Water Sorption and Solubility of Different Commercially Available Dental Cements. (An in Vitro Study)

Ahmed Ghanim M.
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Keywords : Water Sorption,Solubility,Available Dental Cements,Vitro Study
Medical Journal of Babylon  7:3 , 2014 doi:1812-156X-7-3
Published :15 June 2014

Abstract

Background: A variety of cements have been used in dentistry through many years for two primary purposes: as restorative filling materials, either alone or with other materials, and to retain restorations or appliances in a fixed position within the mouth. In addition, certain cements are used for specialized purposes in the restorative, endodontic, orthodontic, periodontic, and surgical fields of dentistry. Cement solubility and water sorption could be a primary cause of restoration failure. Aim of study: To evaluate the water sorption and solubility of different commercially available dental cement materials. Materials and Methods: Thirty disks (9×2 mm) of zinc polycarboxylate, zinc phosphate and glass ionomer cements (ten disks for each one) were prepared according to manufactures instructions. After setting, they were desiccated and weighed and each specimen were immersed in distil water for 7 days, then removed and weighed again. Then disks were again desiccated and weighed. Solubility and water sorption values were calculated from these different measures. Results and Conclusion: The results shows that the polycarboxylate cement show the highest value of water sorption and water solubility followed by zinc phosphate cement. Glass ionomer cement shows the lowest values of the three materials tested regarding both water sorption and water solubility.

Introduction

Although dental cements are used in small quantities, they are the most important materials in clinical dentistry because of their application as luting agents, orthodontic attachments, cavity linings and bases, and restorations for teeth. These multiple uses of dental cements require more than one type of cement; since no one material has yet been developed that can perform all the desirable requirements, these different applications require different physical properties and appropriate clinical manipulative characteristics [1]. Solubility and water sorption is an important feature in assessing the clinical durability of dental cements. Consequently, solubility of dental cements has been widely evaluated both in vitro and in vivo [2-4]. Water sorption and solubility may cause degradation of the cement, leading to debonding of the restoration and recurrent decay [2, 5, 9]. However, most of these tests are static solubility tests, unrelated to the conditions found in the oral environment, and in particular, applied only to short-term solubility, While some investigators study the solubility in dynamic state (different pH) [6, 7]. It’s clear that the clinical success of fixed partial prostheses is heavily dependent on the cementation procedure, because dental cement must be used to act as a barrier against microleakage [8, 15]. Dental cements can degrade when exposed to saliva in the mouth, and the resulting gap between the tooth and the restoration predisposes the tooth to caries, post operative hypersensitivity, pulpal inflammation and periodontal disease [9]. Water sorption and solubility of cements leads to dimensional changes, loss of retention, staining and breaking in margin contours and may affect the mechanical behavior such as the flexural strength, Vickers hardness and mechanical stability [10-13]. The solubility of dental luting cements influences both their rate of degradation and their biological compatibility [14]. Because of this, the water sorption and solubility of dental cements are of considerable clinical importance and can not be overlooked.

Materials and methods

The ADA specification #8 (zinc phosphate cement solubility) [24] was adapted with few modification to design the methodology used in this study, distilled water used as storage media as the ADA specification #8 suggests , and the storage time were 1 week [16].
The materials used in this study and its composition are listed in table (1) and shown in figure (1).
Thirty discs were prepared (ten discs for each material) measured (9 mm in diameter and 2 mm in thicknesses). The powder –liquid ratio and mixing of the components of each material was carried according to manufacturer instructions.
The samples were prepared using a specially designed plastic syringe (with a stopper on its body) (figure 2), the resulting space inside the syringe has 9 mm diameter and 2 mm thickness. The syringe were loaded with the cement material with slight excess and pressed against a polyester strip placed on glass slab, after setting of the cement we remove the excess material and remove the stopper of syringe and push the plunger to extrude the disc of cement. Then the samples weighed with precision weighing scale (Denver instruments MXX-123-USA) (figure 3), the initial weight is termed (W1). Immediately after weighing the samples, they were immersed in individually numbered distilled water tubes and held in stand (figure 4) at 37 ?C for 1 week in an incubator (Memmert, Germany) (figure 5), removed and weighing again (W2). The samples then dehydrated in an oven at 37?C for 24 h and weighed again (W3).
The loss of material (solubility) was obtained from the difference between the initial and final drying mass of each sample (W1-W3).
The water sorption was obtained from the difference between initial weighing and the wet weighing (W2-W1).
The values of water sorption (Wsp) and solubility (Wsol), in µg/mm3 for each sample were calculated using the following equations [10, 17]:
Wsp = (W2-W1) / V
Wsol = (W1-W3) / V

