The use of the operating microscope in general dental practice part 1: magnification in general

Advantages of magnification

There are many advantages of utilizing magnification in clinical dentistry. First, and most obviously, the clinician enjoys improved vision with respect to clarity (detail) and definition of the image as the image is larger and therefore easier to see. This reduces operator eye fatigue and so eye strain is minimized. Furthermore, as the eyes are covered they are protected from airborne foreign bodies and aerosols which may be created during operative procedures. Secondly, owing to their design, most optical aids force the clinician to sit in a more comfortable and ergonomic position, otherwise the object will be out of focus. This has the effect of reducing neck and back strain of both the dentist and dental nurse due to their improved posture. Thirdly, there is evidence that magnification gives the clinician the ability to perform more precise work,3 both in diagnosis and operative interventions. Better treatment outcomes with respect to quality, predictability and longevity can therefore result, with a commensurate increase in job interest and satisfaction for all members of the dental team.

Importance of illumination

To improve the operator's vision further by complementing this magnification, good illumination is essential. Increased illumination causes the iris to constrict which increases the operator's depth of vision by up to 33%. Resolution of detail is also enhanced and so eye fatigue is also reduced. A properly angled light source will ensure that the clinician is never working in a shadow so that he/she has an optimum freedom of movement and with it the correct working posture and position. Good illumination is especially important when performing highly detailed work. For this reason, both loupes and microscopes intended for dental use utilize a light source which either comes as an integrated feature or may be added to the system as an accessory. However, it is important that the light intensity is not too powerful as this can lead to eye strain and fatigue and may cause after-images, like a camera flash effect. The hue (colour) of this light may also detrimentally affect the actual appearance of tooth structures and soft tissues and the clinician should be mindful of this possibility.

Loupes

The most commonly used magnification aid in dentistry are (binocular) loupes (Figure 1) and these instruments are most dentists' first experience of magnification.1^,4 It is important to note that eyesight will not be damaged by wearing loupes; they will in fact lessen eye strain and reduce eye fatigue.

Loupes are lenses either inset into (‘through the lens’), or are flipped down over, the protective spectacles of the operator. These can offer a magnification from x2 up to x6.5. The ‘through the lens’ models require the interpupillary distance and working distances (dentist's eye to patient's mouth) of the wearer to be measured with the result that a customized instrument is produced. This ensures that the dentist is forced to sit correctly, which is advantageous as mentioned earlier. The ‘flip-up’ models are recommended when it is important for the operator to switch (often) between magnification and the naked eye.

The optical systems most commonly utilized in dental loupes are Keplerian and Galilean. The former allows greater magnification with edge-to-edge clarity, whereas the latter is a telescopic lens arrangement enabling optimum depth of field and field of vision. The detail regarding dental loupes is outwith the scope of this article and so the reader is referred to other papers and, in particular, a review done by Shanelec.5

Many models are compatible with a headlight which may also be purchased (Figure 1). The original light source was a halogen bulb which had to be housed in a bulky mains-powered unit on an adjacent work surface as the large amount of heat energy produced by the bulb had to be dissipated by means of a cooling fan. The light was transmitted to the headlight by an umbilical fibre-optic cord. Unfortunately, these cords were readily damaged during usage. The constant daily use of these bulbs caused deterioration of the output of the halogen bulb with time and their longevity was poor. Light Emitting Diodes (LEDs) are now used in preference and these offer a number of advantages:

It is true to say that, once clinicians become accustomed to using magnification, they will find it virtually impossible to revert back to using the naked eye. This, in many cases, will stimulate an interest and curiosity to increase magnification further as they appreciate the many benefits for themselves. The next step is to use an operating microscope.

Operating microscope

Operating microscopes have been used for some years in many branches of surgery. These include:

Their use offers the advantages of loupes but on a much larger scale. The ability of the surgeon to perform procedures which require fine detail is therefore increased.7^,12 This results in fewer post-operative complications with an improved surgical outcome.10 This has been extrapolated to dentistry13 with the result that the use of operating microscopes is becoming more widespread, both in general dental practice and in various dental specialties.

Features

The operating microscopes used in dentistry have many features. Each magnification setting is called a step. For example, a five-step microscope would have settings at, for example, x3, x5, x8, x13, x20 (Figure 2). Clearly, it is critical that the optics afford the clinician excellent vision. Clarity of view, good contrast and depth perception are all therefore important, as is wide-field stereoscopic vision, all for obvious reasons. It is advantageous for an apochromatic lens system to be used as this eliminates chromatic aberration. This is the phenomenon of different colours focusing at different distances from a lens. Apochromatic lenses are designed to bring three wavelengths (typically red, green and blue) into focus in the same plane to correct this phenomenon. Other optical features may be present on some instruments. These include wide field, adjustable cup eyepieces with dioptre settings. These are suitable for prescription and discrepancy non-prescription wearers, so allowing the operator to wear prescription spectacles, if necessary, or safety glasses if no prescription is required. A motorized zoom and autofocus may also be available. Adjustment of focal lengths (including a range of focal lengths) is advantageous as it will allow the operator to work at his/her ideal working distance. Some products now incorporate lens arrangements which give an increased depth of field. Most final objectives have a depth of field of approximately 30 mm and therefore any increase results in better posture and obviates the need for continuous repositioning of the microscope for gross focusing.

