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CASE REPORT
Year : 2006  |  Volume : 24  |  Issue : 1  |  Page : 30-39
 

Long term results of mandibular distraction


Maxillofacial and Dental Department, Great Ormond Street Hospital for Children NHS Trust

Correspondence Address:
Puneet Batra
Maxillofacial and Dental Department, Great Ormond Street Hospital for Children NHS Trust

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-4388.22835

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  Abstract 

Mandibular distraction osteogenesis has become a popular surgical modality due to its many advantages over conventional orthognathic surgical procedures. However, in spite of the technique having been used for over 15 years, no concrete long term results are available regarding the stability of results. We discuss the various studies which have reported either in favour or against the stablility of results after distraction. We report a series of 6 cases (3 unilateral and 3 bilateral distraction) where distraction was carried out before puberty and followed them up to seven years after removal of distractors. This case series shows that results achieved by distraction osteogenesis are unstable or best unpredictable with respect to producing a permanent size increase in the mandible. The role of the distraction osteogenesis in overcoming the pterygomassetric sling is questionable. We suggest a multicenter study with adequate patient numbers treated with a similar protocol and documented after growth cessation to have meaningful conclusions on the debate of distraction osteogenesis versus orthognathic surgery.


Keywords: Functional matrix, Mandibular distraction, Regenerate


How to cite this article:
Batra P, Ryan F S, Witherow H, Calvert M L. Long term results of mandibular distraction. J Indian Soc Pedod Prev Dent 2006;24:30-9

How to cite this URL:
Batra P, Ryan F S, Witherow H, Calvert M L. Long term results of mandibular distraction. J Indian Soc Pedod Prev Dent [serial online] 2006 [cited 2020 Nov 26];24:30-9. Available from: https://www.jisppd.com/text.asp?2006/24/1/30/22835


Distraction osteogenesis is the process of generating new bone in a gap between the two bone segments in response to the application of graduated tensile stress across the bone gap. Bone lengthening by osteotomy (corticotomy) and distraction osteogenesis of the long bones was first described in 1905 by Codvilla[1] and popularized by Illizarov.[2],[3] Mandibular lengthening by gradual distraction was reported by Synder et al[4] who used an extraoral device in a canine study: new bone formation at the elongated site was demonstrated later by Karp et al .[5] In 1992 McCarthy et al[6] successfully elongated the mandible by up to 24mm. It was proclaimed that distraction osteogenesis would affect the entire facial milieu with an increase in soft tissue envelop due to expansion and muscle hypertrophy. Molina and Monasterio[7] stated that "skeletal distraction proceeds parallel to an expansion of all the soft tissues of the face and upper neck (skin, muscles, vessels and nerves), achieving esthetic results much superior to those obtained by skeletal surgery, by soft tissue surgery done independently, or by a combination of both." Since then numerous papers and reports have been published on distraction.

Distraction osteogenesis has now been advocated as an effective and safe technique for mandibular lengthening. However, the regenerate in distraction osteogenesis is subjected to a number of external forces during consolidation, including those from muscles of mastication and the soft tissue envelope. These external forces can alter the postdistracted position, size and shape of the mandible.[8]

Long term followup studies have been documented by various authors. The followup period in these studies has varied from 3 months to 6 years. The results are diverse as different methods of evaluation and different timings have been used. Authors have used photographs, cephalograms (lateral, PA, 3 dimensional cephalometry), CT scans and panoramic radiographs to study the long term results following distraction. In a comprehensive review of distraction by Swennen et al (2000),[9] they found that only 62 cases had been followed up for a year or longer and only 6 relapses were reported in the congenital micrognathia sample. Among the acquired micrognathia cases only 9 cases were followed up for one year or longer, none of the cases showed a skeletal relapse.

Studies reporting stable results



• Molina and Monasterio[7] evaluated 106 (87 unilateral and 19 bilateral) cases and after clinical and radiographic evaluation were convinced that no relapse had occurred in the 3 months -3.5 years followup.

