Occlusion sheet # 6 - Muna yanis

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Occlusion sheet # 6 - Muna yanis

Post by Shadi Jarrar on 13/4/2011, 3:05 am

First we need to know that the anatomy of the teeth affect the occlusion.(this is the most imp factor)
We add also TMJ, muscles and ligaments.
We are going to talk about:
-factors affect mandibular movement. (introduction and definition)
-static occlusion
-angle`s classification of occlusion
-intra arch tooth alignment
-the baccolingual contact relationship and mesiodistal contact relation ship
-dynamic occlusion: how teeth come in contact with each other during function
-occlusal contact during mandibular movement
-control of mandibular movement ,which done by: 1-ant controlling factor (ant guidance) 2-post controlling factor
-vertical determinant of occlusal morphology, used in case: 1-we are restoring a large # of teeth 2-complete denture 3- partial denture restoring large # of teeth
-horizontal determinant of occlusal morphology
Definitions :
Supporting cusps: lingual cusp of maxillary post teeth, Buccal cusp of mandibular post teeth. Normal adult dentition the supporting cusps is : maintain centric stop contact with the opposing fossa and interproximal embrasure. So the cusp either it occlude with :opposing fossa or marginal ridge or opposing embrasure. The point of contact of the supporting cusp with the opposing teeth should be well established because they affect:
-occlusal stability : which is maintained by centric directed forces which are forces applied by the centric stops.
- mastication
-contact occurs in both the inner and outer aspects of those cusps
-maintaining the vertical dimension height.
If these cusps are lost so the vertical dimension (lower third of the face) will be reduced.
When viewed from the occlusal, the position of the supporting cusps is: 1/3 the total distance into the buccolingual width of the tooth.
Ya3ne : mandibular Buccal cusps …… 1/3 from the Buccal side maxillary lingual cusps……… 1/3 from the lingual side
The rest cusps called guiding cusps: maxillary buccal cusps, mandibular lingual cusps . these also called non centric cusps :
-they are relatively sharp - non definite cusps -located 1/6 the distance (which is 5/9 of total buccolingual width which we use during carving in dental anatomy )
The major role of non centric cusps is:
_to minimize tissue impingement: Buccal cusps of maxillary post teeth remove the check away from the functioning cusps so prevent check biting. Lingual cups of mandibular post teeth remove the tongue from the functioning cusps so prevent tongue biting.
-Maintain the bolus of the food on the occlusal table for mastication
-give the mandible stability so that when teeth are in full occlusion there is tied definite occlusal relationship.
Guiding inclines: they are the planes of occlusal ridges that determine the path of the supporting cusp during normal lateral and protrusive movements.
Incisal guidance: the influence of the palatal surface of maxillary ant teeth during protrusive movement .
Condylar guidance angle: the angle btw condyle and horizontal plane during function
Cusp angle: the angle btw slopes of the cusps and the plane that (passes through the tip of the cusps and perpendicular to a line bisecting the cusp)
Curve of spee: if we look at the teeth fro sagital plane they display a curve.

Plane of occlusion: which is an imaginary plane touches the incisal edges of mandibular central incisors and the tips of the DB cusps of the mandibular 2nd molars. It is curved plane where is the convex toward the mandible and the concave toward the maxilla
Curve of Wilson: when observing the denture arches from frontal view , the maxillary post teeth have a buccal inclination and the mandibular post teeth have lingual inclination

