Effect of OT-Bridge System versus Multiunit Abutment on the Passive Fit and Stresses Induced by CAD/CAM Fabricated All-on-Four Screw-Retained Prostheses: In Vitro Study
This in vitro study demonstrates that the OT-Bridge system provides superior passive fit and induces significantly lower peri-implant stresses compared to the traditional multi-unit abutment system in CAD/CAM All-on-4 screw-retained prostheses, suggesting enhanced long-term stability and reduced risk of complications.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
When a person loses all their teeth, modern dentistry offers a powerful solution: a full arch of replacement teeth anchored directly into the jawbone by just four metal posts. This approach, known as the All-on-4 concept, is a triumph of engineering that allows patients to walk away with a new smile on the same day as their surgery. However, the success of this procedure relies on a delicate mechanical truth. The four posts are rarely perfectly parallel; the two at the back are often tilted to find the strongest bone, creating a complex, angled landscape. To connect a rigid bridge of teeth to these uneven posts, dentists must use a set of intermediate connectors. If these connectors do not fit together with absolute precision, even a microscopic gap can create stress. Over time, that stress can loosen the screws holding the teeth in place or damage the bone supporting the implants. The central question for clinicians is which type of connector system creates the tightest, most stress-free fit.
A team of researchers at Ain Shams University in Egypt set out to answer this question by comparing two specific systems used to bridge the gap between the implants and the replacement teeth. One system uses traditional angled connectors called multi-unit abutments, which rely on screws to correct the angles. The other uses a newer system called OT-Bridge, which utilizes a unique mechanical ring to lock the pieces together without needing to correct the angle with a screw. To test these systems, the researchers did not work on human patients. Instead, they built two identical, high-tech models of a lower jaw using 3D printing technology. These models contained four digital replicas of dental implants arranged in the standard All-on-4 pattern.
The scientists then created fourteen different sets of replacement teeth frameworks for these models. Seven sets were built to fit the traditional screw-based connectors, and seven were built to fit the newer ring-based connectors. All the frameworks were manufactured using advanced computer-aided design and metal printing, ensuring that every piece was made with the same high level of precision. To make the test realistic, the team covered the models with a layer of soft silicone that mimicked human gum tissue. They then installed the frameworks onto the models and subjected them to rigorous testing. First, they checked how well the frameworks sat on the connectors by tightening just one screw on each side and measuring the tiny gaps that appeared at the other connection points. Next, they applied heavy, static loads to the teeth, simulating the force of biting down, while sensors glued to the jaw models measured the microscopic strain or stress transferred to the bone.
The results revealed a clear difference between the two approaches. The frameworks using the traditional screw-based connectors showed a noticeable gap where they met the implant, measuring an average of 72.57 micrometers. In contrast, the frameworks using the ring-based OT-Bridge system fit much more tightly, with an average gap of only 31.61 micrometers. This difference was not just a minor variation; it was statistically significant. The researchers found that a larger gap directly correlated with higher levels of stress on the surrounding bone. When the teeth were loaded with force, the traditional system transferred significantly more strain to the implants than the ring-based system did. Under the heavy biting forces used in the test, the traditional system generated an average stress of 281.86 units, while the ring-based system kept that stress lower at 247.14 units.
The study also looked at how the stress was distributed across the four implants. In both groups, the back implants on the side being bitten took the most pressure, while the front implants on the opposite side were pulled in the opposite direction, a natural result of the leverage involved in chewing. However, the distribution of this force was more consistent and balanced in the ring-based group. The traditional system showed more extreme peaks of stress, suggesting that the rigid screw connections might be concentrating the force in specific, vulnerable spots. The researchers concluded that while both systems are clinically acceptable and fall within safe limits for bone health, the ring-based OT-Bridge system offers a superior fit and creates less strain on the jawbone. This finding suggests that for patients receiving this type of full-arch restoration, choosing the ring-based connector could potentially reduce the long-term risk of screw loosening or bone loss, leading to a more stable and durable result.
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