April 3, 2019
by David Hornbrook, DDS
The prospect of replacing an anterior tooth with an implant-supported restoration presents both esthetic and clinical challenges for dentists.1,2 These include – but are not limited to – ensuring an ideal shade match among adjacent natural teeth or all-ceramic restorations (e.g., veneers or crowns) and the implant restoration, which is greatly affected by the optical characteristics of the abutment.3-5 Additionally, maintaining the health and stability of underlying periodontal structures (e.g., bone and gingival tissues) is a significant concern, particularly when cement-retained restorations and abutments are placed.6
Historically, esthetic all-ceramic restorations supported by metal abutments allow show-through of the underlying structure, thereby requiring a higher level of opacity in order to mask the dark color of the abutment, resulting in compromises to the restoration’s vital appearance.2,5 Esthetics can be further compromised when a dark grey colour emanates from the metal abutment through the gingival tissue, which is particularly problematic in patients with a thin biotype.2,5 Clinically, cement-retained implant restorations are prone to residual cement along the implant margins, which has been shown to be a contributing factor to peri-implantitis and subsequent implant failure.6
Fortunately, the availability of pressable lithium disilicate enables the fabrication and placement of a “hybrid” implant abutment (or “H” abutment) with the requisite esthetic and physical characteristics for anterior implant-supported restorations.2,5,7 An ideal substructure for translucent and life-like all-ceramic restorations, an “H” implant abutment is comprised of a pressed lithium disilicate suprastructure that is bonded extraorally to a machined titanium (Ti) base (i.e., platform and cylindrical sleeve) using resin-based cement and a metal primer.2,5
As a result, the “H” abutment resolves the esthetic and clinical challenges that can plaque anterior implant restorations. First, because a pressed ceramic overlying restoration can be placed with supragingival margins, the cement-abutment interface falls several millimeters above the implant itself, enabling proficient removal of excess cement and easy polishing to help respect the gingival and periodontal tissues. Additionally, because the screw is ultimately torqued against the titanium platform at the base of the abutment – and not against ceramic (i.e., as with zirconium abutments) – the challenges associated with fractures of the abutment and/or at the implant/abutment interface are eliminated.2,5,8,9
A female patient presented with an unaesthetic smile that she desired to improve (Fig. 1) and a pre-existing porcelain-fused-to-metal (PFM) full-coverage crown restoration on her maxillary left central incisor (i.e., tooth #9) (Fig. 2). She had previously undergone root canal therapy, followed by an apicoectomy, on tooth #9. Due to the vertical root fracture (Fig. 3), the treating endodontist advised that the tooth be extracted and an implant placed.
Following a thorough clinical and esthetic evaluation, the patient’s periodontal health and surrounding teeth were found to be within acceptable and normal limits, and a comprehensive treatment plan was presented to and accepted by the patient. Given the complex nature of this anterior esthetic case, the treatment plan involved:
1. Redesigning the smile of her maxillary anterior arch (i.e., teeth #7 through #10);
2. Extracting tooth #9, placing an implant and bone graft, and allowing four months for healing and osseointegration;
3. Placing a long-term laboratory-fabricated PMMA provisional bridge on the maxillary incisors (Fig. 4); and
4. Preparing the remaining teeth for lithium disilicate (e.g., IPS e.max, Ivoclar Vivadent) restorations and provisionalizing them using a Shrink-to-Fit technique.
Custom “H” Abutment Fabrication
After four months of healing, the provisional restorations were removed (Fig. 5) using a hemostat, after which the preparations were cleaned and evaluated for complete removal of provisional cement. A custom impression transfer post created using flowable resin (Fig. 6) was placed at #9, and an impression was taken to transfer the desired soft tissue contours to the laboratory for use when creating the custom abutment (Fig. 7).
At the laboratory, the custom implant “H” abutment (i.e., lithium disilicate cemented to a titanium base) was designed by using a Ti-base abutment, waxing the ideal abutment contours over the Ti-base, and investing and pressing a lithium disilicate material (e.g., IPS e.max Press, Ivoclar Vivadent). The custom abutment was then custom-stained (Fig. 8). To enhance the surface area for bonding, the Ti-base was sandblasted (Figs. 9 & 10), after which a metal-primer was applied to enhance bonding of the custom abutment to the Ti-base (Fig. 11). Then, the internal aspect of the custom lithium disilicate abutment was etched with 5% hydrofluoric acid (Fig. 12), rinsed, and dried. A silane coupling agent was then applied to the internal surface an allowed to sit for 60 seconds (Fig. 13).
A dual-cure resin cement was placed inside the custom lithium disilicate abutment, after which it was seated onto the Ti-base (Fig. 14). Excess cement was removed, and the abutment and base were then light polymerized (Fig. 15).
Abutment Placement & Provisionalization
In addition to the “H” abutment, the laboratory also fabricated new individual PMMA provisionals for the custom abutment and three remaining incisors. The original provisionals were removed, the preparations cleaned, and the custom “H” abutment placed at #9. The new PMMA provisionals were also placed using a resin-based provisional cement.
The final tissue contours around the abutment and individual provisionals were evaluated and approved after four weeks. The provisionals were removed, and definitive master impressions were taken of the abutment and remaining incisor preparations and forwarded to the laboratory for fabrication of the definitive lithium disilicate restorations. The individual PMMA restorations were then re-cemented onto the preparations.
