This study evaluated the effect of CO2 laser irradiation and topical fluoride therapy in the control of caries progression on primary teeth enamel. 30 fragments (
Application of fluoride compounds has been used to control dental caries in primary teeth under different forms [
Higher incidence of dental caries in primary teeth associated with rapid progression of these lesions due to lower mineral content [
CO2 laser irradiation is more appropriate to dental enamel because it produces radiation in the infrared region (9.3, 9.6, 10.3, and 10.6
The CO2 laser may control caries progression in permanent [
As creation of an acid-resistant surface seems to be a promise in the control of caries lesions, the aim of this study was to evaluate
The factor under investigation was surface treatment at 3 levels: L: CO2 laser irradiation; APF: 1.23% acidulated phosphate fluoride; C: no treatment (control). The sample consisted of 30 fragments of human primary enamel distributed among three surface treatments (
This research was approved by the Ethics in Research Committee of the School of Dentistry of Ribeirão Preto, University of São Paulo (Process number 2010.1.1373.58.9). Freshly extracted sound primary canines were obtained from Human Tooth Bank of the same institution.
Primary teeth were hand scaled and cleaned with water/pumice slurry, in rotating bristle brushes at low speed (N270, Dabi Atlante, Ribeirão Preto, SP, Brazil) to remove calculus and surface-adhered debris and stored in 0.1% thymol solution. The absence of cracks, hypomineralization, and hypoplasia was confirmed under an ×20 magnifier (Leica S6 D Stereozoom, Mycrosystems Leica AG, Switzerland) and teeth with structural defects were discarded. Afterwards, the selected teeth were sectioned in the cement-enamel junction in precision cutter water-cooled (Isomet 1000, Buehler, Lake Bluff, IL, USA), to separate the root and coronal portions. The buccal surface of each tooth was sectioned to obtain a fragment of enamel measuring
The fragments were fixed in acrylic resin blocks using melted wax (Wax Sculpture Fixed Prosthodontics, Aspheric Chemical Industry Ltda., São Caetano do Sul, SP, Brazil) with the subsurfaces facing the external environment. The subsurfaces were then flattened with #1200-grift silicon carbide paper in a water-cooled polishing machine (Politriz, DP-9U2, Struers A/S, Copenhagen, Denmark) (Hermes Abrasives Ltd., VA, USA) and polished with 0.3
For obtaining initial microscopic lesions of standardized white spot lesion, simulating patients with high caries activity, an artificial caries challenge was performed in all fragments. The specimens were repositioned with the buccal surface facing the external environment in resin blocks and fixed with wax. All surfaces except the buccal were covered with melted wax and stored individually in plastic containers. The initial cariogenic challenge was performed during 5 days according to the protocol proposed by Argenta et al. 2003 [
According to a complete block design and randomized, the specimens were divided according to treatment in three groups (
The CO2 laser with
0.1 g of 1.23% acidulated phosphate fluoride gel (DFL Industry, Rio de Janeiro, RJ, Brazil, pH 3.6) was weighed on analytical balance (AUW220D, SPLABOR, Presidente Prudente, SP, Brazil) and applied to the dry surface deciduous enamel using microbrush (KG Sorensen, Cotia, SP, Brazil). After 1 minute [
The control group did not receive any treatment, being kept in artificial saliva at 37°C for 24 hours.
The samples were replaced in plastic containers and all surfaces, except for the treated surface, and were covered with melted wax. The same pH cycling that was applied before the laser or the fluoride treatment was repeated 5 times, at a rhythm of one per day, in order to simulate the conditions of cariogenic severe challenge.
