• Jirawadee Narkdee D.D.S., M.Sc. (Orthodontics)
• Niramol Chamnannidiadha D.D.S. (Hons), Dr.med.dent., Diplomate, Thai Board of Orthodontics
• Piyarat Apivatanagul D.D.S., M.S. (Orthodontics)

Objective The purpose of this study was to investigate incidence and characteristics of skeletal
Class II malformation in both male and female in Thai population and to investigate difference
between gender.

Materials and methods One hundred initial lateral cephalometric films of 50 males and 50 females,
aged between 18-43 years, were selected from patients, who presented for orthodontic treatment at
Faculty of Dentistry, Chulalongkorn University based on ANB angle (ANB ≥ 6 degree). All films were
traced and measured for the cephalometric parameters: anteroposterior characteristics of maxilla
and mandible (SNA, maxillary length, maxillary depth, SNB, mandibular length, and facial depth),
and vertical characteristics (facial axis, Frankfort mandibular plane angle, lower facial height,
posterior facial height, and mandibular arc). All parameters were then analysed and compared with
accepted Thai norms, which were used in this department to classify the position and relationship
of maxillary and mandibular arches into 3 anteroposterior categories (passing 2 out of 3 criteria):
orthognathic, prognathic, and retrognathic; and 3 vertical categories (passing 3 out of 5 criteria): normal
bite, open bite, and deep bite. The incidences of all categories were also compared between genders
using Chi's square statistics.

Results The most common anteroposterior characteristic of skeletal Class II was orthognathic maxilla
combined with orthognathic mandible for both males and females (44% and 46%). The second most
common characteristics in males and females were prognathic maxilla combined with orthognathic
mandible (24%) and orthognathic maxilla combined with retrognathic mandible (26%), respectively.
The most common vertical characteristic was skeletal normal bite (46%) followed by skeletal open
bite (41%). No statistical significant difference of anteroposterior or vertical characteristic was found
between genders.

Conclusion The study of Class II skeletal characteristics in a group of Thai patients found that
both male and female had normal position of the maxilla and mandible. No differences were found
in the relationship between gender and skeletal characteristics.

(CU Dent J. 2009;32:39-52)