Delivery & Cementation of Final Restorations
When the definitive restorations were returned from the laboratory, the provisionals were removed (Figs. 16 & 17). The lithium disilicate restorations were then evaluated on the master model and dies to confirm accuracy of marginal fit, contour, anatomy, incisal edge characteristics, and shade (Figs. 18 & 20). Each restoration was then evaluated individually for complete seating intraorally (Fig. 21), after which all four restorations were tried in without try-in gel to verify complete seating and proximal contacts (Figs. 22 & 23).
In order to evaluate the shade intraorally, a water soluble, glycerin-based try-in gel was used. The restorations for #7 and #8 were evaluated using a translucent shade (Fig. 24), while #9 and #10 were evaluated using a warmer shade (e.g., shade A5) (Fig. 25). Due to the translucency of the lithium disilicate material used to fabricate the restorations, the shade could be altered slightly using different values of resin cement. After placement, excess try-in gel was removed using a light water spray (Fig. 26), after which the shade was evaluated (Fig. 27). It was determined that the patient preferred the translucent shade (i.e., #7 and #8), rather than the warmer shade (i.e., #9 and #10).
Therefore, the decision was made to try-in the restorations on the left side (i.e., #9 and #10) using a higher value try-in gel to determine what effect that might have on the overall shade. These restorations were carefully removed, the higher value gel applied (Fig. 28), and the restorations reseated intraorally. A slightly higher value at the gingival third on the left side was observed when the lighter try-in gel was used (Fig. 29). However, the patient again preferred the translucent cement. At this point, the restorations for #9 and #10 were again removed and rinsed, and the translucent shaded try-in gel was placed into these restorations, which were then reseated intraorally. To verify the shade, the seated restoration shade was compared to the shade tab chosen at the preparation appointment (Fig. 30).
The restorations were then removed, excess try-in gel rinsed, and a phosphoric acid gel used to thoroughly clean and acidify the internal aspects, which were then rinsed and dried thoroughly (Fig. 31). Then, a silane coupling agent (e.g., Monobond Plus) was applied to the internal surfaces to enhance adhesion between the resin cement and the ceramic (Fig. 32), allowed to sit undisturbed for 60 seconds, and then air dried thoroughly. Next, a light-cure resin cement (e.g., Variolink Esthetic) that matched the Translucent try-in gel was placed onto the internal surfaces of the restorations, after which they were placed in a light-protective container.
Using the “total etch” technique, the preparations – including the custom “H” lithium disilicate abutment – were etched with 35% phosphoric acid (Fig. 33). After 15 seconds, the etch was rinsed away, and the preparations allowed to remain moist. Excess moisture was removed by waving high-speed evacuation over the tooth and abutment surfaces, with care taken not to desiccate them (Fig. 34). Multiple coats of a universal dental adhesive were then dispensed and applied to the preparations and abutment (Fig. 35), after which the adhesive solvent was evaporated using a moisture-free air/water syringe (Fig. 36). The adhesive was then light polymerized for 10 seconds per preparation (Fig. 37).
All four restorations were placed on the preparations and, using a Benda Brush, seated completely in an upward/inward direction. Each restoration was then “tack” cured into place for 1 second per restoration using a 2.0-mm diameter light guide (Fig. 38). After each restoration was tacked, all margins were “wave” cured for a total of five seconds using a 13.0-mm light guide at approximately 1 inch away from the teeth (Fig. 39). Excess cement was then gently peeled away from the margins using a Bard Parker #12 Blade (Fig. 40), after which dental floss was used interproximally to gently remove additional excess cement (Fig. 41). Then, prior to final light polymerization, an oxygen inhibiting medium (e.g., Liquid Strip) was placed at all margins (Fig. 42).
Final polymerization of the resin cement was achieved using two curing lights for one minute per tooth (Fig. 43), after which excess oxygen inhibition gel was rinsed away, and any excess cement on the ceramic removed using a Bard Parker #15 Blade (Fig. 44). Gingival interproximal margins were then polished using a narrow finishing strip (Fig. 45), and the occlusion was evaluated and adjusted using polishing diamonds.
The patient’s immediate postoperative photographs revealed excellent esthetic results (Fig. 46). The patient was re-appointed in seven days for further evaluation and final photographs.
The ability to fabricate and place an “H” abutment when anterior teeth are replaced with an implant-supported restoration enables clinicians to enhance the predictability of the esthetic and functional outcomes associated with these treatments. The “H” abutments readily integrate into a natural smile appearance based on their dentin color and ability to be customized with staining near the gingival margins. Simultaneously, “H” abutments can also be custom designed in terms of their shape and contours to accommodate specific case requirements. Additionally, the supragingival nature of margin location and extraoral bonding when “H” abutments are used contribute to periodontal health by reducing the likelihood of residual cement around the margins that could otherwise contribute to peri-implantitis.
Oral Health welcomes this original article.
Acknowledgement: The author would like to thank Phil Nebeker from Utah Valley Dental Laboratory (Lindon, Utah) for his artistry in fabricating the all-ceramic restorations and “H” abutment” presented in this article.
About The Author
Dr. David Hornbrook graduated from UCLA School of Dentistry and has been in private practice in San Diego, California for 30 years. He is a pioneer in Live-patient, esthetic dental treatment programs and founder and director of LVI, PAC~live, the HornbrookGroup, and Clinical mastery. He has lectured internationally on all facets of dentistry. He was editor of the Journal of the AACD and is an Accredited and Fellow of the ACCD, Fellow and Diplomate of the American Society of Dental Aesthetics, a Fellow of the Academy of Comprehensive Esthetics, and honored with Lifetime achievement awards by the Crown Council and the Academy of Comprehensive Esthetics. He has developed materials, techniques, and consulted many manufacturers and is Clinical Director of Education at Utah Valley Dental Lab.