1. Therapeutic dentistry, as a general dental discipline, topics, goals and objectives of propaedeutic course. Types of dental units. Safety work on the dental unit. Dental instruments, their usage. The concept of ergonomics in dentistry.

1. Therapeutic dentistry, as a general dental discipline, topics, goals and objectives of propaedeutic course. Types of dental units. Safety work on the dental unit. Dental instruments, their usage. The concept of ergonomics in dentistry.

Therapeutic Dentistry– is a part of dentistry that studies the reasons and mechanisms of teeth diseases, periodontium tissues diseases and oral mucosa diseases, theirs diagnosis, treatment methods and prevention.

 

Therapeutic Dentistry include such chapters:

– Propaedeutic course;

– Preventive dentistry (deals with dental caries, developmental disorders and Endodontics);

– Periodontology (deals with diseases of periodontium);

– Oral Pathology (deals with oral mucosa diseases).

 

Propaedeutic course – deals with the history of dentistry, study the anatomical and physiological features of the oral cavity, dental instruments and dental office equipment, ergonomics issues, ethics and deontology, structure of Ukraine dental service.

 

AN ERGONOMIC ENVIRONMENT IN DENTISTRY

Ergonomics – is the science that studies the relationship between people and their work environment.

 

Position of operator relative to chair.

 

Ergonomics is defined as ‘the study of man in relation to his working environment: the adaptation of machines and general conditions to fit the individual so that he may work at maximum efficiency’. The application of these principles concerns every aspect of design within the building and streamlining of procedure. Within the surgery, the contemporary dental unit is a masterpiece of design incorporating as many ergonomic features as possible to enable the operator, dental nurse and patient to experience the minimum of stress and fatigue. It is evident, furthermore, that this environment must facilitate a high standard of dental treatment as clinical techniques become ever more complex and exacting.

This transformation began with the general adoption of a comfortable, supported and seated position for the operator and the consequent supine positioning of the patient. However, the necessary changes in posture and working procedures were largely overlooked and, despite the convincing work and publication of Paul1, it would seem that many dentists persist in working in inefficient, distorted postures that must frequently lead to excessive fatigue if not skeletal damage.

The operator’s chair

This should be fully adjustable and mobile, provide a broad, preferably anatomically contoured seat and give support in the lumbar region. It should be adjusted in height to suit each individual operator in order to distribute the weight equally between the thighs and feet. The dental nurse chair differs only, but importantly, in that it must adjust to at least a 10 cm increase in height and provide a corresponding ‘bar stool’ type rim rest for the feet.

 Operator and nurse positions

The dentist will normally work within a range from the 12 o’clock to the 9 o’clock position relative to the patient’s head. However, most operative procedures are completed from, at, or near, the 12 o’clock position. The dental nurse will normally remain in a fixed position at  4 o’clock (Fig. above) but at a considerably higher position in order to look down or forward to the mouth. This height not only facilitates the different tasks, but enables the nurse to visualise the back of the mouth and remove any accumulation of debris or water.

Operator’s vision

There can be no doubt that any tooth is best visualised by direct vision (Figure below). However, the nature of operative dentistry demands that, whenever possible, the line of vision is perpendicular to the tooth  surface. Clearly, those surfaces inaccessible by direct vision must be visualised indirectly through a mirror. Nevertheless, it remains important, however difficult, to position the mirror and attempt a near perpendicular view. Magnification of the working area provides a major advantage in both the reduction of eye strain and the promotion of high standards.

 

 Patient position

Adoption of the supine patient position by most dental practitioners has focused attention on the optimal position of the patient’s head in relation to the seated operator.

 

WORKING POSITION

It is important to have a good working position to allow efficient, effective working, to maximise patient comfort and to prevent the development of back and neck problems for the operator and dental nurse. When taking a history or discussing treatment with a patient, the operator should sit facing the patient who should also be in a sitting position in the dental chair. Sitting behind or standing in front of the patient reduces opportunities for non-verbal communication and may threaten or even distress the patient.

For carrying out treatment, the patient should be put into a supine position and the operator should sit behind the patient. The operator should sit with his/her thighs parallel with the floor, feet flat on the floor, back against the chair support and elbows close to the rib cage.

The right-handed operator usually sits in the 11o’clock position with the nurse at 1 o’clock. The nurse’s chair should be slightly higher than that of the operator to give her/him good vision of the mouth. The operator should be able to move between 1 o’clock and 8 o’clock positions. The 8 o’clock position may be used for working on the lower right quadrant. The nurse should be able to move from the 1 o’clock to 4 o’clock positions.

Most dental surgeries are designed for right-handed operators, which means left-handed operators have to try to adapt to the surgery in which they are working.

 

CLOSE SUPPORT (FOUR-HANDED) DENTISTRY

An operator and a dental nurse working as a team will result in efficient delivery of dental care in as pleasant a manner as possible for patients, with improved safety.

The nurse maintains a clear, dry field for the operator by retracting the lip, cheeks and tongue and by aspirating the water from the high-speed handpiece. The dental nurse may also keep the operator’s mirror clear of spray by using the air stream of the three-in-one. The nurse passes and collects instruments from the operator. Instruments should be passed in front of the patient and not over the face, particularly the eyes.

