INTRODUCTION:

In the modern era, bleaching has gained a lot of popularity because of increased demand for beautiful teeth and smile in the community. It is also one of the most popular dental procedures amongst the general population¹ .Home applied carbamide peroxide bleaching agents are generally indicated for night time use for 6-8 hrs². Studies have indicated discolouration of teeth due to acids^3,4.

A typical oral hygiene pattern is to remove the tray and use a dentrifice for brushing the teeth which may be abrasive. The bleaching agent will be washed away during brushing. If the bleaching agents penetrate the hard tissues, it could result in various changes to these vital teeth. To improve the remineralization of enamel after exposing the teeth to carbamide peroxide bleaching agents, Attin et al. recommended the application of fluoride varnish or mouthwash which acts by enhancing the quality of enamel as in erosive lesions^5,6. Application of fluoride after bleaching also helps prevent formation and progression of dental caries as a part of preventive modality protocol of minimal invasive dentistry^7,8,9.

Bleaching solutions of 10% carbamide peroxide have become the standard agent used in dentist-prescribed, home-applied, vital bleaching techniques¹⁰. These materials release hydrogen peroxide, the active whitening agent. Much concern has been expressed by the American Dental Association and the United States Food and Drug Administration (FDA) regarding the safety of carbamide peroxide and other bleaching agents used in home whitening and self-applied bleaching systems. The FDA initially limited its use until safety and efficacy were established. Although this decision was later rescinded, concerns about the safety of the materials remain^11,12.

This prohibition includes carbamide peroxide, zinc peroxide, and any other agent which releases H2O2, in concentrations greater than 0.1%. The bleaching agents are prohibited due to mutagenic and carcinogenic potential4. The prohibition does not apply to whitening agents applied by dentists in their office or agents used to treat non-vital teeth via endodontic preparations. Many of the dentists feel that the widespread use of hydrogen peroxide as a mouthwash and oral rinse, a practice carried out earlier from the 1850s, provides sufficient evidence of safety^10,11. Others feel the benefits of use outweigh the potential risks. More research examining the effects of bleaching agents on hard and soft tissues is required^13,14.

According to a survey by the Clinical Research Associates (CRA), at-home carbamide peroxide bleaching is recommended by 62% of the dentists. The organic content could play a major role in the bleaching process, although the dental hard tissues are highly mineralized¹⁵.

Therefore, the present study attempted to evaluate changes in enamel surface roughness after bleaching and brushing at three times intervals and storing the specimens in artificial saliva during the study period.

MATERIAL AND METHODS:

Ninety extracted human permanent pre molars were collected for the study. They were stored in 0.5% chloramine T solution until use. The teeth were disinfected according to OSHA regulations. Intact pre-molars without caries were included in the study. Fractured teeth, teeth with cracks and restored teeth were excluded from the study.

The roots were cut at the cemento-enamel junction, subsequent to cleaning the teeth.2mm thick enamel slabs measuring 6x4mm were prepared from the middle third of buccal and lingual aspects with the use of double sided diamond discs. One hundred eighty enamel slabs were prepared from ninety permanent extracted human pre molars. The specimens were stored under distilled water at 37ᵒC after cutting and then placed with the enamel surface on top, inside cold cure acrylic resin in a cylindrical mould with a diameter of 1.5cm. The enamel was smoothened, finished and polished with the help of a hand piece under water spray. The specimens were placed on an ultra sonic device containing distilled water for 10 minutes to remove the polish debris.

Furthermore the enamel slabs randomly were divided into 3 groups (n=60) based on 3 percentages of carbamide peroxide- 15%, 25%, 35%. Every group was divided further into 3 subgroups (n=20) - A, B, C. The subgroup A served as control wherein no tooth brushing was done after bleaching, subgroup B wherein the teeth were immediately brushed after bleaching and subgroup C wherein the teeth were brushed 1 hour after bleaching.

