Journal of Dental Biomaterial最新文献

Statement of problem: Fixed orthodontic appliances in the oral cavity make tooth cleaning procedures more complicated.

Objectives: This study aimed to compare the efficacy of computerized oral hygiene instruction with verbal technique among fixed orthodontic patients referred to the evening clinic of Orthodontics of Shiraz Dental School.

Materials and methods: A single-blind study was performed in Orthodontic Department of Shiraz, Islamic Republic of Iran, from January to May 2015 following the demonstrated exclusion and inclusion criteria. The sample size was considered 60 patients with 30 subjects in each group. Bleeding on probing and plaque indices and dental knowledge were assessed in the subjects to determine pre-intervention status. A questionnaire was designed for dental knowledge evaluation. The patients were randomly assigned into the computerized and verbal groups. Three weeks after the oral hygiene instruction, indices of bleeding on probing and plaque index and the dental knowledge were evaluated to investigate post-intervention outcome. The two groups were compared by chi-square and student t tests. The pre- and post-intervention scores in each group were compared using paired t-test.

Results: In the computerized group, the mean score for plaque index and bleeding on probing index was significantly decreased while dental health knowledge was significantly increased after oral hygiene instruction, in contrast to the verbal group.

Conclusions: Within the limitations of the current study, computerized oral hygiene instruction is proposed to be more effective in providing optimal oral health status compared to the conventional method in fixed orthodontic patients.

Statement of problem: Acrylic teeth of dentures are prone to discoloration due to frequent exposure to different colouring solutions in the oral environment. Thus, in order to maintain their aesthetic appearance, they must possess high colour stability while exposed to colorant solutions.

Objectives: To compare the colour stability of three different brands of acrylic teeth following immersion in coffee, tea and cola.

Materials and methods: This in vitro experimental study was conducted on 90 acrylic teeth in three groups (n = 30) of Ivoclar (Italy), PolyDent (Slovenia) and Apple (Iran). The teeth were immersed in coffee, cola and tea for one, three and six weeks (the teeth were not in contact with each other). Colour parameters were assessed before and after immersion using a spectrophotometer, and overall change in colour parameters was calculated. The overall colour change (ΔE) of the three groups at different time points was analyzed using one-way ANOVA. Pairwise comparisons were performed using Tukey's test.

Results: Coffee caused the greatest colour change in Apple acrylic teeth after six weeks (mean ΔE of 4.6 for coffee and 3.4 for tea and cola). Tea caused an almost equal colour change in the three groups. The greatest colour change in the Ivoclar teeth occurred in cola after six weeks (mean ΔE of 3.3, 3.4 and 2.8 for cola, tea and coffee, respectively). The greatest ΔE occurred at six weeks and was the highest in Apple, followed by PolyDent and then Ivoclar teeth in coffee (mean ΔE of 4.6, 3.4 and 3.3, respectively p < 0.001).

Conclusions: Despite the significant colour change in the three groups, ΔE in Ivoclar group was within the clinically acceptable range of ≤ 3.3. A slight colour change was expected regarding the Apple and PolyDent acrylic teeth clinically.

Statement of problem: Pit and fissure sealant therapy has been approved as an effective measure in the prevention of occlusal dental caries. Resin based materials are the most common materials used worldwide. A variety of resin based fissure sealants are produced and used. Most of them have been presented with ideal results in research environment. However, their effectiveness in the real life, especially in a mass application program such as Iran's oral health reform plan is not clear.

Objectives: To evaluate the longevity of different fissure sealant applied in Iran's oral health reform plan in Fars Province (south of Iran) after one year.

Materials and methods: Seven counties were selected. One hundred 6- to 8-year-old school children who had undergone fissure sealant therapy in spring 2015 were randomly selected from each county. Their first molars were examined to evaluate the status of the fissure sealants which were applied one year ago. Data on the type/brand of fissure sealant materials, type and experience of clinicians who applied them, existence of a chair-side assistant, and whether the children were caries-free at the time of fissure sealant application were collected from the existing reports.

Results: Data of 1974 teeth from 598 children were used for the final analysis. The effects of type/brand of the material was significant on the final results and remained significant (p < 0.001) after adjustments for the level of fluoride, urban/rural area, upper/lower jaw, type of clinician who applied the sealant, existence of a chair-side assistant, and child's gender, age, and being caries-free.

Conclusions: Many factors affect the success rate of a fissure sealant therapy program. The type/brand of the material remained significantly related to the success rate of the fissure sealant even after adjustments for other influencing factors. In this study, ClinproTM Sealant (3M/ESPE, USA) showed better longevity after one year of application.

Statement of problem: It is necessary to use irrigation solutions during cleaning and shaping of root canals to efficiently reduce the number of micro organisms. Sodium hypochlorite is used as an effective antibacterial endodontic irrigants. However, the extract of pennyroyal plant has also shown anti-bacterial characteristics comparable with antibacterial drugs.