Fig. Exchange of instruments in the transfer zone.

LIGHTING

The operating light should be positioned to give maximum light to the area in which treatment is being carried out; the position is different for the upper and for the lower arches. Additional light may also come from fibreoptic light in the high-speed handpiece.

WORK SURFACES

There are a number of possible positions for work surfaces: beside the operator, beside the dental nurse, behind the head of the chair and as a bracket table over or beside the patient. Instruments, materials and patient records and radiographs need to be placed in appropriate positions around the operator, nurse and patient and therefore a number of surfaces are normally used. Patients’ records should be kept well away from instruments to prevent contamination of the notes.

MANAGEMENT OF ANXIETY

ASSESSMENT OF ANXIETY

Dental anxiety can be measured both qualitatively and quantitatively. The qualitative measures can be made by observation: the patient may be shaking, sweating and be unwilling or uncertain about sitting in the dental chair. Patients who are nervous often talk incessantly, often avoid eye contact or may even appear aggressive. Important information can also be gained through the dental history that the patient gives. There may have been a previous bad dental experience which has affected the patient’s confidence in dental treatment. Dental anxiety can be measured quantitatively using a questionnaire. There are many dental anxiety questionnaires but the quickest and simplest is the Modified Dental Anxiety Scale (MDAS). This questionnaire has five questions relating to different aspects of dental treatment including scaling, drilling and local analgesic injections. The range of scores is from 5 to 25. The average score is around 11, with those with high anxiety scoring 20+.

Prevention of anxiety

Considerable patient anxiety follows a bad dental experience. It can take only one distressing episode to affect a patient’s attitude for many years. It is therefore particularly important to try to prevent any experience that may colour a patient’s attitude to dentistry in the future.

There are two situations that tend to recur as bad experiences. The first is where a procedure becomes unexpectedly more complex, for example caries removal may result in pulp treatment. The second is where a patient feels pain during a procedure. The key elements to preventing any patient developing anxiety are therefore careful planning and good pain control.

INSTRUMENTS FOR CAVITY PREPARATION

Conventionally, cavities are prepared using a combination of hand instruments and rotary instruments.

HAND INSTRUMENTS

Examination of teeth

1.                 Mirrors: used for indirect examination of teeth, to retract tissues and to direct light to specific areas of the mouth.

2.                 Straight probe: used to check the margins of restorations and to examine carefully for dentine caries.

3.                 Briault probe: used to detect deficiencies and ledges on proximal surfaces.

 

 

 

Cavity preparation

1.                Excavators: used to remove soft dentine caries, particularly from the floor of the cavity. Excavators may also be used to remove temporary dressing materials.

2.                Small excavators may be employed for carving fissure patterns in plastic materials, such as amalgam.

3.                 Chisels: used to remove unsupported enamel.

4.                 Gingival margin trimmers: used to remove unsupported enamel at the base of proximal cavities.

Material placement

1.                 Flat plastic: used to place plastic restorative materials (i.e. those that are soft on placement and subsequently set and harden in the cavity). They can be used to place temporary dressings, linings, glass ionomers and composites. Flat plastics are not suitable for carving amalgams as their blades are too thick and the amalgam is smeared rather than cut and removed.

2.                 Round-ended plastic: used for placing and shaping plastic materials such as temporary dressings and composite.

3.                 Amalgam carrier: used to carry amalgam to the cavity.

4.                Amalgam plugger: used to condense the amalgam into the cavity.

Material shaping

■ Amalgam carvers: examples include Ward’s carvers and the 1/2 Hollenbach. These instruments have thin cutting blades that cut through the amalgam.

■ Composite instruments: specific instruments with non-stick coatings, such as Teflon or titanium-nitride, have been developed for placing and shaping composite resins.

Material mixing

■Metal spatula: is used to mix dental cements (e.g. glass ionomer cements, zinc-phosphate cements, polycarboxylate cements).

■Resin spatula: is used to mix chemically activated composite material.

ROTARY INSTRUMENTS

Slow speed

The slow-speed handpiece is driven either by compressed air or directly by an electric motor. The speed of the handpiece ranges from 0 to 40 000 rpm. The most efficient cutting is achieved with a straight handpiece, but this is difficult to use in the mouth and is therefore restricted to extraoral use, such as adjusting temporary crowns and dentures. The contra-angle handpiece is used for the removal of caries, polishing and finishing.

High speed

The high-speed handpiece is driven by compressed air and is sometimes referred to as an air-turbine or air-rotor.

It is used for cutting through enamel and dentine and removing previous restorations. It has a speed of 250 000–500 000 rpm and, to keep it cool, a water spray is directed at the cutting part of the bur which is held in the head of the handpiece by friction. A fibreoptic light in the head of the handpiece aids visibility.

