成人牙根唇舌侧牙槽骨的厚度

doi:10.3969/j.issn.2095-4344.2013.15.008

中国组织工程研究

• 口腔组织构建 oral tissue construction • 上一篇下一篇

成人牙根唇舌侧牙槽骨的厚度

丁继群¹，方建强²，袁昌青¹，陈杰¹

1青岛大学医学院附属医院口腔科，山东省青岛市 266003；
2杭州口腔医院正畸中心，浙江省杭州市 310006

收稿日期:2012-11-04 修回日期:2012-11-05 出版日期:2013-04-09 发布日期:2013-04-09
通讯作者: 通讯作者：袁昌青，硕士，副主任医师，主要从事口腔临床医学的研究，青岛大学医学院附属医院口腔科，山东省青岛市 266003
作者简介:丁继群★，女，1977年生，安徽省宣城市人，汉族，2009年温州医学院毕业，硕士，主要从事口腔临床医学的研究。

Labial and lingual alveolar bone thickness of adult tooth root

Ding Ji-qun¹, Fang Jian-qiang², Yuan Chang-qing¹, Chen Jie¹

1 Department of Stomatology, Affiliated Hospital of Qingdao University Medical College, Qingdao 266003, Shandong Province, China
2 Department of Orthodontics, Hangzhou Stomatological Hospital, Hangzhou 310006, Zhejiang Province, China

Received:2012-11-04 Revised:2012-11-05 Online:2013-04-09 Published:2013-04-09
Contact: Yuan Chang-qing, Master, Associate chief physician, Department of Stomatology, Affiliated Hospital of Qingdao University Medical College, Qingdao 266003, Shandong Province, China chenfjq2010@163.com
About author:Ding Ji-qun★, Master, Department of Stomatology, Affiliated Hospital of Qingdao University Medical College, Qingdao 266003, Shandong Province, China chenfjq2010@163.com

摘要/Abstract

摘要：

背景：牙根在牙槽骨的位置及周围骨板厚度影响着口腔治疗，治疗过程中如果对牙齿控制不当可造成医源性并发症。以往对颌骨的研究主要针对解剖学、骨厚度或骨密度，对于牙根在牙槽骨内的空间位置及其与周围骨骼的关系，研究关注较少。
目的：建立颌骨的数字化计算机三维模型，测量牙根的唇舌侧牙槽骨厚度。
方法：选择牙列完整无明显骨骼吸收的年轻成人70例，采用牙科专用锥形束CT机进行颌面部扫描，将扫描中采集的容积信息传入计算机工作站，以及冠状位或矢状位多平面重建，获得高质量的重建图像，原始数据以DICOM格式导入计算机，并输出到整合的3D设计软件Invivo5软件进行测量。
结果与结论：重建的颌骨数字化模型可从多平面进行观察及测量，实验测得70 例患者各个牙根唇舌侧牙槽骨厚度的均值：上下前牙舌侧牙槽骨厚度大于唇侧(P < 0.05)；除上前磨牙的牙颈部唇侧牙槽骨较厚外, 其他前磨牙舌侧牙槽骨厚度大于唇侧(P < 0.05)；上磨牙和下颌第一磨牙唇舌侧牙槽骨厚度接近，下第二磨牙唇侧牙槽骨厚度大于舌侧(P < 0.01)。结果证实，成人不同牙位的唇舌侧牙槽骨厚度差异较大。

关键词: 组织构建, 口腔组织构建, 锥形束CT, 牙根, 牙槽骨, 舌侧, 颊侧, 厚度, 正畸, 牙齿移动, 拔牙, 牙折

Abstract:

BACKGROUND: Oral treatment is affected by the root position and the surrounding bone plate thickness of the alveolar bone, and the improper teeth control can cause iatrogenic complications. The scholars have conducted the research about the jaw, such as anatomical observation, bone thickness or bone density. However, the research regarding the spatial position of the root within the alveolar bone and its relationship with the surrounding bone is less of a concern.
OBJECTIVE: To establish a digital three-dimensional computer model of the jaw, and then to measure the thickness of labial and lingual alveolar bone around the tooth root, providing a reference for orthodontic tooth movement design and tooth extraction.
METHODS: A total of 70 young adult orthodontic patients were selected with complete dentition and with no bone absorption shown on panoramic radiographs. The maxillofacial region was scanned using dental cone beam CT machine. Collected data were input into a computer workstation to implement coronal or sagittal multi-planar reconstruction with high-resolution three-dimensional images, and then raw data at DICOM format were outputted to the integrated three-dimensional design software, Invivo5 software, for measurement.
RESULTS AND CONCLUSION: The digital and virtual reconstruction model of the jaw could be observed and measured from the multi-plane, and the mean alveolar thickness was measured with every root in 70 patients. The mean lingual alveolar bone thickness of anterior tooth was thicker than the labial (P < 0.05). Besides the dental cervix of upper premolars, the mean lingual alveolar bone thickness of premolars was thicker than the labial (P < 0.05). There were no differences when the bilateral measurements were compared for upper molars and mandibular first molar (P > 0.05), but a significant difference between labial alveolar bone and lingual alveolar bone was noted in the mandibular second molar (P < 0.01). The results confirmed that the significant difference exists between lingual and labial alveolar bone thickness of the young adults at different tooth positions.

