ORIGINAL RESEARCH | https://doi.org/10.5005/jp-journals-10024-2684 |
Effect of CO2 Laser and 1.23% Acidulated Phosphate Fluoride on Acid Resistance and Fluoride Uptake of Human Tooth Enamel: An In Vitro Assessment
1,2Department of Pediatric and Preventive Dentistry, Nair Hospital and Dental College, Mumbai, Maharashtra, India
3,4Department of Pediatric and Preventive Dentistry, Government Dental College and Hospital, Mumbai, Maharashtra, India
5Department of Pediatric Dentistry, Jamia Millia Islamia, New Delhi, India
6Department of Pediatric and Preventive Dentistry, Bharati Vidyapeeth Dental College and Hospital, Sangli, Maharashtra, India
Corresponding Author: Parag Kasar, Department of Pediatric and Preventive Dentistry, Nair Hospital and Dental College, Mumbai, Maharashtra, India, Phone: +91 9619345878, e-mail: parag.pedopg@gmail.com
How to cite this article Kakade A, Kasar P, et al. Effect of CO2 Laser and 1.23% Acidulated Phosphate Fluoride on Acid Resistance and Fluoride Uptake of Human Tooth Enamel: An In Vitro Assessment. J Contemp Dent Pract 2019;20(9):1082–1089.
Source of support: Nil
Conflict of interest: None
ABSTRACT
Aim: To evaluate the effectiveness of CO2 laser treatment before applying 1.23% acidulated phosphate fluoride (APF), through topically applied 1.23% APF solution, and after applying 1.23% APF on acid resistance and fluoride uptake of the enamel.
Materials and methods: Sixty non-carious human premolars were extracted due to the orthodontic reason and stored in distilled water solution under refrigeration. Using a water-cooled diamond disc, enamel slabs of 4 mm × 4 mm × 1.5 mm were cut from the buccal surface of each tooth. Sixty samples were randomly divided into one control group and five test groups of 10 premolars each. Solution was prepared for wet chemical analysis followed by fluoride analysis that was carried out using a fluoride ion selective electrode (Thermo Scientific Orion 4-Star Plus ISE Meter). The weight of enamel (WE) was determined from the amount of calcium (Ca) etched away considering the fact that the Ca content of the human enamel is 37.4 wt%. The subgroups were statistically analyzed using ANOVA for fluoride determination and evaluation of acid resistance.
Results: There was a significant increase in acid resistance of enamel slabs when treated individually or in combination of a low-power CO2 laser and 1.23% APF solution. Application of 1.23% APF solution after low-power CO2 laser treatment showed maximum increase in acid resistance.
Conclusion: Application of a low-power pulsed CO2 laser through topically applied 1.23% APF solution resulted in a detrimental effect of the human tooth enamel with resultant decrease in acid resistance. High fluoride uptake does not necessarily indicate increased acid resistance.
Clinical significance: The present study provides evidence that a low-power CO2 laser can be used effectively in combination with topically applied 1.23% APF solution in order to make the enamel more resistant to acid attack, thereby helping in controlling dental caries.
Keywords: 1.23% Acidulated phosphate fluoride, Acid resistance, CO2 laser, Fluoride uptake, Human tooth enamel.
INTRODUCTION
Acidulated phosphate fluoride (APF) is most effective among all topical fluorides.1–3 But it has been reported that APF when applied for 4 minutes is insufficient for the optimum effect.4 Prevention through increased acid resistance as a result of the laser occurs due to decreased enamel permeability,5 alterations in chemical composition,6 or both.7 CO2 laser irradiation of the human dental enamel at 10.6 microns and the continuous8–11 as well as the pulsed12–15 wave mode led to significantly reduced dissolution rates. Similar results have been found when investigating the effect of additional fluoride application before or after laser treatment, leading to an increased fluoride uptake and a decreased rate of dissolution in acidic solution.11,16–18
Spontaneous conversion of hydroxyapatite to fluorapatite by irradiation with a high-energy CO2 laser in the presence of sodium fluoride has been reported.19 Also, 1.23% APF application followed by laser shows high fluoride uptake and acid resistance in comparison to NaF.16 Several advantages have been reported when laser is performed in combination with fluoride application.20
Hence, the present study aimed at evaluating the effect of a CO2 laser before applying 1.23% APF, through topically applied 1.23% APF solution, and after applying 1.23% APF on acid resistance and fluoride uptake of the enamel.
