Three-dimensional comparison of mandibular morphology in young people with Treacher Collins syndrome and Pierre Robin sequence

Introduction

Treacher Collins syndrome (TCS) and nonsyndromic Pierre Robin sequence (PRS) share mandibular deficiency as a similar clinical finding. This study aimed to compare the mandibular size and morphology of subjects with TCS and PRS.

Methods

Group TCS was composed of 17 subjects (7 male, 10 female) with a mean age of 11.5 years (standard deviation, 4.4) from a single center. Group PRS was composed of 17 subjects paired by age and sex with group TCS. Preorthodontic cone-beam computed tomography examinations of all patients were evaluated using Mimics Innovation Suite 17.0 (Materialise, Leuven, Belgium). Nine 3-dimensional measurements were performed in segmented 3D images of the mandible. Intragroup comparisons were performed using paired t tests. Intergroup comparisons were performed using analysis of variance and Tukey tests. The significance level considered was 5%.

Results

TCS showed a significant dimensional difference between less and more affected sides for ramus, condyles, and mandibular body. The mandibular dimensions in PRS were more symmetrical. Group TCS presented a smaller mandibular effective length and mandibular body length compared with PRS. The condyle width and height and the ramus width were also decreased in TCS. The gonial angle was greater in TCS compared with the PRS group.

Conclusions

Young subjects with TCS presented a smaller, more vertical, and more asymmetrical mandible compared with nonsyndromic PRS.

Highlights

  • Subjects with Treacher Collins syndrome (TCS) and Pierre Robin sequence had micrognathia.

  • Mandibular shape differed significantly in the 2 groups.

  • Mandibles were more asymmetric in subjects with TCS compared with Pierre Robin sequence.

  • Mandibles were smaller and more hyperdivergent in subjects with TCS.

Severe micrognathia induces both esthetic and functional clinical implications. Treacher Collins syndrome (TCS) and Pierre Robin sequence (PRS) show a small and retrognathic mandible. , In both situations, micrognathia may cause airway reduction or obstruction. Inability to feed, malnutrition, airway obstruction leading to respiratory failure, and growth deficiency were also related to the small mandible in TCS and PRS. Infant interventions include mandibular distraction, endotracheal intubation, continuous positive airway pressure, or use of prone position. At the end of growth, surgical procedures for mandibular advancement are frequently required both in TCS and PRS.

TCS was first described in 1900 by Edward Treacher Collins. Its estimated incidence is 1:50,000 births. , As a result of mutations in the TCOF1 gene, TCS originates from abnormalities in the development of craniofacial structures derived from the first and second branchial arches. TCS presents variable phenotypic expressiveness, and the most characteristic finding is malar and mandibular hypoplasia, frequently with limited formation of the zygomatic complex.

PRS is a congenital anomaly characterized by a triad of clinical signs: micrognathia, glossoptosis, and obstruction of the upper airways, frequently associated with cleft palate. , The incidence ranges from 1:8,500 to 1:14,000 in the general population. , It is a heterogenic pathologic entity, and it can be found as an isolated condition or in association with other syndromes. The most associated syndromes are Stickler syndrome, velocardiofacial syndrome, and TCS in 5% of patients.

Children with TCS and PRS present the mandibular deficiency as a similar clinical finding. TCS presents a short mandibular ramus and a relatively normal mandibular body, whereas PRS presents a reduced mandibular body and a relatively normal mandibular ramus. Mandibular size and shape have not been compared between TCS and PRS through 3-dimensional (3D) evaluation. The phenotypic refinement between TCS and PRS is important for the differential diagnosis between these craniofacial anomalies. In addition, morphologic data contribute to surgical planning and esthetical-functional outcomes. Therefore, this study aimed to compare the mandibular size and morphology of subjects with TCS and nonsyndromic PRS. The hypothesis was that both craniofacial anomalies present similar mandibular size and shape.

