# Retainers ## Clasp assembly Dr. Matsubara #### Components of the Clasp Assembly A clasp assembly is a fundamental component of a removable partial denture, designed to provide retention, stability, and support. It typically consists of several integrated parts working together to secure the prosthesis while protecting the abutment teeth. - **Rest**: Provides vertical support and prevents the denture from moving toward the tissue. - **Retentive Arm**: Engages the undercut of the abutment tooth to resist dislodgment. - **Reciprocal Arm (Stabilizing Component)**: Counters the forces exerted by the retentive arm during insertion and removal. - **Minor Connector**: Joins the clasp assembly components to the major connector or denture base. The logo of The University of Western Australia, featuring a shield with a swan and the motto 'SEEK WISDOM' below it, accompanied by the text 'THE UNIVERSITY OF WESTERN AUSTRALIA'. The logo of the Oral Health Centre of Western Australia, consisting of a stylized butterfly design in blue and yellow, with the organization's name written in blue text. A close-up photo of a dental retainer with a clasp assembly, showing artificial teeth attached to a pink gum-colored base and a metal clasp mechanism designed for securing the retainer in place. # Retainers – Retentive unit Components of a RPD that engage abutments and resist dislodging forces Provide resistance to displacement by deformation of the retentive arm <img src="image.png" alt="A partial denture with two clasps attached to artificial teeth, set against a black background." /> Components of a Removable Partial Denture (RPD) that engage abutments and resist dislodging forces. - Provide resistance to displacement by deformation of the retentive arm. A close-up photo of a partial denture retainer with two clasps attached to artificial teeth, set against a black background. The retentive arms are metallic and curve around the teeth, demonstrating how they engage abutments to resist dislodging forces. # Retainers # Forces Displacement can occur through gravity, sticky foods or functional jaw movements <img src="image.png" alt="Two images of dental retainers on a blue background. The larger image shows a full dental arch with metal retainers on the molars, with yellow arrows indicating forces. The smaller image shows a close-up of a retainer with a red arrow pointing upwards."> Displacement can occur through gravity, sticky foods, or functional jaw movements. A photo of a dental retainer model on a blue background, showing a dental arch with metal retainers on the molars, with yellow arrows indicating forces. A close-up photo of a dental retainer on a blue background, with a red arrow pointing upwards, highlighting a specific area of the retainer. <div class="image-container"> <img src="image.png" alt="Flowchart of Retainers classification"> </div> Retainers are classified into various categories based on their location, construction, and function within the prosthesis. A flowchart titled 'Retainers' that categorizes retainers into Intracoronal and Extracoronal types, with further subdivisions including Precision Attachments, Retentive Clasp Assemblies, and Extracoronal Attachments. A close-up photo of a dental retainer with a metal clasp attached to a tooth, illustrating an extracoronal attachment. A detailed photo of a dental retainer with a metal component and a yellow attachment, showing an intracoronal attachment. A photo of a dental retainer with multiple metal clasps attached to teeth, demonstrating an extracoronal attachment in a patient's mouth. A photo showing a dental instrument being used to adjust a metal retainer, illustrating the application of an extracoronal attachment. A photo of two precision attachments, one with a cross-shaped component and another with a rectangular slot, used in dental retainers. A photo of a dental retainer with a gold-colored metal framework and pink gum-colored material, showing an intracoronal attachment. A diagram showing a dental retainer with a yellow component and red attachments, illustrating the placement of precision attachments on teeth. # Direct Retainers - **Intracoronal** - Precision Attachments - **Extracoronal** - Retentive clasp Assemblies - Extracoronal Attachments ## Disadvantages of clasp-retained partial dentures 1. Strain on the abutment teeth often is caused by improper tooth preparation or clasp design 2. Clasps can be unaesthetic, particularly when they are placed on visible tooth surfaces 3. Caries may develop beneath clasp components, especially if the patient fails to keep the prosthesis and the abutments clean. - **Intracoronal** - Precision Attachments - **Extracoronal** - Retentive clasp Assemblies - Extracoronal Attachments 1. Strain on the abutment teeth often is caused by improper tooth preparation or clasp design. 2. Clasps can be unaesthetic, particularly when they are placed on visible tooth surfaces. 3. Caries may develop beneath clasp components, especially if the patient fails to keep the prosthesis and the abutments clean. A hierarchical diagram illustrating the classification of direct retainers in dentistry. The diagram shows 'Direct Retainers' at the top, branching into 'Intracoronal' and 'Extracoronal' categories. 