# A 68-year-old male patient presents with a Kennedy’s class III partially edentulous arch. What is the nature of support in this situation?
A. Tooth supported
B. Bilateral distal extension
C. Tooth tissue supported
D. Unilateral distal extension
The correct answer is A. Tooth supported.
Clinical Reasoning
In Kennedy’s Class III, the edentulous area is bounded both anteriorly and posteriorly by natural teeth. Because there are functional abutments at both ends of the span, the occlusal forces are transmitted directly through the teeth to the alveolar bone via the periodontal ligament.
Unlike Class I or Class II (Distal Extension) cases, there is no "extension" base that relies on the compressibility of the soft tissue (mucosa) for support.
Breakdown of Support Mechanisms
| Classification | Support Type | Rationale |
| Class I & II | Tooth-Tissue Supported | Includes a distal extension; support comes from both abutment teeth and the residual ridge/mucosa. |
| Class III | Tooth Supported | Bounded by teeth; the abutments bear the entire functional load. |
| Class IV | Tooth or Tooth-Tissue | Depends on the length of the span; short spans are tooth-supported, while long spans may involve tissue support. |
Abutment Selection: In Class III, the primary requirement for an abutment is its ability to resist vertical and horizontal forces. Because it is tooth-supported, the "lever" action seen in distal extension cases (Class I & II) is virtually non-existent.
Stress Breakers: These are generally not indicated in Class III situations because there is no differential in displacement between the teeth and the ridge during function.
Applegate's Rules: Remember Rule #5—the most posterior edentulous area(s) always determine the classification. A Class III situation specifically implies that the most posterior space is bounded by a tooth.
