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The word ‘luting’ is derived from a latin word ‘Lutum’ which means ‘mud’. ‘Luting’ is a word that is often used to describe the use of a mouldable substance to seal a space or to cement two components together. Therefore in view of the clinical importance of dissolution of luting cements in the oral environment, an in vitro study was designed to compare the sorption and solubility of commercially available luting cements mainly zinc phosphate, Glass Ionomer cement, Resin Modified Glass Ionomer Cement and Resin Cement after immersion in artificial saliva of different ph values of 5 and 7.
To Compare and Evaluate the sorption and solubility of four luting cements after immersion in artificial saliva of different pH values.
A total of 120 test samples were prepared of which 30 samples of each luting cement were prepared for the purpose of assessing the water solubility and sorptionThese luting cements were grouped as: GROUP- A (Zinc Phosphate cement), GROUP- B (Glass Ionomer Cement), GROUP-C (Resin Modified Cement), GROUP- D (Resin Cement) In these groups, based on immersion of artificial saliva of acidic pH 5 and neutral pH7, the luting cement specimens were subdivided into 2 groups of 15 samples each. The volume (V) of each specimen was calculated using mathematical formula.
Resin cement had the highest resistance to solubility and sorption followed by resin modified GIC, Conventional GIC, and Zinc Phosphate which exhibited the least resistance to solubility in both artificial saliva of pH 5 and pH 7.
The luting procedure is a key to the long-term success of fixed restorations. Dental luting cements in conjunction with the geometry of the tooth preparation provide the basis for the retention of the casting on the tooth. The clinical success of fixed prosthesis is heavily dependent on the physical properties of the luting cement.
For luting cement, its clinical performance and durability hinge on many determinants – among which are the dimensional stability and structural integrity of the cement in the oral environment. Dimensional change and structural integrity, on the other hand, are a function of the sorption and solubility properties. A critical property of the luting cement is its solubility and sorption in oral fluids. Solubility and sorption are important properties in assessing the clinical durability of the luting cements.
A total of 120 test samples were prepared of which thirty samples of each luting cement were prepared for assessing the water solubility and sorption [Figure 1]. These luting cements were grouped as:
Group A (zinc phosphate cement), Group B (glass ionomer cement [GIC]), Group C (resin-modified cement), and Group D (resin cement)
In these groups, based on immersion of artificial saliva of acidic pH 5 and neutral pH 7, the luting cement specimens were subdivided into two groups of 15 samples each. Transparent plastic molds with two circular cavities, an inner diameter of 10 mm, and thickness of 3 mm were selected for the purpose. Cement discs of the four luting cements – (zinc phosphate cement, GIC, resin-modified GIC, and resin cement) were prepared using the molds.
The powder/liquid ratios used were in accordance with the manufacturer's recommendations. The materials were placed in the mold and pressed between two plastic matrix strips and a glass microscopic slides under hand pressure to extrude any excess material. During setting, the specimens were then placed in an oven with a relative humidity of 95%-100% at 37 ± 1° for 1 h.
After 1 h, the samples were then transferred to a desiccator to cool down to room temperature. Then, the specimens were removed from the mold, and any excess material was removed by gentle dry grinding with 400 grit silica carbide paper on both the sides. After dry grinding, each specimen was weighed (W1) using an electronic analytical scale with accuracy up to 0.1 mg [Figure 2]. Diameter and thickness were measured using a digital micrometer [Figure 3]. The volume (V) of each specimen was calculated as follows in cubic millimeters using the mean thickness and diameter:
V = π × r2 × h
Where, “r” is the sample radius (diameter/2) and “h” is the mean sample thickness.
After that, the artificial saliva was titrated by the addition of buffers to prepare an acidic pH of 5 and neutral pH of 7. The pH is adjusted by adding buffers and verified at first with pH paper and later with a pH meter. After that, the specimens were immersed in 50 ml of artificial saliva of acidic pH 5 and neutral pH 7 at 37°C for 7 days [Figure 4].
After 7 days, the specimens were dabbed with blotting paper to remove visible moisture and loose debris from decomposition after the immersion period. The specimens were then weighed. The weight thus obtained was termed as W2. The specimens were then dried at 37°C for 24 h in the hot air oven and thereafter transferred to the desiccator. The dried specimens were again weighed on the electronic weight analyzer with readability up to 0.1 mg. This weight was considered as W3.
The values of sorption (Wsorp) and solubility (Wsol) were calculated using the following equations (ISO 4049: 2000):
Where, V is the volume of the specimen before immersion.
For each group, the means and standard deviations for solubility and sorption (μg/mm3) were calculated. The analysis of the sorption and solubility values was performed using two-way ANOVA and Student's t-test at a significance level of 0.05.
Within the parameters of the materials used and the study design, the following results were obtained:
Restorations that are made outside the patient's mouth using indirect technique and are subsequently cemented in the mouth require a luting agent to aid in retention and to fill cement space between the restoration and the permanent tooth. The probability that dental cements suffer dissolution in the mouth is of considerable concern to prosthodontists restoring the teeth with both intracoronal and extracoronal restorations.
Mesu devised a method whereby luting cements were tested in thin films for degradation that was visualized and measured. Another method was reported by Beech and Bandyopadhyay, who subjected the specimens to a continuous jet of water or lactic acid solution to the test solubility of the luting cements.
Swartz et al. studied in vitro degradation of luting cements by comparison of three test methods, i.e., by weight loss, by loss in the area of the films, and by a reduction in transverse strength.
Iwaku et al. compared the solubility of three luting agents and found that the disintegration was much greater in lactic acid than in distilled water. Therefore, the clinical significance of the information obtained from a standard laboratory test for solubility that utilizes distilled water as a medium has been criticized by some investigators. One reason this test has been criticized is because acid producing bacteria is found in the oral cavity. Lactobacilli and Streptococcus mutans also affect the solubility of luting cements.[7,8] These microorganisms predominantly produced lactic acid generally with a pH of 5 in the oral cavity which hastens the dissolution of the luting cements in the oral cavity.
Mesu used acetic acid, lactic acid, and citric acid medium to evaluate the degradation of luting cements in vitro. Therefore, a test which utilized an acidic medium was suggested by many investigators.[4,5,7,9,10] Knobloch et al., did a study which compared the 7-day water sorption, water solubility, and lactic acid sorption and lactic acid solubility of composite and resin modified GICs.
The present study was designed to compare and evaluate the solubility and sorption for commercially used luting cements zinc phosphate (Dental Products of India), glass ionomer (GC Lining and Luting, Radiopaque), resin-modified GIC (RelyX luting, 3M ESPE), and resin cement (RelyX U200, 3M ESPE) after immersion in the artificial saliva of pH 5 and pH 7. This study used artificial saliva titrated to a pH of 5 as a test medium so as to mimic as close as possible the clinical situation where lactobacillus and streptococcus mutans produced predominantly lactic acid of the same pH value.
Resin cement had the highest resistance to solubility and sorption followed by resin-modified GIC, conventional GIC, and zinc phosphate which exhibited the least resistance to solubility in both artificial saliva of pH 5 and pH 7.
There are no conflicts of interest.