|Occlusion lecture 8
Vertical Determinants of Occlusal morphology
When we talk about the vertical & horizontal determinants of occlusal morphology, we talk about full mouth rehabilitation like complete denture or we are restoring most of the post teeth, this means that we are changing the occlusion of the patient so in this case we need to change the cuspal height, we change them in their componetive way (this means we only change the occlusion in the cases like occlusal problems or large number of teeth are involved in the restorative procedure or vertical dimension was reduced due to attrition,abrasion&due to loss of most of the post teeth) in addition if we are talking about complete denture or partial denture involving most of post teeth.
So we have the effect of condylar guidance on the cusp height, effect of anterior guidance, effect of curve of spee, effect of Bennet movement & plane of occlusion.
Condylar Guidance =>
The steeper the angle allows longer cusps due to increase the angle during downward movement there will result in more separation between posterior teeth so by this we can make the cusps “high” & we don’t need to be flat or reduce the cusps height.
Anterior Guidance on cusps height =>
It has 2 components vertical & horizontal; they depend on over jet & over bite.
As the horizontal overlap increases the anterior guidance angle decreases this means when the horizontal overlap increases this will make maxillary incisors more labial to the mandibular incisors & the mandibular incisors have to travel in a longer way this means that the posterior cusps should be flatter because if the cusps were high this means it will result in interference during movement , decrease of the horizontal overlap leads to decrease anterior guidance angle & less vertical component of mandibular movement so this will result in flatter posterior cusps.
Plane of occlusion =>
The relation of plane of occlusion to the angle of eminence influences the steepness of the cusps result in occlusion more nearly parallel to the angle of the eminence; the posterior cusps should be made flatter.
Bennet Movement =>
Has 3 components 1.timing 2.amount 3.direction
It’s the movement on the working side downward & inward movement, it’s rotation & slight shift
Amount & timing are determined by the degree to which the medial wall of mandibular fossa is away from the condyle.
The direction of movement depends on the direction taken of the rotating condyle during the body movement.
Bennet movement which is rotation & slight movement (body shift)on the working side laterally; this lateral body shift either direct or indirect or in other way immediate & progressive (Immediate means quick & on the onset of movement) BUT (Progressive means step by step or slowly)
As Bennet movement decreases the body of mandible dictates shorter body shift, the posterior cusps should be shorter or flatter, the movement occurs to about 60 degrees & the apex is rotated at the axis of rotation, this means that the movement on the working side either it’ll be to the side or upward or slightly downward or rotation & the slight body shift either horizontal, upward & downward also we have sup,inf,ant & post direction so we have a combination movements because we already said that the movement is in 3 dimension; the horizontal movement between the grooves & the distance between the cusps “not” the height , it’s the function of orbiting condyles & the tightness of attachment to TM ligament , this factor has the greatest effect on the morphology of the posterior teeth movement which has little effect on the occlusal morphology.
If we are talking about time we care mostly about immediate time shift not progressive, if it occurs early it has more influence, the more immediate the side shift the shorter the cusps.
Horizontal determinants of occlusal morphology include the relations that influence the direction of movement of the ridges & grooves, because during the lateral movement we know that the mandibular cusps pass along the grooves in-between cusps of maxillary teeth; since during eccentric mandibular movements the cusps pass between ridges & over the grooves then they influence the placement.
The influence of the placement of cusps as well each cusp generate laterotrusive & mediotrusive , the angle between these can be compared (the dr mentioned that we are not concerned to know them in details but we have to know their meanings & horizontal components & what do they mean).
Mediotrusive movement means if we are talking about shifting toward the left for example this means that the cusps on the non-working side & even the cusps on working side will move toward the left.
Laterotrusive means toward the working side, the cusps will move laterally but in the case of non-working side they’ll move medially so by this case the non-working side is mediotrusive movement & the working side is laterotrusive movement, now in this case we made laterotrusive movement & we want to go back to the center so here the non-working side will move in laterotrusive way so an angle will result between these 2 pathways.
**So the influence of the distance of the teeth from the center of rotation & from the mid sagittal plane also we have the effect of intercondylar distance , the effect of Bennet movement on the ridge & the groove placement because as we said that Bennet movement had vertical & horizontal components which is ant, directly in the center & posterior.