'Intracoronal' leads to 'Precision Attachments,' while 'Extracoronal' branches into 'Retentive clasp Assemblies' and 'Extracoronal Attachments.' The diagram is presented in a flowchart format with rectangular boxes and connecting lines. # Clasp Assemblies ## Components of Clap Assembly 1) **Rest** 2) **Retentive arm** 3) **Reciprocating arm** 4) **Clasp body: proximal plate** 5) **Minor connector** <figure> <img src="image_with_labels.png" alt="Diagram showing components of a clasp assembly on a tooth with numbered labels"> </figure> 1. Rest 2. Retentive arm 3. Reciprocating arm 4. Clasp body: proximal plate 5. Minor connector A colored diagram illustrating the components of a clasp assembly on a tooth, with numbered labels corresponding to the rest, retentive arm, reciprocating arm, clasp body, and minor connector as listed in the text. A detailed diagram showing a clasp assembly on a tooth, with colored sections highlighting different components such as the rest, retentive arm, reciprocating arm, clasp body, and minor connector, with corresponding numbers. # Clasp Assemblies ## Suprabulge - Retentive arm approach the undercut region of the abutment from the Occlusal direction <img src="image1.png" alt="Suprabulge clasp assembly"> ## Infrabulge - Retentive arm approach the undercut region of the abutment from the apical direction <img src="image2.png" alt="Infrabulge clasp assembly"> #### Suprabulge Clasps - Retentive arm approaches the undercut region of the abutment from the occlusal direction. #### Infrabulge Clasps - Retentive arm approaches the undercut region of the abutment from the apical direction. A photograph showing a suprabulge clasp assembly on a dental model, where the retentive arm approaches the undercut region of the abutment from the occlusal direction, highlighting the metal clasp engaging with the tooth structure. A photograph illustrating an infrabulge clasp assembly on a dental model, where the retentive arm approaches the undercut region of the abutment from the apical direction, demonstrating the clasp's positioning on the tooth. # Clasp Assemblies ## Classification According to the retention - Direct retainer: adjacent to the edentulous area - Indirect retainer: away from the edentulous area, makes indirect retention #### According to Retention - **Direct retainer**: Adjacent to the edentulous area. - **Indirect retainer**: Away from the edentulous area, provides indirect retention. A dental model showing a clasp assembly with metal retainers. The image highlights three specific areas with red circles, illustrating the placement of direct and indirect retainers in relation to the edentulous area, as described in the accompanying text. # Clasp Assemblies ## Classification ### According to the retention - Direct retainer: adjacent to the edentulous area - Indirect retainer: away from the edentulous area, makes indirect retention ### According to the construction - Adapted, wrought wire - Cast - Adapted, wrought wire - Cast Close-up photo of a dental clasp assembly on a patient's teeth, showing a direct retainer adjacent to an edentulous area with a visible metal clasp. Close-up photo of a cast clasp assembly, illustrating a metal framework with a clasp arm designed to provide retention in a dental prosthesis. # Clasp Assemblies ## Requirements for the retentive unit 1. **Support**: mainly provided by the rest. It distributes loading through the abutment - teeth protects the soft tissues & periodontium #### Support - Mainly provided by the rest. - Distributes loading through the abutment teeth. - Protects the soft tissues and periodontium. A diagram illustrating the concept of support in dental clasp assemblies, showing a prohibited downward force on a tooth with a rest, emphasizing that support should be provided by the rest to distribute loading through the abutment teeth and protect soft tissues and periodontium. A close-up photo of a dental clasp assembly on a tooth, showing a metal clasp engaged with the tooth structure, demonstrating the retentive unit's function in a dental prosthesis. A close-up photo of a dental clasp assembly, highlighting a metal clasp engaging with a tooth, illustrating the retentive unit's role in securing a dental prosthesis. # Clasp Assemblies ## Requirements for the retentive unit 2. Stabilization: bracing effect resists horizontal forces evenly through all abutment teeth - Reciprocating arm - Proximal plate (minor connector) - Initial third of the retentive arm Bracing effect resists horizontal forces evenly through all abutment teeth. Components involved include: - Reciprocating arm - Proximal plate (minor connector) - Initial third of the retentive arm A diagram illustrating the stabilization of a clasp assembly, showing a dental arch with a retentive arm and arrows indicating the bracing effect that resists horizontal forces evenly through all abutment teeth. The diagram includes components like the reciprocating arm, proximal plate (minor connector), and initial third of the retentive arm. A close-up photo of a dental clasp assembly in situ, showing a metal retentive arm engaging with a tooth, demonstrating the practical application of the clasp design discussed in the text. # Clasp Assemblies ## Requirements for the retentive unit 3. **Retention**: resists occlusal displacement and is provided by the terminal third of the retentive arm. - Retention should be distributed throughout the arch. - Depth of undercut is determined by the flexibility of the alloy used. <image> - Resists occlusal displacement. - Provided by the terminal third of the retentive arm. - Retention should be distributed throughout the arch. - Depth of undercut is determined by the flexibility of the alloy used. A diagram showing a prohibited upward movement, indicated by a red circle with a diagonal line over an upward arrow, placed between two cylindrical objects, likely illustrating a restriction on vertical displacement in a mechanical or dental context. A close-up photo of a dental clasp on a tooth, with a red circle highlighting the retentive arm's engagement with the tooth's surface. A diagram of a tooth showing labeled areas for buccal and lingual height of contour, illustrating the anatomical reference points for clasp placement. A diagram of a dental model with a clasp assembly, highlighting the suprabulge and infrabulge regions in relation to the tooth's contour. A close-up photo of a dental clasp assembly on a tooth model, showing the clasp's fit and interaction