Jochen Könneker, CDT, outlines the production process for implant-supported or retained restorations made with titanium



Titanium in combination with CAD/CAM technology has become a cost-effective alternative material choice due to the current exorbitant cost of precious metals and the high labor costs of traditional manufacturing processes. Implant-supported and/or retained full-arch/full-mouth restorations made with titanium bars and substructures present unique challenges with regard to techniques and materials.

Nobel Biocare™ pioneered this concept with the All-on-4™ (fixed-detachable hybrid denture) and Procera® Implant Bridge (PIB) treatment modalities. Today, there are many variations and sources for titanium substructures and bars, ranging from other implant manufacturers to independent third-party suppliers such as Cagenix™. The production process to produce the aforementioned restorations is the same regardless of the subframe manufacturer.

First, a full-arch stone master model with soft-tissue moulage is poured from the impression that was made following either a full-arch direct or indirect impression technique. The soft-tissue moulage material needs to be flexible and removable from the stone master model. Although several manufacturers offer this kind of material, it is important to choose a product with a high elasticity, such as Gingifast Elastic (Zhermack®). A rigid material such as Gingifast Rigid (Zhermack®) is too brittle and may not withstand the rigors of repeated removal and repositioning of the soft-tissue moulage.Models poured without soft tissue may not be suitable because the scanning procedure requires clear access to the analog/scan peg interface.

After the model is poured and trimmed, a base plate and wax rim are fabricated. Non-indexed (non-engaging) temporary cylinders may be incorporated into the base plate to facilitate a more predictable bite record procedure. The number of temporary cylinders to be incorporated could be argued. Utilizing two or more cylinders may place the implants under undue stress because the model on which the base plate was fabricated has not been verified for accuracy at this time. Executing the base plate with only one cylinder would avoid any inaccuracy, but renders the base plate less stable.

Overcoming the inherent potential of distortion from impression taking to model fabrication combined with the difficulty of sectioning and lasering titanium necessitates the fabrication of a verification index or jig. The verification index consists of non-indexed temporary cylinders (preferably metal) connected to each analog and joined with light-cured acrylic. This index is then tried in the patient’s mouth, and seating of the cylinders is documented with a pano. In case of ill fit, the jig is sectioned and reluted intraorally. Upon return of the index and the master model to the laboratory, the offending analogs (if any) are carefully removed from the model and repositioned with the aid of the verification index.



Denture teeth are now set in wax for try-in with a lingualized, lingual-contact occlusion1 in a conventional fashion onto the previously manufactured base plate. The dentist will then verify proper occlusion, phonetics, and esthetics of the wax try-in in the patient’s mouth. Barring any major reset of the wax try-in, a silicone matrix is created over the set-up, covering the vestibular and occlusal aspect of the set-up. The silicone matrix and the set-up are removed from the model after the matrix is cured. The matrix is repositioned onto the model without the wax-up in place, and the vertical height availability and screw access path of the analogs in relation to the proposed tooth position are surveyed. A minimum height of 12-15 mm is required to accommodate the substructure or bar in combination with acrylic and denture teeth.

Now the anteroposterior spread distance is determined by measuring the distance between the most anterior analogs to the most posterior analogs and multiplying the measured distance by a factor of one and a half. First, a line connecting the two most posterior implants on each side of the ridge is drawn through the distal aspect of the implants, followed by drawing a second line parallel to the first through the center of the most anterior analog. Measuring the distance between the two lines and multiplying the measurement gives a guideline of the length of any possible distal cantilever. Other factors, such as patient gender, age, and opposing dentition (natural or prosthetic) influence the decision-making process in determining a patient’s specific cantilever length.



The future substructure may be fastened directly to the implants or intermediate abutments (abutment for screw, BioHorizons®, and others) to either overcome excessive tissue height (≥ 2 mm) over an implant and/or to change the screw-access path of the fixation screw.

Once the appropriate modus of fixation is resolved, the model is scanned for digital design or sent to a milling center. If the model is scanned on the premises, implant manufacturer-specific scan pegs are attached to each analog to record their relationship in space to each other and render a virtual three-dimensional model for computer-aided design of the framework. Many design options are available to achieve restoration objectives. A multitude of attachments (Locator®, Hader, ball-type and others) and combinations thereof are possible for overdenture bars. Fixed detachable frames may be designed as wraparound, with a metal tissue side or a metal lingual. After the virtual design is finished, the digital design file is sent to a milling center to mill the substructure out of a solid piece of titanium (CAM).

Upon delivery of the finished frame to the laboratory, its accuracy and fit are checked and verified on the master model. The original wax try-in is then transferred with the aid of the silicone matrix onto the model with the titanium frame installed. Acrylic is processed in a restoration-type specific method over or around the substructure and finished in a conventional fashion.
At the time of delivery, the dentist transfers the intermediate abutments to the patient’s mouth in their corresponding locations and orientations, and then seats the final restoration, or if no intermediate abutments were utilized, fastens the restoration directly to the implants. The occlusion and lateral contacts are checked and calibrated. Screw-access holes are obturated with acrylic or composite in the case of a hybrid denture.




For further information in regard to implant procedures and components, visit genieoss.com. The fine art of acrylic denture fabrication may be explored at personalizeddentures.com.

Bio

Jochen Könneker is a certified dental technician (Dental Technician Guild, lower Saxony, Hannover, 1986) from Germany, first introduced to the field of implant technology more than 20 years ago as an in-house, all-around technician for a prosthodontist in Beverly Hills, CA. Today he leads the implant department in one of the United States’ largest dental laboratories. He was granted fellowship in the ICOI, graduated from Dr. Carl Misch’s International Implant Institute’s prosthetic courses I, II, and III, and founded genieoss.com in 2010.

Reference

1. Lang BR, Lauciello FR, McGivney GP, et al (2010) Contemporary Complete Denture Occlusion NA3600311 Rev. 2. Ivoclar Vivadent. For a copy of this manual, contact Ivoclar Vivadent at 800-533-6825.