“Do you think people with old ‘silver’ fillings should have them removed and replaced by more up-to-date materials?”
– Question from Tony of Mango Hill, Brisbane
Dr David Kerr replies:
That’s a very common question and it’s one that is difficult to give a definitive yes or no answer. Although there has been no conclusive research that shows that silver mercury fillings are harmful to your health (regarding mercury leeching), in our experience we have seen a lot of problems that occur underneath these old fillings. These are problems are not easily observed from the surface or with X-Rays and is primarily to do with decay getting under the fillings and cracks in the teeth.
Silver fillings can hide decay
Because silver fillings are opaque to X-Rays, it’s difficult to see a cavity under the filling until they are quite extensive. Research has shown that when you’re examining a patient with silver fillings, if you don’t use any X-Rays you can see 50% of what is going on and with a full set of X-Rays you will still only see about 80 – 85% of what’s going on. So there is 15% – 20% of cavities that we wont be able to see because the metal blocks out this damage.
In some cases, this can mean the difference between getting another filling or having to have a root canal treatment.
Silver fillings are also a factor in teeth cracking
Another factor to consider is the cracks in the teeth, which also won’t show on X-Rays at all. We see this commonly in people in their 40’s or 50’s. For instance Darryl had some fillings put in when he was in his teens and at his last hygiene appointment Robyn noted some cracks coming off those teeth. He has had some sensitivity, which means the cracks are getting deeper, and closer to the nerve and he will have to have those teeth crowned. In his case there’s no new decay there, it’s just a wear and tear issue that is unavoidable with aging.
Do tooth coloured fillings prevent teeth cracks or decay?
We know from the research that silver fillings do not strengthen teeth at all. So a silver filling in a tooth, essentially acts like a wedge, and when you bite down on the filling the forces are transmitted to the remaining tooth structure. If the filling is more than about a half of the width of the tooth there is a good chance that the tooth is going to crack, break or chip. If the filling is a third of the size of the tooth it is less likely but still a risk.
Because the silver filling material was usually just packed in, there is no adhesion of the silver filling to the tooth, which we get with the tooth coloured materials. This adhesion means that the chewing forces are distributed over a greater amount of tooth, making the tooth about 15 – 20% stronger with the tooth coloured compared to silver filling.
The force of biting down with the chewing is also distributed across the whole tooth structure more evenly than it is with silver filling, meaning less likelihood of tooth cracking.
The complexities of horizontal and vertical teeth cracks
If you get cracked teeth, the cracks can sometimes be horizontal, which means a piece of tooth will fall off, and that looks very spectacular, but it’s usually self limiting. The real problem is when the crack is oblique or vertical (where a tooth splits in half and goes down to the nerve). This can lead to tooth abscesses, fractures into the roots and lots of other potential complications. All of this can come with little or no warning at all.
The advantage of tooth coloured fillings in detecting dental problems
There is a lot of variation in the materials that tooth coloured fillings are made from and how they show on X-Rays, so I can’t unequivocally say they are all better to see dental problems using X-Rays.
Where their advantage lies is that on the tooth coloured fillings you can see the problems starting more easily because of staining around the edges. This means the seal between the tooth and the filling is breaking down, which is a sign that something needs to be done. With silver fillings they tarnish and corrode so its much more difficult to identify when there is a problem.
The bottom line: Replacing silver fillings depends on your dental proactivity
Ultimately, whether you replace all your fillings depends on how proactive you want to be. Some patients approach is to only come to the dentist when they are in pain and this isn’t for them.
For other people their approach might be: “My teeth are more important to me and I know it’s going to be more cost affective in the long run. Yes I have to pay more upfront, but its going to be more cost affective to fix problems when they are small rather than when they are big, so I’ll do it sooner rather than waiting till it hurts.”
The different strategies for replacing silver amalgam fillings with white fillings
The strategies I have seen people use vary and there is no ‘one size fits all’. Some people will want to do everything at once and then sleep tight knowing that it’s all sorted out. Others will pick the part of their mouth that is worst and together we will break it up into sections: do the top right this year, the bottom left next year, and so on.
If you are replacing your fillings in stages I would recommend that you replace the bigger ones first as these cause more problems. If you think of your jaw like a nut cracker, you have the hinge at the back, the forces on those molar teeth are eight times the force on the incisor teeth, so those molars are always under more load. The fillings in those teeth also tend to be bigger and better at hiding or decay or causing tooth cracks.