The Animal Study On The Effect Of The Miniscrew Implant-aided Rapid Maxilly Expansion(RME)

Maxillary transverse deficiency, mild crowding and crossbite of posterior teeth are very common in the clinical work. In these situations, a expansion is needed to stimulate the growth of maxilla.Maxillary expansion treatments have been used for more than a century and can be categorized by different ways. It can be divided into osteo-anchorage, dental-anchorage and dentalosteo-anchorage, or RME and SME, or orthopedic and orthodontic expansion. Among all the methods, RME, which is first come up with by Angle, is the most extensively-used one. It is generally accepted that RME is effective as long as the suture system is still growing.Traditionally, bilateral first premolars and molars are utilized to supply anchorage. This dental-anchorage method has been proved to be effective, however, some limitations associated with it have been reported, including bite opening, relapse, microtrauma of the temporomandibular joint and the midpalatal suture, root resorption, tissue impingement and pain, excessive tipping of anchorage teeth or even a failure of expansion. So it has been greatly concerned that how to reduce the tipping of teeth and maximize the splitting effect of midpalatal suture.Experiment 1 to observe the expansion effect of our appliance.Animal Experiment on palatal implant anchorage applied in expanding narrow dental arch8 dogs of six months old and about 10kg were matched into two groups randomly, with 4 dogs in each group. In experiment group, we fabricate an expansion appliance with two stainless-steel boards and a screw welding together. Then this appliance is fixed in dog's palatal area with some titanium mini-screws with a scale of 6mm in length and 4mm in width. In control group, we use the traditional RME method of utilizing bands on bilateral premolars and molars. Both groups load force every two days, 180 every time. Then we set plaster cast for every dog before and after the experiment, and measure the distance between maxillary central insiors, canines and first premolars and the axial angles of maxillary canines,premolars and first molars before and after experiment.the result showed that the distance of central incisors had no obvious differences in experimental group and control group before and after experiment (p﹥0.05) . However, canines and premolars in experimental group and control group showed p value <0.05. Variance of the distance between dog's canines and first molars in experimental group before and after experiment was less than in the control group, and there were differences between the two groups. It was considered that the width of the maxilla in lateral direction was all expanded in experimental group and control group. After anchorage was used to expend ordinary tooth's arch, the expanded distance among anchorage teeth was wider than among homonym teeth when micro-implant was used as anchorage. The traditional rapid maxillary expansion with tooth as anchorage was more advantageous in increasment than that of maxilla arch width using micro-implant anchorage to assist expansion screw's rapid maxillary expansion. The tilting angles of dog's canines, first premolars and first molar's buccal surface showed different extent of increasement. However, while those in experimental group showed almost no change. The difference of the groups was significant (p﹤0.05). The result indicated that there was no labial inclination in experimental group. Although the increasement of control group's maxillary width was greater than that of experiment group, some increasement was bought by anchorage teeth's labial inclination instead of the desirable pure expansion of palatal suture. Labial inclination of anchorage teeth had an unstable effect with a high incidence of relapse. The over inclination of teeth could cause the failure of arch expansion. To better observe the proportion of increasement of palatal suture width before and after arch expansion to the total quantity of arch expansion, we designed the second experiment.2. The research on tetracycline fluorescent staining method before and after palatal implant anchorage was applied in expanding narrow dental arch.The experimental animal and arch expansion method was the same as in the first experiment. The two groups were given intravenous tetracycline (10mg/kg) twice every day before and after experiment, two days before arch expansion and at the end of arch expansion. After the experiment, the dogs were all killed. We made slices from horizontal line of first molars and made tetracycline fluorescent labeled undecalcified ground bone of 7-10um width. They were observed under the fluoroscope and the result was input into computer analyzer to measure the width of palatal suture.In tetracydine stained undecalcified ground bones, we explored the tetracydine's characteristic of chelating with calcium ion and employed the fluorescence microscope to observe two tetracydine fluorescent staining bands before arch expansion and after maintenance. With the help of computer, we measured the distance between two fluorescent striate bands and got the real quantity of expansion of palatal suture. Its proportion of the expanded quantity among anchorage teeth to the first experiment model was just the proportion of palatal suture's expansion quantity in two arch expansion methods to the whole arch expansion effect. The result showed that, in control group, the proportion of palatal suture's expansion in total arch expansion was 70%. However, the figure was 95% in the experimental group. The result showed that the expansion quantity among anchorage teeth in the experimental group model was completely caused by the expanded width of palatal suture. For the expansion quantity among anchorage teeth in the control group model, the expanded width of palatal suture was only a part of the complete effect causes. The rest effect was caused by the labial inclination effect of anchorage teeth.In the process of maxillary expansion, we can't aimlessly seek the total expansion quantity. The anchorage expansion with over inclination of teeth as its focus is unstable and will lead to failure finally. We shall concentrate on the expansion of palatal suture and integral movement of teeth.This study establishes the RME model with implant anchorage on dogs. In comparison with the traditionally teeth anchorage RME appliance, the expansion and anchorage-protecting effects are proved. That will provide some reference for the future clinical application.