| Abstract|| |
Background: Distraction osteogenesis (DO) emerges to be a promising alternative to the traditional method of bone lengthening, by which a significant skeletal and soft tissue enlargement can be obtained in the hypoplastic area in a short period. Manipulations of the newly created callus (regenerate), during DO or as a single step molding procedure at the end of the distraction process, may be necessary to correct the mandibular position.
Aim: To report the efficacy of callus molding (CM) - floating bone concept in the vertical lengthening of ramus by DO and creating a gonial angle in the difficult case of vector selection or surgically induced asymmetry.
Materials and Methods: Retrospective analysis of patients who underwent DO of mandible followed by CM for correction of mandibular asymmetry at authors centers from 2008 to 2014 formed the study group. Only the mandibular distraction cases were included in the study. After the 5 days of latency period, the mandible was distracted at the rate of 1 mm/day. At the end of DO, CM was completed in the 1-3 weeks before consolidation. CM was done either by removing the lower screws with distractor in place or after removal of distractor based on case selection. Secondary maxillary correction by Le Fort I osteotomy using bone graft and further occlusion is corrected by postorthodontics if necessary. Splints were used during CM for predetermined occlusion. In all the cases, postoperative intermaxillary fixation was maintained for 8 weeks for stable ossification of the callus.
Results: The study group consist of four and five cases of external and internal distraction, respectively. Of the 9 patients who underwent DO, 6 were females and 3 were males. The mean age of the population ranged from 10 to 21 years with a mean age of 18 years. The average distracted length of the mandible was 23.55 mm ranging from 20 to 26 mm with the standard deviation of 1.95. The mean deviation of the mandible (crossbite) at the end of distraction was around 8.23 mm ranging from 5 to 12 mm with the standard deviation of 2.17. Of the total 9 cases, only in 3 cases CM is done during DO and the rest 6 cases the CM is done after removal of the distractor. Secondary maxillary correction by Le Fort I osteotomy was done for 4 cases, and postorthodontic correction was done in 3 cases. In all the 9 cases, 100% results (as assessed clinically and radiographically) achieved with the creation of perfect gonial angle.
Conclusions: CM plays a crucial role in those cases where proper vector orientation is hindered because of anatomical difficulty for osteotomy cuts and parallel fixation of the distractor to ramus resulting in cross-bite with deviation toward the undistracted side. Manipulation of the regenerates would provide a precise achievement of gonial angle, minimizing the need for secondary corrections, and diminishing treatment duration and costs.
Keywords: Callus molding, distraction osteogenesis, facial asymmetry, floating bone technique, vector
|How to cite this article:|
Balaji S M. Callus molding in external and internal distraction of mandible. Indian J Dent Res 2015;26:603-8
Distraction osteogenesis (DO) emerges to be a promising alternative to the traditional method of bone lengthening, by which a significant skeletal and soft tissue enlargement can be obtained in the hypoplastic area in a short period. 
Although simultaneous DO is a promising technique in the treatment of craniofacial deformities, even meticulous planning may not avoid deviations from preplanned results. ,,
However, accurate planning, patient selection, implementation, and follow-up are necessary to avoid unfavorable results. The unfavorable results may arise from many factors ranging from improper patient selection, planning and use of inappropriate distraction device, and vector planning.
The orientation of the vector with respect to the anatomic axis of the bone is one of the vital concepts of the distraction. The vector of elongation should be mainly vertically downward, with slight anterior protrusion of the hypoplastic mandible and any deviation in the vector orientation might result in distraction failure or malocclusion. In case of occlusal disasters due to vector deviation, several authors have proposed the "callus manipulation," at the beginning of the consolidation phase, to attain the desired occlusion.
Callus molding - The floating bone technique
"Direct manual shaping of the callus," as suggested by Pensler et al.  was opted to prevent further deviation of mandible or occlusal discrepancy. At the end of the distraction period, after attaining the desired mandibular length, the lower screw of the distraction device was removed, and the callus was manipulated to obtain the desired position of the mandible and proper occlusion thereby correcting the malocclusion taking advantage of the moldability of the callus.
Various authors have adopted the technique of callus molding (CM), at the activation or early consolidation phase, to restore any occlusal changes caused by vector deviation. This technique is based on the "floating bone concept" introduced by Hoffmeister et al. 
This concept emphasizes on the property of moldability of the callus at the early consolidation phase so that the mandible is floated into the desired position, to correct the occlusal changes. The Floating bone method consisted of removal of the distraction devices 2 weeks after the distraction phase and the mandible were guided into the desired occlusion by means of elastics.
