BACKGROUND: An accurate anteroposterior measurement of jaw relationships is critically important in orthodontic diagnosis and treatment planning. There are some disadvantages in current cephalometric methods.
OBJECTIVE: To introduce a new cephalometric measurement, named the r angle, in order to express the sagittal relationship between maxilla and mandible with accuracy and reproducibility.
METHODS: One hundred and eighty patients aged 13-25 years were selected to take the pre-treatment cephalometric radiographs. They were divided into skeletal Ⅰ, Ⅱ, and Ⅲ groups on the basis of four standards. The different malocclusion types for the r angle were calculated. Finally, the differences between genders were analyzed.
RESULTS AND CONCLUSION: ①The r values of skeletal Ⅰ, Ⅱ, and Ⅲ were (40.84±3.10)°, (48.85±3.09)° and (26.12±4.76)° respectively. ②There were no statistically significant differences of r value between genders. It indicates that r angle can express the sagittal relationship with good repeatability. r angle between 35 and 45 degrees can be considered to have a Class Ⅰ skeletal pattern. With an angle less than 35 degrees, patients are considered to have a skeletal Class Ⅲ relationship and with an angle greater than 45 degrees, patients have a skeletal Class Ⅱ relationship.