Monea M, Hantoiu T, Stoica A The impact of operating microscope on the outcome of endodontic treatment performed by postgraduate students. Eur Sci J. 2015; 11:305-311
Setzer FC, Kohli MR, Shah SB Outcome of endodontic surgery: a meta-analysis of the literature – part 2: Comparison of endodontic microsurgical techniques with and without the use of higher magnification. J Endod. 2012; 38:1-10 https://doi.org/10.1016/j.joen.2011.09.021
Nagi SE, Khan FR, Rahman M. Practice of endodontic re-treatment in four cities of Pakistan. J Ayub Med Coll Abbottabad. 2017; 29:445-449
Kersten DD, Mines P, Sweet M. Use of the microscope in endodontics: results of a questionnaire. J Endod. 2008; 34:804-807
von Arx T, Frei C, Bornstein MM. Periradicular surgery with and without endoscopy: a prospective clinical comparative study. Schweiz Monatsschr Zahnmed. 2003; 113:860-865
Taschieri S, Del Fabbro M, Testori T, Weinstein R. Microscope versus endoscope in root-end management: a randomized controlled study. Int J Oral Maxillofac Surg. 2008; 37:1022-1026 https://doi.org/10.1016/j.ijom.2008.07.001
Setzer FC, Shah SB, Kohli MR Outcome of endodontic surgery: a meta-analysis of the literature – part 1: comparison of traditional root-end surgery and endodontic microsurgery. J Endod. 2010; 36:1757-1765 https://doi.org/10.1016/j.joen.2010.08.007
Setzer F. The dental operating microscope. In: Kim S, Kratchman S (eds). Hoboken, NJ: John Wiley & Sons; 2018
AAE Position Statement. Use of microscopes and other magnification techniques. J Endod. 2012; 38:1153-1155
von Arx T, Steiner RG, Tay F. Apical surgery: endoscopic findings at the resection level of 168 consecutively treated roots. Int Endod J. 2011; 44:290-302
Creasy JE, Mines P, Sweet M. Surgical trends among endodontists: the results of a web-based survey. J Endod. 2009; 35:30-34
Kratchman S. Endodontic microsurgery. Compend Contin Educ Dent. 2007; 28:399-405
García Calderón M, Torres Lagares D, Calles Vázquez C The application of microscopic surgery in dentistry. Med Oral Patol Oral Cir Bucal. 2007; 12:311-316
The direct operating microscope has completely revolutionized the field of endodontics, leading to increased success in both non-surgical and surgical cases. In low- and middle-income countries, microsurgical endodontics is still a developing field and procedures that fall within this category employ higher magnification. Currently, less than 25% of dentists in developing countries employ any sort of magnification in their practice. Basic concepts, such as microscope positioning and operator's ergonomics, are still confusing to many dentists, novice or experienced alike. This article introduces the benefits and general principles of direct operating microscope use in endodontic microsurgeries.
CPD/Clinical Relevance: A better understanding of the use of dental operating microscopes in endodontic microsurgical techniques may facilitate a more efficient workflow.
Article
Faizan Javed Saqib Habib
Endodontic practice has always been an art of precision and attention to detail, thereby making every millimetre count. With minute inconsistencies in root-canal filling resulting in failures, it was only natural that endodontists would employ magnification for their day-to-day cases. Dental operating microscopes (DOM) were introduced in endodontics in the early 1990s,1,2 but saw routine use after being mandated in postgraduate endodontic programmes by the American Association of Endodontics in 1998. This use led to a significant increase in successful clinical outcomes in both non-surgical and surgical endodontics.3,4
For dentists who were trained without magnification, the introduction of any sort of magnifying device/magnification was met with reservation.5 Clinicians had to weigh the benefits of a new technique against the cost and time involved in making it an effective investment. In a 2017 review of endodontic re-treatment practices, Nagi et al6 reported that less than 25% of dentists in a developing country employed any sort of magnification. In contrast, the use of microscopes by endodontists in the US was 90% in 2008.7
In low- and middle-income countries, the introduction of microsurgery in endodontics is still in a nascent state. The procedures that fall within the category employ higher magnification by virtue of the operating microscope, or less commonly the endoscope.8,9 While foremost consideration is given to non-surgical endodontic treatment when a patient presents with persistent periapical disease, endodontic microsurgery may be more appropriate, if not the only option available in certain cases. A list of indications for endodontic microsurgery are given below:
Endodontically treated teeth with clinical and/or radiographic signs of failure, where orthograde re-treatment is unlikely to improve upon previous results.
Iatrogenic or developmental anomalies that prevent access and, by extension, disinfection of the apical third. Such cases include irretrievable separated instruments, non-negotiable ledges, and pulp canal obliteration.
