Premolar extraction protocols Part 2 What you may not know…

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Premolar extraction protocols Part 2 What you may not know…

"M pattern vs frog pattern"

Which one is better?

Case report by Sun et al. 2023 compares identical twins utilising different extraction staging patterns...

The Case Study:

• Identical twins

• Reason for extraction:

• Convex profile

• Protrusive lips

• Strong muscle strain

• Excessive OB and OJ

• Both U4 and L4 exo

Patient 1:

• Frog pattern adopted (the more severe OB and OJ twin)

• 2.8mm maxillary anterior intrusion and 3.2mm of mandibular incisor intrusion overcorrection planned (AOB of 1mm)

• Class II elastics 3.5oz for retraction (when incisors started to retract)

• LRT 2 degrees on mandibular incisor

Patient 2:

• M-Pattern adopted

• 3mm maxillary anterior intrusion and 2.8mm of mandibular incisor intrusion overcorrection planned (AOB of 1mm)

• 3.5oz elastics (only when incisors started to retract)

• LRT 5 degrees max. incisors and 3.5 degrees on mandibular incisors

Result:

• Patient 2 had more of a bowing effect (mesial tilt of the lower 6’s especially) however maintained a class I pattern

• Patient 1 ended up losing posterior anchorage which turned into a class II hence treatment time was longer

Note: Patient 1 had more exaggerated OJ/OB, frog staging takes longer which could explain the anchorage loss.

The wear protocol was 10 days/aligner.

Would have been useful to check the Tooth Movement table to see how much

retraction was needed

Result:

• M pattern was more effective for anchorage preservation in the sagittal plane

• Frog pattern is a useful protocol to reduce the bowing effect

Suggestions for overcorrection by Author:

• The mean accuracy of maxillary incisor torque was 42% (Simon et al. 2014)

• In other words, if you want to improve the incisor torque from 110 → 112 then you would overcorrect by probably 5 degrees of LRT

• If torque was already high then you may not add any additional LRT

• Intrusion should be to AOB at the end of treatment

• Attachments: larger size (rectangular > optimised)