Design Enhances Soft-Tissue Architecture

Osseointegration of dental implants has had a highly predictable outcome in the process of replacing missing teeth for the adult dentition.¹ It would seem that many assessments of dental implants define the success of such procedures in functional but not necessarily aesthetic terms.² The architecture of peri-implant tissues, both soft and hard, is of critical importance to the aesthetic outcome.³ Although the author has attempted many methods (such as the ovate pontic technique⁴) to train the peri-implant tissue for more appealing cosmetics, experience has shown that implant design is a far more important consideration in this area for the long term. This article will describe how implant design, specifically as it relates to the abutment/implant interface (“the connection”), has the most profound influence on peri-implant tissue architecture and thus the aesthetics of this framework.

INTERNAL HEX VERSUS MORSE TAPER
The internal hex configuration has been the most common abutment/implant connection for some time because of its stability in physically retaining the abutment on an implant.⁵ However, on a micro level, the seal of that connection is just as important a factor when it comes to the development and preservation of peri-implant tissues because the presence or absence of bacterial infestation within the connection has a direct effect on those tissues.⁶ Another type of connection (Figure 1), the true Morse taper (invented in 1864 by Stephen A. Morse [Figure 2]), provides a stability of retaining an implant abutment equal to that of the internal hex with a seal against bacterial colonization that is virtually hermetic.⁷ This connection is also so secure as to be completely anti-rotational without the segmented surfaces of the internal hex.⁸ The Ankylos system (Dentsply Implants) did add an “index” to its abutments in the North American market for dentists accustomed to the internal hex, but the Morse taper’s exceptional seal is retained as that index is positioned at the apical portion of the abutment, away from the connection’s outer surface. As an example of the physical engineering capabilities of the Morse taper, note that it is commonly used to affix jet engines to the wings of the planes they power (Figure 3).

Figure 1. The Morse taper connection of the Ankylos system (Dentsply Implants).	Figure 2. Stephen A. Morse (1828–1898), inventor of the true Morse taper.
Figure 3. The Morse taper connection as used to mount jet engines onto their wing assemblies.	Figure 4. A graphic representation of bacterial toxin effluence onto peri-implant tissues from colonization within the abutment/implant interface. (Image copyright Dr. Paul Weigl, University of Goethe, Frankfurt am Mein, Germany. Used with permission.)

I have been using a true Morse taper connection system (Ankylos) now for the last 6 of the 25-plus years that I have been restoring dental implants, obtaining clinical results that are far superior to any other system previously used in my office. As noted above, the reason for this is that the abutment/implant interface with this system is so stable that no significant microbial invasion of the connection occurs, thus preventing the effluence of bacterial toxins within the surrounding peri-implant tissues. A graphic representation of the effects of bacterial toxins on peri-implant tissues is shown here (Figures 4 and 5). When spared exposure to these toxins, peri-implant osseous tissues are not only maintained, but can actually grow coronally. This provides the ideal scaffolding for peri-implant soft tissues that then comprise the ultimate pink aesthetics framework about implant restorations.

A Previously Documented Internal Hex Case
The internal hex systems that I have used in the past (having had experience with most of the major systems available) routinely provided disappointing results in the long term with regard to perpetuation of peri-implant tissues and thus maintenance of the original aesthetic outcome, rather than continued function. I documented a case that turned out after the fact to be a typical example of this type of cosmetic failure in the peer-reviewed literature about 11 years ago.⁹ I had used a new type of interim prosthesis with ovate pontic contours during the healing period to replace the tooth extracted before implant placement. The gingival contours so developed exhibited an ideal soft-tissue frame for the definitive restoration that lasted less than 18 months (Figure 6). Thereafter, recession became evident with darkening of the soft tissue and a slight exposure of the head of the implant clinically (Figure 7). Even though the patient did not complain about this cosmetic problem with a mandibular tooth that showed only the incisal half when he spoke or smiled, I still came to consider the case an aesthetic failure.

