Microscope-Assisted Precision (MAP) Dentistry -- A Challenge for New Knowledge

The purpose of this paper is to acquaint the dentist with the learning needs associated with the use of microscope-assisted precision dentistry (MAP) and identify certain concepts that will assist in the education process. Although the learning curve is considered to be lengthy and often difficult, the authors believe that the clinical benefits of MAP dentistry are well worth the necessary effort to achieve a level of competency with this methodology.

In a recent publication, the authors of this paper introduced the term "microscope assisted precision (MAP) dentistry" to distinguish an advanced level of operator exactness with the aid of a microscope.¹ The surgical microscope not only provides a variety of magnification options, but also the control of coaxial illumination for a shadow-free visual field. In addition, it allows the dentist and auxiliary to work in precise concert with one another because they share the same visual access to the procedure being performed.

Fig 1. A small group of senior dental students experience making a cavity preparation on the dental simulator using a surgical microscope.

Interestingly, at a local school of dentistry two surgical microscopes are being used by a very limited number of faculty as a teaching methodology utilizing video networking to demonstrate the fine detail of operative dentistry. This allows an instructor to perform a procedure in real time (or videotape), while the student gains a perspective of the procedure from the faculty's point of view. However, the use of the microscope is not taught as a part of the regular curriculum at this time. A "handful of senior students" were given minimal instruction in the use of a surgical microscope. They were asked to use it as an adjunct to making a cavity preparation (MO inlay) on a plastic tooth in a simulator manikin head. The outcomes of this exercise suggest that as part of their formative training, students could be taught to use the surgical microscope in a minimal amount of time and achieve a reasonable level of proficiency at improving their level of precision (Fig. 1).
In general dentistry, there are numerous opportunities to take advantage of better vision for both diagnostic and restorative intervention. Well-documented human subject studies are essential in order to validate the efficacy of the surgical microscope for use in general practice. Nonetheless, it appears that when a general dentist has received basic training, and subsequently has a period of time to adjust to the technical differences inherent with the microscope, it enhances his/her ability to discern more detail and perform with greater precision. In a recent paper on microdentistry, Mora states "... that to reach a comfort level with maximum productivity can be time consuming and frustrating."² The authors believe that the clinical benefits of of MAP dentistry are well worth the necessary effort to achieve a level of competency with this methodology.

History

Today, the specialties of otolaryngology, ophthalmology, neurosurgery and other medical subspecialties use surgical microscopy as an everyday procedure in order to achieve improved vision and illumination. This approach of handling diminutive hard and soft tissues with precision has generated new requirements for micro-instrumentation.^3-9 As a natural extension from medical microsurgery, MAP dentistry has gained acceptance in the areas of endodontics and, to a lesser extent, periodontology.^10-21

Although there are a few individuals who have been early adapters, the use of surgical microscopy in performing conventional restorative procedures in operative dentistry and fixed/removable prosthodontics is a relatively unexplored area for investigation. In a book published by Martignoni and Schonenberger in 1990, the authors describe the clinical use of an operating microscope in restorative dentistry.²² Chou and Pameijer, in 1985, described how a laboratory technician can more accurately trim stone dies more accurately with the aid of microscopy.²³ Leknius and Geissberger²⁴ demonstrated that students make approximately one-half the number of clinical and laboratory errors with the introduction of 2X magnification loupes in the fabrication of a fixed prosthesis. They further suggested that "magnifiers" should become an integral part of the instrumentation used by students of dentistry.