MATERIALS AND METHODS
The present in vitro study was carried out in the Department of Pediatric and Preventive Dentistry, Nair Hospital Dental College, Mumbai, in collaboration with Department of Earth Sciences and Department of Sophisticated Analytical Instrument Facility, Indian Institute of Technology, Powai, Mumbai, to assess the effect of a CO2 laser and 1.23% APF solution on the human tooth enamel. All subjects enrolled in this research responded to an informed-consent protocol, which had been approved by the Ethics Committee, Nair Hospital Dental College, Mumbai.
Preparation of Enamel Slabs
Sixty non-carious human premolars were extracted due to the orthodontic reason and stored in distilled water solution under refrigeration. The teeth were then cleaned and polished with nonfluoridated polishing paste and rubber cup. The selected teeth were checked for surface cracks, white spots, or mottling using contrast light (Fig. 1). Enamel slabs of 4 mm × 4 mm × 1.5 mm were cut using a water-cooled diamond disc on the buccal surface of each teeth (Fig. 2). A vernier caliper was used to standardized the dimensions. The enamel slabs were embedded in acrylic blocks (Fig. 3).
Fig. 1: Comparison of the mean Ca content of solutions from different groups
Fig. 2: Comparison of mean WE loss from each group
Fig. 3: Comparison of mean enamel depth from different groups
Preparation of 1.23% APF Solution
Four grams of sodium fluoride were added in 200 mL of 0.1 M phosphoric acid in a plastic beaker. The 48% hydrofluoric acid was added to adjust the pH between 3 and 3.5 using a Eutech pH meter and fluoride concentration at 1.23%. Constant stirring using a magnetic stirrer and fischer was done to prepare the solution.
Carbon Dioxide Laser
Commercially available dream pulse III surgical laser system (Daeshin Enterprise, Korea) was used at super pulse setting and mode A (having pulse duration of 800 μs), each pulse separated by 100 ms with energy output of 5 W per pulse. The laser system operated at a wavelength of 10.6 μm.
Lasing the Samples
The entire enamel surface of the samples was irradiated for 15 seconds by moving the laser probe tip continuously at a distance less than 1 mm from the sample surface by a single operator. Sixty samples were randomly divided into one control group and five test groups of 10 premolars each as follows:
- Group I: control samples, sound tooth enamel slabs receiving no treatment.
- Group II: enamel slabs treated with 1.23% APF solution for 4 minutes.
- Group III: enamel slabs lased for 15 seconds using super pulse setting and mode A (having pulse duration of 800 μs), each pulse separated by 100 ms and energy output of 5 W per pulse.
- Group IV: enamel slabs that were treated with 1.23% APF solution for 4 minutes before lasing for 15 seconds.
- Group V: enamel slabs that were treated with 1.23% APF solution for 4 minutes after lasing for 15 seconds.
- Group VI: enamel slabs that were lased for 15 seconds immediately through the topically applied 1.23% APF solution at the end of 4-minutes application.
All the 60 samples underwent the following procedures.
Method of Preparation of Solution for Wet Chemical Analysis (Fig. 4)
One layer of the enamel in samples was etched away by exposure to 1 mL of 0.5 M perchloric acid contained in plastic beakers for 30 seconds. The 0.5 M perchloric acid was prepared by adding 4.4 mL of 70% pure perchloric acid to 100 mL of double distilled water. After removing the sample subsequent to etching with 0.5 M perchloric acid, the enamel slab was washed carefully with 4 mL of total ionic strength adjustment buffer (TISAB) solution dispensed through a plastic syringe, in such a way that all the solution was collected in a beaker containing perchloric acid. The solution in a beaker was then prepared to 10 mL by adding distilled water. This analysis was done to evaluate calcium levels of all the groups.
Fluoride Analysis (Fig. 4)
The fluoride analysis was carried out using a fluoride ion selective electrode (Thermo Scientific Orion 4-Star Plus ISE Meter). The same solution (mixture of 0.5 M perchloric acid and 4 mL TISAB was mixed and prepared to 10 mL by adding distilled water) was used to evaluate the fluoride level in all groups.
Fig. 4: Comparison of the mean fluoride content of solutions from different groups
Estimation of Calcium Content
The weight of enamel (WE) was determined from the amount of calcium (Ca) etched away considering the fact that the Ca content of the human enamel is 37.4 wt%. The thickness of the enamel layer removed was also determined using the following formula:21
where, 37.4 wt% is the calcium content in the enamel, 2.95 g/cm3 is the density of the enamel, and 16 mm2 is the surface area of the enamel slab.
