Occlusal Reduction: How Much Space Does the Material Need on the Occlusal Surface?

Occlusal Reduction: How Much Space Does the Material Need on the Occlusal Surface?

Insufficient occlusal reduction is the beginning of problems. The dentist prepares, the lab prepares, but if there's <1.0 mm of clearance on the occlusal surface, the technician only has bad options: making it too thin (risk of fracture) or changing the design during processing (risk of misfit).

Problem: Insufficient Occlusal Reduction

Clearance < 1.0 mm = two bad options for the technician:

1. Making it too thin (physics: material won't withstand occlusal forces)
2. Changing the design during processing (milling tolerance, creating a boss)

Result: fractures, misfits, complaints, costs for everyone.

The Role of Clearance in the Success of the Restoration

Proper thickness on the occlusal surface ensures:

• Durability: the material has a reserve for occlusal forces (200–500 N standard, 1000 N bruxism)
• Natural Occlusal Point: the technician doesn't have to create artificial convexities; the occlusal point is natural
• Ease for the Technician: processing without risk; any dimension outside tolerances can be implemented
• Aesthetics: possible characterization and anatomy without risk of layer chipping

Reduction Standards

• e.max: 1.5–2.0 mm (optimally: 1.8 mm for bruxism)
• HT Zirconia: 1.0–1.5 mm (optimally: 1.2 mm)
• UL Zirconia: 0.7–1.2 mm (only for anterior teeth without bruxism)

How to Practically Check Preparation

Method 1: Silicone Index (reference point)

1. Make an index of the prepared tooth (impression material)
2. Place it on the natural tooth, mark the contour
3. Transfer to the prepared tooth
4. Index thickness = approximate occlusal reduction

Method 2: Bite Registration (in dynamic)

1. Apply bite registration material (e.g., polyether)
2. Patient closes naturally
3. Apply to the prepared tooth and mark the contact points
4. Material height = actual reduction (considering patient's dynamics)

Material Variants and Their Requirements

FAQ

Is e.max 1.5–2.0 mm always necessary?

Optimally for e.max it's 1.5 mm minimum, but 1.8–2.0 mm is safer (especially for bruxers). Below 1.5 mm, the risk of fracture increases; a series of delaminations in patients with dynamic occlusion.

Can I prepare below the norm for a patient without bruxism?

You can work at the minimum (e.max 1.0 mm, zirconia 0.7 mm), but if the patient later develops bruxism or is a dentist (high forces), the law may be on their side in a complaint.

How does the lab check if the reduction is sufficient?

A good lab uses a CAD scanner to map the thickness. If the lab doesn't check, that's a red flag. Always ask: "Do you have enough space on the occlusal surface?"