By Hugo Sousa, Head of Education, Nexus Dental Laboratory
A few weeks ago, a dentist asked us to mill a deprogrammer. He was specific about it, and he is far from the only one. The milled request comes in often enough now that it has become a pattern worth explaining rather than simply accommodating.
The instinct behind it is easy to read, and it is fair. Milled sounds denser and tougher. Something cut from a solid block ought to outlast something grown in layers out of a tank of resin. That instinct has a real history in the academic literature, and for a long time, the data backed it plainly.
The honest answer today, though, is more interesting than a straight yes or no. It depends on the appliance, on the material, and on the process behind it. Most labs either wave the question away or quietly do what they were going to do anyway. We would rather explain it.
A milled appliance is carved out of a factory-made block that was polymerised under industrial conditions. The material is dense, uniform and fully cured before the cutter ever touches it. Think of it as sculpture: the block arrives finished at a molecular level, and the machine removes what is not the appliance.
A printed appliance is closer to bricklaying. It is built up in layers from liquid resin and post-cured, so the resin formulation, build orientation, and post-processing quality determine its final properties. The structure is created and finished on our floor rather than in a factory.
That one difference explains most of what the studies find. Block materials begin with a mechanical head start, while printed materials depend heavily on process control.
It also explains where printing genuinely wins: complex geometry at no extra cost, minimal material waste, quicker turnaround, and identical reprints whenever a patient needs another one.
The earlier bench work gave milling a genuine edge. A 2022 wear study found milled PMMA had the highest wear resistance, with heat-cured close behind and printed materials some way back. It also found that build angle mattered, with 0-degree prints outperforming those built at 45 and 90 degrees (Grymak et al., 2022).
Strength studies pointed in the same direction. Prpic and colleagues (2023) found that printed splints were generally lower in flexural strength and hardness, and a 2023 study in Materials reported the highest fracture strength after ageing in the milled splint (Abad-Coronel et al., 2023).
However, the current picture has moved. A study in the Journal of Prosthetic Dentistry ran a 400,000-cycle wear test across 10 materials and found that rigid printed occlusal device materials wore at a similar rate to milled, heat-polymerised, and light-polymerised materials. The materials that wore fastest were the flexible printed resins (Lawson et al., 2025).
So the meaningful divide in current wear data sits between rigid and flexible, rather than between milled and printed. Clinically, a 2023 randomised pilot trial in 47 patients found printed and milled splints performing similarly on patient-reported outcomes and complications (Herpel et al., 2023), and a randomised crossover trial testing whether printed splints are non-inferior to milled ones is registered and underway in Freiburg (Rabel et al., 2024), so stronger clinical data is coming.
Here, the bench evidence still favours milling, and by a clear margin. A 2025 systematic review and meta-analysis in Scientific Reports, covering 38 studies, found milled denture bases had the highest flexural strength and surface hardness.
Conventional heat-cured PMMA came second, and printed bases showed wide variability. The review puts this down to the pre-polymerised block: less porosity, better polymerisation and greater homogeneity.
Print orientation partly explained the spread in the printed results, and the authors also noted printing's compensating strengths in customisation, production efficiency and reduced waste.
Printed denture bases are advancing rapidly and offer real workflow advantages, but milled denture bases remain the mechanical benchmark today.
This is the most contested category, and the one that breaks the pattern. A 2022 systematic review and meta-analysis in Polymers compared printed provisional resins with milled and conventional ones and found that the printed materials were mechanically stronger, while their physical properties were weaker, particularly colour stability (Jain et al., 2022). That result runs counter to the splint and denture base evidence, and it is worth reporting exactly as it stands.
On fit, the workflow decides it. A 2024 study in the Journal of Esthetic and Restorative Dentistry compared DLP-printed interim crowns with milled controls and found that printing at a 50-micron layer thickness with ultrasonic post-processing matched the milled marginal fit almost exactly, whereas other print settings did not (Moron-Conejo et al., 2024). Reviews of the wider printing literature note that layer-by-layer building reduces polymerisation shrinkage at the margins, which is part of why printed margins can measure surprisingly well.
Milled leads on colour stability, too, which matters most on provisionals that have to serve for months. Printing competes on strength and marginal accuracy, and wins on speed and cost. It is the process quality that swings the result either way.
The studies are one input. The stronger signal, for me, is what surgeons and this lab are seeing in the wild.
