Expression Of RANKL And OPG In Peri-implant Tissues During Unloading Period

Objective:The aim of this study was to observe the morphology and activity of osteoclast in peri-impplant tissues and to observe the expression of RANKL (receptor activator nuclear factor kappa B ligand) and its decoy receptor, OPG (osteoprotegerin) during unloading period of dental implants dynamicly, and to provide referrence for clinical or basic studies on dental implants.Methods:6adult healthy male Beagle dogs (1-or2-year-old) were fed in1week of acclimation. The mandibular second and fouth premolars of all the dogs were randomly divided into two groups: experimental group and control group, each comprised of12teeth. The study was divided into six stages:the1st day, the30th day, the60th day, the75th day, the84th day and the87th day. In each stage2teeth of the control group were extracted randomly, at the same time teeth at the opposite side were extracted and implants were inserted immediately in order to establish animal models of dental implants as the experimental group. RANKL and OPG mRNA expression were quantified by real-time PCR, all the animals were sacrificed after three months and then mandibular bones were taken out. Tissue samples were prepared and observed, experimental parameters were evaluated as the followings:(1) Crestal bone changes of X radiograph, changes of bone-implant interface, bone density and bone resorption in peri-implant;(2) Some sections were stained with hematoxylin and eosin to observe the morphological change of peri-implant tissues, an image analysis system was used to measure the length and depth of bone resorption lacunaes;(3) Some sections were observed by hard tissue slice, bone ingrowth fraction (BIF) and osseointergration idex (01) were calculated, the data was analyzed with the statistics softeware SPSS13.0. The results were statistically significant based on P<0.05.Results:1. All the24dental implants healed well and no loosen or failed, no inflamma response was found in peri-implant tissues.2. Observation of X-ray:no obvious gap between implants and bone; bone density increased as time increase; no obvious resorption was found in peri-implant tissues. Bone remodelling of experiment group was better than control group.3. Real-time PCR:Both OPG and RANKL were detected in peri-implant tissues, The most prominent period of bone remodeling occured at7day after the placement of implants. The mRNA expression of RANKL and OPG in alveolar bone increased in a time-dependent manner. After7days it gradually decreased and then was in balance. The mRNA expression of RANKL and OPG in experiment group were higher than the control group, and there was significant difference between them (P<0.05)4. Histological staining:On the3rd day, broad and disordered resorption lacunaes was observed in peri-implant, the resorption area concentrated a large number of multi-nucleared odontoclasrs. Resorption lacunaes became deeper and wider on the7th day. After15days, plum osteoblast-like matrix was observed at the bottom of the resorption lacunaes, the surrounding alveolar bone resorption lacunaes were less and neonatal line around showed the repair of new bone. The control group observed wider and deeper resorption lacunaes, and new bone formation was delayed.5. Image analysis:There was statistic difference about average length and depth among goups (P<0.05).6. Observation of hard tissue slice:New bone formation was observed on the30th day, trabecular arranged in an disordered and rarefaction way, new bone growed activly. On the60th day, new bone formation was distinct, trabecular arranged more regularly. After90days, bone remodelling was finished on the whole, trabecular arrangement of the experiment group was more regular than the control group. Quantitation histological analysis showed that BIF and OI on the90th day were higher than that of the30th day, and there was statistic difference (P<0.05).Conclusions:1. Insertion of dental implants can change the process of bone healing for tooth extraction wound, thus can decrease the resorption of alveolar bone.2. Both OPG and RANKL were expressed in peri-implant tissues, and the chanj tendency of RANKL and OPGmRNA was consistent with the change of bone remodeling, which indicates that RANKL and OPG may play an important role in the bone remodeling after placement of dental implants.3. The active stage for bone remodelling in peri-implant tissues during unloading period is about7days after implantation, so we can restraint bone resorption of peri-implant by using some inhibitior for RANKL at the time of osteoclast active phase.