Dentaltown November 2020 - 30

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Why Not Prep Undercuts
for Occlusal Composites?
A Townie wants to know the benefits of not utilizing undercuts to improve retention of restorative materials

kenwylie
Member Since: 06/22/04
Post: 1 of 78

I recently posted a poll about this and more dentists answered that they don't prep undercuts
for occlusal composites. What's the benefit of no undercuts? ■
7/1/2019

teethdood
Member Since: 12/29/05
Post: 2 of 78

I'll start with amalgam. Many schools teach students to prep amalgams in a way to minimize unsupported enamel rods (parallel to the rods), such that the prep forms a 90-degree
angle to the cavosurface. What that means is that there's going to be a natural undercut for the
amalgam restoration at the expense of more tooth removal. Other schools teach parallel walls
and 90-degree box forms instead to be more conservative at the expense of possible unsupported
enamel that could fracture.
With composites, a restoration does not necessarily require any retentive undercuts or box
forms due to bonding, although it would be nice in certain circumstances like buccal Class V.
The point is to be minimally invasive. Remove all caries and most of the time you're good to go.
Most of the time. ■
7/1/2019

Profitable GP's
Member Since: 05/14/19
Post: 4 of 78

I finish all my composite cavity preps with medium-grit diamonds. The diamond particles
leave groves everywhere and that's plenty of physical retention and increased etching and bonding surface. No undercut needed. I still cut groves for big Class V with a 34 carbide. The tooth
flexes a lot there so locking it in helps. ■
7/1/2019

jmslps
Member Since: 11/30/05
Post: 5 of 78

I think you should ask the other question, "What is the benefit of prepping undercuts for
occlusal composites?" With materials that are not bonded, there are very specific reasons for
undercuts. My reasons for not specifically prepping undercuts for any composite restoration is
that they are not needed and only remove healthy structure for no purpose. I do not remove all
undercuts, though. ■
7/1/2019

Brett Mansfield
Member Since: 08/19/05
Post: 6 of 78

Intentionally creating undercuts for a Class I composite removes additional tooth structure,
creates stress points within the tooth structure, and creates areas that are potentially more difficult to fully seal and fill, depending on your technique. Well-done Class I and II composites
don't fall out. ■
7/1/2019

AZCrazy
Member Since: 12/20/01
Post: 19 of 78

An occlusal composite surrounded on all sides by enamel and dentin should never have
a hope of coming loose. The bond on that should be strong enough to hang a patient up by
his tooth.
Class IV and Class V composites, which have to hold on to the tooth with pure adhesion or
against flexural forces, can be aided by undercuts in retention. ■
7/1/2019

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