Figure 5. Another graphic representation of the bone loss that results from exposure to such toxins. (Image copyright Dr. Paul Weigl, University of Goethe, Frankfurt am Mein, Germany. Used with permission.)	Figure 6. A one-month follow-up photo showing the restoration of an implant at the No. 22 position.
Figure 7. An 18-month follow-up photo showing that same restoration with discolored and receding gingiva that reveal the head of the implant caused by exposure of the peri-implant tissues to bacterial toxins.	Figure 8. The one-month follow-up radiograph of No. 22 implant.

Figure 9. The 18-month follow-up radiograph of No. 22 implant showing interproximal bone loss down to the first thread.

A radiographic comparison of the implant when it was restored and after the described peri-implant tissue changes had occurred revealed apical migration of the crestal bone that is commonly referred to as remodeling, which is the normal turnover of osseous tissues through osteoblastic and osteoclastic activity in healthy individuals that does not alter tissue size or shape,¹⁰ but is simply bone loss (Figures 8 and 9). It has been my experience with internal hex connection systems that this loss of hard tissue regularly results in crestal bone levels that approximate the most coronal thread of the implant, if not more. I have come to refer to these systems as members of The First Thread Club (this term is a registered trademark of Seacoast Dental Seminars).

Effects of Functional Loading on Internal Hex Versus Morse Taper Design
I learned the reason for this all-too-typical outcome after seeing radiographic videography done by Dr. Paul Weigl and colleagues at the University of Goethe (Frankfurt am Mein, Germany). These videos showed what happens comparatively when the abutment/implant interface of the average internal hex connection and a Morse taper connection are put under functional loads. Internal hex connections were seen to develop a gap under function which has the potential to allow bacterial invasion. The system pictured here is the same one as in the clinical case noted above (Figures 10 and 11). The true Morse taper connection of the Ankylos system showed no such gap formation under equivalent functional loading (Figures 12 and 13). System designs that employ the “platform switching” concept with the internal hex connection have shown no statistically significant difference in their peri-implant bone levels when compared to their conventional counterparts.¹¹ In my view, they merely delay this inevitable bone loss by moving the connection somewhat further away from the peri-implant tissues without addressing the fundamental issue of connection stability and gap formation.

Figure 10. A freeze-frame of radiographic videography showing an abutment/implant interface from the same system as used in the case of No. 22 implant in its static state.	Figure 11. A freeze-frame of radiographic videography showing that interface under a functional load. Note the accompanying gap formation.
Figure 12. A freeze-frame of radiographic videography showing an abutment/implant interface from the Ankylos system in its static state.	Figure 13. A freeze-frame of radiographic videography showing the Morse taper interface under a functional load. Note the absence of gap formation.
Figure 14. A radiograph at the No. 30 position of a restored Ankylos implant at 14-month follow-up.	Figure 15. A radiograph of the same No. 30 implant at 24-month follow-up. Note the bone level over the shoulder of the implant contacting the base of the abutment in both images.
Figure 16. A worst case scenario with the Ankylos system. A 19-month radiographic follow-up of an implant at the No. 18 position showing bone levels at (but not over) the shoulder of the implant.	Figure 17. Another worst-case scenario showing a 23-month radiographic follow-up of an Ankylos implant at the No. 19 position. Again, this shows bone levels at (but not over) the shoulder of the implant.

Advantages of the Morse Taper Design
The clinical benefits of this most stable Morse taper abutment/implant interface are immediately apparent intraorally and radiographically. Comparing radiographs at subsequent recalls after single-tooth or full-denture implant restorations are started and then years later in my practice typically shows bone levels encroaching on the shoulders of the implants (Figures 14 and 15). Such an osseous base provides ideal support for the soft-tissue peri-implant architecture necessary for an aesthetic restorative outcome that will stand the test of time as well as the necessary foundation for implant-retained or -supported denture prostheses. Worst case scenarios with the Morse taper connection in my practice still show bone levels well above the first thread (Figures 16 and 17). It is especially remarkable, with regard to implant-retained dentures on the mandible, that the Morse taper connection will sustain bone levels despite the distal leveraging forces applied to the 2-implants-at-the-canine-positions format typically used in these cases (Figures 18 and 19).¹²

