In Part I of this series, I introduced a 21-year-old patient that was missing teeth 8-11 and 21-27 due to a life-threatening car accident. I demonstrated the results we could achieve for him, but he was very particular about the esthetic outcome and felt that he wanted to get other opinions.
He returned to our office 13 months later – now missing teeth 6-11 and 21-27 with four Nobel Replace Select dental implants placed in both the maxillary and mandibular anterior segments. Once again, the diagnostic matrix was evaluated intra-orally during the discussion of the restorative treatment options. The healing abutments were visible through the clear thermoplastic matrix to demonstrate the position of the dental implants relative to the position of teeth on the surgically altered dental arch but not relative to facial landmarks. A specific restorative treatment plan was discussed that would connect the dental implants to provide support for the prosthetic teeth and soft tissues of the upper and lower lips.
Integral to the process of the restorative treatment, the planned design of the prosthesis with acrylic provisional restorations was evaluated to determine tooth position, lip support and adaptation to speech sounds. The provisional restoration was made with information provided by a diagnostic evaluation of the anterior teeth that tested the appearance and soft tissue support of the lower third of the face. A silicone matrix was made on the working model to transfer the arrangement of the teeth and requirements for tissue support to the provisional restoration. Non-indexed titanium provisional abutments were placed on the working model and attached to the teeth with auto-polymerizing polymethyl-methacrylate using the silicone matrix.
The provisional restoration was modified on the intaglio surface to create a smooth convex surface to allow for hygiene maintenance with dental floss. The goal was to create an optimal shape of the residual alveolar ridge prior to construction of the definitive restoration. The soft tissue was surgically modified in the areas of the dental implants to accommodate the intaglio surface of the provisional. Following an intra-oral evaluation period, the adjacent maxillary premolars were re-contoured on the mesial surfaces to provide an optimal transition between the natural teeth and the definitive prosthesis.
Materials for implant-supported fixed prostheses include frameworks made of a metal alloy that is cast, or it can be made of titanium or zirconia made by computer aided milling procedures. A framework can be made for a porcelain-fused-to-metal restoration to create a customized result and an optimal tissue response at the intaglio surface (Chan & Weber JPD 1986).
Due to the technical skill and time involved to create a customized result, porcelain-fused-to-metal restorations of this nature increase the overall cost of the prosthesis. The heating and cooling cycles required, along with multiple firings of the porcelain with a large metal framework, will likely result in some distortion of the restoration that can be adjusted prior to cementation (Karl JPD 2005).
Chan C & Weber H. Plaque retention on teeth restored with full-ceramic crowns: A comparative study. Journal of Prosthetic Dentistry 1986; 56: 666-667. Plaque accumulation was measured using Silness & Loe plaque index:
- All ceramic (Cerestore) – least plaque accumulation
- Metal ceramic
- Complete gold crown
- Acrylic resin provisional
- Natural tooth – most plaque retention!
Karl M, et. al. Static implant loading caused by as-cast metal and ceramic-veneered superstructures. Journal of Prosthetic Dentistry 2005; 93(4): 324-330. "Conventional procedures were unable to produce superstructures with absolute passive fit. Ceramic veneering appeared to increase the strain development and, thus, the inaccuracy of the fit. The technique of cementing superstructures to prefabricated components directly on the implants may compensate for dimensional errors caused by the impression making and superstructure fabrication".
Douglas G. Benting, DDS, MS, FACP, Spear Visiting Faculty [ www.drbenting.com ]