Relationship between the apices of the lower molars and mandibular canal--a radiographic study

The study was performed on forty-six randomly chosen dry mandibles. The molar areas of each mandible were radiographed by the paralleling technique, and an additional radiograph at -20 degrees angulation of the same area was taken. Measurements of the distance between the upper border of the mandibular canal and the root apices of the first and second molars were taken. The location of the mandibular canal in the buccolingual plane was determined. The obtained data were statistically evaluated. Statistically significant symmetry of the relationship of the mandibular canal to the root apices was established between the right and left sides of the same mandible. In the majority of cases the mandibular canal was buccal to the apices of the second molar, and in the first molar area the canal was lingual to the root apices in almost half of the cases. Most frequently, the upper border of the mandibular canal was located 3.5 to 5.4 mm below the root apices of both first and second molars. In no case was the mandibular canal found in close proximity, both in the vertical and in the buccolingual planes, to the first and second molar apices.     

下颌矢状劈开截骨术相关下颌管空间定位的三维CT研究

目的：应用三维CT影像测量下颌管解剖位置与骨皮质和磨牙的关系,为避免下颌矢状劈开截骨术中损伤下齿槽神经血管提供指导。方法：选择50名正常成人下颌骨三维CT扫描图像,应用AW4．4图像处理软件分别在第二前磨牙,第一、第二磨牙正中,下颌磨牙后区处测量下颌管的解剖位置。结果：通过获得的CT数据研究中国人下颌神经管的解剖位置与骨皮质和磨牙的联系,在第二磨牙区域下颌管距离颊侧骨皮质最远（平均7．82mm,最小4．9mm）。结论：在第二磨牙区域下颌体最厚,对于下颌矢状劈开截骨术的颊侧垂直切口须在下颌第二磨牙区域,这个区域骨质最厚并且下颌管距离颊侧骨皮质最远。对于下颌矢状劈开截骨术颊侧垂直切口的安全深度是4．9mm。     

A study of the internal structure of the Japanese edentulous mandible

With the aim of improving understanding of the transition the mandible internal structure undergoes between the dentulous and edentulous states, the thickness of the substantia compacta, the ratio of trabecular bone to the total substantia spongiosa, and the thickness of the trabecular bone were measured in 9 edentulous mandibles aged 45 to 65 years. The measurements were made with an image-treatment device outfitted with a personal computer. Results 1. Thickness of the substantia compacta The thickest zones (3.00-3.81 mm) were located on the lingual side of the anterior teeth; the second thickest zones (2.20-2.48 mm) were located on the superior lingual and buccal side of the molars. The thinnest zones (1.66-1.67 mm) were located on the labial side of the anterior teeth; the second thinnest zones (1.71-1.75 mm) were located on the buccal side of the premolars. Little difference (1.90-2.18 mm) was observed in the bases of the mandibular areas. In the region of the lingual side, the thickest zones occurred in the premolars. Little difference in thickness was observed between the premolar and molar zones. On the labial-buccal side, thicknesses increased from the premolar to the molar zones (which were the thickest) and decreased gradually from the mental to the premolar zones. Comparisons showed that the anterior teeth zoon in the edentulous mandible the substantia compacta is thinner on the labial side and thicker on the lingual side than it is in the dentulous mandible. Little difference between the dentulous and edentulous mandibles was observed in the lingual side of the molar zone, although the buccal side was thinner in the edentulous than in the dentulous mandible. 2. Ratio of trabecular bone to the total substantia spongiosa The highest ratios (74.03-89.62%) occurred in the mental zone; the second highest (69.07-82.92%) occurred in the incisor zone. The lowest ratios (30.61-39.61%) occurred in the superior and middle regions of the premolar zone. The inferior area of the premolar zone, however, was relatively wider (42.83-55.66%) than the superior and middle areas. The following ratios of trabecular bone to total substantia spongiosa were observed: The highest ratio occurred in the zone of the anterior teeth, the next highest ratio in the molar zone, and the lowest ratio in the premolar zone. Although, differences in ratios between dentulous and edentulous mandibles were only slight, a lower ratio occurred in the inferior area of the premolar zone. 3. Thickness of trabecular bone within the substantia spongiosa.(ABSTRACT TRUNCATED AT 400 WORDS)     

