• Loss of Lamina Dura: The lamina dura is the thin layer of dense bone that lines the tooth socket (alveolus). In hyperparathyroidism, the loss of lamina dura can be observed due to the increased osteoclastic activity and bone resorption.

• Ground Glass Appearance: This refers to a radiographic appearance of bone that looks hazy or "ground glass" rather than having a clear, well-defined structure. This appearance is due to the alteration in bone density and the presence of fibrous tissue replacing normal bone.

Other Options:

1. Osteogenesis Imperfecta: This condition is characterized by brittle bones due to a defect in collagen formation. Radiographically, it may show thin cortices and osteopenia, but not typically a ground glass appearance.

2. Osteopetrosis: This is a condition of excessive bone density due to impaired osteoclast function. Radiographically, it shows increased radiopacity (dense bones) rather than a ground glass appearance.

3. Osteitis Deformans (Paget's Disease): This condition is characterized by disorganized bone remodeling. Radiographically, it can show a "cotton wool" appearance and enlarged bones, but it does not typically present with a loss of lamina dura or a ground glass appearance in the early stages.

• 1) Provide vertical stop: True. Internal rests prevent vertical displacement of the RPD by engaging the ridge.
• 2) Provide horizontal stabilization: True. They resist lateral forces and stabilize the prosthesis.
• 3) Act as occlusal rests: False. Occlusal rests are placed on the occlusal surfaces of abutment teeth for vertical support. Internal rests are not occlusal; they are intraoral (e.g., cingulum or palatal rests).
• 4) Provide retention: True. They contribute to retention by engaging undercuts or providing frictional resistance.