Welcome, ortho warriors! 🎭 Today, we’re diving into the world of space analysis—a topic as old as orthodontics itself but still as relevant as ever. If you’ve ever struggled to fit all 32 teeth into a jaw that seems to have space for only 28, you’ll understand why this is such a big deal!

Space analysis is nothing new. For years, orthodontists have tried to predict and manage space within the arch. Some key contributions include:

1️⃣ Predicting the size of unerupted canines and premolars (a.k.a. fortune-telling for teeth 🔮)
2️⃣ Assessing space required to flatten an occlusal curve (because we love smooth arches, not rollercoasters 🎢)

And then came some of the big names in space analysis:

Merrifield’s Total Dentition Space Analysis 🎯

Divides the dental arch into anterior, midarch, and posterior areas

Uses Tweed’s diagnostic triangle to assess space deficits or surpluses

Even suggests extraction patterns based on findings! (Because sometimes, it’s off with their heads! 🦷⚔️)


Merrifield et al’s Cranial Facial Dental Analysis 🏗️

Built upon the Total Dentition Space Analysis

Incorporated Cranial Facial Analysis

Assigned a difficulty score for Class II cases (because ortho isn’t already stressful enough 🤯)


Royal London Space Planning (1985) 🇬🇧👑

Developed at Royal London Hospital

Based on Andrews’ Six Keys to Normal Occlusion 🔑🔑🔑🔑🔑🔑

Helps quantify space needs for treatment in permanent/mixed dentition

Unlike Merrifield’s method, it doesn’t tell you where the teeth should be or how to move them—it’s more flexible, like an ortho version of “choose your own adventure”! 📖😆

Why Space Planning is a Game-Changer? 🎯

A well-thought-out space plan isn’t just for neat-freak orthodontists (though we love our perfectly aligned brackets ✨). It serves multiple purposes:

✅ Disciplined treatment planning – No more “let’s wing it” approaches! 🚫🦷
✅ Realistic treatment goals – Can we actually achieve that Hollywood smile? 🎬
✅ Anchorage control – Avoid unwanted tooth movement (because molars love to wander!) 😵‍💫
✅ Extraction decisions – To pull or not to pull? That is the question! ⚖️
✅ Arch relationship correction – Ensuring upper and lower arches play nice together! 🤝
✅ Better patient communication – No more confused patients nodding along in fear 😅
✅ Informed consent – Patients need to know what’s coming before we go full ortho mode! 📜

How Do We Plan Space Like a Pro? 🏗️

The space planning process happens in 2 stages:

1️⃣ Assessing Space Requirements 📏

How much space is needed for proper alignment?

Is there excess space or a deficit?

What about crowding or spacing issues?


2️⃣ Creating or Utilizing Space 🏗️

Predicting how much molar movement is required 🦷➡️🦷

Considering future growth (because kids don’t stay tiny forever! 👶➡️🧑)

Deciding if we need extractions, distalization, expansion, or IPR


📋 Fun Fact: This isn’t just a one-time calculation! Space planning is an ongoing process recorded for every patient before starting treatment.

ASSESSMENT OF SPACE REQUIREMENT

Why Assess Space? 🤔

Before you even think about which appliance to use (no, don’t grab that bracket just yet! ❌🦷), you need to define treatment goals:
✅ How wide should the arch be?
✅ Where should the incisors be positioned?
✅ Is there extra space, or are we playing dental Tetris?

How to Measure Crowding & Spacing? 📏

1️⃣ Place a clear ruler over the occlusal/labial surface of study models.
2️⃣ Measure mesiodistal widths of misaligned teeth.
3️⃣ Compare with available arch space in the archform selected.
4️⃣ Record values in mm:

Positive (+) = Space present or created (e.g., incisor advancement)

Negative (-) = Crowding or space required (e.g., incisor retraction)

🚨 Warning: Do NOT measure 3 or more teeth together using a straight-line method! Why?

A straight-line (chord) underestimates space compared to the actual curved archform (arc).

This can make you think there’s more space than there actually is = bad treatment planning! 🚨

Why Does the Curve of Spee Eat Up Space? 🍽️

When you level an occlusal curve, you’re not just straightening teeth like a 2D line. It’s a full-blown 3D puzzle! 🧩

📌 Key Fact:

The Curve of Spee forms because of vertical “slippage” at contact points between teeth.

When you level it, these contact points shift back into alignment—and that eats up space in the arch.

🛑 Common Mistake:

People assume space required = difference between arc (curved line) and chord (straight line). ❌

But this underestimates the space needed because teeth aren’t perfect cylinders—they’re bulbous! (Thanks, anatomy. 🤦‍♂️)

How Much Space Do We Need? 📏

Orthodontists used to think:
📢 “1 mm of space for every 1 mm of curve depth.”