When a clinician keeps asking me for milled, it is usually because something came back to their chair and stuck in their memory. A controlled study gets run in clean conditions by knowledgeable operators working to a defined protocol, which is what makes the data worth having in the first place. It is also a very tidy version of the world. None of it accounts for the patient who eats a madras and then sleeps in the guard, or for the appliance that spends a fortnight drying out on a windowsill. Nobody has yet run a trial of the chairside adjustment that removes the polish from a surface that one of my technicians spent an hour finishing.
Bench data and lived results can honestly disagree. When they do, our own returns bench is data too, and I take it seriously.
I have no verdict to offer here, and I am comfortable with that. The question is legitimate on its own terms, and I would rather ask it openly than pretend it is settled.
We run 16 printers, and we still choose not to print everything.
That decision is made case by case, based on the material chosen for the indication, the demands the appliance will face in the mouth, and how long it needs to serve.
Heavy occlusal duty on a long-service appliance points one way. Fast replacement, an identical reprint, or complex geometry points the other way. Also, every generation of resin narrows the gap a little further, which is why any absolute claim about either method ages badly.
So, when a dentist asks us to mill something, the answer is never defensive. Sometimes, milled is exactly what we would have chosen ourselves. Sometimes printing serves the case better, and we can tell you precisely why.
Whichever camp you sit in, we cater to it. Pick your route, and if you want to know which one we would take and why, ask us. We will always tell you.
And if you are seeing something come back that the literature has not yet caught up with, tell us that, too. It is the kind of evidence this lab pays attention to.
Most of this thinking has gone into n.guard, our nightguard line, where the whole point is protecting restorative work from parafunction rather than just supplying an appliance. n.splint is available now for occlusal work and follows it.
If you want to talk through which is right for a particular patient, or how we would make it and why, get in touch, and we will walk you through it.
Grymak A., Waddell J.N., Aarts J.M., Ma S., Choi J.J.E. Evaluation of wear behaviour of various occlusal splint materials and manufacturing processes. Journal of the Mechanical Behaviour of Biomedical Materials, 2022; 126: 105053. doi: 10.1016/j.jmbbm.2021.105053
Prpic V., Spehar F., Stajdohar D., Bjelica R., Cimic S., Par M. Mechanical properties of 3D-printed occlusal splint materials. Dentistry Journal, 2023; 11(8): 199. doi: 10.3390/dj11080199
Abad-Coronel C., Ruano Espinosa C., Ordonez Palacios S., Paltan C.A., Fajardo J.I. Comparative analysis between conventional acrylic, CAD/CAM milled, and 3D CAD/CAM printed occlusal splints. Materials, 2023; 16(18): 6269. doi: 10.3390/ma16186269
Lawson N.C., Brown P., Hamdan S., Alford A., Nejat A.H. Wear resistance of 3D printed occlusal device materials. Journal of Prosthetic Dentistry, 2025; 133(2): 576.e1-576.e6. doi: 10.1016/j.prosdent.2024.10.021
Herpel C., Kykal J., Rues S., Schwindling F.S., Rammelsberg P., Eberhard L. Thermo-flexible resin for the 3D printing of occlusal splints: a randomised pilot trial. Journal of Dentistry, 2023; 133: 104514. doi: 10.1016/j.jdent.2023.104514
Rabel K., Luchtenborg J., Linke M., et al. 3D printed versus milled stabilisation splints for the management of bruxism and temporomandibular disorders: study protocol for a randomised prospective single-blinded crossover trial. Trials, 2024; 25: 589. doi: 10.1186/s13063-024-08437-7
Azab A., Abdelhady W.A., Elwakeel E., Ashraf M., Wally R., Soliman A., Mohamed M.A., Abozaid D. Systematic review and meta-analysis of mechanical properties of 3D printed denture bases compared to milled and conventional materials. Scientific Reports, 2025; 15(1): 29207. doi: 10.1038/s41598-025-14288-2
Jain S., et al. Physical and mechanical properties of 3D-printed provisional crowns and fixed dental prosthesis resins compared to CAD/CAM milled and conventional provisional resins: a systematic review and meta-analysis. Polymers, 2022; 14(13): 2691. doi: 10.3390/polym14132691
Moron-Conejo B., Berrendero S., Bai S., Martinez-Rus F., Pradies G. Fit comparison of interim crowns manufactured with open and proprietary 3D printing modes versus milling technology: an in vitro study. Journal of Esthetic and Restorative Dentistry, 2024; 36(12): 1693-1703. doi: 10.1111/jerd.13295
van Lingen C., Tribst J.P.M. 3D-printed occlusal splints: a narrative literature review. Journal of Advanced Oral Research, 2025; 16(1): 25-33. doi: 10.1177/23202068251317825
