Removable Partial Prosthodontics
Kennedy Classification · RPD Components · Design Principles · Clasps · Surveying
TL;DR
A removable partial denture (RPD) is a removable prosthesis that replaces one or more missing teeth while deriving support and retention from the remaining natural teeth and mucosa. RPD design is governed by biomechanical principles aimed at protecting the abutment teeth, preserving the residual ridges, and restoring function. Kennedy classification categorises the edentulous space pattern; the RPD framework is designed to address the specific biomechanical challenge each class presents.
- Kennedy classification categorises partially edentulous arches by the most posterior edentulous area: Class I — bilateral posterior free-end (distal extension) — the most demanding biomechanically because the denture base must bear occlusal load without tooth support distally; the framework is a tooth-mucosal supported (tooth-tissue-borne) prosthesis. Class II — unilateral posterior free-end (one side only). Class III — bounded (intercalated) edentulous space with teeth both anterior and posterior to the space — the most favourable biomechanically (tooth-borne from abutments on both sides of the space). Class IV — single edentulous space crossing the midline anteriorly (only one class — no modifications). Modification spaces (additional edentulous areas in the arch beyond the primary class) are designated by modification numbers (e.g., Class II Mod 1). The class is always determined by the most posterior edentulous space — not the most anterior, and not the most extensive.
- The major connector is the fundamental structural element of the RPD framework: The major connector connects all components of the RPD into one rigid unit. For maxillary RPDs: the palatal bar (narrow, posterior, for small edentulous spaces), the palatal strap (broader, for better load distribution), the anteroposterior palatal strap (two straps joined by lateral connectors — for Class I and II), or the complete palatal coverage (horseshoe connector + palatal coverage — for cases with poor remaining tooth support). For mandibular RPDs: the lingual bar is the most common choice — it sits below the gingival margin of the anterior teeth with its superior border at least 3mm below the free gingival margin; the sublingual bar (for shallow lingual sulcus — bar sits deeper); the lingual plate (covers cingulae of anterior teeth — indicated when lingual sulcus is too shallow for lingual bar or when anterior teeth require support, or when all anterior teeth may be lost); the labial bar (only when lingual anatomy absolutely prevents any lingual connector — rare, poor aesthetics).
- The IPSILATERAL I-bar (RPI clasp) is the clasp of choice for Class I and II Kennedy mandibular free-end cases: The clasp assembly for a distal extension (free-end) RPD must allow the denture base to move inferiorly under occlusal load (because no distal tooth support exists — the denture must settle into the tissue slightly on loading) while still retaining the denture in place. The RPI clasp (Rest, Proximal plate, I-bar retentive arm) achieves this: (1) Mesial rest — the rest is on the mesial surface of the abutment tooth (not distal), so that when the denture base settles under load, the rest can tip mesially and not torque the abutment tooth distally; (2) Proximal plate — minor connector that contacts the tooth’s guiding plane surface; (3) I-bar (modified gingivally-approaching Akers clasp) — the retentive arm approaches the undercut from below (gingivally), not occlusally; this allows the retentive arm to disengage from the undercut as the denture base settles inferiorly during function, reducing tipping forces on the abutment tooth. In contrast, a conventional circumferential (Akers) clasp with a distal rest on a free-end abutment creates a Class I lever — loading the denture base causes the distal rest to fulcrum, torquing the abutment distally and apically.
- Surveying determines the path of insertion and identifies the height of contour for clasp design: A dental surveyor is a mechanical parallelometer — it consists of a horizontal arm with a vertical analysing rod that moves parallel to a fixed vertical axis over the dental cast. The cast is tilted to determine the survey line (height of contour) for each tooth: the survey line divides each tooth into a suprabulge area (above the height of contour — retentive area where clasp tip engages) and an infrabulge area (below — where the clasp body and reciprocating arm pass). The path of insertion is the direction along which the RPD is placed and removed — chosen to: (1) provide a uniform undercut for the retentive clasp tips; (2) maximise guiding plane surfaces (the proximal surfaces of abutment teeth that become parallel to the path of insertion — guiding planes prevent lateral movement on insertion); (3) minimise tissue interference (prevent soft tissue displacement on insertion). The path of insertion and removal are the same — a single path from which the denture can be placed and removed without binding.