The initial surface roughness was evaluated using Stylus Profilometer. Three traces were made and the main reference value was achieved on each slab and statistically analyzed. After the initial surface roughness was measured, bleaching process was instituted. Then the specimens were stored in artificial saliva. The bleaching, brushing and rinsing procedures were continued for 21 days in all the groups. At the end of this period the surface roughness values of the specimens were measured again. After storage, the specimens were transfered to the Stylus Profilometer individually and then subjected to surface roughness evaluation.

The statistical analysis was performed with a non parametric Kruskal-Wallis test and non parametric Mann Whitney U test.

RESULTS:

In control group (subgroup A): The mean change in surface roughness values in Group1, 2 and 3 was found to be 0.1395, 0.0995,0.0655 respectively. P value is <0.001. The Kruskal wallis test and Man whitney U test showed that there the control group did not significantly differ from each other.

Group 1: The surface roughness value in subgroup A was 0.477 in Subgroup B it was 0.632 and in Subgroup C it was 0.327 i.e. Subgroup B > Subgroup A > Subgroup C. P value is <0.001. Kruskal wallis test and Man whitney U test did not show much significant difference with each other. Subgroup C showed the least surface roughness.

Group 2: The surface roughness value in subgroup A was 0.558 in subgroup B it was 0.779 and in subgroup C it was 0.324 i.e subgroup B> subgroup A > C. P value is <0.001. Kruskal wallis test and Man whitney U test did not show much significant difference with each other. Subgroup C showed the least surface roughness.

Group 3: The surface roughness value in subgroup A was 0.603 in subgroup B it was 0.849 in subgroup C it was 0.639 i.e.subgroup B>subgroup A > subgroup C. P value is < 0.001. Kruskal wallis test and Man whitney U test showed significant differences with each other. Here subgroup A showed the least surface roughness.

Analysis by Mann Whitney U test was done to compare the surface roughness values between the

Groups (1, 2 and 3). Therefore 15% carbamide peroxide was found to be better and safer than 20% and 35% carbamide peroxide.

Graph I: The linear and bar graphs of the mean differences in the enamel surface roughness values before and after intervention in Group I.

Graph II : The linear and bar graphs of the mean differences in the enamel surface roughness values before and after intervention in Group 2.

Graph III: The linear and bar graphs of the mean differences in the enamel surface roughness values before and after intervention in Group 3.

Table I: The significance in the enamel surface roughness values before and after intervention

Multiple comparisons

Bonferroni : Change

		P
gp 1-A	gp 1-B	p < 0.001	HS
	gp 1-C	p < 0.001	HS
	gp 2-A	0.002	HS
	gp 2-B	p < 0.001	HS
	gp 2-C	1.000
	gp 3-A	p < 0.001	HS
	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 1-B	gp 1-C	p < 0.001	HS
	gp 2-A	p < 0.001	HS
	gp 2-B	p < 0.001	HS
	gp 2-C	p < 0.001	HS
	gp 3-A	p < 0.001	HS
	gp 3-B	p < 0.001	HS
	gp 3-C	1.000
gp 1-C	gp 2-A	p < 0.001	HS
	gp 2-B	p < 0.001	HS
	gp 2-C	0.020	Sig
	gp 3-A	p < 0.001	HS
	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 2-A	gp 2-B	p < 0.001	HS
	gp 2-C	p < 0.001	HS
	gp 3-A	0.024	sig
	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 2-B	gp 2-C	p < 0.001	HS
	gp 3-A	p < 0.001	HS
	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 2-C	gp 3-A	p < 0.001	HS
	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 3-A	gp 3-B	p < 0.001	HS
	gp 3-C	p < 0.001	HS
gp 3-B	gp 3-C	p < 0.001	HS

DISCUSSION:

The present in-vitro study attempted to simulate a clinical course of at-home bleaching procedures as exactly as possible. The procedure was carried out for 21 days, 6 hours every day, with 15%, 20% and 35% carbamide peroxide. This was followed by daily routine tooth brushing which was carried out with a low-abrasive fluoridated toothpaste suggested by the manufacturer followed after by each daily bleaching procedure. During the bleaching period, artificial saliva was used to store the specimens to simulate the physiologic conditions of the oral cavity.

