Resin cements: what they are, types and clinical applications

Composite resin cements are now the solution of choice for the adhesive cementation of indirect restorations thanks to their superior mechanical, adhesive and aesthetic properties compared to conventional cements.

These materials are characterised by a resin matrix based on methacrylic monomers reinforced by inorganic filling particles, which provide strength, hardness and dimensional stability over time (1,2).

Their versatility allows bonding to various substrates – enamel, dentin, ceramics, metals and composite materials – making them suitable for a wide range of clinical applications (3,4). However, the choice of cement type and adhesion protocol remains crucial for long-term clinical success.

The introduction of universal dual-curing resin cements (light-curing and self-curing) in the dental market has led to increasingly simplified cementation systems in order to standardise the cementation procedure, which is complex and dependent on the operating technique (5).

However, some of them present chemical incompatibilities with some universal adhesives (6), leading companies to produce systems consisting of resin adhesives together with self-adhesive cements, which can be used individually or together (7).

In this sense, a new division of resin cements into three categories (7) has been proposed: (1) multi-step adhesives; (2) one-step self-adhesives; (3) universal (one-step or multi-step depending on the clinical protocol).

Multi-step adhesive cements

Multi-step adhesive cements were the first resin cements introduced on the dental market and require the usual steps for adhesion to dental tissue – etching (15-30 seconds depending on whether dentine or enamel is involved), priming the dentine and application of the bonding agent (bonding) (8).

Multi-step adhesive cements have shown higher adhesion values to dentin than self-adhesive cements, both initially and after ageing; (9) characteristics that are clearly evident in the case of cementation of partial restorations (10) but not in the case of fully covered crowns in zirconia or lithium disilicate (11).

However, compared to self-adhesive cements, multi-step adhesive cements, if used in combination with “etch and wash” systems, may expose the patient to post-operative sensitivity, usually transient and destined to resolve within a few days or weeks after cementation (12).

One-step self-adhesive cements

Research and development in the field of dental materials have allowed the introduction of “one-step” self-adhesive cements which no longer require the usual procedures of pre-adhesion to the dental tissue (13). These self-etching resin cements contain modified methacrylate monomers with acids such as phosphoric acid on their side chains (8).

These, in turn, have an etching effect and can bind to the calcium in the dental tissue (7). However, it has been demonstrated that resin cements that involve multiple steps and phases guarantee higher tensile strength values than one-step self-adhesive cements (9).

From a clinical point of view, this is relevant only in cases of partial preparations, presence of enamel and short abutments (14). Furthermore, it is necessary to pre-treat some materials such as composite or ceramic with silane agents, such as 10-MDP for zirconia.

Universal cements

Then there are the so-called “universal cements”, which have the following characteristics (7):

• They bind to various substrates, dental tissues and metallic, resin and ceramic restorative materials;
• They can be used both in multi-step and one-step mode, similarly to adhesive cements (self-etching, which require selective etching on the enamel or etch & wash adhesive systems) and self-adhesive depending on the clinical case and the dentist’s preferences (7);
• They are dual (both light-curing and self-curing);
• Either the cement itself or its possibly associated adhesive system can contain etching acids and silane molecules to create chemical bonds between different substrates;
• They can be combined with primers or bonding agents to improve adhesion on different substrates, without the need for other priming systems.
  

These cements have a lower hardness than the other two categories of resin cements and a greater tendency to absorb water, making them more susceptible to ageing (15).

Light-cured and dual-cured cements: Advantages and limitations compared

Most of these three types of cements are dual-polymerised, i.e. self-curing and light-curing. Light-curing cements are less widespread due to the risk of incomplete polymerisation under non-translucent prostheses. They are therefore used almost exclusively for the cementation of veneers of glass ceramic (16).

Light-curing cements, with initiators based on camphorquinone and aliphatic amines, are less subject to chromatic changes than chemically polymerized cements, based on aromatic amines and benzoyl peroxide (17).

Some light-cured cements also exhibit a higher level of conversion and microhardness than dual-cured ones, probably due to different polymerization kinetics and differences in the composition and type of filler (18). However, the mechanical and polymerization properties of resin cements are strongly dependent on the type of resin polymer (19), so no generalisable conclusions can be made.

How to choose a resin cement

The clinical performance of resin cements is however influenced by multiple factors, including the chemical composition, the type of substrate, the clinical conditions and the application technique.

An in-depth knowledge of the different types of cements, their characteristics and indications, allows the clinician to select the most suitable material for the specific context, optimising the effectiveness of the treatment and reducing the risk of prosthetic failure.

Despite the progress made, there remain many opportunities for development and improvement in this constantly evolving field.

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References:

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