Written by Jonathan H. MacArthur, DDS Wednesday, 31 October 2007 19:00
The world is too much with us; late and soon, Getting and spending, we lay waste our powers: Little we see in Nature that is ours...”
These are the words of discontent written by the great William Wordsworth 200 years ago, and in many ways the sentiment is more alive today than ever. Some might say that we are endlessly grappling with collateral cumulative difficulties that stem from central technological advances, that we end up creating more activity than progress, more noise than signal. The truth is that progress in any field is fraught with this difficulty. Martin Luther King, Jr. indicated that in social change, “All progress is precarious, and the solution of one problem brings us face to face with another problem.”
All too often in dentistry we see ourselves “getting and spending” in technologies that seem to bring with them diminutive, nagging problems that “lay waste our powers” and diminish our energy as the day proceeds. Given that the goals of most practitioners are to feel fulfilled about the service they provide, be well compensated for their efforts, and still have something left at the end of the day to “see in nature” what is theirs, technological advances may appear to fall short of their intended benefit. However, having said this, it is important to remember that frustrations and setbacks should not stifle progress; they must be handled in a positive way. These problems should simply be seen as opportunities in work clothes.
At the 20th anniversary of CEREC gala event in Las Vegas in August 2006, the inventor of CEREC, Dr. Werner Mormann, spoke of his involvement in the technology since its inception. He traced his involvement from its early and groundbreaking days to the impressive technology that it represents today. He described many of the problems and some of the resistance that he encountered along the way, and I couldn’t help but to be reminded of a quote by Frances Hodgson Burnett, the English-American playwright and author: “At first people refuse to believe that a strange new thing can be done, then they begin to hope it can be done, they then see it can be done, then it is done and all the world wonders why it was not done centuries ago.”
It seems that after all things are considered and despite the appearance of collateral problems, our facility to provide dental care has and continues to be more efficient; our ability to emulate nature in the delivery of strong and aesthetic restorations both anterior and posterior continues to grow. I believe that our ability to embrace new technologies and conquer the inevitable problems that can arise from them is the key to the continuation of this trend.
In this article you will see how CAD/CAM technology combined with magnification, soft-tissue lasers, and certain alternatives to conventional approach can expedite the delivery of care that traditionally would require a 2-week treatment span, temporary restorations, and more than one session of anesthesia. The facility to stain and glaze these restorations will be shown to directly control the final aesthetic outcome. A new technique for holding indirect restorations that is reliable, dependable, and simple will be introduced, this being an example of an innovation that solves a problem created by the wake of advancing technology.
In the past, the handling of inlays and onlays either at try-in or final placement was often stressful because the dental assistant and dentist would both be on proverbial tender hooks, hoping that after various manipulations the restoration would not fall off at the most inopportune moment. Since the restoration in question is the culmination of advanced technological CAD/CAM application, it has been carefully etched, silanated, and dried, a highly evolved luting agent has been mixed to ideal proportion, and the recipient tooth prepared and isolated with extreme attention, it seems ludicrous for the final placement step to hinge on such tenuous unreliability.
Efforts have been made to circumvent this difficulty. Some have advocated seating CEREC units with the sprue still attached to serve as a handle, subsequently to be removed after bonding. This technique makes it difficult to achieve the level of final polish that is more easily achieved extraorally. It also precludes staining and glazing, as the final result would inevitably be marred during sprue removal. Using the fingers to place these small restorations is messy and unnecessarily difficult. This problem is not exclusive to the CEREC approach. It applies to any indirect restoration, gold or tooth colored. Many products have been developed in an effort to solve this lingering problem.
CLINICAL TECHNIQUE, METHODS, AND MATERIALS
Figure 1. Preoperative photo of teeth Nos. 28 and 29 with interproximal decay, yet occlusal anatomy is still intact.
Figure 2. Teeth coated with silica dioxide powder to create a uniform reflective surface required for the infrared camera.
|Figure 3. The optical impression of the existing anatomy is captured.|
Figures 4 and 5. The Isolite System used to illuminate and isolate the teeth to be restored.
This author has developed a technique that uses a light-weight, portable heating device to activate a green-colored adhesive pellet. The adhesive pellet is carried to the restoration and quickly heated in place, whereupon an end-tufted bendable brush is submerged into the molten adhesive to create a handle within 5 seconds. In this case, teeth Nos. 28 and 29 exhibit pronounced interproximal decay, but the occlusal anatomy and marginal ridges are intact (Figure 1). Exact duplication of pre-existing anatomy using CAD/CAM CEREC technology in correlation mode is only one of the several available modes that can be selected when using CEREC 3-D software. In this case, the teeth are coated with silica dioxide powder to achieve a uniform reflective surface, and the exact morphological characteristics in question will be captured by an optical impression and stored in the database (Figures 2 and 3). A shade is then taken prior to isolation to avoid the effects of dehydration on tooth color. The Vita block itself is used as a shade guide. It is general procedure to err on the lighter side since staining and glazing can be used to darken more easily than to lighten.
As in all situations regarding bonded dentistry, isolation is critical. In this case an Isolite Dryfield Illuminator (Isolite Systems) was utilized successfully (Figures 4 and 5). Initial preparation and excavation was rapidly achieved using high-speed carbide 557 and No. 2 round burs (Brasseler). Tapered, round-ended diamonds were then used to refine internal wall tapers and prep margins; 5x magnification using loupes (Orascoptic) greatly enhances the ease with which this is achieved. A 810-nm diode laser (Odyssey [Ivoclar Vivadent]) was used to refine the gingival margins so that they are easily read by the optical scanner (Figure 6). The versatility of the laser can be vastly improved by frictionally fitting a syringe tip to the end of the laser stylus (Den-Mat). The fiber-optic is supported within the metal lumen of the syringe tip, and hence does not break when the tip is bent, allowing the creation of any desired angle (Figure 7).
