April 1, 2006
by David J. Clark, DDS and Jihyon Kim, DDS
As patients become increasingly aware of the esthetic potential through cosmetic dentistry, there is an increasing demand for smile makeovers with porcelain. In our efforts to create beautiful smiles, we tend to focus on tooth color, shape, proportion and alignment as we are bombarded with restorative choices.
However our efforts for an ideal restorative outcome will fall short if we are distracted from the larger picture to focus on teeth and somewhat neglect the importance of gingival health and contour. The goal of modern esthetic dentistry is to achieve both “white” and “pink” esthetics.1 “White esthetics” refers to natural dentition or tooth colored restorations. “Pink Esthetics” refers to the surrounding soft tissues (Figs. 1 & 2).
Every dentist has experienced the disappointment of a cosmetic case that starts out beautifully then is marred by receding or inflamed tissue. The question is how do we increase our chances for optimal tissue response and long term health? Our focus in this article for this broad question will be our microscope centered approach for porcelain precision and the role of high level magnification in assisting ideal gingival esthetics.
HOW MUCH MAGNIFICATION IS “ENOUGH MAGNIFICATION”?
Today most restorations are still performed with little or no magnification. However, critical analysis of some esthetic compromises will show progressive decline of gingival color from ideal salmon pink to bluish purple typical of chronic mild inflammation. In our practice we are surprised at the number of patients who report to us for re-treatment of cases because of mildly red or purple gingiva (Fig. 3). Such requests are evidence that non-ideal tissue responses impact patient acceptance of cases much more than dentists would have thought. We may be underestimating the importance of “pink” esthetics to overall treatment success.
Numerous studies have shown that gingival and subgingival marginal discrepancies greater than 50 microns cause untoward tissue response with increased crevicular fluid flow, altered bacterial flora, and poor esthetics.2-5 Carr has demonstrated that the unaided human eye cannot distinguish two discrete lines closer than 200 microns.6 Not surprisingly many restorative margins have average discrepancies of 200 microns and sadly we often see gross discrepancies much greater in failing restorations.
Carr has also demonstrated that 4x magnification is required for the human eye to distinguish two black lines 50 microns apart. However, 4x loupes may not be sufficient in consideration of three important issues.
1) Less visual contrast is available to distinguish a tooth colored restorative margin from a tooth finish line than two black lines separated by white. Therefore 4x magnification may be insufficient in porcelain or resin restorations. In fact many clinicians who take our microscope courses comment that they need at least 10x magnification to discern the marginal integrity of porcelain laminates.
2) Magnification of 4x or greater require better quality light beyond what can be provided by a traditional operatory light. At higher magnifications a microscope makes more sense than adding a headlamp to loupes that have insufficient power.
3) Magnification needs can routinely escalate to 16x or 24x when working with challenging circumstances such as posterior areas, difficult isolation, or indirect vision.
Thus in order to achieve marginal precision with consistency in porcelain or resin restorations, magnification of 8x or higher is recommended. Such magnification and light requirements are difficult to attain with loupes and a separate light source.
FUNDAMENTALS OF CLINICAL MAGNIFICATION
The operating microscope offers not just higher magnification than oculars (loupes) but better magnification. Oculars have been very helpful and may always have a role in dentistry, but the optics is crude when compared to the Infinity Corrected Optics of a stereoscopic microscope (Figs. 4-7). When combined with the shadowless coaxial light source, they transform the clinician’s potential for accuracy in nearly every aspect in the different disciplines in dentistry.
Most importantly, increasing levels of magnification produce a squared, not linear relationship to visual acuity. In other words, 10x magnification allows the human retina to acquire 100 times more information and 20x allows 400 times the visual information.
PRINCIPLES OF TOOTH PREPARATION AND PORCELAIN MARGINS FOR GINGIVAL ESTHETICS
The enormous advantage the operating microscope offers is ability for acute visual inspection. This precision along with skill and recognition enables us to readily identify the cemento-enamel junction (CEJ), create more appropriate finish lines for the rigors of porcelain adaptation, and eliminate noxious tissue irritants.