The importance of good illumination was discussed earlier and, with microscopes, this is provided by a co-axial radiating light source which will provide a shadow-free light. If the bulb is halogen, then a back-up bulb should be available and easy to switch to if the one being used fails during the procedure. Often, xenon sources are now commonly used which provide light which is equivalent to ‘daylight’. As mentioned earlier, colour filters may be incorporated. An orange filter will remove the specific wavelength of light which initiates the setting of light-cured dental materials, whilst green makes a surgical site easier to visualize, known as ‘red free’.

To ensure maximum comfort for the operator, inclinable binoculars are often provided to minimize neck and back strain. Some microscopes have a motorized positional mechanism which facilitates the adjustment of the microscope during use so that the operator does not need to exit the mouth to adjust the position of the microscope. This is more efficient and results in less eye strain as the need to accommodate the eyes is much reduced.

Many microscopes are available with a choice of mounting: wall, ceiling or on a moveable stand. The decision between a wall or ceiling mounting will depend on the dimensions of the surgery: how much space is available, the height of the ceiling, or the distance from the nearest wall. A ceiling mount may not be advisable if the room above the surgery is populated as vibrations from people walking about may cause the microscope to move, so adversely affecting its use. A high ceiling, for example in older buildings, may also preclude the use of this mounting type. The moveable stand offers the advantage that the microscope is portable and may be used in more than one surgery in the practice or clinic.

Ideally, the microscope should allow the mounting of a (digital) camera on the microscope, by means of a lateral output port and beam splitter, or have an inbuilt camera. This allows still or video photography to be done and allows real time viewing for the dentist, dental nurse and possibly the patient. The many advantages of this are discussed later in detail.

It is important to note that not all of the features listed above may be available on every instrument, with some only being available on the higher specification models.

The use of photography and video

A good quality digital camera is strongly recommended to be used in conjunction with the microscope. This camera is connected to a monitor or PC by means of a USB or HDMI or incorporated into the microscope. This will permit a television screen to be placed in direct eye line for the dental nurse to watch the procedure in real time (Figure 3). This will enhance a dental nurse's interest in his/her work and will improve his/her ability to assist the dentist. Some operators mount a television screen on to the ceiling above the dental chair so that the patient may also watch the procedure. The advantage of this is that the patient's head is kept still as there is no temptation for them to look at the screen intended for the dental nurse, so moving the head out of the operator's field of view. Any movement (particularly at a higher magnification) is both counterproductive and annoying from the operator's perspective. In the experience of this author, patients react to the ability to view their treatment in usually one of two ways: they either find the experience very interesting or highly disconcerting. It is therefore advisable to ask patients whether they wish to watch or not and adjust the television accordingly. The availability of a camera also allows the dentist to record material,14 so enhancing the quality of the clinical records. Whether this is captured as stills or video footage, it may be used in many ways. The information can be digitally attached to the patient's clinical notes with the result that, for example, both hard and soft tissue lesions may be more easily monitored over a period of time (Figure 4), or sent electronically to another colleague if the patient is being referred for further advice or treatment. Other information may be captured and stored which may not be seen subsequently, such as a fracture line on a cavity floor which has then been restored (Figure 5). The recording and retention of such material may also be useful from a medico-legal perspective as evidence of a particular situation or as justification for a decision.

Many colleagues use images as a patient education tool with the old adage of a picture painting a thousand words being very true. The ability to show and explain clinical photographs to patients can engage them far more in their treatment, so making any future discussion of treatment options more meaningful and less abstract (Figure 6). The critical importance of prevention in clinical dentistry can never be stressed enough and clinical photographs are an effective motivational and educational tool. The obvious example would be to show a patient the presence of plaque in an area difficult to see and to demonstrate the appropriate cleaning technique. Clinical photographs can also be used to demonstrate a particular clinical situation (for example, a heavily restored tooth) and to recommend a particular treatment (in this example, the provision of a crown) (Figure 7). Documentation of clinical cases may be used by the dentist as a portfolio of evidence to be submitted as case reports for qualifications such as postgraduate degrees. Likewise, the information may be used for publication in journals, such as case reports or research, as a teaching tool to professional colleagues, or as a library of the dentist's work to be kept for his/her own interest.

Instruments

Various instruments are available which are specifically designed to be used intra-orally in combination with the operating microscope. These instruments are essential to achieve the full advantages of a less invasive procedure15 and also to decrease the potential for other objects (such as the fingers of the operator) to obstruct the line of vision. Examples include:

Front surface dental mirrors are recommended as they produce a clearer single image, unlike conventional mirrors. A front surface mirror is a mirror with the reflective surface being above a backing, as opposed to the conventional mirror with the reflective surface behind a transparent substrate such as glass. The ‘silvering’ on a dental front surface mirror is usually aluminium. No ‘ghosting’ effect is seen with the front surface mirror, unlike the conventional mirror (Figure 9).

