Techniques to Optimize Color Esthetics, Bonding, and Peri-implant Tissue Health With Titanium Implant Abutments
Chandur P.K. Wadhwani, BDS, MSD; Todd Schoenbaum, DDS; Kirk E. King, DDS; and Kwok-Hung Chung, DDS, PhD
Abstract: Due to their exceptional biological and mechanical properties, titanium and its alloys are commonly used in both dental implants and implant abutments, upon which prostheses can be attached. The gray color of titanium metal, however, can elicit esthetic problems, as it has the potential to show through a translucent ceramic restorative material. Various solutions have been proposed and used to attempt to overcome esthetic issues associated with titanium. This article describes a simple, economical technique to color titanium abutments and components utilizing anodization, resulting in light reflection and color enhancement through a natural physics phenomenon known as light interference patterns. A technique for improving the bonding capabilities of cement to the abutment is also discussed.
Titanium, a truly remarkable metal named after the Titans, Greek gods of myth, is considered to be a standard biocompatible material for human use. It has a proven record for being effective in both osseointegration1,2 and soft-tissue integration.3,4 Titanium (Ti) and its alloys have exceptional biological and mechanical properties, allowing their use in both a dental implant and implant abutment, upon which a prosthesis can be attached.
When a titanium abutment is used, for example, in a single-unit restoration, most implant systems have a screw joint to assemble it to the implant, and a cemented crown is then used as the restoration. Recently, however, a trend has emerged toward a return to the use of a screw-retained, implant-supported crown. This has been mostly due to the increasing prevalence of cement-induced peri-implantitis, a condition that can ultimately lead to implant failure.5
Cement-induced peri-implantitis, which initially was identified as a clinical anomaly originally thought to have occurred in a few isolated reports,6 has become a major risk factor affecting the long-term health of peri-implant tissues. Unfortunately, cement-induced peri-implant disease has been reported to take, on average, 3 years, but in some instances up to 9 years, before it becomes a clinically identifiable condition.7
Several approaches have been developed to overcome this issue. These include more careful management of the cemented margin depth,8 better control of cement flow,9 use of more microbiologically compliant cements,10 new abutment designs,11 and cementing the implant restoration extraorally as a hybrid cement-screw–retained crown.12
The cement-screw implant crown presents a simple method to eliminate excess cement extrusion. The crown is fabricated to fit the titanium abutment with a hole incorporated to allow for screw access. The crown and abutment are cemented extraorally, which enables complete access to the cement margins. All cement extruded through the crown abutment margin is removed before the crown is delivered to the patient. This crown and abutment complex is then screwed onto the implant.
The use of this “hybrid” abutment/restoration provides the good esthetics of ceramics with the advantages of titanium, which include:
Biology—Other abutment materials, including zirconia, have been associated with more biological complications than titanium,13 which has been proven to have less bone and soft-tissue loss than any other abutment material.
Economics—Prefabricated or stock titanium abutments are less costly than custom-fabricated cast gold UCLA-type abutments.14
Fit—Titanium abutments are machined to fit the implant with a very high level of fidelity. Conversely, cast gold abutments may suffer from poor handling and finishing in the laboratory, which can affect long-term screw stability.15,16
Strength—Wear and fracture resistance of a titanium-based implant abutment is superior to a zirconia-based one.17
Zirconia also presents problems with cementation bonding because it cannot be etched, and airborne particle abrasion may have detrimental effects on flexural strength.18 However, with the titanium base comes the potential for esthetic issues, especially in cases where the facial soft tissues are thin or when the restorative material used may be highly translucent, such as lithium disilicate, allowing gray show-through. A study has shown that zirconia offers advantages over its titanium counterparts when evaluating esthetics with a pink esthetic score.16 The gray color of titanium metal showing through a translucent ceramic material is an issue such that, even if a colored opaque cement is used as the luting agent, there is no way to know if it will fully mask the metal.
To overcome this issue, some manufacturers use an additive gold coloring layer in the form of a titanium nitride coating. Although this improves the esthetics, a risk of allergy to this coating material has been reported in the literature.19
The purpose of this article is to describe a simple and economical technique to color titanium abutments and components. The coloring of titanium is routinely used in the dental implant industry mainly to identify componentry (Figure 1). Recently, implant manufacturing companies have realized some of these colors can be useful for esthetics also. Unlike the titanium nitride coating that may alter the biocompatibility of the abutment, anodization is a procedure that simply thickens the biocompatible titanium oxide layer resulting in light reflection and color enhancement by a natural physics phenomenon known as light interference patterns. Environmental light is reflected off the titanium oxide surface, producing esthetically pleasing yellow and pink shades. This has been extensively explored in ophthalmology, where it is used to color titanium keratoprosthesis.20 In vitro and in vivo results suggest that the anodized titanium is equally as biocompatible and safe as standard, non-anodized titanium. This provides the potential to improve the esthetics of both peri-implant gingival tissues and the restoration with no known risk to the peri-implant tissues.21
Additionally, this article describes a technique for improving the bonding capabilities of the cement to the abutment. Easy to apply on a routine basis, inexpensive, and reversible, these techniques can be used in both the laboratory and the dental office environment.
Colorizing Titanium Through Anodization
The armamentarium needed for this process includes an electrolyte and low voltage applied between the implant abutment and liquid. Essentially, the electrolyte can be any liquid that allows current to flow through it. The voltage supply can be as simple as a series of batteries as shown in Figure 2 or a dedicated voltage generator. The titanium abutment should be clean and free of residue. It can be anodized selectively by placing wax on areas where color change may be unwanted (Figure 3). This is especially important when abutments are to be dual-colorized, as will be described later in this article.