One of the most common offenses to delicate gingival architecture is when the clinician fails to follow the undulating contour (Fig. 8) of the CEJ and instead creates a flat margin from facial to lingual. This is often exacerbated or initiated by rubber dam placement, which flattens the papillae and leads to misinterpretation of the appropriate placement for the interproximal finish line.
Thus begins a series of mistakes. The interproximal margin is cut too deep, followed by aggressive tissue retraction. When two approximating teeth are prepared in this manner and the tissue is subsequently retracted with cord, electrosurgery or ablation, the papilla is often obliterated. The papilla sometimes returns but sometimes not.
In a classic study, two interdental papillae were excised from16 dental students.7 Of the 32 specimens, 22 papillae did not return to the original shape. This 69 percent attrition rate should serve as a wakeup call. The dreaded “black triangle” usually ensues, which can be both an esthetic and functional nightmare. Exotic regenerative techniques or bulky porcelain contours are a poor substitute for conservative tooth preparation and delicate micro-manipulation of tissues.
With the benefit of high-level magnification, a series of delicate and physiologically appropriate steps can occur.
MICROSCOPE ASSISTED PRECISION AND ENAMEL FINISH LINES
The fear of marginal esthetics (Fig. 9) has driven clinicians to “bury” their margins, creating a whole new set of problems, which include pulpal, periodontal and microleakage issues.
Whenever possible a porcelain-enamel marginal interface is the goal in bonded porcelain restoration (Figs. 1 & 2). This will place the finish line either slightly supragingival, equa-gingival or slightly subgingival. In cases of gingival recession, it is preferable to cover exposed dentin with gingiva (in lieu of porcelain or composite) via procedures such as connective tissue grafts.
Periodontists using high-level magnification have demonstrated predictable and breathtaking root coverage. Afterwards, a porcelain margin can be placed on enamel, nestled neatly near robust gingiva.
The Contact Lens Effect has become a popular term. One interpretation relates to the ability to create invisible porcelain margins that need not be hidden. We see that the optimal combination is 1) translucent porcelain, 2) a translucent luting agent, and 3) translucent tooth structure, preferably enamel. Once the finish line for a porcelain laminate is placed on dentin, the contact lens effect loses some of its magic because dentin is more opaque than enamel.
Dentin margins pose other difficulties as draw becomes more of a problem, the pulp is further traumatized, and a strong enamel bond is sacrificed for a tenuous dentin bond. Maintaining a minimum of a 750 micron distance from the CEJ during preparation requires high levels of magnification.
MARGINAL PRECISION OF PORCELAIN
Volumes of information are bandied about when debating which porcelain has the best marginal accuracy. I
n the end, most of these arguments are moot because other factors create discrepancies that are significantly more critical. A poll done by CRA revealed that 90 percent of impressions received in U.S. laboratories contained portions that did not capture the finish lines. In these cases we will see gross inaccuracies that will lead to micro leakage and poor tissue response.
Additionally, microscopic inspection reveals that many restorations are not fully seated during cementation. The culprit is often improper contacts, hardly a microscopic issue, but floss alone is not enough to make a proper assessment. High magnification provides complete visual information required to trouble shoot all causes of incomplete seating, including a “lifting” contact. Once these factors are controlled, a legitimate analysis of porcelain margins can begin.
Once microscopic accuracy becomes a reality for both clinician and ceramist, a constant dialogue between the two parties is of paramount importance (Fig. 12). Simply describing a porcelain laminate margin as “poor” or “open” or “bulky” is insufficient information to help coach a ceramist who is using microscopic visualization. For example it is possible for a porcelain margin to be “plus” and yet have an overall under-contoured emergence profile.
