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4 Aesthetics and Simple Implant-Abutment Modifications

4 Aesthetics and Simple Implant-Abutment Modifications

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C. P. K. Wadhwani et al.



b



Fig. 14.4 (a) Zirconia abutment fracture at the implant-abutment connection, considered a weak

site. (b) This fracture has left some of the zirconia still within the implant itself, which can be challenging to remove



Fig. 14.5  Abutments have

been anodized using

batteries and diet soda. By

varying the voltage applied,

yellow/gold colors can be

used for the core abutment

color. Pink hues can be

produced for the abutment

beneath the tissues. Both

pink and yellow can also be

produced by selective

anodization



An improved way of coloring titanium has been described in the literature, which

uses a very different technique to provide aesthetic-colored abutments (Fig. 14.5).

Anodization is a physicochemical controlled method of thickening the titanium

dioxide surface layer. This is the same layer that naturally and sponaneously evolves

if the titanium is left in air and is the basis of the biocompatibility of titanium itself.

This is a simple, fast, and inexpensive technique for coloring the titanium that has

been described in the dental literature and can be done by anyone, using common

materials. When the titanium dioxide layer is thickened, a physical phenomenon

occurs, whereby natural white light is absorbed and reflected back as a thin film



14  Delivery of the Definitive Abutment/Prosthesis



287



Fig. 14.6  Anodization uses

the properties of reflected

light passing through a clear

film—the same effect is seen

when a CD-ROM is rotated. It

has no intrinsic color, but

colors are seen through this

effect



Fig. 14.7  Some of the

many colors that can be

produced by anodization of

titanium and titanium alloy,

simply by using different

voltages



interference pattern, similar to what is commonly seen with oil films on water or

when a CD-ROM reflects colors (Fig. 14.6). A series of colors can be produced,

each of which is dependent upon the thickness of the titanium dioxide layer. Some

of the colors are very useful for improving abutment aesthetics, either relative to the

soft tissues, the restoration, or both. The anodization can easily produce many different colors including clinically useful yellows, golds, and pinks (Fig. 14.7) all of

which are dependent upon the applied electrical direct current voltage. This natural

phenomenon is easily achieved using common electrolytes—usually acids, including products such as diet cola (Fig. 14.8).

The process involves placing a positive electrical charge on the titanium to be

anodized and placing it in an electrolyte which has a negative electrode immersed



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C. P. K. Wadhwani et al.



Fig. 14.8  Using weak

acids, including diet soda

which contains food-grade

phosphoric acid, as an

electrolyte for anodization.

Note the aluminum cooking

foil provides the negative

terminal for the solution



Fig. 14.9  Flat, 9 V

household batteries are ideal

to use for the electrical power

with anodization. Generally,

linking them in series by

“connecting them” allows the

voltages to be increased in

increments of 9 V. Nine of

these batteries produce a

“pink” hue, and seven linked

gives a “yellow” hue



in it. The negative electrode can pass electrical current through the electrolyte if

attached to aluminum cooking foil (Fig. 14.8). The electrical supply can be a dedicated direct current generator or simply common household batteries (Fig. 14.9).

Because electric current must flow onto the surface of the titanium, it must be clean

and free of oils. Similarly, at the conclusion of the anodization process, the abutment must be thoroughly washed with deionized water to remove any residue left

by the electrolyte used. At 63 V (seven 9 V batteries connected in series), a gold

color is produced. At 81  V (nine 9  V batteries connected in series), a pink hue

results (Fig. 14.5). This technique is highly effective, does not change the biocompatibility of the titanium, and is fast (taking less than 10 s). However, care must be



14  Delivery of the Definitive Abutment/Prosthesis



a



289



b



Fig. 14.10 (a) This abutment has HF (hydrofluoric acid 9.5%) applied. Within seconds the titanium surface starts to bubble (b). This is hydrogen being liberated. It can be used to etch the abutment; red wax is applied as a protective barrier at sites where etching is undesirable



exercised whenever electrical currents are employed, even household batteries can

induce an electric shock if incorrectly handled.

Titanium has other very useful properties also, for example, in contrast to zirconia,

titanium can be acid etched with 9.5% hydrofluoric acid for 30 s (Fig. 14.10a, b). This

results in an increase in surface area which improves micromechanical bonding.



14.5 Delivery of the Restoration

Many implant restorations provided by the laboratory have residual contamination

present. This may result from machining processes as described by Kelly or from

simply handling the components in a contaminated environment. Because these

items come into close proximity with the tissues, and in an ideal situation have some



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C. P. K. Wadhwani et al.



cellular attachment, these materials should be biocompatible, clean, and sterile.

