Systemic Changes in Palatal Rugae Landmarks During Orthodontic Treatment

Orthodontists have long sought immovable fiducial points on dental casts against which developmental and orthodontic movements of teeth can be measured. Unfortunately, prior studies show that all landmarks on a dental cast are themselves moving to varying degrees during treatment, but claims continue to be published that rugae patterns—the 3 pairs of transverse fibrotic ridges in the front of the palate—are "stable enough" to be used as fiducial landmarks to gauge tooth movements. Objectives: We studied 122 orthodontic cases treated with 4-premolar extractions to test the stability of rugae landmarks and differences due to whether first or second premolars were extracted. Methods: Cases were Class I or Class II/1 and were treated to a Class I molar relationship. Homologous features were marked on pre- and posttreatment casts, which then were photographed in a standardized manner and enlarged 2X to improve landmark identification. Landmarks were digitized as Cartesian coordinates, and the differences in spatial relationships were evaluated statistically. Results: The fibrous tissue covering the palate, including the rugae, drifts quite noticeably when teeth are moved to correct the malocclusion: 1) Rugae are pushed distally, especially the anterior ridges and more so in P1 extraction cases. 2) Breadths of the individual rugae changed in different directions; anterior rugae were narrowed but the distal ones were stretched. 3) Transverse distances across rugae increased as they were stretched into a broader segment of the arch. 4) Millimetric changes were greater in the incisor-canine region, apparently because of greater dental movements in this area. 5) Differences often were bilaterally asymmetric, typically with greater changes on the right side. Conclusion: The researcher needs to exercise extreme caution when using rugae landmarks as registration points since they patently are mobile, and the amounts of drift are proportionate to the orthodontic correction.