Material and methods

This retrospective study was approved by the Institutional Research Ethics Committee of Hospital for Rehabilitation of Craniofacial Anomalies, University of São Paulo, Bauru, Brazil (process no. 1.938.354). Informed consent for the use of records was obtained from all subjects. A sample of cone-beam computed tomography (CBCT) scans of subjects with TCS and nonsyndromic PRS was selected from the files from a single center. The sample size calculation was based on a standard deviation for mandibular ramus height of 2.0 mm, a minimum intergroup difference of 2.0 mm, an alpha value of 5%, and a statistical power of 80%. The sample size for each group was 17 subjects.

The inclusion criteria were the diagnosis of either TCS or PRS confirmed by the team of geneticists and age varying from 7 to 20 years. The exclusion criteria consisted of a history of previous facial surgical intervention, except palate repair; history of previous facial orthopedic treatment; inadequate quality of CBCT, including motion or metal artifacts or excessive artifacts.

Group TCS was composed of 17 subjects (7 male, 10 female) with a mean age of 11.5 years (standard deviation, 4.4) ( Fig 1 ). Group PRS was composed of 17 subjects paired by age and sex with group TCS (mean = 11.6; standard deviation, 4.2) ( Fig 2 ). CBCT examinations from all subjects were analyzed using Mimics Innovation Suite 17.0 (Materialise, Leuven, Belgium). The thresholding tool was used to achieve differentiation between bone and soft tissue. For bone segmentation, a Hounsfield units threshold varying from 226 to 17,079 HU was used. The mandible of each subject was digitally isolated from the skull. Seven landmarks were assigned on the right and left sides of the mandible ( Fig 3 ). Nine mandibular dimensions were measured ( Fig 4 ). Landmarks and linear variables were based on previous studies by Hilgers et al and Fernandes et al. Volumetric measurements were automatically performed for each mandible using the same software.

Fig 1
Right, frontal, and left side views of some mandibles in group TCS.

Fig 2
Right, frontal, and left side views of some mandibles in group PRS.

Fig 3
Cephalometric landmarks. A, lateral surface of the condyle—landmark placed in the most lateral surface of the condyle in the frontal view of the mandible; B, medial surface of the condyle—landmark placed in the most medial surface of the condyle in the frontal view of the mandible; C, condylion—landmark placed in the most superior and posterior surface of the condyle in a lateral view of the mandible; D, coronoid—landmark placed in the most superior surface of the coronoid process in a lateral view of the mandible; E, mandibular notch—landmark placed in the most inferior surface of the coronoid process and mandibular notch in a lateral view of the mandible; F, gonion—landmark placed in the most posterior and inferior surface of the gonial angle in a lateral view of the mandible; G, pogonion—landmark placed in the most anterior and inferior surface of the symphysis in a lateral view of the mandible.

Fig 4
Linear cephalometric variables. A-B , condyle width; C-E , condyle height; C-D , ramus width; C-F , ramus height; F-G , mandibular body length; C-G , mandibular effective length; C-F-G , gonial angle; C-F/F-G , ramus/body ratio.

Statistical analysis

The sample normal distribution was tested using the Shapiro-Wilk test. Intragroup side comparisons were performed using paired t tests or Wilcoxon tests. For intergroup comparisons, the less affected and more affected sides of TCS were considered separately. Intergroup comparisons were performed using 1-way analysis of variance and Tukey test or Kruskal-Wallis tests. The significance level considered was 5%. All the analyses were performed using SPSS IBM (version 16.0, SPSS, Chicago, Ill).

The study error was conducted by remeasuring 9 patients from each sample group that were randomly selected in both groups by 2 examiners (RMK and PPM) after a 30 days interval. Interexaminer and intraexaminer reproducibility was calculated using the intraclass correlation coefficient and Bland-Altman plots.

Results

Variables had an excellent intraexaminer agreement, with intraclass correlation coefficients varying from 0.932 to 0.997 ( Table I ). The variable with the greatest limits of agreement was the right gonial angle for both intraexaminer (−4.00 and 5.04) and interexaminer assessments (−3.27 and 14.19).