🚨 Turns out, that’s an overestimate! 🚨

What’s the Real Deal?

Studies5-7 have shown space required increases nonlinearly as the curve deepens.

The first millimeter of leveling takes less space than later increments.

Space depends on tooth shape—bulbous teeth = more space needed!

Royal London vs. Other Methods 🏆

1️⃣ Traditional Methods 🏛️

📏 Use a reference plane from the second molars → Curve appears deeper → More space estimated.

2️⃣ Royal London Space Planning 👑

📏 Uses a reference plane from first molars → Looks like a shallower curve → More realistic space estimate.

💡 Why?

Second molars tend to level by moving backward (distally)—which doesn’t affect anterior/midarch space.

Royal London focuses on anterior & midarch space needs—which is what we care about for space planning!

🔢 Fun Fact:

Rarely does the Curve of Spee exceed 4 mm (excluding second molars).

That’s why Royal London’s approach makes more sense for treatment planning.

What to Watch Out For! 🚦

🔹 1️⃣ Don’t Double Count! ❌

If premolars are already crowded, don’t also count them in space required for leveling!

That’s like counting your Netflix subscription twice in your budget. 🫠


🔹 2️⃣ Not Every Case Needs a Flat Curve! 😲

Clinical judgment is key! Do you really need to flatten it completely? 🤔

Some deep curves are functional—flattening them could cause occlusal instability! ⚠️

The Great Space Expectation vs. Reality Check 🏗️

What We Assume:

“Broaden the arch, and BOOM—more room for all the teeth!” 🏠➡️🏡

What Actually Happens:

🔬 Studies (Adkins et al.12, Akkaya et al.13) found that even with Rapid Palatal Expansion (RPE):

Each 1 mm expansion → Only ~0.7 mm increase in arch perimeter! 😲

Why? Because not all teeth expand equally!

First premolars? Expanded 6.1 mm

Canines? Only 2.9 mm

Anterior arch form isn’t fully expressed during expansion alone!

How Does Expansion Really Affect Space?

👨‍🔬 O’Higgins’ ex vivo experiment (bracketed teeth on an acrylic model) taught us:
📏 Every 1 mm increase in intermolar width → 0.28 mm reduction in anteroposterior arch depth.

💡 Translation:

Arch gets wider, but also shorter!

The result? Arch perimeter increases by just ~0.56 mm per mm of molar expansion!


Key takeaway: Expansion gives space, but NOT a 1:1 ratio.

How Should We Use This in Space Planning? 🤓

👑 The Royal London Space Planning Approach:
✅ For every 1 mm of molar expansion, assume ~0.5 mm space creation.
✅ If palatal suture is split, expect slightly more space gain.
✅ Don’t count individual tooth movements as “expansion”—that’s just crowding adjustment!

Wait… What About Contraction? 😨

If expansion reduces arch depth, contraction (like using a TPA for anchorage or reducing arch width) can make things even tighter! 🚧

Moral of the story?
🚫 Don’t overpromise your patient “Oh, we’ll just expand your arch for space!”—because it’s NOT that simple!

Incisor Position: The Space Creator & Consumer 📉📈

Think of incisors like chess pieces—a single move forward or backward shapes the entire game (or arch)!

Why Would We Change Incisor A/P Position?

✅ Reduce excessive overjet (Class II cases)
✅ Proclination in cases of crowding
✅ Maintain proper interincisal angle
✅ Achieve ideal incisor inclination (cephalometric harmony)

How Much Space Does Incisor Movement Really Create? 🧐

👨‍🔬 O’Higgins & Lee (ex vivo model):

They removed first premolars (7.2 mm per side) & closed spaces

Incisors retracted ~7.7–8.0 mm! 😱

Why more than 7.2 mm? Because the archform changed too! (Intercanine width expanded slightly)


What does this mean for us in practice?

🔹 For every 1 mm of incisor retraction → 2 mm of space gained!
🔹 For every 1 mm of incisor advancement → 2 mm of space used!

📌 Moral of the story? Small incisor changes eat up or free up space twice as fast as you might think!

Practical Space Planning 🔢

1️⃣ Assess the lower incisor position first!

If they need retraction, you’ll GAIN space.

If they need advancement, you’ll LOSE space.

2️⃣ Adjust the upper incisors accordingly (to maintain a 2-3 mm overjet).

3️⃣ Beware of unwanted side effects!

Incisor retraction may lead to molar mesialization (which reduces space)

Excessive advancement can lead to lip strain & instability

The Space Implications of Tooth Angulation 🔄

Think of teeth like bookends on a shelf—upright ones take up less space, while tilted ones can hog more.

How Does This Work?

