Dimensional accuracy of mock-ups fabricated using conventional, additive, and subtractive manufacturing techniques: an in vitro study
This in vitro study found that while all three manufacturing techniques (conventional, additive, and subtractive) produced similar linear dimensions for anterior mock-ups, subtractive manufacturing demonstrated the highest surface-to-surface matching accuracy, whereas conventional molding exhibited significantly lower depth deviations.
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
In the world of modern dentistry, the goal has shifted from simply fixing broken teeth to crafting smiles that look and feel completely natural. To achieve this, dentists often rely on a temporary simulation called a mock-up. Think of this as a trial run: a thin, plastic-like shell is placed over a patient's teeth to show exactly how a new smile will look before any permanent work begins. This step is crucial because it allows the patient to see the future result and helps the dentist plan exactly how much of the natural tooth needs to be shaved down to make room for the final restoration. If the mock-up is too thick, the dentist might remove too much healthy tooth; if it is too thin, the final result might look flat or feel wrong. For years, these trial shells were made by hand using a silicone mold and liquid resin, a process that relied heavily on the skill of the person making it. Recently, however, technology has introduced two new ways to create these shells: one that builds them up layer by layer using a 3D printer, and another that carves them out of a solid block using a computer-controlled machine. The question facing the field is whether these high-tech methods produce a more accurate guide than the traditional hand-made approach.
A team of researchers at Trakya University set out to answer this question by comparing the dimensional accuracy of mock-ups made with these three different methods. They did not work with patients directly but instead used digital data from ten individuals who were planning to receive cosmetic veneers. For each person, the team created a six-tooth mock-up using three distinct techniques: the traditional hand-molding method, a subtractive method where a machine mills the shape from a solid disc, and an additive method where a printer constructs the shape layer by layer. To see how well each mock-up matched the original digital design, the researchers scanned every single specimen with a high-precision industrial scanner. They then compared the physical object to the perfect digital blueprint, measuring how closely the surfaces matched and checking the thickness at specific points across the teeth.
The results revealed that the way a mock-up is made significantly changes its shape. The machines that carved the mock-ups from solid blocks produced the most accurate results, matching the digital design on nearly 75 percent of the surface area. The 3D-printed mock-ups came in second, matching the design on about 59 percent of the surface, while the traditional hand-molded ones matched on only about 43 percent. The difference between the machine-carved and hand-molded groups was statistically significant, meaning the gap was too large to be random chance. Interestingly, while the overall surface shapes varied, the basic measurements of the teeth—such as the width of the front teeth or the distance between the canine teeth—were surprisingly similar across all three groups. This suggests that while all methods can get the general size right, the smoothness and exact contour of the surface differ greatly depending on the technique used.
Perhaps the most clinically important finding concerned the thickness of the mock-ups, which acts as a guide for how much tooth to remove. The researchers measured the depth at nine different spots on each tooth and found that the 3D-printed and machine-carved mock-ups stayed very close to the intended thickness, with their average deviation hovering near zero. In contrast, the hand-molded mock-ups showed a consistent tendency to be thinner than the design, particularly as one moved from the gum line toward the biting edge. This inward deviation was most pronounced in the hand-made group, suggesting that the manual process of pressing the resin into the mold and removing excess material tends to shrink the final shape. The study also found that the shape of the tooth mattered; the canine teeth, which are more pointed and curved, showed the largest deviations in thickness, while the flatter central incisors were more consistent.
These findings suggest that for procedures where the mock-up serves as a precise guide for shaving down teeth, the digital methods offer a distinct advantage in consistency. The machine-carved approach provided the highest surface accuracy, while the 3D-printed method offered a middle ground with thickness that closely matched the plan. The traditional hand-molding technique, while still useful for simple previews, introduces more variability that could lead to uneven tooth preparation if used as a strict guide. The researchers noted that their study was conducted in a controlled laboratory setting, so factors like saliva or body temperature were not present, but the data clearly indicates that the manufacturing process itself is a major factor in the final accuracy. For dentists aiming to preserve as much natural tooth structure as possible, choosing a fabrication method that minimizes these thickness errors could be the key to a more predictable and successful outcome.
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