The Experimental And Applied Research Of Rapid Orthodontic Tooth Movement Through Distraction Osteogenesis

ObjectivesMalocclusion is one of the three major stomatological diseases confirmed by WHO (The World Health Organization), it affects craniofacial development, oral function, psysical and psychological health seriously. The prevalence of malocclusion is 71.21% in mixed dentition and 72.92% in permanent dentition in China (FU minkui, 2000). More and more malocclusion patients appealed to orthodontic treatment. Up to now, the traditional techniques showed the general velocity of orthodontic tooth movement (OTM) of 1mm/month, therefore, the process of orthodontic treatment usually lasted about 2 years or even longer. For that reason, scholars all over the world focused on how to accelerate the tooth movement and to shorten the duration of orthodontic treatment.Distraction osteogenesis (DO) is a method to induce new bone formation by applying mechanical strains on the preexisting bone. The formation of new bone is achieved through stretching of the callus in the osteotomy or corticotomy gap with distraction devices. It is suggested that the formation of the new bone in the osteotomy or corticotomy site with a width of approximately 1 mm per day can be achieved by this method. In 1992, DO was first applied to the human mandible by McCarthy et al, and since then it has been applied to all the bones of the craniofacial skeleton. Resently, DO has been used in orthodontics to achive rapid OTM. In 1998, Liou and Huang put forward the concept of periodontal ligament distraction(PDLD). They demonstrated the rapid distalization of 26 canines in human subjects using distraction of the periodontal ligament aided by alveolar surgery undermining the interseptal bone. They achieved an average 6.5 mm of distraction of the canines within 3 weeks without severe side effect. In 2002, Ki?ni?ci et al put forward the technique of dentoalveolar distraction(DAD), they made a corticotomy around the apex of the canine and a fracturing of the surrounding spongious bone around its root, so a fully mobilizing dentoalveolar segment that inclouded the canine is made, and then the canines ccould be distracted rapidly in a speed of 0.8mm/day, while the anchorage teeth could withstand the forces with minimal anchorage loss. But Sukurica et al reported that 14 out of 20 canines were negative to vitality test 6 months after the completion of DAD. Although a few researches on rapid tooth movement have been published, systemic research is scarce.This study will set up experimental animal models of PDLD and DAD firstly. The periodontium histological changes of moved tooth will be observed by light microscope to investigate the difference between the two new techniques and the traditional way. The number of TRAP positive cells were counted on the periodontium. Further more, the BMP-2 in the periodontium will be measured by using well- known immunohistochemistry and in situ hybridization techniques, so we can explore the BMP-2 change in protein and molecular level which help us understand deeply about periodontium remodeling and molecular biology mechanism of moved tooth. Based on study of experimental animal model, we choose PDLD technique to be used clinically,we will study the surgery procedure, mode of activation, speed of tooth movement, effectiveness and safety through model analysis, X-ray and vitality testing.Methods:1 To establish the experimental animal models of rapid orthodontic tooth movement through distraction osteogenesis by PDLD and DAD with Beagle dogs.Animal and grouping. Twelve male Beagle dogs were randomly devided into 4 groups: group A (1-week activating), group B(2-weeks activating), group C (2-weeks activating, 2-weeks retention) and group D(2-weeks activating, 4-weeks retention), with 3 dogs in each group. Of the 3 dogs in each group, the 2nd lower premolars were extracted, totally 6 lower 1st premolars were defined as moved teeth, and they were randomly devided into PDLD, DAD and routine fixed orthodontic tooth movement(routine control). The establishment of experimental animal models.The establishment of PDLD experimental animal model.After the 2nd lower premolar were extracted, grooves were made from the mesial of the extracted socket to the buccal and lingual cortical bone of the 1st lower premolar, and from bottom of the socket towards the apical proper alveolar of the 1st lower premolar by dental chisel. A costom-made, tooth borne distractor