In the day-to-day practice of dentistry, the dental assistant is exposed to a wide variety of chemicals. All chemicals that are used for treatment procedures, cleaning of instruments and surfaces, disinfection and sterilization, laboratory procedures, and dental x-ray processing are capable of causing serious health consequences if they are absorbed into the body in sufficiently large amounts.

The heart, kidney, liver, and lung tissues can be seriously damaged by chemicals. Results range from short-term discomfort, such as burns or rashes, to life-threatening conditions, such as cancer or organ failure.

As a dental assistant, it is important for you to understand the proper use, storage, handling, spill cleanup, and disposal methods for all chemicals used in the dental office. In addition, you should know the first aid procedures associated with chemicals. You must be aware of the hazardous materials that may be regulated under federal, state, or local environmental guidelines and the requirements associated with the disposal of these hazardous materials. Common examples of items that require special disposal procedures include x-ray processing solutions, lead foil backing from film packets, scrap dental amalgam, and elemental mercury.

This chapter also discusses the Occupational Safety and Health Administration (OSHA) Hazard Communication Standard and the procedures necessary to develop the safe working habits that will become part of your daily routine in the dental office.

Hazardous Chemicals

A hazardous chemical is defined as any chemical that can cause a physical or a health hazard. A chemical is considered hazardous if it (1) can ignite (catch fire), (2) can react or explode when mixed with other substances, (3) is corrosive, or (4) is toxic (Fig. 23-1).

FIG. 23-1 Chemical hazard warning labels.

Exposure to Chemicals

The three primary methods of chemical exposure are inhalation, skin contact, and ingestion.

How Chemicals Enter the Body

• Inhalation of chemical vapor

• Absorption of chemical through the skin

• Ingestion of chemical (eating or drinking)

Inhalation of the gases, vapors, or dusts of chemicals can cause direct damage to the lungs. Some chemicals may not affect the lungs but are absorbed by them and are then sent through the blood to other organs, such as the brain, liver, or kidneys, where they may cause damage.

Skin is an effective barrier against many chemicals, but some chemicals can be absorbed through the skin. In general, you must have direct skin contact with the chemical for absorption to occur. Sometimes, after repeated contact with a chemical, a skin condition called dermatitis may develop.

Ingestion (swallowing) is another way in which chemicals can enter the body. Common ways of ingesting harmful chemicals in the workplace include eating lunch in an area in which chemicals are used or eating with hands that are contaminated with chemicals. It is important to wash your hands thoroughly after contact with any chemical.

Acute and Chronic Chemical Toxicity

The potential for a chemical to cause harm and the extent of harm depend on the amount of the dose and the duration of exposure to the chemical. Chemical toxicity may be acute or chronic.

Acute chemical toxicity results from high levels of exposure over a short period. Acute toxicity is often caused by a chemical spill, in which exposure is sudden and often involves a large amount of the chemical.

The victim of acute toxicity feels the effects immediately. Dizziness, fainting, headache, nausea, and vomiting are symptoms of acute overexposure to chemicals.

Chronic chemical toxicity results from many repeated exposures, generally to lower levels, over a much longer time (months or even years). Many effects of chronic toxicity are possible, including liver disease, brain disorders, cancer, and infertility. Always check the material safety data sheet and the product label for information on potential dangers associated with the chemicals included in the products you use.

The difference between acute and chronic toxicity can be illustrated by considering the effects of acute exposure and chronic exposure to the same chemical. For example, a single exposure to a high concentration of benzene (acute toxicity) may cause dizziness, headache, and unconsciousness, whereas long-term daily exposure to low levels of benzene (chronic toxicity) may eventually cause leukemia.

1 What types of health consequences could develop as a result of exposure to chemicals?

2 Why is it important for the dental assistant to understand how to handle chemicals?

3 What are three primary methods of chemical exposure?

4 What is the difference between acute and chronic chemical exposure?

Hand Protection

When using chemicals, be certain to wear utility gloves made from a chemical-resistant material, such as natural rubber, neoprene, or industrial grade nitrile (Fig. 23-2).

FIG. 23-2 Clean room nitrile gloves provide protection and dexterity when handling chemicals. (Courtesy Lab Safety Supply, Janesville, WI.)

These chemical-resistant gloves are essential because the latex gloves worn during patient care do not provide adequate protection when one is handling chemicals. When exposed to chemical disinfectants, the latex in the glove degrades and creates a wicking (sucking) action that will actually pull contaminants and chemicals through the glove and onto the hands.

Eye Protection

Serious damage to the eyes, even blindness, can result from chemical accidents. It is crucial to protect the eyes from fumes and splashes while pouring chemicals such as x-ray processing solutions, ultrasonic solutions, disinfectants, and sterilants.

A variety of safety eyewear is available. The ideal goggles have soft, vinyl flanges (rims) at the top and bottom and fit the face snugly (Fig. 23-3).

FIG. 23-3 Dental assistant wearing chemical goggles.

Protective Clothing

When caustic or staining chemicals are used, it is best to wear a rubber or neoprene apron when mixing or pouring the chemical. The material safety data sheet (MSDS) for each product (see later discussion) provides specific information regarding the need for additional personal protective equipment (PPE).

Inhalation Protection

Depending on the quality, the masks worn during patient care may or may not provide adequate protection when one is working with chemicals. The proper face mask should be fluid repellent and should provide respiratory protection.

If your job requires you to pour or mix chemicals frequently, or if you are sensitive or allergic to substances, you might require a mist respirator face mask approved by the National Institute of Occupational Safety and Health (NIOSH) (Fig. 23-4).

FIG. 23-4 Disposable respirator has tapered angle to fit facial contours around nose and chin to protect against dusts and chemical mists. (Courtesy Lab Safety Supply, Janesville, WI.)

Control of Chemical Spills

Accidents and spills should not be common occurrences. Planning and practice in dealing with such spills should minimize employee exposure to harmful chemicals. Refer to the MSDS for the specific product for accurate information on how to manage spills.

Mercury spill kits should be available in all dental offices in which amalgam is used. Exposure to even small amounts of mercury is very hazardous to the health of dental personnel. Mercury can be absorbed through the skin or through inhalation of mercury vapors. The spill kit for small amounts of mercury should contain mercury-absorbing powder, mercury-absorbing sponges, and a disposal bag (Fig. 23-5). A mask and utility gloves should be worn whenever one is cleaning up a mercury spill.

Precautions When Working with Mercury

• Work in a well-ventilated space.

• Avoid direct skin contact with mercury.

• Avoid inhaling mercury vapor.

• Store mercury in unbreakable, tightly sealed containers, away from heat.

• When preparing amalgam for restorations, use preloaded capsules. (This avoids exposure while measuring mercury.)

• When mixing amalgam, always close the cover before starting the amalgamator.

• Reassemble amalgam capsules immediately after dispensing the amalgam mass. (The used amalgam capsule is highly contaminated with mercury and is a significant source of mercury vapor if left open.)

• Leftover scrap amalgam (that was not used) is stored dry in a tightly closed container.

• Scrap amalgam (that has been retrieved from dental unit traps) is disinfected in a solution of bleach and water. Then it is placed in the container with other scrap amalgam.

• Clean spills using appropriate procedures and equipment. Do not use a household vacuum cleaner or the high-volume evacuator. (Dangerous fumes from the mercury can be released into the air.)