Introduction:
Replacement of missing teeth with osseointegrated (bone-implant fusion or contact) implants has become a predictable option with a high survival rate. An abutment is a connecting prosthetic element for a fixed bridge, partial denture, or, most importantly, for dental implant fixation. The versatility of zirconium abutments is due to the precision with which they can be designed by CAD or CAM technology (computer-aided designing or computer-aided manufacturing). Also alternatively, a wax-up can be scanned before milling a zirconium abutment. Hence, the use of 3D technology or CAD or CAM makes zirconia abutments effectively milled.
The grayish-blue tint in titanium abutments causes gingival discoloration in patients with thin gingival biotype. In cases of peri-implant soft tissue recession, the exposure of metal abutment severely compromises appearance. Hence zirconia abutments for this same reason (as they are of almost the same color as the natural teeth) are preferred by many patients and the operator for addressing esthetic concerns after implant fixation. A dental implant crown is anchored securely in place only as long as the implant abutment, the ceramic or titanium or zirconium abutment, is correctly fitted into the implant head portion. Also, it is used to facilitate proper bite and force distribution (masticatory forces) through the osseointegrated implant into the jaw bone.
Titanium vs Zirconium Abutments
Usually, titanium abutments require intra-sulcular placement of prosthetic margins to mask the gray appearance. Notably, this may lead to complications, such as cement residues. When it comes to the point of a zirconium abutment, especially in patients having thin gingival biotype, zirconia offers an esthetic advantage over the bluish-gray tint of the titanium abutment. Zirconia abutment can block the reflected light in thin gingival biotype patients that will produce a pleasing outlook or aesthetic appearance. Compared to titanium abutments, zirconia abutments have become the prime or preferred abutments mainly due to their excellent biocompatibility, mechanical strength, and insolubility in water. Moreover, zirconia abutments could limit bacterial adhesion (as they accumulate less dental plaque compared to titanium) compared with metal abutments. They exhibit soft tissue integration comparable with that of titanium abutments and have thus been noted as a viable alternative to metal abutments.
What Influences an Abutment Success?
Concerns for the success of a zirconium abutment always lie at the level of the internal connection of the abutment. Superior qualities of the abutment can be produced during manufacturing this zirconium abutment, especially regarding the internal connection by attaching a secondary metallic component. This may be essential even more when used for posterior teeth, as in premolars and molars, as the masticatory forces that produce stress on the abutment can cause the internal connection to weaken and abutment to eventually fracture. Certain preventive measures can avoid this by the implantologist during fixation mentioned below and also by the additional attachment of the metal component to the internal connection. Even in vitro studies or research cannot fully simulate the mechanism of actual intraoral fracture of zirconia abutments; hence this is a useful measure to counteract fracture forces. The dental laboratory's primary considerations for a zirconium abutment are:
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Implant abutment connection.
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Crown to implant ratio.
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Restoration vertical height (RVH).
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Occlusal design.
What Are the Fracture Preventive Measures?
Even in case, a zirconia abutment either due to patient preference or the dentist recommendation is adopted for posterior teeth. The following precautionary measures are a must:
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Careful seating is the zirconia implant abutment.
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Use of torque control instruments.
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The minimal wall thickness should not be reduced beyond 0.5-0.7mm.
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Proper case selection (anterior vs. posterior area, prior occlusal scheme, and avoidance of unfavorable parafunctional habits).
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Use of copious irrigation when modifying the abutment using high-speed rotary instruments.
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Radiographic confirmation of complete abutment seating before the application of torque to the abutment screw.
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Maintenance of a minimal abutment thickness of 0.5 mm.
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Use of other materials, such as titanium or metal alloy, when the thickness required is not met.
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In the presence of parafunctional habits and unfavorable biomechanical parameters, external or internal zirconia abutments with metal components should be considered as the first choice to reduce the risk of clinical failures.
How to Ensure Long-Term Stability of Zirconia Abutments?
In order to ensure long-term stability, a minimum wall thickness of 0.8 mm is required throughout the zirconia abutment structure. Patients with zirconia abutments are usually advised not to eat very hard food (owing to higher fracture rates accidentally on chewing too hard foods). Any abutment in a dental laboratory is primarily milled, taking into accord both the anatomic and functional characteristics (the shape, size, angulation, and diameter of the implant). The dental implant needs a supra structure that cannot only bear adequate stress or force of mastication (that is transmitted to the implant and to the jaw bone, just as in the case of a natural tooth). Also, it should have an aesthetic finish, especially in patients who have a thin gingival biotype (where the light gets reflected easily through the thin gingival tissue). Zirconium abutments' primary goal is always to suit the patient's gingival margins. The casting of zirconium abutments in the laboratory is also by advanced high-tech injector technology that gives appropriate durability over a lifespan.
Conclusion:
Selection of an eligible dental laboratory and modification of the abutment with appropriate mentioned fracture prevention measures should be adopted to withstand stress distribution during masticatory forces. The dental implantologist should consider both the esthetic and functional aspects of seating a zirconium abutment for an implant before fixation for the patients who opt for zirconia abutments. Also, by adopting fracture-resistant criteria, a competent dental implantologist or dental surgeon can definitely ensure the long-term success of zirconium abutments.
