L8-YI-RPD Lecture-Advanced Prosth 2023_updated.pdf

Anna Yi, BDSc, MSD, DMSc, FACP Clinical Applications of Removable Partial Dentures Advanced Prosthodontics 2023 Anna Yi, BDSc, MSD, DMSc, FACP Clinical Assistant Professor Department of Prosthodontics Rm 631-S [email protected] Adapted from Dr. A. Soni’s lecture Anna Yi, BDSc, MSD, DMSc, FACP Any questions ➡ please email me and I will collate and organize the answers to be shared during our panel discussion Anna Yi, BDSc, MSD, DMSc, FACP Lecture Objectives • Be able to discuss the di erences between the various types of major connectors and select the most appropriate major connector for a given arch. • Be able to utilize di erent clasp designs as required • *Reason: ideal survey lines cannot always be achieved* Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • ff Be able to discuss the various types of rests available using the criteria of force distribution to correctly select the appropriate rests ff • Anna Yi, BDSc, MSD, DMSc, FACP Lecture Objectives • Be able to discuss the di erences between the various types of major connectors and select the most appropriate major connector for a given arch. • Be able to utilize di erent clasp designs as required • *Reason: ideal survey lines cannot always be achieved* Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • ff Be able to discuss the various types of rests available using the criteria of force distribution to correctly select the appropriate rests ff • Anna Yi, BDSc, MSD, DMSc, FACP Maxilla Anna Yi, BDSc, MSD, DMSc, FACP Maxillary Major Connectors 1. Palatal bar connector 2. U-shaped (horseshoe) 3. Palatal Strap 4. Anteroposterior palatal bar 5. Anteroposterior palatal strap 6. Complete palatal plate *remember: there are 6 for maxilla my friends* Anna Yi, BDSc, MSD, DMSc, FACP Mx: Palatal bar connector • Crosses the palate • Relatively narrow anteroposteriorly Cue for discussion points Consider the mechanical consequences of this narrowness on cross-arch bracing action Anna Yi, BDSc, MSD, DMSc, FACP Mx: Palatal bar connector Discussion points • If placed too anteriorly will interfere with the action of the tongue • Not rigid as it is narrow in size • A palatal bar is not a good choice Anna Yi, BDSc, MSD, DMSc, FACP Mx: U-shaped connector • Consists of a thin sheet of metal • Exposed palate = patients sometimes prefer this 😊 fl fi Cues for discussion points Consider the mechanical consequences of a thin sheet of metal on exure What are the bene ts of exposed palate? Anna Yi, BDSc, MSD, DMSc, FACP Mx: U-shaped connector Discussion points • Thin sheet of metal ➡ less resistance to exure • Hence ➡ poor choice for • Distal extension RPD, or • Extensive edentulous span • Flexure ➡ torsional force ➡ may damage the abutment teeth (periodontium) • Exposed palate: pt comfort (gag re ex pts), minor salivary glands, eating fl fl experience (sensory ➡ proprioception, temperature, “taste”) Anna Yi, BDSc, MSD, DMSc, FACP Mx: Palatal strap • Variations • Anterior palatal strap / Posterior palatal strap • Dimension • Antero-posteriorly 13 - 20 mm, minimum 8 mm • Rigidity can be increased by thickening the mid section to approx. 1.5mm • Design • Directly or obliquely traverses the palate • Generally located in the area of the second premolar and rst molar • Placing it in two planes increases its rigidity fi Cues for discussion points Consider the indications given the design features Compare the comfort level cf. palatal bar Anna Yi, BDSc, MSD, DMSc, FACP Mx: Palatal strap • Discussion points • Strap is thinner than bar • • More comfortable to patients Indications • Presence of torus - can circumvent it • Anterior strap: missing anterior teeth • Posterior strap: tooth borne RPD especially in Kennedy class lll Anna Yi, BDSc, MSD, DMSc, FACP Mx: Antero-posterior palatal strap/bar • A maxillary major connector having an anterior/posterior strap/bar • Dimension • Both anterior and posterior straps width should be minimum 8 mm Cue for discussion point *Flex your RPD knowledge muscles* ➡ Consider the indications given the design features Anna Yi, BDSc, MSD, DMSc, FACP Mx: Antero-posterior palatal strap/bar • Indications • Can be used for both ‘tooth borne’ or ‘tooth and tissue borne' RPD • Used when torus is present and is not to be removed • For long-span distal extension bases where rigidity is critical Anna Yi, BDSc, MSD, DMSc, FACP Mx: Complete palatal plate • A maxillary major connector covering the entire palate • Complete cast metal covering the entire palate • Combination of anterior metal and posterior