Removable Partial Denture Planning PDF

# Removable Partial Denture Planning ## Assoc. Prof. Dr. Simge Taşın ## Resources - HAREKETLİ BÖLÜMLÜ PROTEZLER (Planning) - McCracken’s Removable Partial Prosthodontics (Twelfth Edition) ## The purpose of planning: - Forces acting on retention and stabilization - equalize - using pros...

# Removable Partial Denture Planning ## Assoc. Prof. Dr. Simge Taşın ## Resources - HAREKETLİ BÖLÜMLÜ PROTEZLER (Planning) - McCracken’s Removable Partial Prosthodontics (Twelfth Edition) ## The purpose of planning: - Forces acting on retention and stabilization - equalize - using prosthetic components - Preservation of remaining tissues - Maintaining oral hygiene ## Tissue Support - Length of residual crest - The contour of the residual crest - Support bone structure - The quality of the mucosa ### Length of residual crest As the length of the edentulous space increases, the tissue support of the denture base will increase. ### Contour of the Residual Ridge Plays an important role in the distribution of forces - Support (force absorption)-Stabilization - parallel side/wide crest - flat crest - Thin, small, knife-edge ### Quality of the Mucosa The area covered by the denture base - Thickness of mucosa - Soft, thin and mobile mucosa - support and stabilization #### Support areas of the Mandibular Jaw - *Buccal Shelf Area* (primary support) - *Retromolar Triangle Area* (Primary/secondary based on tissue density) - *Slopes of the residual ridge* (secondary support) #### Support areas of the Maxillary Jaw - *Posterior crest of the residual ridge* (primary support) - *Horizontal area of the hard palate* - *Slope of the ridge* (secondary support) ## Tooth Support ### Periodontal Health - Clinical & Radiographic - Quantity and quality of alveolar bone support (additional force) - Infection, luxation - Crown & root ratio | Ratio | |:---| | 1:2 | | 1:1 | | 2:1 | - Crown & root length and angulation - Crown-root morpholgy - cylindrical-thin-pointed root ### Position in the arc - Positioned outside the arc - Incomplete eruption - Tipped teeth ## Opposing occlusion: - Type of opposing jaw occlusion - Teeth in contact in opposing occlusion - Number of teeth in opposing jaw - Complete denture ## Tooth-supported, Class III RPD - Takes all support from the teeth like fixed prosthetics - Periodontal tissues - Bone ### Difference - No rigid connection - Movement during function - Non-axial forces ## Tooth-Tissue Supported Class I, II, IV RPD Support - In the areas close to the tooth, from the teeth - In the far region, from the crest / tissue ## Denture base movements depend on the following: - Degree of mucosa resiliency - Mount of bone resorption - Denture base fit-width - Characteristics of chewing forces ## Ability of the supporting tooth to withstand forces - Axial forces - Tilting and rotational forces ## Planes and Axes: - Movement in the human body occurs in three planes: - Horizontal - Sagittal - Frontal These planes intersect each other at *right angles*. - The intersection of any two planes creates a linear axis. - The rotational motion of an object around any of the three axes occurs in a plane passing perpendicular to the planes. ## While the removable partial denture is in function, the movements that occur as a result of the forces should be known, and the prosthetic components should be planned to prevent these movements. ## Inclined Plane and Lever Systems Forces are transmitted to the oral tissues according to the principles of the inclined plane and the lever. - Occlusal rests should be designed to prevent slipping **Lever:** A long bar supported from any region along its length. - The point at which it is supported is called the *fulcrum*. - The lever rotates around the fulcrum. - Three types of leverage are available ### Types of leverage - *First Class Leverage*: Fulcrum=support (F) in the middle, Force (K) & Resistance (D) = Load at both ends. Example: seesaw. - *Second Class Leverage*: Resistance (D) = load in the middle, Fulcrum = Support (F) at end & Force (K) at other end. Example: wheelbarrow movement. - *Third Class leverage*: Force (K) in the middle. Fulcrum-Support (F) & Resistance=Load (D) at the ends. Example: Fishing rod. #### First Class Lever Systems - *Disto-occlusal rest and circumferential clasp*: Disto-occlusal rest makes the fulcrum, Force distal to denture base, Clasp tip on the equator line, The support tooth is forced distally. - *Rotational movement of distal-extension denture*: The rotational movement of distal-extension denture around the axis of the primary fulcrum towards and away from the tissue. - The most harmful forces for RPD are first class leverage #### Second Class Lever systems - *Mesio-occlusal rest and bar clasp*: Less leverage and denture base movement, When the denture moves away from the tissue, the bar clasp tip moves away from the tooth. No harmful effects. #### Third Class Lever Systems - Tooth-supported cases: The denture base movements and the forces applied to the support teeth are very low. ## Mechanical Advantage - Leverage system's potential to increase force - Leverage action increases when the MA grows - Denture base movements increases - Damage to tissues increases - **It is an UNWANTED situation** - Mechanical Advantages= Force arm / Resistance arm ## Distal extension (free-end) prostheses do NOT have rigid supports. - Since it receives support from tissues with two different resilience (tooth and mucosa on the edentulous crest), it is exposed to many different forces and movements and creates more harmful