The Philosophy of MAP Dentistry

Traditional dental techniques have historically placed a major diagnostic emphasis on the tactile input received from the tip of a sharp explorer traversed over the surface of a tooth, or junction of a restoration on or within the tooth. This tactile evaluation process is often the sole criteria by which a restoration is deemed clinically adequate or defective. The subjective information obtained from this type of inspection is also the only criteria for developmental caries detection in the absence of definitive radiographic evidence. In some instances, this assessment method is the major parameter for smooth surface caries detection as well. The diversity of such clinical data collection can vary significantly depending upon the condition of the explorer tip, the angle of contact with the tooth, the force applied and the specific location(s) of the explorer during the inspection process. Most important of all is the interpretation of this tactile data by the clinician.²⁵

The brain's interpretation of the tactile information received from an explorer can be compared to a blind person using their hands on the face of another individual to "see" what they look like. The brain develops certain mental "pictures" based upon sensory input from the digits. In restorative dentistry, we naturally use a combination of visual and tactile information to make our assessments. Quite often, the final decisions are based more on the tactile information than on the visual information.²⁶ This is because the areas of assessment are frequently not accessible to direct vision (e.g. subgingival margins) or our unaided visual acuity cannot adequately resolve the necessary detail to make an accurate assessment. A common example of this decision process is the diagnosis of occlusal caries on a restoration-free tooth. If the radiograph is ambiguous and the explorer does not demonstrate a definite "stick", the tooth is usually designated as a "watch-monitor-recheck" category even if dark "suspicious" stains are highly suggestive of incipient caries development. It is reasonable to speculate that with better visual inspection methods of the occlusal surface of teeth, the ambiguity often associated with an explorer inspection may be greatly reduced.

Learning to use the Surgical Microscope

There are five distinct challenges that must be overcome by the dental team when incorporating a microscope into the treatment operatory. The first consideration is how the instrument should be set up into the specific working environment.

Fig 2. Typical microscope mounting from the ceiling affords ease in maneuverability without restricting the working environment when not being used.

To be practical in restorative dentistry, the microscope needs to have adequate maneuverability around the head of the patient without restricting access to the oral cavity for the dentist or the auxiliary. This requires a well-balanced arm that supports the weight of the microscope head. As more accessories are added to the head (observer tube, inclinable binoculars, camera, etc.) the counter-balance support becomes more critical for the head to maintain fluid yet steady movements. The instrument can be mounted on a floor stand, on a wall or from a ceiling mount (Fig. 2). The floor stand allows for transport of the instrument from one area to another. However, the vast majority of practitioners prefer a ceiling or wall mount. The natural hysteresis (oscillating movement) of the microscope head is distracting to the observer. To reduce this effect, every attempt should be made to insure that the microscope is firmly affixed to a rigid surface. It should be installed in a position that will minimize excessive extension of the support arm during normal working conditions.

Fig 3. Simple rock switch on the microscope handle is wired to the chair base motor allowing focusing to be performed without moving the microscope.

Another element that becomes apparent when using a microscope is the importance of patient-to-microscope positioning and repositioning that takes place during treatment. Experience has demonstrated that although microscopes manufactured for dentistry are easily repositioned in an infinite manner, whenever possible it is much more efficient to move the patient's head or the dental chair rather than the microscope head. A small rocker switch can be attached to the microscope handle to activate the dental chair base motor (Fig. 3). A light touch of the switch will raise or lower the chair base which acts as a coarse focus adjustment. The authors have found this an invaluable modification by greatly reducing the need to reposition the microscope vertically during a procedure.

Fig 4. Using the rubber eyecups, the operator makes minor position corrections by tilting or moving the head slightly, which saves time and does not require hand contact. Eyeglass corrections can be dialed in as needed.

A specialized foot control can also be configured for this operation. By reducing the need to change the microscope's vertical positioning, the operator and assistant can maintain ideal posture throughout a procedure. Furthermore, a well-balanced microscope can easily be moved left or right with slight tilt of the head by maintaining pressure on rubber eyecups. If the operator wears corrective glasses, they can be removed because the oculars have a built-in compensation adjustment (Fig. 4). Such repositioning with slight head movements results in greater efficiency.

Fig 5. To minimize microscope movements and gain complete access to the oral cavity, the 12 o'clock position is ideal for restorative dentistry. Deviation from that position forces the auxiliary (using a binocular) to move as well.

