Dental Apptitude
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Kennedy's Classification
Simulator

Removable Partial Denture Design Suite Component

Kennedy's Classification System and Applegate's Rules

When designing a Removable Partial Denture (RPD), we use two matching systems to describe a mouth with missing teeth. Kennedy's system tells us exactly where the empty spaces are located. Applegate's rules help us decide which of those spaces actually need to be filled or used to anchor the framework. Use this introductory guide to master both before using the interactive tools!

1. The Four Base Kennedy Classes

Every jaw with missing teeth falls into one of these four core categories. The classification is always determined by the most posterior edentulous area in the mouth.

Key Concept 1: Free-End vs. Bounded. A free-end saddle means there are no natural teeth standing posterior to the edentulous saddle; the posterior/distal part of the saddle is tissue-borne (i.e., it rests directly on the gum tissue). A bounded saddle means the edentulous area has natural teeth remaining at either end of it, acting as abutments. These areas should be tooth-borne (i.e., with occlusal or cingulum rests on each abutment).

Key Concept 2: Bilateral vs. Unilateral. These terms describe how missing spaces relate to the dental midline. Bilateral means the edetulous area crosses the midline (as seen in Class I and Class IV). Unilateral means the edentulous area exists strictly on one side of the midline only, leaving the opposite side of the midline anatomically different (as seen in Class II and Class III).

Class I

Definition: Bilateral edentulous areas located posterior to the remaining natural teeth.

Bilateral Free-End: Teeth are missing at the back on both the left and right sides. No natural back teeth remain behind these two posterior gaps. Because there are no posterior tooth pillars to anchor to, the denture framework must rely heavily on the tissue of the residual ridges for support.

Class II

Definition: A unilateral edentulous area located posterior to the remaining natural teeth.

Unilateral Free-End: Teeth are missing at the back on only one side of the mouth. The opposite side of the arch still features an intact line of natural back teeth. This creates an asymmetrical design challenge where one side behaves like a tissue-supported saddle and the other side acts as a tooth-supported anchor.

Class III

Definition: A unilateral edentulous area with natural teeth both anterior and posterior to it.

Bounded Space: An edentulous area located on one side that has healthy, natural teeth standing at either end. This is a completely tooth-supported scenario—the adjacent teeth act as solid pillars (abutments) to fully carry the forces of chewing without pushing into the gums.

Class IV

Definition: A single bilateral anterior edentulous area crossing the midline.

Anterior Midline: A single edentulous area in the anterior of the mouth that crosses the exact center line (midline). Crucially, to stay a Class IV, it must be the only missing space in the entire arch. The denture teeth replace incisors or canines, while the framework reaches back to the posterior teeth for retention.

Understanding "Modifications" (Mods)

What happens if a patient fits a base class but has extra missing gaps elsewhere? We call these extra spaces Modifications.

Once you look at the furthest-back gap to choose your primary Class (I, II, or III), you simply count the number of extra missing spaces left over in the rest of the mouth. If there is 1 extra space, it's a "Mod 1". If there are 2 extra spaces, it's a "Mod 2"—regardless of how many individual teeth are missing inside those spaces.

2. Applegate's Sorting Rules

These rules act as filters. Apply them in order from 1 to 8 to solve tricky clinical cases without guessing.

Rule Definition What It Means In Simple Terms
Rule 1 Classification should follow rather than precede extractions. Plan ahead. If any bad teeth need to be pulled out, pretend they are already gone before figuring out the classification.
Rule 2 If a third molar is missing and is not to be replaced, it is not considered in the classification. If a wisdom tooth is missing and you aren't going to place a denture tooth there, completely ignore it. It does not count as a gap.
Rule 3 If a third molar is present and is to be used as an abutment, it is considered in the classification. If a wisdom tooth is healthy and you plan to clasp it, it counts as a natural abutment tooth.
Rule 4 If a second molar is missing and is not to be replaced, it is not considered in the classification. If a second molar is missing and the patient doesn't need it replaced (e.g., they have no chewing tooth opposing it), cross it off and ignore it.
Rule 5 The most posterior edentulous area (or areas) always determines the classification. Always scan the mouth from back to front. The empty space furthest back in the jaw dictates your main Class (I, II, III, or IV).
Rule 6 Edentulous areas other than those determining the classification are designated as modifications and are designated by their number. Any extra edentulous areas outside of your main class choice are simply called modifications.
Rule 7 The extent of the modification is not considered, only the number of additional edentulous areas. Count the number of missing gaps, not the individual teeth. A gap missing 3 teeth in a row counts as exactly one single modification space.
Rule 8 There can be no modification areas in Class IV arches. To be a Class IV, the front midline gap must be the only gap. If there is even one single missing tooth space behind it, that back space takes priority due to Rule 5, changing the whole class.
Fully Present
Missing & Replaced (Saddle Area)
Missing & Ignored (Applegate Exception)
Maxillary Arch
Mandibular Arch
Select a Kennedy Class Scenario
Click any scenario block on the right to visualize explicit arch layouts. Repeatedly clicking cycles through variations showing how Applegate rules resolve potential paradoxes.

Case Portfolios

Click to cycle variants

Click each scenario below to see examples in the canvases and clinical breakdowns in the description card below. Repeatedly clicking a card cycles through variants.

Var 1/3
Class I Scenarios
Definition: Bilateral distal extension saddles located posterior to remaining natural teeth.
Var 1/3
Class II Scenarios
Definition: A unilateral distal extension saddle located posterior to remaining natural teeth.
Var 1/3
Class III Scenarios
Definition: A unilateral bounded space with natural teeth both anterior and posterior.
Var 1/2
Class IV Scenarios
Definition: A single bilateral anterior space crossing the midline.
Var 1/4
Applegate Rule Explanations
Definition: Dedicated examples resolving Molar presence/absence rules.
Fully Present
Missing (To Be Replaced)
Missing (Ignored)
Maxillary Arch
Mandibular Arch
Classification Space

Click the teeth in the arch to change their status and view the real-time computed classification below. Use the hide button above to mask the result and test yourself or your classmates!

Tooth Status