Comparative Evaluation of Erosive Potential of Different Pediatric Liquid Medications on Primary Tooth Enamel and Tooth Coloured Restorative Materials

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 dental erosion is complex and multifactorial, and it may be either extrinsic or intrinsic. Some intrinsic causes of dental erosion include recurrent vomiting in eating disorders such as bulimia, anorexia and gastric regurgitation due to gastrointestinal problems. Extrinsic sources include regular use of products with high titratable acidity, low endogenous pH, with low quantity of calcium, phosphate and fluoride ions.Among these products are acidic drinks and foods, and acidic medicines that come in direct contact with the teeth.²

Pediatric liquid analgesics are very commonly prescribed and are easily accepted by parents and children.³ Although the contact of solution with teeth during intake is shorter when compared to the liquid being rinsed, at least one of the daily medication doses are usually prescribed to be taken at bedtime. Also, the clearance time for liquid medicines from mouth is longer compared to tablets and capsules.¹ Since self-medication with over-the-counter medicines, especially non-steroidal anti-inflammatory drugs, has increased in recent times, and therefore there is an increased risk of dental erosion even in healthy children who take these medicines infrequently and for shorter periods.³

When the substance loss caused by erosive wear reaches a certain degree, restorative materials such as glass ionomer cements and composite resins can be used for restoring tooth structure, function and aesthetics.⁴ The durability of the material and its properties, such as surface roughness, wear resistance, integrity of the tooth-restoration interface and hardness determines the longevity of dental restorations.⁵ In the oral cavity, degradation of these restorative materials can occur due to low pH, water sorption, erosion, and wear, leading to increased surface roughness and wear rate.⁶ The surface roughness of a material is of considerable importance, as roughened surface may promote plaque accumulation and staining, thereby decreasing the longevity of restoration, and potentially increasing the risk of secondary caries.⁷

Even though previous published studies ^8,9,10 have reported pediatric liquid analgesics to be erosive, very limited knowledge on their effect on primary enamel and restorative materials is available. Therefore, the present in vitro study was conducted to evaluate the erosive potential of commonly prescribed pediatric liquid analgesics on primary enamel, and tooth coloured restorative materials and to compare their resistance to the erosion by these medications.

Materials And Methods

Selection of medications

The pediatric liquid medications chosen for this study are two commonly used NSAIDs: Calpol® ( Paracetamol) and Ibugesic® (Ibuprofen). The above medicines were selected on obtaining the data of commonly prescribed NSAIDs for children from paediatricians practicing in the area.

Measurement of pH and titratable acidity

Both the selected medications were analysed in triplicate with regard to pH and titratable acidity. The pH values were determined using a calibrated digital pH meter (HI-2215 pH Meter, Hanna Instruments, USA). After calibration, three samples of each freshly opened pediatric medications were analyzed and average of the three measurements was considered as the pH value. Titratable acidity was measured according to the method adopted by the Association of Official Analytical Chemists (1984),¹¹ that is, the amount of 0.1N Sodium hydroxide solution needed for the product to reach a neutral or basic pH.

Tooth selection and preparation of primary enamel specimens

The teeth selected for the study were nine recently exfoliated/extracted human primary second molars free of dental caries, restorations and hypoplasia which were stored in 0.1% thymol solution. When present, the roots were removed at the cemento-enamel junction and the crowns were sectioned longitudinally in a mesiodistal direction through the centre of the crown using watercooled low speed diamond cutter (Struers-Minitom, Denmark) and eighteen enamel blocks were prepared. The enamel blocks were then embedded in acrylic resin using PVC ring moulds with the buccal and lingual/ palatal surfaces facing toward the ring base. After acrylic resin polymerization, the enamel of samples were wet ground using 600, 800 and 1200-grit abrasive discs and polished with alumina slurry to produce an optically flat area. Polishing debris was then cleaned off the samples using deionized water. Each sample was then coated with two layers of acid-resistant nail varnish except for an exposed window (3×2mm).

Preparation of restorative material specimens

The restorative materials selected for the study were composite resin (3M ESPE FILTEK^TM Z250XT Nano Hybrid Universal restorative) and glass ionomer cement (GC Gold Label HS Posterior 9 Extra^TM).

Eighteen specimens from each of these two restorative materials were prepared. Each material was placed into a cylindrical plastic mould (5 mm diameter and 3 mm thickness) placed on a glass slab and was covered with polyester strip to remove the excess and standardize the finish of samples. Glass ionomer cement was mixed according to the manufacturer’s instructions and left to set under a polyester strip. Composite resin was placed into the mould in increments and light polymerized from the top through the polyester strip using LED unit (COXO DB-685 PENGUIN, Foshan COX Medical Instrument Co. Ltd, China) with an irradiance of 1200 m W/cm2 for 20 seconds as per manufacturer’s instructions. All the specimens were then coated with two layers of acid-resistant nail varnish exposing a window of 3×2 mm.