Most general practitioners recognize that an operating position that approximates 12 o'clock is the most convenient when working on the scope. This not only places the operator at the most ideal position, but it also allows the auxiliary to work from the most efficient and comfortable position as well. Most dental units are designed for the assistant to be positioned approximately 90 degrees from the head of the chair. Working from the head of the chair exclusively means that for the operator to visualize the complete oral cavity, he/she must take advantage of the mouth mirror and position the patient in a relatively supine position (Fig.5).

Fig 6. A freshman dental student automatically assumes ideal posture and arm support when using the microscope for the first time. Notice the support of the upper arm and shoulder with the wrist support stool. Fig 7. The same student in figure 6 assumes a less than ideal posture in order to gain a "comfortable" distance from the mannequin. Notice the position of the neck and lack of support for the shoulder, arm and wrist.

One immediate benefit that will be realized from this configuration is that the operator works in a completely relaxed and posture-correct position, regardless of which quadrant of the oral cavity is being treated. Some manufacturers have introduced operator stools with wrist supports to enhance ergonomics and contribute to ideal posture while working with the microscope. These wrist supports reduce fatigue and make it more comfortable for the operator, but they also decrease intention tremor by reducing the distance from the fulcrum to the fingertips. This extra support acts to steady hand movements when working on the microscope and it likely reduces muscle fatigue in the shoulder, back and neck since these muscle groups will not be enlisted to help support the weight of the arm and forearm (Figs. 6-7). Care needs to be exercised when using these operator stools since the wrist extension can inadvertently contact the patient's head or face as the operator rotates the stool.

Fig 8. It is critical that the operator does not rotate a wrist support chair without first moving away fro the patient's head. Otherwise, an accidental contact from the wrist support with the patient's face can occur. Fig 9. When using an auxiliary binocular, the assistant will be working from a slightly greater distance from the oral cavity than usual. It may be appropriate to redesign an auxiliary chair specifically for MAP dentistry.

It is important to always move the stool backward before rotating it to avoid accidental contact with the patient (Fig. 8).

Operating with the microscope offers new challenges to the dental team relative to instrument transfer because the assistant does not approach the oral cavity in the exact same manner to which she/he is accustom. With the proper objective lens (typically 200 - 250 mm), there is more than adequate access to the oral cavity for routine instrument transfer. However, with the observer attachment, the assistant will likely be working from a slightly increased distance from the oral cavity (Fig. 9). The most striking adaptation that becomes apparent is that normal peripheral vision is eliminated. For this reason, the operator must rely heavily upon the skills of the assistant to pass instruments and materials more accurately and efficiently than ever before. The actual instrument transfer will never be visible even at the extreme edges of the visual field. The assistant needs to be aware of this visual constraint and reduce the diameter of the transfer area to the region of the objective lens. If the dentist removes a finger rest to reach for an instrument, it is more difficult to regain it when looking into the oculars of the microscope. Even minor wrist movements will take an instrument out of the visual arena. It is extremely beneficial if the assistant uses the observer attachment so that she/he can see the magnified field as well. Without having access to the same magnified perspective as the operator, an understanding of the detail transpiring within the working arena is lost. One of the unique elements of using the surgical microscope for restorative dentistry procedures is the ability to allow both the operator and the assistant to see precisely the same visual image with the same illumination at the same exact time. Working with a dual binocular system gives the sense that the operator and the assistant have an "invisible Ethernet" connection. Since they see the same image at the same time from the exact same perspective, the assistant can anticipate actions more precisely. For example, if the mirror surface has debris obscuring the dentist's view of the operative field, the assistant's image is unclear as well and she/he will be inclined to clean the mirror before being asked to do so. This synergism proves to be positive for both the operator and the assistant. However, it should be kept in mind that the patient's well being cannot be assessed while observing the operative field through the microscope. Therefore, either the assistant and/or the dentist must, from time to time, check to insure that the patient is comfortable and not exhibiting any signs of distress.

