Complete lower dentures are a source of concern for many denture patients. The reasons for lower denture
Instability are complex. Some of these reasons are listed below. Lower dentures are harder (more difficult) to secure, because unlike an upper denture, suction is not possible with a lower denture. The denture bearing area is smaller than the upper jaw and continues to decrease over time due to bone loss called resorbtion. The lower ridge has movable tissue (tongue and cheek) with flexible muscle attachments impinging on the denture bearing area. Accurate recording of the maximum denture bearing boundary is essential for lower denture stability. An over extension of the denture base due to an inaccurate impression technique, will result in a denture that moves about as the muscles move during talking and eating.
When dentures meet in a non-harmonious manner, the lower denture tends to slide over the tissues till the dentures meet evenly, causing instability and discomfort. Recording the relationship between the upper jaw and the lower jaw is complex due to the nature of the joint being both double hinged and having the ability to slide forward and side to side. Accurate recording of your jaw relationship (bite) is essential for a stable lower denture.
Denture teeth wear flatter with use. This wear, combined with changes in the size of the lower jaw due to resorbtion, causes changes in the relationship of the upper and lower dentures. This change in how the dentures bite together results in the lower denture becoming unstable, with the lower denture sliding over the tissues as described above. Worn out dentures are a very common cause of lower denture instability.