Occlusion

‫بسم ال الرحمن الرحيم‬ Lec #9, crowns & bridges. Occlusion in fixed prosthodontics .

What is occlusion ? Occlusion (in simple words) is the teeth contact relationship which might be dynamic or static , means that any teeth movement like closure, protrusion , excursion ...is considered as occlusion . There is something called masticatory system ,(this system includes teeth, supporting structures like bone and periodontium, and the articulatory system) all of these together form the masticatory system). If you play with any of these components then you are affecting the whole masticatory system .

All of these structures work together in harmony, and there is a complex relationship between all of these components which is difficult to be understood fully .so what you need to do is to avoid any thing that could affect this harmony ,the only part of occlusion which you can play with( in your clinic) is teeth, if you affect teeth then you are affecting occlusion , and definitely the masticatory system .

**What are the possible complications when you create disharmony ? Each person have been created in a way that these structures works together in harmony, if you create a disharmony, there will be sort of complications to your patient like : Page | 1

Fractured teeth or restorations //Accelerated tooth wear // Tooth migration // Tooth mobility // TMJ As general dentist, you are in a position to prevent those from happening ,and you are expected to diagnose any disharmony in this system if created by other dentist ,and to treat some of these problems , while it is a must not to be the one who create anyone of these complications for your patient .To understand your job regarding this subject, you have to know the basic principles of occlusion , and the applied science of these basic principles .

**Occlusion is devied into : 1-static :  



ICP/CO : intercuspal position ,which is the habitual maximum intercuspation (it’s old term was centric occlusion). RCP/CR: retruded contact position , it is the teeth relationship when the mandible is at most retruded position (centric relation). Freedom of CO : freedom of centric occlusion , (look at the picture page1,slide6), patient in B, though he is in his habitual position (maximum intercuspation),he’s got sort of freedom to move his teeth a little bit forward, this is what is called freedom in centric occlusion .

2-dynamic : it is when the mandible moves, where there is a relationship between mandibular and maxillary teeth, this movement of the mandible is controlled by 2 things : 

neuromuscular control (your brain ask your mandible to move), and other

thing called: 

guidance system .

This guidance system, once your brain ask your mandible to move ,this mandible will move controlled by two things : 1- posterior thing which will ask it how to move . 2- anterior thing which will ask it how to move as well. Page | 2

Now this posterior guidance together with anterior guidance are totally in harmony, and if there is any disharmony we will go forward for the complications . The posterior guidance ,is your tempomandibular joint ,which is composed of :condyle , glenoid fossa , articular eminence ,articular disc (look to the diagram page2,slide 3). _The condyle will move in the joint depending on the morphology of the joint itself , in your edentulous patient, there is nothing to guide mandibular movement except this joint, so the patient in this case will not be able to put his mandible in the proper position , so for this reason we ask him to go to centric relation because it is the only thing which is reproducible in that patient (there is no anterior guidance). In case of dentate patient, mandible is not totally free to move because there is another factor beside the TMJ guides its movement. _Your posterior guidance ,the condyle, could move forward , medial,or lateral. _ If your condyle moves forward it will create something called protrusive condylar guidance.There is another movement called lateral condylar guidance, associated with something called Bennet angle , and Bennet movement .(Dr said refer to the book and read about them and more important to know why do we need them ).

_Working side versus non-working side :working side means that the movement is toward it , when you move your mandible to the right, the right side is your working side and the left is the non-working side . _(Look to the diagram page2,slide5)..movement laterally will create something called lateral condylar guidance, there is Fischer angle , Bennet angle , adjustable intercondylar distance....ALL these complex structures which you have to read about them are important to CHOSE YOUR ARTICULATOR .

**Why do we need to learn about posterior guidance ? _To chose your articulator ,for example , if you have chosen to use a semiadjustable articulator, then you can adjust these measurements on the articulator according to the patient records or measurements , this is Page | 3

because I know that semiadjustable articulator gives me the benefit of adjusting them. If your articulator can do the whole stuff (movements and angels ),then your articulator is perfectly the joint of your patient, and the more complex the articulator , the closer to the posterior guidance . _For example, fullyadjustable articulator can simulate the whole movements of your mandible, then it is exactly your posterior guidance, and depending on the movements which are provided by the articulator, you can classify them into fully adjustable, semiadjutable , average value , and simple hinge articulator .

