Establishment Method of Retention Force of Mandibular Complete Dentures and Examination of Factors Related to Retention Force

Purpose: Various aspects of the retention of mandibular complete dentures are unclear, as no evaluation method has been established to date. This study aimed to clarify the effect of suitable mouth opening, the shape of the residual ridge, and the form of the denture on retention when measuring retention of mandibular complete dentures. Methods: The subjects were 37 individuals wearing mandibular complete dentures. The central incisor was loaded 45° downward toward the occlusal plane. The force needed to dislodge the denture was measured using a digital force gauge. The size of the mouth opening was defined as 1, 2, and 3 cm, and was measured four times. Retention forces were compared based on the shape of the molar residual ridge and the relative position of the anterior residual ridge crest. Results: As the size of the mouth opening increased, the retention decreased (P<.05). The variation index was the lowest when the mouth was opened to 1 cm. Denture retention increased as the viscosity of the oral moisturizer increased (P<.05). Retention decreased when the residual ridge in the anterior mandibular region was positioned relatively backward (r = -0.608, P<.01). There was a significant relationship between the height of the residual ridge in the molar region and denture retention. Conclusions: As the viscosity of the oral moisturizer increased, denture retention increased. The size of mouth opening needs to be defined when measuring retention. The size of mouth opening is stable at 1 cm; therefore, this is the optimal size. Retention was associated with the height of the molar region residual ridge and the relative position of the crest of the anterior residual ridge.