by Jeffrey B. Dalin, DDS, FACD, FAGD, FICD
For more on this topic, go to www.dentaleconomics.com and search using the following key words: lab technician, Matt Roberts, Jeff Dalin, zirconia, porcelain, implants, shade matching.
Dr. Dalin: I tell patients that I consider my lab technician an equal partner in the design and construction of the top-quality crowns and bridges I provide them. Excellent restorative dentistry requires the highest levels of communication and rapport between the dentist and the lab technician. In this feature, we will speak with Matt Roberts, one of the premier ceramists in the country. Matt, let's begin by talking about the relationship between a lab technician and a dentist. Should there be some groundwork laid before a relationship between the two is developed? Do you have a checklist that you send to prospective dentists?
Roberts: When starting a new relationship with a dentist, it is important to establish parameters for communication, as well as expectations of performance for the dentist and ceramist. It also helps if you happen to like each other! We do issue an introductory package that defines our communication protocol, as well as our prescheduling requirements and general philosophy on restorative dentistry. I conduct a phone conversation with each new dentist to learn what his or her needs are and to get an idea if the person is compatible with our lab. In general, I want to see if this is someone whose phone call I will look forward to receiving. It is important to understand that a laboratory can't be all things to all people, and that there are many models for dental practices. All of these models are needed in the marketplace, but not all of them are compatible with our style of dentistry. Fees charged and time taken to fabricate the case need to be compatible with a dentist's price structure and relationship with his or her patients. Occlusal philosophies need to be understood, and each part must understand the depth and complexity of the treatment method. A systematic approach to achieving our patients' needs must be agreed upon so that dentist, ceramist, and patient are rewarded by the experience.
Dr. Dalin: Let's talk about preparation designs. Are there any tips and tricks you can give readers regarding the ways dentists prepare teeth for veneers, inlays, onlays, and crowns?
Roberts: This could be the subject of an entire book, but I will cover the obvious points in an abbreviated form. Preparation design varies with restorative material. Some materials, such as porcelain-fused-to-metal or zirconia-based restorations, have a preferred design for preparation that is always the same. Bonded restorations, on the other hand, change dramatically based on the color and position of underlying tooth structure. There is no fixed design that works in every situation. The clinician must understand the properties of the restorative material being used and appropriately select a material that fills the patient's restorative needs.
Matt Roberts
First, preparation design must be based on patient need, then be optimized for restorative material. A patient's restorative needs can be evaluated by completing an additive-reductive diagnostic wax-up while considering the patient's functional and esthetic goals. Areas in which tooth structure must be removed to accomplish these goals are marked for reference during the preparation phase of treatment. This process will determine the teeth involved in treatment and the number of surfaces of each tooth that must be restored to achieve the contour and position to accomplish the patient's functional and esthetic goals. Ideally, the form and function of the reconstruction is tested by taking a putty matrix impression of the diagnostic wax-up, and clinically relieving any areas of the dentition in which tooth structure was removed during the additive reductive process to allow the matrix to be completely seated in the patient's mouth. This matrix is then filled with a material such as Luxatemp, placed in a patient's mouth, and allowed to cure. In this way, the details of the additive reductive wax-up are transferred to the clinical environment. Form, function, esthetics, and phonetics can be evaluated in the patient's mouth.
Individual preparation design now can be considered based on the teeth's condition and position. Teeth that are fully covered with composite will need some kind of full crown while teeth that are only partially covered with Luxatemp can be treated with veneers or onlays. The marginal placement on these restorations is determined by looking at the periphery of the areas in which wax was added or tooth structure was removed during the completion of the additive-reductive wax-up. I like to approach treatment from a mindset that preserves as much natural dentition as possible. So, where possible, I like to see treatment with bleaching, composite bonding, or bonded ceramic inlay, onlay or veneer-type restorations. The depth of preparation for these restorations is determined by the existing color of the patient's tooth structure and the projected thickness of ceramic that will be required to accomplish the final desired shade. The more color change desired, the more preparation depth required.
Reconstructive materials may now be selected based on masking requirements, strength requirements, and bondability of the underlying dentition. Ceramic materials vary in strength: feldspathic ceramic has a flexural strength around 80 mpa, lucite-reinforced pressables (Empress, Authentic, etc.) fall into the range between 125 mpa and 175 mpa, lithium disilicate restorations (E Max Press or Blue) exhibit a strength of 350 mpa to 450 mpa.
