| [Objective]1. The purpose of this study was to analyze three-dimensional(3D) changes of midfacial skeleton, sutures and dental arch after trans-sutural distraction osteogenesis(TSDO) and to explore the mechanism in this process, which may eventually help to optimize its clinical utility.2. By the cephalometric measurement at each postoperative follow-up time point, the position of midfacial skeleton was analyzed to evaluate the long-term skeletal stability after TSDO and then futher to propose effective strategies for preventing relapse.3. By establishing the animal model of TSDO for midfacial skeleton with internalized distractor in dogs, the long-term osteogenesis outcome of TSDO were analyzed to provide some biological bases to strategies for preventing relapse in clinical.Meanwhile based on the success of animal experiments, the aim of this preliminary study was to design an internalized distractor for the treatment of midfacial hypoplasia in growing patients with cleft lip and palate (CLP) by the technique of TSDO.[Methods]1. All growing patients with CLP who underwent bone-borne TSDO for midfacial hypoplasia from 2005.1 to 2014.12 were reviewed in this retrospective study.3D morphological and quantitative measurement analyses were performed to evaluate the changes of midfacial skeleton, sutures and dental arch by super imposition of preoperative and postoperative computed t omograph i c (CT) i mage s.2. All growing patients with CLP who underwent bone-borne TSDO for midfacial hypoplasia from 2005.1 to 2015.12 were reviewed and their lateral cephalographs at each postoperative follow-up time point were also collected. The changes in the position of midfacial skeleton were analyzed by cephalometric measurement to assess the long-term skeletal stability after TSDO.3. Three-month-old beagle dogs were treated with midface TSDO using a self-designed internalized distractor. The feasibility was evaluated and the effects of the midface advancement were measured using radiography and CT. In addition, the regenerated bone in sutural area was examined with Micro-CT, biomechanical testing, and histology 1 year after the TSDO. Meanwhile based on the animal experiments, a personalized internalized distractor of TSDO for clinical application was preliminarily designed according to the skull 3D-CT images of patients and its feasibility would be further verified.【Results】Part 1:1. A total of 26 patients met the inclusion criteria and their data were reviewed. The average age at the time of distraction was 11.5 years, the average unilateral maximum traction force was 4.45kg and the average distraction time was 40.0 days. All of these patients achieved improvement in midface convexity and positive overjet with the advancement of the midfacial skeleton.2. The 3D morphological analysis was performed on superimposition images. The intuitionistic analysis findings exhibited the most significant suture stress changes at the pterygomaxillary suture area with obvious bone generation in all patients. The whole midfacial skeleton had progressively increased advancement in a craniocaudal direction along the midface segment associated with morphological changes in skeleton itself.3. The 3D quantitative measurement findings were consistent with morphological findings. And it also showed differential advancement of each landmark on midfacial skeleton with a decreasing tendency at the maxillary alveolar, zygomatic bone, orbital rim, and nasal bone. In the vertical dimension, the temporal process of zygomatic bone and the lower part of maxillary tuberosity showed significant downward displacement, while the nasal bone showed significant maximal upward displacement. But in the transverse dimension, the nasal dorsum and nasal base became widen and the width of maxillary occurred mild growth. Accordingly, the 3D quantitative measurement findings of dental arch exhibited the significant increasement in the maxillary tuberosity, while the length of dental arch showed no obvious changes; the width of anterior and medial arch was obviously increased but the posterior arch changed slightly; finally in the vertical dimension, all the landmarks on the dental arch showed the downward displacement with an increasing tendency from front to back.Part 2:1. A total of 76 consecutive growing CLP patients with midfacial hypoplasia were treated with bone-borne TSDO between 2005.1 to 2015.12. The clinical outcomes showed 2 patients with treatment failure and 4 mixed dentitions bilateral CLP patients with skeletal anterior open bite, all the other patients achieved a satisfactory improvement in the midface convexity and positive over jet. The results of long-term follow-up showed 1 patient lost and 8 patients with retraction or relapse.2. The cephalometric measurement results of 66 patients exhibited that the A-point was significant advanced in horizontal direction, and the SNA angle and SNB angle were also significant increased after the distraction. But the A-point showed no obvious changes in vertical direction as well as the SNB angle and MPA angle. At each postoperative follow-up time point, the position of A-point remained stable in horizontal direction and showed the tendency of downward movement in vertical direction. The SNA angle, SNB angle, ANB angle and MPA angle fluctuated smoothly in some ranges with no significant difference.Part 3:1. In experiments of TSDO with internerlized distractor on dogs, the gross observation of the experimental group showed the development of dolichocephaly, enophthalmos and class II malocclusion after the distraction. The distance of the maxillary antedisplacement measurements from radiography increased significantly and the CT images showed active bone metabolism along the zygomaticomaxillary suture and maxillary contrast against the surrounding bone area. With 1 year of observation after the distraction, we found that the face appearance had gradually trended toward harmony and the occlusal relationship had also returned to a class I malocclusion, and the CT images showed that the structure of the new bone formation area tended to be stable but still had decreased integrity that assumed a cribriporal and thinning anterior wall of the maxillary in the experimental group while it was intact in the control group. Further testing the zygomaticomaxillary sture and adjacent bone, the Micro-CT showed more incompact structure with the disordered bone trabecular alignment and bone volume/total volume was significantly less in the experimental group. Biomechanical testing also showed a significantly lower yield but with no difference in stiffness. Histologic staining found that there were more fibroblasts and capillaries in the suture area with stretched collagen fibrils that connected the bone. Along the suture on both sides, a belt-shaped area of less bone matrix mineralization with high osteocyte density was identified, and the osteoclasts were deposited mainly in the border region of the suture and bone.2. For the clinical research, a 9 yeas old male CLP patient with midfacial hypoplasia was treated with TSDO using an internalized distractor with skull anchorage. This device was designed combined the skull 3D-CT images with the technique of computer assisted surgery. The installation of device was to insert the anchorage rods into the oral beneath the zygomatic arch through small scalp incision. The clinical outcomes showed that the patient’s appearance and malocclusion achieved improvement.[Conclusions]1. TSDO allows the growth and advancement of the whole midfacial skeleton to achieve occlusal correction and facial harmony through the mechanism of both suture remodeling and bone remodeling.2. TSDO can achieve good long-term skeletal stability, the position of maxillary remain stable in horizontal direction and show the tendency of downward movement in vertical direction. The effective stragedies for preventing relapse after TSDO should include moderate overcorrection, prompt orthodontic treatment and timely facemask therapy.3. TSDO using an internalized distractor with skull anchorage for the treatment of midfacial hypoplasia in growing CLP patients has been demonstrated practicable, but it still has much room for improvement. Moreover, the long-term osteogenesis analysis findings suggest that the metabolism of sutural area still remain active, which provides reliable biological bases to prevent relapse in clinical. |
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