with the tooth's surface. # Clasp Assemblies ## Requirements for the retentive unit 4. **Reciprocity**: Insertion force of the retention arm must be opposed by reciprocating arms and/or other components of the RPD. Optimally the reciprocating arm should contact the tooth when the retentive arm engages. It contributes to bracing of the RPD - Insertion force of the retention arm must be opposed by reciprocating arms and/or other components of the RPD. - Optimally, the reciprocating arm should contact the tooth when the retentive arm engages. - Contributes to bracing of the RPD. Two labeled diagrams (a and b) illustrating the reciprocity principle in clasp assemblies. Diagram (a) shows a retentive clasp engaging a tooth with a reciprocal element opposing the insertion force. Diagram (b) depicts a similar setup with a retentive clasp and reciprocal element, emphasizing the interaction between components during insertion. # Clasp Assemblies ## Requirements for the retentive unit 5. **Engagement**: Components must encircle more than 180° of the tooth to prevent movement of the abutment out of the assembly Components must encircle more than 180° of the tooth to prevent movement of the abutment out of the assembly. Close-up photograph of a dental clasp assembly on a tooth, showing a metal component encircling the tooth to provide retention. The image illustrates the engagement requirement where components must encircle more than 180° of the tooth. Another close-up photograph of a dental clasp on a tooth, demonstrating the retentive unit's engagement. This image shows a metal clasp securely fitting around the tooth structure, emphasizing the need for encirclement to prevent movement. # Clasp Assemblies ## Requirements for the retentive unit 6. **Passivity**: when fully seated the clasp assembly exerts no force on the tooth When fully seated, the clasp assembly exerts no force on the tooth. A line drawing illustration of a dental clasp assembly on a tooth, showing the retentive unit in a seated position. The diagram visually represents the concept of passivity, where the clasp exerts no force on the tooth when fully seated, as described in the accompanying text. # Clasp Assemblies ## Retention Arm Correct location: - Middle and/or gingival third - 3 sections: (S) Shoulder, (M) Midsection (T) Terminal third: Flexible clasp terminus (T): Bellow the height of contour – Retentive area #### Correct Location - Middle and/or gingival third. #### Sections of the Arm 1. **Shoulder (S)** 2. **Midsection (M)** 3. **Terminal third (T)**: Flexible clasp terminus located below the height of contour (retentive area). A diagram illustrating a retention arm on a tooth, showing three sections labeled (S) Shoulder, (M) Midsection, and (T) Terminal third. The terminal third is noted to be below the height of contour, serving as the retentive area. A detailed diagram of a retention arm with a yellow flexible terminus extending from the tooth. The arm is shown in cross-section, highlighting its placement and structure relative to the tooth's surface. # Clasp Assemblies ## Retention Arm ### Shape - Tapered uniformly - Cross-sectional form: half-round form - Tapered uniformly. - Cross-sectional form: half-round form. A close-up photo of a dental clasp assembly on a model of teeth, showing the retention arm in place. The clasp is metallic and has a half-round cross-sectional form, as described in the text. A technical drawing illustrating the shape of the retention arm, showing it as tapered uniformly with a half-round cross-sectional form. The diagram includes multiple views, including side and end views, with annotations indicating dimensions and taper angles. A set of four schematic diagrams illustrating different aspects of a clasp assembly. The diagrams show a clasp component, a cross-section, and a force distribution pattern, likely representing the engagement and force application of the retention arm. # Clasp Assemblies ## Retention Arm **Flexibility (capacity to suffer elastic deformation)** - Length of the arm: longer = more flexible - Circumferential: point of origin in the clasp body - Bar clasp: from metal base or resin base - Degree of taper: lengthwise and widthwise - Cross-section form - Diameter: greater = less flexible - Type of material: Flexibility is the capacity to suffer elastic deformation. Factors include: - **Length of the arm**: Longer arms are more flexible. - Circumferential: Measured from the point of origin in the clasp body. - Bar clasp: Measured from the metal or resin base. - **Degree of taper**: Both lengthwise and widthwise. - **Cross-section form** - **Diameter**: Greater diameter results in less flexibility. A diagram showing a clasp arm with a curved retention arm extending from a clasp body, illustrating the concept of flexibility in dental clasp assemblies. The arm is depicted with a dashed line indicating its path and a shaded area representing the clasp body. A schematic diagram illustrating the forces acting on a clasp arm, showing a circular object being pushed by the clasp arm with arrows indicating upward and downward forces, and a horizontal arrow indicating the direction of movement or force application. # Clasp Assemblies ## Retention Arm ### Flexibility - All cast alloys show some degree of flexibility - Cast gold alloys have greater resiliency than Cr-Co alloys - Cast alloys flexibility is inversely proportional to bulk - Wrought wire clasp has higher tensile strength than cast clasps. It can be used in smaller diameter to provide greater flexibility without fatigue and fracture. <img src="https://i.imgur.com/9Z4YQ5l.png" alt="Partial denture with a clasp assembly"> - All cast alloys show some degree of flexibility. - Cast gold alloys have greater resiliency than Chrome-Cobalt (Cr-Co) alloys. - Cast alloy flexibility is inversely proportional to bulk. - Wrought wire clasps