| Abstract|| |
Objective: Evaluate the changes in alveolar bone as a result of maxillary and mandibular incisor retraction in patients with bimaxillary protrusion by means of using lateral cephalograms and computed tomography (CT) scans and to investigate any occurrence of bony defects like dehiscence and fenestration.
Subjects and Methods: Ten patients (age 15 ± 3 years) with bimaxillary protrusion treated by extraction of four first premolars were investigated by lateral cephalograms and CT scans during pre-treatment (T1) and after 3 months of completion of incisor retraction (T2). The labial and lingual cortex of all the incisors were assessed on the CT scan with measurements taken at site adjacent to widest point of the labiolingual root in three slices separated by 3 mm at crest level (S1), mid root level (S2), and apical level (S3).
Result: In the mandibular arch, after lingual movement of the incisors, the bone labial to the anterior teeth decreased in thickness at the coronal level of the left lateral and left central incisors. Left lateral incisor showed significant changes in all the three levels. In the maxilla the change in the labial bone thickness was not statistically significant. Lingual bone of all the incisors showed significant changes in S1 level and S3 levels. Few patients demonstrated bone dehiscence that was not visible macroscopically or cephalometrically.
Conclusions: When incisors are retracted, the risk of adverse effect is present. This must be carefully monitored to avoid negative iatrogenic effects. This study needs follow up after 6 months or 1 year after completion of the orthodontic treatment to assess the long-term consequences.
Keywords: Alveolar bone thickness, computed tomography, dehiscence, orthodontic treatment, retraction
|How to cite this article:|
Nayak Krishna U S, Shetty A, Girija M P, Nayak R. Changes in alveolar bone thickness due to retraction of anterior teeth during orthodontic treatment: A cephalometric and computed tomography comparative study. Indian J Dent Res 2013;24:736-41
Bimaxillary protrusion is a malocclusion which is routinely treated by extraction of first premolars in both the jaws followed by retraction of anteriors is a widely accepted method of treatment, , but it is not without controversies. The debate and controversy is whether the alveolar bone follows in the direction of tooth movement or there is an actual loss of supporting alveolar bone. In the case of severe protrusion where maximum retraction is required, the tooth tends to breach the cortical plate exposing roots and also leading to loss of alveolar bone.  Compensation for the bone loss that occurs by remodeling capacity of alveolar bone is questionable in each and every case. Autopsy findings have also shown that the dehiscence and fenestration occur in those individuals who have undergone tooth retraction. The bony defects are not evident on radiographs, nor by clinical examination. , Investigators have studied the effect of incisor retraction on the palatal cortex using laminography and found that the palatal cortex could not be detected immediately after retraction of the incisors.  The effect of various incisal movements within the symphysis have been studied in cephalometrics and laminograms. The differences in axial inclinations and perforations were not readily discernible by other types of radiographs.  The different imaging qualities of cephalograms and computed tomography in the region of the lower incisors were compared with the microscopic and histological finding of specimen being compared with the corresponding radiological findings, by Fuhrmann,  who concluded that CT scanning is the only imaging technique giving three dimensional quantitative evaluation of the labiolingual alveolar bone width and the facial and lingual cortical bone plates. Kobayashi  found cone-beam CT to be a useful tool for preoperative evaluation in dental surgery, because of the relatively small field size of its images limiting the patients exposure to radiation.
|How to cite this URL:|
Nayak Krishna U S, Shetty A, Girija M P, Nayak R. Changes in alveolar bone thickness due to retraction of anterior teeth during orthodontic treatment: A cephalometric and computed tomography comparative study. Indian J Dent Res [serial online] 2013 [cited 2019 Oct 23];24:736-41. Available from: http://www.ijdr.in/text.asp?2013/24/6/736/127623
The aim of present study is to investigate the following after orthodontic retraction of anterior teeth
- Evaluate the changes in alveolar bone as a result of maxillary and mandibular incisor retraction in patients with bimaxillary dentoalveolar protrusion by means of using cephalograms and computed tomography
- Evaluate any occurrence of the bony defect like dehiscence and fenestration.
| Subjects and Methods|| |
The criteria for selection were as follows.
