Pages From Management of Temporomandibular Disorders and Oc

111

6C H A P T E R

“Developing teeth that successfully permit efficient mas-ticatory function is basic to dentistry and survival.”

—JPO

In health the occlusal anatomy of the teeth func-tions in harmony with the structures controllingthe movement patterns of the mandible. The

structures that determine these patterns are thetemporomandibular joints (TMJs) and the anteriorteeth. During any given movement the uniqueanatomic relationships of these structures com-bine to dictate a precise and repeatable pathway.To maintain harmony of the occlusal condition, theposterior teeth must pass close to but must notcontact their opposing teeth during mandibularmovement. Importantly, the clinician should exam-ine each of these structures carefully and appreci-ate how the anatomic form of each can determinethe occlusal morphology necessary to achieve anoptimum occlusal relationship. The structures thatcontrol mandibular movement are divided into twotypes: (1) those that influence the movement of theposterior portion of the mandible and (2) thosethat influence the movement of the anterior por-tion of the mandible. The TMJs are considered theposterior controlling factors (PCFs), and the anteriorteeth are considered the anterior controlling factors(ACFs). The posterior teeth are positioned betweenthese two controlling factors and thus can beaffected by both to varying degrees.

Determinants of OcclusalMorphology

POSTERIOR CONTROLLING FACTORS(CONDYLAR GUIDANCE)

As the condyle moves out of the centric relationposition, it descends along the articular eminenceof the mandibular fossa. The rate at which it movesinferiorly as the mandible is being protrudeddepends on the steepness of the articular emi-nence. If the surface is quite steep, the condyle willtake a steep, vertically inclined path. If it is flatter,the condyle will take a path that is less verticallyinclined. The angle at which the condyle movesaway from a horizontal reference plane is referredto as the condylar guidance angle.

Generally, the condylar guidance angle gener-ated by the orbiting condyle when the mandiblemoves laterally is larger than when the mandibleprotrudes straightforward. This is because themedial wall of the mandibular fossa is generallysteeper than the articular eminence of the fossadirectly anterior to the condyle.

The two TMJs provide the guidance for the pos-terior portion of the mandible and are largelyresponsible for determining the character ofmandibular movement posteriorly. They havetherefore been referred to as the PCFs of themandibular movement. The condylar guidance is con-sidered to be a fixed factor because it is unalter-able in the healthy patient. It can be altered,

112 Functional Anatomy

however, under certain conditions (trauma, patho-sis, or a surgical procedure).

ANTERIOR CONTROLLING FACTORS(ANTERIOR GUIDANCE)

Just as the TMJs determine or control the mannerin which the posterior portion of the mandiblemoves, so the anterior teeth determine how theanterior portion moves. As the mandible protrudesor moves laterally, the incisal edges of themandibular teeth occlude with the lingual surfacesof the maxillary anterior teeth. The steepness ofthese lingual surfaces determines the amount ofvertical movement of the mandible. If the surfacesare quite steep, the anterior aspect of the mandiblewill take a steep-incline path. If the anterior teethhave little vertical overlap, they will provide littlevertical guidance during mandibular movement.

The anterior guidance is considered to be avariable rather than a fixed factor. It can be alteredby dental procedures such as restorations, ortho-dontia, and extractions. It can also be altered bypathologic conditions such as caries, habits, andtooth wear.

UNDERSTANDING THE CONTROLLINGFACTORS

To understand the influence of mandibular move-ment on the occlusal morphology of posteriorteeth, one must consider the factors that influencemandibular movement. As discussed in Chapter 4,mandibular movement is determined by theanatomic characteristics both of the TMJs posteri-orly and of the anterior teeth anteriorly. Variationsin the anatomy of the TMJs and the anterior teethcan lead to changes in the movement pattern ofthe mandible. If the criteria for optimum functionalocclusion are to be fulfilled, the morphologic char-acteristics of each posterior tooth must be in har-mony with those of its opposing tooth or teethduring all eccentric mandibular movements.Therefore the exact morphology of the tooth isinfluenced by the pathway it travels across itsopposing tooth or teeth.

The relationship of a posterior tooth to the con-trolling factors influences the precise movement ofthat tooth. This means that the nearer a tooth is tothe TMJ, the more the joint anatomy will influenceits eccentric movement and the less the anatomyof the anterior teeth will influence its movement.Likewise, the nearer a specific tooth is to the ante-rior teeth, the more the anatomy of the anteriorteeth will influence its movement and the less theanatomy of the TMJs will influence that movement.