Feldspathic veneers constructed on foil or refractory dies can be fabricated in thicknesses under 0.5 mm and are useful for conservative veneers and inlay/onlay applications with good underlying support. As occlusal involvement increases and restorative thickness increases, the added strength and stability of pressed ceramic restorations becomes more desirable. Materials like Empress can be fabricated with a minimum of 0.7 mm of reduction. The higher strength of these materials allows for greater success with thicker restorations lacking underlying support.
The new class of lithium disilicate restorations provides the strongest etched and bonded restorative material available, and can be used in thin applications (as small as 0.1 mm), as well as having the strength to survive in bridge application in the anterior or thicker single restorations. Lithium disilicate restorations that are translucent enough to use without layering are new materials. Time will test the various applications, but the possibilities are exciting.
Nonbondable surfaces, like metal posts or sclerotic dentin, require cementable full crowns with a high strength core material. This class of restoration, whether the core is zirconia, alumina or metal, requires conventional preparation design with 1.5 mm of axial reduction, resistance form retention, and a shoulder preparation with a rounded internal line angle.
Once material selection is accomplished and the mock-up is in place, preparation can begin by doing depth cuts into the mock-up that will provide the amount of restorative room necessary for the material that has been chosen. This will develop the final color and look desired by the patient. This process of depth cutting through a mock-up to a specific restorative thickness relative to the goals of treatment not only optimizes the success of the case, but is also the approach that is the most conservative of natural tooth structure. With this technique, prepared teeth are oriented to the desired position of the future restorations rather than being centered in the location of the preexisting dentition.
Dr. Dalin: Now we have some prepared teeth. Do you have any preferred materials or methods in terms of taking impressions?
Roberts: That is a scary question. If a doctor is comfortable with an impression material and technique, and is getting good results, I would not encourage the doctor to change impression materials. With conventional materials, I see more consistent results with polyether materials than I do with the polyvinyl siloxane materials although I see clinicians who get excellent results with either material.
Dr. Dalin: While we are discussing impressions, would you discuss the new digital impression devices — the Lava Chairside Oral Sanner by 3M ESPE and the iTero Scanner by Cadent?
Roberts: Digital impressions are an exciting development. Currently, we are working with iTero by Cadent, as well as with 3M ESPE's new Lava COS system. Each provides predictable results and speeds up the fabrication process. In current form, each is reliable and accurate for the fabrication of models. What is key about the future of this technology is the potential for integration with current and future virtual technologies, as well as CAD/CAM milling or deposition fabrication technologies. We now have the ability to take a digital impression, view it on a monitor to evaluate completeness, upload it to a site where the lab can look at it and mark the margins (the dentist can do this also), then order the fabrication of the models either by milling or stereolithography. The models then are mailed to the laboratory the next day.
In addition, since we have the surface of the prepared tooth in a digital format, we can send this data to a compatible milling system and start milling a zirconia coping or lithium disilicate dentin form before we get the model in the lab. If the concept of open architecture between systems proliferates, conceptually we can create a virtual patient in the digital environment and the potential for integrated treatment becomes mind boggling. We can record CAT scan data of hard tissue, TMJ joint movement with the Digma system from KaVo, integrate optical scanning of dentition, use software to place any implants in a virtual environment generated from the CAT scan, look at infrared-based scanning technology for the subgingival scanning of hard tissue, and produce physical models and articulator settings that replicate everything that exists in the patient's oral environment. We also have the ability to continue with treatment with this data set.
Dr. Dalin: We have prepared the teeth and have taken an impression. Now it is time to design the final restoration, but we need some shade selection guidance. What is your opinion of digital shade matching devices? Do you think a dentist can do a good job with digital photography?
Roberts: They are a useful tool if combined with a good quality digital photograph that has a shade guide positioned next to the tooth. I have worked the most with ClearMatch, which actually works in harmony with good digital photography and gets good results. ShadeVision from X-Rite also has been a useful tool. There are now many systems on the market. Unfortunately, I haven't had the opportunity to work with all of them. The feedback I hear from people who use the various systems has been positive. Currently, my preference still is to have several good quality digital photographs with a shade guide in the picture. I have an open mind in this area, and reserve the right to change my opinion as I work with the technology.
Dr. Dalin: We are now ready to discuss how to select the best material for the restoration. What are your thoughts about zirconium vs. porcelain?
Roberts: We discussed material selection in the question about preparation design. With respect to zirconia vs. porcelain, zirconia is quickly replacing metal as a core material for cemented restorations. It also shows favorable biocompatibility for the fabrication of implant abutments. I think that with the development of stronger etched and bonded systems, like the lithium disilicate materials, we will see less need for high-strength core materials like PFM or zirconia. There will continue to be a need for these materials in situations in which composite bonding of restorations is impractical, or as long as we are fabricating bridges rather than placing implants.
