Assertion: Aptyalism patients have higher than normal incidences of dental caries.
Reason: Aptyalism is caused by the action of parasympa- thetic nervous system

Answer

### Step-by-Step Solution:

1. **Understanding Aptyalism**:
- Aptyalism refers to the condition where there is a deficiency or absence of saliva in the mouth. Saliva plays a crucial role in oral health by helping to neutralize acids and wash away food particles.

2. **Impact of Saliva on Dental Health**:
- Saliva contains enzymes and antibacterial compounds that help control the growth of bacteria in the mouth. Without adequate saliva, harmful bacteria can proliferate, leading to an increased risk of dental caries (tooth decay).

3. **Assertion Evaluation**:
- The assertion states that patients with aptyalism have a higher incidence of dental caries. This is true because the lack of saliva means that bacteria can thrive, leading to more tooth decay.

4. **Reason Evaluation**:
- The reason given is that aptyalism is caused by the action of the parasympathetic nervous system. This is incorrect because the parasympathetic nervous system actually stimulates saliva production. If the parasympathetic nervous system is functioning properly, saliva should be produced, preventing aptyalism.

5. **Conclusion**:
- The assertion is correct (aptyalism patients do have higher incidences of dental caries), while the reason is incorrect (aptyalism is not caused by the parasympathetic nervous system).

### Final Answer:
- The assertion is true, and the reason is false.