BURS

 

BURS ARE DESCRIBED BY:

 

 

Rotary Cutting Instruments

The original rotary cutting instruments were hand driven and very slow. The introduction of the electric motor allowed speeds up to 2000rpm with mild steel burs and these remained the method of choice until the late 1940s. Improvements in gearing the rotating handpiece and the introduction of air/water coolants and lubricants lead to rapid improvements in the 1950s18. Speed of rotation has increased from the standard 500-2000rpm up to 400,000rpm and is now recognised in three different groups9.

1. Slow speed handpiece and bur rotates at 500 – 5000rpm. Steel burs are indicated in this speed range and the use of a lubricant is optional. Visibility is better without a lubricant but cutting is faster and cleaner with an air/water spray. Diameter of steel burs can range from 3.0mm down to 0.5mm. The size should be selected to fit the task in hand. Tasks include removal of caries and development of retentive designs, placement of pins, grooves and ditches, as well as all stages of polishing to a final finish.

2. Intermediate high speed rotates at 30,000 – 120,000rpm. Diamond burs with a medium to fine grit are the most efficient in this range and use of a lubricant is mandatory. Air alone for very short periods is acceptable because it will enhance visibility but cutting will be faster under air/water spray. Tungsten carbide burs tend to “chatter” at this speed and may cause micro-cracks in enamel and steel burs will not cut at these speeds. There is a very fine tactile sense available within this speed range and the risk of over-cutting is minimal. Therefore it should be used in the development of small cavities as well as to refine final cavity outline for all restorations. It is also useful for initial contouring of most restorations leading to a final polish. It is the correct speed group for refining the occlusion.

3. Ultra-high speed rotates at 250,000 – 450,000rpm. Tungsten carbide burs are at their most efficient in this range but diamond burs are also very useful. Lubrication is mandatory with a copious water jet being the most efficient for temperature control. Tungsten carbide burs cut dentine very smoothly providing they are not chipped or eccentric. They can also develop a fine margin in enamel although it must be noted that they cut more smoothly along the margin where the rotating bur enters the cavity. The opposite, exit margin, is likely to chip more readily. As they are essentially a side cutting bur they should not be used to enter through healthy enamel into a new lesion. They cut old metal restorations well. Diamonds are more versatile and a coarse end cutting diamond is the preferred bur to enter a new lesion or remove bulk enamel, even though both entry and exit margins will be relatively rough depending upon the grit size being used. The diameter of burs for use in this speed group range from 2mm down. Initial entry to extensive lesions and the removal of old restorations is achieved best in this speed range. The tactile sense is minimal and over cutting is possible if visibility is at all limited. Use these speeds for gross reduction of tooth structure only and then step back to intermediate high speed to refine the cavity.

A combined air/water spray is used at the higher speeds always as a coolant and lubricant and can be used at slow speed also if desired. Selection of the correct bur for the appropriate function is important because none of the three types of cutting method is universal and each has its place.

1. Steel burs

These were the burs originally used when rotary cutting instruments were developed well over one hundred years ago. They are still valuable for removal of caries and development of retentive elements in dentine and are designed for slow speeds under 5000rpm. Each bur generally has eight blades and some of them have a positive rake angle to facilitate the cutting of the dentine or removal of caries. This, however, makes them relatively fragile and subject to chipping along the leading edge and they should not be expected to have a long life iormal practice.

2. Tungsten carbide burs

Following the development of higher speed handpieces there was a need for stronger steel burs to withstand the heavier stresses involved and to lengthen their useful life. Tungsten carbide burs are designed almost exclusively for friction grip handpieces because concentricity is essential and they only cut efficiently at greatly increased speeds. In fact, they do not begin to reach effective cutting capacity until 100,000rpm and are best used at speeds beyond 300,000rpm. One of the main variations in these burs in recent years has been to increase the number of blades and to vary the rake angle of the blades. The usual bur has six blades and a negative rake angle to provide better support for the cutting edge. For the same reason many have a radial clearance as well. They cut metal and dentine well but are prone to produce micro-cracks in enamel thus weakening the cavo-surface margin. They are not indicated for minimal intervention type cavities.

Probably only a new bur will be truly concentric because any loss of a blade, or even a piece of a blade, will alter the balance so that only every third or fourth blade will actually contact the tooth and remove a piece. This means that the clinical life is generally quite short.

3. Diamond stones

Diamonds abrade tooth structure rather than cut or chip it and are therefore more efficient over a greater range of speeds and are less likely to chip or break either themselves or the tooth. They are most efficient when used against hard materials such as enamel and porcelain although very fine diamonds are excellent for reducing enamel and dentine to a fine finish. Initially diamond burs were covered with large diamond particles and were regarded as rather coarse leaving a finish with a surface roughness index of up to Rt. 50µm. In recent times there have been considerable improvements in the methods of embedding the diamond particles in the metal of the bur head so they last longer and there is a far better distribution of particle size. Large particle size ensures rapid removal of porcelain and enamel but leaves a rough surface. Fine particles leave fine scratches and it is possible now to produce a polished surface with particles down to a surface roughness index of Rt. 4µm. There are a variety of grit sizes in between to be selected according to the task in hand. They are the preferred choice for development of minimal cavity designs. Also as adhesion is greatly enhanced in the presence of smooth surfaces, it should be regarded as mandatory to finish all cavity margins with a fine diamond stone of 25µ grit, or less, at 40,000rpm.