resin • Design • Metal should be extended to the vibrating line and beaded • Posterior palatal seal (PPS) • Create PPS if combination of anterior metal and posterior resin is used (e.g. planning for complete denture) • No PPS needed if no CD is contemplated Cues for discussion points Consider pros, cons and indications Anna Yi, BDSc, MSD, DMSc, FACP Mx: Complete palatal plate • Pros • Provides ultimate rigidity and support for the RPD • Full metal palate ➡ thermal conductivity • Prevents bacterial overgrowth (eg. C. Albicans) • • Since metal = non-porous (cf. acrylic resin) ➡ healthier to the tissue Cons • Potential phonetic problem due to extensive coverage • Indications • • Few anterior teeth are remaining No tori are present Anna Yi, BDSc, MSD, DMSc, FACP Steps for designing RPD 1. Outline denture bearing areas (denture base areas) 2. Outline non-bearing areas 3. Outline bar areas 4. Select the bar type fi 5. Uni cation Also important • Minor connectors • Clasps • Rests • Guide planes Adapted from L. Blatterfein Anna Yi, BDSc, MSD, DMSc, FACP Considerations for Maxillary Major Connectors • Comfort • Minimum bulk • Positioned so that it is least detectable e.g. posterior strap • Rigidity • Double/A-P straps, full coverage: provide maximum rigidity • Edentulous saddle location • Choice of bar is dictated by the location of the edentulous region • Indirect retention • Mostly needed in the free-end saddle cases • Long edentulous span • Ridges lacking vertical height Anna Yi, BDSc, MSD, DMSc, FACP Mandible Anna Yi, BDSc, MSD, DMSc, FACP Mandibular Major Connectors • Lingual bar • Sublingual Bar • Lingual Plate • Interrupted Lingual Bar • Kennedy Bar or cingulum bar • Labial Bar Anna Yi, BDSc, MSD, DMSc, FACP Functional depth of lingual sulcus Measuring functional depth of lingual sulcus • Measurement is made from the oor of the mouth to the gingival margin of teeth • Ask patient to raise tongue and gently touch the vermillion border of upper lip fl • Anna Yi, BDSc, MSD, DMSc, FACP Lingual major connector: Relief • A: if the soft tissues are vertical or nearly so, only minimal relief is required A • Lingual Plate B: tissues that slope toward the tongue require the greatest amount of relief B Anna Yi, BDSc, MSD, DMSc, FACP Md: Lingual bar • Most common design • Indication • Functional depth of the lingual sulcus ≥ 7 mm • Design • Half pear shaped bar with 4 mm in height and 2 mm in width • Inferior border is rounded so as not to impinge on the lingual tissue in the oor of the mouth • Should be relieved on the tissue surface with fl 28 G wax Anna Yi, BDSc, MSD, DMSc, FACP Md: Sublingual bar • Variation of the Lingual Bar • Indication • Functional depth of the lingual sulcus is 5 mm • When the space does not allow to place a Lingual Bar • Design • Essentially a lingual bar but rotated 45 to 90 degrees • Half-pear shape with 2 mm in height and 4 mm in width because of this it is more rigid than the Lingual Bar in the horizontal direction Anna Yi, BDSc, MSD, DMSc, FACP Md: Lingual plate • Design • Superior margin is placed near the junction of Middle and Gingival third, extending interdentally to the contact points. *Should not be placed above the middle third.* • Superior margin should be thin and must contact the tooth • In the presence of overlapping/crowded teeth the lingual interproximal surfaces must be recontoured • There should be relief between the tissue surface of the plate and soft tissue • Terminal abutments must have rest seats to prevent facial movement of teeth 👉 Given the images and design considerations, think about its clinical indications 👈 Anna Yi, BDSc, MSD, DMSc, FACP Md: Lingual plate • Indications • Functional depth of the lingual sulcus < 5mm • Presence of Lingual Tori • High Lingual Frenum • Future loss of anterior teeth are anticipated (allows for addition of teeth to RPD) Anna Yi, BDSc, MSD, DMSc, FACP Md: Interrupted lingual bar • Interrupted Lingual Bar is basically the same as the Lingual Plate • Used when there are diastema (plural – diastemata) in the anterior teeth Anna Yi, BDSc, MSD, DMSc, FACP Md: Kennedy bar/double lingual bar/cingulum bar • Kennedy Bar is another variation of Lingual Bar • In addition to the Lingual Bar, it includes the Cingulum Bar • Not a good choice because of the large open space between the Lingual Bar and the Cingulum Bar leading to food impaction • Closing the open space with metal eliminates the food impaction and becomes a Lingual Plate which is a better choice Anna Yi, BDSc, MSD, DMSc, FACP Md: Labial bar • Indications • Severely