1. Dentoalveolar Flashcards
3 most common teeth to be missing
Third molars
Second premolars
Maxillary lateral incisors
4 most common teeth to be impacted
Third molars
Maxillary canines
Mandibular premolars
Maxillary premolars
Second molars
Development of third molars:
-When are follicles first visible?
- When is crown formation done?
- When is 50% of the root formed
- When are 95% of molars in final tooth position
- Age 6-9 follicles become visible
- Crown formation done at age 14
- 50% root formation at age 16
- 95% of molars in final tooth position at age 24
Why do teeth become impacted?
- differential growth rate of roots causes over- or under-rotation leading to impaction
- arch length: impacted third molars are larger than erupted third molars
- ectopic position: abnormal germ position puts teeth in contact with denser external oblique ridge
- late mineralization: tooth growth lags behind maturation of jaws
- attrition: softer diet leads to less attrition maintaining MD space
What are two classification systems for third molars?
- Pell and Gregory based on radiographic review
- Winter’s classification (most common)
Pell & Gregory Classification
A-C based on relation to second molar occlusal plane
A: occlusal plane in line with second molar
B: occlusal plane between occlusal plane and CEJ of second molar
C: occlusal plane below cervical junction second molar
1-3 based on relation to anterior border of the ascending ramus
1. MD diameter of crown anterior to ascending ramus
2. half of crown is covered by ramus
3. Tooth is completely within ramus
Winter’s classification
Most commonly used classification system for third molars.
Angle between occlusal plane and longitudinal axis of third molar.
>0 degrees= inverted (rare)
0-30 degrees= horizontal impaction
31-60 degrees= mesioangular impaction
61-90 degrees= vertical impaction
<90 degrees= distoangular impaction
Indications for removal of third molars
- Pericoronitis (most common over age 20). Inflammation of operculum.
- Orthodontic needs (dental crowding may not be associated with third molars but can interfere with orthodontic treatment).
- Pericoronal pathology (pericoronal radiolucency >3mm is suggestive of a dentigerous cyst)
- Caries
- Fracture
- Unexplained pain
- Overlying prosthesis
- Periodontal disease
Inferior alveolar nerve injury after third molar extraction %
1%
Lingual nerve injury after third molar surgery
0.6-2.0%
Lingual nerve location in relation to third molar
2.8mm below crest and 2.5mm medial to lingual cortex
In 4.6-21%, lingual nerve is at or above crest of bone
22% reported at lingual plate of bone
Turns toward tongue at region of first and second molars
Rood’s Criteria
Describe intimacy of IAN with roots of mandibular third molar:
1. Darkening of Root
2. Deflection of Root
3. Narrowing of Root
4. Bifid Root Apex
5. Diversion of Canal
6. Narrowing of Canal
7. Interruption in white line of canal
Darkening of root
Diversion of canal
Interruption of white line
Most predictive
Theory of alveolar osteitis
Risk factors
Incidence
Timing
Symptoms
Increased fibrinolytic activity leading to breakdown of clot.
Risk factors: tobacco smoke, increased age, pericoronitis, birth control, female gender, inexperienced surgeon, inadequate irrigation.
Incidence 1-30%
Timing 3-7 days after EXT
Symptoms: referred pain to ear, eye, temple, foul odor, extreme tenderness
Treatment: eugenol on gel foam or iodoform gauze (inhibit neural transmission). Do not place eugenol on IAN. Can use topical lidocaine instead.
What is Gelfoam?
Absorbable gelatin sponge
Matrix for blood clot formation
Made from purified porcine skin
May cause excessive granuloma or fibrosis
What is Avitene?
Microfibrillar collagen
Mechanically broken down bovine collagen
Aggregates platelets onto fibrils and acts as matrix for blood clot formation
What is HemCon and ChitoFlex?
Chitosan dressing
Polysaccharide from shellfish, positively charged to attract erythrocytes. Acts as scaffold for clotting. New dental formulation dissolves in 48 hours.
What is Thrombin?
Promotes clot formation through activated bovine prothrombin. Activates factor IIA. Acts as serine protease converting fibrinogen to fibrin.
What is Surgicel?
Oxidized regenerated methylcellulose
Binds platelets
Negative pH is bacteriostatic
Precipitates fibrin
More efficient at hemostasis than gelatin sponge
Can be packed into socket to aid in pressure hemostasis
Does cause some prolonged healing
Be cautious when using in lower third molar sockets as surgicel creates an acidic milieu which can be toxic to the inferior alveolar nerve.
What is a Collaplug?
Cross linked collagen that promotes platelet aggregation
What is a Tanin?
Found in tea bag, serves as vasoconstrictor
What is aminocaproic acid mouth rinse?