 

DENTAL UNITS

1. — Headrest. The headrest provides adjustment features for easy access to the oral cavity and increased patient comfort.

 Dental Chair. The chair could be adjusted as up and down, backrest front and back for different requirement.

2.— Assistant Console. Assistant to control the function of the water heating and spraying. Saliva ejector and high-volume suction.

3.— Foot switch. To control the dental chair move and instruments which on instrument tray work

4.— Imaging System. The imaging system for diagnosing

5.— Light Adjusting Arm. The arm to adjust angle and direction of operation light

6.— Operation Light. Operation light for diagnosing, operation or examining

7.— Balance Arm. The arm to connect the instrument tray

8.— Instrument Tray. Assistant device receptacle

9.— X-Ray Viewer. A device to check the x-ray film

10.— Extended Tray. A tray which set some stuff during using.

11.— Foot Control. The foot control button to control the moving of dental chair

12.— Spittoon-bowl.

13.—Post-mounted service console. The main control system of the dental unit

14.— Chair Base. The main base of the dental chair

15. — Armrest. The armrests are designed to allow easy access for both you and the patient.

Patient Entry/Exit. Lift the armrest slightly to unlock it, and lower it into the entry/exit position.

To reposition the  armrest, lift the armrest back into the standard position.

 

16. —Cup-filler nozzle

Cup filler Switch.

Momentarily press the cupfiller switch (     ), water will come out from the cupfiller nozzle for 3 seconds and stops automatically.  Also the bowl flush starts and will run for 6 seconds and stops automatically. While the cupfiller is working, by momentarily pressing the cupfiller  switch (      ) the cupfilling will cancel. Also, when the cupfiller starts, the spittoon water flushes 6 seconds and stops automatically.(Synchronized Bowl Flush)

 

Bowl Flush Switch.

Momentarily press the bowl flush switch (), water flushes for 6 seconds and stops automatically. (Timer Mode)  Press the bowl flush switch for  2 seconds, water flushes continuously. (Continuous mode) While the bowl flush is working by momentarily pressing the bowl flush  switch (      ) the bowl flush will stop.

Chair Manual Control Switches.

a.       Seat Lifting. Press the switch until the seat is lifted up to the desired position.

b.      Seat Lowering. Press the switch until the seat is lowered to the desired position.

c.       Backrest Reclining. Press the switch until the backrest is reclined to the desired position.

d.      Backrest Raising. Press the switch until the backrest is raised up to the desired position.

 

 

MAINTANANCE AND INSPECTION

 

MOISTURE CONTROL

Fig. 1 Tips for high-volume suction, low-volume suction (saliva ejector), cotton wool rolls, dry guards (flat triangular pads).

Why is moisture control important?

The water spray of the high-speed handpiece and three-in-one syringe and the patient’s own saliva result in large volumes of fluid accumulating in the mouth. This needs to be removed for the following reasons:

■ Patient comfort.

■ Visibility for the operator and assistant.

■ Avoidance of contamination of dental materials.

■ To reduce or prevent bacterial contamination of cavities.

■ For overall operating efficiency.

METHODS OF MOISTURE CONTROL

ASPIRATION

Suction is used to remove fluids from the mouth. High-volume suction is used with high-speed handpieces and ultrasonic and sonic scalers. Low-volume suction, such as a saliva ejector, is used for smaller volumes of fluid such as patients’ saliva.

Air

The air spray from the three-in-one tip is used to blow excess moisture from cavities and the surfaces of the teeth. It can also be used to keep water off the mouth mirror to improve vision for the operator.

Absorbent materials

Cotton wool rolls are a common method of moisture control. They may be placed in the buccal and lingual sulcus to absorb saliva. They also act to retract soft  tissues, such as the lips and tongue. Care should be taken when removing cotton wool rolls from the oral cavity. The cotton wool roll must be soaked with water before removal, otherwise the mucosa may be damaged, resulting in a ‘burn’ of the soft tissues.

Dry guards are flat triangular pads of absorbent material that are placed inside the cheeks over the parotid duct to absorb saliva and water.

Care of instruments and hand-pieces

Dental instruments and handpieces need regular maintenance if you want them to work effectively. Hand instruments designed for cutting enamel or dentine should be kept sharp. Chisels may be sharpened against a lubricated stone or against a stone bur in a slow-speed straight handpiece. Excavators and probes are best sharpened against an abrasive disc held in a slow-speed straight handpiece. It is also essential that they are sterilised between patients to prevent cross-infection:

■ Obvious debris, such as excess dental cement, should be removed immediately after use of the instrument by cleaning with an impregnated wipe.

■ Cleaning is a vital step as it removes the nutritive material on which bacteria survive. This may be achieved by manual washing, ultrasonic baths or the use of a washer-disinfector. The washer-disinfector  is the most reliable technique for decontamination of instruments.

■ Sterilisation is best carried out in an autoclave. Instruments should be clean before they are placed in the autoclave. Sterilisation is achieved by direct contact of the instruments with saturated steam at 134°C for a minimum of 3 minutes.