• Klein and Howaldt[10] evaluated their 9 cases (6 unilateral and 3 bilateral) and after 3-17 months of followup found stable results.

• Grayson et al[11] followed up 10 cases (5 unilateral and 5 bilateral) of mandibular distraction with serial cephalometric tracings from 12-70 months after distraction and found continued growth on the distracted side without relapse. However they recommended overcorrection in growing children.

• Carls and Sailer[12] evaluated 14 cases (5 unilateral and 9 bilateral) and followed them up from 0.3 to 6.5 years. They found that the articulare to pogonion length showed addition growth.

• Hollier et al[13] followed up 8 patients for an average of 32.6 months (range 12-92 months) and suggested that to minimize the need for repeat distraction, it would seem intuitive that overcorrection would be beneficial.

• Kusnoto et al[14] observed 6 cases (5 unilateral and 1 bilateral) using three dimensional cephalograms and concluded that the ramal height decreased by 1mm and the mandibular body was found to resume its growth with a faster rate at the distracted side after 18 months of followup.

• Ko et al[15] followed up their 11 cases of unilateral distraction for one year and found that the new saggital jaw relation and mandibular body length were stable, and the achieved occlusal interdigitation was well maintained. However the ramus and chin deviation demonstrated some relapse.

Studies showing relapse

• Marquez et al[16] reported a two year followup of uniplanar distraction in a 7 year old boy and concluded that antero-posterior elongation of the mandible was relatively stable, whereas the vertical ramal lengthening was minimal. There was a relapse of 87% of the 15mm of vertical distraction. They stated that "distraction osteogenesis does not accelerate growth and does not predictabily increase length in the mandibular ramus".

• Rachmiel et al[17] followed up 11 cases for 1 year and using clinical and radiographic observation concluded that some relapse does occur in vertical ramus height.

• Stucki-McCormick et al[18] reported long term followup of one case operated on early and concluded that bony improvements which resulted were not maintained during growth.

• Huang et al[19] evaluated their 5 cases (4 unilateral and 1 bilateral) and followed them up for 1 year and found that the Co-Gn (mandibular length) was stable, Co-Go (ramus) showed nearly 50% relapse and the Go-Gn length (body length) showed some growth.

Thus it can be seen that inspite of the procedure of distraction osteogenesis being invogue for over 10 years, no definitive conclusions have been reached on the long term stability of the results. We report the cephalometric data and superimpositions of 6 cases (3 underwent unilateral distraction and 3 bilateral) which were followed up for 7 years or longer.


  Case Report Top


A retrospective analysis of all cases which underwent distraction in the Great Ormond Street Hospital for Children NHS Trust was done. Patients who underwent distraction prepuberty and were now in CVMI Stage V or VI in their lateral cephalograms were first short listed. Then the available records were analysed and patients who had serial cephalograms (lateral cephalogram as well as postero-anterior) predistraction, immediately after distractor removal, 1 year post distractor removal, 3 years, 5 years and 7 years post distractor removal were included in the study. Only 6 patients (3 unilateral and 3 bilateral) could be included in the study after applying the stringent inclusion criteria [Table - 1].

All radiographs were traced independently under optimum conditions by one investigator (PB). Three measurements for each variable were taken and the mean recorded for the different time intervals. Changes in each measurement at the different intervals were calculated from the measurements from each set of radiographs and compared. The different time intervals were labeled from T0 to T5 as under

• T0: Predistraction

• T1: Immediately after distractor removal

• T2: 1 year after completion of distraction

• T3: 3 years after completion of distraction

• T4: 5 years after completion of distraction

• T5: 7 years after completion of distraction

The lateral cephalograms were used to analyze the bilateral cases which underwent distraction whereas in unilateral distraction cases measurements were done on both lateral as well as PA cephalograms. Superimposition of pre-distraction, post-distraction and the 7 year followup radiographs were done.

