A Plethora of Options for Implants
Everyday abutment selection and bar designs
Oscar D. Galvis, CDT, MDT, MS
It is safe to say that digital and implant dentistry, along with their growing impact on the industry, are of paramount importance to dental professionals across the country. CAD/CAM technology is frequently a foundational element of an integrated digital workflow for dental implant placement and restoration.1 As intriguing as these topics are, dental professionals must not forget that proper treatment planning and case design are pillars to the success of all cases. This is especially true in the arena of implant and digital dentistry, where the prosthetics play a major role in propelling the demand for dental implants through oral rehabilitation.2 Given the vast amount of restorations and designs available, this article will discuss the more common options and solutions in regard to abutment selection and bar/full-arch designs.
Abutment Selection
According to the American College of Prosthodontics, single crowns are the most common restoration procedure, with approximately 2.3 million implant-supported crowns made annually.3 Partial edentulism affects the majority of adult Americans and is predicted to affect more than 200 million individuals in the next 15 years.3 With such a large demand and opportunity for single-crown and small bridge implant restorations, it is the dental professionals' responsibility to choose the best components available to customize a quality restoration for each patient. There is a plethora of implant companies that offer restorative components; most of these manufacturers offer the following:
Stock abutments
Although each manufacturer has its own proprietary implant system, stock abutments are fairly standard across the industry and are available for purchase for immediate use, no design specifications necessary. Available in a variety of materials, most commonly PMMA, titanium, and zirconia, they usually come in the following varieties:
• Engaging: These stock abutments are used for
the traditional single-implant restoration that seats into/onto the implant platform, engaging in a select few positions. Engaging abutments may be used for cement- or screw-retained restorations (Figure 1).
• Non-engaging: These abutments are meant for screw-retained bridge work specifically due to their ability to seat passively in situations when implants are not placed exactly parallel to one another into or onto the platform of an implant. This is made possible due to a smooth, often cone-shaped abutment base. Non-engaging abutments are usually designated for small bridges with fairly parallel implant placement that allows for ideal screw access hole placement outside the esthetic zone and minimum tissue depth of the implant (Figure 1).
• Variety of abutment heights: Different abutment heights are available dependent upon the manufacturer. The purpose of this is for the slight customization in association to restorative space (Figure 1). Note: It is a good practice to stock taller abutment heights since they can always be reduced at the bench.
• Variety of gingival heights: The different gingival heights pertain to the height of the base of the abutment and its emergence profile from the platform of the implant. This gives the ability to restore implants with deep gingival emergence profiles (usually up to 3-mm depths) without having to design a custom abutment or having to augment tissue in order to seat intraorally (Figure 1).
The use of these combinations of stock abutment designs can not only enable the production of a quality restoration, but it may also aid in reduction of material costs. Scanning these abutments and designing crown and bridge restorations on them—later attaching them to the abutments as screw-retained restorations—may significantly reduce costs in comparison to using custom abutments.
Custom abutments
Even with the use of digital implant planning software and the use of surgical guides, implant placement is not always as predictable or ideal as dental professionals would hope. Custom abutments aid with creating a personalized structure to support the restoration itself, as well as fully resolving the problems created by a difficult emergence profile at the gingiva. They can be used in both cement- and screw-retained restorations, and are offered in titanium and zirconia (Figure 2).
Angulated abutments
These abutments are used for screw-retained restorations that are impacted by poor implant position relative to a properly placed restoration. Angulated abutments can usually change the screw access hole up to 30˚. This can make the difference between an access hole impinging on the incisal edge of an anterior tooth, to allowing access back toward the cingulum. These systems usually require the manufacturer's proprietary screw and driver in order to make use of that specific angulated abutment.
Multi-unit abutments
Multi-unit abutments are made available mainly for full-arch restorations, but they may also be used in smaller bridges. They are especially useful when implants are placed with the platforms at different gingival heights while also being significantly divergent. When the restoration integrity is compromised along with hygiene, these multi-unit abutments can turn a divergent implant-level restoration into a passively seated, fixture-level restoration. The multi-unit abutment is available not only in different gingival heights (often up to 5 mm), but also in degrees of angulation (generally 15˚, 17˚, and 30˚), which aid in the elimination of divergence and allow a more esthetically placed access hole. The gingival heights and degrees of angulation correction vary dependent on the manufacturer. With proper multi-unit abutment selection, full-arch restorations have numerous capabilities in association with bar designs (Figure 3).
Full-arch Bar Designs
Similar to the demographics on single-tooth loss and implant restorations, full-arch rehabilitation has its own window of opportunity in regard to implant restorations. Currently, it is estimated that about 23 million people are completely edentulous and about 12 million are edentulous in one arch.3This leaves a large market for full-mouth/full-arch rehabilitation, which is commonly done using bar designs. The following are some of the more common ways to restore full arches on implants.
