Written by Ray M. Becker, DDS Wednesday, 31 August 2005 19:00
Dentistry has always had a variety of cliche´s that define its direction and espouse its purpose. The latest catchphrase, high tech/high touch, is no different. Essentially, not only does it advise us that it is important to incorporate the latest technologies to improve the delivery of dental care, but it also reminds us to consider the patient's overall experience and interaction with us while receiving that care.
Tremendous technological advances have been made in dentistry over the past few years, advances that have the potential to completely change the traditional patient experience. A big advantage of the high-tech/high-touch dental office is not merely an additive one; when these technologies are used together, as this case illustrates, it is actually possible to deliver high-tech/no-touch dentistry.
|Figure 1. Preoperative view of tooth No. 18.|
This 45-year-old female patient presented with a broken tooth previously restored with a very large restoration over a composite base/liner (still partially intact) that was originally placed 11 years ago (Figure 1). Most of the remaining tooth structure either approximated or was below the gumline. Besides the obvious prosthetic challenge, the patient had a strong desire to save and treat the tooth in the most conservative manner possible. After testing to determine tooth vitality, and thorough, extensive co-diagnosis and treatment planning, the patient chose a CEREC crown.
The tooth was prepared with a DELight Er:YAG hard-tissue laser (Hoya ConBio). The laser light cuts the tooth structure without any physical contact with the tooth itself, unlike traditional handpiece/bur technology. The subsequent crown was then fabricated from a 3-D virtual model using the CEREC 3D CAD/CAM System (Sirona), which uses an infrared camera to image and fabricate a virtual die of the prepared tooth instead of the typical impression materials, trays, and dies associated with traditional crown fabrication.
As a result, the first true physical contact with the tooth structure was during try-in of the resulting crown for finalization of the restoration. The unique advantages of each independent system were able to yield a synergistic result considered impossible just a few years ago. In fact, the completely broken-down tooth was imaged, restored, and finalized in just one sitting, having only made direct physical contact with the tooth at the try-in/final insertion phase of the completed restoration (hence, high tech/no touch).
The advantages of these technologies include the following:
• complete fabrication of restorations in only 1 visit,
• detailed and accurate results via a digitized library created by ceramist Lee Culp,
• use of well-proven restorative materials whose manufacture is tightly controlled,
• elimination of potential human error associated with the fabrication of traditional crowns,
• defect-based restorations, allowing conservative treatment of teeth without unnecessary reduction of otherwise healthy tooth structure, and
• fewer visits and less invasive procedures yielding less postoperative discomfort and fewer sequelae.
• extremely concise and accurate cutting of hard and soft tissues,
• true sterilization of lased tissues versus limited disinfection with solutions alone,
• no introduction of a debris-laden smear layer typical with bur preparation of the tooth,
• a 40% increase in bond strength over conventionally prepared surfaces,
• less pulpal edema, fewer postoperative sequelae, particularly in extremely deep restorations, and
• selective and very concise ablation of distinct materials via laser settings alone.
Together, as this case illustrates, the advantages of these 2 systems allowed for the greatest probability of successful, conservative, and aesthetic restoration of this extremely compromised tooth. This is a result of the laser's ability to yield the best possible bonding surface with the smallest probability of exposure and negative postoperative pulpal response.
Additionally, a beautiful restorative result was achieved predictably and easily in only 1 step and visit using the CEREC 3D CAD/CAM System with the Lee Culp library. Reducing the amount and degree of tissue manipulation while definitively treating in just one visit further reduces the possibility of postoperative sequelae.
Although there have been reports of hard-tissue anesthesia of an unknown etiology occurring with Er:YAG lasers, in order to guarantee comfort throughout the entire procedure and at the patient's request, local anesthetic was administered in this case (1.8 cc 4% Articaine with 1:100,000 epinephrine) at the mucogingival junction, buccal, and lingual via infiltration. The remaining composite resin base was then removed using the Hoya DELight Er:YAG hard-tissue laser at the factory default "caries" settings of 70 mJ and 30 Hz. Use of these settings allowed easy and selective removal of the remaining composite resin without removing or altering the surrounding tooth structure. This is an important phenomenon unique to lasers and a significant benefit in this particular case, since it was all but impossible to determine the full extent of the recurrent decay beneath the composite base and how extensive the base was originally. A unique and valuable property of all lasers is that, by definition, they deliver an extremely pure wavelength of light energy. The absorption of this energy by oral tissue has been well-defined, and it is this precision that allows the efficacy of the laser for dental applications. Knowledge of the specific, typical properties of the targeted tissue allows selective removal of those tissues, even when different types of tissue are in close proximity.