Many offices do not possess plasma equipment to pretreat components. However,

some chemical cleansing is possible. Citric acid, a natural food substance, is readily

available from many grocery stores. Made into a 40% solution, it has been used to

effectively decontaminate implant surfaces affected by peri-implantitis. Placing the

abutment in an ultrasonic bath for 5 min and then rinsing thoroughly with deionized

water provide a cheap and effective decontaminant.

During the final stages of the implant restoration being delivered, irrespective of

the type (cement- or screw-retained), the contact points with the adjacent dentition

should always be carefully evaluated. They should allow floss to pass through, but

not be too light especially at the mesial contact site where natural teeth exist. Recent

data suggest that these will often present issues in the future with open contacts

developing as a result of the natural anterior mesial drifting that occurs with natural

teeth, but not with implants.

Also, routinely radiographs must be made, to confirm component fit, and no

excess cement remains (Fig. 14.2b) as well as providing a baseline for evaluating

bone changes that may occur.



14.6 Implant Restorations

The vast majority of implant abutments are held onto the implant body via a screw,

although a few manufacturers use friction grip connections, but these can be problematic if the componentry must be removed. Restoring the implant superstructure,

such as a crown or a bridge, is generally undertaken either by a screw-retained or

cement-retained restoration.

Although there are proponents of each technique, neither is ideal, and both systems involve the use of a screw attaching to the implant body. The cemented restoration is separated to an abutment screwed onto the implant. It introduces more

variables into the system, with two attachment sites, the abutment and the crown, as

well as introduce another material into the system, namely, the cement which is

known to cause biological issues in some cases. The screw-retained option has only

one attachment as the abutment and restoration are an integral component. It may

have aesthetic issues associated with the screw access channel and has an access

hole with the potential to compromise the structure of the restoration.

With either of the systems discussed, the screw and how it works has been reported

on. Early implants tended to have screw loosening issues, predominantly related to

the poor tightening techniques involved. The screws were usually tightened to finger

tight, which produces a very inefficient use of the screw mechanics. Eventually, engineering principles were employed with the introduction of dedicated torque wrenches.

These are used to deliver a specific torque, known as preload, which is dictated by the

screw manufacturer. What this essentially does is cause a mechanical stretch within

the screw itself, turning the screw into a “spring”-type device that pulls the components tightly together and makes the most effective joint. However, there is still a lack

of understanding on how best to provide the preload with some authorities



14  Delivery of the Definitive Abutment/Prosthesis



291



suggesting waiting up to 10  min between repeated torque application. When one

evaluates how other industries approach screw loosening of critical components, it

appears waiting between torque applications is not needed. A prime example is the

motor racing industry, where formula one tires are replaced within seconds, using

torque devices and a single screw. They never wait 10 min! The authors consider

tightening torque should be repeated but within a second or so during the development of the preload and always to the manufacturers specifications.



14.7 M

 echanics of the Implant-Abutment Connection:

Delivery of Componentry

The screw connection must be very carefully considered, as it is a potential site of

implant failure, with screw loosening or breakage occasionally occurring.

Factors that can negatively affect this joint include how the components match or

fit together. Manufacturers design their joints to fit perfectly with predefined

machining tolerance, using specific metal alloys. If the tolerance or the alloy used

differs from the prescribed dimensions, then the joint may not work as intended.

Enlarged discrepancies at the implant-abutment junction will compromise the seal

and lead to premature screw loosening and larger microgaps which may harbor

pathogenic bacteria. For these reasons, prosthetic components should be made by

the implant manufacturer; predictable joints are essential to implant success.

Even with original componentry, errors can occur in the mechanics of the joint,

if, for example, a damaged screw is used or an incorrect torque delivered or the joint

is not fully seated. Care must be taken with all these aspects, and where a joint cannot be physically inspected by tactile probing, or visualized well made, radiographs

are essential.

Once the screw has been tightened, the screw head should be covered to maintain

the ability to use a screw driver in the event that the screw needs to be re-torqued.

Several materials have been proposed to do this, ranging from cotton wool, wax,

impression material, gutta-percha, and zinc oxide/eugenol; however, the authors

consider polytetrafluorethylene (PFTE)—also known as plumbers tape—to be a

good alternative. It is readily available, is inexpensive, can be autoclaved, and has

been shown not to support bacteria in an in vitro experiment when used as an access

hole spacer for endodontics.



14.8 Summary

Delivery of the final abutment/prosthesis is at the control of the clinician; he or she

may improve the biologics, esthetics, and mechanics by the choices made.

Understanding the value of the physical properties of the materials such as titanium,

as well as knowing how to make simple modifications, can vastly improve these

factors, usually in a simple, inexpensive, and clinically useful way.



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Planning is always essential; knowing where to place margins, how to control

cement flow, and choice of materials in situations where cementation is necessary

will help reduce the incidence of cement issues. A correct understanding of how the

joint works will also improve the long-term stability and outcome of the implant

restoration.



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