An interesting side effect of working on the microscope is a sense of increased attentiveness due to the reduced visual field. Without peripheral images that can be distracting and interrupt concentration, the operator can focus his/her complete attention on the task at hand. For example, in a noisy restaurant one has to expend extra effort to block out background noise when trying to carry on a conversation with a specific individual. A quiet corner table allows for that conversation to continue more easily without the distraction of the added noise from the other patrons. Viewing through the microscope eliminates all peripheral visual distractions. A sense of increased concentration from automatically blocking out competing peripheral visual activity or "visual noise" in and around the treatment area is realized after only a few minutes on the microscope.¹ This is an intriguing element of MAP dentistry that bears further scientific investigation.

Fig 10. When using an auxiliary binocular, the assistant will be working from a slightly greater distance from the oral cavity than usual. It may be appropriate to redesign an auxiliary chair specifically for MAP dentistry. Fig 11. Unfortunately, no manufacturers yet provide restorative materials specifically for MAP dentistry. The smallest composite delivery system orifice covers Mr. Lincoln's nose, mouth and chin simultaneously.

A third element that the dental team must adapt to is how the magnified field influences everything used in a procedure. Traditional instruments appear bulky, awkward and often obscure vision significantly. This is most evident with the dental turbines. Their head sizes make it difficult to see around them. Often, by extending the bur shanks, the turbine head can be positioned to the periphery of the constricted visual field, allowing the operator to see the contact of the bur/diamond with the tooth at all times. Similar to the experiences in other fields of specialty, restorative dentistry will likely see new instruments and delivery systems specifically designed for MAP. Smaller instruments and modified materials will be needed to take full advantage of this treatment modality. Even if an extra-small access cavity is achieved with the aid of a microscope and "micro" burs, there are no restorative material delivery systems capable of taking advantage of such small diameter openings (Figs. 10-11).
One immediate challenge to the operator is developing a strategy for instrument placement that does not limit visualization of the operative field. This is particularly important when using the mouth mirror. With the unaided eye and even with low power (2Xû4X range) magnification loupes, the visual radius is wide. The natural tendency is to position the mouth mirror in close proximity to the tooth or the object being visualized. Intuitively, the operator will move his/her head appropriately to gain an ideal optical axis from which to see clearly. It is also possible to look above or to the side of the dental turbine or dental instrument and the broad peripheral field presents an infinite number of repositioning possibilities relative to head position. In sharp contrast, the relatively fixed position of the microscope restricts such movements. It is axiomatic that as the level of magnification is increased (6X-12X range), the visual radius and depth of field are reduced, while at the same time all items within the field are magnified. Therefore, the mirror head, air turbine or dental instruments can easily obscure the view of the tooth surface. In addition, as these elements are brought into closer proximity due to a reduced visual circumference, they can obstruct one another making movements more difficult. For this reason, the operator must intentionally take a different approach to positioning the mirror in relationship to the tooth, turbine and instruments.

Fig 12. Based on the rule of proximity, the turbine head will obscure the mirror image as it enters the field because the mirror is placed in proximity to the object of focus (the distal pit). Fig 13. The mirror is positioned away from the root surface allowing full view of the object of focus without interfering in the placement and movement of the turbine and bur.

Learning to maintain the correct distance and position of the mirror surface relative to the other instruments and the primary object of focus is the single most difficult component of the learning curve for MAP dentistry. The most ideal position of the mirror is when it takes full advantage of the entire viewing circumference at a specific magnification. As the position of the critical elements come into closer proximity to one another, they begin to overlap making it difficult to see each one of them separately. The further the mirror is positioned from the object of focus the less interference will be created from the turbine head or any other instruments in the working area. Often, the position of the mirror may need to be at the perimeter or even outside of the oral cavity for optimum visual and working access. However, due to the magnification effect, it may appear as if the mirror is in close proximity to the object of focus (tooth, soft tissue, etc.). The authors have termed this concept the rule of proximity that states, "as the level of magnification is increased, the distance from the mirror to the object of focus must also be increased." (Figs.12-13)