Conversely, a porcelain crown or veneer can possess a grossly over-rounded emergence profile and still be “sub” (Figs. 13-15). Another critical problem is an over-reliance on porcelain glaze to create smoothness. This quick fix creates the illusion that the surface is smooth and glossy, but high level magnification and oblique lighting reveal the unacceptable surface created with glaze alone.
Upon microscopic inspection and re-treatment, many failing cases that were suspected to be biologic width violations were actually violation of factors in Tables 1 and 2. Clinicians working with microscopic precision report that fewer cases result in tissue responses requiring crown lengthening or periodontal surgery. The biologic width for a tooth is determined by individual factors which cannot be predicted or controlled. Individual biology will determine how much tissue is needed to protect crestal bone. However working with microscopic precision may enable us to encroach further into the gingival sulcus and yet maintain optimum tissue health.
INSPECTION OF FINISH LINES
One of the startling revelations to come from high magnification work is that finish lines prepared at low magnification commonly rest on calculus, composite or heavy plaque. The resultant residual roughness and marginal inaccuracy of porcelain will result in compromised tissue health. For tooth colored restorations, we find 4x, 8x and 12x power to be the workhorse operation steps of magnification. Brief utilizations of 16x and 24x for inspection are now considered essential for a growing number of clinicians for various nuances of aesthetic dentistry.8,9
GINGIVAL RETRACTION… LESS IS MORE
Microscopic visualization allows an extremely delicate level of treatment of hard and soft tissues. Figures 16 and 17 demonstrate two very different levels of retraction. Figure 16 shows a crisp finish line with over two millimeters of apical impression profile (impression of tooth surface apical to finish line). This traditional retraction protocol creates an easier environment for both impression taking and die trimming.
The problem is that gingiva rarely returns to preoperative form. With extreme magnification, a completely different approach and mindset are possible. Figure 17 shows a crisp finish line with only 3/4mm of apical impression profile. The finer apical profile requires:
1. Microscopically milled finish lines;
2. Extremely high-level magnification during retraction to provide the absolute minimum level of tissue displacement;
3. Die trimming at extreme magnification of 10x-20x (Fig. 18);
4. Case specific use of brownie points for careful die trimming.
We spend significant time engaged in delicate tissue retraction at high magnification, and subsequently at the die trim in many cases. The maintenance of intact and unchanged papillae and attachment levels is a worthwhile goal. The additional time invested by the clinician should be factored into an appropriate fee for this level of treatment. Another tangible benefit of microscope dentistry is reduced postoperative discomfort for patients.10
TECHNICIANS CAN BE THE MISSING LINK
Microscope dentists, enjoying newfound precision with preparations and impressions, may well become frustrated with ceramists whose work becomes the weak link in precision. We tried many labs and toiled with ceramists who, though they had lab microscopes, were unwilling to treat our cases with special care. Many labs have microscopes with poor optics, dim light, filthy lenses, and are in such a state of neglect that they are nearly worthless.
One of the most challenging steps in the quest for precision in porcelain is the visual challenge of minimal contrast. In addition to the stark color contrast it offers, gold casts a useful shadow when viewed directly on the tooth or die. Unfortunately, most technicians use the visual approach that works well with gold when analyzing porcelain. While gold may be analyzed by looking directly at the margin/die interface, we have found that porcelain must be evaluated in profile.
Together with our ceramists we have created a protocol to consistently produce porcelain and porcelain fused to metal restorations that hold up to the scrutiny of 16x magnification. One component of the system is the three die protocol that gives us a virgin die for evaluation and final sculpting of the finish lines. In order to implement this new protocol, Chuck Rickabaugh at Twin Lakes/ DTI actually created a lab within a lab. With the right team, it can be done!