have higher tensile strength than cast clasps. They can be used in smaller diameters to provide greater flexibility without fatigue and fracture. A partial denture with a clasp assembly, showing a pink acrylic base with artificial teeth and metal clasps designed to retain the denture on natural teeth. The image illustrates the retention arm component discussed in the text about flexibility and material properties of clasp assemblies. # Clasp Assemblies ## Reciprocal Arm - To resist tooth movement in response to deformation of the retentive arm - Must be in contact during the entire period of retentive clasp deformation - Stabilize the framework against horizontal movements during deformation of the retentive arm <img src="image.png" alt="Diagram showing a dental clasp assembly with labels for the retentive clasp and reciprocal element, and a diagram of a dental arch with red arrows indicating forces." /> - Resists tooth movement in response to deformation of the retentive arm. - Must be in contact during the entire period of retentive clasp deformation. - Stabilizes the framework against horizontal movements during deformation of the retentive arm. Close-up photograph of a dental clasp attached to a tooth, showing the retentive clasp and its interaction with the tooth surface. Another close-up photograph of a dental clasp on a tooth, illustrating the reciprocal element and its positioning relative to the tooth. Diagram showing a dental arch with a clasp assembly, using red arrows to indicate forces and movements related to the reciprocal arm and retentive clasp. Schematic diagram illustrating the components of a clasp assembly, including the retentive clasp and reciprocal element, with arrows indicating forces during deformation. # Clasp Assemblies ## Reciprocal Arm - Rigid - Half-round form - Average diameter (AD) > AD opposing retentive arm - No taper or Taper in one dimension (lengthwise) - Above the height of contour. - Rigid construction. - Half-round form. - Average diameter (AD) is greater than the AD of the opposing retentive arm. - No taper, or taper in only one dimension (lengthwise). - Positioned above the height of contour. A diagram illustrating a reciprocal arm on a dental prosthesis, showing its placement above the height of contour with a yellow highlighted area indicating the arm's position relative to the tooth. The diagram includes labels indicating 1/3 divisions along the tooth's surface. A technical drawing of a reciprocal arm, depicted in two views: a top-down view and a side view, showing its half-round form and tapering design. The drawing includes dimension lines and annotations indicating the arm's geometry and taper. A close-up photograph of a metallic reciprocal arm attached to a dental prosthesis, showing its rigid, half-round form and placement on a model of teeth. The arm is positioned above the height of contour, demonstrating its function in a real-world application. # Clasp Assemblies ## Clasp body - Union of arms and rest to the framework - Above the height of contour - Rigid - It will be in contact with guiding planes (frictional retention) <img src="image.png" alt="Diagram of a clasp body with red lines indicating guiding planes"> - Represents the union of arms and rest to the framework. - Positioned above the height of contour. - Rigid structure. - Contacts guiding planes to provide frictional retention. A diagram illustrating a clasp body, showing its union of arms and rest to the framework, with red lines indicating the guiding planes for frictional retention. The diagram is positioned next to a textual description of the clasp body's characteristics. # Clasp Assemblies ## Guiding planes - Flat parallel surfaces prepared on abutment teeth (occlusal one/two thirds) - Guide planes provide a single path of Insertion (POI). - GP are used to control and limit the directions of movement of RPD during insertion, removal or function. - Components of the denture start to contact the abutments in the guiding planes area - Flat parallel surfaces prepared on abutment teeth (occlusal one-third to two-thirds). - Provide a single Path of Insertion (POI). - Used to control and limit the directions of movement of the RPD during insertion, removal, or function. - Denture components initiate contact with abutments at the guiding plane area. A diagram showing flat parallel surfaces prepared on abutment teeth, illustrating the concept of guiding planes with arrows indicating the direction of insertion. A detailed illustration of a denture component interacting with abutment teeth, highlighting the guiding planes and the path of insertion (POI) during denture placement. A schematic diagram depicting the movement of a removable partial denture (RPD) along guiding planes, showing the controlled path of insertion and removal. # Clasp Assemblies ## Guiding planes Most effective: - Parallel - Include more than one common axial surface (e.g. proximal and lingual surfaces) - Placed on several teeth - Cover a large surface area (long and/or broad) Guiding planes are most effective when they: - Are parallel. - Include more than one common axial surface (e.g., proximal and lingual surfaces). - Are placed on several teeth. - Cover a large surface area (long and/or broad). A black and white line diagram illustrating the concept of guiding planes in clasp assemblies, showing two opposing teeth with vertical bars representing guiding surfaces and arrows indicating the direction of movement. A close-up photograph of a dental clasp assembly in the mouth, highlighting a metal clasp attached to a tooth, with a red circle emphasizing the clasp's position on the lingual surface. A clinical photograph showing a dental clasp assembly in place on the upper teeth, demonstrating the structure of the clasp and its attachment to the teeth within the oral cavity. # Clasp Assemblies ## Types: Based on