Bonwill and mosin said that mandibular arch is part of an equilateral triangle which is part of hemisphere btw the two joint and the central incisors anteriorly
angle`s classification of occlusion
-most commonly used but it has some problems like it is dependent only on the position of the teeth and the relationship to each other without considering the position of the condyles
-dosen`s classifications : consider both teeth and condyles.
angle`s classification of occlusion
-class I: normal relationship (bcs it gives maximum esthetics and maximum functions) it affected by the size of dental base(normal size) determined by:
Relation btw upper and lower 1st molar
Relation btw ant teeth
-classII and class III are abnormal relationship but that doesn’t mean that these are bad for the patient
Class II : -when the mandible is too distal
-Maxillary arch is too big and the mandible is normal
-Maxilla is big and the mandible is small
-Maxilla is normal and the mandible is too small
Class III:
-maxilla small and mandible has normal size
-maxilla small and mandible larger in size
-maxilla is normal and the mandible is larger in size
notes Relation btw ant teeth Relation btw U&L 1st molars class
Mand teeth in the class I are mesial than max teeth bcs ant teeth are smaller so lower 1st molar is mesial to upper 1st molar
-doesn’t occlude bcs it is nonfunctioning cusp
-each mand tooth occlude with its counterpart and the one that is mesial to it. They occlude with one opposing tooth which is max central incisor -MB cusp of mandibular 1st molar occlude in the embrasure area btw the max 2nd premolar and the 1st molar
-MB cusp of max 1st molar is aligned over the baccal groove over the mand 1st molar
-ML cusp of max 1st molar occlude with the central fossa of mand 1st molar
Class I
-Max teeth are more mesial
-man teeth more distal -MB cusp of man 1st molar occlude with the central fossa of max 1st molar and is aligned with the Buccal groove of it
-DL cusp of max 1st molar occlude with the central fossa of the man 1st molar Class II
-man teeth are more mesial than in class I -DB cusp of the mand 1st molar is in the embrasure btw the max 2nd premolar and 1st molar
-ML cusp of the max 1st molar is in the mesial pit of the mand 2nd molar Class III




Class I arch relationship allows good function, good esthetics and stability if it is in harmony with the completed seated position of the condyle
Class I doesn’t mean stability bcs sometimes there a problem in the condyles
Stable occlusion means :
-Ant guidance free of post deflective contact
-Canine guidance on the lateral excursions
-Centric occlusion there is stops that are the same intensity
If these are available that means that class I is in harmony with function.
For example if we have ant guidance and post there is a contact then this means it is not stable occlusion or in harmony with function, then we have a problem either with the teeth or the condyles .
Another example is that upon lateral move there is no canine guidance it is group function in post teeth at the same side or the other side, these contact that interfere with the harmonious function are called deflective contact.
Sometimes that we have class II or III that more stable and in harmony with the function TMJ .
After a lots of research they found :
Occlusal factors contribute to TMJ disorders
Deflective interferences to complete seating maybe a normal characteristic in some patients but it can also be problematic in some.
Maybe there is no problem until now and problems appear later on or never appear .So we can`t decide if it problem or not so we should examine : TMJ, muscles and occlusion for signs like bruxism...
Teeth in the dental arches they are not straight every tooth have certain angulation .
BL angulation MD angulation teeth

buccally mesially ant
labially mesially post
max
labially mesially ant
lingually distally post
man





Occlusal surface of post teeth can be divided into :
Area btw Buccal and the lingual cusp called occlusal table: it is the area where occlusion happened and it represent 50% to 60% of the total buccolingual dimension. It is considered the inner aspect of the tooth since it is btw the inclines which called the inner aspect of the tooth.
Where is outside occlusal table is called the outer aspect.
The inner and outer aspect of the teeth are extend to the crest of contour baccally or to the central fossa lingually, so we can say outer incline of the cusp or inner incline
Inner incline means toward the occlusal table.
Outer incline means toward the outside of the tooth.





We can also name according cusp names : outer incline of the Buccal cusp, inner incline of the lingual cusp of max 1st molar.
Inter arch tooth alignment : relation of the teeth in one arch in relation to those in the other one.
when the tow arches come to contact the occlusal relationship of the teeth is established. the max and mand teeth occlude in a precise manner …. Always during closing we come to the same position which is the area of centric occlusion.
Arch length: both arches have approximately the same length with the mand being slightly smaller this is due to the narrower MD distance of the mand central incisors.
Arch width: -two lingual surfaces of tow teeth opposing each other (right and left) -max arch is little bit wider than the mand arch.
Curve of Wilson: caused by :
-Maxillary post teeth are buccally inclined
-mand post teeth are lingually inclined
How do we protect the surrounding tissue?
The presence of buccal cusps of max post teeth and lingual cups of mand post teeth will protect the cheeks and the tongue.
Cross bite:
maxillary buccal cusps contact in the central fossa area of the mandibular teeth because of discrepancies in skeletal arch size or
eruption patterns
maxillary is narrower in class III and the max post teeth goes inside where post mand teeth goes out (reverse to class I) this called cross bite.

