Final answer:
The opacity on dental X-rays can change due to dental fillings and the severity of tooth decay or cavities.
Step-by-step explanation:
Opacity on dental X-rays can change due to a variety of reasons.
One reason is the presence of dental fillings or restorations. These materials may have different radiodensities than natural teeth, causing variations in opacity on the X-ray.
Another reason is the severity of tooth decay or cavities. Decay can lead to demineralization of the tooth structure, making it less dense and more transparent on X-ray images.