The Foundation of Practice Hygiene
Cleaning - Disinfection - Sterilization

Infection control is based on the three fundamental concepts of cleaning, disinfection, and sterilization. They form the foundation for health and safety in the practice. However, the diverse methods result in variables that leave open several questions. What are the various procedures and which are preferred? Where and how are they employed? What can make the reprocessing easier? These are just some of the questions that will be addressed in this chapter.

Infection control is at the heart of quality management in any dental office. In order to determine the correct infection control practices, both a detective-like instinct and a prophetic sense of clairvoyance is required. All possible health hazards must be identified, and appropriate protective measures must be implemented. This search is a continuing process and to be expanded and enhanced at all times. The owner of the practice must establish a hygiene plan that outlines all work processes and functions. Yet he cannot do this alone. He must get his entire team on board – only then can the “Hygiene Ship” sail in safe waters. A thorough hygiene orientation for all staff and quick information updates when changes are made are as important as the general training of employees.

The Hygiene Plan –  The Essence of the Practice

The Five Questions of a Hygiene Plan

The hygiene plan must itemize each individual activity that is relevant for the upkeep of hygiene within the practice. Besides cleaning, disinfection, and sterilization, the hygiene plan also covers the disposal of waste, and the execution of protective measures, such as putting on gloves or safety goggles. It must also include occupational health precautions and plans in the event of an emergency. The hygiene plan should answer questions regarding processes, procedures, and responsibilities in the practice.
The Federal Chamber of German Dentists and the German Committee for Hygiene in Dentistry (DAHZ) have published a framework of a hygiene plan that can be adapted to the specific needs of an individual practice.

Cleaning: Armed with a Brush

Cleaning is the mechanical elimination of unwanted residue from an object. This can be any kind of dirt or soil that can be either of chemical or organic nature. To clean an object, water is used with a cleaning agent that supports the process through enzymatic active agents or detergents. This helps lower the surface tension between the object and the dirt, allowing the dirt particles to be dissolved. Cleaning agents can neither kill germs nor stop their reproduction – they can, at the most, physically remove part of a germ population. Cleaning is a process that can be performed either manually with the help of brushes of various sizes or an ultrasonic device or mechanically by means of a washer disinfector.

Disinfection: The First Step toward Protection

Disinfection reduces the number of germs of a contamination by such a degree that the risk of infection is eliminated. This requires a reduction of germs by at least a factor of 10⁵. In some cases (mycobacteria, Candida albicans, viruses), a reduction of germs by a factor of 10⁴ suffices. In other words, if there were originally 100’000 germs (or 10’000 for 10⁴), only one germ may survive the disinfection process. In such a case, this single germ is no longer pathogenic. This is only a temporary condition that changes once the germ begins to reproduce. Primarily, chemical methods are employed for disinfection, although some fields require the use of thermal disinfection or UV lamps.

The Process of Disinfection 

Active Agent, Concentration, and Application Time

Chemical disinfection kills or deactivates germs by inorganic means; these disinfectants are either bactericidal, tuberculocidal, sporicidal, fungicidal, or virucidal. Disinfectants are composed of various ingredients, each of which has its own effective spectrum. The large selection of active substances or the combination of agents makes it possible to develop the right formula for a specific application.

Besides the effective spectrum, other attributes such as the exposure time, material compatibility and dosage determine its usefulness. The manufacturer provides any pertinent product information. Accuracy of the information is reconfirmed by independent parties. Compliance with the manufacturer‘s instructions is required for proper disinfection and for the protection of people and the environment. Microcidal properties of the disinfectants can also have negative impacts on larger organisms. Using the disinfectant according to the instructions helps avoid any damage to the health or the environment.

Opponents with Varying Qualities

Bacteria, viruses, fungi, prions. The goal is always the same: to break the chain of infection. In the case of microorganisms with their own metabolism (bacteria in reproductive stage and fungi), it is a question of elimination, whereas with other biological agents (viruses, bacteria in spore stage, and prions), it is a process of deactivation. The pathogens have different levels of resistance, and cannot all be treated alike.

A bacteria spore requires a considerably longer application time for deactivation than, for example, a Gram-negative bacteria with a thin cell wall. The Gram-positive tuberculosis bacteria is also relatively resistant and is able to survive small doses of disinfectant. Polioviruses, adenoviruses, and noroviruses are examples of highly stable viruses; non-enveloped viruses such as the influenza virus are less stable. Aspergillus niger is one of the most resistant fungi.

The human immune system is fundamentally better equipped to fight bacteria and fungi than viruses. For a viral infection to be pathogenic, a considerably lower number of germs is required than with bacterial or fungal infections. Even 10 hepatitis B viruses in the bloodstream are enough to cause an infection 50 percent of the time. For this reason, the virucidal properties of a disinfectant are particularly important.

