SPACE
CALCULATOR
Am I extracting?
The most crucial question in every treatment plan. We all know the those good old formulas that help you make the call:
For every 1 mm of incisor retraction/protrusion, we require/create 2 mm of space.
For every 1 mm of maxillary expansion, we create 0.7 mm of space.
Since there are so many factors to consider all at once, I have created the Maxillary and Mandibular Space Calculators to help you keep track of all your thoughts and feel confident that you’ll be able to correct any tooth size arch length discrepancies (TSALDs).
The calculator is divided into five sections:
Section I — Space Analysis
In the first section, you simply write down what you see:
Crowding
Spacing
Leeway space
This should be calculated in relation to the line of the arch that reflects your planned incisor position and arch shape. This assessment of crowding / spacing gives us our baseline TSALD.
Section II — Planned Incisor Position (PIP)
In the second section, plan where you want the incisors to finish in terms of A-P position of the incisal edge. I view this step as the KEY step for two important reasons:
Incisor position drives aesthetic outcomes, which are of the utmost importance to our patients
We must respect bony limits and ensure incisor roots remain safely contained within the alveolar housing to avoid periodontal complications
Consider using the N-A line to guide your planned incisor position (Creekmore, 1997):
L1s — on the N-A line
U1s — just ahead of the N-A line
The Class II div 1 patient in this example requires mild procilnation of the lower incisors, and a fair bit of retraction of the upper incisors to satisfy the above criteria.
Section III — Space CreatION
In the third section, you get to have some fun and play around with all the different ways you can create space to account for any TSALDs:
Expansion / Uprighting
Derotation
Distalization
Interproximal Reduction (IPR)
Extraction
Keep playing until your “Total crowding / spacing” hits zero (or moves into the positives) indicating you have enough (or excess) space to carry out your incisor-driven treatment plan.
A few notes:
The value you punch in for expansion can be determined using the Expansion Calculator
Sometimes, Space Creators 1 through 4 are not enough to resolve the TSALD and you must resort to the 5th option — extractions
If this is the case, jump over to the Extraction Calculator page to determine which extraction pattern will be most beneficial based on the current A-P relationship of the buccal segments
If you still cannot create enough space (e.g. extractions are contraindicated), you may have to adjust your PIP (e.g. less retraction) to minimize your space requirements
This SECTION Ends by displaying a
total score
from sections 1-3
If your score = 0
You created exactly enough space to carry out your treatment plan
You have no residual space (i.e. 0mm)
You do NOT need to burn anchorage, and can skip to Section V
If your score is > 0
You created excess space
You have residual space left over
You MUST head to Section IV to burn anchorage (i.e. slip the molars forwards)
Section IV — burning anchorage
In the fourth section, you must:
Burn anchorage by mesializing the molars
Eliminate all residual space (down to 0mm)
You placed the incisors where you want them in Section II, so all remaining space must be closed from the back.
Continue to mesialize the molars (evenly for a symmetric case) until the score for Residual Space hits 0. At this point in your treatment planning, all TSALDs have been resolved and no space remains.
Section V — anchorage REQUIREMENTS
In the final section, you simply review the results to learn what your anchorage requirements are in each quadrant. This was calculated based on the ratio of:
Incisor retraction
Molar mesialization
The sensitivity for anchorage within the calculator is set as follows:
evidence-based
The formulas utilized by the calculators are based on my review of the literature and wisdom passed down by my instructors at the University of Toronto.
If you are curious about where the values come from, click the button below to see the main references I based these calculators on.
Now that you understand the theory behind the space calculators
Click on the Calculators below and start crunching the numbers!
MANDIBULAR SPACE CALCULATOR
MAXILLARY SPACE CALCULATOR