Biomechanics of Complete Dentures PDF

# Biomechanics of Complete Denture ## Batterjee Medical College **For Science and Technology** **Marketing Department** **Mon. Feb. 21. 2018** ## Biomechanics of complete denture - Retention - Stability - Support - Factors affecting retention, stability, support ### Retention - The resistance to...

# Biomechanics of Complete Denture ## Batterjee Medical College **For Science and Technology** **Marketing Department** **Mon. Feb. 21. 2018** ## Biomechanics of complete denture - Retention - Stability - Support - Factors affecting retention, stability, support ### Retention - The resistance to removal in a direction opposite to that of insertion (vertical tissue away movement) ### Stability of complete denture - The ability of the denture to withstand horizontal forces (quality of the denture to be firm and steady when functional forces are applied, resistance to horizontal and rotational forces) ### Support of complete denture - Support: Resistance to vertical forces of mastication, occlusal forces and other forces applied in a direction towards to denture bearing area. ## Factors affecting retention ### Anatomical Factors - **Size of the denture bearing area:** Retention increases with increase in size of the denture bearing area. The size of the maxillary denture bearing area is about 24 cm2 and that of the mandible is about 14 cm2. More retention than mandibular denture. - **Quality of the denture bearing area:** The displaceability of the tissues influence the retention of the denture. Tissues displaced during impression making will lead to tissue rebound during denture use leading to loss of retention. ### Physiological Factors - **Saliva:** The viscosity of saliva determines retention. Thick and ropy saliva gets accumulated between the tissue surface of the denture and the palate leading to loss of retention. Thin and watery saliva can also lead to compromised retention. ### Physical Factors - **Adhesion:** (The physical attraction of unlike molecules to another). The role of saliva is very important for adhesion. Saliva wets the tissue surface of the denture and the mucosa. This thin film helps to hold the denture to the mucosa. The amount of adhesion present is proportional to the denture base area. - **Cohesion:** "The physical attraction of like molecules for each other". The cohesive forces act within film of saliva. The effectiveness of these forces increase with increase in denture bearing area. - **Interfacial surface tension:** Is the resistance to separation possessed by a film of liquid between two well-adapted surfaces. The cohesive forces acting at the surface of the liquid. Close adaptation of the denture base to the mucosa will enhance these forces. If the shape of the palate is high and vaulted, it will be easier to displace a denture base than if the palate is flatter. - **Atmospheric pressure & peripheral seal (intimate contact):** Atmospheric pressure can act to resist dislodging forces applied to dentures, if the dentures have an effective seal around their borders. Retention produced by an atmospheric pressure is directly proportional to the denture base area. Peripheral seal is the area of contact between the peripheral borders of the denture and the resilient limiting structures. This peripheral seal prevent air entry between the denture surface and the soft tissue. ### Mechanical Factors - **Under Cuts:** Unilateral undercuts aid in retention while bilateral undercuts will interfere with denture insertion and require surgical correction. - **Magnetic Forces:** Intra-mucosal magnets aid in increasing retention of highly resorbed ridges. - **Denture Adhesives:** They are available as creams or gels or powders. They should be coated on the tissue surface before wearing the denture. The action of adhesive is: Increasing the adhesive and cohesive properties and viscosity of the medium lying between the denture and its basal seat. Eliminating voids between the denture base and its basal seat. - **Suction Chambers & Suction Discs:** In the past suction chambers in the maxillary dentures were used to aid in retention. They are avoided now due to their potency for creating palatal hyperplasia. ### Neuromuscular Factors - The muscles apply supplementary retentive forces on the denture. - There is a balance between the forces acting from the buccal musculature and the tongue. - The balance is obtained in the neutral zone. - The artificial teeth should be arranged in the neutral zone to achieve the best retention possible. - The occlusal plane should be parallel to the residual ridge ## Factors affecting complete denture stability - **Vertical height of the residual ridge:** The residual ridge should have sufficient vertical height to obtain good stability. Highly resorbed ridges offer the least stability. - **Quality of soft tissue covering the ridge:** The ridge should provide a firm soft tissue base with adequate sub-mucosa to offer good stability. - **Quality of the impression:** An impression should be accurate as possible. The impression surface should be smooth and duplicate all the details accurately. It should be devoid of voids and any rough surfaces. It should be dimensional stable and cast should be poured as soon as possible. - **Occlusal plane orientation:** Occlusal plane should be oriented parallel to the ridge. If the occlusal plane is inclined, then the sliding forces may act on the denture, reduce its stability. - **Arrangement of teeth:** The position of the teeth and there occlusion play an important role in the stability of the denture. Balanced occlusion facilitates the even distribution of forces across the denture. The teeth in the denture should be arranged in the neutral zone. - **Contour of the polished surfaces:** The polished surfaces of the denture should be harmonious with the oral structures. They should not interfere with the action of the oral musculature. ## Factors affecting support of complete denture - The anatomical and histological factors of the ridge - The way of pressure direction on the ridge during impression making procedure - The maximum coverage provides the greater the support, which distributes applied forces over as wide an area as possible. - The best support for denture is the compact bone covered with fibrous connective tissue # Thank You