颌切牙牙胚自牙胚发育起始期至钟状晚期不同发育阶段组织Notch1的分布情况进行免疫组织化学染色。结果 Notch1在小鼠下颌切牙发育蕾状期牙胚的口腔侧上皮中表达,而在和间充质相邻的牙胚上皮中没有表达。从帽状期至钟状期,Notch1在牙胚的中间层表达,而在内釉上皮中没有表达。钟状期的唇侧颈环部位星网状层和部分牙上皮细胞也表达Notch1。此外,Notch1还在牙胚发育不同时期的间充质、牙乳头和早期牙髓中表达。结论 Notch1可能在小鼠下颌切牙发育过程中的牙上皮,特别是内釉上皮的细胞分化,以及牙囊和牙乳头细胞分化及分化完成后的牙髓干细胞的稳定性方面有重要作用。