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Table of Contents   
ORIGINAL RESEARCH  
Year : 2022  |  Volume : 33  |  Issue : 3  |  Page : 277-281
Comparison of mandibular buccal shelf bone characteristics between two facial types using cone beam computed tomography


1 Department of Orthodontics, Faculty of Dental Sciences, M S Ramaiah University of Applied Sciences, Bengaluru, Karnataka, India
2 Consultant Orthodontist, Private Practitioner, Bengaluru, Karnataka, India

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Date of Submission29-Dec-2021
Date of Decision18-Jun-2022
Date of Acceptance03-Aug-2022
Date of Web Publication17-Jan-2023
 

   Abstract 


Background: Mandibular buccal shelf (MBS) offers good quality and quantity of bone for orthodontic bone screw (OBS) insertion. Despite several reports of treated patients, there are numerous variables in selecting the exact placement site for OBS placement in the MBS. There are also anatomical variations in this area which must be considered. Objectives: This study aims to measure and compare the MBS bone characteristics for OBS placement using cone beam computed tomography (CBCT) between two different facial types. Materials and Methods: Eighty CBCT samples were collected (40 samples of group A horizontal growers and 40 of group B vertical growers). Each CBCT image was reconstructed and oriented with CS 3D CBCT software. The cortical bone thickness, the slope of the MBS, and buccolingual inclination of mandibular second molar were measured and analysed. Result: Cortical bone thickness among horizontal growers was 5.23 ± 0.58 mm and among vertical growers was 4.85 ± 0.37 mm. The slope of MBS among horizontal growers was 60.83 ± 6.15 degrees and among vertical growers was 66.75 ± 6.27 degrees. In both the parameters there was a statistically significant difference between the groups. There was no significant difference between the groups for the buccolingual inclination of 2nd molar. Conclusion: Increased cortical bone thickness and the flatter slope of MBS at the 2nd molar region allows for easier placement of OBS in horizontal growers than in vertical growers.

Keywords: Buccal shelf implant, cone beam computed tomography, mandibular buccal shelf anatomy

How to cite this article:
Ramasamy P, Sabrish S, Pattabiraman V, Shivamurthy PG, Sagarkar R, Mathew S. Comparison of mandibular buccal shelf bone characteristics between two facial types using cone beam computed tomography. Indian J Dent Res 2022;33:277-81

How to cite this URL:
Ramasamy P, Sabrish S, Pattabiraman V, Shivamurthy PG, Sagarkar R, Mathew S. Comparison of mandibular buccal shelf bone characteristics between two facial types using cone beam computed tomography. Indian J Dent Res [serial online] 2022 [cited 2023 Feb 5];33:277-81. Available from: https://www.ijdr.in/text.asp?2022/33/3/277/367873



   Introduction Top


In recent years, miniscrews have been widely used for skeletal anchorage because they require minimal patient compliance while providing maximum anchorage. Primary stability is the key factor for successful mini-screw placement as they do not undergo osseointegration.[1] Although interradicular sites are routinely selected for miniscrew placement, they have a few limitations.[2] As an alternative, different anatomic structures (i.e., extra alveolar sites distant from dental roots) that includes hard palate, infrazygomatic crest (IZC) and mandibular buccal shelf (MBS) are used because of their increased bone density and consecutively improved stability of the implant. Mandible has greater compact cortical bone than the maxilla and the MBS area which is present from the region of 1st molar to the external oblique ridge, allows the clinician to insert the orthodontic bone screw (OBS) in an orientation parallel to the long axis of molar roots.[3]

The mandibular buccal shelf offers good bone quality and quantity for bone screw insertion. Cortical bone thickness increases from the anterior to the posterior alveolar bone region.[4] Other studies revealed that the slope of the MBS becomes flattened from the anterior region to the posterior region.[5],[6] The flatter the slope, the easier it is to place the orthodontic bone screw. However, the degree of this slope varies among different individuals.[5] Accordingly, the thickness of the cortical bone can provide an insight into the forces it experiences and is expected to vary in subjects with different vertical facial dimensions.[6] According to Chang et al, there is a need to study the anatomic characteristics involved in MBS orthodontic bone screws placement.[7],[8] Also, contact of OBS with a root/roots is considered as one of the most frequent causes of failure.[8] Hence it is important to understand the relation between the inclination of the mandibular buccal shelf and the long axis of molars.

