PLACEMENT AGAINST WEAK CUSPS
If cusp structure is weak, e.g., almost devoid of dentin support, this Handbook recommends that it be deliberately supported before being exposed to large contraction forces. The following protocol has been proven effective clinically in avoiding “crazing”, that is, the development of visible, light-diffracting lines in the enamel on the reverse side of a weak cusp.
The goal is to build a triangle, from pulpal floor to cusp arm, using a very small initial increment of flowable to just coat the dentin. After cure, place a second very small increment of flowable linking the cusp to the pulpal floor in a radius that final resin will adapt to readily, and cure fully. Complete the triangle with paste resin.
This triangle or “fillet” forms a strut that reinforces the cusp against contraction forces pulling inwardly on the cusp. Flowable is used to ensure perfect adaptation, but in very small quantities, to avoid teh excessive contraction inherent in flowables, i.e., usually over 4 % relative to under 2% in our best paste resins.
After the cusp is supported, avoid linking it to the rest of the the subsequent resin build-up intercuspally by retaining a small isthmus of open space until only a small final increment is required. This “decoupling” of intercuspal contraction forces has a consensus among many composite authorities. Evidence in the literature for its efficacy, like many clinical habits, cannot be quoted at this time, because contraction is inherently invisible. See Problems in the Composite Field