Rehabilitating an Edentulous Lower Anterior Ridge Segment

A 54-year-old male patient with a noncontributory medical history presented to the practice without lower incisors, having lost them all by his mid-20s as a result of caries. He was wearing an old, removable cast partial denture that he wished to replace in favor of a different option. As would be anticipated after almost 3 decades, his residual anterior ridge was extensively resorbed (Figure 1 through Figure 3); however, his remaining lower dentition exhibited no significant periodontal disease or active decay, and his occlusion was stable. His chief concern at the time was to replace the missing incisors without involving his removable cast partial denture, and the possibilities for doing so were explained to him. After considering the alternatives, the patient elected implant placement and was referred out for a surgical consultation. He decided against implant-supported bridgework, stating that he knew that he would not floss such a prosthesis consistently and that he wanted the end result to mimic natural teeth as closely as possible.

After the surgical consultation, the case was discussed in the context of the patient's preferences and certain financial constraints that he had to see if implantology was still a viable route. Although the patient accepted the fees that would be charged for the implant placement and restoration, his financial situation was such that he declined to have any kind of hard- or soft-tissue augmentation performed prior to those procedures. This would leave the clinicians little room for error in terms of the angulation, abutment design, and orientation of the four implants that would be placed. Developing some semblance of natural-looking gingival architecture about the implants without being able to preserve the contours that can be achieved with immediate protocols^3,4 would be daunting. The fact that these implants would be located less than 3.0 mm apart from each other was another critical consideration because issues regarding close proximity have been described in the literature.^5,6

Due to these concerns, the choice of implant system and restorative material were crucial to the success of this case. With these factors in mind, an implant system (Ankylos Implant System, Dentsply Sirona) with well-documented hard- and soft-tissue preservation (and even growth) qualities^7,8 was chosen along with custom abutments (Atlantis Abutments, Dentsply Sirona). The implant crowns (Captek^® Crowns, Argen) were selected for their well-documented positive soft-tissue response properties.⁹

Prior to the placement appointment, the surgical doctor sent computed tomography (CT) scans (Figure 4) of the patient to the dental laboratory for the fabrication of a surgical stent to guide the implant placement. Using these records, the laboratory generated the stereolithography (STL) files necessary for the CAD/CAM process to fabricate the stent (Figure 5 and Figure 6).¹⁰ This was a critical step for the surgical procedure because the limited available volume of alveolar bone due to the lack of any hard- or soft-tissue augmentation necessitated exceedingly precise implant locations (Figure 7).

In the two-stage protocol that was selected, the implants would remain submerged after insertion while osseointegration ensued, and the patient would continue to wear his removable cast partial denture during that time period. Once osseointegration was confirmed and the implants were exposed by the restorative doctor, the intaglio surface of the patient's existing cast partial denture was modified to accommodate the healing abutments (Figure 8) and allow the patient to continue wearing it during the soft-tissue healing and initial maturation phase of treatment. These healing abutments are sometimes referred to as "sulcus formers" because, when appropriately sized to the specific implants used in a case, they commence to form the soft-tissue emergence profile, creating natural-looking papillary and marginal contours.¹¹ In addition, it has been shown that healing abutment configuration can have a positive effect on peri-implant tissues.¹² The two practices involved in the case closely coordinated so that the modification appointment was scheduled to occur immediately after the exposure appointment.

Once the soft-tissue healing and initial maturation phase was complete, which took about 3 weeks in this case, the healing abutments were replaced with transfer pins to acquire an impression and a shade reading was taken. At this point, rudimentary papillae formation can be seen that is typical of sulcus former action (Figure 9). The healing abutments were placed back on the implants after the impression was taken. During the period that the case was away at the dental laboratory, the patient continued to wear his cast partial denture, so it was important that the intaglio modification not only made room for the healing abutments but also prevented any soft-tissue impingement. Two weeks later, the case arrived back from the laboratory with four custom abutments, four implant crowns, two insertion jigs, and four cementation dies (Figure 10 through Figure 13).

