The defects, risks and countermeasures of clear aligner Zhihe Zhao. Episode 52.IOC 2020

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Hosted by
Farooq Ahmed


Defect in material

  • Not 3D printed
  • Membrane material same for all patients – different malocclusions, aligners provide same force


Defect in efficiency Kravitz 2009, Simon

  • Anterior intrusion and extrusion
  • Canine and premolar rotation
  • incisor torque
  • Anchorage


Efficiency of aligners

  • Distalisation
  • Alignment
  • Anterior expanded


Defect in mechanics

  • Force placed at a distance from the CoR = tipping in space closure = roller coster effect


Gate Spring – single tooth torque auxillary crimped onto the wire


Overbite correction Zhao 2019

  • Aligner efficiency in OB correction = 50%
    • Aim for openbite
    • Additional 100% anterior intrusion
  • Anchorage for overbite – premolar extrusion efficiency poor
    • As lower anterior intrude the lower premolars extrude
    • To ensure the lower premolars extrude – horizontal attachments are placed on the premolars


  • Bite ramps
    • On upper 3-3
    • Maintains occlusal contact of upper incisors – preventing over eruption


  • Staging of intrusion for deepbite – anchorage efficiency is poor
    • Intrude lower 2-2 first
    • 2nd stage lower canine intrusion


  • Anterior tooth torque efficiency poor 15% Zhao 2019
    • For 1mm of retraction 2.50 of anterior torque loss
    • Overcorrect anterior torque loss


  • Power ridge
    • Produce counter moment effectively – to aid bodily movement.
    • Power ridge force closer to the CoR
    • Can lose tracking with power ridge


  • Attachment placement tips
    • Extrusion of teeth = attachment on tooth to be moved
    • Intrusion of teeth = attachments on anchorage teeth (not teeth to be intruded)
    • Attachment to match movement type
      • Horizontal rectangular for vertical movement / molar uprighting
    • Not cause occlusal interference
      • If they will – place lingually
    • Prevent undesired mesial tip
      • Use class 2 elastics
      • First molar cut out placed on the mesial side


Clinical case of space closure


  • Distalisation of posterior teeth
    • Reactionary proclination of upper incisors
      • Resolved by use of class 2 elastics
    • Retraction of anterior teeth
      • Reactionary torque loss of the upper incisors
        • Resolved by over correcting upper anterior torque with power ridges
      • Reactionary extrusion of upper and lower molars
        • Due to upper molar distalisation
        • Due to lower molar class 2 elastics
          • Resolved by intrusion upper and lower molars
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