There's a concept in modern medicine and dentistry of "informed consent". Basically, it means knowing the ins and outs of something before you get into it . . . . . . .
If you're considering composites (white fillings), it's worth going through the history first, so that you understand the properties of the material. Those properties still matter today. Read on - it's actually quite interesting!
White filling material is made of a mixture of a fancy variation on acrylic mixed with a grit made of something like glass or silica. It's basically a miniature variation on concrete - pebbles in cement, but tiny. The very early versions, in the early 1980s were two pastes mixed together. The setting time was unpredictable and they were a nightmare if the area got wet. The grit was large and the resin was soft - so they were difficult to polish and became rough very easily. The resin was unstable, so it went off, going yellow with age. Also, because the resin was soft, it wore away and left a rough surface which collected stain. In short, they weren't very good. (But - they WERE vaguely tooth coloured!)
The fundamental problem with dental composite materials is that they shrink. They shrink about 5 or 6% by volume as they set. So, if you put the stuff in a hole, as it sets, it'll shrink away from the sides and leave a gap around the edge. Result - sensitivity - and a brown line around the filling after a while. If you're unlucky, the filling leaks and decay creeps in around it.
The cure was to bond the filling onto the tooth. We do this by etching the surface of the enamel with a weak acid. It creates a rough surface that we can paint resin onto. The resin locks into the tooth surface and the filling grabs onto the resin. So we get a seal at the edge of the cavity - progress! It also allows us to grip hold of a broken tooth a stick a piece of tooth coloured material to the surface
About 1983, the big advance was light cure. Suddenly, we could shine a blue light on the filling and it would set in 40 seconds - predictably.
Same tooth! Front tooth, patient's left. Not perfect, if we're honest - it's actually a repair on a porcelain veneer. (The red spots are ink used for checking the bite)
BUT - setting the material with light doesn't stop the shrinkage. It's still there. And it shrinks towards the light. So if we're not careful, it pulls up off the bottom of the cavity and leaves a tiny space. Later advances in the mid 1980s added a bond to the dentine, deep in the tooth, but it's not as strong as the bond to the outside enamel.
- The bonding materials are currently on the 9th generation, but there's a great deal of
argument over which are the best. They appear to have gone downhill over
the past few generations, so we elect to use a 4th generation material,
which has worked very well for us for many years. Are the manufacturers
trying to get us to change for the sake of it? (To increase profits?)
We consciously use a brand of material that's tried and tested in clinical
practice because we know it works. To our minds, two
years testing in a laboratory isn't good enough a test, whereas looking at fillings that have been used in real mouths for 20 years ago is as good a test as there will ever be.
Over the years, we've seen advances in the material. It's far more colour stable. It's far better to polish because the size of the grit was changed. It doesn't stain so easily due to change in the resin base and we've had great advances in the way we bond to the enamel and dentine. We've gone from one shade - Universal, which was basically magnolia to a plethora of shades from white and cream through to brown, pink and blue.
In short - composite grew up. But it's not perfect. It's not as hard wearing as good old fashioned silver amalgam, or gold alloy or porcelain - but it's not bad at all. It still shrinks - but we've worked out ways to get around most of it. We've done many thousands of white fillings in our Practice over the past 23 years, so we have a very good idea of what will work, and what won't. It undoubtedly looks good - it's the perfect material for many fractured front teeth, but we do have to understand the limitations.
Large fillings will shrink a lot because of the 5% thing. So, we place the filling in diagonal layers to allow it to shrink without pulling on the tooth substance so hard that it can crack. The bond strength is high enough to grip the tooth and can literally pull the sides off it. So how about we make the filling on the bench and then set it before we cement it into place? If we do this, it's effectively pre-shrunk. Then we can fix it in with a tooth coloured cement that fills up the space.
This technique is called an inlay or onlay. We take an impression of the tooth to create a model of it and then the inlay/onlay is made on the model. Lots of advantages with some disadvantages - It takes two visits - preparation and fit. So it has to have a temporary restoration placed. Most cavities are naturally larger inside than out, so more tooth has to be cut away to allow a solid material to be slid into place. Cost - the work is made by a laboratory so it attracts a laboratory bill of £80 - £100.
So, composite! We love it! If a dentist ever got the chance to be creative without involving a laboratory, this is how we do it. It can look magnificent in the right hands - even better than porcelain at times, and with far less destruction as it can be simply bonded on.
Don't just dive into porcelain without asking about composite first. You may save a small fortune financially and you may prevent the destruction of your teeth.
© Hesslewood Lodge Dental Practice, 2nd October 2012