The relation between salivary properties and in vivo solubility of dental cements

Microleakage of various cementing agents for full cast crowns

OBJECTIVES

To evaluate microleakage and marginal gaps in full cast crown restorations bonded with six different types of cementing agents.

METHODS

Sixty non-carious human premolars and molars were prepared in a standardized manner for full cast crown restorations. The mesial and distal margins were located in dentin, while the vestibular and palatal/lingual margins were located in enamel. Crowns were made from a high-gold alloy using a standardized technique. The specimens were randomized to six groups of cementing agents: one zinc-phosphate cement (Harvard cement), one conventional glass-ionomer cement (Fuji I), one resin-modified glass-ionomer cement (Fuji Plus), two standard resin cements (RelyX ARC, Panavia F), and one self-adhesive universal resin cement (RelyX Unicem). After 4 weeks of storage in distilled water at 37 degrees C, the specimens were subjected to 5000 thermocycles ranging from 5 to 55 degrees C. Then, they were placed in a silver nitrate solution, embedded in resin blocks, and vertically cut in buccolingual and mesiodistal direction. Subsequently, the objects were evaluated for microleakage and marginal gap using a high-resolution digital microscope camera.

RESULTS

A number of inter-group differences were statistically significant. RelyX Unicem showed the smallest degree of microleakage both in enamel and in dentin. Panavia F und RelyX Unicem were associated with significantly larger marginal gaps than all other cementing agents. No association was observed between microleakage and marginal gap other than a weak direct correlation when using Harvard cement on enamel.

SIGNIFICANCE

The cementing agents investigated revealed different sealing abilities. These differences were not associated with specific types of materials.

Effect of an acid environment on leakage of root-end filling materials

One hundred fifty-six single-rooted human extracted teeth received root canal treatment, apicoectomy, and ultrasonic root-end preparations. The roots were divided into six groups of 24 teeth. The groups were filled with Amalgam, Geristore, Super-EBA, Mineral Trioxide Aggregate (MTA), Calcium Phosphate Cement (CPC), or MTA with CPC matrix, respectively. Immediately after root-end filling, 12 teeth from each group were exposed to a pH of 5.0 for 24 h, and 12 teeth were exposed to a pH of 7.4 for 24 h. Twelve teeth served as controls. All teeth were exposed to Pelikan Ink for 5 days and cleared. Linear dye leakage was recorded. Data were statistically analyzed. An acid pH significantly reduced dye leakage of Geristore (0.67 vs. 3.93 mm) and MTA with CPC matrix (0.54 vs. 2.41 mm), whereas leakage of all other materials was not affected by pH. In conclusion an acid environment did not hinder the sealing ability of any of the materials tested, and enhanced the sealing ability of Geristore and MTA with CPC matrix.

Short-term contamination of luting cements by water and saliva

OBJECTIVES

The aim of this study was to determine the effect of water, artificial saliva and natural saliva on the hardening process of three dental luting cements.

METHODS

Cement samples, 1 mm thick and 5 mm in diameter, were subjected to various storage conditions in an oven maintained at 37 degrees C. Some samples were aged in 100% humidity or water for up to 1 wk. The other samples were covered with water, artificial saliva or natural saliva at various times after mixing. The Knoop hardness values of the cement surfaces were measured. Differences between groups were evaluated with an ANOVA followed by a Tukey multiple comparison at the 5% level of significance. The hardness ratio of the contaminated samples was calculated using the 30 min mean KHN of the samples aged in 100% humidity as the divisor.

RESULTS

The glass ionomer samples were significantly harder (48.3 +/- 3.8) than the zinc phosphate (38.9 +/- 7.5) or composite cements (35.4 +/- 10.2) after 1 wk in 100% humidity storage condition. When immersed in water, the hardness of both the glass ionomer and the zinc phosphate decreased to almost half that of the specimens stored in 100% humidity (26.2 +/- 2.7 and 16.9 +/- 2.5, respectively). Contamination decreased the hardness of zinc phosphate and glass ionomer (hardness ratio, water contamination at 5 min: 0.39 +/- 0.10 and 0.52 +/- 0.12, respectively) but had very little effect on the composite. Overall, water had a greater softening effect than artificial or natural saliva on the cements.

SIGNIFICANCE

In light of these results, glass ionomer cement should be protected from water and saliva for the first 15 min after mixing.

