Removable Partial Denture PDF

CHAPTER 1: Partially Edentulous Epidemiology, Dental cast surveyor Instrument used to determine the Physiology, and Terminology relative parallelism of two or more axial surfaces of teeth or...

CHAPTER 1: Partially Edentulous Epidemiology, Dental cast surveyor Instrument used to determine the Physiology, and Terminology relative parallelism of two or more axial surfaces of teeth or other parts of a cast of a dental arch; also used to locate and Removable Partial Denture delineate the contours and relative positions of abutment - A component of prosthodontics teeth and associated structures - Branch of dentistry pertaining to: restoration and maintenance of oral Denture base Part of a denture (whether it is metal or is function, made of a resinous material) that rests on the residual bone comfort, covered by soft tissue and to which the teeth are attached. appearance, and health of the patient Direct retainer Component of a removable partial denture by the restoration of natural teeth and/or the used to retain or prevent dislodgment; consists of a clasp replacement of missing teeth and craniofacial assembly or precision attachment. tissues with artificial substitutes. Guiding planes Two or more vertically parallel surfaces of abutment teeth shaped to direct a prosthesis during Objective of Prosthodontic Treatment placement and removal; surfaces are parallel to the path of the placement and parallel to each other; preferably these Elimination of oral disease to the greatest extent surfaces are made parallel to the long axes of abutment teeth. possible Preservation of the health and relationships of the Height of contour Line encircling a tooth, designating its teeth and the health of oral and para-oral structures, greatest circumference at a selected position determined by a which will enhance the removable partial denture dental surveyor. design Preservation of the health and relationships of the Indirect retainer Part of a removable partial denture that teeth and the health of oral and para-oral structures, assists direct retainers in preventing displacement of distal which will enhance the removable partial denture extension denture bases by resisting lever action from the design opposite side of the fulcrum line. Abutment A tooth, a portion of a tooth, or a portion of an Major connector Part of a removable partial denture that implant that serves to support and/or retain a prosthesis. connects the components on one side of the arch to the components on the opposite side of the arch. Angle of cervical convergence Angle viewed between a vertical rod contacting an abutment tooth and the axial surface Prosthesis A denture, an obturator, a fixed partial denture, or of the abutment cervical to the height of contour. a crown Bar clasp Type of extra-coronal retainer that originates from Removable partial denture (RPD) Prosthesis that replaces the denture base or framework, transverses soft tissue, and some teeth in a partially dentate arch and can be removed approaches the tooth undercut area from a gingival direction. from the mouth and replaced at will. Basal seat Oral tissues and structures of the residual ridge Residual ridge Residual bone with its soft tissue that covers supporting a denture base. the underlying area of the denture base; the exact character of the soft tissue covering may vary, but it includes the mucous Circumferential clasp Term used to designate a clasp arm membrane and underlying fibrous connective tissue. that originates above the height of contour and approaches the tooth undercut from an occlusal direction. Rest Any component of the partial denture that is placed on an abutment tooth, ideally in a prepared rest seat, so that it Clasp assembly Part of a removable partial denture that acts limits movement of the denture in a gingival direction and as a direct retainer and/or stabilizer for a prosthesis by partially transmits functional forces to the tooth. encompassing or contacting an abutment. Retention Quality inherent in the denture that resists the Clasp (or direct retainer) Component of the clasp assembly vertical forces of dislodgment (e.g., the force of gravity, the that engages a portion of the tooth surface and either enters adhesiveness of foods, the forces associated with opening of an undercut for retention or