The primary drawback of using conventional PMMA (Polymethyl methacrylate) as a denture base material is its high water sorption.

- PMMA is widely used in prosthodontics due to its good esthetic qualities, ease of manipulation, and biocompatibility.
- However, one significant limitation is its tendency to absorb water over time.
- This high water sorption can lead to dimensional changes, such as swelling or distortion, which may affect the fit and function of the denture.
- Additionally, absorbed water can lead to reduced mechanical properties and increased potential for microbial colonization, compromising the longevity and hygiene of the denture base.

Other options considered:
- Low flexural strength: While PMMA has moderate strength, its flexural strength is generally adequate for denture bases. Improvements through fiber reinforcement exist but are not the primary drawback.
- Excessive polymerization shrinkage: Polymerization shrinkage does occur but is relatively minimal and manageable with proper processing techniques.
- Poor esthetic appearance: PMMA is actually preferred for its excellent esthetics, closely mimicking the natural oral tissues.

Therefore, the key limitation remains its high water sorption, which impacts the dimensional stability and durability of the denture base.

Reference: Contemporary Fixed Prosthodontics*, 5th Edition, Chapter 6: Denture Base Materials/Page 178