MD occlusal contact relationship : centric cusps contact opposing teeth in central fossa or marginal ridge or embrasure area
Cusp tip fossa contact when two unlined surfaces meet, only certain point come in contact with each other.
Ya3ne: if cusp tip to fossa we need 3 point of contact but it is impossible to have the fossa coincide with the cusp tip these contact help in function.
If the cup tip contact with the marginal ridge (convex surface with convex surface) so we get powerful function for better grinding of the food and penetration!!!!
Each tooth in the dental arch occludes with two opposing teeth except the mand central incisors and the max third molar.
This relationship helps in distributing occlusal forces to several teeth and there for to the entire arch.
Ya3ne:when each tooth is occluding with two opposing teeth when one of them was lost there is still contact that helps to distribute the forces in all the teeth.
Mand teeth are usually position slightly lingual and mesial to the counterparts and this applies for post and ant teeth.
Max ant teeth are normally positioned labial to mand ant teeth: overjet.
Both max and mand teeth are labially inclined with an average 12 to 28 degrees.
Normally the incisal edge of mand incisor contact the lingual fossa of the max incisors with an overbite of 4 mm
Contact in ant teeth in centric occlusion are much lighter and sometimes absents as that in post teeth..why?? advantage??
Bcs of different inclination and space btw them. If they have continuous force in centric occlusion this force will not be along the long axis of the tooth so it is higher force and the tooth couldn’t stand it.
Sometimes there is deviation of the ant relationship (overlap and overjet each by 2-3mm),
classII maxilla is too big so the space is big so ovejet would be bigger and also overbite.
Maybe teeth are edge to edge , or space btw max central and mand central incisor (ant open bite)
Maybe post teeth be in class I but ant no occlusion.
During movement the masticatory system is extremely dynamic and we have movement all the time in all plane (horizontal, sagital, frontal) along with these movements come potential tooth contact which called eccentric contact. Three basic movement are present:
-protrusive -retrusive -latrotrusive
(forward) (backward) (to the sides)
Protrusive mand movement
Protrusive contact: there is contact ant and disocclusion post. Anterior guiding planes for this movement: mandibular incisors move against lingual fossa of maxillary incisor and incisor edge
Posterior : the protrusive movement causes the mandibular centric cusp to pass ant across the occlusal surfaces of the max teeth. They don’t touch ideally but movement occur the max post teeth.
Post occlusal contact occur Distal inclination of maxillary lingual
cusp and mesial inclination of opposing fossa and marginal ridge (try this with your teeth).
They can also occur btw the Mesial inclination of mandibular buccal cusp against distal inclination of opposing fossa and marginal ridge


Latrotrusive mand movement
The right and left mand post teeth move across, as we said before the only contact is on the canine known as canine guidance or group function contact may occur on the canine with 1st premolar or 2nd premolar or mesiobuccal cusp of the 1st molar only if it was more post so we have deflective contact
During left lateral move: Left molar
-contact occur in two contact areas one btw the inner inclines of the maxillary buccal cusps and outer inclines of mandibular buccal cusps
- then other is btw the outer inclines of maxillary lingual cusps and
the inner inclines of mandibular lingual cusps
both these contact are called "latrotrusive contact" or "Working contact"


Mand teeth on the right side assume a mesial movement across the opposing teeth
- contact occur at the inner inclines of maxillary lingual cusps and inner inclines of mandibular buccal cusps.
This is called “balancing contact or non working contact”
Ant teeth play an imp guiding role during right and left lateral move. In normal occlusal relationship max and mand canine contact during right and left lateral move so we have a latrotrusive contact which occur btw the labial surface and the incisal edges of the mand canine and the lingual fossa and incisal edges of the canine which called "canine protected occlusion".
Retrusive movement
It is opposing to the latrotrusive. Mandible moves more toward the distal that means Mandibular buccal cusp moves distal along occlusal surface of opposing max teeth (max mesial inclines cross the mand distal inclines )


