A lateral cephalogram is a standard tool used in orthodontic diagnostics to assess the position of the central incisors. Treatment decisions involving anterior-posterior incisor movements inside the jaws are frequently influenced by the central incisor’s inclination and their relationship to the surrounding alveolar bone, which are easily measured on a lateral cephalogram. Crowding in an arch increases the risk of ectopic tooth eruption, which may affect the apparent thickness of the alveolar bone around the roots. Malocclusions may also be linked to aberrant myofunctional behaviours, natural dental compensations, and other environmental factors that might negatively affect the incisor’s visible locations inside the alveolar processes.1

The limitations of the orthodontic movement are defined by the thickness of the alveolar bone, and pushing these boundaries could have unfavourable side effects for the periodontal tissues.2

Proffit and Ackerman addressed the limitation of tooth movement with a widely accepted diagram described as the ‘‘envelope of discrepancy.’’ With orthodontic tooth movement alone, they estimated that the limits of extrusion, retraction, intrusion, and protraction of mandibular incisors were 2, 3, 4, and 5 mm, respectively. These parameters were determined by the anatomical boundaries of the alveolar bone width. Alveolar bone morphology must be assessed prior to orthodontic therapy in order to minimise the undesirable consequences like dehiscence and fenestration that may arise during orthodontic treatment due to anatomical and iatrogenic reasons.3

It is usual practice to consider the palatal cortical plate as the limit of retracting maxillary anterior teeth. Approximation of the incisive canal and upper central incisor should also affect orthodontic retraction of the anterior teeth. Nakada et al. observed that mesial displacement of the root apex during orthodontic retraction can lead to its contact with the IC cortical plate and cause apical root resorption.4

In orthodontic tooth movement, force induces alveolar bone resorption on the pressure side and bone formation on the tension side. A classical theory in orthodontics is that the alveolar bone follows the direction of tooth movement and the width of alveolar bone remains unchanged. According to Sun et., al. the retraction of anterior teeth causes a decrease in both alveolar bone height and width, indicating that alveolar bone remodelling does not necessarily follow the course and magnitude of orthodontic tooth movement.5

Edwards' studied a large group of individuals with Class II malocclusion and bidental protrusion. He noted that despite prolonged palatal retraction and root torquing of incisors, the width of the anterior palate at the level of the apex remained unchanged. The alveolus can, however, remodel at the mid-root level and at the alveolar margin when the lingual cortex is approached and passed. He postulated an anatomic barrier against further tooth movement in the higher areas at the anterior palatal curvature as it approaches the horizontal vault.6

The need of this study is to evaluate and compare the changes in alveolar bone thickness with change in incisor position pre and post operatively in Class II div 1 patient undergoing fixed orthodontic treatment after extraction of maxillary first premolars.

15 Pre and Post treatment Lateral cephalograms of patients with Class II div 1 malocclusion who had undergone fixed orthodontic treatment were acquired from the Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Sciences, Bareilly International University, Bareilly. Sample Size: Sample size has been scientifically estimated using G Power V 3.1 Software which yielded a minimum sample size of 15. Patients having Class 2 Div 1 malocclusion treated with extraction of first premolars bilaterally. Pre and post treatment cephalometric image quality sufficient to recognise important anatomic landmarks were taken, Patients with no history of previous orthodontic treatment and having healthy periodontal status were included in study. Lateral cephalograms of 15 subjects with Class II div 1malocclusion that were treated with extraction of upper first premolars were taken. Pre and post lateral cephalograms were used to assess various parameters. All lateral cephalograms were digitally traced in dolphin software by one examiner. The structures traced included the maxilla, mandible, inner and outer cortical surfaces of the mandibular symphysis, first molars, and central incisors. Pre and post treatment lateral cephalograms readings for Maxillary Central Incisor Root Position, Maxillary Alveolar Process Thickness, Mandibular Central Incisor Root Position, Mandibular Alveolar Process Thickness, Incisor Inclination Interincisal Angle and AP Jaw Relationship were measured and compared for the changes after orthodontic treatment. Maxillary Central Incisor Root Position The measurements were taken perpendicular to the tooth's long axis, measuring the lengths (in millimetres) between the root midpoint and the outer cortical surface of the alveolar process on the labial (U1-lab) and palatal (U1-pal) sides. Maxillary Alveolar Process Thickness In order to determine the overall thickness of the maxillary alveolar process (Mx-Alv), the distances U1-lab and U1-pal were taken at the midroot level and added. Fig .1 & Fig 2. Mandibular Central Incisor Root Position On the labial (L1-lab) and lingual (L1-ling) sides, the distances (in millimetres) between the root apex and the alveolar process's outer cortical surface were measured parallel to the occlusal plane. Mandibular Alveolar Process Thickness The sum of the lengths L1-lab and L1-ling was used to determine the overall thickness of the mandibular alveolar process (Md-Alv) Fig.1 & Fig.2. Incisor Inclination. U1- occlusal plane-Angle between long axis of Maxillary central incisor and occlusal plane. L1 – occlusal plane--Angle between long axis of Mandibular central incisor and occlusal plane. Interincisal Angle- Angle formed between long axis of maxillary and mandibular incisors. Fig .3. AP Jaw Relationship The AP jaw relationships were evaluated using the Wits appraisal (Wits). Where a perpendicular drawn from point A and point B on occlusal plane and the distance between the two points measured. Statistical Analysis: The data are tabulated in Microsoft excel and analysed with SPSS V.24 software. The continuous variables are presented with mean and standard deviation. The categorical variables are presented with frequency and percentage. Paired t test is used for the statistical analysis. The p value ≤0.05 is considered statistically significant.

