Background & Aim: One of the induced major problem after bleaching treatments is enamel surface roughness increase, which can lead to increased risk of dental caries, plaque accumulation and later enamel discoloration. In this study the effect of adding CPP-ACP to home bleaching gel on enamel roughness was evaluated.Methods & Materials: in this experimental study, premolar teeth have been used. The samples divided in three groups (n=13) randomly. The roughness of each group was evaluated before the bleaching process with ATOMIC FORCE MICROSCOPY. Samples was kept in Carbamide peroxide 20%, CP 20% and CPP-ACP (with 1: 1 ratio), CP 20% and CPP-ACP (with 1: 2 ratio) for 14 days, each day 4 hours. The roughness was evaluated two times after bleaching and the results were evaluated statistically. The gained data in each group were evaluated by PAIRED T-Test, and for intra-group analysis ANOVA and POST HOC test was used.Results: Surface enamel roughness before bleaching was same in all three groups. (p<0.4) The surface roughness after bleaching was increased in Carbamide peroxide 20% and decreased in group 1, significantly The increase was significant in first group (p=0.01), the decrease was not significant in second group, but significant in third group. (p=0.01) Conclusion: The 20% CP and CPP-ACP with 1: 2 ratio can significantly decrease the surface roughness in comparison to the primary roughness.

In the present research, higher resonance frequencies are employed to improve the performance of the ATOMIC FORCE MICROSCOPY in the non-contact mode. Conventional models already used in the literature to study AFM microcantilever dynamics such as point-mass approach are not only incapable of modeling higher vibrational modes but also fail to predict microcantilever complicated dynamics with a sufficient accuracy. In this paper, the Hamilton’ s extended principle is used to obtain equations governing the nonlinear oscillations of the AFM probe. Euler-Bernoulli beam assumptions and small deflection theory are assumed. The resulting partial differential equation is often converted to a set of ordinary differential equations and then this set is solved either numerically or based on perturbation methods. In the present research, however, the partial differential equation is attacked directly by a special perturbation technique. The accuracy of the present method is then verified by a combination of the Galerkin discretization scheme and a Rung-Kutta numerical solution. Finally, different behaviors of the AFM probe including static behavior, linear mode shapes and frequency response curves are investigated through several numerical simulations. It is found out that higher vibrational modes have smaller frequency shift. It is also found out that higher modes are faster in gathering surface information and also more sensitive to the excitation.

Nitriding of steels, using plasma environments has been practiced for many years. A lot of efforts have been put on developing new methods, such as plasma immersion ion implantation (PI3) and radio frequency (RF) plasma nitriding, for mass transfer of nitrogen into the surface of the workpiece. This article presents the results obtained from an in depth investigation of the surface morphology of the treated samples, carried out using an ATOMIC FORCE microscope (AFM). Samples from microalloyed steel were treated by both methods for 5 hours at different temperatures ranging from 350 to 550 °C in 75% N2 -25% H2 atmospheres. It has been found that the surface of the samples treated by PI3 technique, although having morefavorable properties, were rougher than the surfaces treated by RF plasma nitriding.