CLINICAL PRACTICE
CASE REPORT |
JADA Continuing Education
An alternative method for restoring single-tooth implants
BARRY F. McARDLE, D.M.D. and
LOUIS F. CLARIZIO, D.D.S.
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ABSTRACT
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Background. Having laboratory technicians prepare soft-tissue casts and implant abutments with or without concomitant removable temporary prostheses during the restorative phase of single-tooth replacement is an accepted practice. It can, however, result in functional and esthetic intraoral discrepancies.
Case Description. Single-tooth implants can be restored with crowns (like those for natural teeth) fabricated at a dental laboratory on casts obtained from final impressions of prepared implant abutments. In the case reported, the restorative dentist restored the patient’s single-tooth implant after taking a transfer impression. He constructed a cast simulating the peri-implant soft tissue with final impression material and prepared the abutment on this model. His dental assistant then fabricated a fixed provisional restoration on the prepared abutment. At the patient’s next visit, the dentist torqued the prepared abutment onto the implant, took a final impression and inserted the provisional restoration. A crown was made conventionally at the dental laboratory and cemented in place at the following visit.
Clinical Implications. This alternative method for restoring single-tooth implants enhances esthetics by more accurately simulating marginal gingival architecture. It also improves function by preloading the implant through fixed temporization after the dentist, rather than the laboratory technician, prepares the abutment to the dentist’s preferred contours.
The viability of a single-tooth implant–supported crown as a treatment option for partial edentulism is well-documented.1 The most commonly accepted method for crowning a single-tooth implant involves intraorally attaching a transfer pin to the implant; taking a final and an opposing impression, as well as an interocclusal registration; and pouring the opposing impression in stone. These clinical records are sent to a dental laboratory where a permanent crown is fabricated. At the laboratory, a technician fabricates a soft-tissue cast because trimming the working cast in the laboratory eliminates soft-tissue details that are critical to properly contouring the final restoration.2 There are, however, steps involved (for example, trimming the stone model, adding the soft-tissue material and seating the prefabricated implant abutment) between clinically taking a standard transfer impression and producing a soft-tissue cast in the laboratory.3 They are technique-sensitive and have the potential to alter the soft-tissue details, which result in discrepancies between the cast and intraoral conditions.4 Finally, the technician prepares the implant abutment on this soft-tissue cast for the permanent crown.
The described method gives the dentist more control over the implant abutment preparation when using prefabricated abutments and preloads the implant through fixed temporization.
There is an alternative to this method that gives the dentist more control over the implant abutment preparation when using prefabricated abutments and preloads the implant through fixed temporization. This method also provides for a greater degree of peri-implant soft-tissue conditioning, which enhances the esthetic zone before the final restoration is inserted.
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CASE REPORT
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In 1999, the restorative dentist (B.F.M.) diagnosed a 45-year-old woman with an unrestorable root fracture at tooth no. 13 that had been caused by accidental trauma. She had no significant periodontal or medical complications. After the dentist determined that the tooth had to be extracted, he discussed with her all treatment options—partial denture use, fixed bridgework and implant placement—as well as the option of no treatment at all.
The patient chose implant placement because she did not want to wear a removable appliance or eliminate the crown on tooth no. 12, which placing bridgework would have required. The dentist referred her to the oral and maxillofacial surgeon (L.F.C.) who placed the implant.
After the oral and maxillofacial surgeon confirmed that the implant had osseointegrated, the dentist obtained all of the clinical records needed to proceed with crown placement at the first restorative visit. Directly after this visit, he connected the implant analog to the transfer pin in the final impression (Figure 1
). He then covered the exposed surface of the transfer pin in the final impression with more impression material (Figure 2). He was careful not to cover any portion of the implant analog or fill in any of the adjacent teeth in the laboratory impression with this additional impression material, as it could compromise the stability of the analog in the cast or the inter-proximal contacts of the provisional restoration fabricated on the cast. His dental assistant then poured the impression—known as a laboratory impression in this method—in stone in his office laboratory.
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Figure 2. The transfer pin is completely covered in additional impression material, which does not engage the implant analog.
