3D printing: Color stability of 3D-printed dentures 

3D printing in dentistry: How do different surface treatments affect color stability? A research team at LMU Munich compared the color stability of a 3D-printed resin for permanent restorations with two veneering composites. The scientists investigated how various surface treatments—varnishing, coating, and polishing—affect discoloration rates and also tested cleaning methods for removing existing discoloration.

Thanks to technological advances in 3D printing, permanent restorations can now be manufactured from 3D-printed resins and used clinically. This cost-effective method represents a potential alternative to conventional metal- or ceramic-based restorations. In addition to single-tooth restorations, 3D-printed resins can also be used as veneering materials to meet aesthetic requirements regarding color and surface texture. However, color instability and discoloration are common problems with 3D printing, leading to replacement of these restorations. Studies show that increased surface roughness and high surface energy promote the adhesion of color pigments and thus negatively affect color stability. Furthermore, rough surfaces increase plaque accumulation, which increases the risk of oral disease.

To improve surface quality and color stability, various post-processing methods such as polishing, varnishing, or coating are available. These can create a smooth, homogeneous surface and optimize material properties. However, there are currently few studies investigating the effects of these treatments on 3D-printed resins after storage in different media.

Additionally, the study investigated the extent to which individual and professional preventive measures can reverse possible changes in these parameters. The study puts forward several hypotheses: 

• The discoloration rates were the same for all test groups regardless of the material type, surface treatment, and choice of color medium.
• Individual and professional prophylaxis did not lead to any improvement in the tendency to discoloration (could not reverse the discoloration)
• Surface parameters such as surface free energy or surface roughness showed no significant differences for all materials, surface treatments, ink media and cleaning methods.

material and methods

The study involved the production of a total of 576 test specimens using three different materials: 

• a 3D printing resin (VarseoSmile Crown^?; BEGO GmbH & Co. KG) and 
• two veneering composites (GRADIA PLUS; GC EUROPE NV and VITA VM LC flow; VITA Zahnfabrik H. Rauter GmbH & Co. KG) that were processed using the layering technique. 

The test specimens were then divided into four groups: painting, polishing, coating (“coated”) or no surface treatment (control group).

OPTIGLAZE color (GC EUROPE NV) and VITA AKZENT LC (VITA Zahnfabrik H. Rauter GmbH & Co. KG) were used for varnishing. Polishing was performed using goat hair brushes and polishing paste or silicone polishers. After surface treatment, the test specimens were stored for up to 14 days in various coloring liquids (red wine, turmeric, cress, water). 

The measurements were taken at four points in time: 

• directly after production (T0), 
• after 14 days of storage (T14) 
• after individual tooth cleaning (IP) and
• after professional teeth cleaning (PP). 

The test specimens were first cleaned with a specially developed toothbrush device to simulate individual prophylaxis (IP), which corresponds to the home use of an electric toothbrush. If severe discoloration (ΔE₀₀ > 1.8), additional professional prophylaxis (PP) was performed using a prophylactic cup and polishing paste – comparable to a professional dental cleaning in a dentist's office. In addition to color stability, the degree of discoloration, surface roughness, and surface energy of the test specimens were examined as part of the study. The statistical analysis of the collected data was performed using IBM SPSS Statistics v29.0. The Kolmogorov-Smirnov test, the Mann-Whitney U test, the Kruskal-Wallis test, and the Friedman and Wilcoxon tests were used. A significance level of α = 0,05 was used.

Results

Painted or coated 3D-printed surfaces showed lower rates of discoloration after exposure to red wine, turmeric, cress, and water. Polishing, particularly with goat hair brushes, also reduced discoloration—both for the 3D-printed resin and the two veneering composites. This underscores the clinical relevance of appropriate surface treatment, especially when exposed to strongly staining substances such as red wine and turmeric. Untreated specimens, in contrast, showed the most pronounced color change. 

For veneering composites, polishing with goat hair brushes resulted in particularly smooth surfaces (roughness ≤ 0,2 µm), which may be clinically relevant in the long term, as smoother surfaces may accumulate less plaque and dye. The type of surface treatment had a greater overall influence on discoloration than the material itself.

Both cleaning methods (IP, PP) improved surface parameters and reduced discoloration. Individual prophylaxis was particularly effective with veneering composite 1, while professional prophylaxis achieved the best results with the 3D-printed resin. However, in addition to the material selection, surface treatment and dietary habits also influence discoloration behavior, as discoloration could not always be completely removed despite prophylactic measures. Furthermore, it was shown that individual prophylaxis with the 3D-printed resin increased surface energy, while professional prophylaxis decreased it. Overall, increased surface roughness and energy were associated with a greater tendency to discoloration, as irregular structures could more easily absorb and bind color pigments.

Conclusion

3D printing of dental prostheses: Since 3D printing resins are currently still prone to discoloration, post-treatment of the material surface is essential to achieve improved color stability. Surface treatments such as varnishing, coating, and polishing contribute to improving color stability and various surface properties, such as roughness, which in turn ensures long-term aesthetic and clinically consistent results. To minimize discoloration, varnishing and polishing with goat hair brushes are recommended for all materials tested.