Case 1

A 13.5 year old female patient with hemifacial microsomia (L) as well as cleft palate underwent unilateral distraction of the left side [Table - 1][Table - 2]. The ANB differential was 5° predistraction and reduced by 2° after completion of distraction. However, at followup the differential was 4° (1° due to increase in SNA and 1° due to decrease in SNB). The mandibular plane angle decreased by 5° but returned to pre distraction value during followup. The vertical position of the pogonion increased by 10mm and the horizontal position increased by 3 mm. However the vertical position of pogonion reduced by 1mm while the horizontal position reduced by 2 mm in the followup period of 7 years.

The mandibular length on the normal side increased by 2 mm after distraction and another 2 mm in the subsequent followup period. On the distracted side the increase in mandibular length was 4 mm after distraction. However in the subsequent followup 1mm of mandibular length was reduced showing a relapse tendency. The body length on the normal side remained stable during distraction but showed an overall increase by 2 mm in the study period. The body length on the affected side increased by 3 mm after distraction and another 1 mm in the followup period. The ramal length was increased by 2 mm on the normal side during the study period, though no change occurred immediately after distraction. On the distracted side the ramal length increased by 12 mm after distraction. However in the subsequent followup period about 3mm of the increase in ramal length was lost (25% relapse). The gonial angle on the normal side opened up slightly by 2° during the study period while on the distracted side it as initially reduced by 9° and subsequently increased slowly and was actually 3° greater than the value which was there predistraction.

The maxillary height on the normal side increased by 2mm after distraction and another 2 mm in the followup period. On the distracted side a net gain of 6 mm was achieved after distraction. However relapse of 3 mm (50%) in maxillary height was noticed in the subsequent followup period. The occlusal height increased by 5mm on the normal side and 12 mm on the distracted side. However at followup there was a further increase in occlusal height by 2 mm on the normal side and a decrease in occlusal height by 2 mm on the distracted side. Maxillary width on the normal side increased by 1 mm during the study period, while the width increased by 3 mm on the distracted side and subsequently reduced by 2 mm in the followup period (66% relapse in maxillary width). The ramus height increased by 4 mm on the normal side after distraction and 2 mm at followup. On the distracted side there was a substantial increase by 19 mm after distraction but at followup about 7 mm of the increase had relapsed (33% relapse in ramal height). The chin point was deviated by 10mm to the right side and after distraction was 1 mm to the right. However in the followup period due to a combination of growth on the normal side exceeding the growth on the affected side as well as relapse of the distracted side the chin point was still deviated to the right by 5 mm. [Figure - 1]

Result

Substantial relapse- Needs More surgery

Case 2

A 10 year old female patient with hemifacial microsomia (L) underwent unilateral distraction [Table - 1][Table - 2]. The ANB differential was 8° predistraction and reduced by 1° after completion of distraction. However, at followup the differential was 6° (2° due to increase in SNA and 3° due to decrease in SNB). The mandibular plane angle decreased by 2° but stabilized to pre distraction value during followup. The vertical position of the pogonion increased by 4 mm and the horizontal position increased by 8 mm. However the vertical position of pogonion increased by 2 mm while the horizontal position reduced (2 mm) to a value even worse than the pretreatment value.

The mandibular length on the normal side increased by 1mm after distraction and another 3 mm in the subsequent followup period. On the distracted side the increase in mandibular length was 5 mm after distraction. However in the subsequent followup 2 mm of mandibular length was reduced (40% relapse in mandibular length gained after distraction). The body length remained stable during distraction but showed an overall increase by 4 mm in the study period. The body length on the affected side increased by 4 mm after distraction and another 1 mm in the followup period. The ramal length was increased by 5 mm on the normal side during the study period, 2 mm increase occurred immediately after distraction. On the distracted side the ramal length increased by 8mm after distraction. However in the subsequent followup period about 3mm of the increase was lost (37.5% relapse in ramal length). The gonial angle on the normal side opened up by 7° (4° after completion of distraction) during the study period while on the distracted side it as initially reduced by 25° and subsequently increased slowly and was actually 8º less than the value which was there predistraction.

