Vol 12, No 9 (2015)
Original Article
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Objectives: This study aimed to evaluate the effect of different ceramic surface treatments after machining grinding on the biaxial flexural strength (BFS) of machinable dental ceramics with different crystalline phases.
Materials and Methods: Disk-shape specimens (10mm in diameter and 1.3mm in thickness) of machinable ceramic cores (two silica-based and one zirconia-based ceramics) were prepared. Each type of the ceramic surfaces was then randomly treated (n=15) with different treatments as follows: 1) machined finish as control, 2) machined finish and sandblasting with alumina, and 3) machined finish and hydrofluoric acid etching for the leucite and lithium disilicate-based ceramics, and for the zirconia; 1) machined finish and post-sintered as control, 2) machined finish, post-sintered, and sandblasting, and 3) machined finish, post-sintered, and Nd;YAG laser irradiation. The BFS were measured in a universal testing machine. Data based were analyzed by ANOVA and Tukey's multiple comparisons post-hoc test (α=0.05).
Results: The mean BFS of machined finish only surfaces for leucite ceramic was significantly higher than that of sandblasted (P=0.001) and acid etched surfaces (P=0.005). A significantly lower BFS was found after sandblasting for lithium disilicate compared with that of other groups (P<0.05). Sandblasting significantly increased the BFS for the zirconia (P<0.05), but the BFS was significantly decreased after laser irradiation (P<0.05). Conclusions: The BFS of the machinable ceramics was affected by the type of ceramic material and surface treatment method. Sandblasting with alumina was detrimental to the strength of only silica-based ceramics. Nd:YAG laser irradiation may lead to substantial strength degradation of zirconia.
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Objectives: The aim of this study was to compare the permeability of dentin after using diamond bur and Er:YAG laser.
Materials and Methods: Seventy-two recently extracted, intact, and restoration-free human permanent molars were used in this study. The samples were randomly divided into three groups of 24 each and class I cavities were prepared as follows. Group 1: High speed diamond bur with air and water spray. Group 2: Er:YAG laser. Group 3: Er:YAG laser followed by additional sub-ablative laser treatment. Each group consisted of two subgroups with different cavity depths of 2mm and 4mm. The entire cavity floor was in dentin. Two samples from each subgroup were observed under scanning electron microscope (SEM). The external surfaces of other samples were covered with nail varnish (except the prepared cavity) and immersed in 0.5% methylene blue solution for 48 hours. After irrigation of samples with water, they were sectioned in bucco-lingual direction. Then, the samples were evaluated under a stereomicroscope at ×160 magnification. The data were analyzed using two-way ANOVA and Tukey’s HSD test.
Results: Two-way ANOVA showed significant difference in permeability between groups 2 and 3 (laser groups with and without further treatment) and group 1 (bur group). The highest permeability was seen in the group 1. There was no significant difference in dentin permeability between groups 2 and 3 and no significant difference was observed between different depths (2mm and 4mm).
Conclusion: Cavities prepared by laser have less dentin permeability than cavities prepared by diamond bur.
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Objectives: The purpose of this study was to evaluate the resistance to fatigue failure of five different nickel-titanium rotary files in three different curved trajectories.
Materials and Methods: A total of 150 Neoniti A1, RaCe 25.06, Mtwo 25.06, Twisted file 25.06 and ProTaper Next X2 files with the tip size of 25 were tested (n=30 for each group). Three groove types simulating curved canals were used differing in radius, arc length and position of the arc, each measuring 1.5 mm in width, 20 mm in total length and 2.5 in depth. Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure. Furthermore, the fragment length of the fractured tips and angle and radius of curvature formed by each file in each trajectory were evaluated. The data were analyzed by t-test, one way ANOVA and Tukey’s HSD test.
Results: Neoniti showed the highest and RaCe showed the lowest number of cycles to fracture (NCF) values (P<0.05), indicating the highest and lowest fatigue resistance, respectively. The highest and lowest curvature angles were seen in RaCe and Neoniti, respectively. Regarding the radius of curvature, Twisted file had the lowest and Neoniti had the highest values. The mean NCF of all rotary files was lower in the more coronally curved trajectory.
Conclusion: The fatigue resistance of the evaluated rotary files was lower in more coronally located curvatures. Neoniti exhibited the highest and RaCe exhibited the lowest fatigue resistance compared to other evaluated files.
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Objectives: Implant primary stability is one of the important factors in achieving implant success. The osteotome technique may improve primary stability in patients with poor bone quality. The aim of this study was to compare implant stability using two different techniques namely osteotome versus conventional drilling in the posterior maxilla.
Materials and Methods: In this controlled randomized clinical trial, 54 dental implants were placed in 32 patients; 29 implants were placed in the osteotome group and 25 in the conventional drilling group. Implant stability was assessed at four time intervals namely at baseline, one, two and three months after implant placement using resonance frequency analysis (RFA).
Results: Primary stability based on implant stability quotient (ISQ) units was 71.4±7 for the osteotome group and 67.4±10 for the control group. There was no statistically significant difference between the two groups in implant stability at any of the measurement times. In each group, changes in implant stability from baseline to one month and also from two months to three months post-operatively were not significant but from one month to two months after implant placement, implant stability showed a significant increase in both groups.
