Prosthodontips – occlusion revisited: part two
We continue the occlusion theme in this month’s Prosthodontips as the Josh Sharpling and Zo Ali discuss static and dynamic occlusion.
In the February column, we went back to the basics of occlusion. Have a quick glance through that as the items discussed are truly the fundamental building blocks of occlusion.
The aim of these columns is to give you a working knowledge of occlusion and to move away from overly complicated or dogmatic approaches.
Hence, I’ll keep things as simple and relatable to everyday practice as possible.
Now that you have an understanding of the key terms, we are going to look at a bit more closely at the features of static and dynamic occlusion.
Before doing that, it is important to understand when all of this information is actually important to collect and record.
Whilst it’s virtually always relevant in some shape or form, it is often not extremely important when carrying out single tooth dentistry. In those situations, it is often possible to simply identify the occlusal contacts for that one tooth and ensure we respect those limitations when restoring. This is because the adjacent teeth provide reference points and help to protect the new restoration/tooth.
However, let’s assume that we are practising quadrant dentistry and restoring multiple posterior teeth in one quadrant in a single visit.
This is quite a common occurrence and in these situations, it is much easier to lose occlusal control. This is because we are essentially resetting the occlusion on that side.
When we restore all those posterior teeth in one visit, we lose those vital reference points. It becomes much more important to reintroduce them in a predictable manner.
The column this month is intended as a practical guide. It is very simple and the aim is to provide you with basic checks you can use on virtually every patient.
However, it is not an exhaustive occlusal assessment. Certain cases will require greater diligence. As always, do get in touch if you have any burning questions or specific queries!
This simply refers to the features of occlusion when the mandible is in ICP, ie maximally interdigitating.
Whilst there are no black and white rules regarding exactly what needs recording, I make note of the following key features that are relevant to daily practice:
- Incisor classification (British Standing Incisor Classificaton, BSI)
- Class I
- lower incisor edges occlude on or lie below the cingulum plateau of the upper incisors
- Class II
- Lower incisor edges occlude behind the cingulum plateau of the upper incisors
- Division one: the upper incisors are proclined
- Division two: the upper incisors are retroclined.
- Class III
- Lower incisor edges occlude anterior to the cingulum plateau of the upper incisors
- Class I
- Overbite and overjet
- This gives additional information on top what we have already learnt from the incisor classification
- If there is increased overjet, then we know immediately that the mandible may have to travel further before the anterior teeth engage and create space between the posteriors. Hence, we would need to be careful when restoring posterior teeth
- A reduced overbite would result in similar problems, just for a different reason. In this situation, there is very little guiding surface available. Although the bite may open immediately once the mandible is moving, the amount of space between the posteriors may be very limited. Effectively we see the same problem as with increased overjet and posterior teeth may be clashing unfavourably (interferences)
- Note that clashing posterior teeth are not always a problem and natural. Unrestored teeth may last a lifetime without any issues. However, large restorations etc significantly weaken teeth and therefore it becomes more important to plan appropriately
- In essence, understanding overbite and overjet gives tells us about the potential for anterior guidance during dynamic movements. Overbite and overjet tell us how close the anterior teeth are to each other and therefore how effective they will be in guiding the mandible
- ICP contacts
- Simply ask the patient to bite together and mark these with thin articulating paper. Check each mark with shim stock and record which teeth hold the shim stock when the patient is biting together (Figure 1)
- This tells how many occluding pairs of teeth there are on each side
- It is also helpful when checking occlusion after completing a restoration as we can confirm the presence of the same pre-op shim stock holds.
Simply put, which teeth are in contact when the mandible is moving forward, left and right. Using two different coloured articulating papers is the easiest way to record this.
For example, with blue articulating paper, ask the patient to bite together and carry out protrusive movements. Then ask the patient to bite together into ICP, but this time with red articulating paper. When you examine the marks left behind, blue marks with no red are the guiding surfaces and you can record these as the guiding teeth during protrusive movements. Repeat this for left and right movements.
Sometimes it is even easier and there is no need to use articulating paper. Using a dental mirror, it is easy to actually visualise which teeth are guiding the mandible as it moves away from ICP.
In most cases, the maxillary incisor teeth tend to guide protrusion.
Lateral movements are usually either canine guided or in group function.
Canine guidance is self-explanatory. Group function is where there are multiple teeth sharing the occlusal load as the mandible moves let or right.
Sometimes the guidance starts in group function but ends solely on the canines, or vice versa. Don’t let this confuse you or allow yourself to over complicate things. Just record what you see.
When you are doing a restoration, in most cases, you will simply be looking to reproduce what was there beforehand. Cases where you might want to change it include heavily restored and root canal treated teeth, or where more delicate restorations (eg veneers) are being placed.
I hope you enjoyed this month’s column, and, as always, please get in contact if you have any questions.
If there are specific topics you would like us to cover in a column, please let us know.