Title: Occlusion in restorative dentistry.
Lec no: 4
Done by: Eman N. Smadi
We will talk about the Occlusion, how to construct the occlusion, what are the occlusion consideration when you are doing direct or indirect restoration.
What is our aim?
Our aim is to provide a restoration that is in harmony with the existing occlusion and that will not have a negative effect on teeth, bone, periodontal ligament, muscular and articular surfaces.
The starting point is the Examination, this is what we always miss, we should start with examination, look at the tooth and see the occlusion on it before start doing your restoration.
For example if you want to do a restoration on a canine, you should look at this canine and examine it … is it a guidance? Does your patient have a canine guidance on that canine I want to restore? What should I aim afterward? Should I restore the guidance on it?
We will start talking about two approaches:
The conformative approach
The re-organised approach
The conformative approach:
It means that the patient happy with his/her occlusion so I wouldn’t change it, I will do the restoration and keep the same occlusion. Around 80% of our work is about conformative approach.
So the definition of the conformative approach is the provision of restorations in harmony with the existing jaw relationships.
That means in your practice the provided restoration does not alter the static or dynamic occlusion relationships. It is the easiest and safest approach.
For example if I want to do single crown on lower 5, which approach should I use and why?
I use the conformative approach I keep the same static and dynamic occlusal relationships, because it is a single tooth and the most important is that the patient is comfortable with his/her occlusion and happy with it, even if there is slight mal alignment or the centric occlusion not coincide with the centric relation but the patient is happy with the existing occlusion so I don’t need to change it.
When it is used?
The patient has an ideal occlusion.. this is very rare to happen only 10% of the population , it is when the patient has the centric occlusion coincide with the centric relation, with anterior guidance free from posterior interferences.
What is the properties of ideal occlusion (comfortable occlusion)?
Simultaneous, well distributed contacts in centric occlusion, stable centric occlusion and there are no interferences in lateral and protrusive movements.
The patient does not have an ideal occlusion however the provided restoration will not change the patient’s existing occlusion.
In reorganizing the occlusion I want to change most of the contacts on occlusal surfaces of a large number of teeth, except sometimes you have to restore a single tooth but still you have to use the reorganized approach not the conformative one and this what you will do in two cases:
If the tooth which I want to restore has interference so I should eliminate the interference in the new restoration.
If the tooth to be restored is a deflective contact, for example tilted lower 7 and it is a deflective contact when the patient occlude in centric relation he/she bites on it then deflects the mandible to the centric occlusion so if I want to restore this tooth why not to eliminate it and give the patient something better.
The dr showed us a picture for patient with non-working side interferences, in such case we should use the reorganized approach and eliminate the interferences.
The interferences are not healthy, what could the interferences do?
At tooth level attrition or fracture of cusps may happen, fracture of restoration, mobility of the tooth, periodontal exaggeration of any disease there and in extreme cases may cause TMJ and muscles problems.
What is an ideal centric contact?
It is a point contact (tripod) not a surface contact, the more surface contact you have the more wear and lateral forces on the tooth, also it should be in line with the long axis of tooth and simultaneous with other contacts. Try to avoid infra or supra occlusion, most of the dentists who want to free there minds do restoration that is infra-occlusion, this is not healthy for many causes, it will lead to over eruption of the opposing tooth and that will lead to interferences later on because it will disturb the curve of Wilson and the curve of spee, in addition to that the tooth will not be in function.
What is the technique of the conformative approach?
We will talk about a principle called ‘’EDEC principle’’, we use it in direct or in indirect restorations. It means:
E= Examine, D= Design, E= Execute, C= check.
EDEC principle for direct restorations:
First of all I should examine the occlusion of the patient and the tooth I’m going to restore it.
Also we can use this principle in indirect restorations, we do pre-treatment records and then you start your preparation then you do provisional restoration to check the new occlusion then you do your final restoration.
