Study On The Influence Of Dentine Bonding Agents Towards Pulp's Biologic Properties

With the improvement of dental bonding materials, from inorganic materials to organic macromolecule materials, they are used to bond from enamel to dentine and even soft tissues. During the past decades, varied dental bonding systems have been brought out, which have changed the concept of dental conservative restoration greatly and made unimaginable progress in clinical therapy. In prosthodontics, dentine bonding agents are mainly used to adhere veeners, crowns and fixed bridges,to repair segmental defect of teeth and broken teeth and to desensitize dentin hypersensitivity. Nowadays, "total-etch", "wet-bonding " and "self-etching" products are commonly used in clinic. Though "total-etch" products developed from this concept have greatly increased dentin bond strength, however, their unpredictable postoperative tooth sensitivity still exist when restorations are very close to pulp tissues. Because of their weaker acidic composition, self-etching bonding adhesives only dissolve smear layers instead of removing them. The remaining smear layers participate in the formation of hybrid layers, which can seal dentinal tubule well, thus decrease the postoperative sensitivity. Self-etching adhesives are key direction of dentin bonding systems due to convenient clinical application and low postoperative sensitivity. However, the self-etching bondingagents in domestic dental materials market are now full of foreign products, whose prices are so high that few clinicians in China use them. Fortunately, the research and development of dental bonding materials have made great progress recently and some new products made in China come out one after another. Recently a new self-etching bonding agent named as U-Bond was developed by the department of dental materials of stomatological college of FMMU, and makes up the deficiency in this area in China.In general, before use in clinic, the biocompatibility of the material should be assessed by a three-step approach. The first step is to screen the candidate material using a series of cytotoxicity assays in vitro. Second, if the material tested is not a cytotoxic one in vitro, it can be implanted subcutaneously and the local tissue reaction evaluated. Finally, the effects of the material on target tissue cells must be evaluated in animals or human beings in vivo. The following research is aimed to evaluate the biologic properties of a new dentin bonding agent (UB) compared with two commercial products(AP and PB) by observing the pH change on their surfaces before and after light-curing and evaluating the influence to standard cells in vitro and direct or indirect effects of them toward animal pulp tissues in vivo. All the results are provided for their rational use in clinic.Here are the main results and conclusions:First, UB and AP showed higher acidity then PB before light-cured, both of presenting pH values below 1 contrasting to PB's pH value of 2.34. After light-curing the elutes from the three adhesives still had low pH values. With the lapse of time after light-curing, the pH values of these elutes decreased gradually especially the following two hours after light-curing. After the two hours their pH values had almost no changes. It was indicated that the three dentin bonding agents still had low acidity even after light-curing and acidity permeability might took place after adhesives were cured in dentin layer which was likely to lead toshort-term acidity irritation towards pulp tissues.Second, MTT assay showed that cytotoxicity of the three dentin bonding agents were 1 grade after light-curing. PB was more toxic than UB and AP (p<0.05 ) ,while the difference between UB and AP was not significant (p>0.05) . Though MTT assay presented quantitative and precise results, its simulation to in vivo situation was limited. The results only demonstrated their slight cytotoxicity after light-curing and couldn't explain their cytotoxicity towards pulp tissues when they were used in vivo. The following studies should evaluate the amount of their ingredients after their ingredients' penetrating through dentine barrier and cooperation and antagonistic effect among these ingredients. This would contribute to comparing the cytotoxicity of varied dentin bonding agents comprehensively.Third, in agar overlay test, parts of decolored zones and some dissolved cells were observed under all test dentine discs and cytotoxicity of the three dentin bonding agents were 1 grade. Agar overlay test was more similar to clinical situation and dentine discs protected cultured cell to some extent from lesion caused by toxic ingredients coming from adhesives. However, it was not clear how many toxic ingredients diffused through dentine discs to target cells. In vivo pulp tissue could reduce toxicity of adhesives due to taking away or diluting toxic ingredients reached in pulp tissues. In a word, further study on the influence of dentin bonding agents towards pulp tissue should be taken.Fourth, the results of direct pulp capping of two self-etching adhesives in dogs teeth indicated that UB, AP and Dycal could cause mild to moderate inflammatory reaction in short observation period(7 days) and the difference among them was not significant (p>0.05) . In long-term observation, most pulp cavities of adhesive groups showed displaced resin particles and persistent chronic inflammatory reaction without or only few reparative dentin formation. No statistical difference was observed between two adhesive groups (p>0.05) . Pulp inflammatory reaction...