Titanium bars
The term hybrid is used often to refer to a final restoration that contains a combination of a metal substructure, while esthetic portions are typically a form of PMMA. Titanium bars are commonly used as substructures in hybrid restorations. These hybrid restorations should have a minimum restorative space of 15 mm, allowing adequate room for the bar, acrylic, and tooth structures.4 (With advancements in selective laser melting [SLM] 3D printing, these bar structures can be printed in chrome-cobalt, allowing for beaded retention where restorative space is an issue.) The following are some of the most popular titanium bar designs:
• Montreal*: This design incorporates a biocompatible, hygienic titanium intaglio surface with mechanical retention such as struts, holes, etc, for its acrylic-bearing cameo surface (Figure 4).5
• Wraparound*: This design is one of the simpler designs that allow acrylic to fully encompass the titanium bar substructure. The biggest benefit of this design is the ability to easily manage the tissue-bearing surface over time since acrylic can be freely removed or added in the case of any hygienic or phonetic situations that may occur post insertion (Figure 5).5
• Telescopic tertiary bar: Although not as common in the US as in other countries, this technique is gaining headway in the industry. This type of design makes use of friction as a retention mechanism. This technique involves a tertiary structure, commonly titanium, that in turn functions as a traditional hybrid restoration, which is also retrievable by the patient for hygiene purposes.
• Overdenture bar: Although this design is not a hybrid, it has been a removable, implant-retained, tissue-supported option in prosthodontics for more than 50 years. This design offers the advantages over other implant removable options of improved stability, easy access for hygiene, cross-arch stabilization, improved lip support from denture borders, etc.5 These metal bars are incorporated with direct retainers, bar attachments, and offset attachments that allow the denture to snap onto the bar (Figure 6).6
* Montreal and wraparound designs incorporate acrylic components that can still require repair (Figure 7) and/or a complete stripping of the acrylic down to the titanium bar that is usually coated in a gingival shade opaque (Figure 5). This allows all the acrylic work to be redone without the need of another substructure fabrication.
Zirconia and PFM arches
While zirconia and PFM arches are not technically bar designs, they fall in the similar arena of common full-mouth implant restorations. Full-contour monolithic zirconia (Figure 8) can be easily copy-milled from a wax or acrylic protype that has been approved by the patient before final fabrication. Although zirconia arches can offer strength and esthetic/functional approval from the patient, the hardness of the material does not distribute masticatory forces as well as other options like PFMs. Chrome-cobalt can be milled into substructures used in full arches that receive the application of porcelain. These types of PFMs commonly incorporate thimble preparations that resemble prepared teeth, allowing for the cementation of individual crowns. This offers an amazing individuality and vitality to a full-arch bridge restoration.
High-performance Polymers
High-performance polymers (HPPs) are newer options available through various companies with their own proprietary formulas. They have been introduced recently into the dental industry and have a broad range of versatility in treatment planning. HPPs can be used as part of overdenture, hybrid, and telescopic tertiary structures, and they can help reduce costs in comparison to titanium. Time will tell on the longevity of these materials. With their characteristics of lighter weight and high esthetic capabilities when used in combination with composites and PMMA, HPPs are definitely worth noting.8
Often, the most difficult part of designing and planning a solution for a patient is knowing what implant component option best suits the ideal restoration for that specific situation. The options and solutions listed above fit a wide range of treatment plans and case designs; however, there are so many different restorative implant components available in the industry that this article only scratches the surface. Use it as a starting point for your own research on how to provide the best care for your patients.
About the Author
Oscar D. Galvis, CDT, MDT, MS, is an owner of Nu-Crown Dental Laboratory Inc. in Totowa, New Jersey, and a faculty member at CUNY New York City College of Technology in Brooklyn, New York.
References
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5. Wade T. Full-Arch restorations on CAD/CAM-milled titanium bars: Part II. Inside Dental Technology. https://www.aegisdentalnetwork.com/idt/2012/04/full-arch-restorations-on-cad-cam-milled-titanium-bars-part-ii. Published April 2012. Accessed December 31, 2019.
6. Dos Santos MBF, Bacchi A, Correr-Sobrinho L, Consani RLX. The influence of clip material and cross sections of the bar framework associated with vertical misfit on stress distribution in implant-retained overdentures. Int J Prosthodont 2014;27:26-32. doi: 10.11607/ijp.3627
7. Overdenture Bars. Preat Corporation website. https://preat.com/attachment_systems/overdenture-bars/. Retrieved December 31, 2019
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