Morphology of open bite

The purpose of this work was to define and illustrate the skeletal morphology of open-bite patients against the background of sagittal jaw relationships on the basis of lateral cephalograms.

Lateral cephalograms of 197 untreated adults were analyzed in dental imaging software (Onyx Ceph 3™; Image Instruments, Chemnitz, Germany). Four groups were formed based on vertical (Index scores) and sagittal (individualized ANB values) parameters. Ninety-nine patients were defined as the control group due to their neutral sagittal and vertical relationships. The remaining patients were found by their vertical relationships to represent open-bite cases and were divided by their sagittal relationships into three study groups: neutral (Class I, n = 34), distal (Class II, n = 26), and mesial (Class III, n = 38). A geometric morphometric approach was used to analyze the x,y-coordinates of 28 skeletal landmarks on each cephalogram. Relative size was captured based on centroid size (CS). The shape-determining factors in the groups were compared by permutation testing after Procrustes transformation, and intergroup differences were visualized in the form of thin-plate splines.

While size (CS) was significantly increased in the Class III group, the other two groups were not different from the control group. After Procrustes transformation, characteristic and invariably significant (p < 0.001) differences in shape were detected. Neutral (Class I) open bite involved compression in the mandibular ramus and the upper anterior facial third, including vertical expansion in the lower molar and anterior nasal spine areas. Mesial (Class III) open bite was associated with pronounced vertical and sagittal size reductions in the upper posterior segments and reduced lengths of the mandibular ramus. Distal (Class II) open bite involved expansion in the pterygoid area and compression in the mandibular ramus.

Open bite is not a homogeneous group. Our geometric techniques of morphometric analysis revealed typical patterns, thus, confirming the differences observed by traditional morphometry. True skeletal overdevelopment appears to be present only in open-bite cases having a mesial jaw relationship. All open-bite groups have in common that the mandibular ramus is compressed, but marked differences are seen in terms of vertical development of the maxilla. This differentiated view of open-bite cases should be taken into consideration during individual etiology assessment and treatment planning.