Table I
Intraexaminer and interexaminer reliability (intraclass correlation coefficients and Bland-Altman)
Measurements Intraexaminer error Interexaminer error
Measurement 1 Measurement 2 ICC Bland-Altman Examiner 1 Examiner 2 ICC Bland-Altman
Mean (SD) Mean (SD) Lower Upper Mean (SD) Mean (SD) Lower Upper
Right side
Condyle width A-B (mm) 12.02 (4.30) 11.90 (4.70) 0.976 −1.79 2.03 12.02 (4.30) 12.32 (3.65) 0.875 −4.16 3.56
Condyle height C-E (mm) 19.19 (4.72) 18.82 (4.82) 0.969 −1.81 2.57 19.19 (4.72) 18.77 (4.46) 0.952 −2.24 3.10
Ramus width C-D (mm) 28.96 (5.44) 28.17 (6.10) 0.932 −3.11 4.68 28.96 (5.44) 29.09 (6.41) 0.902 −5.28 5.02
Ramus height C-F (mm) 41.11 (9.64) 41.17 (9.29) 0.994 −2.03 1.91 41.11 (9.64) 40.73 (9.32) 0.955 −5.15 5.93
Mandibular body length F-G (mm) 69.48 (7.72) 69.22 (7.78) 0.995 −1.21 1.74 69.48 (7.72) 68.26 (6.87) 0.955 −2.32 4.78
Mandibular effective length C-G (mm) 100.43 (12.6) 99.98 (12.38) 0.996 −1.68 2.58 100.43 (12.60) 96.74 (10.28) 0.912 −2.57 9.95
Gonial angle C-F-G (°) 129.52 (7.13) 129.00 (7.04) 0.944 −4.00 5.04 129.52 (7.13) 124.06 (6.96) 0.607 −3.27 14.19
Ramus/body ratio C-F/F-G 0.59 (0.10) 0.59 (0.10) 0.985 −0.04 0.03 0.59 (0.10) 0.59 (0.12) 0.894 −0.10 0.09
Left side
Condyle width A-B (mm) 12.34 (3.96) 12.30 (3.87) 0.956 −2.23 2.32 12.34 (3.96) 12.19 (3.85) 0.979 −1.38 1.69
Condyle height C-E (mm) 18.03 (5.42) 17.98 (5.68) 0.961 −3.01 3.10 18.03 (5.42) 18.94 (3.71) 0.742 −7.26 5.43
Ramus width C-D (mm) 28.90 (5.32) 28.29 (6.09) 0.932 −3.35 4.56 28.9 (5.32) 29.40 (6.25) 0.947 −4.07 3.06
Ramus height C-F (mm) 43.98 (7.52) 43.69 (7.19) 0.977 −2.78 3.36 43.98 (7.52) 41.74 (7.76) 0.913 −2.32 6.79
Mandibular body length F-G (mm) 68.25 (9.80) 68.10 (9.55) 0.997 −1.25 1.56 68.25 (9.80) 67.23 (7.58) 0.940 −4.56 6.60
Mandibular effective length C-G (mm) 101.13 (12.45) 100.55 (12.33) 0.995 −1.55 2.70 101.13 (12.45) 96.04 (10.93) 0.887 0.01 10.15
Gonial angle C-F-G (°) 128.11 (7.04) 127.53 (6.25) 0.951 −3.34 4.50 128.11 (7.04) 122.41 (5.99) 0.634 −0.33 11.75
Ramus/body ratio C-F/F-G 0.65 (0.09) 0.64 (0.08) 0.941 −0.05 0.06 0.65 (0.09) 0.62 (0.09) 0.755 −0.08 0.14
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Dec 24, 2021 | Posted by in Orthodontics | Comments Off on Three-dimensional comparison of mandibular morphology in young people with Treacher Collins syndrome and Pierre Robin sequence
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