Third Molars (1) Flashcards
Radiographically, the crowns of upper third molars can be seen beginning to calcify at what age?
upper third molars = between 7 - 9yrs old
Radiographically, the crowns of lower third molars can be seen beginning to calcify at what age?
lower third molars = between 8 -10yrs old
By what age does the crown of third molars appear fully calcified radiographically?
usually by 18 years old
Between what ages can root calcification be seen?
18 - 25yrs old
What does agenesis mean?
Failure of an organ to develop
Why is there increased frequency of third molar agenesis?
It is an example of human evolution
Third molar agenesis incidence varies between populations - which population has reached nearly 100% third molar agenesis?
The Indigenous Mexicans
Which gene has been shown to be involved in third molar agenesis?
PAX9 gene
(there are other genetics involved also)
Is agenesis of third molars more common in the maxilla or mandible?
more common in the maxilla
Is agenesis of third molars more common in females or males?
more common in females
By which age - if you cannot see third molar development will it be almost always likely that they will completely fail to develop?
14 years old
What does M3M stand for?
Mandibular Third Molar
What does it mean if a third molar is impacted?
Failure of the third molar to erupt - either into full or partial functioning positioning or tooth fails to erupt at all
What is the most common reason for third molar failure to come through?
impacted third molar
Name 4 reasons why a third molar can be impacted?
- Impacted against adjacent tooth
- Impacted against alveolar bone
- Impacted by surrounding soft tissue
- Combination of all of these factors
Name 3 forms of eruption an impacted third molar can be found?
- Unerupted
- Partially erupted
- Fully erupted
Describe an unerupted impacted third molar
tooth completely enclosed around bone + soft tissue
Describe a partially erupted impacted third molar
Some of it has managed to erupt into the oral cavity, but not all of it
Describe a fully erupted impacted third molar
Whole occlusal surface right through the oral mucosa + exposed to oral cavity
Third molar partially erupted but no tooth evident on clinical examination. Radiograph shows caries in third molar - how?
This suggests that there is a communication between the oral cavity + third molar - allowing bacteria to pass through and cause caries
Name 3 problems related to impacted teeth
- Caries
- Pericoronitis
- Cyst formation
Name 4 nerves at risk during third molar surgery
- Inferior Alveolar Nerve
- Lingual Nerve
- Nerve to Mylohyoid
- Long Buccal Nerve
Which 2 nerves are much less commonly affected + effects are less obvious?
- Nerve to Mylohyoid
- Long Buccal Nerve
What type of nerve is the Inferior Alveolar Nerve?
peripheral sensory nerve
What nerve is the IAN formed from?
The mandibular division of the trigeminal nerve
What does the IAN supply?
All mandibular teeth on that side, mucosa of lower lip + chin
What is the Lingual nerve a branch of?
Branch of the mandibular division of the trigeminal nerve
What does the Lingual nerve supply?
Anterior 2/3rds of dorsal + ventral mucosa of tongue
Lingual gingivae
Floor of mouth
In Pogrel (1995) study, what was the mean vertical distance of the lingual nerve from the crest of the lingual plate + mean horizontal distance?
Distance from crest of lingual plate = 8.32mm
Mean horizontal distance = 3.45
In Kiesselbach (1984) study, what was the distance of the Lingual nerve vertically from the alveolar crest + from the lingual plate?
2.8mm (+/- 1.9mm) vertically from alveolar crest
0.58mm (+/- 0.9mm) from lingual plate
What structure does the lingual nerve have a close relationship to?
Lingual plate in the mandibular + retromolar area
What % of cases is the lingual nerve positioned at or above the level of the lingual plate?
15-18% of cases
What distance in mm does the lingual nerve run medial to the mandible?
the lingual nerve runs 0.3 - 5mm medial to the mandible
What 3 guidelines are related to third molars?
