OBJECTIVES: This study was designed to test the hypothesis that a reduction in occlusal rests and minor connectors decrease the stress transmitted to the residual ridge.

METHODS: Two extracted first upper molars, two first and two second upper premolars were used. The roots were double coated with Solithane (Uniroyal Chemicals) and then embedded in PL-2 resin (Measurement Group)obtaining the study model. A first removable partial denture (RPD) was constructed with 8 occlusal rests and 4 minor connectors (experimental), as control, a second RPD with 12 occlusal rests and 8 minor connectors was made for the same model. Both share 4 casts circumferential claps and the same mayor connector. The experimental and control RPDs were subjected to stress analysis in a circular polariscope (Photolastic Inc) where a 20 and then a 40 kg. inclined load (35 and 45 degrees) was applied on the central incisors interproximal cervical area of the artificial teeth, and the fringe patterns were recorded. Then, the cast claps were replaced with wrought wire circumferential claps, and the protocol of loading and photography was repeated.

RESULTS: Both designs showed higher stress transmitted to the residual ridge when loaded with 40 kg. at 45 degrees. In all the conditions of the study, control RPD showed higher stress transmitted to the ridge than the experimental one. The stress intensity to the residual ridge was the same for each RPD, regardless of the clap's material. For each RPD, stress distribution was not modified in any of the study.

CONCLUSION: The number of occlusal rests and minor connectors are directly related with the stress transmitted to the residual ridge. Moreover, stress distribution could be related to the residual ridge morphology.

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