PPD essays | Topics 64 - 71 PDF

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Propaedeutics Prosthetic Dentistry final exam // Essays 64- 71...

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PPD 64. FULL REMOVABLE DENTURES. STABILIZATION.

THEORETICAL EXAM ELEMENTS OF FULL DENTURE. PRINCIPLES OF RETENTION

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Definition: The replacement of natural teeth in the arch and their associated parts by artificial substitutes restore aesthetics, mastication and speech Elements of full denture Denture has 3 surfaces and 4 component parts → Surfaces of complete denture

1. Impression surface (Intaglio surface) –portion of denture surface which has its contour determined by impression Refers to the surface of the denture which will be in contact with the tissues when the denture is seated in the mouth ⋅ Negative replica of the tissue surface of the patient ⋅ Must be free of void and nodules to avoid injury to tissues 2. Polished surface (cameo surface) Refers the external surface of the lingual, buccal and labial flanges and external palatal surface of the denture ⋅ Surface should be well polished and smooth to prevent collection of food debris 3. Occlusal surface - occlusal surface of the denture teeth → Components (1) Denture base (2) Denture flange (3) Denture teeth (4) Denture border

Denture base Forms foundation of the denture, rests on the oral mucosa, helps distribute and transmit all forces acting on the denture teeth to basal tissues –made from acrylic resin and metal Responsible for retention and support Denture flange Buccal and labial vertical extension of the upper or lower denture base, and lingual vertical extension of the lower one Functions include, providing peripheral seal and horizontal stability to denture - Flanges are named based on the vestibule they extend into ✴ Labial flange - lip support ✴ buccal flange - cheek support ✴ lingual flange - mandibular denture, in contact with the floor of the mouth to provide peripheral seal, overextended lingual flanges can lead to loss of retention !

Denture border –margin of the denture base at the junction of polished and impression surface ⋅ Responsible for peripheral seal

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Should be devoid of sharp edges and nodules to avoid soft tissue injury overextended borders - hyper-plastic tissue damages under-extended borders - loss of peripheral seal

Denture teeth Functions of the denture teeth: aesthetics, mastication and speech Usually made of acrylic resin or porcelain anatomic, semi-anatomic, non-anatomic, cross-bite, and metal insert teeth

→ Principles of retention and stability Retention in complete dentures refers to the ability of that denture to resist displacement in the direction opposite to path of insertion Results from fit and forming a border seal [Providing retention is difficult to achieve with lower dentures where stability and muscular control must be optimized t compensation]

Physical forces: (a) Adhesion: physical attraction between unlike molecules e.g. denture-saliva-mucosa, if there is a flat alveolar ridge, small jaws = less adhesion (b) Cohesion: attraction between like molecules e.g. high mucous saliva increases cohesion which in turn decreases retention; normal saliva is not very cohesion, unless modified. (c) Interfacial surface tension: tension/ resistance to separation possessed by the film of the liquid between two well adapted surfaces Low surface tension - maximizes contact ! high surface tension - minimize contact (d) Capillarity: state due to surface tension, causes elevation/ depression of the surface of a liquid that is contact with the solid Close adaptation between base and mucosa - thin film of saliva in the space - Saliva acts as a separating media between dental flanges and mucosa Concave meniscus forms between saliva and air, when denture sits on that side an intimate contact is formed –this contributes to retention of the denture (e) Undercuts enhance retention - resiliency of the mucosa and submucosa; exaggerated bony undercuts, which compromise retention (f) Gravity - retentive force for the mandibular and displace for the maxillary when person is upright ! Heavy maxillary prosthesis unseat if the other retentive forces are suboptimal (g) Parallel walls - prominent alveolar ridge with parallel buccal and lingual walls will increase the surface area and maximize interfacial and atmospheric forces. (h) Atmospheric pressure resists dislodging forces to dentures with an effective seal (suction) Most effective in retention when denture has a perfect seal around entire border Pressure between the tissues and the dentures drops below the atmospheric pressure - resists displacements

Secondary retention –indirect retention obtained when stability and support of denture is optimum, external factors which tend to unseat denture are eliminated