lingually tilted mandibular teeth • Extremely large tori which cannot be removed • Design considerations • Must have adequate labial sulcus depth > 7 mm to fabricate a Labial Bar • Superior border 4 mm from gingival margin • Check for interferences with labial or buccal frenum • Need relief under the bar as all mandibular major connectors Anna Yi, BDSc, MSD, DMSc, FACP Lecture Objectives • Be able to discuss the di erences between the various types of major connectors and select the most appropriate major connector for a given arch. • Be able to utilize di erent clasp designs as required • *Reason: ideal survey lines cannot always be achieved* Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • ff Be able to discuss the various types of rests available using the criteria of force distribution to correctly select the appropriate rests ff • Anna Yi, BDSc, MSD, DMSc, FACP Clasps fi Anna Yi, BDSc, MSD, DMSc, FACP Types of Clasps • Suprabulge or Circumferential clasps • Akers clasp / cast circumferential / circlet • Hairpin clasp / C clasp / shhook clasp /reverse loop • • Ring clasp Embrasure clasp • • Extended arm clasp • Overlay clasp / onlay clasp Infrabulge / bar clasps/ roach clasps/ vertical projection • • L, I, S, T, U, Y Combination clasps • Cast clasp with wrought wire clasp Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps Akers Clasp / Cast Circumferential (CCC) / Circlet • CCC most commonly used • Rest - Bracing Arm – Retentive Arm – Minor Connector • Design of choice for tooth supported RPD Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps Hairpin Clasp / C Clasp / Fishhook Clasp / Reverse loop • Used when Atypical A survey line exists • Undercut in the near zone at the facial or lingual • Superior margin of the retentive arm must not interfere with the occlusion • Cannot be used in short teeth • Disadvantage: food trap Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps MESIAL Ring Clasp • Indicated on tipped mandibular molars • Retentive clasp engages the ML or MB undercut BUCCAL Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps Embrasure Clasp Two CCC clasp joined together in the body facing in opposite directions • Mostly indicated when there are no edentulous space on the other side of the arch • Rest seats must be prepared with su cient depth to accommodate the rests to prevent interference with the occlusion • Need to prepare marginal ridges to create space for adequate bulk of metal, or else the clasps will fracture • When preparing, marginal ridges should maintain contact points ffi • Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps Extended Arm Clasp Similar to CCC but covers two teeth • Remains above the survey line on the rst tooth and crosses into the undercut of adjacent tooth fi • Anna Yi, BDSc, MSD, DMSc, FACP Suprabulge clasps Overlay / Onlay Clasp • The rest covers the occlusal surface of a tilted molar from which the clasps originate • Helps in establishing the proper plane of occlusion • Eliminates the need for a crown Anna Yi, BDSc, MSD, DMSc, FACP Infrabulge clasps AKA Infrabulge / bar clasps / roach clasps / vertical projection • There are many variations of the Infrabulge clasps • They are often referred to by the names of the letters they resemble • The most common types used are the I, T • In an RPI Removable Partial Denture the I bar is used • The infrabulge clasp approaches the undercut from the gingival direction • They exhibit a push type (Tripping action) rather than pull type of retention of the suprabulge clasps • The push type exerts a tripping action L I S T U Anna Yi, BDSc, MSD, DMSc, FACP Infrabulge: RPI Assembly RPI = Rest, Proximal Plate and I Bar • Esthetic advantage • Used in tooth mucosa borne partial dentures • Concept of mesial rest • As the rest is moved mesially the forces on the RPD become vertical and less damaging to the abutment tooth and the ridges • Mesial vs distal rest - a well fabricated RPD supported by abutments with healthy periodontium and 70% or more bone support, and adherence to a 6 month regular recall program, is an acceptable treatment modality (Kapur KK, Dent RJ, JPD 1994) Anna Yi, BDSc, MSD, DMSc, FACP Infrabulge: RPI Assembly R F E R 1st class F R F E E E F R 2nd class Anna Yi, BDSc, MSD, DMSc, FACP Infrabulge: RPI Assembly RPI = Rest, Proximal Plate and I Bar • Contraindications • Insu cient vestibular depth ➡ A functional vestibular depth of 5mm is required • Deep tissue undercut ➡ A deep undercut forms a food trap • Lack of facial undercut ➡ Due to buccal or lingual tilt of abutments • Mesial