Refinement...Friend or Foe? Part 2 of 2

In the second part of this series, I will review examples of movements that may require refinement and why. I will also provide tips on how to avoid a refinement.  In all cases, I cannot overstate the importance of monitoring progress of treatment.  

In part 1 of this series, I reviewed the definition of a refinement, the nature of movements with aligner therapy, and factors that could affect the predictability of aligner treatment therefore leading to refinements. In the second part of this series, I will review examples of movements that may require refinement and why. I will also provide tips on how to reduce the need for refinement. In all cases, I cannot overstate the importance of monitoring progress of treatment. Close monitoring will allow you to minimize "tracking" issues and finish cases more predictably.  

Movements that May Require Refinement 

Examples of orthodontic malocclusions that may require a refinement are: Class II div 2, deep bite, big residual spaces, divergent crowns, excessive premolar and canine rotations.  Furthermore, existing restorations, such as veneers and crowns, also increase the likelihood of a case needing a refinement. This is because the aligner has to transmit forces through the restoration so the movement intended on the crown/root is less predictable. You must also inform your patient that during treatment, the restorations can become dislodged or worse, be damaged.  

Class II Div 2 

Palatally inclined incisors (retroclined upper and lower incisors) are challenging because to achieve uprighting, the apex has to move through the bone which is one of the most difficult movements in orthodontics. When correcting this with aligners, it’s considerably more difficult due to the material separation experienced from the area closest to the center of rotation. 

 Reduce the likelihood of refinement for Class II Div 2 by:  

• Ensuring long periods of wear time will increase predictability 
• Good patient compliance is necessary  
• Use of chewies  
• Good staging protocol that drives the forces in the correct direction and the correct sequence—guaranteed by Six Month Smiles 

Deep Bite

Deep bites are also difficult malocclusion because the need of apical movement through the bone to intrude the teeth in need, added to the potential vertical plane correction on the posterior segment (extrusion). This malocclusion will rely on two potentially challenging movements:

1. Intrusion of the anterior segments
2. Extrusion of posterior segment
   - Possible class II div 2 correction
   - Skeletal discrepancies will play a limiting factor

Intrusion movements can be difficult for aligners if the patient isn't compliant, as the forces won't be constant enough to achieve the apical/root movement or if the anchorage to help aligners produce this force isn't prescribed correctly. Six Month Smiles reduces the likelihood of refinement for Deep Bites by ensuring:

• Good anchorage systems to ensure the predictable intrusion
• Good extrusion systems to ensure predictable posterior extrusion
• Possible bite ramp requirements
• Limiting and identifying the predictable movements involved in achieving deep bite reduction/correction on each patient

Reduce the likelihood of refinement for Deep Bites by: 

• Use of chewies
• Good patient compliance
• Over intrusion/extrusion at digital planning stage
• Review patients every 4-6 weeks and identify aligners not fitting perfectly
• Allow the patient to wear aligners slightly longer if the aligners aren't fitting well

Big Residual Spaces

Requires bodily movements and moving the apex through the bone at the same rate in the same direction at the same time as the clinical crown… this is challenging with aligners since the control and forces are only dependent on the clinical crown shape and size.

• Avoiding mesial or distal crown tipping is challenging
• 20 aligners can fall short to fully close some spaces (more than 3 mm)

Six Month Smiles will reduce the likelihood of refinement for Big Residual Spaces by:

• Good root control attachment placement
• Good planning sequence protocol
• Potentially sequential movements planned
• Auxiliary techniques (class II/III buttons and elastics)
• Good monitoring to avoid mesial or distal crown tip (to be done by provider)

Divergent Crowns/Roots

The main challenge occurs when the roots need to be uprighted rather than the crowns tilted. Moving apex through the bone requires a long time and can be unpredictable. Any teeth with ceramic restorations will make this almost impossible to achieve.

Reduce the likelihood of refinement for Divergent Crowns/Roots by:

• Ensure the correct movement is planned
• If crown tilting is needed, do not plan root uprighting
• Good root control attachments needed in place
• No ceramic restorations. If so, remove them and bond directly to tooth
• Close monitoring to avoid aligner separation

Premolar & Canine Rotation

De-rotation of a “round” tooth like canines and premolars can be challenging due to the unfavorable labial/buccal surface shape. In some cases where the crowns are smaller than average this challenge will increase.

Reduce the likelihood of refinement for premolar & canine rotations by:

• Good attachment placement
• Do not attempt too much de-rotation and root torquing at the same time
• Chewies and close monitoring

Avoiding Refinements 

Avoiding refinements is directly related to the control of these variables:

• During treatment, follow routine monitoring steps to help reduce the lack of movement tracking. 
• Check interproximal contact points at each appointment and break tight contacts between teeth that are supposed to move. Some contact may require slight relief to allow tooth movement even if IPR was not prescribed. 
• Use chewies to seat trays. Aligners not fully seating is a sign that there is a tooth or teeth not moving as planned. 
• Do not continue changing aligners if they aren't fitting perfectly and seek troubleshooting advice on the Six Month Smiles Provider Resource Center.

Refinement Considerations & Summary

• Refinements are aimed to correct movements that did not track towards the end of treatment.
• Movements or fitting issues at the beginning or mid-treatment need to be addressed by seeking clinical support.
• Stubborn teeth may require extra help (auxiliary techniques).