Stabilizes clot by inhibiting plasmin
What is tranexamic acid 5% mouth rinse
Antifibrinolytic that inhibits conversion of plasminogen into plasmin
When to use apically positioned flap for impacted maxillary canine?
For labial impactions
Maintains keratinized gingiva
Use if less than 3mm of keratinized gingiva is expected after an open window technique
Do not use if high in alveolus (high labial impactions should be treated with closed technique).
When to use open exposure technique (window technique) for impacted maxillary canine?
Crown is uncovered and left exposed.
Ortho bracket may or may not be placed at time of surgery (tooth may spontaneously erupt or site can be packed with periodontal packing open with or without bracketing (speak to orthodontist preference). Packing is normally left for 2-3 weeks.
When to use a closed technique for impacted maxillary canine?
Used when teeth are not in a position to allow for repositioning of the flap after the crown is exposed.
Palatal impaction that is not close to the alveolar ridge.
Describe nerve anatomy (layers)
Endoneurium: connective tissue sheath that surrounds group fo fibers to form a fascicle.
Perineurium: surrounds a bundle of fascicles
Epineurium: outermost layer of a peripheral nerve, surrounding multiple fascicles and blood vessels
What is the rate of PERMANENT injury to the lingual nerve from third molar surgery?
0.04-0.6%
What is the rate of PERMANENT nerve injury to the IAN after third molar surgery?
0.1-1%
What is the incidence of persistent nerve impairment of the IAN 1 year after BSSO?
33%
What is the Seddon classification?
Classifies severity of nerve injuries based on histology
- Neuropraxia
- Axonotmesis
- Neurotmesis
- Neuroma
How quickly does nerve recovery progress?
1mm/day
(1 inch/month)
What is the Sunderland classification?
Classifies severity of nerve injuries based on level of anatomic injury and expands on Seddon’s classification to five degrees
1: neuropraxia, temporary disturbance in nerve conduction caused by nerve trunk traction or compression.
- Loss of axonal continuity, endoneurium and perineurium intact. Forceful compression or traction. Wallerian degeneration distal to nerve injury.
- Endoneurium and axonal loss of continuity. Perineurium intact. Severe crush, puncture, chemical, thermal, or needle-track injury.
- Loss of endoneurium, perineurium. Epineurium intact.
- Complete transection
- Mackinnon used sixth degree to describe a neuroma in continuity
What is allodynia?
Pain from a non-painful stimulus
What is anesthesia?
Absence of any sensation
What is anesthesia dolorosa?
Deafferentation pain is pain felt in an area which is completely anesthetic to touch
What is hyperalgesia?
Increased response to stimulation that is normally painful
What is hyperpathia?
Prolonged pain following a repetitive noxious stimulus that lingers beyond expected duration
What is hypoalgesia?
Diminished response to a normally painful stinulus
What is hypoesthesia?
Decreased sensitivity to stimulation
What is paresthesia?
Abnormal sensation, whether spontaneous or evoked and is not unpleasant
What is Tinel sign?
Tingling or “pins and needles” sensation elicited upon tapping on distribution of the nerve. Thought originally to be an effect of regenerating nerves and also may be misinterpreted as neuroma formation.
What is Wallerian degeneration?
Distal degeneration of the axon and its myelin sheath after injury may result from passive wasting of the distal axonal fragment due to lack of nutrient supply.
What is Level A neurosensory testing?
Fibers?
Tests?
Level A: spatiotemporal perception
A-alpha and A-beta fibers
Moving brush stroke
Two-point discrimination (anything greater than 6.5 is considered abnormal)
Stimulus localization (touch with tip of cotton stick and ask to localize stimulated area with finger. 1-3mm off is normal)
What is Level B neurosensory testing?
Fibers?
Tests?
Level B - Static Light Touch
A-beta fibers
Touch skin with end of cotton tip (if able to detect, normal, if can feel only when skin indented, this is increased threshold which is abnormal).
Semmes-weinstein monofilaments, von Frey hairs to compare to normal side.
What is Level C Neurosensory Testing?
Fibers?
Tests?
Level C - Nociception
A-delta and C fibers
27 gauge needle without indentation of skin should evoke painful response
May discriminate A-delta with heated gutta percha vs. cold from ethyl chloride for C fibers.
Indications for nerve repair
- Observed nerve transection
- Complete postoperative anesthesia
- Persistent anesthesia > 1 month without improvement
- Presence or development of dysesthesia
- Paresthesia without improvement > 3 months
- Foreign body in canal
- Patient unable to tolerate hypoesthesia
How much of a lingual nerve gap and IAN gap is possible to close with direct repair (without interpositional graft)?
1cm lingual nerve gap
5mm IAN gap
How much longer should your nerve graft be than the defect?
25% longer than defect due to shrinkage.
Where is the sural nerve located and how much can be harvested? Describe the morbidity.