Significantly, even the same tissue in differing states of health will absorb the energy differently, allowing for the selective removal of diseased tissues. This property proved extremely valuable in this particular case, since selective removal of composite resin and carious dentin was possible with a greater degree of security. Additionally, the tissues are sterilized by using the laser, and the resulting bonding surface—and subsequent bonding strength—is much improved.
Finally, even with extensively damaged teeth such as in this case, the operation of the Er:YAG laser has been found to lower the intrapulpal temperature while cutting the tooth structure. This is in marked contrast to the well-documented increase in pulpal temperature noted with traditional bur/handpiece preparation. This phenomenon further reduces the risk of postoperative sequelae on severely compromised teeth.
|Figure 2. Creating butt margin with Er:YAG laser.|
To prepare the required butt joint margin for an all-ceramic crown, the enamel settings of 240 mJ and 25 Hz were used, holding the laser tip perpendicular to the long axis and surface to create a circumferential "slot" around the remaining tooth sections (Figure 2). The lower aspect of the resulting slot then defined the margin of the crown preparation itself. This slot is typically created to a depth of 1.0 to 1.5 mm; it is gauged via visual landmarks or by using permanent pen to create a mark of that depth on the cutting tip.
|Figure 3. Further refinement with Er:YAG laser.|
Next, working from the occlusal aspect, the remaining segment of buccal tooth was worked away until it separated upon meeting the circumferential slot created earlier. Following removal of these segments, some practitioners advocate using a diamond bur to define the margins further. In this case, the Er:YAG laser was solely utilized to define, create, and prepare the entire crown preparation (Figure 3). This is a straightforward procedure when approached in the manner indicated here, even though lasers do not remove tooth structure as efficiently as burs. When the preparation is defect-based, as is typical with CEREC-based restorations, there is less reduction of otherwise healthy tooth structure from the outset. Furthermore, defining the margin with the circumferential depth slot allows precise control of the position and integrity of the margin. Significantly, the sometimes irregular appearance of laser-prepared surfaces is primarily due to the lack of tactile feedback, not the actual cutting action of the laser itself, which is extremely precise. Creating the circumferential margin-defining slot first eliminates this concern, since the peripheral cutting action is easily gauged and defined.
|Figure 4. Subgingival margin before diode laser.||Figure 5. Subgingival margin after diode laser.|
After complete removal of the residual composite and refining of the crown margin, the defect and necessary preparation positioned the clinical margin substantially below the gumline. The Odyssey Diode soft-tissue laser (Ivoclar Vivadent) at the 1.2-W continuous pulse setting was used. The laser quickly and easily corrected this defect and provided proper parabolic contouring. Additionally, it sterilized the area, providing better access to the clinical margin for subsequent patient hygiene. This laser also provided exquisite hemostasis of the area throughout the subsequent steps required to fabricate the restoration (Figures 4 and 5).
As stated previously, laser energy is absorbed selectively by different tissues. The Odyssey Diode laser at the 810-nm wavelength selectively absorbs into melanin and hemoglobin. This wavelength has relatively little absorption into hydroxylapatite and water, the predominant components of bone and tooth structure. Therefore, using this laser allowed the desired effect of gingival recontouring and hemostasis, with no negative effect on the previously defined tooth preparation.
The next step in the procedure was to image the tooth preparation and create the crown using the CEREC 3D system. A registration of the preparation was taken using GC America Exabite II NDS to capture accurately the anatomy and cuspal guidance of the opposing teeth. This registration was then cut to expose the appropriate margins of the prepared tooth. The Isolite dry field illuminator system (Iso-lite) was utilized throughout the entire preparation, imaging, and bonding sequences. The Isolite system is a significant aid in all phases of CEREC dentistry, due to its comfortable isolation, efficient evacuation that effectively prevents intraoral lens fogging, and its ability to provide a stable and repeatable platform from which to capture the required images. These measures greatly assist in guaranteeing a quick and accurate capturing of the required images.
|Figure 6. CEREC 3D showing crown proposal in TriLux Block.|
After the crown was designed on the acquisition unit of the CEREC 3D System, the appropriate size block was designated by the computer. A Vita TriLuxe block (Vident) in the designated size was selected, matching the desired shade. As the name suggests, the TriLuxe block features 3 zones of shade within the individual block (Figure 6). Using the software, the exact degree of variation necessary to match the clinical circumstance was selected within the block by altering the position of the proposed milling within an outline of the block on the screen. This provides for impeccable aesthetic control of the final polychromatic restoration. The milling data was then sent via a high-speed wireless network to the milling unit, where the crown was created in approximately 15 minutes.
