We require enough enamel  to disperse contraction , recognizing that enamel can only absorb so much resin polymerization contraction before it is  destroyed adhesively or cohesively. Pursuing an ethos of minimal invasion,we want to remove the least amount of tooth structure . But we need to remove enough to get the job done.  A correct proportionality for each preparation is dictated by clinical understanding; it varies according to

  • intrinsic resin factors:  polymerization attributes of the resin used
  • tooth size –  larger teeth versus smaller teeth,  teeth with lesser or greater thickness of  enamel
  • resin volume – replacement of whole cusps versus half-cusps.

Starting with any generic enamel margin design, the inclination of bevels may need to be increased when placing a higher-contraction resin, on a larger tooth, with a large amount of resin.In these cases,  we increase the bevel to present  a greater number of rod ends for bonding.

As restorations grow larger with more carious destruction, the proportion of resin to tooth increases.  Because composite mass enlarges, contraction forces increase, and there is less tooth to receive these forces.

Important reductions in contraction forces can be achieved by understanding C-factor, by careful incrementing, by decoupling increments as they are placed and cured, and by choosing modern lower-contraction resins.

But, in the preparation itself, two factors can be exploited to resist contraction damage:

  •  terminate margins in thicker enamel to increase the number of rod-ends recruited to lessen strain at the marginal interface i.e., increase thickness of enamel
  • Adapt the degree of bevel, i.e.,Increase inclination 

For further elaboration of this, see Cusp Shoes and Bevels


Enamel is crystalline and fragile. To disperse resin polymerization contraction into enamel without invoking   adhesive  or cohesive destruction, there must be a proportionality between the resin volume and the enamel volume. This must be assessed clinically in each preparation. It will vary according to prep design, resin volume, and polymerization attributes of the resin used. See Contraction Quotient Hypothesis.

No amount of careful incrementing offsets  violation of preparation enamel axioms. Fresh-cut rod-ends of sufficient depth for lifespan, extending continuously to underlying dentin are basic cornerstones to well-executed composite preparations. Proportionality completes these clinical precepts.  Only when thin enamel adjacent to a large mass of resin is properly prepared is there hope for long term success. At this point and at this point only can careful incrementing avoid damage to the enamel. Follow the clinical technique below for long-lasting MODB restorations emanating from a CEJ margin.


A thin margin, such as a 60-degree CEJ finish line, is  incremented in the following steps

  1. Warmed flowable is placed over all preparation dentin axial walls to  distribute contraction over a wide area and prevent dentin sensitivity from excessive bond stress. See Heated Resins. Flowable also provides intimate adaptation and lower stress in a thin layer (< 0.3 mm.,) than paste resin in thicker layers (>1mm thickness). High viscosity of  paste resins is also offset by heating.
  2. The band is placed and a Wet-Pack Margin Placement Method is used to close the margin. The acute angle between band and 60 degree margin is otherwise difficult to seal without voids or bubbles, which will subsequently appear, disfigure,leak, and fail.
  3. This flowable “lubrication” solves the integrity problem of an acutely convergent margin.
  4. It is indicated only on buccal and lingual surfaces where instrumentation of overfill is beautifully visible.
  5. Remember to use a brush to remove flowable to a minimum. This avoids compressing excess flow past the band and excessive finishing time subsequently. It also prevents a stripe of flowable along the gingival margin in the final restoration if the flowable is not expressed out past the band.
  6. Only a small amount of paste resin(<1mm thick) in used for the initial wet-pack increment.
  7. Once the margin is sealed and unified with the axial wall, larger increments become feasible, because contraction is now being delivered to an increasingly wide substrate of well-bonded flowable, not to a fragile CEJ margin.