Key words: tissue construction, oral tissue construction, cone-beam CT, root of tooth, alveolar bone, lingual, buccal, thickness, orthodontics, tooth movement, tooth extraction, tooth fracture

中图分类号:

R318

丁继群，方建强，袁昌青，陈杰. 成人牙根唇舌侧牙槽骨的厚度[J]. 中国组织工程研究, doi: 10.3969/j.issn.2095-4344.2013.15.008.

Ding Ji-qun, Fang Jian-qiang, Yuan Chang-qing, Chen Jie . Labial and lingual alveolar bone thickness of adult tooth root[J]. Chinese Journal of Tissue Engineering Research, doi: 10.3969/j.issn.2095-4344.2013.15.008.

图/表（结果） 2

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引言

Improper operation or physicians are not familiar with patient’s anatomy can result in iatrogenic complications such as root absorption and root out of the alveolar bone during orthodontic treatment process[1] as well as root rupture or alveolar bone fracture during extraction process.
Orthodontic braces are used in orthodontics to align and move teeth to the desired positions
with regard to a person’s bite. Alveolar bone defects are very common prior to orthodontic treatment[2]. During tooth movement, three-dimensional cone-beam CT images are important to avoid iatrogenic periodontal support loss of anterior teeth, especially the lingual bone
plate of lower incisors[3].

Anchorage control is a key determinant for the success of orthodontic treatment, while movable anchorage is often ineffective because of poor cooperation from patients. Mini-implant anchorage as an “absolute anchorage” has been widely favored by clinicians, but how to safely and effectively use it is a clinical issue of concern. Mini-implants are small in size and easy to be implanted into most region of the jaw as needed. It is crucial to avoid some important anatomic structures during implantation, such as the mandibular canal, maxillary sinus and root, then to find a safe area, thereby improving the success rate of the mini-implant and reducing complications. In purpose of providing guidance for the use of mini-implants, clinical studies have been focused on the bone mineral density[4-5] and cortical bone thickness[6-7].

Oral implantology is a minimally invasive surgery involving alveolar surgery that implants dental implants into the alveolar bone with the edentulous ridge (artificial tooth root), to prepare implant-supported dentures and complete dental restorations till implant survival after implantation. Implant-supported dentures that have been widely used can significantly improve patient’s chewing function and feeling similar to natural teeth. Tooth socket depth and alveolar ridge width are the anatomical basis of alveolar surgery and dental implant design and application. Anatomical observations of the permanent tooth sockets of skull specimens show that the mandibular fossa is not connected with the inferior alveolar tube, while it is common seen that the tooth sockets of the maxillary posterior teeth are interlinked with the maxillary sinus; the alveolar ridge in the molar area is the widest, which is corresponding to the function of the teeth, stress distribution of the jaw bone and its internal mechanical structure. Fully understanding alveolar bone height, width, density, shape and adjacent anatomical structures prior to implantation is to ensure the success of oral implantology. Generally, the panoramic X-ray film and tooth model are used to the assessment and planning of surgical implants, but the panoramic radiograph is a two-dimensional image that can enlarge images to some extent and result in anatomical distortion, thereby impacting the design accuracy.

Cone-beam CT offers an undistorted three-dimensional view of the implanting area that can be used to accurately locate the examined site and its surrounding anatomical structures, determine bone mineral density, measure the line distance and angle, and simulate implanting design of surgical implants, which greatly increases the implantation accurate. CT images of the alveolar ridges and corresponding teeth are useful for the designation and preparation of surgical guides for dental implants, placement, depth and direction of template guide holes, as well as implanting angle[8]. Alveolar bone thickness data relevant to the Chinese people are less, and maxillofacial anatomical differences exist between nationalities, therefore which should be considered when conducting oral implantology and maxillofacial surgery.

