PDF: Effect of water storage on tooth displacement in maxillary complete dentures

Since the introduction of acrylic resin in Dentistry in 1937, a certain lack of dimensional accuracy has been accepted as one of the disadvantages of complete denture construction, resulting from the unavoidable denture base shrinkage during acrylic resin polymerization.

Loss of retention and stability of dentures under clinical conditions is caused by dimensional changes that occur in the acrylic resin base due to undesirable warpage and distortion upon resin base water loss or uptake, stress release and base flexural fatigue.

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Water sorption seen in clinical use following denture processing occurs during the first three months, and the consequent expansion partly compensates the curing shrinkage. As a result, water balance and dimensional stability of the denture base are frequently attained. Good wetting characteristics of the denture base are important because materials with different surface energies have distinct wettabilities.

According to the diffusion theory for assessing the quantitative aspects of water sorption kinetics, the diffusion coefficient governs water sorption rate and the time required to reach equilibrium, which is also proportional to the thickness of the specimen. This suggests that the denture should fit better after water uptake than immediately after processing because the shape of oral tissues remains the same.