A dental crown is an example of an extra coronal restoration. The vast majority are indirect for which you require an imprint or impression to be taken prior to construction of the crown. Dental crowns can be classified in different ways but generally according to their use, their aesthetics and the material.
Posterior crowns on premolars and molars need to be strong enough to withstand biting forces; however , anterior crowns require superior aesthetics. Crowns can be divided into their coverage such as full coverage crowns, three-quarter crowns and inlays/onlays.
The earliest crowns for posterior teeth were full gold crowns and porcelain jacket crowns for interiors. The porcelain jacket crown for anterior teeth was not strong enough sometimes so an alumina core was placed but this resulted in a compromise to appearance. Eventually, this underlying core was made out of metal resulting in porcelain fused to metal crowns.
All-ceramic crowns nowadays are strong enough to use in most posterior situations and the aesthetics are more superior to traditional porcelain fused to metal crowns.
Here Are The Advantages Of Dental Crowns
- In order to provide protection for the tooth. A tooth which has been ravaged by extensive dental caries or has a large restoration which is failing, needs extra-coronal protection.
A crown is able to provide this protection so that the tooth will last longer against functional occlusal forces. In addition, if a tooth has been root-treated, it needs extra protection because as a rule, root-treated teeth are generally weaker than teeth which have not been root- treated. This is for two reasons. Firstly, without dental pulps, there are no odontoblasts to produce dentinal fluid so dentine loses its moisture content and becomes more brittle.
Secondly, the teeth that need to have root canal treatment will usually have been extensively weakened by the restoration after removal of dental caries. With crowns, teeth can even be saved when there is very little coronal tooth structure left. Extra retention may be necessary such as a dentine and bonding agent, dentine pins and root posts.
- The crown can provide superior aesthetic results compared to a large composite filling. Some patients may even ask for a crown on a premolar or molar tooth where the existing filling such as amalgam is causing concern with regards to their appearance.
Dental Crowns Do Have Disadvantages And It Is Important To Know About These Before You Embark On This Course Of Treatment
- It is important to know that 20% to 30% of all vital teeth which are crowned will become non-vital and need root canal treatment in the future. This is because a tooth which needs a crown, will at some point have had extensive caries and extensive restorations.
Although the dental pulp does have remarkable regenerative qualities, nevertheless, caries and dental treatment does produce significant stress and the dental pulp then not be able to recover adequately. The stress produced may be a one off sudden stress such as having a deep filling or a large restoration or it could be due to repeated restorative treatment. Sometimes, it is the preparation which also produces stress on the tooth which is the last straw that breaks the camel’s back.
When a tooth which is a crown then requires a root canal treatment, this is usually carried out through the existing crown structure. This has disadvantages. It is more difficult to carry out a root canal through an existing crown as compared to a tooth without a crown on. This is because a dentist has to drill through the crown structure first and also estimate where the dental pulp is. The other disadvantage relates to appearance and structural integrity.
Where the access cavity has been made, it then has to be sealed up using a material such as composite or glass ionomer. The restoration into the access cavity is easy to spot especially if it is on the occlusal surface.
In addition, the procedure of carrying out the root canal treatment will have weakened the tooth and the tooth is more likely to fracture unless the underlying tooth core is reinforced further.
- A crown is most susceptible at its margins. Ideally, the marginal gap must be microscopic and is usually filled in with the luting cement.
If the gap is large and the cement washes away, this creates a gap where dental caries can develop or produce sensitivity. The luting cement is also vulnerable especially if moisture was present during the cementation stage of the crown.
- A crown takes two visits to make whereas a filling can be done in one visit. Each appointment in addition will be a long appointment so quite considerable time is spent making a crown for a patient as compared to a normal filling. In addition, problems can arise between visits while the crown is being constructed in the dental laboratory.
For instance, the temporary crown can come off and cause irreversible pulpal damage or sensitivity effects. If the temporary crown comes off and is not put back on immediately, this can result in movement of the adjacent teeth through mesial drift of opposing teeth or from over eruption. Even worse, the crown margins cannot be maintained if the gingiva grows over the margins.
- Dental x-rays can have limited value in assessing caries under a crown. The best way to assess a crown is by probing with good direct vision and to check the proximal margins with the bite wing radiographs. Unfortunately, often when caries are spotted on the radiographs, it becomes too late to save the tooth. At the very least, additional root canal treatment becomes necessary.
- The cost of the dental crown is approximately five times that of an equivalent filling. This means that you could have 5 fillings before you get up to the cost of a dental crown.
There is another important factor to also consider and that is that over a lifetime, a dental crown will need to be replaced every 10 – 15 years. This is partly offset by a filling requiring replacement every 5 – 15 years but nevertheless the difference is significant.
Before having a dental crown, patients should sit down with a dentist and have a thorough assessment and discussion with regards to all treatment options and if that indeed is the best treatment available.