Discussion

Various types of RPE appliances; tooth & tooth-tissue borne are available [3,4,30]. Due to maturation and adjacent articulations in the midpalatal suture region [31,32]; palatal expansion in nongrowing individuals has been shown to be less fruitful as compared to RPE in younger individuals [33-35]. This potential risk of toothborne appliances has been recognized in the literature and linked to resorption of buccal cortical bone, fenestrations, and gingival retraction [36].

Age is a vital factor in successful accomplishment of skeletal effects, as palatal expansion rapidly becomes inefficient after the early teens [1,37]. Thus, it was then believed that surgery is the only option for orthopaedic transverse correction [5]. Though, there are a few studies which show successful expansion in adults [4,38,39], there are still doubts whether they will represent general clinical situations.

Mouth breathing is a significant problem caused by nasomaxillary deficiency [40]; studies demonstrate that orthopaedic expansion can change the breathing pattern to nasal breathing [41,42]. RPE increases the nasal cavity volume [29,43], nasopharynx volume and cross-sectional areas of the upper airway [44-46].

More recent MARPE cases provide a clear picture using measurements from computed tomography [39,47]. Rigid interdigitation of palate in adults previously compelled clinician to perform limited lateral and midline osteotomies combined with fixed palatal expanders (SARPE) to effectively expand the maxillary skeletal base [48,49].

However, SARPE approach is a more invasive procedure; increases risk and the treatment costs for the patient [50,51]. The skeletal gain with MARPE appliances has been variable and was reported by Clement A as 61% of total expansion and was higher than that reported by Profitt (50%) [5,52], Kartalian, et al. (40%) [53], Lim, et al. (43.2%) and Garrett, et al. (55%) [54,55]. This can be attributed to the better anchorage potential of miniscrews which Lee, et al. in 2017 in their FEM study claim can be enhanced by bicortical engagement of palatal miniscrews [56]. Tausche, et al. has documented that in their sample [57], 85% - 91% of expansion achieved was skeletal in nature which can be ascribed to surgical intervention done along with MARPE. Dental tipping in the buccal direction has been reported in previous studies of conventional RPE as well as MARPE [8,58]. Gurgel, et al. and Garib, et al. also reported some amount of buccal tipping with MARPE [48,59]. Thus, using a MARPE appliance, some amount of buccal tipping is inevitable though much less as compared to RPE, as teeth are still used as anchor units alongside miniscrews. Tendency of buccal tipping is directly proportional to resistance exerted by midpalatal suture. Moon, et al. in 2010 and later Kolge, et al. in 2018 reported greater changes in the degree of molar inclination than that of premolar inclination [20,26]. The higher density of the buccal cortical bone in the maxillary canine and premolar regions might have resulted in the greater buccal inclination of the first molar in comparison with that of the first premolar [58,60,61].

A conventional RPE is advantageous compared to MARPE appliances as they can be placed or removed in the outpatient clinic, does not usually require administration of local anaesthesia and are economical [50]; while placement of a MARPE appliance can be time consuming. Hygiene can be better maintained with MARPE appliances as compared to the conventional RPE appliances; since they were smaller in size, have less food retentive areas and permit better brushing and flossing [62].

Though, some claim MARPE to be more efficacious than conventional RPE [8,15,63], Lagravere MO in 2010 evaluated and compared treatment efficiency between MARPE and conventional RPE devices and affirmed that both have a similar skeletal expansion potential [8]. Thus, he further said; the decision to use a MARPE device should be based on operator preference and specific patient variables like missing/compromised anchor units. MARPE independent of any anchor units also allows a full bonded orthodontic therapy to be done at the same time as expansion. MARPE has been proved to be a viable treatment modality to correct a transverse maxillary deficiency in adults; with a considerably good success rate and stability [8,9,16,50,52,58,59,63-65].

While zygomatic arch expanded to a lesser extent, expansion of nasal cavity was much more evident, and thus can result in improvement of nasal breathing owing to increased air flow. Thus, by effectively increasing the nasal cavity volume, treatment with a MARPE appliance can improve the constricted airway, thus aiding in long-term stability [66,67].