Disinfectants are made up of various active agents that employ different mechanisms.
One mechanism is based on protein-dissolving substances that denature the proteins of the microorganisms. This denaturing occurs as a structural change of the protein molecules so the pathogen can no longer accomplish its biological function. Protein-dissolving agents are highly effective and can also destroy resistant germs. Examples of protein-dissolving agents are alcohols, aldehydes, aldehyde separators, oxidizing agents, halogens, and phenols.

Protein-dissolving Disinfectants 

Other disinfectants are based on fat-dissolving substances. Bacteria and fungi cell walls are partly composed of lipids (fats), and some viruses possess a lipid-based envelope, such as HIV, the herpes virus, and the influenza virus.

Fat-dissolving Substances 

The lysis (disintegration) of the cell wall or the lipid envelope destroys the pathogen. Examples of fat-dissolving substances are alkylamines/alkylamine derivatives, quaternary ammonium compounds, guanidines/guanidine derivatives, pyridine derivatives, and tensides. These substances are often used in combination with other active agents.

Making the Right Choice

Disinfectants undergo extensive testing before being placed onto the market.
The product must run through various test phases. In the active substance screening, the bactericidal, fungicidal, and virucidal effects of the disinfectant are tested on apathogenic test organisms. In the second phase, the same test is performed using pathogenic organisms under practice near conditions. At the same time, the toxicity of the product against humans and animals, the tolerance on skin and mucous membranes, and the biodegradability are tested. Disinfectants should have no protein errors (loss of effectiveness from contact with proteins) or any other possible errors (e.g., loss of effectiveness from contact with cleaning agents). In the third and final phase, the disinfectant is tested in the medical field.
European standards and national legislations have laid out the requirements disinfectants must fulfill. In order to provide full transparency on the compliance with standards, disinfectants have to be labelled  and itemized:

• CE Marking (with or without number)
• Marking according to the Chemicals Act
• Identification according to the Biocidal Product Regulation
• List of the German Society of Hygiene    and    Microbiology (DGHM) / Association for Applied Hygiene (VAH)

CE Marking

The CE symbol stands for conformité Européenne, which further means “conformity with EU standards.” The symbol can be found on products recognized for compliance with EU standards. This compliance to EU standards refers to both the effectiveness and the safety of the product. (Since 2002, Switzerland has applied the same product requirements as the European Community.)

Disinfectants are assigned a CE marking and a number (e.g., CE 1250). They are registered as medical devices class IIA due to their potential risks. An independent notified body tests every product and its manufacturer for their compliance with regulations and the correctness of the product information. In Switzerland, hand disinfectants are not considered as medical devices and therefore do not bear a CE marking.
A CE marking without a number can be found on cleaning agents that belong to the medical devices Class I due to their lower level of risk. The CE marking signalizes that the manufacturer has conformed with all applicable standards.

Identification According to the Chemicals Act and the Disinfectant List of the German Society of Hygiene and Microbiology (DGHM) / Association for Applied Hygiene (VAH)
Since 2005, all disinfectants in Switzerland are subject to the Chemicals Act, which is entirely concordant with the valid EU-wide chemical law (REACH). The product must be filed with the Federal Ministry of Health together with test reports regarding the material properties of the disinfectant. Only after a positive evaluation and registration may they be sold in Switzerland. They then receive an identification marking that will be included on the label and product information alongside one or more danger symbols, declaration of contents, hazard warnings, and safety tips.

Published by the German Society of Hygiene and Microbiology (DGHM), the DGHM/VAH list is a widely accepted reference throughout Europe. The clear layout and the thorough introduction in the study of active agents are some of its strongest points. New products may be included in the annually updated list after a disinfectant has received two positive expert reports regarding the effectiveness and application time. These products are then “DGHM/VAH-listed.” Testing must be done in accordance with the regulations of the Robert Koch Institute and the German Association for the Control of Viral Diseases (DVV).

The Choice Is Yours

Unfortunately, there is not one single universal disinfectant for all materials and purposes. There are many factors that must be considered when choosing a disinfectant:

Purpose
Medical instruments, hands, surfaces, suction units, or dental impressions? Which area requires disinfection? For the orientation of the consumer, disinfectants are color-coded for specific work areas:

• Red – mucous membrane, hands, gloves
• Blue – instruments
• Green – surfaces
• Yellow – special areas (for example, suction unit, water systems, dental impressions, dental tools)

Handling
Work processes are made easier if a flawless disinfection can be achieved in the shortest possible time. Active agents should not coagulate (cluster) with proteins. This can result in adhesions on the materials that contain germs and require further cleaning. Products that clean and disinfect at the same time ease the process.