All the enamel, glass ionomer and composite resin specimens prepared were stored at 37ºC at 100% relative humidity for 7 days. The specimens were then immersed in artificial saliva for 24 hours at 37ºC to simulate clinical conditions before baseline surface roughness measurements. The artificial saliva used in the study was prepared in the laboratory as described by Gupta G et al (2011)¹² with a pH of 6.75.

Baseline surface roughness evaluation

Before the immersion cycling protocol, the surface topography of all specimens was analysed using a 3D optical profilometer (Veeco, Wyko NT 9100, Tucson, AZ, USA) to determine surface roughness (Ra). Ra value (µm) is the height parameter that represents the arithmetical mean of roughness of a surface. Three scan areas (233 µm × 311 µm) were obtained within the window for each specimen. Two linear measurements (one vertical and one horizontal) were performed in each scan area of the specimen and the average of these two linear measurements was used to determine Ra of that area. Mean of the three Ra measurements was recorded as the baseline surface roughness value for that specimen.

Immersion cycle protocol

Eighteen primary enamel, eighteen glass ionomer cement and eighteen composite resin specimens were randomly distributed according to immersion media into three groups (n=6) as follows: Group 1 – Calpol®, Group 2 – Ibugesic® and Group 3 – Artificial saliva (control).

The following immersion cycling protocol was followed to simulate the usual number of intakes of NSAIDs selected for this study: the specimens were immersed with the exposed area up for 1 minute in 10 ml of the medication, under stirring (30 rpm) using a magnetic stirrer 3 times daily with 6-hour intervals between immersion cycles, during 5 days. After each immersion cycle, specimens were washed with deionized water and maintained in artificial saliva at 37ºC until the next immersion cycle. Fresh medicines and artificial saliva were taken for each immersion. The control specimens were placed in artificial saliva during experiment and the solution was refreshed daily.

Post experimental surface roughness evaluation

After 5th day, all the specimens were cleaned using deionized water, gently blotted dry and the surface roughness was measured in the same way as baseline measurement. Figure 1 depicts the 3D profilometry scheme representation of the surfaces tested before and after immersion cycles.

Statistical analysis

The surface roughness values (Ra) obtained from the baseline and post immersion measurements of all the specimens in different immersion media were tabulated and subjected to statistical analysis using SPSS. Surface roughness measurements at baseline and after immersion cycle were compared using paired t-test. One-way analysis of variance was used to compare means of experimental and control group followed by Tukey’s post hoc analysis to determine differences between groups. P ≤0.05 was considered statistically significant. The tested null hypothesis was that exposure to pediatric liquid analgesics would not influence the surface roughness of primary enamel and tooth coloured restorative materials included in the study.

Results

pH and titratable acidity of pediatric liquid analgesics tested

The pH of Ibugesic® and Calpol® was 4.80 and 6.24 respectively. The titratable acidity (%) recorded was higher for Ibugesic® (1.15) when compared to Calpol® (0.28). The results indicated Ibugesic® to be more acidic when compared to Calpol®.

Baseline surface roughness values (Ra) of the tested surfaces

Of all the surfaces tested, the highest baseline mean surface roughness was observed for glass ionomer cement with a mean value of 0.19±0.07 (ranging between 0.11- 1.07µm) followed by enamel and composite with mean surface roughness values of 0.03±0.01 (ranging between 0.01-0.05µm) and 0.006±0.003 (ranging between 0.002- 0.01µm), respectively.

Post immersion surface roughness values

The post immersion surface roughness of the test materials is presented in Table 1. On comparison of test materials, it is observed that glass ionomer cement exhibits highest post immersion surface roughness followed by primary enamel and composite resin. A statistically significant difference was found between the surface roughness of glass ionomer when compared to primary enamel and composite. No significant difference was observed between the post immersion surface roughness values of composite resin and primary enamel.

Mean surface roughness of test materials in various immersion media (Intergroup comparison) (Table 2)

On comparison of mean surface roughness change of glass ionomer cement in various immersion media, highest mean change was noticed with Ibugesic®. On evaluation of mean change of surface roughness in composite group, Calpol® produced greater mean surface roughness change and in enamel group, greater surface roughness change was observed with Ibugesic®.

Discussion

Dental erosion involves chemical removal of superficial hard tissue from tooth by acids due to intrinsic factors such as eating disorders and gastric reflux and extrinsic factors such as dietary sources.⁴ Increasing use of pediatric liquid medications can be considered as one of the major extrinsic factor causing dental erosion in children. 

Several studies have attempted to investigate and establish the erosive potential of commonly used pediatric liquid medications. Many of these investigations were focused on analysing the erosive potential of medications such as antitussives,^2,10,13 antihistamines,^1,2 antiasthmatics^14,15 that are usually used in chronically ill children for a prolonged duration. However, other healthy children who take medicines infrequently and for shorter duration also could be at risk. Pediatric liquid analgesics are widely prescribed by pediatricians and pediatric dentists and forms one of the most common over-the-counter medications given to children.³ Even though they are used for shorter duration, it is essential to evaluate them considering their rampant use. Therefore, in this study, we attempted to evaluate the erosive potential of pediatric liquid analgesics and their effect on primary enamel, glass ionomer and composite resin restorations.

