White Fillings versus Dental Amalgam Fillings
I have been staring at old dental amalgams for nearly 30 years wondering why the teeth containing them fracture or break up & why there is almost always dental decay beneath them when I go to fix them.
Silver Fillings vs White Fillings
At Milford Dentists, North Shore, I haven’t placed a Dental amalgam (silver/metal) filling since 1999. I have placed white fillings aka composite resin fillings successfully instead – this is because white filling bio-mimics tooth structure i.e. it behaves very similarly to the tooth that has decayed or snapped off that it is replacing
But what is going on here? Why have I opted for Milford Dentists to be Mercury Amalgam Free since 1999?
Over the last couple of years clever researchers, some of whom are dentists have worked out why dental amalgam fillings end up making teeth snap, fracture & decay; eventually making the tooth fail. This has reinforced my own theories that Mercury Dental amalgam fillings are a disaster for teeth & conversely white composite resin fillings are a much better more biomimetic (life like) alternative.
There are a few physical processes going on when you have a dental amalgam filling sitting in your tooth.
- Temperature changes making the filling expand & contract
- The tooth cusps & dental amalgam filling all moving in different directions during chewing
- The actual dental amalgam cavity preparation destroying parts of the tooth that actually hold the tooth together
Temperature Change in Mercury
Around 50% of dental amalgam is made up of mercury. Mercury has been used in thermometers for years because it expands and contracts a great deal with temperature change. So when you, say, have a hot drink, the mercury in your dental filling heats up & expands making the filling bigger. This puts a whole lot of pressure on your tooth & eventually your tooth can’t take the strain & cracks/fractures/snaps.
Conversely when you have something cold to eat or drink – say ice cream, your filling contracts leaving a gap around it. Conversely, white bonded composite resin fillings have a similar coefficiency of expansion as the tooth with temperature change i.e. composite resin expands & contracts just like your tooth with temperature variations. White fillings are also bonded or “glued” into the tooth cavity which means there are no gaps around the edges.
Everything is moving when you chew
When you chew you are putting a lot of pressure on your teeth (approximately 150-newton centimetres of torque). Surprisingly, for something so solid, a tooth will twist and bend a little under this pressure. In tests on teeth (in vitro), a tooth with a medium sized amalgam filling will flex 26 times more than a tooth with a similar sized bonded white filling.
In fact, the tooth with a bonded white filling will flex almost the same amount as a healthy tooth. This is because the white filling not only fills the cavity, it also bonds the tooth back together again biomimetically, so the tooth & white filling are swaying & twisting as one.
Essentially the teeth tested with the amalgam fillings are twisting & bending in all different directions i.e. the cusps are moving away from each other & the amalgam filling is jiggling around in the cavity, as the mercury amalgam is just a hole filler & does not “glue” anything to anything.
In the first part of this film clip a rubber band ball illustrates what happens when any object is put under pressure - the ball obviously squashes a lot. The same thing happens to seemingly solid objects like teeth, but by a smaller amount ie when you chew, your tooth is bending, flexing & squashing - 26 times more so if there is a medium sized mercury amalgam filling in your tooth.
The second part of the clip shows a chewing machine & how the information about how teeth with various fillings behave when chewed on is gathered.
The actual dental amalgam cavity preparation
Because mercury dental amalgam is a hole filler it needs to be “keyed” or locked into the tooth by undercuts so that it doesn’t fall out. At dental school, this type of dental cavity preparation is called a “G V Blacks” cavity. The cavity shape destroys “girders” of enamel that hold the tooth together.
In the last 10 years, dentists have discovered that the tooth is a lot more complicated structurally than we had thought. There is a complex framework of stronger enamel spokes that connect together within a strong enamel rim running around the tooth on the biting surface. If the spokes and or the rim is cut during a dental amalgam cavity preparation the tooth is weakened, eventually leading to the tooth snapping.
Imagine trying to ride a bike with some of the spokes broken or part of the wheel rim missing.
As already mentioned a bonded composite resin filling glues the tooth back together & because white fillings are bonded they do not need to be “keyed” into the tooth. This means cavities for white fillings are smaller than corresponding cavity shapes for an amalgam filling.
A lot of the time teeth can be repaired using white composite resin filling material. As well as strengthening the tooth with the bond or "glue" holding each part of the tooth to the rest of the tooth these restorations look very natural -
If the tooth is weakened by tooth cracks or decay sometimes the optimal option to strengthen & hold the tooth together for the longer term & at the same time improving its appearance is a dental porcelain crown or overlay. This acts like a crash helmet for the tooth holding everything together.
Posted by Andrea Clarke BDS
Milford Dentists is proud to help the good people of the North Shore with all their dental requirements - From Devonport and Belmont up through Takapuna, Castor Bay, Mairangi Bay & Browns Bay as well as Albany, Northcote, Hillcrest & the Whangaporoa Peninsula.