the position of the retentive arm - Suprabulge - Infrabulge Clasp assemblies are categorized based on the position and approach of the retentive arm: - Suprabulge - Infrabulge Close-up photo of a dental clasp assembly on a model, showing a suprabulge design with a metal arm extending over the tooth's bulge. Photo of a dental clasp assembly on a model, illustrating an infrabulge design with a metal arm positioned below the tooth's bulge. Photo of a dental clasp assembly on a model, depicting a suprabulge design with a metal arm extending over the tooth's bulge, highlighting the retentive arm's position. # Clasp Assemblies ## Types: ### Suprabulge **CIRCUNFERENCIAL CLASPS** - Continuous contact with the crown - From occlusal to gingival - Retention arm needs to be pull over the height of contour ### Inflabulge **BAR CLASPS** - Short contact of retentive arm with the crown - From gingival to occlusal - Retention arm needs to be push over the height of contour --- Suprabulge vs Inflabulge <img src="image.png" alt="Diagram showing suprabulge and inflabulge clasp assemblies"> #### Circumferential Clasps - Continuous contact with the crown. - Approaches from occlusal to gingival. - Retention arm must be pulled over the height of contour. #### Bar Clasps - Short contact of the retentive arm with the crown. - Approaches from gingival to occlusal. - Retention arm must be pushed over the height of contour. A line drawing illustrating a suprabulge circumferential clasp assembly, showing a retentive arm (labeled 'S') in continuous contact with the crown from occlusal to gingival, with a retention arm (labeled 'T') and a major connector (labeled 'M'). A line drawing depicting an inflabulge bar clasp assembly, showing a short contact of the retentive arm with the crown, with a retention arm (highlighted in yellow) that needs to be pushed over the height of contour. # Clasp Assemblies ## Circumferential clasps 1) Simple circumferential design - The most simple and versatile clasp - Clasp assembly has one retentive arm opposed by a reciprocal arm originating from the rest **Indication:** - Molars e premolars - Intercalated edentulous area - Canines with no aesthetic restriction **Limitation** Abutment is tilted toward the edentulous space <img src="image.png" alt="Three images showing circumferential clasps on dental models"> #### Simple Circumferential Design - The most simple and versatile clasp. - Assembly consists of one retentive arm opposed by a reciprocal arm originating from the rest. **Indications:** - Molars and premolars. - Intercalated edentulous areas. - Canines where there are no aesthetic restrictions. **Limitations:** - Not ideal if the abutment is tilted toward the edentulous space. A photograph showing a circumferential clasp assembly on a dental model, illustrating a simple circumferential design with a retentive arm and reciprocal arm. The image is part of a presentation on clasp assemblies, specifically for molars and premolars. A close-up photograph of a circumferential clasp on a dental model, highlighting the retentive arm engaging the tooth. This image demonstrates the application of a simple circumferential design in a dental prosthesis. A photograph displaying a circumferential clasp on a dental model with multiple teeth, showing the clasp's position and interaction with the abutment tooth. This image is used to illustrate the design and placement of a simple circumferential clasp. # Clasp Assemblies ## Circumferential clasps ### 2) Reverse circumferential design - Rest and body opposite to the edentulous area and the arms run towards the edentulous space - Need a proximal plate **Indication:** - Abutment is tilted to the edentulous space **Limitation** - Short clinical crown - No space for the connector <img src="image.png" alt="Two images showing a dental clasp assembly with a proximal plate labeled in the top image. The clasp is designed to fit around a tooth with a mesh-like structure extending towards the edentulous space. The bottom image shows a similar view from a different angle." /> - Rest and body are located opposite to the edentulous area; arms run towards the edentulous space. - Requires a proximal plate. **Indications:** - Abutment is tilted toward the edentulous space. **Limitations:** - Short clinical crowns. - Lack of space for the connector. A photo showing a dental clasp assembly with a proximal plate, illustrating a reverse circumferential design. The clasp is fitted around a tooth model with a mesh-like structure extending towards the edentulous space, as described in the text. A second photo of the same dental clasp assembly from a different angle, highlighting the mesh structure and the proximal plate. This image provides a clearer view of the clasp's design and its relation to the tooth model. # Clasp Assemblies ## Circumferential clasps 3) Ring clasp design - Mesial and distal rests - Encircle nearly all tooth **Indication:** - Intercalated edentulous area - Molars tipped in a mesiolingual direction **Limitation** - Free end saddle - Features mesial and distal rests. - Encircles nearly the entire tooth. **Indications:** - Intercalated edentulous areas. - Molars tipped in a mesiolingual direction. **Limitations:** - Not suitable for free-end saddles. Close-up photograph of a dental prosthesis with a ring clasp design, showing the metallic clasp encircling a tooth model. The image illustrates the mesial and distal rests and the circumferential nature of the clasp, as described in the text. Another close-up photograph of a dental model with a ring clasp, highlighting the clasp's engagement with the tooth. This image provides a detailed view of the clasp's fit and design, relevant to the indication of molars tipped in a mesiolingual direction. A diagram showing the ring clasp design, illustrating how the clasp encircles nearly all of a tooth. This visual