Sural nerve 11-12 fascicles (IAN 18-21, Lingual 15-18)
2.1mm diameter (IAN 2.4, lingual 3.2).
20-30cm can be harvested
Found below and posterior to lateral malleolus between the gastrocnemius tendons.
Anesthesia of heel and lateral foot, temporary gait disturbance.
Overall success rate of nerve repair.
What percentage of patients with painful neuromas are helped regardless of surgical technique?
50% overall success rate
70% of patients with painful neuromas are helped regardless of surgical technique.
How do you determine positioning of an impacted canine without CBCT?
Periapical “shift shots” with the SLOB rule
Same lingual opposite buccal (as cone of X-ray machine is moved anteriorly or posteriorly)
What is allodynia?
Allodynia is pain due to a stimulus that does not normally produce pain.
What is dysesthesia?
Dysesthesia is an unpleasant abnormal sensation, either spontaneous or evoked.
What is anesthesia dolorosa?
Anesthesia dolorosa is pain in an area or a region that is anesthetic.
What is a positive Tinel’s sign?
A provocative test of regenerating nerve sprouts in which light percussion over the nerve elicits a distal tingling sensation; it is often interpreted as a sign of small fiber recovery, but following LN injury with complete severance, this response likely represents proximal stump neuroma formation and phantom pain.
In patients with abnormal pain sensations (allodynia, anesthesia dolorosa, dysesthesia), is there a diagnostic test to determine if pain relief from microneurosurgical repair is possible?
Perform a local anesthetic block of the involved nerve. If pain is abolished during duration of anesthetic block, there is a reasonable possibility of pain relief from microneurosurgical repair of the injured nerve.
Level A neurosensory testing
Level B neurosensory testing
Level C neurosensory testing
A: Directional and two-point discrimination (direction of soft cotton swab and single vs. two point stimuli)
B: Contact detection (repetitive application of touch/pressure)
C: Pain sensitivity (response to pin-prick, noxious pressures, heat)
Seddon nerve injury classification
Neurapraxia, axonotmesis, neurotmesis
Sunderland nerve injury classification
First degree (neurapraxia, no axonal damage, no demyelination, no neuroma)
Second, third, fourth degree (some axonal damage, demyelination, possible neuroma)
Fifth degree (severe axonal damage, nerve discontinuity, neuroma formation)
Procedural steps in microsurgical peripheral nerve repair
- External decompression (remove bone, scar, foreign material, expose nerve)
- Internal neurolysis (incision of epineurium, inspection of internal nerve structure, removal of scar tissue)
- Preparation of nerve stumps (excision of neuroma or scar tissue, mobilize distal and proximal stumps to allow approximation)
- Neurorraphy (approximation and suturing of nerve stumps without tension)
- Reconstruction of nerve gap (autogenous nerve graft, processed allogeneic nerve graft, alloplastic nerve guide)
- Nerve sharing procedure (when proximal nerve not available, anastomosis to nearby nerve e.g. great auricular nerve to viable distal stump of injured nerve)
- Irreparable nerve injury (nerve capping, nerve redirection, neurectomy)
Absolute contraindications to zygomatic implants
Medical condition making the patient an unsuitable candidate for surgery and general anesthesia or IV sedation.
Restricted mouth opening.
Relative contraindications to zygomatic implants
Presence of mandibular anterior teeth (making proper alignment of the drill difficult
Active maxillary sinus pathology or sinusitis (chronic sinusitis is not a contraindication)
Describe how you place zygomatic implants
- Local anesthesia
- Mouth opened maximally
- Crestal incision with anterior midline and bilateral posterior vertical releases
- Subperiosteal exposure of anterior maxillary sinus wall to the zygomatic buttress
- “Slot” prepared through the maxillary sinus wall to allow visualization of the trajectory of the implant and allow for emergence at the crest in the premolar/first molar area
- Apex of slot flattened with round bur to allow drilling into body of zygoma
- Zygomatic retractor placed, drill w/ 2.9mm drill until drill bit is seen exiting zygomatic body. Transitional drill then 3.5mm drill.
- Depth gauge to determine length of implant needed
- Zygoma implant placed into position
- Closure
Zygoma implants length and width
Typical integration length
Typical angulation
Typically range 30-55mm
Shaft diameter may taper 4mm superiorly to 5mm at fixture level
Integrated length in range of 15-20mm within body of zygoma. May have additional zone of integration at level of alveolus but not necessary.
Fixture typically angulated 45 or 55 degrees
Must use cross-arch stabilization due to long moment arm.
Bedrossian’s classification of maxillary atrophy
Zone 1: alveolus in incisor region of the arch
Zone 2: premolars
Zone 3: molars
Inadequate bone in zone 3 is contraindication to conventional implants and requires combination of sinus augmentation and bone grafting vs. zygomatic implants.
