Evaluating Equipment Designs

The basic dental unit designs available today include the side delivery, rear delivery, split unit/cabinet, and transthorax. Figures 14–17 provide schematic examples of the four common unit styles.

Transthorax Delivery

The transthorax unit design (Figure 14a) meets the requirements of time and motion and promotes favorable ergonomics. With the dental unit positioned over the patient’s thoracic area, the dental assistant can easily retrieve the handpieces and transfer them to the operator (Figure 14b). This eliminates the shift of the operator’s vision away from the operating site. Repeated shifting of vision from a brightly illuminated operative field at close range to a darker area outside of the oral cavity, located at a greater distance, forces the eyes of the operator to accommodate for these lighting and distance changes. This can lead to eye fatigue and subsequent headache.

A mobile cabinet with a moveable top that slides over the seated assistant’s knees serves as the primary source of supplies and instruments located well within the comfortable reach of the assistant. There are no hoses to interfere with the assistant’s position. This type of unit has been designed for the practice of the most effective four‑handed dentistry (Figure 14c).

A fixed cabinet in the back enables the assistant to use a Class IV or V motion, if necessary, to obtain infrequently used items (Figure 14d).

Figure 14a.
fig14a transthorax delivery
Figure 14b.
fig14b
Figure 14c.
fig14c
Figure 14d.
fig14d

Side Delivery

This unit (Figure 15a) has been a popular concept for many decades. In fact, several dental schools use this style of unit, often supplied with a bracket tray, since dental students often have to work without a dental assistant. Some units of this style even include a cuspidor that interferes with the assistant’s position and creates an infection control problem as well as a physical challenge for a patient if they were to actually use it. In private practice this style limits productivity, since the dentist must perform so many tasks him or herself and additional stress results.

This style unit requires the dental operator to retrieve and replace the handpieces which, in turn, forces the shift of vision from the treatment site, twists the upper body to turn to grasp the wanted instrument, and then refocus the eyes back on the operative field. This can result in physical stress and eye fatigue.

The side delivery style configuration prohibits the assistant from reaching the instruments to exchange handpieces or change burs that requires more unnecessary movement by the operator, thus, reducing productivity. Often in this arrangement, high velocity evacuation (HVE) is placed on the assistant’s side of the chair that, in turn, forces the assistant to be positioned too far away from the patient. At times, HVE hoses are located on the assistant’s mobile cabinet. The concern here is whether the addition of the hoses to this cabinet diminishes the cabinet’s effectiveness. The hoses may impede the function of a sliding top or encroach on valuable storage space in the cabinet.

As with the previous unit a fixed cabinet in the back enables the assistant to use a Class IV or V motion, if necessary, to obtain infrequently used items (Figures 15b).

Figure 15a.
fig15a side delivery
Figure 15b.
fig15b
Fixed cabinetry provides back up materials and equipment.

Rear Delivery

The operator may be forced to retrieve and replace the handpieces with this style of unit (Figure 16). This requires extensive twisting and turning as well as eye-strain as the operator is forced to turn from the operating field to pick up a handpiece. It is often necessary to transfer the handpiece from the retrieval hand to the operating hand in order to use it. The units are mounted in a fixed position that cannot be moved to accommodate for the changing working positions of the operator or for ease of use for the assistant.

HVE hosing and air/water syringes are permanently affixed to an assistant’s work area. Since it is in the rear, it requires the assistant to lean forward. When a mobile cabinet is used with the rear delivery unit concept, it may interfere with access to the sink or to the HVE and air/water syringe. For the assistant, this can provide undue stress and strain and limit access for increased productivity.

Despite the ergonomic disadvantages, rear delivery units remain popular because they are attractive furnishings for the treatment room and hide the dental unit from the patient’s view.

Figure 16.
fig16 rear delivery

Split Unit/Cabinet

The split unit/cabinet (Figure 17a) concept places part of the dental unit on the operator’s side and the HVE and air/water syringe on the assistant’s mobile cabinet. As in the side delivery unit, it requires the dentist to retrieve the handpieces and makes them inaccessible to the assistant, thus, reducing productivity.

The assistant can only use the HVE and the air/water syringe that are attached to the mobile cabinet and is unable to transfer handpieces or change burs for the operator. The hoses also often impede the approach areas and interfere with the assistant’s zone.

The assistant can only use the HVE and the air/water syringe that are attached to the mobile cabinet and is unable to transfer handpieces or change burs for the operator. The hoses also often impede the approach areas and interfere with the assistant’s zone.

Again, a fixed cabinet in the back enables the assistant to use a Class IV or V motion, if necessary, to obtain infrequently used items.

Figure 17a.
fig17 split unit cabinet
Figure 17b.
fig17b