Ultrasonic instruments are commonly used in conjunction with the operating microscope as their use permits much more precise usage than conventional rotary instrumentation. A more conservative preparation can therefore be achieved both of tooth tissue during a dental procedure and bone removal during a surgical procedure.

Operating position

When dentists work on a patient with an operating microscope, they require extra chairside help from the dental nurse. The dentist and dental nurse should sit as they would when ‘close support (four-handed)’ dentistry16^,17 is being practised (Figure 10). Both the dentist and dental nurse should be seated with their backs straight and their knees bent at a 110° angle with their feet flat on the floor. Furthermore, their legs are intertwined, so permitting them both to sit closer to the head of the patient. It is recommended that the dentist's stool is supplied with arm rests to reduce fatigue. This may also reduce any tremulous movement as the arms are more able to relax, particularly during a long procedure.

The patient is placed in the normal supine operating position (Figure 10). The dental team's vision may be improved by asking the patient to move his/her head from side-to-side or by tilting the head up and down. Should the operator find that he/she has to crane the neck to look into the eyepieces then the dental chair may be lowered to facilitate vision and reduce neck strain. Clearly, those patients who are unable to be placed in the supine position, for whatever reason, would not be candidates for those procedures which require an operating microscope.

The proximity of the dentist and dental nurse facilitates their ability to see and to pass instruments between them. This is particularly important when the microscope is being used. To avoid eye fatigue by constant accommodation between near and further away objects, the operator should only look down the eyepieces. The help of the dental nurse is invaluable to guide instruments into the hand of the operator and then into the patient's mouth and thus into view (Figure 11). Clearly, this is most important when sharp instruments are being handled, such as dental probes (explorers), needles or scalpel blades. The role of the dental nurse in the retraction of the oral soft tissues to improve access and vision is also critical. This may be done by the dental nurse holding the aspirator in one hand and the 3 in 1 syringe in the other. Both these instruments may be used to retract the soft tissues, with the 3 in 1 syringe being used to blow air on to the dental mirror to prevent fogging (Figure 12).

Maintenance and care

Just like any other piece of dental equipment which is used frequently, it is wise to have the microscope serviced annually. Fixing bolts and screws can work loose from regular movement during usage and other problems, such as the microscope ‘drifting’ or rubber eyepieces perishing, can occur over time. Regular servicing will minimize problems, which can be highly inconvenient should a problem occur unexpectedly. It is sensible to ensure that, when purchasing a microscope, that the vendor company is willing to provide such a service or can recommend another which can. The unwillingness or reticence of a vendor to provide this service may influence the decision of the dentist to buy from a given company. Sadly, some companies are very keen for the sale then let themselves down with their after sales service. Customers should therefore be wary and satisfy themselves that back-up is in place with respect to maintenance and breakdown.

The optics of the microscope should be looked after carefully. Cleaning of the various lenses and glasses should only be done using products recommended for such use, otherwise scratches may result which will compromise the optics. These products may be purchased at opticians' shops. When not in use, the microscope should be kept covered to reduce any dust from the atmosphere falling on to the glasses (Figure 13).

Costs and finance

As would be expected, an operating microscope is an expensive item. The initial outlay (purchase price) can start from approximately £5000, rising steeply for top of the range models. Many companies (both microscope vendor companies and specialist dental finance houses) offer finance to allow the practice to pay for the equipment over a period of months or years, so spreading the cost of the initial outlay. This should be viewed as an investment with a return being realized over a period of years. This is not only in financial terms, but also clinically and personally. This is because a microscope will facilitate an increased satisfaction in one's work, as well as providing a tool which will make clinical dentistry easier and reduce back, neck and eye strain.

Inevitably, there are some associated ongoing running costs. Periodic servicing has already been discussed, but other costs may not be so apparent, such as the replacement of halogen bulbs. These will fail from time-to-time and will need to be replaced. When considering purchasing a microscope, the dentist should enquire how often this may occur and the cost of replacement bulbs.

Clearly, such an investment in a business will require to be recouped. Generally speaking, two approaches are used by colleagues in private practice to that end. Some practitioners charge the patient a fee for each case requiring the use of the microscope, whilst others prefer to include the cost into the general running expenses of the practice and charge indirectly by increasing their hourly charge-out rate. Clearly, those dentists working solely in NHS general dental services are not able to use the latter method and so will have to make it clear to the patient at the outset that an extra (private) charge will be levied or, alternatively, absorb the extra cost themselves. That said, notwithstanding the costs, the satisfaction of using an operating microscope with its other many advantages will pay for the instrument in non-monetary ways in the long term.

Conclusion

The incorporation of an operating microscope system into dental practice offers many advantages to the dental team and offers great potential for improving the clinical care which the patient receives. The second paper in this series will discuss the specific potential uses of the operating microscope in general dental and specialist practice.