| The restorative therapy for residual root and crown resulting from early childhood caries (ECC) has been very difficult in clinic until now. The therapy for residual root and crown of permanent teeth always takes metal or fiber post to enhance retention by root canal to repair the dental shape and function. But the restorative treatment for residual root and crown of deciduous teeth will affect the dental replacement using the no-absorbable post. The dental replacement is a special physiological process in childhood. The root of deciduous teeth will be absorbed with the development of permanent tooth germ, and be replaced by permanent teeth. For the dental replacement, we must think whether it will affect the eruption of permanent teeth to take root canal treatment of internal fixation therapy for severe early childhood caries (SECC). Domestic data showed that dentist sometimes takes semeiological treatment or extraction for residual roots and/or crowns of deciduous teeth. But the conservative treatment, affect not only the young patients aesthetic and development, but also the normal permanent teeth's eruption and jaw's growth which will result in malocclusion. In order to solve the problem, the most important problem for pediatric dentist is to choose proper root canal post for repairing the S-ECC aesthetically, functionally and physiologically. Now medical bioabsorbable materials have began to be widely used in clinic treatment, such as orthopedic fixations and surgical scaffold. The bioabsorbable materials have good biocompatibility and mechanical properties, and the right biodegradable properties, so it can be applied to the replacement of the tissues and organs, which can improve the function or promote healing. Moreover, Polylatic Acid (PLA) materials have been the hot-spot due to the excellent physical, chemical and biological properties. In this experiment, we would explore the feasibility of PLA post application by the experiments of cellular biocompatibility and animal model, and further observe and assess the postoperative effect by clinical trials. We wished to set up a novel restorative method in repairing ECC, and provide the experimental basis on the management of the bioabsorbable post.Experiment one: The basic studies on biocompatibility of PLA postIn this experiment, we firstly made bioabsorbable intracanal post with PLA materials and then made the leaching liquor from PLA post of different concentrations. In the next, Human dental follicle cells, dental pulp cells and periodontal ligament fibroblasts of deciduous teeth were cultured and identified by immunohistochemistry methods. The leaching liquor from PLA post was added to the three kind of culture medium to observe its effects on morphological changes, cell proliferation and apoptosis by the histological methods, MTT test and flow-cytometry technology. The experimental results showed: The leaching liquor from PLA post had no significant effects on cellular life compared with the normal cultured group; the cytotoxicity assessment of different experimental groups were detected at grade one, and there was no significant difference comparing with the control; the flow-cytometry analysis suggested that the early apoptosis and late apoptosis, the apoptosis index had no significant differences statistically among all groups. Further, the randomized Kunming mouse were injected with leaching liquor from PLA post of different concentration, while the mouse injected with saline were regarded as the control group. the acute behavioral response to toxicity were observed and recorded, and then the activity changes of the inflammatory factors were analyzed in the experimental animal's serum by IL-1 Elisa method, finally mouse liver samples were prepared with conventional histological method, and the liver cell's toxicity to PLA were observed by HE staining. The results showed: firstly, the mouse in experimental group all had no obvious acute behavioral response to toxicity; secondly the inflammatory factor in serum, IL-1 activity analysis had no significant difference between the experimental group and control group; thirdly the histological observation of liver found no obvious cell swelling or necrosis, congestive tissue, invasion of inflammatory cells and other abnormality. In all, the results suggested that the prepared PLA intracanal post had no significant effect to the related cells of human dental replacement. It had good biocompatibility and biological security, no biological toxicity in experimental animal was detected. So it could be used for further clinical research.Experiment two: the experiment of PLA post application in animals.In this experiment, the three-month-old dog was chosen as the experimental animal, and the lower deciduous anterior teeth were used to make the the experimental model of intracanal restoration with PLA post. Then the dental and periodontal clinical manifestation and restoration's situation of the restored deciduous teeth were observed, and the changes in the tissues around the root were detected by periapical radiograph. Two month later, the experimental animal was killed by the painless way, the jaw's tissue samples were placed, and specimens were prepared by conventional histological method. The influence of PLA post to the root absorption and the eruption of permanent tooth germ were observed by histological method, and the biological response of deciduous periapical tissue was detected. Experimental results showed that the deciduous anterior teeth restored by PLA intracanal post had no obvious abnormalities such as pathological tooth loosening, gingival hyperemia, periodontal abscess and other abnormalities; the X-ray showed that deciduous apical tissue had no abnormal shadow of pathological absorption and inflammation, and the underlying permanent tooth developed normally; the histological observation found that the physiological absorption occurred in restored deciduous tooth's root, the underlying permanent tooth germ erupted normally, and the schedule of dental replacement had no significant difference comparing with the control tooth. There were not pathological abnormalities in deciduous periapical tissue, including obvious disordered tissue structure, congestion of capillary vessel, invasion of inflammatory cells, and tissue necrosis. The results of experimental animal suggested the intracanal restoration application of PLA post had no obvious effect to physiological replacement of primary and permanent tooth.Experiment three: the preliminary study on the PLA post's clinical trialBecause the mechanical properties of the PLA post produced by casting mold method is not very good, the bioabsorbable implants used in surgical treatment are usually modified. In this experiment, we took SmartPin (Linvatec, Finland) as the materials of clinical trial for deciduous teeth restoration, which is made of the PLA polymer and synthesized by special drawing and weaving technique, and has high strength and toughness. Firstly the 2mm diameter SmartPin (Linvatec, Finland) were cut into the 10mm-length root canal posts by sterile cutting method, and then the posts were stored at room temperature and sterilized condition. 48 S-ECC children at age 3 ~ 4 year were selected as the clinical samples. And their severely carious maxillary anterior teeth could be not restored by conventional treatment options, which were total 100 teeth. In the informed consent, Firstly the decayed teeth were endodontically treated, and then the posts were implanted into root canals and cemented with adhesive glass ionomer, finally full-coverage restorations with resins were placed to rebuild teeth crown. In periodic follow-up of half a year, the patients was examined by clinical test and evaluated by USPHS&Ryger assessment, in order to analyze the success rate of PLA post's application. They were observed by periapical radiographic examination to detect the clinical sequelae or complications, including apical inflammation, pathological root absorption of deciduous teeth, abnormal eruption of permanent tooth germ and so on. One-year review shows the success rate of restoration of teeth was 96.8%, however the incidence rate of apical inflammation wass only 6.3%, and no other abnormalities were found. Results suggested bioabsorbable canal post should be a kind of desired intracanal fixation device for the restoration of S-ECC. Certainly, long-term follow-up will be needed to guarantee sustainable result. |
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