Configuration factor

In dentistry, the configuration factor (or c-factor) refers to the number of bonded surfaces in an adhesive dental restoration. Because adhesive dental restorative material will adhere to all of the walls of a cavity preparation made available to it during polymerization, competing forces can arise during restoration of the tooth that can have both short and long term effects that correlate to the configuration of the cavity preparation.

Adhesive dental materials are generally used in a semi-liquid or semi-solid state that is then changed into a solid state during or after placement of the material into the cavity preparation. This modification of state can occur automatically after a given time period after the material is discharged from the cartridge (referred to as self-polymerization) or this change can be activated by certain wavelengths of light (referred to as light-cured or light-sensitive material) or the material can be activated in both ways (referred to as dual curing).

For example, for a class I preparation there would be 5 bonded surfaces and only 1 un-bonded surface; the net result would be a c-factor of 5. With an increasing C factor the developing curing contraction stresses of bonded restorations (resin composites) increases too (Feilzer et al. 1987). The developing curing contraction in a bonded restoration generate stress on the bonded interface that are in competition with the developing bond strength of the setting restorative to the cavity surfaces, which may result in (partial) debonding, marginal leakage and post-operative pain (Davidson et al. 1984).

Internal stress can be reduced in a restoration subject to potentially reduce high disruptive contraction forces by using:

• "soft-start" polymerization instead of high-intensity light curing
• incremental layering to reduce the effects of polymerization shrinkage; and
• a stress-breaking liner, such as filled adhesive, flowable composite, or resin-modified glass ionomers
• the application of non or low shrinking restorative materials

References

• Roberson, Theodore; Haymann, Harold; Swift, Edward (2002), Sturdevant's Art and science of Operative Dentistry, St. Louis, Missouri: Mosby

• Feilzer, Albert J; de Gee, Anton J; Davidon, Carel L (Nov 1987), "Setting stress in composite resin in relation to configuration of the restoration.", J Dent Res, 66 (11): 1636–9

• Davidson, Carel L; de Gee, Anton J; Feilzer, Albert J (Dec 1984), "The competition between the composite-dentin bond strength and the polymerization contraction stress", J Dent Res, 63 (12): 1396–9
• Davidson, Carel L (1986), "Resisting the curing contraction with adhesive composites", J Prosthet Dent, 55 (4): 446–44