دکتر همایون علاقه مند

This study assessed the effect of different concentrations of 4‑methacryloyloxyethy trimellitate anhydride (4‑META) added to silane on microtensile bond strength (μTBS) of light‑cure and dual‑cure resin cement to hybrid and zirconia‑reinforced lithium silicate ceramics.

This in vitro, experimental study was conducted on 32 Celtra Duo and 32 VITA Enamic ceramics bonded to Allcem Veneer light‑cure and Allcem dual‑cure resin cements using silane impregnated with 4‑META in 0%, 2.5%, 5%, and 10 wt% concentrations in 16 groups (n = 4). The μTBS of specimens was measured by a universal testing machine and analyzed by the Kruskal–Wallis and Mann–Whitney tests, and the mode of failure was determined under a stereomicroscope and analyzed by the Chi‑square test (alpha = 0.05).

The lowest mean μTBS was recorded in the Enamic ceramic group with 4‑META (0%) bonded to dual‑cure cement (14.26 MPa), and the highest mean μTBS was recorded in Enamic ceramic with 4‑META (10%) bonded to light‑cure cement (18.59 MPa) (P < 0.001). The μTBS of Celtra Duo was significantly higher than that of Enamic in bonding to light‑cure cement using 4‑META (2.5%) (P = 0.003). All failures (100%) were adhesive in most groups. The frequency of adhesive failure was the lowest (90%) in Celtra Duo bonded to dual‑cure cement with 4‑META (5%).

According to the results of this pilot study, the addition of 4‑META (10%) to silane caused a significant improvement in μTBS to light‑cure cement. The addition of 4‑META in all concentrations significantly improved the μTBS to Enamic ceramic in the use of dual‑cure cement; however, it had no significant effect on μTBS of Celtra Duo. Nonetheless, the results should be interpreted with caution due to the relatively small sample size.

Ensuring the long-term stability of orthodontic treatments and preventing tooth relapse remains a significant challenge in orthodontics, often addressed through the extended use of retainers. Given the pivotal role of retainers' physical and mechanical properties in this regard, this study aimed to investigate the tensile strength, flexural strength, and deflection of three distinct types of fixed orthodontic retainers.

In this laboratory study, each group comprised 12 samples of twisted, flat, and coaxial retainer wires, each measuring 8 mm in length. These samples were affixed onto the polyethylene blocks using cyanoacrylate adhesive and subsequently subjected to compressive loads using a universal testing machine. The maximum bending strength and deflection rate were recorded from stress-strain diagrams. To evaluate the tensile strength, the identical samples underwent tensile loading. Statistical analysis was performed utilizing SPSS software, employing analysis of variance tests to compare data between groups.

Significant differences were observed in the bending strength (P=0.004), deflection (P<0.001), and tensile strength (P<0.001) among the investigated retainer wires. The flat retainer wire exhibited the highest bending strength, averaging 822.876±136.07 MPa, while the coaxial retainer wire showed the lowest, with an average of 673.65±73.35 MPa. Regarding deflection, the flat retainer wire displayed the highest average at 4.04±0.6 mm, surpassing the other two types of retainers. However, the tensile strength of the twisted retainer wires, averaging 699.7±83.46 MPa, exceeded that of both the flat and coaxial retainer wires.

The flat retainer wires demonstrated the highest bending and deflection strength, while the twisted retainer wires exhibited the highest tensile strength. Overall, the bending strength, deflection, and tensile strength of the 3-strand twisted and flat retainer wires outperformed those of the 5-strand coaxial retainer wires, increased flexural and tensile strengths imply a higher resistance of the wires to the forces induced by harder and more viscous foodstuffs.

Graphene oxide (GO), a product of graphite, is a candidate for nano‑reinforcing cement‑based materials due to its good water dispersibility and excellent mechanical properties. On the other hand, zinc oxide (ZnO) is well‑known for its antibacterial characteristics as well. Therefore, we aimed to evaluate the impacts of adding ZnO and GO nanoparticles on the antibacterial properties of flowable composites.

In this, in vitro experimental study was designated into five groups containing:(1) no nanoparticles as control group,(2) 1 wt.% ZnO nanoparticle,(3) 1 wt.% GO,(4) 1 wt.% physical compound of ZnO and GO, and (5) 1 wt.% chemical compound of ZnO and GO. The antibacterial properties of composite resin discs were evaluated by direct contact test. Data were analyzed using a one‑way analysis of variance, followed by Tukey’s post hoc tests (P = 0.05).

Streptococcus mutans colony counting in the first 24 h showed the least growth rate in the chemical compound group (2.2 × 105 ). However, in 7 days, the least colony number was observed in the GO group (2 × 103 ). Moreover, the physical compound showed the least bacterial adhesion.

Adding GO alone to composites, compared to adding ZnO or physical and chemical compounds of GO‑ZnO, was more helpful to increase the antimicrobial characteristics.