■ Handpieces must be oiled before being placed in the autoclave and should be maintained according to the manufacturer’s instructions.

 

PROTECTIVE CLOTHING

Protecting dental healthcare personnel from potential exposure to microorganisms requires a combination of controls, one of which is the use of personal protective equipment (PPE) (Kohn et al., 2003). The wearing of PPE helps to prevent contact with infectious microorganisms or body fluid by creating a barrier between the worker and the infectious material. National health and safety authorities require workers, including healthcare professionals, to wear PPE when there is a risk of exposure to potentially infectious diseases. PPE should never be worn outside the clinical environment.

 

GLOVES

Gloves protect the dental healthcare worker’s hands from exposure to microorganisms while performing dental procedures. However, they do not protect against percutaneous injuries. A variety of disposable gloves are available for this purpose, the majority of which are made of latex, vinyl or nitrile. Non-sterile, ambidextrous, disposable, latex examination gloves are the most frequently used type of glove in modern dental surgeries. The use of powdered gloves has been discontinued in many healthcare institutions to reduce exposure to latex powder that can cause allergy (Korniewicz et al., 2005).

Sterile surgical gloves are worn for surgical procedures or for procedures requiring a sterile field. Auxiliary dental staff frequently wear disposable latex gloves when cleaning environmental surfaces in the dental clinic; however, they are not suitable or intended for this purpose. Reusable heavy-duty gloves made of latex or nitrile are more appropriate and individual pairs should be provided for each worker concerned and not used by many different individuals. It is important to appreciate that gloves only protect you provided you do not touch environmental surfaces, face or hair with contaminated gloves. Care should be taken to ensure not to touch and thus cross-contaminate items such as pens, case notes, X-ray films, telephones, computers (screen, keyboard and mouse, etc.) with contaminated gloves. Gloves should be changed after each patient and should never be washed or reused. Gloves should also be changed if they become heavily soiled, even if being used during treatment of the same patient, or torn during use. Gloves should also be worn when handling or cleaning items or surfaces contaminated with body fluids, e.g. used clinical gowns and the DCU spittoon. Hand hygiene procedures should be under-taken before putting on and after removal of gloves. Care should be taken to limit self-contamination when removing gloves. Remove gloves by grasping the outside edge of the glove closest to the wrist; peel the glove away from the hand and in so doing, the glove will be turned inside out. Then slide an ungloved finger under the cuff of the remaining glove and peel it off from inside (Fig. – below).Discard used gloves into a contaminated waste bin.

 

 

GOWNS

Clean gowns should be worn to prevent cross- contamination of the clothes of dental healthcare staff during dental procedures. It is important to emphasise that uniforms (e.g. dental nurses’ or dental hygienists’ uniforms, etc.) are not protective clothing and protective gowns should be worn over uniforms during dental  procedures. There are many different views regarding whether gowns should have long or short sleeves; however, long-sleeved gowns protect the forearms from contamination and are recommended. Gowns should protect the torso and be long enough to cover the knees of operators while in the seated position. Gowns should also be fluid resistant and, in the case of reusable gowns, be able to withstand high-temperature washing with  a good-quality detergent. Gowns should be changed if they become visibly soiled. Gowns should be removed by loosening the ties or snap fasteners at the back of the gown, which should be uncontaminated, and then peeling the gown away from the neck and shoulders. During this process the contaminated outside part of the gown should be facing away from the wearer. The gown may then be rolled into a bundle and placed in a designated package.

 

FACEMASKS

Facemasks are used to protect the mucous membranes of the mouth and nose from spray, splashes, spatter and aerosols. They are secured in place with either string ties at the back of the head and base of the neck or by adjustable elastic tapes. The mask should be adjusted to fit snugly against the face and nose so that there are no gaps. The mask should not be touched during procedures to prevent contamination from gloves. Face shields may also be worn and should protect the forehead, extend below the chin and also wrap around the sides of the face. Masks should be changed hourly or if visibly soiled or wet. Facemasks should not be worn around the neck as a necklace as this serves no useful purpose. Masks should be removed by untying the strings from the bottom first and then the top and then discarding into a designated waste bin.

PROTECTIVE GLASSES

 

Fig. 3 Protective glasses

Protective glasses or goggles should be worn during dental procedures by both dental healthcare workers and patients to prevent physical injury and transmission of microorganisms to the eyes. Eyes are particularly vulnerable to injury by high-velocity particles/debris generated during use of high-speed handpieces and scalers. Prescription glasses do not usually provide sufficient protection, so protective goggles or glasses should be able to fit snugly over the top of them. The  goggles or glasses should have top and side shields to provide best possible eye protection. They should be washed with soap and water after each use. If glasses are disinfected, care should be exercised to ensure that they are thoroughly rinsed, as chemical residues may cause irritation to the skin and eyes of the wearer. Contact lenses do not protect the eyes and can increase the risk  of exposure to microorganisms if contaminated fluids gain access beneath the lens. Protective glasses should not be pushed up on to the head as this may result in cross-contamination of the hair.

