Denture Bearing Areas Lecture 8 PDF

Support - definition In general, it is the foundation area on which a dental prosthesis rests support also refers to the amount of resistance that the prosthesis can have against occlusal/functional forces In complete dentures, it is the area of mouth available for supporting a denture...

Support - definition In general, it is the foundation area on which a dental prosthesis rests support also refers to the amount of resistance that the prosthesis can have against occlusal/functional forces In complete dentures, it is the area of mouth available for supporting a denture Otherwise, supporting areas are those areas in the mouth that are best suited for absorbing the functional forces during mastication Parts of complete denture 1. Denture base/ denture foundation – this is the part of the denture that closely contacts the supporting area (denture bearing area) – also called as impression surface or intaglio surface, recorded and reproduced by final impression and have three subdivisions a) Support areas b) Relief areas c) Peripheral seal/ border areas 2. Denture flange – this surface lies outside denture base and is called cameo /art surface – it is the surface that is developed by the dentist – this surface influences esthetics only and function is not affected in most cases 3. Occlusal surface – this surface is formed by the artificial teeth that we use in the denture and is used to create balance for dentures during mastication Denture bearing area This refers to all the surfaces that are contacted by the denture base The picture on the right shows the denture base or the fitting surface of the denture which will contact the oral tissues The denture bases usually made of hard materials like acrylic and they do not change shape during function Thus, all the occlusal forces are transferred completely to the denture bearing areas by the denture base  Forces in complete dentures Forces that are perpendicular to occlusal plane are generated in complete dentures during mastication These forces are transmitted to the underlying supporting tissues as compressive forces In bone, these forces cause bone resorption In tissues, these forces cause ischemia (reduction of blood flow) Bone resorption and ischemia are long term problems However, in some cases pain, ulceration and irritation occur instantly or in a short-term use What happens when we make an impression? In general, a dental impression is a procedure that records the anatomy of oral cavity by using some appropriate materials that are carried by impression trays The material must be pressed against the structures in the oral cavity to record them – pressing against the structures is nothing but compression It is logical to assume that the denture base applies as much force as that was applied for making an impression Some structures can withstand this pressure (ex: teeth, bone) some structures cannot withstand pressure and they get compressed ( ex: mucosa, muscle attachment etc) How to manage compression in denture bases? To manage this situation, we need to fabricate a customized tray which contacts only those areas that can resist pressure This type of tray is fabricated with a first duplicate (primary cast) made from an initial/preliminary impression On this duplicate we place wax sheets in all places where we want to reduce pressure during impression – this wax is called relief wax On this, we will fabricate a special tray with acrylic Then, the wax inside is removed before making the final impression It is also possible to reduce the pressure further by making some holes in the tray – these holes are called relief holes GRAPHIC REPRESENTATION OF SELECTIVE PRESSURE Anatomical landmarks These are visible/palpable anatomical structures seen in oral cavity of an edentulous patient These structures can be appreciated both in impressions and casts that are prepared from the impressions It is essential to have a knowledge about how these structures are classified and how the classification helps in making a custom tray that can apply selective pressure during impression making 1. Support areas – primary and secondary 2. Relief areas 3. Border areas/ peripheral seal areas Favourable characteristics of supporting areas 1. A thick cortical bone – cortical bone is avascular and is resistant to resorption and thus, an excellent supporting structure 2. A thick keratinized attached mucosa – if the mucosa is thick, attached and keratinized, it can resist trauma/ulceration caused by movements that happen with denture bases 3. Direction in relation to occlusal plane - support and resistance are maximum when the supporting area is parallel to occlusal plane (or, perpendicular to occlusal forces) Relief areas Sometimes, even when you may find that there are some favourable support criteria in some places, they will not be used to provide support 1. Nerve canals ( mental nerve canal, incisive nerve canal) 2. Sharp bony edges ( canine prominence, interdental bony peaks in fresh extraction sites, mylohyoid rigde ) 3. Fresh extraction socket spaces 4. High frenal attachments 5. Ridge crest with soft medullary bone 6. Areas of thin mucosa ( mid palatine raphae, External oblique ridge) Peripheral seal areas These are places which determine the denture flange length and thickness They are classified as 1. Frenal areas – areas where muscles take attachment 2. Sulcus areas – the areas between the attachment where the muscles move in function Maxilla – support and relief Primary support 1. Horizontal surface of posterior 2/3 of the palate Secondary support 1. Anterior and lateral slopes of palate 2. Residual ridge slopes Relief areas 1. Residual ridge crest 2. Incisive papilla 3. Mid palatine raphae 4. Canine eminence 5. Undercuts, if any Maxilla – peripheral seal areas Labial sulcus Labial frenum Buccal sulcus Buccal frenum Hamular notch Posterior palatal seal area Mandible – support and relief Primary support 1. Buccal shelf Secondary support 1. Residual ridge slope Relief 1. Residual ridge crest 2. Mental foramen 3. Mylohyoid ridge 4. Genial tubercles Mandible – peripheral seal areas Labial frenum Labial sulcus Buccal frenum Buccal sulcus Retromolar pad area Lingual frenum Alveolo-lingual sulcus