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Measurement of Buccal Bone Plate Thickness Using C

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    RESEARCH ARTICLES

    Measurement of Buccal Bone Plate Thickness Using Computed Tomography in Maxillary Tooth

    Guangchun Jin, Youcheng Yang*

    Abstract: The distance from the apex to the buccal bone plate was measured from the computed tomography (CT) images of 1,806 teeth from 66 patients who were treated in the department of Oral & Maxillofacial Surgery at Dental Hospital affiliated to Binzhou Medical College in order to evaluate their accessibility during apical surgery. An image analyzer program (Image-Pro Plus, Ver. 4.0, Media Cybernetics, U. S. A.), optic lens, and digital caliper (Mitoutoyo Co, Tokyo, Japan) were used. The distance between the apex to either the buccal bone plate or the lingual bone plate was measured from the axial CT images for each tooth. The measurements were averaged and divided according to gender. In the maxilla, the largest distances from the second molar mesio-buccal and disto-buccal root to the buccal bone plate were 4.63mm and 3.61mm, respectively. The other measurements were < 3mm. In particular, the anterior teeth were all < 2mm. The average distances from the palatal apex in the maxillary first molar and the second molar to the buccal bone plate were 10.69mm and 10.17mm, respectively. The average distances from the palatal apex to the palatal bone plate in the maxillary first and second molars were 3.15mm and 3.08mm, respectively. Sometimes the lingual approach, bony lid approach or replantation needs to be made when there is a surgical need in the second molar and the disto-lingual root of maxillary molars because the normal buccal bone approach and retrograde filling would not be feasible. When it comes to diagnosis, the axial CT images were quite helpful in determining the spatial relationship between the apex and surrounding bone compared with the conventional radiographs, which means that it would be ideal to take a CT for each apical surgery case.

    Key words: apical surgery; computed tomography; buccal bone plate; surgical approach

    The appropriate method for accessing and securing the surgical field is very important for accurate apical surgery. Manipulating the surgical instruments and securing the surgical field are limited in many ways during apical surgery, which is performed in a cramped space and in a bleeding situation. From a clinical point of view, the thickness of the buccal bone plate is always of concern. Obtaining good surgical accessibility becomes increasingly difficult particularly when the buccal bone plate is thick such as in the mandibular molars or palatal roots of the maxillary molars. If a large amount of buccal bone plate needs to be sacrificed in order to reach the apex by boring through the thick buccal bone plate, the overall prognosis for the tooth can become poor even after successful apical surgery. Moreover, the root canal isthmus can still remain open even when the apex is reached reasonably but retrograde filling is not performed appropriately. The same problems are also encountered in the palatal root of the maxillary molars that is remote from the buccal bone plate. Although the approach differs according to the ability of each practitioner, either the lingual approach or replantation is recommended to secure the appropriate retrograde filling [1, 2]. However, lingual surgery is also restricted when there is a nearby dangerous anatomical structure such as a greater palatine foramen. Therefore, it is important to be familiar with the anatomical structure of the buccal bone plate when planning apical surgery.

    CT provides valuable information about the jawbone anatomy and the root apex before apical surgery. Sliced or reconstructed CT images show the detailed structure of the tooth from various directions [3-6]. The diagnostic value of CT is expected to increase because of its being able to show 3-D images of the tooth location and apex anatomical structure for apical surgery. The aim of this study was to evaluate the accessibility of each tooth during apical surgery by measuring the anatomical distance from the apex to either the buccal or lingual bone plate on CT in the China population.

    MATERIALS AND METHODS

    66 patients (1, 806 teeth), who underwent a CT examination at the department of Oral & Maxillofacial Surgery at Dental Hospital affiliated to Binzhou Medical College, were enrolled in this study. The subjects included 33 men and 33 women, whose ages ranged from 14 to 80 years (average age: 37 years for men and 35 for women). Those patients with the prosthesis, the restoration or the third molar that may hinder the measurements, along with those showing vague CT images were excluded.

    1. CT data collection

    The CT images were obtained using a CT Hi-Speed Advantage (GE Medical System, Milwaukee, U.S.A.) at the Department of Oral and Maxillofacial Surgery at Dental Hospital affiliated to Binzhou Medical College by taking 1mm thick serial cross-sectional slice images under a high-resolution bone algorithm with a 9.6cm diameter field of view (DFOV) at 200mA and 120 kV for 1 sec. A gantry angulation of 0 was used, and the reconstruction matrix contained 512x512 pixels.

    2. Apex confirmation, measured items and method of measurement

    In order to measure the apex on the 1mm cross sectional axial CT images, the last root apex observed on the previous cross section but no longer observed in the next image was considered the apex. When there were two mesial root canals, the center of the line connecting the two canals was used as the reference. The measurements were made using a digital sliding caliper (Mitutoyo Co., Tokyo, Japan) up to 1/20mm detail. In order to compensate for the magnification of the radiographic images, the measured values were converted according to the measured values from CT to calculate the actual distance (Fig.1).

