# Abstract

 

## Background The aim of this study was to assess the effect of Nd:YAG laser irradiation following casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) application on calcium and phosphate concentration and surface microhardness (SMH) of enamel surface in artificial white spot lesions of primary teeth. 

## Material and Methods Eighty teeth with artificial white spot lesions were randomly divided into four groups: (A) distilled and deionized water, (B) Nd:YAG laser, (C) CPP-ACP crème, & (D) CPP-ACP plus laser. SMH was measured using Vickers diamond indenter in Vickers Hardness Number (VHN). Two samples of each group were analyzed using scanning electron microscope (SEM). The results were analyzed with the SPSS 17/win. 

## Results The subjects of group D demonstrated a significant increase in the calcium and phosphate contents of enamel surface compared to those of groups A (P < 0.001, P < 0.001), B (P < 0.001, P < 0.001) and C (P = 0.024, P = 0.04), respectively. A statistically significant difference was seen for mean VHN between groups A and B (P = 0.002). SEM evaluations confirmed the results. 

## Conclusions The combination of Nd:YAG laser and CPP-ACP crème could be recommended as an effective preventive modality for remineralizing of white spot lesions in primary teeth. \*\*Key words:\*\*CPP-ACP, enamel remineralization, microhardness, Nd:YAG, primary teeth, SEM. # Results -Total weight percentage of calcium, phosphate and enamel surface micro hardness The mean enamel VHN and total weight percentage of calcium and phosphate, resulting from the EDX analysis of enamel surface in treatment groups are given in [ Table 1](#). ::::table-wrap

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## Comparison of mean values (mean ± SD) of surface microhardness, calcium weight percentage, and phosphate weight percentage in the studied groups.

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![](<>):::: Mean total weight percentage of calcium was higher in group D compared to other groups ([ Table 1](#)). Also mean total weight percentage of phosphate was higher in group D compared to other groups. The difference in the mean values were statistically significant between groups A and D and also between groups A and C, while the difference was not significant between groups A and B ([ Table 1](#)). The highest mean VHN was recorded in group C ([ Table 1](#)). The results showed a statistically significant difference in the mean values of VHN between groups A and B, while the difference was not significant between groups A and other groups. Mean VHN in groups D and C were significantly higher than that in group B; meanwhile, this difference was not significant between groups D and C the p values are listed in [ Table 1](#). -SEM micrograph findings Figure [1](#)a shows a sound enamel surface from the negative control group demonstrating relatively smooth area with frequent enamel prism ends present on the surface. The surface presented shallow depressions and fine porosities within these depressions. The enamel surfaces were devoid of any surface deposits. <figure> <p><img src="" /></p> <figcaption>a) SEM image of control group showing enamel surface. b) SEM image of enamel surface irradiated with Nd:YAG laser showing melted enamel (large arrow) and fine cracks (small arrow). c) SEM image of enamel surface treated with CPP-ACP showing granular particles and amorphous crystals (arrow). d) SEM image of enamel surface treated with combined application of CPP-ACP and laser showing smooth and more homogeneous lazed surface (large arrow) with a few cracks coating by granular and globular particles and amorphous homogenous crystals (small arrow).</figcaption> </figure> The SEM image of enamel irradiated with Nd:YAG laser (group B) showed an irregular roughened surface (Fig. [1](#)b). In this group, typical melting appearance with occasional areas of fine surface cracking, discontinuities, coalescence of globules and holes could be observed. The surface was peppered with cavitations and craters leading to an irregular undulated surface. The surface did not show any of the usual enamel prism ends seen in the control group. Numerous cracked surface coatings covered almost the entire surface. In the SEM image of the enamel surface treated with CPP-ACP (group C), numerous granular particles and amorphous crystals were arranged on the enamel surface, those crystals seemed to be homogeneous, and there was no obvious intercrystalline space (Fig. [1](#)c). In the CPP-ACP plus laser samples (group D), a relatively smooth, more homogeneous surface compared to those in the groups treated with laser and CPP-ACP alone were noted (Fig. [1](#)d). Fewer cracks were observed on the glazed enamel surface, probably due to the application of CPP-ACP before laser irradiation, consistent with the numerous occurrences of granular and globular particles and amorphous homogenous crystals arranged on the enamel surface.


Extracted trial result:
Outcome: Total weight percentage of phosphate (continuous)
Intervention: CPP-ACP plus laser (group D)
Comparator: Nd:YAG laser (group B)
Intervention mean: 20
Comparator events: 20
Notes: All numerical values are in a graphical format of table.