The occlusal surfaces of posterior teeth consistof a series of cusps with both vertical and horizon-tal dimensions. Cusps are made up of convexridges that vary in steepness (vertical dimension)and direction (horizontal dimension).

Mandibular movement has both a vertical and ahorizontal component, and it is the relationshipbetween these components or the ratio that issignificant in the study of mandibular movement.The vertical component is a function of the super-oinferior movement, and the horizontal compo-nent a function of the anteroposterior movement.If a condyle moves downward two units as it movesforward two units, it moves away from a horizontalreference plane at an angle of 45 degrees. If itmoves downward two units and forward one unit,it moves away from this plane at an angle ofapproximately 64 degrees. The angle of deviationfrom the horizontal reference plane is what clini-cians study in mandibular movement.

Fig. 6-1 represents the mandible as it movesfour units in the horizontal plane and zero units inthe vertical plane, resulting in a deviation awayfrom horizontal of 0 degrees. Fig. 6-2 shows themandible moving four units in the horizontal andfour units in the vertical plane. The result here is adeviation away from horizontal of 45 degrees.

In Fig. 6-3 the mandible moves four units in thehorizontal plane, but in the vertical plane the PCFmoves four units and the ACF moves six units. Thisresults in a 45-degree movement of the PCF and a57-degree movement of the ACF. Points betweenthe factors will deviate by different amounts fromthe horizontal plane depending on their proximityto each factor. The nearer a point is to the PCF,for example, the more its movement will approach45 degrees (because of the greater influence ofthe PCF on its movement). Likewise, the nearer a

point is to the ACF, the more its movement willapproach 57 degrees (because of the greater influ-ence of the ACF on its movement). A point equidis-tant between the factors will move away fromhorizontal at an angle of approximately 51 degrees(which is midway between 45 and 57 degrees), and

one that is 25% closer to the ACF than to the PCFwill move away from horizontal at an angle of54 degrees (one fourth of the way between 57 and45 degrees).

To examine the influence of any anatomic varia-tion on the movement pattern of the mandible, it

HRP

HRP

PCF 4 units forward 0 units downward

ACF 4 units forward 0 units downward

Units ofvertical

movement

Units ofhorizontal movement

Units ofvertical movement

Fig. 6-1 Horizontal reference plane (HRP) of the mandible at both the posterior (PCF)and the anterior (ACF) controlling factor. The mandible moves horizontally four units from aposition marked by the dotted line. No vertical movement occurs. The solid line representsthe position of the mandible after the movement has taken place.

HRP

HRP


ACF 4 units forward 0 units downward

45

45

45

Fig. 6-2 Movement of the mandiblefour units horizontally and four unitsvertically at both the posterior (PCF)and the anterior (ACF) controllingfactor. When the mandible movesfour units down, it moves four unitsforward at the same time. The netresult is that it is at a 45-degree anglefrom the horizontal reference planes.Because both the PCFs and the ACFsare causing the mandible to move atthe same rate, each point on themandible is at a 45-degree angle fromthe horizontal reference plane at theend of a mandibular excursion.

Determinants of Occlusal Morphology 113


is necessary to control all factors except the onebeing examined. Remember that the significanceof the anterior and condylar guidances lies in howthey influence posterior tooth shape. Because theocclusal surface can be affected in two manners(height and width), it is logical to separate thestructural influence on mandibular movement intofactors that influence the vertical components andthose that influence the horizontal components.The anatomy of the occlusal surface is also influ-enced by its relationship with the tooth thatpasses across it during movement. Therefore thelocation of the tooth to the center of rotation isalso discussed.

VERTICAL DETERMINANTS OF OCCLUSAL MORPHOLOGY

Factors that influence the heights of cusps and thedepths of fossae are the vertical determinants ofocclusal morphology. The length of a cusp and the

distance it extends into the depth of an opposingfossa are determined by three factors:1. The ACF of mandibular movement (i.e., anterior

guidance)2. The PCF of mandibular movement (i.e., condylar

guidance)3. The nearness of the cusp to these controlling

factorsThe posterior centric cusps are generally devel-

oped to disocclude during eccentric mandibularmovements but to contact in the intercuspal posi-tion. For this to occur, they must be long enough tocontact in the intercuspal position but not so longthat they contact during eccentric movements.

