On the interaction between incisor crown-root morphology and third-order angulation.
OBJECTIVE
To evaluate the significance of crown-root angles (CRAs) by testing the null hypothesis that there are no significant differences in deviations of third-order angles to axial inclination values between Angle Class II division 2 incisors and a neutral occlusion control sample.


METHODS
The study group comprised n(total) = 130 whites with either Angle Class II division 2 (n(1) = 62; group A) or neutral (n(2) = 68; control group B) occlusal relationships. Upper central incisor inclination (U1) was assessed with reference to the cephalometric lines NA and palatal plane (U1NA/deg, U1PP/deg). Craniofacial sagittal and vertical relations were classified using angles SNA, SNB, ANB, and NSL-PP. Third-order angles were derived from corresponding dental cast pairs using an incisor inclination gauge. Welch's two-sample t-tests (alpha-level: .05) were used to test the null hypothesis. Single linear regression was applied to determine third-order angle values as a function of axial inclination values (U1NA, U1PP) or sagittal craniofacial structures (ANB angle), separately for group A and B.


RESULTS
The discrepancy between axial inclination (U1NA, U1PP) and third-order angles is significantly different (P < .001) between groups A and B. Regression analysis revealed a simply moderate correlation between third-order measurements and axial inclinations or sagittal craniofacial structures.


CONCLUSIONS
The hypothesis is rejected. The results of this study warn against the use of identical third-order angles irrespective of diminished CRAs typical for Angle Class II division 2 subjects. Routine CRA assessment may be considered in orthodontic treatment planning of Angle Class II division 2 cases.
Knösel
Michael
M
Department of Orthodontics and Dentofacial Orthopedics, Center of Dentistry, Georg-August-University, Robert-Koch-Str. 40, Göttingen, Germany 37099. mknoesel@yahoo.de
Jung
Klaus
K
Attin
Thomas
T
Engelke
Wilfried
W
Kubein-Meesenburg
Dietmar
D
Gripp-Rudolph
Liliam
L
Attin
Rengin
R
D000293:Adolescent; D002508:Cephalometry / Q000706:statistics & numerical data; D003766:Dental Occlusion; D005260:Female; D006801:Humans; D007180:Incisor / Q000473:pathology*; D008297:Male; D008312:Malocclusion, Angle Class II / Q000473:pathology / Q000628:therapy; D008334:Mandible / Q000473:pathology; D008437:Maxilla / Q000473:pathology; D009295:Nasal Bone / Q000473:pathology; D010159:Palate / Q000473:pathology; D012658:Sella Turcica / Q000473:pathology; D019228:Tooth Crown / Q000473:pathology*; D014087:Tooth Movement Techniques / Q000379:methods*; D014092:Tooth Root / Q000473:pathology*; D014716:Vertical Dimension