FAQs

One would have thought that someone as old as I, would know exactly how long a given lecture would take to present! Apparently not, given that, at a recent lecture for the BDIA virtual meeting, I over-ran and agreed to respond to Frequently Asked Questions (FAQs) by publishing my responses later. The questions related to resin composite restorations, so here we go!

Historically:

The contemporary view² is that:

Research to back up these comments includes the following. Von Fraunhofer and co-workers³ found an increase in microleakage, post-operative sensitivity and potentially secondary caries when a lining was present under a posterior composite restoration. Blum and colleagues¹ found that prevalence of post-op sensitivity after placement of posterior composite restorations was 20% greater when a lining was placed. Last, Schwendicke et al,⁴ in a systematic review, concluded that there was insufficient evidence to recommend cavity linings based on their antibacterial effects, adding that dentists should be aware that the use of cavity liners is not recommended by clinical studies.

Is that sufficient to answer the questions on the need for a base? I realize that it is difficult for clinician to change what they were taught at dental school, especially if they have been placing a liner or base under composite restorations for years. The message today, however, is to trust your bonding agent! In this regard, I will shortly publish a positive follow-up to my 2017 publication⁵ in which I considered universal adhesives were an advance on many of the bonding agents that we had previously. On the other hand, if you feel that you could not sleep at night if you didn't place a base under composite restorations, then, for goodness sake, use one that is adhesive (for example, the resin modified glass ionomer (RGMI), Vitrebond, 3M, MN, USA) rather than one which is not (for example Dycal, Dentsply, Milford, DE, USA), given that it has been suggested⁶ that the physical properties of Dycal are not sufficient and that it should always be covered with a layer of RMGI to protect it.

Another FAQ asked for details of the ‘optimum core build-up material for a molar, whether root-filled or not’.

Let's go back to basics! The purpose of the core build-up is to replace missing tooth structure and to create optimal resistance and retention form for the crown preparation. It should have:⁷

Which materials fit the bill? Dental amalgam has been widely used in the past, but bonding it to tooth structure is problematical, and the use of dentine pins to retain it is now discouraged. Conventional glass ionomer (GI) materials, while having satisfactory compressive strength, are poor in flexion, which rules those out. Reinforced GIs are probably sufficiently rigid and the manufacturers of the most recent GIs such as Equia Forte (GC) claim improved physical properties over reinforced GIs, so that would probably work.

However, if one looks at the list of ideal properties, resin composite fulfils all but one (cariostasis) of the ideal criteria. Dual-cured composite materials have been introduced as core build-up materials because these have the advantage of being placeable in bulk, and provide complete curing in areas that may be out of reach of the curing light. Resin composite for use as a core build-up should have a contrasting colour, so that the clinician will be able to visualize where the core ends and the tooth starts, given that the margin of the crown preparation should always be on tooth substance rather than on the core (as that makes for two interfaces rather than one).

Hope that helps! A couple more FAQs in the next issue.

Finally, as always, thanks to all our authors, but a special thank you again to Martin Kelleher for enlightening us regarding more dental fallacies. I make no apologies for his paper being a lengthy one, but readers will find that it is full of tips and tricks (one that I particularly enjoyed was to chill the composite material to make it more sculptable!), and common sense.