Impact of rapid maxillary expansion on palatal morphology at different dentition stages

Abstract

Objective: Rapid maxillary expansion (RME) is an established and frequently used procedure to overcome maxillary constriction. In-depth studies about morphological changes of the alveolar process and its immediate surroundings are missing. Therefore, the aim of the present study was to examine the treatment effects of a dentally anchored, rapid maxillary expander at different dentition stages upon palatal width, height and shape.

Material and methods: The dental casts of 114 patients-taken immediately before and after RME-were three-dimensionally analysed. Depending on the dentition stage, the patients were divided into two groups (each n = 57, group 1, early mixed dentition; group 2, late mixed or permanent dentition).

Results: The width increases were highly significant, both in the overall and in the individual groups (p < 0.001). While the width increase was greater in the posterior area than anteriorly in the early group, the widening in the late group happened significantly greater anteriorly than posteriorly. Palatal height increased anteriorly and posteriorly in both groups to a significant extent (p < 0.001). The height increase was more pronounced in the anterior region than in the posterior region in the late group. The palatine index according to Kim revealed a change in palatal morphology both anteriorly and posteriorly in the early group but only anteriorly in the late group.

Conclusions: Maxillary expansion occurs more parallel in early treatment compared to V-shaped opening in the later treatment approach.

Clinical relevance: RME is more advantageous in an early dentition.

Keywords: Median palatine suture; Palatal morphology; Rapid maxillary expansion (RME); Transverse palatine suture.

Fig. 1

a, b Representative clinical pictures of the RME appliance in a patient a out of PG1 and b PG2

Fig. 2

a–c Quantification of the transverse palatal dimension. a Analysis of dental arch width with standard reference points on the premolars or deciduous molars and on the first permanent molars. b and c Palatal width to assess the gingival-alveolar plane, measured between the most coronal points of the gingival margin at the first premolar or deciduous molars (b) and the first permanent molars (c). The width was measured in the cranial direction at different heights. The spacing of the individual measurements was always 2 mm and ended at a maximum height of 6 mm. Level 1: dental width, level 2 gingival-alveolar, level 3: level 2 + 2mm cranial movement; level 4 : level 2 + 4mm cranial movement; level 5 skeletal-basal = level 2 + 6mm cranial movement. The anterior/posterior ratio was calculated on three planes to qualify the expansion as parallel or triangular.

Fig. 3

a, b Determination of palatal height: A point on the median raphe was connected perpendicularly to the most coronal point of the gingival margin on a the 1st premolars or deciduous molars and b the first permanent molars. For the height at the median raphe, the mean value was calculated of measurements at the reference teeth in both quadrants. a For the first deciduous molars or first premolars, the same measurement was taken 5 mm to the right (to the 1st quadrant) and to the left (to the 2nd quadrant) of the palatal centre, and b on the first permanent molars, 5 mm and 10 mm to the right and to the left of the palatal centre

Fig. 4

a, b Modified palatal index according to Kim [24] to determine the palatal shape: from the first quadrant, the angles between the horizontal reference line from the gingival margin of opposing a 1st premolars or deciduous molars and b 1st molars and the lowest point in the centre of the palatal vault were measured