Normal dental development, Tooth eruption and Interceptive ortho Flashcards
At birth what are the characteristics of the mouth?
- Gum pads
- Upper rounded
- Lower is U shaped
- Appear Class II
- AOB
What is the eruption pattern of deciduous teeth?
- Erupts from 6months to 2.5years
- a-b-d-c-e
- Lowers before uppers
What are the characteristics of deciduous dentition?
- Incisors more upright
- Spaced
- Wear
What is a natal/ neo-natal tooth?
- Abnormal dental development
- Lower incisors (most common natal tooth) present at, or just after birth
When should a natal/neo-natal tooth be extracted?
- If it is mobile and presents risk of inhalation
- Is causing difficulty breastfeeding
What are the processes of tooth eruption? x3
- Pre-eruptive phase
- Eruptive phase
- Post-eruptive phase
What is the pre-eruptive phase?
- Starts when crown starts to form
- Ends when crown formation complete/ root formation about to start
What is the eruptive phase?
- Starts when root starts to form
- Ends when teeth reach occlusal plane
- Split into Intra-osseous stage and Extra-osseous stage
What is the post-eruptive phase?
- Tooth movement/ eruption continues as root forms and throughout life in extremely small increments
- Movement after tooth has reached occlusal plane
What are the characteristics of Pre-eruptive phase? (Movement of crown)
- Developing crowns move constantly in jaw
- Small mesial and distal movement occur
- Developing crowns reposition themselves in response to increasing length, width and height of jaws
Where does the movement of tooth crowns occur in pre-eruptive phase?
- Contained within bony crypts
What does movement of tooth occur in response to during eruptive phase?
- Positional changes of neighbouring crowns
- Growth of mandible and maxilla
- Resorption of deciduous tooth roots
what would alter the relative position of deciduous and permanent teeth
- eruption of the deciduous teeth
- increase in height of the surrounding alveolar bone
What occurs during Intra-osseous eruptive phase?
- Root formation - starts with proliferation of HERS (Hertwig’s epithelial root sheath) and continues with production of dentine and pulp
- Movement of developing tooth - in occlusal or incisal direction (slow)
- REE Reduced enamel epithelium fuses with oral epithelium
What occurs during extra-osseous eruptive phase?
- Penetration of tooth’s crown tip through epithelial layers (fast 1-2weeks)
- Crown continues to move through mucosa in occlusal direction until contacts opposing tooth (slow several months)
- Environmental factors like muscles forces from cheeks, lips and tongue help determine final tooth position
What is the eruption pathway?
- Within dental follicle degeneration occurs
- Blood vessels decrease
- Nerve fibres break up into pieces
- This area is eruption pathway
What is the Gubernacular cord?
- Fibres from dental follicles formed in periphery of eruption pathway
- Theory is it guides teeth to erupt in oral cavity
What happens to the bone during Intra-osseous eruptive phase?
- Adjacent to and overlying, teeth bone loss keeps pace with occlusal movement of teeth
- Osteoclasts and osteoblasts constantly remodelling bone
Why does post-eruptive movement occur?
- In response to increases in height of growing alveolar bone and jaw
- In response to attrition and abrasion (due to occlusal wear compensation )
- In response to loss of opposing teeth (can cause over-eruption)
What does proximal surface tooth wear lead to?
- Mesial drift
Theories of tooth eruption
Multifactorial and likely combo of;
- Root formation
- Remodelling of alveolar bone
- Development of periodontal ligament (membrane)
- Genetics
What are the roles of dental follicle?
- Initiates resorption of bone overlying teeth
- Facilitates connective tissue degradation and creates eruption pathway
- Promote alveolar bone growth at base of tooth
- Provides traction forces within PDL
- Ectomesenchymal cells from dental follicle contribute to root formation
cytokines that control the tooth eruption (signalling cascade of cytokines)
- Interleukin1
- CSF1
- RANKL/ Osteoprotegerin (OPG) pathway
What is Interceptive orthodontics?
- Any procedure that will reduce or eliminate severity of developing malocclusion
When can ectopic upper permanent canines be treated with interceptive ortho?
- Extraction of deciduous canine ages 10-13
When would we intercept early mixed dentition? (Case)
- Impacted 6’s
- Potential crowding
- Early loss of deciduous teeth
- Carious 6’s
- Cross-bites
- Transposed teeth
- Habits
When is the best time to extract deciduous to encourage permanent teeth to erupt?
- 1/2 to 2/3rds root development of permanent tooth
What are the eruption dates?
