Kennedy’s Classification of Edentulous Space and Applegate’s Rules

The Kennedy method of classification was originally proposed by Dr. Edward Kenedy in 1925. Like the Bailyn classification and also the Skinner classification, it is to classify the partially edentulous arch in a manner that will suggest certain principles of design for a given situation. the classifications don’t just make it easy for students but for the dental surgeons later to communicate about the condition and decide the line of treatment of partially edentulous jaws.

Kennedy divided all partially edentulous arches into four main types. Edentulous areas other than those determining the main types were designated as modification spaces.

Kennedy Classification

The Kennedy classification is as follows:

  • CLASS I: Bilateral edentulous areas located posterior to the remaining natural teeth
  • CLASS II: A unilateral edentulous area located posterior to the remaining natural teeth
  • CLASS III: A unilateral edentulous area with natural teeth remaining both anterior and posterior to it
  • CLASS IV: A single, but bilateral (crossing the midline), edentulous area located anterior to the remaining natural teeth

One of the principal advantages of the Kennedy method over the others is that it permits immediate visualization of the partially edentulous arch. Those schooled in its use and in the principles of partial denture design may immediately compartmentalize their thinking concerning the basic partial denture and is, therefore, a logical method of classification.

Kennedys classification of edentulous space

Applegate’s rule for applying the Kennedy classification

The Kennedy classification would be difficult to apply to every situation without certain rules for application. Applegate has provided the following eight rules governing the application of the Kennedy method.

RULE 1: Classification should follow rather than precede any extractions of teeth that might alter the original classification.
RULE 2: If a third molar is missing and not to be replaced, it is not considered in the classification.
RULE 3: If a third molar is present and is to be used as an abutment, it is considered in the classification.
RULE 4: If a second molar is missing and is not to be replaced, it is not considered in the classification (for example, if the opposing second molar is likewise missing and is not to be replaced).
RULE 5: The most posterior edentulous area (or areas) always determines the classification.
RULE 6: Edentulous areas other than those determining the classification are referred to as modifications and are designated by their number.
RULE 7: The extent of the modification is not considered, only the number of additional edentulous areas.
RULE 8: There can be no modification areas in Class IV arches. (Another edentulous area lying posterior to the “single bilateral area crossing the midline” would instead determine the classification)

Whereas it is true that there is some confusion in the mind of the student initially as to why Class I should refer to two edentulous areas and Class II should refer to one, the principles of design make this position logical. Either by design or by accident, presumably, the former, Kennedy placed the class II unilateral distal extension type and the Class III tooth bounded classification. Any change in this order would be illogical for the following reasons. The Class I partial denture is designed as a tooth- and tissue supported denture.

Three of the features necessary for the success of such a denture are: 1. Adequate support for the distal extension bases, 2. Flexible direct retention, and 3. Some provision for indirect retention.

The Class III partial denture is designed as a tooth-borne denture, without need generally (but not always) for indirect retention, without base support from the ridge tissues, and with direct retention, the only function of which is to retain the prosthesis. An entirely different design is, therefore, common to each class because of the difference in support.

However, the Class II partial denture must embody features of both, especially when tooth-borne modifications are present. Having a tissue-supported extension base, it must be designed similarly to a Class I denture, but frequently there is a tooth-supported, or Class III, component elsewhere in the arch. Thus the Class II partial denture rightly falls between the Class I and the Class III because it embodies design features common to both. In keeping with the principle that design is based on the classification, the applicaton of such principles of design is simplified by retaining the original classification of Kennedy.

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