Effect of Deep Cryogenic Treatment on Cyclic Fatigue of Endodontic Rotary Nickel Titanium Instruments

Introduction: Cyclic fatigue is the common reason for breakage of rotary instruments. This study was conducted to evaluate the effect of cryogenic treatment (CT) in improving the resistance to cyclic fatigue of endodontic rotary instruments. Methods and Materials: In this in vitro study, 20 RaCe and 20 Mtwo files were randomly divided into two groups of negative control and CT. CT files were stored in liquid nitrogen at -196°C for 24 h, and then were gradually warmed to the room temperature. All files were used (at torques and speeds recommended by their manufacturers) in a simulated canal with a 45° curvature until breakage. The time to fail (TF) was recorded and used to calculate the number of cycle to fail (NCF). Groups were compared using independent-samples t-test. Results: Mean NCFs were 1248.2±68.1, 1281.6±78.6, 4126.0±179.2, and 4175.4±190.1 cycles, for the Mtwo-control, Mtwo-CT, RaCe-control, and RaCe-CT, respectively. The difference between the controls and their respective CT groups were not significant (P>0.3). The difference between the systems was significant. Conclusion: Deep CT did not improve resistance to cyclic fatigue of the evaluated rotary files.Keywords: Cryogenic Treatment; Cyclic Fatigue; Instrument Fracture; Rotary Nickel Titanium File

Porcelain color alteration after orthodontic bonding using three different surface preparation methods

Background: By increasing the number of adults seeking orthodontic treatment bonding orthodontic brackets to the surfaces other than intact enamel has become necessary. The purpose of this study was to evaluate the effect of three different surface preparation methods associated with orthodontic bonding on porcelain color alteration. Materials and Methods: In this in vitro study forty-five porcelain discs (6- mm diameter, 2- mm thickness) were fabricated. The color of the specimens was evaluated by means of a Vita Easyshade. Commision Internationale de I'Eclairage (CIE) L* a* b* system was used for color measurement. Then, the specimens were randomly divided into three groups (n = 15) with respect to the surface preparation methods including a 9.6% hydrofluoric acid (HF) + silane, sandblasting, and sandblasting + 9.6% HF + silane. Metal orthodontic brackets were bonded. Samples were stored in 37° c water for 24 hours. Afterward, the brackets were debonded with a debonding plier and porcelain surfaces were polished with a tungsten-carbide bur. The color assessment was done, and ΔE values were measured. ΔE = 3.7 units were considered as an acceptability threshold. Data were analyzed with Paired t-test and one-way ANOVA. Level of significance was set at P < 0.05. Results: Orthodontic bonding changed the color parameters significantly. Mean L*, a* and b* difference were 1.35 ± 2.41, 0.19 ± 0.80, 0.89 ± 1.27 units, respectively (P = 0.003 for L*, P < 0.001 for a* and b*). There was not any significant difference in ΔE units between the groups (P = 0.456). In all the groups the mean ΔE values were below 3.7 units and within the clinically acceptable limit. Conclusion: Orthodontic treatment changed the CIE color parameters of porcelain surface. However, the color alteration is below the clinically acceptable threshold. With regard to color alteration, there is no difference between different surface conditioning methods