- The rest is the most important component of the RPD — it determines where occlusal load is directed: A rest is a rigid extension of the RPD framework that contacts a prepared rest seat on the abutment tooth. Its function: to direct occlusal forces along the long axis of the abutment tooth. Without rests, occlusal forces are transmitted to the mucosa and residual ridge only (mucosal-borne prosthesis) — this produces accelerated ridge resorption and abutment tooth tipping. Rest seats must be prepared in enamel (or in metal restorations): the marginal ridge must be reduced by 1.5mm at the rest seat to create a seat that holds the rest in position (if the marginal ridge is not reduced and the rest sits on the marginal ridge, occlusal force will tip the tooth). Occlusal rests are placed in posterior teeth. Cingulum rests (cingulum, lingual surface near the CEJ) are placed on maxillary canines or incisors — the lingual surface must have adequate bulk; an incisal rest notch at the incisal edge is an alternative for canines.
Key Facts
What Is Removable Partial Prosthodontics?
Removable partial prosthodontics is the branch of prosthodontics concerned with the design, fabrication, and maintenance of removable partial dentures (RPDs) — removable prostheses that replace some but not all natural teeth in an arch where some natural teeth remain. Unlike complete dentures (which support entirely on mucosa and bone) and fixed prostheses (which are cemented or implant-supported), RPDs derive support and retention from a combination of the remaining natural teeth (via rests and clasps) and the oral mucosa (via denture bases). This mixed support mechanism creates unique biomechanical challenges that drive the principles of RPD design.
RPDs remain an important treatment option in clinical practice — they are more affordable than implant-supported restorations, can replace multiple non-adjacent missing teeth in one prosthesis, are reversible (removable by the patient), can accommodate future tooth loss by addition, and are appropriate for patients with medical, economic, or anatomical contraindications to implant surgery. However, they also carry risks: caries and periodontal disease in abutment teeth (plaque accumulation under clasps), accelerated ridge resorption (if denture bases transmit excessive mucosal forces), and abutment tooth tipping (if lever forces are not controlled by good design).
Why It Matters
RPD design is heavily tested on the INBDE and NBDE — particularly Kennedy classification and Applegate’s rules, the components of an RPD and their functions, the distinction between free-end (Class I/II) and bounded (Class III) biomechanics, clasp assembly design (RPI vs. Akers, mesial vs. distal rest), and the surveying process. Clinically, poor RPD design is a common cause of abutment tooth loss — particularly when clasps torque abutment teeth or when rests are not placed correctly to prevent tissue-borne force transmission.
Kennedy Classification
The Kennedy classification (E.H. Kennedy, 1925) categorises partially edentulous arches by the position and number of edentulous areas. The class is determined by the most posteriorly located edentulous space in the arch. Additional edentulous areas beyond the most posterior are called “modifications” and are numbered by count (Mod 1, Mod 2, etc.).
