Dental Anatomy - Exam 1

What is the name of the system of teeth for chewing?

Masticatory System

What approach should you have in complete dentistry?

Identify and treat causative factors rather than just the symptoms (in these cases, it may be occlusal interference)

4 Parts of Complete Dentistry

• Optimum Oral Health

• Anatomic Harmony

• Functional Harmony

• Occlusal Stability

Optimum Oral Health

• Plaque control

• Periodontal status

• Finding cause of problems

• Fixing misdirected occlusal forces

Anatomic Harmony

• Muscles and TMJ function as expected w/o interference

• Anatomic shape of teeth corresponds with function

Functional Harmony

• Mastication w/o interference

• Can easily function to limit or remain at peace

Occlusal Stability

• Horizontal stability of teeth (tongue muscle)

• Vertical stability of teeth (opposing arch)

Benefits of Complete Dentistry

• Increased patient comfort

• Restoration longevity

• Occlusal stability

• More accurate treatment planning

• Improved esthetics

• Increased productivity

• Decreased stress

Diagnostic Appointment Steps

• Chief Complaint

• Medical History

  • Conditions affecting treatment methodology

  • Systemic Conditions w/ Oral manifestations

  • Conditions affecting treatment plan

  • Risk factors to dentist and auxiliary personnel

  • Review of systems

  • Dental History

• Comprehensive Dental Exam

  • Maxillary/Mandibular Alginate Impressions (one of many tests done to examine oral health)

Alginate Impression General Info

• Irreversible Hydrocolloid where alginic acid solution is converted to calcium alginate as gel

• Water makes up 50% of composition

• Hydrocolloid should be poured 12 minutes before removal

Alginate Impression Tools

• Impression material

• Rubber bowl

• Beaver Spatula

• Disposable Tray

• Adhesive for Alginate

• PPE

• Any other equipment for modifications like Hanau Torch or rope wax

Impression Tray Details

• Perforated for retention

• Need adhesive

• Can be disposable or metal and size small, medium, or large

• Ideally have ¼ inch alginate thickness

Alginate Impression Technique

• Select tray and adhesive

• Add powder to water and mix for 45-60 seconds

• Load the tray

• Position yourself in front of patient for mandibular and behind patient for maxillary

• Use mirror to retract cheek and seat tray in rolling motion from posterior to anterior without applying pressure

• Remove tray carefully with fingers under vestibular flange

Features to see in Impressions

Maxillary

• Vestibule Roll

• Buccal Frenulum

• Hamular Notch

Mandibular

• Vestibule Roll

• Buccal Frenulum

• Lingual Frenulum

• Lingual Vestibule

• Retromolar Pads

Pouring and Making Cast

• Impression must be removed within 12 minutes of being made

• Rinse disinfectant from impression and remove excess water

• Use exact W/P ratio

• Vacuum mix stone for 15 seconds

• Carefully vibrate into impression and use 2-step pour technique

• Remove from alginate in 45-60 minutes

• Trim casts to fit base former

• Use super-sep to index grooves

Facebow

• Instrument to record spatial relationship of maxillary arch to reference point

• Orients dental cast to opening axis of articulator

Components of Facebow

• Nasion Relator

• Ear Piece

• Metal Earbow

• Cross Bar

• Bite Fork

• Toggle Assembly

Facebow Record Equipment

• Clean facebow and bitefork

• Toggle Assembly

• Blue Mousse

• Red Handle Knife

• Necessary PPE

Interocclusal Record

• Spatial relationship between max and man teeth

• Reproduces patient’s occlusal plane and arc of closure

• Reference points used: Maximal Intercuspal Position and Centric Relation

Articulator Classes

• Class 1 - Vertical motion only and non-adjustable

• Class 2 - Permits horizontal and vertical motion but no TMJ movement

• Class 3 - Simulates condylar pathway using mechanical equivalents of motion (semi-adjustable)

  • Arcon type have adjustable Bennet angle corners

• Class 4 - 3D dynamic registrations used to orientate the cast to TMJ and simulate mandibular movements (adjustable)

Articulator Settings

• Condylar Guidance is 30 degrees

• Immediate Sideshift should be set to 0

• Latch is closed

• Pin set to 0 mm

Temporomandibular Joints

• Right and left TMJs are interdependent

• Changes in occlusion, attrition, or loss of teeth affects loading patterns of TMJ

Structures around TMJ

• Mandibular Fossa

  • Has V-shaped contour to allow medial pole of condyle to fit and have rotational movement

• Articular Surface of Condyle

  • Posterior aspect has greater articular surface

• Soft Tissue Components

  • Articular Disc

  • Retrodiscal tissue

Muscles of Mastication and other structures

• Deep Portion

  • Lateral Pterygoid

    • Superior head

    • Inferior head

  • Medial Pterygoid

• Superficial Portion

  • Temporalis

  • Masseter

• Suprahyoids

• Tongue muscle

• Buccinator

• Capsule of Temporomandibular Joint

Temporalis

• Origin - Inferior temporal line and fossa

• Insertion - Coronoid Process and anterior ramus

• Action - Elevates mandible (anterior and middle fibers) or retrudes mandible (posterior fibers)