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When the transfer pin was removed from the cast—known as a laboratory cast in this method—the peri-implant tissue had been reproduced accurately in the final impression material (Figure 3). Also, the gingival architecture recorded in this cast essentially replicated the cuffing of peri-implant tissues produced by the healing cap fixture on the exposed implant and the presence of the transfer pin in the final impression. After the dental assistant articulated the laboratory cast with its opposing cast and connected the implant abutment to the implant analog, the dentist prepared the abutment as if it were a natural tooth. He was careful not to disturb the impression material simulating soft tissue around the preparation (Figure 4).
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Figure 3. Only the peri-implant soft tissue on the cast is represented in impression material, while the adjacent teeth remain in stone.
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Figure 4. The prefabricated implant abutment is prepared by the dentist to his or her preferred contours.
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Once the implant abutment had been prepared to the dentist’s preferred contours, the dental assistant prepared a fixed provisional crown. She thoroughly coated the prepared implant abutment and the impression material immediately adjacent to it, including that representing the peri-implant crevicular space, with a separating medium. She obturated the tool access at the top of the implant abutment before fabricating the provisional crown just as the dentist would for the transfer pin when taking a laboratory impression. She then filled the peri-implant crevicular space to the height of the peri-implant tissue crest in the impression material with slightly diluted liquid acrylic resin before she situated a prefabricated provisional crown filled with more viscous acrylic resin for best possible tissue adaptation. She made this adaptation to maintain peri-implant tissue architecture for a more esthetic emergence profile and so that tissue rebound would not make final restoration seating difficult for the dentist or uncomfortable for the patient. The dentist checked the margins and contacts of the provisional crown after the dental assistant fabricated it on the articulated casts (Figure 5).
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Figure 5. A preformed polycarboxylate provisional crown lined with acrylic is customized on the cast in light occlusion, which supports and enhances the peri-implant soft tissue, while providing appropriate preloading for the implant itself.
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Before the patient’s next visit, the dental assistant removed the implant abutment and provisional restoration from the implant analog in the cast and sterilized them. At this next visit, the dentist attached the prepared implant abutment to the implant intraorally using a torque wrench. He then took the final impression, using the double-arch technique as he usually does for a natural tooth preparation before provisional crown insertion. He then sent the final impression to the crown and bridge laboratory that fabricated the final restoration for the implant as if it was a natural tooth. The dentist cemented the final restoration at the next visit (Figure 6).
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Figure 6. The final restoration in place with a natural emergence profile and peri-implant soft-tissue contour.
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DISCUSSION
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There are several advantages to using our method to restore single-tooth implants. Extraorally preparing the implant abutment virtually eliminates the possibility of sanguineous contamination in the final impression phase of crown placement. Since the dentist, rather than the oral and maxillofacial surgeon or laboratory technician, prepares the implant abutment, the preparation form he or she prefers is fully realized. Ultimately, prosthetics are the province of general dentists or prosthodontists, and those clinicians should be responsible for the restorative phase of implant treatment.5
Using the proper impression materials, such as polyvinylsiloxane and polyethers, with this method will generate an effectively accurate cast6 that, in our experience, is less likely than a cast from an outside laboratory to harbor any divergence from intraoral conditions.
Taking a final impression of the implant abutment after it has been torqued in place intraorally eliminates the possibility of any microdiscrepancies that may occur between its stance on the implant analog in the laboratory and its connection to the implant intraorally. While this is-not a factor in the accuracy of the provisional restoration (in which a transfer impression is involved), it does foster the likelihood that the fit and contacts of the final crown will be correct.
Although this has been an extremely rare occurrence in our experience, any variance that may occur between soft-tissue contours in the mouth and those on the master cast can be compensated for by simply removing the prepared abutment from the implant in the mouth, reseating it on the cast and altering the abutment preparation to compensate. The previously fabricated provisional crown then can be adjusted to match any alteration. Using a triple tray is an option for the final impression, though usually not for the laboratory impression, as the height of most transfer pins precludes inter-cuspation when they are connected to implants intraorally.
Placing the implant abutment and preparing it intraorally may subject the peri-implant bone to dangerous heat levels.
