Lecture 13- TMJ Disorders and Restorative Dentistry

TMJ anatomy

Mandibular head (condylar process) articulates with mandibular fossa of temporal bone; synovial joint with 2 compartments

TMJ function

Mandibular head moves rostral + ventral during opening; maximal opening stretches capsule + lateral ligament; masseter/temporalis/pterygoid maintain congruity

TMJ dysplasia definition

Abnormal development → excessive joint laxity → subluxation/luxation; rostral shift → coronoid contacts zygomatic arch ipsilaterally

Open‑mouth locking

Intermittent inability to close mouth due to coronoid–zygoma interlock; hallmark of TMJ dysplasia

TMJ dysplasia anatomic changes

Shallow fossa; flattened mandibular head; abnormal obliquity; capsule/ligament laxity; excessive movement → soft tissue laxity → joint incongruity

TMJ dysplasia chronicity

Bony proliferation; DJD; reduced ROM

TMJ dysplasia presentation

Intermittent inability to close mouth; spontaneous reduction; visible coronoid bulge; mandibular shift ventrally + toward affected side; temporalis atrophy

TMJ dysplasia age/breeds

Young adults; Irish Setters, CKCS, Cocker Spaniels

TMJ dysplasia diagnosis

CT or CBCT; radiographs NOT advised (poor soft tissue detail, unlikely to capture disarticulation)

TMJ dysplasia treatment

Surgery to prevent locking; NOT stabilization; condylectomy NOT advised (destabilizes TMJ)

Zygomatic arch resection

Semilunar rim ostectomy of rostral ½ arch length + ½–⅔ arc height; performed during jaw locking or with assistant opening/closing jaw

Coronoid reduction

Concurrent with arch ostectomy; blunt dissection deep masseter; incise temporal fascia; remove ½–¾ coronoid height

TMJ dysplasia complications

Facial asymmetry; recurrence (inadequate removal/regrowth); bilateral disease missed

Dislocation definition

Joint displacement with components still within capsule

Luxation definition

Complete dislocation; articular surfaces fully separated

Subluxation definition

Partial/incomplete dislocation

TMJ fracture classification (AO‑CMF)

Condylar process fracture (line caudal to notch); mandibular head fracture; fragmentation grades 0–3; displacement grades 0–2

TMJ fracture exam finding

Jaw shifts BACK and TOWARD side of fracture

TMJ luxation presentation

Inability to open/close mouth; malocclusion; mandible shifts AWAY from side of luxation; traumatic history possible

TMJ luxation differentials

Traumatic luxation/sublux; mandibular fracture; TMJ dysplasia; oral FB; dynamic malocclusion (PD); trigeminal neuropraxia

TMJ luxation diagnosis

Radiographs + CT/CBCT; subluxation = widened joint space; luxation = condylar displacement (rostrodorsal most common); caudal displacement → retroarticular process fracture

Trauma workup

Thoracic rads + abdominal US; CBC/chem/UA

TMJ luxation closed reduction

Pencil fulcrum between 2nd–3rd molars on luxation side; gently close mouth + push mandibles caudally with counterclockwise rotation; digital pressure on coronoid also works; confirm via CT; apply MMF or tape muzzle

TMJ luxation open reduction

Lateral recumbency; ventral incision caudal zygomatic arch; incise capsule if intact; remove torn/folded disc; preserve intact disc; condylectomy only for chronic/non‑reducible cases; MMF 2–3 weeks

TMJ fracture treatment

Non‑surgical preferred unless fragment blocks opening/closing; MMF 7–14 days (young), 2–3 weeks (adult)

MMF rigid fixation

Composite with 10–20 mm opening; disadvantages: delayed function, feeding tube, poor hygiene, hyperthermia, aspiration

MMF elastic fixation

Elastic bands guide occlusion; better blood supply; faster function return; less thermoregulation/aspiration risk

Severely displaced fractures

Miniplate reconstruction indicated

TMJ fracture healing time

Dogs 10–13 weeks; cats 4–8 weeks

TMJ fracture complications

Ankylosis; fibrous healing (no treatment if normal function); DJD (slow chewing, weight loss, crepitus → NSAIDs)

TMJ ankylosis definition

Bony or fibrous fusion of mandibular head to fossa; intra‑articular disc destruction + narrowed joint space

TMJ pseudoankylosis definition

Extra‑articular fibrous/bony encapsulation; minimal intra‑articular involvement; coronoid–zygoma bridging common