representation supports the textual description of the clasp's structure and function in circumferential clasps. # Clasp Assemblies ## Circumferential clasps ### 4) Embrasure clasp design - Essentially two simple circumferentials joined at bodies - There should be enough occlusal clearance through the embrasure form - Occlusal rest seats should not create wedging forces between the teeth #### Indication: - Indirect retention - Molars and premolars #### Limitation - Extensive preparation of marginal ridges, involving facial inclines - Essentially two simple circumferential clasps joined at the bodies. - Requires sufficient occlusal clearance through the embrasure. - Occlusal rest seats must not create wedging forces between teeth. **Indications:** - Indirect retention. - Molars and premolars. **Limitations:** - Requires extensive preparation of marginal ridges, involving facial inclines. A line drawing diagram illustrating the embrasure clasp design, showing two simple circumferential clasps joined at their bodies, designed to fit around adjacent teeth. A photographic image of a dental model with a metal clasp assembly attached, demonstrating the placement of an embrasure clasp on a maxillary model. A close-up photograph showing a dental clasp on a tooth model, highlighting the fit and structure of the embrasure clasp design. # Clasp Assemblies ## Bar clasps ### 1) T-clasp design - Approach arm originates from components in the edentulous area - Retention arm cross gingival margin at 90° - Two horizontal projections **Indication:** - Intercalated or free end edentulous area **Limitation** - Interference with frenulum - Severe soft tissue undercut (Risk of food entrapment and soft tissue irritation) - Height of contour near the occlusal surface #### T-Clasp Design - Approach arm originates from components in the edentulous area. - Retention arm crosses the gingival margin at 90°. - Features two horizontal projections. **Indications:** - Intercalated or free-end edentulous areas. **Limitations:** - Potential interference with the frenulum. - Severe soft tissue undercuts (risk of food entrapment and irritation). - Height of contour located near the occlusal surface. Close-up photo of a dental prosthesis with a T-clasp design, showing the metal clasp attached to a tooth model, illustrating the retention arm crossing the gingival margin at 90 degrees. Two diagrams illustrating the T-clasp design: diagram (a) shows the approach arm originating from components in the edentulous area, and diagram (b) depicts the retention arm crossing the gingival margin at 90 degrees, highlighting the two horizontal projections. # Clasp Assemblies ## Bar clasps ### 1) T-clasp design - Approach arm originates from components in the edentulous area - Retention arm cross gingival margin at 90° - Two horizontal projections **Indication:** - Intercalated or free end edentulous area **Limitation** - Interference with frenulum - Severe soft tissue undercut (Risk of food entrapment and soft tissue irritation) - Height of contour near the occlusal surface - Approach arm originates from components in the edentulous area. - Retention arm crosses the gingival margin at 90°. - Features two horizontal projections. **Indications:** - Intercalated or free-end edentulous areas. **Limitations:** - Interference with frenulum. - Severe soft tissue undercut (risk of food entrapment and soft tissue irritation). - Height of contour near the occlusal surface. A close-up photograph of a dental model showing a T-clasp design on a tooth, with the clasp attached to a denture base. The image highlights the retention arm crossing the gingival margin at a 90-degree angle and the approach arm originating from components in the edentulous area. A line diagram illustrating the placement of a bar clasp on a dental model, showing the clasp's approach arm originating from the edentulous area and the retention arm crossing the gingival margin at 90 degrees. The diagram also depicts the two horizontal projections of the clasp. # Direct Retainer ## Bar clasps 2) Modified T-clasp design - Only one horizontal projection - Design to avoid significant soft tissues undercuts ### Indication: - Intercalated or free end edentulous area ### Limitation - Interference with frenulum - Severe soft tissue undercut (Risk of food entrapment and Soft tissue irritation) - Height of contour near the occlusal surface - Features only one horizontal projection. - Designed to avoid significant soft tissue undercuts. **Indications:** - Intercalated or free-end edentulous areas. **Limitations:** - Interference with frenulum. - Severe soft tissue undercut (risk of food entrapment and soft tissue irritation). - Height of contour near the occlusal surface. Close-up photo showing a modified T-clasp design on a dental model, highlighting the single horizontal projection and its placement near the gingival margin to avoid soft tissue undercuts. Clinical photo of a modified T-clasp in situ on a patient's dentition, demonstrating its placement in an intercalated or free-end edentulous area with visible soft tissue and tooth structure. Another clinical photo showing a modified T-clasp on a dental arch, illustrating its design and interaction with the surrounding soft tissues and teeth, particularly near the occlusal surface. # Direct Retainer ## Bar clasps ### 3) I-clasp design - Cross perpendicular the gingival margin - Should be placed mesially to the midfacial prominence of the abutment ### Indication: - Intercalated or free end edentulous area ### Limitation - Interference with frenulum - Severe soft tissue undercut (Risk of food entrapment and Soft tissue irritation) - Height of contour near the occlusal surface - Crosses perpendicular to the gingival margin. - Should be placed mesially to the midfacial prominence of the abutment. **Indications:** - Intercalated or free-end edentulous