    Fig. 1 Maxillary axial CT images for measurement

    a: Distance between the central incisor, lateral incisor, 2nd premolar apex and the buccal bone plate. MB: Distance between the first molar mesial apex and the buccal bone plate; DB: Distance between the first molar distal apex and the buccal bone plate. b: P(B): Distance between the first molar palatal apex and the buccal bone plate; PP: Distance between the first molar palatal apex and the palatal bone plate. c: Distance between the canine apex and the buccal bone plate.

    3. Statistical analysis

    The non-parametric Kruskal Wallis test (Chi-Square Approximation) is performed using the SAS 6.12 version to evaluate the statistical significance of the distance from the apex to the buccal and lingual plates according to gender. The difference is significant at the levels of p<0.05.

    RESULTS

    From the buccal root, the distances from the mesiobuccal and distobuccal root of the maxillary second molar to the buccal bone plate were the largest at 4.63mm and 3.61mm, respectively. The remaining maxillary teeth were < 3mm, and were within 2 mm particularly with the anterior teeth. When the palatal root was present, the distances between the buccal and palatal root of the first and second premolars were 4.15mm and 3.94mm, respectively. The average distances from the palatal apex to the buccal bone plate in the maxillary first molar and second molar were 10.69mm and 10.17mm, respectively. The average distances between the palatal apex and the palatal bone plate in the first and second molars were 3.15mm and 3.08mm, respectively (Table 1).

    Table 1. Distance between the root apex to the outer surface of the buccal

    and palatal cortical plate in maxilla

    MaxillaCentral

    incisorLat, incisorCanine1st premolar2nd premolar1st molar2nd molarRoot areaR (2)R (1)R (2)R (1)MDP (B)PPR (3)R (2)FRBP (B)BP (B)MDP (B)PPMP (B)PP

    Male

    2.02

    

    0.471.78

    

    0.401.62

    

    0.411.94

    

    0.514.56

    

    1.362.17

    

    0.722.36

    

    0.844.43

    

    1.713.32

    

    1.423.12

    

    1.172.92

    

    2.4210.75

    

    2.423.17

    

    1.054.77

    

    1.343.70

    

    1.2010.34

    

    1.873.19

    

    0.954.09

    

    1.20

    8.9

    

    3.49

    3.59

    

    1.016.37

    

    1.80Female2.09

    

    0.511.89

    

    0.541.66

    

    0.481.42

    

    0.493.74

    

    1.332.22

    

    0.631.62

    

    0.543.44

    

    1.503.43

    

    1.342.82

    

    0.982.54

    

    1.0510.64

    

    2.663.14

    

    1.074.49

    

    1.323.52

    

    1.0210.01

    

    2.842.98

    

    0.915.06

    

    1.389.38

    

    1.483.58

    

    1.104.33

    

    1.09Total2.05

    

    0.491.84

    

    0.471.64

    

    0.451.68

    

    0.504.15

    

    1.352.19

    

    0.681.99

    

    0.693.94

    

    1.613.38

    

    1.382.97

    

    1.092.73

    

    1.7410.69

    

    2.543.15

    

    1.064.63

    

    1.333.61

    

    1.1110.17

    

    2.353.08

    

    0.934.57

    

    1.299.19

    

    2.73 3.59

    

    1.065.35

    

    1.45 All data are expressed in S. B: Buccal, M: Mesial, D: Distal. R (1): One root, R (2): Two roots, R (3): Three roots, FR: Fused root. P (B): Distance between the palatal apex and the buccal bone plate. PP: Distance between the palatal apex and the palatal bone plate.

    DISCUSSION

    Other than in special cases, the jawbone is normally approached from the labial or buccal side, during apical surgery. The thickness of the buccal bone plate is an important variable for either reaching the apex or securing the surgical field particularly in the case of molars. Even when the apex can be accessed safely, failure can occur if the isthmus cannot be retro-filled appropriately.

    There are few reports showing the thickness of the buccal bone plate. Eberhardt et al. examined CT and reported that the distance between the mesial apex and the buccal bone plate in the maxillary second molar was 4.45mm, which was the thickest, while the maxillary first premolar was 1.63mm, being the thinnest [7]. Their results were similar to those obtained in this study where the average distance in the maxillary first premolar and maxillary second molar was 1.64mm and 4.63mm, respectively. They also reported that the distance between the apex and the palatal bone plate was 3.01mm in the maxillary first molar and 2.76mm in the second molar. These values were also similar to those obtained in this study, which were 3.15mm and 3.08mm, respectively. Frankle et al. (1990) examined 33 cadaver mandible halves and reported that the average distance from the mesial apex to the buccal bone plate in the second molars was 4.18mm. Therefore, it is believed that the measurements obtained from CT are comparable to those obtained from the actually sectioned cadaver specimens. Within the range of these limited data, the thickness of the buccal bone plate between the Chinese and other ethnic groups do not seem to be different.

