Implant-retained overdentures have emerged as an effective treatment option for edentulous patients (those who have lost all teeth), especially the ones who struggle with conventional removable dentures. Implants offer a less time-consuming, aesthetically pleasing, and minimally invasive approach to restoring missing teeth.
However, most implant-supported types of dentures, including overdentures that fit on existing natural teeth, snap-in dentures that are held in place by implants, and all-on-four dentures that use mini-implants are still removable, meaning that they must be taken out at the end of the day for cleaning before going to bed.
Hybrid implant-supported dentures, on the other hand, can be permanently fixed, such that you don’t have to remove it from your mouth for cleaning or when going to bed.
What is a hybrid denture?
Hybrid prostheses or hybrid dentures are usually recommended for patients who cannot adapt to traditional complete dentures, or experience difficulties with removable implant overdentures.
Hybrid dentures provide a fixed restoration option and have been utilized since the 1980s, offering a state-of-the-art solution for fixed implant-supported restorations.
A hybrid denture is constructed using a metal framework and retained in place by screws threaded into the implant abutments. The front portion of a lower hybrid denture is fixed to implants, while the posterior part extends and cantilevers from the implants. This design allows for stability and improved functionality.
There are two common approaches to designing hybrid prostheses:
- The first involves metal frameworks as the primary component, with artificial teeth and minimal denture bases being non-metallic.
- The second approach utilizes acrylic resin denture bases and artificial teeth, with smaller metal frameworks (known as a wraparound design).
As fixed restorations, it means that the dentures cannot be removed by the patient and are retained by cements, screws, or a combination of both. As a stable restoration option, they provide improved function, aesthetics, and the preservation of alveolar bone, enhancing the overall oral health and quality of life for individuals with complete tooth loss.
Number of Implants and Positions for Hybrid Dentures
In order to distribute the masticatory load and prevent bending moments that may lead to bone loss, an increase in the number of implants is recommended for edentulous patients in the upper jaw.
Upper jaw
A minimum of 6 to 8 implants with a minimum of two centimeters spread from front to back is recommended. The implant in the back should be at least 10 millimeters long and placed in the position of the missing teeth.
Lower Jaw
For the lower jaw, 4 to 6 implants in the front of the jaw, anterior to the mental foramen, are recommended. This is due to the dynamics of the lower jaw during chewing, with occlusion (contact) occurring at the first molar and a distal (rear) cantilever extending up to 15 millimeters.
Frameworks for Hybrid Dentures
Frameworks play an important role in hybrid dentures as they provide support and retention for the functional and esthetic components of the prosthesis. The design and fabrication of metal frameworks are crucial for long-term success. Different methods and materials can be used for framework design in implant prosthodontics.
These include:
- Cast noble alloys (such as gold, palladium, silver, and platinum)
- Cast base metal alloys (nickel, chromium, cobalt, and iron-based alloys)
- Milled titanium frameworks
- Milled zirconium frameworks
CAD/CAM (computer-aided design/computer-aided manufacturing) frameworks are more precise and can be milled from titanium or zirconia. They have been shown to have similar clinical results to cast gold alloy frameworks but require fewer maintenance appointments.
CAD/CAM frameworks may be less expensive as they do not contain noble metals, but the labor costs for developing the wax/resin framework patterns should be taken into account.
Framework Design
The design of the framework is important to prevent fractures and ensure optimal strength. Different designs, such as I-beam, L-beam, elliptical, and oval, have been used successfully.
- I-beam designs have been shown to strengthen cantilevered portions of the framework and provide rigidity and strength with minimal increased bulk and weight.
- CAD frameworks with modified I-bar or elliptical designs have also been proposed, providing support for the artificial teeth and denture base.
The choice of framework design depends on various factors, including the specific case and patient needs.
Thinning of the framework is recommended to allow for the retention of acrylic resin denture teeth and to minimize the potential fracture of the acrylic resin base material. However, strategic thinning should not compromise the bulk of the framework.
Cantilevered segments should not exceed 20 millimeters, and the framework should provide adequate access for oral hygiene while minimizing the display of metal on the facial and occlusal surfaces. High-strength casting alloys and appropriate cantilever lengths are ideal to ensure structural integrity and resistance to stress.
Esthetic Material Used upon Metal Frameworks
Acrylic denture teeth are commonly used for hybrid prostheses. Over time, the occlusal surfaces of the denture teeth may show signs of wear and abrasion, leading to decreased chewing efficiency and exposure of the framework.
Traditional acrylic resin denture teeth typically last around 7 to 9 years before needing replacement. Micro-ceramic composites are alternative materials with improved wear resistance, water absorption, polymerization shrinkage, and high fracture strength. These materials can enhance the durability and esthetics of the hybrid prosthesis.
Hybrid Dentures vs. Removable snap-in dentures
Implant overdentures or snap-in dentures offer significant advantages over conventional complete dentures in terms of stability, retention, bite force, chewing efficiency, and oral health.
However, the fact that they are removable may be seen as a disadvantage by some patients. The forces exerted by natural teeth can potentially lead to fractures in implant overdentures and advanced bone loss.
In cases where patients have an extreme gag reflex, this treatment option may become more complicated.
On the other hand, hybrid prostheses can be designed with a shorter palatal border in the upper jaw, reducing or eliminating the gag reflex.
Hybrid prostheses are considered to be the most predictable treatment option for improving patient satisfaction in terms of oral pain and chewing functionality compared to implant overdentures.
