QUESTION

How can I design a denture so that it won't move around in the patient's mouth?

ANSWER

There are two key aspects to designing a denture that will help resist dislodgement: 1. The denture base extensions 2. Placement of the teeth in relation to the ridges and each other.

Denture Base Extensions

On the maxillary denture, stability is more easily achieved due to the suction created between the denture and the palate. Also, there is usually adequate remaining bone on the ridge to support the denture. Over-extension of the periphery and the posterior borders are the most likely causes for instability problems. Beware of over-extending in these areas especially near the buccal and labial frenae, where muscle attachments are located. It is more difficult to achieve mandibular stability of the denture base.Bone resorption may leave little residual ridge and the ridge may be knife-edged. The floor of the mouth moves with tongue function and if the denture is over-extended here, the denture will easily dislodge. Also, attention must be paid to the muscle attachments in the buccal and labial vestibule. They too will cause dislodgement of the denture if the peripheral extensions intrude upon them.

Tooth Placement

Natural teeth erupt into an area called the neutral zone. In this zone, the pressure of the tongue pushing outward on one side is balanced by the pressure of the cheek and lip muscles pushing inward on the other side. When you put the denture teeth in this zone, the equilibrium between opposing forces helps keep the denture in place. If you place the teeth outside this zone, the added pressure on that side may dislodge the denture. For greatest stability, the ideal place for the teeth is over the crest of the ridge. Unfortunately, sometimes due to ridge resorption, you must compromise some stability to achieve a satisfactory appearance and comfort, but remember, do so only with caution. When you place teeth off of the ridge, the torquing created when upper and lower teeth come together in chewing may dislodge the denture on the opposite side of the mouth. Likewise, when the mandibular anterior teeth are set too far forward on the ridge, the pressure created when the patient incises will cause the posterior part of the denture to lift up off of the tissue. This pressure can accelerate bone resorption as well as contribute to fatigue fractures in the denture base.