You may have noticed that initially your new porcelain veneers were perfect in colour but over time it is now not the case. The main causes of discolouration of porcelain veneers over time are the following.
1. Decay developing under the veneer.
2. The underlying tooth becoming non-vital.
3. Discolouration due to ageing.
4. Discolouration due to the underlying veneer cement.
Before we look at the above in more detail, it is important to note that colour is quite a complex subject in dentistry and can be divided into three components which are chroma, hue and value.
When decay/ dental caries develops under a porcelain veneer, it will normally begins with discolouration around the edges of the veneer. The edges may be around the gum line, adjacent to the neighbouring teeth or along the tip of the veneer also called the incisal edge.
The discolouration that occurs will be dark brown or black in colour and as the dental decay progresses, the discolouration area also becomes larger. Discolouration usually develops because you have a diet high in sugar but it can also develop in a moderate diet if gaps appear under the veneer where bacteria can easily get inside. In these circumstances, it is important to get this treated as soon as possible before the decay gets even worse. If it is caught in time, you will need just a new veneer rather than needing more extensive treatment. If the decay however is much deeper, the treatment will be more extensive and it may mean that you need a crown and even a root canal treatment. If the decay has been there for a long time then it can also mean that it has progressed so far that the tooth can no longer be saved. Fortunately, this scenario does not happen often where the tooth needs to be extracted.
If a non-vital tooth becomes discoloured because the underlying dentine no longer has any nutrition going into it from the dental pulp, this will happen gradually. A tooth which has had a porcelain veneer will become non-vital for two reasons. The first reason is if extensive decay/ caries develop underneath it but probably the more common reason is that about 20% of all teeth which are crowned or veneered become non-vital. Unfortunately in these cases, it becomes necessary to carry out the full root canal treatment and a full coverage crown will become necessary also. If this is not carried out, infection due to non-vitality will spread into the surrounding periodontal periapical tissues which can lead to a dental abscess.
Age is an important factor and patients will compare their teeth from 10, 15 or even 20 years ago. All teeth discolour over age and this is due to 2 factors. The first factor is related to the enamel of your teeth which provides translucency. With time, the enamel over your teeth becomes thinner and this means that the underlying dentine which is more yellow in colour becomes more apparent. The other factor is that with time, your tooth lays down secondary and tertiary dentine which is darker than primary dentine but also the thickness of the overall dentine layer will be greater. This results in the teeth becoming more yellow and there isn’t much that can be done with regards to this. However on the average, porcelain veneers will last 10 years so after 10 years you could have your porcelain veneers replaced with new ones that you prefer.
Finally, another reason for porcelain veneers to become discoloured is due to the cement that is used to bond the veneer onto the your teeth. This is due to the degradation of the bond polymerised matrix of the resin component of the porcelain veneer. Once again unfortunately not much can be done with this but this occurs and is only apparent after several years of having veneers done and if you are going to have your veneers replaced after 10 years, then this doesn’t become much of an issue. It is also known that light cured cements have less cement degradation than chemically cured or dual cured cements. However, light cured cements also can have disadvantages and it is up to the dentist’s discretion as to which cement is used for your porcelain veneers.