remains entirely above the height the jaws). of contour to act as a reciprocating element; generally used to stabilize or retain a removable prosthesis. Stability Quality of a prosthesis of being firm, stable, or constant and resisting displacement by functional, horizontal, or rotational stresses  Physiologic A. Major connector What are we replacing when we consider managing missing B. Rest teeth? C. Direct retainer ANSWER: D. Minor connector E. Guide plane the physical anatomic tools for mastication F. Indirect retainer the oral capacity for neuromuscular functions to manipulate food The most sensitive input, which means the input that provides the most refined and precisely controlled movement, comes from periodontal mechanoreceptors (PMRs), with additional input coming from the gingiva, mucosa, periosteum/ bone, and temporomandibular joint (TMJ) complex. TOOTH LOSS AND AGE Chewing – generated from within the central nervous system. Key points: - Tooth loss and age are linked FUNCTIONAL RESTORATION WITH PROSTHESES - An INTERARCH difference: MAXILLARY loss before MANDIBULAR teeth Mastication - An INTRA-ARCH difference: POSTERIOR teeth Mastication involves two discrete but well-synchronized lost before ANTERIOR teeth activities: - Last remaining teeth in the mouth are the MANDIBULAR ANTERIOR teeth (especially (1) subdivision of food by applied force; mandibular canines) (2) selective manipulation by the tongue and - Common finding to see an edentulous maxilla cheeks to sort out coarse particles and bring opposing mandibular anterior teeth. them to the occlusal surfaces of teeth for - Partially edentulous conditions are more further breakdown. common in the maxillary arch; the most commonly missing teeth are first and second Process of mastication is greatly influenced by factors that molars affect physical ability to reduce food and to monitor the reduction process by neurosensory means. Food Reduction CONSEQUENCES OF TOOTH LOSS Masticatory Efficiency Anatomic - ability to reduce food to a certain size in a given time frame. - With the loss of teeth, the residual ridge no longer benefits from the functional stimulus it Swallowing Threshold once experienced. (loss of ridge volume both - The point at which an individual is prepared to height and width—can be expected unless a swallow the food bolus. dental implant is placed) Note: BONE LOSS is greater in the mandible than in the maxilla and Superior masticatory ability that is highly correlated more pronounced posteriorly than anteriorly, and it produces with occlusal contact area also achieves greater food reduction a broader mandibular arch while constricting the maxillary at the swallowing threshold. Conversely, a diminished ability arch. to chew is reflected in larger particles at the swallowing threshold. Loss of bone is an accompanying alteration in the oral mucosa. The attached gingiva of the alveolar bone can be replaced with When the loss of posterior teeth results in an less keratinized oral mucosa, which is more readily unstable tooth position, such as distal or labial migration, traumatized. tooth replacement should be carefully considered.  CURRENT REMOVABLE PARTIAL DENTURE USE Key points: - In the maxilla, lack of stability was seven times more prevalent than lack of retention. - In the mandible, lack of stability was 1.8 times more prevalent than lack of retention. - Common flaws associated with poor removable partial dentures: Rest form Denture base extension Stress distribution Framework fit FAQs There are different forms of “indirect retainers” and one of the most common forms is a “rest”. Those rests located farthest from the edentulous space are usually the ones acting as indirect retainer. CHAPTER 2: CONSIDERATIONS OF PARTIAL DENTURE preparations) and verification of adequate fit of the frame to the teeth Tooth Replacements from the Patient’s Perspective PHASES OF PARTIAL DENTURE SERVICES (DTS EIP) Shared Decision Making 1. DIAGNOSIS AND EDUCATION OF PATIENT Multiple outcomes combine to describe the overall impact of prosthetic care for all patients. These include “The process of informing a patient about a health matter to secure informed consent, patient cooperation, and a high level of patient technical outcomes compliance.” physical outcomes 2. TREATMENT PLANNING, DESIGN, TREATMENT SEQUENCING, esthetic outcomes