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Stability is the ability of the prosthesis to resist displacement by function horizontal or rotational forces Establishing a balanced occlusion is key to maintaining stability and in turn the border seal [Lower dentures are particularly vulnerable to instability as a result of poor retention] Occlusal force should be transmitted at a 90o to alveolar and primary masticatory teeth –located in the deepest part of the alveolar Denture teeth should be positioned to create: ⋅ A stable denture by positioning teeth over central portion of alveolar ridge ⋅

Stability during chewing by centering the primary chewing teeth over the favorable part of ridge → When marking the stable position on the patient’s alveolar ridge this will ensure the first molar tooth occupies this space ∴ ensuring stability

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Stability of the lower denture by creating agreeable, non-antagonistic contacts between mandibular and maxillary teeth during lateral and protrusive movements

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Retention by ensuring the denture teeth and held within the neutral zone/ potential denture area –an area existing between the forces exerted by the muscles of cheek, lip and tongue

Total edentulism - complete tooth loss due to bone reposition: mandible inclines outwards and becomes progressively wider maxilla resorbs upwards and inwards making it smaller - gives the prognathic appearance in long-term edentulous patient lip and cheek support must be restored by the denture the denture must have high adhesion to the tissue for good retention and stability mechanical retentive components can be added to improve the retention of the denture spring, intra-mucosal magnets and suction discs - these components are avoided because they produce tissue damage Available denture - bearing area for an edentulous mandible - mandible 14cm; maxilla 24cm buccal shaft area - between the buccal frenum and anterior border of the masseter serves as primary stress-bearing area, as it lies at right angles to the occlusal force Relief areas mylohyoid ridge - runs along the lingual surface of the mandible Mental foramen - due to rifge resorption, it may lie close to the ridge - can never be sequeezed Genial tubercules - pair of bony tubercules found anteriorly on the lingual side of the body of the mandoble Torus mandibularis - abnormal bony prominence found bilaterally on the lingual side, near the premolar region

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https://www.slideshare.net/mahakralli/stability-in-complete-dentures-52718407 https://www.slideshare.net/deepthipramachandran/retention-of-complete-dentures

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65. FULL REMOVABLE DENTURES -IMPRESSIONS AND CUSTOM TRAY DESIGN. An individualized impression tray made from a cast recovered from primary impression - used in making a final impression To achieve a good quality working impression, a well-designed custom tray along with the appropriate impression material should be used

Criteria A customised impression tray should: ⋅ Allow easy control and guides the impression material, provides an even layer ⋅ Stiff to prevent distortion ⋅ Altered in areas hindering the ridge ⋅ Supports impression material to provide even contact with oral tissues and enable pressure on selected areas of denture-bearing area ⋅ Be rigid and retain its shape throughout the impression procedure and during the pouring of model Design of tray ⋅ Periphery of tray designed to allow impression material to flow into buccal and labial sulci without displacement of soft tissue ⋅ Allows free movement of muscle attachment ⋅ Tray is spaced appropriately for amount of undercut present Workable thickness ≈ 4mm Borders ≈ 2mm short of vestibule (so green stick compound can be used to do border moulding) ∗

Perforated edentulous stock trays are used for alginate impressions

Materials for custom tray fabrication: polystyrene, shellac, cold cure resin

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A. Close-fitting tray It is adapted directly on the cast without any wax spacer ✓ When majority of denture-bearing area is free from large undercuts → Allow pressure to be exerted on denture-bearing area during procedure Compresses the mucosa and adapts the relaxed mucosa closely to underlying alveolar bone, this allows masticatory forces acting on denture to be transmitted directly and comfortably to alveolar bone ✓ Allows a thin uniform layer of impression to be used Impression material –non elastic, rigid once set: ZnO and eugenol paste Usually used with impression materials that have a light viscosity to obtain a wash impression B. Spaced tray –used in presence of undercuts Use a wax spacer to provide space for the impression material, because the material used here need extra space as they have higher viscosity: Alginate, medium and heavy bodied elastomers The greater the depth of undercut, the more likely the material will tear or exceed its limit of elasticity on removal In presence of large undercuts greater spacing is required − Amount required depends on tear strength of impression material

C. Windowed tray –used in presence of fibrous ridges Customised tray is designed to have a window cut around the fibrous ridge area

