Mastering Shade Selection in a Limited Area of the Smile Zone by Dr. Scott Finlay

Dentaltown Magazine

by Scott Finlay, DDS, FAGD, FAACD


The restoration in a limited area of the smile zone is one of the most challenging situations of dentistry. The micro-aesthetics of a restoration—the subtle intricacies of shade, textures, translucencies and surface effects that make teeth look natural—can be difficult to harmonize when the optics of indirect restorative materials are adjacent to natural tooth structure.

The partnership between a restorative dentist and laboratory ceramist is a key part of treatment success. The Achilles’ heel of this dynamic is that our colleagues on the lab bench don’t often have the luxury of directly observing the clinical condition, yet they are presented with the shared responsibility of matching what they can’t see.

The restorative dentist and laboratory ceramist need to communicate in a progressive and quantitative way to optimize function and aesthetics through innovative techniques, such as using cross-polarization filters to remove visual artifacts to visualize color three-dimensionally, and to calibrate images through RAW digital photography with a white balance card to determine the color coordinates of the desired shade.

The power of cross-polarization

Diagnostic photographs are one of the essential tools used to facilitate communication between the restorative dentist and the lab ceramist by bringing stone models to life on the lab bench. The use of twin point flash dental macro photography creates reflective zones and patterns that are useful to illustrate texture and contours. This gives technicians valuable information about surface morphology.

However, these same reflections are a liability when trying to select shade as they essentially mask our ability to see shade three-dimensionally. The elimination of these spectral reflections with management of the polarization of the light removes these artifacts. Specular reflections (or reflection zones) can impede our ability to see underlying idiosyncrasies of the tooth shade. Eliminating these reflective distortions through cross-polarization helps us to visualize the histological stratification of shade (Figs. 1a and 1b).

The eye can only interpret the perceived shade with available light that’s reflected from the surface. Therefore, we would like to observe our subjects under the fullest spectrum of light at 5,500 degrees Kelvin with a color rendering index (CRI) of 95% or better when selecting shades.

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Figs. 1a and 1b: Images are recorded in RAW format with and without the cross-polarization filters in place to facilitate illustration of the stratification of shades and surface finish/texture.
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Fig. 1b

Re-creating accurate shades

It is important that shade communication images are captured with consistency in angulation, magnification and exposure in the RAW format. This facilitates the recording of an image without compression, and allows the file to be calibrated with image management software to a known color coordinate. This known color coordinate is the introduction of a white-balance gray reference card into the field of view.

Once the image has been color-corrected, the user can then select any other site within that image and determine what the shade is relative to the correct color coordinates. This technique eliminates the use of traditional shade tabs that require interpolation to harmonize a shade. Rarely does the desired shade of the teeth actually match any single traditional shade tab.

Once the desired color coordinates have been determined through the use of proprietary software, the corrected formulations of dentin and enamel shades for the ceramics can be selected. This innovative technique was developed by the team at eLab through extensive research and clinical trials (Fig. 2).

The newly developed indirect restorations can then be placed on the custom shaded dies with the appropriate try-in paste, which serves as a quality control check of what will be anticipated clinically. The lab technician can then replicate the same series of photographic images on the lab bench that were recorded clinically in a virtual environment. Only then can the restorations be delivered to the dentist with predictable aesthetic outcomes related to micro-aesthetics.

Using the “virtual try-in” technique

The technologies of dental materials have evolved to the level of strength and beauty that now rivals nature. These restorations can be created in very thin cross-section and can impart a high degree of natural translucency. Our challenge involves dealing with discolorations of underlying tooth structure and the influence they may have on the final restoration once it’s delivered. This often requires interpolation and guesswork by the ceramist. This can be overcome and tested in the laboratory by creating custom color dies. These dies are fabricated from materials available to the ceramist that replicate the shades of the clinical preparations and are determined once again from the photographs that the restorative dentist provides of the preparations.

With the color-correct dies in hand, the newly fabricated indirect restorations can be placed onto these dies with the same try-in paste that the clinician will use to try the restorations in chairside (Fig. 3).

Photographing in the RAW format with the restoration on the virtual die, these images can also be color corrected with the white balance gray reference card.

The two images—the clinical condition and the lab bench result—can then be overlaid and determined if our goals of micro-aesthetics have been met. Only then, with this quality control in place, can the restorations be forwarded to the clinician for try in and delivery. The intention is to eliminate the multiple chairside visits sometimes necessary to dial in the shade for a single central incisor.