areas. **Limitations:** - Interference with frenulum. - Severe soft tissue undercut (risk of food entrapment and soft tissue irritation). - Height of contour near the occlusal surface. Close-up photo of a dental model showing an I-clasp design on a tooth, with arrows indicating the clasp's position and direction of engagement. Close-up photo of a dental retainer with a bar clasp attached to a tooth, highlighting the clasp's placement and connection to the denture. Photo of a dental model showing a direct retainer with a bar clasp, illustrating its fit and interaction with the surrounding teeth and tissue. # Direct Retainer ## Bar clasps ### 4) RPI clasp design - Comprises of rest (R), proximal plate (P) and I bar (I). - The I bar is located in the mesio-buccal undercut - Need preparation of guiding planes #### Indication: - Kennedy Class I and II #### Limitation - Need to reduce tooth structure - Tipped teeth require severe axial reduction <img> <img> - Comprises a Rest (R), Proximal plate (P), and I-bar (I). - The I-bar is located in the mesio-buccal undercut. - Requires preparation of guiding planes. **Indications:** - Kennedy Class I and II. **Limitations:** - Requires reduction of tooth structure. - Tipped teeth may require severe axial reduction. A diagram showing the occlusal view of an RPI clasp design, illustrating the components: I-Bar in mesial undercut, proximal plate, and mesial rest, with labels indicating their positions on the tooth. A diagram depicting a dental clasp design with a proximal plate, rest, and minor connector, showing how the components fit around a tooth, with labels identifying each part. # Direct Retainer ## Bar clasps ### 4) RPI clasp design #### Proximal plate: - Wide minor connector touching the distal guiding plane - Junction of the occlusal and middle third of the guiding plane - 1 mm thick - Joins the framework at a right angle. - A wide minor connector touching the distal guiding plane. - Located at the junction of the occlusal and middle third of the guiding plane. - Approximately 1 mm thick. - Joins the framework at a right angle. A detailed diagram showing the distal view of an RPI clasp design, illustrating the proximal plate (PP) with a 1.0mm overlap of the guide plane, a 2-3mm height, and a 2/3 width of cusp. The diagram includes a buccal view of the clasp engaging the tooth. A buccal view diagram illustrating the RPI clasp design, showing the wide minor connector touching the distal guiding plane and the clasp joining the framework at a right angle, with a focus on the occlusal and middle third junction. # Direct Retainer ## Bar clasps ### 4) RPI clasp design #### Proximal plate: - Improves stabilization of the prosthesis - Improves retentiveness by limiting the path of insertion and removal - Provides reciprocation - Reduce food impaction (when guide plane are properly done) No guiding plane preparation - Improves stabilization of the prosthesis. - Improves retentiveness by limiting the path of insertion and removal. - Provides reciprocation. - Reduces food impaction (when guide planes are properly prepared). *Note: These benefits are not achieved without proper guiding plane preparation.* A detailed diagram illustrating the RPI clasp design, showing a distal view with labeled components including the proximal plate (PP), guide plane (GP), and a 1.0mm overlap of the guide plane. The diagram also indicates dimensions such as 2-3mm for the proximal plate and 2/3 width of cusps. A diagram depicting an I-bar clasp design on a tooth, highlighting the guiding plane and a 3mm depth of the clasp. The diagram shows the relationship between the clasp and the tooth structure, with annotations indicating the guiding plane and the I-bar. A diagram showing a dental setup with a triangular space and a bar clasp, illustrating the concept of 'No guiding plane preparation.' The diagram depicts the relationship between the clasp and the tooth, emphasizing the absence of a guide plane. # Direct Retainer ## Telescopic Crown retained removable partial dentures ### Retention Principles: - Parallel-sided inner and outer crowns - Rigidly connected to the abutment teeth - High treatment costs - Increased risk for tooth fracture - Treatment and laboratory procedures are highly complex Wostmann et al. 2007 Long-term analysis of telescopic crown retained removable partial dentures: Survival and need for maintenance #### Retention Principles - Utilizes parallel-sided inner and outer crowns. - Rigidly connected to the abutment teeth. #### Considerations - High treatment costs. - Increased risk for tooth fracture. - Treatment and laboratory procedures are highly complex. *(Reference: Wostmann et al. 2007)* Close-up photo showing a telescopic crown retained removable partial denture in situ, with gold-colored inner crowns attached to abutment teeth and a pink denture base. Photo of a telescopic crown retained removable partial denture, highlighting the pink denture base and gold-colored telescopic crowns, demonstrating the structure of the prosthesis. # Direct Retainer ## Aesthetic clasps: Flexible removable partial dentures Thermoplastic materials: Nylon, Acetal resin (Polyoxymethylene), PMMA, Polypropylene Hill et al 2013 Flexible Removable partial dentures: an overview #### Flexible Removable Partial Dentures Utilize thermoplastic materials such as: - Nylon - Acetal resin (Polyoxymethylene) - PMMA - Polypropylene *(Reference: Hill et al. 2013)* A close-up photo of a flexible removable partial denture with pink thermoplastic material and artificial teeth, held by a gloved hand against a green background. A photo of a flexible removable partial denture with a U-shaped design, showing pink thermoplastic material and artificial teeth, placed on a green surface. # Direct Retainer ## Aesthetic clasps: PEEK (polyether ether ketone) (CAD-CAM partial dentures) ### PRESENT / FUTURE? - Good