EFFECT OF CONDYLAR GUIDANCE(ANGLE OF THE EMINENCE) ONCUSP HEIGHT

As the mandible is protruded, the condyle descendsalong the articular eminence. Its descent in relationto a horizontal reference plane is determined by the


HRP

54�51�

HRP ACF 4 units forward 6 units downward

57�

45�

x y

Fig. 6-3 RESULTANT MOVEMENT OF THE MANDIBLE WHEN THE CON-TROLLING FACTORS ARE NOT IDENTICAL. The posterior controlling factor (PCF)causes the posterior portion of the mandible to move four units forward (horizontally) and four unitsdownward (vertically). However, the anterior controlling factor (ACF) causes the anterior portion ofthe mandible to move four units forward and six units downward.Therefore the posterior portionof the mandible is moving away from the reference plane at a 45-degree angle, and the anterior por-tion is moving away at a 57-degree angle. A point (x) that is equidistant from the controlling factorswill move at a 51-degree angle from the reference plane. Another point (y) that is one fourth closerto the ACF than to the PCF will move at a 54-degree angle.Thus it can be seen that the nearer thepoint is to a controlling factor, the more its movement is influenced by the factor.


steepness of the eminence. The steeper the emi-nence, the more the condyle is forced to moveinferiorly as it shifts anteriorly. This results ingreater vertical movement of the condyle,mandible, and mandibular teeth.

In Fig. 6-4 the condyle moves away from a hori-zontal reference plane at a 45-degree angle. Tosimplify visualization, anterior guidance is illus-trated at an equal angle. The cusp tip of premolarA will move away from a horizontal reference planeat a 45-degree angle. To avoid eccentric contactbetween premolar A and premolar B in a protrusivemovement, cuspal inclination must be less than45 degrees.

In Fig. 6-5, condylar guidance and anterior guid-ance are presented as being 60 degrees to the hor-izontal reference planes. With these steepervertical determinants, premolar A will move away

from premolar B at a 60-degree angle, resultingin longer cusps. Therefore a steeper angle of theeminence (condylar guidance) allows for steeperposterior cusps.

EFFECT OF ANTERIOR GUIDANCEON CUSP HEIGHT

Anterior guidance is a function of the relationshipbetween the maxillary and mandibular anteriorteeth. As presented in Chapter 3, it consists of thevertical and horizontal overlaps of the anteriorteeth. To illustrate its influence on mandibularmovement and therefore on the occlusal shape ofposterior teeth, some combinations of vertical andhorizontal overlap appear in Fig. 6-6.

Parts A, B, and C present anterior relationshipsthat maintain equal amounts of vertical overlap.

45

45

4545

45

45

A

A B

B

Fig. 6-4 A, The posterior andanterior controlling factors arethe same, causing the mandible tomove away from the referenceplane at a 45-degree angle. B, Forpremolar A to be disoccludedfrom premolar B during a protru-sive movement, the cuspal inclinesmust be less than 45 degrees.


By comparing the changes in horizontal overlap,one can see that as the horizontal overlapincreases, the anterior guidance angle decreases.

Parts D, E, and F present anterior relationshipsthat maintain equal amounts of horizontal overlapbut varying amounts of vertical overlap. By com-paring the changes in vertical overlap, one can seethat as the vertical overlap increases, the anteriorguidance angle increases.

Because mandibular movement is determined toa great extent by anterior guidance, changes in thevertical and horizontal overlaps of the anterior teethcause changes in the vertical movement patterns ofthe mandible. An increase in horizontal overlapleads to a decreased anterior guidance angle, lessvertical component to mandibular movement, andflatter posterior cusps. An increase in vertical over-lap produces an increased anterior guidance angle,

a more vertical component to mandibular move-ment, and steeper posterior cusps.

EFFECT OF THE PLANE OFOCCLUSION ON CUSP HEIGHT

The plane of occlusion is an imaginary line touch-ing the incisal edges of the maxillary anterior teethand the cusps of the maxillary posterior teeth. Therelationship of the plane to the angle of the emi-nence influences the steepness of the cusps. Whenthe movement of a mandibular tooth is viewed in relation to the plane of occlusion rather than in relation to a horizontal reference plane, theinfluence of the plane of occlusion can be seen.