- Patients with bimaxillary dentoalveolar protrusion requiring extraction of first premolars with minimal anterior crowding
- All patients required distalization of canines
- Gingival showed no signs of inflammation
- Periodontal healthy teeth with generalized probing depths less than 3 mm and no radiographic evidence of bone loss pre-treatment
- Patients treated using preadjusted edgewise appliance.
- Age group selected was 15 ± 3 years
- Sex of the patient was not taken as criterion for case selection.
The research was approved by independent ethical committee and informed consent was obtained from the patients.
For each patient pre-treatment and post-retraction lateral cephalograms, orthopantomograms and full mouth periapical radiographs were obtained. In addition, contiguous 1 mm slice thickness CT scan were obtained for both maxillary and mandibular incisors at 120 KV, 160 MVA, with window width set at 2444 level 364 from spiral CT (GE medical systems). CT scanning was done perpendicular to the long axis of the central incisor on each jaw. This angle was determined by setting the gantry angle according to the lateral scanogram of the head position [Figure 1]. For each tooth, the thickness of the labial and lingual alveolar plates were measured to nearest 0.2 mm. Measurements were taken at site adjacent to widest point of the labiolingual root in three slices separated by 3 mm (S1, S2, and S3) [Figure 2]. Thus six measurements for each tooth, three labial, and three lingual were taken at T1. The same measurements were repeated 3 months after anterior retraction was completed (T2). CT scans were done by same machine and operator. Measurements were taken from images generated with maximum zoom, according to the size of maxillary and mandibular segments. T2 measurements were taken at the same slice level as those at T1, using the first slice on the incisal edge of tooth as a reference point.
|Figure 1: CT scanning was done perpendicular to the long axis of the central incisor on each jaw. This angle was determined by setting the gantry angle according to the lateral scanogram of the head position|
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|Figure 2: Location of bone thickness measurements before and after retraction|
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Angular and linear measurements of the central incisor were also evaluated on the lateral cephalograms to determine the amounts of lingual movement and to differentiate between tipping and bodily retraction. The cephalometric measurements (in mm) are the incisor point of U1 to pterygoid vertical U1-PTV, the cervical point of U1-PTV, apical point of U1-PTV, the incisor point of U1-FH, the incisor point of L1 to pterygoid vertical L1-PTV, the cervical point of L1-PTV, apical point of L1-PTV, the incisor point of L1-FH. The measurements on the lateral cephalograms were made by same investigator.
The appliance of choice was preadjusted edgewise appliance with 0.022-inch Roth prescription (Omrco, USA). Initial leveling was achieved with 0.016 nitinol (3M unitek) arch wires. Anchorage was reinforced using TPA and lingual arches in upper and lower arches, respectively. The initial leveling and alignment took an average of 2 months. Separate canine distalization was done on 0.018'' round A. J. Wilcock S.S wire with adequate anchor curves using close coiled NiTi spring (Ortho Quest, USA) with constant force levels of 150 g. After canine distalization 0.017 × 0.025 inch rectangular wire with reverse curve of spee was engaged in all the bracket slots in both the arches for 1 month. Maxillary and mandibular anterior retraction was done by sliding mechanics with light continuous forces from elastomeric chains (about 100 g). Force was uniformly maintained through out the retraction by measuring with Dontrix gauge. Anterior retraction was completed within 5 months. After incisor retraction a mean rest period of 3 months for remodeling to take place was allowed before T2 CT scans.
| Results|| |
The statistical analysis for the study was assessed as follows.
- Mean difference values
- Standard deviation of mean value
- Wilcoxon signed rank sum test was used for statistical analysis.
Results of cephalometric analysis
The results of the lateral cephalometric measurements listed in [Table 1] and [Table 2]. In most patients there was a significant difference between the mean T1 and T2 cephalometric measurements.
|Table 1: Mean values measured from lateral cephalograms for maxillary anterior teeth before and after retraction |
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|Table 2: Mean values measured from lateral cephalograms for mandible anterior teeth before and after retraction |
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The angles U1-SN, U1-FH, U1-NA and U1-A Pog decreased significantly (P = 0.005).
The U1-NA and U1-A Pog distance also decreased significantly (P = 0.005).
The decrease in U1 incisal points-PTV distance (P = 0.005) is highly significant.
