Different Types of Autoclaves for Effective Sterilization

Sterilisation is a process whereby all forms of microbial life including bacterial spores are killed, it can be accomplished by physical or chemical means.

Sterilisation is essential in the dental field to ensure all equipment is free from harmful microorganisms. One of the most efficient methods to achieve sterilisation is autoclaving, which uses high-pressure steam to eliminate bacteria, viruses, and other pathogens. SOURCE: BAILEY AND SCOTT’S DIAGNOSTIC MICROBIOLOGY 10TH EDITION PG.NO.20

ANSI/AAMI, which provides standards and guidelines for the processing of medical devices, refers to autoclaves for healthcare specifically as Steam Sterilizers

In this blog, we will explore the different types of autoclaves used in dentistry, their principles, working mechanisms, advantages, and the instruments they sterilize.

What is an Autoclave?

An autoclave is a machine that utilizes steam under pressure to sterilize dental instruments. By increasing the pressure inside the autoclave, the boiling point of water is raised, allowing the steam to reach a higher temperature.

 Sterilizing Conditions:

• Temperature: 121°C (250°F)

• Pressure: 15 lb per square inch (psi)

• Time: 15 minutes

The Principle of Autoclaving

The autoclave operates on the principle of Moist heat sterilization. When steam comes into contact with a cooler surface, it condenses to water, releasing latent heat to the surface. This condensed water creates moist conditions that effectively kill the microbes present on the instruments. This process ensures that dental instruments such as handpieces, impression trays, orthodontic pliers, and surgical instruments are sterilized properly, making them safe for use.

Phases of Sterilization

The sterilization process in an autoclave generally includes the following phases:

1. Pre-Heating Phase: Water is heated until steam is produced.

2. Sterilization Phase: Steam under pressure is introduced to kill microorganisms.

3. Exhaust Phase: Pressure is released from the chamber, and the sterilized instruments are ready for removal.

Advantages of Autoclaving

Autoclaving is a widely preferred method of sterilization in dentistry due to its many advantages:

• Economical.

• Fast Process

• Effective Penetration

• No Chemicals Needed

Disadvantages of Autoclaving

Despite its many benefits, autoclaving does have some drawbacks:

• Moisture Retention/ Presence of air  is the greatest enemy of steam sterilization, as it can prevent the steam from thoroughly getting rid of all potentially infectious foreign materials present on medical items and waste

• Damage to Carbon Steel instruments  

• Heat Sensitivity: Only instruments made from stainless steel or heat-resistant plastics can be autoclaved.

Types of Autoclave /Sterilizers

The most significant differentiating factor between types of autoclaves is their sterilization method. There are two principal types of sterilizers:-

1. Gravity Displacement – Class N

2. Vacuum-induced or Pre-vacuum- class B

Note: some autoclaves use both methods to sterilize

Autoclaves come in different types, each designed to meet specific sterilization needs.

In gravity cycles, A completely air-free environment cannot be guaranteed, which is why the steam can only treat certain parts of certain materials.

However, as their name implies, this is not an issue with pre-vacuum autoclaves – also known as “class B” autoclaves.

1. Pressure Cooker Type / Laboratory Bench Autoclaves (N-Type)

These are basic autoclaves that resemble domestic pressure cookers. The chamber is typically made of metal, and the lid is sealed with a rubber gasket. A pressure gauge, air and steam discharge tap, and a safety valve are essential components. These autoclaves are commonly used in regions where advanced models may not be readily available.

Key Features:

• Simple and basic design

• Affordable

• Manual operation

2. Gravity Displacement Type Autoclave

The gravity displacement type is one of the most common autoclaves used in dental practices. In this type, steam is created inside the chamber via the heating unit and moves around for sterilization. It is affordable and widely used in laboratories.

Key Features:

• Simple mechanism

• Cost-effective

• Suitable for basic sterilization needs

3. Positive Pressure Displacement Type (B-Type)

This autoclave generates steam in a separate steam generator, which is then passed into the autoclave. The process is faster compared to gravity displacement types because steam can be generated almost instantly. B-type autoclaves are faster and more efficient, making them ideal for busy dental practices.

Key Features:

• Faster steam generation

• More efficient than gravity displacement types

4. Negative Pressure Displacement Type (S-Type)

The S-type autoclave is equipped with both a steam generator and a vacuum generator. Class S autoclaves are something of a hybrid between Class B and Class N autoclaves. Their specifications are determined by the manufacturer, and they often incorporate features from both classes, offering more flexibility in terms of what they can sterilize. The vacuum generator removes all air from the chamber before steam is introduced, ensuring thorough sterilization.

Key Features:

• Most accurate and reliable

• High sterility assurance level

• Expensive but highly effective

Manual or Automated Autoclave

Manual autoclaves require time to be spent on tasks that are effortlessly performed with automated autoclaves. For example, pre-programmed cycles remove the need to set sterilization parameters. Other examples include automated door-locking and release, a water-fill function, and digital documentation for the sterilization log.

Nonetheless, manual autoclaves can be simple to use and are less expensive.

How Do I Ensure the Autoclave is Functioning Properly?

For this last phase, there are a series of tests that ensure the step is functioning correctly:

• Physical Tests

• Chemical Controls: These are indicators that change colour or form when exposed to certain conditions.

• Biological Controls: These are the most reliable ways to validate the effectiveness of sterilization since they use highly resistant bacterial spores for verification. They are performed every 3 months.

• Vacuum Test: It is performed every 15 days and checks the ability to maintain the vacuum.

Conclusion

Understanding the types and principles of autoclaving can help dental professionals make informed decisions about which sterilization method is best suited for their practice.

FAQ

What is the role of an autoclave in dental sterilization?

Autoclave sterilises dental instruments by exposing them to high-temperature steam under pressure, to kill all the harmful microorganisms like bacteria, viruses, and fungi from dental instruments including spores, ensuring they are safe to use intraorally. Thus preventing cross-contamination between patients; is considered a vital tool for maintaining hygiene standards in Dental practice.

Can all dental instruments be sterilised in an autoclave?

We can't sterilise all the dental Instruments like chairs or X-ray machines. These instruments need to be disinfected with solution or fumigation methods to reduce germs. Generally, they are soaked in or wiped down with a disinfectant.

How does autoclaving keep dental instruments safe for use?

The autoclave uses high-pressure steam to penetrate all surfaces of the instrument, ensuring even the most hidden areas are sterilised. Instruments are typically wrapped in special sterilisation pouches to allow steam penetration while protecting them from contamination post-sterilisation.

What is the best way to store sterilised dental instruments?

Sterile instruments should be stored in sealed pouches in closed cabinets. They should not be stored under sinks or in other places where they become wet. If a package has been compromised(wet, torn, punctured) the contents should be reprocessed.