Graphene oxide (GO), a product of graphite, is a candidate for nano‑reinforcing cement‑based materials due to its good water dispersibility and excellent mechanical properties. On the other hand, zinc oxide (ZnO) is well‑known for its antibacterial characteristics as well. Therefore, we aimed to evaluate the impacts of adding ZnO and GO nanoparticles on the antibacterial properties of flowable composites.

In this, in vitro experimental study was designated into five groups containing:(1) no nanoparticles as control group,(2) 1 wt.% ZnO nanoparticle,(3) 1 wt.% GO,(4) 1 wt.% physical compound of ZnO and GO, and (5) 1 wt.% chemical compound of ZnO and GO. The antibacterial properties of composite resin discs were evaluated by direct contact test. Data were analyzed using a one‑way analysis of variance, followed by Tukey’s post hoc tests (P = 0.05).

Streptococcus mutans colony counting in the first 24 h showed the least growth rate in the chemical compound group (2.2 × 105 ). However, in 7 days, the least colony number was observed in the GO group (2 × 103 ). Moreover, the physical compound showed the least bacterial adhesion.

Adding GO alone to composites, compared to adding ZnO or physical and chemical compounds of GO‑ZnO, was more helpful to increase the antimicrobial characteristics.

The aim of this study was to investigate the effect of different surface treatments on the microtensile bond strength (µTBS) of two types of composite substructures with Vita Mark II ceramics by resin cement.

Sixty-four substructure specimens were molded from two dual-cure composites Core.it and Build-it, equally, and cured by LED light. The specimens of each group were randomly divided into 4 subgroups (n=8) treated by one of HF acid 10%, air abrasion, Er: YAG laser, and one group without any treatment (control group), and then the specimens of each group were bonded to Vita Mark II CAD/CAM ceramic blocks using two Duo-Link and Panavia F 2.0 resin (n=4 and 20 slice in any group). Each final specimen was thermocycled between 5 °C and 55 °C for 2500 cycles and then cut by a slow speed saw to obtain 5 sticks with cross-section dimensions of about 1×1 mm². The µTBS test was done at a speed of 0.5 mm/min by Universal Testing Machine. The fracture pattern was then determined using a stereomicroscope. Statistical differences between groups were determined by one-way ANOVA using Tukeychr('39')s multiple comparison tests.

Among all 16 groups, the highest µTBS was observed in the group with Core.it substructure composite and Duo-link resin cement without any surface treatment and after that in the second step in build-it substructure composite group and Panavia resin cement without surface treatment. The most common fracture pattern in all groups was cohesive in resin cement (P value<0.05).

According to this study, composite substructure surface treatment by hydrofloridric acid, laser and air abrasion reduced µTBS between substructure- ceramic and so  is not recommended.

This study aimed to assess the effect of graphene oxide (GO) nanoparticles mouthwash on oral mucosa, Streptococcus mutans (S. mutans) count in the saliva of rats, and human enamel surface microhardness, in comparison with fluoride mouthwash.

This study was conducted in two phases namely an animal study, and an in vitro experimental study. GO mouthwash (0.005%), sodium fluoride (NaF) mouthwash (0.05%), and a combination of both (0.05% NaF-0.005% GO) were prepared. The oral cavity of 36 rats was inoculated with S. mutans, and they were randomly divided into 4 groups according to the type of mouthwash. The control group received saline mouthwash. Fourteen days after using the mouthwashes, all rats were sacrificed, and the salivary S. mutans count was measured. The buccal and tongue mucosa were also histologically examined for the type and severity of inflammation, number of blood vessels, epithelial thickness, and epithelial keratinization. For microhardness testing, 40 sound extracted human premolars were randomly assigned to four groups (n=10) of culture medium with S. mutans and different mouthwashes. The enamel microhardness was measured at 7 and 14 days, and compared with the baseline value.

The mean S. mutans count in the saliva of rats in GO and NaF-GO groups was significantly lower than that in other groups (p<0.001). Enamel microhardness in NaF and NaF-GO groups significantly increased at 7 and 14 days, compared with baseline.

Addition of GO nanoparticles improved the antibacterial properties without causing adverse mucosal effects such as ulceration, acute inflammation or atrophy of the epithelium of the oral mucosa, but had no effect on surface hardness of the enamel.

Today, chitosan has a wide usage in Dentistry. Due to its penetration into tooth tissues, inhibition of the acid penetration and anti-demineralization capabilities, chitosan may interfere with the etching mechanism in the bonding restorations. The aim of this study was to evaluate the effect of chitosan with different concentrations and molecular weight on the shear bond strength (SBS) of composite to deciduous teethchr('39')s enamel.

In this in vitro trial, 50 deciduous anterior human maxillary teeth, which extracted because of orthodontic treatment plan, were selected and divide evenly between groups. In the control specimens, Filtek Z250 composite were packed on buccal teeth surfaces after using self-etch primer  single bond universal and light-cured. In four next groups the teeth were immersed into chitosan solution with low and high molecular weights and 5 mg/ml and 2.5 mg/ml concentrations for 60 seconds and restored with composite as control groups. The SBS of composite to the teeth enamel were determined with Universal testing machine. Data was analyzed by SPSS-18 software using one-way ANOVA and p<0.05 was considered significant.  

