Table of Contents:
When we talk with our patients about full-arch rehabilitation, we should give enough attention and detail to every phase of the procedure including, treatment planning, surgical, provisional prosthesis as well as the All-on-X final restoration. Different final restorative options exist to accommodate various functional and esthetic needs, but they also vary in terms of convenience and financial considerations. Therefore, we need to take into consideration the advantages and disadvantages of all the available treatment modalities to determine which would be the ideal choice for each case. By doing so and sharing with the patient, we ensure more sustainable clinical outcomes of the restorative treatment as well as higher patient satisfaction rates.
We will be exploring 5 of the currently available final restorations and what are the pros and cons of each one of them.
1. Screw-Retained Hybrid Denture
Also known as Fixed Complete Denture/Bridge; is an implant-supported final prosthetic option that has been in use for some time now. First, a metallic framework is made (e.g. cobalt-chrome alloy), followed by the addition of acrylic resin pink material and denture teeth with the desired shade. Porcelain teeth can also be used to mitigate strength-related issues of acrylic teeth.
- Relatively low manufacturing cost.
- Minimal repair-associated costs; only chairside application of resin is needed to fix defects. No need for lab repairs.
- The most popular final prosthetic option for full-arch cases.
- Restorative space (i.e. from the ridge to the occlusal surface) of at least 12-15 mm is required to give the acrylic enough bulk for strength.
- Increased risk of breakage if adequate space is not provided.
- Faster rate of wear especially if the opposing arch has natural or porcelain teeth; this will negatively affect function and esthetics by reducing the occlusal vertical dimension if left untreated.
2. Metal Framework with Single Crowns
In this final prosthesis, we start with a metallic base that has single crown preparations. Each crown is designed, fabricated and attached to the base resulting in a single-unit All-on-X final restoration.
- Enhanced esthetics with a more life-like appearance due to individually-attached crowns.
- Implants don’t have to be in the exact position of the teeth.
- Improved load-distribution qualities thanks to porcelain crowns with less staining and higher translucency.
- Increased risk of breakage due to chipping and cracking of porcelain crowns.
- Complex repair process and higher costs (unless digital CAD/CAM methods are used from the start).
3. Zirconia Framework with Porcelain Overlay
Instead of metal, zirconia is used to fabricate the framework which then allows for porcelain to be attached on top. Alternatively, the zirconia base can be used to accommodate the cementation of single porcelain crowns to decrease potential repair fees.
- Zirconia has superior biocompatibility, durability and esthetics.
- The whiteness of zirconia is far better than the metallic color which might show under the porcelain.
- If the single-unit porcelain overlay method is used, the entire restoration has to be removed and sent to the lab for repairs in case of any breaks or cracks.
- Costly repairs as multiple visits will be needed to fix the restoration.
4. Full-Contour Zirconia Bridge
No porcelain is used in this treatment option; a single block of zirconia is milled into a complete bridge. The full-contour zirconia prosthesis is then stained in the desired pink and white shades in order to replicate the natural gingival tissues and teeth. Due to the high strength of this All-on-X final restoration, fractures are relatively rare. However, in some cases, the zirconia denture can break into two pieces; in which case the prosthesis has to be removed and remade. Fortunately, the original STL files from the CAD/CAM phase can be used to make a replacement quickly and efficiently.
- Maximized strength, durability and esthetics.
- Reduced chances of attrition, chipping or cracking.
- Reduced translucency of zirconia results in suboptimal esthetics.
- The entire bridge has to be removed and remade in case of a serious fracture.
- High cost of replacement as well as longer waiting times.
5. Partial Implant-Supported PFM Bridges
Conventional porcelain-fused-metal (PFM) bridges can also be used to restore a fully-edentulous arch. Multiple partial fixed bridges are retained using implants as abutments. This is similar to the implant-supported crown and bridge procedure in partially-edentulous cases. However, it can be a complex treatment option because of the need for final adjustment of different contact points which can hinder the passive fit of the All-on-X final restoration.
- Separations between bridges in the midline and other areas along the arch make for a more life-like appearance.
- Ease of replacing a single bridge individually as opposed to having to take a complete denture out.
- At least 2 implants are needed for a 3-4 unit fixed bridge as opposed to the All-on-4 cases where a complete bridge will fit only 4 implants in the whole arch.
- Adequate remaining bone volume is needed to place implants anteriorly and posteriorly.
- Bone grafting may be required for implant placement.
The convenience of CAD/CAM final restorations lies in the fact that even in the unfortunate case of prosthesis fracture, the re-fabrication process doesn’t take long. The STL design files are already there and can be used immediately for re-milling or reprinting. Therefore, the patient isn’t inconvenienced by having to wait without his or her denture for an extended period of time. For the same reason, although single-unit final restorations have higher durability, the fracture of their framework will require removal and in some cases, remaking, which is not ideal for the patient.
One important factor to be taken into consideration is the status of the opposing arch. This will largely determine the choice of material to use in the final prosthesis. At first sight, zirconia might seem like an ideal option due to its durability and wear resistance. However, if the opposing denture has acrylic teeth, the chances of wear will be increased in the acrylic restoration resulting in flattened incisal edges and cusps as well as the decreased vertical dimension. If left without treatment, this will result in reduced chewing ability as well as compromised esthetics.
To help minimize these disadvantages, denture teeth made of porcelain are preferred to acrylic ones since they can withstand wear better. Alternatively, metallic occlusal rests (or metal islands) can be added posteriorly in order to achieve proper cusp-fossa contact. However, it should be noted that this may lead to higher treatment and repair costs as well as suboptimal esthetics due to the grey color of metal showing through.