Buccal bone plate thickness of the Asian people

Distances from the apex to the buccal bone plate were measured on the computed tomography (CT) images of 1806 teeth from 66 patients, using an image analyzer program (Image-Pro Plus, Ver. 4.0, Media Cybernetics). In the mandible, the mean distance from the distal apex of the mandibular second molar to the buccal bone plate was the largest distance measured, at 8.51 mm, followed by distance from the mesial root to the buccal bone (7.34 mm). In the mandibular first molar, the mean distal and mesial bone thicknesses were 5.18 mm and 4.09 mm, respectively. However, when there were two distal roots, the distance of the disto-lingual root to the buccal plate was found to be 9.52 mm, which constitutes the greatest measured thickness. In the maxillary buccal roots, the distances from the mesio-buccal and disto-buccal root of the second molar to the buccal bone plate were the largest, at 4.63 mm and 3.61 mm, respectively. The average distances from the palatal apex of the maxillary first and second molars to the buccal bone plate were 10.69 mm and 10.17 mm, respectively, while, from the palatal bone plate, average distances of 3.15 mm and 3.08 mm were measured. Special considerations, such as bony lid approach, lingual approach, or intentional replantation may be required, especially when a patient has a surgical need in the second molars and the disto-lingual root of the mandibular first molar, or in the palatal root of the maxillary molars.     

Investigation of the root canal configurations of mandibular permanent teeth in the Turkish population

AIM: To investigate the root and canal morphology of mandibular permanent teeth collected from an indigenous Turkish population. METHODOLOGY: A total of 1400 extracted mandibular permanent teeth were evaluated. The teeth were divided into seven groups as central incisors, lateral incisors, canines, first premolars, second premolars, first molars and second molars in order to evaluate their root canal configurations. Access cavities were prepared and pulp tissue removed using 5.25% sodium hypochlorite solution. The teeth were stored in 5% nitric acid solution for 5 days, then rinsed under running water for 4 h and placed in increasing concentrations of ethyl alcohol. The teeth were rendered transparent by immersion in xylene solution for 3 days until complete transparency was achieved. Following this procedure, India ink was injected in the root canal systems and their configurations were examined and compared with the classification of Vertucci. The following observations were made: (i) root canal classification of mandibular teeth; (ii) morphology of the mandibular permanent teeth. The classification of Vertucci was taken as a reference during the evaluation; however additional canal morphological types were evaluated as separate groups. RESULTS: The presence of a second canal was detected in 68% of mandibular central incisors and 63% of lateral incisors. Lateral canals were found in 6.5% of mandibular central incisors and in 13% of lateral incisors. Overall, 62% of mandibular first premolar teeth had a single canal whereas 71% of second premolars had a single canal. The mandibular first and second molar teeth exhibited similar root canal configurations except for a group of second molar teeth that had a single root and canal. CONCLUSIONS: The morphological characteristics of teeth in this Turkish population were consistent with those of other studies performed on different populations using similar methodology.     

基于CBCT对下颌管位置的测量分析

目的：应用CBCT对正常人群下颌管在第二前磨牙及第一、二磨牙根尖处位置的测量,来确定其正常位置关系。方法：测量120例18岁以上正常人群第二前磨牙及第一、二磨牙根尖处位置的3个距离：①下颌管中心（ A）到下颌骨下缘最下点（ B）的距离;②下颌管中心（ A）到与A点在同一水平线的颊侧点（ C）的距离;③下颌管中心（ A）到与A点在同一水平线的舌侧点（ D）的距离。每个距离测量3组,取其平均值。结果：男性第二前磨牙根尖处的下颌骨下缘骨壁最厚,其舌侧骨壁厚于颊侧骨壁。在第一磨牙及第二磨牙处,下颌骨下缘骨壁、舌侧骨壁、颊侧骨壁均增厚,且颊侧骨壁厚于舌侧骨壁;女性测量结果及规律与男性相同,其骨壁厚度略较男性骨壁为薄。结论：利用这3个空间距离来确定正常人下颌管在第二前磨牙及第一、二磨牙根尖处的位置,对正颌手术中下颌骨矢状劈开术,囊肿刮治术,种植术等提供理论依据。     

Proximity of the mandibular canal to the tooth apex

Introduction

Knowledge of the inferior alveolar nerve (IAN) position is important in avoiding nerve damage during invasive dental procedures. Because the exact position of the nerve bundle can vary in patients, this study evaluated the distance from the apices of mandibular premolar and molar teeth to the superior border of the mandibular canal.

Methods

Cone-beam computed tomography (CBCT) scans from 139 patients were analyzed to evaluate the proximity of the mandibular canal to the root apices of 743 mandibular second premolar and first and second molar teeth. Subjects were subgrouped by age and sex. A random intercept model was used to account for multiple measurements within a patient.

