Studies Of Biodegradable Micro-implants As Orthodontic Anchorage In Experimental Animals

Objective:In orthodontic treatment, the securing of an anchor is one of the most importantaspects that must be carefully considered when developing and executing a treatmentplan.In1980s, traditional implants were known as a very reliable source for clinicalanchorage.In recent years, titanium alloy implants are known as the orthodontist’s“master key” and widely used because of its small size, easy to use and providingabsolute anchorage.The implants can be open or closed to provide a stable anchorage,however, providing closed anchorage, they need to be remove outside our bodies andcause secondary damage.The biodegradable implants offer a promising alternativefor patients, as they avoid implant removal and intracranial implant migration,absentimaging interference, and they provide temporary support and degrade at a ratematching tissue formation, and thus, eliminate the need for secondary surgeries.Against this backdrop of problems and complications surrounding orthodonticimplants, there arises the need for a bioabsorbable material.Methods:Seventy-two micro-implant anchorages of2.0mm diameter×10.0mm lengthwere provided by the manufacturer. The micro-implants composed of poly(l-lacticeacid), poly(D, L-lactic-co-glycolic acid) and hygroxyapatite were implanted to themandible of6weight13-15kg male beagle dogs. The surgical site was themandibular body in the premolar and molar regions, known to have high cortical totrabacular bone ratio.The left hemi-arch of the mandible was used for theexperimental groups and the right hemi-arch for the control groups.Themicro-implants were planted under mucous membrane.The animals were sacrifcedat2,4and6months after surgery.Before the animals were sacrificed14days and4days, respectively intramuscular tetracycline hydrochloride. The animals were killedby anesthesia overdose, and the mandibles remained in4%paraformaldehyde solution. The mandibles were observed by CBCT，then dissected,and blockscontaining a micro-implant and the adjacent bone were sectioned to have at least2mm of surrounding bone.Mechanical properties of the micro-implants were done bythe universal mechanical testing machine. Histological evaluation was done usingHE staining and toluidine blue staining techniques.Each micro-implant was carefullyexcised from the mandible2，4and6months after installation.Surface propertieswere then observed with SEM.Results:No significant foreign body reactions were seen in the mandibles. CBCTshowed that the micro-implants were gradually radiopacity with the extension oftime.No significant difference between the experimental and contral groups. Overtime,mechanical properties showing a downward trend, expecially the experimentalgroups. Histological observation showed that the inflammation around the implantsdid not happen. It can be found that the micro-implants and surrounding bone areconnected,but the combination rate is relatively low.Tetracycline mark also showsthat there are new bone formation around the micro-implants between10days.SEMshowed that the micro-implants surface morphology changed significantly,micro-implants degradation occurs gradually.Conclusion:The micro-implants examined maintain adequate strength for the orthodontictreatment period, producing no harmful foreign body reactions.The compositesshowed good biocompatibility and biodegradability,and did not found the localinflammatory response, but there are still some problems for improvement.