The Ca content in the solution was determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The same solution (mixture of 0.5 M perchloric acid and 4 mL TISAB was mixed and prepared to 10 mL by adding distilled water) was used to evaluate the Ca content level in all groups.
Statistical Analysis
The subgroups were statistically analyzed using ANOVA for fluoride determination and evaluation of acid resistance. Individual post hoc comparisons were performed using a unpaired t test. Significance was set at 95% (p ≤ 0.05).
RESULTS
Among all the groups, group V showed lowest values of mean Ca content in prepared solution (16.58 ± 2.03 ppm), mean WE (44.34 ± 5.44 ppm), and mean enamel depth (25.12 ± 3.08 μm) suggestive of maximum acid resistance (Tables 1 to 7, Figs 5 to 7). The fluoride content of prepared solutions was highest in group VI (10.87 ± 0.79 μg) (Tables 1 to 7 and Fig. 8). Fluoride uptake was highest in group IV (15372.10 ± 4277.46 ppm) with comparable fluoride uptake in group V (14509.00 ± 1625.53 ppm) and group VI (14226.90 ± 1543.75 ppm) (Table 7 and Fig. 9).
DISCUSSION
Fluoride prevents dental decay by inhibition of demineralization and promoting subsurface remineralization.22–25 The human enamel is considered the substrate of choice for preparing the enamel slabs, because it is identical, or nearly so, to the substrate it is intended to represent. Use of premolars intended for extraction also has the advantage that they are in the functional and natural state.26 So, enamel slabs for the present study were prepared from sound human premolars extracted for the orthodontic reason. Synthetic hydroxyapatite shows high-energy CO2 laser treatment converting hydroxyapatite into fluorapatite in the presence of fluoride.19 Thus, APF solution was used in the present study.
Oral hard tissues absorb light in the infrared spectrum.13 The radiation produced by a CO2 laser in the infrared spectrum coincides with the apatite absorption bands.26 For this reason, a CO2 laser was used in the present study. At a continuous wave11 mode or a pulsed wave15 mode, a CO2 laser shows high resistance to acids. Energy is dissipated if the pulse duration is short, whereas if it is longer, some amount of heat is deposited in upper layers. So, a pulsed wave CO2 laser was used in the present study. A low-power surgical laser system was used in this study. The test groups were lased with a CO2 laser at 10.6 μm wavelength, energy level of 5 J/cm2 for 15 seconds with pulse duration of 800 μs and each pulse separated by 100 ms.27–30
Among the various methods of fluoride estimation, acid etch biopsy along with the use of a fluoride ion selective electrode is comparatively easier31 and has been used previously by various authors like Mellberg,32 Mellberg and Loertscher,33 Margill,34 Hattab and Frostell,21 Hattab,35 Crall and Bjerga,36 and Tepper et al.11
While determination of fluoride using acid etch biopsy, sharp etch is of interest because an irregularly removed layer directly influences the fluoride profiles in the enamel. The 0.5 M perchloric acid was used for acid etch biopsy in this study because of its ability to give a sharper etch pattern.37 Fluoride ion concentration in biopsied solutions from test and control groups was determined using a fluoride ion selective electrode. Same solutions were then used for the estimation of the Ca content, which was then used for the determination of the dissolved enamel, i.e., WE etched away. Weight of the dissolved enamel was calculated considering the Ca content of the human tooth enamel to be 37.4%. The resultant fluoride content of test and control solutions and calculated enamel weight etched away were then used for the calculation of the fluoride content in human tooth enamel slabs using the formula given by Hattab and Frostell:21
