Effects of the Position of Artificial Teeth and Load Levels on Stress in the Complete Maxillary Denture

Statement Of Problem: Complete maxillary dentures are subjected to significant variations in force. The influence of tooth position on the stress patterns of a complete maxillary denture during gradual load increases has not been determined.

Purpose: This study was designed to measure the effects of the position of artificial teeth and load levels on stress patterns in the complete maxillary denture.

Material And Methods: For this study, 2 groups of complete maxillary dentures were fabricated with different tooth positions (Group 1 with teeth on the crest of the ridges; Group 2 with buccal position of the teeth) using commercial casts, with 3 identical dentures in each group. Two rosette strain gauges were cemented onto the mid-line of each denture, one on the anterior palatal area and the other on the posterior palatal area. The dentures were loaded from 0 N to 110 N in steps of 10 N, and the strains induced were measured. Values were substituted into standard equations to calculate principal stresses. A Student t test was used to quantify the differences of the stress magnitudes between the 2 groups and the coefficient of variation for each magnitude, with the level of statistical significance set at a probability value of.05.

Results: The anterior stress field of the maxillary denture was dominated by a principal tensile stress and a smaller compressive stress, both of which had stable orientations that were independent of load and tooth positions (coefficient of variation of angle Phi of the anterior stress field was 2.00% and 1.23% for Groups 1 and 2, respectively). In contrast, the posterior stress field was unstable. It was dominated by a large compressive principal stress (with a much lower principal tensile stress) that changed direction during loading (the coefficient of variation of angle Phi of the posterior stress field increased to 17.84% and 13.54% for Groups 1 and 2, respectively). The outer placement of the maxillary posterior teeth in Group 2 caused a significant increase in the principal compressive stresses in the anterior stress field, whereas in the posterior stress field, this caused a significant decrease of both principal stresses.

Conclusion: Within the limitations of this study, the results suggest that the high anterior tensile stress with stable orientation and the lower posterior stresses with variable orientations during loading may be responsible for denture base fractures that initiate from the anterior palatal area. The pattern of these stresses might also be responsible for the clinically observed characteristics of crack propagation.