Measurement of Stresses in Fixed-Bridge Restorations Using a Brittle Coating Technique

¹ School of Dentistry, University of Michigan, Ann Arbor, Michigan

The magnitude and direction of strains and stresses were determined on fixed-bridge restorations, using a brittle lacquer-coating technique. A maxillary anterior six-unit bridge having pin-ledge preparations on the cuspids, a mandibular anterior six-unit bridge having -crowns on the cuspids and a see figure in pdf four-unit maxillary bridge having a -crown and full crown on the first biscuspid and second molar, respectively, were used in the study.

The maxillary and mandibular anterior bridges were loaded on the incisal edge and were shown to deflect downward and to tip forward during loading. The two anterior bridges, therefore, when loaded sustained tensile strains in a vertical direction on the lingual aspect and in a horizontal direction on the labial aspect. The pin-ledge preparations were not particularly satisfactory, since often the cement failed at the abutments during loading. The -crown preparation appeared to be more suitable, since the mandibular bridge having these preparations withstood loading up to 60 pounds. The posterior bridge when loaded deflected in a typical transverse manner, since little if any tipping occurred. The stress and direction of the strain were found to be a function of load, position of the force application, and mass and shape of the restoration.