Journal of Dental Materials and Techniques
Volume:12 Issue: 2, Spring 2023

Low tensile strength is one of the problems of tissue conditioning materials used in complete prostheses. This study aimed to explore the impact of silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs) on the tensile strength of a tissue conditioner. Ag and ZnO NPs were synthesized using the light bulb method and verified by scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy (FTIR). The prepared NPs were mixed with the tissue-conditioner fluid at weight percentages (wt%) of 0.675, 1.25, 2.5, 5, and 10. The NPs were added either individually (Ag or Zn alone) or in combination (at a ratio of ½ Ag and 1/2  ZnO). Tensile strength was measured on rectangular cube specimens with dimensions of 2 x 20 x 200 mm using a universal testing machine according to the ISO 17025 standard. The results were analyzed by one-way analysis of variance (ANOVA) and Tukey test at a significance level of P<0.05. The concentration of 5% and 10% Ag NPs increased the tensile strength of the tissue conditioner (P<0.05), but the addition of ZnO NPs at any concentration (up to wt. of 10%) did not (P>0.05). The combined application of Ag and ZnO NPs at concentrations of 5% and 10% was also effective in enhancing the tensile strength (P<0.05). The addition of Ag or Ag-ZnO NPs at concentrations of 5% and 10% may be suggested to enhance the tensile strength of the tissue conditioning materials. (J Dent Mater Tech 2023;12(2):55-60)

The present study evaluated the effect of different surface treatments of fiber posts on the micro-push-out force between posts and various composite core materials. A total of 80 fiber posts were divided into 16 groups according to the surface treatment and core material. Four different surface treatments were applied on fiber posts including Al2O3 sandblasting, CoJet sandblasting, ytterbium-doped fiber (YbPL) laser roughening, and control (no surface treatment). The core materials were Bis Core, Core Flo, Clearfil DC Core, and Clearfil Photo Core, which were applied in a transparent mold on the surface-treated posts. The light was applied for a total period of 120 seconds. Four 1-mm sections were obtained from each post-core structure. The micro-push-out test was then performed and the results were recorded in Newtons and converted to megapascals (MPa). The type of surface treatment (P<0.001) and core material (P<0.001) significantly affected the bond strength. The highest bond strength was found in the combined application of Al2O3 sandblasting and Core Flo material (132.84 MPa) and the lowest was observed in YbPL laser-treated posts combined with Bis Core material (59.46 MPa). Among the core materials, Clearfil Photo Core showed the highest bond strength with no significant difference from the Core Flo material. Clearfil Photo Core or Core Flo may be preferred for clinical use. Among the surface treatments, sandblasting with Al2O3 showed the highest bond strength.  (J Dent Mater Tech 2023;12(2): 61-67)

Candida albicans and Candida tropicalis are the most common fungal species in humans. The present study aimed to investigate the effect of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser on inhibiting the growth of Candida albicans and Candida tropicalis in vitro.  Candida albicans and Candida tropicalis species were cultured in sub-dextrose agar containing chloramphenicol and exposed to Nd:YAG laser (1064 nm). The laser was emitted at the pulse frequency of 1 Hz (1 pulse per second) for 7 or 13 seconds. At each pulse duration, the energies of 40, 60, 80, or 100 mJ were delivered to microbial plates. After radiation, the number of colonies was counted and reported as colony-forming units per milliliter (CFU/mL).  There was a significant reduction in the number of Candida albicans and Candida tropicalis colonies after Nd:YAG laser radiation, compared to the control group (P<0.05). At the pulse duration of 7 seconds, there was a significant difference in the number of Candida albicans colonies between the pulse energy of 40 mJ with other pulse energies (P<0.05). At the pulse duration of 13 seconds, the energies of 80 mJ and 100 mJ were significantly more potent at killing Candida tropicalis than other pulse energies (P<0.05). Increasing the duration of irradiation from 7 to 13 seconds was effective at killing Candida species at most pulse energies (P<0.05).  Nd:YAG laser is effective in inhibiting the growth of Candida species. Under the conditions of this study, the antifungal effect of Nd:YAG laser improved with increasing pulse energy and duration of laser irradiation. (J Dent Mater Tech 2023;12(2): (68-72)

High-quality pit and fissure sealant (PFS) treatment can promote public oral health. The present study aimed to compare the success and survival rates of PFS treatments performed by dental students and postgraduate students in pediatric dentistry, and to evaluate the associated patient-related factors. Patients who had received at least one PFS treatment performed by an undergraduate or postgraduate student during 2016-2018 were recalled. The age and gender of the patients, caries risk, oral hygiene status, DMFT, dmft, and the status of the PFS treatment in terms of retention rate and caries development were evaluated. The chi-square test, multiple logistic regression model, and Weibull accelerated failure time regression model were applied for statistical analysis. The success and survival rates of PFS treatments in the postgraduate group were significantly higher than those in the undergraduate group (P<0.05). Moderate caries risk and permanent tooth type were significantly associated with lower success rates of PFS therapy (P=0.02 and P=0.003, respectively). Additionally, increased dmft, moderate caries risk, and permanent tooth type were associated with shorter survival times (P<0.001, P=0.01, and P=0.009, respectively). High caries risk also decreased both success and survival rates of PFS treatment, but these alterations were not statistically significant (P=0.26, and P=0.55, respectively). The success rate of PFS therapy is influenced by patient-, tooth-, and operator-related factors. PFS treatment is assumed to be more successful when performed by postgraduate students in the primary teeth of patients with low caries risk. (J Dent Mater Tech 2023;12(2):(73-81)

