DENTURE RETENTION It is the resistance to displacement of the denture base away from the ridge.
DENTURE RETENTION A number of forces and factors combine to retain complete dentures in position in the mouth. These factors can be considered as : 1- physical. 2- anatomical. 3- physiological. 4- mechanical.
DENTURE RETENTION 1- Physical factors : a) Adhesion. b) Cohesion. c) Atmospheric pressure. d) Gravity.
DENTURE RETENTION a) Adhesion : It is the force of attraction existing between dissimilar bodies in close contact. i.e. attraction between the saliva and the denture base.
DENTURE RETENTION Adhesion acts most powerfully at right angles to the surface, and is proportional to the area of the surfaces in contact.
DENTURE RETENTION b) Cohesion : It is the force of attraction existing between similar bodies in close contact or the surface tension of the saliva. Cohesion is effective in direct proportion to the area covered by denture, if other factors are equal.
DENTURE RETENTION Viscosity of the saliva ??? The adaptation of the denture base to the mucosa must be as close as possible. So, thick saliva ( contains a larger percentage of mucin ) prevents the denture and tissues coming into sufficiently close contact.
c) Atmospheric pressure : When the denture is seated in the mouth, air is expelled from between it and the mucosa and provided that there is an intact border seal, a pressure differential is established which provides a positive force to maintain the denture. Atmospheric pressure contributes very little to the retention of the denture until an attempt is made to move it away from the tissues.
DENTURE RETENTION d) Gravity : Working against the upper denture and for the lower denture.
DENTURE RETENTION For the maximum utilization of physical forces in denture retention, the following principles must be remembered: 1. The denture should cover the maximum area of mucosa compatible with functional muscular activity. 2. The saliva film must be as thin as possible. 3. The meniscus must be uniformly thin around the entire denture, and peripheral and facial seals must be effective in preserving it.
DENTURE RETENTION 2- Anatomical factors: These include : A. Shape of the edentulous ridge. B. Undercuts. C. Anatomy of the border tissues.
DENTURE RETENTION 3- Physiological factors: These include : A. Neuromuscular control. B. Viscosity and volume of saliva.
DENTURE RETENTION A. Neuromuscular control : For oral and facial musculature to be most effective in providing retention for complete dentures, the following condition must be met: 1. Denture bases must be properly extended to cover the maximum area possible without interfering with the health and function of the structures that surround the denture. 2. The occlusal plane must be at the correct level. 3. The arch form of the teeth must be in the neutral zone between the tongue and cheeks.
DENTURE RETENTION 4- mechanical factors : These include : A. Balanced occlusion. B. Contour of the polishing surfaces. C. Position of the occlusal plane ( the vertical distance of teeth from ridge ). D. Position of the teeth in respect to the ridge.
DENTURE RETENTION A. Balanced occlusion : The bilateral, simultaneous, anterior and posterior occlusal contact of teeth in centric and eccentric position.
DENTURE RETENTION B. Contour of the polishing surfaces : The polished surface of the lower denture faces outward and upward on the buccal surface and inward and slightly upward on the lingual surface.
DENTURE RETENTION B. Contour of the polishing surfaces : In the upper, the buccal surface faces outward and downward, the palatal surface follows the contour of the palate. Thus, the buccal surface of the upper and lower dentures and teeth present a concave surface to the buccinator muscle of the cheek.
DENTURE RETENTION c. Position of the occlusal plane : The occlusal plane of the lower denture must be at the correct level, the corners of the mouth provide the anterior landmarks for the correct height of the occlusal plane while the distal end of the occlusal plane should be at a level two third the way up the retromolar pad.
Biological factors : 1. Intimate tissue contact, obtainable by accurate impression. 2. Peripheral seal : A. Posterior palatal seal is most important in maintaining seal on maxillary denture. B. Lingual flange area. Proper adaptation is important for seal on the mandibular denture especially in the anterior lingual region.
DENTURE STABILITY It is the resistance to horizontal or rotational forces. Factors that promote stability : 1. Residual ridge anatomy ( size and height). 2. Relationship to facial muscles. 3. Polished surface and borders of denture. 4. Occlusion.
DENTURE STABILITY Residual ridge anatomy ( size and height) : Larger, square, broad ridges offer greater resistance to lateral forces than narrow, tapered ridges.
DENTURE STABILITY Relationship to facial muscle : The posterior lingual flange slopes medially away from the mandible to allow for action of the mylohyoid muscle.
DENTURE SUPPORT It is the resistance to vertical movement of the denture base toward the ridge.