Soft tissue contours are critical to fabrication of fixed and removable implant prosthetics. Without this information aesthetics and hygiene may be compromised in the final prosthetics.
To ensure that the emergence profile of fixed abutments replicates natural tooth aesthetics, the laboratory technician must be able to see the gingival margin and know the thickness of the soft tissue. Fixed prosthetics on natural teeth provides a margin at or slightly below the gingival margin. The resulting cast fabricated from the impression, is sectioned to provide individual dies. These dies are then ditched and marked to expose the die margins. Thus allowing the technician to wax and finish the metal portion of the abutment. Conversely, implant fixed prosthetic abutments utilize prefabricated metal components that are modified or cast. Soft tissue models can be fabricated in the laboratory or in the office. Soft tissue depth can vary due to bone loss and implant plateform placement. Often the width of the implant is significantly less then the needed cervical width of the restoration. Emergence profile may require the prosthetics to increase from 4mm at the plateform to 7mm at the cervical region with a soft tissue depth of 6mm or more. Without the soft tissue present for the technician it is difficult to determine where the cervical region needs to be placed, especially when natural teeth are not present in the arch adjacent to the implant.
Removable prosthetics retained with overdenture bars also present challenges with respect to hygiene and where the bar will connect to the abutment head. If the joint between the abutment head and bar is too close to the gingiva, seating of the bar may be difficult and chronic inflammation may result. A soft tissue model can provide valuable information to the technician allowing them to design the bar at the ideal height in relation to the soft tissue surrounding each abutment providing better long-term gingival health.
METHODS AND MATERIALS
The healing screws are removed from the implants and impression heads are affixed (Figs. 1 & 2). A full arch Exaflex, polyvinyl siloxane impression (GC America, Alsip, IL) is taken in a stock plastic tray (GC America, Alsip, IL) (Fig. 3).
Implant analogs are affixed to the impression heads encased within the polyvinyl siloxane impression (Fig. 4). The cartridge of GI-Mask, (Coltene/ Whaledent, Mahwah, NJ) a silicone based soft tissue replicating material is bled prior to initial use. Bleeding the cartridge ensures that the two components will flow into the mixing tip without plugging the tip (Fig. 5). A mixing tip is placed on the cartridge and an intraoral tip is placed on the end of the mix tip (Fig. 6). The next step is critical to prevent adhesion of the GI-Mask to the polyvinyl siloxane as they are chemically similar and will bond. GI-Mask lubricant is sprayed over the entire impression and analogs (Fig. 7).
The GI-Mask is injected around each analog (Fig. 8). Material should be confined to the coronal third to allow sufficient length of the analog within the model stone. After completion of set, a scalpel is used to trim the mesial and distal of the soft tissue material to ensure that adjacent proximal contacts are in stone (Fig. 9). A die stone, Kromotypo 3, is then poured into the impression to complete the cast. (Kromopan USA, Inc., Des Plaines, IL) After setting it is trimmed and the soft tissue model is complete (Figs. 10 & 11).
CONCLUSION
Without the knowledge of where the gingival margin is the technician cannot determine where connector joints need to be placed in the framework or the emergence profile of fixed cases. Soft tissue modeling can provide critical information to the laboratory technician that can improve the aesthetics and hygiene of the completed implant prosthetics.OH
Dr. Kurtzman is in private practice in Silver Spring, MD and is an Assistant Clinical Professor at the University of Maryland School of Dentistry, Department of Restorative Dentistry.
Dr. Schneider is in private practice in Springfield, VA. He is a consultant to various dental companies. He is also a consultant in prosthetics at the Veterans Administration at Martinsburg, WV.
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Soft tissue modeling is critical for accurate aesthetics and hygiene when fabricating fixed and removable implant prosthetics. Gingival morphology is an important detail to be communicated to the laboratory technician. This article shall address a method of fabricating a soft tissue implant model.