Extrusion of obturation material or instruments beyond the apex not amenable to orthograde retrieval
Heavily restored teeth where disassembly of the coronal structure would risk rendering the tooth unrestorable.
Disassembly and orthograde re-treatment would incur excessive cost and longer re-treatment time.
Unclear diagnosis of peri-apical lesion where specimen needs to be obtained for histopathological analysis.
As a diagnostic adjunct for suspected root fracture or perforation.
A landmark systematic review and meta-analysis by Setzer et al10 showed that modern microsurgical methods resulted in 95% success, compared to a 59% success achieved with traditional endodontic surgery. In this review, the benefits and general principles of DOM use in endodontic microsurgery are discussed.
Advantages of the operating microscope
The DOM offers a range of magnification, usually an increase in the order of 8–40 times.11 Compared to magnifying loupes, where any magnification over x4 requires the practitioner to remain in a narrow range to stay in focus, the DOM remains stable and allows the operator to continue the procedure in an ergonomically non-stressful position. In loupes, the monocles are angled inwards in order to focus on the object. This process requires constant short distance accommodation from the eyes and results in fatigue and soreness of the eye muscles. Conversely, the DOM uses distance vision, thereby negating the stress encountered by the use of dental loupes. However, by far the most important benefit offered, is a shadow-free, illuminated field of view that helps achieve the highest standards of clinical operation and documentation.12
In surgical endodontics, the use of DOM has led to changes in all aspects of surgery (Figure 1). It has substantially decreased the risk of severance of nerve bundles and vessels. It allows for smaller osteotomies (3–4 mm) compared to traditional access (8–10 mm), thereby preserving cortical bone. A smaller resection at a minimal angle can now be made, offering two-fold benefits: preservation of root structure; and visualization of additional anatomical variations and defects.13 The root surface is inspected in detail for presence of additional canals, isthmus, cracks, frosted dentine and gaps at the tooth restoration interface, the detection and management of which leads to better surgical outcomes.14
Figure 1. Clinical use of DOM in surgical endodontics. (a) Flap reflection and initial osteotomy preparation. (b) Root-end resection. (c) Root-end preparation. (d) Retrograde ultrasonic preparation. (e) Inspection of prepared root end following application of methylene blue dye. Note the crack (arrow)on the palatal root surface. (f) Root-end filling. Photo courtesy of Dr Fahad Umer.
Basic anatomy of DOMs
There are three principal components to the DOM.
Supporting structure: allows a microscope to be either free-standing, wall- or ceiling-mounted. Its purpose is to keep the microscope stable, while still keeping it manoeuvrable with ease and precision.
Body of the microscope: includes components (Figure 2) that make use of the lenses and prisms. These include the eyepieces, binoculars, magnification change factor and the objective lens.
Light source: current microscopes are usually fitted with either xenon or LED light sources.
Figure 2. DOM components: (A) body of the microscope; (B) six-step magnification changer; (C) brightness adjustment scale; and (D) DSLR camera attached to the digital adapter.
Eyepieces, binoculars and magnification
Eyepieces
Eyepieces are available in various magnifications, with x10 and x12.5 being the most common.15 These eyepieces have modifiable dioptre settings. Correct dioptre settings are important because they allow the clinician to maintain focus while switching between different magnification settings.
Binoculars
The binoculars allow adjustment of the inter-pupillary distance. These need to be manipulated until two different circles of light merge to form a single circle. They employ a focal length of 125 or 160 mm. The dioptre settings and inter-pupillary distance together, are the foremost considerations in customizing a microscope for personal use. For surgical endodontics, a DOM should be equipped with 180-degree tiltable binoculars to address the angulation requirements. Similarly, the attached tubes should also be inclinable to achieve a comfortable working position.
Magnification change factor
A series of magnifications is available with the DOM. These may be available as a three-, five-or six-step manual or power-zoom changers. The manual changers (Figure 2) can be manipulated by rotating a dial located at the side of the microscope. Manipulation of the power-zoom changer is carried out with a foot control or a manual override control knob usually placed at the head of the microscope. The manual changers have the disadvantage of momentary disruption in image visualization when jumping from one magnification to another. However, the change in magnification is faster in comparison to power-zoom changers.
Objective lens
The distance between the microscope and the surgical field is determined by the focal length of the objective lens. For surgical endodontics, an average focal length of 200–300 mm usually suffices. This is basically the working distance from the operating field. The decision is usually based on the height of the practitioner and their most comfortable working position. Most microscopes come with charts explaining the impact of each component on the total magnification. A formula to calculate the total magnification is as follows:
TM=(BFL/OLFL)×EM×MF
Where TM: total magnification; BFL: binocular focal length; OLFL: objective lens focal length EM: eyepiece magnification; MF: magnification factor.
It is important to note that any change in components that result in an increase in total magnification will simultaneously decrease the field of view. This is also the reason why the highest magnification settings are used for documentation purposes only.