AND MOUTH PREPATION various maintenance needs initial and future costs, and even physiologic outcomes -Medical and dental histories. that suggest to what extent prostheses “feel” like teeth Complete oral examination must include: (CCP RV) In summary, tooth replacement prostheses should provide a combination of several features of natural teeth: caries, the condition of existing restorations, acceptable in appearance, periodontal conditions, comfortable and stable in function, responses of teeth (especially abutment teeth) and and maintainable throughout their serviceable lifetime at a residual ridges to previous stress, and reasonable cost the vitality of remaining teeth. AVAILBLE OPTIONS FOR PARTIALLY EDENTULUOS PATIENTS: Dental cast surveyor – absolute necessity - Natural-tooth supported FPD 3. SUPPORT OF DISTAL EXTENSION DENTURE BASES - RPD - Implant-supported FPD Only for distal extension Certain soft tissue in the primary supporting area should be TOOTH-SUPPORTED PROSTHESES recorded or related under some loading so that the base may be The major categories of partial tooth loss (see Chapter 3) are those made to fit the form of the ridge when under function. 1. with teeth both anterior and posterior to the space (a 4. ESTABLISMENT AND VERIFICATION OF OCCLUSAL FORCES AND tooth-supported space), and TEETH ARRANGEMENT 2. with teeth either anterior or posterior to the space (a tooth- and tissue-supported space) Tooth-supported partial denture, ridge form is of less significance than it is for the tooth- and tissue-supported prosthesis, because the It should be obvious that careful planning and execution of the ridge is not called on to support the prosthesis necessary natural tooth contour modifications are required to 5. INITIAL PLACEMENT PROCEDURE ensure movement control and functional stability for removable Patient is given possession of the removable prosthesis. partial dentures supported by teeth Inevitably it seems that minute changes in the planned occlusal relationships occur during processing of the dentures. TOOTH-AND TISSUE SUPPORTED PROSTHESES 6. PERIODIC RECALL It is necessary that the residual ridge be used to assist in the 6 months recall period functional stability of the prosthesis Healthy residual ridge (masticatory) mucosa, movement from 1 The proof of the merit of this type of restoration lies in the to 3 mm can be expected knowledge that: CLASP – RETAINED PARTIAL DENTURE – most commonly used RPD (1) it permits treatment for the largest number of patients at a Disadvantages: Strain on abutment teeth, clasps can be unesthetic, caries reasonable cost; may develop beneath clasp (2) it provides restorations that are comfortable and efficient over a long period of time, with adequate support and maintenance of INTERNAL ATTACHMENTS – eliminates some disadv of clasps occlusal contact relations; (3) it can provide for healthy abutments, free of caries and Advantage: Esthetic periodontal disease; Disadvantages: Higher cost, excessive torsional load (4) it can provide for the continued health of restored, healthy tissue of the basal seats; and Most commonly cited problem associated with RPD is INSTABILITY (5) it makes possible a partial denture service that is definitive and Control of combined vertical (tissue-ward) and horizontal not merely an interim treatment movement is most critical and places a premium on tooth modifications (rest and stabilizing component CHAPTER 3: CLASSIFICATION OF PARIALLY CHAPTER 4: BIOMECHANICS OF REMOVABLE PARTIAL EDENTULUOS ARCHES DENTURES Open ended means that problems typically have more than one The purpose of this system of classification is to facilitate treatment solution, decisions on the basis of treatment complexity. Ill structured means that solutions are not the result of standard mathematical formulas used in some structured manner. Complexity is determined from four broad diagnostic categories: location and extent of the edentulous areas, condition of the abutments, BIOMECHANICAL CONSIDERATIONS occlusal characteristics and requirements, RPD supporting structures: (abutment tooth, residual ridges) and residual ridge characteristics Whether the supporting structures are capable of resisting the applied forces depends on: KENNEDY METHOD – most widely accepted classification (1) what typical forces require resistance, (2) what duration and intensity these forces have, Dr. Edward Kennedy (1925) (3) what capacity the teeth, implant(s) and/or mucosae have to resist these forces, REQUIREMENTS OF AN ACCEPTABLE METHOD OF CLASSIFICATION (4) how material use and application influence this teeth-tissue resistance, and 1. It should permit immediate visualization of the type of partially (5) whether resistance changes over time edentulous arch that is being considered. 