inclination of Abutments ➡ No undercut present gingival to the distal proximal guide plane. The proximal plate cannot disengage from the tooth during function • Combined with a lingual plate ffi ➡ Will produce buccal torquing during function Anna Yi, BDSc, MSD, DMSc, FACP Combination clasp • Consists of a Rest, Cast reciprocal arm and a Retentive Wrought Wire Clasp • Advantage of this clasp is its exibility and can be easily adjusted • Commonly used on weak abutments which cannot tolerate a cast clasp • Since used in smaller diameter are more esthetic compared to cast clasps fl Due to its exibility ➡ less chances of fracture fl • Lingual Buccal Anna Yi, BDSc, MSD, DMSc, FACP Surveying Anna Yi, BDSc, MSD, DMSc, FACP Ideal Survey Line Anna Yi, BDSc, MSD, DMSc, FACP Type of survey lines Anna Yi, BDSc, MSD, DMSc, FACP Type of surveylines and location of undercuts Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps Treatment option for Atypical A Survey line • Hairpin Clasp / C Clasp / Fishhook Clasp / Reverse loop • Undercut is in the near zone at the facial or lingual • Superior margin of the retentive arm must not interfere with the occlusion • Cannot be used in short teeth • Disadvantage: food trap 👉 If you haven’t paid attention: same notes as slide 34 👈 Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Treatment option for Atypical A Survey line • Reverse Circlet / Reverse attachment clasp arm • Occlusal rest: far side • Terminal 1/3 of retentive clasp: engages into undercut at near side • Must create space between the embrasure between the contact area where the clasp crosses the occlusal surface ffi • Insu cient space will interfere with opposing occlusion Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Treatment option for Atypical A Survey line • Use Roach Clasp / Infrabulge Clasp L or T to engage the undercut • Cannot be used if the sulcus depth is shallow Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Please provide 3 clasp options for Atypical A Survey line Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Please provide 3 clasp options for Atypical A Survey line Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Treatment options for Atypical B Survey line • Recontour tooth to move the survey line • Fabricate a survey crown Anna Yi, BDSc, MSD, DMSc, FACP Atypical survey lines and clasps • Treatment option for Atypical C Survey line • Extended arm clasp Anna Yi, BDSc, MSD, DMSc, FACP Lecture Objectives • Be able to discuss the di erences between the various types of major connectors and select the most appropriate major connector for a given arch. • Be able to utilize di erent clasp designs as required • *Reason: ideal survey lines cannot always be achieved* Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • ff Be able to discuss the various types of rests available using the criteria of force distribution to correctly select the appropriate rests ff • Anna Yi, BDSc, MSD, DMSc, FACP Rests Anna Yi, BDSc, MSD, DMSc, FACP Rests • Rest Seat: The prepared recess in a tooth or restoration created to receive the occlusal, incisal, cingulum, or lingual rest Anna Yi, BDSc, MSD, DMSc, FACP Types of Rests 1. Occlusal rests • Conventional • Extended 2. Incisal rests • Overlay / Onlay 3. Cingulum rests • Interproximal • Auxiliary or Secondary Anna Yi, BDSc, MSD, DMSc, FACP Occlusal rests • Maintains components of RPD in their planned positions • Prevents settling of the dentures • Prevents impingement of the tissues • Directs and distributes occlusal loads to abutment teeth • Transmits forces along the long axis of the abutment teeth • Help transmit lateral or horizontal forces applied to RPD during function • Prevents food impaction where the rest is adjacent to the abutment tooth Anna Yi, BDSc, MSD, DMSc, FACP Overlay / onlay rest • Tipped Molars • Establish occlusal plane • Eliminate the need for cast restoration on abutment tooth • Prevents further tipping • Clasps may originate from the overlay rest to engage the undercuts Anna Yi, BDSc, MSD, DMSc, FACP Interproximal rest • Embrasure preparation > 1.5 mm • An embrasure clasp is essentially two CCC joined at their bodies • Frequently used on the side where there is no edentulous space • Clasps originate from a minor connector that traverses the marginal ridges between teeth Anna Yi, BDSc, MSD, DMSc, FACP Interproximal rest Marginal ridges and adjacent facial inclines must be prepared to ensure a su cient metal bulk for clasp strength • Inadequate preparations will result in thin metal that causes fracture of the clasp • Occlusal