| Class | Description | Biomechanical Demand | Support Type | Mods Possible? |
|---|---|---|---|---|
| Class I | Bilateral posterior free-end — missing teeth posterior to all remaining teeth on both sides | Highest — no posterior tooth support; denture base must transmit occlusal load to ridge and posterior abutments; rotational axis passes through the most posterior abutment teeth on both sides (fulcrum line) | Tooth-mucosa (tooth-tissue-borne) | Yes — Mod 1, 2, etc. |
| Class II | Unilateral posterior free-end — missing teeth posterior to all remaining teeth on one side only | High on the free-end side; the unilateral free-end creates tipping forces toward the free-end side under load; cross-arch stabilisation via major connector is critical | Tooth-mucosa on free-end side | Yes — Mod 1, 2, etc. |
| Class III | Bounded (intercalated) space — missing teeth with natural teeth both anterior and posterior to the space (on the same side) | Lowest — abutments on both sides of each space → tooth-borne prosthesis; framework rests on abutments on both sides → minimal mucosal loading | Tooth-borne (most favourable) | Yes — Mod 1, 2, etc. |
| Class IV | Single edentulous space crossing the anterior midline — anterior to all remaining teeth | Moderate — bilateral abutments, but anterior aesthetics and incisal forces create unique demands; single tooth-borne Class IV if abutments on both sides are sound | Tooth-borne | No modifications — by definition, Class IV cannot have modifications (any additional edentulous area would reclassify the arch to a posterior class) |
Applegate’s 8 Rules for Applying Kennedy Classification
- Classification should follow (not precede) extractions that might alter it — classify only after all extractions affecting the arch are complete.
- If the third molar is missing and not to be replaced, it is not considered in the classification.
- If the third molar is present and is to be used as an abutment, it is considered in the classification.
- If a second molar is missing and not to be replaced, it is not considered in the classification.
- The most posterior edentulous area always determines the classification.
- Edentulous areas other than those determining the classification are referred to as modifications and are designated by their number.
- The extent of the modification is not considered — only the number of additional edentulous areas.
- There are no modifications in Class IV.
RPD Components
Major Connector
The major connector is the primary connecting element — it rigidly unites all other components on both sides of the arch. Requirements: rigid (must not flex under load — any movement of the major connector transfers forces differently to different parts of the arch, causing imbalanced loading); positioned to avoid impinging on free gingival margins (at least 3–4mm from free gingival margin) or soft tissue relief areas; should not impinge on moving tissues (frenal attachments, floor of mouth). Common maxillary designs: (a) palatal bar — narrow, anterior-to-posterior, does not cover palate — simple, good tissue response, but limited rigidity for large bilateral cases; (b) palatal strap — wider than a bar, good rigidity; (c) palatal plate — full palatal coverage — maximum rigidity and support distribution; (d) horseshoe — U-shaped, avoids midpalatine torus — poor rigidity alone (add anterior coverage or posterior strap to stiffen). Common mandibular designs: (a) lingual bar — standard choice; (b) lingual plate — covers lingual surfaces of anterior teeth — when lingual sulcus is shallow, anterior teeth need stabilisation, or future anterior tooth loss is anticipated.
Minor Connector
Minor connectors are the structural elements that join the denture base, clasps, rests, and other components to the major connector. They must also be rigid. The proximal plate is a specific minor connector that contacts the guiding plane surface of the abutment tooth — it stabilises the RPD against lateral forces and also prevents food impaction between the natural tooth and the RPD base.
Rests and Rest Seats
Rests are rigid extensions of the framework that transmit occlusal forces to the abutment teeth. Rest seat preparation is the most important mouth preparation step. For an occlusal rest seat: shape is a rounded triangular or spoon-shaped depression in the marginal ridge area; minimum 1.5mm depth at the marginal ridge; floor inclined lingually and toward the center of the tooth (so that the rest “seats” and cannot slide off); marginal ridge must be reduced by 1.5mm minimum so the rest does not create a premature occlusal contact. For a cingulum rest seat: prepared on the lingual surface near the CEJ of maxillary anterior teeth; requires adequate lingual enamel bulk — not feasible on mandibular incisors (insufficient enamel thickness).
