Minimally Invasive Dentistry
By Irwin Smigel, DDS
This past October, I was the keynote speaker at an outstanding esthetic symposium in Turkey. One of the participants, the world renowned authority on dentures, Dr. Kunihide Terakawa, suggested that denture usage would intensify as a consequence of our aging population. There's no doubt many of us in this country would debate that assumption, but Dr. Terakawa demonstrated that throughout the world, denture construction has unfortunately kept pace with the world's growing geriatric population.
There have been many attempts to intercept this phenomenon, and several, such as an emphasis on proper home care and water fluoridation, have been particularly successful. However, the denture problem still exists, and in this article, I will discuss a treatment modality I believe could be a leap forward in the long-term maintenance of teeth minimally invasive dentistry.
I am a strong advocate of full coverage; it has been and still is a major part of my practice. Nevertheless, 40 years have demonstrated that even under the best of circumstances, a percentage of crowned teeth will devitalize from the insult of preparation and/or cementation, and another percentage will be periodontally challenged from trauma to the tissues. It has long been wished that lost teeth could be replaced without completely preparing their "adjacents." Today,. in many instances, it is a reality, and as the following three cases attest, with measurably less trauma to the hard and soft tissues.
CASE I
The young man in this case was congenitally missing both maxillary lateral incisors (Figure IA). As demonstrated in Figure IB, there is not sufficient room for adequately sized lateral incisor replacements. To obtain the necessary space, we orthodontically moved his maxillary centrals, closing the diastema and creating room for normal laterals (Figure IC). The orthodontic treatment, although relatively uncomplicated, was carefully executed to make certain the closure would be stable.
Approximately 4 months later, we commenced final treatment. Our intent was a minimally invasive reinforced composite/porcelain "Encore Bridge'." The composite superstructure would be bonded to the lingual surfaces of the centrals and canines, and porcelain veneers would be bonded to the composite pontics.
The Encore Bridge is itself unusual. It is composed of an 81% filled composite with a glass fiber reinforcement (Sculpture/FibreKo, Jeneric/Pentron, Inc). The framework has sufficient flexure to attain a Class I mobility. Flexure is important Class I mobility allows the bridge to move (flex) with the teeth. An all-porcelain bridge, for example, has no flexure, and when natural teeth flex, it is subject to fracture.
Tooth Preparation
Tooth preparation for the Encore Bridge is minimal. It is essentially a lingual surface preparation with a small proximal extension. The preparation (Figure ID) starts I mm from the most distal aspect of the lingual surface and extends into the proximal area.
Using a football-shaped diamond, my associate, Dr. Bijan Gohari, initiated the preparation with a 0.5-mm reduction of the lingual surface; 1 mm of natural tooth structure was maintained at the incisal, gingival, and distal areas. Slightly more reduction (0.8 mm to 1.0 mm) was needed at the proximal/lingual interface where the pontic connects to the abutment. This connector site is a critical area and must have a minimum clearance of I mm.
Finally, we used a 0.4-mm depth cutter to create a horizontal groove halfway between the incisal and cervical areas. This increased the retentive properties, strengthened the structure of the wings, and transferred stress to the long axis of the abutment teeth (Figure IE).
Bonding the Framework
For this case and the others in the article, a polyether (Permadyne, ESPE) was used to take the impressions. After shade determination, the impression and prescription were sent to daVinci Dental Studios (Woodland Hills, Calif), the designers and inventors of the Encore Bridge.
The returned framework was carefully seated and the veneers tried in. After verifying the fit, the framework was bonded into place with C&B-Metabond (ParkelI) (Figures IF and IG), after which the veneers were bonded onto the composite pontics with UltraBond (Den-Mat). Figure IH demonstrates our minimally invasive completed case.
CASE 2
David, age 50, presented with discomfort in the area between his mandibular right second molar and second premolar (Figure 2A). The mesiogingival area of the molar was engorged and had a pocket depth of 4 mm. David also felt his occlusion had changed during the past year. He was "no longer connecting properly" on his right side and wanted his missing tooth replaced.
