Brazilian Journal of Oral Sciences Piracicaba Dental School - UNICAMP EISSN: 1677-3225 Vol. 9, Num. 1, 2010, pp. 20-24

Braz J Oral Sci, Vol. 9, No. 1, January-March, 2010, pp. 20-24

Original Article

Erosive effect of an antihistamine liquid formulation on bovine teeth: Influence of exposure time

Viviane Santos da Silva Pierro¹, Beatriz Romeiro Furtado², Michele Villardi³, Lúcio Mendes Cabral⁴, Eduardo Moreira Silva⁵, Lucianne Cople Maia⁶

¹ DDS, MS, Graduate student, Department of Pediatric Dentistry and Orthodontics, Dental School, Federal University of Rio de Janeiro, Brazil
² DDS, Undergraduate student, Department of Pediatric Dentistry and Orthodontics, Dental School, Federal University of Rio de Janeiro, Brazil
³ DDS, Undergraduate student, Department of Medicaments, Pharmacy School, Federal University of Rio de Janeiro, Brazil
⁴ MSc, PhD, Pharmacist, Associate Professor, Department of Medicaments, Pharmacy School, Federal University of Rio de Janeiro, Brazil
⁵ DDS, MS, PhD, Associate Professor, Department of Restorative Dentistry, Dental School, Federal Fluminense University, Brazil
⁶ DDS, MS, PhD, Associate professor, Department of Pediatric Dentistry and Orthodontics, School of Dentistry, Federal University of Rio de Janeiro, Brazil

Correspondence Address: Lucianne Cople Maia, Rua Gastão Gonçalves, 47/501 - Santa Rosa, 24.240-030 - Niterói, RJ Brazil, rorefa@terra.com.br

Date of Submission: 13-Oct-2009
Date of Acceptance: 25-Mar-2010

Code Number: os10005

Abstract

Keywords: tooth erosion, pharmaceutical preparations, hydrogen-ion concentration, child

Introduction

Dental erosion is the irreversible loss of dental hard tissue due to a chemical process of acid dissolution that does not involve bacterial plaque acid, and is not directly associated with mechanical or traumatic factors ^[1] . The etiology of erosion is related to different behavioral, biological and chemical factors and it can have extrinsic or intrinsic causes. Extrinsic erosion is the result of exogenous acids, and dietary acids are, undoubtedly, its main causative factors. The most frequently consumed potentially damaging beverages are fruit juices and soft drinks ^[2] . However, several cases of tooth erosion have been attributed to oral administration of medicines ^[3] .

Medicines usually have low endogenous pH, high titratable acidity, and absence or low concentrations of ions including those of calcium, fluoride, and phosphate in their composition. The risk of dental erosion is increased when medications are used for treatment of chronic diseases with a high frequency of ingestion (two or more times per day), at bedtime, or when they have side effects such as reduction of salivary flow rate, which happens with antihistamines ^[4],[5],[6] .

Although the contact of a solution with the teeth during intake is usually not as long as when the liquid is rinsed ^[3] , at least one of the daily medication doses are designated to be given at bedtime. Additionally, liquid medicines usually take a longer time to clear from the mouth compared to tablets and capsules ^[7] .

The pH of liquid oral medicines may be formulated to optimize efficacy and patient acceptability. The solubility of weak acids and bases is pH dependent, and acidic preparations are often necessary for drug dispersion. Additionally, these acidic medicines often taste pleasanter, which may enhance patient compliance, especially children ^[8] .

Previous studies have already pointed out the erosive potential of liquid medicines or soluble tablets ^{[4],[5],[8],[9],[10],[11],[12]} , but few of them evaluated the effect of oral medication on tooth surface ^{[4],[9],[10],[12]} , and only one study investigated the effect of exposure time on the development of dental erosion ^[9] . Therefore, this study aimed to evaluate, in vitro, the effect of an oral antihistamine liquid formulation on roughness and topography of bovine enamel and the influence of exposure time on its erosive effect, if any.