Also, contact of OBS with roots is considered as one of the most frequent causes of failure. Hence it is important to understand the relation between the inclination of the MBS and the long axis of molars.

Despite numerous reports of treated patients, there is inconsistency regarding the selection of the placement site in the MBS. Few recommendations include placement adjacent to the first molar, between first and second molars, and adjacent to the second molar.[8] This wide range of recommendations may be due to strong local anatomic variations at the buccal shelf or the lack of studies that investigated the local anatomy.[9] So, this study aims to measure and compare the MBS bone characteristics such as cortical bone thickness, the slope of the MBS, and the buccolingual inclination of the 2nd molar for OBS placement using cone beam computed tomography (CBCT) between two different facial types.


   Methods Top


The study protocol was approved by the ethics review committee of the Institutional Review Board (EC-2019/PG/014). This cross-sectional study was conducted on full skull CBCT scans taken from the patient archives. The scans were obtained for general dental purposes and not specifically for this study. All the scans in the archives were made using the same machine and using Carestream software (Carestream 9300, Carestream Dental LLC, Atlanta) with parameters of 6.3 mA, 90 kvp and 300 microns resolution with a full field of view (FOV) of 17 × 13.5 cm.

The sample size was calculated using software G-power (version 3.1). Based on previous literature[10] with power as 90%, alpha error as 0.05, and effect size as 0.64, the sample size was calculated to be 40 per group. A flowchart for sample selection and study design is shown [Figure 1].
Figure 1: Flowchart for sample selection

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The inclusion criteria were as follows: patients with age of 16 years or more, presence of lower first and second molars, no alveolar bone loss, and no posterior crossbite or scissor bite. The exclusion criteria were any case with a pathology or developmental anomalies. From the oriented lateral ceph view of CBCT images, subjects were classified into horizontal and vertical growers based on Frankfurt mandibular plane angle (FMPA) and basal plane angle (BPA).[11],[12] Subjects with FMPA ≤18.42° and BPA less than 25° were considered horizontal growers and subjects with FMPA ≥28.54° and BPA more than 25° were considered vertical growers. Forty samples were selected in each group. Each CBCT image was reconstructed and oriented in the coronal view, axial view and the sagittal view as shown [Figure 2]. In the coronal view, the axial plane (yellow line) passed through the mesiobuccal cusp of the mandibular first molars. In the sagittal plane (green line) passed through the central grooves of molars. In the axial plane (yellow line) passed through first molars and first premolars occlusal contact points.
Figure 2: Orientation of CBCT image in three planes

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In both the groups, three parameters which were the cortical bone thickness, slope of MBS at the mesial aspect of mandibular second molar and buccolingual inclination of the second molar were measured using the CBCT images and were compared. Method of measurement of the three parameters used is shown in [Figure 3] and [Figure 4]. In [Figure 3], the measurement of the cortical bone thickness of the MBS on the insertion path (green line) is shown. In [Figure 4], the slope of the MBS was the angle formed by a line tangent to the MBS and the axial plane in the coronal view (an angle formed by two green lines).
Figure 3: Drawing an orthodontic anchoring screw insertion path (green line) with an angle of the 70° to the axial plane (horizontal line)

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Figure 4: Measurement of buccolingual inclination of 2nd molar

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Statistics

The values obtained for each parameter were recorded in an MS Excel file, tabulated and subjected to statistical analysis.

