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An Analysis of Mandibular Volume in Treacher Collins Syndrome

Terner, Jordan S. B.A.; Travieso, Roberto B.A.; Chang, Christopher M.D.; Bartlett, Scott P. M.D.; Steinbacher, Derek M. M.D., D.M.D.

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Plastic and Reconstructive Surgery: April 2012 - Volume 129 - Issue 4 - p 751e-753e
doi: 10.1097/PRS.0b013e318245e903
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Sir:

Figure
Figure

The mandibular deformity in Treacher Collins syndrome is characterized by microretrognathia and a deep antegonial notch (Fig. 1). The ramus is short, with a steep mandibular and occlusal plane.1,2

Fig. 1
Fig. 1:
The mandibular deformity in Treacher Collins syndrome is characterized by microretrognathia and a deep antegonial notch.

Previous studies have described two-dimensional cephalometric3 and qualitative three-dimensional descriptors.4 Attention has not before been paid to mandibular volume in Treacher Collins syndrome.

The purpose here is to volumetrically characterize the Treacher Collins syndrome mandible in children. We hypothesize a structural diminution in Treacher Collins syndrome compared with controls. We also investigate the contribution of the dental-bearing and proximal segments.

This is a retrospective analysis of Treacher Collins syndrome and control children. Demographic and computed tomographic scan information was obtained. Children without a computed tomographic scan or with confounding surgical intervention or abnormality were excluded.

The mandible was digitally isolated from the craniofacial skeleton (Materialise). A digital osteotomy segmented the central incisor–midsymphyseal and the antegonial notch–ramal intersections (Fig. 2).5

Fig. 2
Fig. 2:
For volumetric analysis, the mandible was digitally isolated from the craniofacial skeleton. A digital osteotomy segmented the central incisor–midsymphyseal and the antegonial notch–ramal intersections.

Volumes were obtained for each segment in cubic millimeters; t tests were performed and a value of p < 0.05 was considered significant. The proximal and dentate percentage contribution was calculated by dividing each segmental volume by the hemimandible.

Computed tomographic scans were identified in 20 Treacher Collins syndrome sides (four girls and six boys) and 30 control sides (five girls and 10 boys). Total volumes were smaller in Treacher Collins syndrome sides compared with controls (Table 1). All Treacher Collins syndrome segments were decreased. There was no difference comparing left and right Treacher Collins syndrome segments. Interestingly, the proportion of proximal to dentate segments showed a smaller ramus volume in Treacher Collins syndrome versus controls.

Table 1
Table 1:
Results

The Treacher Collins syndrome mandibular dysmorphology is of interest. Becker et al.1 described antegonial notching and the obtuse body–to-ramus relationship.

Arvystas and Shprintzen noted short ramus and body lengths and a clockwise mandibular rotation.5 Marsh et al.4 descriptively evaluated a wide-age-range group of Treacher Collins syndrome patients, commenting on the variable condylar deformity and, interestingly, an asymmetric pattern.4 Chong et al.3 analyzed Treacher Collins syndrome teenagers, reporting subnormal sella, nasion B point; short mandibular length; steep mandibular plane angle; and a deep antegonial notch compared with norms. Steinbacher and Bartlett quantitatively described a steep mandibular plane (mean, 38.25) and obtuse ramus–body angle (mean, 150.28) in a young Treacher Collins syndrome population.2

Here, we volumetrically quantified the Treacher Collins syndrome mandible, and its subdivisions, in young children, compared with aged-matched controls. We also inspected the relative contributions of the proximal and distal mandible. Not surprisingly, the Treacher Collins syndrome mandible is statistically smaller than controls, in all segments. We found a symmetric and bilaterally equivalent mandibular structural deficiency, in contrast to previous studies.4 Interestingly, we demonstrate that the proximal mandible shows a greater proportional diminution in Treacher Collins syndrome mandibles compared with controls. That is, the ramal contribution to total mandibular structure is less in Treacher Collins syndrome mandibles than in controls. These ratio comparisons were not statistically significant, but the trend indicates a smaller proximal contribution to total mandibular volume. This may represent a surrogate of shortened ramus height contributing to the clockwise rotation and steep mandibular plane. The surgical implication is that both ramal and mandibular body bony structure must be increased when attempting to normalize the Treacher Collins syndrome morphology.

This study volumetrically characterizes the Treacher Collins syndrome mandible. As expected, the Treacher Collins syndrome mandibular volume is significantly decreased compared with controls. The diminution was bilaterally symmetric in the Treacher Collins syndrome group. Interestingly, the proximal segment is proportionally further diminished in Treacher Collins syndrome versus controls.

Jordan S. Terner, B.A.

Roberto Travieso, B.A.

Plastic Surgery, Yale University School of Medicine

Christopher Chang, M.D.

Plastic Surgery, Yale University, New Haven, Conn.

Scott P. Bartlett, M.D.

The Children's Hospital of Philadelphia, Philadelphia, Pa.

Derek M. Steinbacher, M.D., D.M.D.

Plastic and Craniomaxillofacial Surgery, Yale University, New Haven, Conn.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.

REFERENCES

1. Becker MH, Coccaro PJ, Converse JM. Antegonial notching of the mandible: An often overlooked mandibular deformity in congenital and acquired disorders. Radiology 1976;121:149–151.
2. Steinbacher DM, Bartlett SP. Relation of the mandibular body and ramus in Treacher Collins syndrome. J Craniofac Surg. 2011;22:302–305.
3. Chong DK, Murray DJ, Britto JA, Tompson B, Forrest CR, Phillips JH. A cephalometric analysis of maxillary and mandibular parameters in Treacher Collins syndrome. Plast Reconstr Surg. 2008;121:77e–84e.
4. Marsh JL, Celin SE, Vannier MW, Gado M. The skeletal anatomy of mandibulofacial dysostosis (Treacher Collins syndrome). Plast Reconstr Surg. 1986;78:460–470.
5. Arvystas M, Shprintzen RJ. Craniofacial morphology in Treacher Collins syndrome. Cleft Palate Craniofac J. 1991;28:226–230; discussion 230–231.

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