The anode (positive) terminal is attached to the abutment (Figure 4). The cathode (negative) is attached to the liquid through a strip of aluminum foil (Figure 5). Common cleaning products, low-grade acids, or even diet cola (which contains phosphoric acid that allows electron flow) can be used as the electrolyte. The abutment is dipped into the solution carefully so as to not contact the negative connection terminal in the bath (Figure 6). Though the voltage/amperage is low, the operator must exercise care to prevent being shocked.
For safety the operator should wear rubber gloves and use insulation around the terminal connectors. The process, which can be completed in 5 to 10 seconds, is self-limiting in that the anodization producing the color stops when the oxide layer is achieved (Figure 7). The titanium should be free of oil and other contaminants that may interfere with the electrical current flow and potentially prevent anodization. Ethanol can be used as a surface cleanser if the titanium becomes contaminated.
Useful to dentistry are the anodization colors of yellow, which is achieved when a voltage of 60 V to 65 V is used, and pink or magenta, achieved at 75 V to 85 V. These color variations are demonstrated in Figure 8 and Figure 9. A variety of titanium colors can be produced, depending on the particular electrolyte used and the type of titanium or titanium alloy being anodized (Figure 10). The abutments can also be dual-colored: pink for soft-tissue esthetics, and gold for maintaining the esthetics of translucent crown materials. This dual coloration is particularly useful in cases where high translucency crowns are to be used (Figure 11).
This process does not change the chemical nature of the titanium; rather, it increases the thickness of the titanium oxide layers. The anodized color is stable and can endure indefinitely if covered by a restoration or by soft tissues. Having been shown to be stable, the colorization has demonstrated that the passivation oxide film is resistant to degradation.20 Additionally, because the colorization effects are directly related to the titanium oxide layer, if desired, the color may be polished away using polish paste. This reduces the thickness of the titanium oxide layer, returning the abutment to its original gray color. This is useful in instances where the anodization has been incorrectly applied and has resulted in an undesirable color change. If cleaned thoroughly, the abutment can subsequently be re-anodized.
Another significant advantage of anodization is that it may be coupled with a roughened surface to further improve both the esthetics and cement retention. The rough surface is particularly useful when considering bonding agents and materials, which, in general, are highly dependent on the surface area. The “as received” titanium abutment is usually machined to a relatively smooth surface with minimal retentive features. The surface can be modified using burs or airborne particle abrasion (sandblasting); however, an easier method to improve micromechanical retention to the abutment is to etch the titanium (Figure 12 through Figure 14). This is accomplished by using porcelain etchant, ie, a 9.5% hydrofluoric gel for 30 seconds, then rinsing thoroughly. Again, care must be taken as this material is highly toxic and corrosive and should only be used extraorally. During the reaction, bubbling at the surface of the titanium occurs, which is the liberation of hydrogen gas. The etching pattern appears as a dull surface; microscopically the etching increases the surface roughness, producing a surface that has been shown to be as effective as airborne particle abrasion when bonded to lithium disilicate.22
Discussion and the ScienceBehind the Phenomenon
Despite their various advantages, titanium abutments present several specific challenges. Restorative materials available, such as translucent forms of zirconia and lithium disilicate, may fail to mask the metallic grey undertones of the abutment. Similarly, soft tissues with thin biotypes may also be problematic, potentially allowing show-through and compromising esthetics. However, this simple laboratory technique, which employs a well-known phenomenon involving light interference patterns, can be used to change the abutment color economically and without altering the biocompatibility of the materials. This technique involves anodization of the abutment using inexpensive, readily available materials.
The gray color of titanium results from light passing through a thin (approximately 20-nm thick) titanium oxide layer, then reflecting off the metallic surface. A titanium oxide layer forms instantly on the surface of the metal upon exposure to air. This natural process provides excellent chemical inertness, corrosion resistance, re-passivation ability, and biocompatibility. Using an electrochemical anodization technique can alter and increase the titanium oxide thickness to the degree that light interference patterns are produced, causing the effect of a colored surface. A similar pattern is noted when viewing items such as compact discs, for example. Although the disc is not actually colored, colors are produced as the angulation of the reflected light is changed (Figure 15 and Figure 16). This process of light passing through and reflecting off the clear layer of titanium dioxide, reinforcing particular color wavelengths, is a physics phenomenon related to thin film interference.
When anodizing titanium and titanium alloys, altering the thickness of the titanium oxide layer results in an optimally colored surface without affecting the surface chemistry while retaining the surface biocompatibility. The induced yellow hue can result in improvement of both soft-tissue appearance and restoration effect, where there is some surrounding translucency. Pink and magenta hues should improve the esthetics of the soft tissues. Bicolored component formation is also possible, with a pink hue for the soft-tissue emergence area and a yellow one for the abutment portion within the definitive restoration. This technique requires knowing which voltage will result in which hue (ie, 60 V to 65 V, yellow; and 80 V to 85 V, pink), and clean titanium surfaces are essential. The process is self-limiting, requiring only 5 to 10 seconds to complete.
About the Authors
Chandur P.K. Wadhwani, BDS, MSD
Affiliate Assistant Professor, Advanced Specialty Education Program in Prosthodontics, Loma Linda University, Loma Linda, California; Clinical Associate Professor, Graduate Periodontics, Oregon Health Sciences University, Portland, Oregon; Private Specialty Practice limited to Prosthodontics, Bellevue, Washington
Todd Schoenbaum, DDS
Associate Clinical Professor, Division of Constitutive and Regenerative Sciences, UCLA School of Dentistry, Los Angeles, California
Kirk E. King, DDS
Private Practice, Renton, Washington
Kwok-Hung Chung, DDS, PhD
Professor, Department of Restorative Dentistry, University of Washington,
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