A cursory exam and history revealed the source of the problem. Twenty years earlier, subsequent to endodontic failure, his first molar had been extracted. "I suffered a lot with that tooth," he said, "and for a long time didn't want anything done to my teeth."
His second molar had drifted mesially. The movement, now both mesial and gingival, was responsible for the tissue irritation and occlusal disharmony. The diminished space between the teeth made the placement of a normal-sized premolar pontic problematic. I treated the engorged area, and after the inflammation subsided, considered the regimen that would best suit David.
Treatment Options
What were my options?
1. A three-unit, full-coverage fixed bridge? I discounted this option quickly. Preparing two healthy teeth for porcelain-fused-to-metal crowns to fill the small pontic area would have been overkill. Furthermore, because of David's previous endodontic trauma, he dreaded even the remote possibility of a similar experience.
2. An implant? His small, closed-in pontic area might have caused an alignment problem, but more importantly, David's first molar had been missing for 20 years. The bone in that area had diminished considerably, and an implant would have necessitated bone replenishment. Knowing David, that was not an option.
3. A gold inlay bridge? At first thought, a very viable option., There would be little trauma to the teeth and no risk to the soft tissues. The problem was esthetics. David watched his diet and worked out regularly. He looked younger than 50. Gold was not an option.
Targis/Vectris
My choice was a material with which I have had considerable success: Targis/ Vectris (Ivoclar Williams). Targis/Vectris, a glass fiber-reinforced composite, has three essential components: silanized glass fibers, a BIS-GMA matrix, and an 85% ceramic-filled composite veneer The material has Class I flexure, exceptional fracture resistance, and esthetic properties comparable to metal-free ceramic restorations.
Tooth Preparation
The first step was proper tooth preparation. With some minor but important differences, the preparation is similar to that for gold inlays. There are no occlusal bevels with Targis/Vectris. The occlusal is a butt-joint finish. With gold inlays, walls are parallel. Retention depends as much on the tenso-frictional grip between the inlay and tooth structure as on the cement. With Targis/Vectris, the walls are divergent, flaring out about 10 degrees (Figure 2B). Retention is derived from the intimate bond between the material and etched tooth structure.
After shade determination, the impressions were sent to Jurim Dental Studio (Great Neck, NY) and were returned with the completed Targis/Vectris bridge (Figures 2C and 2D). The undersurface must not be etched, only roughened. If possible, sandblasting is best, otherwise, roughening the undersurface with a diamond is sufficient.
Variolink 11 System
Although the Variolink 11 (Ivoclar Vivadent) kit was not developed solely for Targis/Vectris (I use it to cement ceramic crowns), it contains everything necessary to complete our case.
After sandblasting, the inlay undersurfaces are silanated with Monobond-S (Ivoclar Vivadent). The teeth are now isolated, and the preparations are etched (Figure 2E). In this instance, the enamel was etched for 30 seconds and the dentin for 5 seconds. The etchant is thoroughly washed away and the preparations dried.
Syntac (Ivoclar Vivadent) dentin primer is applied for 15 seconds (Figure 2F), after which the teeth are dried. Syntac dentin adhesive is then applied for 10 seconds and dried (Figure 2G). Heliobond (Ivoclar Vivadent) is applied to both the preparations (Figure 2H) and the undersurface of the inlays (Figure 2I). It is not light cured.
We are now ready to cement. Variolink 11 cement offers a high- and low-viscosity catalyst and a reasonable range of base colors.
For this inlay bridge, the high-viscosity catalyst was my choice. The inlay wings were thick enough to withstand the cement thickness, and I preferred the feel of a more viscous cement as I inserted the bridge.
Jurim Dental Studio had almost perfectly matched the color, so a translucent base was selected to attain a neutral color. Equal amounts of base and catalyst were mixed, and the cement was placed onto the inlay wings (Figure 2J). The bridge was inserted into the preparations, and after the excess cement was removed, it was thoroughly and completely cured.