Results

In all groups, root apices of the mandibular second molars were closer to the mandibular canal than other teeth. The mesial root of the second molar was closer to the nerve in female patients compared with male patients. Root apices in younger patients (<18 years) were generally closer to the mandibular canal than in older patients.

Conclusions

The CBCT scan is an accurate, noninvasive method to evaluate the position of the mandibular canal. The variable position of this structure between patients suggests the need for CBCT to determine the proximity of the nerve bundle before attempting invasive treatment in this area. Dental practitioners should consider potential differences of mandibular canal position as a result of age and gender when performing these procedures in this area.     

Use of cone-beam computed tomography to evaluate root and canal morphology of mandibular first and second molars in Turkish individuals

Objective: The aim of this study was to investigate the root and canal morphology of mandibular first and second molars in a Turkish population by using cone beam computed tomography (CBCT). Study design: CBCT images of mandibular first (n = 823) and second molar (n = 925) teeth from 605 Turkish patients were analyzed. The root canal configurations were classified according to the method of Vertucci. Results: The majority of mandibular molars (95.8% of first molars, 85.4% of second molars) had two separate roots; however, three roots were identified in 2.06% of first molars and 3.45% of second molars. C-shaped canals occurred 0.85% of first molars and 4.1% of second molars. Three canals were found in 79.9% of first molars and 72.8% of second molars. Most distal roots had a simple type I configuration, whereas mesial roots had more complex canal systems, with more than one canal. The most common root morphology of first and second molars is the two rooted morphology with three canals. Both the mesial and distal roots showed wide variations in canal anatomy with type IV and type I canal configuration predominating in the mesial and distal roots, respectively. Conclusion: Vertucci type I and IV canal configurations were the most prevalent in the distal and mesial roots, respectively, of both the mandibular first and second permanent molar teeth. Key words:Cone-beam CT, Turkish, mandibular molars, root and canal morphology.     

Risk Assessment Before Extraction for Immediate Implant Placement in the Posterior Mandible: A Computerized Tomographic Scan Study

Background: Controversy exists in treatment planning relative to the attempt of saving a tooth with unfavorable prognosis or extracting it and placing an immediate or delayed implant. Preextraction radiographic assessments of teeth are traditionally performed using two‐dimensional periapical and panoramic radiographs. These can reveal bone loss around a tooth, but have limited use in assessing implant risk before tooth extraction. Three‐dimensional radiographs or cone‐beam (CB) or computerized tomographic (CT) scans are often taken after tooth extraction and socket healing to assess the healed ridge as a potential implant site. However, when treatment planning for an immediate implant in the posterior mandible, a CT scan taken before tooth extraction can be of value in assessing the available bone and anatomy of the area. This allows the clinician and patient to consider alternative options, such as treating and maintaining the tooth or using a delayed implant protocol, when the site presents a high risk for immediate implant placement (IIP). The purpose of the present study is to assess the prevalence of sites associated with the mandibular second premolar, mandibular first molar, and mandibular second molar teeth that present high risk for IIP using a preextraction CT scan to assess the available apical bone and the anatomy of the posterior mandible in the area of the anticipated extraction site. Methods: One hundred consecutive CT scans were obtained and screened from the New York University College of Dentistry, Office of Quality Assurance–Approved Implant Dentistry Database. Forty‐one of these CT scans were further assessed because they included the presence of ≥2 of the following tooth types: mandibular second premolars, mandibular first molars, and mandibular second molars. Measurements were obtained on the axial sections of the selected teeth to evaluate the amount of bone available apical to the root apices to determine the frequency of sites where an IIP protocol presented a high risk for inferior alveolar nerve injury or lingual plate perforation. Results: Of the 135 teeth assessed from 41 CT scans, 65% of the mandibular second premolars, 53% of the mandibular first molars, and 73% of mandibular second molars had <6 mm of bone available for IIP, presenting high risk for inferior alveolar nerve injury. Of the sites in which the inferior alveolar canal did not limit available bone for IIP, 7% of the second premolars, 9% of the first molars, and 31% of the second molars presented high risk for lingual plate perforation. Conclusions: Preextraction CT scans may present a useful diagnostic aid to assess the risk of inferior alveolar nerve injury and lingual plate perforation for IIP in the posterior mandible. This information may be used for assessing risk when deciding whether to retain a questionable tooth or replace it with an implant with either an IIP or delayed protocol.     

A clinical and histological evaluation of titanium mini-implants as anchors for orthodontic intrusion in the beagle dog.

