If you are working with Locator abutments and attachments and everything is working with no problems, I am happy for you and your patients. This article is not intended for you at this point.

The Locator Implant Attachment System is well-known and recognized for a wide range of applications in the treatment of edentulous patients. The treatment planning concepts capturing my interest focuses on the boundaries or limits of application in this scenario. Specifically working with individual Locator abutments working with four dental implants to support a mandibular overdenture.

Why does the Locator abutment/attachment system work so well?

The gold Locator Abutment is connected to the dental implant like an abutment screw using a torque wrench. The metal housing (cap) and the replaceable nylon insert are incorporated into the removable over denture prosthesis.

The low profile helps to accommodate for restorative space limitations. Specifically, the requirements include 2 mm of the denture base acrylic surrounding the metal housing for the materials to work as intended.

Figure 1: The low profile helps to accommodate for restorative space limitations
Figure 1: The low profile helps to accommodate for restorative space limitations.

The advertised features of the Locator abutment/attachment system include several levels of retention, easy to use, and the ability to manage dental implants that are angled relative to one another. It all sounds great — until it doesn’t work.

At what point will this system not work, where is the line with Locators?

The patient shown in Figure 2 had her remaining lower teeth removed and following insertion of the lower prosthesis has made several trips to have the Locator attachments changed. The patient describes going through this process every two weeks or so and is curious if something else can be done to improve the retention and stability while decreasing the time invested in maintenance.

Figure 2: Maxillary restored dentition opposing mandibular implant
Figure 2: Maxillary restored dentition opposing mandibular implant “supported” overdenture.

What do you see?

  1. Missing lateral incisors … potential arch width discrepancy.
  2. Upper natural dentition opposing and perhaps overpowering the lower overdenture.
  3. Locator Abutments appear divergent … extended range attachments have less retention as they do not engage the middle of the gold Locator Abutment.
  4. The mandibular arch could be described as advanced alveolar ridge resorption with limited vertical height and limited horizontal width of the hard and soft tissue supporting structure.
  5. One of the implants (#23 or 3-2) contains a cover screw rather than a Locator Abutment.
  6. Two implant Locator Mandibular over denture likely not the right choice with opposing maxillary dentition — on track with four dental implants in this scenario.
  7. The arrangement or position of the dental implants is less than ideal — prefer more space between the implants specifically the goal would be to have a more posterior position for the terminal implants.
Figure 3: Occlusal view of mandibular arch with three locator abutments and one cover screw.
Figure 3: Occlusal view of mandibular arch with three locator abutments and one cover screw.

When thinking about the position of the dental implants, would a connecting bar work for this patient? Any treatment scenario will likely require an accommodation for angle correction of the dental implant fixtures. What about an implant supported lower hybrid (all-on-X)?

What else is possible? Think about this patient, they have invested in their dental health, and it seems to be a stretch financially, and the result is a high-maintenance Locator over denture where she is required to come to the dental office every two weeks to change the attachments.

If the patient presented with an upper complete removable denture, it is possible to work with the anterior implants as an “indirect retainer” to limit the rocking of the lower overdenture prosthesis. The two terminal or most posterior implants are positioned to create a fulcrum where a lower overdenture would rock anterior posteriorly working with only soft tissue support in the anterior segment.

This patient has a full natural dentition in the maxillary arch — the recommendation would not be to remove the upper teeth to make this work. Removing and replacing implants or simply adding additional implants if the restorative space is adequate with the existing implants comes to mind. The goal would be to create the appropriate foundational support expected of four or more dental implants for a removable prosthesis.

What about a phased approach to treatment?

The question is … is there a way to help this patient out of a frustrating outcome that provides the opportunity to make treatment decisions resulting in a long-term, low-maintenance result?

The Conus Abutment/Attachment system is based on a friction-fit telescopic (conometric) design providing a non-resilient connection with removable prostheses supported by a minimum of four dental implants. The limit for the available angle correction with the Conus system is 30 degrees.

In this scenario, the plan is to work with customized Conus Abutments to correct for the relative angulation of the existing mandibular dental implants. The goal is to create a single path of insertion for the removable over denture prosthesis.

Figure 4: Cross-over between the analog and the digital world — creating custom
Figure 4: Cross-over between the analog and the digital world — creating custom “angle correcting” Conus abutments.

Working through this process requires a modified workflow with the ability to cross over between the traditional analog techniques and the virtual realm enhanced by computer aided design techniques.

Working virtually requires the identification of the desired tooth position relative to the position of the dental implants — information that is identified and recorded clinically. The information is sent to the dental laboratory for the digital design and construction of the custom “angle correcting” Conus Abutments.

Figure 5: Evaluating the proximity of the dental implants and Conus Attachments.
Figure 5: Evaluating the proximity of the dental implants and Conus Attachments.

The computer design software creates an opportunity for improved communication using screenshots where the technician highlights an area of concern prior to moving forward with milling the customized “angle corrected” Conus Abutments.

The question is, can we work with this or not? We can measure virtually and evaluate from multiple angles to help decide prior to proceeding with the treatment plan.

Figure 6: Clinical evaluation of Conus Abutments with the Syncone friction fit attachments.
Figure 6: Clinical evaluation of Conus Abutments with the Syncone friction fit attachments.

The prefabricated Syncone caps are designed to work with the five-degree taper designed into the customized Conus abutment. The Syncone caps are available with aggressive retentive features as shown in the photo.

The Syncone caps are also available with a smooth surface designed for cementation into a metal intaglio framework. When picking up the Syncone caps into an acrylic denture base using auto-polymerizing resin, it is recommended to work with Syncone caps with retention.

In this scenario, the Syncone caps have been modified to create space for the acrylic where the dental implants were placed in proximity. This was identified and discussed in the planning stages as the virtual design software identified the concern allowing the opportunity to communicate with the technician.

Figure 7: Chairside pick-up of the friction fit Syncone caps.
Figure 7: Chairside pick-up of the friction fit Syncone caps.

White auto-polymerizing acrylic to pick up the prefabricated Syncone caps in a “chairside” technique. The color difference improves the visibility for clean-up of excess resin that may form a thin veneer of material on the intaglio of the removable over denture prosthesis.

The space requirements as advertised include 5.5-mm vertical height for the Conus Abutment and Syncone cap, and an additional 5 mm to account for the acrylic and denture tooth. Working with space measurements beginning at the restorative platform of the dental implant on one end and the incisal edge or cusp tip of the denture tooth, 14-mm provides a practical recommendation for space requirements when working with an acrylic based removable overdenture. 15-mm would be recommended when incorporating a metal intaglio framework into the design.

The modification to the existing overdenture design was changing the abutments from Locator to Conus. The point was to determine if altering one variable could make a difference in the outcome in this scenario. This patient has gone from having to have the nylon Locator Attachments replaced on a two-week interval to a point where it is a challenge to have the patient come into the office for an evaluation.

It’s understandable that a break from the dental office was needed! We now have the opportunity to plan for continued care with the confidence generated from a proof-of-concept style prototype.

Douglas G. Benting, D.D.S., M.S., F.A.C.P. is a member of Spear Resident Faculty.



Comments

Commenter's Profile Image John P.
April 28th, 2021
Very nice digest post! When it comes to conus abutments, I am not aware of any Straumann options. Are you? I have always recommended authentic Straumann abutments for their implants so their replacement warranty remains valid.