SHOES

The wearing of open-toed sandals and shoes made from fabric is to be discouraged in the dental clinical environment to minimise the potential for cross-infection or physical injury from dropped instruments, other items or chemicals falling on to the exposed foot.

 

PROCESSING AND HANDLING OF DENTAL INSTRUMENTS

 

The majority of instruments used in dentistry are double ended and can also be very sharp. For this reason they should be handled with appropriate care and attention. All instruments should be used only for the purposes for which they are intended.

 

INSTRUMENT DECONTAMINATION

 

All reusable medical devices, including dental instruments, must be decontaminated following each use. Dental surgeries should have dedicated space allocated for instrument decontamination and processing. The purpose of the designated area is to minimise opportunities for cross-infection of patients and clinical staff and cross-contamination of the working environment. The designated area should be made up of receiving, cleaning, decontamination, packing, sterilisation and storage areas. The area for processing of contaminated instruments should be segregated into contaminated and clean areas and contaminated instruments should be processed unidirectionally from the contaminated to the clean area to avoid recontamination of clean items. Enough space should be provided in the decontamination area to accommodate equipment, sinks and work benches.

It is vital that the appropriate method of decontamination is applied to all dental instruments and equipment. Generally, dental instruments and equipment may be divided into three risk categories: high, medium and low risk, according to the risk of infection associated with the subsequent use of each item of equipment.

For high-risk items (e.g. instruments that become contaminated with blood), cleaning followed by heat sterilization is the method of choice. In certain circumstances, it may be necessary to use chemical disinfection for heat-sensitive items such as photographic mirrors. For dental procedures it is best to use only instruments that will tolerate sterilisation by the moist heat method (i.e. autoclaving), as this is one of the safest and easiest to monitor and validate.

Medium-risk items consist of instruments or equipment used in contact with mucous membranes in the oral cavity, such as a light-curing units, that are not suitable for heat sterilisation and should be barrier protected prior to use. For reusable medium-risk items, the appropriate means of decontamination is cleaning followed by high-level disinfection or sterilisation. In fact, the majority of instruments and equipment used in dentistry come into direct contact with the patient’s oral cavity so decontamination followed by sterilisation is the method of choice.

Low-risk items include instruments, equipment or other items/surfaces in the dental clinic that come into contact with a patient’s healthy intact skin, and equipment that does not have close contact with the patient. For these items, cleaning is sufficient. However, disinfection may be necessary if there is a known infection risk. Examples of low-risk items include door handles and surfaces, including floors, walls and sinks.

 

INSTRUMENT COLLECTING AND TRANSPORTATION

 

After use in dental procedures, contaminated dental instruments have to be removed from the clinic and transported to the designated processing area for cleaning, decontamination and sterilisation. Steps in the collection and transportation process are outlined below:

■ Instruments should be removed from the surgery or clinical environment using a defined procedure.

■ To prevent injuries during transportation and during the decontamination process, instruments should be arranged in kits or cassettes for set procedures, e.g. examination kit, scaling kit, etc.

■ Instruments should not be transported uncovered, as there is the likelihood of dropping the instruments enroute or, indeed, colliding with patients or staff.

■ Depending on how long the instruments are stored prior to cleaning, it may be necessary to store them in a disinfectant solution. However, some commercial disinfectant products recommended for this purpose cause corrosion if in contact with instruments for prolonged periods. Ideally, instruments should be cleaned and disinfected immediately or shortly after use. In the case of heavily contaminated instruments it is best to adopt a policy of removing as much of the contamination as possible prior to collection for transport to the decontamination area, e.g. instruments heavily contaminated with blood should be wiped carefully with damp gauze using a single-handed technique.

■ Remove all disposable items from the kit prior to dispatch, e.g. disposable needles, cartridges, polishing cups.

 

HAND WASHING OF INSTRUMENTS

 

Cleaning should remove all visible dirt, dust or other foreign materials. Hand washing of instruments is the least preferred method of instrument decontamination and should be strongly discouraged due to the high risk of percutaneous injury during cleaning. Unfortunately this hazardous approach is still widely practised. A scheme for hand washing of instruments is outlined below:

■ Instrument decontamination should take place away from food, beverages or sterile items.

■ Wear protective clothing: goggles, facemask, water resistant over-gown or plastic apron and heavy-duty protective gloves.

■ Gloves should be able to withstand instrument abrasion, should be cut, tear and puncture resistant. In reality, heavy-duty utility gloves are regularly used. However, even when wearing heavy-duty utility gloves, care should be taken to prevent percutaneous injuries or cuts when washing sharp instruments. In case of an injury, follow the protocol for such injuries detailed by your hospital or surgery.

■ Use deep sinks to prevent splash-back and if possible have a splash screen situated in front of the sink. Ensure that it does not impede your vision of the instruments. A double sink unit is preferable, one for washing instruments and the other for rinsing.

■ Use a low-foaming detergent that is approved for instrument decontamination according to the manufacturer’s instructions.

■ A wide range of autoclavable cleaning brushes is available for cleaning both lumened and non-lumened instruments. Steel brushes should not be used to clean instruments as they can scratch instrument surfaces, providing refuge areas for microorganisms that lead to an inability to decontaminate.

