The evolution of restorative materials plays a huge role in simplifying and streamlining dental procedures, which have become a priority in modern-day dentistry.
By Prof Brian Millar, pictures and case by Dr Stephen Denny
There has been a sustained move from conventional cementation to adhesive luting as clinicians move away from cast restorations to aesthetic materials (Fig. 1). In line with this, there has been a shift away from conventional cements to dual-curing, resin-based luting materials.
Ideally, adhesive luting materials should bond to both tooth tissue and restoration, tooth coloured, and are easy to use: syringeable, dual-cure, suitable viscosity and no need for separate etch and bond stages.
One of the first was ParaCore (COLTENE) and although this was designed as a core build-up material, its flow properties, dual-cure feature and colour also made it suitable as an adhesive cement. Even if most of the requirements mentioned above were met, ParaCore, like many earlier resin-based luting materials (e.g., Nexus, Calibra, Panavia), required an additional bonding agent.
Therefore, further development resulted in built-in adhesives bringing us to the popular current materials in this range: the self-adhesive cements, such as RelyX Unicem (3M) or SoloCem (COLTENE). These are designed to be used directly onto the tooth without the need for neither acid-etching nor the application of a separate bonding agent.
However, the bond strengths resulting from self-adhesive cements were lower than the ones from adhesive luting materials which have been used with additional bond. Whereas in some situations, the bond strengths resulting from a self-adhesive protocol would be sufficient, in other situations they are not.
This is why the newest evolution in adhesive cementation is the universal luting materials (e.g., RelyX Universal, 3M). Companies recognised that in some situations additional bond strength may be required and made their self-adhesive luting materials compatible with bond.
Solocem (originally a self-adhesive material) can now be used with a layer of the universal bond ONE COAT 7 UNIVERSAL (COLTENE) if the clinician chooses to improve bond strength on enamel and dentin. Even if ONE COAT 7 UNIVERSAL is light-curing, its acidity does not affect the curing properties of the luting material SoloCem. This means that there is no need of using an additional activator for ONE COAT 7 UNIVERSAL.
In order to improve bond strengths on enamel even more, I recommend the use of selective etch technique. I would consider this essential when bonding a metal-framed resin-bonded bridge to enamel. Etch the enamel (not dentin) with standard 35% phosphoric acid gel (e.g., Etchant Gel S, COLTENE) for 25 seconds, wash and gently dry. Be careful not to get the acid on adjacent teeth, otherwise, clean-up becomes more difficult. Ideally, the adjacent teeth should be protected with a barrier before proceeding with the adhesive luting protocol (Figs. 12 to 18).
Note that as the bonding agent needs to be light-cured, this has to be carried out before placing the restoration. Therefore, the bond layer must be very thin, otherwise, it can prevent the seating of the restoration.
Conclusion
There is a good reason to simplify luting restorations. The new universal self-adhesive luting composites are helpful to clinicians. Reduced bond strengths when using them self-adhesively can be enhanced by adding the options of:
- Use with acid-etching enamel where necessary
- Use an additional bond layer to improve bond strength
Reference
1 Olley RC, Andiappan M, Frost PM. An up to 50-year follow-up of crown and veneer survival in a dental practice. J Prosthet Dent 2018 Jun;119(6):935-941.
Published in Dental Asia January/February 2022 issue.
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