Introduction
The concept of angulated dental implants has evolved significantly over the years. Angulated dental implants refer to the placement of dental implants at an angle rather than perpendicular to the occlusal plane. This technique is often employed to address anatomical constraints, improve esthetics, or maximize the use of available bone in areas where traditional implant placement might be challenging. The use of angulated implants became more prominent in the late 1980s. Professor P.I. Brånemark played a crucial role in this development, particularly for creating prosthesis stability in maxillary arches compromised by trauma or oral cancer. Angulated implants have since evolved to become a standard practice in many cases. They offer significant benefits, such as eliminating the need for grafting procedures and allowing for immediate loading of provisional prostheses in specific situations.
Biomechanical Considerations
Load Distribution
Angled Load Transmission: Angulated implants alter the direction of force transmission. Forces are directed along the axis of the implant and need to be carefully managed to avoid excessive stress on the bone-implant interface. Studies have shown that the stress around tilted implants varies with the angle of inclination and the length of the cantilever. For example, a 45-degree tilted implant tends to exhibit lower stress levels compared to a vertically placed implant under similar loading conditions. For example, a study using photoelastic models demonstrated that a 45-degree tilted implant showed the lowest stress levels when loaded at the central fossa of the mandibular first molar, compared to a vertically placed implant. Another finite element study found that a 45-degree inclination resulted in lower stress values compared to a 30-degree inclination, primarily due to the shorter cantilever (references are available in the book).
Stress Concentration: There is a potential for higher stress concentrations at the cervical region of the implant, which may increase the risk of bone resorption or implant failure. Tilting implants can help distribute occlusal forces more evenly across the implant and surrounding bone. This can reduce the risk of bone resorption and implant failure. The length of the cantilever also plays a significant role. Longer cantilevers can increase stress around the implant, potentially leading to higher stress concentrations. The type of implant-abutment connection can influence stress distribution. Monoblock implants, for instance, tend to accumulate higher stress compared to conventional angled multiunit abutment-implant connection systems. Proper planning and placement of tilted implants are essential to minimize stress concentration and ensure the longevity of the implant. This includes considering factors like the angle of inclination, cantilever length, and type of implant-abutment connection.
Bone-Implant Interface
Osseointegration: Proper osseointegration is critical, regardless of the implant angle. Angulated implants must achieve sufficient primary stability to ensure successful osseointegration. The healing process for tilted implants involves the same stages as for vertical implants, including initial bone remodeling and the gradual formation of a stable bone-implant interface. Studies have shown that tilted implants can achieve successful osseointegration similar to vertically placed implants. The angle of the implant does not significantly affect the osseointegration process, provided that the implant is placed correctly and the bone quality is adequate. The macro-design of the implant, including its angle, can influence the initial stability and stress distribution, which are crucial for osseointegration. Properly designed tilted implants can distribute occlusal forces more evenly, reducing stress concentrations and promoting better bone integration.
Bone Quality and Quantity: The quality and quantity of bone in the implant site play significant roles in the success of angulated implants. Denser bone (e.g., in the anterior mandible) generally offers better support than less dense bone (e.g., in the posterior maxilla). Implants placed in dense bone (Type I or II) tend to have higher success rates compared to those in less dense bone (Type III or IV). The thickness of the cortical bone also plays a crucial role. Thicker cortical bone can provide better initial stability for the implant.
Implant Design
Implant Shape and Surface: The design of the implant, including its shape and surface characteristics, influences its ability to withstand forces. Some implants are specifically designed to accommodate angulated placement. Tapered implants are often preferred for tilted placements as they mimic the natural tooth root shape and provide better stability in areas with limited bone volume. The overall shape, including the body and apex of the implant, is designed to maximize bone contact and stability. For example, some implants have a conical shape that helps in achieving bicortical anchorage, which is beneficial for tilted implants. A roughened surface increases the surface area for bone contact, promoting better osseointegration. Techniques like sandblasting and acid etching are commonly used to create a rough surface.