Objectives: To compare the anti-bacterial effect of spearmint extract on Enterococcus faecalis bacteria with that of sodium hypochlorite 5.25%.

Materials and methods: In this experimental study, Muller Hinton medium, including 5% sheep blood was prepared. The two solutions used including sodium hypochlorite 5.25% and spearmint extracts were put adjacent to Enterococcus faecalis bacteria after preparing. Two groups, each containing 10 samples, with the total of 20 samples were used. The disks, including each solution were placed 2 cm apart on a plate containing Muller Hinton medium and the bacteria. The plate was subsequently incubated at 37°C for 48 hours. After incubation, the mean diameter of the halo around each disk, which represents the lack of bacterial growth, was measured and compared using a ruler. Penicillin disk was used for positive control and a sterile blank disk containing physiologic serum was utilized as the negative control. This process was repeated 10 times for each solution. Data were analyzed in SPSS 17 statistical software using t-test.

Results: The results showed that the mean diameter of halo in the spearmint extract group was zero and in the sodium hypochlorite group it was 23.7 ± 1.49 mm. There was a significant difference between the mean diameter of the lack of growth halo of the spearmint extract and that of hypochlorite sodium 5.25% on Enterococcus faecalis bacteria (p ≤ 0.001).

Conclusions: Considering the limitations of an experimental study, it seems that spearmint extract does not have any anti-bacterial effect against Enterococcus faecalis bacteria, in contrast to hypochlorite sodium 5.25%.

Statement of problem: Dental resin composites are becoming prevalent in restorative dentistry and have almost replaced amalgam nowadays. Consequently, their mechanical properties and durability are critical.

Objectives: The aim of this study was to produce Pyrex glass nano-particles by wet milling process and use them as reinforcement in dental resins for anterior restorations and then examination of fractographic properties of these composites.

Materials and methods: The glass nano-particles were achieved via wet milling. The surface of the particles was modified with 3-(Trimethoxysilyl) propyl methacrylate (γ-MPTMS) silane in order to improve their surface. Fourier transform infra-red (FTIR) analysis showed that the silane groups provided double bonds to the surface of the particles and prevented agglomeration. Then, the composite resins were made with different weight percentages of Pyrex glass. The mechanical properties of samples flexural test were evaluated. The required energy for fracture of the specimens was achieved via this test. The fracture surfaces of the samples were analyzed using a scanning electron microscope (SEM) in order to explain the mechanisms of fracture.

Results: The results and analysis showed that increasing the glass nano-particles mass fraction had a great effect on mechanical properties of the composites due to the mechanisms of crack propagation and crack deflection as well as preventing void formation. The effective energy dissipation mechanisms such as crack pinning and deflection, was observed in SEM micrographs.

Conclusions: Void formation in the low filler content composite is one of the mechanisms to decrease the energy required for fracture of these composites and eventually weaken them.

Statement of problem: The bond strength between restorative material and tooth structure is so important for conduction of durable restoration. Considering the recent attention to low shrinkage composite resins, evaluation of micro tensile bond strength of these materials would be valuable.

Objectives: To compare the microtensile bond strength of silorane composite resin (Filtek P90) with the conventional methacrylate composite (Filtek Z250) with and without applying acid etch before application of bonding system.

Materials and methods: In this experimental study, 24 intact primary canines were used. After the dentin was exposed, the teeth were randomly divided into four groups as follows: the first group (silorane bond system + composite Filtek P90); the second group (etch + silorane bond system + composite Filtek P90); the third group (Single bond + composite Filtek Z250); and the fourth group (etch + Single bond + composite Filtek Z250). The teeth were cut on the longitudinal axis and the interface between the composite and dentin were grinded buccolingually and mesiodistally. The samples were subjected to a microtensile force until breakage. The obtained values were recorded in MPa; data were analyzed using One-way ANOVA and Tamhane's T2 statistical tests.

Results: The average microtensile bond strength in all groups had a statistically significant difference with each other (all p < 0.05). The highest bond strength belonged to the second group (etch + silorane bond system + composite Filtek P90) and the lowest value was related to the third group (Single bond + composite Filtek Z250).

Conclusions: As the second group (etch + silorane bond system + composite Filtek P90) exhibited higher microtensile bond strength, it may prove that using composite Filtek P90 is preferable to be used in primary dentin in comparison with composite Filtek Z250, and using etch + silorane bond system is more advantageous than single bond system.

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.

Statement of problem: For many years, application of the composite restoration with a thickness less than 2 mm for achieving the minimum polymerization contraction and stress has been accepted as a principle. But through the recent development in dental material a group of resin based composites (RBCs) called Bulk Fill is introduced whose producers claim the possibility of achieving a good restoration in bulks with depths of 4 or even 5 mm.

Objectives: To evaluate the effect of irradiation times and bulk depths on the degree of cure (DC) of a bulk fill composite and compare it with the universal type.

