Development And Relevant Performance Of Provisional Crown And Bridge Composite Resin In Dentistry

Composite provisional restorative materials have got rapid development in recent years. Due to their remarkable performance in many aspects, these kind of materials have been widely applied for many therapeutic fields in dentistry. However, the researches of provisional restorative materials are relatively laggard in our country. And till now, there are no domestic-made composite resins used for provisional restoration. Despite good performace, these materials depend on import completely with high price which increase the cost of therapy and economic burden of patient.So the major objective of the study is to develop a provisional crown and bridge composite resin with better performance compared to the same kind of imported commercial products. Firstly, we systematically evaluated the effect of resin matrix, catalyst system and filler system on the relevant properties of provisional composite resin. From these results, we got an acceptable prescription of composite resin. And then we performed a series of biological safety experiments and some comparative studies on the properties closing the clinical situation. At last selected clinical trials were performed to see how its therapeutic effect is.The study can be divided into 4 main parts as below:PartⅠDevelopment of provisional crown and bridge composite resin. This part consists of 5 experiments: In Exp.1, four kinds of dental monomers including UDMA,Bis-EMA,Bis-GMA and TEGDMA were mixed in different proportions. After adding chemical curing agent and hybrid fillers, standard specimens were fabricated. The flexural strength, elastic modulus, diametral tensile strength and monomer conversion were tested to investigate the optimal ratio of resin matrix. In Exp. 2, different ratio of initiator, accelerator and inhibitor were added to the optimal ratio team and standard specimens were fabricated. The flexural strength, monomer conversion, gel time and set time of experimental composites were tested to detemine chemical curing system. A kind of chain transfer agent was then added into the experimental composite in order to control the polymerization exotherm. In Exp.3, the barium glass of hybrid filler was treated with different content of KH-570. The barium glass before and after modification were characterized by virtue of several analysis means. In Exp.4, the nano-sized silica combining the modified barium glass with various content of silane coupling agent were added into resin matrix, following that the effect of different filler contents with different silane concentrations on some properties of experimental composite were evaluated. In Exp.5, lots of preliminary experiments were performed to determine the basic formula for provisonal crown and bridge composite resin based on the early experimental results. After synthesizing, we evaluated the relevant properties compared with imported commercial products. The results are showed as follows:1.Varying the relative amounts of UDMA,Bis-EMA,Bis-GMA and TEGDMA had a significant effect on the mechanical properties of the experimental composite. Combined with literatures and clinical manipulation, we determined the mass fraction of UDMA,Bis-EMA,Bis-GMA and TEGDMA was 0.55, 0.30, 0.05, 0.10, respectively when the flexural strength was 98.02 MPa, the elastic modulus was 3.58GPa, the diametral tensile strength was 35.72 MPa and the monomer conversion was 75.3%, respectively.2.BPO/DHET/BHT-chemical curing-initiating system had significant influence on flexural strength, monomer conversion, gel time and set time of experimental composite. When the mass proportion of BPO, DHET and BHT was 1%, 1% and 0.04%, respectively, the experimental composite had appropriate gel time and set time, with the optimal flexural strength (98.7MPa) and monomer conversion (76.6%). When 0.1% DPMP was added, the maximum polymerization temperature was below the critical temperature 38℃. At the mean time, the gel time and set time were still within the normal range of ISO standard.3. The surface performance of barium glass modified with silane coupling reagent (KH-570) had changed from hydrophilic to hydrophobic, the KH-570 was bound on the surface of barium glass powder, a firm chemical bonding of KH-570 to barium glass film and a layer of organic coating layer formed. The maximum mass fraction of KH-570 coated on the surface of barium glass measured was only about 2.86%.4. The concentration of silane coupling agent, the content of hybrid filler, and their interaction had significant influence on physical and mechanical properties of experimental composite. When the content of 3wt% silane-treated barium glass filler reached 40wt%, simultaneously added 3wt% nano-sized silic into resin matrix, the experimental composite obtained optimal mechanical properties and suitable viscosity.5. According to early experimental results, we established the basic prescription for provisonal crown and bridge composite resin. The new composite resin, Fast-Temp exhibited good physico-mechanical properties, appropriate gel time and set time, with low temperature rise during polymerization.PartⅡEvaluations on the biological safety of provisional crown and bridge composite resin.Biological tests were carried out to evaluate the biological safety of new provisional crown and bridge composite resin according to standards YY/T 0268-2001. The results of biological tests was as below:In the cytotoxicity test, the result showed that the cytotoxicity index of Fast-Temp was in gradeⅠ, which indicated that the new provisional composite resin has no cytotoxicity. In the acute systemic toxicity test, no significant difference was showed between experimental group and control group in utilization rate of food and increase rate of body mass. Histological observation showed there was no abnormal condition for the histopathology of the important viscera in experimental material group. It means that Fast-Temp has no acute systemic toxicity. In oral mucosa stimulation test, the mucous membrane contacting to the tested material did not exhibit any abnormality and pathological reaction, which indicates that Fast-Temp has no oral mucosa stimulation. In pulp and dentine applying test, slight inflammation reaction was observed in experimental material group. And after a long time, the dental plups of experimetal material group were able to return to normal the same as control group. It can be concluded that the Fast-Temp has no pulp and dentine irritation. In a word, the new composite, Fast-Temp has good biocompatibility. PartⅢComparative study on the relevant properties of provisional crown and bridge composite resin.In this part, three properties of provisional composite resin such as intrapulpal temperature rise, color stability, marginal accuracy and composite repair strength which have tight relation with clinic were studied. The results were as below: 1. Like other 3 commercial bis-acryl composite resins, Fast-Temp had low maximum intrapulpal temperature rise during polymerization process, which made them preferable for fabrication of provisional restoration by a direct method. 2. The bis-acryl composite resins including Fast-Temp had good marginal accuracy superior to PMMA resins. 3. As to provisional composite resins, keeping an oxygen-inhibited layer was helpful to increase composite repair strength when resin-based bonding agents were applied between two composite layers. However, if resin-based bonding agents were not used, the presence of oxygen-inhibited layer could compromise the composite-composite bond.PartⅣClinical study on the new provisional crown and bridge composite resinFast-Temp was used to fabricate provisonal restorations on 42 patients. After finishing fabrication, the provisional crown and bridge restorations were evaluated conformed to the Califomia Dental Association's (CDA) criteria and questionnaire. The results showed that Fast-Temp had satisfying clinical effect. The provisional restorations had good surface smoothness, marginal accuracy, anatomic form, gingival health and easy to operate. It's a highly acceptable material which can be used widely in dental clinic.