The Animal Experiment Of A New Optimized Distraction Implant

Dental implantation has drawn attention for its long-term functional and estheticpreponderances, and has become one of the most common and efficient practice. However,the insufficient alveolar bone height resulted from tooth extraction, trauma, periodontaldisease, or tumor resections etc., makes the dental implantation difficult insertion, estheticdefects or even failure. The nature of this deficiency poses either structural or aestheticobstacles to successful dental prosthesis.In such cases, alveolar ridge augmentation was required to restore a favorable alveolarridge height and to create an appropriate environment for the placement of endosseousimplants. Many methods have been proposed to reconstruct the alveolar ridge, including onlay or sandwich bone graft, guided bone regeneration (GBR), and alveolar distractionosteogenesis (ADO). Among these methods, ADO has received considerable interest since1996, when the first experimental and clinical application of ADO was reportedrespectively. Compared with other methods, ADO has many advantages, such assimultaneous augmentation of hard and soft tissue, no bone harvesting, avoidance ofdonor site morbidity, and less bone resorption versus with free bone graft.However, the conventional procedure of ADO included three surgical steps: placementof a distractor, removal of the distractor, and insertion of one or more implants8~16weeks after the distraction. After the insertion, another4~6months of bone-implantosseointegeration were needed before the application of prostheses. All mentioned abovehad disappointed both the dentists and patients, and a new technique was needed urgentlyto simplified the surgery procedure. Thus, a new device named as Distraction Implant (DI),which could act as both a distracter and an implant, had shortened the whole treatmenttime obviously.Although DI had its special advantages, the complicated structure of previous DIlimited its clinical usage. Firstly, the coronal function portion was the main load bearingpart, but it was too short to support the occlusal force. Secondly, the central distractionscrew could be easily broken under long-time stress. Thirdly, it was difficult to take outthe apical support portion in case the implantation failure occurred. Thus, in order topromote the DIs’ clinical application, it was necessary to optimize the current DI and takea comprehensive evaluation.In this study，we aimed to examine the feasibility of a new optimized DI to correct theinsufficient alveolar height in adult mongrel dogs by X-ray, Micro-CT, histological, andbiomechanical evaluations.Part one: Design and manufacture of the new optimized DIExperiment one: Design and manufacture of the new optimized DIMethod： The problems of existing DI were found after analysis, and the optimizationof the structure and materials was done to solve these problems. After that the specificparameters of each part were determined, and the optimized DI was manufactured according to the optimization results.Results: We have found the problems of existing DI in structure, biomechanicalproperties and transformation from distracter to implant. After optimization of previouslyDI structure, and according to the aim of DI, the improvements were establishedrespectively: firstly, the length ratio of the TP: SP was8:2; secondly, the diameter of DS≥2mm; thirdly, manufacturing SP with absorbable materials. Finally, we have successfullyproduced an optimized DI.Conclusions of part one1.After optimization, the problems of previous DI were found, and improvements weremade.2. R=8:2and D≥2mm were the optimal choices. And according to these results, theoptimized DI was made.Part two：In vitro study of DIExperiment two: Biomechanical testing of the Optimized DIMethod：Comparative analysis of the in vitro biomechanical properties between theoptimized DI and normal implant were conducted: axial pull-out test and cyclic loadingfatigue test.Results: After in vitro biomechanical testing, the optimized DI and normal implantshad similar biomechanical properties. Test results: axial pull-out test, maximum pulloutforce of DI was1106±75.22N, maximum pullout force of normal implant was1094±114.3N. There was no statistically difference between them. Fatigue test: after2,400,000continuous load (to simulate10years of chewing), all DIs and normal implants were notfailed.Experiment three: In vitro canine mandibular distraction test of the Optimized DIMethod：On a fresh alveolar defect canine mandible, the osteotomy and insertion of DIwere conducted, after that, the DI was distracted with FP.Results: The operating procedure was successful. And we used some innovativesurgical approach to avoid the drawbacks happened in the previous surgery. Thesimulation surgical procedure was successful, and FP promoted successfully. Conclusions of part two1. The biomechanical property of the optimized DI was as good as the normalimplant.2. The optimized DI had reliable distraction osteogenesis capability.Part three: in vivo animal experimentExperiment four: Establishment of insufficient alveolar height animal modelMethod:6dogs were involved in the experiment. All the mandible premolars wereextracted and an alveoloplasty was performed. After3months of bone healing, theinsufficient alveolar height animal models were built up.Results: The innovative anesthesia method improved the surgical efficiency and safety.3months after tooth extraction, visual observation and X-ray examination showed that theinsufficient alveolar height animal model was successfully established.Experiment five: The insertion of the optimized DI and distraction osteogenesisMethod： The6insufficient alveolar height dog models were involved in thisexperiment. A horizontal incision in the vestibule and ultrasonic osteotomy were used tocomplete the DI insertion. Five days after insertion the distraction osteogenesis wasconducted at a rate of1mm/2d, a total of12days,6mm.Results: Successfully completed the DI insertion with innovative use of surgicalmethods, and avoided some of the drawbacks of previous surgery; the alveolar ridge wassuccessful promoted6mm height.Experiment six: evaluation of bone regeneration of in vivo experimentMethod: One month,2months and3months after distraction, the dogs were examinedby X-ray, CT scanning, Micro-CT scanning and histological analysis, to evaluate the resultof distraction osteogenesis of the optimized DI.Results：The visual observation: none of the DIs was lost or loose during the healing,the height of the transport bone segment remained in position. X-ray, CT scanning,Micro-CT scanning, and hard tissue histological analysis showed new bone graduallyregenerated in the distraction gap3months after distraction. The new bone was noobvious difference compared with the native bone around, at3months after distraction. Conclusions of part three1. Innovation surgical methods of DI insertion, and optimized DI could effectivelyreduced the trauma of the hard and soft tissue, shortened operating time, reduced thesuffering of the patients, and provided protection to the transport bone segment and DIstability.2. The results of animal experiments confirmed that the optimized DI had reliablecapability of distraction osteogenesis.