|Figure 7. Initial try-in with no adjustments (note intact milling sprue).|
After milling, the restoration was then tried in to verify the margins, contacts, and occlusion. In this case, as is typical with these restorations, absolutely no adjustment was required to fit the restoration internally. The margins were impossible to detect with even the sharpest perpendicularly placed explorer, the contacts were exactly as defined on the virtual die, and only a few minor brushes of the diamond bur were required to finalize the occlusion to guarantee the desired cuspal guidance and inclination (Figure 7). This was the very first direct physical contact that occurred with this particular tooth throughout the entire treatment process: high tech...no touch!
|Figure 8. Stained/glazed and cemented final restoration, postoperative view.|
Finally, using the Akzent stains and glazes with the fully automatic Vita Vacumat 40 firing oven (both from Vident), the restoration was stained and glazed. The restoration was then etched with HF acid and silanated with 3M ESPE Sil silane coupling agent. The tooth was then touched for only the second, yet final time to rewet the tooth surface with Hemaseal & Cide (Advantage Dental Products) and to cement the crown with 3M ESPE Unicem (Figure 8). While it has been documented that no additional bond strength is obtained from using Hemaseal & Cide with Unicem, it is used routinely as a rewetting agent with all dentinal bonding agents due to its exceptional disinfection properties, which are well-documented in both clinical and university-based research.
Using the database/antagonist mode of CEREC 3D with the Lee Culp library allows the precise definition and fabrication of the entire restoration to fit the clinical tooth margins, contacts, and occlusion accurately. One has unprecedented control of all design aspects of the crown. Many unique perspectives can easily be visualized by limitless manipulation of the virtual die from practically any conceivable viewing and editing angle. A unique quality of CEREC 3D-designed restorations is the use of highly accurate imaging and computer technologies to eliminate the multiple steps that are otherwise performed manually in the traditional creation of a crown.
While it is entirely possible to create an accurate crown using lost wax-based techniques, many steps must still be done manually. Unfortunately, the more individual steps involved and the more manual input required, the greater the possibility of introducing error; the overall negative impact is magnified the earlier in the sequence the particular error occurs. Considering many factors, from simple air bubbles in impression and die materials to the variable expansion and contraction of the impression and die stone material, it is a true testament to the skill of laboratory technicians that restorations in a recent study were found, on average, to be inaccurate by only 100 µm in margin error.
With the CAD/CAM technology described, the entire sequence of fabrication from initially capturing the tooth preparation through manufacturing the actual crown is done virtually within a computerized system resolution of 25 µm. There are no physical dies, impressions, or manual steps involved. All that needs to be done is remove the unhealthy structure, clean up the outline form, verify that the minimal material clearances and thicknesses have been met (typically, a minimal dimension of 1 mm), capture the preparation, then fabricate the corresponding restoration.
This quality was highly beneficial in this particular case, as minimal reduction of the remaining healthy tooth structure was necessary. This approach also elegantly overcomes the subsequent concern that lasers are less efficient in absolute tooth removal when compared to a traditional bur. Since it is only necessary to clean up the defective and diseased tooth structure, bulk reduction of otherwise healthy tooth structure is not only undesirable, but completely unnecessary. The Er:YAG laser is notable for creating an ideal bonding surface with the least amount of trauma and postoperative sequelae. Er:YAG lasers are not known for their tooth-cutting efficiency, but this is not an issue due to the defect-based restorative capabilities of the CEREC 3D System. Additionally, the extra steps and expense associated with the traditional multiple-visit core build-up and crown process are eliminated.
This case highlights the unique advantages of 2 technologies, which when used together yield a result better than either could produce independently. The illustrated solution demonstrates the most predictable means of controlling the many unique variables factoring into this difficult prosthetic challenge. Taking advantage of the laser's ability to prepare and sterilize the preparation while improving the bond strength, combined with the ability of CAD/CAM to design and create a single-visit crown, adds up to a unique treatment opportunity for today's dental patient.
Besides the obvious benefits of treating a tooth definitively in a single visit with true sterilization and improved bondability, one should not overlook the distinct advantage that fewer visits provide to an already nervous dental populace. Restoring this case traditionally would mean at least 2, possibly even 3, separate dental visits, each representing yet another unwelcome rescheduling of the patient's personal life. Considering the amount of time required for travel to and from the office for a single visit, the inevitable wait, and the repetition of the cycle for subsequent visits to insert the final restoration, it is easy to understand patients' disenchantment with taking a half day from their busy lives for each of these appointments.
Understanding, respecting, and actually addressing these very real patient concerns would truly be lending credence to the cliche´ "high tech/high touch." In fact, one could even say that "high tech/no touch" as demonstrated in this case might actually be the ultimate delivery of that goal.
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