At the patient's next appointment, the custom abutments were torqued into place using the insertion jigs (Figure 14 and Figure 15), and then the implant crowns (Captek^® Crowns, Argen) were luted (RelyX^™ Unicem Self-Adhesive Universal Resin Cement, 3M) to the abutments using the cementation dies. The insertion jigs ensure the correct orientation of the custom abutments with respect to the individual implants on the first placement attempt and preclude any movement of the abutments during torqueing. The cementation dies prevent the extrusion of excess cement beyond the margins of the crowns and onto the heads of the implants or peri-implant tissues during luting by eliminating any excess outside of the mouth.¹³ After the cement is inserted into the implant crowns, they are then situated on the cementation dies (Figure 16). Any surplus cement that extrudes from the crowns is wiped away with gauze before the crowns are subsequently removed from their cementation dies and seated on the abutments. The abutments used were uniquely fabricated to arrive at the most versatile configurations and angulations possible with regard to how these implants needed to be positioned within this particular edentulous ridge segment.¹⁴ The implant crowns chosen for this case displayed superior esthetics, even when compared with other porcelain-fused-to-metal (PFM) restorations that the manufacturer is known for¹⁵ that rival or surpass ceramic ones in terms of gingival esthetics.¹⁶

The distinct advantage of the conical connection using a true Morse Taper (ie, 5.7°) that is employed in the abutment/implant interface of the implant system is the absence of micromovement during function.¹⁷ This micromovement, which is typically seen with internal hex connection systems, can permit bacterial infestation and colonization at the abutment/implant interface. Micromovement discharges bacterial toxins from the abutment or implant interface via a pumping action, triggering osseous defects to occur around the implant. Such defects are usually characterized by bone levels that descend down to the implant's first thread and sometimes even further. This deficit is routinely more pronounced between implants, especially when they are less than 3.0 mm apart. Of course, when a loss of bony scaffolding occurs, gingival recession inevitably follows, creating the "black triangle" effect. Although often euphemistically termed "remodeling," more accurately, this phenomenon should be considered bone loss. Conversely, the abutment/implant interface of the implant system used in this case is considered to be hermetically sealed,^18,19 so no such deficits were anticipated.

At a 1-week follow-up appointment, the gingival tissue appears pink and healthy despite the less than ideal oral hygiene that was being performed by the patient (Figure 17). At 7 weeks, further maturation of the soft tissues was apparent along with noticeable improvement in the patient's at-home care (Figure 18). At 6 months, further gingival maturation was noted with more fully developed papillae (Figure 19). At 1 year, the soft-tissue heights have been maintained with further marginal refinement (Figure 20), and a radiograph obtained at the same time revealed interimplant bone levels well above the first threads of all four implants and, most significantly, between the implants (Figure 21). All of the inter-implant distances in this case were less than 1.5 mm.

This case exemplifies the type of considerations and challenges that both restorative and surgical dentists face daily in a typical practice. The patient was not a good candidate for fixed bridgework because of the span that such a restoration would have entailed, and he wished to discard the removable cast partial denture that he was already wearing. Given these parameters, placing dental implants was the patient's only real option, but the existing physical and financial limitations that were central to this case made realizing an acceptable clinical outcome (both functionally and esthetically) a difficult proposition.

However, with proper treatment planning, an appropriate implant system and abutment design choice, and the right restorative material, as well as conscientious implementation, a clinically acceptable result was achieved. Although all dental practitioners would like to complete treatment for their patients under ideal conditions, all too often, this simply is not possible, and certain compromises need to be made. In the end, it is the dentist's duty to try, to the best of his or her ability, to attain the best result possible for patients given their circumstances.

The authors would like to thank the technicians at NuCraft Dental Arts in Watkinsville, Georgia, for their expertise in the fabrication of the surgical stent used in this case and the technicians at Arrowhead Dental Laboratory in Sandy, Utah, for their expertise in the fabrication of all of the restorative components.

Barry F. McArdle, DMD
Cofounder
Seacoast Esthetic Dentistry Association
Portsmouth, New Hampshire
Private Practice
Portsmouth, New Hampshire

Daniel H. De Tolla, DDS, MD
Private Practice
Portsmouth, New Hampshire