Data were analysed using the Statistical Package for Social Sciences (SPSS) version 20 (SPSS 22.0, IBM, Armonk, NY, USA). Percentages, means and standard deviations (SD) were computed for descriptive purposes. Normality of data was assessed using a Kolmogorov–Smirnov test and appropriate statistical tests were applied. The Chi-square test was used to find out the differences in the distribution of demographic variables. The student's t-test was used to compare the mean of age, cortical bone thickness, buccolingual inclination of molar, and slope of the MBS. A P value of < 0.05 was considered statistically significant.


   Results Top


The mean age of horizontal growers and vertical growers were 23.50 ± 6.41 years and 24.78 ± 6.53 years, respectively and the mean differences did not differ significantly (p = 0.38) [Table 1]. [Table 1] also shows that there were 20 (50.0%) males and 20 (50.0%) females among horizontal growers and 23 (57.5%) males and 17 (42.5%) females in the vertical grower's group. There was no significant difference between the number of males and females in both the groups (p = 0.50). The mean FMPA among vertical growers (28.88° ± 0.82°) was significantly higher than horizontal growers (15.48° ± 1.15°) (p < 0.001). The mean BPA among horizontal growers was 21.75° ± 2.06° and this was significantly lesser when compared to that of vertical growers (28.25° ± 2.30°) (p < 0.001).
Table 1: Mean age among the study groups and distribution of study groups based on gender

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Cortical bone thickness among horizontal growers was 5.23 ± 0.58 mm and vertical growers was 4.85 ± 0.37 mm, which was statistically significant. There was no significant difference between the groups for the buccolingual 2nd molar inclination [horizontal grower: 72.95° ± 3.67°; vertical growers: 73.93° ± 5.02° (p = 0.32)]. The slope of MBS among vertical growers was 66.75° ± 6.27° and among horizontal growers was 60.83° ± 6.15° which was again statistically significant (p < 0.001) [Table 2].
Table 2: Mean values of cortical bone thickness, buccolingual inclination of 2nd molar and slope of MBS among the study groups

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   Discussion Top


The success of orthodontic treatment greatly depends upon the anchorage control. The most important factor determining the primary stability of bone screws is the jaw bone morphology which is influenced by the masticatory muscles. The form of maxilla and mandible, specifically the density and thickness of the cortical bone is determined by the masticatory muscle force.[13] The thickness of the cortical bone is closely related to the vertical facial patterns.[6] The MBS has a greater cortical bone thickness as compared to other sites on the mandible.[14] Thus, screw placement in the MBS should provide greater primary stability and implant success. Literature states that the cortical bone thickness between the left and right sides of an individual is similar.[15] The MBS lies lower and lateral to the second molar region. Hence, all the measurements were made on the side which had the best alignment of first and second mandibular molars.

Parinyachaiphun et al.[5] measured the cortical bone thickness at two sites: contact point between mandibular first and second molar; and mesial aspect of the second molar in mandible. They concluded that cortical bone thickness at the mesial aspect of the second molar was thicker than that of the first/second molar contact point site. The mesial side of the mandibular second molar was considered as a safe zone for placement of MBS orthodontic anchorage screw, as its slope was flatter and this region provides more distance from the molar root than the first/second molar contact point site. Hence, we selected this area to study the properties of bone for the placement of the buccal shelf implant. In orthodontic research, there are numerous reports on the relationship between lower incisor inclination and mandibular symphysis and also the mesiodistal changes of the mandibular molar axis during treatment.[16] However, the buccolingual inclination of molars is not yet fully understood. Sato et al., conducted a study using CT images obtained from the dry skulls and reported that the buccolingual inclination of mandibular molars was related to the facial types which was characterized by ramus height, gonial angle, and mandibular plane angle.[10] The subjects with a smaller gonial angle and mandibular plane angle were found to have more vertically positioned molars. These findings were similar to a study done by Masumoto et al.,[6] who stated that facial type was associated with the cortical bone thickness of the mandibular body, buccolingual inclination of first and second molars, and the standing position of mandibular molars, which in turn were affected by masticatory function. Hence, we assessed the association between facial types and buccolingual inclination of the 2nd molar using CBCT.