U1cervical-PTV distance (P = 0.021) significant.
U1apical point-PTV distance was not significant.
The increasing FMIA was highly significant (P = 0.007).
The angles IMPA was highly significant (P = 0.008)
The angles L1-NB was also highly significant (P = 0.007)
L1-A Pog was also significant (P = 0.013)
There were also significant decrease in L1 incisor points-PTV distance (P = 0.011).
L1 cervical point to PTV distance and L1 apex to PTV distance were not significant.
Results of CT analysis
The results being the changes in alveolar bone thickness as measured on the CT scans from T1 to T2 are listed in [Table 3], [Table 4], [Table 5], [Table 6].
|Table 3: Comparison of mean values of maxillary labial alveolar bone width measured form CT scans before and after retraction of maxillary anterior teeth |
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|Table 4: Comparison of mean values of maxillary lingual alveolar bone width measured form CT scans before and after retraction of maxillary anterior teeth |
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|Table 5: Comparison of mean values of mandibular labial alveolar bone width measured form CT scans before and after retraction of mandibular anterior teeth |
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|Table 6: Comparison of mean values of mandibular lingual alveolar bone width measured form CT scans before and after retraction of mandibular anterior teeth |
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In the maxilla [Figure 3] the change in the labial bone thickness was not statistically significant. The width of the labial bone to the maxillary left lateral incisor decreased significantly at S2. The maxillary bone thickness lingual to the both the left lateral incisors showed significant values at S3 level; lingual to both the central incisors showed a significant change in the S1 level and also maxillary left central incisors showed a significant change in S2 and S3 levels. The changes were significant at the coronal level S1 in maxillary left lateral incisor where as S3 measurement showed the minimal change. But the maxillary right lateral S3 showed a significant change.
|Figure 3: Pre-treatment (T1) and post-anterior retraction (T2) slices of maxillary arch at S1, S2, and S3. Bone dehiscences are clearly visible at T2 lateral incisors in all three levels|
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In the mandible [Figure 4], after lingual movement of the incisors, the bone labial to the anterior teeth decreased in thickness at the coronal level of the left lateral and left central incisors. There was a significant change in left central incisor at the coronal level S1 and mid root level S2. Left lateral incisor showed significant changes in all the three levels. The lingual alveolar bone of the mandible decreased significantly after retraction of the incisors. The decrease was significant at S1 for both the central incisors. There was also a significant decrease in the bone width lingual to the mandibular right central incisor at S1 and S3 levels and also left central incisor showed significant changes in coronal level (S1) and mid root level (S2) and both the lateral incisors also showed significant changes at the S3 level.
|Figure 4: Pre-treatment (T1) and post-anterior retraction (T2) slices of mandibular arch at S1, S2, and S3.Bone dehiscence are clearly visible at T2 at S1 level for lower incisors|
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| Discussion|| |
Our goal was to evaluate the changes in labial and lingual alveolar bone during incisor retraction in maxilla and mandible thus it was decided to evaluate the maximum incisor retraction in bimaxillary dentoalveolar protrusion patients. 
Cephalometric radiographs are mid sagittal projections. Thus the actual limits of the palate and the symphysis at the midline may be narrower than the traced image.  The cortical plate that is observed could represent the superimposition of any other tooth that did not denude the alveolar bone. And they do not allow for evaluation of sites of dehiscence. CT analyzing method gives both quantitative and quantitative assessment of the labial and lingual bony support of the tooth, also three-dimensional interpretations of the alveolar osteodynamics, especially the development and repair of orthodontically induced bone dehiscence. ,, The CT findings have proven to be statistically similar to histological measurements. ,,
Considering all these points this study is done by using CT measurements to more accurately evaluate bone width changes. Use of the CT scan allowed us to evaluate every tooth at three different levels. If the teeth were moved bodily in the alveolar process over a distance, the remodeling would take place and form new healthy bone.  Our results demonstrate that lingual movements of the maxillary and mandibular incisor teeth reduced the lingual alveolar bone in both the arches. According to De angles,  mechanics that induces alveolar distortion triggers a coordinated opposition and resorption of the alveolar bone, retaining its structural characteristics and size as it moves. In our patients the maxillary and mandibular alveolar thickness did not remain the same. There was 1 mm of reduced thickness of alveolar bone from pre-treatment to post-treatment. Our findings agree with the results of Wainwright, Ten Hove and Mullie Vardimon et al.