Clasps
A clasp assembly has three components: (1) the retentive arm — engages the tooth undercut below the survey line; the tip of the retentive arm is the only part of the clasp that should be in the undercut; (2) the reciprocal arm — contacts the tooth above the survey line (in the suprabulge); it provides reciprocation (counters the forces generated by the retentive arm during insertion/removal so the tooth is not tipped); (3) the rest — directs occlusal load axially. Clasp designs:
| Clasp Type | Approach | Best For | Retentive Undercut | Key Feature |
|---|---|---|---|---|
| Circumferential (Akers) | Occlusally-approaching — arm descends from the rest to the undercut from above the survey line | Class III bounded spaces; posterior teeth with adequate buccal undercut at junction of middle and gingival thirds | 0.01–0.02 in. (metal); 0.01–0.03 in. (wrought) | Simple, rigid, good retention; retentive tip engages the undercut below the survey line on the buccal. Distal rest + Akers on free-end = bad — creates Class I lever |
| RPI (I-bar) | Gingivally-approaching — I-bar contacts tooth from below the survey line (gingival third) | Class I/II free-end (distal extension) cases — mesial rest essential | 0.01 in. (Co-Cr) — shallow, gingival 1/3 | Allows denture base to settle under load without torquing the abutment; retentive arm disengages as the base settles; RPI = Rest (mesial) + Proximal plate + I-bar |
| Embrasure (internal) | Enters the embrasure between two teeth; two retentive arms — one per tooth in adjacent embrasure | When adjacent teeth have no suitable buccal undercut but parallel proximal surfaces exist for guidance; aesthetically superior (less visible than buccal clasps) | No undercut required — retention from bilateral proximal guidance | Requires parallel proximal guide planes on both adjacent teeth; less visible; does not rely on undercut; requires very careful path of insertion design |
| Ring clasp | Encircles most of the crown (used for tilted or isolated posterior teeth) | Isolated molar teeth (often tilted mesially after tooth loss); when the only suitable undercut is on the mesio-lingual surface | 0.01–0.02 in. at the terminal tip only | Requires a support spur from the major connector to prevent distortion; wraps ~¾ of crown circumference; most flexible section is the long arm — must not engage excessive undercut |
Denture Bases
RPD denture bases are the acrylic sections that bear the artificial teeth and contact the mucosal residual ridge. They may be: (a) metal (Co-Cr or gold) base — used in Class III tooth-borne cases where minimal ridge coverage is needed; rigid; easier to clean; cannot be relined because metal does not bond to new acrylic without special provisions; (b) acrylic resin base — used for free-end (Class I/II) extension cases because they can be relined as the ridge resorbs; tissue surface can be adjusted; indirect retention provided by extending the base sufficiently to resist displacement.
Surveying and Path of Insertion
Surveying is performed on a diagnostic cast (before any mouth preparation) and then on the master cast (after mouth preparation is complete, to verify and finalise the framework design). The surveyor is used to: (1) determine the height of contour (survey line) of each tooth for clasp placement; (2) identify blocking undercuts that must be blocked out with wax in the laboratory before casting; (3) establish guiding planes by marking parallel surfaces on adjacent abutment teeth; (4) determine the optimal path of insertion by tilting the cast. The tilt of the cast is recorded by noting the angle of the cast table at the chosen path of insertion — this tilt is reproduced on the master cast to ensure the framework is designed and cast to the same path of insertion as the mouth preparation.
The height of contour changes with cast tilting — tilting the cast anteriorly raises the anterior survey line and lowers the posterior survey line; tilting posteriorly does the opposite. The clinician selects the cast tilt that provides: optimal undercuts on the preferred clasp teeth; minimal undesirable undercuts on non-clasp teeth; maximum guide plane surfaces; and the most acceptable path of insertion for patient-friendly placement and removal.
RPD Biomechanics
The biomechanical behaviour of an RPD is determined primarily by whether it is tooth-borne, tissue-borne, or tooth-and-tissue-borne (tooth-mucosa supported):
Class III (tooth-borne): Occlusal forces are transmitted entirely through the rests to the abutment teeth — the denture base does not contact the mucosa under load (or contacts it only minimally). The framework acts like a small bridge. The fulcrum of rotation passes through the most posterior rests. Forces on the anterior extension of the framework tend to lift it toward the mucosa (indirect retainer needed anteriorly to prevent this).