**Anterior guidance system : _Posterior guidance is considered as something which you cannot affect directly while you are performing your prosthetic work. But you can easily affect teeth which are the anterior guidance of your patient. _This anterior guidance can be divided into : Posterior teeth; there function is chewing, and they are subjected to the maximum occlusal load.  Anterior teeth; which are responsible for guiding the movement of the mandible, and the ideal tooth to be the main anterior guidance is your canine. This is because canines are: 

>> strong teeth. >>far away from the joint, and the longer the distance from the joint, the longer

the resistance arm , the better the resistance to the applied force (coming from TMJ movement). >> the threshold of proprioceptors in the PDL of canine is quiet low , means if there is a

high spot on the canine this will easily cause an opening reflex of the mandible, and it is a very protective reflex to minimize complications. So all of these tell that the best occlusion I can create for the patient is a canine guided occlusion .

Posterior teeth when they bite in the habitual bite, they are actually protecting anterior teeth, while during excursion when anterior teeth(canines) _This anterior guided occlusion is manifested mainly through are in contact they(*there are protecting posterior teethmovements -which are not in contact- retrusive from being loaded. excursion are 4 main excursion : protrusive, , left lateral , this is called mutual protection system ,which is the ideal occlusion . Page | 4

,if you protrude your mandible the only teeth which are allowed to be in contact are the anterior teeth(incisors mainly). When you move your teeth to the working side( lateral excursion), the only tooth which is allowed to be in contact is the canine, the rest of the teeth (ideally)should be out of contact .So this excursion movement should be controlled by the canine, but canine is connected as other teeth with the posterior guidance, so the idea is : a problem in the occlusion on this anterior guidance (high spot for example) will affect the posterior guidance and create a form of disharmony . and right lateral )

_ This means ;the best is to have your canine in contact during excursion and other teeth are not .There is also another concept called Christensen’s phenomenon during excursion , the only teeth which contact are the guiding teeth which are canine ideally , or all anterior teeth in some situations. With time ,people who have canine guided occlusion could become group function guided ,this is because with time , canine start to suffer from attrition and Posterior teeth start to guide occlusion ,and this is called group function guided occlusion , this is still good , but the best is canine guided. _As you start having posterior contact (posterior guiding) then you are closer to the TMJ which is the fulcrum of mandible movement, so this increase the resistance arm , increase the load ,then you may end with tooth wear, fractured restorations , or TMJ problem.When the mandible moves, a sort of harmony exists between posterior and anterior guidance , this harmony could be easily spoiled by interferences (in case of removable prosthodontics they are called premature contacts).

...Interferences ...: tooth to tooth contact/s which will prevent smooth guidance during excursion ,or cause deviation during closure into ICP. If Page | 5

there is anything preventing canine from coming into contact during excursion this called interferences .

**Types of interferences : • 1-working side interferences . • 2-non-working side, the worst interference in term of possible complications, we will talk about them later in this lecture. • 3-prutrusive. • 4-retruded contact position: which is called deflective contact because it cause the mandible to move some distance in order to come in the habitual bite . Or it can be called sometimes premature contact, means that the patient has a premature contact on some of his teeth when he try to make intercuspation so prevent him from doing that.(interferences is the term which we use commonly in fixed prosthodontics) .

_ (look to the upper left figure page3,slide4) : this patient is trying to occlude in his retruded contact position , but since there is an interference from the 2ed molar ,patient moves his mandible slightly forward in order to bite in the maximum intercuspation . _(the same slide, lower pictures) : patient is trying to go to the left side ,ideally this should be controlled by canine ,but if you notice , there is an interference created by the 2ed molar in the non-working side prevents canine from coming into contact in the working side . The significance here is that when you have interferences , your anterior and posterior guidance don’t work in harmonious way , and if the mandible tries to go simply through glenoid fossa , teeth will prevent it because there is a premature contact on the 2ed molar , so patient is supposed to manipulate his joint to let his bit come in the correct way.This manipulation will affect the joint ! *The most bearable interferences are the centric and working side interferences . and the most destructive interference is the nonworking side ,then the protrusive interference . Page | 6

**Why do you need to learn about anterior guidance ? _To fabricate a proper restoration without creating disharmonies (interferences) using a proper articulator.You have - as a dentist- to make your restorations and prostheses in a way not to create these interferences in particular , and the whole interferences in general . sometimes you could create a high spot in your amalgam restoration ,or your crown , and this will be an interference which causes complications for the patient .One of the indications of doing crowns is unstable occlusion (drifting for example) , and if this drift has caused an interference it has to be treated.

