Join me for a podcast exploring the limits of
orthodontic tooth movement. This podcast is a summary of two intriguing
lectures, by Dr Yanqi Yang and Carlos Flores Mir from this year’s International
Orthodontic Symposium by the IOF. This podcast explore the anatomical and
periodontal boundaries of orthodontic tooth movement
Anatomical boundary
·
Distalisation: Alveolar boundary lower
molar distalization
·
Horizontal: Atrophic ridge.
·
Vertical: Maxillary sinus
boundary for lower molar distalization.
o
Coronal level: Anterior border of
mandibular ramus
o
Apex level: lingual plate
o
Variable – distance from second
molar distal root and inner lingual cortex
§
Favourable Class 3 greater retromolar
space, class 2 least Fan 2022
§
Unfavourable High angle have
shorter distance Kim 2021, Victoria 2022
Side effects of lower molar distalisation
o
Mainly tipping
o
Distalisation achieved at apical
level approximately 1mm AJODO 2016
o
Lingual plate contact 1/3 of cases Kim
et al 2014
Horizontal movement: atrophic ridge
·
Change in width and height of
extraction site
o
Loss of 40-60% width and height
Pagni 2012
§
Width 3.79mm Tao 2012
§
Height 1.24mm Tao 2012
o
Mostly within 6 months Schrepp 2003
·
Changes when orthodontic tooth
movement into atrophic edentulous site
o
Increase bone height 2.2-5.2mm,
duration 24 months Elif 2004
o
Increase in width 0.8-1.6mm
Stokland 2011
o
Greater height increase buccally,
less lingually Dos Santos 2017
·
Side effects
o
Root resorption – lateral
§
0.7mm
o
Dehiscence
§
Slight in all cases, thinning of
alveolar bone Patricia dos Santos 2017
o
Reduced bone height compared to
non-edentious area
Vertical:
·
Maxillary sinus prevent tooth
movement?
o
Increased tipping, slower rate of tooth
movement
·
Side effects
o
Mild increase in RR
o
No difference in relapse, vitality
or periodontal differences
o
6 buccal roots closest . (Qin et al
2020)
·
Understanding
o
Maxillary sinus remodels itself
with tooth movement
o
Increase in resistance to tooth
movement, greater tipping.
Periodontal boundaries
Carlos Flores Mir started the topic with a thought proving
question, that we are well aware of Proffit’s envelope of lower incisor dental
movements; but the question of what
is the periodontal limit, is still yet to be clearly defined.
The difference between the gingival biotype and phylotype,
there has been a focus on biotype but it
·
Biotype – thickness of gingiva in
bucco-lingual direction
·
Phenotype – contour gingiva,
underlying bony architecture, and width of keratinised tissue
Thin gingival biotypes are likely to have more chances
of recession.
Factors to consider
·
Extraction Vs non-extraction: in
both scenario the bone height decreases, but in different locations, anterior
extraction treatment = 2mm reduction, non-extraction = 1.2mm. www.orthoinsummary.com/blog
·
Dehiscence exist pre treatment
·
Thicker the gingiva, the better Yared
2006
·
Initial position of the tooth
decides its periodontal future
·
Thickness varies in various areas
of the mouth.
·
Oral hygiene major factor of
recession Melsen 2005.
CBCT
·
Aren’t really telling us the whole
story –
·
Size of the image of a CBCT is
limited by the radiation dose, and typically is 0.3-0.6mm3 of voxel size
·
Tissue less than 0.6mm appears as a
absent in CBCT giving false positive results ( Redua 2020)
Lower incisor proclination and recession:
·
Systematic review Kalina no correlation
between proclination and gingival recession. (Kalina 2022)
Understanding
Recession = Thin gingiva + proclination +
periodontitis
Contents– Shanya Kapoor
Editing and Production – Farooq Ahmed