The test and control samples were evaluated by ICP-AES for relative acid resistance. The calcium levels were used to calculate the WE etched away and enamel depth penetration. Calcium analysis was performed using an atomic emission spectrometer. Use of an atomic emission spectrometer for analysis of the Ca content has also been done by Jetpurwala and Damle.38
Group II samples showed reduced enamel solubility when compared to the control group. On comparing with the WE of the control group, i.e., 68.17 ± 5.19 ppm, the difference was statistically significant similar to findings of authors such as Bibby,1 Mellberg,32 Garcia-Godoy et al.,39 and Delbem and Cury.40 Significant increased resistance to acid attack and changes in enamel permeability have been obtained after lasing the tooth samples with a high-energy CO2 laser.5,7,9,15,41 The findings of these authors cannot be correlated with the present study due to the difference in the methodology and the type of CO2 laser used. High acid resistance after exposure to a low-power CO2 laser has been reported by Hsu,27 Whitters and Strang,28 Tepper et al.,11 and Oliveira et al.29
| Group I | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 25.14 | 67.22 | 38.08 | 0.03 | 0.27 | 406 |
| 2 | 25.87 | 69.17 | 39.18 | 0.02 | 0.25 | 359 |
| 3 | 23.25 | 62.17 | 35.22 | 0.03 | 0.34 | 552 |
| 4 | 26.02 | 69.57 | 39.41 | 0.03 | 0.31 | 450 |
| 5 | 25.01 | 66.87 | 37.88 | 0.03 | 0.29 | 438 |
| 6 | 22.13 | 59.17 | 33.52 | 0.03 | 0.34 | 581 |
| Group II | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 18.22 | 48.72 | 27.60 | 0.31 | 3.10 | 6361 |
| 2 | 23.73 | 63.45 | 35.94 | 0.26 | 2.63 | 4146 |
| 3 | 22.19 | 59.33 | 33.61 | 0.27 | 2.68 | 4518 |
| 4 | 19.98 | 53.42 | 30.26 | 0.30 | 3.03 | 5675 |
| 5 | 20.18 | 53.96 | 30.57 | 0.44 | 4.43 | 8218 |
| 6 | 17.22 | 46.04 | 26.08 | 0.46 | 4.58 | 9957 |
| 7 | 17.59 | 47.03 | 26.64 | 0.30 | 3.03 | 6446 |
| 8 | 20.62 | 55.13 | 31.23 | 0.38 | 3.83 | 6952 |
| 9 | 19.6 | 52.41 | 29.69 | 0.50 | 4.99 | 9513 |
| 10 | 17.29 | 46.23 | 26.19 | 0.42 | 4.23 | 9148 |
| Mean | 19.66 ± 2.17 | 52.57 ± 5.79 | 29.78 ± 3.28 | 0.37 ± 0.09 | 3.37 ± 1.25 | 6546.82 ± 2659.15 |
| Group III | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 18.75 | 50.13 | 28.40 | 0.05 | 0.54 | 1081 |
| 2 | 19.98 | 53.42 | 30.26 | 0.04 | 0.42 | 791 |
| 3 | 20.3 | 54.28 | 30.75 | 0.02 | 0.18 | 336 |
| 4 | 20.57 | 55.00 | 31.16 | 0.08 | 0.75 | 1370 |
| 5 | 20.43 | 54.63 | 30.94 | 0.06 | 0.60 | 1104 |
| 6 | 19.97 | 53.40 | 30.25 | 0.04 | 0.38 | 717 |
| 7 | 17.1 | 45.72 | 25.90 | 0.09 | 0.85 | 1867 |
| 8 | 19.87 | 53.13 | 30.10 | 0.06 | 0.55 | 1041 |
| 9 | 15.2 | 40.64 | 23.02 | 0.07 | 0.65 | 1607 |
| 10 | 16.2 | 43.32 | 24.54 | 0.06 | 0.62 | 1436 |
| Mean | 18.84 ± 1.96 | 50.37 ± 5.24 | 28.53 ± 2.97 | 0.06 ± 0.02 | 0.56 ± 0.20 | 1141.00 ± 480.28 |
| Group IV | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 19.81 | 52.97 | 30.01 | 0.84 | 8.39 | 15844 |
| 2 | 20.25 | 54.14 | 30.67 | 1.44 | 14.38 | 26555 |
| 3 | 18.04 | 48.24 | 27.32 | 0.79 | 7.86 | 16299 |
| 4 | 21.27 | 56.87 | 32.22 | 0.89 | 8.87 | 15591 |
| 5 | 20.69 | 55.32 | 31.34 | 0.69 | 6.86 | 12406 |
| 6 | 21.17 | 56.60 | 32.07 | 0.89 | 8.89 | 15709 |
