From conception to implementation: Efficient production of a hybrid implant-supported full-arch restoration

From conception to implementation: Efficient production of a hybrid implant-supported full-arch restoration

A metal-acrylic hybrid prosthesis has been a traditional choice for implant-supported full-arch restorations. A newer development has centred around the use of zirconia. While acrylics are lighter and cheaper, zirconia offers the greatest combination of strength and aesthetics. This article describes a protocol for the fabrication of hybrid prostheses consisting of a primary structure made of titanium and a secondary structure made of zirconia.
The tooth and gum morphology were digitally designed in DentalCAD (exocad, Germany) (Figure 1). Next, a passive bar was designed in a new project (Figure 2), manufactured in aluminium and sent to the clinic for testing and adjustment.
Unlike teeth, that are connected to the bone via the periodontal ligament, implants have a rigid connection to the bone. Therefore, a passive fit of the suprastructure is very important.

Fig. 1: Complete teeth and gum design in exocad.

Fig. 2: Bar on implants with passive connection.

Fig. 3: Cut and splinted aluminium bar.
Fig. 4: Printed test on model created with split cast.
Fig. 5: The primary structure in titanium. Care was taken that around the screw hole, the material had a minimum thickness of 0.8 mm.

Fig. 6: The secondary zirconia structure was milled from a 25 mm Initial Zirconia Disk Multilayer Elite.

A misfit of the suprastructure can have negative effects, such as detrimental stresses on the bone- titanium junction or prosthetic problems, such as screw loosening. The dentist verified the seating of the aluminium bar, cut and splinted it in the new position for a perfect passive fit (Figure 3) and sent it back to the lab. Then, the analogues were placed and the new position was fixed using a silicone base former and FujiRock Polar White gypsum. This was scanned with scanbodies and overlap meshes in exocad to have the new position of the analogues located in the three-dimensional space of the original design.

A prototype based on the digital design and with the optimised implant positions was then 3D-printed (Figure 4). This step served to verify the gum pressure, function, and aesthetics intraorally. After verification of the passive structure and intraoral mock-up, the primary and secondary structure were designed in Blender4Dental (Blender). The primary structure consists of a titanium bar (Figure 5) that needs to be screwed onto the prosthetic abutments and is then completed with a secondary zirconia structure. This secondary structure was milled from Initial Zirconia Disk Multilayer Elite from GC, Shade A2 (Figure 6).

Next, the zirconia structure was customised. In this case, a manual vestibular reduction was carried out in both the white and pink parts using different burs and stones to achieve an individualisation effect between the teeth (Figure 7). Such manual changes are always done in the green state of the material. After sintering (Figure 8), further internal characterisation of the gum and teeth was done with Initial IQ Lustre Pastes ONE (GC) and Initial Spectrum Stains (GC). For the teeth, L-NFL was used as a fluorescent base. Different colours were then applied on top to create different chromatic areas and effects. The cervical areas of the teeth were coloured with L-B.

Fig. 7: Zirconia framework after removal from the disk and manual cut-back.

Fig. 8: Initial Zirconia Disk Multilayer Elite framework after sintering (Shade A2).

In the middle area of the central and lateral incisors, a light refracting zone between the cervical area and the incisal area was created with a mixture of L-V and L-1. This effect adds to the natural appearance. In the incisal area, a light absorption zone was created at the free edge with L-5 and a mixture of L-6 and L-3.

The mamelons were created with a mixture of L-V, L-1, L-B and SPS-4. Finally, a non-fluorescent L-N base was used for the gingiva, and different gum shades were added to create naturalness.

Figs. 9-10: Application of Initial IQ Lustre Pastes ONE with Initial Spectrum Stains (GC).

Fig. 11: Initial IQ Lustre Pastes ONE with Initial Spectrum Stains: result after firing.

Fig. 12: Application of different masses of Initial Zr-FS: EOP-2, EOP-3, E-58, CT-22, FD-92, Dentin A2, CL-F; GM-24, GM-34, GM-36 and GU.

The free gingiva was coloured with G-23+ LP-M4 and G-24, while G-35 was used for the attached gingiva. The alveolar mucosa was coloured last with G-36 (Figures 9-10).

After firing, we already see the beautiful, natural colour and gloss appearing (Figure 11). Further characterisation was done with Initial Zr-FS (Figure 12). These beautiful feldspar-based masses add depth and vitality to the structure. Enamel Opal shades EOP-2 and EOP-3 and E58 were used to mimic the enamel.

Cervical translucent shade CT-22, Fluo Dentin FD-92, Dentin DA2, CL-F were used for the teeth. Gum shades GM-24, GM-34 and GM-36 were combined with gum universal (GU) to finish the gingiva.

Figs. 13-14: Result after glazing.

Fig. 15: The bluish 3D-effect on the incisal edge adds to the vividness of the teeth.

A high-end prosthesis, comprising a high-precision titanium bar and zirconia stands out as the premium choice for a full-arch prosthesis. It is resistant to staining and its smooth, polished surface is less likely to attract bacteria, resulting in easy maintenance and optimal hygiene. (Figures 13-14)

TIP: the blue effect on the edges comes from the combination of the internal characterisation and putting EOP-3 in the same zone, creating that three-dimensional area (Figure 15).

Initial offers a complete system to achieve the highest quality in the most efficient way. The most notable factors are: stability, reproducibility, time and aesthetics.

01. Stability: The Initial materials act reliable and predictable; combined with a good protocol, this gives great control over your work.

02. Reproducibility: That same protocol and materials give reproducible results, minimizing possible errors.

03. Time: Workflows that can be customised to fit the need of each work enable to be more efficient and productive.

04. Aesthetics: Due to the right protocol, the vibrant shades and the consistency in results, a very aesthetic and natural-looking outcome can be achieved, time after time.

CONCLUSION

Considering all these advantages, it stands out as an exceptional choice for delivering durable and satisfying dental solutions (Figures 16-18). By prioritising quality and precision, we can ensure our work leaves a lasting impact on both patients and practitioners alike.

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