On the normal side the maxillary height increased by 1mm during the study period. On the distracted side a net gain of 2mm was achieved after distraction. However relapse of this 2mm increase (100% relapse in maxillary height) was noticed in the subsequent followup period. The occlusal height increased by 1mm on the normal side and 7mm on the distracted side. However at followup there was a further increase in occlusal height by another 1mm on the normal side and a decrease in occlusal height by 3mm on the distracted side (42.8% relapse in occlusal height). Maxillary width on the normal side remained unchanged during the study period, while the width increased by 1mm on the distracted side and subsequently reduced by 1mm in the followup period (total relapse in maxillary width). The ramus height increased by 4mm on the normal side after distraction and remained stable at followup. On the distracted side there was an increase by 12mm after distraction but at followup about 8mm of the increase had relapsed (66% relapse in ramal height). The chin point was deviated by 8mm to the left side and after distraction was 1mm to the left. However in the followup period due to a combination of growth on the normal side exceeding the growth on the affected side as well as relapse of the distracted side the chin point was still deviated to the left by 5 mm [Figure - 2].

Result



Substantial relapse- However patient satisfied with result

Case 3

A 10 year old male patient with hemifacial microsomia (L) underwent unilateral distraction [Table - 1][Table - 2]. The ANB differential was 4° predistraction and reduced by 2° after completion of distraction. However, at followup the differential was 4° (1° due to increase in SNA and 1° due to decrease in SNB). The mandibular plane angle decreased by 4° but stabilized to pre distraction value during followup. The vertical position of the pogonion increased by 5mm and the horizontal position increased by 5mm on the distracted side. However the vertical position of pogonion increased by 3mm while the horizontal position reduced by 3mm at followup.

The mandibular length on the normal side increased by 4mm after distraction and another 3mm in the subsequent followup period. On the distracted side the increase in mandibular length was 7mm after distraction. However in the subsequent followup 1mm of mandibular length was reduced (14.3% relapse in mandibular length). The body length showed an overall increase by 2mm in the study period. The body length on the affected side increased by 4mm after distraction and reduced by 1mm in the followup period (25% relapse in body length). The ramal length was increased by 3mm on the normal side during the study period, 2mm increase occurred immediately after distraction. On the distracted side the ramal length increased by 19mm after distraction. However in the subsequent followup period about 5mm of the increase was lost (26% relapse in ramal length). The gonial angle on the normal side opened up by 9° (8° after completion of distraction) during the study period while on the distracted side it as initially reduced by 13° and subsequently increased slowly and was actually 5° less than the value which was there predistraction.

On the normal side the maxillary height increased by 1mm during the study period. On the distracted side a net gain of 2mm was achieved after distraction. However relapse of this 1mm increase was noticed in the subsequent followup period (50% relapse in maxillary height). The occlusal height increased by 3mm on the normal side and 9mm on the distracted side. However at followup there was no further change in occlusal height on the normal side and a decrease in occlusal height by 5mm on the distracted side (55.5% relapse in occlusal height). On the normal side, maxillary width increased by 1mm during the study period. The width increased by 3mm on the distracted side and subsequently reduced by 1mm in the followup period (33% relapse in maxillary width). The ramus height increased by 2mm on the normal side (no change after distraction) at followup. On the distracted side there was an increase by 14mm after distraction but at followup about 5mm of the increase had relapsed (35.7% relapse in ramal height). The chin point was deviated by 9mm to the right side and after distraction was 3mm to the right. However in the followup period due to a combination of growth on the normal side exceeding the growth on the affected side as well as relapse of the distracted side the chin point was deviated to the right by 10mm (more deviated than before the procedure). [Figure - 3]

Result

Substantial relapse- Patient and parents satisfied with result

Case 4

An 8 year old male patient with Oto-Palato-Digital Syndrome Type II underwent bilateral distraction [Table - 1]. Extraoral bilateral unidirectional distractors were placed after bilateral ramus osteotomies had been performed. Distraction was started after a 5 day latency period at a rate of 1mm per day and continued bilaterally for 3 weeks until the desired antero-posterior movement had occurred. At this stage, chin point was displaced to the left. Distraction was continued on the left side until symmetry was restored. After a 6 week consolidation period, the devices were removed. The patient was kept under review until the permanent teeth had erupted. At that point, orthodontic treatment was carried out to achieve arch alignment. The patient presented with many missing teeth (18, 27, 28, 38, 37, 35, 32, 42, 45, 48). The lower second deciduous molars are retained and infraoccluded. These teeth will be restored using composite onlays. The patient is now 8 years post distraction.

