Unique Attachment System for Implant-Supported Dentures

INTRODUCTION
Implant-supported full dentures today (as opposed to implant-retained units)¹ are normally supported by either a bar (Figure 1) or male-female attachments that are connected to at least 4 endosteal implants. These contemporary attachment systems can make oral hygiene more difficult and are often vulnerable to failure because of corrosion.² In addition, they may be less stable than other attachment approaches.3 There is a system now on the market that eliminates these issues through a unique attachment that places the bar within the denture acrylic, preventing such deterioration from corrosion and making home care significantly simpler.

CASE REPORT
Diagnosis and Treatment Planning
A 58-year-old male, with an unremarkable medical history other than light tobacco use, presented to my practice with an older complete maxillary denture opposed by a periodontally-compromised lower dentition anchoring a relatively new cast partial denture (Figure 2). His chief complaint was discomfort and dysfunction during mastication. My initial examination revealed that he had moderate to severe periodontal disease of the mandibular teeth. No other abnormalities in the soft or hard tissues were noted. His upper denture was excessively worn and, though the lower cast partial denture was serviceable, the considerable mobility present with these teeth made the prosthesis unstable, with the patient stating that chewing was very uncomfortable. After the examination appointment was completed, the patient was reappointed for a consultation visit in which his condition would be reviewed and all treatment options discussed.

At the subsequent consultation appointment, I told him that I thought treatment of his periodontitis would be a heroic effort with a long-term prognosis being uncertain at best, with or without supporting a cast partial denture. Full-denture treatment was also discussed, both immediate and delayed, with or without implant support or retention. Based on this information, and considering that his financial resources were limited, the patient elected to first have an immediate full lower denture placed that would later be converted to an implant-supported prosthesis. A new conventional full upper denture would be fabricated after the lower occlusion was stabilized.

Figure 1. An example of a traditional Hader bar attachment for an implant-supported full denture.	Figure 2. Preoperative panoramic radiograph.
Figure 3. Exposed implants with their sulcus formers in place.	Figure 4. Transfer pins in place ready for impression.

Clinical Protocol
After he consulted with the specialist to whom I refer my patients for implant placement, a treatment plan was developed. The treatment would consist of 5 implants (ANKYLOS [DENTSPLY International]) that would be placed at the time the immediate full lower denture was inserted. This system was chosen due to its well-documented tissue-scaffolding properties as well as its advanced attachment method (SynCone [DENTSPLY International]). These implants would be located in the mandibular midline and at both canine and second premolar positions as immediates in replacing some of the remaining lower dentition.

The implant surgery proceeded uneventfully several weeks later, and 3 months later, after confirmation of osseointegration, the implants were uncovered with placement of sulcus formers (as healing abutments are known in the ANKYLOS system due to their tissue training capabilities [Figure 3]). The immediate lower denture’s intaglio was adjusted by the surgeon to adapt to these abutments at the uncovering.

Figure 6. The impression taken for laboratory modification of the denture prior to insertion.	Figure 7. The modified denture, as sent back from the laboratory team, with the bar integrated into its base (black arrows) and the created retention cap adaptations (red arrows).
Figure 8. The soft-tissue model was sent back from the lab team with the custom ATLANTIS (DENTSPLY International) abutments and the mounting jig.	Figure 9. The soft-tissue model with the SynCone (DENTSPLY International) retention caps on the custom ATLANTIS abutments.
Figure 10. Implants before abutment insertion. (Note the excellent tissue health that was fostered by the sulcus formers.)	Figure 11. The abutments positioned in the mouth on the implants using the mounting jig.
Figure 12. The SynCone retention caps embedded in the denture with cold-cure acrylic.	Figure 13. The abutments in the mouth were filled with a semi-flexible light-cured resin provisional restorative material (Fermit [Ivoclar Vivadent]) followed by a layer of flowable light-cured composite (Revolution Formula 2 [Kerr]) to complete the seal.
Figure 14. The final clinical result with the implant-supported full lower denture and standard full upper denture.	Figure 15. Panoramic radiograph, taken at the one-year follow-up appointment, showing bone growth over the shoulders of the implants.

The patient returned to my office and the sulcus formers were removed and transfer pins affixed to the implants (Figure 4) for an impression (Examix NDS [GC America]) that would be sent to my implant laboratory team without the denture in order to minimize the patient’s time spent without it. Using this impression, the laboratory team fabricated the custom abutments (ATLANTIS [DENTSPLY International]) to be used for the case in conjunction with the retention cap (sleeve-like) attachments of the system that would be embedded in the denture on insertion of the abutments.

The ANKYLOS system is exceptionally suited to such cases, both due to the SynCone attachment and its Morse taper implant connection. The Morse taper connection design (also used to mount jet engines on airplanes) is the most stable on the market and directly responsible for the system’s excellent hard- and soft-tissue response.⁴ It is so stable as to be anti-rotational, even without an internal hex. However, it also comes in an indexed (located at the bottom of the abutment [Figure 5]) version for positional purposes. In its pure form, unlike internally hexed designs, the ANKYLOS Morse taper connection allows its abutment to be situated at any of 360° on the implant. This is particularly advantageous for relating the abutments in the mouth to the attachments in the denture, since the abutments can be positioned at any stance along the implant’s circumference to best integrate with those attachments.