The three-dimensional reconstruction using spiral CT technology is very effective in the diagnosis of diseases, but the higher inspection costs and the larger body irradiation dose limit its clinical use. Spiral CT runs via a fan-beam scanning and the resolution is relatively low. In particular, it is unsatisfactory to image the fine structure of the bone[9]. In addition, the spiral CT is easy to produce volume effects and radial artifacts when scanning tissues with large interface and poor density. Cone-beam CT is the fifth generation of CT technology, and runs via a cone beam scanning, which greatly improves the scanning speed, axial ray utilization efficiency and reconstructed image resolution, as well as use fewer rays and has no amplification errors[10]. The cone-beam CT is also insensitive to the movement artifacts, applicable to dynamic space reconstruction.

The present study enrolled 70 patients undergoing cone-beam CT reconstruction and measurement of CT scan measurements, and then we positioned the root in the alveolar bone and measured labial and lingual alveolar bone thickness, in purpose of providing a reference for clinical orthodontics and alveolar surgery.

材料方法

Design
A observational experiment.

Time and setting
The experiment was conducted in the Department of Orthodontics, Hangzhou Stomatological Hospital, China from October 2010 to May 2012.

Subjects
Seventy adult patients with malocclusion from the Department of Orthodontics, Hangzhou Stomatological Hospital were enrolled, including 35 females and 35 males.

Inclusive criteria
Patients aged 18-25 years had complete dentition in the study area (excluding third molars) confirmed via clinical and X-ray examination, and presented no significant bone absorption (Figure 1).

Exclusion criteria
Patients with dental disease, apical shadow, jaw cysts or tumors were excluded. Patients who took drugs affecting bone metabolism within 6 months or those with hyperthyroidism and diabetes mellitus were excluded.

All subjects were informed about the experimental program and its potential risks before starting and informed consent was obtained according to the Administration Regulations of Medical Institution, formulated by the State Council of China[11].

Experimental instruments for measurement of adult alveolar bone thickness are as follows.

Methods
Cone-beam CT scanning and establishing a digital three-dimensional model of the adult jaw
Dental cone beam CT machine was adopted for maxillofacial scanning. Patients sat to place their heads on the scan head frame, and the infraorbital line was parallel to the ground.

Scanning parameters: Tube voltage 120 kV, tube current 5 mA, field of view 13 cm×16 cm, standard scanning exposure time: 8.9 seconds, slice thickness 0.2 mm. A multi-plane reconstruction mode was employed for sagittal, coronal, axial plane and three-dimensional image reconstruction with reconstruction thickness of 0.2 mm. Images were saved at DICOM format. Reconstructed model was a high-definition three-dimensional image, could be used for three-dimensional cephalometric analysis, as well as the traditional two-dimensional measurement, which is better than the routine analysis means and convenient to transfer all images into digitized dental models.

Cone-beam CT images could accurately position the teeth, and visualize the teeth within the alveolar bone, its relative position corresponding to adjacent teeth and important adjacent anatomical structures, such as the mandibular canal, maxillary sinus wall and cortical bone boundary, providing a reference for location of the implant and dental abutment as well as for accomplishment of the whole repair process. This three-dimensional model could be arbitrarily rotated, scaled, of perspective, and sectioned to observe a part of the model using different planes and bodies. It could not only increase the diagnostic accuracy of positioning, but also improve the accuracy of qualitative diagnosis, as shown in Figure 2.

Measuring the labial and lingual alveolar bone thickness of the tooth root and relevant parameters
In vivo 5 image analysis software was employed for three-dimensional image processing. Reconstruction images were cut according to the reference line and angle, and alveolar bone thickness was measured according to Lee’s method[12], as shown in Figure 3.

Measurement parameters for labial and lingual alveolar bone thickness are as follows.

(1) Thickness of the alveolar bone plates Measurement method.
(2) Labial alveolar bone thickness of the dental cervix: the distance from the most former (outside) point to the most-back (inner) point along the cervix vertical line.
(3) Lingual alveolar bone thickness of the dental cervix: the distance from the most former (outside) point to the most-back (inner) point along the cervix vertical line.
(4) Labial alveolar bone thickness of the middle of the root: the distance from the most former (outside) point to the most-back (inner) point along the central vertical line of the root.
(5) Lingual alveolar bone thickness of the middle of the root: the distance from the most former (outside) point to the most-back (inner) point along the central vertical line of the root.
(6) Labial alveolar bone thickness of the root apex: the distance from the most former (outside) point to the most-back (inner) point along the apical vertical line.

Measurement of parameters is shown in Figures 4-6.