■ Begin by cleaning from the centre of the item using an outward motion. Hold the instrument under the water to avoid generation of aerosols.

■ After cleaning, the instruments should be thoroughly rinsed and dried.

 

ULTRASONIC CLEANING

 

Ultrasonic cleaners can be used to decontaminate dental instruments and their use is far safer than hand washing instruments. Contaminated instruments in an open  basket or tray are immersed in an enzymatic solution designed to digest biological material. Ultrasonic waves are then passed through the solution resulting in the removal of contaminating material on the surface of instruments by a process called cavitation. Ultrasonic cleaning is suitable for stainless steel instruments but not suitable for plastic items. There are many different types of ultrasonic baths available ranging from the small bench-top variety to larger baths used more frequently in hospitals. Some important considerations concerning the use of ultrasonic baths are outlined below:

■ The ultrasonic cleaning units or bath should be operated with a well-fitting lid to prevent release of aerosols.

■ Fill the bath according to the manufacturer’s instructions and drain and rinse twice daily or more often, depending on the frequency of use.

■ Use an enzymatic detergent recommended by the unit’s manufacturer.

■ The unit should be thermostatically controlled (43–45°C: 3–4 minutes) to prevent coagulation of proteins on to instrument surfaces.

■ Ensure that all items to be treated are fully immersed.

■ Hinged instruments should be opened.

■ Do not overload trays.

 

WASHER DISINFECTOR

 

This is an automated machine similar to a domestic dish-washer that is specially designed to clean, decontaminate and thermally disinfect instruments and equipment.

Washer disinfectors should conform to approved standards (e.g. UK standard HTM 2030). The washer/disinfector runs a washing cycle, followed by a disinfection phase. Disinfection is performed by flushing with hot water of approximately 90°C for 1–10 minutes. The machine renders equipment clean, disinfected, dry and safe for further handling. The machines are fast and are easy to operate. They usually have set programmes for different types of loads and allow for minimum instrument handling. However, they are unsuitable for use with heat-sensitive items. Care should be takeot to over-fill the washer disinfector as this can cause some items to be shielded and result in them not being cleaned or disinfected properly.

 

HANDPIECES

 

After each patient use, any dental handpiece that is connected to the DCU air/water system should be operated to discharge water and/or air for at least 30 seconds; care should be takeot to inhale the aerosol. This procedure is designed to dislodge any patient-derived material that may have been retracted into the air and/or waterlines due to failure of antiretraction valves. These valves are designed to prevent material or fluids from being retracted or siphoned back into air and/or waterlines. In reality, modern antiretraction valves are very reliable and failure of antiretraction valves is more likely to be a problem in older chair units or dental handpieces.

Following air and waterline purging, handpieces should be detached, cleaned, decontaminated and sterilised according to the manufacturer’s instructions and local policy. Automated pre-sterilisation cleaning is the preferred method of handpiece decontamination.

However, manual cleaning is still widely practiced. Clean the outside of the handpiece with detergent and warm water (follow the manufacturer’s instructions with regard to type of detergent advised). If recommended by the manufacturer, lubricate the handpiece with pressurized oil until clean oil appears from the chuck (wear protective clothing including gloves, glasses and a facemask).

Cover the working end of the handpiece with disposable paper towel to absorb the residual oil and clean away any excess oil. Following cleaning, sterilise in an autoclave with a pre-sterilisation vacuum phase.

 

X-RAY

 

Intraoral X-ray films should always be barrier protected prior to insertion into the oral cavity. The barrier should be disposed of in contaminated waste after removal.

Bite-blocks and film-holders should be autoclavable and a sterilised block and holder should be used for each patient.

 

SINGLE-USE AND SINGLE-PATIENT-USE ITEMS

 

If an item is marked single-use, it means that it must only be used on a single occasion and then it should be discarded into contaminated waste or a sharps box, as appropriate. Single-use item products will often be labelled with the symbol . A single-use item or device must not be used on multiple occasions either on a single patient or on a different patient. Examples of single-use items include plastic syringes used for irrigation, suction tips and polishing cups. The use of single-patient-use items is recommended where possible. If a medical device is marked for single-patient use, the item may be used on several occasions with the same patient then must be discarded. Before using a pre-packed sterile single-use or single-patient-use item, check that the packaging is intact and the product is within its use-by date. These devices must be stored in clean, designated areas where there is no risk of aerosol and droplet contamination. It should be noted that only reusable medical devices should be reprocessed. Never reprocess medical devices designated for single-use only.

 

PACKAGING OF INSTRUMENTS

 

After cleaning and decontamination, dental instruments have to be appropriately packaged prior to sterilization by autoclaving. Instruments should be packed before sterilisation, because otherwise as soon as they are removed from the autoclave, they become recontaminated with dust and microorganisms from the environment. Packaging allows the instruments to be safely stored and transported within the clinical environment following sterilisation. All instruments should be thoroughly dry before packaging and sterilisation. The packaging material should be compatible with the sterilisation process (i.e. allow passage of air and steam) and should provide an effective barrier against recontamination by microorganisms (i.e. the packaging should be robust and permit handling and transportation while maintaining the sterility of the packaged instruments).

