Th 314029

Delivery systems: Which one is right for you?

March 1, 2009
Rear, side, over-the-patient, or over-the-head delivery ...

by Bethany Valachi, MS, PT, CEAS

For more on this topic, go to and search using the following key words: Bethany Valachi, rear delivery, side delivery, over-the-patient delivery, over-the-head delivery, preventing pain in dentistry.

Rear, side, over-the-patient, or over-the-head delivery ... While manufacturers frequently tout the esthetic and productivity features of different delivery systems, there is a paucity of literature regarding the impact of each type on dentists' musculoskeletal health, or the impact on productive capacity. Each delivery system has advantages and disadvantages. Understanding them can help dentists select the right systems for their teams.

From a productivity standpoint, the assistant's ability to function with a delivery system should be a primary consideration. This is often overlooked when doctors select room options at a trade show or dealer showroom. Assistants should be able to easily retrieve suction, syringes, instruments, and handpieces. This enables you (or the hygienist, if using assisted hygiene) to operate without shifting your field-of-view to retrieve instruments and handpieces or change burs.

The most frequently used handpieces should be placed closest to the assistant. It should be noted, however, that handpieces actually comprise no more than 15% of a typical procedure, thus their placement ergonomically is of far less importance than that of the entire treatment arrangement.

Hoses on all delivery systems should be lightweight and flexible to avoid muscular strain. This is usually achieved with a silicone, low voltage, straight six-pin or ISO-C tubing. Although fiber-optic bundles have better light output, they also add weight and rigidity.

Rear-delivery systems

Rear-delivery systems accommodate all clinical instruments behind the patient, which frees up space for larger pieces of equipment in the operatory. It is the least expensive way to connect to utilities, and keeps equipment out of view of the patient, which decreases anxiety. Functionally, rear delivery works fairly well when true four-handed dentistry is practiced (i.e., equipment is within reach of the assistant, who transfers instruments, retrieves handpieces, and changes burs).

However, rear delivery is the poorest method of delivery in two-handed function. More often than not, rear-delivery systems encourage operators to extensively reach, lean, or twist their torsos to retrieve instruments from behind the patient's head, which can contribute to low-back pain. Operators should try to retrieve instruments with the closest (nondominant) hand to avoid repeated twisting or reaching across the body (Fig. 1) and then transfer the instrument to the dominant hand. If rear-delivery rooms are designated for even a moderate amount of two-handed use, they should be reconfigured to an alternative delivery system.

Fig. 1: Operators with rear delivery should retrieve instruments with the nondominant hand and transfer the piece to the dominant hand.
Click here to enlarge image

The ability to frequently reposition and move around a patient's head is imperative to musculoskeletal health. Some rear-delivery systems limit access from 11 o'clock to 12 o'clock positions, which generally offers the best ergonomic access during a procedure. In addition, when positioned from the 7 o'clock to 9 o'clock positions, it is difficult, if not impossible, to reach the rear-delivery system without leaning or extended reaching, a risk factor for neck and shoulder pain.

Side-delivery systems

When placed correctly, side-delivery systems require less trunk-twisting for the doctor than rear delivery to retrieve instruments. However, since the assistant cannot reach the instruments, the dentist must remember to squarely face the system when changing burs, rather than sustaining a twisted posture.

The main ergonomic concern I see with dentists who use side delivery is the tendency to “lock” into one working position that is relative to the patient. They do this hour after hour and day after day. This overworks and fatigues certain areas of the body and leads to pain. The best practice with any delivery system is to change positions as frequently as possible during procedures.

Proximity of the system is also a concern. As operators move around a patient's head, they do not reposition the side-delivery system, and repeatedly lean or twist to one side to retrieve instruments. Keep in mind that, from a resale perspective, most side-delivery units are not interchangeable for left- and right-handed dentistry.

Also, since the dentist retrieves the handpieces and the assistants cannot reach them, productivity is often compromised. There is an emerging concern with side delivery as it relates to high technology.

Fig. 2: Over-the-patient delivery systems allow freedom of movement around the patient's head, but may require repeated upward reaching for those with short torsos.
Click here to enlarge image

Side-delivery units obstruct the egress of equipment, such as lasers and CAD/CAM units, in the operatory, a problem likely to increase over time as more capabilities emerge.

Over-the-patient systems

Over-the-patient (OTP) delivery systems allow you to move freely from the 8 o'clock to 12 o'clock positions around the patient's head. The unit is located over the chest of the patient, so handpieces and other instruments are within easy reach for both you and the assistant, minimizing your movement and shift of vision (Fig. 2).

However, this system is highly visible and in close proximity to the patient. It may also be bumped by the patient, which makes it especially undesirable for most pedo offices. It can require raising the arm repeatedly at the shoulder, which is an ergonomic risk factor for rotator cuff injury.

The design may be less ideal for operators with short torsos. When it is placed over a large patient, shorter operators may be forced to repeatedly reach upward for instruments, which risks neck and shoulder pain. Using a microscope with OTP delivery may compromise access to the delivery system at the 11 o'clock and 12 o'clock working positions. Selecting a unit with long arms that permits the unit head to be located beside the patient will reduce this problem.

Unfortunately, then the problems of side delivery come into play. Also, for your assistant's health, don't position the system too far down the patient's abdomen, since this means the assistant must twist to retrieve instruments.

These systems can be designed to convert flexibly with right- and left-handed adjustability, which not only impacts ergonomics, but helps in the resale of your practice, specifically for left-handed dentists who most likely will find a right-handed buyer. Should right-left convertibility be a significant objective, make sure that the rest of the operatory is designed to support this goal.

Over-the-head systems

Over-the-head delivery systems, developed by Dr. David Ahearn of Design Ergonomics, Inc., have recently become recognized as a unique solution to dental delivery. Combining many of the benefits of over-the-patient and rear-delivery systems, over-the-head systems allow the operator to practice from the 7 o'clock to 1 o'clock positions.

Supplies are in an ideal position for assistant access, while handpieces are more accessible than in rear-delivery layouts, reducing the ergonomic challenges of two-handed function. Also, when properly configured, over-the-head layouts rapidly convert from right- to left-handed function.

Often it is not only the design of ergonomic equipment, but the use and adjustment of it that contribute to ergonomic problems. These guidelines may help you determine which type of delivery system best suits your staff's needs.

Bethany Valachi, PT, MS, CEAS, is a physical therapist, dental ergonomic consultant, and CEO of Posturedontics®, a company that provides research-based dental ergonomic education. A clinical instructor of ergonomics at OHSU School of Dentistry, Bethany lectures internationally at dental meetings. She covers the above topics and more in her new book, “Practice Dentistry Pain-Free,” available at or by calling (503) 291-5121.

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