Main outcome measurements
Labial and lingual alveolar bone thickness of the dental cervix; labial and lingual alveolar bone thickness of the middle of root; labial and lingual alveolar bone thickness of the root apex.

Statistical analysis
Measurement data were expressed as mean±SD, and data analysis was performed using SPSS 17.0 statistical software. Mean differences between groups were compared using paired t-test, and a value of P < 0.05 was considered significant.

讨论

Teeth are positioned in the tooth socket of the alveolar bone, and the root of teeth is enveloped with the alveolar bone inherent onto the peripheral wall of the tooth socket, which is the foundation for the stable location of the tooth within the mandible. Meanwhile, the tooth root is strictly limited by the anatomical structure of the bone and soft tissue.

Reliability of cone-beam CT and features of the alveolar bone
Reliability of cone-beam CT
Conventional anatomy is mainly focused on the maxilla general form, and there is lack of therapeutic guidance for clinical orthodontics and alveolar surgery. X-ray imaging is an important means of research. However, because of the serious overlap of the two-dimensional images, such as conventional cephalometric films, low resolution, and high radiation, ordinary CT cannot clearly display the fine structure of local bone tissues and any tooth points, leading to physician’s difficulty in determining the relationship between the teeth and surrounding structures[13-14]. Cone-beam CT provides the best choice[9, 15-18]. Domestic scholars have reported cadaveric anatomic studies focusing on the alveolar height[19], and CT studies of bone mineral density[4-5] and cortical bone thickness[6-7]. But, there is still a lack of data regarding the spatial location of the root within the alveolar bone and its relationship with the surrounding bone, which is worthy of attention.
Cone-beam CT is flexible for three-dimensional imaging, minimizes the radiation dose to obtain high-resolution three-dimensional scanning results, provides a smooth soft tissue image, displays the hard tissue and bone structure detail and contrast to the maximal extent, and clearly show the tooth, root apex, alveolar bone, maxillary sinus and mandibular canal, providing a full range of diagnostic information for dental, periodontal, implanting, orthodontic, maxillofacial surgery, and repair treatment[20]. Cone-beam CT has high resolution[8], clear image quality, shorter scan time, and low ray dose[21-22] to supply low-radiation-dose and high-definition images for dentistry, greatly improving the diagnostic accuracy and cure rates of oral diseases, with a wide range of applications.

Characteristics of labial and lingual alveolar bone thickness of the tooth root
Gross observation showed non-equivalent thickness of the labial/buccal and palatal/lingual bone plates of the maxillary tooth socket. The present study found that labial bone plate thickness of the upper teeth showed a gradual thickening from front to back, while the lingual bone plate thickness gradually decreased at the middle and apex of the tooth root, especially in the cervical part of the canine and first premolar at the lingual side and in the root middle of the first and second premolars at lingual side, showing a narrowing phenomenon. Labial/lingual bone plates of the lower teeth gradually thickened from front to back, showing a gradual thickening tendency from the cervical to the apical side. This measurement results were consistent with those of Zhao et al [23].

Labial/lingual alveolar bone thickness in the same tooth position showed significant difference in the thickness of labial/lingual bone plates of the maxillary anterior teeth, that is, the lingual bone plate was thicker than the labial bone plate at the tooth neck, and also dramatic difference existed in the middle and apex of the teeth. These findings are consistent with cone-beam CT studies[24-25].

Mandibular anterior teeth had the greater lingual bone plate thickness than the labial. It was noted that patients exhibited no bone-covered labial bone plate of the neck of the mandibular anterior teeth on the cone-beam CT images during orthodontic treatment of anterior tooth malocclusion[2-3]. The stress of the periodontal ligament gradually increased with the loss of the alveolar bone, and patients with alveolar bone resorption should pay attention to tooth apex health. Maxillary and mandibular premolars exhibit thicker labial and lingual bone plates at the tooth neck, respectively. Lingual bone plates at the middle and apex of the premolars were thicker than the labial ones. Maxillary molars had similar lingual bone plate thickness as the mandibular first molar. For the mandibular second molar, the labial bone plate at the tooth neck was thicker than the lingual. The lingual bone plate at the apex of the posterior mandible was thicker, exhibiting the physiological sexual lingual inclination of the posterior mandible.