However, there is a risk of mucositis (inflamed mouth), periimplantitis, and acrylic fracture with fixed implant hybrid prostheses.
| Hybrid Dentures | Removable Snap-in Dentures | |
|---|---|---|
| Advantages | – Improved stability, retention, bite force, chewing efficiency, and oral health | – Improved stability, retention, bite force, chewing efficiency, and oral health |
| – Can be designed with shorter palatal border to reduce or eliminate gag reflex in upper jaw | – | |
| – Predictable treatment option for improving patient satisfaction in terms of oral pain and chewing functionality | – | |
| Disadvantages | – Risk of mucositis (inflamed mouth), periimplantitis, and acrylic fracture with fixed implant hybrid prostheses | – |
| – | – Removability may be seen as a disadvantage by some patients | |
| – | – Forces exerted by natural teeth can potentially lead to fractures in implant overdentures and advanced bone loss | |
| – | – Complications may arise for patients with an extreme gag reflex |
Hybrid Prosthesis vs. Fixed Metal Ceramic Restorations
Metal-ceramic fixed implant restorations are recommended when there is minimal bone loss and a sufficient number of implants can be distributed along the edentulous arch.
However, these restorations may have negative effects on aesthetics, implants’ axial load, occlusal stability, and resistance of the veneering material around screw access holes.
In cases where there is a lack of osteomucosal support, fixed-detachable hybrid prostheses are considered the treatment of choice. In the atrophic maxilla (upper jaw with severe bone loss), hybrid prostheses have been reported to be superior to fixed metal ceramic restorations in terms of providing lip support, phonetics, and esthetics.
Cement-retained restorations are indicated when the crown height space (CHS) is between 8-15 mm. For CHS lower than 8 mm, there is not enough abutment height for cement retention, and for CHS greater than 15 mm, there are challenges in fabricating a metal casting that can support the porcelain without resulting in porosities or porcelain fractures.
In such cases, screw-retained hybrid prostheses are the treatment of choice. They are also more affordable than implant-supported fixed bridges but have higher maintenance costs compared to full arch fixed bridges.
However, it should be noted that hybrid prostheses may pose challenges in the maxilla in terms of speech and hygiene, as the design and contours can impact phonetics and compromise hygiene.
| Hybrid Prosthesis | Fixed Metal Ceramic Restorations | |
|---|---|---|
| Recommended Cases | – Lack of osteomucosal support | – Minimal bone loss with sufficient implants |
| – Atrophic maxilla (severe bone loss) | – | |
| Advantages | – Provides lip support, phonetics, and esthetics in atrophic maxilla | – |
| Disadvantages | – Challenges in speech and hygiene | – Negative effects on aesthetics, axial load, occlusal stability, and veneering material |
| – | – Challenges with crown height space (8-15 mm) | |
| – More affordable than implant-supported fixed bridges | – | |
| – Higher maintenance costs compared to full arch fixed bridges | – |
FAQs
Can you get same-day hybrid dentures?
Although patients can obtain their fixed dentures on the same day of implant placement, there are concerns about damaging the surgical site and irritating the freshly sutured tissue during the impression procedure. As such, your orthodontist may recommend an alternative method that involves an adjustable acrylic resin framework, which allows for maximum adaptability to your jaw size and shape. This method can accelerate the fabrication of the final metal framework of the prosthesis, resulting in a shorter treatment time.
How much should the denture extend from the last implant?
When deciding on the cantilever length and anterior-posterior spread of the framework for a hybrid prosthesis, several factors need to be considered, including the number and distribution of implants, arch placement, and the optimal design for the specific case. In the lower jaw, it is recommended that the extension from the most distal (last) implant should not exceed 15 millimeters. It’s also worth noting that hybrid dentures typically have fewer back teeth compared to a conventional complete denture. These considerations help ensure the stability and functionality of the prosthesis for the individual patient.
How do you ensure balanced occlusion with hybrid dentures?
Occlusion refers to the way the upper and lower teeth come together when you bite. With a balanced occlusion, the bite should be evenly distributed between the upper and lower jaws to help preserve the bone in the upper jaw. If any contact is noticed on the front teeth during check-ups, adjustments can be made to relieve pressure.
Are hybrid dentures suitable for patients with limited mouth opening?
Yes, fixed hybrid prostheses are often the preferred treatment option for patients with limited mouth opening caused by tumor removal. This is especially beneficial for younger patients with oral tumors as it can improve their speech, appearance, and overall oral function. Removable implant prostheses are not recommended in these cases due to the difficulty of daily removal and reduced saliva flow. It’s important to assess the patient’s maximum mouth opening before the tumor resection and provide appropriate care and support during the treatment process.
What is computer-aided engineering in the fabrication of hybrid prostheses?
Computer-aided engineering (CAE) is a technology used to create hybrid prostheses. It involves using sophisticated algorithms to guide the fabrication process, starting from acquiring clinical records to developing provisional complete dentures and radiographic templates. This technology improves the accuracy and efficiency of creating the prosthesis, resulting in better alignment of the teeth and overall treatment outcomes.
How should hybrid prostheses be maintained?
Regular maintenance is crucial for the longevity of hybrid prostheses. Studies have shown high implant survival rates but relatively lower denture survival rates. The denture may require replacement or repair due to wear on the false teeth. To minimize costs, the original frameworks can often be reused, although this process takes time and may require patients to be without their prostheses temporarily. It’s important to follow a maintenance schedule and seek professional care to ensure the prostheses remain in good condition.
Final Thoughts
Proper diagnosis and treatment planning are crucial for successful tooth replacement with permanent hybrid dentures. Dentists must consider the advantages and disadvantages of available options and align them with the patient’s expectations.
Overall, the choice between hybrid prostheses and removable overdentures depends on various factors such as patient preferences, oral health conditions, aesthetics, functional demands, and cost considerations.
It is important for patients to discuss these options with their dentist to determine the most suitable treatment approach for their specific needs.
Reference
https://msadj.journals.ekb.eg/article_301120_22ca9a50a0c67c8a3b2dfce8dcc736bd.pdf