Conclusion: The results of this study revealed that in both techniques, good implant stability was achieved and osteotome technique did not have any advantage compared to conventional drilling in this regard.
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Objectives: The purpose of this experimental study was to evaluate the efficacy of low level laser therapy (LLLT) for pain reduction after midpalatal expansion in rats.
Materials and Methods: Sixty male Sprague six-week old rats weighing 180±10g were divided into seven groups (two experimental groups of 24 rats and one control group of 12 rats). The experimental groups were subjected to expansion with or without LLLT. The health status of each rat was monitored starting seven days prior to the experiment and evaluated by regular body weight monitoring during the study period. Diode laser with 810nm wavelength and 100 mw output power was used. Laser therapy and body weight monitoring were performed on days 0, 2, 4, 6, 8, 10, 12 and 14. The data were analyzed by One-way repeated measures ANOVA.
Results: The body weight of the experimental groups significantly decreased in the first two days because of the pain and difficult nutrition with the new appliance. Within the next two days, the body weight of all rats increased but this increase was significantly higher in the irradiated compared to the non-irradiated group. This significant improvement continued until day 14 and then between days 14 and 30 the rats gained weight similarly in the irradiated and control groups.
Conclusion: The study results showed that laser irradiated group continued to gain weight easier than the control group. This may be due to more efficient pain control due to laser irradiation after midpalatal expansion.
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Objectives: Saliva plays an important role in prevention of dental caries. Neutrophils are the first defense mechanism of the immune system. Interleukins (ILs) can regulate the activity of neutrophils. This study aimed to assess the neutrophil count and level of IL-lβ and IL-8 in the saliva of children with and without dental caries.
Materials and Methods: This case-control study was performed on 90 preschool children between three to five years. Children were divided into three groups of caries-free, early childhood caries (ECC) and severe early childhood caries (S-ECC). Saliva was collected in tubes by the spitting method. Neutrophil count was assessed by Giemsa staining and the levels of IL-lβ and IL-8 in the saliva were assessed using ELISA. Data were analyzed by the Kruskal-Wallis and post hoc Games-Howell test.
Results: The mean levels of IL-1β and IL-8 and the mean neutrophil count in the caries free group were found to be 59.2± 59.15 pg/mL, 86.04± 96.12 pg/mL and 1342.66± 2222.412 pg/mL, respectively. These values were 36.78± 40.88 pg/mL, 76.12± 107.01 pg/mL and 2500± 3834.61 pg/mL in the ECC group and 48.75±47 pg/mL, 76.77± 70.63 pg/mL and 2353.1± 4583.81 pg/mL in the S-ECC group, respectively. There were no significant differences among the three groups in terms of the levels of IL-1β, IL-8 or the neutrophil count (P>0.05).
Conclusion: Since no significant difference was noted in the salivary levels of IL-1β and IL-8 or the neutrophil count among the groups, development of dental caries may be related to neutrophil chemotaxis defect.
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Objectives: Repairing composite restorations is a challenging procedure especially when two different types of composites are used. This study aimed to compare the repair strength of silorane-based composite (SC) (Filtek P90) with that of preheated SC, methacrylate composite (MC)(Z250), flowable MC (Filtek Supreme Plus) and different adhesive/composite combinations.
Materials and Methods: Eighty-four SC specimens were fabricated and randomly divided into seven groups (G). In the control group (G7), SC was bonded immediately to SC. The other specimens were water-aged for two months and were then roughened, etched and repaired with the following materials: G1) Silorane Adhesive Bond (SAB)/SC;
G2) Preheated SC; G3) SAB/MC; G4) Adper Single Bond (SB)/MC; G5) Flowable MC/MC; G6) Preheated MC. After water storage and thermocycling, the repaired specimens were subjected to shear bond strength testing. The data were analyzed using ANOVA and Tukey’s test.
Results: Preheated SC and MC, flowable MC and SAB/SC resulted in bond strength comparable to that of the control group. Preheated SC showed significantly higher bond strength when compared to SAB/MC (P=0.04) and SB/MC (P<0.001). Bond strength of SB/MC was significantly lower than that of the other groups (P<0.05), except for SAB/SC and SAB/MC.
Conclusion: All repairing materials except for SB/MC resulted in bond strength values comparable to that of the control group. Repair with preheated SC yielded the highest bond strength.
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Objectives: Considering the adhesion of some microorganisms such as Streptococcus mutans (S. mutans) to restorative materials and the unrecognized consequences of this phenomenon, and due to the controversies in this regard, it is important to discover the materials to which the lowest adhesion of S. mutans occurs. The objective of this study was to assess the level of adhesion of S. mutans to glass ionomer (GI), BisCem Cement and enamel.
