Kennedy Classification and Applegate's Rules in RPD

On 12-04-2021 | Read time about 9 Minutes

Removable partial denture is a prosthesis that replace some missing teeth in the maxilla or/and mandible. They can be removed by the will of the patient.

For planning a prosthesis, the partial edentulous arch needs to be classified to make them easier for diagnosing, planning, communicating and designing a denture.

Kennedy’s classification is so far the easiest and widely used classification for partially edentulous arch. The classification is based on the relationship of edentulous arch to the adjacent abutment teeth.

They are classified as follows:

Kennedy Class I: Bilaterally located edentulous spaces, posterior to natural teeth.

In a Kennedy Class I scenario, there are edentulous spaces on both sides of the arch, and they are located posterior to the remaining natural teeth. When planning a prosthesis, the appliance should have some features that keep the denture fixed and perform their function efficiently. The partial denture is designed as follows:

Direct retention: Kennedy Class I dentures are generally tooth and tissue supported. They get retention from the tissue as well as the abutment teeth.
Clasps: two retentive clasps are placed on each abutment which is always the last tooth near the edentulous space. The type of clasp depends on the location of undercut. To more learn about about Clasps used in RPD designing, check this page.
Rests: teeth selected for rest should provide maximum support to the prosthesis and are generally placed next to the edentulous space.
Major connector: they connect all other components of the partial denture. They are generally antero posterior palatal strap or full palate for the maxilla and lingual bar or lingual plate for the mandible.

Kennedy Class II: A unilateral edentulous space located posterior to the remaining natural teeth.

In a Kennedy Class II scenario, the edentulous space is similar to class I but present only on one side of the arch. The partial denture is designed as follows:

Direct retention: they are tooth and tissue supported. They get support from tissue as well as the abutment teeth.
Clasps: three retentive clasps are placed. One on the abutment teeth on the edentulous side and two on the opposite dentulous side.
Rests: teeth selected for rest should provide maximum support to the prosthesis and are generally placed next to the edentulous space. To more learn about about Clasps used in RPD designing, check this page.
Major connector: they connect all the components of the denture. They are generally anteroposterior palatal strap in the maxilla and horse-shoe, lingual bar or lingual plate in the mandible.

Kennedy Class III: A unilateral edentulous space with natural teeth remaining both anterior and posterior to it.

In a Kennedy Class III scenario, the edentulous area is on one side, but have teeth anterior and posterior to the edentulous space. The partial denture is designed as follows:

Direct retention: retention can be achieved from abutment teeth on either side of the edentulous area.
Clasps: 4 clasps are placed in a quadrilateral position to get maximum support and prevent the denture for dislodging.
Rests: teeth selected for rest should provide maximum support to the prosthesis and are generally placed next to the edentulous space.
Major connector: they generally use palatal strap or palatal bar for maxilla and lingual bar for the mandible.

Class IV: A single, but bilateral (crossing the midline), edentulous space located anterior to the remaining natural teeth.

A Kennedy Class IV scenario has missing teeth in the anterior region, with the missing teeth on both sides of the midline together. Design configuration with Kennedy Class IV is unique compared to other classes. They require esthetic consideration to make them look as natural as possible. Clasps and other retentive features are places in area with least visibility and the major connector should be rigid and broad palatal coverage is used in the maxillary arch.

Applegate’s rule for Kennedy Classification

Type and number of teeth missing is different from patient to patient. Therefore, correlating every partially edentulous case to 4 simple groups in a classification is difficult. Applegate provided eight rules to govern the application of Kennedy’s system.

Rule 1: Classification should follow rather than precede any extractions of teeth that might alter the original classification.

All extractions that are required needs to be completed before planning a partial denture because extractions in the posterior region could alter the classification.

Rule 2: If a third molar is missing and is not to be replaced, it is not considered in the classification.

Third molars if missing, are not replaced- they are not considered while planning the dentures.

Rule 3: If a third molar is present and is to be used as an abutment, it is considered in the classification.

In case the third molars are present and can be used as abutment, they are 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 (e.g., if the opposing second molar is likewise missing and is not to be replaced).

If second molars are missing, they are not replaced and not considered in the classification.

Rule 5: The most posterior edentulous area (or areas) always determines the classification.

Missing teeth in the most posterior area determines the classification. An edentulous area should be classified as Kennedy Class I first, before moving on to classify as Kennedy Class II. An edentulous area should be classified as Kennedy Class II first, before moving on to classify as Kennedy Class III. An edentulous area should be classified as Kennedy Class III first, before moving on to classify as Kennedy Class IV.

Rule 6: Edentulous areas other than those that determine the classification are referred to as modifications and are designated by their number.

Missing teeth after classifing the scenario, into Kennedy Class I, II III or IV are referred to as modification and are designated by the number of such spaces (not number of missing teeth).

Rule 7: The extent of the modification is not considered, only the number of additional edentulous areas.

Only the number of edentulous area present are counted, not the number of missing teeth.

Representation of Modifications of Applegate’s rule 6 and 7 are as below.

This is Kennedy class III with a single edentulous area anteriorly, hence designated as class III modification 1.

This is Kennedy class III with two edentulous area - the second premolars and first molars are missing posteriorly and lateral incisor and canine missing anteriorly, hence designated as class III modification 2.

Rule 8: No modification areas can be included in Class IV arches.

The other edentulous areas will be having to be posterior to this edentulous space and will hence determine the classification.

Merits and demerits of Kennedy classification

Merits

The classification is simple and universally acceptable.
They make writing and diagnosing the condition of the oral cavity in which missing teeth are to be replaced easier.
They permit visualization of the type of edentulous arches considered without clinically checking them.
Classification is based on the relationship of the edentulous spaces to the abutment teeth so type of support can be easily determined.
The number and location of edentulous spaces can be identified.
The classification provides design for each class. Guidelines and principals for each class have been proposed.

Demerits

They do not indicate the number of missing teeth in each edentulous area.
Assessment of the hard and soft tissue status are not included in the classification.
They do not indicate the position of individual tooth.
They do not permit assessment of occlusion.