Material and Methods

Medicine selection, pH analysis, titratable acidity and mineral content of the tested media

The most widely distributed antihistamine liquid formulation (Histamin^® , Neo Quimica, Anapolis, GO, Brazil) by the pharmacies of public Pediatric Hospitals and other Healthcare Services in the city of Rio de Janeiro, Brazil, was chosen for this study because of its possible impact on the oral health of children who usually seek for medical assistance at these facilities. Negative (distilled water) and positive (0.6% citric acid) controls were also tested.

All the 3 tested media were analyzed in triplicate with regard to pH, titratable acidity, calcium, phosphate and fluoride contents. The pH was measured with a calibrated pH meter (Quimis Q-400MT, Diadema, SP, Brazil), which was also used to determine titratable acidity by adding increasing quantities of 0.1 N sodium hydroxide (NaOH) solution to 25 mL of the medicine and controls, followed by agitation and equilibration (2 min) for further pH measurements. A correction factor of 0.95 was obtained by factorizing 0.1 N NaOH solution with potassium biphthalate standard. The total volume of 0.1 N NaOH solution required to neutralize medicines and controls (raise their pH to 7.0) multiplied by the correction factor of 0.95 corresponded to the titratable acidity value. All the media were used in an undiluted form.

Phosphate and fluoride contents of the antihistamine formulation and controls were analyzed by ion chromatography ^[13] , while calcium content was determined by flame atomic absorption spectrophotometry ^[14] .

Preparation of bovine enamel specimens

Forty-one enamel blocks (3 x 3 x 3 mm) were prepared from bovine incisors stored in a 2% formaldehyde solution (pH 7.0) at room temperature. Crowns were sectioned from the roots and enamel blocks were obtained with water-cooled diamond double-faced disk at low-speed.

All enamel blocks were then embedded in acrylic resin using PVC rings as moulds with the labial surfaces facing toward the ring base. After resin acrylic polymerization, the labial enamel of samples were wet ground using 600, 800 and 1200-grit abrasive discs (3M, Sumare, Brazil) for 10 min each and polished using felt discs (Arotec Ind.& Com. Ltda; Sao Paulo, Brazil) and 1 and 0.3 μm aluminum oxide suspension (South Bay Technology Inc.; San Clemente, USA) in a water-cooled grinding machine (Panambra DPU-10, Struers; Copenhagen, Denmark) to produce a flat surface.

After the polishing procedure, samples were cleaned with an ultrasonic device and viewed under an optical microscope (Aus Jena, model 444181, with a 40 objective; Astro Optics Division, Montpelier, USA) in order to confirm that the surfaces were flat, polished, and free of irregularities that could interfere with roughness evaluation.

Red nail polish (two coats, 24 h drying) was then placed over the enamel blocks, except for a 0.8 mm ² window of exposed enamel.

Treatment groups

Thirty-nine specimens were randomly divided into three treatment groups, as follows: antihistamine liquid formulation (Histamin^® , Neo Quimica, Anapolis, GO, Brazil), 0.6% citric acid (Crystal Pharm, Niteroi, RJ, Brazil) - positive control, and distilled water - negative control. The specimens were immersed in 100 mL of each solution for 5, 15, and 30 min at 37 ^° C and maintained upon agitation during the experiment.

Two additional specimens were set aside and kept in humid environment at 37°C to represent baseline on further SEM analysis.

Roughness Evaluation

All measurements of enamel loss were made using a surface roughness tester (Surftest SJ 201, Mitutoyo Co., Kawasaki, Japan) to determine surface roughness (R _a - μm) due to media exposure.

Before roughness measurements, all specimens were ultrasonicated both at baseline and after the experimental periods. Three roughness measurements spaced at 60° were recorded for each specimen (cut-off length of 0.25 mm) at baseline and after each treatment period (5, 15 and 30 min). Therefore, a mean roughness value was obtained for each sample according to treatment and exposure time (n=9), for both experimental and control groups.