2. It should permit immediate differentiation between the tooth- supported and the tooth- and tissue-supported removable partial Consideration of the forces inherent in the oral cavity is critical. denture. This includes the direction, duration, frequency, and magnitude of 3. It should be universally acceptable the force. The longer the handle, the less effort it takes IMPACT OF IMPLANTS ON MOVEMENTS OF PARTIAL DENTURES Use of an implant should be directed toward the most beneficial movement control 3 desired principles demonstrated by prostheses: support, stability, retention But major functional demand is chewing Greatest benefit- resisting instability by improving support SIMPLE MACHINES RULES GOVERNING APPLICATION OF THE KENNEDY METHOD TWO GENERAL CATERGORIES: simple, complex (1) Classification should follow rather than precede any Complex: combination of simple machines extractions of teeth that might alter the original Simple: LWS WPI classification. (1) LEVER – rigid bar supported somewhere along its length (2) If a third molar is missing and is not to be replaced, it is not Fulcrum – support point of the lever, and lever can move around the considered in the classification. fulcrum (3) If a third molar is present and is to be used as an THREE TYPES OF LEVERS: abutment, it is considered in the classification. Rule 4 If a First class- fulcrum positioned between load and the force second molar is missing and is not to be replaced, it is not Second class- fulcrum is on one end of the machine and the one in considered in the classification (e.g., if the opposing between in load/ resistance second molar is likewise missing and is not to be replaced). Third class- fulcrum is on one end of the machine and one in (4) The most posterior edentulous area (or areas) always between is the force or effort determines the classification. (5) Edentulous areas other than those that determine the (F) fulcrum/ occlusal rest, (R) resistance, (E) direction of force/ classification are referred to as modifications and are effort, occlusion or gravity designated by their number. (6) The extent of the modification is not considered, only the Cantilever beam- beam supported at one end that can act as first- number of additional edentulous areas. class lever, should be avoided (7) No modification areas can be included in Class IV arches. (2) WEDGE (Other edentulous areas that lie posterior to the single (3) SCREW bilateral areas crossing the midline would instead (4) WHEEL AND AXLE determine the classification; see Rule 5. (5) PULLEY (6) INCLINED PLANE Machines that should be avoided in RPD: CHAPTER 5: MAJOR AND MINOR CONNECTORS Lever, wedge, inclined plane Components of a typical removable partial denture : 1. Major connectors A tooth is apparently better able to tolerate vertically directed 2. Minor connectors forces than nonvertical, torquing, or horizontal forces. This 3. Rests characteristic is observed clinically, and it seems rational that more 4. Direct retainers periodontal fibers are activated to resist the application of vertical 5. Stabilizing or reciprocal components (as parts of a clasp assembly) forces to teeth than are activated to resist the application of 6. Indirect retainers (if the prosthesis has distal extension bases) nonvertical force 7. One or more bases, each supporting one to several replacement teeth POSSIBLE MOVEMENTS OF PARTIAL DENTURES (3) 1) SAGITTAL Rotation around a fulcrum line passing through the The chief functions of a major connector include: most posterior abutments when the denture base moves 1) unification of the major parts of the prosthesis, vertically toward or away from the supporting residual ridges; 2) distribution of the applied force throughout the arch to -can be controlled in tooth bound denture selected teeth and tissue, 2) FRONTAL Rotation around a longitudinal axis formed by the 3) and minimization of torque to individual teeth crest of the residual ridge; and -much less in tooth bound denture bc of posterior abutments CROSS-ARCH STABILITY – 3) HORIZONTAL Rotation around a vertical axis located near the center of the arch. ROLE OF MAJOR CONNECTORS OF PROSTHESIS -occurs in all partial dentures, it stabilizes components against MOVERMENT horizontal movement MAJOR CONNECTOR – provides cross-arch stability Connects the parts of the prosthesis LOCATION 1. Major connectors should be free of movable tissue. 