The SBS to enamel in the control specimens were 20.98 ± 6.31 MPa. The values were 17.92 ± 7.25, 16.02 ± 6.03, 13.26 ± 5.18 and 17.67 ± 8.95 MPa in the pretreatment with low molecular weight chitosan in 2.5 mg/ml , low molecular weight chitosan in 5 mg/ml , high molecular weight chitosan in 2.5 mg/ml and high molecular weight chitosan with 5 mg/ml concentrations respectively. No significant differences were found regarding SBS between groups. (P>0.05)

Despite a slight reduction in SBS of the composite to the enamel of the treated compare to control, use of chitosan in different concentration and molecular weight did not interfere with the SBS of composite to the enamel of deciduous teeth.

This study aimed to evaluate the effects of hydrofluoric acid (HF) concentration and etching time on the surface roughness (SR) and three-point flexural strength of Suprinity and to analyze the surface elements before and after etching.

To measure the SR, 70 specimens of Suprinity (2×4×5mm3) were assigned to seven groups (n=10). Six groups were etched for 20, 60, and 120 seconds with 5% and 10% HF and 7th group was the control group. Specimens were evaluated using atomic force microscopy (AFM). One specimen from each group was used to analyze the surface elements using scanning electron microscopy (SEM). For measuring the three-point flexural strength, 60 specimens were divided into six groups (n=10) and etched as previously described. The flexural strength was measured using a universal testing machine. T-test, one-way analysis of variance (ANOVA), and two-way ANOVA were used for statistical analyses (P<0.05).

The 10% concentration of HF caused higher SR compared to the 5% HF. The effect of HF concentration on the flexural strength was significantly different in the 20- and 60-second etching groups. Different etching times had no significantly different effect on the SR. With 5% HF, the flexural strength was significantly higher for 20-second etching time than for the etching times of 60 and 120 seconds. With 10% HF, there was a significant difference in flexural strength between etching times of 20 and 120 seconds. 

The best surface etching protocol comprises 10% HF used for 20 seconds.

 Dental ceramics are considered as materials that can restore the appearance of natural teeth. Etching the inner surface of a ceramic restoration with hydrofluoric acid (HF) followed by using a silane coupling agent is a well-known and recommended method to increase the bond strength. The aim of etching on ceramic structure is to enhance the surface roughness (Ra) and energy and to cleanse the bonding area. The aim of this study was to evaluate the effect of different HF concentrations and etching times on the Ra of IPS e.max CADTM and Vita mark IITM.

 Two HF concentrations (5% and 10%) and three etching times (20, 60 and 120 seconds) were evaluated. Etched patterns were observed by scanning electron microscopy (SEM) and Ra was measured using atomic force microscopy (AFM). Surface element analysis was performed using energy dispersive X-ray spectroscopy (EDAX). Data were analyzed on SPSS 20 using ANOVA and T-test.

 The Ra had no significant difference among various Vita mark IITM specimens (P=0.973). Among IPS e.maxTM specimens etched with 5% HF, the AFM results showed that 20-s etching time had the lowest Ra and among those etched with 10% HF and 120-s etching time had the most Ra. In IPS e.maxTM specimens etched with acid for 20 s, a significant difference was observed in Ra of 5% and 10% acid concentrations (5% HF lower than 10% HF) (p=0.012).

  Among IPS e.maxTM specimens etched with 5% and 10% HF, increasing the etching time lead to higher Ra. For both IPS e.maxTM and Vita mark IITM, 20-s etching with 5% HF provides acceptable Ra for the bond.

The purpose of this study was to evaluate the addition of sodium fluoride to fifth-generation adhesive (Solobond M) on the degree of microleakage and type I collagen content of dentin.

The present in vitro study was conducted on 120 orthodontically extracted human premolars devoid of decay and anatomical defects. Two series of 20 premolars were selected to test immunohistochemistry (IHC) and two series of 40 premolars to evaluate microleakage in two time points of 24 hours and 3 months. In both tests and at both time points, the tests were performed on the samples divided  into four groups: 1-control (only Solobond M), 2-bonding group (Solobond M) containing fluoride, 3-bonding group (Solobond M) containing Chlorhexidine (CHX) after acid etching, and 4-bonding group (Solobond M) containing fluoride+CHX after acid etching.

The IHC score at 24 hours and 3 months was significantly higher in the CHX, Fluoride, and Fluoride+CHX groups compared to the control group. The IHC score in the CHX+fluoride group was higher than that in the CHX group (p=0.04). The degree of microleakage at 24 hours and 3 months was significantly lower in the Fluoride+CHX and Fluoride groups compared to the control group. The degree of microleakage in the Fluoride group was lower than in the CHX group. The IHC score and the microleakage degree had no significant difference in 24 hours and 3 months between the Fluoride+CHX, Fluoride and CHX groups.

It seems that the effect of fluoride on non-degradation of collagen is greater than that of the CHX.