TMJ ankylosis causes

Post‑traumatic; neoplasia; infection; CMO

TMJ ankylosis presentation

Gradual reduced opening; drift toward affected side; complete inability to open; tongue entrapment; TMJ pain; reduced ROM; anesthetic concerns (tracheostomy)

TMJ ankylosis diagnosis

CT/CBCT: reduced/absent joint space; bony proliferation; pseudoankylosis shows coronoid–zygoma bridging; 3D reconstruction helpful

TMJ ankylosis surgical considerations

Young: gap arthroplasty preferred (avoid refusion); forced opening + steroids NOT advised

Condylectomy technique

Cut from mandibular notch caudal + ventral in semilunar configuration

Gap arthroplasty components

Zygomectomy (remove central arch segment); coronoidectomy ± condylectomy (ventral osteotomy avoiding mandibular foramen); fossectomy (medial fossa osteotomy to zygomatic–cranial junction)

Salvage mandibulectomy

Extreme bone proliferation involving cranial base

TMJ ankylosis complications

Further ankylosis (prevent by reintroducing hard food at 3–5 days); traumatic malocclusion (manage with extractions or crown reduction)

MMM definition

Autoimmune inflammatory myopathy of 2M fibers (temporalis, masseter, pterygoids, rostral digastricus); trigeminal mandibular branch innervation

MMM imaging

CT shows contrast enhancement in temporal, masseter, pterygoid; digastricus spared

MMM clinical signs

Lethargy, anorexia, fever, bark change; pain opening mouth; swelling/atrophy; inability to open mouth; exophthalmos/enophthalmos; blindness (optic neuritis)

MMM diagnosis

CT; 2M antibody titer (Antech); muscle biopsy

MMM treatment

Prednisone taper: 2 mg/kg q24h ×2w → 1 mg/kg ×4w → 0.5 mg/kg ×10w → 0.25 mg/kg ×16w → 0.25 mg/kg q48h ×16w → taper 2–4w; discontinue after 1 year if asymptomatic + negative titers

MMM prognosis

Determined by fibrosis + treatment response; excellent–good if improvement within 1–3 days of prednisone

MMM complications

Muscle atrophy; fibrosis → inability to open mouth (end‑stage); relapse

Restoration definition

Sealing exposed dentinal tubules to reduce sensitivity + prevent pulpitis/pulp necrosis

Dentin composition

72% mineral, 18% organic, 10% water; odontoblast‑produced; primary/secondary/tertiary dentin; 45,000 tubules/mm²

Dentinal tubules

Contain odontoblastic processes; exposed tubules → sensitivity + contamination; tertiary dentin from chronic wear not sensitive

Restoration indications

Uncomplicated crown fractures; occlusal caries on MxM1 without pulp exposure; root canal access restoration; enamel defects (hypoplasia/hypocalcification)

Restoration contraindications

Pulp exposure; near‑pulp exposure; endodontic disease; periodontitis; cats with tooth resorption

Bonding agent components

Etchant (35–37% phosphoric acid); primer (hydrophilic monomers); adhesive; fillers; solvent

Bonding generations

5th gen = phosphoric acid + primer/adhesive; 6th–7th gen = self‑etch (faster, weaker bond)

Bonding equipment

Radiography; high/low‑speed handpiece; scaler; explorer; Arkansas stone; sanding discs; pumice; contra‑angle; etch; microbrush; curing light

Bonding procedure: evaluate

Probe sulcus; radiograph; compare canal width; check for apical lucency; transilluminate for vitality

Bonding procedure: clean

Ultrasonic clean; remove calculus; avoid pulp exposure; pink area = near pulp exposure

Bonding procedure: pulp check

Explorer/file/needle; pulp exposure → extraction or endodontics

Bonding procedure: enamel edges

Arkansas stone to remove sharp enamel

Bonding procedure: smooth dentin

Polishing discs (coarse → fine → ultrafine); check with explorer; rinse between discs

Bonding procedure: polish

Non‑fluoride pumice; fluoride reduces etch efficacy

Bonding procedure: isolate

Gauze or rubber dam

Bonding procedure: etch

37% phosphoric acid; 15 sec dentin, 30 sec enamel; rinse gently (no air blast)

Bonding procedure: apply agent

Microbrush; follow manufacturer instructions

Bonding procedure: air dry

Gentle compressed air 5–10 sec

Bonding procedure: cure

Light cure 10 sec (“One‑Step®”)

Bonding procedure: repeat

Apply 1–2 additional layers; air dry; cure

Bonding procedure: final check

Explorer smoothness; dentinal tubules sealed; sensitivity reduced; bacterial ingress prevented