Scanning Electronic Microscopy (SEM) Analysis

SEM analysis was performed to assess the topography of enamel surface at baseline and after each treatment period for the three tested media. Two enamel specimens from each treatment group according to exposure time were prepared for SEM analysis. The two specimens were mounted on aluminum stubs, fully-dried, sputter-coated with a thin layer of gold-palladium and examined with a JEOL JSM-35 scanning electronic microscope (Tokyo, Japan) with an acceleration voltage of 15kV. SEM micrographs were made at 500x and 2000x magnification.

Statistical Analysis

Statistical analysis was performed using SPSS software version 11.0 (SPSS Inc., Chicago, USA). After verifying that the roughness data presented a non-normal distribution for all treatment groups, Kruskal-Wallis test was used for comparison among the three treatment groups, and then the Mann-Whitney test using Bonferroni correction ((=.017) was employed for group comparisons.

Results

The chemical parameters of the media tested in the present study are shown in [Table - 1].

The results of surface roughness are shown in [Figure - 1] and [Table - 2]. Kruskal-Wallis test detected significant difference for media (P<0.001). Mann-Whitney test with Bonferroni correction showed that specimens immersed in citric acid presented the highest roughness values (P<.001) at all time periods, followed by the antihistamine liquid formulation and distilled water, without significance between them after the 5-min (P=.66), 15-min (P=.60) and 30-min (P=.66) exposures.

Qualitative analysis of SEM micrographs showed that specimens immersed in citric acid presented the most severe erosion pattern with time [Figure - 2], followed by those immersed in antihistamine liquid formulation [Figure - 3]. It seemed that specimens immersed in water did not suffer erosion irrespective of exposure time [Figure - 4].

Discussion

Erosive damage to the permanent teeth in early childhood may compromise the dentition for the child′s entire lifetime and this will certainly require expensive dental treatments in adult life ^[15] . However, individual susceptibility should be taken into account due to structural variations in enamel. Bovine teeth were used in the present study based on a morphological investigation on progression of enamel erosion, and it has been shown that the surface ultrastructure of erosive lesions in prismatic human enamel did not differ from that observed in bovine tooth specimens ^[16] .

Previous in vitro studies have already shown that oral medicines could be related to dental erosion ^{[4],[5],[8],[9],[10],[11],[12]} . Additionally, Johansson et al.17, in an in vivo investigation with Saudi children, pointed out that high intake of acidic drinks and fruits, upper respiratory tract problems and frequent medications may constitute possible etiological and/or aggravating factors for severe dental erosion.

The medicine selected for this study is an antihistamine liquid formulation extensively handled in public Pediatric Hospitals and Healthcare Services of Rio de Janeiro city and, therefore, consumed by a significant number of children that do not have access to private medical assistance. This antihistamine liquid formulation, like others, is most commonly used for treatment of respiratory allergies, which are usually present as a chronic health problem. As this medication is used chronically by allergic children, it is important to study its chemical properties to verify their role in children′s dental health.

Factors mostly related with the ingested substances per se could modify erosion patterns. pH and dissociation constants of the acids allied to the general chemical composition of the solutions may modify the degree of enamel dissolution ^[16] . In the present study, the specimens immersed in citric acid (positive control), presented remarkable changes in enamel surfaces than those immersed in antihistamine liquid formulation and distilled water [Figure - 2],[Figure - 3] and [Figure - 4]. At a first glance, this finding could be related to the low pH of this acid [Table - 1]. However, it is well-known that the pH gives only the initial concentration of H+ ions, and does not represent the presence of undissociated acid in the medium ^{[15],[18],[19],[20]} . Valinoti et al.[21] using two acidic medicines with pH close to the same value (Claritin/antihistamine - 2.57 and Dimetapp/elixir - 2.51) showed, under SEM, that Claritin/antihistamine caused more surface alterations on some resin-based composites. According to these authors, the dissimilar results of these medicines were due to the differences in the titratable acidity between the medicines, 41.83 and 36.31 mL NaOH, respectively. Based on this, it is clear that the higher titratable acidity of citric acid in the present study have contributed more than pH to the changes produced in the enamel surfaces. In fact, titratable acidity can be claimed as a more accurate measure of the total acid content present in substances, and calcium-chelating properties may greatly enhance the erosive potential of beverages ^{[15],[18],[19],[20]} . The studied antihistamine liquid formulation presented a pH slightly lower than distilled water, but it showed higher buffering capacity and ability to resist pH changes than distilled water because of its amount of neutralizing agent was tenfold greater than that of water. This probably explains the different patterns of erosion found in SEM images, that is, eroded areas were present in antihistamine (pH 5.1; 1.6 mL NaOH) treated enamel specimens, while no erosive pattern was verified in the samples treated with distilled water (pH 5.6; 0.1 mL NaOH).