In Fig. 6-7, condylar guidance and anterior guid-ance are combined to produce a 45-degree move-ment of a mandibular tooth when compared with

60

60

60

60 60

60

A

B

A B

Fig. 6-5 A, Posterior and ante-rior controlling factors are identi-cal and cause the mandible to moveaway from the reference plane at a60-degree angle. B, For premolarA to be disoccluded from premo-lar B during a protrusive move-ment, the cuspal inclines must beless than 60 degrees. Thus it canbe seen that steeper posteriorand anterior controlling factorsallow for steeper posterior cusps.


the horizontal reference plane. However, when the45-degree movement is compared with one planeof occlusion (POA), it can be seen that the tooth ismoving away from the plane at only a 25-degreeangle, which results in the need for flatter poste-rior cusps so that posterior tooth contact will beavoided. When the tooth movement is compared

with the plane of occlusion (POB), it can be seenthat the movement away from this plane is 60 degrees. Therefore the posterior teeth can havelonger cusps, and we have determined that as theplane of occlusion becomes more nearly parallelto the angle of the eminence, the posterior cuspsmust be made shorter.

41 38

28

56

3821

VO

VO

HO

HO

A B C

D E F

Fig. 6-6 The anterior guidance angle is altered by variations in the horizontal and verticaloverlap. In A to C the horizontal overlap (HO) varies, whereas the vertical overlap (VO)remains constant. When the HO increases, the anterior guidance angle decreases. In D to Fthe VO varies, whereas the HO remains constant. As VO increases, the anterior guidanceangle increases.


EFFECT OF THE CURVE OF SPEEON CUSP HEIGHT

When viewed from the lateral, the curve of Spee is ananteroposterior curve extending from the tip of themandibular canine along the buccal cusp tips ofthe mandibular posterior teeth. Its curvature canbe described in terms of the length of the radius ofthe curve. With a short radius, the curve will bemore acute than with a longer radius (Fig. 6-8).

The degree of curvature of the curve of Speeinfluences the height of the posterior cusps thatwill function in harmony with mandibular move-ment. In Fig. 6-9 the mandible is moving away froma horizontal reference plane at a 45-degree angle.Movement away from the maxillary posterior teethwill vary depending on the curvature of the curve

of Spee. Given a short radius, the angle at whichthe mandibular teeth move away from the maxil-lary teeth will be greater than with a long radius.

The orientation of the curve of Spee, as deter-mined by the relationship of its radius to a hori-zontal reference plane, will also influence how thecusp height of an individual posterior tooth isaffected. In Fig. 6-10, A, the radius of the curveforms a 90-degree angle with a constant horizontalreference plane. Molars (which are located distalto the radius) will have shorter cusps, whereas pre-molars (located mesial) will have longer cusps. InFig. 6-10, B, the radius forms a 60-degree anglewith a horizontal reference plane (rotating thecurve of Spee more forward). By moving the curvemore forward with respect to the horizontal plane,one can see that all the posterior teeth (premolars

45

45

60

25

15

45

POB

HRP

POA

A

B

Fig. 6-7 A, The anterior and poste-rior controlling factors create amandibular movement of 45 degreesfrom the horizontal reference plane.B, The tooth moves at a 45-degreeangle from the reference plane (HRP).However, if one plane of occlusion(POA) is angled, the tooth will moveaway from the reference plane at only25 degrees. Therefore the cusp mustbe relatively flat to be disoccludedduring protrusive movement. Whenthe angle at which the tooth movesduring a protrusive movement is com-pared with another plane of occlusion(POB), a much greater discrepancy isevident (45 + 15 = 60 degrees). Thisallows for taller and steeper poste-rior cusps.


and molars) will have shorter cusps. In Fig. 6-10, C,if the perpendicular line from the constant hori-zontal reference plane is rotated posteriorly (curveof Spee placed more posteriorly), one can see thatthe posterior teeth (especially the molars) canhave longer cusps.

EFFECT OF MANDIBULAR LATERALTRANSLATION MOVEMENT ONCUSP HEIGHT

The mandibular lateral translation movement is abodily side shift of the mandible that occurs during

lateral movements (previously called Bennett movement). During a lateral excursion the orbitingcondyle moves downward, forward, and inward inthe mandibular fossa around axes located in theopposite (rotating) condyle. The degree of inwardmovement of the orbiting condyle is determinedby two factors: (1) morphology of the medial wallof the mandibular fossa and (2) inner horizontalportion of the temporomandibular (TM) ligament,which attaches to the lateral pole of the rotatingcondyle. If the TM ligament of the rotating condyleis tight and the medial wall is close to the orbitingcondyle, a pure arcing movement will be made

A B

Fig. 6-8 CURVE OF SPEE. A, A longer radius causes a flatter plane of occlusion. B,A shorter radius causes a more acute plane of occlusion.