Advantages of special tray ⋅ Economy in impression material - uses less material than special tray ⋅ More accurate impression and adapted to the oral vestibules - better retention ⋅ Provide even thickness of impression material - minimize tissue displacement and dimensional changes of impression material ⋅ Easier to work with and quicker than modifying stock tray ⋅ less bulky than stock trays - more comfortable for patient Light cure acrylic resin ⋅ less hazardous than cold cure acrylic ⋅ reduce preparation time ⋅ easy to use and has good handling properties Disadvantages of cold cure acrylic custom tray ⋅ Polymerization shrinkage ⋅ A time interval must be allowed between the fabrication and the use of these custom trays ⋅ The hazardous effects caused by the monomer include dermatologic reactions

Fabrication of custom tray Preparation of the primary cast Undercuts should be found with the help of surveyor and should be blocked out. Outline the border of the tray should be marked with pencil which is 2/3 mm short of the reflection. The relief areas should be marked in the cast. The border of the tray should be marked on the cast and may be grooved deeper using a carver. Adapting the relief wax - should be adapted over the relief areas marked on the cast Materals for giving relief - baseplate wax; non - asbesos casting liner

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Adapting the spacer A spacer should be adapted throughout the extent of special tray (coincide with the second line), except posterior palatal seal area in maxilla and buccal shelf area in mandible Function of spacer ⋅ Allows the tray to be properly positioned in the mouth during border molding procedure ⋅ Allow the impression to have an even thickness of impression material ⋅ Prevent distortion of the material at final stage The use of stops The spacer should be cut out in 2-4 places so that the special tray touches the ridge in these areas. The size of the stoppers can be 2mm square/ 2 by 4 mm rectangle/ 2mm mesiodistally, palatally over the crest of the ridge and buccaly half way into the sulcus Function of tissue stops - to orient the tray and for uniform thickness of the impression material Application of separating medium - apply separating media on the cast so that acrylic resin does not stick to the cast. Acrylization - monomer ratio is 3:1 in 5 distinct stages: sandy, stringy, dough, rubbery/ elast, stiff

Fabrication of handle The handle should be parallel to the long axis of the teeth that are to be replaces. it should not arise horizontally from the tray because it may interfere with lip movement. It should be 3-4mm thick, 8mm long and 8mm high, the vertical distance from the sulcus to the handle is 2cm. The handle up-stand must be made long enough for the handle to exit through the oral commissure. for mandibular tray two posterior handle should be given as finer test Function of the handle is to support the lip while making impression and are helpful when loading, placing and orientating custom tray in the mouth The function of the finer rest is to stabilize tray in mouth, to equale distribution of pressure and to reduce pressure applied to the tissue Preparing the tray for border molding procedure - tray periphery should be 2-3mm thick, the edge should be rounded. the rest of the tray should be ~2mm thick. Close fit tray skips the spacer and stop making.

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TRAY - Def. Is a device used to carry, confine and control the impression material from the patient’s mouth. During impression taking the tray facilitate insertion and removal of impression material from the patient’s mouth. Classification (1) According to the material ! Metalic trays (stainless stess, aluminum)! Non-metallic trays (plastic, acrylic resin)

(2) According to the method ! Stock trays (full arch, sectional, Custom tray/ special tray

quadrant)!

(3) According to the present/ absent teeth ! Edentulous trays - square cross-section for patient with teeth ! Dentulous trays - rounded cross-section for patient without teeth

(4) According to the method of interlocking of material ! Perforated trays! Non-perforated trays! Rim-lock trays (Water/ non-water cooled)

Stock tray - ready - made and comes in specific sizes. must be selected for best fit. Are reusable after sterilization! Custom trays - are fabricated on the particular patient’s cast thereby making it unique to the patient. always have better fit than stock tray Stock tray - Impression tray that serve to carry the impression material to the mouth and support it in the correct position while it is hardening. used for making the primary impression. Material - Al, Tin, Brass, Plastic. Tray is available in 5 sizes: 1U - 5U - for upper jaw; 1L - 4L - for lower jaw; 1-small, 5-large Factors effect in selection of stock tray (1) Material types used in primary impression procedure ! impression compound used with non-perforated tray, because it will stick on the tray! Alginate used with perforated stock tray (2) Size of the arch (3) Form of the arch - round/ square/ taper (4) The stock tray must cover all the anatomical landmarks needed in complete denture !!! (5) Stock tray should give sufficient space for impression material in all direction