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Fig 2: The introduction of a white balance gray reference card (www.emulation.me) with a known color coordinate facilitates the calibration of images.
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Fig. 3: The fabrication of color-correct dies by the laboratory technician simulates the clinical condition on the lab bench to allow for interpolation of the underlying tooth structure.

Case example

This patient presented with a history of traumatic injury to her anterior teeth. She previously had bonding to correct the defects of teeth #8 and #9; these restorations had interproximal extensions to repair previous caries and began to discolor with time. Her end goal was to improve the appearance of her anterior teeth with the most durable option possible (Fig. 4).

In all aesthetic cases, it is critical to follow our understanding of the criteria of smile design. The American Academy of Cosmetic Dentistry’s Contemporary Concepts in Smile Design provides us with the gold standard of this commonly accepted nomenclature. These criteria of smile design are conceptually organized from our broadest field of view and progressively narrowed.

1. Global aesthetics. Those criteria that focus on elements of smile design that are observed in unretracted smiles and how the smile orients to the face and the lips that drape the smile.

2. Macro-aesthetics. Those criteria that focus on the shapes and contours of the teeth and their relationship to each other.

3. Micro-aesthetics. Those criteria that relate to the subtle intricacies of shade, textures, translucencies and surface effects that make teeth look like teeth.

By speaking the same language, both restorative dentists and lab ceramists will ensure the best opportunity to create a predictable, aesthetically pleasing result for the patient.

Diagnosis and treatment planning

After the initial assessment, a clinical examination, including hard- and soft-tissue evaluations, a complete radiographic survey, diagnostic photographic series, a T-Scan occlusal survey and mounted diagnostic models was completed.

The treatment options included an equilibration to optimize and balance occlusal forces and to meet the requirements for a stable occlusal design. A diagnostic design was also created to simulate the intended changes in contour for teeth #8 and #9. Preparation and provisionalization stents were then fabricated for this design (Figs. 5 and 6).

The restorative treatment plan included a conservatively prepped lithium disilicate layered veneer for tooth #8 and a lithium disilicate layered porcelain jacket crown was planned for tooth #9.

Choosing the right shade

The teeth were observed under a full spectrum of light of 5,500 degrees Kelvin with a CRI of 95% or better, without the opportunity to dehydrate. A white-balance gray card was introduced into the field, and the images were captured in RAW format both with and without the cross-polarization filters. After preparation, additional images were captured with the same protocol to help the ceramist manage and interpolate the influence of the underlying tooth.

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Fig. 4: Clinical preoperative condition, requiring limited restoration within the smile zone.
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Fig. 5: A diagnostic design creates a blueprint that affords predictability and ef?ciency in preparation and provisionalization.
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Fig. 6: The fabrication of prototypes is a diagnostic opportunity. The use of tints and a bilaminar layering technique of bisacryls creates an aesthetic enhancement during the provisionalization phase.
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Fig. 7: Innovative advanced photographic techniques bring to life the clinical condition on the lab bench to create better predictability in creating excellence in micro-aesthetics.

Creating prototypes and using color correction

The mounted models and diagnostic design provided a blueprint for the intended changes and construction of the provisional matrix. Prototypes were fabricated with a lock-on technique from a silicone stent that captured the diagnostic design with bilaminar technique to establish a natural gradation of shade: A1 for the cervical half and BL3 for the incisal half.

In this case, blue tint was used in the incisal aspect to simulate translucency and white opaque was diluted to create the milky hypocalcification observed in the adjacent teeth. A final glaze was then placed. These prototypes allowed the intended contours to be tested clinically and detailed prior to final restoration (Fig. 7).

In the fabrication of the final restorations, the laboratory ceramist utilized the above described protocol to calibrate the shade selection and complete the virtual try-in before forwarding the restorations for delivery.

The final try-in

Once received, the restorations were tried in for fit and accuracy. They were then tried in with the anticipated neutral try-in paste as a cement simulator, while evaluating the shade clinically through photography (again, with and without cross-polarization filters). Once accepted, the teeth were cleaned, conditioned and the restorations delivered with an aesthetic luting system.

Predictability of managing micro-aesthetics can be greatly facilitated with effective communication between the clinician and the ceramist, through the use of innovative advanced photographic techniques to synchronize the reality of the clinical condition with the lab bench.


Author Bio
Author Scott Finlay, DDS, FAGD, FAACD, is the resident expert of aesthetics and has been a senior faculty member at the Dawson Academy since 2007. Finlay authored AACD Guide to Accreditation Criteria: Contemporary Concepts in Smile Design, which serves as the primary reference for credentialing for accreditation within the American Academy of Cosmetic Dentistry. He is a full-time practicing dentist in Annapolis, Maryland, and Los Angeles.
 

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