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Objective: To determine the effect of acidulated phosphate fluoride “APF” and casein phosphoprotein amorphous calcium phosphate “MI paste” on the flexural modulus of two super elastic orthodontic wires. Material and Methods: Preformed round and rectangular NiTi and Cu NiTi were immersed in either APF, MI paste or artificial saliva (control) for 4 minutes. The wires were then subjected to a 3-point bend test in accordance with the American National Standard/American Dental Association Specification No. 32 (2006) Results: NiTi wires were significantly affected by the prophylactic agents’ application with a more substantial effect for those treated with APF. The effects were less in magnitude however still significant for the tested Cu NiTi wires. Conclusion: Mechanical properties of NiTi wires are significantly affected by the application of remineralizing agents. Clinically it would preferable to use Cu Niti wires if it is predicted that the patient will need a prophylactic agent. (74) Islam Tarek Hassan, et al. E.D.J. Vol. 63, No. 1 satisfy orthodontic requirements, yet these properties are liable to change under various manipulations and conditions5. One such condition affecting the mechanical properties of arch wires is the use of dental re-mineralizing agents which is sometimes mandatory to preserve the dental structure6. These agents are also used to enhance the patients’ oral hygiene and as a prophylaxis to reduce the incidence of the white spot lesions commonly associated with orthodontic fixed appliances7,8,9. Products containing fluorides and casein phosphoprotein are the mainly prescribed prophylactic agents used for such purposes7-9. Different protocols including professional in-office as well as home use applications are advocated throughout the orthodontic treatment period. Therefore, it is important to understand their effect on the various components of the orthodontic fixed appliances. The unique properties of superelastisty and shape memory allow titanium-based wires to deliver a constant force over a wide range of activation making them ideal for orthodontic tooth movement4,13. Accurate knowledge of the mechanical properties of these wire is essential in their utilization to deliver ideal forces for tooth movement14,15. Titanium and titanium based alloys are known for their excellent corrosion resistance attributed to their protective oxide6,13. However previous studies have recorded discolorations, surface changes as well as changes in mechanical properties of superelastic titanium based wires in response to fluoride applications5,6. Therefore, this study was conducted to test and compare the effects of acidulated phosphate fluoride “APF” and casein phosphoprotein amorphous calcium phosphate “MI paste” on the flexural modulus of NiTi and Cu NiTi wires as well as any possible influence wire cross section might have on that interaction. MATERIAL AND METHODS Preformed Ormco pseudo nickel titanium (NiTi) round and rectangular wires as well as thermoplastic copper nickel titanium wires (Cu NiTi) were chosen for their superelastic properties and popularity. TABLE (2) Number of wire samples distributed according to; wire alloy and wire crosssection Material Cross-section in Inches Number of Wires Group 1 Niti 0.016 50 Group 2 Niti 17x25 50 Group 3 Cu-Niti 0.016 50 Group 4 Cu-Niti 17x25 50 The fluoride agent used was 1.23%APF, Sorbet ,Dental Resources, a division of Key Stone Industry, Myerstown, Pennsylvania, USA and the casein phosphoprotein was MI Paste, GC International, Itabashi-Ku, Tokyo, Japan. (table 1) TABLE (1) Prophylactic agents; composition and manufacturing company Prophylactic Agent Composition Manufacturer APF “Sorbet”TM Acidulated phosphate fluoride. Flouride ion 1.23% available from 2.09% sodium fluoride and hydrofluoric acid Dental Resources, A division of Key Stone Industry, Myerstown, Pennsylvania, USA “MI Paste” TM Casine phosphoprotein amorphous calcium phosphate GC International, Itabashi-Ku, Tokyo, Japan EFFECT OF REMINERALIZING AGENTS ON THE FLEXURAL MODULUS OF ELASTICITY (75) Each wire specimen was cut from the straight portion of preformed arch wires with a round crosssectional dimension of 0.016 inch and a rectangular crosssectional dimension of 0.017x0.025 inch and were cut to the length of 20 mm. The wire specimens were divided into four equal groups of 50 according to the wire alloy and cross section. (Table 2) Wire treatments From each sub-group 10 wire specimens were allocated to be used as control samples. These wires were immersed in separate vials containing artificial saliva for 5 minutes prior to their testing. The remaining wires from each sub–group were randomly selected to be treated with either; APF or MI Paste rendering 20 wires for each treatment. The treatment consisted of a four-minute application of the prophylactic agent (total emersion of the wire in the agent in a glass bowl). After that, 10 wires of each treatment subgroup (no. of wires per sub group 20) were randomly allocated to