Materials and Methods:In this in vitro experimental study, 12 specimens including five GI blocks (GC America Inc., Alsip, IL, USA), five BisCem blocks (Bisco Inc., Schaumburg, IL, USA) and two enamel blocks were exposed to a bacterial suspension (1×106 mg/mL). After incubation for one hour at 37˚C, the swab samples were taken and cultured in blood agar. The S. mutans colonies were counted by unaided vision after 48 hours of incubation. The results were analyzed using ANOVA followed by the Tukey’s test.
Results:The number of colonies attributed to enamel, GI, and BisCem blocks was 24±2, 24.2±2.7 and 14.8±1.7 colonies/mm2, respectively. There was no difference between enamel and GI in terms of adhesion of S. mutans (P=0.08 and P>0.001, respectively); however, the difference between these two and BisCem was statistically significant (P= 0.00075 and P<0.001, respectively).
Conclusion:Within the limitations of this study, BisCem cement is superior to GI for the cementation of indirect restorations.Objectives: Considering the adhesion of some microorganisms such as Streptococcus mutans (S. mutans) to restorative materials and the unrecognized consequences of this phenomenon, and due to the controversies in this regard, it is important to discover the materials to which the lowest adhesion of S. mutans occurs. The objective of this study was to assess the level of adhesion of S. mutans to glass ionomer (GI), BisCem Cement and enamel.
Materials and Methods:In this in vitro experimental study, 12 specimens including five GI blocks (GC America Inc., Alsip, IL, USA), five BisCem blocks (Bisco Inc., Schaumburg, IL, USA) and two enamel blocks were exposed to a bacterial suspension (1×106 mg/mL). After incubation for one hour at 37˚C, the swab samples were taken and cultured in blood agar. The S. mutans colonies were counted by unaided vision after 48 hours of incubation. The results were analyzed using ANOVA followed by the Tukey’s test.
Results:The number of colonies attributed to enamel, GI, and BisCem blocks was 24±2, 24.2±2.7 and 14.8±1.7 colonies/mm2, respectively. There was no difference between enamel and GI in terms of adhesion of S. mutans (P=0.08 and P>0.001, respectively); however, the difference between these two and BisCem was statistically significant (P= 0.00075 and P<0.001, respectively).
Conclusion:Within the limitations of this study, BisCem cement is superior to GI for the cementation of indirect restorations.
Keywords: Bacterial Adhesion; Streptococcus mutans; Glass Ionomer Cements; BisCem cement
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Objectives: Because of poor bond between resin cement and zirconia ceramics, laser surface treatments have been suggested to improve adhesion. The present study evaluated the effect of CO2 and Nd:YAG lasers on the shear bond strength (SBS) of resin cement to zirconia ceramic.
Materials and Methods: Ninety zirconia disks (6×2 mm) were randomly divided into six groups of 15. In the control group, no surface treatment was used. In the test groups, laser surface treatment was accomplished using CO2 and Nd:YAG lasers, respectively (groups two and three). Composite resin disks (3×2 mm) were fabricated and cemented to zirconia disks with self-etch resin cement and stored in distilled water for 24 hours. In the test groups four-six, the samples were prepared as in groups one-three and then thermocycled and stored in distilled water for six months. The SBS tests were performed (strain rate of 0.5 mm/min). The fracture modes were observed via stereomicroscopy. Data were analyzed with one and two-way ANOVA, independent t and Tukey’s tests.
Results: The SBS values of Nd:YAG group (18.95±3.46MPa) was significantly higher than that of the CO2 group (14.00±1.96MPa), but lower than that of controls (23.35±3.12MPa). After thermocycling and six months of water storage, the SBS of the untreated group (1.80±1.23 MPa) was significantly lower than that of the laser groups. In groups stored for 24 hours, 60% of the failures were adhesive; however, after thermocycling and six months of water storage, 100% of failures were adhesive.
Conclusion: Bonding durability of resin cement to zirconia improved with CO2 and Nd:YAG laser surface treatment of zirconia ceramic.
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Objectives: The aim of this study was to assess and compare the characteristics of commonly used initial archwires by their load deflection graphs.
Materials and Methods: This study tested three wire designs namely copper nickel titanium (CNT), nickel titanium (NiTi), and multi-strand NiTi (MSNT) archwires engaged in passive self-ligating (PSL) brackets, active self-ligating (ASL) brackets or conventional brackets. To evaluate the mechanical characteristics of the specimens, a three-point bending test was performed. The testing machine vertically applied force on the midpoint of the wire between the central incisor and canine teeth to obtain 2 and 4mm of deflection. The force level at maximum deflection and characteristics of plateau (the average plateau load and the plateau length) were recorded. Two-way ANOVA and Tukey’s test were used at P <0.05 level of significance.
Results: Force level at maximum deflection and plateau length were significantly affected by the amount of deflection. The type of archwires and brackets had significant effects on force level at maximum deflection, and plateau length. However, the bracket type had no significant effect on the average plateau force.
Conclusion: With any type of brackets in deflections of 2 and 4mm, MSNT wire exerted the lowest while NiTi wire exerted the highest force level at maximum deflection and plateau phase. The force level at maximum deflection and the plateau length increased with raising the amount of primary deflection; however the average plateau force did not change significantly.
