What position places the chair back until the patient is almost lying down?

The supine position involves reclining the patient so they are almost lying flat on their back, with the chair back positioned at a near-horizontal angle. This position is commonly used in dentistry as it allows for optimal access to the oral cavity, making it easier for the dental professional to work effectively. It promotes comfort for the patient during procedures that may take some time and helps ensure proper blood circulation.

In contrast, the subsupine position is typically even more reclined than supine, often used in emergency situations to facilitate optimal blood flow to vital organs, but it's not the standard position for most dental procedures. The Trendelenburg position, where the body is laid flat on its back with the legs elevated, is also not standard for general dental procedures and is reserved for specific clinical situations. Lastly, the upright position maintains the patient in a vertical posture, which is not conducive to most dental procedures as it restricts access to the mouth.