    Considering the presence of significance between men and women in this study, all the maxillary teeth showed thicker bone plate in men than in women. However, the thicknesses were not significantly different (p>0.05). Therefore, different surgical protocols do not seem to be needed for men and women during apical surgery.

    Considering the results of this study in relation to clinical applications, the thicknesses from the palatal root to the buccal bone plate in the maxillary first and second molars were 10.69mm and 10.17mm, respectively. A great deal of difficulty is anticipated in this region during the apical surgery. Considering the fact that the usual length of a maxillary molar root is approximately 10mm, a significant amount of bone removal needs to be done in order to access the palatal root from the buccal side. Therefore, approaching the surgery site through the palatal side is recommended unless there are anatomical obstacles such as the greater palatine foramen.

    According to the results of this study, the palatal root of the maxillary first premolar was 2.47mm (4.15mm-1.68mm) away from the buccal root, which was more distant than the 1.95mm (3.94mm-1.99mm) in the second premolar. Accordingly, care should be taken so as not to miss the palatal root during apical surgery of the maxillary first premolar.

    Rather than forcefully forming a bone cavity, it would be wise to use a bony lid approach. This approach involves removing the buccal bone plate in a block and then replacing it after surgery. However, when the bony lid approach is not even achievable with the case of bulky buccal bone plate, replantation may need to be considered.

    One of the problems encountered during the measurements was that the entire apices could not be observed on a single axial plane because the lengths of teeth were all different. In this study, the last root apex observed on the previous cross section but no longer observed in the next image was considered the identified apex. However, considering that not all the surgical access was made parallel to the axial plane, there was a limitation to reproduce the actual surgical distance using this study protocol. Therefore, securing a 3-D image that can demonstrate the actual distance from any surgical approach will be necessary for this type of study. The values measured on the axial CT images in this study were also not the actual values of the jawbone but were reduced in scale. A ratio of 0.81:1 was used to convert the measured values to actual ones.

    Compared with the conventional radiographs, the axial CT images were quite helpful in determining the spatial relationship between the apex and the surrounding bone, which means that it would be ideal to take a CT for each apical surgery case. However, considering that the patient would be exposed to large amount of radiation, and a great deal of time and expense would be required, further studies will be needed to overcome these drawbacks, so that CT can be used in extensive clinical applications.

    REFERENCES

    1. Gutmann JL, Harrison JW. Surgical endodontics (1st edition). Boston: Blackwell Scientific Publications. 1991.

    2. Kim S, Pecora G, Rubinstein RA, et al. Case Selection: Indications and contraindications. In: Kim S, Saunders W B, Pecora G, edited. Color atlas of microsurgery in endodontics (1st edition). Philadelphia: W. B. Saunders Company. P: 19.

    3. Alder ME, Deahl ST, Matteson SR. Clinical usefulness of two-dimensional reformatted and three-dimensionally rendered computed tomographic images: Literature review and surgeons' opinions. Journal of Oral and Maxillofacial Surgery. 1995, 53: 375-386.

    4. Jung HJ, Kim HJ, Kim DO, et al. Quantitative analysis of three-dimensional rendered imaging of the human skull acquired from multi-detector row computed tomography. Journal of Digital Imaging. 2002, 15: 232-239.

    5. Kim ES, Kim KD, Roh BD, et al. Computed tomography as a diagnostic aid for extracanal invasive resorption. Journal of Endodontics. 2003, 29: 463-465.

    6. Kim KD, Ruprecht A, Jeon KJ, et al. Personal computer-based three-dimensional computed tomographic images of the teeth for evaluating supernumerary or ectopically impacted teeth. Angle Orthodontist. 2003, 73: 614-621.

    7. Berhardt JA, Torabinejad M, Christiansen EL. Computed tomographic study of the distances between the maxillary sinus floor and the apices of the maxillary posterior teeth. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology & Endodontics. 1992, 73: 345-346.

    (Edited by Yang Zhao, Lian Hu, Yanling Xiao and Yingqi Zhao)

    Guangchun Jin, PhD, associate professor, Binzhou Medical College, 661, 2nd Huanghe Rd, Binzhou, Shandong, China, 256603

    * Corresponding to Youcheng Yang, male, PhD, professor; Address: Binzhou Medical College, 661, 2nd Huanghe Rd, Binzhou, Shandong, China; Postcode: 256603; Tel: 13455774888; Fax: 0543-3257792; E-mail: jingc88@hanmail.net

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