Final Result
The result (Figure 2K) fulfilled my expectations. The bridge is typical of minimally invasive dentistry. It required minimal tooth reduction and yielded little trauma to the teeth and surrounding soft tissues. From David's perspective, the mesiogingival drift was halted, and his occlusion returned to normal. He is free of pain and enjoys an esthetic, durable restoration.
CASE 3
Calvin, a 23-year-old rock singer, had been my patient for 11 years. His mandibular centrals were congenitally missing, and he absolutely revered his deciduous centrals. At 15, as he became more conscious of his appearance, I bonded them to make them look more like permanent teeth.
I constantly warned him that his deciduous teeth could not last indefinitely, and when he was 21 I took this x-ray (Figure 3A) to show him their limited bone support. Nevertheless, Calvin, an organic eater and naturalist, believed natural healing could salvage any disorder.
A Late Night Call
Late one Saturday night, my answering service called me frantically. Calvin, who was appearing that night in Birmingham, Alabama, told them while eating a sandwich he had pulled out both deciduous teeth. By the time I reached him, he had already seen a dentist.
"Doc," he said, "I lost my two beautiful teeth, and they want to drill down the good ones alongside them." It was difficult to talk to him, but I finally got him to drive to Tuscaloosa, where the late Dr. Dudley Davis, a fine dentist and cherished member of the American Society for Dental Aesthetics, practiced.
The Encore Bridge
Dr. Dudley came to the office that Sunday intending to make a provisional for Calvin, but it was to no avail. Calvin was bereft - he could not tolerate the possibility of an invasion of his teeth and was much too upset for any treatment. Dr. Dudley took a photo (Figure 3B) and called me. After listening to Calvin for 10 minutes, I calmed him by promising to replace the missing teeth benignly. That was 8 years ago; the Encore Bridge' was just being developed and I had no experience with it.
By the time Calvin returned to New York, his tissues had healed (Figure 3C), and I had learned the Encore preparation technique from Dan Materdomini of daVinci Studios. The preparation technique used for Calvin is similar to that shown in Case 1. Calvin's case, however, is best demonstrated by showing it step-by-step on the model and mouth simultaneously.
Step-by-Step
Figure 3D demonstrates the preparation (lingual with a horizontal groove in the center) on the model, and Figure 3E shows the preparation in the mouth.
Figure 3F shows a lingual view of the Encore Bridge framework try-in on the model, while Figure 3G shows a lingual view of the framework bonded to Calvin's teeth in the mouth.
Figure 3H shows the Encore Bridge' framework try-in from a facial view of the model, and Figure 3I shows the facial view of the framework bonded onto Calvin's teeth in the mouth.
A polyether impression of the permanently bonded bridge was then taken. Esthetics was very important to Calvin, so I had my in-office technician construct the laminates. Figure 3J demonstrates the model of this impression with the dies prepared for laminates. Figure 3K shows the laminates on the model, and Figure 3L is the completed case with the refined laminates bonded onto the composite pontics.
Rewarded With Results
I don't doubt that other alternatives could have been considered for this situation; however, Calvin might not have accepted any of them. Even leaving Calvin out of the mix, the Encore Bridge proved worthy.
The most treacherous teeth to prepare are lower anteriors. Sufficient reduction for ideal esthetics invariably raises the specter of devitalization. We avoided that pitfall.Today, implants are a viable alternative. But Calvin's case was 8 years ago. Presently, implants are an integral part of my practice; 8 years ago, I was not nearly as secure.In any event, just I week after he returned from Alabama, Calvin looked and functioned better than he had in years and, 8 years later still does today.Minimally invasive dentistry, as shown here, is not a panacea, but it is an important alternative to traditional dentistry and will be even more so in the future.
ACKNOWLEDGEMENT
The author would like to thank Ivoclar Williams/Vivadent for introducing Targis/Vectris and Variolink 11 to the dental profession, Adrian Jurim of Jurim Dental Studio for his invaluable technical support, and Dan Materdomini and Uri Yarovesky of davinci Dental Studios for their development of The Encore Bridge.