Material Compatibility
Disinfectants must be compatible for use with the material of the object to be disinfected. For example, phenol-based disinfectants reduce the illumination level of polymerization lamps.

Economical Aspect
One must compare the relative costs for a liter of working solution from the various manufacturers while keeping in mind the application time and effective spectrum.

Ecological Aspect
Substances should be biodegradable but must remain active during usage.

Sterilization

Sterility means the absence of all microorganisms. The probability that one germ survives must be smaller than 1:1’000’000. The various types of sterilization include steam, hot air, gas, plasma, as well as radiation sterilization. In dental clinics, steam sterilization is used as the default method of sterilization.

During steam sterilization (autoclave), the object requiring sterilization is put into a closed high-pressure system and exposed to high-temperature saturated steam. A vacuum system ensures that there is no air in the autoclave, which allows for a uniform diffusion of the steam. The sterilization takes place at 134° C and at a pressure of 2 bar.

The required sterilization time depends on the type of germ population and from the assumed number of germs – the so-called bioburden. The higher the level of contamination, the longer the sterilization takes. A logarithmic calculation helps determine the required time period. Within a certain amount of time, the so-called decimal reduction time, 90 percent of the germ population is eliminated. In the same amount of time, the population is reduced again by another 90 percent, resulting in a total elimination of 99 percent of the germs. When the decimal reduction time is repeated six times, 99.9999 percent of the germs are eliminated. The product is then sterile.

Decimal Reduction Times for Microorganisms in Steam Sterilizer  

An effective disinfection and cleaning of medical devices is necessary to create a proper starting point for the elimination of the germs, i.e., not having to unnecessarily raise the decimal reduction time. The bioburden is reduced by this cleaning and the germs are no longer protected from the steam by residue.

Steam sterilizers that are used in a dental practice must meet the European standard EN 13060. This standard classifies the devices according to their various levels of performance into classes N (for large, unpackaged objects), S (for certain objects that the manufacturer names), and B (for packaged, large, and hollow objects).
The Robert Koch Institute, the Federal Ministry of Health, and Swissmedic recommend Class B autoclaves.

The Discoveries of Ignaz Semmelweis

Ignaz Semmelweis (1818–1865), founder of modern hand hygiene, stated in 1861: “It is safer not to dirty one’s finger as to try to clean one’s dirtied finger.” What he meant by this was that prevention is possibly the most important aspect of infection control.

The first step in prophylaxis is the case history of every patient before treatment in order to get an accurate risk assessment.

This applies especially to high-risk patients. The prevention of injuries of both patient and dental team is of great importance and must be taken into account. Work processes that help to lower contamination include:

• Prepare all required instruments and tools before the treatment begins. Opening drawers during treatment must be avoided.
• Use instruments sensibly.
• Use barriers such as gloves, safety goggles, and face masks.
• Avoid the perforation of gloves and sterilization pouches.
• Adhere to the systematic suction technique to minimize aerosol clouds.
• Use dental instruments to move patient’s lips, cheeks, and tongue rather than using your hands.
• Use dental dams.
• Do not place any unnecessary objects near the dental chair.
• Use the foot-switch rather your hand than control the chair.
• Follow the process of safe disposal of trash.
• Disinfect the oral cavity before any treatment.

Oral Antisepsis: Disinfection of the Oral Cavity

Oral antisepsis reduces the germ population in the oral cavity thereby lowering aerosol contamination, which is particularly high when working invasively with the mucous membranes. An oral antisepsis is normally used for invasive procedures and at-risk patients, such as those with immunodeficiencies or elevated risk of endocarditis.

Solutions for the oral antisepsis are medications and therefore must be approved for this purpose. Many products are based on active agents such as Jodophore, Octenidin, Triclosan, or Chlorhexidin. The disinfection of the oral cavity occurs through a soaked swab, spray, or rinsing of the oral cavity. Depending on the disinfectant, the application time ranges between 30 and 120 seconds. For a treatment that lasts longer than 30 minutes, the disinfection measures should be repeated.

Quality Assurance and Self-Monitoring

The legal requirements and duty to protect oneself and others can only be accomplished by means of the complete realization of all hygiene measures. The quality can be secured at a consistently high level by means of a flawless examination of the results. Weaknesses are detected if close monitoring and ongoing training is in place. At the same time, these procedures fulfill the official and legal burden of proof.

Some methods for the evaluation and improvement of the practice’s hygiene measures include the following:

• Documented and written hygiene plan
• Specific documentation of all measures taken (e.g., the sterilization dossier)
• The use of Petri Dishes to check for possible contaminations
• An internal microbiological analysis
• The use of bioindicators (e.g., autoclave tape) to document the success of sterilization
• Revalidation of all technical devices on a on-going basis