Titanium-Zirconium Implants: A Case Report: Immediate Provisional and Restoration Using a Small-Diameter System

INTRODUCTION
The original implant protocol required an undisturbed healing period of 6 months before exposure and loading.¹ Reducing this waiting period was believed to prevent osseointegration and cause implant failure.² The timing options for the placement of a provisional restoration and loading of dental implants have since expanded.^3-5 Currently, there is increased interest in immediate and accelerated loading protocols; that is, shortening the amount of time between implant placement and rehabilitation with a provisional implant-supported restoration. The fabrication of the definitive prosthesis is then usually delayed for 8 to 12 weeks.⁶ Success rates of these procedures appear to be similar to traditional ones.^7-10 In addition, this approach can reduce total treatment time, eliminate the need for an interim removable prosthesis, and improve overall efficiency.¹¹

A novel implant material has been recently introduced to increase the range of treatment options with small-diameter implants (Roxolid [Straumann USA]).¹² The material is an alloy of titanium and zirconium and is purported by the manufacturer to combine high tensile and fatigue strengths while providing faster osseointegration.¹² Although no clinical research on humans is available at this time to support these claims, the properties of titanium-zirconium alloys seem promising. In vitro studies have shown them to have significantly greater hardness than pure titanium or zirconium alone, with tensile strength tests showing a similar tendency.^13,14 It would be expected that biomaterials fabricated with these metals could withstand higher loads than either material alone. These alloys appear to have high biomedical potential due to the combination of biocompatibility¹⁵ and biomechanical properties.¹⁶ The availability of a small-diameter implant with increased elongation and fatigue strength compared to pure titanium would be mechanically advantageous when limited interdental space makes the placement of a regular diameter implant impractical. Faster osseointegration would also help shorten the time between placement of the provisional prosthesis and the definitive restoration, likely increasing the patient’s satisfaction.

This article illustrates the immediate provisional restoration of a small-diameter titanium-zirconium implant replacing a maxillary canine and the definitive restoration with a zirconia abutment and crown at 6 weeks.

CASE REPORT
Diagnosis and Treatment Planning
A 39-year old woman, with nonremarkable medical history, presented to a private practice requesting the aesthetic enhancement of the primary maxillary right canine (Figures 1a to 1c). The radiographic examination revealed an unfavorable crown-to-root ratio. The treatment options discussed by the treating prosthodontist included restoring the primary canine with a ceramic crown; or extracting the tooth and replacing it with a removable partial denture (RPD), a tooth-supported fixed partial denture, or an implant.

The first option was deemed unpredictable since the tooth had a small clinical crown and an unfavorable crown-to-root ratio that would be exacerbated by the anatomy of the new restoration. In addition, the patient did not want a removable prosthesis or a restoration that would involve the adjacent teeth. Therefore, a dental implant was considered the best option to provide a predictable and long-term aesthetic correction, thus addressing her chief complaint. After the treatment plan and clinical procedures were explained, the patient requested to minimize the time she would wear a provisional RPD, as well as the overall treatment time.

The permanent maxillary right canine had been removed more than 20 years earlier because of impaction. The primary canine presented with gingival recession and lack of keratinized tissue. The mesiodistal space was limited at 6.7 mm, compared to an average permanent maxillary canine width of 7.6 mm.¹⁷ The alveolar ridge was narrow buccolingually, with a buccal undercut. In addition, the patient wanted to avoid hard- and soft-tissue augmentation procedures to widen the residual ridge, further increasing the challenge of placing a regular diameter implant. For these reasons, a small-diameter (3.3 mm) implant was chosen for the site. The purported enhanced mechanical attributes of the titanium-zirconium implant alloy over titanium¹³ were expected to offset the apparent biomechanical compromise of using a small-diameter implant in the canine position. In addition, the narrow diameter would allow a safer placement along the canine eminence in close proximity to the premolar roots, maintaining a greater thickness of the buccal plate of bone needed to preserve gingival aesthetics. To avoid an aesthetic compromise due to the restricted mesiodistal space, the definitive restoration would be fabricated with a slight mesial overlap. A 2-week delayed implant placement approach was planned to allow keratinized gingiva to migrate over the socket. This gain in soft tissue would eliminate, or reduce, the need for gingival grafting or flap advancement over the exposed buccal socket gap. In addition, this would decrease variations in the final position of the gingival margin, while the minimal manipulation would facilitate synchronous soft-tissue maturation and osseointegration. This timing protocol addressed the patient’s goals of short treatment time without augmentation procedures, and followed basic biologic principles in healing.

Clinical Treatment Protocol
The initial phase of treatment involved the removal of the primary tooth, which was not ankylosed. At this time, the anatomy of the ridge was assessed clinically with direct visualization and an interim RPD was placed. The denture tooth (SR Phonares [Ivoclar Vivadent]) in the prosthesis was shaped as an ovate pontic to contour the gingiva while awaiting implant placement (Figure 2).