The ANB differential at presentation was 12° which reduced to 6° after completion of distraction. The ANB differential after 7 years remains at 7°. The mandibular plane opened up by 3 degrees after completion of distraction but returned to the predistracted value and subsequently reduced by 2 degrees. Thus the normal growth vector continued. The pogonion position altered by 6 mm horizontal advancement while the vertical increase was 14 mm. The change in pogonion position remained stable and after cessation of growth there was an overall increase by 8 mm in the horizontal plane and 19 mm in the vertical plane. The change in the inclination of the symphysis plane was maintained.

The mandibular length was increased by 15mm and continued to increase and after 7 years showed an overall increase of 18mm while the maxillary length increased by 3mm in the followup period. The ramal length increased by 8mm and during the subsequent 7 years showed an overall increase of 12 mm. Initially after distraction the gonial angle opened up by 13° but reduced by 7° and the overall change after 7 years was a change in gonial angle by 4° opening. The increase in lower anterior facial height was 14mm after completion of distraction and 17 mm at the end of 7 years. Thus after the completion of distraction the changes appear to be stable even 8 years later. [Figure - 4]

Result

Stable results

Case 5

A 6 year old female patient with TMJ Ankylosis underwent bilateral distraction osteogenesis [Table - 1]. The initial ANB differential was 14° which reduced to 7° after distraction. The ANB differential at the end of 7 years followup was 12° (2° increases in SNA and 3° decreases in SNB). Thus the ANB differential after cessation of growth was substantial and the net gain of 2° could be achieved by the distraction procedure undertaken at 6 years. The mandibular plane increased by 4° after distraction but reduced to the pre distraction value after the followup period. Thus the pre distraction growth vector remained stable. The pogonion was displaced 4mm horizontally and 12 mm in the vertical plane. After followup the pogonion position increased by 4 mm in the vertical plane while the horizontal pogonion position worsened and was actually displaced back by 17 mm. This worsening could be attributed to the vertical vector of growth, the increase in gonial angle and the relapse of distraction. The inclination of the symphysial plane increased by 7° and continued to increase and was overall increased by 10° at followup.

The mandibular length showed an increase of 7mm which remained stable even at the end of followup while the maxillary length increased by 2 mm. The ramal length increase of 4mm was achieved at the end of distraction. However the length of the ramus reduced to even less (2 mm) than the predistracted value and eventually stablised. The body length increased by 3 mm and showed an eventual increase by 5 mm at followup. This along with the gonial angle contributed to the stability of the overall mandibular length. The genial angle initially reduced by 2° after distraction but subsequently increased by 9° partially compensating for the change in mandibular spatial relationship. The lower anterior facial height increased by 8mm after completion of distraction and continued to increase in the followup period. The results seen in this patient are disappointing. [Figure - 5]