In this study, there was no significant difference in the buccolingual inclination of molars between the groups [horizontal grower: 72.95° ± 3.67°; vertical growers: 73.93° ± 5.02° (p = 0.32)]. Our results were comparable to those of a study done by Masumoto et al.,[6] where they used CT images of mandibular first and second molars. They found that the inclination of the second molar in long face subjects was lesser (more lingually inclined) than in short face and average subjects but this was not statistically significant.[6]

Our results revealed that the cortical bone thickness measured at the mesial aspect of the mandibular second molar was 5.23 ± 0.58 mm among horizontal growers and 4.85 ± 0.37 mm for vertical growers. There was a significant difference in the cortical bone thickness between the groups. These findings were similar to those of a recent study which reported that mandibular buccal cortical bone at all inter radicular sites from canine to the second molar of hypodivergent subjects was thicker than in hyperdivergent subjects.[3] Masumoto et al.,[6] found that the buccal cortical bone thickness was significantly different between hyperdivergent and hypodivergent groups at only two out of nine vertical levels of the mid-second molar site. Swasty et al.[17] reported no significant difference in cortical bone thickness between long-faced and average-faced subjects, measured at first and second mandibular molars. A possible explanation for these differences in results is that Swasty et al.[17] had a small field of view of CBCT images and used only Palatal Plane to Mandibular Plane as the criteria for vertical skeletal classification. Whereas, the other two studies used different criteria, such as SN to mandibular plane, FMA and gonial angle.[3],[6] In our study, we included two criteria to classify the horizontal and vertical growers – FMPA and BPA. The reason for measuring cortical bone thickness at 70° angulation to the occlusal plane is that this measurement is more representative of the final implant position and is more perpendicular to the occlusal plane compared to other studies that measured it in a more horizontal direction.[3] Deguchi et al.[18] studied the effect of insertion angles in the same style as vertical levels. As the insertion angle increased, the cortical bone thickness measured along with the OBS insertion path also increased. Inaba also revealed that the implant-cortical bone contact was higher when placing the OBS at a higher angulation to the cortical bone surface.[19] The thickness of the cortical bone is a crucial parameter for the successful placement of OBS. Motoyoshi et al.[20] suggested that cortical bone thickness of more than 1 mm was essential for a success rate of 6 months. In this study, we found that the cortical bone thickness was 5.23 ± 0.58 mm in horizontal and 4.85 ± 0.37 mm in vertical growers. Thus, our results showed that the cortical bone thickness was significantly higher in hypodivergent subjects than in the hyperdivergent subjects.

In this study, we found a significant difference in the slope of the MBS between horizontal and vertical growers. The slope of the MBS is important during OBS placement. It is easier to insert the OBS on a flatter MBS, especially when the clinician tries to place it as perpendicular to the occlusal plane as possible. Our results suggest that the MBS slope had a flatter anatomy in the region of mesial aspect of second molar with a statistically significant difference between the two groups. This was consistent with previous literature reports.[5] The measured values for the slopes were relatively higher for vertical grower (66.75° ± 6.27°) compared to that of horizontal growers (60.83° ± 6.15°). This supports the statement of Lin, who concluded that the slope of the MBS greatly varies between different individuals.[7] Angular measurements of the slope of the MBS region show a flatter buccal shelf area in the hypodivergent group (increased angular measurements) as compared to the hyperdivergent group. Thus, in hypodivergent individuals, because of the flatter and hence broader buccal shelf area, OBS can be placed farther from the dentition compared to the hyperdivergent individuals.

One of the drawbacks of this study was that inter and intra observer variability was not assessed.