After my laboratory team reported that the abutments and attachments were ready, an impression (Examix NDS) was taken with the patient’s lower denture (Figure 6) and it was sent to the lab. This was done so that the dental technician could reinforce the denture with an integral bar to propagate occlusal forces over the entire denture base and adapt it to the retention cap attachments (Figure 7) of the SynCone system. The case was returned to our office in 4 working days (Monday to Friday) with a soft-tissue model, the abutments (ATLANTIS), a jig (Figure 8) to orient those abutments on the implants in the mouth, and the retention caps (Figure 9). The patient was then reappointed to insert the abutments onto the implants and the SynCone retention caps into the denture.

At the next appointment, the sulcus formers were removed for the final time (Figure 10). The abutments were arranged on the implants using the lab-fabricated jig (Figure 11) because these abutments were not indexed so as to give them the ultimate positioning flexibility, as mentioned above. At this point, the abutments were hand tightened to place through the jig, and then the SynCone retention caps were placed on them. The modified denture was then tried in over the retention caps, and fit was confirmed. Next, the retention caps were embedded in the denture with cold-cure acrylic, and excess acrylic was trimmed after curing. Any small voids were then sealed using flowable composite to create a constant intaglio surface (Figure 12). With the denture in the mouth, fit was again confirmed and then the implants were finally torqued in through the jig. After this, the screw holes were nearly filled with a light-cured, semi-flexible, resin provisional material (Fermit [Ivoclar Vivadent]), and then a layer of flowable composite resin (Revolution Formula 2 [Kerr]) was placed over the top of the Fermit and light cured to complete the seal (Figure 13).

The resulting attachment between the implants and the denture through the retention caps was so secure that the patient had extreme difficulty retrieving the prosthesis after insertion. The patient needed to practice this procedure multiple times with the retention caps lubricated using petroleum jelly on insertion in the morning before removal became routine. Palpating any aspect of the denture after placement in the mouth elicited no detectable movement, and the patient reported that he perceived none himself on occlusion, speech, or mastication.
A new conventional full-upper denture was fabricated to this stabilized lower occlusion in subsequent weeks (Figure 14). A year later, radiographic follow-up revealed bone levels over the shoulders of the implants; this is typical for the ANKYLOS system, in this author’s experience (Figure 15).

DISCUSSION
The advantages of this implant system and attachment apparatus are many. Its Morse taper abutment connection is so stable that no clinically significant microgaps between the abutment and implant arise during function. This prevents bacterial invasion⁵ with the spewing of toxins that cause the bone resorption to the first thread that is often seen in other systems. The well-established SynCone system,⁶ which has been updated with the use of ATLANTIS custom abutments, is at the same time ingenious and straightforward. The stability of its attachment, which originally had been shown to be comparable with other systems,⁷ is, in my opinion and experience, now unequaled. The abutments can be cleansed in the mouth even more easily than a freestanding, implant-supported crown, as the bar is sealed within the acrylic of the denture, which also protects it from possible corrosion. That’s right, the bar is in the denture!

IN SUMMARY
The patient in the case described herein was provided with an implant-supported unit that was more stable than any other that this author has seen in a 20-plus year history of placing such prostheses. Furthermore, the patient found it to be a prosthesis that is much easier to keep clean.

Acknowledgements
The author would like to thank James Spivey, DDS, MS, (Portsmouth, NH) for his expertise in dental implant surgery with this case. The author would also like to thank Mr. David Avery and his talented team of technicians at Drake Precision Dental Laboratory (Charlotte, NC) for the removable prostheses and laboratory implant procedures described in this article.

References

1. Kreyer R Jr. Implant retained overdentures. Dental Products Report. March 2007:30-31.
2. Waddell JN, Payne AG, Swain MV, et al. Scanning electron microscopy observations of failures of implant overdenture bars: a case series report. Clin Implant Dent Relat Res. 2010;12:26-38.
3. Kobayashi M, Srinivasan M, Ammann P, et al. Effects of in vitro cyclic dislodging on retentive force and removal torque of three overdenture attachment systems. Clin Oral Implants Res. 2014;25:426-434.
4. 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.
5. Weigl P. Current concepts in implant dentistry [lecture]. Presented at: Goethe University; June 26, 2012; Frankfurt, Germany.
6. May D, Romanos GE. Immediate implant-supported mandibular overdentures retained by conical crowns: a new treatment concept. Quintessence International. 2002;33(1):5-12.
7. Zhang RG, Hannak WB, Roggensack M, et al. Retentive characteristics of Ankylos SynCone conical crown system over long-term use in vitro. Eur J Prosthodont Restor Dent. 2008;16:61-66.

Dr. McArdle graduated from Tufts University School of Dental Medicine in 1985 and has been practicing general dentistry on the New Hampshire seacoast ever since. He has served on the active medical staff in dentistry of Concord Hospital in Concord, NH, and on the board of directors of Priority Dental Health (prioritydental.com), 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. 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. He can be reached at (603) 430-1010, at drmcardle@seacoastdentalseminars.com, seda@dentalesthetics.com, or by visiting the Web site mcardledmd.com.

Disclosure: Dr. McArdle discloses that DENTSPLY International, manufacturer of the ANKYLOS implant system, has supported several of his lectures and has paid for continuing education programs that he has attended.