What is C-Factor?
C-Factor is the cavity configuration factor. It is the “ratio of bonded to unbonded surfaces of the dental cavity, and its value is supposed to be directly related to the stress developed at the interface bonding area” (1). It’s very important in adhesive dentistry because it is related to the incidence of polymerization shrinkage in composites during light curing when the composite pulls away from the bonded surface toward the direction of the curing light. Polymerization shrinkage is a problem because it leads to post-op sensitivity and bond failure leaving many composite fillings acting as “white amalgams” and even more vulnerable to recurrent decay than amalgams (2).
How do you minimize C-Factor Stress?
Preparation design is key. The retentive, GV-Black-style features taught to us in dental school were intended for amalgams and are actually detrimental to composites and C-factor stresses. Avoid sharp line angles and corners with composites.
Decoupling with time and Incremental fill. Waiting at least 5 minutes after placing bond on your freshly cut dentin will allow the dentin bond to mature. Then layering incrementally in “thin horizontal layers of composite that are 1mm or less” which “ensures that decoupling with time is properly achieved and that the flow of the composite is not moving away from the deep dentin during the early stage of horizontal layer development” (3).
Fiber-reinforcement as stress-breaker, “fiber nets allow the composite on either side of the net to move in different directions via micro shifting of the woven fibers” (3). Studies on the Ribbond page show increased dentin bond strength in cavities with high C-factor stresses (4).
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