2. Impingement of gingival tissue should be avoided. 3. Bony and soft tissue prominences should be avoided during placement and removal. 4. Relief should be provided beneath a major connector to prevent its settling into areas of possible interference, such as inoperable tori or elevated median palatal sutures. 5. Major connectors should be located and/or relieved to prevent impingement of tissue that occurs because the distal extension denture rotates in function. - Superior border of a lingual bar connector be located a minimum of 4 mm below the gingival margin(s) - Borders of the palatal connector minimum of 6mm away from gingival margins MANCDIBULAR MAJOR CONNECTORS (LLS LCL) 1. LINGUAL BAR half pear shaped, usually made up of reinforced, 60guage, half pear-shaped wax/ plastic pattern, 2. LINGUOPLATE should be made thin as possible, not serve as indirect retainer. (Interrupted linguoplate – presence of interproximal spaces) 3. SUBLINGUAL BAR use when 4mm is not allowed Contraindication- interfering lingual tori 4. LINGUAL BAR WITH CINGULUM BAR 5. CINGULUM BAR excessive block out of interproximal undercuts, wide diastema 6. LABIAL BAR Swing-lock design - consists of a labial or buccal bar that is connected to the major connector by a hinge at one end and a latch at the other end Combination anterior and posterior palatal strap–type connector Palatal plate-type connectors: A. Single Broad Palatal Major Connector B. Complete Palatal Coverage Major Connector DESIGN OF MANDIBULAR MAJOR CONNECTORS Step 1: Outline the basal seat areas on the diagnostic cast Step 2: Outline the inferior border of the major connector Step 3: Outline the superior border of the major connector Step 4: Connect the basal seat area to the inferior and MINOR CONNECTORS serve as the connecting link between the major connector or the base of a removable partial denture and the other components of the prosthesis, such as the clasp assembly, indirect retainers, occlusal rests, or cingulum rests FUNCTIONS: serve 2 purposes 1. Transfers functional stress to the abutment teeth: superior borders of the major connector, and add minor 2. Transfers the effects of the retainers, rests, and connectors to retain the acrylic resin denture base material stabilizing components throughout the prosthesis MAXILLARY MAJOR CONNECTORS (SCP USA) FORM AND LOCATION 1. EMBRASURE MINOR CONNECTOR 1. Single palatal strap denture base framework -Bilateral tooth-supported prostheses, (may 2. PROXIMAL GUIDING PLATE also be unilateral w/ provision of cross arch minor connector must be wide enough that the guiding plane -class III can be used to fullest advantage 2. Combination anterior and posterior 3. DENTURE BASE FRAMEWORK palatal strap–type connector acrylic-resin denture attaches bases -Used in any max PD, flat and min of 8mm -angles formed at the junctions of the connectors wide should not be greater than 90 degrees, thus ensuring the -class II and IV most advantageous and the strongest mechanical connection 3. Palatal plate-type connector between the acrylic-resin denture base and the major -class I connector. -covers 2/3 Complete coverage palatal major connector TISSUE STOPS 4. U-shaped palatal connector -retention of acrylic-resin bases - least rigid type, used in inoperable palatal -preventing distortion of the framework torus 5. Single palatal bar FINISHING INDEX TISSUE STOPS - most widely used and yet the least logical of all palata -located distal to the terminal abutment and continuation of major connector the minor connector contacting the guiding plane Less than 8mm – Palatal bar More than 8mm – Strap FINISHING LINES - retention latticework. 