Appropriateness of standard cephalometric norms for the assessment of dentofacial characteristics in patients with cleidocranial dysplasia

Objectives: Cleidocranial dysplasia (CCD) is a rare skeletal syndrome affecting craniofacial and dental development. As a consequence, conventional cephalometric landmarks may not be valid for CCD patients, and the appropriateness of norms used for the general population should be critically discussed. Methods: Five patients 9-to 22-year old (three females, two males) with CCD were included. Lateral-cephalograms, orthopantomographies, and intra oral photos were retrospectively analysed. Lateral-cephalograms of 50 normal controls (ten for each CCD patient) matched for age and sex were selected from an online database. Cephalometric measurements of each CCD patients were compared with average values of matched controls using Wilcoxon signed rank test for paired values (alpha = 0.05). Results: In CCD patients, a shortening of the cranial base was present (Delta SN = -17.1 mm, p = 0.043). Thus, the mandible (Delta SNPg = +9.5 degrees, p = 0.043) and the maxilla (Delta SNA = +11.2 degrees, p = 0.043) showed protrusion compared to the cranial base, despite a reduced maxillary (Delta Co-A = -15.1 mm, p = 0.043) and mandibular (Delta Co-Gn = -15.2 mm, p = 0.080) length. The mandibular divergence was reduced (Delta SN/GoGn = -6.4 degrees, p = 0.043), a reduced overbite was present (Delta Overbite = -2.9 mm, p = 0.043), and the interincisal angle was increased (Delta InterincisalAngle = +13.7 degrees, p = 0.043), mainly due to retro-inclination of lower incisors. Conclusions: Standard cephalometric norms for the assessment of horizontal jaw position may not be applicable to CCD patients because of a reduced anterior cranial base length compared to normal subjects. Vertical relationships may not be affected, and mandibular hypodivergency was confirmed.