When it comes to adjacent implants in the aesthetic zone, this type of interface provides cosmetic results that are far beyond what can normally be expected from an internal hex connection system, platform switched or not. It has been claimed that when dental implants are placed less than 3.0 mm apart, predictably aesthetic peri-implant architecture cannot normally be expected.^13,14 I have found this contention to be irrelevant when using the Ankylos system as I have also documented cases in the peer-reviewed literature where adjacent implants in the aesthetic zone less than 3 mm apart developed full interproximal papillary anatomy that has remained constant throughout several years (Figures 20 to 22).¹⁵ This was accomplished at a long edentulous site where no hard- or soft-tissue grafting of any kind was used (Figure 23). In my practice, I have also been able to obtain such results routinely (Figures 24 and 25).

Figure 18. A panoramic radiograph of Ankylos implants at the lower canine positions at the start of prosthetic treatment where an implant-retained lower full denture would be placed.	Figure 19. A panoramic radiograph of the lower canines retaining that full denture after 16 months in function reveals bone levels over the shoulders of both implants despite the leveraging forces applied to them.
Figure 20. Ankylos implants at the Nos. 5 and 6 positions 2.8 mm apart after one year in function. Note the bone level almost up to the shoulders between implants.	Figure 21. A follow-up radiograph of those Nos. 5 and 6 implants after 38 months shows a slight increase in inter-implant bone level with a significant maturation of the crestal lamina dura.
Figure 22. A follow-up photo of those Nos. 5 and 6 implant restorations (Captek [Argen]) after 38 months reveals a soft-tissue framework between the implants that is indistinguishable from that about the adjacent natural teeth.	Figure 23. A presurgical photo of the long edentulous site in the Nos. 5 and 6 implants case reveals its initial topography. No hard- or soft-tissue grafting of any kind was done in this case.
Figure 24. Ankylos implants at the Nos. 4 and 5 positions 1.8 mm apart after 2 years in function. Note the bone level up to the shoulders between implants.	Figure 25. A follow-up photo of the Nos. 4 and 5 implant restorations (Captek) after 2 years also reveals a soft-tissue framework between the implants that is indistinguishable from that about the adjacent natural teeth.

CLOSING COMMENTS
In short, the true Morse taper connection as utilized in the Ankylos dental implant system affords the clinician a sense of confidence due to long-term peri-implant tissue stability. As a practicing clinician, I have never had this level of consistency and predictability with any of the other implant systems, no matter what their design. My earlier cases with systems from The First Thread Club almost invariably proceeded to lose crestal bone with the concomitant recession, graying of the peri-implant soft tissue, and even exposure of the head of the implant in some cases. I considered many of those cases to be failures due to the concurrent aesthetic issues.

It has been said that, “The tissue is the issue, but the bone sets the tone.”¹⁶ I now say, “If the bone stays home, or gets grown, you get to pick your own.” This phrase (also a registered trademark of Seacoast Dental Seminars) refers to the fact that the choice of restorative material as well as abutment design and fabrication are not made related to anticipated peri-implant tissue deficits. I do not feel the need to use all-ceramic abutments, some of which are more prone to fracture than metal ones,¹⁷ because my experience with the Morse taper connection gives me the certainty that peri-implant tissue loss is just not a problem.

All of the implant crowns shown in this article as depicted by clinical photographs are supported by metal abutments (Atlantis [Dentsply Implants]). Previously, my implant system choice was dictated by cost and flexibility concerns as I was experiencing similar results with any of the ones on the market that I had tried. I now base my choice on the performance that I have been consistently achieving with the Ankylos system.F

Acknowledgment
The author would like to thank Drs. James Spivey and Daniel De Tolla (Portsmouth, NH) for their expertise in implant placement for the cases shown in this article.