6. Anterior-posterior palatal bars Sharp, definite, butt-type finish DESIGN OF MANDIBULAR MAJOR CONNECTORS lines are incorporated into Step 1: Outline of primary bearing areas: the metal because it is here Step 2: Outline of nonbearing areas that the acrylic resin meets Step 3: Outline of connector areas: the metal. Step 4: Selection of connector type -should take the form of an Step 5: Unification: angle not greater than 90 degrees, therefore being somewhat undercut CHAPTER 6: REST AND REST SEATS Rest: A rigid component of a removable partial denture which rests in a recessed preparation on the occlusal, lingual or incisal surface of a tooth to provide vertical support for the denture. a. Occlusal rest - a rest placed on the occlusal surface of a bicuspid or molar. b. Lingual (cingulum) rest - A rest placed on the cingulum of an anterior tooth (usually the canine). Rests may also be placed on the lingual of posterior teeth by creating a ledge of the tooth surface (prescribed for surveyed crowns). c. Incisal rest - A rest placed on an anterior tooth at the incisal edge. d. Intracoronal (precision) rest - A rest consisting of precision manufactured attachments that are placed within the coronal EXTENDED OCCLUSAL REST AND REST SEATS – Kennedy cII, contours of a crown or retainer m1 and Kennedy class III, extend occlusal rest to minimize further tipping of abutment Rest Seat: A portion of a tooth selected and prepared to INTERPROXIMAL OCCLUSAL REST AND REST SEATS – occlusal receive an occlusal, incisal or lingual rest. support is derived from floor of seat, horizontal stabilization near vertical walls FUNCTIONS OF RESTS INTERNAL OCCLUSAL REST 1. To direct forces along the long axis of the abutment tooth. 2. To prevent the denture base from moving cervically and impinging gingival tissue. 3. To maintain a planned clasp-tooth relationship. 4. To prevent extrusion of abutment teeth. 5. To provide positive reference seats in rebasing and/or impression procedures. 6. To serve as an indirect retainer by preventing rotation of the partial denture (Class I or II RPD’s only) PREPARATION OF REST SEATS Rests seats should be prepared using light pressure with a high-speed handpiece with or without water spray. Since minimal preparation is usually performed, minimal heat is generated. Good visibility is required so that water coolant can be eliminated. Since preparations are usually entirely in enamel it is best to avoid anesthesia so the patient can inform the dentist when sensitivity is felt. Occlusal rest seats can be prepared with medium round burs (#2 and primarily the #4 sizes). or diamonds (e.g., 801-016, 38006-135) Guiding planes and cingulum rest seats can be prepared with a long, medium diameter cylindrical bur or diamond (e.g., #57L; 8837K- 014) CHAPTER 7: DIRECT RETAINERS A removable dental prosthesis that engages an abutment tooth or implant to resist displacement of the prosthesis away from basal seat tissue. 2 MEANS OF PROVIDING RETENTION 1. PRIMARY RETENTION - mechanically by placing retaining elements (direct retainers) on the abutment teeth. 2. SECONDARY RETENTION - intimate relationship of the minor connector contact with the guiding planes and denture bases and of the major connector (maxillary) with underlying tissue BASIC PRINCIPLE OF CLASP DESIGN 1. PRINCIPLE OF ENCIRCLEMENT – more than 180 in the greatest circumference of the tooth In addition to encirclement, other basic principles of clasp design are as follows: 1. The occlusal rest must be designed to prevent movement of the clasp arms toward the cervical 2. Each retentive terminal should be opposed by a reciprocal component capable of resisting any transient pressures exerted by the retentive arm during placement and removal. Stabilizing or reciprocating arm will always be above 3. Clasp retainers on abutment teeth adjacent to distal survey line extension bases should be designed so that they If case is distal extension, minor connector should avoid direct transmission of tipping and rotational only be located mesiolingual, mesial lingual portion forces to the abutment of tooth 4. Unless guiding planes will positively control the path The terminal end should only be contacting the of removal and will stabilize abutments against undercut rotational movement, retentive clasps should be Mesiolingual of the tooth, not on the embrasure bilaterally opposed (i.e., buccal retention on one side of the arch should be opposed by buccal retention on the other, or lingual on one side opposed by TYPED OF DIRECT RETAINERS lingual on the other) EXTRACORONAL INTRACORONAL 5. The path of escapement for each retentive clasp -Most used for rpd -May be cast/ attached terminal must be other than parallel to the path of -Uses mechanical totally restored natural removal for the prosthesis to require clasp resistance contours of an abutment engagement with the resistance to deformation that -has 3 principal forms tooth is retention 1) clast-type retainer -Internal/ precision 6. The amount of retention should always be the 2)manufactured attachment minimum necessary to resist reasonable dislodging attachments forces. 