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ADEX exam

ADEX Class II Preparation – Step-by-Step Exam Guide

A clear, simple breakdown of how to prepare a pass-level Class II (MO/DO) for the ADEX manikin exam — dimensions, criteria, and mistakes to avoid.

Quick Answers

What bur should I use for the ADEX Class II?

Use a 330 or 245 bur for outline and initial depth; switch to a 56 or 169L for refining walls.

What is the ideal pulpal floor depth?

Roughly 1.5 mm from the DEJ (≈2 mm occlusal reduction), following tooth anatomy.

How wide should the proximal box be?

Enough to break contact — generally 0.5–1 mm clearance. Over-widening loses points.

What causes automatic failure in the Class II prep?

Pulp exposure, adjacent tooth damage, open gingival margin, or incorrect tooth selection.

How to avoid breaking the adjacent tooth?

Use a wedge before breaking contact and remove enamel carefully with hand instruments.

What is the biggest mistake candidates make?

Over-prepping the box, creating unsupported enamel, and “chasing perfection” until they overcut.

1. Why the Class II is the most failed ADEX preparation

The MO/DO preparation looks simple, but in ADEX it tests multiple competency areas at once: outline accuracy, depth control, proximal box management, and safety. Most failures come from overcutting or ignoring the scoring sheet.

2. Step 1 – Establish ideal outline form

Start with a 330 or 245 bur and follow these principles:

  • Maintain conservative outline; do not “balloon” the cavity.
  • Keep the occlusal isthmus around 1.0–1.5 mm.
  • Maintain smooth curves, no sharp irregular edges.
  • Stay centered over the groove anatomy — drifting loses points.

High-yield outline rules

● Don’t guess the shape — mark with pencil first.
● Stay inside enamel until you intentionally break contact.
● Slightly rounded internal line angles are preferred.

3. Step 2 – Prepare the pulpal floor

The ADEX floor should be flat, smooth, and anatomically appropriate, around 1.5 mm from the DEJ.

  • Keep the bur parallel to the long axis of the tooth.
  • Avoid “dips” — inconsistent depth is a deduction.
  • Do not over-deepen; it risks pulp exposure and automatic failure.

4. Step 3 – Breaking contact safely

Breaking contact is where most candidates lose points or fail outright.

  • Insert wedge before entering the proximal box.
  • Use hand instruments after initial bur passes to avoid adjacent tooth damage.
  • Your clearance should be just enough to pass the explorer tip (≈0.5–1 mm).
  • Avoid over-widening — a very common deduction.

Automatic failures in this step

● Adjacent tooth damage
● Contact not fully broken
● Gingival margin open / unsupported enamel

5. Step 4 – Proximal box dimensions

Examiners look for consistency, not perfection. The ADEX box should follow these principles:

  • Gingival floor flat and 1.0 mm thick.
  • Axial wall depth ≈1.0 mm, gently following contour.
  • Buccal–lingual dimension controlled, not excessive.
  • No unsupported enamel at margins.

6. Step 5 – Final refinement

Use slower speed instruments for finishing:

  • Mini 56 bur for smoothing walls.
  • Hatchets/hoes for enamel smoothing at margins.
  • Clear unsupported enamel with hand instruments only.

Your goal is a preparation that looks clean, controlled, and safe — not “perfect”. Over-polishing tends to lead to over-reduction.

7. High-yield mistakes to avoid (examiner perspective)

The ADEX team consistently reports these as the top reasons for lost marks:

  • Excessive box width (the most common deduction)
  • Unsupported enamel left at the gingival margin
  • Inconsistent axial wall depth
  • Occlusal isthmus too wide
  • Failure to fully break contact
  • Over-reduction leading to pulp proximity

8. Linking this to ADEX scoring

If you haven’t read our main overview yet, start with the ADEX Exam 2025 guide so you understand how Class II fits into the overall scoring system and what counts as a critical error versus a minor deduction.

After mastering the Class II prep, move to the ADEX Class III preparation guide and the Treatment Planning OSCE guide to complete the core manikin and decision-making set.

9. How DentAIstudy helps you practise Class II preps

DentAIstudy can convert the entire Class II criteria list into:

  • Short checklists you can use beside the manikin
  • Flashcards for critical vs. standard errors
  • OSCE-style scenarios related to proximal boxes
  • Step-by-step refinement notes for common mistakes

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References

  • ADEX Candidate Manual – Latest Release.
  • Standardised preparation criteria from licensure boards.
  • Examiner calibration summaries and performance reports.