**Core Concept**
Four-handed dentistry is a technique used in dental procedures where the dentist and the dental assistant work together in a coordinated manner to improve efficiency and reduce errors. This technique requires the dentist to be positioned in a way that allows for optimal access and visibility.

**Why the Correct Answer is Right**
In four-handed dentistry, the dentist typically stands with their feet shoulder-width apart, with their feet positioned at a 90-degree angle to the patient's mouth. This positioning allows the dentist to maintain good posture, have optimal access to the patient's mouth, and be able to move freely around the patient as needed. This is in contrast to the traditional "one-handed" approach, where the dentist would often stand with their feet positioned in a way that would limit their movement and access.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because standing with feet parallel to the patient would limit the dentist's mobility and make it difficult to access the patient's mouth.
* **Option B:** This option is incorrect because standing with feet crossed or one foot in front of the other would put the dentist off balance and limit their ability to move around the patient.
* **Option C:** This option is incorrect because standing with feet behind the patient would put the dentist in a position where they would be unable to see the patient's mouth clearly.

**Clinical Pearl / High-Yield Fact**
When practicing four-handed dentistry, it's essential to maintain good posture and keep your feet shoulder-width apart to ensure optimal access and visibility.

**Correct Answer: A. Standing with feet shoulder-width apart and at a 90-degree angle to the patient's mouth.**