Comparison of Mx-Alv measurements between the pre-treatment and post-treatment periods shows the mean pre-treatment Mx-Alv value was 8.27 ± 1.17, while the post-treatment mean value increased to 9.87 ± 1.59. The observed change was statistically significant, with a P value of 0.003.(Table 1)

 On Comparing of Md-Alv measurements before and after treatment, the mean pre-treatment Md-Alv value was 8.67 ± 1.76, whereas the post-treatment mean value slightly decreased to 8.41 ± 1.32. However, this change was not statistically significant, as indicated by a P value of 0.542. (Table 2)

U1-Pal values in the pre-treatment and post-treatment phases indicates the mean pre-treatment value was 5.06 ± 0.88, which reduced to 3.88 ± 0.97 post-treatment. This increase was statistically significant, with a P value of 0.001. (Table 3)

Data on U1-Lab values before and after treatment showed the mean pre-treatment U1-Lab value was 4.27 ± 0.77, increasing to 4.94 ± 1.28 post-treatment. However, the observed change was not statistically significant, with a P value of 0.075. (Table 4)

L1-Ling values in the pre-treatment and post-treatment periods. The mean pre-treatment value was 3.82 ± 0.82, which decreased slightly to 3.41 ± 0.86 post-treatment. The change, however, was not statistically significant, as indicated by a P value of 0.225. (Table 5)

Study also showed comparison of L1-Lab values before and after treatment. The mean pre-treatment L1-Lab value was 4.85 ± 1.36, and the post-treatment mean value was 5.00 ± 1.31. The change was not statistically significant, with a P value of 0.701.(Table 6)

Wits values in the pre-treatment and post-treatment periods showed the mean pre-treatment value was 5.33 ± 2.07, which decreased to 3.65 ± 2.15 after treatment. This reduction was statistically significant, with a P value of 0.002. (Table 7)

The comparison of U1-occlusal plane values before and after treatment indicate the mean pre-treatment value was 48.65 ± 7.23, while the post-treatment mean value significantly increased to 61.11 ± 5.14. This increase was statistically significant, with a P value of less than 0.001. (Table 8)

Comparison of L1-occlusal plane values in the pre-treatment and post-treatment phases showed the mean pre-treatment value was 55.47 ± 6.69, increasing to 58.03 ± 8.81 post-treatment. However, this change was not statistically significant, as indicated by a P value of 0.306. (Table 9)

Interincisal angle measurements before and after treatment indicates the mean pre-treatment interincisal angle was 103.09 ± 11.57, which increased significantly to 119.00 ± 9.97 post-treatment. This increase was statistically significant, with a P value of 0.001. (Table 10)