The provisional phase of treatment is an important, yet often underemphasized, aspect of implant dentistry.7 Having a fixed provisional restoration in place for a period before the final restoration is placed provides suitable preloading8 to augment osseointegration and, if fashioned correctly, will promote proper peri-implant tissue contours.9 In the case of anterior teeth in which a removable provisional prosthesis often is employed during surgical preparation of the implant site, use of the ovate pontic design also may enhance peri-implant soft-tissue contours. A system is available that can create a custom healing abutment to serve the same purposes, but its use cost significantly more than our method does.10 The additional technician time needed with the other system to fabricate these custom abutment components, not the price of the component materials themselves, composes most of the additional cost. Tailoring prefabricated abutments using our technique is less costly and less time-consuming than using custom abutments,11 and we believe it is preferable.
Although it may seem tempting, placing the implant abutment and preparing it intraorally may subject the peri-implant bone to dangerous heat levels. The kind of heat that can be generated during intraoral implant abutment preparation has been shown to compromise the alveolus in implant placement when inadequate irrigation is used.12 In our experience, even using copious irrigation during implant abutment preparation in the mouth may not cool the underlying bone sufficiently to protect it.
Using this technique, dentists’ nonchairside time commitment to cases can be minimized through the proper use of auxiliary personnel. An appropriately trained dental assistant can process laboratory impressions, articulate casts with interocclusal registration and fabricate provisional crowns on an articulator. The assistant can fabricate provisional crowns on implant abutments using the method the dentist prefers.
We use a prefabricated provisional crown (poly-carboxylate for anterior teeth and premolars or stainless steel for molars) lined with acrylic resin, or, for patients who have removable temporary prostheses, we use a stent made from the prosthesis to fabricate a custom provisional crown in acrylic resin. If the dentist does not use the double-arch technique and will be sending that cast out with the case, coating the relevant occlusal contacts on the opposing cast with clear nail polish before provisional fabrication can help negate any abrasion that might occur during that process.
After cases have been completed, auxiliary personnel can recover implant analogs and transfer pins for sterilization and reuse in subsequent cases. This can reduce overhead and build up a readily available inventory of implant components in the office as more cases are completed.
Having auxiliary personnel perform the previously mentioned tasks will leave covering the exposed surface of the transfer pin in the final impression with more impression material and preparing the abutment as the dentist’s only laboratory responsibilities besides verifying the auxiliary personnel’s performance.
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CONCLUSION
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This method does require a greater time commitment from the dentist. However, despite the extensive means that dentists use to relay intraoral conditions to the laboratory through clinical records in traditional implant restoration procedures,13 inconsistencies do occur. We believe the more predictable results (both functionally and esthetically) we have been able to achieve using this method are well worth the additional work involved.
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Dr. McArdle is a general dentist in private practice, 118 Maplewood Ave., The Captain Moses House, Suite B-7, Portsmouth, N.H. 03801, e-mail "drmcardle{at}mcardledmd.com". Address reprint requests to Dr. McArdle.
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Dr. Clarizio is an oral and maxillofacial surgeon with private practices in Portsmouth, N.H., and Somersworth, N.H.
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FOOTNOTES
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The authors thank Dr. Craig Leffingwell for his invaluable assistance with the preparation of this manuscript.
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REFERENCES
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- Saba S. Soft tissue transfer models: the patient-dentist-laboratory connection. J Can Dent Assoc 1998;64(8):584–5.
- Wilkinson MR, Woody RD. A soft tissue simulated cast for implant prosthesis. J Prosthet Dent 1992;68(3):553–4.[Medline]
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- Beyak BL, Chee WW. Compatibility of elastomeric impression materials for use as soft tissue casts. J Prosthet Dent 1996;76(5):510–4.[Medline]
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- Kerstein RB, Castellucci F, Osorio J. Ideal gingival form with computer-generated permanent healing abutments. Compend Contin Educ Dent 2000;21(10):793–801.
- Giglio GD. Abutment selection in implant-supported fixed prosthodontics. Int J Periodontics Restorative Dent 1999;19(3):233–41.[Medline]
- Haider R, Watzek G, Plenk H. Effects of drill cooling and bone structure on IMZ primary implant fixation. Int J Oral Maxillofac Implants 1993;8(1):83–91.[Medline]
- Derbabian K, Marzola R, Arcidiacono A. The science of communicating the art of dentistry. J Calif Dent Assoc 1998;26(2):101–6.
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