mechanical and biological properties - Denture clasps made of PEEK have lower retentive forces compared to cobalt–chromium (Co–Cr) clasps Najeeb et al 2016 Applications of polyetheretherketone (PEEK) in oral implantology and prosthodontics #### CAD-CAM Partial Dentures - PEEK offers good mechanical and biological properties. - Denture clasps made of PEEK have lower retentive forces compared to cobalt–chromium (Co–Cr) clasps. *(Reference: Najeeb et al. 2016)* A photo of a CAD-CAM partial denture with aesthetic PEEK clasps, showing the denture's design and fit on the teeth. The image illustrates the use of PEEK material for clasp fabrication in dental prosthetics. Retainers are essential components used to maintain the position of teeth after orthodontic treatment has been completed. They ensure that the corrected alignment is preserved while the surrounding bone and gingival tissues adapt to the new tooth positions. #### Types of Retainers - **Fixed Retainers** - Typically consist of a stainless steel wire bonded to the lingual surface of the anterior teeth. - Commonly used for the mandibular arch to prevent relapse of lower incisor crowding. - Provide continuous retention without requiring patient compliance for insertion or removal. - **Removable Retainers** - **Hawley Retainers**: Constructed from acrylic and metallic wires (labial bow and clasps). They are durable and allow for minor adjustments to tooth position. - **Vacuum-Formed Retainers (VFRs)**: Clear, plastic appliances that cover the entire dental arch. They are highly esthetic and popular among patients due to their near-invisibility. #### Clinical Considerations - **Duration of Wear**: The retention phase is often long-term. Initially, full-time wear may be required, followed by a transition to nighttime-only wear as the occlusion stabilizes. - **Maintenance and Hygiene**: Patients must be instructed on proper cleaning techniques to prevent plaque accumulation and dental caries, particularly around fixed retainer wires. - **Follow-up Appointments**: Regular monitoring is necessary to ensure the integrity of the retainer and to check for any signs of dental relapse. Thank you The logo of The University of Western Australia, featuring a shield with a black swan on a yellow background, flanked by two open books, and the text "THE UNIVERSITY OF WESTERN AUSTRALIA" in blue. [^1]: Original PDF page 1: [[L4 Clasp Assembly.pdf#page=1|L4 Clasp Assembly, p.1]] [^2]: Original PDF page 2: [[L4 Clasp Assembly.pdf#page=2|L4 Clasp Assembly, p.2]] [^3]: Original PDF page 3: [[L4 Clasp Assembly.pdf#page=3|L4 Clasp Assembly, p.3]] [^4]: Original PDF page 4: [[L4 Clasp Assembly.pdf#page=4|L4 Clasp Assembly, p.4]] [^5]: Original PDF page 5: [[L4 Clasp Assembly.pdf#page=5|L4 Clasp Assembly, p.5]] [^6]: Original PDF page 6: [[L4 Clasp Assembly.pdf#page=6|L4 Clasp Assembly, p.6]] [^7]: Original PDF page 7: [[L4 Clasp Assembly.pdf#page=7|L4 Clasp Assembly, p.7]] [^8]: Original PDF page 8: [[L4 Clasp Assembly.pdf#page=8|L4 Clasp Assembly, p.8]] [^9]: Original PDF page 9: [[L4 Clasp Assembly.pdf#page=9|L4 Clasp Assembly, p.9]] [^10]: Original PDF page 10: [[L4 Clasp Assembly.pdf#page=10|L4 Clasp Assembly, p.10]] [^11]: Original PDF page 11: [[L4 Clasp Assembly.pdf#page=11|L4 Clasp Assembly, p.11]] [^12]: Original PDF page 12: [[L4 Clasp Assembly.pdf#page=12|L4 Clasp Assembly, p.12]] [^13]: Original PDF page 13: [[L4 Clasp Assembly.pdf#page=13|L4 Clasp Assembly, p.13]] [^14]: Original PDF page 14: [[L4 Clasp Assembly.pdf#page=14|L4 Clasp Assembly, p.14]] [^15]: Original PDF page 15: [[L4 Clasp Assembly.pdf#page=15|L4 Clasp Assembly, p.15]] [^16]: Original PDF page 16: [[L4 Clasp Assembly.pdf#page=16|L4 Clasp Assembly, p.16]] [^17]: Original PDF page 17: [[L4 Clasp Assembly.pdf#page=17|L4 Clasp Assembly, p.17]] [^18]: Original PDF page 18: [[L4 Clasp Assembly.pdf#page=18|L4 Clasp Assembly, p.18]] [^19]: Original PDF page 19: [[L4 Clasp Assembly.pdf#page=19|L4 Clasp Assembly, p.19]] [^20]: Original PDF page 20: [[L4 Clasp Assembly.pdf#page=20|L4 Clasp Assembly, p.20]] [^21]: Original PDF page 21: [[L4 Clasp Assembly.pdf#page=21|L4 Clasp Assembly, p.21]] [^22]: Original PDF page 22: [[L4 Clasp Assembly.pdf#page=22|L4 Clasp Assembly, p.22]] [^23]: Original PDF page 23: [[L4 Clasp Assembly.pdf#page=23|L4 Clasp Assembly, p.23]] [^24]: Original PDF page 24: [[L4 Clasp Assembly.pdf#page=24|L4 Clasp Assembly, p.24]] [^25]: Original PDF page 25: [[L4 Clasp Assembly.pdf#page=25|L4 Clasp Assembly, p.25]] [^26]: Original PDF page 26: [[L4 Clasp Assembly.pdf#page=26|L4 Clasp Assembly, p.26]] [^27]: Original PDF page 27: [[L4 Clasp Assembly.pdf#page=27|L4 Clasp Assembly, p.27]] [^28]: Original PDF page 28: [[L4 Clasp Assembly.pdf#page=28|L4 Clasp Assembly, p.28]] [^29]: Original PDF page 29: [[L4 Clasp Assembly.pdf#page=29|L4 Clasp Assembly, p.29]] [^30]: Original PDF page 30: [[L4 Clasp Assembly.pdf#page=30|L4 Clasp Assembly, p.30]] [^31]: Original PDF page 31: [[L4 Clasp Assembly.pdf#page=31|L4 Clasp Assembly, p.31]] [^32]: Original PDF page 32: [[L4 Clasp Assembly.pdf#page=32|L4 Clasp Assembly, p.32]] [^33]: Original PDF page 33: [[L4 Clasp Assembly.pdf#page=33|L4 Clasp Assembly, p.33]] [^34]: Original PDF page 34: [[L4 Clasp Assembly.pdf#page=34|L4 Clasp Assembly, p.34]] [^35]: Original PDF page 35: [[L4 Clasp Assembly.pdf#page=35|L4 Clasp Assembly, p.35]] [^36]: Original PDF page 36: [[L4 Clasp Assembly.pdf#page=36|L4 Clasp Assembly, p.36]] [^37]: Original PDF page 37: [[L4 Clasp Assembly.pdf#page=37|L4 Clasp Assembly, p.37]] [^38]: Original PDF page 38: [[L4 Clasp Assembly.pdf#page=38|L4 Clasp Assembly, p.38]] [^39]: Original PDF page 39: [[L4 Clasp Assembly.pdf#page=39|L4 Clasp Assembly, p.39]] [^40]: Original PDF page 40: [[L4 Clasp Assembly.pdf#page=40|L4 Clasp Assembly, p.40]] [^41]: Original PDF page 41: [[L4 Clasp Assembly.pdf#page=41|L4 Clasp Assembly, p.41]]