- NICE - Guidance on Extraction of Wisdom Teeth, 2000
- SIGN Publication Number 43 - Management of Unerupted + Impacted Third Molar Teeth, 2000
- FDS RCS - Patameters of Care for patients undergoing mandibular third molar surgery
Summarise the NICE and SIGN guidelines for extraction of wisdom teeth
Consensus from both documents - due to risk factors involved with third molar surgery, you must be able to justify surgical removal
What is the most recent guidance on third molars
FDS RCS 2020 - parameters for care for patients undergoing mandibular third molar surgery
Summarise the FDS RCS 2020 guidelines for third molars
acknowledges that by not removing impacted third molars - we are often postponing inevitable surgery, can result in procedure being more difficult
Recommend changing from solely therapeutic approach to mixed range of interventions for patients with M3M based on a more holistic + informed approach which should be agreed by patient
Name 11 indications for third molar extraction
- Infection
- Cysts
- Tumours
- External reposition of 7 or 8
- Surgical indications
- High risk of disease
- Medical indications
- Accessibility
- Patient age
- Autotransplantation
- General Anaesthetic
What is the most common reason for wisdom tooth extraction?
Infection
Name 4 forms of infection in third molars
- Caries
- Pericoronitis
- Periodontal disease
- Local bone infection
In what scenarios of ‘infection’ should third molar extraction always be considered
- Pericoronitis (acute or chronic)
- One or more episodes of infection (e.g. abscess)
- Untreatable pulpal or periapical disease
Which is the more common reason for extraction - caries or pericoronitis?
caries
What would make restoration of a third molar with caries difficult?
Limited access
Moisture control
Why is peridontal disease an indication for third molar removal?
Because of the relative position of the lower 2nd + 3rd molars
Untreated horizontal, mesial angular impaction is prone to causing bone loss distal to 7
What age are cysts related to third molars most common in patients
20-50yrs old
What is the most common cyst associated with impacted third molars
dentigerous cyst
How does a dentigerous cyst arise
arises from reduced enamel epithelium separation from the crown
are cysts more common in the mandible or maxilla
mandible
(x10 more likely)
When do symptoms of cysts usually occur?
often no symptoms associated until cyst becomes very large + infected
Describe the management of a cyst related to third molars
Prophylactic removal or coronectomy of a disease free impacted M3M would often prevent development of a cyst - however number prevented small… therefore not usually an indication for removing a symptom free M3M
What indications related to a tumour may third molars be extracted?
- if close to 8
- extracted as part of cancer (may be part of resection)
- if patient diagnosed with cancer elsewhere in body + undergoing radiotherapy (extraction after tx commenced may result in osteoradionecrosis)
What is external resorption
destruction of tissue
What happens if resorption is left untreated
usually progressive
How does resoprtion occur
Cause of inflammation usually unclear
Can be external resorption of third molar or second molar, caused by the third
Relatively rare
Resorption is relatively rare, however what ages does it usually occur between?
21 - 30 years old
(risk of developing after 30 is small)
Describe the management of resorption in third moalrs
should always consider removal of third molar in these cases
Provide some surgical indications for third molar removal
- If the third molar is within the surgical field
(if the M3M is in the line of the mandibular split - can lead to poorer outcome) - If M3M is unerupted - extraction allows primary closure post-op
- If there is a fracture at the angle of the mandible - removal may be req. to allow adequate open reduction + internal fixation
What medical indications may require removal of third molars
- patient awaiting cardiac surgery + need to be ‘dentally fit’ to avoid post-op complications
- Immunosuppression
- Starting course of bisphosphonates to avoid MRONJ
How does accessibility affect indication for third molar removal?
If the patient has limited access to the dentist (e.g. astronaut, gap year, travelling) - may not be able to attend dentist for some time therefore removal of third molars may be indicated
How might patient age be an indication for third molar extraction?
complications + recovery increase with age therefore may indicate removal before the patient gets older
Describe the autotransplantation of third molars
If a third molar is sound it can occasionally, but rarely, but used for autogenous transplantation.
Usually third molar –> first molar socket site.
