Introduction:
Dental implants are currently regarded as the most advanced prosthetic solutions for individuals with one or more areas of tooth loss. When compared to conventional dentures, dental implants offer superior support for both aesthetic appearance and chewing functionality. It is understood that the implantologist may choose between an immediate loading or a delayed loading protocol, based on the anticipated success of the integration between the bone and the implant.
The All-on-Four concept, developed by Malo et al. by various manufacturers in contemporary implant dentistry, is fundamentally based on an immediate loading protocol designed for comprehensive arch dental rehabilitation. This approach involves the placement of two tilted posterior implants and two anterior implants without the need for bone augmentation (increase the height of the bone), utilizing surgical planning software or CBCT (cone beam computed tomography) technology. Preoperative planning can be conducted by storing patient data as DICOM (Digital Imaging and Communications in Medicine) files obtained from CT scans (computed tomography), which are then processed through Virtual Surgical Planning (VSP) to determine the precise orientation and location for implant placement in the edentulous jaw regions. However, the All-on-Four concept is contraindicated for patients with a high smile line, where bone reduction may be necessary, or in cases where there is insufficient space for implant prosthetics in the edentulous area. Additionally, this concept can be adjusted for individuals who smoke, those with parafunctional habits or bruxism (unnatural grinding of teeth), and patients with an edentulous maxilla opposing natural dentition for an extended period.
What Is a Fixed Full-Arch Prostheses in All-On-Four?
According to the research conducted by Malo et al., the all-on-four concept allows for the provision of high-density acrylic resin prosthetics as provisional solutions for patients, utilizing titanium cylinders during immediate loading on the day of implant surgery. This approach enables the immediate rehabilitation of either the entire mouth or all four quadrants of the jaw.
Further studies by Lopes et al. have explored this protocol, demonstrating that removable prostheses can be transformed into fixed prosthetic bridges made entirely of acrylic resin, thereby facilitating immediate functionality for patients. These definitive prostheses can be implemented in various clinical situations, typically utilizing titanium acrylic resin prosthetics, titanium ceramic prosthetics, or all-ceramic zirconia crowns. The choice of prosthetic materials is at the discretion of the dentist, taking into account the patient's financial considerations and aesthetic preferences, while also considering the specific clinical context.
For healthy individuals who do not engage in harmful habits and exhibit signs of effective osseointegration (joining of bone and implant) the optimal approach is to deliver a definitive screw-retained prosthesis within 24 hours following the placement of the dental implant. The All-on-Four loading protocols facilitate the rehabilitation of the final definitive prosthesis, which can be constructed using either acrylic resin or cast metal frameworks. These prostheses are referred to as fixed full-arch prostheses (FFA). The advantages of fixed full-arch restorations are largely attributed to the implant tilting concept, which is designed to reduce the length of the cantilever, alleviate peri-implant bone stress, and ensure an optimal distribution of forces across the underlying jawbone, particularly in healthy individuals without detrimental habits.
Why Smoking or Bruxism Can Commonly Lead to Implant Failure?
Recent studies have thoroughly examined the direct relationship between tobacco smoking and the harmful effects of nicotine on fibro-osseous integration, or connective tissue integration, with dental implants rather than traditional bone osseointegration. This has been linked to higher failure rates of dental implants in smokers. Dental professionals, including implant dentists and oral surgeons, must evaluate the likelihood of a patient quitting smoking, as failure to do so can lead to significant risks of implant failure. For patients who can gradually reduce their smoking or who smoke infrequently, dental surgeons may consider the all-on-four treatment approach. This consideration also applies to individuals who are chronic bruxists or have long-standing parafunctional habits. Dentists typically exclude these patients from candidacy due to the associated risks of increased stress on implants. They might still look into functional rehabilitation choices for cases without teeth that are made worse by natural bone loss, which adds to their dental problems. However, studies on dental implants show that these factors can lead to high failure rates if patients don't manage to stop or cut back on their long-term habits.
How to Rehabilitate All-On-Four Cases in Smokers and Bruxists?
According to the clinical research conducted by Acocella et al., dental implants can be successfully loaded in the edentulous mandible (lower jaw bone) of both smokers and bruxists using titanium cast electrode screw-retained prosthetics. This protocol is also applicable to the edentulous maxilla (upper jaw bone), provided that some natural teeth are present in the opposing Implementing this approach is feasible when there is potential for natural dentition in the opposing arch. Following a successful verification of osseointegration by the implant dentist within a timeframe of three to six months—using intraoral radiography, panoramic radiography via CBCT scanning, or multidetector CT scanning—the dentist will proceed to arrange for the final prosthesis. However, the doctors should encourage the patient to give up smoking. Regular smoking may lead to increased bone destruction and loss of osseointegration. Typically, the definitive prosthesis is delivered as a fixed bridge polyetheretherketone (PEEK) prosthesis for individuals who smoke or grind their teeth. Along with this, perforated splints can be advised to the patients. Such splints reduce stress on the implant surface. Also, light occlusal contacts must be maintained. Any type of occlusal disharmony must be eliminated in such cases.
Conclusion:
Recent dental research has demonstrated significant outcomes with the FFA prosthesis for patients who do not engage in harmful habits such as smoking or bruxism. In healthy individuals without any medical complications, a 100 percent success rate has been achieved, along with favorable surgical outcomes and numerous advantages associated with the FFA prosthesis. Conversely, in cases involving smokers or patients exhibiting parafunctional habits, including bruxism, the results have been inconsistent even after the definitive prosthesis was loaded. Studies indicate that those who continued smoking or had a history of periodontal disease experienced long-term failures of the prosthetic implants, despite the use of definitive titanium acrylic or metal-ceramic bridges over four to six months.