45

45

45

45

A B

Fig. 6-9 The mandible is moving away from a horizontal reference plane at a 45-degreeangle. The flatter the plane of occlusion (A), the greater will be the angle at which themandibular posterior teeth move away from the maxillary posterior teeth and therefore the taller the cusp can be.The more acute the plane of occlusion (B), the smaller will be theangle of the mandibular posterior tooth movement and the flatter the teeth can be.


around the axis of rotation in the rotating condyle.When this condition exists, no lateral translationof the mandible occurs (and therefore no mandibu-lar lateral translation movement) (Fig. 6-11). Sucha condition rarely occurs. Most often there is somelooseness of the TM ligament, and the medial wallof the mandibular fossa lies medial to an arcaround the axis of the rotating condyle (Fig. 6-12).When this occurs, the orbiting condyle is movedinwardly to the medial wall and produces amandibular lateral translation movement.

The lateral translation movement has threeattributes: amount, timing, and direction. Theamount and timing are determined in part by thedegree to which the medial wall of the mandibularfossa departs medially from an arc around the axisin the rotating condyle. They are also determinedby the degree of lateral movement of the rotating

C

A

B

Fig. 6-10 ORIENTATION OF THE CURVE OF SPEE. A, Radius perpendicu-lar to a horizontal reference plane. Posterior teeth located distal to the radius will needshorter cusps than those located mesial to the radius. B, If the plane of occlusion is rotatedmore posteriorly, it can be seen that more posterior teeth will be positioned distal to theperpendicular from the reference plane and can have shorter cusps. C, If the plane is rotatedmore anteriorly, it can be seen that more posterior teeth will be positioned mesial to theperpendicular and can have taller cusps.

TightTM ligament

Medial wall

Fig. 6-11 With proximity of the medial wall and a tighttemporomandibular (TM) ligament, there is no lateral trans-lation movement.


condyle permitted by the TM ligament. The moremedial the wall from the medial pole of the orbit-ing condyle, the greater the amount of lateraltranslation movement (Fig. 6-13); and the looserthe TM ligament attached to the rotating condyle,

the greater the lateral translation movement.The direction of lateral translation movement dependsprimarily on the direction taken by the rotatingcondyle during the bodily movement (Fig. 6-14).

Effect of the Amount of Lateral TranslationMovement on Cusp HeightAs just stated, the amount of lateral translationmovement is determined by the tightness of theinner horizontal portion of the TM ligamentattached to the rotating condyle, as well as thedegree to which the medial wall of the mandibularfossa departs from the medial pole of the orbitingcondyle. The looser this ligament and the greaterits departure, the greater the amount of mandibu-lar translation movement. As the lateral transla-tion movement increases, the bodily shift of themandible dictates that the posterior cusps beshorter to permit lateral translation without creat-ing contact between the maxillary and mandibularposterior teeth (Fig. 6-15).

Effect of the Direction of the Lateral TranslationMovement on Cusp HeightThe direction of shift of the rotating condyle duringa lateral translation movement is determined bythe morphology and ligamentous attachments of

LooseTM ligament

Medial wall

Fig. 6-12 When there is distance between the medial walland medial pole of the orbiting condyle and the temporo-mandibular (TM) ligament allows some movement of therotating condyle, a lateral translation movement occurs.

3 2 1

321 321

Fig. 6-13 The more medial the medial wall is from thecondyle, the greater will be the lateral translation movement.Therefore when the medial wall is in position 3, it will allowmore lateral translation of the mandible than in position 1.

21

21

Fig. 6-14 The direction of the lateral translation move-ment is determined by the direction taken by the rotatingcondyle. When the rotating condyle follows pathway 1,the central fossa of the teeth will need to be wider thanpathway 2 to disengage the opposing teeth.


the TM joint undergoing rotation. The movementoccurs within a 60-degree (or less) cone, the apexof which is located at the axis of rotation (Fig. 6-16).Therefore in addition to lateral movement, therotating condyle may also move in (1) a superior,(2) an inferior, (3) an anterior, or (4) a posteriordirection. Furthermore, combinations of these canoccur. In other words, shifts may be laterosu-peroanterior, lateroinferoposterior, and so on.

