Rapid palatal expansion. Part 2: Dentoskeletal changes in cats with patent versus synostosed midpalatal suture

Intercanine expansion (C-C) following rapid palatal expansion is made up of sutural displacement (S d-S d), tooth tip (T t-T t), tooth displacement (T d-T d), and alveolar process tipping and bending (A t+b-A t+b). The involvement of these four components was studied on 10 rapid palatal expansion treated and two control cats during an active phase (25 days), a retention phase (60 days), and a relapse phase (60 days). The midpalatal suture was analyzed for linear measurements, radiopaque versus radiolucent zones and optical density from occlusal radiographs. Nine treated cats exhibited sutural split and one treated cat showed no split as a result of synostosis of the suture. The contribution of the four constituents [(S d-S d):(T t-T t):(T d-T d):(A t+b-A t+b)] to the C-C expansion changed from active to relapse phase from [45%:15%:25%:15%] to [50%:25%:25%:0%] in the animals with sutural split and from [0%:40%:60%:0%] to [0%:0%:100%:0%] in the cat without sutural split, implying the major role of sutural displacement in patent suture, and tooth displacement in synostosed suture. The latter indicates the potential buccal corticalis fenestration, dehiscence or perforation in synostosed suture undergoing RPE. In patent suture (animals with sutural split), optical density increased during rapid palatal expansion (soft tissue build-up) and decreased during retention (remineralization) and relapse phases (medial convergence of the palatal processes). In the animal without sutural split, a continuous decrease in the optical density (predetermined ossification) was found. The progressive six-fold surge in coefficient of variation of C-C expansion during the relapse phase indicates limitation in predicting rapid palatal expansion stability. Clinically, the use of serial occlusal radiographs during rapid palatal expansion is recommended to evaluate patency and extent of retention period. (Am J Orthod Dentofacial Orthop 1998;113:488-97.)