When managing a deep overbite, we often think about intrusion arches, curve of Spee leveling, or anterior bite turbos. But have you met the “base arch”?
This humble-looking yet biomechanically brilliant appliance does more than you expect — especially when molar control and occlusal plane leveling are your goals.
🔍 What Is the Base Arch?
Also called the intrusive arch, the base arch shares design features with the tip-back mechanism:
- Buccal segments: 0.018 × 0.025 inch stainless steel
- Anterior segment (from canine to canine): 0.016 inch or larger
- Lingual arch: mandatory to stabilize molars
- The base arch wire (0.017 × 0.025 inch TMA or 0.018 × 0.025 inch SS) includes helices or stops/washers.
But here’s the twist:
- The base arch is tied back.
- This fixes the hook in place — no sliding anteroposteriorly as in tip-back.
- The center of rotation (Crot) shifts mesially, closer to the mesial root of the first molar.
💡 Clinical Scenario 1: Deep Bite Without Flaring Incisors
👩⚕️ Patient:
- 14-year-old female
- Deep curve of Spee, increased overbite
- Incisors well-aligned, not flared
- Goal: Level curve of Spee without proclination
Treatment Plan:
A base arch is used with a lingual arch in place. The base arch is:
- Preactivated and tied back
- Not sliding (fixed helices or stops used)
- Calibrated with a Dontrix gauge to deliver ~200g (100g per side)
What Happens Biomechanically?
- The tied-back base arch applies an eruptive force to posterior teeth.
- The Crot shifts mesially → molars rotate and erupt, reducing the curve of Spee.
- Incisors remain stable, no flaring, thanks to tie-back ligature through helices.
- You get vertical leveling without anterior dentoalveolar protrusion.
💡 Clinical Scenario 2: Deep Bite with Slight Incisor Flaring👨⚕️ Patient:
👨⚕️ Patient:
- 15-year-old male
- Class I molar, but deep overbite
- Mild lower incisor flaring, crowding resolved
- Posterior bite is underdeveloped
Treatment Plan:
Use a base arch without tying it back, and no lingual arch is placed (intentional).
What Happens?
Incisors become more upright, which is desired in this case. Without a tie-back, the anterior segment is free → some lingual crown torque may develop. The lack of a lingual arch allows posterior eruption and rotation to happen more freely. Curve of Spee flattens.
How to Decide When to Use Base Arch and How to Modify It
| Clinical Goal | Use Base Arch? | Tie Back? | Lingual Arch? | Expected Result |
|---|---|---|---|---|
| Deep bite, no flaring | ✅ Yes | ✅ Yes | ✅ Yes | Eruption of molars, anterior stability |
| Deep bite with incisor flaring | ✅ Yes | ❌ No | ❌ No | Posterior eruption + anterior uprighting |
| Need arch length gain | ❌ No (use tip-back instead) | ❌ | ❌ | Base arch doesn’t increase arch length |
| Avoid incisor flaring | ✅ Yes | ✅ Yes | ✅ Yes | No anterior proclination |
🧠 Ask Yourself Before Using a Base Arch:
- Is anterior flaring acceptable or not?
- Do I need posterior eruption and rotation to flatten the curve?
- Will the lingual arch block or assist the desired moment?
- Is there any need to increase arch length (then consider tip-back instead)?
Dentowesome 