Despite its pathogenic heterogeneity, it is often assumed that the small mandible in a neonate with Robin sequence will not grow normally. The purpose of this study was to determine mandibular length and position in patients with nonsyndromic versus syndromic Robin sequence.
Lateral cephalograms of 51 children with Robin sequence were analyzed. Group I consisted of nonsyndromic (NS) subjects and group II consisted of subjects with the 4 most common syndromic (S) diagnoses. Cephalometric measurements included sella-nasion-A point (SNA), sella-nasion-B point (SNB), sella-nasion-pogonion (SNPg), articulare-gonion-pogonion (ArGoPg), temporomandibular joint-pogonion (TmPg), articulare-gonion (ArGo), and gonion-pogonion (GoPg). Differences between groups and subgroups were compared using t test.
There were 26 NS patients (mean age, 6.8 yrs) and 25 S patients (mean age, 8.7 yrs); mean age was statistically different between groups (P = .04); therefore, cephalometric measurements were compared with age-matched normal values. Syndromes included Stickler (n = 10), bilateral facial microsomia (n = 8), velocardiofacial (n = 4), and Treacher Collins (n = 3). SNA was statistically different from normal in both groups (NS, P = .017; S, P = .007); however, SNB was not different from normal for either group (NS, P = .175; S, P = .537). SNPg (0.007) was significantly greater than normal in NS (P = .007) but not in S (P = .702) patients. SNA, SNB, and SNPg were not significantly different between groups. In both groups, mandibular length was short (P = .00), especially in S patients (P = .049), mandibular body was small (NS, P = .00; S, P = .00), and the gonial angle more obtuse (NS, P = .006; S, P = .000) than normal. Ramus length was significantly shorter than normal only in S patients (P = .019). Mandibular length (TmPg) was smaller than normal in all S subgroups but with wide variability. There were statistically significant differences among S subgroups with respect to mandibular sagittal position (SNB, P = .00; SNPg, P = .00) and mandibular length (TmPg, P = .008). There were no differences in S subgroups with respect to age, SNA, ArGo, GoPg, and ArGoPg.
Mandibular morphology and position are variable in Robin sequence, based on the presence and type of associated syndromic diagnosis.