Physical properties of some zinc phosphate and polycarboxylate cements

Dental Luting Cements: An Updated Comprehensive Review

The cementation of indirect restoration is one of the most important steps in prosthetic and restorative dentistry. Cementation aims to bond the prosthetic restoration to the prepared enamel or enamel and dentine. Successful cementation protocols prevent biofilm formation at the margin between tooth and restoration and minimize mechanical and biological complications. With the advancements in dental cements, they have been modified to be versatile in terms of handling, curing, and bond strengths. This review presents updates on dental cements, focusing on the composition, properties, advantages, limitations, and indications of the various cements available. Currently, dental restorations are made from various biomaterials, and depending on each clinical case, an appropriate luting material will be selected. There is no luting material that can be universally used. Therefore, it is important to distinguish the physical, mechanical, and biological properties of luting materials in order to identify the best options for each case. Nowadays, the most commonly used dental cements are glass-ionomer and resin cement. The type, shade, thickness of resin cement and the shade of the ceramic, all together, have a tangible influence on the final restoration color. Surface treatments of the restoration increase the microtensile bond strength. Hence, the proper surface treatment protocol of both the substrate and restoration surfaces is needed before cementation. Additionally, the manufacturer's instructions for the thin cement-layer thickness are important for the long-term success of the restoration.

Mechanical properties of dental luting cements

STATEMENT OF PROBLEM

Dental luting cements fail by microcrack formation and bacterial ingress or by gross failure and crown dislodgment. Both of these failure modes are related to mechanical properties and deformation.

PURPOSE

This study evaluated those mechanical properties of cements. METHODS AND MATERIAL. Elastic modulus for 8 representative cements (zinc phosphate, polycarboxylate, glass ionomer, encapsulated glass ionomer, resin-modified glass ionomer, resin composite, and adhesive resin composite) was measured by using a nondestructive technique and evaluated for cement type and storage time (1 hour, 1 day, 1 week, 1 month, 1 year) by 2-way ANOVA (P <.05). Compressive properties (proportional limit, resilience, and toughness), ultimate strengths (compressive, diametral tensile, and flexural), and flexural toughness were determined and evaluated by 2-way ANOVA for 2 crosshead testing rates (5 and 0.5 mm/min) and cement type (P <.05).

RESULTS

Cements varied with respect to elastic moduli, compressive proportional limit, compressive resilience, compressive strength, compressive toughness, diametral tensile strength, flexural strength, and flexural toughness. Storage time affected the elastic moduli of different materials in different ways. Elastic moduli of polycarboxylate and glass ionomer cements increased over time, whereas the other materials changed little after the first day. Crosshead rate only significantly affected compressive proportional limit and resilience.

CONCLUSIONS

Luting cements differed considerably with respect to mechanical properties.

Effects of the porcelain firing sequence on the bond strengths of cements

Bond strengths for the retention of ceramic bonded to metal alloys to the tooth structure involve cavity preparation variables, cement variables and ceramic bonded to metal alloy variables. The aim of this work was to evaluate the retentive strength differences between alloy surfaces, unfired and fired, for porcelain alloys retained with different dental cement compositions. The clinical situation was stimulated by using standardized tooth preparations, extracted teeth and castings cemented with zinc phosphate and polycarboxylate cements, which were debonded on an Instron. Jelenko O, Cameo, Jelstar and Genesis II alloys were compared unfired and fired to simulate porcelain application. Fired Jelenko O casting alloy cemented with polycarboxylate cement produced the greatest bond strengths (6.0 +/- 1.0 MPa). Polycarboxylate cemented castings had greater bond strengths for all alloys whether fired or not. The only effect of firing was an improvement with Jelenko O alloys produced with both cements. All of these differences were statistically significant at the P less than 0.01 level using Tukey's post hoc evaluation. The improvements observed were related to the oxide formation on the internal surfaces of the casting and the ability of polycarboxylate cement to adhere chemically to those layers.

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.