Of importance as a determinant of cusp heightand fossa depth is the vertical movement of therotating condyle during a lateral translation move-ment (e.g., the superior and inferior movements)(Fig. 6-17). Thus a laterosuperior movement of therotating condyle will require shorter posterior cuspsthan will a straight lateral movement; likewise, alateroinferior movement will permit longer poste-rior cusps than will a straight lateral movement.

Effect of the Timing of the Lateral TranslationMovement on Cusp HeightTiming of the lateral translation movement is afunction of the medial wall adjacent to the orbitingcondyle and the attachment of the TM ligamentto the rotating condyle. These two conditionsdetermine when this movement occurs during alateral excursion. Of the three attributes of thelateral translation movement (amount, direction,and timing), the last has the greatest influence onthe occlusal morphology of the posterior teeth. If the timing occurs late and the maxillary andmandibular cusps are beyond functional range, theamount and direction of the lateral translationmovement will have little, if any, influence onocclusal morphology. However, if the timing of this

2

2

21

3

3 3

1

1

Fig. 6-15 The greater the lateral translation movement,the shorter is the posterior cusp. Pathway 3 will requireshorter cusps than pathway 1.

60

Fig. 6-16 The rotating condyle is capable of moving later-ally within the area of a 60-degree cone during lateral trans-lation movement.

1

11

2

22

3

33

Fig. 6-17 The more superior the lateral translation move-ment of the rotating condyle (1), the shorter the posteriorcusp. The more inferior the lateral translation movement(3), the taller the cusp.


movement occurs early in the laterotrusive move-ment, the amount and direction of the lateraltranslation movement will markedly influenceocclusal morphology.

When the lateral translation movement occursearly, a shift is seen even before the condyle beginsto translate from the fossa. This is called an imme-diate lateral translation movement or immediate side shift(Fig. 6-18). If it occurs in conjunction with an eccen-tric movement, the movement is known as a pro-gressive lateral translation movement or progressive sideshift. The more immediate the side shift, the shorterthe posterior teeth.

HORIZONTAL DETERMINANTS OF OCCLUSAL MORPHOLOGY

Horizontal determinants of occlusal morphologyinclude relationships that influence the direction ofridges and grooves on the occlusal surfaces. Becausecusps pass between ridges and over grooves duringeccentric movements, the horizontal determinantsalso influence the placement of cusps.

Each centric cusp tip generates both lat-erotrusive and mediotrusive pathways across its

opposing tooth. Each pathway represents a por-tion of the arc formed by the cusp rotating aroundthe rotating condyle (Fig. 6-19). The angles formedby these pathways can be compared and will befound to vary depending on the relationship of theangle to certain anatomic structures.

EFFECT OF DISTANCE FROM THEROTATING CONDYLE ON RIDGE AND GROOVE DIRECTION

Because the position of a tooth varies in relationto the axis of rotation of the mandible (i.e., rotat-ing condyle), variation will occur in the anglesformed by the laterotrusive and mediotrusivepathways. The greater the distance of the toothfrom the axis of rotation (rotating condyle), thewider the angle formed by the laterotrusive andmediotrusive pathways (Fig. 6-20). This is consis-tent regardless of whether maxillary or mandibularteeth are being viewed. Actually, the angles areincreased in size as the distance from the rotatingcondyle is increased because the mandibularpathways are being generated more mesially (see Fig. 6-20, A) and the maxillary pathways arebeing generated more distally (see Fig. 6-20, B).

1 1

1

2 2

2

Fig. 6-18 TIMING OF THE LATERAL TRANS-LATION MOVEMENT. 1, Immediate lateral transla-tion movement (immediate side shift); 2, progressive lateraltranslation movement (progressive side shift). The moreimmediate the lateral translation, the shorter the posteriorcusp.

B

B

B

B

B

A

A

A

A

A

Fig. 6-19 The pathway that the cusp of a tooth follows inpassing over the opposing tooth is a factor of its distance(radius) from the rotating condyle. Mediotrusive pathway(A) and laterotrusive pathway (B).


EFFECT OF DISTANCE FROM THEMIDSAGITTAL PLANE ON RIDGEAND GROOVE DIRECTION

The relationship of a tooth to the midsagittal planewill also influence the laterotrusive and mediotrusive

pathways generated on the tooth by an opposingcentric cusp. As the tooth is positioned fartherfrom the midsagittal plane, the angles formed bythe laterotrusive and mediotrusive pathways willincrease (Fig. 6-21).