The aim of this study was to determine the anchorage potential of the titanium mini-implant for orthodontic intrusion of the mandibular posterior teeth. Six mini-implants were surgically placed around the mandibular third premolars on each side in 3 adult male beagle dogs. On the buccal site, three mini-implants were placed distal to the apex of the distal root of the third premolar, at the interradicular septa of the third premolar, and mesial to the apex of the mesial root of the third premolar, as linearly as possible. The same procedure was performed at the lingual site on both sides of the mandibular third premolars in each dog. Bilateral interradicular mini-implants on both the buccal and the lingual sites were used as the anchorage for the intrusion of the third premolars (loaded implants) and the other mini-implants were used as control (unloaded) implants. In 6 weeks, an intrusive force (150 g) was applied between the interradicular implants on the buccal and the lingual sites by closed coil springs run across the crowns of the third premolars. After 12 to 18 weeks of orthodontic intrusion, the animals were killed and their mandibles were dissected and prepared for histologic and fluorescent observation. The results indicated that the mandibular third premolars intruded 4.5 mm, on average, after 12 to 18 weeks of orthodontic force application, with mild root resorption at the furcation area as well as the root apex. All the mini-implants remained stable during orthodontic tooth movement without any mobility or displacement. The morphometrical findings indicated that the calcification of the peri-implant bone on the loaded implants was equal to or slightly greater than those of the controls. In addition, 6 of the 36 mini-implants were removed after tooth movement, and all of them were easily removed with a screwdriver. These findings suggest that mini-implants are effective tools for the anchorage of orthodontic intrusion in beagle dogs.     

Root canal morphology of mandibular first premolars in an Indian population: a laboratory study

Aim  To determine the root canal morphology of mandibular first premolar teeth in an Indian population using a decalcification and clearing technique.
Methodology  One hundred extracted adult mandibular first premolar teeth were studied following decalcification and clearing. The shape of the canal orifice, root canal pattern and length of the teeth were determined.
Results  The mandibular first premolars were identified to have a round orifice (38%), oval orifice (44%), flattened orifice (17%) and C-shaped orifice (1%). The canal patterns were classified as Type I (72%), Type II (6%), Type III (3%), Type IV (10%) and Type V (8%) according to Vertucci's classification. C-shaped canals were identified in one tooth (1%). The average length of the teeth was 21.6 mm. Fourteen per cent of the teeth had mesial invaginations of the root.
Conclusions  Type I canal patterns were the most frequently occurring in mandibular first premolars amongst the Indian population. 85.7% of the teeth with mesial invagination of the root had either two canals or division of canals.     

Bone dimensions in the posterior mandible: a retrospective radiographic study using cone beam computed tomography. Part 1--analysis of dentate sites

This retrospective radiographic study analyzed the dimensions of the alveolar bone in the posterior dentate mandible based on cone beam computed tomography (CBCT) images. A total of 56 CBCT images met the inclusion criteria, resulting in a sample size of 122 cross sections showing posterior mandibular teeth (premolars and molars). The thickness of the buccal and lingual bone walls was measured at two locations: 4 mm apical to the cementoenamel junction (measurement point 1, MP1) and at the middle of the root (measurement point 2, MP2). Further, alveolar bone width was assessed at the level of the most coronal buccal bone detectable (alveolar bone width 1, BW1) and at the superior border of the mandibular canal (alveolar bone width 2, BW2). The vertical distance between the two as well as the presence of a lingual undercut were also analyzed. There was a steady increase in buccal bone wall thickness from the first premolar to the second molar at both MP1 and MP2. BW1 at the level of the premolars was significantly thinner than that for molars. Alveolar bone height was constant for all teeth examined. For the selection of an appropriate postextraction treatment approach, analysis of the alveolar bone dimensions at the tooth to be extracted by means of CBCT can offer valuable information concerning bone volume and morphology at the future implant site.     

Anatomic Study of Mandibular Posterior Teeth Using Cone-beam Computed Tomography for Endodontic Surgery

Introduction

The present study aimed to anatomically assess mandibular posterior teeth using cone-beam computed tomographic (CBCT) imaging for endodontic surgery.