Figure 2. Removal of interim removable partial denture reveals gingival scalloping supported by ovate pontic.	Figure 3. Provisional abutment after preparation. Provisional shell to be relined with acrylic resin to fabricate screw-retained interim restoration.

Two weeks later, the small primary canine socket was covered with keratinized gingiva. The anatomy of the ridge was reassessed with sounding and palpation. The attending dentists believed this provided sufficient information for implant placement, making 3-dimensional imaging of the site unnecessary. A flapless osteotomy through the newly formed keratinized gingiva was made in Type III bone with cooled saline irrigation. This approach was preferred over raising a flap, which could result in gingival recession. A surgical stent was utilized to guide implant placement. The socket contours were followed to help preserve the original canine eminence. During the osteotomy, a buccal bone fenestration was created apical to the socket of the primary tooth. Its location and size were determined using depth gauges (Depth Gauge [Straumann USA]) and a curette (Lucas Surgical Curette [Hu-Friedy]). After completion of the drilling sequence, the fenestration was grafted through the osteotomy with a bovine bone graft replacement material (Bio-Oss [Ostheohealth]). A small-diameter, 3.3- x 12-mm implant (SLActive Roxolid Bone Level NC [Straumann USA]) was placed with primary stability using the handpiece set at 40 Ncm, and hand torqued to the final position. This implant is purported by the manufacturer to be made of an alloy of titanium and zirconium and has a hydrophilic, airborne-particle abraded and acid-etched surface. The implant-abutment connection is platform-switched. A healing cover (Straumann USA) was placed, and the patient returned on the same day to the prosthodontist’s office for immediate placement of a provisional restoration.

Immediately after implant placement, the healing cover was removed and a polymer provisional abutment (NC Temporary Abutment [Straumann USA]) was connected to the implant. The abutment was prepared intraorally using an electric handpiece (NuTorque Electric System [DentalEZ Group]) (Figure 3). To fabricate a provisional crown shell, a diagnostic cast was made, followed by a full-contour diagnostic wax-up of the maxillary right canine. An impression was taken of the wax-up with vinyl polysiloxane (Exafast [GC America]), and the maxillary canine was prepared on the diagnostic cast before the surgery. A small amount of acrylic resin (Jet Acrylic [Lang Dental]) was placed in the corresponding area inside the impression, then seated over the prepared diagnostic cast and allowed to polymerize. Cotton was placed inside the access hole of the abutment to avoid acrylic resin from blocking access to the retaining screw. Next, a thin mix of acrylic resin was placed inside the shell. Then, the shell was seated over the implant provisional abutment intraorally and allowed to polymerize to fabricate a screw-retained restoration. Copious water irrigation was used to prevent the heat of polymerization from affecting the implant. A small perforation was made with a 557 carbide bur (DENTSPLY Caulk) on the lingual side of the provisional restoration to remove the cotton and to gain access to the abutment screw. Occlusal contacts in maximum intercuspation, lateral, and protrusive excursions were eliminated, replicating the occlusal scheme of the deciduous canine. The provisional crown was adjusted only on the lingual side, thus avoiding any aesthetic compromise. The preoperative group function occlusal scheme on the right side and the incisal length of the incisors allowed premolars and anterior teeth to provide lateral and anterior guidance, respectively, until the insertion of the definitive restoration. The provisional crown was polished to a high shine with medium and fine grade flour of pumice (Whip Mix), and connected to the implant with an abutment screw torqued to 15 Ncm. The screw access hole was sealed with a light-polymerizing semi-rigid composite resin (Fermit [Ivoclar Vivadent]). The patient was recalled at one week. No complications were observed, and excellent peri-implant gingival health was evident (Figures 4a and 4b).

Approximately 4 weeks after implant placement, the provisional restoration was removed, a closed-tray impression post (NC Impression Post [Straumann USA]) was connected to the implant and an impression was made with heavy and medium body vinyl polysiloxane (Exafast [GC America]). Notes and photographs of the desired shade, contours, and surface texture were forwarded to the dental laboratory team. In the dental laboratory, the definitive cast was scanned (Etkon Es 1 Scanner [Straumann USA]) and specially devised software (Etkon visual 5.0 CAD/CAM Software [Straumann USA]) was used to design a custom-milled zirconia abutment (CAD/CAM abutment [Straumann USA]) with the desired emergence profile, optimal retention, resistance, and support. The abutment was then scanned to fabricate a zirconia coping (Lava CAD/CAM system [3M ESPE]), which was veneered with a compatible porcelain (Creation ZI-F [Jensen Industries]) to obtain proper anatomy, aesthetics, and function.
Six weeks after implant placement, the definitive restoration was inserted after all necessary adjustments were made. The zirconia abutment was torqued to 35 Ncm, the access hole sealed with gutta-percha (Autofit [SybronEndo]) and composite resin (Esthet·X [DENTSPLY Caulk]). Then, the zirconia crown was adhesively cemented with a resin cement (Multilink [Ivoclar Vivadent]) (Figures 5a to 5c).