Herein, the manuscript intends to describe our experience in manipulating the newly formed regenerate for correction of mandibular asymmetry in cases of difficult vector selection and surgically induced asymmetry.
| Materials and Methods|| |
This retrospective study was performed from the archival records of the center from January 2008 to December 2013. Only those cases with mandibular asymmetry treated by mandibular distractor with at least 1-year follow-up were included in the study. Patients of either gender, who have not been previously operated on were included in the study. Those cases with bilateral mandibular hypoplasia and simultaneous maxillomandibular distraction cases were excluded from the study. Measurement of the amount of mandibular hypoplasia and the amount of distracted length, deviation of mandible to the undistracted side was routinely noted down in the records, which were collected. Besides patient's demographic data, the type of distraction procedure, secondary maxillary cant correction, and postoperative orthodontics details were noted down [Table 1], [Table 2], [Table 3]. Patients without such data were excluded from the study.
All distractor fixation procedures were performed under standard general anesthesia care. In to achieve ramus lengthening without shift in occlusion, the vector (device) should be parallel to the desired direction of lengthening, and the osteotomy cut perpendicular to it. After the latency period of 5 days, intermaxillary fixation (IMF) was done, and distraction was initiated at a rate of 1 mm/day up to 20-26 days depending on the required vertical length. At the end of DO, CM is completed in the 1-3 weeks before ossification.
Postoperative secondary maxillary correction by Le Fort I osteotomy using bone graft and further occlusion are corrected by postorthodontics if necessary in some cases. Splints were used during CM for predetermined occlusion in certain cases. In all the cases, postoperative IMF was maintained for 8 weeks for stable ossification of the callus.
| Results|| |
A total of 9 patients with mandibular asymmetry treated by mandibular distractor were included. Study group consist of 4 and 5 cases of external and internal distraction, respectively. Of the 9 patients who underwent DO, 6 were females and 3 were males. The mean age of the population ranged from 10 to 21 years with a mean age of 18 years. The average distracted length of the mandible was 23.55 mm ranging from 20 to 26 mm with the standard deviation of 1.95. The mean deviation of the mandible (crossbite) at the end of distraction was around 8.23 mm ranging from 5 to 12 mm with the standard deviation of 2.17. Of the total 9 cases, only in 3 cases the CM is done during DO and the rest 6 cases the CM is done after removal of distractor. Secondary maxillary correction by Le Fort I osteotomy was done for 4 cases, and post orthodontic correction was done in 3 cases. In all the 9 cases, 100% results (as assessed clinically and radiographically) achieved with the creation of perfect gonial angle.
| Discussion|| |
DO is a dynamic process interacting with changing soft tissue resistance and vector forces. Its principle is based on the studies of Ilizarov, , who showed that osteogenesis could be induced if the bone is expanded (distracted) along its long axis at the rate of 1 mm/day. This process induces new bone formation along the desired vector without requiring the need for the additional bone graft. The technique also provides the added benefit of expanding the overlying soft tissues, which are frequently deficient in affected patients. 
In DO, accurate planning, patient selection, implementation, and follow-up are necessary to avoid unfavorable results. The unfavorable results may arise from many factors ranging from improper patient selection, planning and use of inappropriate distraction device and vector planning.
The crucial factors that dictate the degree of development of deformity depend on several factors including but not limited to (i) age of development of deformity. (ii) The rate of residual tissue and bone growth. (iii) The degree of growth of adjacent structures such as tongue and developing dental apparatus. (iv) The development of oral musculature and degree of tonicity of the muscles of mastication. These factors are crucial as they influence the vector pattern of the MDO device. As these factors are not uniform universally, the study samples could not be measured using previously described measures. Hence, often in such studies, the outcome measures are often subject to subjective results rather than being objective in outcomes. This probably, is the single most limitation of similar studies, as also in this study. However, the subjective result, being esthetics and achievement of near normal occlusion - Class-1 molar relationship with no crowding of denta-alveolar structures and correction to acceptable gonial angle remains as the most common objective. In this regard, this study also relies on the subjective perception of the esthetics, achievement of Class-1 molar relationship with minor deviations.
In addition, the vector design of the affected mandible takes into the account of growth potential, "V" principle of growth of mandible, the age of the patient, existing minor occlusal anomalies such as crowding or proclination of tooth besides the differential rate required between length, width, and height of the mandible. Hence, the treatments are often customized. The resultant neo-bone or the regenerate and rate of the movement of teeth into such regenerate by themselves are an issue of contention in literature. The limited number of cases leads to nonavailability of standard treatment protocols for such disorders and associated risk factors. Customization of the procedure to each case remains the only alternative. Furthermore, there are no known factors that could predict the development of the abnormal growth preoperative to MDO placement. In such a scenario, relying on the surgeon's expertise and training becomes crucial. The surgeon during the formation and management of regenerate has to be on watch for the regenerate's quantity and moldability. Should an asymmetry or malocclusion develops; use of the callus molding technique, either during or post MDO becomes a necessity.
At this situation, the control of distraction vectors during a distraction of mandible for the correction of facial asymmetry could be a problem of major impact, if the orientation of vector is miscalculated. The altered vector resulted in the transverse growth of the mandible leading to deviation of mandible to the undistracted side and the resultant crossbite. Hence, the CM - the floating bone technique has been successfully used for the undesired effects of vector manipulation.