3)lient extra coronal 7. Reciprocal elements of the clasp assembly should be located at the junction of the gingival and middle attachment thirds of the crowns of abutment teeth CRITERIA FOR SELECTING A GIVERN CLASP DESIGN The terminal end of the retentive arm is optimally placed in CIRCUMFERENTIAL CLASP ARM – tooth bounded the gingival third of the crown, retentive RPI/ I-BAR CLASP ARM – distal extension CLASP ASSEMBLY Plate- refers to prosthesis 1/ more minor connectors Plane – refers to tooth The pricincal test Retentive clasp Reciprocal clasp  2 STRATEGIES TO CHANGE THE FULCRUM LOCATION MESIAL REST CONCEPT – to give further support 3 BASIC APPROCHES TO APPLICATION OF RPI 1) guiding plane and the corresponding proximal plate minor connector should extend the entire length of the proximal tooth surface, free gingival margin 2) guiding plane and the corresponding proximal plate minor connector should extend from the marginal ridge to the junction of the middle and gingival thirds of the proximal tooth surface 3) The third approach favors a proximal plate minor connector that contacts approximately 1 mm of the gingival portion of the guiding plane, retentive clasp arm located in a 0.01-inch undercut RPI Rest, proximal plate, I-bar RPA Rest, proximal, aker’s retentive arm(always wrought c) 4mm from the gingival down connecting to the I-bar wire) (shallow buccal or labial vestibules) CLASP DESIGN TO ACCOMMODATE FUNCTIONAL MOVEMENT CLASP DESIGN TO ACCOMMODATE WITHOUT 1)RPI –(a) mesio- occlusal rest w minor connector FUNCTIONAL MOVEMENT placed mesiolingual embrasure but not contacting 1) Circumferential (Circle or Akers) clasp adjacent tooth -(a)most simple and versatile clasp - the retentive arm begins above the height of contour, and curves and tapers to its terminal tip, in the gingival 1/3 of the tooth, well away from the gingiva 2. Ring clasp BAR CLASP – (b) roach clasp arm, contact 1mm of gingival portion of GP 2)RPA – (a) used when there is an insufficeient vestibule depth/ width, iindicated when a bar-type clasp is contraindicated and a desirable undercut is located in the gingival third of the tooth away from the extension - (b) Encircles nearly the entire abutment tooth base area - used when a proximal undercut cannot be approached by other means. 3. Embrasure (Double Akers) Clasp - no edentulous spaces are available on the opposite side of the arch to aid in clasping. 3)COMBINATION CLASP – (b) used for its adjustability when precise retentive requirements are unpredictable and later adjustment to increase/ decrease retention may be necessary CHAPTER 8: INDIRECT RETAINERS distance of a resisting element from the fulcrum line. - a RPD that prevents rotational displacement of the denture about the rests of the principal abutment teeth Cingulum bars (continuous bars) and linguoplates - usually take the form of rests, on the opposite side of a Ø Technically, these are not indirect retainers because they fulcrum line rest on unprepared lingual inclines of anterior teeth. The indirect retainers are actually the terminal rests at either end that occur in the form of auxiliary occlusal rests or canine rests. Modification areas Ø The occlusal rest on a secondary abutment in a Class II partial denture with modification may serve as an indirect retainer. This use will depend on how far from the fulcrum line the secondary abutment is located. Rugae support The fulcrum line on a Class I partial denture as passes through Ø Usually part of a palatal horseshoe design. The coverage of the rest areas of the most posterior abutment on either side the rugae area of the maxillary arch of the arch (A and B). On a Class II partial denture, the as a means of indirect retention is considered because the fulcrum line