Low incidence of success, therefore only used in specific circumstances
How may general anaesthetic indicate removal of a third molar
If patient is undergoing third molar removal under GA, may indicate also removing opposing/contralateral third molars as you dont want to have to carry out this similar procedure down the line
What is pericoronitis
inflammation around the crown of a partially erupted tooth
what is the operculum?
flap of gum sitting over the tooth - often the source of the problem in pericoronitis
how does the operculum often cause pericoronitis
difficult to clean, food/plaque/bacteria can get trapped underneath
How can pericoronitis be described
transient + self limiting
What age group are usually affected by pericoronitis
20 - 40 yrs
Which health condition can impact the incidence of pericoronitis?
Upper Respiratory Tract Infection (URTI)
(seems to be an increase in cases of pericoronitis)
starts off as URTI then develops into pericoronitis
(reason unclear)
What is the second most common indication for M3M extraction?
pericoronitis
what are the majority of microbes involved in pericoronitis?
anaerobes
(e.g. streptococci, actinomyces, staphylococci etc.)
Signs + Symptoms of pericoronitis
- pain + swelling (most common)
- bad taste
- pus discharge
- occlusal trauma to operculum
- ulceration of operculum
- cheek biting
- foetor oris
- limited mouth opening
- dysphagia
- pyrexia
- malaise
- regional lymphadenopathy
How can the pain associated with pericoronitis be described?
very variable
often ‘throbbing’
often increases in intensity as it develops
In severe cases of pericoronitis which result in extra-oral swelling, where can the swelling occur?
commonly starts at the angle of the mandible + extend…
- usually to submandibular area
- laterally into cheek
- disto-bucally under masseter (sub-masseteric abscess)
- sublingually
- around tonsils + pharyngeal space
If swelling due to pericoronitis extends under the masseter - what is this known as and what are the associated characteristics?
= sub-masseteric abscess
characteristic signs: profound trismus (unable to open mouth)
If swelling due to pericoronitis extends to tonsils / pharyngeal space - what difficulty can the patient experience?
can lead to dysphagia
(difficulty swallowing)
Patient may present with drooling if unable to swallow comfortably
how might a patient present if they are systemically unwell due to pericoronitis
pyrexia (fever)
malaise (generally run down)
lymphodenopathy (swollen lymph nodes)
What are tx options if a patient is acutely symptomatic due to pericoronitis?
- incision of local area of infection
- irrigation with warm saline (or perhaps chlorhexidine mouthwash)
- removal of upper third molar
How would you irrigate to treat pericoronitis?
- LA may/may not be indicated (patient preference)
- use syringe + blunt needle
- fill syringe with warm saline
Why may chlorhexidine be contraindicated for irrigation in pericoronitis
Previous reports of anaphylaxis (rare - but some health boards are wary of use)
Therefore check with health board / use saline
How does removal of upper third molar relieve pericoronitis of M3M?
eases trauma to lower operculum
may also give space for M3M to erupt
Post op instructions after tx of pericoronitis
- tell Pt to frequently rinse with warm saline or chlorhexidine (to prevent reoccurrence of pericoronitis)
- give advise regarding analgesia (do not exceed dose / check MH)
- advise patient to drink plenty fluids + eat at regular intervals (soft diet may help)
Can lower 8 be removed during pericoronitis episode?
Generally, we don’t remove lower 8 until acute episode of pericoronitis has resolved
What is an operculectomy?
removal of the operculum causing pericoronitis
Why are operculecomties not carried out nowadays?
because the operculum just grows back to where it was within weeks/months therefore not much to be gained from an operculectomy. (although may be indicated in specific cases)
when would you consider referral to A&E or maxfax during pericoronitis?
- large extra-oral swelling
- Pt systemically unwell (significant cases of dysphgia, breathing difficulty, trismus)
Pre-disposing factors for pericoronitis
- Partially erupted tooth
- Vertical or distoangular impaction
- Opposing 2nd/3rd maxillary molar causing trauma
- Upper Respiratory Tract Infection
- Stress
- Fatigue
- Poor OH
- Insufficient space between ascending ramus of lower jaw + distal aspect of lower 7 - more likely to have impacted tooth - more likely to suffer from pericoronitis
- White race
- Full dentition
