Intro to Occlusion and TMD

Lecture from 8/7/2025

maximum intercuspal position (MIP)

the complete intercuspation of the opposing teeth independent of condylar position, sometimes referred to as the best fit of teeth regardless of the condylar position

is the habitual position for dentate patient, requires posterior teeth to hold VDO

you can hand articulate the dental models to this position

centric relation

the maxillo-mandibular relationship in which the condyles articulare with the thinnest avascular portion of their respective disks within the TMJ complex in their anterior-superior positions against the slopes of the articular eminences

it rarely coincides with MIP in dentate patient

is the position that we use for complete denture or when MIP does not exist

it is a repeatable position as it is independent of tooth contact

what are the characteristics of natural dentition?

32 teeth, PDL proprioception, mutually protected occlusion, non-working side, curve of spee, CR vs MIP

what are the characteristics of complete dentures?

2 plastic entities, no PDL proprioception, bilateral balanced occlusion, balancing side (not working side), compensating curve, CR=MIP

dental articulator

a mechanical device that duplicates certain important diagnostic and border movements of the mandible

necessary to allow communication between dentist and lab technician, allows transport and transmission of the information back and forth with the lab

why do we need an articulator?

replicates patients mandibular movements, saves patients time, diagnostic purposes which dictates the treatment plan (no influence of neuromuscular control, lingual visualization, no tongue/saliva), communication with the lab, saves chair time (no/minimal adjustments at the appointment), educational for students and patient (wax up for esthetic cases, helps to set realistic patient expectations)

what can an articulator replicate?

open-close movement (rotation)

protrusive movements with condylar guidance (translation)

lateral movements (orbiting condyle with immediate and progressive side shift and rotating condyle with laterotusion)

intercondylar distance

what determines posterior mandibular movements?

right and left TMJs

the measurements and the reproduction of those condylar movements is the basis for the use of articulators

what determines anterior mandibular movements?

teeth of the maxillary and mandibular arches

rotation

the process of turning around an axis (disco ball)

translation

movement in which every point of the moving object has simulatenously the same velocity and direction (a plane flying)

terminal hinge axis

the axis in which the movement of the condyles are in their most superior position in the articular fossae and the mouth is purely rotated open occurs

what are the 3 rotational axes of the jaw?

horizontal, frontal (vertical), sagital

condylar guidance angle

the angle formed by the steepness of the articular surface of the temporal bone as related to a horizontal reference plane

affects on the fossa depth and cusp height of the posterior teeth

if the condylar guide inclination is steeper, the condylar guidance angle will be…?

bigger

posterior controlling factors of the mandibular movement

the 2 TMJs provide the guidance for the posterior portion of the mandible and are largely responsible for determinging the character of mandibular movements posteriorly

they are a fixed factor in healthy patients (unalterable)

mandibular lateral translation

a movement of the mandible to one side that occurs during lateral movements

also known as bennet movement

bennet angle

the angle formed between the sagittal plane and the average path of the advancing nonworking side condyle as viewed in the horizontal plane during lateral mandibular movements

there is a _____ relationship between the pattern of bennet’s side shift and the anatomy of the teeth because…

close, during the movement the cusps must not interfere with the antagonist ones

what does mandibular lateral translation look like on a non-adjustable articulator?

no side shift

what does mandibular lateral translation look like on a semi-adjustable articulator?

duplicates immediate and progressive side shift, bennet angle is straight-fixed or adjustable

what does mandibular lateral translation look like on a fully adjustable articulator?

precise anatomy and side shift

intercondylar distance

the distance between the rotational centers of the condyles

what does the intercondylar distance look like on a non-adjustable articulator?

not a close duplicate (very narrow)

what does the intercondylar distance look like on a semi-adjustable articulator?

very close duplicate but fixed

what does the intercondylar distance look like on a fully adjustable articulator?

precise mm distance

what is the average intercondylar distance?

about 110 mm

non-adjustable articulator

open and close in a fixed horizontal axis, referred to as cast holders, stephen’s articulator

only need bite registration (MIP)

casts are maintained in MIP, intercondylar distance is no accurate, cannot replicate eccentric movements

semi-adjustable articulator

have fixed intercondylar distance, arcon or non-arcon

need centric relation and facebow records (necessary to make articulator accurate for excursions)

fully adjustable articulator

have adjustable intercondylar distance, condylar inclination, progressive side shift, immediate side shift, rotating condylar movement

need an exact axis location, a pantographic recording, and a CR interocclusal record

both fully and semi-adjustable articulators allow for some adjustment for…

side shifts and condylar inclination

arcon

articulating condyle

the condylar element on the articulator is on the lower member and the guiding track is on the upper member (similar to the TMJ)

non-arcon

non articulating condyle

the condylar element on the articulator is on the upper member and the guiding track is on the lower member (opposite to the TMJ)

facebow registration

an instrument used to record the spatial relationship of the maxillary arch to some anatomic reference point or points and then transfered to the opening axis of the articulator

*what does the facebow registration relate?

the maxillary arch to the horizontal hinge axis and cranial base

what are the posterior reference points for facebow registration?

hinge axis of each condyle

arbitrary hinge axis is the external acoustic meatus

what are the anterior reference points for facebow registration?

orbital

fixed distance from nasion (-23mm), an arbitrary point is measured up from the incisal edge of the maxillary lateral incisor (Denar is +43mm)

an incorrect facebow record can…

misalign the maxillary cast, misrepresenting the true occlusal plane and condylar position, leading to occlusal errors and poor restorative outcomes

*how do we locate the hinge axis for a fully adjustable articulator?

requires hinge axis locator, patients used to be tattooed so that the facebow could be repeated

*how do we locate the hinge axis for a semi- adjustable articulator?

an arbitrary hinge axis can be used (determined by manufacturer of facebow and articulator system)

Denar is auditory meatus

average distance from ear to hinge axis is 10-13mm, which the manufacturer has taken into account

*how do we located the anterior reference point?

measuring 43mm from the incisal edge of maxillary lateral incisor

what are the steps of facebow record and transfer?

determine anterior reference point

stabilize bitefork

separate bitefork and transfer jig assembly from facebow

assemble transfer jig table

position and secure transfer jig assembly

mount maxillary cast

mount mandibular cast

condylar inclination on fully adjustable articulators

capable of adjusting the condylar pathway to duplicate the angle and specific curvature of the patient’s condylar movements

accurately duplicates mandibular movement

*what can our (Denar Mark 320) articulator do?

condylar inclination adjustment is straight (not curved like fully adjustable)

fixed progressive side shift is 15 degree bennet angle

fixed condylar distance is 110 mm

arcon (condylar element is on lower member)

arbitrary hinge axis (external auditory meatus)

anterior reference point is 43 mm above incisal edge of #7

needs facebow transfer for accuracy

virtual articulators

mathematically simulated- 3D virtual articulators with average values, not feasible to obtain individualized movements, more user friendly and less expensive

completely adjustable- can record and reproduce the precise movements of the mandible using an electronic jaw registration system