Dental Anatomy 2 - Final Exam

TMJ

• Bilateral ginglymodiarthroidal joint

  • Ginglymo (hinge rotation) - Open and close around horizontal axis; teeth separation and occlusion with no positional change

  • Diarthroidal (translation) - When rotation ends, inferior head of lateral pterygoid pulls condyle forward against articular eminence

• Upper compartment (translation) - superior surface and temporal bone

• Lower compartment (rotation) - inferior surface and condyle

Mandibular Movement Steps

Opening

1. Depressor muscles contract, elevators relax, hinge movement begins

2. Pure hinge movement stopped by temporomandibular ligament

3. Inferior head of lateral pterygoid contracts, pulling disk and condyle. Digastric and hyoid muscles contract

4. Condyle slides on crest of eminence as inferior head of lateral pterygoid relaxes

Closing

1. Temporalis contracts to move mandible back and up

2. Superior head of lateral pterygoid contracts to bring disc to anterior surface of condyle

3. Depressor muscles relax

4. Elevator muscles contract to pull condyle up until condyle hits superior position

Anatomical Planes and Axes of Rotation

Horizontal Plane

• Rotation of the horizontal axis - Hinge motion. Horizontal axis is called terminal hinge axis when condyle is sitting in mandibular fossa.

Frontal Plane

• Rotation of frontal (vertical) axis - One condyle moves anteriorly while other condyle remains in terminal hinge position. Considered unnatural because of articular eminence inclination.

Sagittal Plane

• Rotation of sagittal axis - One condyle moves inferiorly while other condyle remains in terminal hinge position. Considered unnatural because of musculature and ligaments of TMJ.

Translational Movement

• Teeth, condyles, and rami move in the same direction and to the same degree

• Mandible moves slightly forward during opening.

• Usually, both rotation and translation occur simultaneously (When mandible rotates around an axis, the axis is also translating)

Ligaments of TMJ

Temporomandibular Ligament

• Outer oblique portion limits opening movement

• Inner horizontal portion limits posterior movement

Stylomandibular and Sphenomandibular Ligaments - Limit opening and anterior movement

Sagittal Plane Movements

Represented in Posselt’s Triangle

1. Posterior Functional Border Movement

2. Anterior Functional Border Movement

3. Superior Contact Border Movement

4. Mastication

Posterior Functional Border Movement

Two stage hinge movement:

• Stage 1 - Pure rotation while condyles are in CR (20-25 mm)

• Stage 2 - Rotation while condyles move anteriorly and inferiorly (causes axis of rotation to translate)

Maximum opening stopped from capsular ligaments (40-60 mm)

Anterior Functional Border Movement

• Condyles remain in anterior and inferior position

• Pure hinge motion moves mandible from maximally opened to maximally protruded position

• Ligaments pull condyles slightly posteriorly as mandible moves to protruded position

Superior Contact Border Movement

• Determined by occluding teeth surfaces

• Factors causing delineation include:

  • CR and MIP variations

  • Cusp inclination steepness

  • Overjet and overbite

  • Maxillary anterior teeth lingual surface anatomy

Horizontal Plane Movements

Recorded by Gothic Arch

1. Left Lateral Border

2. Continued Left Lateral Border

3. Right Lateral Border

4. Continued Right Lateral Border

Frontal Plane Movements

Makes a shield pattern

1. Left Lateral Superior Border

2. Left Lateral Opening Border

3. Right Lateral Superior Border

4. Right Lateral Opening Border

Gothic Arch Tracing

• CR-CO should be down midline and be short

  • If adjusted, long centric or freedom in centric may occur which is undesirable and may need orthodontic treatment

Anterior Guidance

• Anterior teeth protect the posterior teeth and TMJs during excursive movements through posterior disclusion

• Effects of anterior guidance are most on premolars

• Anterior teeth are protected by distance from TMJ because forces are closest near joint

Condylar Guidance

• Functional relation of hard and soft tissue in TMJ

• The steeper the articular guidance, the taller the cusps may be

• Anterior guidance must be equal to or greater than condylar guidance for excursive movements

Mandibular Movement Rules

• Memorize Picket Fence of Dentistry

• Tooth types occlude with the same tooth type of opposite jaw (ex: first premolars only occlude first premolars)

• Arrows on maxillary quadrant represent direction of mandibular movement; arrows on mandibular quadrant are opposite of mandibular movement

• Side of lateral excursion is working side; side opposite of lateral excursion is non-working (balancing side)

  • Arrows pointed to supporting cusps are balancing movement; arrows pointed to non-supporting cusps are working movement