**How patient could cope with these interferences? _If you created an interference in the filling , the patient tries to adapt, and this adaptation could be in the posterior guidance by doing morphological changes , like thickening in capsule , or the ligament ...adapting the disharmony which you have done . Or it can be in the anterior guidance, in the teeth, and this adaptation is manifested as widening in the periodontal ligament space . Or if this interference is so severe , this could lead to myofacial pain dysfunction syndrome , tooth fracture , tooth mobility , or decementation of you crown . *There is something you will read it also in Shillinberg : Being under stress , will reduce the threshold of adaptation .when you are under stress ,then your joint is less capable to adapt interferences ,so some patients may experience myofacial pain dysfunction syndrome only in periods of real stress like during exams .

**How do you manage occlusal surfaces ? _By two ways : 1-Comformative approach : when you do a simple amalgam filling for a patient , you should return the bite as it was , because your patient in this case have enough centric stops and contacts , it is much easier, and if a Page | 7

patient came with upper and lower bilateral free-end saddles (Kennedy class1), it is not required to (‫)تتفنن‬...and take the vertical dimension and retruded position , it is enough to see how the patient bite while the record block in his mouth , and to join them out of his mouth at the same bite. 2- Reorganized approach : there is no enough contacts or no contact at all like edentulous patients , in this case , you recreate the vertical dimension , centric relation and other records .so you forget the existing occlusion and you create your own occlusion . _How could you know that your patient has interferences ? This is done by occlusal examination, to assess the patient’s occlusion if it is ideal . Ideal occlusion rarely exist , and is measured at many levels : 1-patient level : any patient who has bearable occlusion whatever interferences are there, as long as he is comfortable with his occlusion functionally and aesthetically , this is considered as ideal occlusion .

2-system level : _First : Maximum intercuspation should be in the centric occlusion to consider the occlusion ideal , and if it is not then there should be interference somewhere .but this interference in not significant because level of adaptation of joint in this case is high. Normally.. about 10% of patients have their maximum intercuspation at the retruded contact position, the majority have interferences and their mandibles slide slightly forward to get into the bite .these interferences if present already in patients dentition then they are adaptable and don’t cause problems , but you should not do them in your restorations._ Second(from slides) : there should be no posterior interferences. _Third: presence of freedom of displacement (Dr *You have to know that you are creating restorations for dentate patients in their maximum intercuspal position regardless if it coincide with retruded contact position or not . 3-toohe level : _ First, the force of occlusion should be at the long axis of the tooth ,and if you are preparing a rest in your partial denture, or a path of insertion , all should be guided in order to make the occlusal load coming along the long axis of the tooth so that a maximum periodontal support will be gained . Second , there should be no inclined plane contact ,means Page | 8 cusp should not meet cusp at an inclined plain , instead , cusp should occludes into fossa to have a proper bite and to direct forces along the long axis. Now if the cusps of your crown meet

*Returning back to non-working side interferences : _(Look at this patient page5 ,slide2) he is trying to move his mandible toward the left side (your left) which is the working side , but a premature contact is present between the upper palatal and lower buccal cusps a the non-working side ,now if you decided to make an all-ceramic crown for this molar ,and make a 1.5 mm occlusal reduction , remember that those 1.5 mm are the casted material+the original interference . _This patient may develop complications of interference after your restoration even if it was present previously as an adaptable one , this is because natural interference are much tolerable than the iatrogenic interference ,this is mainly because your crown is not perfectly simulating the natural morphology of the cusp. So if your bridge abutment has any interferences you could end up with failure of the bridge because of affecting occlusion, and it could be decementated , you could chip the porcelain ,or TMJ dysfunction and pain.

**How can I know the type of guidance in my patient ?? Two dimensional records :by using articulating paper and asking the patient to bite, doing excursion and sided movement. If there is a high spot on the canine then the patient is canine guided occlusion , also you can use photographs , or drawing .  Three dimensional records : this is done using study models ,but errors in this records are abundant , start from errors in taking impression, accuracy in registration , articulator, and face bows . To get proper three dimensional record you should start from a proper primary impression , then proper pouring ,proper bite. If these were taken wrongly, your 3D records on the study cast are useless ! 

So accuracy in inter-occlusal registration essential for mounting .in many cases ,these registrations will reduce the accuracy of Page | 9

mounting , so you need sometimes anterior and lateral guidance on top of ICP.

