Summary: part 1 set out the indications and rationale for posterior indirect adhesive restorations. This part covers the technique: the principles of the Morphology Driven Preparation Technique, the butt-joint thickness threshold, the role of immediate dentin sealing, and what the laboratory needs to see on the model to reproduce the design correctly.

1. Morphology-driven preparation

The preparation technique described by Veneziani (Int J Esthet Dent, 2017) does not begin from a requirement for mechanical retention, as classical cavity designs did. It begins from two features of the tooth itself: the maximum contour line and the cuspal inclination.

The practical consequence is that the finish line is no longer placed by a fixed rule but according to its position relative to the maximum contour line:

Above the maximum contour line — a continuous inclined plane in the form of a hollow chamfer or concave bevel on the axial walls. This zone is still in enamel, and the inclined plane cuts the enamel prisms at an angle favourable for bonding.
Below the maximum contour line — a butt-joint of approximately 1.2 mm in the proximal box and on the walls. This threshold ensures adequate material thickness rather than creating thin margins prone to fracture.

The occlusal surface is prepared anatomically — cusps and grooves retained — rather than flattened. All transitional angles are rounded, with no undercuts or sharp line angles.

2. Designs to avoid

Three familiar features of classical cavity design no longer suit a restoration retained by adhesive bonding:

Shoulders around the cusps — remove a large volume of tissue in an area that could have been preserved.
Occlusal grooves — create mechanical retention that is unnecessary once bonding is in place, while introducing stress-concentrating angles.
Pins — expose dentine without need.

What all three have in common: they trade tooth structure for mechanical retention, when retention is already provided by the adhesive interface.

3. Immediate dentin sealing

Immediate dentin sealing means applying the adhesive layer to dentine right after preparation, before the impression, rather than at the cementation appointment. The protocol described in the literature involves etching dentine with 37% phosphoric acid for about 15 seconds, rinsing and suctioning so the surface remains visibly moist, applying a universal adhesive for 20 seconds, air-drying and light-curing for 10 seconds.

The reported benefits are improved dentine bond strength and reduced risk of debonding. A systematic review and meta-analysis protocol is synthesising its effect on the fracture strength of posterior indirect restorations, and an in vitro study examines its effect across different luting agents.

From the laboratory’s side, what matters is that sealing changes the preparation surface. If it has been performed, say so when sending the case — the technician will calculate cement space differently.

4. Preparation design and marginal adaptation

Preparation design directly affects the marginal adaptation of the finished restoration. An in vitro study comparing three preparation designs for lithium disilicate overlays found significant differences in marginal adaptation between designs — meaning design selection is not only a question of tissue preservation but of accuracy.

This is also why a butt-joint is recommended below the maximum contour line: a thick, square margin can be reproduced far more accurately by both scanning and milling than a thin bevelled one.

5. Clinical advantages reported in the literature

Better bond quality — the inclined plane optimises the cut of enamel prisms and increases the available enamel bonding surface.
Less dentine exposure — fewer bonding and sensitivity problems.
Maximum preservation of hard tissue — the cavity is designed for reinforced composite luting, improving flow and excess removal.
Better aesthetic integration — the inclined-plane design allows a smoother shade blend at the tooth–restoration transition.

6. What the laboratory needs to see

The boundary between bevelled and butt-joint zones — if the model does not show the transition, the technician has to guess and will produce the wrong margin type.
A clear, unchipped butt-joint margin, sufficient to verify 1.2 mm of thickness.
Anatomic occlusal morphology retained — a flattened occlusal surface removes the reference for rebuilding cusps and grooves.
A note on whether immediate dentin sealing was performed.
Opposing model, bite registration and a note on bruxism.

FAQ

Is 1.2 mm a hard number?

It is the threshold cited for the butt-joint in the morphology-driven technique, intended to avoid thin fracture-prone margins. Total restoration thickness also depends on the material — lithium disilicate and zirconia do not share a threshold.

Is immediate dentin sealing mandatory?

Not mandatory, but the bond-strength benefit is consistently reported. If performed, tell the laboratory.

Does this apply to endodontically treated teeth?

Yes, and this is the group that benefits most, because tissue preservation retains structure that is already reduced.

Can intraoral scanning read a butt-joint margin?

Yes, and usually better than a thin bevel, because a square margin gives a crisp boundary. The condition is still that soft tissue is controlled and the margin is not obscured by blood or fluid.

References

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