Light source
Current microscopes usually employ either xenon or LED light sources and light intensity can be varied using an adjustment scale (Figure 2). Xenon lights appear very close to natural daylight and offer high light intensity, which allows for crisp documentation. These lights, however, generate heat and have short lifespans. LED light sources have comparable colour temperature to that of xenon lights and therefore appear similar to daylight. Heat is vented from the back of the light source, resulting in increased surrounding temperatures. LEDs, on average, have long lifespans.
Most light sources have an orange filter that is designed for working with light-sensitive material, such as resin composite. This prevents premature setting of the materials. A green filter allows for better contrast between blood and tissues during surgeries. Some microscopes also come equipped with fluorescence for caries detection.
Individual microscope adjustment (parfocaling)
Parfocaling refers to objective lenses that can be adjusted with minimal or no refocusing. When a microscope has parfocalled objectives, it is possible to switch from one magnification to another with no disruption to the focus as the magnification is changed. Failure to parfocal microscope objectives can be inconvenient for the operator and can increase eye strain.
The clinician should follow the following steps for parfocal adjustment:
For operators who wear glasses, the rubber cups on the eyepiece should be completely screwed in, and the process carried out with the corrective glasses worn.
The operator should then determine the dominant eye. Different techniques exist for this process; however, the authors recommend the ‘superimposition technique’ because of its simplicity. The clinician chooses a distant object to focus on, while simultaneously holding a finger or pencil with extended arms, superimposing the near object over the distant object. After this, one eye is closed while the other remains open. If the near object stays centred on the distant object, then the eye that was open is the dominant eye.
Set the dioptre settings to extreme positive.
Set the microscope at the lowest magnification.
Looking through the eyepiece with the dominant eye, adjust the dioptre setting where the reticle, appearing as lines or concentric rings, becomes completely focused.
Place a flat, non-reflecting object such as a currency note, business card, or an ‘X’ marked on a piece of paper under the microscope. Without changing the dioptre settings, adjust the microscope at the correct vertical distance until a focused image is seen.
Switch to the highest magnification. Use fine focus to account for minor changes due to focal distance. The dominant eye is now calibrated throughout the entire range of magnifications.
Look through the non-dominant eye and change the dioptre settings slowly until the object under the microscope becomes focused. This calibrates the non-dominant eye to the dominant eye.
Adjust the inter-pupillary distance, until two different circles of light merge to form a single circle
For ideal results, video output should be from the same side as the dominant eyepiece. This will result in an exact match in what is seen.
Focal plane
When focusing an object using stereomicroscopes, we observe a particular focal plane. We can also see an area above and below the focal plane with similar clarity. This distance between the nearest and farthest object that appear acceptably focused under the microscope is called the depth of field (DOF). It is always preferable to work with microscopes that offer a high DOF as this allows for better spatial orientation. However, DOF is governed by several parameters:
Magnification: the lower the magnification, the greater the DOF;
Working distance: the greater the working distance, the greater the DOF;
Aperture of objective lens: the smaller the aperture of the objective lens, the greater the DOF;
Accommodation of the eye: the better the adaptability of the eye, the greater the DOF. This decreases with age.
At higher magnifications, the depth of field narrows significantly. For patients who move often during the course of treatment, maintaining focus can become difficult, and the operator has either to reset the microscope assembly or encourage the patient back to their original position. In such cases, a microscope with a variable objective lens can be used as a fine focus knob to allow for minor adjustments, and to save time.
The treatment field that can be viewed under the microscope is termed the field of view (FOV). It is most convenient to work with a large FOV. Parameters governing the FOV are as follows:
Magnification: the lower the magnification, the greater the FOV;
Working distance: the greater the working distance, the greater the FOV;
Lens system: FOV varies with lens design.
Cycling through magnification
Magnification can range significantly between different microscopes, but is usually in the range of x3–30. For surgical endodontics, the recommended magnification factors are listed in Table 1 for different procedures.
Magnification
Range
Procedures
Low
<5x
OrientationAssessment of the surgical siteIncisionDetermining location of the root apexSuture placement
The beam splitter, aptly named, splits the light into two portions so that one goes to the eyepiece (observer) and the other portion goes to the documentation device (eg camera). The beam splitter's eyepiece to documentation port ratio varies, but is usually 50:50, 80:20 or 95:5. Some cameras are able to work with low levels of light and use the 80:20 or 95:5 ratio. This allows more light to be diverted to the eyepiece, which retains a bright field for the observer. Some newer cameras, with more pixels, require more light for adequate documentation, and hence work better with the 50:50 beam splitting ratio. The adapter simply connects the beam splitter to the documentation device. Customized camera adapters may be needed because the diameter of the connection varies with different manufacturers, that is to say a Nikon Digital single lens reflex (SLR) camera will not fit the adapter made for a Canon Digital SLR camera. Dedicated SLR cameras can take high-quality photos, but may fail to document videos with similar finesse. Some users therefore prefer having a second port for a dedicated video camera. These cameras can be attached to an LCD monitor that can display live feed and allow the clinician to review images as soon as they are taken.