| 7 | 22.26 | 59.52 | 33.72 | 0.69 | 6.86 | 11531 |
| 8 | 15.96 | 42.67 | 24.17 | 0.61 | 6.06 | 14204 |
| 9 | 18.86 | 50.43 | 28.57 | 0.63 | 6.32 | 12537 |
| 10 | 20.19 | 53.98 | 30.58 | 0.70 | 7.04 | 13045 |
| Mean | 19.85 ± 1.82 | 53.07 ± 4.88 | 30.07 ± 2.77 | 0.82 ± 0.24 | 8.15 ± 2.41 | 15372.10 ± 4277.46 |
| Group V | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 13.03 | 34.84 | 19.74 | 0.53 | 5.30 | 15218 |
| 2 | 14.65 | 39.17 | 22.19 | 0.61 | 6.13 | 15654 |
| 3 | 16.31 | 43.61 | 24.70 | 6.26 | 14359 | |
| 4 | 17.66 | 47.22 | 26.75 | 0.62 | 6.21 | 13155 |
| 5 | 16.53 | 44.20 | 25.04 | 0.56 | 5.61 | 12694 |
| 6 | 18.11 | 48.42 | 27.43 | 0.64 | 6.36 | 13139 |
| 7 | 15.73 | 42.06 | 23.83 | 0.69 | 6.89 | 16387 |
| 8 | 17.86 | 47.75 | 27.05 | 0.64 | 6.36 | 13323 |
| 9 | 20.33 | 54.36 | 30.79 | 0.74 | 7.40 | 13617 |
| 10 | 15.63 | 41.79 | 23.67 | 0.73 | 7.33 | 17544 |
| Mean | 16.58 ± 2.03 | 44.34 ± 5.44 | 25.12 ± 3.08 | 0.64 ± 0.07 | 6.39 ± 0.67 | 14509.00 ± 1625.53 |
| Group VI | ||||||
|---|---|---|---|---|---|---|
| Sample no. | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
| 1 | 26.77 | 71.58 | 40.55 | 1.00 | 10.03 | 14011 |
| 2 | 29.44 | 78.72 | 44.59 | 1.10 | 10.97 | 13940 |
| 3 | 32.34 | 86.47 | 48.98 | 1.00 | 9.97 | 11531 |
| 4 | 30.17 | 80.67 | 45.70 | 1.00 | 9.97 | 12361 |
| 5 | 29.1 | 77.81 | 44.08 | 1.05 | 10.47 | 13459 |
| 6 | 28.36 | 75.83 | 42.96 | 1.20 | 11.98 | 15792 |
| 7 | 27.42 | 73.32 | 41.53 | 1.20 | 12.05 | 16434 |
| 8 | 28.68 | 76.68 | 43.44 | 1.07 | 10.74 | 14004 |
| 9 | 26.96 | 72.09 | 40.84 | 1.10 | 11.05 | 15328 |
| 10 | 27.91 | 74.63 | 42.27 | 1.15 | 11.50 | 15409 |
| Mean | 28.72 ± 1.68 | 76.78 ± 4.48 | 43.49 ± 2.54 | 1.09 ± 0.08 | 10.87 ± 0.79 | 14226.90 ± 1543.75 |
| Group | Ca in solution (ppm) | WE in solution (ppm) | Calculated depth (μm) | Fluoride in solution (ppm) | Total fluoride content in solution (μg) | Calculated fluoride in tooth (ppm) |
|---|---|---|---|---|---|---|
| Group I | 25.50 ± 1.94 | 68.17 ± 5.19 | 38.62 ± 2.94 | 0.03 ± 0.01 | 0.27 ± 0.06 | 399.90 ± 112.86 |
| Group II | 19.66 ± 2.17 | 52.57 ± 5.79 | 29.78 ± 3.28 | 0.37 ± 0.09 | 3.37 ± 1.25 | 6546.82 ± 2659.15 |
| Group III | 18.84 ± 1.96 | 50.37 ± 5.24 | 28.53 ± 2.97 | 0.06 ± 0.02 | 0.56 ± 0.20 | 1141.00 ± 480.28 |
| Group IV | 19.85 ± 1.82 | 53.07 ± 4.88 | 30.07 ± 2.77 | 0.82 ± 0.24 | 8.15 ± 2.41 | 15372.10 ± 4277.46 |
| Group V | 16.58 ± 2.03 | 44.34 ± 5.44 | 25.12 ± 3.08 | 0.64 ± 0.07 | 6.39 ± 0.67 | 14509.00 ± 1625.53 |
| Group VI | 28.72 ± 1.68 | 76.78 ± 4.48 | 43.49 ± 2.54 | 1.09 ± 0.08 | 10.87 ± 0.79 | 14226.90 ± 1543.75 |
Also, there was statistically significant difference between WE of groups II, III, and IV (52.57 ± 5.79 ppm, 50.37 ± 5.24 ppm, and 53.07 ± 4.88 ppm, respectively) and group V (44.34 ± 5.44 ppm); group V reported more acid resistance than other groups. These findings are in agreement with Tagomori and Morioka,42 Kakade et al.,17 and Flatiz et al.43
An interesting finding was seen when WE of group VI (76.78 ± 4.48 ppm) was compared with WE of all other groups. There was a significant difference between WE of group VI and all other groups suggesting that the acid resistance of enamel slabs had decreased after exposure to a low-power laser system through topically applied fluoride solution. Meurman et al.19 showed that phase transformation of hydroxyapatite into fluorapatite is possible when a CO2 laser was used with the threshold energy density of 38 J/cm2 through topically applied sodium fluoride solution.