was bonded. The distractor was activated 90°, twice a day for 2 weeks and followed by retention period.The establishment of DAD experimental animal model. After the 2nd lower premolar were extracted, a mucoperiosteal flap was made along the buccal vestibule to expose the cortex of the 1st and 2nd premolar. The buccal wall of the extracted socket was removed and the socket was smoothed by dental chisel but the lingual cotex was retained. An corticotomy was made 5mm below the root apex and mesial of the 1st premolar, larger osteotomes were used to fully mobilize the alveolar segament by fructuring the surrounding spongious bone off the lingual cortex, which like an transport disc.A costom-made, tooth borne distractor was bonded right after stitching up the wound. After a latent period of 3 days, the distractor was activated 90°, twice a day for 2 weeks and followed by retention period.The establishment of routine orthodontic tooth movement experimental animal model.To extract the 2nd lower premolar, and nickel-titanium coin spring were bonded between the 1st and 3rd premolar with a force of 150g for 2 weeks and followed by retention period.Measurement indicators. The distances of movement of moved teeth and anchorage teeth were masured, and radiograph pictures were taken every week.2 Histological Study of periodontium remodeling of rapid orthodontic tooth movement through distraction osteogenesis. The dogs of group A were killed after activation for 1 week; group B after activation for 2 weeks; group C after activation for 2 weeks, retention for2 weeks; group D after activation for 2 weeks, retention for 4 weeks. Dentoalveolar segments including the 1st and 3rd premolars were then dissected out separately, fixed in 10% buffered formalin, and decalcified with EDTA. They were embedded in paraffin. Sections(5μm) were stained with hematoxylin and eosin . The number of osteoclasts in the periodontium of moved teeth were caculated by TRAP staining.3 The expressions of BMP- 2 protein and mRNA in periodontium of moved teeth of rapid orthodontic tooth movement through distraction osteogenesis.Making the sections on different period of time and processing by immunohistochemical and in situhybridization of BMP- 2 as well as analyzing diagram.4 An applied research of rapid canine distalization through PDLD after reducing interceptal bone resistance.20 canines in 11(8 male and 3 female, mean age 15.8 years) patients who required first premolar extractions. A tooth-borne, custom-made distractor was bonded right after the premolar was extracted and the interseptal bone distal to the canine was undermined. The distractor was activated 0.1mm, 3 times a day. Orthodontic models, panoramic radiographs, periapical radiographs, electrical vitality test were taken.Results:1 The establishment of the experimental animal models of rapid orthodontic tooth movement through distraction osteogenesis by ways of PDLD and DAD with Beagle dogs.After 2 weeks'activation, the average distal movements of moved teeth in PDLD and DAD were 3.98mm and 3.87mm separately compared with 0.68mm in routine control(P<0.01), and the average distal movements of moved teeth in PDLD was 2.73mm compared with 1.25mm in DAD in the 2nd week(P<0.05) . After 2 weeks activation, the average anchorage loss were 0.52mm in PDLD, 0.38mm in DAD and 0.65mm in routine control separately(P﹥0.05).The distal inclination of the moved teeth were 13.75°in PDLD, 3.97°in DAD and 8.33°in routine control separately (P<0.05).X-ray on PDLD: during the activating period, the PDL on tension side of the moved tooth widened rapidly and the PDL on pressure side compressed slightly, the interceptal bone bended into the distracted socket with the moved tooth. During the retention period, the density of the widened PDL on tenside increased, the width of PDL gradually regain normal and new proper alveolar formed.X-ray on DAD: during the activating period, bone disc moved into the bone defect area with moved tooth rapidly, and the PDL on tension side of the moved tooth widened simultaneously. During the retention period, the density of the distraction gap increased, the width of PDL gradually regain normal.X-ray on routine control: during the activating period, the PDL on tension side of the moved tooth widened and the PDL on pressure side compressed. During the retention period, the width of PDL gradually regain normal.There were no evidence of severe root resorption and alveolar bone loss in each modes.2 Histological