According to the results obtained in the present study, the group which demonstrated a significant increase in surface roughness following bleaching in comparison with the control group was Subgroup B(brushing immediately after bleaching) — in other words, delaying of brushing the tooth for one or two hours daily after bleaching procedures and the specimens stored in artificial saliva during the waiting period led to surface roughness values comparable to those in the control group.

Bleaching agents may exert negative influences on the integrity of the organic structures of the tooth, including proteins and collagen¹⁶. Urea and hydrogen peroxide are the by-products of carbamide peroxide breakdown. Urea could denature tooth structure proteins by getting penetrated the enamel structure and influencing prismatic and the interprismatic structure and also by increasing the permeability and ultrastructural changes. This process results in pore formation and can increase the diameter of the pores of enamel and dentin surface. On the other hand, free oxygen present in hydrogen peroxide increases the surface porosity and reacts with the organic structure of dental tissues. Increase in surface porosity facilitates the movement of oxygen radicals beyond the enamel and dentin and also the breakdown of stained larger molecules into light-coloured micro molecules.^17,18

The present study tried to simulate clinical conditions. In-between and after the bleaching treatments, artificial saliva was used to store the teeth. The oral environment provides conditions for enamel remineralization, and demineralization and enamel are more susceptible to remineralization¹⁹. In most of the studies on bleaching, the specimens have been stored in remineralizing solutions containing phosphate and calcium with concentrations similar to that of human saliva^20,21. According to some studies, artificial saliva can mimic oral saliva in vitro and play a role in remineralization^22,23. According to the results of the present study, if the teeth have the opportunity to be in contact with artificial saliva before toothbrushing and after bleaching, the surface roughness values would be comparable to that of the control group. It is to be likely that precipitation of the minerals present in artificial saliva on tooth surfaces could play a vital role in declining surface roughness of the bleached enamel, however, further studies are required to determine the effect of various other storage environments, such as artificial saliva and plain water, on changes in surface roughness of bleached enamel^24-29. In the present study, the specimens were stored in artificial saliva one or two hours before tooth brushing, which did not result in significant differences.

Considering the methodology applied, the results of the present study indicated that regardless of whether or not the enamel had been exposed to bleaching agent for home use with 15% 20% 35% carbamide peroxide, the performance observed in the different brushing subgroups resulted in different Ra values. In the present study, the enamel slabs were smoothened and polished to allow for standardized profilometric measurements along with the flat reference surfaces. Considering that specimen preparation process in the surface roughness tests could have influenced the results, it may not be completely possible to extrapolate the conclusions of in vitro studies to the clinical setting.

The results from the present study indicates that an increase in the concentration of the bleaching agent increased the surface roughness as well as delaying tooth brushing after bleaching resulted in a reduction of the surface roughness.

CONCLUSION:

Treatment modalities for discoloured teeth varies depending upon the extrinsic and intrinsic cause of staining³⁰. Although veneers and laminates provide a long term solution and are the chosen treatment options, they do have disadvantages such as high cost, inability to be used in misaligned cases and polymerization shrinkage with composite veneers which limits its use; due to which bleaching is the most sought after option for management discoloured teeth as well as a part of cosmetic dentistry.³¹

Within the limitations of the presented study, it can be concluded that lower concentrations of carbamide peroxide are generally safer and do not produce significant changes in the enamel surface roughness and delaying tooth brushing after 1 or 2 hours after bleaching can produce better results comparable to that of the control group. Among the different concentrations of bleaching agents available today, it is always better to use bleaching agents with lower concentrations and delaying the oral hygiene procedures after bleaching should always be considered to help achieve better results.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 04.09.2019 Modified on 09.10.2019

Research J. Pharm. and Tech 2020; 13(5): 2112-2116.

DOI: 10.5958/0974-360X.2020.00380.7