Clinical / Chairside Assisting Procedures
Zones and positioning
Four-handed dentistry rests on a fixed map of the treatment area. The operator works from roughly 7 to 12 o'clock, the assistant from 2 to 4 o'clock, and the static zone (12 to 2 o'clock) holds the unit, bracket table and light. Instruments pass through the transfer zone at 4 to 7 o'clock - near the patient's chin and chest - never across the patient's face. Deliver an instrument with the working end oriented for immediate use and the handle toward the operator's hand, retrieve it in the same motion, and keep the suction tip positioned so the field stays dry without traumatizing tissue. High-volume evacuation is used whenever a handpiece, air-water syringe or ultrasonic scaler is running; a saliva ejector alone does not clear aerosols.
Materials and moisture control
Know the setting reactions and working times of what you mix. Alginate is an irreversible hydrocolloid that sets by chemical reaction, so it is spatulated quickly and poured promptly. Elastomers (vinyl polysiloxane, polyether) are more dimensionally stable and tolerate delayed pouring. Zinc oxide-eugenol is sedative but interferes with composite polymerization. Glass ionomer bonds chemically to tooth structure and releases fluoride. Composite is placed in increments (generally no more than about 2 mm) and cured with the light tip held close to the surface.
Traps candidates miss
Questions love to ask who maintains the visual field (the assistant), which evacuation device is appropriate, and the sequence of placing a matrix band and wedge. Expect bur identification too: the shank engages the handpiece, the neck connects, and the head cuts - bur names describe the head shape, not the shank.
Rule of thumb: if your hand would cross the patient's face or the field, the pass is wrong - re-route through 4 to 7 o'clock.