What are the limits of orthodontic movement?

orthodontics In summary

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