In our study we waited for an average of 3 months before we did the T2 scans. The aim was to allow osteoblasts activity to start the repair process. It would be valuable to reassess these patients years from now to determine whether repair has taken place. Whereas famous authors like Remmelink and van der Molen  studied the patients of Ten Hove and Mullie after several years after the original study and they have found well-defined dense cortical plate in association with relapse of torque of the anterior teeth.
The macroscopic evaluation of patients in our study revealed no bony dehiscence or poor periodontal health. The force we used in our study was within the acceptable limits prescribed by other authors. , The kind of movement we brought was bodily retraction of anterior teeth however it was not complete translation but by controlled tipping. It can be appreciated in the cephalometric readings, by the finding that apex-ptv of both maxillary and mandibular incisors has not changed. It gives the same value during pre- and post-treatment. The post-treatment records show that the maxillary incisors moved in lingual direction 4 mm at coronal level, 3 mm at cervical level, and 1.5 mm at the apical level. The mandibular incisors moved in the lingual direction 3.5 mm at coronal level, 3 mm at cervical level, and 1.5 mm at the apical level. These differences indicate that some degree of tipping was involved in the combined movement. These finding agrees with the result of Vardimon et al.  who observed that in patients subjected to retraction with torque, the result was a combined movement with some tipping rather than pure translation. In our study alveolar bone loss was more evident in the marginal and mid root regions than it was at the apical region because of more controlled tipping. The retraction forces applied to the incisors was concentrated at the alveolar crest, leading to greater accumulation of pressure in the marginal region.
The thickness of bone lingual to maxillary lateral incisors decreased more than that of central incisors. Reason may be that force applied to all four incisors was spread equally, but periodontal ligament area of maxillary central incisors was larger compared to that of laterals. So there was more concentrated pressure on the alveolar cortical plate of the maxillary lateral incisors leading to greater reduction in the thickness of the cortical plate lingual to these teeth. All four mandibular incisors showed similar amount of bone loss in the mandibular anterior region probably because of the four incisors having the same amount of periodontal ligament area and had received the same amount of pressure. Our data indicate that cortical alveolar bone changes are so minimal that they can be attributed to measurement error. Hence all the pre- and post-readings are taken by the same machine and same operator. According to our measurements the labial bone width changes were between 0.2 and 0.5 mm. Such minute changes cannot be quantified accurately and are within the margins of error. Fuhrmann et al. also suggest that measurements are accurate only to the nearest 0.5 mm. 
Some individual variations: Some patients showed dehiscence in the direction of tooth movements in both the jaws after incisor retraction. The mean value for bone thickness changes in our study samples did not indicate any bony dehiscence, only reduction of alveolar bone width. In some of the cases negative bone width changes were found indicating these patients had marginal bone loss. Wehrbein et al.,  who noted this iatrogenic damage stated that histological changes were substantially more pronounced than radiographic and microscopic evaluation reveal.
| Conclusion|| |
High forces used in orthodontic practice do not necessarily produce most efficient tooth movement. In contrast, they might overload the periodontal tissues and cause negative effects that will hinder the tooth movement.
The results of our study indicate that when maxillary and mandibular incisors are retracted, the risk of adverse effect may be present. Further research into application of our knowledge of biomechanics and refinement in our appliances is needed to avoid such clinical situations from arising. Until then, would delineation of the limits of the orthodontic tooth movement prior to the start of treatment would be beneficial? The lateral cephalograms, though two-dimensional radiography however fails to provide a record of any single incisor. High resolution computed tomography has proven to be useful in assessing labial and lingual alveolar bone structure and diagnosing dehiscence. Although computed tomography is not yet available for routine orthodontic screening because of technical and financial aspects and additional radiation risks, it may contribute toward clarifying scientific issues and be used as an additional diagnostic aid.
