Extraction CALCULATOR
The extraction CALCULATOR is based on two important concepts
1) Katz classification of malocclusion
Katz MI. Angle classification revisited 1: is current use reliable? American Journal of Orthodontics and Dentofacial Orthopedics 1992;102(2):173-79.
Katz MI. Angle classification revisited 2: a modified Angle classification. American Journal of Orthodontics and Dentofacial Orthopedics 1992;102(3):277-84.
2) Creekmore’s Rules of Thumb for space closure
Creekmore TD. Where teeth should be positioned in the face and jaws and how to get them there. Journal of Clinical Orthodontics: 1997;31(9):586-608.
Let’s review each of these concepts and then explore how they can be used in tandem to calculate the optimal extraction pattern for your case.
Katz classification of malocclusion
The extraction calculator uses the Katz method of classifying malocclusion, which assigns a millimetric value to the anterior-posterior discrepancy of the arches.
It compares the 4th tooth back in each arch—ideally, the cusp of the 4th tooth back in the Mx will contact the distal aspect of the 4th tooth back in the Md.
This is Katz = 0
Any deviation from this point is measured:
Deviations in the Class II direction are given a positive value
Deviations in the Class III direction are given as negative value
Creekmore’s Rules of Thumb for space closure
The extraction calculator also relies upon the anticipated pattern of space closure based on Dr. Creekmore’s observations, as well as the research of many others. Please see “Extractions” section on the References page for more info—although challenging, I have tried to make this calculator as evidence based as possible.
Without any specific mechanics for anchorage control (e.g. powerchain 6-6), extraction spaces can be expected to close as shown in the image to the right. The difference in Mx vs Md is largely due to differences in bone density.
Different combinations of upper and lower extractions will result in various “differentials” which can improve the Katz malocclusion, or in other words, bring it closer to zero (Class I).
Planning your extractions based upon these principles simplifies anchorage considerations. Clinically, what this translates to is a decreased dependence on patient compliance with rubber band wear to sock in the occlusion.
Watch the video below for examples of space closure with a Class II and a Class III extraction pattern
If the buccal segments are well aligned (Katz = 0) and all other factors have been considered (arch shape, arch coordination, Bolton discrepancies, torque, etc.), you should end with ideal anterior coupling.
Remember, the extraction calculator can be seen as the third step in the calculator sequence:
If the Space Calculator indicates no TSALD, but there is an A-P discrepancy (Katz ≠ 0) between the arches, you may choose to extract to improve the Katz malocclusion. If this is the case, you should then go back to the space calculator and rework the numbers knowing that you will gain space from extractions.
If the Space Calculator indicates a TSALD which requires extractions, but there is no A-P discrepancy (Katz = 0), you may choose to extract U4s/L5s, which has a net differential of 0, to keep the Katz at 0.
If there is a TSALD and an A-P discrepancy (Katz ≠ 0), extractions can help resolve both issues.
