The Research On Impregnating HA/TCP With Silver: An Antibacterial Strategy For The Scaffold Of Tissue Engineering

Defect of dentition is very common in humans. It is recorded that people hadtried to complete the defective dentition with artificial materials since1600s.Today, more than400years later, although dentists focus more and more on bothesthetic and function of gnathostomatic system, the materials have developedfrom animal bones, wood or ivory to metal, resin and porcelain, the processingtechnic has changed from hand-crafted to computer-aided-design andcomputer-aided-manufacture, it is still similar to the old technique of replacement,because it can only replace the crown. In1980s, Branemark,a Swedishorthopedist built the theoretical and technical system of dental implant, whichopen up a new epoch of dental and maxillofacial reconstruction. But thesynostosis between implant and alveolar bone can’t buffer the occlusal force asmuch as the natural combination between tooth root and alveolar bone bypericementum. It can also not protect the implant out of the destructive occlusalforce and keep the reconstruction physiological. So, how to regenerate teeth has become a dream of mankind for a long time.The development of stem cells and tissue engineering technique bringsbright sunshine to the tooth regeneration. Tooth is a complex organ whichcontains enamel, dentin, cementum and pulp. The stability and success rate ofwhole tooth regeneration is far from the clinical therapy because of thecomplicated control mechanism. Tooth root regeneration, which based on the3D tissue engineering technique, makes a breakthrough in recent years. In2006, areport on tooth root regeneration was presented by Sonoyama. They used humanSCAP to regenerate dentin on a HA/TCP carrier, while using human PDLSCs toregenerate PDL on a Gelfoam which was covered around the HA/TCP carrier.CT examination revealed a HA/SCAP Gelfoam/PDLSC structure forming insidethe alveolar bone with mineralized root-like tissue formation and periodontalligament space. However, shortly after the root in conjunction with the dentalcrown, they found there was a deep periodontal pocket around the root, withsome inflammatory tissue inside the pocket, which looked likes the symptom ofperi-implantitis. In order to promote the long term effect of tissue engineeringtooth root, it is essential to research the combination between gingival and theroot.The natural combination between tooth and gingiva contains two parts, theone is epidermis, while the other is gingival lamina propria. Epidermis attach theenamel or cementum of dental cervix by hemidesmosome, and the gingivallamina propria, which mainly consists of collagenous fibre, can adhere to thetooth tightly by compact connective tissue to protect the clearance betweengingival and tooth from the bacterial attack. It can also inhibit the epidermismove to the root apex direction. So, the gingival lamina propria may plays a moreimportant role in the soft tissue closure on dental cervix. According to current result, the inflammation on the periodontal pocket may be the most importantfactor of interrupting gingival tissue to adhere to the root. If the inflammationwas removed, the combination between gingival and the root may be better.Nowadays, silver has become a kind of very important antimicrobial in dentalcare, because of its wide antimicrobial spectrum, long-acting antibiotic activityand low drug resistance. Furthermore, the toxicity of silver is selective, it canresist the bacterial specially, while the cell is relatively safe.So, the aim of this research is to explore an antibacterial strategy of theHA/TCP scaffold which is on the gingiva-crossing part of the tooth root. Basedon the pre-research by Sonoyama, our research work can be devided into threepart,(1) The biological behaviour of GFs and DPSCs when they are cultured onthe HA/TCP.(2) The preparation of Ag+-HA/TCP and the research of itsantibacterial activity.(3) How the Ag+-HA/TCP affect the biological behaviour ofGFs and DPSCs. The results is reported as follows.1. HA/TCP is a kind of innoxious material. Both SEM andimmunofluorescence shows that the GFs and DPSCs which cultured on theHA/TCP extends well, and the cytoplasm is full.2. Irradiate by UV-light after marinated in AgNO3is a new way ofpreparing Ag+-HA/TCP. The content of Ag+in Ag+–HA/TCP can be adjusted bychanging the viscosity of AgNO3。Ag+releases abruptly in the beginning24h,and goes slowly after24h, finally it tended towards stability. There is a positivecorrelation between the released Ag+and the viscosity of AgNO3in the first24h.3. Ag+–HA/TCP can inhibit the growth of bacterial.0.5mol/L group showeda weaker antibacterial activity than the other3groups (1mol/L group,1.5mol/Lgroup and2mol/L group), but there is no remarkable difference between thelatter3groups. It is indicated that there maybe also a positive correlation between the antibacterial activity and the viscosity of AgNO3, but the minimalantibacterial viscosity still needs to be researched.4. Use MTT method to investigate the safety of Ag+–HA/TCP. The RGR ofthe4groups were83.22%，51.01%，38.67%and19.84%. It means that the0.5mol/L group has a little cytotoxicity and is qualified for the biologicalexperiment, while the other3groups are not fit for the clinical use.5. According to the immunofluorescence, the GFs cultured on the0.5mol/Lgroup grows much better than the other3groups, there is only a little cellsdissolved, while most cells cultured on the other3groups died. Similar situationoccurs in the DPSCs. So we conclude that0.5mol/L group has a goodbiocompatibility with both GFs and DPSCs.