Aerated Soft Drinks: Its Effects On Cement Solubility

INTRODUCTION

Oral cavity has a diversity in function and with each function it is subjected to many variations like the change in microorganisms' flora, pH levels etc. One of the important factors is the low pH level and its effect on the teeth and restorative materials. Alow pH of the oral cavity is due to the acids produced by microorganisms as the food is broken down and also due to some acids being taken into the mouth as food and drinks. Modernized people are fascinated by the soft drinks and the consumption rate has increased day to day with or without knowing its effect on oral cavity and the general health.

The solubility of cements in the oral cavity has been considered as a primary cause of failure of the fixed restorations, due to micro-leakage, recurrent caries and loss of retention. The solubility and disintegration of luting cement depends upon variables such as,

i. Composition of the luting cement

ii. Film thickness of the cement, and

iii. pH of the medium

The pH of aerated soft drinks is considerably low, and for fresh Coco Cola is 2.6.¹ The erosive activity of citric, malic and phosphoric acid in non –alcoholic beverages, and other acids as ingredients of beverages and foodstuffs has been demonstrated in many studies and reported to be significant². Hunter conducted a study to show the relative susceptibility of deciduous and permanent dental tissue to erosion by a low pH fruit drink in vitro³. The fact that the pH of the oral cavity remains low for some time even after consumption of the aerated soft drinks has been proven by Moazzez et.al.⁴, who correlated the oral pH during ingestion of a carbonated Cola drink in a group of adolescents and dental erosion. In their study, the pH fell below 5.5 and 4 in the incisors and the upper molar regions respectively, after the consumption of the drink.

The luting cements can be susceptible to dissolution in acidic pH environment. The above studies show that the acidic pH created by the aerated beverages may also have deleterious effect on the solubility of the luting agents used under fixed restorations. Hence a study was undertaken to evaluate the effect of aerated soft drinks' on cement solubility.

OBJECTIVES OFTHE STUDY

i) To identify the least soluble cement under the fixed restoration when exposed to acidic pH environment created by aerated soft drinks

ii) To evaluate and compare the solubility in terms of loss in weight of the cement due to immersion in various soft drinks in vitro.

MATERIALS AND METHODS

Three permanent luting cements and one temporary cement were chosen in the present study and were grouped as follows.

Group A- Resin cement (PANAVIA-F, Kurrary Co. Ltd. Japan),

Group B - Glass ionomer luting cement (GC-Fuji GC Corporation, Japan),

Group C- Poly carboxylate cement (Hardvard CC, Herstellungs, Germany),

Group D- Intermediate restorative cement (IRM Dentsply, Germany). 

A total of 20 specimens were prepared for each type of luting cement as per manufacturer's instructions. Each specimen measured one centimeter in diameter and one millimeter in thickness (fig:1). They were numbered for identification and weighed in an electronic balance which showed + or – 0.1 mg precision (Precisa PAG –Switzerland) (fig:2).

The most available and consumed aerated soft drinks were chosen for the study. They were Coco-cola, Limca, and Maaza. Distilled water was used as a control. Five specimens of each luting cement were immersed separately in a glass beaker containing 50 ml of respective soft drinks (fig:3). After 24 hours of immersion, these specimens were dried and weighed, the initial and final readings were recorded in grams and the difference of the initial and final reading was calculated. The results were tabulated and subjected to the statistical analysis.

RESULTS

The mean and standard deviation of loss in weight (in grams) of pellets of these cements immersed in different aerated soft drinks for 24 hours (Table-1) was calculated. The statistical comparison by ANOVA for loss in weight for various cements at 1 % ( Table-2) was compared. The Mean of loss in weight in grams was plotted on the bar diagram (Graph 1). The Group - A [Resin cement] was found to be least soluble, and group C [polycarboxylate cement] was the most soluble. All the specimens showed the least solubility when immersed in distilled water. Glass ionomer cement and intermediate restorative cement showed highest solubility when immersed in Coco Cola drink. Of all the cements, Polycarboxylate cement showed the highest solubility and this was observed when it was immersed in Limca drink.

DISCUSSION

The erosive potential of soft drinks on the teeth and cement restorative materials both in vivo and in vitro has been reported in the literature^5,6,7,8. The effect of soft drinks on the luting cements has been given lesser attention. This study was an attempt to compare the solubility of luting cements in aerated soft drinks. Four types of luting cements i.e. Resin cement, Glass ionomer cement, Polycarboxylate cement and intermediate restorative cement were chosen for the study. IRM was chosen as it is commonly used as the temporary luting cement. Pellets of same dimensions were fabricated and weighed. These pellets were immersed in three aerated soft drinks. Distilled water was used as the control as it was expected to cause least solubility as compared to soft drinks. After 24 hours, the samples were dried and weighed again for calculating the weight loss.

All the cements were least soluble in distilled water and this showed that the acidic pH of the aerated soft drinks was responsible for increased solubility of the luting cements. As believed, Resin cement, showed the least solubility as compared to all the other cements used in the study. Properly cured resin cement is not soluble in oral fluids; however, the weight change after immersion in water is caused by leaching of the unreacted monomer or loss of the filler particles. As the filler content of the resinous cement increases, the dissolution and solubility in the liquids decreases⁹.

The solubility of glass ionomer and intermediate restorative cement was the most in Coco cola drink. The solubility of Glass ionomer cement could be explained due to the matrix dissolution in the periphery of the glass particles, which could result from dissolution of the siliceous 5 hydrogel layer. The surface of glass ionomer becomes rough and dull which indirectly attaches the plaque and there by the chemical reaction continues². Polycarboxylate cement was the most soluble of all the cements and this was seen when immersed in Limca drink. Some studies have proved that the solubility of zinc Polycarboxylate cement increases when it is exposed to organic acids of less than pH 4.5⁹. Polycarboxylate cement manipulation is believed to be very critical as the material is thixotropic. So if appropriate consistency is not achieved, then the cement will show reduced strength and increased solubility^10,11.

The rate of solubility of the luting cements in the oral cavity can be considered proportional to this in-vitro solubility. The results of the study is of clinical significance as the Resin cement being least soluble should be the luting cement of choice for people who are habituated to aerated soft drinks. Individuals with fixed restorations should be advised against over consumption of aerated soft drinks as all the cements showed increased solubility in soft drinks as compared to distilled water.

Consumption practice was not simulated in the study and it can vary from person to person. Although in-vivo results are expected to match the in-vitro findings of the study, it is to be considered that the soft drinks consumed are diluted or buffered with saliva immediately after consumption into the oral cavity. The entire mass of the cement was taken into consideration in this study; where as in clinical practice only the cement film at the margins underneath the veneer is exposed to the oral fluids. The exposed cement is very minimal in well adapted restorations. But the surface area exposed to the oral fluids would affect the amount of the cement dissolved and not the rate at which it is dissolved.

CONCLUSION

This study evaluated a method of comparing the in vitro solubility of luting cements in a low pH environment as created by soft drinks in the oral cavity. All the luting cement specimens showed increased solubility when immersed in soft drinks. For the habituated aerated soft drinkers, it is advised to taper the intake of the carbonated drinks and for such people who need fixed restorations, resin cement followed by glass ionomer should be the luting cement of choice.

ACKNOWLEDGEMENT

My sincere gratitude to my esteemed Professor Late Dr. Narendra P. Patil for the knowledge he has shared and for his kind support in finishing this work.