Ions like calcium, phosphate and fluoride have a protective effect against erosion ^[15] . However, despite the presence of fluoride and calcium in the antihistamine liquid formulation, and of fluoride, calcium and phosphate in citric acid [Table - 1], their ionic concentrations were not high enough to prevent the erosive effect viewed in the enamel surfaces [Figure - 2] and [Figure - 3] on teeth treated with those substances. Here, again, it seems obvious that the high titratable acidity overcame the probable positive effects of ions F ^3- , Ca ⁺⁺ and PO4 ^3- on preventing enamel erosion.

The etiology of dental erosion can also be influenced by biological and behavioral factors, unusual eating, drinking and swallowing habits, for example holding an acid beverage in the mouth before swallowing, increase the contact time of an acid substance with the teeth and thus increase the risk of erosion ^[15] . Furthermore, it should be emphasized that some oral medicines are usually given at bedtime without subsequent toothbrushing or water rinse, and oral clearance is usually also compromised during sleep. Therefore, it seems reasonable to evaluate how exposure time could influence erosive dental patterns. The choice for 5-, 15- and 30-min exposure times were intentionally proposed because they seem to be less aggressive than the time intervals proposed by Babu et al.^[9]. On this matter, the SEM results of the present study differed from those of Babu et al.[9] because our images showed that severity of erosion′s increased with exposure time for both the positive control and the tested antihistamine liquid formulation, while those authors found more severe lesions after a 10-min than an 8-hour immersion period. This could probably be explained by the great difference between these time periods, which could have been enough to promote saturation of the liquid medium.

Quantitative methods are usually employed for determination of erosion severity along with SEM evaluation ^[15],[22] and roughness analysis has already been used to evaluate the effect of acidic medicines, under pH-cycling conditions, on the surface degradation of composite resins ^[21] . However, in this study, roughness measurement was not sensitive enough to detect the alterations shown by SEM analysis in enamel immersed in antihistamine liquid formulation. This was a limitation of the present study with regard to the quantification of mineral loss. Further studies would benefit from combining SEM evaluation with techniques that enable ultrastructural mineral loss quantification.

The difficulty in reproducing the clinical situation in in vitro studies must be borne in mind. This is due to complexity of the oral environment. The absence of salivary pellicle and buffering by saliva may overestimate the in vivo occurrence of erosive demineralization ^[4] . However, antihistamine-containing medicines are known to reduce salivary secretion and it is important to alert for their erosive potential even, based mainly on in vitro studies ^[5] . In the present study, enamel specimens treated with the antihistamine liquid formulation showed erosion in SEM images when compared to distilled water, and their erosive pattern increased with increasing exposure time. Further studies testing low-pH antihistamine liquid formulations should be encouraged because allergic children make regular use of these medicines and could present dental erosion as an undesirable effect of oral medication.

Based on the experimental conditions of this study, the following conclusions can be made: among the tested media, only 0.6% citric acid produced a significant increase in enamel roughness. The SEM analysis showed that antihistamine liquid formulation and 0.6% citric acid were capable of producing erosion in enamel and was influenced by exposure time.

Acknowledgements

The authors are grateful to Prof. Paulo Barrocas and Leticia Alves da Silva for their support in the phosphate and fluoride content analysis at ENSP/FIOCRUZ (Escola Nacional de Saude Publica/Fundaqao Oswaldo Cruz). The authors also would like to thank CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico) for the research grant (302382/2009-7), and FAPERJ (Fundaqao Carlos Chagas de Amparo a Pesquisa do Estado do Rio e Janeiro) (E-26/ 110.486/2010) for the financial support.

References

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