study of periodontium remodeling of rapid orthodontic tooth movement through distraction osteogenesis.PDLD: along with the activation, the PDL on tension side widened significantly, fibroblasts enriched in PDL and new bone trabeculae formed actively with the same direction of distraction. No hyalinization zone of PDL or resorption of cementum were discovered on the pressure side, the interseptal bone was compressed into the extraction socket rapidly and remodeled gradually. During the retention period new trabeculae bone were mature gradually and the PDL in both sides reverted to normal.DAD: new trabeculae bone were seen along the direction of distraction in distraction area, at the same time the PDL on tension side widened gradually and cells accumulated, hyalinization zone and resorption of cementum were found occasionally on the pressure side. During the retention period new trabeculae bone were mature gradually and the PDL in both sides reverted to normal.Routine control: along with the activation, the PDL on tension side widened, hyalinization zone of PDL and resorption of cementum were discovered on the pressure side. The formation of new bone were weak compared with PDLD and DAD. During the retention period new trabeculae bone were mature gradually and the PDL in both sides reverted to normal.The pulp tissues showed mild hyperemia or edema during activate period and recovered during retention period.The osteoclasts activity significantly increased to peak in 2nd week on PDLD, while it increased to peak in 1st week on DAD and kept on a high level for relatively long period.3 The expressions of BMP- 2 protein and mRNA in periodontium of moved teeth of rapid orthodontic tooth movement through distraction osteogenesis.The expression of BMP-2 protein expressed mainly in osteoblasts near alveolar bone, cementoblasts near cementum, fibroblasts and new bone matrix, and its mRNA expressed mainly in osteoblasts, cementoblasts, fibroblasts and a few osteoclasts.The positive expression of BMP-2 protein and mRNA reached peak at 2nd week in PDLD, DAD and routine control, seperatedly, and the intensity of expression in PDLD and DAD are higher than routine control side, while there is no statistic significance between PDLD and DAD.During retention period, the intensity of expression reduced gradually in PDLD and routine control, while it kept on a high level for relatively long period in DAD.4 A clinical study of rapid canine distalization through PDLD after reducing interceptal bone resistance.The distraction procedure was completed in 18 to 35 days(mean 25.6±4.74 days). The distal displacement of the canines ranged from 0 to 2.27mm(mean 0.76±0.75 mm).The canines showed a mean of 12.2o distal tipping and a mean of 18.52o rotation.There was no significant root resorption and pulp vitality change after distraction.Conclusions:1 Two kinds of experimental animal model of rapid orthodontic tooth movement through distraction osteogenesis were established successfully by means of PDLD and DAD.2 Rapid orthodontic tooth movement were achived safely by means of PDLD (3.98mm in 2weeks)and DAD(3.87mm in 2weeks).3 The histological changes on moved tooth of rapid orthodontic tooth movement by means of PDLD are: after the resistance of interceptal bone was weaken, the moved tooth and the PDL on pressure side and the interceptal bone moved into the distract socket rapidly, while under the reinforced tension force, the PDL on tension side was distracted rapidly,new bone formation were activated and the periodontium rebuilded rapidly.4 The histological changes on moved tooth of rapid orthodontic tooth movement by means of DAD are: bone disc moved rapidly with moved tooth by interval force, and then regenerate bone formed in the distraction area.5 Mode of traditional orthodontic tooth movement was involved in both PDLD and DAD simultaneously.6 Rapid tooth movement through PDLD showed minor truma, root resorption and pulp symptom and better anchorage.7 We established a clinical procedure of reducing interseptal bone, and made a tooth-borne distractor for rapid canine distalization.8 The key technology of PDLD is the vertical osteotomies connected with an oblique osteotomy extending towards the base of the interseptal bone to weaken the resistance of ooth movement.9 Rapid orthodontic tooth movement through PDLD showed fewer truma and effective to shorten the duration of orthodontic treatment and to diminish the anchorage loss, it can be used in clinical extensively.