forces in the supporting tissues. ### Components of Distal Extension - "Fulcrum line" - "fulcrum axis" - "rest line" - "support line" ### Fulcrum lines are classified and named in different ways: - **According to planes** - In distal extension (free-end) RPDs, rotational movements occur around three different fulcrums according to the planes. - The prosthesis components should be placed in a way that prevents these movements, considering that the denture can move in a combined way around these three fulcrums. - **According to the structural elements of the prosthesis** - The *primary retentive fulcrum (RF)* passes through the retainer ends of the clasps applied to the abutment teeth, is formed by the displacing forces in the gingivo-occlusal direction. - The *stabilizing fulcrum* passing through the rests applied to the abutment teeth is formed by the biting forces in the occluso-gingival direction. - The *primary stabilizing fulcrum (PDF)* passes through the primary tooth abutments adjacent to the edentulous space. - The *secondary stabilizing fulcrum (SDF)* passes through the rests located on the secondary abutments for indirect retention. - **According to the position and number of support teeth on the arch** - *Radial fulcrums*: are formed when there is a single abutment tooth. - *Unilateral fulcrum* is formed when the supporting teeth are on one side of the arch. - *Bilateral diametrical fulcrum* is formed between two abutment teeth located symmetrically on both sides of the arch. - *Bilateral diagonal fulcrum* is formed between two abutment teeth located asymmetrically on its two sides of the arch. - **When the number of supporting teeth is more than two, instead of a fulcrum, a sustentation plane is formed, and the prosthesis does not rotate, and there is a more stable placement.** - *Triagular sustentation plane*: formed between three abutment teeth on either side of the arch. - *Quadrangular sustentation plane*: formed between four support teeth on both sides of the arch. ## Planning: - Classification of the case - Support zones - Guiding planes - Direct retainers - Indirect retainers - Major connector - Minor connectors - Denture bases and artificial teeth ## Case Classification: - **Teeth-supported (CI III)** - Supported by teeth on both sides of the edentulous cavity, like FPD - The tooth-supported base transmits occlusal forces directly to the abutment teeth via the rests. - The resilience of the mucosa and the structure and properties of the bone supporting these tissues *do not affect the prosthesis support*. - If the abutment teeth are healthy enough to face the additional loads, the support is provided by the teeth even if the edentulous area is long. - The movement away from tissue must be controlled with prosthetic components. - **Teeth-Tissue Supported (CI I-II-IV)** - The denture base near to the teeth is supported by the teeth, and the tissue support increases as it moves away from the teeth. - They are exposed to greater stress, as they provide most of their support from the tissues under the base and a limited amount from the abutment teeth. - These prostheses are dependent on the bases not only for support *but also for retention*. - **Stresses**: Maximum tissue coverage, the right choice and advantageous placement of direct and indirect retainers and other prosthetic components needs to be checked. ## Identifying support zones: - **Teeth support**: Terminal supports, Cross arch stabilization (C.A.S) - **Mucosal Support**: Tooth-supported cases with a large edentulous space. The free-ended bases are largely mucosa-supported and should cover as large an area as possible. *The amount of load per unit area should be reduced*. - **Occlusal rests**: - **CL I and CL II**: Placed on molar and premolar abutment teeth adjacent to each edentulous space. It is advantageous to place them in the rest seat so that the functional forces can be transmitted along the long axis of the tooth. It is placed on the mesio-occlusal surfaces of the teeth adjacent to the edentulous space. - **CL III**: Occlusal rests are placed in the areas of the teeth close to the edentulous crest. - **CL IV**: The rests are attached to the abutment teeth adjacent to the edentulous space. One or two are placed on the supporting teeth in the posterior of the prosthesis. - **Exceptions**: Rests are never placed in areas that conflict with natural occlusal contact. *Paced on the other side or adjacent tooth. If all teeth are in tight occlusal contact, a minimum preparation is required for rest placement*. - **However**: Rest seat is not opened for teeth with insufficient enamel thickness or abraded teeth. *They are restored with crowns* - **In the presence of periodontally weak abutment teeth**: Load is distributed by placing the rest between two abutment teeth. - **Singulum Rests**: Rest; It is placed on the cingulum or put in place of the cingulum in cases where anatomy does not limit it. *When there is contact with opposing teeth, anywhere between the point of contact and 2mm above the gingival margin*. ## Identifying Direct Retainers - The parts that are applied directly to the abutment teeth and prevent the prosthesis from displacing from the tissues and moving. - Direct attachments are divided into *intra-coronal and extra-coronal*. ### Direct retainer criteria: - Stabilization should be good. - Should remain passive *when not in function*. - Must have the flexibility to allow limited movement of the denture base without transmitting torque to the abutment tooth. - **Placing the direct retainer**: - The most ideal choice is to place three retainers as far from each other as possible with a triangular arrangement, which will make the retention system more stable. - If the existing undercuts or undercut depths on the abutment teeth are below average and the guiding planes are short and few in number, *more direct retainers should be used*. - Direct retainers are placed first, starting from the posterior region of the arch. The use of retainers in the anterior region is avoided as much as possible. - Using more than two retainers on the same plane does not provide any mechanical advantage, and is inconvenient in terms of plaque accumulation and stresses on the supporting tooth. - Free-end RPDs require two direct retainers in cases where only two abutment teeth are present, and are placed diagonally *if the undercuts and guide planes are suitable*. - Occlusal rests placed on other teeth that are not clasped serve as indirect retainers. ### Type of direct retainer: - Condition of the abutment tooth - Mount of flexibility - Effective use of equator lines - Localization of retentive areas - Undercut depth and amount - Soft tissue contour - Aesthetic ### Condition of abutment tooth: - Periodontal support - Casted clasp - Wrought wire (bended)clasp ### Amount of flexibility: - Long-short clasp - Thick-thin clasp - Casted-Bended Clasp ### Effective use of equator lines: - The only flexible part of the RPD is the retentive end of the clasp, which is located in the undercut area of the equator line. - Appropriate undercut area provides both aesthetic and mechanical advantages. ## Identifying Indirect Retainers - Indirect retainers are elements that assist direct retainers *to prevent the displacement of partial dentures around their rotational axes.* - **Contributes to stabilization.** - **Prevents the prosthesis from embedding and separating from the tissue.** - The *denture base should be stabilized with indirect retainers that prevent the movement of the free-end (distal extension) bases away from the tissues around the rotation axis*. - The retentive fulcrum axis passing through the direct retainers is determined, and a straight line is drawn perpendicular to this axis. - The indirect retainer is the rest of this line placed at the farthest point *from the fulcrum axis*. - Lingual plate and Kennedy bar - **Optimal indirect retainer position relative to the fulcrum axis**: Two centrals, Sloped surface, incisal rest, aesthetic. The most suitable option? - **In the presence of modification in the anterior region**: anterior cingulum rest. - **In the area where the primary fulcrum line cuts the cross arch**: Indirect retainer on the first premolar or canine rest (IT= indirect retainer). - **Indirect retainer is not used in tooth-supported CL III prostheses unless necessary for the rigidity of the major connector.** - **CL IV**: Ideally points A and B. Point A; excessive mucous membrane, ineffective mucosal support. Point B; It is NOT possible. Occlusal rests on molar teeth as indirect retainer. Direct retainers placed on the mesiobuccal anterior undercuts of the molar teeth on both sides also act as indirect retainers. ## Placement of minor connectors: - Minor connectors must be rigid except for the bar- gingival clasp approaching arm. - When placing minor connectors: - Comfort - Ability to be cleaned - It is intended to facilitate the placement of artificial teeth. ## Planning of denture base and artificial teeth: ### Denture Base - **Borders**: It will distribute occlusal forces over a wide area. Will not restrict the function of surrounding tissues. ### Artificial Teeth: - Missing anterior single tooth- facing tooth - Premolar single tooth missing- tube tooth - Metal tooth or metal body in case of absence of lower molars and narrowing of the space ## Major Connector - **Anatomical features of the case**: Position and number of edentulous spaces, Need for splinting of teeth, The necessity of providing indirect retention with the major connector. - **When the remaining teeth have adequate periodontal support and the need for additional tissue support is reduced**: palatal/ anteroposterior bar. - **In free-end cases**: In the presence of two or fewer incisors, When the abutment teeth show asymmetric placement, If periodontal support is weak, *Full palatal plate*. - **Free-end cases with long edentulous spaces**: The main connector must be rigid. *Full palatal plate, antero posterior bar*. - **Few abutment teeth anterior to the fulcrum line**: Rest placement is not appropriate. *Indirect retainer- U-plate, Anteroposterior bar, Full palatal plate*. - **Anterior edentulous space**: Number and location of missing posterior teeth, Periodontal support, Opposing occlusion type. *U-plate, Anteroposterior bar, Full palatal plate*. - **Presence of Torus**: *Anteroposterior bar/ U-plate*. ### Major connector in tooth supported cases: - **Lingual bar**: - **If the undercut on the buccal of the canine teeth is distal and the tissue undercut allows, the clasps can be worked as gingival clasps.** - **Lingual Plate**: - When there is not enough distance between the gingival margin and the floor of the mouth (6-8 mm). - Periodontal support of anterior teeth is poor and needs splinting. - If there is a diastema, *interrupted lingual plate*. - **In the presence of only anterior teeth**: indirect retainer, Lingual plate, Kennedy bar. There should be sufficient distance between the gingival margins and the floor of the mouth. *6-8mm* ## AIDENTAL: - **Digital Learning Applications**: RPD Design, RPD Game, TX Planning.