"Direct manual shaping" of the callus was another method advocated by Pensler et al.  and Kunz et al.  were the first to report on the immediate manipulation of a newly created regenerate to correct minor deviations in a 1-step procedure in 6 of 9 patients. In this method, the distraction devices were removed once the planned mandibular lengthening had been achieved. The open bite is then closed by the manual shaping of the callus to achieve optimal occlusion.
Grayson and Santiago, Hanson and Melugin, , initiated the technique of "molding the generate" as yet another option to control an open bite. In contrast to the previous methods, molding is carried out during the activation phase rather than the consolidation phase of DO. According to the authors, the fresh regenerate revealed considerable ability to be molded, allowing the creation of well-shaped gonion angles and correct occlusion and proposed that this method offers corrective options in cases with severe vector deviation and also could be integrated into a plan for correction of complex mandibular deformities.
Various study demonstrates that molding of the generate during active distraction can be performed to reduce the mandibular plane angle and control an open bite. ,,, During active mandibular distraction, intermaxillary elastic traction was considered essential to achieve skeletal change and a precise occlusal outcome. Yen et al. reported in a study where experimentally produced open bites were closed with heavy coils placed between the maxilla and mandible in rabbits taking advantage of the activation possibilities of a multiplanar distraction device, similar to the ones used in this case series, with possible control of distraction vectors (force and direction). 
Under stable conditions, a fresh regenerate can be molded to a considerable extent without permanently endangering osseous healing.  To prevent unwanted dentoalveolar changes from occurring during elastic use, skeletal elastic anchorage rather than dental anchorage is recommended. However, if orthodontic appliances are used for the intermaxillary molding elastics, heavy rectangular wires or a bonded occlusal splint are recommended to prevent distortion of the dental arches.  Noticeable postoperative correction of crossbite with marked improvement in facial asymmetry can be achieved. Representative images are shown in [Figure 1] and [Figure 2]. The mandibular distraction and the callus manipulation had no influence on temporomandibular joint function in those cases. Mouth opening and mandibular movements were in the normal range, and there was no articular noise or pain.
|Figure 1: (a) Preoperative image showing marked left side deviation of the jaw while smiling. (b) Preoperative orthopantomogram showing hypoplastic left condyle with midline shift toward left. (c) Postoperative image showing external distractor in place placed after osteotomy cuts. (d) Callus formation after distraction of about 25 mm which resulted in right side open bite with marked deviation. (e) External distractor in place. (f) Postoperative image showing crossbite and deviation toward undistracted side. (g) Removal of external distractor. (h) Intermaxillary fixation done after positioning in determined occlusion. (i) Callus molding phase. (j and k) Postoperative image showing achieved stable occlusion and profile. (l) Postoperative orthopantomogram showing treated mandibular deviation and crossbite by callus molding|
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|Figure 2: (a) Case of hemifacial microsomia showing deviation toward left. (b) Computed tomography image showing deficient left mandibular ramal height. (c) Placement of intraoral distractor. (d) Orthopantomogram showing distractor in place with newly formed callus bone by distraction. (e) Overcorrection achieved. (f) Callus molding. (g) Corrected crossbite and occlusal cannot by callus molding. (h) Postoperative image with improved facial profile|
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The complexity of the disease process and treatment methods coupled with the lack of uniformity in either rendered nonavailability of a distinct variable to measure the outcome. This issue was further complicated by nonavailability of a large number of cases or uniform operating procedures. However, the knowledge that emanates from the experience of effectively managing the complex cases gives a fair idea how the callus needs to be handled in dire situations. The outcome of this study indicates the effectiveness of the interference of handling callus during or before its ossification to avoid disastrous or asymmetrical esthetics. Thus, the manipulation of the callus for corrective options of unfavorable deviation following vector deviation yields favorable clinical results.
| Conclusion|| |
It is concluded that the vector orientation is a vital aspect of the successful outcome of DO process, and "direct manual shaping of the callus" can be a reliable option to correct occlusal discrepancies resulting during the DO, especially with deviation of the vector.
The vector of distraction needs to be carefully planned so as to maximize the beneficial effects of DO in terms of achieving the functional and occlusal goals. This determination of movement of the osteotomized bone segment is planned preoperatively with the help of clinical examination, cephalometry, model analysis, and three-dimensional computed tomography. The vector of distraction also needs to be carefully evaluated during the process of distraction to make sure that the distracted bone is moving along predetermined path.
Manipulation of the regenerates would provide a precise achievement of gonial angle, minimizing the need for secondary corrections and diminishing treatment duration and costs.
Declaration of patient consent
The author declares that all appropriate patient consent forms are obtained. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. S M Balaji
Department of Oral and Maxillofacial Surgery, Balaji Dental and Craniofacial Hospital, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]