What is the Procedure for a Filling?
The procedure for having a filling involves many stages.
The time taken to complete the fillings depends on size; difficulty, material used and the experience of the dentist, but between twenty minutes for something very simple and an hour for something quite complex could be expected.
First the area is made numb using a small injection of anaesthetic – . This is necessary most of the time but not always- times when it may not be needed could be:
1. If an existing filling has fallen out and there is no decay, a dentist may be able to simply be able to bond some material in to restore the tooth.
2. If the tooth has been root filled (i.e. it no longer has a nerve in it) then a filling won’t be painful, but sometimes the bands we put around the teeth to shape the filling and stop it sticking to the tooth next door, may be.
3. If the reason for the filling is tooth wear on the top or side of the tooth, or for sensitivity and there is no decay.
4. Baby teeth- we can often fill baby teeth without anaesthetic by just explaining what the child is likely to feel while we are doing it.
Removal of caries (decay)
The decay or ‘caries’ needs to be removed from the tooth. We use two main drills - a fast one called an ‘airotor’ which emits the high pitched classic dental drill noise and sprays lots of water to keep the spinning tip cool and a slow speed drill. The high speed is usually used to cut the hard enamel- this is often necessary to access the decay. The slow speed drill is used to remove the decay and softened dentine. Whilst it doesn't sound as bad, it creates quite a vibration inside your tooth and feels a bit like we are getting in there with a mini jack hammer. Those of you who have had fillings will totally understand that description.
With fluoride and the natural defense of saliva, the top part of the tooth often looks pretty intact but decay is occurring underneath- this has either come from the pattern on the top of the tooth or from the side of the tooth. It is only when this gets really large that the enamel finally collapses and you can feel a hole with your tongue. Your dentist will use a combination of the two drills to remove all the decay from the tooth.
If the decay goes so deep that it exposes the nerve (you won’t feel it because the area will be numb), a root canal maybe necessary to save the tooth. Otherwise the dentist will simply fill it up. In slightly deeper cavities, a layer of special lining material will be placed before the tooth is filled up. This will help seal the dentine and protect the nerve. The most common are:
- Calcium hydroxide lining (dycal is a common example) which has a high pH killing helping to neutralise any remaining bacteria.
- Vitrabond (glass ionomer cement)
- ledermix: a cortico-steroid cement that helps to decrease more severe inflammation in the nerve. This tends to be reserved for situations deeper cavities where there is a possibility of irreversible pulpitis.
Filling the tooth
If your dentist is using a white composite filling, the procedure involves a couple of steps, which will vary slightly depending on the particular system used. They will first select the right shade for your tooth, using a shade guide which has a number of different coloured tabs to see how white or yellow your tooth is. The colour will then be matched carefully.
Moisture control for this type of filling is very important, so expect your dentist to pad you out with cotton wool rolls, dry guards or tips (to stop saliva from your cheek) and salivary ejectors (suction that goes next to your tongue) to keep everything dry. Some dentists will use the most effective moisture control system we have- rubber dam (used in root canal treatment). If the filling gets blood or saliva in it before it is finished, it is not likely to bond properly and is likely to have to be redone. This is can be a problem with children as they have lots of saliva and tiny mouths.
The main stages are etching, priming, bonding and filling- which I will now explain. Etching means applying a special acid to the tooth, this creates lots of mini ditches or indentations in the tooth's crystal surface. This may need to be washed and dried, or just dried depending on the particular system the dentist uses. The tooth is then primed and bonded. Priming involves lowering the surface tension to allow the bond to penetrate efficiently down into the little holes. The bond layer is rather like Velcro on a microscopic scale providing multiple little tags which stand up, ready to grip the filling material. This layer needs to be set hard with a special blue light before the filling is added. Your dentist may use a system where all of these are separate steps, or where they are combined into one or two bottles which they apply one at a time.
Filling material is then placed into the tags to secure it firmly to the tooth. The special blue light can only cure or set thin sections of filling materia,l so your dentist will often need to add a bit of material at a time, curing it after each increment, then adding some more. Depending on the size of the filling and the speed of the curing light (a basic one may take 20 seconds to cure a segment, the latest high tech plasma or LED light a mere 5 seconds), this can take some time.
If your dentist is using amalgam- which is very safe and still used a lot- they will simply have it mixed and passed to them by the nurse. It will then be pushed firmly into the tooth with various instruments, most often an 'amalgam packer' of one size or another. So expect lots of pushing even though the area itself will most likely be numb. This type of filling is held in by mechanical retention (or undercuts) so the wider base stops the material from coming out.
Glass iomer cement
If a glass ionomer cement (GIC) is used, the tooth is normally cleaned with a special conditioner and the material applied straight to the tooth. It bonds strongly with the calcium and phosphate of the tooth and either sets on its own or with the help of the blue dental light. Those that are set with the dental curing light are examples of what we call compomers- a combination of composite and GIC generally in the ratio of about 80% to 20% respectively. As such the composite part sets rapidly with the light and the glass ionomer part via a chemical reaction over the next 24 hours.
If the filling involves the side of the tooth, which nowadays is more likely than not, we have to put a little band around the tooth to prevent the material from flowing out or sticking to the tooth next door. We need to keep the tooth shape! We call these bands matrices or matrix bands.
Different types are available and different dentists prefer different ones, but they all do the same job. The dentist may squeeze your gum a little when the band is tightened and there may be a bit of pressure when your dentist puts in a little wedge to help push away the neighbouring tooth and ensure the material isn't going to leak out.
Shaping, polishing and adjusting the bite
Once the tooth has been filled up, it is time to shape the filling material so that it looks like a normal tooth again. We also need get your bite right. To do this, the dentist will use a range of burs or little fine discs if it is a white filling. They will carve the shape with hand instruments if it is a silver filling.
Finally they will continue with this procedure until your bite feels normal again- they test your bite with articulating or bite paper which they will place in your mouth and ask you to bite down onto. Your teeth will mark the paper and show any high spots that need adjusting. You should feel your teeth meeting on all sides and at the front (assuming they did so before) if the bite is right.
A little roughness is common but this will smooth off during normal eating and chewing. If it is very rough or doesn’t feel right, let the dentist know so he can make it more comfortable for you.