A possible explanation for decreased acid resistance after lasing through applied fluoride solution in the present study can be attributed to the use of insufficient power of the laser. Due to presence of the water content of 1.23% APF solution on the tooth enamel slab, the low-power laser failed to raise the surface temperature adequately and may have led to increased permeability of the enamel rendering it less resistant to acid attack. The heat generated by exposure to the CO2 laser may have been dissipated in the applied solution itself rendering increased activity of H+ and F− ions in solution that has led to dissolution of apatite crystals and formation of soluble calcium fluoride-like deposits.
Fig. 5: Comparison of mean fluoride content of the teeth in different groups
Fig. 6: Tooth being checked for surface cracks, white spots, or mottling using contrast light
Fig. 7: Preparation of enamel slabs
Fig. 8: Enamel slabs mounted in acrylic resin
Fig. 9: Samples prepared for fluoride analysis and wet chemical analysis
Moreover, formation of calcium phosphate and conversion of hydroxyapatite to fluorapatite or fluorohydroxytapatite are spontaneous reactions and are exothermic in nature. But conversion of fluorapatite to calcium fluoride and calcium phosphate is an endothermic reaction. Heat generated after CO2 laser treatment through applied 1.23% APF solution might have been used for conversion of fluorapatite to calcium fluoride and calcium phosphate with resultant decrease in acid resistance. There was marked increase in uptake of fluoride in group II tooth enamel slabs, difference being statistically significant. These findings are in agreement with Mellberg32 and Mellberg and Loertscher.33 The fluoride content of group III enamel slab was 1141.00 ± 480.28 ppm while that of the control group was 399.90 ± 112.86 ppm. There has been an increase in the fluoride content of the surface enamel suggesting redistribution of fluoride that was already present in the human tooth enamel slabs.
There has been an overall increase in fluoride uptake of group IV, group V, and group VI (15372.10 ± 4277.46 ppm, 14509.00 ± 1625.53 ppm, and 14226.90 ± 1543.75 ppm, respectively) human tooth enamel slabs as compared to the control group (399.90 ± 112.86 ppm) human tooth enamel slabs, difference being statistically highly significant. This suggests that there is definite increase in fluoride uptake of human tooth enamel after treatment with a CO2 laser. Other authors who have reported increased fluoride uptake after laser treatment are Tepper et al.11 and Tagomori and Morioka.42 However, Hattab35 did not notice any significant difference in fluoride uptake by lased and unlased human tooth enamel. The observed difference might be attributed to the use of an argon laser by the author that has poor absorption in the human tooth enamel.
Observed increase in fluoride uptake of the tooth enamel after lasing with a CO2 laser through topically applied fluoride solution in the present study is in accordance with Meurman et al.19 and Tepper et al.11 But the resultant decrease in acid resistance of group VI human tooth enamel slabs in the present study suggests that increased fluoride uptake may not be necessarily associated with increased acid resistance. As per findings of Sterns and Berndt,44 reliance on fluoride uptake data alone in considering the reaction of human apatite with 1.23% APF solutions can lead to false or misleading conclusions. Often high fluoride uptake data are interpreted as indicating a high conversion of fluorapatite, whereas they could indicate considerable destruction of the apatite to calcium fluoride. Occurrence of this phenomenon in group VI human tooth enamel slabs of the present study can be possible considering the decrease in their acid resistance.
CONCLUSION
The present study concludes that a low-power CO2 laser can be used effectively in combination with topically applied 1.23% APF solution in order to make enamel more resistant to acid attack, thereby helping in controlling dental caries process. However, clinical safety of the CO2 laser in caries prevention is yet to be proven. Also, “does the same amount of acid resistance is obtained after the combination of CO2 laser and topically applied fluoride in oral cavity?” is yet to be determined.
ACKNOWLEDGMENTS
We would sincerely like to thank Prof Dhanesh Manik, Department of Mechanical Engineering, IIT, Powai; Mr Arijit Laik, Department of Material Science Division, Bhabha Atomic Research Centre, Trombay; and Mrs Shilpa, Earth and Science Department, in providing insight and expertise that greatly assisted our research study.
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