6’s = 6years
1’s = 7years
2’s = 8years
4’s = 10years
3’s and 5’s = 11-12years
7’s = 12-13years
How is space created for larger anterior teeth from decidious?
- Increased in intercanine width though lateral growth of jaws
- Upper incisors erupting onto wider arc (more proclined)
- Leeway space
In relation to primary teeth how do the permanent incisors erupt?
- Develop palatal/lingual to primary teeth
How is leeway space calculated for upper arch?
(c+d+e) - (3+4+5) = 1to1.5mm
How is leeway space calculated for lower arch?
(c+d +e) - (3+4+5) = 2to2.5mm
What is a diastema?
- Space separating two upper centrals
What is the prevalence of diastema?
6Yrs 96% have diastema
12years 7% have diastema as 3’s erupted
- If <2.5mm should close
What is this called
Ugly duckling phase
Unerupted canine pressing against lateral (so flare out)
When canine erupt, it’ll sort out itself
How can ectopic eruption affect first permanent molar?
- Permanent first molar gets stuck behind e
- Fails to fully erupt
What are the management options for ectopic eruption of 6 beneath e?
- If <7 years wait 6months (90% self correct)
- Orthodontic separator
- Attempt to distalise first molar
- Extract E
- Distal disking of e
Possible causes of unerupted CI
- supernumerary
- trauma to primary (dilaceration of permanent )
- congenital absence (rare)
What to do if unerupted central incisors? (Assessment)
- Case history e.g. regarding trauma
- E/O and I/O
- Palpate labially and palatally
- If primary retained, is it mobile/discoloured
- Radiograph PA / AOM
What are the management options for supernumerary unerupted central incisor?
- Remove primary teeth and supernumerary
- Create/ maintain space
- Monitor 12months (<9= immature root apex)
- still fail to erupt/ pt > 9yo (mature root apex)
- Expose/bond gold chain and apply orthodontic traction
What is balancing extraction?
- Removal of tooth from opposite side of same arch
- To maintain position of dental centreline (preserve symmetry)
- mainly C
What is compensating extraction?
- Removal of tooth from opposing quadrant
- To maintain buccal occlusion
- don’t really do on primary
What does early loss of deciduous teeth cause?
- Localised crowding
What is the management of early loss of A’s and B’s?
- Has little impact
- Don’t balance or compensate
What is the management of early loss of C’s?
- Balance
- Compensating extraction not required
What is the management of early loss of D’s?
- Small CL Shift, balance under GA?
What is the management of early loss of E’s?
- tend not to balance
- Major space loss
- Upper > lower
- Consider space maintainer (prevent 6 mesial tipping)
What are the two types of space maintainers?
Removable (passive URA)
- retention: Adams/ labial bow/ southend 0.7mm HSSW
- baseplate: extend acrylic around teeth to prevent unwanted mesial drift
- +/- mesial stop 0.6mm HSSW
Fixed
- palatal and lingual arches
- band and loop
What do you need to consider when extracting first molars of poor prognosis?
- Age/stage of dental development
- Degree of crowding
- Malocclusion type
- Condition of other teeth
- LA or GA
What conditions give most ideal result when extracting first molars?
- 7’s bifurcation calcifying
- 8’s present
- angulation of 7
- Class I av/reduced OB
- Moderate lower crowding
- Mild/mod upper crowding
What are the general rules to follow when extracting 6’s in Class I patient?
- If extract lower take upper
- Don’t balance with sound tooth
- Don’t balance if well aligned or spaced
- If extract upper don’t need to take lower
when should you consider temporising upper FPM of poor prognosis
- crowding
- space needed for class II incisors correction
- consider temp until 7 erupt
- then use trans-palatal arch to prevent mesial drift of 7
- (no spontaneous closure needed)
When should you treat a (ant/ post) cross bite?
- IOTN 4c
- > 2mm discrepancy of RCP and ICP
What is a URA to help fix posterior unilateral cross bite?
- Active component is Hyrax screw or coffin spring
- Retention is no retentive component across midline
- Baseplate is Posterior bite plane to disclude teeth
What is the digit habit management?
- Positive reinforcement
- Bitter-tasting nail varnish
- Glove on hand, elastoplast
- Habit breaker appliance (habit deterrent) fixed or removable
What’s the idea position of unerupted 5 if XLA carious 6?
- If it lies below and distal to roots of E, likely to erupt to 6’s socket
- In this case,XLA both 6 and E
- Encourage normal path of 5 eruption
What’s the rate of relapse of post crossbite
50%