Masseter

• Origin - Zygomatic Arch

• Insertion - Lateral surface of ramus and angle of mandible

• Action - Elevates mandible

Medial Pterygoid

• Origin - Medial surface of lateral pterygoid plate, pyramidal process of palatine, maxillary tuberosity

• Insertion - Medial surface of ramus and angle of mandible inferior to mandibular foramen

• Action - Elevates Mandible

Superior Head of Lateral Pterygoid

• Origin - Greater wing of sphenoid and infratemporal crest

• Insertion - Articular disc and neck of condyle

• Action - Protrudes, moves mandible side to side

Inferior Head of Lateral Pterygoid

• Origin - Lateral surface of lateral pterygoid plate

• Insertion - Pterygoid fovea on the neck of condyle

• Action - Depresses mandible

Which muscle is responsible for elevating, closing, or raising jaw?

All muscles of mastication except inferior head lateral pterygoid.

Which muscle is responsible for depressing or opening jaw?

Inferior head of lateral pterygoid and suprahyoid muscles.

What is responsible for elevation, depression, retrusion, protrusion, and lateral excursion?

Elevation

• Ipsilateral Medial Pterygoid

• Contralateral Masseter

• Contralateral Temporalis

Depression

• Contralateral Inferior Head of Lateral Pterygoid

• Suprahyoid (such as anterior belly digastric and mylohyoid)

• Infrahyoid

Retrusion

• Temporalis

• Masseter (deep)

Protrusion

• Lateral Pterygoid

• Medial Pterygoid

• Masseter

Lateral Excursion

• Ipsilateral Masseter

• Contralateral Medial Pterygoid

Condylar Movement in Working and Balancing Side

• Working Side

  • Rotation

• Balancing Side

  • Orbiting (involved in translation and rotation of condyle)

Full Intercuspation, Opening Phase, End of Closing Phase

Full Intercuspation

• Buccal cusps of mandibular molars are medial to buccal cusps of maxillary molars

Opening Phase

• Buccal cusps of mandibular molars on working side is more lateral than usual

End of Closing Phase

• Mandible is drawn toward midline

• Bolus is subjected to vertical and horizontal shear forces by opposing molar cusps

What is considered as the power stroke during mastication?

The end of the closing step when teeth are crushing food bolus while resting between opposing cusps and fossae

Random Additional Info at the end of Spears Lecture

• Articular disc rotates relative to condyle

• Forces are transmitted to mandibular condyle during chewing and biting

• Temporomandibular Disorder (TMD) causes clicking, internal derangement, joint degeneration, limited movement, and pain

• Anatomical (occlusal contact area, malocclusion), physiological (muscle strength, gender, age), and psychological components all affect occlusion

• Masticatory performance is objective and affects, food breakdown, nutrition, digestion, and much more

• Number of occlusal contacts influences maximum bite force

• Class II and III patients have lower masticatory performance but not cared for clinically if patient is not compromised

Occlusion and Determinants of Occlusion

• Occlusion - Contact between maxillary and mandibular teeth

• Determinants - Both TMJs, permanent dentition, and neuromusculature

  • Anterior teeth are active determinants; posterior teeth are passive determinants

Intercuspation and Interdigitation

• Intercuspation is the cusp-to-fossa relationship of upper and lower teeth

• Interdigitation is intercuspation but for multiple teeth

  • Each tooth interdigitates with two opposing teeth (provides dental arch stability)

  • Less distinct in molar region than other regions

  • Mandibular teeth interdigitate with same tooth and tooth medial to it (maxillary do opposite)

  • Exceptions are mandibular central incisors and maxillary third molars

Centric Occlusion

Occlusion of teeth when mandible is in centric relation

• Maxillary buccal cusps line up with buccal embrasures and developmental grooves

• Mandibular lingual cusps line up with lingual embrasures and developmental grooves

Maximal Intercuspation

• Complete intercuspation of opposing teeth independent of condylar position

• Used in articulators when occlusions can be restored in current mandibular position and no changes are planned on occlusal plane or vertical dimension

Centric Relation

• Position independent of tooth contact

• Condyles are in anterior-superior position against posterior slopes of articular eminence

• Mandible can only rotate in this position

• Bone-to-disk-to-bone relationship

• Use in articulators when you plan to reorganize occlusion, when you plan to use extensive indirect restorations, or you want to make a new occlusal plane

Centric Stop

Opposing cusp/fossae contacts maintaining occlusal vertical dimension between opposing arches

• Take the form of cusp to marginal ridge, cusp to fossa, or cusp to occlusal embrasure

• They are usually found under or over line of central groove

Which teeth are classified as closure stoppers? What teeth protect others during protrusive movement? What teeth protect others in lateral excursion?

• Closure Stoppers - Posterior Teeth

  • Protect anterior teeth in Centric Occlusion

  • Minimize load on TMJ’s

• Protrusive Movement - Incisors

• Lateral Excursions - Canines

  • Canine Protected Articulation (form of Canine Guidance or Cuspid Rise) is involved in lateral movement

  • Uses vertical and horizontal overlap of tooth as well as canine eminence (thick facial plate of bone) for protection

  • Has longest root in mouth

Anterior Guidance

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

• Anterior teeth are considered steering wheel of occlusion

• Effects of anterior guidance are most on premolars

• Effects of condylar guidance are most in molars

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

What happens when canine guidance fails?