Since the long-term consequence of these alveolar bone losses and some dehiscence are unknown, this study needs follow up after 6 months or 1 year after completion of the orthodontic treatment.
| References|| |
|1.||Farrow AL, Zarinna K, Azizi K. Bimaxillary protrusion in black Americans- esthetic evaluation and treatment consideration. Am J Orthod Dentofacial Orthop 1993;104:240-50. |
|2.||Scott SH, Johnston LE. The perceived impact of extraction and non extraction treatments on the matched samples of African American patients. Am J Orthod Dentofacial Orthop 1999;116:352-8. |
|3.||DeAngelis V. Observations on the response of alveolar bone to orthodontic force. Am J Orthod 1970;58:284-94. |
|4.||Wehrbein H, Furhmann RA, Diedrich PR. Human histologic tissue response after longer term orthodontic tooth movement. Am J Orthod Dentofacial Orthop 1995;107:360-71. |
|5.||Wingard CE, Bowers GM. The effects of facial bone from facial tipping of incisors in monkeys. J Periodontol 1976;47:450-4. |
|6.||Mulie RM, Ten Hoeve A. The effect of incisor retraction on a palatal cortex with severe class II malocclusions under treatment with Begg's technique. J Clin Orthod 1975;10:882-99. |
|7.||Mulie RM, Ten Hoeve A. The limitations of tooth movement within the symphysis studied with laminagraphy. J Clin Orthod 1976;10:882-99. |
|8.||Fuhrmann R. Three-dimensional interpretation of labiolingual bone width of the lower incisors. Part II. J Orofac Orthop 1996;57:168-85. |
|9.||Kobayashi K, Shimoda S, Nakagawa Y, Yamamoto A. Accuracy in measurement of distance using limited cone-beam computerized tomography. Int J Oral Maxillofac Implants 2004;19:228-31 |
|10.||Vardimon AD. Cortical bone remodeling/tooth movement ratio during maxillary incisor retraction with tip versus torque movements. Am J Orthod Dentofacial Orthop 1998:114:520-9. |
|11.||Handelman CS. The anterior alveolus: its importance in limiting orthodontic treatment. Angle Orthod 1996;2:95-110. |
|12.||Katagiri S, Yoshie H, Hara K, Sasaki F, Sasai K, Ito J. Application of computed tomography for diagnosis of alveolar bony defects. Oral Surg Oral Med Oral Pathol 1987;64:361-6. |
|13.||Wainwright WM. Faciolingual tooth movement: Its influence on the root and cortical plate. Am J Orthod 1973;64:278-302. |
|14.||Ten Hoeve A, Mulie RM. The effect of antero-postero incisor repositioning on the palatal cortex as studied with laminography. J Clin Orthod 1976;10:804-22. |
|15.||Sarikaya S, Haydar B, Ciðer S, Ariyürek M. Changes in alveolar bone thickness due to retraction of anterior teeth. Am J Orthod Dentofacial Orthop 2002;122:15-26. |
|16.||Quirynen M, Lamoral Y, Dekeyser C, Peene P, van Steenberge D, Bonte J, et al. The CT scan reconstruction technique for reliable jaw bone volume determination. Int J Oral Maxillofacial Implants 1990;5:384-9. |
|17.||Fuhrman RA, Wehrbein H, Langen HJ, Diedrich PR. Assessment of the dentate alveolar process with high resolution computed tomography. Dentomaxillofac Radiol 1995;24:50-4. |
|18.||Remmelink HJ, Van der Molen AL. Effects of anteroposterior incisor positioning on the root and cortical plate: A follow up study. J Clin Orthod 1984;18:42-9. |
|19.||Storey E, Smith R. Force in orthodontics and its relation to tooth movements. Aust J Orthod 1952;56:11-8. |
|20.||Ricketts RM, Bench RW, Gugino CF, Hilgers JJ, Schulhof RJ. Bioprogressive therapy. Denver: Rocky Mountain Orthod; 1979. |
|21.||Wehrbein H, Bauer W, Diedrich PR. Mandibular incisors, alveolar bone, and symphysis after orthodontic tooth movement: A retrospective study. Am J Orthod Dentofacial Orthop 1996;110:239-46. |
Departments of Orthodontics and Dentofacial Orthopedics, AB Shetty Memorial Institute of Dental Sciences, Mangalore
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]