As dental science progresses, we learn many valuable new pieces of information that help people have longer lasting, healthier, more beautiful teeth and smiles. Dental implants are relatively new to dentistry, and full mouth implant-based restorations are even newer. As such, new discoveries and innovations are common and not all dentists are going to know about each of them as they are found.
Early Full Arch Dentistry
When dental implants were first used to restore a full arch or teeth, the prevailing wisdom was that the implants across the mouth needed to be splinted to each other to provide extra support for the implants and prevent failure. This is called cross-arch stabilization. It was believed that too much pressure on an individual implant would cause the bond between the bone and the implant to separate, causing the implant to fail. The common method was to place a single unit prosthetic across all the teeth, distributing and reducing the stimulation forces that each implant receives.
It is technically true that extreme pressure on an implant can cause it to fail, but this is also true of natural teeth. So why don’t dentists recommend connecting (or splinting) our natural teeth? It is because they understand that our jawbone needs the stimulating forces that come from chewing to keep our bone healthy.
Bone Adaption
In 1892, German anatomist and surgeon, Julius Wolff, published his scientific research, The Law of Bone Remodeling. The most groundbreaking part of his work is that he established the concept of bone change in relation to physical stress placed upon them. His research stated that bones will become thicker and stronger over time to adapt to forces placed on them. Inversely, bones will become weaker and thinner over time without those forces.
Wolff’s findings were later built upon by American orthopedic surgeon, Harold Frost. Frost developed the Mechanostat model to demonstrate the effect that forces have on either bone loss (resorption) or growth (formation). His work further reinforced the idea that the mass, strength, and geometry of bone adapts to its everyday needs.
We can see this in everyday life. Tennis players have more bone mass and density in their dominant hitting arm. Paraplegics in wheelchairs have decreased bone mass in their legs. This is also why a patient in a denture will continue to lose bone in their mouth. Even if they can eat with the denture, the distributed and decreased pressures cannot create significant enough force and stimulation to maintain bone levels.
The Problem with Full Arch Prosthetics
Cross-arch stabilization (splinting) is important while the implants heal. This is like putting a cast on a broken arm. While the implants are healing and fusing to the bone, a full arch prosthetic will shield the bone from excess forces that could disrupt that process. However, much like an arm in a cast, once the bone is healed, the splint (or cast) should be removed.
As single-unit full arch prosthetics (like the All-on-4) have been very popular for the last two decades, many dentists watched as their patient’s bone resorbed during the years after treatment. The development of gaps between the tissue and an All-on-4 or All-on-X prosthetic are quite common. This has led many dentists to believe that bone loss with full arch dental treatment is inevitable.
This erroneous belief has contributed to many dentists removing healthy bone from their patient’s mouth and replacing it with artificial gums. From their estimation, the gaps that form can be ignored because they’re hidden behind the lips when smiling. They don’t realize that the large prosthetic is the likely cause of the bone loss as it prevents adequate bone stimulation to the implants.
The Benefits of Segmented Bridges
Science teaches us and experience has shown that when we increase the pressures on implants, we can maintain and even form new bone. By segmenting a full arch of teeth into multiple bridges like with the 3 on 6, it allows each implant to receive increased stimulation from biting forces. For example, if you bite an almond with your left molars, the implants on the left side receive all the pressure without distributing those forces to the front or right side of the mouth.
This is like physical therapy for the bone in your mouth. When you segment the bridges, you take off the cast and have the bone do the work that it was designed to do. Examinations and x-ray imaging of 3 on 6 patients that had treatment 5 and 10 years ago show very positive results for long-term bone health.
In addition to the bone building properties of 3 on 6 treatment, there are many other benefits.
Full-arch prosthetics made in a single piece generally need to be made thicker to prevent them from breaking and can feel less natural in the mouth when speaking or eating.
Studies have shown that a full-arch bridge is approximately 6 times more likely to fracture over a 5-year period than a 4-unit bridge (Stomatologija 2008;10:133-139). In a follow up study conducted on 3 on 6 patients, Smile Systems found that in a 6-year period, only 3 zirconia bridge fractures were found out of 5,000 bridges placed, or .0006%.
If a full arch prosthetic breaks, or if an implant fails, the entire prosthetic must be replaced. This can cost thousands of dollars. In the unlikely event of a fracture of a 4-unit zirconia bridge, just the individual bridge can be replaced and at a fraction of the price.
Conclusion
Bone is like muscle: if we don’t use it, we lose it. Understanding the laws of bone formation and resorption, we know that bone will shrink and dissolve without consistent exposure to significant forces. When we leave a patient in a single-unit full arch prosthetic, we can expect bone loss and resorption over time. Segmented bridges in full arch restoration has shown to be effective at long-term bone maintenance and development.
If you have questions about segmented bridges or would like to learn more, schedule a free consultation with a 3 on 6 provider at https://www.3on6.com/providers
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