It is widely accepted that whenever orthodontic tooth movement occurs, the bone around the alveolar socket remodels. However, non-orthodontic tooth movements do not follow this rule. During eruption of the dentition, teeth emerge from the alveolar process, and alveolar ridge augmentation occurs simultaneously. It is not clear whether the bone remodelling-to-tooth movement ratio is actually 1:1in all orthodontic tooth movements so this study was conducted with the aim to evaluate and compare incisor position, Maxillary Alveolar Process Thickness, Mandibular Central Incisor Root Position, Mandibular Alveolar Process Thickness, AP Jaw Relationship in pre and post treatment in class II div 1 malocclusion treated by fixed orthodontic treatment.7 The present study evaluates and compares the changes in alveolar bone thickness around root of maxillary and mandibular central incisors with changes in its inclination after fixed orthodontic treatment. Cephalometric analysis based on lateral cephalograms has been a mature and widely used tool for the studies of craniofacial anatomical structures. Since lateral cephalometric radiography was introduced in 1931, studies have been widely conducted and cephalometric normative value has been accumulated, which provides useful information in orthodontic diagnosis. However, although CBCT provides more extensive information, it still cannot replace the widely used lateral cephalometric radiography due to studies of the normative value data are insufficient. CBCT is likely to replace lateral cephalograms completely as the field progresses. However, the current two-dimensional normative reference value of lateral cephalograms is an important criterion for diagnosis.5 Cephalometric tracings can be performed by manual and/or computerized methods. The manual method was, for a long time, the only method used for implementing and obtaining cephalometric tracings, and angular and linear measurements required for their interpretation. The main disadvantage of this method lies in the fact that it is relatively time-consuming, particularly for orthodontists. In 1994, during the 2nd Symposium on Computers in Orthodontics, held during the 9th Brazilian SPO Orthodontic Conference, Dolphin Imaging software was first introduced in Brazil. This computer program features high technology and works with cutting-edge graphics software. It provided an alternative way to perform cephalometric tracings without using conventional cephalometric radiographs and therefore paved the way for the use of 3D Cephalometry.8 Considering the advantages of computerised methods dolphin imaging software was used in our study. The anterior alveolar bone defines the boundary for the retraction of the anterior teeth in orthodontic treatment. Though theoretically bone remodelling occurs during tooth movement, it remains controversial whether the changes in the anterior alveolar bone always follow the direction and quantity of tooth movement.5 Although severe skeletal class II cases require surgical intervention, not all patients agree for the same. In such cases, extraction treatment can be used as an alternative to slightly improve the profile.9 The anatomical limits set by the cortical plates of the alveolus may be regarded as orthodontic walls. Since the cortical plates of the palate and the symphysis are represented only in 2 dimensions on lateral cephalograms, the examiner cannot rule out iatrogenic sequelae during or after tooth movement based on these films. Unlimited tooth movement is not possible during retraction of the incisors, especially the mandibular incisors. This is due to the restriction imposed by the symphyseal bone. It consists of a dense cortical plate on the labial and lingual surfaces near the roots of the incisors. In fact, the incisors can be moved labially or lingually to only a very limited extent. Our goal was to evaluate the changes in labial and lingual alveolar bone during incisor retraction in the maxilla and mandible.7 In this study the cephalometric tracing of pre and post treatment lateral cephalogram was done using dolphin software. All the landmarks were marked and traced on the lateral cephalograms. Maxillary central incisor root position, maxillary alveolar process thickness, mandibular central incisor root position, mandibular alveolar process thickness, incisor inclination, interincisal angle, AP jaw relationship were the parameters used to evaluate and compare the changes in alveolar bone thickness in class II div 1 patient after extraction of maxillary first premolars. After retraction of maxillary anteriors change in root position in incisors occurs which resulted in change in total alveolar bone thickness. The alveolar bone thickness in maxillary alveolar process is measured from the midroot level of maxillary central incisors while the mandibular alveolar process thickness was measured from the root tip of mandibular central incisor. As the retraction of anterior was done the root of central incisors move towards center of alveolar process. In ideal condition the root should be placed in center of alveolar process and the labial and lingual alveolar thickness of the maxillary and mandibular process should be equal. According to the results of our study there was an increase in value of maxillary alveolar process which shows statistically significant change after retraction of maxillary incisors. There was significant decrease in palatal alveolar bone thickness in maxilla after treatment while the labial maxillary bone thickness increased. The results of our study were in accordance with the study performed by Ahn et al, Marian D et al.10,11 who also showed an increase in labial maxillary bone thickness and decrease in palatal maxillary bone thickness. The total mandibular alveolar bone thickness was found to be reduced in which the thickness decreased on lingual side and increased on labial side of mandibular alveolar process. This result is similar to the results by the study performed by Wainwright, Ten Hoeve and Mu lie,Vardimon et al, and Wehrbein et al. 12,13,14,15 which showed that alveolar bone thickness reduces in the direction of tooth movement. Wits value which show the anteroposterior jaw relationship shows decrease in post treatment cephalogram which show statistically significant change. The decrease in wits appraisal is also similar like a study performed by Shashidhar K et al.9 as there is remodelling of Point A after extraction of premolars and retraction of maxillary anteriors. Inclination of maxillary and mandibular central incisors with the occlusal plane both increases after change in inclination of incisors which also shows statistically significant changes. On comparing the interincisal angle in pre and post treatment samples the parameter shows increase in value after retraction by correcting the angulation of incisors. This increase in interincisal angle shows statistically significant changes. This result is in accordance with the results of study performed by Kusnato et,al ,Sayuti E,et al.16,17 which shows increase in value of interincisal angle after retraction of anteriors in Class II div 1 cases after extraction of maxillary first premolars.

  This study concluded that after orthodontic treatment in class II div 1 case with premolar extraction. Total maxillary alveolar process thickness increases where it decreases on palatal side and increases on labial side. Total mandibular alveolar process thickness decreases where it decreases on lingual side and increases on labial side. Decrease in Wit’s appraisal. Inclination of maxillary and mandibular central incisors increases. There is increase in interincisal angle.