Bite records, that what we do, we record the occlusion of the patient. We have two dimensional and three dimensional bite records.
two dimensional bite records: photographs or written records (more precise) or occlusal sketching. In clinic when we want to record the occlusion of the patient we should have an idea about many things such as the static stops when the patient closes in centric occlusion where are the stops and we should see on right lateral if there is a guidance and if there are any interferences, the same thing on the left side and if there are interferences in protrusive movement.
How could we see the interferences in eccentric movements?
First thing we train the patient to do the movements then we use an articulating paper and ask the patient to bite in centric occlusion then we flip the paper and ask the patient to do the movements if any lines showed on non-working side this means there are interferences on that side. You can also ask the patient if there are any interferences and he/she can tell us.
This is very important especially in the comprehensive cases, we should take proper history and examination, study models, radiographs and occlusal records.
Three dimensional bite record: you record the spatial relationship of the prepared tooth to its antagonist, other teeth should contact as before. When you put the biting material on the prepared teeth the other teeth should occlude on each other.
Note: the biting material could be hard wax, elastomer, acrylic resin (the acrylic resin we don’t put it on all teeth only on the prepared teeth). We should put little amount of biting material only on the occlusal surfaces of teeth and not to interfere with the mucosa and cheeks to avoid over stimulation of the soft tissues and as a result the patient will bite wrongly. It is preferred to put the biting material on the prepared teeth only if there are enough teeth in the mouth to occlude on them, but still we can use horse shoe on all teeth, in this case we should make sure that the sheet is perforated if we take the bite at centric occlusion or maximum intercuspation.
If only we have the sex anterior teeth and there are no posterior teeth, in this case we lost the centric occlusion and we have to build a new CO on the CR, we should put base plate as if we do a complete denture.
Occlusal practice in advanced dentistry:
We will talk about something more advanced not simple restoration or simple crown. In most patients the existing occlusal scheme is usually functional, comfortable and cosmetic, therefore the most appropriate way is to adopt a conformative approach, it means to provide treatment within the existing envelope of static and dynamic relationships of the teeth however there will be situations where this can’t be adopted, that means when treating advanced restorative cases, the conformative approach might be not appropriate or even possible.
When multiple posterior teeth are missing or they are prepared, in this case we lost the reference starting point making it impossible to return to the pre-existing occlusion when trying to record the inter-arch relationship, but there is a way make us able to bypass this problem, for example I have a patient who want to prepare his teeth from first premolar to second molar, if I prepare all teeth together at the same time and ask the patient to bite in CO at this point the patient doesn’t have a clear CO reference as was before the preparation and we will go for reorganized approach, to bypass this problem and use the conformative approach (because the patient is happy with his/her occlusion) I will prepare two teeth at first (for example the 4 and 6) and then take a bite record and then I prepare the other two teeth, by doing that I preserve the occlusal relationships of the patient. Also we can prepare 3 teeth (4, 5, 6) out of 4 (4, 5, 6, 7) and if we think about it the most important tooth of these 4 teeth is the last one (second molar), that means we prepare the first 3 teeth and keep the last one and we record the bite then we prepare the last tooth.
When the conformative approach is not appropriate? (Indications for reorganized approach):
1-When we need to change the actual occlusal relationships.
2-Increasing the vertical dimension of occlusion, it is impossible to increase the vertical dimension without changing the occlusal surfaces of at least one arch.
3-Most of teeth are significantly out of position.
4-Change in appearance wanted, for example when the patient tells you that he/she wants to change the appearance of anterior teeth from right premolar to left premolar.
5-History of occlusion repaired or fractured existing restoration, this means the patient has heavy interferences and I should think about reorganized approach.
6-Recurrence of TMD that has relapsed after successful splint therapy. Not every patient has TMD we do reorganization of his/her occlusion because very small percentage (<10%) of the TMDs related to dental problems.
When the conformative approach can’t be used we need to plan the new restoration to the different occlusion before the work started.
Changing the occlusion without having a plan for new occlusion and jaw relationship is an unorganized approach.
The aim of reorganized approach:
To provide a restoration which although change the occlusion, but it will be tolerated by the patient.