📏 Upright incisors take up less space in the arch.
📐 Properly angulated incisors need more space (but look and function better).
🛠️ Over-angulated incisors may actually free up some space (though this is rare).

The Evidence: Tuverson’s Wax Setup Experiment 🕵️

🦷 2 mm of excess space can be absorbed by properly angulating overly upright upper incisors!
🦷 But… not every angulation issue = space problem!

A 5° distal tilt doesn’t necessarily take up more space than a 5° mesial tilt.

🧐 Royal London Hospital (Unpublished Study):
🔹 Confirmed Tuverson’s findings but estimated a maximum of 0.5 mm per incisor.
🔹 For canines: Small angulation changes don’t impact space much (due to their curved mesial & distal surfaces).

So, What Does This Mean for Us? 🤔

💡 Angulation correction isn’t a game-changer for space—MAX 2 mm total from all four upper incisors!
💡 The bigger clinical concern? Anchorage loss from mesiodistal apical movements (especially with canines).

How Torque Affects Space 🔄

📏 Palatal root torque → Incisal edges shift forward → Arch perimeter increases
📐 Proclined incisors (tipped forward) → Need less space to retract
🛠️ Retroclined incisors (tipped back) → Need more space to torque upright

The Science Behind It

Tuverson’s Demonstration Set-Up

🔹 Applying palatal root torque can absorb 1 mm of excess space in the maxillary arch.

O’Higgins et al’s Ex Vivo Model

🔹 Bracketed acrylic teeth with fixed posterior segments showed:

Palatal torque → Increased arch perimeter

Overjet increases if buccal segments aren’t distalized

🔹 Incisor morphology matters!

Large/Parallel-sided incisors → Need more space

Triangular incisors (contact points near incisal edge) → Need less space

Barrel-shaped incisors → Need an intermediate amount

🔹 Archform also plays a role—3D space dynamics are complex, making simple calculations tricky!

How Much Space Do You Need? 🤔

1️⃣ Bodily retraction of upper incisors by 5 mm → Needs 10 mm of space (5 mm per buccal segment).
2️⃣ Proclined incisors (simple tipping) → 5 mm incisal edge movement, 4 mm contact point movement → Needs 8 mm of space.
3️⃣ For every 5° of incisor torque in average-shaped teeth → Expect 1 mm of space requirement.
4️⃣ Retroclined incisors (Class II Div 2) → Need space to apply apical torque, even if incisal edges stay in place.
5️⃣ Lower incisors? Minimal space effect because their contact points are closer to the incisal edges.

Key Space-Influencing Factors 🚀

1️⃣ Crowding & Spacing → Most significant
2️⃣ Arch Width Changes → Expansion creates ~0.5 mm per mm of intermolar width increase
3️⃣ Incisor Anteroposterior (A/P) Changes → 1 mm of A/P movement = 2 mm of space change

👉 These three have the biggest impact on total space needs!

Minor Space Contributors 🔍

4️⃣ Occlusal Curve Leveling → Nonlinear relationship with space (~1 mm per 1 mm curve depth is an overestimate)
5️⃣ Tooth Angulation (Tip Changes) → Max 0.5 mm per incisor
6️⃣ Incisor Inclination (Torque Changes) → 1 mm per 5° of torque for upper incisors

👉 These three have minimal impact on total space.

Upper vs. Lower Arch: Why the Difference?

🚩 The missing factor? Molar A/P relationship!
✔️ In Class I, space requirements should be equal for both arches (unless tooth-size discrepancies exist).
✔️ In Class II, upper arch needs more space due to molar distalization needs:

Full-unit Class II molars → Upper arch needs 14 mm more space than lower

Half-unit Class II molars → 7 mm discrepancy
✔️ Any mismatch between upper and lower space needs could signal an analysis error or Bolton discrepancy (tooth size discrepancy).

Clinical Takeaways 📌

✅ Focus on major space factors first (crowding, arch width, incisor A/P change).
✅ Use molar relationship as a final check—Class II cases often need more upper arch space.
✅ Small adjustments (angulation, torque, curve leveling) play a role but don’t majorly impact total space calculations.

💡 Final Thought: A well-planned space analysis isn’t just about numbers—it ensures a stable, functional, and esthetic occlusion!

🔑 Takeaway:
Space planning is not just about measuring gaps—it’s about strategizing movement to ensure stable, functional, and aesthetic outcomes. Whether it’s through expansion, extractions, IPR, or torque control, every decision impacts the final smile. 😁✨

💬 Final Thought:
Next time you analyze space, think beyond numbers—factor in growth, anchorage, and occlusion to craft a truly individualized treatment plan!

👉 So, fellow ortho warriors, how do you approach space planning in your cases? Let’s discuss! 🚀💬