Result

Substantial relapse- Needs More surgery

Case 6

A 10 year old female patient with mandibular deficiency underwent bilateral distraction osteogenesis [Table - 1][Table - 3]. The ANB differential was 13° pre-distraction and was reduced to 6° post distraction. At the end of followup the differential was 8° (1° increase in SNA and 1° decrease in SNB). The mandibular plane angle reduced initially after distraction but returned to the predistraction value showing the return to the original growth vector. The pogonion was displaced by 9mm in the vertical plane and 4mm in the horizontal plane. However at followup the vertical position increased by another 10mm while the horizontal position was worse than the predistraction position and reduced to 2mm worse than the position predistraction. The inclination of the symphyseal plane increased by 3° and increased further by 5° in the followup period. The mandibular length increased by 15mm after distraction and increased by another 5mm in the subsequent followup period while the maxillary length increased by 4mm in the study period. The ramus length increased by 7mm after distraction and increased by another 3mm in the subsequent period. The body length increased by 2 mm after distraction and continued to increase (4 mm) in the followup period. The gonial angle did not change post distraction and showed an overall increase by 4º at the end of followup. The lower anterior facial height increased by 5mm after distraction and increased by another 5mm in the followup period. [Figure - 6]

Result



Little relapse-Optimistic result; thought not in terms of horizontal pogonion position


  Discussion Top


The role of the functional matrix on the growth and development of the mandible and craniofacial structures is well known.[20],[21] The components of the face do not develop as individual units. Rather, development proceeds as a functional unit, with growth of one area dependent upon the growth in other areas. The retrognathic or asymmetric mandible influences the growth of the adjacent structures. Dental compensations occur to camouflage the effect of this retruded mandible. The asymmetric mandibular growth leads to secondary growth compensations and a progressive distortion of both ipsilateral and contralateral skeletal structures including the maxilla.[22],[23],[24],[25],[26]

According to Hollier et al[13],[27] by normalizing mandibular dimensions at a young age, it is hypothesized that the maxilla and the overlying muscle and soft tissue envelope may have a longer period of time in which to develop with a bilaterally balanced functional matrix providing for overall facial harmony. Proponents of mandibular distraction believe that an early intervention would prevent the secondary compensations from taking place or would unravel the compensations at the onset.[28] This would prevent the long orthodontic decompensation phase followed by orthognathic surgery. Early treatment by osteodistraction should have a positive effect on the "functional matrix" and would produce more stable results. However this still remains to be proven.

Distraction osteogenesis is advantageous because of minimal operative time, low risk of complications, minimum hospitalization time, no donor site morbidity, no need for blood transfusion and no intermaxillary fixation required.[9] Repeated osteodistraction has already been undertaken frequently and has shown that mandibular reconstruction is not stable with growth, whether due to relapse or due to growth impairment.

Muscle function can alter the development and growth of the craniofacial skeleton.[29],[30] It is possible that abnormally shortened muscles or those with abnormal insertions produce specific mandibular conformation over the long term. Thus, the restrictive soft tissue forces and the innate growth of the bone dictate the final mandibular structure after distraction has been undertaken to alter its morphological characteristics. During the initial phase of distraction, the forces of active distraction are able to alter the entire shape of the mandible even beyond the immediate regenerative zone. This is because, during distraction, the bony regenerate extends beyond the borders of the osteotomy. However this regenerate is capable of being remodelled beyond the period of consolidation. Three dimensional CT scans were used by one author[31] to evaluate the effect of distraction three years after the procedure in hemifacial microsomia patients. A small increase in the volume of the affected side masticatory muscles was found. Perceptable relapse was seen one year after distraction and was progressive in nature when evaluated at 3 years post distraction.

According to Stelnicki et al ,[32] the underlying genotype and the musculoskeletal milieu must be taken into account when planning distraction. These factors tend to remodel the mandible into its preoperative shape over time despite the fact that the increased mandibular volume and projection are maintained. It becomes obvious that the intrinsic pattern of growth together with the forces of the musculature try to return the ramal length to its predistraction position and size. Though the process of distraction tries to guide the mandibular structure along the pathway of the vector of distraction, over the long term post distraction the mandible has a tendency to remodel to a predistraction form especially in high angle cases. Van Strijen et al[33] found that high angle cases are at a greater risk of relapse after distraction compared to the normal to low angle cases. The most likely reasons for relapse in the high angle group are the myoskeletal balance, habitual mouth posture as well as the soft tissue balance between the lips and the tongue.