C-shaped root canal in a maxillary first molar: a case report

AIM: This case report presents an unusual C-shaped root canal system in a maxillary first molar tooth. SUMMARY: Although C-shaped root canals are most frequently seen in the mandibular second molar, they may also appear in maxillary molars. A literature search revealed only a few case reports of C-shaped root canal systems in maxillary molars. The present case describes a C-shaped canal in the buccal root of a maxillary first molar. The endodontic access cavity displayed two canal orifices, one leading to the canal system in the buccal root, the other into the palatal root canal system. In the buccal root, what appeared to be the mesial and distal canals joined to form a single C-shaped canal. KEY LEARNING POINTS:--Careful examination of radiographs and the internal anatomy of teeth is essential.-- The location and morphology of root canals should be identified at high magnification under the microscope.     

华东地区汉族人下颌第一前磨牙根管弯曲度的测量

目的 采用显微CT精确测量下颌第一前磨牙根管的弯曲度,为临床根管治疗提供依据。方法 收集华东地区汉族人154颗离体下颌第一前磨牙并进行显微CT扫描,采用Mimics 10.01（Materialise,Leuven,比利时）对牙齿及根管系统进行三维重建,在平行投照模式下,采集根管系统颊面观及邻面观的影像并测量根管的弯曲度。结果 下颌第一前磨牙单根管在颊面观上初次弯曲的平均角度仅为11.1°（Schneider法）,二次弯曲出现率较低,在颊面观出现6例,邻面观出现4例。下颌第一磨牙双根管时,重度弯曲（>20°）主要位于邻面观,颊、舌根管初次弯曲的平均角度分别为17.5°和28.7°,二次弯曲的发生率分别为19.1%（9/47）和85.1%（40/47）。舌侧副根管的弯曲半径和圆心角均值分别为6.6 mm和54.2°;舌侧根管的根管口离根尖的平均距离为6.6 mm。结论 下颌第一前磨牙舌侧根管多出现在根中及根尖1/3,在邻面观常有重度弯曲。     

不同方法研究第一、第二磨牙的根管解剖形态

目的研究第一、第二磨牙根管解剖特点,为提高根管治疗的效果提供解剖学根据。方法采用肉眼、放大镜、牙科显微镜和透明牙标本观察四种方法,研究第一、第二磨牙的根管解剖特点。结果①经χ2检验,肉眼与放大倍数下对上颌第一磨牙近中颊侧第二根管（MB2）的检出率在统计学上有显著性差异（P〈0.05）。②152颗离体牙中,上颌第一磨牙64.91%存在MB2,下颌第二磨牙21.21%为＂C＂形根管。70.83%～77.55%的根尖孔为侧向开口。结论熟知第一、第二磨牙根管解剖特点对根管治疗的临床操作有指导意义。     

Root and canal morphology of the mesiobuccal and distal roots of permanent first molars in a Kuwait population--a clinical study

Aim To identify the number of roots and canal configurations in permanent first molars of the indigenous Kuwaiti sub‐population and compare them against a similar group of non‐Kuwaiti population in different age groups and gender, and to determine the frequency of a second canal in the mesiobuccal root of maxillary first molars and distal root of mandibular first molars that could be located and treated in routine practice without using magnification or special lighting conditions. Methodology A total of 220 permanent first molar teeth of patients scheduled for root canal treatment over a period of 1 year were included. Patients were identified and grouped according to their nationality as Kuwaiti and non‐Kuwaiti (which included Filipinos, Indonesian Indians, Srilankans, Egyptians, Saudi Arabians and Syrians). In both nationality groups, patients were successively distributed into four groups based on their age. The first age group included patients below 20 years, the second 21–30 years, the third 31–40 years and the fourth were over 40 years. The first three groups comprised of 15 male and 15 female patients whilst the fourth group had 10 patients of each gender. Teeth with open apices, resorptions and calcification were excluded from the study. The teeth included were both clinically and radiographically examined for number of roots, the canal configuration and the presence of the additional mesiobuccal and distal canals and recorded. The simplified classification of canal configurations proposed by Weine was utilized. Results The incidence of a second canal in the mesiobuccal (MB) root of maxillary first molars and the distal root of mandibular first molars was not influenced significantly by nationality and gender. All the 110 maxillary first molars treated had three roots; 58% of MB root had one canal and 42% had two canals. The majority of the mesial roots had Weine type II canal configuration when the second mesiobuccal canal was present. All distobuccal and palatal roots had a single or type I canal configuration. Of the 110 mandibular first molars that were treated, 96% had two roots and 4% had three roots. When present, the third root was located either buccal or lingual to the main distal root. Overall 51% of the single distal roots had one canal whilst 49% had two canals. The mesial root frequently had a Weine type II canal configuration as did the distal root when a second canal was present. Pearson’s correlation analysis of both molars revealed a significant (P < 0.05) negative correlation (r = ?0.274, r = ?0.144) between age and number of canals as well as the type of canal. Conclusions The incidence of a second canal in distal roots of permanent mandibular first molars was 49% in the Kuwaiti population and this was similar to other Asian ethnic populations. Adopting modified access and troughing procedures revealed a 42% frequency of MB2 canals in maxillary first molars. The incidence of a second canal in both mesiobuccal roots of maxillary molars and distal roots of mandibular molars decreased significantly with age; no differences were noticed amongst the nationalities and gender studied. The possibility of extra roots should be anticipated in mandibular molars.     

