Written by Andrew Sedler

Written by Andrew Sedler

Written by Andrew Sedler

Solutions for Undesirable Screw Access Positioning
IN IMPLANT RESTORATIONS
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NobelProcera ASC Abutments®

One of the perennial problems that we encounter at Burbank Dental Lab is when our clients are restoring implant restorations that do not have ideal screw access hole positioning. It is particularly important to have solutions for this challenge since there is an increasing trend in implant dentistry moving back towards screw-retained restorations. However, too often the case must be done as a cementable crown. Screw access hole issues could be challenging, until the introduction of Nobel's Angulated Screw Channel® (ASC). Nobel's ASC allows many restorations to be restored as screw-retained that otherwise would have required a less desirable abutment and a cementable crown option.

For the purpose of this article, we will discuss the features and benefits of Nobel's ASC®, as well as what are the indications for prescribing this restoration.

The ASC abutment is proprietary to Nobel Biocare® and is fabricated via the Procera® design workflow. These restorations are only available for use with Nobel's Conical Connection® implant systems. Burbank Dental Lab can use the Procera design software (Figure 1) to create a zirconia restoration (FCZ) that has an angled access hole. This is made possible in conjunction with the ASC titanium base and the Omnigrip® driver and screw system.

ASC design in procera software
Figure 1
Burbank Dental Lab
Burbank Dental Lab
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4 Elements of the ASC Abutment

1. The Adapter for Zirconia Abutment Conical Connection

This is the titanium base used in the ASC system. The interface that engages the zirconia coronal portion is lower profile than most titanium bases. The titanium base uses a one-of-a-kind anti-rotational tri-lobe base that secures the zirconia crown to the base, forming an integrated hybrid restoration.  (Figure 2)

Titanium base for ASC abutment
Figure 2

2. Zirconia Procera Full-Contour Zirconia

The Full-Contour Zirconia (FCZ) of an ASC restoration is designed with an angled screw access hole up to 25º. The zirconia can be fabricated for use as a monolithic or layered restoration. (Figure 3)
Full Contour Zirconia used with ASC abutment
Figure 3

3. & 4.  Omnigrip Driver and Screw

The ASC Abutment employs the use of the Omnigrip driver that fits your Nobel torque wrench. The Omnigrip driver and screw are what allows the ASC system to torque the retaining screw into a torque of 35 N, with a screw to driver angle up to 25º. (Figure 4)
Omnigrip and screw used for ASC Abutments
Figure 4

Features of the ASC

  • Allows for driver access to screw from 0º to 25º
  • Low profile height of titanium base
  • Cement-free seating
The FCZ is designed to interlock with the tri-lobbed titanium base and is seated without using cement. When placed, the Omnigrip screw holds the zirconia locked onto the top of the titanium base. (Figure 5)
Omnigrip screw holds zirconia to titanium base
Figure 5

Benefits of the ASC

Benefits for Anterior Restorations

When restoring anterior restorations, several critical elements are important to control in order to maximize esthetic results:

  • Allows for the access hole on the cingulum, this benefits the cosmetics since the access hole must be positioned on the lingual. The ASC delivers the ability to reposition the access hole in most cases.
  • Place cement-free screw-retained crowns without compromising esthetics or occlusal function. The ASC facilitates the avoidance of cement-retained restorations. This is critical since it has been recognized that screw-retained restorations are safer than cemented restorations on implant abutments.
  • Easy technician handling – the adapter is retained mechanically (without cement), allowing for easy removal and replacement during the veneering process in the lab, and in case any re-firing is required after try-in.
  • The low profile of the titanium interface limits the adverse effect on the color of restoration and tissue from titanium interface.
  • It is particularly beneficial to be able to screw-retained restorations in the anterior since anterior restorations typically require the ability to manage the soft tissue more than posteriors. Achieving the correct soft tissue contour and ceramic esthetics to mirror the natural adjacent central incisor is the key to success. The ASC increases the ability to place screw-retained restorations that can facilitate tissue shaping.

Benefits for Posterior Restorations

  • Retrievability - valued by most clinicians.
  • When encountering posterior restorations that have limited vertical opening, the ASC allows angled access to the screw rather than straight access vertical access parallel to the implant root form. (Figures 6 & 7)
Straight access to screw-retained restoration
Figure 6
Angled access to posterior restoration
Figure 7

Indications to Prescribe an ASC Restoration 

  • Anterior restorations that require a lingually-positioned access hole, but the placement and angulation of the implant direct the screw access hole in a less than ideal position.
  • Anterior implant restorations where pressure is required for tissue shaping.
  • Posterior restorations that have limited vertical access.
  • Posterior restorations that have a poor screw access angle.
 
 
In today’s dental practice, implant restorations have become an essential component of everyday treatment. Screw-retained restorations are generally preferred for most treatment needs, and the ASC facilitates the expanded use of screw-retained options and increases the success of your anterior as well as many posterior implant restorations. Burbank Dental Lab has over 10 years of experience with Nobel Procera design systems and nearly 30 years of implant restoration experience.
Burbank Dental Lab

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