Where V is the volume of sample in mm3 = (127.17 mm3).
The data were subjected to one-way ANOVA, and LSD test at a 0.05 significance level.




Results

The Mean values of W1, W2, W3, for all materials used in this study are shown in table (2). The water sorption and water solubility are shown in table (3). The mean values shows that the polycarboxylate cement show the highest value of water sorption and water solubility followed by zinc phosphate cement. Glass ionomer cement shows the lowest values of the three materials tested regarding both water sorption and water solubility as shown in figure (6) and figure (7).The water sorption values showed correlation with the solubility values: the higher the water sorption, the greater the solubility for the evaluated materials. The data were subjected to one-way ANOVA, and LSD test at a 0.05 significance level. For water sorption, ANOVA test shows significant difference among the materials tested (p <0.05) (table (4)).Post hoc (LSD) test for water sorption values shows a significant difference between all materials (p <0.05) except between zinc phosphate and glass ionomer cements (table 5).For water solubility, ANOVA test shows non significant difference among the materials tested (p <0.05) (table (6)), however the mean values shows that zinc poly carboxylate has greater solubility values followed by zinc phosphate, the glass ionomer has the least values.Post hoc (LSD) test for water solubility values shows a non significant difference between all materials (p <0.05) (table (7).

Discussions

the water sorption and solubility of dental restorative materials are of considerable clinical importance and cannot be neglected [10, 18]. according to tae hyung kim [19], high strength and low solubility are desirable for any base or lining material. a strong base material is needed to support the overlying restoration and the subsequent occlusal forces acting upon it during clinical function. some reduction observed in compressive strength may be attributed to dissolution or water sorption during storage. moreover, marginal infiltration may influence on liners hardness, which reinforces the need for studies related to their physical properties. the water sorption measurements actually measured the net gain in weight of a specimen as a result of the ingress of water molecules and egress of monomers and other small molecules [20]. from an atomic point of view diffusion mechanisms are a stepwise migration from one site to another. generally two patterns are known for diffusion of water through polymeric materials [21]: one is the pattern following the (free volumetric theory), in which the water diffuses through a microvoids without any mutual relationship to the polar molecules in the material. the other pattern is called (interaction theory), in which water diffuses through material binding successively to the hydropinghilic groups. in the case were there was a negative correlation between the diffusion and equilibrium water uptake, the later pattern of diffusion was supposed to occur mainly. recently it has been assumed that both approaches could be valid, each one for a defined specimen family or both simultaneously. solubility is the ability of a substance to dissolve in another, expressed as the concentration of saturated solution of the former in the latter. when solubility is tested, there is no particle in suspension (the solvent remains limpid) [30]. this study was aimed at elucidating essential values for the evaluation of the quality of each employed material, which is of important clinical applicability. in fact, lining, base and luting materials have to be resistant to dissolution in water, organic solvents and acid-etching solutions, in order to maintain their pulp protective effect [22]. in addition, dissolved and smeared cement may contaminate acid etched enamel, and produce an inferior bond, which is not desirable [23]. the choice for the three kinds of cements here evaluated was based on the fact that zinc phosphate, zinc polycarboxylate and glass ionomer cement are the most commonly used conventional lining and luting materials in the clinical practice. water sorption and solubility tests were applied according to the ada’s #8 specification [24], though with few alterations to meet the objectives of this study. the results of this study shows higher mean values (both sorption and solubility) for poly carboxylate cement followed by zinc phosphate and the least values were for glass ionomer cement. the results of yoruc and karaaslan [1] showed that commercial dental polycarboxylate cements absorbed most of the water within 1st day of water storage. they continued to absorb the water at a slower rate for 28 days until equilibrium was reached. they