**In border movement of the mandible we took it in the last lecture so you must be familial with it.
Posselt envelope =>
All the movements of the mandible occur within this envelope, maximum opening is reached when the capsular ligament prevent further movement at the condyle.
We have to know that the mandible especially the mandibular head is connected to ligaments.
Maximum protrusive position is determined by stylomandibular ligament & here we have to know the importance of ligaments to stop further movement & affect the hinge movement & posture of the mandible which is done by tempromandibular ligament
The superior movement of the mandible is determined by characteristics of occluding surfaces which are anterior teeth changes in teeth will result in changes in the nature of border of movement for example loss of teeth height or more bulky in the palatal surface of longer this will affect superior part of posselt envelope, its precise shape affect the amount of variation between CR & CO,the steepness of cuspal incline of the posterior teeth, the amount of over jet & overbite of anterior teeth, the lingual morphology of maximum ant teeth & general interarch relationship.
**NOW we want to talk about new subject which is
In clinical examination of occlusion when the patient comes to us we don’t make examination on the teeth only but also we examine the condyle, the range of movement,TMJ,muscles,ligaments in addition to the extra oral examination like posture so all of this have effect on the oral cavity so we have to examine occlusion in static & dynamic.
Static means we only ask the patient to close his mouth together & dynamic we have to ask the patient to move from side to side, mediotrusive & laterotrusive movement as to see the contact between teeth & the relationship between each other & separation the teeth on the non-working side & so on.
This includes clinical examination which is through the eye or using radiographs if needed & the study models
**The advantages of the study models that they give us idea &when we put them (the casts) on the articulators we can see what’s behind, we can see the relation of the lingual cusps to each other.
**Palpation of TMJ & the related muscles:
Through the mandibular movements such as opening & closing movements, range of movements, how much the opening, how much the lateral movements & protrusive movement. In the mandible, there are limitations of jaw opening & the path of movement may be straight or it starts as straight then it takes an angle.
During TMJ movements sometimes we hear sounds like crepitus or click movement, clicking means during opening & closing we have only one loud sound BUT with crepitus we hear multi sounds like the sounds of rubbing the glass paper.
Then we have the clinical examination or what’s called the dental examination by taking the history from the patient in addition we take or we look to the teeth, static occlusal structures, dynamic occlusal structures & arch organization.
In Dental examination, the history, the number & the position of the teeth, missing extracted teeth, then we have to detect the anomalies of the tooth structure if the patient has amelogenesis imperfecta or pathological conditions & the shape of teeth sometimes maybe pig-shaped lateral incisors also we are concerned with the status of the teeth(caries), rotated or hard structures or abnormal structures, hard tissues infections wither it’s from the origin of the teeth or from peridontium or gingiva.
The cusp tips are functional, internal cusp ridges marginal ridges of maxillary & mandibular teeth, this means that we ask the patient to close the teeth together on “horse shoe articulating paper” & we see where are the points of contact between the maxillary & mandibular teeth & we check the function & the stability of CO position; is it stable, does it go each time to the same contact or each time it’s in different side, also we look at the distribution of occlusal stresses axially whether the occlusal stops are well distributed or whether some areas have forces more than other areas, we should examine the masticatory function we also observe the mechanical tooth loss like abrasion due to habits like pen biting or fracture of the teeth , type of occlusion, cusp to fossa relationship or cusps to marginal ridges there must be homogenous, the intensity must be equal laterally this means the occlusal stops must be equal in intensity.
Changes in the occlusal morphology or tooth contact from the original one this’ll affect occlusal stability, masticatory function or closure interferences.
Dynamic occlusal structures; we have incisal border of mandibular incisor,becoz they affect the protrusive movement, cusp caries,affect the canine because they’ll affect lateral excursion & lingual surface of maxillary ant teeth , function of these structures is to guide mandibular movement through various excursions & masticatory function so we should observe whether these are functional healthy ant teeth (ant guidance).
The importance of dynamic structures because they alter static structure; they will influence occlusal stability; alteration in the dynamic structural cusps could result in dynamic functional occlusal consequences & will lead to problems.
Arch examination =>
Intra-arch relationship we should observe the anomalies in position such as rotation & drifting of the teeth that could result in interferences for example if one of the teeth is missing, this may result in tilting or lose of the tooth which is mesial to it; may result or may have distal movement of mesial neighbor & this may result in (for example if we have a slight shifting will lead to distal side of the tooth is higher than mesial side) so this will make interferences during function.
