The Prevalence of Alveolar Bone Dehiscence and Fenestration among untreated patients with different patterns of vertical growth using cone-beam computed tomography

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INTRODUCTION
Alveolar bone is the primary structure of the dentition, as it develops along with the tooth.It continuously remodels itself to accommodate the functional and physiological needs of the dentition.Alveolar bone dehiscence is the V shaped defect located along the alveolar bone margin toward the apex on the buccal and lingual side of a tooth. 1 On other hand, fenestration can be described as localized defects of the alveolar bone covered only by periosteum and gingiva or occasionally exposed underlying root structure. 1Previous studies have reported dehiscence and fenestration are commonly found in the alveolar bone with mal-positioned teeth or buccally prominent teeth and considered as nonpathological conditions. 1,2In malocclusion, alignment of teeth is deflected from normal relation within the arch or to the opposing arch during teeth development. 3rthodontic treatment is done for the correction of the The Prevalence of Alveolar Bone Dehiscence and Fenestration among untreated patients with different patterns of vertical growth using cone-beam computed tomography malocclusion for proper function of teeth, esthetic and maintaining the overall oral health.As tooth movement in orthodontics is a continuous process of remolding of alveolar bone, there is high risk of development of alveolar bone defect especially dehiscence and fenestration which can cause decrease in tooth support. 4[7] Cone-beam computed tomography (CBCT) is a digital three-dimensional radiograph.[13][14][15][16][17][18][19] In previous studies alveolar bone dehiscence and fenestration has been evaluated using dry skull and after orthodontic treatment but there have been only few studies evaluating alveolar bone dehiscence and fenestration among untreated patients according to vertical growth pattern using CBCT. 20,21The predictability of the prevalence of alveolar bone dehiscence and fenestration in different growth pattern before orthodontic treatment can help the dental professionals in formulating effective treatment plan and preventing unwanted complication during the treatment along with long-term stability of the treatment. 19,21According to severity of the alveolar bone dehiscence and fenestration was classified into mild, moderate and severe types.We considered the range of 2mm-3mm as mild, 3mm-4mm as moderate and >4mm as severe for alveolar bone dehiscence.Subsequently, for fenestration the range of mild was 2.2mm-3mm, moderate was 3mm-4mm and severe was >4mm. 20atistical analyses were performed with the statistical package for social science (SPSS) version 18.0.Percentage of Incidence of alveolar bone dehiscence and fenestration according to vertical growth pattern in different tooth was calculated.Pearson chi square was performed and the statistical test was concluded to be significant when the p value was less than 0.05.To evaluate the stability and consistency of the measurement, test-retest reliability was calculated using intra-class correlation coefficient (ICC).
Severity of dehiscence was found mild in nature, while moderate severity was seen in fenestration.we found that mild, moderate and severe degree of severity was seen in 63.35%, 21.14%, 15.51%, while that in fenestration was 22.62%,44.35%,33.03%respectively.(Table 3) Pearson chi square test was performed to test the association between alveolar bone dehiscence and fenestration with different vertical growth patterns (Table 1).There was a significant association between alveolar bone dehiscence and fenestration with different vertical growth pattern dX2= 3814, fX2 =1178 and p < .001)This shows that the prevalence of alveolar bone dehiscence and fenestration was different among patients with different vertical growth patterns.The ICC was estimated to be 0.93 (95% confidence Interval: 0.88-0.97)were calculated using SPSS statistical package version 18 based on single-rating, absolute agreement, 2-way random effects model.7][28][29][30] However, studies on prevalence in dehiscence and fenestration among untreated patient according to vertical growth patterns using CBCT is still less.
CBCT is a routine dental radiography, efficient in identification of alveolar bone defect along with other periodontal disease.Compared to other conventional radiography CBCT is highly accurate in detection of alveolar bone dehiscence and fenestration. 11,12Even some study reported that CBCT overestimate the presence of alveolar bone defect, [11][12][13] it is clinically used due to three-dimensional visualization and low  Dehiscence was commonly seen than fenestration since natural defects have more gradual and tapering margins along with thin alveolar bone which might easily expose alveolar bone to inflammatory process. 4,11Watson et al also said that Alveolar bone dehiscence might be formed due to inflammatory processes induced by Chronic gingivitis. 3While fenestration is isolated defect exposing the underlying root which is more related with the position of tooth. 5In our study, the prevalence of dehiscence was also seen higher than fenestration.

Hypo
In study done by Enhos et al. in patients with different vertical pattern dehiscence andwas prevalent in normo -divergent group (8.18%) and hyper-divergent group (8.35%).whereas fenestration was prevalent in hypodivergent and hyper-divergent groups 21 .Studies have found that higher the alveolar bone density, lower the alveolar bone defects.The thickness of alveolar bone is higher in hypo-divergent compared to hyper-divergent growth pattern. 20,32,33 suggesting as common finding. 14The main factors for occurrence of alveolar bone defect are position of tooth along with alveolar bone thickness.The thickness of cortial plates varies significantly from tooth to tooth throughout the arches.Tooth position in arch such as buccoversion, linguoversion, superuption, supereruption, intrusion etc appears to be the major determinant of cortical plate thickness and contour. 32,33n  21 Jin et al. investigated the bone thickness of canine and premolars in normal occlusion and found that the thickness of canine and first premolar were was lower than 2mm in relation to second premolars. 32,33In mandible central and lateral incisors were mainly present with the alveolar bone defect compared to posterior teeth as a result of presence of thin anterior alveolar bone compared to posterior alveolar bone. 9,32

LIMITATIONS
The limitation of the current study is its dependence on only one observer in detecting bone defects using CBCT images therefore inter-observer reliability in detecting these alveolar bone defects was not evaluated.As inter-observer reliability in interpreting CBCT images when diagnosing orthodontic-related problem can significantly affect the diagnosis accuracy of the imaging technique. 34

CONCLUSION
The dehiscence and fenestration are innately prevalent in all three hyper-divergent, normo-divergent, and hypodivergent groups.The prevalence of alveolar bone dehiscence and fenestration were less in hypo-divergent group compared to hyper-divergent and normodivergent group.Dehiscence was more prevalent in first premolar in maxilla and central incisors in mandible.Fenestration was more prevalent in canine in maxilla and lateral incisors in mandible.

Figure 1 :
Figure 1: Measurement of dehiscence and fenestration in Materalise Mimics research 21.0

Percentage of severity of the Alveolar bone dehiscence and fenestration according to Vertical growth pattern
21,21tration.Study has been done on alveolar bone defect with different vertical growth.20,21Enhosetal. found the prevalence of dehiscence and fenestration was 8.35% in hyper-divergent group, 8.18% in normodivergent group and 6.56% in hypo-divergent group.21 We used CBCT to find the Prevalence of alveolar bone dehiscence and fenestration among patients having different patterns of vertical growth.