further assumed that the results of their investigation showed that the water absorption of the commercial dental polycarboxylate cements was significantly depend on material composition. zinc polycarboxylate cement is a water-based material that hardens following an acid-base reactions between zinc-rich powder and an aqueous solution of polyacrylic acid [25]. the hydropinghilic nature of a polymer is a function of the chemistry of its monomers and polymerization linkages. the presence of hydroxyl, carboxyl and phosphate groups in monomers and their resultant polymer make them more hydropinghilic and more prone to water sorption [13], these cements include water in their formulation.glass ionomer cements are sensitive to water erosion [26] it may be duo to same hydrolysis of the cement components, this phenomenon is apparently aggravated in oral environment duo to presence of aggressive compounds in saliva. clinical success of glass ionomer cements depends on early protection from hydration and dehydration it’s weakened by early exposure to moisture, while desiccation on the other hand causes shrinkage and cracks [10]. deniz et al [27] found that higher levels of solubility were associated with earlier exposures of mixed cement to water, and glass ionomer luting cements were highly sensitive to water contact during the first 6 minutes after mixing. it was reported in previous studies that long–time storage of dental cements in water affected the mechanical properties of the cements [1, 14]. cattani-lorente et al [11] found that deterioration of the physical properties of the cements after long–term storage in an aqueous environment could be related to the water absorption of these materials. part of the absorbed water acted as a plasticizer, inducing a decrease in strength. weakening resulted from erosion and plasticizing effect of water. the results of this study are agreed with that of hajmiragha etal [6], yanikoglu et al [7], keyf et al [10], tuna etal [14], nomoto et al [29], nomoto etal [30] and eisenburger et al [31], however some of these researchers use different storing solution and different specimen preparation technique and size. hajmiragha et al [6] uses artificial saliva at ph 5 and ph 3 and found that weight changes of polycarboxylate cement were greatest, and there were significant differences among all the materials (p<0.05). solubility of the cements in the two medium decreased in the following order: polycarboxylate, zinc phosphate and glass ionomer. solubility of the cements were more in the acidic medium (p<0.05). yanikoglu etal [7] uses artificial saliva at different ph values and found that statistically significant differences were found among the specimens stored in acidic, basic and neutral artificial saliva, it was observed that the cements were more soluble in acidic media and more stable at ph 7. the highest solubility found in zinc phosphate followed by zinc polycarboxylate and the least is glass ionomer cement. keyf et al [10] found that the water sorption of zinc poly carboxylate more than zinc phosphate and the two is more than glass ionomer cement, while for solubility he found that glass ionomer has greater solubility than zinc poly carboxylate and the least is zinc phosphate. tuna et al [14] has exactly the same finding of keyf et al [10]. nomoto et al [29] found that the erosion (using 0.1 and 0.02 lactic acid solution) of three different kinds of cement zinc phosphate, polycarboxylate and glass ionomer, were evaluated by measuring the depth loss of the cement in a cavity. differences in the eroded depths of the three types of cements clearly emerged. the depth losses of polycarboxylate cements (up to 300 ?m) were more than those of zinc phosphate cements (up to 200 ?m), which were more than those of glass ionomer cements (up to 100 ?m) after 24 h immersion in 0.1 m buffer solution. nomoto et al [30] found that the eroded depth are in the same order zinc polycarboxylate more than zinc phosphate more than glass ionomer cement and stated that the volumetric method for investigation are more applicable than gravimetric method. eisenburger et al [31] stated that profilometric measurements show a higher susceptibility of zinc phosphate cement than glass ionomer cement for acid erosion. comparison with erosion depth of enamel and dentine measured in vitro reveals a higher substance loss of zinc phosphate cement at all ph values, whereas glass ionomer cement shows a lower erosion depth than the dental tissues.

Conclusions

Within the limitation of this study, zinc poly carboxylate has greater values of water sorption and solubility than zinc phosphate, and the least values were found in glass ionomer cement.

References

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