Observation of occlusal curve in curve of Wilson & curve of spee:
Maximum intercuspation position => stability of CO is maintained by lateral & homogenous contact on all the teeth due to each tooth is maintained in place by the forces acting on it from different adjacent structures this means for example mandibular first molar is maintained in place by its mesial & distal neighbors & by the opposing one so if one of these contact are lost this means that the tooth won’t stay stable in position or for example if the patient has the facial nerve is affected which will result in “palsy” ; which result in loss of the tone of the muscle or in the tongue so one of the teeth may move from its place or if a cut occur in the lingual nerve this means that pressure from lingual nerve to the teeth will be lost & the teeth might tilt toward lingual side .
Rapid closure of the mandible from opening position to the maximum intercuspation should move in one line & always should result in the same position.
Palpation of muscles of elevation during closure:
All elevator muscles’ tone must be the same because if we had muscles tighter from other muscles this means that more force on that area.
Palpation of the teeth:
Which is accomplished ,once closure occur, by putting one of the fingers on the labial surface of the teeth & ask the patient to bite on his teeth together, so if we felt that there’s movement in one of the teeth closure “when contact occurs” this means that this tooth undergoes (premitus) which is excessive load on the tooth or periodontitis .
Displacement of CR & CO position:
Measuring ant-post & lateral shift of the aspect by working on the vertical & horizontal lines on the incisors ; this means that we ask the patient to close into CR & then we ask him to move to the CO & we mark this movement, we measure it & see its direction ant –post & lateral.
When the lateral component exists then this is indicator to a problem in the centering of the mandible since it must be directly to the posterior of CO area but if it’s more than 2 mm ((max 2 mm & the normal 1 mm)) in magnitude it’s usually associated with signs & symptoms.
Examination of anterior guidance , presence of harmonious ant guidance, we see the contact on the incisors during protrusive movement by checking contact with articulating paper either in the clinic by asking the patient to move or on the casts (semi-adjustable articulator & face-bow transfer).
Examination of vertical dimension of occlusion; we have to know that the height of lower third of the face is important for speaking &esthetics because if the lower facial height is lower than normal this means that it’ll affect the speech in addition to esthetics.
Loss of the vertical dimension of occlusion could result from pathological loss of tooth structure or loss & migration of the teeth.
Pathological loss of the tooth structure like having excessive wear of the incisal edges of maxillary ant & mandibular ant teeth this would cause problems from an esthetic point of view as well as from problems of neuromuscular system.
Para functional habits:
Habits involving that type of swallowing such as infantile swallowing (if u look at an infant below 1 year they push the tongue between arches in order to close ant part of the mouth to be able to swallow), if this type of swallowing is maintained through adulthood this will cause problems like open bite.
Nail biting, lip biting, tongue biting can have an influence on the occlusal stability & function, we may have for example protruded upper incisors , this would result for eventual changes in tooth morphology & abnormal tooth position, “Nail biting, lip & tongue biting “cause changes in the structure of the teeth due to continuous pressure on the teeth.
As we said before, we can use an articulator as we can see anterior guidance CO & so on, so it’s a complementary step to compare or it’s a step for clinical observations, it’s advantages: No cheeks, no soft tissues so we can place the articulating paper easily without any push from the soft tissues & structures, it’s sometimes easier to locate occlusal contact independent from tissue interferences.
The selective grinding or any type of occlusal modification, should be done on the articulating paper systematically before any irreversible changes are done in the mouth, sometimes when the patient has occlusal interferences, he has signs & symptoms like pain & clicking.
One of the treatment options is selective grinding, we change the contour of certain cusps & teeth to reach an occlusion free of interferences this should be done on the articulating paper because sometimes we remove the wrong cusp tips or we remove one & still we have other interfered cusp tips, we need an accurate study models which are taken by alginate impression & then mount them on the articulator (semi-adjustable articulator with the use of face-bow) & must be in CR.
**So what are the criteria of functional occlusion?
Minimal shift between CR & CO.
Harmonious vertical dimension of occlusion.
Stable contact in the maximum intercuspation position.
Multi-bilateral homogeneous contact on maximum number of post teeth.
Functional anterior guidance free of posterior interferences.
“All corrections are welcomed ,I tried my best to write every word the Doctor mentioned “
Done by : Dareen Matarweh