Abstract
Objective: The position of the denture base outline is an important factor that affects the retention and stability of complete dentures. However, positioning of the outline of lower complete dentures in particular varies among different practitioners.
We conducted a series of studies, of which this is the first report. In this study, we used a traction device to determine the effect of the position of the denture base outline on retention of lower complete dentures. Here, we describe changes in retentivity for different amounts of retromolar pad area coverage by the denture base.
Methods: The distal border of the experimental trial plate was trimmed in a phased manner to reduce the amount of coverage. The distal border was positioned at the distal end dome of the retromolar pad, at posterior border of the retromolar pad, at its 2/3 coverage, at its center, and at its anterior border. During this process, traction was applied to the experimental trial plate with a digital force gauge while it was inserted in the mouth, and the pulling force required to separate the denture base from the alveolar ridge was measured. The measured values obtained were used to compare the effect on retention of the positioning of the distal border of the denture base outline. At the same time, we also measured the dimensions of the retromolar pad area, and attempted to quantify the positioning of the denture base outline.
Results: Measured values declined as the position of the distal border of the denture base was shifted proximally from the distal end dome of the retromolar pad. The values were highest when the border of the denture base was positioned on the distal end dome of the retromolar pad, and it was significantly higher than when it was positioned at the anterior border of the retromolar pad(p<0.01).
Conclusions: To obtain a stable border seal in the retromolar pad area, the distal denture border should be positioned so as to cover at least 2/3 of the retromolar pad(approximately 7 mm posterior from the anterior border of the retromolar pad), and if possible, should be extended to the distal end dome of the retromolar pad (approximately 15 mm posterior from the anterior border of the retromolar pad).
