Aim: One of the problems which repaired complete denture is refracturing at the same repaired point. To solve this problem, different methods have been introduced. The following study will show the success rate of these methods.Method & Material: In this study has been used 40 test specimens (15.3.70 mm) in 4 groups and all of them made of heat cure acrylic material. Three of the four groups have been cut and beveled at the center. The first group was repaired with selfcure Acrylic material. In second group, monomer has been applied the edges for 180 seconds, and in third group chloroform has been applied for 5 seconds to achieve etching and then repaired. All 3 groups have been compared with the fourth group for transverse strength on ANOVA and t- test.Results: The result of this study determined the transverse strength in second and third groups, to be increased than the first group. However a significant difference was found in third group (P<0.05) and the transverse strength was about 97% of the fourth group.Conclusion: This study showed that, using of chloroform for 5 seconds were caused the most reinforcement in repaired acrylic resin than other methods.

Introduction: PMMA has been the most popular denture base material because of its advantages including good aesthetics, accurate fit, stability in the oral environment, easy laboratory and clinical manipulation and inexpensive equipments since the 1930’s. However, its fracture resistance is not satisfactory. Aim: The aim of this study is to improve the fracture resistance of denture bases made of PMMA by assessing the effect of resin type, packing and processing variables on biaxial flexural strength (BFS).Materials & methods: 930 discs, 12 mm diameter and 2 mm thick were prepared with the following variables: a. Veined (V) and Plain (P) PMMA. b. 5 different powder/liquid ratios by volume (1.5:1, 2:1, 2.5:1, 3:1, 3.5:1). c. Conventional (C) and Injection packing methods (I). d. Dry heat (D) Water bath (W); and e. different curing times. The discs were trimmed and stored in 37°C tap water for 50 hours before carrying out BFS test, according to BS EN ISO 1567: 2001. BFS test was carried out using a tensile-testing machine (Lloyd LRX, Lloyd instruments Ltd) (Figure.1 b), with a x-head speed of 1mm/min. ONE-WAY ANOVA analysis and TUKEY’S comparison were carried out (MINITAB). The temperature within the curing baths and inside of curing resin was evaluated by using a thermocouple. Results: BFS of Powder/liquid ratio of 1.5:1 is significantly lower than the other four ratios. Among the last four ratios, 2.5:1 was the strongest one although the difference was not significant. BFS of the plain type of PMMA is significantly higher than the veined type· BFS of conventionally packed PMMA discs was greater than the injectional packed ones and the difference is significant. Water bath cured resin showed a significant higher BFS compared with dry heat curing. · Changing the curing time in the dry heat bath from 7h @ 75º C and 2hrs @ 95º C to 5hrs @ 75º C and 3hrs @ 95º C and then 2hrs @ 95º C improves BFS of PMMA. In the water bath the trend is identical although the difference is not significant. Analysis of the temperature climb and hold within the curing bathes showed a consistent performance with the water bath irrespective the number of the flasks being cured. Meanwhile, the dry heat bath showed very inconsistent results.Conclusion: 1. Type of resin, packing procedure and processing variables can have major effect on BFS of PMMA. 2. Using plain resin, conventional packing, water bath curing with two hours at 95 ºC are recommended conditions.  

Introduction: Fractures of acrylic resin dentures are quite common. It is favorable to securely repair the denture to prevent re-fracture. The aim of this study was to evaluate the flexural strength of heatcured acrylic resin samples repaired with Iranian and foreign self-curing acrylic resins alone and impregnated with uni-directional fiberglass.Materials and Methods: In this experimental study 40 specimens with a dimension of 65x10x2.5 mm were fabricated from Meliodent heat-cured acrylic resin. Eight specimens were left intact as the control group. The other specimens were first fractured and then 8 specimens were repaired with selfcuring Acropars acrylic resin; 8 specimens were repaired with self-curing Acropars acrylic resin impregnated with fiberglass; 8 specimens were repaired with self-curing Meliodent acrylic resin and finally, 8 specimens were repaired with self-curing Meliodent acrylic resin impregnated with fiberglass. Then the flexural strengths of repaired and intact specimens were measured by DARTEC machine. The results were analyzed with one-way ANOVA, and Tukey and two-sided Dunett tests (a<0.05).Results: An increase in the flexural strengths was observed only in Meliodent groups repaired with self-curing acrylic resin without fiberglass and with fiberglass (p value<0.008), with no significant differences between other groups (p value>0.05).Conclusion: Based on the results of the present study, the use of Acropars and Meliodent selfcuring acrylic resin impregnated with fiberglass in repaired site increased the flexural strength only in self-curing Meliodent group.