Class I/II (tooth-mucosa-borne): Occlusal forces are transmitted partly through posterior rests to the abutment teeth and partly through the denture base to the residual ridge mucosa. Under load, the free-end base settles inferiorly (compressing the mucosa). The fulcrum line passes through the posterior abutment rests (the most posterior rests on each side for Class I). As the free-end base settles, the anterior portion of the RPD tends to be lifted away from the mucosa — this is prevented by indirect retainers (rests on anterior teeth, placed as far anteriorly as possible on the opposite side of the fulcrum line from the free-end). The distance of the indirect retainer from the fulcrum line determines its effectiveness: the further from the fulcrum, the greater the moment arm and the better the indirect retention.
Clinical Steps and Abutment Preparation
The clinical sequence for RPD fabrication: (1) Preliminary examination and treatment planning — diagnose caries, periodontal disease, pathology; identify abutment teeth; plan any needed extractions, endodontic treatment, crown lengthening; (2) Mouth preparation — includes rest seat preparation (occlusal or cingulum), enameloplasty or restoration of guide plane surfaces, removal of interference undercuts, restoration of abutment teeth as needed; (3) Final impressions — primary impressions (alginate in stock tray) for diagnostic cast and custom tray fabrication; final impressions (alginate or PVS in custom tray) for master cast; (4) Laboratory construction — surveying master cast, designing framework, casting (Co-Cr), finishing; (5) Try-in — framework try-in in mouth: check seating, occlusal rests, guide planes, clasp fit, retention; (6) Record base and occlusal rim construction — for jaw relation records (CR record, OVD assessment); (7) Teeth arrangement and wax try-in; (8) Processing and delivery; (9) Post-insertion adjustments and maintenance — check occlusion, adjust base extensions, schedule recall at 6–12 months.
Implant-Retained RPD (Implant-Assisted RPD)
When appropriate implants are placed in strategic positions in a partially edentulous arch, they can provide additional support or retention for an RPD — eliminating the free-end problem, reducing mucosal loading, or replacing clasps for improved aesthetics. A single implant placed in the distal free-end region of a Class I/II RPD converts it from a distal extension (mucosa-borne distally) to a tooth-borne prosthesis on both sides — significantly reducing ridge resorption and abutment tooth torque. The implant may provide retention via a ball-and-socket attachment or Locator attachment incorporated into the RPD framework. This hybrid approach is increasingly used as an intermediate-cost alternative to full implant-supported fixed bridges.
Clinical Considerations
- Plaque control and caries prevention around abutment teeth are the most critical long-term maintenance factors: Abutment teeth for RPDs have a higher caries rate and higher periodontal bone loss rate than adjacent non-abutment teeth in the same patient. Clasp arms and rest seats create areas where plaque accumulates and cannot be effectively reached by standard brushing. All patients receiving RPDs must have: (a) intensive oral hygiene instruction specific to RPD care; (b) fluoride supplementation (professionally applied fluoride varnish every 3–6 months for abutment teeth; home fluoride toothpaste; fluoride gel application in high-caries-risk patients); (c) diet counselling; (d) regular recall (every 6 months) to check for early caries at clasp contact sites. The RPD should be removed every night to allow tissue recovery — continuous wearing is associated with increased Candida colonisation and RPD stomatitis (similar to complete denture stomatitis).
- The rest seat is the most important irreversible mouth preparation step — plan it carefully before drilling: Rest seat preparation removes enamel — this cannot be undone. Before preparing rest seats, confirm: (a) the Kennedy classification is correct and will not change; (b) the planned path of insertion is finalised; (c) the selected abutment teeth are periodontally sound and caries-free; (d) the rest seat location is on the correct abutment tooth and in the correct position (mesial vs. distal — important for free-end cases). Preparation on the wrong tooth, too shallow, or on an unsupported marginal ridge creates a non-functional rest and may require a cast metal restoration on the abutment.