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Metal trays ⋅ Provide maximum support for impression material; are rigid ⋅ Durable and long lasting; can be perforated or solid ⋅ Can be used with all elastomeric materials ! Plastic tray ⋅ Disposable, eliminate cross0contamination ⋅ Can be modified! ⋅ Rigid, thick walls to provide lateral support fo the tray impression material to prevent distortion when pouring the model Tray selection ⋅ Always selected for the best fit ! ⋅ Dentulous mouth - use dentulous trays ⋅ edentulous - edentulous trays ⋅ partially edentulous - combination trays ⋅ elastic impression material - perforated trays ⋅ inelastic materials - non-perforated trays

IMPRESSIONS Primary impression → Primary cast → Special tray → Secondary impression Negative replica of oral tissue, plaster or stone can be poured into it to form the positive replica –cast Cast acts as a template used to fabricate the complete denture ×

Diagnostic impression Diagnostic impressions are a part of treatment planning Negative replica of oral tissue used to prepare diagnostic cast ∗ Diagnostic casts are used for study purposes –locating path of insertion, measuring undercuts, not fabrication processes Used to estimate amount of pre-prosthetic surgery required Articulate the casts on tentative jaw relation and evaluate the inter - arch space ×

Primary impression An impression made for the purpose of diagnosis or for the construction of a tray First step in the fabrication of a complete denture There should be at least 5 mm clearance between the stock tray and the ridge The tray should extend over hamular notch and maxillary tuberosity. Mandibular tray should cover the retromolar pad - tray can be extended using modeling wax Material: impression compound, alginate or impression plaster ×

Secondary impression Clinical procedure used to prepare master cast, done after mouth preparation is complete - Makes use of custom tray prepared from primary cast Records denture-bearing area in great detail and also records the muscular peripheral tissue in function Peripheral structures are recorded by ‘border moulding’ process: Movements of lip, cheek and other muscles are stimulated passively to record the length and width of vestibule Border molding is the shaping of the border areas of an impression tray by functional or manual manipulation of tissue adjacent to the borders to duplicate contour and size of the vestibule Terminating denture borders on soft resilient tissue will allow mucosa to move with the denture base during function and thereby maintain peripheral seal

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Low viscosity impression material should be used to record structures accurately Material: ZnO eugenol paste and medium-bodied elastomeric impression material Classification Depending on theories pf impression making ∗ mucostatic/ passive impression ! Made with he oral mucosa membrane and the jaws in a normal, relaxed condition. border moulding is not done here. the impression is made with an oversized tray ! Material: impression plaster. ! Results in a denture, which is closely adapted tot he mucosa of the denture - bearing area but has poor peripheral seal ∗

mucocompressive ! Records the oral tissue in a functional and displaced form. ! Material: impression compound, waxes and soft liners ! The oral soft tissue are resilient and this tend to return to their anatomical position once the forces are relieved. ! Dentures made by this technique tend to get displaced due to the tissue rebound at rest. ! During function, the constant pressure exerted onto the soft tissues limit the blood circulation leading to residual ridge resorption

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selective pressure ! The impression is made to extend over as much denture- bearing area as possible without interfering with the limiting structures at function and rest ! This technique makes it possible to confine the forces acting on the denture to the stress bearing areas - achieved through the design of the special tray in which the non stress bearing areas are relieved and the stress bearing areas are allowed to come in contact with the tray

Depending on the technique ∗ Open mouth ! Built in tray which carries the impression into the desired contact with the supporting tissues and into an relation to the peripheral tissues when the mouth open and without applied pressure. ! The rationale behind this method is that the dentures do not dislodge when subjected to biting force ! It develops a contour of impression surface which in harmony with the relaxed supporting tissues, and which may be out of perfect adaptation with these tissues when the denture is subjected to occlusal loading ∗

Closed mouth ! Wax occlusal rims to be fa...