Why do we restore occlusal morphology? Why to do carving ?
All because of dynamic movements along with the centric occlusion so the occlusal morphology must be in harmony with the movements.
When closure the mandible in the musculoskeletal stable position creates an unstable occlusal condition the neuromuscular system quickly feedbacks back appropriate muscle action to locate a mandibular position that will result in more stable occlusal position.
Ya3ne: it is impossible for the mouth closure to be on one fixed spot only even if it was the stable position according to the TMJ. The stability should be considered according to teeth even if it was over the stability of TMJ as consequence they found that problems in the occlusion cause problems in the TMJ.
Optimal occlusal condition during mand closure will be achieved by even simultaneous contact of all teeth (occlusal analysis)
Forces applied to should be directed along the long axis and this is achieved by two methods :
-tooth contact occurs either on the cusp tips or relatively flat surfaces that are perpendicular to the long axis of the tooth (flat surfaces mainly the crest of the marginal ridges or bottoms of the fossa )
-Tripodization
In tripodization , each cusp contacting on opposing fossa should produce 3 contacts surrounding the actual cusp tip to be stable .
** In both methods the resultant force is directed through the long axis of the tooth and axial loading is achieved.
The TMJ permits lateral and protrusive excursions which allow the teeth to contact during different types of eccentric movements and this allows horizontal forces to be applied to the teeth. The teeth that could accept the horizontal forces are the canine and the ant teeth to a lesser extent.
These horizontal forces are not well accepted by supporting structures of the tooth.
Ant teeth can with stand horizontal forces bcs of : mandible is as a lever system the fulcrum of it is the TMJ……. If we are closer to the fulcrum the forces are higher so the post teeth could tolerate axial loading but not horizontal loading …… but ant teeth are away from the fulcrum so it can with stand of axial loading.

Canines are best suited to accept the horizontal forces which occur during eccentric movement . Why ?

1-They have the largest and the longest roots (best crown/ root ratio )
2- they are surrounded by dense compact bone which tolerates forces better than the bone found around post teeth .
3- fewer muscles are active when canines contact during eccentric movement s than when post. Teeth contact .

So , when the mandible is moved in a right or left laterotrusive excursion , the maxillary and mandibular canines are appropriate teeth to contact and dissipate the horizontal forces while disocluding or disarticulating the post. Teeth. This condition called canine guidance.

Many patients don’t have canine guidance , other teeth must contact during eccentric movements . the most favorable alternative is group function ( a group of teeth contacting during lateral excursions ) when the canine cusp is lost or the canine itself is lost .

The most desirable group function consists of :canines , premolars , and sometimes the mesiobuccal cusp of the first molar . ( this occurs on the working side ) .

Any latero trusive contacts more posterior than the mesial portion of the first molar are not desirable because teeth and supporting structures could be injured .

Buccal cusp to buccal cusp contacts latero trusive movements are more desirable than lingual cusp to lingual cusp contacts

It is important that the Canine guidance or group function provide enough guidance to disocclude the teeth on the non working side which are non desirable contact (no contact on the non working side )

If we have during lateral movement to the left side if there is no contact on the left side and contact happened on the right side this is called deflective contact bcs it inhibit normal occlusion on the working side ……
if we have contact on both left and right in the same movement then this called non working side contact bcs it didn’t interfere with the normal contact on the working side.

During protrusive movement only ant teeth should come in contact and not post teeth.





Summary:

 All anterior teeth and post. Teeth act differently .
 Post. Teeth can withstand forces applied during closure of the mouth ( during axial loading ) .
 They are positioned well in the arches to accept heavy forces applied to their long axis .
 Ant . teeth are not , they accept off axial loading why ? because they are labially inclined . So , during closure of the mandible the touch on them is minimal except in post. bite collapse ,where one looses all his post teeth and so all the function is on ant. Teeth . so the patient closes on the anterior teeth ,ant. Teeth will deteriorate and they will flare ( become more labially inclined and the bone around them changes ) .

