| Class II hyperdivergent malocclusion is a kind of malocclusion with varying degrees of anteroposterior and vertical dysplasias, which is one of the difficulties in orthodontic treatment[1, 2]. A large number of studies indicate that most of these patients are accompanied with mandibular retrusion and backward rotation [3]. Therefore, the key to the treatment of these patients is the vertical control of maxillary and mandibular molars [4], so that counterclockwise rotation can occur in the mandible[5, 6]. However, the traditional anchorage,such as TPA,Nance arch, J hook and headgear,is not an efficient way in vertical control of molars[5, 6]. In recent years, implant anchorage has been widely applied in orthodontic treatment, and has achieved satisfactory outcomes in the treatment of class II hyperdivergent malocclusioncases.This study was conducted to compare different outcomes of vertical control in patients with Class II hyperdivergent malocclusion treated with implant anchorage system or conventional anchorage system, in search of a better choice of anchorage for this type of cases.ObjectiveOur aim is to explore and discuss different changes of mandibular position and soft-tissue profile with implant anchorage system or conventional anchorage system for vertical control of molars in the treatment of adult patients with Class II hyperdivergent malocclusion.Material and methods1.Material The subjects in this study included 32 adults with Class II hyperdivergent malocclusion,treated in the Department of Orthodontics, the stomatological hospital of the Fourth Military Medical University from 2010 to 2015. All were required extraction.Lateral cephalograms of each patient were taken before and after treatment. The subjects were divided into two groups. Group 1 subjects received implant anchorage(16 patients;age,18-35 years) and group 2 subjects received conventional anchorage(16 patients;age, 18-35 years).2.Methods1)There were 19 representative measurement indexes,including 7 teethrelated indicators,7 skeletalrelated indicators and 5 softtissue related indicators.All statistical analyses were based on comparison of mandibular rotation,molars intrusion and facial soft-tissue profile changes measured on the pre-(T1) and post-treatment(T2) lateral cephalograms.2)All statistical analyses were performed with SPSS software(version 17.0). All the data fitted normal distribution by single sample K-S test.For each variable,the mean and standard deviation values were calculated.A paired-samples t test was used to determine the significance of the treatment changes between the pre-treatment and post-treatment within each group.Treatment changes between the 2 groups were compared with an independent-samples t test.And the levels of statistical significance were α=0.05.Results1.Teeth related indicators1.1. Variation of upper molarsFor the implant anchorage group,comparing the lateral cephalograms before(T1) and after(T2) treatment,upper molars was significantly intruded 1.59±1.28 mmin vertical movements(P<0.05),while moving 0.60±1.20 mm mesially in anteroposterior movements with no statistic significance(P>0.05), thus confirming that the upper molars were controlled preferably in both anteroposterior and verticaldirection by implant anchorage. For the conventional anchorage group, maxillary molars was significantly extruded 0.17±0.51 mm and moved 1.63±1.04 mm mesially after treatment(P<0.05),which implied that there was a certain extent of anchorage loss in anteroposterior direction and the conventional anchorage was of no effecton the veritical control of molars.1.2 Comparison of anterior teeth retractionThere were statistic significant differences in anterior teeth retraction between before and after treatment in both 2 groups.The change in the measurement of upper incisor edge(Lo-SV) retraction in G1 was significantly lager than that in G2(5.53±2.46 mm Vs 3.35±3.13mm),with statistic significance(P<0.05),indicating that the implant anchorage was better for anterior teeth retraction compared with conventional anchorage.2. Skeletal related indicators2.1Statistically significant increases in FA(0.65±0.94°),SNB(0.38±0.47°) and decreases in SN-MP(0.57±0.45°),AFH(1.63±2.45mm) were noted in G1(P<0.05).All these data indicated that counterclockwise rotation occurred in mandible.2.2 There were no statistically significant changes after treatment in G2(P>0.05). However, with regard of the value numbers,there was a decrease of 0.08±0.62° in SNB, an increase of 0.18±0.45° in SN-MP, and also an increase of 0.04±0.89 mm in AFH. Therefore, the position of mandible cannot be improved after extraction with conventional anchorage in the treatment of adults with Class II hyperdivergent malocclusion.2.3 Statistically significant differences in SNB,SN-MP,FA and AFH between G1 and G2 were recorded(P<0.05). This result showed that implant anchorage provided vertical control of molars more efficiently than conventional anchorage,accompanied with counterclockwise rotation in mandible.3.Variation in facial soft tissue profileComparing the outcomes between G1 and G2,there was not any statistical significance in the changes of Li-Sn Pos and the depth of clypeogenal sulcus(P>0.05). From the view of lip’s protrusion,using implant as an anchorage was not more effective than conventional anchorage.However,the data of pogonion(Pog’-SV) and face angle of soft tissue have statistical significance(P<0.05).Pogonion and face angle of soft tissue are the signals of position changes in soft tissue ofchin. In G1, the point Pog’ moved forward 0.88±2.15 mm,while the face angle of soft tissue increased 0.91±2.08°. In G2, point Pog’ moved backward 0.34±0.67 mm, while the face angle of soft tissue decreased 0.41±0.95. The results suggested the soft tissue of chin could be more prominent and the facial profile could be more concertedby using implant anchorage than conventional anchorage, which further proved that mandible rotated upward and forward.Conclusion1.From the view of the sagittal direction, the amount of anterior teeth retraction could be larger with implant anchoragethan conventional anchorage,and the molars anchorage could be better protected.2.Fromthe view of the vertical direction,implant anchorage can improve the counterclockwise rotation of mandibular, and decrease the FH-MP and AFH by controlling upper molar vertically in Class II hyperdivergent malocclusion cases.In contrast,there was no significant effect on vertical control with conventional anchorage.3.Implant anchorage can provide effective vertical control, so that it can increase the face angle of soft tissue, make chin move upward and forward, and the facial profile of soft tissues more concerted and aesthetic. |
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