Figure 6. Gingival margins clearly delineated with the use of a 810-nm diode laser.
Figure 7. The fiber-optic tip of the laser can be bent to sharp angles without breakage using a metal syringe tip (DenMat).
Figure 8. Optical image of the preparations captured.
Figure 9. The outline of the preparation is traced using the automatic margin-finding function.
Figure 10. The correlation mode restoration proposal is an exact duplication of the preoperative morphology of the tooth.
Figure 11. The distal contact being refined.
Once the preparation was complete, another optical image or series of images were taken so that they duplicated the position of the preoperative image. This again was stored in the database (Figure 8). The accuracy of this duplication can be determined by clicking and dragging the image in the occlusion (preoperative) category over the top of the prep image. The images behave as transparencies so that the degree of duplication of position can be assessed. With practice, consistently accurate duplication can be achieved with ease.
In the design mode the area to be restored was outlined (Figure 9). The software automatically proposes a restoration (Figure 10). The contact was refined (Figure 11), and the restoration was virtually seated so that the restoration on tooth No. 28 could be designed while the unit for tooth No. 29 was being milled (Figure 12). In this case a size No. 12 block of shade 2M2C as prescribed by the software was used. Note that the restoration proposal in Figure 10 is an exact duplication of the preoperative morphology of the tooth due to the accuracy of the pre-/post-optical im-age duplication. If it is anticipated that this duplication may be difficult intraorally, a pre-preparation impression can be taken and poured in Snap acrylic (Parkell). The occlusion image can then be taken extraorally to match the prep image. Snap acrylic is fast-setting and very accurate in its replication of occlusal detail. Unlike stone, it is not subject to bubbles or fracture upon removal from the impression.
Figure 12. The first restoration has been virtually seated and is being milled while the second restoration is being designed.
Figure 13. A Thermagrip pellet being retrieved from the cassette.
Figure 14. The adhesive pellet is activated on the restoration using the Thermagrip unit.
Figure 15. An attachment handle is created by plunging the end-tufted brush into the activated adhesive. The entire attachment process should take no more than 5 seconds and provides a secure means of carrying the restoration to the preparation during the bonding procedure.
Figure 16. The glazed restorations are attached to the platinum pins using Quick-Peg material so that they may be supported during firing.
Figure 17. The restoration on tooth No. 29 being placed using the Thermagrip system.
Figure 18. The attachment, although secure, is easily removed with brush and adhesive as one unit, leaving no residue on the restoration.
Figure 19. Immediate postoperative photo.
Figure 20. One-year postoperative photo.
At try in, the Therma-grip (Alesar) heating device was activated for 1 to 2 seconds; an adhesive pellet was retrieved from the storage cassette by simply touching it with the tip of the heating device (Figure 13). It was then transferred to the restoration, where it was again heated for 5 seconds until it converted into a molten state (Figure 14). The tuft-ended flexible handle was then submerged into the adhesive (Figure 15). The restoration can immediately be turned over so that it may be etched with 9.5% buffered hydrofluoric acid for 90 seconds, silanated, dried with hot air, and have bonding paste applied. It is important to note that single-bottle silanes generally have a 1- to 2-month shelf life, as they will chemically condense in the bottle, making them ineffective. The author strongly suggests using 2-bottle systems. Overetching will promote the deposition of hexa fluorosilicate salt, which can severely reduce bond strengths to porcelain. The attachment handle can be bent to any appropriate angle to facilitate placement. The attachment is very durable, eliminating the fear of untimely “drop offs.” The adhesive has “smart properties” that prevent it from flowing onto the internal, to-be-bonded portion of the restoration, which is critical when dealing with very small inlay restorations.
In this case the restorations were tried in and interproximal contacts adjusted. CEREC restorations can be polished to high gloss with very little effort using grey and yellow cups and points (Perladia). This is done regardless of whether a stain and glaze will be utilized. These restorations were lightly stained and glazed. To do so they were mounted on platinum pins using Quick-Peg paste (Vident; Figure 16), and the appropriate Vita stain and Vita glaze were applied using a fine sable hair brush. Both were baked simultaneously in an Automatic Glazing Furnace (Vident) oven at 950°C for 10 minutes.
The Thermagrip technique was again employed during insertion, using the Isolite for isolation (Figure 17). Variolink (Ivoclar Vivadent) was used as a bonding agent. After insertion the attachment handle was pulled off along with the adhesive (Figure 18). On rare occasions some adhesive may remain on the restoration, but this can be readily identified by its green color and easily peeled away.
As can be seen by the immediate postoperative and one-year postoperative photos the final result is truly a duplication of the original tooth form and function (Figures 19 and 20). In our efforts to emulate nature, this is as close as it gets.
The advent of technology in dentistry has benefitted both the dentist and patient. But as technology advances, like a great vessel it creates a wake of smaller collateral problems that can undermine our ability to fully appreciate the gravity of the technological advancement. These problems can erode our potential, and in the words of Wordsworth, “lay waste our powers.”
Similarly, advances in technology can often eclipse smaller, more mundane problems that need to be addressed. The fact that man walked on the moon long before he walked in an airport with wheels on his suitcase is astounding, but similar paradoxes occur in our own profession daily. Not withstanding these concerns, the advancing frontier of dental technology affords the profession the opportunity to “tuck in the loose ends” by solving mundane but ubiquitous problems. I feel privileged to have perhaps contributed in small measure to this process.
Disclosure: Dr. MacArthur is president and chairman of Alesar Dental and is the inventor of the Thermagrip and Thermaflect.
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