Prosthodontics Lecture 8 & 9 (BDS IV) PDF

Module: Prosthodontics 3 (BDS IV/Semester 7) Lecture 8 & 9 – Denture bearing areas of maxilla & mandible Dr Vinothkumar Sengottaiyan (@Dr_VK) Lecturer, Department of Prosthodontics Oman Dental College Learning outcomes Differentiate the denture bearing areas of maxillary and mandibular arches in...

Module: Prosthodontics 3 (BDS IV/Semester 7) Lecture 8 & 9 – Denture bearing areas of maxilla & mandible Dr Vinothkumar Sengottaiyan (@Dr_VK) Lecturer, Department of Prosthodontics Oman Dental College Learning outcomes Differentiate the denture bearing areas of maxillary and mandibular arches into supporting, relief and limiting areas. Plan and condition the denture bearing areas to receive the complete dentures. Understand various possible preprosthetic surgeries that may be required for denture construction. Identify situations that require referral to a specialist for further management. 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 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 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 aesthetics only and function is not affected in most cases 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 for a longer time (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 Graphical representation of selective pressure impression 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 Tissues of edentulous oral cavity Mucosa – Keratinized attached mucosa – present on the residual ridge and palate – Non keratinized unattached mucosa – present in vestibule, cheeks, floor of the mouth, soft palate, uvula and tonsillar pillars Submucosa (not seen in mid palatine raphe) – Fibrous – seen on the anterior palate, tuberosities and residual ridges – Fatty/glandular – seen on posterior palate and some areas of floor of the mouth – Muscular – seen along vestibule, cheek and floor of the mouth Bone – Cortical bone – present in most areas except crest of the residual ridges – Medullary bone – present along the crest of residual ridges Favourable characteristics of supporting areas 1. A thick cortical bone – cortical bone is avascular and is OCCLUSAL resistant to resorption and thus, an excellent FORCES 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. Maxillary anatomical landmarks *** - A.Tuberosity I. Buccal frenum B.Buccal vestibule J.Crest of the C.Buccal frenum residual ridge D.Labial vestibule K.Hamular notch E.Labial frenum L.Fovea palatini F.Incisive papilla M.Post palatal seal ! · area (junction of m G.Mid palatine raphe hard & soft palate) H.Rugae with no muscle slope > - cortical bone PPS attachment & - posterior peripheral seal area Raphea (connect muscle no muscle Tendon ligument (bone 1o muscle (bone to bone) ! pengomandibular raphal D buccinator muscle 2 superior pharyngeal constrictor muscle  Classification of anatomical landmarks – maxilla Supporting structures Limiting structures Relief areas (areas that I - (structures that provide (structures along the require relief from pressure resistance to masticatory borders that will limit the of denture base during rest forces) extension of denture base) and function) Required characteristics: – Labial frenum – Incisive papilla 1. Bone should be cortical – Labial vestibule – Mid palatine raphe 2. Mucosa – keratinised, attached – Buccal frenum – Canine eminence 3. Should be placed perpendicular – Buccal vestibule – Pterygoid Hamulus to occlusal forces – Hamular notch – Crest of the alveolar ridge – Primary support– posterior – Posterior palatal seal area 2/3rd of palate (has all 3 characteristics) – Secondary support – anterior 1/3rd of palate, slopes Border areas/tissue - - * of residual ridge (has at least 2 peripheral - characteristics) * seal areas All same meaning which is limiting structures. Anatomical landmarks of mandible – self assessment refer to next slide and try labelling the picture by yourselves  Classification of anatomical landmarks – mandible Supporting structures Limiting structures Relief areas (areas that (structures that provide (structures along the require relief from resistance to masticatory borders that will limit the pressure of denture base forces) extension of denture base) during rest and function) Required characteristics: – Labial frenum – Mental foramen area 1. Bone should be cortical – Labial vestibule – Crest of residual ridges 2. Mucosa – keratinised, attached – Buccal frenum – Canine and premolar 3. Should be placed perpendicular – Buccal vestibule eminences to occlusal forces – Pterygo-mandibular raphe – Genial tubercles - I – Primary – Buccal shelf – Lingual frenum – Mylohyoid ridges (satisfies all 3 criteria for – Lingual vestibule supporting structures) – Secondary – slopes of ↓ ① attut residual ridge (satisfies at connect humular least 2 criteria) notch t retro- molar pad. 1. Pre prosthetic surgeries Alveoloplasty – to reduce sharp bony g extensions of the alveolar ridge. - >invasive 2. Vestibular extension/Sulcus deepening – to Procedures increase depth of the sulcus – usually - achieved with skin or mucosal grafting. - O 3. Tuberosity reduction - to create vertical space in posterior ridge, to accommodate posterior denture base extension, without prosthetic teeth. ⑦ 4. Debulking of flabby tissues – for achieving a - firm mucosal support. ↓ - mobility of soft tissue ⑤ 5. Ridge augmentation – to increase the height of the alveolar ridge - increases stability of the dentures – if achievable, implants can be considered instead of removable dentures. Thanks for listening! TEXTBOOK FOR REFERENCE: 1) Zarb, G.A., 2012. Prosthodontic Treatment for Edentulous Patients: South Asia Reprint-E-book. Elsevier Health Sciences.