Marginal leakage of cast gold crowns luted with zinc phosphate cement: an in vivo study

Marginal gaps of cast restorations are filled with luting agents that are soluble in intraoral fluids. This study investigated the marginal openings in eight extracted teeth with cast crowns that had been intraoral for 20 years or more. These teeth were extracted either because of periodontal disease or to facilitate insertion of a removable partial denture. Initially, the roots of the teeth were sealed with two coats of fingernail polish within 2 mm of the crown-tooth interface. Next, the teeth were immersed in a 0.05% aqueous solution of basic fuchsin die for 24 hours. Finally, each tooth was sectioned at four locations 1 mm apart. At each of these four sections, cement film thickness between tooth and casting, and microleakage were determined. The results of this study showed a mean cement film thickness of 74 microns on the mesial surface and 57 microns on the distal surface. Mean microleakage values were 432 microns on the mesial surface and 274 microns on the distal surface.

An investigation of dental luting cement solubility as a function of the marginal gap

The purpose of this study was to investigate the rate of type I zinc phosphate cement solubility as it relates to the degree of marginal opening. Standardized test samples were constructed that would simulate clinically relevant marginal gaps of 25, 50, 75, and 150 microns and their subsequent cement lines. The study was divided into two phases. Phase 1 evaluated the effects of simple diffusion on cement solubility in a static environment, whereas phase 2 investigated the effects of convective forces on cement dissolution in a dynamic environment. Both the phase 1 and phase 2 studies demonstrated no significant difference in the rate of cement dissolution for the 25-, 50-, and 75-micron test groups. The 150-micron test groups for both studies, however, demonstrated an increase in the rate of cement dissolution. The results of the phase 1 and phase 2 studies should not be compared because different methodologies were used.

The biocompatibility of glass-poly(alkenoate) (Glass-Ionomer) cements: a review

The literature describing the biocompatibility of glass-poly(alkenoate) ('Glass-Ionomer') cements has been reviewed. This literature shows that these materials have generally good biocompatibility for both dental and orthopaedic use, this latter observation being very recent. There have, though, been a few reports showing that in certain circumstances these materials may cause pulpal irritation and the reasons for these particular findings are considered. Following discussion of the biocompatibility of Glass-Ionomer cements, consideration is given to the likely underlying causes of this feature. Three factors are identified as contributing to the biocompatibility of these cements. They are: (i) minimal exotherm on setting; (ii) rapid neutralization following mixing; and (iii) slow release of ions which are generally biologically beneficial or, at least, benign. This last point is considered in some detail. Previous studies of leaching of ions from Glass-Ionomer cements have shown that only inorganic species are released. The biological effects of each of these inorganic ions are described and their influence on biocompatibility discussed.

Dissolution mechanism of zinc phosphate dental cement in acetic and lactic acid buffers

When zinc phosphate cement was immersed in 0.1 M acetic and lactic acid buffer solutions adjusted to pH 4.1, its dissolution rate was determined by chemical analysis. The eroded surface of the cement was examined by X-ray diffraction and SEM observation. The dissolution process of the cement immersed in the acetic acid buffer solution was mainly controlled by the diffusion of releasing species through the cement matrix and that of the cement immersed in the lactic acid buffer solution by the decomposition of the cement matrix at the surface.

The mechanism for erosion of glass-ionomer cements in organic-acid buffer solutions

The behavior and mechanism for erosion of glass-ionomer cements in organic-acid buffer solutions were studied as a function of time, pH, and citric-acid concentration. In acidic solutions, the dissolution of the cement was controlled by the diffusion of the eluted species in the cement matrix, which depended on H+ ion concentration. In citric-acid solutions, the dissolution of the cement was controlled by both the diffusion and the surface reaction between the acid anion and the eluted species. Contribution of the latter reaction was larger with the increase in the acid concentration.

Dental cements

The manifold uses of dental cements-as (a) luting agents, (b) cavity linings and bases, and (c) restorations for teeth—make them perhaps the most important materials in clinical dentistry. The research of the last 10 years has resulted in four main types, classified by matrix-forming species: (1) phosphate, (2) phenolate, (3) polycarboxylate, and (4) polymethacrylate. The zinc phosphate cements continue to be widely used for luting in an essentially unchanged form. Acidity and oral dissolution remain as problems. The zinc-oxide eugenol cements and their modifications are useful as linings and temporary materials but are susceptible to hydrolytic breakdown. Vanillate cements may be an improvement. Calcium hydroxide-salicylate cements are widely used as cavity linings, especially on exposures, and show improved resistance to acid dissolution. Polycarboxylate cements as both zinc polycarboxylate and glass-ionomer cements show adhesion potential, good physical properties, fluoride release, and, generally, good biological properties. Glass-ionomer cements when correctly manipulated show minimal oral dissolution. Polymethacrylate cements have been used principally for bonding etched cast metal restorations to etched enamel. Recently, adhesive crown-and-bridge cements have been developed. There are no well-established correlations between laboratory measurements of apparently relevant properties and clinical performance. More clinically-based research is needed to facilitate the development of new cements.