Lateral cephalometrics in southern Chinese

Abstract

The lateral cephalometric radiograph (LCR) is an important tool in orthodontics to aid diagnosis, inform treatment planning and to evaluate treatment outcomes. Following identification of frequently used cephalometric analyses in the literature, the aims of this thesis were: (i) to establish cephalometric norm values for 12-year-old southern Chinese children for the modified Björk’s analysis, Jacobson’s Wits appraisal, Pancherz’s Sagittal Occlusal (SO) and Vertical Occlusal (VO) analyses (Paper I and II); (ii) to identify gender and racial/ethnic variations in cephalometric norm values (Paper I and II); (iii) to extrapolate from the cephalometric norm values of 12-year-old southern Chinese to produce norm values for 10, 11, 13 and 14-year-old - for these common aforementioned cephalometric analyses and McNamara’s analysis (Paper III); (iv) to investigate variations in the cephalometric characteristics of southern and northern Chinese children (Paper IV); and (v) to study the relationship between common cephalometric reference planes and the True Horizontal Plane (THP), and variations with respect to gender (Paper V).

Extant LCRs from a community based sample of 200 male and 205 female 12-year-old southern Chinese in Hong Kong; 86 Caucasian children and 100 northern Chinese children, were traced and digitized twice employing the Computer Assisted Simulated for Orthognathic Surgery (CASSOS) program. Cephalometric norm values were created and extrapolated for 10 to 14-year-old. Gender and racial/ethnic variations were determined. In addition, the relationship between some common cephalometric reference planes (Sella Nasion Plane - SNP; Constructed Horizontal Plane - CHP; Frankfurt Horizontal Plane - FHP; Upper Occlusal Plane - UOP; Functional Occlusal Plane - FOP) and the THP was determined; and gender differences examined.

Cephalometric norm values for modified Björk’s analysis, Jacobson’s Wits appraisal and Pancherz’s SO & VO analyses were produced for 12-year-old southern Chinese children. Variations in cephalometric norm values with respect to gender (P<0.05) and race/ethnicity (P<0.05) were observed. Extrapolated cephalometric norm values for modified Björk’s analysis, Jacobson’s Wits appraisal, Pancherz’s SO & VO analyses, and McNamara’s analysis were produced for 10 to 14-year-old. Variations in cephalometric norm values with respect to age (P<0.05), gender (P<0.05) and race/ethnicity (P<0.05) were observed. Furthermore, variations in cephalometric values between southern and northern Chinese children were evident (P<0.05), and between Caucasians and both Chinese groups (P<0.05). The mean inclination between THP and the conventional cephalometric planes differed significantly from zero: SNP/THP (P<0.05), UOP/THP (P<0.05), FOP/THP (P<0.05); and gender differences were apparent (P<0.05).

In conclusion, norm values for frequently used cephalometric analyses were produced for 12-year-old southern Chinese, and extrapolated to produce norm values for 10 to 14-year-old. Age, gender and racial/ ethnic differences were apparent, supporting the need for age, gender and racial/ethnic specific norms. Common cephalometric reference planes differed to THP, and this warrants consideration in cephalometric analyses.