Importance of the alveolar bone to orthodontic treatment and periodontal health
The scope and significance of orthodontic tooth movement
No definitive conclusion has been defined for the scope of orthodontic tooth movement. Concept of dentition boundaries gives a rough reference for orthodontic tooth movement, but，with regard to disputes, there is no quantitative standard. Generally, thickness of the alveolar bone around the root is considered as the boundary of tooth movement that refers to the dense cortical bone plate at the same level. Apical tooth movement should not exceed this boundary. Lingual alveolar bone plate of the lower incisors was significantly thicker than the labial, confirmed by CT measurements[2]. The lingual alveolar bone plate of the upper incisors was thicker than the labial thicker, indicating that appropriate incisor adduction can improve the prognathism face commonly seen in Chinese people[1]. It is often necessary to control the root of the maxillary anterior teeth facing to the tongue, but the key is to grasp the adductor limit and anatomy restrictions for the alveolar bone cannot be ignored. Excessive adduction can result in the contact between the root and dense cortical bone plate to increase the risks. The labial bone plate of the neck of the anterior teeth, especially the lower incisors, was very thinner, and even presented no bone coverage; and a thinner bone plate was also found at the labial side of the middle of the root. During the process of tooth movement, biological alterations in the alveolar bone are mainly focused on bone resorption, and bone hyperplasia is very limited[26], prompting that we will attach importance to the labial inclination of the anterior teeth. Excessive labial inclination can result in gingival recession, washboard-shaped root and even fenestration of the tooth apex via the alveolar bone plate. In the present study, the alveolar bone thickness of the maxillary first premolar at the root neck was (1.35±0.67) mm, and the labial bone plate thickness of the first molar at the root neck was (2.85±0.80) mm. During rapid palatal expansion, it should pay attention to preventing against dehiscence and gingival recession in elderly patients. In clinical orthodontic tooth movement, in particular, in patients accompanied with a certain degree of bone abnormalities, conceal orthodontic treatment often requires a certain compensation for the location and angle of the teeth[27]. It should pay attention to the relationship between the root and the alveolar bone, especially in high-risk groups with poor anatomical structures and periodontal status. When necessary, CT assessment can be used to prevent against iatrogenic problems that affects tissue health and treatment stability[28].

Implant design and the significance of orthodontic anchorage screws
Labial area of the maxillary second premolar and first molar is the most common region for orthodontic anchorage screw implantation[29-31]. In the present study, the region with the thickest buccal bone plate was the appropriate site for orthodontic anchorage screw implantation. The labial bone plate at the root apex of the maxillary second molar was thinner than that of the maxillary first molar, which is inconsistent with the result of Liou et al [32]. It is likely associated with the observed region in the present study only focusing on the apical parts rather than the zygomatic crest area. Under the relevant tips from Lin et al [33], orthodontic anchorage implantation outside of the tooth root should be carefully performed at the maxillary first and second molar area to move the upper dentition as a whole. However, the number of cases may be low for this method. The maxillary palatal space is generally higher than the labial, providing more space for implantation. The second premolar region is the thickest in the palatal parts of the maxillary posterior teeth, suggesting patients who are difficult in buccal application can select this region for implantation. The buccal parts of the mandibular molars, especially the buccal bone plate of the mandibular second molar, significantly become thicker, rendered as a platform, which is called as “buccal shelf area”[34]. In fact, the corresponding anatomical structure is the external oblique, providing sufficient implant space, which is an ideal area for anchorage screw implantation.

Force direction for tooth extraction and its significance
Root fracture is the most common complication of tooth extraction surgery, which is mainly caused by no fully understanding about anatomical structures surrounding the extracted teeth and use of violence. Extraction force should be applied directing to the small bone resistance and avoid violence. This study showed that the lingual bone plates of the root of the anterior teeth and premolars were generally thicker than the labial; the palatal bone plate of the maxillary molar region was significantly thickened, indicating that extraction force should be applied towards the labial and buccal sides, to avoid bone resistance. Meanwhile, extraction force should be soft to avoid root fracture and even damage to the maxillary sinus, as the root of the maxillary molar was approaching the maxillary sinus[35]. Because of the obvious thickening of the buccal bone plate in the mandibular molar region, extraction force should lean to the lingual part with small bone resistance, which is conducive to tooth dislocation, and not easy to cause root fracture or jaw fracture[36].

In short, there exists a great difference between the labial/lingual bone plate thickness in different tooth positions, which affects implantation of anchorage screws, and tooth movement range and manner. It should pay attention to the range of orthodontic tooth movement during conceal orthodontic treatment to avoid excessive compensation or randomized over-correction. Direction for extraction force and tooth dislocation should be selected depending on tooth position, which is the direction of small bone resistance.

成人牙根唇舌侧牙槽骨的厚度

Labial and lingual alveolar bone thickness of adult tooth root

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