The application with the most favorable clinical research supporting the use of zirconia is implant abutments. With this application, the white color avoids gray through the tissue and we see favorable hard- and soft-tissue response to the material. Frequently, we create custom abutments with natural emergence form, then fire etchable porcelain to the surface of the zirconia to create an etchable surface with the optical qualities of the adjacent prepared teeth to receive veneers. In this way, the implant is treated with the same restorative material as the adjacent natural teeth and a harmonious result is achieved.
Dr. Dalin: Do you have any advice regarding CAD/CAM systems such as CEREC and E4D?
Roberts: I think the in-office business model will replace laboratory-fabricated single crown and onlay needs in the next few years. With existing systems, I don't think there will be as much impact on anterior restorations. These still need the final touch of a skilled ceramist; however, there may be business models in which an on-site ceramist accomplishes these final improvements while the patient waits in the dentist's office. Currently, though, there is a serious shortage of skilled ceramists for this application. We need to redefine our educational system in dental technology to work with new technology. Future labs won't look or function as they do today.
I would approach any technology with a business plan that pays for itself within two years, or I wouldn't buy it. The pace of development is so rapid that I wouldn't want to still be paying for technology that has already been bypassed by something newer and better.
Dr. Dalin: How about the rapid growth of implants? Is there anything restorative dentists need to think about with implants?
Roberts: Implant treatment needs to be tied to CAT scan technology and computer planning of placement. I think we will soon see a proliferation of guided surgery techniques based on imaging technology. We have already seen Nobel Biocare's "Teeth In A Day." I also am involved with an implant treatment planning and execution company, Smart Implants, LLC, that provides CAT scan-based treatment planning, surgical guides, parts ordering support with an implant company, and immediate patient restorations to wear on the day of surgery. This provides a level of support to boost the practitioner's confidence.With training, it allows the conversion of denture patients with appropriate clinical situations into implant-supported, fixed restorative situations. Having all this happen for the patient in a single appointment is a powerful advantage. Obviously, my opinions in this area reflect a proprietary interest. Objectively, Nobel's system and Smart implants are impacting patients' lives positively.
Dr. Dalin: What do you think about the controversy with offshore labs and the lead found in crowns fabricated in China?
Roberts: The single posterior restoration should be on the "endangered species list," as far as laboratories are concerned. Those not done in-office by CEREC or E4D systems can be mailed to China or other relatively inexpensive labor market for fees much lower than the fabrication cost by a skilled technician in the U.S. Many dentists are happy with the quality of this result for individual crowns. I know this is a strong statement and could initiate emotional arguments, but the result is inevitable and predictable. If we want to stay in business in this country, we need to provide a level of communication and technological integrations that negate the price advantage of overseas markets.
Technology costs the same in the U.S. as it does overseas. Let's use it to our advantage to make our skilled ceramists more productive. The more we can use automation to free up the time of talented ceramists to plan and finish cases at a high level, the more competitive we will be. Remember, with our lifestyle in this country, we can't compete with inexpensive labor on an hour-by-hour basis. We need to produce a level of efficiency and professional excellence that makes it worth spending the money that it costs to do it here.
The offshore situation is a limited time proposition until the standard of living in those countries increases to the point that it brings the labor costs to a level in which it is no longer financially beneficial to ship work halfway around the world. There will always be the next developing country that has invested in education but does not yet have the standard of living that drives labor costs up. This will serve as the next source of inexpensive restorations. Who knows — it may be us if things keep going in the direction they have been. This is just a provocative thought to encourage investment in infrastructure and education.
Matt Roberts is one of the most recognized dental ceramists in the United States. He became interested in dentistry while growing up and working in his father's dental practice. He attended college at Idaho State University. In 1979, he founded CMR Dental Laboratory. Roberts is also the founder of Team Aesthetic Seminars, and holds advanced level training classes for dentists and ceramists. An Accredited member of the American Academy of Cosmetic Dentistry, he lectures nationally and internationally.
Jeffrey B. Dalin, DDS, FACD, FAGD, FICD, practices general dentistry in St. Louis. He is the editor of St. Louis Dentistry magazine, and spokesman and critical-issue-response-team chairman for the Greater St. Louis Dental Society. He is a cofounder of the Give Kids A Smile program. Contact him at [email protected].
