## Core Concept
The cap stage in tooth development is a critical phase where the dental epithelium proliferates and forms a cap-like structure around the dental papilla. During this stage, signalling molecules play a crucial role in regulating the interactions between the dental epithelium and the dental mesenchyme, guiding tooth morphogenesis.

## Why the Correct Answer is Right
The correct answer, **.**, involves the expression of specific signalling molecules that are crucial for the development and patterning of teeth. One key signalling pathway involved in this process is the Wnt/β-catenin pathway, but more specifically, during the cap stage, the **Sonic Hedgehog (SHH)** signalling pathway is pivotal. SHH is expressed in the dental epithelium and plays a significant role in the development of the tooth, including the regulation of cell proliferation and differentiation. It also influences the formation of the dental cusps and the overall shape of the tooth.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while other signalling pathways like Wnt/β-catenin are indeed important in tooth development, they are not the primary pathway highlighted for cap stage signalling in odontogenic epithelium.
- **Option B:** This option is incorrect as it does not accurately represent the key signalling molecule involved in cap stage signalling.
- **Option D:** This option is incorrect because it does not specify the correct signalling molecule critical for odontogenic epithelium signalling during the cap stage.

## Clinical Pearl / High-Yield Fact
A key point to remember is that disruptions in signalling pathways during tooth development can lead to various dental anomalies, such as tooth agenesis or abnormalities in tooth shape and size. The **Sonic Hedgehog (SHH)** pathway is particularly crucial, and its dysregulation has been associated with developmental defects.

## Correct Answer Line
**Correct Answer: C. Sonic Hedgehog (SHH).**