A primary molar is below the occlusal plane, has no mobility, gives a solid high-pitched percussion note, and shows no PDL space radiographically. This is most consistent with:

Ankylosis is fusion of tooth to bone with loss of the PDL, so the tooth is immobile, 'submerged' (infraoccluded) as adjacent teeth keep erupting, and gives a solid higher-pitched percussion note with an absent PDL space. Ankylosed primary molars often fail to exfoliate normally.Other options: Normal exfoliation shows mobility; vertical root fracture and hypercementosis have different features (hypercementosis = excess cementum, not infraocclusion).Key exam takeaway: Infraoccluded, immobile tooth with solid percussion and no PDL space = ankylosis.