By Dr George Druttman

When and why does a dentist recommend a crown for a tooth?

It is important to fully understand the rationale for the recommendation that a tooth be crowned. Like fillings, crowns ‘restore’ the integrity of a tooth after it has been damaged either by trauma or disease (e.g. decay).

There will be times when the dentist recommends a filling, others when a crown is indicated and obviously, times when one or other can fulfill the requirements.

What are the differences?

Function

Basically, a filling ‘fills a hole’. Usually, the hole is created by decay (infected caries) penetrating through the tooth enamel layer into the underlying dentine.

This decayed tooth material needs to be removed (‘drilled’ out) and replaced with a sealed synthetic (preferably tooth coloured) material. Generally, this is a quartz composite. If the ‘hole’ is not too large and is surrounded by at least two thick and strong enough enamel walls of the natural crown of the tooth … then the filling is the ‘appropriate’ restorative material.  Such a filling is ‘supported’ by the tooth.

The function of the crown is quite different to that of the filling.”

On the other hand, if the tooth is very damaged and a large proportion of the natural crown of the tooth is either already missing or needs to be removed because it is so badly decayed (infected), then one needs a restoration that actually strengthens and supports such a tooth. The function of the crown, therefore is quite different to that of the filling.

Most teeth that have undergone root canal treatment are already very damaged and gaining ‘accesses to the root canals for such a procedure (that ‘saves’ the tooth) inevitably has to remove even more of the ‘inside’ (or central part) of the tooth, so further weakening it. Finally, the process of root canal treatment dehydrates a tooth to a degree, rendering it more ‘brittle’ and so even more prone to fracture or splitting as a result of normal functional forces.

That is the reason that, very often, the dentist strongly recommends that the patient does not delay too long before protecting a tooth with a crown after the root canal procedure has been completed.

Process

Usually, a filling needs to be placed in a tooth prior to the tooth then being restored with a crown subsequently. This would then be termed a ‘core’ filling as it acts as a supporting and retaining core for the crown. This is because the crown replaces the outside surfaces (about 1.5mm) of the tooth crown; the core filling fills the missing ‘inside’ of the tooth.

In the event of a root canal treated tooth, there may be an additional requirement for one or two metal or fibre posts to be placed within the (root filled) canal/s of the tooth to help retain the core filling.

If the tooth is ‘alive’ (has not had root canal treatment) and the core filling needs additional retention … one or more tiny titanium pins would need to be ‘drilled and placed’ into the tooth before the core filling is placed around them.

Materials

There are a number of permutations available… ‘overlays’ that are bigger than fillings but more ‘conservative’ than full crowns, and these restorations can be made of different materials. Generally, nowadays, dental restorative materials are almost always visually ‘tooth coloured’. Quartz composite material is the most commonly used for fillings and has well and truly taken over from the very old-fashioned silver-mercury amalgam.

Porcelain or its stronger ‘version’ and zirconium can also occasionally be used for fillings. These latter materials are laboratory produced and certainly far harder and stronger than composite. So, they are certainly used for overlays and crowns. Not infrequently, particularly for very heavily damaged and root canal treated teeth a full porcelain over metal-based crown will be used.

The good old-fashioned gold overlay or full gold crown is still the best restorative material but is usually only used in areas which really are never ‘seen’… such as upper back part of the mouth.

Cost

Any restorations that involve gold, other metals, porcelain or zirconium (certainly such as crowns) generally need to be made by a dental technician in a separate laboratory. Consequently, unlike composite fillings which are placed and hardened by the dentist in one appointment, these need two appointments (one to ‘prepare’ and one to ‘fit’) and the fees tend to be far higher. A large composite filling can be £180- £325 and a full crown in the region of £850-£1,500.