[Fatigue strength and marginal adaptation of composite fillings]

Threshold load tests have shown that the fatigue strength of Class I composite fillings may be increased up to 150 N by the application of a base material. This effect varied only with the consistency of the composite, not with the type of base material used. However, differences were found in the depths at which losses of marginal adaptation occurred: where glass ionomer cement base (polyalkenoate) was used, marginal leakage demonstrated by pigment penetration tests stopped at the interface between filling and base, while in those cases where phosphate cement was used as base material, pigment penetration was shown to extend down to the floor of the cavity. Mesiodistal sections through Class II MOD restorations with the same combinations of materials after 24 hours of storage in pigment solutions and without loading revealed that a close marginal fit in the area of the cervical step can be obtained with the use of glass ionomer cement as base material. In contrast to this observation the use of phosphate cement as base material is associated with marginal leakage down to the area of the floor of the cavity in about one half of the restorations.