Two ways to quantify the acid content and erosive potential of any liquid or beverage includes titratable acidity and pH. In the present study, both the liquid analgesics showed pH values below 7 indicating their acidic nature. Ibugesic® demonstrated a lower pH compared to Calpol®. This is similar to the findings of Subramaniam P (2012)3 who demonstrated Ibugesic® to have lower pH (4.57) when compared to Calpol® (6.08). Ibugesic® even exhibited much higher titratable acidity than Calpol® indicating its higher erosive potential.

The increased risk of dental erosion with these medications highlights the need for understanding the phenomena of degradation of restorative materials and their effect on tooth surface. The materials tested in the study included conventional glass ionomer cement and composite resin as these are most commonly used restorative materials in pediatric dentistry. The restorative specimens were stored for 7 days before the baseline measurements and immersion cycle regimen, to allow post-irradiation hardening of composites and stabilization of the acid-base reaction of glass ionomer cements.¹⁶ The 24-hour storage period in artificial saliva was essential for the elution of unreacted components from the composites¹⁷ and to simulate oral conditions before baseline measurements.

It is common knowledge that, during consumption, food or drink only comes in brief contact with tooth surfaces before it is washed away by saliva.¹⁸ However, in previous studies, substrates usually contacted acidic medicines for a prolonged period of time^9,19 or did not account for the role of saliva.⁹ Therefore, the present study was designed to simulate the washing effect of saliva by cyclic specimen immersion protocol.

In the current study, the immersion cycle protocol used was based on the frequency of medication ingestion. The specimens were immersed for 1 minute in 10 ml of medication, under stirring, 3 times daily with 6-hour intervals between immersion cycles, for 5 days. Based on the observation that the pH of oral fluids returned to neutral in 1 to 3 minutes after one single sip of acidic beverage,20 the 1-minute exposure in each cycle was selected.

In the present study, surface roughness evaluation was chosen because it is well documented that surface micromorphology can play a role in bacterial colonization and maturation of plaque on tooth and restorative surfaces.²¹ Measurement of surface roughness was done using a 3D non-contact optical profilometer. The use of 3D optical profilometer is advantageous because it does not produce grooves on the sample surface and is sensitive²² and specific.²³ This method allows for quantification of tooth depth and its accuracy was compared to scanning electron microscopy.²⁴

Based on the results of the present study, when the baseline surface roughness values of glass ionomer, composite resin and primary enamel were compared, GIC showed highest surface roughness. The rough surface of GIC and lower homogeneity could be attributed to its composition with presence of glass particles. Furthermore, conventional glass ionomer cements are handled manually, which can create porosities due to the inclusion of visually imperceptible air bubbles.⁵ Following the exposure of the restorative materials and primary enamel to the immersion cycle regimen, highest post immersion surface roughness was observed in glass ionomer which showed statistically significant difference from the composite resin. This agrees with findings of Honorio et al (2008)⁴ , Carvalho et al (2012)⁶ , Francisconi et al (2008)¹⁸, Yu et al (2009)²⁰ who observed conventional glass ionomers to have higher susceptibility to erosive challenges when compared to composite resins. These results could be explained by the matrix dissolution peripheral to glass particles of the glass ionomer, which could result from dissolution of the siliceous hydrogel layer.^18,21 On the other hand, composites were more stable under acidic conditions, probably due to the formulation of material and morphology of filler particles, which are nanosized and regular, allowing the incorporation of large inorganic volume.⁵ In addition, the presence of Bis-EMA can promote hydrolytic and biochemical stability as a result of hydrophobicity of this monomer when compared to Bis-GMA.⁶

On analysis of mean surface roughness change among all the materials, though statistically insignificant, all the test surfaces have shown an increase in surface roughness when exposed to pediatric liquid analgesics tested. It should be emphasized that unlike previous studies^9,19 exposing substrates to acidic medicines for prolonged period, our soaking protocol based on the frequency of medication ingestion was relatively short; 15 cycles of 1 minute immersion in acidic medicines over 5 days period, with immersion in artificial saliva in between the cycles. There could also be a possibility of diffusion of calcium and phosphate ions to the surface after prolonged immersion in artificial saliva as suggested by Wongkhantee S et al (2006).¹⁶

Limitations of the study: Despite the cyclic specimen immersion protocol adopted in our study, in vitro models do not allow accurate mimicking of all the events that occur in the oral cavity. It is possible that the period of immersion cycle regime (5 days) which was based on the frequency of medication ingestion was not long enough to cause significant surface changes and if the duration of immersion cycle regime was increased, significant changes in the surface roughness could be found.

Scope for future research: Longer periods of erosive cycle mimicking the oral conditions with consideration to the dynamics of oral cavity and effects of saliva can be considered in future studies.

Conflict of Interest

None.