The tissue side of a pontic in a fixed partial denture should be smooth to ensure proper hygiene and patient comfort. A smooth surface minimizes plaque accumulation and reduces irritation or injury to the underlying mucosa. Rough, porous, or grooved surfaces can trap food debris and bacteria, leading to inflammation, infection, and tissue breakdown. Maintaining a smooth tissue surface promotes healthy soft tissue adaptation and facilitates easier cleaning by the patient, which is critical for the long-term success of the prosthesis.

Reference: Prosthodontics, Shigli & Hegde, 2nd Edition.