- Never deliver an RPD without checking the occlusion carefully on both sides simultaneously: RPDs commonly create supracontacts (premature contacts) because: (a) artificial teeth were processed at a slightly different OVD than the wax try-in; (b) the acrylic base flexed slightly during processing; (c) the articulation was not perfectly transferred from the mounting. Use 40 µm articulating foil to identify heavy contacts and adjust with a high-speed handpiece and polishing. Bilateral balance in centric occlusion and no lateral interferences on the RPD teeth is the target.
- Clasps should never be adjusted chairside by bending — this work-hardens and may fracture the clasp: Cast Co-Cr clasps are brittle — they cannot be adjusted by bending without risk of fracture (work-hardening). If a clasp requires adjustment (too tight, too loose, impinging on gingiva), the options are: (a) return to the laboratory for professional adjustment (very limited bending possible for gross issues); (b) replace the clasp with a wrought wire clasp (which is more ductile and can be bent carefully); (c) reline or remake the framework. Wrought gold wire clasps (Type IV gold — half-round or round wire) are more flexible and can be adjusted carefully, but they are weaker than cast clasps and may distort over time.
- Indirect retainers must be as far from the fulcrum line as possible to be effective: The effectiveness of an indirect retainer is proportional to its distance from the fulcrum line (the line through the most posterior rests). An indirect retainer placed immediately adjacent to the fulcrum line provides almost no benefit. For a Class I mandibular RPD (bilateral free-end), the fulcrum line passes through the most posterior mandibular abutment rests. Indirect retainers should be placed as far anteriorly as feasible — on the mesial surfaces of the premolars or on the cingula of canines or incisors. Anterior rest placement also prevents the anterior portion of the framework from “seesawing” away from the mucosa as the posterior free-end bases settle under occlusal load.
Common Mistakes & Misconceptions
- Misconception: “Kennedy classification is determined by the most anterior edentulous area.”
Correction: Kennedy classification is always determined by the most posterior edentulous area — not the most anterior, not the most extensive. A patient missing both upper first molars (bilateral, posterior) and both upper central incisors would be classified as Kennedy Class I (bilateral free-end posterior), not Class IV (anterior), because the most posterior spaces determine the class. The anterior edentulous space becomes a Modification (Mod 1, in this case). - Misconception: “A distal rest is always preferred on a posterior abutment for a free-end RPD.”
Correction: For a distal extension (Kennedy Class I/II) free-end RPD, a distal rest on the most posterior abutment creates a Class I lever: as the free-end base settles under occlusal load, the rest acts as a fulcrum and torques the abutment distally and inferiorly — highly destructive. A mesial rest is required for the RPI (or other gingivally-approaching) clasp assembly on free-end abutments — so that loading settles the base without creating a distal torque. This is the most commonly tested RPD concept on board examinations. - Misconception: “The horseshoe (U-shape) maxillary major connector provides adequate rigidity for large bilateral cases.”
Correction: The horseshoe connector covers only the anterior and lateral palate — it does not have a posterior palatal strap. This makes it the least rigid of all maxillary major connectors and inherently prone to flexion under bilateral occlusal load. It is only appropriate when a palatal torus or other midline obstruction prevents palatal coverage, and even then, it should be avoided if any alternative can be designed. For Class I or II cases requiring maximum rigidity, the anteroposterior palatal strap or full palatal coverage should be used. - Misconception: “More clasps provide better retention for an RPD.”
Correction: The number of clasps needed depends on the retention demands of the specific design — usually two to four clasp assemblies are sufficient. Additional clasps beyond what is needed do not improve retention significantly and increase: (a) the amount of metal visible (aesthetics); (b) plaque accumulation sites; (c) forces transmitted to abutment teeth on insertion/removal; (d) the possibility of destroying abutment teeth via excessive clasping forces. Good retention depends on proper undercut engagement, correct path of insertion, well-designed guide planes, and appropriate clasp type for the abutment — not simply on the number of clasps. - Misconception: “Class IV has modifications just like the other classes.”
