ABSTRACT

The aim of this study was to determine the norms of SNA, SNB and ANB angles and the limits of their symptomatics and to test whether they give consistent information within different growth stages. Totally 72 lateral cephalograms and hand-wrist radiograms of skeletal Cl I (n=11; 3 males, 8 females) and skeletal Cl II (n=13; 5 males, 8 females) subjects were evaluated. Sample were selected according to the prepeak ANB angle values which was in reference to Steiner norms. Hand-wrist radiograms were evaluated according to Helm criteria and cephalograms were grouped in accordance with these criteria as prepeak, peak and postpeak growth periods. SNA, SNB, ANB angles, maxillary and mandibular corpus, corpus ramus dimension and their ratios to anterior and posterior cranial bases were used in cephalometric evaluation. Repeated measures Variance Analysis and Bonferroni Test were used for statistical evaluation. The results of this study revealed that the norm value of ANB angle could be used in all growth periods, and this norm was indicative for discrepencies between jaw dimensions. Evaluation of mandibular position by SNB angle in Cl II cases may be misleading. The distinguishing spesification for mandibular dimension in Cl II group was Go-Me/S-Ba ratio, and with this ratio, which is determined in prepeak growth period and remain stable, the diagnostic value of SNB angle may be increased. The 82° norm of SNA angle indicated that maxillary dimension also increase in higher angle values. However, SNA angle did not indicate the increase in maxillary dimension in reference to anterior cranial base. This finding points that one should be aware while evaluating the treatment effects on maxilla by SNA angle during growth. ANS-PNS/S-N ratio norms in prepeak or peak stages would give more valid information about stimulated or inhibated maxilla.