Structures that control mandibular movement are divided into 2 types :
1. post controlling factor which is the TMJ/shape of the joint, relation of the muscle, ligament.
2. form of ant teeth and the relationship to each other


1. Posterior controlling factors ( condylar guidance) :
-don’t change all through life.
-The rate at which the mandible moves inferiorly as it is being protruded depends on the steepness of the articular eminence .
-The articular eminence differs from one individual to another , on avg. it’s 45 degrees .
-condylar guidance angle : mostly affects posterior teeth because they are closer to the condyles than the anterior ones . it is defined as the rate at which the condyle moves away from the horizontal reference plane .


2. anterior controlling factors ( anterior guidance)
-change through life /filling, crowns, extraction
- just as the TMJ determines the manner in which the posterior of the mandible moves , the anterior teeth determine how the anterior portion of the mandible moves .

- As the mandible moves laterally or protrudes , the incisal edges of the mandibular teeth occlude with the lingual surfaces of the maxillary anterior teeth , the mandible consequently will move downwards below the horizontal plane , the angle that the mandible does with the horizontal plane is called the incisal guidance angle.
- the incisal guidance angle depends on both : the vertical and the horizontal overlap.
- The larger the over jet ( the horizontal overlap ) the less the angle because the mandible should travel a longer distance forward and shorter distance downwards
The italic point above are from last year sheet

the teeth that are toward mesial (ant teeth) they affected by ant controlling factors while the post teeth are affected by the post controlling factors

determinants of occlusal morphology:
1- Factors affects the cusp height and the depth of the fossa and factors affect the distance btw the cusps and the grooves
factors :
1. Anterior controlling factors ( ant. Guidance)
2. Posterior controlling factors (post. Guidance): on the cusp height
3. Nearness of the cusp to these controlling factors
4.plane of occlusion
5. curve of spee
6.bennett movement

Effect of condylar guidance on cusp height :
- As the mandible is protruded , the condyle descends along the articular eminence .
- It’s descent in relation to a horizontal reference plane is determined by the steepness of the eminence which could allow more separation btw the jaws .
- Conclusion : A steeper angle (bigger) allows for longer cusp


Effects of anterior guidance on cusp height :
- it dependents on overjet and overbite
- An increase in horizontal overlap (overjet) soothe teeth will travel more distance before they occlude so shorter cusps (leads to decreased anterior guidance angle
- An increase in vertical overlap (overbite) produces an increased anterior guidance angle , more vertical component to mandibular movement and longer cusps (they travel more during opening)

Effects of the plane of occlusion on cusp height :
Relationship of the plane of occlusion to the angle of the eminence influences the steepness of the cusp height
As the plane of occlusion becomes more nearly parallel to the angle of the eminences the post cusp should be flater.

Effect of Bennett movement on cusp height :

Bennett movement has 3 factors :
A) Amount : movement of the condyle ( working side )…….if the inner incline of mandibular fossa taller then the amount of movement would be bigger on the non working side
If the downward inward more then the separation is bigger and so this allow for longer cusps
As Bennett movement increases the body shift of the mandible dictates that post teeth should be shorter
B) Timing : immediate , progressive….determined by the anatomy of the medial wall of the fossa of the orbiting condyle and the tightness of attachment of TM ligament (convert from rotation to translation)
C) Direction : if it was downward and straight /downward upward then there is little separation so fatter cusps
If it was side and downward then there is enough separation so longer cusps .

*Horizontal determinants of occlusal morphology :
-the doctor said that they are difficult not necessary to memorize them:)
-they include the relationship that influences the direction of the ledges and grooves since during the mand eccentric the opposing cusps pass in them
-Each centric cusp tip generates both laterotrusive ( working side) and mediotrusive ( non working side ) pathways across its opposing tooth… during movements functioning cusps moves inward and outward so they pass through certain path so no cusps touch each other which cause deflective movement

What affects the positioning of the groove and the cusps???
1-Effects of distance of the teeth from the center of rotation and from the mid sagital plane
2- intercondyler distance
3-bennett movement

Border movement of the mandible (we took it earlier)

_These pictures for angle`s classification of occlusion



Class I



Class II


Class III


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Shadi Jarrar
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عدد المساهمات : 997
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تاريخ التسجيل : 2009-08-28
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الموقع : Amman-Jordan

http://jude.my-rpg.com

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