Kennedy Class II Modification 1 RPD With Compromised Abutments
A 62-year-old man is missing mandibular teeth 35, 36, 37, and 46. The remaining teeth include 34, 38, 45, and 47. Tooth 34 has a 3-mm ferrule and 4-mm probing depth; 45 has a composite core, 2-mm ferrule, grade I mobility, and 5-mm probing depth. The periodontal condition is stable after scaling, but the patient smokes 12 cigarettes/day. The maxillary arch has a complete denture. He wants a removable partial denture and refuses implants because of cost. The edentulous ridge on the left is 6 mm wide and 10 mm high; the right modification space is 8 mm wide. The opposing complete denture has worn posterior teeth.
1. Design the RPD for this Kennedy Class II modification 1 mandible. Specify rests, clasps, major connector, and how you would manage the distal extension.
Read the worked answer
The main edentulous space is the left distal extension (35–37); the right side has a bounded modification space (46). The design must respect the difference: the left base is tissue-supported, while the right space is tooth-supported.
- Major connector: a lingual plate is reasonable because it provides rigidity and some cross-arch stabilization for periodontally involved abutments, but it must not impinge on the gingival margin. A lingual bar is an alternative if hygiene access is poor.
- Left distal extension: use 34 with a mesial rest and a stress-releasing clasp (RPI or wrought-wire retentive arm) to allow the base to move without torquing 34. Do not use a conventional circumferential clasp on 34 as the only retainer for a distal extension. The distal base should be an altered-cast, functional impression.
- Right modification space: 45 and 47 can be used with rests and a circumferential clasp on 47; 45 should receive a rest and possibly a survey crown if the composite core is inadequate. Because this space is tooth-supported, it does not need the same stress release as the left side.
- 38: assess whether it is a suitable abutment; if it is tipped or has poor crown form, do not force it into the design.
The framework should be tried in before processing to verify rest seating and no torque.
2. Evaluate the prognosis of 45 and 34 as abutments. Would you modify the design or recommend extraction/implant?
Read the worked answer
Tooth 34 is the better abutment: 3-mm ferrule and 4-mm probing depth are acceptable if the periodontal condition is stable, though the patient’s smoking worsens long-term prognosis. Tooth 45 is more compromised: 5-mm probing depth, grade I mobility, a composite core, and only 2-mm ferrule. Mobility alone is not an absolute contraindication, but it signals reduced support, and using 45 as a terminal abutment for a clasp-retained RPD could increase torque.
I would not immediately extract 45. I would first reassess periodontal stability, consider a survey crown or core build-up to improve contour and ferrule, and use 45 with a rest and a less rigid retentive element rather than a heavy clasp. If 45 remains mobile or has increasing pocket depth, I would shorten the span or extract it and extend the base, accepting a less favorable design. Because the patient refuses implants, I would explain that the RPD is a maintenance-oriented solution, not a definitive replacement for missing teeth, and that 45 may fail.
3. How would you minimize torque and tissue displacement on the distal extension, and what instructions for hygiene and smoking cessation would you give?
Read the worked answer
I would use an altered cast technique with a functional impression of the left distal extension, so the base is made to fit the loaded tissue. The framework should have a mesial rest on 34 and a stress-releasing clasp; the base should be relieved slightly and then adjusted at insertion. Occlusal contacts should be checked with the opposing complete denture, and the patient should be seen for post-insertion adjustments.
Hygiene instructions:
- remove the RPD after meals and clean it with a brush and nonabrasive cleanser;
- use interdental brushes around 34, 45, and 47 and under the lingual plate;
- massage the ridge and inspect for sore spots;
- do not wear the RPD at night if the tissues need rest.
Smoking cessation is important because 12 cigarettes/day worsens periodontal prognosis and healing. I would refer for cessation support and explain that continued smoking increases the chance of abutment loss. I would also schedule a 6-month recall and consider a reline if the distal extension loses adaptation.