Previous studies have commented on the necessity of comparing the growth of the distracted mandible to the non distracted side and the overall growth potential of the distracted mandible after the active treatment. Mary Trahar et al[34] showed that in unilateral distracted cases of hemifacial microsomia, the ramus height on the treatment side as well as control side tended to follow the same pattern of growth; however the treatment side length never approached the control. They concluded that no significant change occurred between distracted and control sides probably because the vertical vector of distraction was insufficient. It is postulated that the improvement in the functional matrix allows the distracted mandible to grow at a rate similar to the normal side.

The vector of distraction obviously plays a role in any change in ramal length and height.[35] A horizontal vector tends to preferentially stretch the strap muscles of the mandible, whereas a vertical vector would tend to stretch the masseter and temporalis muscles. This means that longer followup of these patients is required. The congenital hypoplastic mandible exhibits multiple variations of deformity.[36] Both vertical ramal and horizontal body discrepancies may be seen. Because of the absence of proper articulation and function, the mandible exhibits an obtuse angle at the gonion. The extent of vertical and body discrepancies vary from patient to patient and it is important to assess the individual extent of ramal deficiency before planning the correction.[37]

The orthodontic management of the patients is critical as a stable occlusion after the distraction could play an important role in the stability of the results. Pre distraction orthodontic phase can lead to decompensating the occlusion and make room to accommodate the newly elongated mandible better within its matrix.[38],[39],[40] It is also important to consider the late mandibular growth as well as other issue associated with growth and then consider over correction in cases where it is deemed necessary.[41] Various other factors have been studied like the type of distraction (extra oral versus intraoral) as well as the methods of fixation.[42],[43],[44]. The generated tissue after distraction appears to be a weak link susceptible to compressive and rotational changes which would remodel the mandibular morphology. This overall change in mandibular morphology may be a result of forces from the abnormal local tissues (Moss),[21],[22] or may be a manifestation of a programmed mechanism intrinsic to the bone itself. Thus inspite of decrease in the acquired mandibular length the spatial orientation appears unaltered. The underlying genotype and the musculoskeletal milieu tends to remodel the mandible into its preoperative shape over time despite the fact that the increased mandibular volume and projection are maintained.[45] The activity or the tension of the strap muscles tends to pull the bone distal to the generated tissue inferior and posterior, whereas the temporalis and the masseter muscles would exert a superior pull on the bone proximal to the generated tissue.[32]

According to Marquez et al[16] it appears that rather than being stimulated the growth that occurs in the area of mandibular ramus on the affected side after distraction is decreased (antero-posteriorly and vertically) or even resorptive (vertically) on the side which receives the distraction. The primary long term effects of unilateral distraction directly attributable to distraction are: a modest increase in AP length of the mandible with improved Pogonion projection, an improvement in the vertical and antero-posterior position of the maxillary and mandibular dentition of the affected side. Indeed, the primary long term effects of distraction are dentoalveolar with minimum secondary changes in the ramus or body. That is, the effects are more orthodontic than orthopedic.

Distraction osteogenesis has become a popular surgical modality due to its many advantages: is a relatively safe, effective, minimally invasive procedure that can be performed at any age with a low complication rate. However, in spite of the technique having been used for over 15 years, no concrete long term results are available. We need to include adequate numbers in samples (possibly multi-centre) treated in a similar way and documented after growth cessation. The protocol for followup and evaluation should be standardized to have meaningful conclusions. This case series shows that results achieved by distraction osteogenesis are unstable or best unpredictable with respect to producing a permanent size increase in the mandible. The role of the distraction osteogenesis in overcoming the pterygomassetric sling is questionable.

 
  References Top

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3.Illizarov GA. The principles of Illizarov method. Bull Hosp Joint Dis Orthop Inst 1988;48:1-11.  Back to cited text no. 3    
4.Synder CC, Levine GA, Swanson HM, Browne EZ Jr. Mandibular lengthening by gradual distraction:preliminary report. Plast Reconstr Surg 1973;51:506-8.  Back to cited text no. 4    
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    Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]

    Tables

[Table - 1], [Table - 2], [Table - 3]


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