Three dimensional printing (3D) is a process of fabricating 3D objects through depositing layers of materials (such as polymers) on previous layers. Currently is considered one of the most important research fields in academic and industrial research centers. Among the various approaches to 3D printing, photopolymerization is of great interest due to the wide range of monomers/oligomers prone to photopolymerization reactions (photopolymers). Photoinitiators and monomers/oligomers are two important components of resins applied for 3D process, which affect not only the possibility of resin printing, but also the functional properties of the part such as mechanical strength, dimensional accuracy, transparency, modulus and others. In this article, the most important group of photopolymers used in the 3D printing process is reviewed from the point of view of reaction chemistry and their advantages and disadvantages. It is obvious that the design and manufacture of photocurable resins requires knowledge about the types of resins available and the challenges associated with them. Therefore, this article can be a good source for active researchers in this field.

The paper reports on the synthesis of water-based alkyd resins and preparation of corresponding water-based paints. Several routes were adapted in the synthesis of alkyd resins. In the first route, non-modified alkyd resins were synthesized at first and then a mixture of the vinyl monomers was grafted on the fatty acid moiety of the alkyd resin via peroxide initiated polyaddition polymerization. In the second route, the vinyl monomers were grafted on fatty acid via peroxide initiated polyaddition polymerization and in the next step the grafted fatty acid was incorporated in the alkyd resin structure through polycondensation polymerization. In the third route, two different methods were adapted. In the first method, the grafted alkyd resins obtained from the first and second routes were reacted with a polyethylene glycol resin (PEG). In the second method, a non-grafted alkyd resin was reacted with PEG and then a mixture of monomers was grafted on fatty acid moiety of the prepared alkyd. Drying time of the films of the prepared resins and paints is similar to that of the solvent-based alkyd resins. The aqueous dispersions of these resins suspend high enough finely-divided titanium dioxide pigment. The gloss of the dried paint film is also high enough. Use of maleic anhydride as dispersing agent is the novelty of this work which is reported for the first time.

Introduction: Low resistance of composite resins to abrasion is a primary concern in the application of these materials for posterior restorations which are prone to high occlusal loads.This study compared the wear resistance of three types of composites.Methods: In this laboratory experiment, five specimens of each of the three types of composites (z250, Heliomolar, Opallis) were prepared separately in brass molds. Composites were placed in 1-mm layers and were cured for 40 seconds. Using an abrasive device, Pedeb 1, with a chromecobalt abrasor, the specimens were abraded under a 20-MPa force, after 5000, 20000, 40000, 80000, 120000 abrasive rotations. Before and after all abrasion cycles, the specimens were weighed with an electronic balance with a precision of 10-4 g. The collected data were analyzed using paired samples statistics t-test and ANOVA analysis.Results: All the specimens showed a reduction pattern from the initial weights to weights after 120000 abrasive rotations. With more abrasive rotations, greater weight reduction occurs and this is of statistical significance. ANOVA analysis showed no significant difference between the three types of composites; yet, the z250 and Heliomolar groups were associated with the least and the greatest amount of wear, respectively.Conclusions: In all specimens, significant weight reduction occurred after abrasion but there were no significant differences between the 3 types of composites.

Background and Aim: When bonding between two different dental materials is impossible due to structural dissimilarity, a third material can be used at the interface to achieve the desired bond. Silanes have been developed for this purpose and can improve bonding strength in dental restorations by preventing debonding at the interface region. The present study reviewed the relevant publications in order to determine the effect of silane on the bond strength of ceramic to resin restorations. Materials and Methods: Multiple internet search engines including Google, AltaVista, and the archives of related Journals were used in order to access information on the properties of silane.Conclusion: Application of silane increases the bonding strength between composite and resin by approximately 25%, regardless of different fabrication and testing methods. Etching with phosphoric acid and treatment with silane emerged as the two most significant factors in the improvement of the bonding strength of cements. However, using an appropriate coupling agent even without etching has also been shown to produce an acceptable bonding strength. Hydrolyzed silanes do not produce methanol and therefore cannot completely vaporize the water generated during chemical reactions. On the other hand, non-hydrolyzed silanes vaporize surface water by producing 3 methanol molecules and thus do not interfere with bonding of adhesive systems. Therefore the bonding strength of non-hydrolized silanes is greater than hydrolyzed silanes. In conclusion, the type of silane (hydrolyzed, non-hydrolyzed), the adhesive used and the technique of its application are considered to be three of the most important factors affecting bond strength.