be tested immediately after prophylactic agent application. Those wires were treated individually (one at a time) with the prophylactic agent then removed with tweezers and washed in a bowl with artificial saliva (the wires of each treatment were washed in a separate artificial saliva bowl) and tested immediately (T0). The prophylactic agent application and washing procedures were repeated for the remaining 10 wires in each subgroup allocated for delayed testing. This was followed by their storage in separate test tubes containing artificial saliva for 3 weeks. These subgroups were then tested at (T1). Testing procedure In our study, all specimens were subjected to a 3-point bending test as described by Miura et al23. Mechanical testing was also based on the current American National Standard/American Dental Association Specification No. 32 for Orthodontic Wires 2006. 5 As indicated in the specification, the wire specimens were submerged and tested in a heated distilled H2O bath (37±1 °C) to simulate the aqueous oral environment. The temperature of the water bath was maintained via a water heater and a thermocouple thermometer. The mechanical testing was performed on a computer controlled universal testing machine (Lloyd Instruments LR 5K Serial No 014441; Load cell 5 KN) and the data was collected using Nexygen version 4.5. The testing procedures were performed at the Dental Biomaterial Department, Faculty of Dentistry, Ain Shams University . During the testing procedure, the wire was supported by a jig, the jig span would determine the length of the wire that was subjected to the bending test. For this test and its clinical applications, the testing procedures were customized for each wire alloy. According to a pilot testing, Titanium based alloys were tested on a 12mm custom made jig span. (Figure 1). Compressive force was applied at a crosshead speed of 1 mm/min by means of a striker (steel rod with a bi-beveled chisel end) placed midway between the two poles of the jig. Each specimen was loaded to a deflection of 3.1 mm and then unloaded at the same crosshead speed until zero deflection was reached. Load in newtons (N) and deflection in Fig. (1) Custom made testing jigs (76) Islam Tarek Hassan, et al. E.D.J. Vol. 63, No. 1 millimeters (mm) were recorded for each specimen with the Nexygen computer software program. Load deflection curves were the generated via MS Excel (2010). The engineering beam theory was used to calculate the flexural modulus of elasticity (E).E for the loading slopes of round cross section specimens was calculated using the following equation: E = 4L3m/3πD4 (GPa). E for the loading slopes for rectangular specimen was calculated using the following equation95: E = L3 m/4bd3 (GPa). P = load at the apparent yield point (N), L = support span (mm), b = width of specimen (mm), d = depth of specimen (mm) and m = slope of the straight-line portion of the loading deflection curve (N/mm of deflection). Statistical Method The Generalized Linear Model was selected because, the dependent variables are continuous (Modulus of Elasticity E,) whilst the independent variables studied (wire dimension, prophylactic agent used and time of testing) were categorical. The Generalized Linear Model was performed using SPSS software version 17. The analysis was performed separately for E, loading YS and unloading YS in each alloy type (NiTi and Cu NiTi). The Generalized linear model was used to study the effect of each of the studied independent variables (wire treatment, cross section and storage time) separately as well as their two-way interactions. RESULTS The results show a statistically significant decrease in the measured Modulus of Elasticity (E) the wires treated with both APF and MI Paste when compared with the control groups. In addition, the measured E values for the groups treated with MI Paste were significantly higher than those treated with APF. This change was less pronounced however still significant for the tested CuNiTi wires. (Curves 1 to 6 and Table 3 to 7) Curve. 1 Modortho NiTi Control Application Load Deflection Curve Curve. 2 Modortho NiTi Fluoride Application T0 Load Deflection Curve Curve. 3 Modortho NiTi Fluoride Application T1 Load Deflection Curve A representative sample of the generated load deflection curves EFFECT OF REMINERALIZING AGENTS ON THE FLEXURAL MODULUS OF ELASTICITY (77) Curve. 4 Modortho Cu NiTi Control Application Load Deflection Curve Curve. 5 Modortho Cu NiTi APF Application T0 Load Deflection Curve Curve. 6 Modortho Cu NiTi APF Application T1 Load Deflection Curve Delayed mododrtho st st 17x25 1 T.M Table (3): GLM analysis showing significance of different variables on modulus of elasticity (E) of NiTi wires Source Type III Sum of Squares df Mean Square F Sig. Corrected Model 43533.192a 27 1612.340 24.132 .000 Intercept 1573819.301 1 1573819.301 23555.686 .000 Main effect Treat 948.850 3 316.283 4.734 .003 Dim 31786.761 1 31

EFFECT OF REMINERALIZING AGENTS ON THE FLEXURAL MODULUS OF ELASTICITY OF NICKEL TITANIUM AND COPPER NICKEL TITANIUM WIRES