Effect of Nd:YAG Laser Irradiation on the Number of Open Dentinal Tubules and Their Diameter with and without Smear of Graphite: An in Vitro Study

Introduction: Dentin hypersensitivity (DH) is characterized by tooth pain arising from exposure of dental roots. In this study the efficiency of neodymium yttrium-aluminum-garnet (Nd:YAG) laser in association with graphite on dentinal surface changes as the alternative to the treatment of DH was evaluated.Methods: Sixteen noncarious human third molars were collected and sectioned into 5 parts from cementoenamel junction (CEJ) to the furcation area. The prepared samples were randomly assigned into five groups (Gs) of each 16: Control (G1), treated by Nd:YAG laser at 0.5 W (G2), irradiation of Nd:YAG with a 0.25 W output power(G3), smeared with graphite and then using Nd:YAG laser at output powers of 0.5 W (G4) and 0.25 W (G5). For all groups the parameters were 15 Hz, 60 s, at two stages and with a right angle irradiation. The number and diameter of dentinal tubules (DT) were compared and analyzed by SPSS software, One way ANOVA and Post hoc LSD tests.Results: The number of open dentinal tubules varied significantly between all groups except among G1 with G3 and G2 with G5. Multiple comparison tests also exhibited significant differences regarding the diameter of tubules between the groups two by two except among G2 with G5.Conclusion: Nd:YAG laser used at 0.25 W and 0.5 W with application of graphite smear was able to reduce the number and diameter of dentinal tubules

Effect of Translucency and Opacity of Fiber Reinforced Intracanal Posts on Fracture Resistance of Compromised Teeth

Background and Aim: Severely damaged teeth with no support at the coronal portion of root canal are very difficult to restore. The aim of this in-vitro study was to evaluate intraradicular reinforcement by dual cure composite resin and two different types of fiber reinforced composite (FRC) posts (translucent and opaque) in structurally compromised roots. Materials and Methods: Root canal therapy was performed for 48 maxillary central inci-sors. The teeth were divided into four groups, and specimens from three groups were pre-pared to simulate the teeth with flared canals. In the 1st group, no weakening was done. In the 2nd group, the compromised area of the root canal was filled with gutta percha. In the 3rd and 4th groups, universal DT light and DT white posts were used respectively in the root canal to 8 mm below the margin of the palatal wall. The posts were cemented with dual-cure composite. In all groups, the access cavity was restored with light-cure compo-site resin. After being mounted, all specimens were pressed at an angle of 45º relative to the long axis of the teeth. The amount of force at fracture was recorded. Results of frac-ture load were evaluated by one-way ANOVA and LSD post hoc test and the results of mode of fracture were evaluated by chi–square test. Results: The mean fracture load for the four groups was 170.12, 71.40, 125.8 and 148.59 kgf, respectively. There was a significant difference between the mean fracture load of 1st and 2nd groups and that of other groups (p=0.001). The mean fracture load of the 4th group was significantly (p=0.002) higher than that of the 3rd group. The frequency of restorable fractures was significantly different between these two groups (p<0.001). Conclusion: Using dual cure composite resin and FRC posts in roots with thin walls will reinforce the compromised teeth but the type of post will affect the outcome

Changes in Bleached Enamel Microhardness After Application of Fluoride and CPP-ACP

Background and Aim : Tooth bleaching decreases enamel microhardness. The aim of this study was to evaluate the changes in microhardness of bleached enamel after applying fluoride and CPP-ACP (casein phosphopeptide –amorphous calcium phosphate ). Materials and Methods : In this experimental study , sixty extracted human molars were divided into six groups (ten each). The flatted occlusal surface was covered with nail varnish. In the second, third and fourth groups, tooth bleaching was performed. The first and second groups were positive and negative control groups. In the third and fifth groups, the specimens were covered with sodium fluoride varnish and the fourth and sixth groups underwent CPP-ACP therapy. Subsurface enamel microhardness was determined on the occlusal surface with 300 micron distance from the buccal or lingual surface. One way ANOVA and Tukey post hoc were used for statistical analysis . Results : Microhardness of bleached enamel was significantly lower than the other groups. The teeth treated by fluoride agent or CPP-ACP after bleaching had a significant increase in their microhardness in contrast with the bleached enamel. CPP-ACP and fluoride treatment had no significant effect on sound enamel microhardness. Although using CPP-ACP and fluoride increases the enamel microhardness, there was no significant differences between them .  Conclusion : Fluoride and CPP-ACP components increase bleached enamel microhardness

Effects of Three Commonly Used Mouthwashes on Color Stability of Bleached Teeth

Background and Aim: Bleached teeth are susceptible to discoloration. The aim of this study was to evaluate discoloration of bleached teeth following short-term use of three mouthwashes. Materials and Methods: In this In-vitro experimental study, 48 extracted maxillary central incisors were selected and divided into four groups of 12. All the teeth were subjected to external bleaching with 38% hydrogen peroxide (H2O2). After bleaching, the teeth were immersed in distilled water (control group or group 1), chlorhexidine (CHX; group 2), Irsha (group 3) or Persica (group 4) for three, seven and 14 days. The color change was assessed by a spectrophotometer at each time point and reported as ΔE1, ΔE2 and ΔE3. The results were analyzed by paired t-test, repeated measures ANOVA, one-way ANOVA and LSD test. Results: Different mouthwashes and immersion times caused significantly different color change in bleached teeth. After 14 days of immersion, the color change of samples in Persica group had significant differences with that of other groups (P<0.001). The results of repeated measures ANOVA was only significant for the Persica group indicating significant color change over time. Thus, paired t-test was applied for pairwise comparison of the time points, which revealed significant differences between ΔE1 and ΔE3 and also ΔE2 and ΔE3 (P<0.05). Conclusion: Persica mouthwash would cause significant discoloration in recently bleached teeth