• Group function occurs, causing contacts between several teeth and distributing occlusal forces

• Restorative dentists consider modifying condylar guidance so no working contacts occur on buccal cusps of first and second molars

Condylar Guidance

• Functional relation of hard and soft tissue in TMJ

• The flatter the articular eminence, the shorter the cusps must be

• 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

Supporting Cusps vs Non-supportive cusps

Supporting Cusps

• They contact opposing centric stops and do most of grinding during mastication

Non-supportive Cusps

• Overlap supporting cusps

• In CO, there is 0.5-1.0 mm of space between supportive and non-supportive cusps

What protects the cheeks and the tongue during mastication?

• Cheeks - Maxillary Buccal Cusps

• Tongue - Mandibular Lingual Cusps

Posselt’s Diagram

Movement of mandibular incisal edge viewed from mid-sagittal plane

• Does not represent mechanics of TMJ because in condylar position, CO may be posterior to CR

Steps of Opening Jaw from Centric Relation

• First - Condyle hinges/rotates about fixed axis (hinge axis)

  • Responsible for recording CR at a vertical dimension

  • End of opening is 20-25 mm from centric relation

• Second - Condyles translate or slide down articular eminences until they are over crests of articular eminences

  • End of opening is 40-60 mm of total opening

Working Side vs Balancing Side

Working Side

• Same side as lateral excursive movement

• Working side condyle rotates (moves forward/backward and upward/downward)

  • Bennett Movement or Immediate Sideshift

Balancing Side

• Opposite side of lateral excursive movement

• Balancing side condyle orbits (moving downward, forward, and medially)

  • Bennett Angle or Progressive Sideshift (measured around 15 degrees) corresponding to angulation of medial wall from lateral checkbite of superior wall

Tracking of Cusps in Working Side and Balancing Side

Working Side

• Mesiolingual cusps of maxillary molars track out of lingual groove of mandibular molars

• Distobuccal cusps of mandibular molars track out of buccal groove of maxillary molars

Balancing Side

• Mesiolingual cusp of maxillary first molars track over distobuccal groove of mandibular first molars

Working vs Balancing Interferences

Working Interference

• Working interferences occur between inner incline of non-supporting cusps and outer incline of supporting cusps

  • Cross-tooth balancing interference is a working interference between maxillary and mandibular lingual cusps

Balancing Interference

• Balancing interferences occur between inner inclines of supporting cusps

Protrusive Movement

• Condyles slide forward and downward on articular eminence

• Mandibular incisal edges slide down lingual surfaces of maxillary incisors

Gothic Arch Tracing

• Aka Gysi’s tracing or crow’s foot

• Detects border movements of articulator in horizontal plane

• 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 othodontic treatment

Maxillary vs Mandibular Crow’s Foot

• Blue - Working

• Green - Non-working

• Black - Protrusive

• Yellow - Lateral Protrusive

Maxillary

Mandibular

Curve of Spee

• Curvature beginning in canine and following buccal cusp tips of premolars and molars

• Flatter curve has less excursive interferences

Curve of Wilson

• Mediolateral curvature of occlusal plane of posterior teeth

• Depresses non-supporting cusps and prevents working interferences

Curve of Spee + Curve of Wilson

Compensating Occlusal Curvature or Sphere or Monson

Shape of Immediate and Progressive Side Shifts

• Not like A, B, or C in this image

• These tracings were made using chinpoint guidance

• Immediate side shift is as much as 3 mm because condyles may be distracted (CR detracts from natural seated position) which can harm TMJ

Orbiting Pathway vs Protrusive Pathway

• Orbiting Pathway is steeper than protrusive pathway to prevent balancing interference

• Since protrusive path is flatter, superior wall settings on protrusive record can be used for all excursive movements which can save chair time when casting restoration

Frontal Plane Border Movements

• Masticatory Loop is vertical and teardrop shaped

• If lateral pterygoid is paralyzed, the mandible will open to affected side

Physiologic Rest Position

Position of mandible when muscles are at minimal contraction

Freeway Space

• Distance between occluding surfaces of maxillary and mandibular teeth when mandible is in rest position

• Usually 2-4 mm

Malocclusion

Deviation from normally acceptable contact between opposing dental arches

Occlusal Prematurity

• Contact of opposing teeth before planned intercuspation

• Brain is signaled and brought to a “new” maximum intercuspation

Occlusal Forces

Should be borne along long axes of teeth to promote stability of occlusion

Primary and Secondary Occlusal Traumatism

• Primary occlusal traumatism - Abnormal force placed on normal structure

  • This causes fremitus (tooth mobility)

  • After being corrected, may take several days to stabilize

• Secondary occlusal traumatism - Normal force on abnormal supporting structures

Other defects that may be found because of occlusal traumatism

• Anterior Diastema

• Gingival Cleft

• The rest of examples are not part of the exam