RELATIONSHIP BETWEEN CRANIOFACIAL SKELETAL MORPHOLOGY AND FREEWAY SPACE IN ADULTS: A CEPHALOMETRIC AND CLINICAL STUDY

Abstract

Abstract Aim: Freeway space (FWS), the difference between rest vertical dimension and occlusal vertical dimension, is a clinically important component of vertical dimension assessment. Because mandibular rest position reflects a dynamic neuromuscular balance, an objective skeletal indicator that complements clinical measurement may be useful. This study aimed to evaluate the relationships of the saddle, articular and gonial angles, and their cumulative Björk sum, with clinically measured FWS in adults. Materials and Methods: Thirty adults with completed growth (20 women and 10 men; mean age 28.06 ± 2.16 years) were included. FWS was calculated using the Niswonger method from repeated measurements between pronasale and soft-tissue pogonion at rest and maximum intercuspation. Manual and digital calipers were used, and measurements were repeated after two weeks by the same clinician. Lateral cephalograms obtained in natural head position, with the jaws in centric relation, were used to measure the saddle (N-S-Ar), articular (S-Ar-Go) and gonial (Ar-Go-Me) angles and their cumulative Björk sum. Results: Agreement between manual and digital measurements was excellent (ICC > 0.90, p < 0.001). Saddle angle (r = 0.002, p = 0.990), articular angle (r = -0.234, p = 0.213) and gonial angle (r = -0.262, p = 0.161) were not significantly correlated with FWS. In contrast, the Björk sum showed a moderate negative correlation with FWS (r = -0.419, p = 0.021). FWS did not differ significantly according to sex or sagittal skeletal class. Conclusion: Individual craniofacial angles were insufficient as isolated indicators of FWS, whereas the cumulative Björk sum showed a significant moderate negative correlation with FWS. A more vertical cumulative skeletal pattern was associated with a smaller FWS. The Björk sum may therefore provide supportive information alongside clinical assessment of vertical dimension. Recommendation: The Björk sum should be considered as a complementary rather than an isolated diagnostic parameter in the clinical assessment of vertical dimension. Further prospective studies with larger and more balanced samples are recommended to confirm its clinical applicability and predictive value.