Composite fillings

Q:In October 1994, I had my amalgam fillings removed as a preventative measure. They were removed in sequence, under proper conditions, by a skilled and highly recommended dentist and replaced with composites.

Ever since, my teeth have been extremely tender and sensitive so sensitive on the right hand side that I am unable to chew on that side at all. I am no longer able to eat anything hard like raw vegetables or nuts, and anything hot or cold is out of the question. The teeth have been checked by two different dentists, who have vouched for the quality of the original work, but at my request, two of the composite fillings were replaced with implants as I felt this would help it didn't.

My teeth did not give me any problems at all before the fillings were replaced (12 in all), and while I am pleased to be rid of the mercury and the teeth now look great, they are no longer able to do the job they were designed for! M C, Perthshire.....

A:To answer the many questions we've received lately about the safety and wearability of composite fillings, we consulted a variety of specialists on the subject, including Dr Stephen Dunne, senior lecturer and consultant, of the department of Conservative Dentistry, Kings Dental Institute in London, who has performed his own research and extensively reviewed much of the literature on the safety and effectiveness of all dental restorative materials.

Composites, which are resin based (a form of plastic) are either applied as a paste to the tooth and hardened in the dental chair with ultraviolet light, or made in a laboratory as a hardened inlay to match the cavity in the tooth.

Whatever the considerable questions about safety, the one advantage of a malleable metal like amalgam is that it it resists any contamination of moisture as the filling is placed, says Dunne. All metals in the mouth corrode that is, rust. Amalgam's adaptation to the tooth also improves with time, as the corrosion products seep into any marginal cracks between the tooth and the filling. While this seepage and the corrosion products isn't doing your health much good, in straight terms of filling the cavity, it works nicely. With most other fillings placed today, says Dr Dunne, the seal between the tooth and filling, a harder substance unable to seep into the tooth's crevices, gets worse over time. Even with gold or ceramic or porcelain inlays, the resin based soluble cement can wash away over time.

With composite fillings, which are all based on resin based materials, saliva, blood or gum fluids, or any sort of moisture at all, can adversely affect its ability to bond properly.

This is why it is vital for dentists to use isolating procedures like rubber dams and to take great care that instruments they are using such as air instruments to blow the tooth dry are not contaminating the cavity. Dr Dunne did a study of dental practices in Britain and found that all air instruments were contaminated with water and half were contaminated with oil. Even rubber dams used to isolate the tooth can have gross contamination, he says.

Another possible reason for your tooth sensitivity is that the fillings have shrunk. When liquid composites are placed in the mouth, these plastic substances must be "cured" or polymerized, which hardens and set the plastic through use of a curing light. When the material is cured, the filling can shrink between 2-5 per cent. If the bond is inadequate, the composite will shrink and have a marginal gap between filling and tooth, which will never improve.

Composites can also hurt when they haven't been properly cured. Some composite fillings have a solid top and what is referred to in dentistry as a "soggy bottom" a liquid like base, with a thin layer of cured material on the top. According to Dr Dunne, a survey found that 60 per cent of curing lights in general practice in the UK are operating below manufacturer's specifications. This is less of a problem if you are getting inlays, which have been moulded to the precise dimension of your tooth's cavity and so are cured in the laboratory.

Dr Dunne maintains that in terms of longevity composites placed directly into the tooth last about half as long in big fillings (gold is the strongest of all), but for smaller ones, do just as well as metal.

However, WDDTY panellist and mercury free dentist Tony Newbury maintains that frequent sensitivity is no longer the case with the newest techniques and materials. Professor Carl Leinfelder of the University of South Carolina, who performs materials testing on humans, says that the 'ideal" restorative materials and least resistent to wear (even over gold, classically considered the hardest substance) are resin based polymers Z100 by 3-M and Charisma by Kulzer, placed in by a careful layering process.

Tony Newbury, who now uses this state of the art method, says that after etching the cavity, he seals it with a resin bond layer, which effectively seals the tooth, preventing sensitivity. Next, he places in a low polymerization (that is, soft), self hardening substance of glass ionomer, which will bend with the base of the tooth as a normal tooth does. The materials of the glass ionomer have minute bits of fluoride, which, for whatever else they may be doing to you, kill bacteria for at least three years, thus helping to avoid breaking the seal. Over that goes more resin bond, then a macrofill material of high polymerization, which needs to be cured with the dentist's light. Another layer of bond follows and then a microfill substance after that, which is very hard wearing.

Through testing on humans with electronmicroscopes, the University of South Carolina has rated this more hard wearing than gold, porcelain or any other composites.

As for older fillings put in without this process which aren't causing sensitivity, Mr Newbury says that your dentist only needs to take off a little layer to refurbish them, not pull out the entire filling.

Tony also makes the point that to place amalgam fillings, dentists have to cut a pyramid shaped wedge in the tooth, with the bottom of the cavity larger than the top for it to stay in place. This seriously undermines the future strength of the tooth and isn't necessary in composite fillings.

Since employing resin sealants a year ago, Tony has had no patients complain of sensitivity.

Of course, another possibility is that your dentist is new to the task. "Many dentists have not been training the placement of resin based fillings," says Dr Dunne. With so many new tooth coloured dental materials recently introduced and with patients clamouring for non amalgam alternatives, many dentists undertake tooth coloured fillings without taking post graduate training, he says.

If you are contemplating having resin based fillings, Dr Dunne recommends that you choose a dentist who uses a rubber dam and meticulous isolating procedures prior to placing the filling. He should also have a system of checking the output of a curing light virtually every day. And he should take care of drying and cleaning of the cavity prior to placing it. Tony Newbury has placed a special filter in his air system to filter out air and oil. Most of all, he should have plenty of experience and lots of contented patients. If you're thinking of having all your silver fillings replaced, it's worth asking how many such jobs your dentist has done, how many patients return with sensitivity problems, and even requesting that you be able to speak to a few patients.

If you're experiencing continued sensitivity, it's very likely that your filling is "leaking" that is, a gap exists between the tooth and its filling. There is also the smaller possibility that the pulp was damaged by the filling, or that your bite has been displaced by the shrinking of the composite.

To determine the cause of your problem, you may have to have x-rays done, which will show up any gaps between tooth and filling. However, if that's not the problem, an x-ray will not show if a filling has been properly polymerized. You might also wish a nerve vitality test, to see if the nerve is healthy or inflamed. You'll also need the bite looked at. Obvious staining around the margins will also indicate a gap. If "leaking" is the problem, unless you are allergic to composites, in Tony's view, the sealant layering method described above should sort out your problem.