| Background: The core idea of orthodontic treatment for patients with dental crowding is the rational development and distribution of the gap so that the teeth and bone mass tend to be coordinated. For some young patients who’s still in . the period of growth and development with bone deficiency, tooth extraction methods can solve the congestion problem, but may lead to further decrease of maxillofacial bone especially relaxation lip,buccal soft tissue loss of hard tissue support and become aggravated concave face type.Maxillary expansion is a clinically important non extraction treatment means, but because of narrow dental arch and crowding for bimaxillary, simply maxillary expansion can lead to upper and lower dental arch width is not adjustable,and can not solve the problem of mandibular crowding and deep spee curve, the clinical application has significant limitations. Therefore, the choice of orthodontic treatment is often determined by the mandibular crowding, because of the special anatomical structure of mandibular unlike palatal suture, the related research reports on the mandibular arch expansion are much less than maxillary. Since 2000, professor of Orthodontics in our hospital, designed a modified model of mandibular screw, and combined mandibular expansion with maxillary in orthodontic clinic work to correct all kinds of malocclusion, achieved satisfactory clinical curative effect. At the same time, the discussion about the existing expansion time also only stay in the maxillary, The related research majorly based on age or dental age for grouping, but the growth and development of young people with individual difference is obvious, the individual growth starting point, growth rate and duration were not the same, the replacement of teeth is also susceptible to variety of interference and external factors,more and more scholars,in recent years,believe that bone age can be regarded as the most accurate assessment of development status of biological age. Therefore, this study aims to analyze changes in width after expansion of patients with different bone age, explore the relationship between bone changes and bone age, to provide a reference for further clinical application of expansion technology.Objective: The aim of this study is to use three-dimensional measurement method to evaluate the dental and skeletal changes in patients different with different Baccetti vertebral bone age after rapid maxillary and mandibular expansion, explore the relationship between bone age and expansion effect of width increased in proportion,For this research, some references are provide for the clinical treatment of timing in orthodontic.Methods: The sample included 39 cases with exclusion criteria was selected in orthodontics department. According to the sharp and lower edge shape in C2, 3, 4(second, third or forth cervical vertebrae) ,they were divided into growth acceleration group, growth peak group and growth deceleration group.Cone-beam computed tomography(CBCT) images were segmented and reconstructed by Mimics 17.0 and Geomagic Studio 12 image processing software to assess the dental and skeletal change before and after treatment,All data was analyzed by MedCalc9.3,SPSS16.0, G*power3.1 software statistically.Result: After rapid arch expansion, the maxillary jaw changes as follows:1.The first molars inclined buccally in three groups of patients after expansion to a certain extent. The growth acceleration and peak group changes with no significant difference (P>0.05), in deceleration growth group ,The first molar was significantly inclined ((P<0.05)).2.The alveolar bone had obvious buccoclination in all three groups after expansion(P<0.05). In growth peak group, the alveolar bone inclination was the smallest, and there was no significant difference between acceleration and deceleration phase (P>0.05).3.In the changes of widest and middle palate width, the acceleration group and the peak group had no significant difference(P>0.05). but both of them were significantly more than deceleration group.4.The mid-palatal suture width in three groups increased with statistical significance after expansion (P<0.05)., both growth acceleration group and the peak group were significantly more than deceleration group(P<0.05)..After rapid arch expansion, the mandibular jaw changes as follows:1.The mandibular first molars had significant buccally tilt in all groups (P<0.05)., and there was no significant difference between the three groups;2.In three groups, the lingual alveolar bone had inclined buccally with significant difference (P<0.05). Patients with acceleration and peak growth were less inclined than deceleration ones(P<0.05).3.The maximum and middle width of mandible after expansion were significantly increased (P<0.05).,and there was no significant difference between the three groups.4.The width of base bone was increased after mandibular expansion in all three groups(P<0.05)., and the increment in acceleration and peak group was higher than that of deceleration group(P<0,05)..Conclusion: 1.The rapid maxillary and mandibular expansion treatment for different growth period patients, can effectively increase the width of the upper and lower dental arch;2. For patients with growth acceleration and peak phrase, the width increment was obtained mainly from alveolar bone inclination, opening of palatal suture, and less incidence of anchorage teeth, in the peak growth period,the inclination alveolar bone was the lowest; 3. Even in the patients in growth deceleration group, rapid maxillary expansion can also open mid-palatal suture to a extent,but the width is mainly due to the inclination of teeth and alveolar bone; 4.The arch width increment is not only entirely obtained from the inclination of anchorage teeth and alveolar bone after rapid mandibular expansion,but also the basal bone width increased with a certain degree; 5.After mandibular expansion,in the growth deceleration group, alveolar bone was more inclined,and the width of the apical basal bone increased less than that of the growth acceleration and peak period group. |
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