Maxillary Rapidly Expanding Preliminary Discussion Of The Influence On The Structure Of The Skull Base And Brain

Rapid maxillary expansion (RME) has been widely used in clinical orthodonticsfor transverse maxillary deficiency or maxillary arch contraction. With rapid heavyforce applied on the posterior teeth in short term, there would not be enough time forthese teeth to move, so the heavy force would be transferred to the mid-palatal sutureand accumulated in it. Then, the suture would be opened up while the teeth movedonly minimally relative to their supporting bone.The maxilla is the biggest Craniofacial bone, which play an important part insupporting. Maxillae are connected via sutures including the frontomaxillary suture,malomaxillary suture, palatomaxillary suture, to respectively neighboring skull bonesincluding frontal bone, zygomatic bone, palatine bone and sphenoid. With increasingage, these sutures become more and more tightly interdigitated and inseparable.During rapid maxillary expansion, a heavy opening force in the midpalatal suture isintended to bring about a transverse widening of the maxilla in a short time.Accordingly, the surrounding construction must be affected. As the Finite ElementeMethode used, researchers including our team found thatRME leads to stresses at thefissure, foramen, and sulcus of the cranial base, such as the Oval foramen and Roundforamen, where maxillary nerve and mandibular nerve distributed. However, whetherthese nerves would be affected by the stress is not known.RME, used in clinical for more than100years, is first introduced by Angell in1860. In this process, RME is used not only for widening the maxilla but also for NEor OSAS in children and proved to be effective. However, the mechanism is not clear.NE is used for girls and boys over the age of five years who wet their beds more thantwo nights per month. Proposed causes for nocturnal enuresis (NE) includeinsufficient arousal response and insufficient vasopressin production during sleep. Aswe known, with the RME used, maxillae are widen. On the one hand, the volume is significantly increased and the airway resistance is significantly decreased. On theother hand, the position of soft tissues especially the levator veli palatini muscle andtensor veli palatine muscle may be changed, which is positive for breathing andresolving CO2accumulation in sleep, and also improve symptoms by changing levelsof AVP and neuropeptides which function on sleep and breathing regulation in brain.The hypothesis would also be suitable for OSAS, which is characterized by repetitivecollapse of the upper airway which could cause reductions in ventilation or totalcessation of ventilation, and followed by hypoxia, hypercapnia and sleepfragmentation.Part ⅠObjective: To evaluate whether rapid palatal expansion (RPE) would affect thebranches of trigeminal nerve by using TSEP in a rabbit model.Materials and Methods: Twenty-four male and3month old New Zealand whiterabbits were selected (mean weight:3.05±0.3kg). A modified acrylic bonded RPEappliance was used as an expansion tool. The TSEP for bilateral maxillary nerve andmandibular nerve were measured before the expansion treatment (1d), on the thirdday of the expansion (3d), at the end of the expansion process (10d) and after tendays’ of retention (20d). The statistical analysis including the Kruskal–Wallis test andt tests was used here.Results: There was no significant difference in bilateral maxillary nerve andmandibular nerve after RME by using TSEP.Conclusions: Rabbit was an idea model for rapid maxillary expansion. And TSEP wasa reliable technique for evaluating the function of trigeminal system. Rapid maxillaryexpansion was a safe method for widen maxilla in growing Adolescence. Part ⅡObjective: To evaluate whether AVP and neuropeptides function on sleep andbreathing regulation were affected by hypercapnia, and to some extent, to explain thefunction of rapid maxillary expansion on brain.Materials and Methods: Fifteen C57BL/6J mice were selected for the test. Theanimals were respectively exposed to moderate hypercapnia (5%CO2balance with95%room air), or severe hypercapnia (8%CO2balance with92%room air) or roomair for3h. The levels of orexin，NPY, galaninA and their receptors and AVP weretested by using western blot and real time PCR. The statistical analysis used here wasANOVA.Results: In hypothalamus, we found that the gene expression, including AVP, galanin,orexin, and NPYR1was downregulated by hypercapnia. However, the protein andmRNA levels of orexin-A receptor were upregulated by severe hypercapnia. In brainstem, it was shown that only NPYR1mRNA expression was decreased in moderatehypercapnia compared with that in severe hypercapnia.Conclusions: These findings presented herein implicated hypercapnia could affectthese neuropeptides and their receptors in the brain stem and especially thehypothalamus, which provided a clue for why RME have a positive effect on NE andOSAS, and on the other side provided a clue to the pathogenesis of OSA.