Abutments: Custom or angulated abutments are often used to ensure that the prosthetic components align correctly with the opposing dentition, improving both function and esthetics. Angulated abutments are specifically designed to correct the angulation of the implant, allowing for proper alignment of the prosthesis. They come in various angles, typically ranging from 15° to 45°, to accommodate different clinical scenarios. Angulated Screw Channel (ASC) Abutments feature an angulated screw channel, enabling the screw to be tightened at an angle. This design helps in achieving a screw-retained restoration even when the implant is placed at an angle. Custom abutments can be fabricated to match the specific angulation and anatomical requirements of the patient. They offer a tailored solution for complex cases.
Prosthetic Considerations
Restorative Angle: The angle of the prosthetic restoration relative to the implant is crucial. Correctly angulated abutments can help distribute occlusal forces more evenly and reduce stress on the implant. Tilted implants are typically placed at angles ranging from 11° to 45°, depending on the clinical scenario and anatomical considerations. Common angles include 30° and 45°, which help avoid anatomical structures like the maxillary sinus and mental foramen. Proper angulation helps in distributing occlusal forces more evenly across the implant and surrounding bone, reducing stress concentrations and enhancing the longevity of the implant. In scenarios like the All-on-4 treatment concept, tilted implants allow for immediate loading, providing patients with a functional prosthesis shortly after implant placement.
Cement vs. Screw Retention: The method of retention (cemented or screw-retained restorations) may also impact the biomechanical behavior of the implant. Screw-retained restorations are often preferred for ease of maintenance and retrievability. For tilted implants, screw-retained restorations can be particularly advantageous as they allow for better management of angulation issues. The main disadvantage of screw retention is the potential visibility of the screw access hole, which can be a concern in the esthetic zone. However, advancements in materials and techniques can help mitigate this issue.
Clinical Outcomes
Studies have shown that angulated implants can have comparable survival rates to traditionally placed implants, provided that biomechanical principles are adhered to. Studies have reported survival rates for angulated implants ranging from 89% to 100% (references available in book). This wide range depends on various factors, including the specific clinical scenario, patient health, and implant system used. For immediately loaded angulated implants, the survival rates range from 86% to 100% for prosthetically splinted implants, with most studies reporting over 93% survival rates. One long term study found that dental implants, in general, have a 93.6% survival rate after an average of 16.5 years, with a cumulative survival rate of 85.9% after 24 years. While this study did not focus exclusively on angulated implants, it provides a good benchmark for long-term success (references available in the book).
Complications
Potential complications include implant fracture, abutment screw loosening, and peri-implantitis. Proper planning and execution can mitigate these risks. If not properly placed, angulated implants can lead to increased stress on the implant and surrounding bone. This can potentially result in bone resorption and implant failure if not properly managed. Improper placement of angulated implants in posterior mandible can lead to nerve damage, causing numbness, tingling, or pain. In the posterior maxilla, angulated implants can sometimes lead to sinus complications, such as tearing of the Schneiderian membrane or sinusitis. The placement and restoration of angulated implants can be technically challenging, requiring precise planning and execution to avoid complications
Advantages of Angulated Implants
Avoiding Anatomical Structures: Angulated implants can help avoid critical anatomical structures such as the maxillary sinus and the inferior alveolar nerve, reducing the need for additional surgical procedures like sinus lifts or nerve repositioning.
Improved Prosthetic Support: By tilting the implants, clinicians can achieve better prosthetic support, especially in cases with limited bone volume. This can enhance the stability and functionality of the prosthesis.
Reduced Need for Bone Grafting: Angulated implants can often be placed in areas with insufficient bone height, reducing or eliminating the need for bone grafting procedures.
Immediate Loading: In treatment concepts like All-on-4, angulated implants allow for immediate loading, providing patients with a functional prosthesis shortly after implant placement.
Conclusion
The angulated implants have become a valuable option in modern dental practice, providing solutions for complex cases and improving patient outcomes. Angulated implants have high survival rates, comparable to vertically placed implants. However, angulated dental implants present unique biomechanical challenges. Successful outcomes depend on thorough planning, appropriate implant selection, and meticulous surgical and prosthetic techniques. Understanding of various above stated aspects is essential for optimizing the use of angulated implants in dental practice.
References
References are available in the hardcopy of the website “Periobasics: A textbook of Periodontics and Implantology”.
Periobasics: A Textbook of Periodontics and Implantology
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