| Clinically, treatment of ClassⅡmalocclusion with anterior crowding usually requires space gaining to achieve Class I molar relationship and align anterior crowding. Common strategies to gain space are to reduce dental material and/or expand arch, which can coordinate dental-skeletal discrepancy and to achieve a functional and aesthetically harmonious occlusion. The reduction of dental material includes teeth extraction and interproximal enamel reduction. The expansion arch involves anteroposterior and tranverse expansions, which are effective measures to create spaces.In recent years, advanced in mechanotherapy and changes in treatment concepts have curtailed the need for extraction in orthodontists. Molar distalizatin techniques, as one of treatment modality in arch expansion, has shown great promise as a simple and more efficient solution for obtaining spaces, which play an important role in non-extraction orthodontic treatment. The appliances used for the purpose of the distalization of molars can be classified as compliance-dependent appliances and non-compliance appliances. When used distalizing appliances to create spaces, they have some undesirable side effects that diminish their clinical effectiveness, including anchorage loss. Especially, these side effects can worsen without patients' compliance when use compliance-dependen appliance. Reducing the need of patient cooperation and placing the treatment result more under the control of the orthodontists are paying more attentions. As a result, micro implants as an absolute anchorage used to distalize molars have gained wider acceptance and utilization.Thus, we conducted this study to investigate the effect of buccal and palatal micro implants on the distalization of maxillary molars, compared with the effect of pendulum appliance. Furthermore, we are looking forward to search a convenient and efficient way to either maintain anchorage or much better controll molar movement in the distalization of maxillary molars. Objective:The aim of this study was to compare the dentoalveolar, skeletal and soft tissue effects obtained with 2 types of molar distalizing appliance with different anchorage designs:buccal and palatal micro implants and conventional pendulum appliance. To explore the clinical features of micro implants in the distalization of molars in order to provide an effective and efficient measures to correct ClassⅡmalocclusion.Methods:20 patients treated at the Department of Orthodontics, Guiyang Stomatology Hospital in Guizhou between 2009 and 2010 were included in the study. The criteria for patient selection were strictly included dentoalveolar ClassⅡmalocclusion with mild to moderate anterior crowding. The patients were divided randomly into two groups of ten: the micro implants group (group A) and the pendulum group (group B). To achieve molar distalization, the group A was provided by 2 micro implants that were placed buccal and palatal region between the first molar and the second permolars, while the group B was provided by conventional pendulum appliance. Lateral cephalograms and study models were taken and analyzed before and after molar distalization. The dental and skeletal changes in the sagittal and vertical planes were measured by using Winceph 8.0 software and the angular and linear changes in the transverse width of the dental arch and rotation of the maxillary first molars were measured on the dental casts.Results:1 Rate of micro implants failure:3 of 20 buccal micro implants (15%) and 2 of 20 palatal micro implants (10%) showed mobility during the first month after placement. Thus, the failure rate was 12.5%.2 Distance of the maxillary first molar:On the dental casts, the mean distalization amounts were 7.10±0.16 mm for group A and 7.50±2.53 mm for group B. There was no statistically significant between two groups (p>0.05).3 Time and rate of maxillary molar movement:The average distalization times were 6.00±0.14 months for group A and 5.17±0.32 months for group B. The rate of molar movement of group A was 1.18±0.04mm per month and 1.45±0.42 mm per month for the pendulum appliance group. There was statistically significant between two groups (p<0.01).4 effects on the maxillary molars:On the cephalograms, the maxillary first molars were tipped distally 4.31±0.60 degrees in group A and 16.54±3.38 degrees in group B, which was statistically significant (p<0.01). The maxillary molars were intruded 2.71±0.12 mm in group A and 2.86±0.60 mm in group B, the differences were not statistically significant (p>0.05) On the dental casts, the mean molars width were increased 0.08±0.22 mm for group A and 0.07±0.04 mm for group B. In group A, the maxillary molars were rotated distopalatally 0.17±0.40 degrees and 2.39±1.06 degrees in group B, which was statistically significant between two groups (p<0.01).5 effects on the anterior teeth:The maxillary anterior teeth were mesially inclined 0.20±0.28 degrees and protruded 0.06±0.07mm in group A and 7.75±1.34 degrees and 1.98+1.05mm in group B. There were statistically different between two groups (p<0.01).6 effects on the soft and hard tissue:the upper lip convexity in the group B showed slightly increase after distalization, whereas there was no statistically significant change in the upper lip convexity in the group A. There was no statistically significant between two groups (p>0.05). The lower anterior facial height (ANS-Me) and the SN to mandibular plane angle (SN-MP) were increased in two groups after distalization. However, no differences were found between the groups (P>0.05)Conclusion:1 Both micro implants anchorage and pendulum are effective and efficient noncompliance appliances to distalize the maxillary first molars2 the tipping of anterior teeth was significantly decreased in the micro implant anchorage group compared with the pendulum group during treatment period. The results might support the use of the micro implants as an absolute anchorage for distal movement of the maxillary molars.3 Significant intrusion of the maxillary first molars produced by both two groups. The micro implant anchorage is a valid alternative distalizing appliance that generates more better controlled molar position transversely and anteroposteriorly than pendulum appliance. |
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