How do you provide the occlusion that is tolerated by the patient?
At tooth level, at PDL level, and at the articular level.
A poorly tolerated reaction could cause TMDs, occlusal trauma to PDL, mobility, fractures, excessive root surface loss and hypersensitivity.
So the reorganized approach provides an ideal occlusion at tooth level, at the articular system level and at the patient level, it means the patient should be happy with the new occlusion.
At tooth level means we try to make multiple, simultaneous, well distributed contacts, cusp to flat fossa contact, no cusp to incline, the occlusal forces directed as you can along the long axis of the tooth.
Smooth shallow guidance contact, for example not to make the angle between the upper and lower canines very steep (upright), and by doing smooth shallow contact we decrease the load on the teeth and relax the muscles.
Articular system level means to have CO coincide with CR as you can, to have freedom in CO (not to have very high cusps because when the patient occludes he/she will have locked maximum intercuspation and this is not comfortable to the patient and he/she will not be able to do the movements easily) and not to have posterior interferences (at two levels, lateral movements and protrusive movements).
How to reorganize the occlusion?
Using EDEC principle, first step is to provide appropriate occlusal scheme before delivering the final restoration by making diagnostic wax up (mock up), it is very important to make wax up for teeth to study the occlusion of the patient and to make provisional restoration.
Examining phase… you record the jaw relationship in CR, in reorganized approach you don’t have any true repeatable reference in patient’s mouth except the CR, so your bite will be a CR bite using bimanual manipulation of Dawson, you position the patient on his/her back, put the two thumps on patient’s chin and your four fingers on the mandible, then you try to do a rotational movement to the mandible but don’t let the patient to close completely (the teeth shouldn’t touch each other, there should be a separating material between upper and lower teeth, for example: wax). Doing this technique in some patients is very difficult, you have to do deprograming for anterior teeth (forgetting the memory of teeth) using piece of resin or cotton roll and ask the patient to bite on it for few minutes, by doing that you tire the muscles to be able to close the mouth incompletely.
Anterior deprogrammer device (Jig of Lucia).
Then you examine static and dynamic occlusion of the patient and mount it on semi adjustable articulator with a face-bow. Then you design doing a wax up, and take the contacts and guidance of your wax up. Sometimes you need to do selective grinding for the cast if you have cusp tip interferences and you not going to change the crown or the indirect restoration then you do the same selective grinding inside patient mouth. We allowed to make selective grinding for very little amount of enamel, if there is heavy interference and it doesn’t disappear using selective grinding you have to think elsewise, you might think in onlays for example.
Then you have to design the curve of spee and curve of Wilson.
Note: the diagnostic wax up is very important step, through it you can discover that the patient needs orthodontic treatment before doing the reorganized occlusion for example, also it helps you to do ideal occlusion, optimal crown preparation, and to verify the treatment plan.
How do a diagnostic wax up help us to verify the treatment plan?
By making provisional restoration that you will leave it in patient’s mouth for weeks or months then the patient will give you feedback if it was good or not.
Sometimes you do selective grinding, sometimes you need to refer the patient to orthodontic department. At the end you do provisional restoration.
make sure your patient is very happy.
Note: the diagnostic wax up helps the technician to copy what you have on your wax up to do the crown. How does he do it? For occlusal features he do index using silicon on your wax up then he transfer it on the crown he makes then he copies it.
How do you copy your anterior guidance?
You put acryl on your incisal table and you make acrylic block on your wax up model, it means you put soft acryl on your wax up model on articulator and you do the lateral and protrusive movements (anterior guidance), when the acryl piece becomes hard the technician can use it to make the crowns to achieve the same anterior guidance you want.
The ideal occlusion is a concept of treatment, it is not a treatment objective by itself.
Examination of patient involves examination of teeth, periodontal tissues and articular system.
There is no such thing as a bad contacts.
The patient occlusion should be recorded before any treatment is done and compare the patient’s occlusion against the ideal occlusion concept.
Conformative is the safest approach.
Ensuring that you are using EDEC principle if you follow reorganized approach.