B

B

B

B

B

B

B

B

B

B

A

A

A

A

A

A

A

A

A

A

A B

Fig. 6-20 The greater the distance of the tooth from the rotating condyle, the wider theangle formed by the laterotrusive and mediotrusive pathways.This is true for both mandibu-lar (A) and maxillary (B) teeth. A, Mediotrusive pathway; B, laterotrusive pathway.

B

BBB

B

B

BB

A

A

A A

A

AAA

Midsagittalplane

Midsagittalplane

A B

Fig. 6-21 The greater the distance of the tooth from the midsagittal plane, the wider the angle formed by the laterotrusive and mediotrusive pathways. This is true for both (A) mandibular and (B) maxillary teeth. A, Mediotrusive pathway; B, laterotrusive pathway.


EFFECT OF DISTANCE FROM THEROTATING CONDYLES AND FROMTHE MIDSAGITTAL PLANE ON RIDGEAND GROOVE DIRECTION

It has been demonstrated that a tooth’s position inrelation to the rotating condyle and the midsagit-tal plane influences the laterotrusive and medio-trusive pathways. The combination of the twopositional relationships is what determines theexact pathways of the centric cusp tips. Positioningthe tooth a greater distance from the rotatingcondyle, but nearer the midsagittal plane, wouldcause the latter determinant to negate the influ-ence of the former. The greatest angle between thelaterotrusive and mediotrusive pathways would begenerated by teeth positioned in the dental arch ata great distance from both the rotating condyle andthe midsagittal plane. Conversely, the smallestangles would be generated by teeth nearer to boththe rotating condyle and the midsagittal plane.

Because of the curvature of the dental arch, thefollowing can be seen: Generally, as the distanceof a tooth from the rotating condyle increases, itsdistance from the midsagittal plane decreases.However, because the distance from the rotatingcondyle generally increases faster than thedecrease in distance from the midsagittal plane,generally the teeth toward the anterior region(e.g., premolars) will have larger angles betweenthe laterotrusive and mediotrusive pathways thanwill the teeth located more posteriorly (molars)(Fig. 6-22).

EFFECT OF MANDIBULAR LATERALTRANSLATION MOVEMENT ON RIDGEAND GROOVE DIRECTION

The influence of the lateral translation movementhas already been discussed as a vertical determi-nant of occlusal morphology. This movement alsoinfluences the directions of ridges and grooves. Asthe amount of it increases, the angle between thelaterotrusive and mediotrusive pathways gener-ated by the centric cusp tips increases (Fig. 6-23).

The direction that the rotating condyle shiftsduring a lateral translation movement influencesthe direction of laterotrusive and mediotrusive

pathways and resultant angles (Fig. 6-24). If therotating condyle shifts in a lateral and anteriordirection, the angle between the laterotrusive andmediotrusive pathways will decrease on both max-illary and mandibular teeth. If the condyle shiftslaterally and posteriorly, the angles generated willincrease.

EFFECT OF INTERCONDYLARDISTANCE ON RIDGE AND GROOVEDIRECTION

In considering the influence of the intercondylardistance on the generation of laterotrusive andmediotrusive pathways, it is important to considerhow a change in intercondylar distance influencesthe relationship of the tooth to the rotatingcondyle and midsagittal plane. As the inter-condylar distance increases, the distance betweenthe condyle and the tooth in a given arch configu-ration increases. This tends to cause wider anglesbetween the laterotrusive and mediotrusivepathways. However, as the intercondylar distanceincreases, the tooth is placed nearer the midsagit-tal plane relative to the rotating condyle–midsagittalplane distance. This tends to decrease the angles

B

B

B

A

A

A

Midsagittalplane

Fig. 6-22 The more anterior the tooth in the dental arch,the wider the angle formed by the (A) mediotrusive and(B) laterotrusive pathways.


generated (Fig. 6-25). The latter factor negates theinfluence of the former to the extent that the neteffect of increasing the intercondylar distance is todecrease the angle between the laterotrusive andmediotrusive pathways. The decrease, however, is

most often minimal and therefore the least influ-enced of the determinants.

A summary of the vertical and horizontal deter-minants of occlusal morphology can be found inTables 6-1 and 6-2.