Ergonomics
Ergonomics is the science that deals with principles and methods employed in order to optimize human well-being and to increase the efficiency of working system. In microsurgical endodontics, one of the most time-consuming tasks is to correctly position the dental operating microscope in relation to the patient and surgical field. The objective of doing so is two-fold: to enhance the visualization of the region of surgical interest; and to reduce the incidence of musculoskeletal disorders in dentists. Microscope-based clinical practices carry the inherent risk of prolonged strained and extended neck positions, which will eventually result in discomfort and pain for the users. A web-based survey by Creasy et al reported that 77% of dentists had difficulty in proper positioning of operating microscopes.16 Proper positioning of the dentist and patient is of paramount importance in performing microsurgical endodontics. Positioning of the patient in the dental chair varies according to site of surgical interest and the patient's medical condition.
Operator position
The operator usually sits between the 10 and 2 o'clock positions around the patient's head depending on the quadrant being treated. The operating chair is adjusted so that the operator's thighs are parallel to the floor. The back of the operator must be kept upright and be well supported by the backrest of chair (Figure 3). Similarly, the operator's elbows are positioned close to the body. Once positioned, the surgeon's elbows should not deviate from this centric position throughout the procedure. This position allows maximum fine control for mechanical instrumentation during the procedure. Some manufacturers have introduced chair designs having the provision of both back support and elbow support.
Figure 3. Operator and patient position. (a) Correct operator position. (b) Incorrect operator position. This will result in strain at the neck and back (c) Patient position for surgery of the anterior teeth. (d) Patient position for surgery of the posterior teeth
Patient position
For endodontic surgery, the patient position in the dental chair is generally supine (Figure 3). However, some clinicians recommend a reverse Trendelenburg position to position the surgical site in an elevated working position. The patient is instructed to lie on their side as if sleeping, this allows the operator to look directly into the area of surgical interest (Figure 3). The tilted position of the patient head is stabilized using the rolled surgical towels, head rest or memory foam pillows. A useful tip while working with high magnification is to have the dental chair's headrest gently touching the operator knee so that by slightly elevating the knee, a minor change in the focal length is obtained, which is enough to produce fine focus. This keeps both of operator's hands free to work during the procedure.17
Generally, endodontic microsurgery is easier to perform in the maxilla as opposed to the mandible. For procedures in the mandibular molars, instructing the patient to slightly move the lower jaw outward (buccally), as in a crossbite relationship, to better visualize the surgical area. This position helps the operator to directly visualize the mesial roots of mandibular molars.17 In order to view the soft tissue of jaws under direct vision, tilting back the headrest of the patient with chin raised is helpful.18
Lastly, when the patient and operator positions are set, the operating microscope is adjusted. The line of sight through the microscope should be perpendicular to the soft tissue of the surgical site. Similarly, the eyepieces are adjusted to the height of the operator.
Four-handed dentistry
To enable efficient and smooth working processes while using the operating microscope, a close understanding between the dentist and the dental nurse/assistant is necessary. The operational layout should provide sufficient room for accommodating the operating microscope.15 Before the start of a procedure, the microsurgical instruments, biomaterials, ultrasonic devices, computers, digital radiographs and scanners, etc should be placed in a manner for easy access by the dental assistant during the procedure. For this purpose, a moving cart or surgical trolley is recommended. There should also be ample unrestricted space to allow passing of instruments to the operator. Ideally, the dental assistant should be able to see what the operator sees so that they know what the operator needs during the procedure. Some manufacturers offer co-observation tubes directly attached to the microscope for the dental assistant to visualize the surgical site.
Clear and effective communication is required between the operator and dental assistant during the instrument transfer process. This can be achieved through verbal or non-verbal communication depending upon the experience of the team. The instrument must be handed over to the operator in an accurate way to ensure proper grip, as the operator eyes are fixed on the microscope, there is risk of personal injury from the sharp instruments if not properly handled. Any disruption in the communication process may affect the quality of the procedure.
Ergonomically designed microscope workstations and a sound understanding of positioning helps the clinician to perform the procedure with minimal stress and discomfort for the patients.
Conclusion
The DOM is an integral part of surgical endodontic practice and elevates the standard of care provided to patients. In low- and middle-income countries, universal adoption of the DOM is not a function of time, but requires a systematic inclusion into curriculum at the specialty level. While the present review has focused on DOM in endodontic microsurgery, the principles of use can be applied to many aspects of restorative dentistry, non-surgical endodontics, periodontal and oral surgery.
