Vol 15, No 6 (2018)

Original Article

  • XML | PDF | downloads: 531 | views: 413 | pages: 339-350

    Objectives: Photopolymerization immediately sets dual-cure cements and prevents the continuation of chemical polymerization. Delayed light-curing allows the chemical process to continue up to the point before starting irradiation; however, there is a controversy in this respect. The present study evaluates the effect of delayed light-curing through a zirconia disc on the microhardness and fracture toughness (KIC) of two types of dual-cure cement.

    Materials and Methods: Samples measuring 25×5×3 mm3 were prepared for fracture toughness test, and discs measuring 5 mm in diameter and 3 mm in thickness were prepared for microhardness test using Bifix and BisCem cements. Light-curing protocols were as follows: immediate light-curing (group A), a 2-minute delay (group B), a 5-minute delay (group C), direct irradiation (group D), and no irradiation (group E). In groups A to C, light-curing was carried out through a zirconia disc. Data were analyzed by two-way and one-way analysis of variance (ANOVA), post-hoc Tukey's test, and Kruskal-Wallis test at 95% confidence interval.

    Results: There was a significant difference in the microhardness of the cements (P=0.00). Delayed light-curing had no effect on microhardness (P=0.080). The microhardness of BisCem in group E was significantly lower than that in group D (P=0.015). The fracture toughness of Bifix in groups B and C was significantly different than that in group E and BisCem groups.

    Conclusions: Under the limitations of our study, delayed light-curing had different effects on microhardness and fracture toughness. Differences in light-curing protocols resulted in different effects based on the cement type. Light-curing is recommended to achieve optimal mechanical properties.


  • XML | PDF | downloads: 505 | views: 461 | pages: 351-357

    Objectives: In clinical conditions, orthodontic brackets are exposed to periodic stresses mainly induced by mastication and intraoral forces. The objective of the present study was to evaluate the effects of cyclic loading to simulate masticatory forces on shear bond strength (SBS) of metal brackets bonded to teeth using self-etch and total-etch bonding systems.
    Materials and Methods: Eighty-four caries- and crack-free bovine mandibular incisors were selected and randomly assigned to two groups based on the type of bonding system. After bonding, all samples were thermocycled (500 cycles) followed by cyclic loading of the half of the specimens in each group by applying 40 N load with 2 Hz frequency for 10,000 cycles. The SBS was measured using a universal testing machine. The adhesive remnant index (ARI) score was calculated subsequently. Data were analyzed using Kolmogorov-Smirnov test, two-way ANOVA and Mann-Whitney test.
    Results: The SBS was 10.09±3.78 MPa and 14.44±6.06 MPa for self-etch and total-etch bonding systems in cyclic loading group, respectively. The SBS was 9.43±5.3 MPa and 11.31±5.42 MPa in self-etch and total-etch groups without cyclic loading, respectively. Cyclic loading did not cause any significant difference in SBS (P>0.05). The ARI scores of the groups were significantly different (P<0.05).
    Conclusions: The present results demonstrated that low masticatory forces at 10,000 cycles did not have a significant impact on bracket-adhesive SBS; however, they significantly changed the ARI score. Even though the total-etch bonding system yielded higher SBS than the self-etch system, the performance of both was clinically acceptable.

  • XML | PDF | downloads: 497 | views: 428 | pages: 358-364

    Objectives: The aim was to evaluate and compare pretreatment serum C-reactive protein (CRP) levels in patients with oral premalignancies and malignancies with that in healthy controls.
    Materials and Methods: The study sample consisted of 90 patients of both genders. The subjects were divided into three groups. Group I comprised 30 healthy controls, while group II included 30 patients with potential oral malignancies including leukoplakia, oral submucous fibrosis (OSMF), and oral lichen planus (OLP), and group III included 30 squamous cell carcinoma (SCC) patients confirmed by histopathological examination. All samples were subjected to CRP analysis. Serum CRP levels were quantitatively determined using the automated immunoturbidimetric method.
    Results: In group I, CRP levels were ranging from 0.1 to 18.3 mg/l with the mean ± standard deviation (SD) CRP level of 3.88±4.50 mg/l. In group II, CRP levels were ranging from 0.8 to 53.9 mg/l with the mean ± SD CRP level of 5.59±9.86 mg/l. In group III, CRP levels were ranging from 3.3 to 96 mg/l with the mean ± SD CRP level of 31.72±31.01 mg/l.
    Conclusions: According to the results, prediagnostic concentrations of CRP are associated with subsequent development of oral cancer and suggest that plasma CRP level is a potential marker of increased risk of cancer.

