Effects of Fluoridated and Non- Fluoridated Bleaching Agents on Bovine Surface Enamel

In the modern era, aesthetic dentistry is becoming famous. The demand of tooth bleaching is increasing day by day and it has become the treatment of choice for tooth discoloration. If there is deposition of chromatogenic material into dentin and enamel during the tooth development stage or after eruption, it leads to intrinsic tooth discoloration [1]. Among various bleaching techniques for intrinsic tooth discoloration, vital and non-vital bleaching techniques are common one. They use oxidizing agents such as hydrogen peroxide to remove intrinsic stains. They are widely used agents as they have safe to use. These properties have made them popular. Further modifications in these agents have opened multiple options for dentists in managing tooth discoloration [2]. Carbamide peroxide (CP) is a perhydrol-urea and hydrogen peroxide carbamide compound which degrades to urea and hydrogen peroxide. This agent with ‘‘night guard’’ bleaching technique, have proved effective and efficient in providing good results. However, altered surface morphology, decreased microhardness and loss of dental hard tissue volume are among few side effects of bleaching as shown by various authors. 10% CP has been proved to decrease the enamel microhardness as compared to higher level [3]. However, a study performed by Potocnik et al. [4] found that 10% CP causes local microstructural changes and there is no affect on enamel microhardness. 10% CP is a safest bleaching agent as demineralization is not clinical evident, moreover, it is soon followed by remineralization. Fluoridated bleaching agents are considered to reduce the adverse effects of tooth whitening. Topical fluoride is used to increase the hardness and acid resistance of demineralized teeth. It may be used in tooth sensitivity peripherally by occluding the dentinal tubules and reducing dentinal fluid flow. Hence, fluoride application may be used for treating post-bleaching sensitivity [5]. The present study was conducted to assess the effects of bleaching agents with and without fluoride as well as the post-bleaching fluoridation on bovine surface enamel.


Introduction
In the modern era, aesthetic dentistry is becoming famous.
The demand of tooth bleaching is increasing day by day and it has become the treatment of choice for tooth discoloration. If there is deposition of chromatogenic material into dentin and enamel during the tooth development stage or after eruption, it leads to intrinsic tooth discoloration [1]. Among various bleaching techniques for intrinsic tooth discoloration, vital and non-vital bleaching techniques are common one. They use oxidizing agents such as hydrogen peroxide to remove intrinsic stains. They are widely used agents as they have safe to use. These properties have made them popular. Further modifications in these agents have opened multiple options for dentists in managing tooth discoloration [2]. Carbamide peroxide (CP) is a perhydrol-urea and hydrogen peroxide carbamide compound which degrades to urea and hydrogen peroxide. This agent with ''night guard'' bleaching technique, have proved effective and efficient in providing good results. However, altered surface morphology, decreased microhardness and loss of dental hard tissue volume are among few side effects of bleaching as shown by various authors. 10% CP has been proved to decrease the enamel microhardness as compared to higher level [3]. However, a study performed by Potocnik et al. [4] found that 10% CP causes local microstructural changes and there is no affect on enamel microhardness. 10% CP is a safest bleaching agent as demineralization is not clinical evident, moreover, it is soon followed by remineralization. Fluoridated bleaching agents are considered to reduce the adverse effects of tooth whitening. Topical fluoride is used to increase the hardness and acid resistance of demineralized teeth. It may be used in tooth sensitivity peripherally by occluding the dentinal tubules and reducing dentinal fluid flow.
Hence, fluoride application may be used for treating post-bleaching sensitivity [5]. The present study was conducted to assess the effects of bleaching agents with and without fluoride as well as the post-bleaching fluoridation on bovine surface enamel.

Materials & Methods
The present study was conducted in the department of Endodontics in year 2015. It included 60 non-carious anterior teeth specimens. The specimens were stored in buffered saline. These teeth were cut into halves using a slow speed rotary saw under water irrigation. After cutting teeth, specimens were embedded in epoxy resin with the labial surface parallel to the horizontal plane.
The enamel surfaces were then ground with 320-grit silicon carbide abrasive paper using a mechanical grinder to create a flat surface

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The specimens of group II, III, IV and V were bleached 8 h/day X 14 days. The bleaching agents were applied on the enamel and stored at 100% humidity at 37 degree C. Rinsing with tap water was done after application of bleaching agent to each specimen for 1 minute and was stored in HBSS at 37 degree C. The color change, microhardness and surface topography were evaluated after 14 days. The color of each specimen was measured as baseline data on Day 0. The color of each specimen was assessed by the CIE-Lab system in L a b mode using a dental colorimeter. The assessed area was the cervical area, 1 mm occlusal to the cemento-enamel junction. After the bleaching treatment, the specimens were again inspected on Days 7 and 14 to measure the color changes.
''L'' represents the degree of gray and corresponds to a value of brightness. The ''a'' is a parameter in the red-green spectrum and ''b'' is a parameter in the blue-yellow spectrum. The microhardness of the specimens used for color measurement was determined with a microhardness tester. Knoop hardness (KHN) was measured with a Knoop indenter three times at a load of 50g for 5s. Specimens from all groups were examined for the surface morphology change on Day 14. All specimens were thoroughly cleaned and air-dried in a desiccator for 24h. Following the desiccating procedure, the specimens were gold sputtered then observed under a SEM.   [10] in their study revealed that bovine teeth treated with CP followed by highdosed fluoridation increased the fluoride uptake even though the structurally bound fluoride was lower than that in teeth receiving fluoridation only. In our study, we compared surface morphology in all groups. Group I showed unchanged enamel surface on the unbleached specimen. Group II and III showed significant alteration with erosion appearance. Group IV and V showed less distinct surface morphologic changes. They demonstrated minor dissolution of the prism core and peripheries [11].

Conclusion
In all groups, whitening efficiency was similar with increase in whiteness and decrease in yellow color saturation. Fluoridated bleaching gel improves whitening efficiency and results in less demineralization changes such as the erosion morphology and hardness loss.