References

1. Adell R, Lekholm U, Rockler B, et al. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg. 1981;10:387-416.
2. Papaspyridakos P, Chen CJ, Singh M, et al. Success criteria in implant dentistry: a systematic review. J Dent Res. 2012;91:242-248.
3. Cooper LF. Objective criteria: guiding and evaluating dental implant esthetics. J Esthet Restor Dent. 2008;20:195-205.
4. McArdle BF. Creating natural gingival profiles using the ovate pontic technique. Dent Today. 2004;23:97-101.
5. Gracis S, Michalakis K, Vigolo P, et al. Internal vs. external connections for abutments/reconstructions: a systematic review. Clin Oral Implants Res. 2012;23(suppl 6):202-216.
6. Taiyeb-Ali TB, Toh CG, Siar CH, et al. Influence of abutment design on clinical status of peri-implant tissues. Implant Dent. 2009;18:438-446.
7. Dibart S, Warbington M, Su MF, et al. In vitro evaluation of the implant-abutment bacterial seal: the locking taper system. Int J Oral Maxillofac Implants. 2005;20:732-737.
8. Goldenberg B. The conical connection: its proven influence in obtaining consistent results preserving soft and hard tissue for the partially and fully edentulous patient. Presented at: Seacoast Esthetic Dentistry Association; May 1, 2015; Portsmouth, NH.
9. McArdle BF. Using a fixed provisional prosthesis during post-extraction healing and implant placement. Compend Contin Educ Dent. 2006;27:179-184.
10. Tatinada A. Medically related osteonecrosis of the jaw. Presented at: New England Dental Society; November 12, 2016; Waltham, MA.
11. Duque AD, Aristizabal AG, Londoño S, et al. Prevalence of peri-implant disease on platform switching implants: a cross-sectional pilot study. Braz Oral Res. 2016;30.
12. McArdle BF. Predictably solving a prosthetic dilemma: a partially edentulous mandible opposed by a worn maxillary denture. Dent Today. 2013;32:62-64.
13. Tarnow D, Elian N, Fletcher P, et al. Vertical distance from the crest of bone to the height of the interproximal papilla between adjacent implants. J Periodontol. 2003;74:1785-1788.
14. Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest. J Periodontol. 2000;71:546-549.
15. McArdle BF. Restoring a long-edentulous maxillary ridge segment with adjacent implants. Compend Contin Educ Dent. 2014;35:518-521.
16. Progebin K. A predictable stepwise approach to treatment planning implant restorations from simple to complex. Presented at: Seacoast Esthetic Dentistry Association; October 3, 2008; Portsmouth, NH.
17. Butz F, Heydecke G, Okutan M, et al. Survival rate, fracture strength and failure mode of ceramic implant abutments after chewing simulation. J Oral Rehabil. 2005;32:838-843.

Dr. McArdle graduated from Tufts University School of Dental Medicine (Boston) in 1985 and has been practicing general dentistry on the New Hampshire seacoast ever since. He has served on the medical staff in dentistry of Concord Hospital in Concord, NH, and on the board of directors of Priority Dental Health, the New Hampshire Dental Society’s direct reimbursement entity. He is a co-founder of the Seacoast Esthetic Dentistry Association (dentalesthetics.com), which is headquartered in Portsmouth, NH, and he is the founder of Seacoast Dental Seminars (seacoastdentalseminars.com), also headquartered in Portsmouth. He has authored numerous other articles internationally in major peer-reviewed publications. Dr. McArdle can be reached at (603) 430-1010, via email at drmcardle@seacoastdentalseminars.com or seda@dentalesthetics.com, or by visiting the website mcardledmd.com.

Disclosure: Dr. McArdle discloses that Dentsply Implants has paid for one continuing education course that he participated in and has monetarily supported several continuing education lectures that he has given.

Also By Dr. McArdle

Aesthetic Implications of Restorative Material Choice: Considering Soft-Tissue Factors

The Immediate Smile: Fixed Provisionalization Using Digital Technology