Effect of metal sleeve integration on implant placement accuracy using additively manufactured tooth-supported surgical guides: an in vitro study

When a dentist needs to replace a missing tooth with an artificial root, the procedure relies on precision. The goal is to place a screw-like implant into the jawbone at a specific angle and depth, perfectly aligned with the patient's bite. To achieve this, many surgeons use a digital plan created on a computer, which is then transferred to the patient's mouth using a custom-made template, or guide. This guide fits over the remaining teeth and has holes that direct the drill exactly where the computer says it should go. For years, the standard way to build these guides involved printing a plastic mold and inserting small, rigid metal tubes into the holes. These metal tubes act as a durable channel for the drill, theoretically preventing the plastic from wearing down or the drill from wobbling. However, adding these metal parts makes the guide more expensive, harder to manufacture, and sometimes difficult to fit in tight spaces inside the mouth. This raises a practical question for the dental world: is the metal tube actually necessary for the drill to stay on course, or can a guide made entirely of printed plastic work just as well?

Researchers at the Universidad Europea de Madrid set out to answer this question by testing the two designs side by side in a controlled laboratory setting. They did not use human patients for this experiment. Instead, they created thirty-two identical resin models of a human upper jaw, each missing a single tooth in the back. These models were made from a digital scan of a real patient's mouth, ensuring that every test started with the exact same anatomical shape. The team split these models into two groups. In the first group, they used surgical guides printed entirely from a special biocompatible plastic, with the drill holes formed directly by the printer. In the second group, they used guides that looked identical but included the traditional metal tubes inserted into the plastic. Both sets of guides were designed from the same computer plan and manufactured using the same high-resolution 3D printing technology.

The experiment proceeded with a single surgeon placing dental implants into all thirty-two models. The surgeon followed the exact same steps for every model, using the guide to direct the drill and then inserting a standard implant. Once the implants were in place, the researchers scanned the models again to see exactly where the implants ended up compared to where the computer plan said they should be. They measured the difference in three ways: how far the top of the implant was from the planned spot horizontally, how far it was vertically, and how much the angle of the implant tilted away from the plan.

The results showed that the metal tubes did not provide a measurable advantage in accuracy. The guides made entirely of plastic performed just as well as the guides with metal sleeves. When looking at the horizontal position of the implants, the plastic-only guides had a median deviation of 0.36 millimeters, while the metal-sleeved guides had a median deviation of 0.28 millimeters. This tiny difference was not statistically significant, meaning it could have happened by chance. Similarly, for the vertical position, the plastic guides deviated by a median of 0.53 millimeters and the metal guides by 0.63 millimeters, a difference that was also not significant. Even the angle of the implant, which is often the hardest part to control, showed no real difference between the two groups; the plastic guides tilted an average of 8 degrees from the plan, while the metal guides tilted 10 degrees, a gap that the researchers determined was not meaningful.

These findings suggest that the rigid metal tube is not the only way to ensure a drill stays on track. The study indicates that a well-designed plastic guide, manufactured with modern 3D printing technology, can achieve the same level of precision as the traditional metal-reinforced version. This does not mean that metal tubes are useless or that they will never be needed, but it does show that for this specific type of tooth-supported guide, the metal component does not significantly improve the final outcome. The researchers noted that both types of guides still had some small errors, which is expected because the process involves many steps, from the initial computer scan to the final drilling, and each step adds a tiny amount of uncertainty. However, the fact that the plastic guides matched the metal ones suggests that dentists might be able to simplify their workflow and reduce costs by using guides without metal sleeves, provided they follow strict planning and manufacturing protocols.

It is important to remember that this study took place in a laboratory on resin models, not in living human mouths. The researchers controlled for variables like saliva, bone density, and patient movement, which are all factors that exist in real surgery. Therefore, while the results are promising, they apply specifically to the conditions tested. The study confirms that under these controlled circumstances, the metal sleeve does not change the accuracy of the implant placement. For now, the choice between a plastic guide and a metal-sleeved guide may come down to other factors, such as the available space in a patient's mouth or the specific equipment a clinic uses, rather than a guaranteed difference in how accurately the implant is placed. The work provides a clear, data-driven alternative to the long-held assumption that metal is always required for precision in guided dental surgery.