Materials and methods: This study was conducted on two groups of dental RBCs including Tetric N Ceram Bulk Fill and Tetric N Ceram Universal. The composite samples were prepared in Teflon moulds with a diameter of 5 mm and height of 2, 4 and 6 mm. Then, half of the samples in each depth were cured from the upper side of the mould for 20s by LED light curing unit. The irradiation time for other specimens was 40s. After 24 hours of storage in distilled water, the microhardness of the top and bottom of the samples was measured using a Future Tech (Japan- Model FM 700) Vickers hardness testing machine. Data were analyzed statistically using the one and multi way ANOVAand Tukey's test (p = 0.050).

Results: The DC of Tetric N Ceram Bulk Fill in defined irradiation time and bulk depth was significantly more than the universal type (p < 0.001). Also, the DC of both composites studied was significantly (p < 0.001) reduced by increasing the bulk depths. Increasing the curing time from 20 to 40 seconds had a marginally significant effect (p ≤ 0.040) on the DC of both bulk fill and universal studied RBC samples.

Conclusions: The DC of the investigated bulk fill composite was better than the universal type in all the irradiation times and bulk depths. The studied universal and bulk fill RBCs had an appropriate DC at the 2 and 4 mm bulk depths respectively and using the recommended curing time of 40s can led to the slightly better value of DC in both composites.

Statement of problem: Shear bond strength (SBS) of home and office bleached enamel will be compromised by immediate application of composite restoration. Antioxidant agent may overcome this problem.

Objectives: This in vitro study assessed the effect of green tea extract on shear bond strength of resin composite to in-office and home-bleached enamel.

Materials and methods: In this experimental study, 40 extracted intact human incisors were embedded in cylindrical acrylic resin blocks (2.5 ×1.5 cm), with the coronal portion above the cemento enamel junction out of the block. Then, after bleaching labial enamel surfaces of 20 teeth with 15% carbamide peroxide 6 hours a day for 5 days, they were randomly divided into two groups: A1 and A2 (n = 10), depending upon whether or not they are treated with antioxidant. Labial enamel surfaces of the remaining 20 teeth were bleached with 38% hydrogen peroxide before being randomly divided into groups B1 and B2 (n = 10), again depending on whether or not the antioxidant was used in their treatment . The experimental groups (A2,B2) were treated with 5% solution of green tea extract before resin composite restoration was done by a cylindrical Teflon mould (5×2 mm). Shear bond strength of the specimens was tested under a universal testing machine (Zwick/Roell Z020). The SBS data were analyzed by using One-way ANOVA and Tukey HSD tests (p < 0.05).

Results: There were no statistically significant differences between shear bond strength of the control group (A1) and treated group (A2), but there were statistically significant differences between the groups B1 and B2 (p < 0.05).

Conclusions: Application of antioxidant did not increase the shear bond strength of home-bleached enamel to resin composite but its application increased the shear bond strength of in-office bleached enamel to resin composite.

Statement of problem: Hemostatic agents may affect the micro-leakage of different adhesive systems. Also, chlorhexidine has shown positive effects on micro-leakage. However, their interaction effect has not been reported yet.

Objectives: To evaluate the effect of contamination with a hemostatic agent on micro-leakage of total- and self-etching adhesive systems and the effect of chlorhexidine application after the removal of the hemostatic agent.

Materials and methods: Standardized Class V cavity was prepared on each of the sixty caries free premolars at the cemento-enamel junction, with the occlusal margin located in enamel and the gingival margin in dentin. Then, the specimens were randomly divided into 6 groups (n = 10) according to hemostatic agent (H) contamination, chlorhexidine (CHX) application, and the type of adhesive systems (Adper Single Bond and Clearfil SE Bond) used. After filling the cavities with resin composite, the root apices were sealed with utility wax. Furthermore, all the surfaces, except for the restorations and 1mm from the margins, were covered with two layers of nail varnish. The teeth were immersed in a 0.5% basic fuschin dye for 24 hours, rinsed, blot-dried and sectioned longitudinally through the center of the restorations bucco- lingualy. The sections were examined using a stereomicroscope and the extension of dye penetration was analyzed according to a non-parametric scale from 0 to 3. Statistical analysis was performed using Kruskal-Wallis test and Mann-Whitney U-test.

Results: While ASB group showed no micro-leakage in enamel, none of the groups showed complete elimination of micro-leakage from the dentin. Regarding micro-leakage at enamel, and dentin margins, there was no significant difference between groups 1 and 2, 1 and 3, and 2 and 3 (p > 0.05). A significantly lower micro-leakage at the enamel and dentin margins was observed in group 3, compared to group 6. No significant difference was observed between groups 4 and 5 in enamel (p = 0.35) and dentin (p = 0.34). Group 6 showed significantly higher micro-leakage, compared to group 4 and 5 (p < 0.05).

Conclusions: Hemostatic agent contamination had no significant effect on micro-leakage of total- and self-etching adhesive systems. Application of chlorhexidine after the removal of hemostatic agent increased micro-leakage in self-etching adhesives but did not affect when total-etching was used.