is always diagonal, passing through the occlusal rugae area is firm and usually well rest area of the abutment on the distal extension side and situated to provide indirect retention for a Class I removable occlusal rest area of the most distal abutment on the other partial denture. side (C). If a modification area is present on that side, the additional abutment lying between the two principal abutments may be used for support of the indirect retainer if it is far enough removed from the fulcrum line (D). In a Class IV partial denture, the fulcrum line passes through the two abutments adjacent to the single edentulous space (E and F). In a tooth and tissue supported Class III partial denture, the fulcrum line is determined by considering the weaker abutment as nonexistent and that end of the base as being a distal extension (G and H) FACTORS INFLUENCING THE EFFECTIVENESS OF AN INDIRECT RETAINER INCLUDE: 1. Proper seating of the denture 2. Distance from the fulcrum line 3. The rigidity of the connectors supporting the indirect retainer 4. The effectiveness of the supporting tooth surface. FORMS OF INDIRECT RETAINER Auxiliary occlusal rest Ø the most commonly used indirect retainer and is located on an occlusal surface and as far away from the distal extension base as possible. Canine rests Ø Used when the mesial marginal ridge of the first premolar is too close to the fulcrum line, or when the teeth are overlapped so that the fulcrum line is not accessible Canine extensions from occlusal rests Ø Finger extension from a premolar rest is used to effect indirect retention by increasing the CHAPTER 9: DENTURE BASE CONSIDERATIONS 4. Low specific gravity, lightweight in the mouth 5. Sufficient strength; resistance to fracture or distortion FUNCTIONS OF DENTURE BASE 6. Easily kept clean 7. Esthetic acceptability 1. Supports the artificial teeth and receives functional forces from occlusion 8. Potential for future relining 9. Low initial cost 2. Adds to the cosmetic effect – more on the bone 3. Stimulates underlying tissue Are flexible dentures ideal - not ideal but esthetically pleasing TOOTH-SUPPORTED PATIAL DENTURE BASE -failed potential for future relining ✓ Serve to prevent horizontal migration of all abutment teeth ✓ Prevent vertical migration of teeth in opposing arch MATERIALS USED IN DENTURE BASE ✓ Future relining or rebasing may not be necessary METAL ACRYLIC RESIN DISTAL EXTENSION PATIAL DENTURE BASE ✓ Thermal conductivity ✓ Ability to reline ✓ Support from the underlying ridge tissue becomes ✓ Accuracy and ✓ Esthetic advantage increasing important as the distance of these bases permanence in form ✓ Repairable from the abutment increases ✓ Hygiene ✓ Rate of resorption – increase bc no support ✓ Weigh and bulk RETENTION OF DENTURE BASES HAS BEEN DESCRIBED AS RETENTION OF DENTURE BASES THE RESULTOF THE FOLLOWING FORCES 1) PRIMARY RETENTION 1. ADHESION – attraction of saliva to denture and tissues Accomplished mechanically by placing retaining 2. COHESION- attraction of molecules of saliva to each other elements (direct retainers, framework itself) on the 3. ATMOSPHERIC PRESSURE dependent on a border seal abutment teeth and results in a partial vacuum beneath the denture 2) Secondary retention base when a dislodging force is applied Provided by the intimate relationship of denture bases and 4. PHYSIOLOGIC MOLDING OF THE TISSUES AROUND THE major connectors (max) w underlying tissues POLISHED SURFACES OF THE DENTURE 5. THE EFFECTS OF GRAVITY ON THE MANDIBULAR SNOW SHOE PRINCIPLE DENTURE If wider support, equal distribution Support is more on the ridge than in the abutment METHODS OF ATTACHING DENTURE BASES Acrylic resin Metal bases bases Attachment attached by integral parts of means of a minor partial denture connector framework Base 1.5mm resin casted together thickness w framework Artificial teeth plastic mesh to follow after casting Acrylic resin – pinhead sticks on pin head, diathoric holes Cement - Proceed directly to metal – metal framework pinhead Cast w/ the framework – when space is too limited Chemical bonding – tribochemical coating Ideal denture base material 1. Accuracy of adaptation to the tissues, w minimal volume change 2. Dense, non-irritating surface capable of receiving and maintaining a good finish. (Mandibular mas dense or compacted) 3. Thermal conductivity