A1

A1

A1A1

A1

B1

B1 B1

B1

B1

A2

A2 A2

A2

A2

A1A2B2

B2 B2

B2

B2

B1 B2

A B

Fig. 6-23 As the amount of lateral translation movement increases, the angle between the(A) mediotrusive and (B) laterotrusive pathways generated by the centric cusp tips increases.This is true for both mandibular (A) and maxillary (B) teeth.

A1

A1

A1

A1

A1

A3

A3

A1

B1B1

B1

B1

B1

B1

A2

A2

A3

A3

A3

A3

A2

A2

A2

A2

B2 B2

B2

B2

B2

B2

B3 B3

B3

B3

B3

B3

A B

Fig. 6-24 Effect of anterolateral and posterolateral translation movement of the rotatingcondyle.The more anterolateral the movement of the rotating condyle, the smaller the angleformed by the mediotrusive and laterotrusive pathways (A3 and B3).The more posterolateral themovement of the rotating condyle, the wider the angle formed by the mediotrusive and laterotrusive pathways (A1 and B1). This is true for both mandibular (A) and maxillary (B) teeth.


Vertical Determinants of Occlusal Morphology (Cusp Height and Fossa Depth)

Factors Conditions Effects

Condylar guidance Steeper the guidance Taller the posterior cuspsAnterior guidance Greater the vertical overlap Taller the posterior cusps

Greater the horizontal overlap Shorter the posterior cuspsPlane of occlusion More parallel the plane to condylar guidance Shorter the posterior cuspsCurve of Spee More acute the curve Shorter the most posterior cuspsLateral translation Greater the movement Shorter the posterior cusps

movement More superior the movement of rotating Shorter the posterior cuspscondyle

Greater the immediate side shift Shorter the posterior cusps

TABLE 6-1

Horizontal Determinants of Occlusal Morphology (Ridge and Groove Direction)

Factors Conditions Effects

Distance from rotating condyle Greater the distance Wider the angle between laterotrusive and mediotrusive pathways

Distance from midsagittal plane Greater the distance Wider the angle between laterotrusive and mediotrusive pathways

Lateral translation movement Greater the movement Wider the angle between laterotrusive and mediotrusive pathways

Intercondylar distance Greater the distance Smaller the angle between laterotrusive andmediotrusive pathways

TABLE 6-2

A1 A1

A1

B1

B1

B1

A2

A2

A2

B2

B2

B2

Fig. 6-25 The greater the intercondylardistances, the smaller the angle formed by thelaterotrusive and mediotrusive pathways. Thegreater the intercondylar distances, the smallerthe angle formed by the laterotrusive andmediotrusive cusp pathways (A1 and B1). Thesmaller the intercondylar distance, the wider the angle between the laterotrusive andmediotrusive cusp pathways (A2 and B2).


RELATIONSHIP BETWEEN ANTERIORAND POSTERIOR CONTROLLINGFACTORS

Attempts have been made to demonstrate acorrelation between the vertical and horizontalrelationships of the condylar guidance with thelingual concavities of the maxillary anterior teeth (vertical and horizontal relationships ofanterior guidance). One philosophy suggests thatanterior guidance should be consistent withcondylar guidance. Consideration is directed prima-rily toward the PCFs that regulate steepness of thecondylar movement (e.g., angle of the eminence andlateral translation movement). This philosophysuggests that as condylar movement becomes morehorizontal (decrease in articular eminence anglewith increase in lateral translation), the lingualconcavities of the maxillary anterior teeth willincrease to reflect a similar movement characteristic.

However, scientific evidence to support a corre-lation between the ACFs and PCFs is negligible.

Instead, studies seem to indicate that the angle ofthe articular eminence is not related to any specificocclusal relationship.1-3 In other words, the ACFsand the PCFs are independent of each other. Theyare independent, yet they still function together indictating mandibular movement. This is an impor-tant concept because the ACFs can be influencedby dental procedures. Alteration of the ACFs canplay an important part in the treatment of occlusaldisturbances in the masticatory system.

References

1. Moffett BC: The temporomandibular joint. In Sharry JJ,editor: Complete denture prosthodontics, New York, 1962,McGraw-Hill, pp 213-230.

2. Ricketts RM: Variations of the temporomandibular joint asrevealed by cephalometric laminagraphy, Am J Orthod36:877-892, 1950.

3. Angle JL: Factors in temporomandibular form, Am J Anat83:223-234, 1948.

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