*To make a proper bite you should:

3- Rigid material is better .

*according to that which material would you chose to take your bite , wax or ZOE ?

2-Use as little material as possible (thin material).

_ZOE because it is thinner.

1- Avoid recording the tips of cusps .

_why should you chose a rigid not flexible material ?? because in case of rigid material the chance for deflection the casts is much less , and the more rigid the material , the less the details(it doesn’t enter fissures and doesn’t take cusp tip in details but relative to each other ).So thin , rigid , and minimum details .Avoid flexible bite and too detailed bite , they will make mounting inaccurate . {Note: You have to take 2 bites , in case if the technician have missed one } _The material which gives this advantages is Duralay Acrylic Resin .it is rigid with very high dimensional stability , and not much accurate . I can use hard wax but it could be distorted , or I can use ZOE which is rigid but the problem is that it takes details and this will cause difficulty in mounting . Or you can use rubbers ,it is less detailed than ZOE but it’s flexibility is the main problem and the two casts could not be stable on each other in the articulator. _So your best choice is Acrylic , it is thin , rigid ,and less accurate( accuracy in the bite should be in the relation between the 2 casts and not in surface details ). *Now after I took the bite, the next step is choosing the articulator , and this is according to what I need from this articulator. If I need full movement , I have to chose a fully adjustable articulator, but if I don’t need that I can use my hands, simply by approaching the two casts together by your hands . *There is also ARCON and Non-ARCON articulator , you need to know that ARCON articulator is better. And that there are two things determine the path of closure ; FACE BOW an ARCON articulator . Page | 10

**What type of articulator ? what type of restoration ? 1-Single crown :

 If it is a determinant of mandibular movement or a last standing molar : if you are preparing single crown on a canine , and canine is guiding the occlusion ,you have to chose a semi-adjustable articulator . If the tooth is not a determinant of mandibular movement : when you have canine guidance and you are preparing a crown on the 1st premolar, in this case , any method of articulation is suitable .

2- if you are preparing up to 3 crowns in different areas in patient’s mouth:

If no one of them is guiding occlusion , then the same thing applies: you can chose any method of articulation . If they are guiding the occlusion (determinant of mandibular movement) , you should use a semi-adjustable articulator .

3-if you are preparing more than 3 crowns : Regardless if they are determinant of mandibular movement or not , you have to use a semi-adjustable articulator .

4-for any bridge work ; you should semi adjustable . Now if you are doing a 3-unite bridge which has a high chance to create an interference, you have to use an articulator which is very close to the posterior guidance in term of movements ,then , after you have chosen your articulator you have to do the next significant step which is : adjusting the movement records on your articulator which include ; protrusive condylar guidance, lateral condylar guidance, and anterior guidance. Page | 11

_How could I set all of these on my articulator ? _by taking the bite : protrusive bite, lateral bite and retruded contact bite or maximum intercuspation . Conclusion 1 : according to your restoration if it is complex or not , you should choose a suitable articulator .Then you go to the next step which is taking a proper bite .The next is setting up your articulator according to your patient posterior guidance( recorded by the bite), and lastly you have to fabricate your restoration which will have the least possible interferences ‫ان‬ Conclusion 2 : you should not create interferences during restoring teeth.

‫مع تمنياتي بالتوفيق للجميع‬ Done by :Alaa Amayreh -References : lecture , Shillinberg chapter 2.

‫واعلممم أنممه ل يممدرك المفمماخر مممن‬..‫وإن هممت فثابر‬.. ‫إذا عزمت فبادر‬ ‫ والمممال ل يجمممع إل‬,‫العلم ل يحصل إل بالنصممب‬.. ‫كان في الصف الخر‬ ‫ ول يحوز أحد لقب الشممجاع إل بعممد‬, ‫ واسم الجود ل يناله بخيل‬,‫بالتعب‬ .. ‫جهد طويل‬ ‫ وإن لممك معممادا ً ينممزل اللممه فيممه‬, ‫ ولممن تممترك سممدى‬, ً ‫إنك لم تخلق عبثا‬ ‫فاجعل من قلبك قلبا ً قويا ً دائم الثأر‬.. ‫ليحكم بين الناس ويفصل بينهم‬ ‫ج مدَ ولمممح‬..‫ فإذا غافله شيطان في غلبة شهوة أو همموى‬...‫من شيطانه‬ ..."‫قول الله تعالى "إن الحسنات يذهبن السيئات‬

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