• Specific rule: If arrow is on mandibular teeth image and it is pointed mesiobuccally or mesiolingually, the mandibular movement is considered non-functional

Occlusal Analysis

• Systematic examination of occlusion that considers the interocclusal relations of mounted casts

• Cast Analysis exercise is used in diagnosis, planning, and treating prosthodontic and TMD patients

CR vs MIP Scenarios and Articulator Settings

Centric Relation

• Reorganize the occlusion, including vertical dimension

• All teeth will be treated by indirect restorations

• When doing occlusal analysis or establishing a new occlusal plane

• Settings: Latched; Pin should not touch surface

Maximal Intercuspal Position

• Stable occlusions restored in the present mandibular position

• No changes to occlusal plane or vertical dimension of occlusion

• Settings: Unlatched; Pin should touch surface

Diagnostic Mounting and Occlusal Analysis Form

• Articulator Condylar Element Settings - How much inclination set on articulator

• Wear - Identify all wear facets (wear line or plane caused by attrition) in teeth

• Centric Occlusion - Verify that CO records is same as what is in the mouth. Check first occlusal contacts. If there is mismatch, restart everything :(

• Maximum intercuspation - Are condyles fully seated in fossa

• Mandibular Displacement - Measures displacement in mm between CR and MIP

  • Vertical displacement is measured by marking maxillary incisor edge in mandibular teeth

  • Horizontal displacement is measured by marking vertical line on reference point in posterior teeth (mandibular is fixed so additional markings are done on maxilla)

  • Frontal displacement is measured with vertical line between central incisors

• Indicate laterotrusive and mediotrusive contacts - Healthy occlusion does not have contacts

• Indicate protrusive interferences - Healthy occlusion has anterior teeth contact for anterior guidance

• Overbite and overjet distance (measured in MIP)

• Anterior teeth coupling - Is there anterior guidance?

• Based on the above, decide whether treatment is needed

Diagnostic Cast Armamentarium

• Diagnostic Mountings

• Red, Blue, and lead Pencil

• mm ruler

• Shimstock - Identifies first point of contact

• Accufilm II (red/black) - Marks contact

Never discussed tbh:

• Boyle Gauge

• Cleoid/Discoid

• Fiberglass eraser and or scalpel

Occlusal Disease

• Deformations or disturbances that prevent occlusion

• Signs precede symptoms and damage progresses if not treated early

• Destructive dental disorder causing tooth loss, discomfort, and decreases orthodontic longevity

Tooth Deformation Mechanisms

• Stress - Produces compression, flexure, and tension resulting in fractures and abfraction

• Friction - Occlusal surface wear in the form of attrition and abrasion

• Corrosion - Chemical/electrochemical degradation (usually with pH < 5.5) appearing as cupped-out dentin area usually on posterior teeth. Caused by:

  • Bulimia - Enamel loss of lingual surface of anterior teeth

  • GERD - Enamel loss of lingual surface of molars where gastric acid could pool

  • Gingival crevicular fluid - Acidic pH affects non-carious cervical lesions

Attrition, Abrasion, and Abfraction

• Attrition

  • Aka bruxism

  • Usually on lower anterior teeth

  • Matching wear facets

  • Anterior Guidance Attrition - Wear on lingual enamel on maxillary anterior teeth

• Abrasion

  • Caused by continuous food chewing, excess toothbrushing or use of foreign objects

• Abfraction

  • Stress-induced, non-carious cervical lesion

  • Another theoretical cause is toothpaste abrasion

Splayed Anterior Teeth

• Forward deflection of mandible from posterior incline interference

• Should be treated early by eliminating the deflective interferences

• Early stages of teeth splaying may present with fremitus and sore teeth

• Also caused by thick lingual restorations of the maxillary anterior teeth and over-contoured mandibular teeth restorations

Advanced Occlusal Disease

• Combination of attritional wear and shifted teeth

Destroyed Dentition

• Includes severe wear, teeth fracture and elongated alveolar processes

Sensitive Teeth

• Occlusal overload produces sensitivity due to pulpal hyperemia or the presence of surface micro-cracks. Exaggerated effect causes soreness

• These teeth are vital; occlusal adjustment provides immediate relief

Split Teeth and Fractured Cusps

• Cusp incline hitting strong occlusal forces causes fracture lines

• This sign precedes cusp fracture or split tooth

Painful Musculature

• Deflective interferences can strain masticatory muscles to achieve MIP

• Interfering posterior teeth aggravate this by causing excessive wear, hyper mobility, fractured cusps, and hypersensitivity