The fourth factor that the restorative team will recognize is that the use of effective isolation techniques greatly enhances success with microscope dentistry. The reliability of the rubber dam for isolation and visualization of the operative field is more critical when working from the head of the patient. It not only reflects the lips and cheeks for better access to the oral cavity, but it reduces the need for the patient to sit up and rinse. If the patient's movements are reduced, repositioning of the microscope is minimized. By contrast, if the operator and assistant are focused on maintaining retraction and isolation of the field, then their attention is continually drawn away from the magnified field. Not only is this tedious and time-consuming, but it will create frustration from having to reposition the microscope excessively, especially on longer procedures. Preparing prepunched rubber dam packs and having the entire set-up ready in advance makes application easy to achieve in a matter of minutes. Furthermore, the dentist who "rediscovers" the advantages of rubber dam will immediately enjoy the reduction of the blood and saliva fog in addition to the greatly improved visibility that this simple step provides. The greater efficiency of high velocity evacuation when using rubber dam also reduces splattering on the microscope and in particular the surface of the objective lens or lens cover. Discontinuing treatment to wipe the objective lens is another avoidable step that interrupts concentration and wastes valuable chair time.

Fig 14. An oral retractor can be used for MAP dentistry procedures in lieu of a rubber dman, but it will reduce operative efficiency.

In circumstances or with patients where a rubber dam is impractical, efficiency of microscope use is greatly reduced. Compromises to rubber dam use are the many oral retractors available. They provide some displacement of the lips and cheeks, but can be removed and replaced easily (Fig 14).

The final challenge that MAP dentistry represents is to the operator's psychomotor skills. This element of the learning curve is difficult to describe. When a dentist first starts to use a surgical microscope, he/she will immediately recognize that there is a need to refine stereotactic and fine motor skills. The vast majority of what dentists do on a daily basis is guided by a combination of both tactile and visual information. With the aid of magnification, vision is enhanced to a level that far exceeds the norms set forth by tactile assessment standards. The shift from a reliance on tactile information to visual information is virtually automatic when working with an operating microscope. Most restorative procedures still require that the operator gain perspective from a non-magnified view as well. Examples would be the assessment of a smile-line or an identification of preparation undercuts for a multiple-unit fixed partial denture. The transition from a tactile to a visual-weighted approach to general dentistry is as exciting as it is challenging. It may expand our knowledge and abilities to provide an unprecedented level of precision in the care of our patients.

Summary

The introduction of a surgical microscope into the dental operatory brings with it many challenges not usually associated with traditional 20th century dentistry. MAP dentistry represents a new technology emphasizing visual information rather than tactile input. Although the learning curve can be lengthy and difficult, the authors believe that the clinical benefits of MAP dentistry for the patient, the operator and the profession are well worth the efforts required. Controlled studies need to be performed with students and practitioners to obtain relevant data on the use of microscopy in general dentistry.

Authors /
Mark J. Friedman, DDS is a clinical professor of restorative dentistry at the University of Southern California School of Dentistry and is on the editorial board of the Journal of Esthetic Dentistry and the Compendium of Continuing Education in Dentistry. He is President-elect of the American Academy of Esthetic Dentistry. He maintains a private practice at the Center for Dental Aesthetics in Encino, California.

Howard M. Landesman, DDS, MEd was appointed Dean of the USC School of Dentistry in 1991 and is the G. Donald and Marian James Montgomery Professor of Dentistry. Dean Landesman is a Diplomate and Past President of the American Board of Prosthodontics, and also serves as the Chair of the Editorial Board of the Compendium of Continuing Education in Dentistry. He has contributed extensively to the literature in prosthodontics and dental education.

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To request a printed copy of this article, please contact / Mark J. Friedman, DDS, Center for Dental Aesthetics, First Financial Plaza, 16850 Ventura Blvd., Suite 258, Encino, CA 91436.