Root and root canal morphology of permanent mandibular first and second molars in a Kuwaiti population: A retrospective cone-beam computed tomography study

AimEndodontic diseases typically affect the mandibular molars. Understanding the complex morphology of the root canal system and its variations is necessary for successful endodontic treatment. The aim of this study was to evaluate the morphology of roots and root canals of mandibular first and second permanent molar teeth in a Kuwaiti population using cone-beam computed tomography (CBCT).Materials and methodsCBCT images of 651 mandibular first and second molar teeth were obtained from specialist government dental centers. The age, sex, root canal configuration, and number and type of roots were recorded. The data were statistically analyzed.ResultsThe most common canal configuration in the mandibular first and second molars was type II (65.6% and 54.4%, respectively), with no significant difference seen between the sexes (p = 0.234). The canal configuration was significantly different between the mandibular first and second molars (p < 0.001). Most teeth had two roots (94.5%); split roots were common (92.6%) and the number thereof varied significantly. Radicular grooves were most common on the lingual side (4.9%). C-shaped canals were present in 43 (6.60%) teeth. Additionally, one tooth had a confluent middle mesial canal and nine (1.4%) had radix entomolaris.ConclusionMandibular molars in our Kuwaiti population typically had two split roots with type II and IV canal configurations. The prevalence rates of C-shaped canals, middle mesial canals, and radix entomolaris were remarkably low.     

下颌第一磨牙种植体解剖式愈合基台的设计与制作

目的探讨下颌第一磨牙种植体解剖式愈合基台的设计与制作,为临床上提供更多愈合基台的选择。方法利用Shining扫描仪技术对离体下颌第一磨牙扫描获得牙颈部的颊舌径和近远中径数据,以及天然离体牙4个轴面牙颈部的坡度数据;统计分析数据后利用计算机辅助设计/计算机辅助制造(computer aided design/computer aided manufacturing,CAD/CAM)原理设计制取下颌第一磨牙解剖式愈合基台。结果测得下颌第一磨牙离体牙釉牙骨质界(cementoenamel junction,CEJ)向下1 mm近远中径与颊舌径均值为(8.54±0.78)mm、(7.87±0.86)mm,离体牙颊、舌、近中、远中各轴面牙颈部坡度分别为17.53°、14.41°、13.40°、13.43°,根据下颌第一磨牙天然牙缩小一定比例获得3种不同周径高度为5 mm的解剖式愈合基台。结论利用Shining扫描及CAD/CAM技术可快速获得下颌第一磨牙解剖式愈合基台。     

因重度牙周炎拔除的磨牙根分叉形态测量及根柱凹陷发生率的调查

目的 :了解因重度牙周炎拔除的磨牙根分叉形态及根柱凹陷的发生情况。方法 :对因重度牙周炎拔除的 3 0个上颌第一磨牙 ,15个上颌第二磨牙 ,3 0个下颌第一磨牙及 10个下颌第二磨牙进行测量 ,记录牙根长度(RL) ,根柱长度 (RTL) ,釉牙骨质界处的近远中径 (MDD)和颊舌径 (BLD) ,根柱凹陷的有无 ,釉牙骨质界到根柱凹陷的距离及根分叉开口下 2mm的宽度。结果 :①无论是上颌还是下颌磨牙 ,第一磨牙牙根长度及根柱长度均较第二磨牙短 ,而第一磨牙颊舌径、近远中径及根分叉开口下 2mm处宽度均较第二磨牙大 ,其中仅 4.71%的牙根分叉开口下 2mm处宽度小于 0 .75mm。②上颌磨牙根柱凹陷发生率高于下颌磨牙 ( p <0 .0 5 ) ,且 89.41%的牙至少在一个面上从根柱凹陷到釉牙骨质界的距离为零。结论 :根柱凹陷可能是造成根分叉病变的原因 ,并可能是导致牙周治疗效果欠佳的原因。