GINGIVAL PORCELAIN FINISHING BURS ARE UNNECESSARY IN A MICROSCOPE-CENTERED APPROACH
Mainstream dentistry is moving toward the creation of two margins, a porcelain and a composite margin. Porcelain that is several hundred microns off in both horizontal and vertical axis are theoretically sealed by the new super viscous composite cements. Margins that are accessible are sometimes “dressed down” with finishing burs. These protocols are the standard of care but when viewed under the microscope we see the following:
* The high luster of porcelain cannot be fully re-established near the sulcus with the ‘dressing down’ of porcelain margins. Additionally the root is often scarred and the gingiva mutilated,
* The cement margin is chalky and becomes even coarser over time,
* The composite margins are prone to microleakage,
* The new super viscous cements are creating ever widening marginal gaps as the crown or veneer cannot be wrestled fully to place.
The concept is different with the microscope-centered approach taught at Precision Esthetics Northwest and Newport Coast Oral Facial Institute. No gingival finishing burs are used. Instead with microscope precision, the excess luting cement is ‘scissored’ away cleanly as the ultra-precise laminate is seated. A surgical #12 blade in a Hartzell round scalpel handle cleaves away excess luting composite. There is only one margin, a laboratory or chair side pre-sculpted and pre-polished porcelain margin.
CHAIRSIDE MARGIN RECONTOURING AND MICROSCOPE ENHANCED SEATING
The final leg of our quest for microscopically ideal esthetics demands another step. While waiting for anesthesia, we evaluate the three parameters of marginal integrity. The marginal interface and emergence angles are evaluated at 12x to 24x in profile while slowly rolling the die and porcelain restoration 360 forwards and backward. “Plus” margins and overly rounded emergence profiles are carefully and quickly sculpted with a Brasseler #0301 medium grit silicone polishing wheel (Fig.
If the integrity of a die is in question, the patient is present for verification. This versatile and inexpensive wheel appears to “melt” the porcelain away without the chattering and potential micro-fractures from burs. Incredibly, it also leaves a very smooth finish.
Try-in, luting, and cement removal under the microscope is a joyful experience. The microscope enables us to visualize problems invisible under low or no magnification (Figs. 20-22). Better yet, a rich array of clues will lead to solutions so that the case can proceed to success instead of starting over or compromising the final result.
Reasonable restorative outcomes can be achieved with amalgam and gold with low or no magnification. In contrast, tooth colored materials require much higher levels of magnification for consistent success. Common clinical magnification simply has not kept pace with dramatic changes in restorative materials and patient expectations. In spite of other advances in dentistry, marginal integrity, emergence profile, and resistance to microleakage have all taken a giant step backward.
Certainly, gifted clinicians exist who operate with little or no magnification and do breathtaking esthetic dentistry. The microscope does not make one dentist better than another. Nonetheless, many accomplished restorative dentists have embraced the use of the microscope because it brings greater predictability and joy to their dentistry. Excellence in dentistry is a choice, and magnification can be a powerful asset in achieving it.
The testimony of doctors who use the microscope daily in their practices confirms its value. An overwhelming majority affirm that it has improved their clinical skill. The microscope, with instantaneous magnification from 2.5x to 24x, no visual noise, and shadowless coaxial light, offers the best means for achieving complete visual information in dentistry. It can nurture great confidence, healthier posture, and better and surer hands for the clinician. In the end, the excellent visual information the microscope offers can help the doctor to create more precise, more healthful, and more esthetically pleasing dentistry.
Dr. David Clark founded the Academy of Microscope Enhanced Dentistry, an international association formed to advance the science and practice of microendodontics, microperiodontics, microprosthodontics and microdentistry. He is a course director at the Newport Coast Oral Facial Institute in Newport Beach, CA. He is co-director of Precision Aesthetics Northwest in Tacoma WA. Dr. Clark maintains a microscope-centered restorative practice in Tacoma, Washington USA.
Dr. Jihyon Kim is a 1999 graduate of the University of Washington School of Dentistry. She is one of the founding members of the Academy of Miroscope Enhanced Dentistry.
Oral Health welcomes this original article.
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