Smart ion-releasing restorative materials may increase the success and survival rate of composite dental restorations. This study aimed to evaluate the impact of sintering temperature on the mechanical properties and ion-releasing behavior of fluorohydroxyapatite (FHA)-filled dental resin composites. The FHA was synthesized via a sol-gel method and sintered at three temperatures (250, 500, and 1000ºC). FHA fillers were characterized using X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy, then coated with citric acid and incorporated (40% w/w) into a photo-curable resin matrix (Bis-GMA, TEGDMA, HEMA; weight ratio 2:1:1). Flexural strength (FS) and diametral tensile strength (DTS) were measured, as well as the depth of cure, which was determined by the Vickers microhardness test. The release of calcium and fluoride ions was monitored for a month in diluted citric acid (pH=4.3), and the effect of acidic storage on mechanical properties was evaluated via DTS testing. The filler distribution was observed via scanning electron microscopy. The influence of sintering temperature on the measured variables was statistically analyzed using one-way and two-way ANOVA (α=0.05). The XRD results revealed increased crystallinity with higher sintering temperatures. Correspondingly, mechanical properties improved with increasing sintering temperature (P<0.05), whereas the depth of cure, as well as ion release (Ca+2 and F-), decreased (P<0.05). Sintering at elevated temperatures yielded a greater amount of crystalline apatite structure, and enhanced mechanical properties of FHA-filled dental resin composites, but reduced ion release. Based on these findings, FHA fillers sintered at approximately 500ºC appear optimal for creating smart dental resin composite. (J Dent Mater Tech 2023;12(2):(82-90)

The present study aimed to determine the insertion torque and fracture resistance of infra-zygomatic crest (IZC) screws as critical factors influencing primary stability. A total of 40 stainless steel IZC mini-screw implants (MSIs) were obtained from two different manufacturers (Bio-Ray, Taiwan, and S. K. Surgicals, India). Each group comprised 20 MSIs of identical dimensions (2 ×14 mm). To simulate a clinical scenario, a customized jig was utilized to embed these screws into human maxillary bone blocks for evaluation of maximum insertion torque (MIT), and into polyacrylic glass blocks for assessment of fracture resistance. A digital torque gauge was used to obtain precise torque measurements. There were significant differences in MIT between the groups at the tip and neck areas of the screws (P<0.05). The Bio-Ray IZC screws manifested significantly greater insertion torque at the tip and significantly lower insertion torque at the neck compared to the S.K. Surgicals group (P<0.05). However, the two groups demonstrated no significant difference in terms of fracture resistance (P=0.484). The evaluated mini-implants displayed a diverse range of insertion torques at various parts of the screws (increasing from tip to mid and neck regions). It is imperative to consider various torque values during screw insertion to mitigate the risk of tissue damage and screw breakage. The present findings revealed no significant difference in fracture resistance between the two brands of mini-implants, suggesting that the fracture torque was primarily influenced by factors beyond the manufacturer of the MSIs. (J Dent Mater Tech 2023;12(2): 91-97)

The efficacy of composite restorations depends on their color stability, with discoloration cited as a principal reason for restoration replacement. The current investigation focused on assessing the influence of various mouthrinses on the color stability of conventional and bulk-fill composites. In this in vitro study, 40 samples (4 mm in diameter and 4 mm in thickness) were constructed from Tetric N-Ceram and Tetric N-Ceram Bulk Fill composites (both from Ivoclar Vivadent). The initial color value of each specimen was recorded using an Easyshade spectrophotometer, in adherence with the CIELab color scale. Subsequently, the specimens were submerged in 20 mL of either distilled water or different mouthrinses including non-alcohol Misswake, alcohol-containing Listerine, or chlorhexidine. After incubating for 24 hours at 37°C, color values were measured again. The data were analyzed by two-way ANOVA, and a P-value<0.05 was considered statistically significant. Tetric N-Ceram demonstrated superior color stability compared to the Tetric N-Ceram Bulk Fill composite after immersion in non-alcoholic Misswake and alcohol-containing Listerine mouthwashes (P<0.05). In both composites, chlorhexidine exhibited the most pronounced color change (P <0.05). The color change was significantly greater in the alcohol-containing Listerine than in the non-alcoholic Misswake mouthrinse (P<0.05). This study suggests that mouthrinses, especially chlorhexidine, significantly affect the color stability of both composite types, with conventional composites showing relatively more resistance to color change than bulk-fill composites.  (J Dent Mater Tech 2023;12(2): 98-103)

This study compared the influence of various adhesive systems and silane application on the adhesion of resin-based luting cement to lithium disilicate, indirect composite resin, and zirconia restorations. Lithium disilicate (n=50), indirect composite resin (n=50), and zirconia (n=50) blocks were divided into five groups (n=10), according to the adhesive protocol applied as follows: 1. Optibond XTR, 2. silane + Optibond All in One, 3. One Coat 7 Universal, 4) Adper Scotchbond Multi-Purpose, and 5) Silane + Single Bond Universal. The blocks were bonded to a resin-based luting cement after surface treatments (silica coating and acid application). The bonded specimens were incubated in 37° C water for 24 hours and thermocycled for 5,000 cycles. The shear bond strength (SBS) was evaluated by a universal testing machine. The adhesion protocols for each type of restoration were compared by one-way ANOVA and Dunnett T3 test. There were significant differences in the bond strength of cement to indirect restorations between various adhesive protocols (P<0.05). In all types of restorations, the highest SBS was observed in group 5, which was silanized and bonded with Single Bond Universal. The bond strength of group 5 in lithium disilicate, indirect composite resin, and zirconia groups were 26.1 ± 4.9 MPa, 20.5 ± 5.7 MPa, and 15.4 ± 4.7 MPa, respectively. It appears that the best adhesive protocol for bonding cement to lithium disilicate, indirect composite resin, and zirconia restorations is the use of silane and a universal adhesive containing silane (Single Bond Universal). (J Dent Mater Tech 2023;12(2): 104-110)