Correction: Class IV (single anterior edentulous space crossing the midline) has no modifications — by definition, per Applegate’s rules. If any other edentulous area exists in the arch beyond the anterior space, the presence of that additional (more posterior) space would reclassify the arch to a different class. Class IV can only apply when there is a single anterior edentulous space with natural teeth on both sides extending posteriorly — any additional space reclassifies the arch.
Related Topics
References & Sources
- Carr AB, Brown DT (2015). McCracken’s Removable Partial Prosthodontics, 13th ed. Elsevier. [The standard RPD text — Kennedy classification, RPD components, design principles, surveying, clinical procedures]
- Kennedy E (1925). Partial denture construction. Dental Cosmos, 67:1103–1109. [Original Kennedy classification paper]
- Applegate OC (1960). The rationale of partial denture choice. Journal of Prosthetic Dentistry, 10(5):891–907. [Applegate’s eight rules for application of Kennedy classification]
- Krol AJ (1973). RPI (rest, proximal plate, I-bar) clasp retainer and its modifications. Dental Clinics of North America, 17(4):631–649. [Original RPI clasp description — mesial rest + proximal plate + I-bar for free-end abutments]
- Frank RP, Brudvik JS, Leroux B, et al. (2000). Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction. Journal of Prosthetic Dentistry, 83(5):521–527. [RPD quality and patient outcomes — clinical performance data]
- Wöstmann B, Budtz-Jørgensen E, Jepson N, et al. (2005). Indications for removable partial dentures: a literature review. International Journal of Prosthodontics, 18(2):139–145. [Evidence-based indications for RPDs vs. implants and fixed options]
- Davenport JC, Basker RM, Heath JR, et al. (2000). A Clinical Guide to Removable Partial Dentures. BDJ Books. [Practical clinical guide — surveying, design, mouth preparation, impression techniques]
- Bergman B, Hugoson A, Olsson CO (1995). A 25-year longitudinal study of patients treated with removable partial dentures. Journal of Oral Rehabilitation, 22(8):595–599. [Long-term RPD outcomes — abutment tooth caries and periodontal disease rates]
Summary
RPDs replace missing teeth while deriving support and retention from remaining natural teeth and mucosa. Kennedy classification organises partially edentulous arches: Class I (bilateral free-end — most demanding), Class II (unilateral free-end), Class III (bounded — most favourable, tooth-borne), Class IV (anterior, no modifications). Key Applegate rule: the most posterior edentulous space determines the class; Class IV has no modifications. The RPD framework consists of major connector (rigid, arch-unifying element), minor connectors, rests (transmit occlusal forces axially to abutment teeth), clasps (retain against dislodgement), and denture bases (bear artificial teeth). For free-end (Class I/II) cases, use a mesial rest + RPI or gingivally-approaching clasp — NOT a distal rest + Akers, which creates a destructive Class I lever. Indirect retainers (anterior rests, far from fulcrum line) prevent seesawing of the free-end base. Surveying determines the path of insertion, survey line, guide planes, and undercut locations before framework design.
Key Takeaways
- Kennedy classes: I = bilateral free-end; II = unilateral free-end; III = bounded (tooth-borne, most favourable); IV = anterior crossing midline, no mods. Most posterior space = the class.
- Free-end biomechanics: Use mesial rest + RPI clasp (or gingivally-approaching clasp). NEVER distal rest on the most posterior free-end abutment — creates Class I lever, torques abutment distally under load.
- Indirect retainer: Anterior rest placed as far from the fulcrum line as possible — prevents free-end base from seesawing away from mucosa during function.
- Surveying: Determines height of contour, path of insertion, guide planes, and undercut positions. Casting cast tilt produces different survey lines — optimal tilt = uniform undercuts + maximum guide planes + patient-friendly insertion direction.
- Maintenance: Abutment teeth have elevated caries/periodontal risk under clasps. Remove RPD nightly; prescribe fluoride; 6-month recall minimum.
About the Author