   Conclusion Top


There was a significant difference in cortical bone thickness between the groups (5.23 ± 0.58 mm in horizontal growers and 4.85 ± 0.37 mm in vertical growers). This increased cortical bone thickness could imply better stability for OBS at the mandibular 2nd molar buccal shelf region in horizontal growers compared to vertical growers. There was no significant difference between the groups in the buccolingual inclination of 2nd molars. MBS was flatter in horizontal growers than in vertical growers, which could allow for easy placement of OBS at the mandibular 2nd molar buccal shelf region.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Vargas EOA, Lopes de Lima R, Nojima LI. Mandibular buccal shelf and infrazygomatic crest thicknesses in patients with different vertical facial heights. Am J Orthod Dentofac Orthop 2020;158:349-56.  Back to cited text no. 1
    
2.
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Parinyachaiphun S, Petdachai S, Chuenchompoonut V. Considerations for placement of mandibular buccal shelf orthodontic anchoring screw in Class III hyperdivergent and normodivergent subjects – A cone beam computed tomography study. Orthod Waves 2018;77:44-56.  Back to cited text no. 5
    
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Chang C, Liu SSY, Roberts WE. Primary failure rate for 1680 extra-alveolar mandibular buccal shelf mini-screws placed in movable mucosa or attached gingiva. Angle Orthod 2015;85:905-10.  Back to cited text no. 8
    
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Huang C, Chang Chris, Roberts W. 3D cortical bone anatomy of the mandibular buccal shelf: A CBCT study to define sites for extra-alveolar bone screws to treat Class III malocclusion. Int J Orthod Implantol 2016;41:74-82.  Back to cited text no. 9
    
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Sato H, Kawamura A, Yamaguchi M, Kasai K. Relationship between masticatory function and internal structure of the mandible based on computed tomography findings. Am J Orthod Dentofac Orthop 2005;128:766-73.  Back to cited text no. 10
    
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Grewal H, Sharma H, Aggarwal N. A cephalometric comparison of horizontal and vertical skeletal parameters in North and South Indian population groups. J Pierre Fauchard Acad 2013;27(1). doi:10.1016/j.jpfa.2013.01.003  Back to cited text no. 11
    
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García-Morales P, Buschang PH, Throckmorton GS, English JD. Maximum bite force, muscle efficiency and mechanical advantage in children with vertical growth patterns. Eur J Orthod 2003;25:265-72  Back to cited text no. 13
    
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Costa A, Raffainl M, Melsen B. Miniscrews as orthodontic anchorage: A preliminary report. Int J Adult Orthodon Orthognath Surg 1998;13:201-9.  Back to cited text no. 14
    
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Ono A, Motoyoshi M, Shimizu N. Cortical bone thickness in the buccal posterior region for orthodontic mini-implants. Int J Oral Maxillofac Surg 2008;37:334-40.  Back to cited text no. 15
    
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Swasty D, Lee J, Huang JC, Maki K, Gansky SA, Hatcher D, et al. Cross-sectional human mandibular morphology as assessed in vivo by cone-beam computed tomography in patients with different vertical facial dimensions. Am J Orthod Dentofacial Orthop 2011;139:e377-89.  Back to cited text no. 17
    
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Deguchi T, Nasu M, Murakami K, Yabuuchi T, Kamioka H, Takano-Yamamoto T. Quantitative evaluation of cortical bone thickness with computed tomographic scanning for orthodontic implants. Am J Orthod Dentofacial Orthop 2006;129:721.e7-12.  Back to cited text no. 18
    
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Inaba M. Evaluation of primary stability of inclined orthodontic mini-implants. J Oral Sci 2009;51:347-53.  Back to cited text no. 19
    
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Motoyoshi M, Inaba M, Ono A, Ueno S, Shimizu N. The effect of cortical bone thickness on the stability of orthodontic mini-implants and on the stress distribution in surrounding bone. Int J Oral Maxillofac Surg 2009;38:13-8.  Back to cited text no. 20
    

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Correspondence Address:
Dr. Sharanya Sabrish
Department of Orthodontics, Faculty of Dental Sciences, M S Ramaiah University of Applied Sciences, MSRIT Post, M S R Nagar, Bengaluru - 560 054, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.ijdr_1201_21

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    Figures

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