The patient was recalled at one week, 2 months, and 6 months. The definitive restoration shared a group function occlusal scheme with the maxillary premolars, and displayed excellent gingival health and natural aesthetics (Figures 6a to 6c).

DISCUSSION
To allow for the immediate placement of a provisional restoration or immediate loading, primary stability is necessary.⁵ This is usually linked to an implant insertion torque greater than 35 Ncm, believed to keep micromovement below 150 µm.¹⁸ Greater mobility is assumed to compromise the healing of the bone and its intergrowth into the implant. However, no clinical trial to date has compared the effect of different levels of stability on implant survival.³ Some authors advise a soft diet during the healing stages, and the use of implants with a platform-switched connection.^4,10,19 The latter refers to an interface between the abutment and the implant that occupies a medial position between a wide implant platform and a comparatively narrow abutment.²⁰ This is purported to help preserve crestal bone levels and to provide better support for the soft tissue. These recommendations were followed for the patient treatment described herein.

Accelerated protocols require that special attention be made to the prosthesis design. In single immediate implant-supported provisional prosthesis, the implant is theoretically protected from overload by eliminating occlusal contact on the interim restoration, although functional forces can be applied during mastication via the bolus.⁵ In addition, a screw-retained provisional crown eliminates the possibility of inadequate cement removal, which could result in bone loss.

The implant used for this patient consisted of an alloy of titanium with 13% to 17% zirconium (Roxolid [Straumann USA]). This material has better elongation and fatigue strength than pure titanium,¹³ potentially making it useful in sites with high mechanical stress.¹² This implant could also be helpful in areas with limited interdental space where a wider implant would be preferable but impractical, or in situations where augmentation procedures are infeasible. It would seem valuable to compare the properties of this material to other titanium alloys used as alternatives to commercially pure titanium. In addition, the manufacturer purports that this implant achieves enhances osseointegration. Although the scientific validity of this claim remains unclear, a recent animal study showed similar or improved bone tissue responses for this implant at 4 weeks compared to the commercially pure titanium control.¹² However, as stated earlier, there are no human studies available at this time.

From a practical perspective, the small-diameter implant used here decreased the need for additional procedures such as soft-tissue grafting to bulk up the highly scalloped thin gingiva and hard tissue grafting to support the soft tissues. While the implant diameter was only 0.7 mm narrower than a conventional 4.0 mm implant, the authors believe that this difference was important. A wider implant would have likely resulted in a larger fenestration than the one created during the osteotomy, with reduction of primary stability, making the immediate insertion of a provisional restoration questionable. A wider implant would have also obliterated the socket with possible buccal crestal bone dehiscence, putting at risk the support for the soft tissue and compromising aesthetics. Primary stability allowed for immediate insertion of the provisional restoration despite the reduced bone volume, thus helping maintain the peri-implant gingival contours. The aesthetic benefits of this approach are evidenced by the rapid and favorable soft-tissue response obtained. Other advantages encountered with this accelerated approach include decreased cost for the clinicians and discomfort to the patient due to the reduced number of procedures and appointments. The insertion of the definitive restoration at 6 weeks allowed the patient to resume normal function earlier, providing additional comfort and abbreviating total treatment time.

SUMMARY
This article presented the immediate provisional and definitive restoration at 6 weeks of a novel small-diameter titanium-zirconium implant, with a 6-month follow up. The manufacturer purports that the implant described herein has superior mechanical and biological properties that could expand treatment options for small-diameter implants, thus benefiting accelerated protocols by further shortening the total treatment time. Human studies are needed to validate these claims.

Acknowledgment
All images except for Figure 2 in this article are courtesy of Straumann USA, LLC, its parents, affiliates or subsidiaries. Straumann USA LLC, all rights reserved. Starget. 2010;(3):30-33.