Primary packaging consisting of sterilisation pouches or bags is generally sufficient for the dental clinic environment. Alternatively, instruments in kits or cassettes may be packaged as required. Packaging should also contain clearly visible chemical indicator strips that give a colour change when sterilising conditions have been achieved during autoclaving. Finally, packaging should be appropriately labelled so that the packaged instrument(s) is clearly identified.

 

STERILISATION OF DENTAL INSTRUMENTS

 

Autoclaving, using equipment that has a pre-vacuum stage, is the most appropriate method of sterilisation for heat-tolerant dental instruments and should be under-taken using equipment that conforms to current European Union (e.g. EN285, EN554 and EN556) or United Kingdom (e.g. HTM2010) standards. The manufacturer’s instructions for correct use of equipment should always be followed and the equipment should be used by trained and competent personnel. Boiling water sterilisers, hot air ovens, ultra-violet light treatment, hot bead sterilisers and chemiclaves are not appropriate for sterilising dental instruments. Furthermore, downward displacement autoclaves are not appropriate for sterilising wrapped loads of instruments or for items that contain a lumen (e.g. dental handpieces), and in the authors’ view should be discouraged in favour of vacuum autoclaves.

Fig. 4 Vacuum autoclave.

When loading the autoclave, instruments and other items to be sterilised should be arranged to permit free circulation of steam and care should be takeot to over-fill the autoclave chamber. Sterilised instrument packs should be allowed to dry inside the autoclave before removing and handling. Fortunately, many modern vacuum autoclaves have a drying cycle that facilitates drying of instrument packs. Autoclaves have to be monitored and validated to ensure they are working correctly and produce a sterile load (Harte and Miller, 2003). Validation is normally undertaken by professionals and this service is usually provided by appropriately accredited commercial companies. Individual autoclave cycles (i.e. packaged instruments, laboratory glassware, etc.) are usually validated separately and autoclave validation should be undertaken at least once a year.

Sterilisation monitoring usually includes a combination of process controls, including mechanical, biological and chemical controls (Fig. below):

■ Mechanical methods for monitoring sterilisation include assessing cycle time, temperature and pressure by observing parameter displays on the steriliser and recording these for each load. Many autoclaves are supplied with integral recording equipment that print out this information. Larger autoclaves, such as those used in hospitals, may also have a remote data archiving facility that allows data for each autoclave run to be recorded in a database on a desktop computer.

Acceptable readings do not guarantee sterilisation, but erroneous readings can indicate a problem(s) with the sterilisation cycle.

■ Chemical indicators are used to evaluate physical conditions (e.g. temperature) during the sterilization process. External indicators applied to the outside of a package (e.g. chemical indicator tape placed on wrapped instrument packages or imprinted chemical markings on instrument packaging pouches) change colour rapidly when exposed to high temperature. Chemical indicator test results can be read by examining the autoclaved packages for the appropriate colour changes on indicator tape or imprint mark when the sterilisation cycle is completed. If chemical indicators or the autoclave parameter readout data indicate inadequate processing, the load should be reprocessed.

■ Biological indicators (i.e. spore tests) are the most acceptable method for monitoring the sterilisation process. These usually consist of highly resistant bacterial spores (e.g. spores from Geobacillus or Bacillus species) that are only killed when adequate sterilisation conditions (i.e. time, temperature and steam pressure) are reached. If the high-density spore preparations found in biological indicators are killed following a sterilisation cycle, this indicates that other microorganisms present in the load have also been destroyed. In general, biological indicators should be used to test proper functioning of autoclave cycles at least once a week for each autoclave. The interested reader should consult the recent CDC guidelines for cross-infection control in dentistry for a more comprehensive overview of indicators and their use for monitoring the efficacy of sterilisation cycles (Kohn et al., 2003).Care should be taken to ensure that water supplied to autoclaves is of good quality to prevent the formation of residue on instruments during the sterilisation process. Residues can result from chemical compounds dissolved or suspended in the supply water or indeed from supply water heavily contaminated with microorganisms. Furthermore, water reservoirs within autoclaves should be drained and cleaned regularly. A variety of approaches for processing autoclave supply water is available, such as reverse osmosis and ion exchange. The autoclave manufacturer’s instructions should be followed in relation to proper maintenance of the equipment, including the quality of the supply water.

 

 

STORAGE OF STERILISED ITEMS

 

Sterilised instruments, other items and disposable single-use items contained in wrapped packages or pouches should be stored in a dry enclosed area, preferably in closed cupboards, cabinets or drawers. They should not be stored under sinks or adjacent to taps or other locations where they may become damp or wet. All sterilised packages should contain the sterilisation date and, if there are multiple autoclaves in a particular facility, the autoclave used. All sterilised packages should be examined prior to use to ensure they are dry and that the packaging is intact. If packaging is compromised, the instruments should be recleaned, repackaged and resterilised.

 

Information was prepared by Levkiv M.O.