After cariogenic challenge period, specimens were sectioned longitudinally and fixed with melted wax and their internal side (sectional) was left exposed and polished in a polishing machine (DP-9U2; Struers S/A, Copenhagen, Denmark). After polishing, specimens were observed under an optical microscope to verify the superficial smoothness and were subjected to ultrasonic cleaning (Dabi Atlante, Ribeirão Preto, SP, Brazil) for two minutes to remove the debris. Then, impressions were made in one of the hemisections, keeping the long axis of the diamond indenter parallel to the external surface of the enamel using a static load of 25 g for 5 sec [
The protocol used in this study is shown in Figure
Schematic design of the methodology presented. (a) Section of the teeth. (b) Obtaining fragments. (c) Fixation of specimens in resin blocks. (d) Planning and polishing the enamel surface. (e) Selection of specimens. (f) Initial cariogenic challenge. (g) Surface treatments. (h) Cariogenic challenge after surface treatment. (i) Section of the fragments. (j) Fixing the fragments into blocks of acrylic resin. (k) Polishing the enamel surface. (l) Microhardness evaluation.
The mean values of microhardness of each specimen were analyzed and showed a normal distribution and homogeneity of variance. Thus, analysis of variance (ANOVA) was employed. The Duncan test was used to investigate differences between the mean of surface treatment factor using SPSS 12.0 for Windows (SPSS Inc., Chicago, IL, USA) with a significant level of 5%.
The results showed that microhardness of subsurface treatments performed on primary teeth enamel was statistically different
Microhardness values (mean and standard deviation) according to the superficial treatments in different experimental groups (
Treatment | Mean | Standard deviation |
---|---|---|
CO2 laser | 324.99a | 33.78 |
1.23% acidulated phosphate fluoride | 309.30a | 68.42 |
No treatment (control) | 209.86b | 67.03 |
Similar letters indicate statistical similarity.
Duncan test showed that surface treatment with CO2 laser showed the highest microhardness values (KNH) on primary teeth enamel, but it was not statistically different from 1.23% acidulated phosphate fluoride application. However, a statistically significant difference from the control group that presented the lowest microhardness values was found.
Acidulated phosphate fluoride [
CO2 laser is responsible for increasing acid resistance on irradiated enamel [
In this study, surface treatment with CO2 laser in primary enamel was statistically similar to 1.23% acidulated phosphate fluoride. The probable reason for the increased acid resistance of the primary enamel after CO2 laser treatment is a consequence of thermal effect [
Thermal variations produced by using the CO2 laser on enamel promote reduction of water and carbonate content [
The thermal effects are responsible for changes in the irradiated tooth surfaces while they may differ from the temperature observed at pulp chamber, due to the support structures present around the teeth and the blood flow of the pulp tissue; this heat could be dissipated [
The low thermal conductivity of the enamel and the rapid decrease in temperature in the lower layer of spent glaze can also contribute to the lack of pulp damage, due to high absorption of this substrate by the appropriate wavelength of 10.6
CO2 laser action on primary and permanent enamel can be distinct, due to the differences between these substrates. The mineralization, calcium, and phosphorus percentage is lower in primary teeth than in permanent teeth [
Carbonate content reduction on permanent enamel, promoted by CO2 laser irradiation [
It has been reported that, after a professional fluoride application, calcium fluoride (CaF2) is formed on enamel surface and fluoride is released to fluid phase. This effect promotes a consequent reduction of enamel demineralization. Also, a dose-response effect is observed between the concentration of CaF2, reservoirs on enamel and fluoride released, to “plaque fluid” and the subsequent inhibition of enamel demineralization [
The amount of fluoride formed in the enamel depends on the concentration and the pH of the product applied and how long it remains in contact with the enamel [
In the present study, as CO2 laser was applied on previously demineralized primary enamel simulating a patient with high cariogenic challenge and high caries risk, it is difficult to make a direct comparison with these results to previous literary studies. Until now, there is no research that performed previously cariogenic challenge on primary teeth enamel, targeting the demineralization controlling and not preventing demineralization, having sound as substrate. Besides, the higher the demineralization is, the more difficult caries control becomes.
CO2 laser with
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to gratefully acknowledge CAPES for the postgraduate scholarship provided to the first author. The authors would like to gratefully acknowledge Professor Sandra Maria Tobias, for reviewing this paper English language.