Join me for a podcast exploring the limits oforthodontic tooth movement. This podcast is a summary of two intriguinglectures, by Dr Yanqi Yang and Carlos Flores Mir from this year’s InternationalOrthodontic Symposium by the IOF. This podcast explore the anatomical andperiodontal boundaries of orthodontic tooth movement

Anatomical boundary

· Distalisation: Alveolar boundary lowermolar distalization

· Horizontal: Atrophic ridge.

· Vertical: Maxillary sinus

boundary for lower molar distalization.

o Coronal level: Anterior border ofmandibular ramus

o Apex level: lingual plate

o Variable – distance from secondmolar distal root and inner lingual cortex

§ Favourable Class 3 greater retromolarspace, class 2 least Fan 2022

§ Unfavourable High angle haveshorter distance Kim 2021, Victoria 2022

Side effects of lower molar distalisation

o Mainly tipping

o Distalisation achieved at apicallevel approximately 1mm AJODO 2016

o Lingual plate contact 1/3 of cases Kimet al 2014

Horizontal movement: atrophic ridge

· Change in width and height ofextraction site

o Loss of 40-60% width and heightPagni 2012

§ Width 3.79mm Tao 2012

§ Height 1.24mm Tao 2012

o Mostly within 6 months Schrepp 2003

· Changes when orthodontic toothmovement into atrophic edentulous site

o Increase bone height 2.2-5.2mm,duration 24 months Elif 2004

o Increase in width 0.8-1.6mmStokland 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 ofalveolar bone Patricia dos Santos 2017

o Reduced bone height compared tonon-edentious area

Vertical:

· Maxillary sinus prevent toothmovement?

o Increased tipping, slower rate of toothmovement

· Side effects

o Mild increase in RR

o No difference in relapse, vitalityor periodontal differences

o 6 buccal roots closest . (Qin et al2020)

· Understanding

o Maxillary sinus remodels itselfwith tooth movement

o Increase in resistance to toothmovement, greater tipping.

Periodontal boundaries

Carlos Flores Mir started the topic with a thought provingquestion, that we are well aware of Proffit’s envelope of lower incisor dentalmovements; but the question of whatis 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 inbucco-lingual direction

· Phenotype – contour gingiva,underlying bony architecture, and width of keratinised tissue

Thin gingival biotypes are likely to have more chancesof recession.

Factors to consider

· Extraction Vs non-extraction: inboth scenario the bone height decreases, but in different locations, anteriorextraction treatment = 2mm reduction, non-extraction = 1.2mm. www.orthoinsummary.com/blog

· Dehiscence exist pre treatment

· Thicker the gingiva, the better Yared2006

· Initial position of the toothdecides its periodontal future

· Thickness varies in various areasof the mouth.

· Oral hygiene major factor ofrecession Melsen 2005.

CBCT

· Aren’t really telling us the wholestory –

· Size of the image of a CBCT islimited by the radiation dose, and typically is 0.3-0.6mm3 of voxel size

· Tissue less than 0.6mm appears as aabsent in CBCT giving false positive results ( Redua 2020)

Lower incisor proclination and recession:

· Systematic review Kalina no correlationbetween proclination and gingival recession. (Kalina 2022)

Understanding

Recession = Thin gingiva + proclination +periodontitis

Contents– Shanya Kapoor

Editing and Production – Farooq Ahmed