References

1. Albrektsson T, Brånemark PI, Hansson HA, et al. Osseointegrated titanium implants. Requirements for ensuring a long-lasting, direct bone-to-implant anchorage in man. Acta Orthop Scand. 1981;52:155-170.
2. Brunski JB. Biomechanical factors affecting the bone-dental implant interface. Clin Mater. 1992;10:153-201.
3. Roccuzzo M, Aglietta M, Cordaro L. Implant loading protocols for partially edentulous maxillary posterior sites. Int J Oral Maxillofac Implants. 2009;24(suppl):147-157.
4. Cornelini R, Cangini F, Covani U, et al. Immediate restoration of implants placed into fresh extraction sockets for single-tooth replacement: a prospective clinical study. Int J Periodontics Restorative Dent. 2005;25:439-447.
5. Esposito M, Grusovin MG, Achille H, et al. Interventions for replacing missing teeth: different times for loading dental implants. Cochrane Database Syst Rev. 2009;(1):CD003878.
6. Romanos GE, Nentwig GH. Immediate functional loading in the maxilla using implants with platform switching: five-year results. Int J Oral Maxillofac Implants. 2009;24:1106-1112.
7. Schnitman PA, Wöhrle PS, Rubenstein JE, et al. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implants. 1997;12:495-503.
8. Calandriello R, Tomatis M, Rangert B. Immediate functional loading of Brånemark System implants with enhanced initial stability: a prospective 1- to 2-year clinical and radiographic study. Clin Implant Dent Relat Res. 2003;5(suppl 1):10-20.
9. Balshi TJ, Wolfinger GJ. Immediate loading of dental implants in the edentulous maxilla: case study of a unique protocol. Int J Periodontics Restorative Dent. 2003;23:37-45.
10. Attard NJ, Zarb GA. Immediate and early implant loading protocols: a literature review of clinical studies. J Prosthet Dent. 2005;94:242-258.
11. Polack MA, Mahn DH. The use of a customized prefabricated zirconia abutment and zirconia crown in the restoration of an immediately provisionalized implant in the esthetic zone. Compend Contin Educ Dent. 2008;29:358-362.
12. Gottlow J, Dard M, Kjellson F, et al. Evaluation of a new titanium-zirconium dental implant: a biomechanical and histological comparative study in the mini pig. Clin Implant Dent Relat Res. 2010 Jun 25. [Epub ahead of print]
13. Kobayashi E, Matsumoto S, Doi H, et al. Mechanical properties of the binary titanium-zirconium alloys and their potential for biomedical materials. J Biomed Mater Res. 1995;29:943-950.
14. Okuno O, Shimizu A, Miura I. Fundamental study on titanium alloys for dental casting. J Jpn Soc Dent Mater Devices. 1985;4:408-715.
15. Albrektsson T, Hansson HA, Ivarsson B. Interface analysis of titanium and zirconium bone implants. Biomaterials. 1985;6:97-101.
16. Wen CE, Xu W, Hu WY, et al. Hydroxyapatite/titania sol-gel coatings on titanium-zirconium alloy for biomedical applications. Acta Biomater. 2007;3:403-410.
17. Scheid RC, Woelfel JB. Woelfel’s Dental Anatomy: Its Relevance to Dentistry. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2007:174.
18. Szmukler-Moncler S, Salama H, Reingewirtz Y, et al. Timing of loading and effect of micromotion on bone-dental implant interface: review of experimental literature. J Biomed Mater Res. 1998;43:192-203.
19. Covani U, Cornelini R, Barone A. Bucco-lingual bone remodeling around implants placed into immediate extraction sockets: a case series. J Periodontol. 2003;74:268-273.
20. Lazzara RJ, Porter SS. Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels. Int J Periodontics Restorative Dent. 2006;26:9-17.

Dr. Polack earned his dental degree in 1995 and his specialty training in prosthodontics and a master of science degree from the University of Minnesota in 2000. He maintains a full-time private practice in Gainesville, Va. In addition, between 2002 and 2004, he was a guest researcher at the Ceramics Division of the National Institute of Standards and Technology where he was involved in several research projects on dental porcelain. Dr. Polack has published more than 30 abstracts and papers on implants, aesthetics, and dental materials in various scientific journals, and lectures internationally, including presentations at the Academy of Osseointegration, American Academy of Periodontology, and American Academy of Implant Dentistry. He is a member of the Academy of Osseointegration, American College of Proshodontics, ADA, and is a founding member of the Gainesville Study Club. Dr. Polack can be reached at (703) 753-8753 or at mpolack@comcast.net.

Disclosure: Dr. Polack reports no disclosures.

Dr. Arzadon, an oral, maxillofacial, and facial cosmetic surgeon, graduated summa cum laude from the University of Maryland School of Dentistry, and received his medical degree from the University of Connecticut School of Medicine. He completed his internship in general surgery and residency in oral and maxillofacial surgery from the University of Connecticut Health Center, where he completed his training in 1996. He is board certified by the American Board of Oral and Maxillofacial Surgery, Fellow of the American Association of Oral and Maxillofacial Surgeons, Fellow of the American Academy of Cosmetic Surgeons, and member of both the ADA and the AMA. He is licensed in both medicine and dentistry, and certified in both oral and maxillofacial surgery and cosmetic surgery. He can be reached at (703) 753-5268 or at jarzadon@novasurgicalarts.com.

Disclosure: Dr. Arzadon reports no disclosures.