**Core Concept**
Self-etching primers are a class of dental materials that combine the etching and priming steps of the bonding process into one step. This simplifies the application process and reduces the number of steps required for bonding. Self-etching primers work by demineralizing both dentin and enamel, creating microporous surfaces that allow for the subsequent bonding of restorative materials.

**Why the Correct Answer is Right**
Self-etching primers contain acidic monomers that release hydrogen ions, which help to demineralize both dentin and enamel. This process creates microporosities in the tooth structure, allowing the primer to penetrate and form a strong bond with the tooth. The primer also contains hydrophobic monomers that help to create a hydrophobic surface, which aids in the bonding of hydrophobic resin composites. By simultaneously etching and priming both dentin and enamel, self-etching primers provide a uniform surface for bonding.

**Why Each Wrong Option is Incorrect**
**Option B:** Self-etching primers do not etch only enamel; they etch both dentin and enamel. This is because the acidic monomers in the primer are able to penetrate and demineralize both tooth structures.
**Option C:** Self-etching primers do not only bond to enamel; they bond to both dentin and enamel. This is because the primer creates a microporous surface on both tooth structures, allowing for the formation of a strong bond.
**Option D:** Self-etching primers do not only remove the smear layer; they etch and prime both dentin and enamel. While the primer does remove the smear layer, this is not its primary function.

**Clinical Pearl / High-Yield Fact**
When using self-etching primers, it's essential to follow the manufacturer's instructions and to use the primer for the recommended amount of time to ensure optimal bonding. Inadequate application or use of the primer can lead to poor bond strength and decreased durability of the restoration.

**✓ Correct Answer: A. Simultaneously etch and prime dentin and enamel**