  • XML | PDF | downloads: 565 | views: 688 | pages: 365-374

    Objectives: The polymerization shrinkage of methacrylate-based composites is among the most important causes of failure of composite restorations. The manufacturers claim that bulk-fill composites have a lower polymerization shrinkage than conventional composites. This study aimed to assess the polymerization shrinkage of five bulk-fill composites in comparison with a conventional composite.
    Materials and Methods: In this in-vitro experimental study, composite discs (n=30) were fabricated using everX Posterior (EXP), Filtek Bulk-Fill Posterior (FBP), SonicFill 2 (SF2), Tetric N-Ceram Bulk-Fill (TNB), X-tra fil (XF), and Filtek Z250 conventional composite at the center of a metal ring bonded to a microscope slide and were covered with a coverslip. This assembly was transferred to a linear variable differential transformer (LVDT). Light-curing (1200 mW/cm2) was performed from underneath the slide for 30 seconds. The deflecting disc method and LVDT were used to assess the dimensional changes of the samples (indicative of polymerization shrinkage) at 1, 30, 60, and 1800 seconds following the onset of light irradiation. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s test.
    Results: The groups were significantly different regarding polymerization shrinkage (P<0.002). The polymerization shrinkage of the tested composites following the onset of light irradiation ranged from 0.19 to 3.03. EXP showed a significantly higher polymerization shrinkage than other composites at 30, 60, and 1800 seconds after light irradiation, while XF showed the lowest polymerization shrinkage at the aforementioned time points.
    Conclusions: The tested bulk-fill composites had a polymerization shrinkage similar to that of the conventional composite. 

  • XML | PDF | downloads: 494 | views: 339 | pages: 375-381

    Objective: This study assessed the effect of shelf life of a ceramic primer containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) monomer on microshear bond strength of zirconia ceramic to composite resin.
    Materials and Methods: Sixty-four sintered zirconia samples (1.5×5×7 mm) were pretreated with Clearfil Ceramic Primer (CCP) at baseline and after one, two and six months of storage at 6°C. Composite cylinders were fabricated using Tygon tubes (1 mm height, 0.7 mm diameter) and placed on treated zirconia blocks, light-cured and subjected to microshear bond strength test. Mode of failure was determined under a stereomicroscope. Fourier-transform infrared spectroscopy (FTIR) was performed at each storage time point. Data were analyzed using one-way ANOVA and Tukey’s test. 
    Results:  Significant differences were noted in microshear bond strength after six months of storage compared to baseline (P<0.05). Significant differences were noted in FTIR spectra at the four time points (P<0.05).
    Conclusions: The effectiveness of one-component ceramic primer in bonding to zirconia was significantly affected by the storage of this material in a time-dependent manner. Visible new peaks and changes in FTIR spectra over time indicated alterations in the composition of ceramic primer affecting its shelf life.  

  • XML | PDF | downloads: 483 | views: 395 | pages: 382-392

    Objectives: The aim of this study was to determine the effect of MTAD on the expression of virulence factors of Enterococcus faecalis (E.faecalis) considering the role of Gutta-percha/AH26 or Resilon/RealSeal SE as root canal obturating materials.
    Materials and Methods: One-hundred and forty-four single-rooted human teeth were instrumented to a standardized apical size. Root canals were infected by E.faecalis (ATCC 29212). Ninety teeth were irrigated with MTAD and randomly divided into three groups. In two groups, root canals were obturated by either Gutta-percha/AH26 or Resilon/RealSeal SE. Root canals were kept unobturated in the third group. The remaining 54 teeth received no final irrigation. All groups were then subdivided into three timepoint subgroups in which dentin powder was obtained from each sample to determine the expression of specific virulence factors of E.faecalis (efa, esp, gel, fsr) using real-time reverse transcription polymerase chain reaction (RT-PCR). Statistical analysis was performed by one-way analysis of variance (ANOVA) and Tukey’s post-hoc test. The statistical power was set at P-value ≤0.05.
    Results: MTAD was effective against the expression of most of the tested virulence factors, and Gutta-percha/AH26 increased the antibacterial efficacy of MTAD.
    Conclusions: MTAD could inhibit the expression of some known virulence factors of E.faecalis at the majority of tested timepoints. This may partly explain some of the mechanisms of antimicrobial efficacy of MTAD against this resistant microorganism which is known as one of the main causes of failure of root canal treatment.

  • XML | PDF | downloads: 497 | views: 470 | pages: 332-338

    Objectives: Temporomandibular joint (TMJ) disorders, known as TMDs, are significant public health problems and may result in pain and disability. In order to determine the prevalence of clinical/subjective TMD in rheumatoid arthritis (RA), we used the research diagnostic criteria (RDC)/TMD axes. We assessed the anti-cyclic citrullinated protein (anti-CCP)-related TMD in RA for the first time.    
    Materials and Methods: Fifty-two RA patients were compared to 47 healthy controls with regard to complete blood count (CBC), serology, acute phase reactants (APR), and TMJ dysfunction. 
    Results: The anti-CCP antibody showed a significant correlation with the development of clinical TMD (P=0.001, 95% confidence interval (CI)=12.4%-35.6%). A prevalence of 50% was calculated through the RDC/TMD for such disorders. In RA patients, statistically significant differences were observed between the groups with and without clinical TMD regarding psychological depression and physical symptoms.
    Conclusions: According to the results, a significant correlation was found between the anti-CCP antibody and TMD. Therefore, when this antibody is detected in the blood serum, the treatment must be initiated. The RDC/TMD used in this study assessed the prevalence of TMJ dysfunction in conformity with RA-associated TMJ findings previously obtained through other conventional methods.  


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