Zygomaticomaxillary modifications in the horizontal plane induced by micro-implant-supported skeletal expander, analyzed with CBCT images

Abstract

BackgroundMiniscrew-assisted rapid palatal expansion (MARPE) has been adopted in recent years to expand the maxilla in late adolescence and adult patients. Maxillary Skeletal Expander (MSE) is a device that exploits the principles of skeletal anchorage to transmit the expansion force directly to the maxillary bony structures and is characterized by the miniscrews’ engagement of the palatal and nasal cortical bone layers. In the literature, it has been reported that the zygomatic buttress is a major constraint that hampers the lateral movement of maxilla, since maxilla is located medially to the zygomatic arches. The objective of the present study is to analyze the changes in the zygomatic bone, maxillary bone, and zygomatic arches and to localize the center of rotation for the zygomaticomaxillary complex in the horizontal plane after treatment with MSE, using high-resolution cone-beam computed tomography (CBCT) images.MethodsFifteen subjects with a mean age of 17.2 (± 4.2) years were treated with MSE. CBCT records were taken before and after miniscrew-assisted maxillary expansion; three linear and four angular parameters were identified in the axial zygomatic section (AZS) and were compared from pre-treatment to post-treatment using the Wilcoxon signed rank test.ResultsAnterior inter-maxillary distance increased by 2.8 mm, posterior inter-zygomatic distance by 2.4 mm, angle of the zygomatic process of the temporal bone by 1.7° and 2.1° (right and left side) (P < 0.01). Changes in posterior inter-temporal distance and zygomaticotemporal angle were negligible (P > 0.05).ConclusionsIn the horizontal plane, the maxillary and zygomatic bones and the whole zygomatic arch were significantly displaced in a lateral direction after treatment with MSE. The center of rotation for the zygomaticomaxillary complex was located near the proximal portion of the zygomatic process of the temporal bone, more posteriorly and more laterally than what has been reported in the literature for tooth-borne expanders. Bone bending takes place in the zygomatic process of the temporal bone during miniscrew-supported maxillary expansion.

<p>A New Methodology for the Digital Planning of Micro-Implant-Supported Maxillary Skeletal Expansion</p>

“…In the protocol developed, the center of MSE appliance and hence the expansion force vector is set by default in the same position as the CM point, defined by the projection of the bizygomatic line (BZL) on the posterior part of the midpalatal suture. In the literature, it has been described that the pterygopalatine suture 28,29 and the zygomatic buttress bone [23][24][25][26]30,31 are two major resistance structures that hamper the lateral maxillary movement. Furthermore, Lee et al 32 have shown that the center of resistance of the maxillary halves is located slightly superiorly and laterally to the root apex of maxillary second molars, close to the most lateral point of the zygomatic process of the maxilla (ZR and ZL) utilized in our protocol.…”

“…The application of the expansion force vector close to the maxillary center of resistance has the scope of maximizing the orthopedic effect on the midface during maxillary expansion. [23][24][25][26] If the CA is moved forward relative to the CM point, the midpalatal suture opening will be less parallel and more V-shaped, since the force vector will act in a more anterior part of the maxilla, away from its center of resistance. 32 Although MSE position relative to the bizygomatic line and CM point is the main objective of the digital planning due to biomechanical reasons, other parameters were taken into consideration.…”

“…Bicortical skeletal anchorage is required for the correct functioning of MSE, since it increases the stability of microimplants. [20][21][22][23][24][25][26] Loss of skeletal anchorage stability and bending of micro-implants is a negative consequence of monocortical anchorage, 22 that seriously compromises the outcome of the therapy in adults and potentially also in growing patients.…”

“…In addition, MARPE devices are used in association with the facemask to enhance the maxillary protraction, especially in patients older than 8-9 years of age. [17][18][19][20] The present paper aims to describe a novel procedure to position a particular type of MARPE appliance, the Maxillary Skeletal Expander (MSE), [20][21][22][23][24][25][26] in the patient's oral cavity through digital planning and workflow.…”

Three-dimensional evaluation of mid-facial soft tissue changes after expansion using micro-implant-supported maxillary skeletal expander

“…The maxilla is located medially and anteriorly relative to this fulcrum. Due to the outward rotation of the zygomaticomaxillary complex around the proximal part of the zygomatic process, each half of the maxilla will be displaced forward and laterally [36]. Additionally, the asymmetrical lateral movement of the cheek points and the alar curvature points between the left and right side could be explained by the unequal movement of the two maxillary bones.…”