Case Report: Screw-Retained Zirconia Implant Restoration

Implant-supported restorations are one of the most commonly utilized alternatives for replacing single missing teeth in partially edentulous patients. Different clinical situations must be considered when selecting the appropriate abutment as the proper design and material enable the clinician to achieve an excellent clinical outcome. Screw-retained zirconia restorations are an excellent alternative for screw-retained metal ceramic restorations because the custom abutment is designed from the final tooth wax up, which provides a more natural esthetic result in single tooth restorations.

This clinical case of a 55-year-old patient treated at the University of North Carolina School of Dentistry Student Clinic is an ideal example of a situation where a screw-retained zirconia implant (Atlantis, Dentsply Professional, York, Pa) restoration was chosen. The patient presented with a previously placed implant (Astra Tech, Dentsply Professional) that lacked an emergence profile, had insufficient interocclusal space, and was placed in a nonideal mesial distal position. This case explores the rationale of using the custom screw-retained zirconia implant (Atlantis) restoration and presents a new alternative for screw-retained metal ceramic restorations.

The patient presented to the 4th-year dental student clinic with a 3.5 mm × 11 mm Astra Tech OsseoSpeed TX implant that had been previously placed by another clinician. Proper osseointegration was noted at the time of the oral examination (Figure 1); however, an insufficient interocclusal space of approximately 5 mm for the implant restoration was noted. The lack of an emergence profile was also observed due to the small implant diameter and insufficient depth of implant placement. More importantly, the implant was placed distal relative to the ideal location (Figure 2). Restorative treatment options were presented to the patient, and based on the patient's desires and the position of the implant, a screw-retained zirconia implant restoration was prescribed to allow for retrievability and an improved emergence profile. Preliminary impressions and diagnostic records were taken to generate an accurate diagnostic wax up. A final impression was made using a stock tray, an impression transfer, and polyvinyl siloxane impression material (3M Express, 3M, St Paul, Minn). A mandibular working cast was generated using soft-tissue moulage and type III dental stone.

The laboratory procedure consisted of a double scanning process where the model was scanned with the occlusal registration material and the diagnostic wax up was then scanned with the fixture locating object to allow for accurate correlation. Once the scanning process was finished, data were sent to the Atlantis design website (http://www.atlantisweborder.com); within a short time the design prototype was sent via e-mail to the clinician. The software allowed the clinician or laboratory technician to modify and design the abutment via an online 3-dimensional editor (Figures 3 and 4). Once the design was approved, the definitive implant restoration was fabricated¹  from a monolithic zirconia block and then sintered. Cutbacks were made to provide for veneering ceramic (Figure 5).

The restoration was tried in, adjusted, inserted, and torqued to 30 Ncm following manufacturer's instructions (Figure 6). To enhance the esthetics and function of the restoration, an access screw hole was covered with a lithium disilicate porcelain (Emax, Ivoclar Vivadent, Amherst, NY) plug in a slightly darker shade (Figure 7), which blended seamlessly with the zirconia. The porcelain plug was etched, silaned, and luted using composite resin cement (RelyX, 3M, St Paul, Minn). Covering the access hole with lithium disilicate allows the clinician to know exactly where the access hole is located, therefore providing easier retrievability if drilling to expose it is required in the future. Esthetics and function were checked and approved by the patient (Figures 8 and 9).

As previously noted, the rationale for using a screw-retained restoration is to provide a retrievable restoration with an optimal emergence profile and proper soft tissue sculpting, a cement-free alternative that maintains a clean oral environment, and an all-ceramic restoration that has excellent mechanical properties and the ability to allow for porcelain stacking, thereby enhancing the esthetics when needed.² 

Traditionally, the objectives of dental implant therapy have been measured by successful osseointegration and function over time. However, in the past decade, restorative parameters, in combination with soft tissue management, have become more important than survival in defining the success of implant restorations.³  Contemporary computerized dental technologies provide a predictable alternative in more challenging restorations.⁴  These technologies have also introduced a variety of new options and materials that the clinician can use in different clinical scenarios in which both function and esthetics can be achieved.^3,5–7 

In the past decades, implant manufacturers have introduced many abutment designs and materials for the restoration of dental implants in every clinical situation. Previously, if a clinician wanted to use a screw-retained restoration, the only options available were a prefabricated abutment or a cast burn-out abutment for a custom design commonly called a “UCLA abutment.”^8,9  This abutment type was primarily recommended for treating malpositioned implants.¹⁰  With the arrival of digital technologies, milling custom abutments became a very predictable and affordable procedure compared with the fabrication of cast abutments.

Currently, implant abutment angulations, the emergence profile, and the abutment axial wall width, height, and angulations can be determined and customized by computer software before the abutment is made.^3,4,11  Custom abutments can be designed for cement-retained restorations, but limited options exist regarding custom screw-retained abutments. Conventional fabrication of screw-retained abutments typically involves waxing, casting, and finishing processes in the dental laboratory.

A computer-aided design/computer-aided manufacturing (CAD/CAM) abutment can be digitally contoured to specifically fit the gingival architecture of the tooth being replaced and to provide the desired emergence profile to enhance esthetics.^3,12,13  Furthermore, if the implant angulation or depth needs to be corrected, the custom abutment provides the flexibility to create an ideal path of insertion with different configurations, such as amount of tissue displacement, finish-line antirotational features, and gingival transitions when the overlying restoration will not have the ideal anatomy and location.¹⁴  Five different zirconia shades are now available through Atlantis, helping to match most shades when making esthetic considerations. The CAD/CAM abutments can be designed, generated, and milled by computer software.^5,6,12,13 

The most important advantage of this approach is that the clinician or technician can control the design virtually before having the final product made. This improves dentist-technician communication and satisfaction because it allows the clinician to review and approve changes before the abutment is milled. Implant abutments generated by CAD/CAM technology are more precise than those created using traditional casting technology. Dimensional inaccuracies of investing and casting are eliminated; therefore, the precision of components could increase prosthetic success and ease of restoration.^12,13,15 

Another advantage is that fabrication of CAD/CAM abutments has a fixed and predictable cost, making this type of restoration more cost effective and affordable for the dentist.^3,15  This option is more cost effective and less time consuming in the long term, thereby increasing production for the dentist and dental technician. In addition, once designed, the file, including the design of the abutment restoration, can be saved and stored for future use if needed, saving time and money for any future treatment. However, most CAD/CAM abutment designs have been fabricated for cemented restorations, which can lead to some discomfort and possible gingival irritation for the patient due to the difficulties in removing all of the excess cement debris. Some clinical scenarios will require a customized screw-retained restoration. In a randomized controlled trial with abutments in the posterior region of the mouth for single restorations, Lops et al¹⁶  found a prosthetic survival rate of 100% for all abutments at 5 years. However, one limitation of restorative abutments is the strength of materials used. Zirconium, when placed in the posterior portion of the mouth, may be susceptible to fracturing or chipping.² 

Overall, screw-retained zirconia restorations can be excellent alternatives for screw-retained metal ceramic restorations because they provide an efficient approach to creating a retrievable custom abutment that will adapt to the final shape of the restoration and offer an excellent solution in situations in which interocclusal space is limited or an emergence profile is lacking.⁴