Effect of shade and light curing mode on the degree of conversion of silorane-based and methacrylate-based resin composites

Statement of Problem: The degree of conversion depends on the material composition, light source properties, distance from light source, light intensity, curing time, and other factors such as shade and translucency

Objectives: In the present study, we evaluated the effects of different light- curing modes and shades of methacrylate and silorane-based resin composites on the degree of conversion of resin composites [DC]

Materials and Methods: The methacrylate-based [Filtek Z250, 3M, ESPE] and low-shrinkage silorane-based [Filtek P90, 3M, ESPE] resin composites were used in three groups as follows: group 1-Filtek Z250 [shade A3], group 2-Filtek Z250 [shade B2], and group 3-Filtek P90 [shade A3]. We used a light-emitting diode [LED] curing unit for photopolymerization. 10 samples were prepared in each group to evaluate the degree of conversion; 5 samples were cured using soft-start curing mode, and the other 5 were cured using standard curing mode. The DC of the resin composites was measured using Fourier Transform Infrared Spectroscopy [FTIR]. The data were analyzed using Kruskal Wallis and one- way ANOVA statistical tests

Results: The degree of conversion of silorane-based resin composite was 70 - 75.8% and that of methacrylate-based resin composites was 60.2 - 68.2% [p = 0.009]. The degree of conversion of the composite with brighter colour [B2] was statistically more than the darker composite [A3]. Higher degree of conversion was achieved applying the standard curing mode

Conclusions: The results of the study showed that the colour and type of the resin composite and also the curing mode influence the degree of conversion of resin composites

Evaluation of solubility of modelling plastic in contiguity of ethanol and plasticizer

In patients with complete denture, some clinicians have used modelling plastic impression compound [MPIC] along tissue conditioner [TC] materials simultaneously. Little information is available on the composition of these materials and the interaction between them. The purpose of this study was to evaluate the influence of two components of MPIC on the structure and chemical composition of TC. In this experimental study, MPIC specimens were provided in 25x2 mm discs. Specimens were randomly divided into three groups and were immersed in ethanol 70%, plasticizer [dibutyl phthalate] and a mixture of them [ethanol 70% and dibutyl phthalate]. All of the discs were weighed with a digital balance before and 2, 4, 6 and 24 hours after immersion. Values were analyzed by non parametric Kruskal-Wallis [alpha= 0.05] and SPSS 16 for Windows [SPSS Inc., Chicago, IL] was used for statistical analysis. Statistical analysis indicated significant differences among all groups [p>.05]. Dibutyl phthalate [DBP] had high impact on the solubility of MP, while the mixture of dibutyl phthalate [DBP] and ethanol demonstrated the highest impact

[ effect of nanoporous fillers and different curing modes on the polymerization shrinkage of an experimental composite]

Statement of Problem: Polymerization shrinkage is one of the major problems of the current dental composites and it can cause marginal gap and post-operative sensitivity

Purpose: The purpose of this study was to investigate the effect of nanoporous fillers on the polymerization shrinkage and degree of conversion of an experimental dental composite in three different curing modes and also comparing its results with another experimental composite containing conventional fillers

Methods and Material: In this study, the experimental composite was prepared by mixing the silane treated fillers with monomers. The monomers consisted of 70% Bis-GMA and 30% TEG DMA by weight. The experimental composite was divided into two groups according to their filler type, i.e. conventional micro-hybrid and nanoporous. In order to make nanoporous fillers, the fillers were sintered in 1300[degree sign]c and grinded Camphorquinon and DMA EMA were used as initiator-accelerator systems. Polymerization shrinkage was measured using bonded disc method in three curing modes [High Intensity, Ramp, Standard]. The degree of convention was measured using FTIR spectroscopy

Result: The results showed that the nanoporous fillers have a positive effect on the reduction of polymerization shrinkage strain. No significant difference was found in polymerization shrinkage of the three curing modes. Neither the type of the fillers nor the mode of cure had an effect on the degree of conversion

Conclusion: Lower polymerization shrinkage strain can be achieved by using nanoporous fillers. The mode of cure does not affect the polymerization shrinkage

[ effect of incorporation of different concentrations of ethanol as a solvent on the microshear bond strength of a solvent-free dentin bonding agent]

Different studies have demonstrated that resin penetration into collagen fibers is influenced and promoted by the presence of a solvent in the bonding agents, but in order to create a reliable bond, it should be removed before curing. This study investigates the effect of adding ethanol as a solvent on the microshear bond strength of a solvent-free dentin bonding agent. After removing the occlusal enamel of 20 caries-free human third molars, midcoronal dentin slices, each about 2 mm thick were prepared then polished by slicion paper. The superficial dentin surfaces were randomly distributed into four groups and treated with James-2 containing different concentrations of ethanol [0, 5, 10, and 20 wt%] in two layers and then light-cured. The micro shear bond strength [micro SBS] was testes using a universal testing machine. The data were finally subjected to one-way ANOVA followed by Tukey's post-hoc test. James-2 containing 5 wt% ethanol provided the highest micro-shear bond strength [32.1 +/- 6.69 MPa]. There were no statistical differences in micro SBS values between other groups [25 +/- 5.8 MPa, 24.8 +/- 4.93 MPa and 21.8 +/- 4.51 MPa, respectively]. Adding ethanol as a solvent resulted in increased micro shear bond strength to dentin. At higher solvent concentrations no significant change was observed indicating that the solvents may not have been completely removed leading to poor polymerization and porosity reflected as lower bond strengths

[A comparision of success rate between Ext. D.C.R and end D.C.R]

Currently, many patients are referred to our department because of continuous or inflammatory tearing; and the diagnosis is Dacriocystitis. Dacriocystitis is an infection of the lachrymal sac and is treated with External Dacriocystorhinostomy [Ext. D.C.R], an operative approach that has a failure rate ranging from 3% to 15%. Most of the failures are related to the incomplete inspection of the intranasal cavity during the operation. Endoscopic D.C.R. is another approach that has two advantages 1] avoid incision and prevent scar formation. 2] According to the perfect inspection of the intranasal cavity, the success rate is expected to increase. The aim of this study is to compare the success rates of End. D.C.R and Ext. D.C.R. This study tries to complete the previous studies that introduced End. D.C.R as a new approach to surgeons. In the previous studies, End. D.C.R was performed by using of YAG Laser that is expensive and inaccessible; whereas, we performed the procedure by using of suction cautery and punch forceps. For collecting the data, we designed a check list that was filled by one physician. Then the data was analyzed. Each of the groups included 43 patients. According to the statistical analysis, overall 28 males and 58 females underwent one of the operational approaches. The difference between the two groups in the duration of the disease and the patient complaints were not statistically significant On the other hand, the difference between the two groups in the duration of surgical approaches, presentation of tearing, regurgitation and bleeding one week after surgery were not statistically significant. But the presentation of the pain in End. D.C.R was less than in Ext. D.C.R. Three months after surgery, the difference between the two groups in presentation of tearing and open ducts were not statistically significant, but the regurgitation in End D.C.R. was less than Ext. D.C.R. Patient satisfaction of elimination of symptoms is not different, but satisfaction of scar in End. D. C.R is significantly less than Ext.D.C.R. The endoscopic approach appears to have two major benefits against the Ext. D.C.R; first, it avoids an external incision; and second, it allows a perfect view of intranasal cavity at the time of surgery so that a common cause of D.C.R. failure could be avoided. With this approach YAG laser is replaced with suction cautery and punch forceps