rests should be properly prepared to accommodate the rests and to avoid occlusal problems ffi • Anna Yi, BDSc, MSD, DMSc, FACP Auxiliary / secondary rests / indirect retainer • A denture base that is supported at one end by a healthy natural abutment and at the other by movable soft tissues will rotate toward or away from the residual ridge when subjected to occlusal forces or the pull of sticky foods • This rotation occurs along an imaginary line called fulcrum line • Indirect retainers are used to prevent this rotation Anna Yi, BDSc, MSD, DMSc, FACP Auxiliary / secondary rests / indirect retainer • Indirect Retainer • • Indirect Retention • ff The component of a partial removable dental prosthesis that assists the direct retainer(s) in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of the fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line The e ect achieved by one or more indirect retainers of a partial removable denture prosthesis that reduces the tendency for a denture base to move in an occlusal direction or rotate about the fulcrum line Anna Yi, BDSc, MSD, DMSc, FACP Auxiliary / secondary rests / indirect retainer • Kennedy Class I, Class II, Class IV RPDs require indirect retention • Kennedy Class lll do not require indirect retention because it is tooth borne RPD Anna Yi, BDSc, MSD, DMSc, FACP Auxiliary / secondary rests / indirect retainer • Any of the following rests can act as an indirect retainer • Occlusal • Cingulum • Embrasure • Incisal Anna Yi, BDSc, MSD, DMSc, FACP Incisal rest • Incisal rests are prepared on the incisal edges • Mostly used on the canines • Dimensions ➡ depth 1.5 mm x width 2.5 mm • Esthetic disadvantage ➡ patient should be informed of its esthetic impact similar to the 20 degree facets / MD Clasp as in the picture on the right • When compared to a cingulum rest (A) the incisal rest (B) may deliver potentially harmful forces because of the greater distance from the abutment’s center of rotation Anna Yi, BDSc, MSD, DMSc, FACP Cingulum rest • Cingulum rest is preferred over the incisal rest • Dimensions ➡ width 2.5 mm x depth 1.5 mm same as incisal rests • Mostly used on Maxillary canines because of the well developed cingulum • Mandibular canines do not have well developed cingulum and a cast restoration may be placed either by a cast metal rest seat bonding, pin inlay or a survey crown Anna Yi, BDSc, MSD, DMSc, FACP Lecture Objectives • Be able to discuss the di erences between the various types of major connectors and select the most appropriate major connector for a given arch. • Be able to utilize di erent clasp designs as required • *Reason: ideal survey lines cannot always be achieved* Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • ff Be able to discuss the various types of rests available using the criteria of force distribution to correctly select the appropriate rests ff • Anna Yi, BDSc, MSD, DMSc, FACP Selecting retentive clasp as related to undercut Given the anatomy and location of retentive undercut, be able to select a retentive clasp with respect to material and con guration fi • Anna Yi, BDSc, MSD, DMSc, FACP Selecting retentive clasp as related to undercut Placing the retentive clasp terminal in a greater horizontal undercut will result in increased retention Angle of cervical convergence (θ) Placing the retentive clasp terminal in a greater angle of cervical convergence will result in increased retention Anna Yi, BDSc, MSD, DMSc, FACP Selecting retentive clasp as related to undercut Materials used in fabricating RPD • Chrome Cobalt • Wrought Wire Anna Yi, BDSc, MSD, DMSc, FACP Selecting retentive clasp as related to undercut Michael D Waldmeier, Joseph E Grasso, George J Norberg, Michael D Nowak. Bend testing of wrought wire removable partial denture alloys Original Research Article. J Prosthet Dent. 1996 Nov;76(5):559-65 Anna Yi, BDSc, MSD, DMSc, FACP Further reading • Dental Technician, Prosthetic, Navy Training Course. (1965 Revised Edition) • Phoenix, Rodney D. Stewart's Clinical Removable Partial Prosthodontics, 4th Edition. Quintessence Publishing (IL), 012008. • Carr, Alan B., David Brown. McCracken's Removable Partial Prosthodontics, 12th Edition. Mosby, 2011 • Michael D Waldmeier, Joseph E Grasso, George J Norberg, Michael D Nowak. Bend testing of wrought wire removable partial denture alloys Original Research Article. J Prosthet Dent. 1996 Nov;76(5):559-65 Anna Yi, BDSc, MSD, DMSc, FACP Good Job & Thank You :)

L8-YI-RPD Lecture-Advanced Prosth 2023_updated.pdf

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