Cytotoxicity of printed resin-based splint materials

OBJECTIVES

Printed splints may be an alternative as a treatment of functional disorders in addition to physical, manual and physiological therapeutics. The objective is to investigate whether different 3D printed splint materials, which are fabricated with different fabrication orientation and post-processing (washing and post polymerisation) exhibit different in vitro cytotoxicity.

MATERIAL AND METHODS

600 discs (n = 25 per group, 5mmx1mm) were printed (P30+ DLP-printer, Straumann, CH; 100 µm layer) from splint materials (M1: Luxaprint OrthoPlus, DMG, G; M2: V-Print Splint, Voco, G). Printing was performed under 90° (A1), 45° (A2) or 0° (A3) alignment to the building platform. Specimens were either automatically washed (W1) (Straumann P Wash, Straumann, CH) or manually cleaned (W2) (Voco Pre-/Main-Clean protocol, Voco, G), and post polymerization was performed (P1: Cure, Straumann, CH; P2: Otoflash N171, Ernst Hinrichs Dental, G). RAW264.7 mouse macrophages were exposed to extracts of the specimens and cytotoxicity was determined as cell survival using a crystal violet assay. Optical density values obtained from exposed cell cultures were normalized to untreated controls (100%), summarized as means and statistically analyzed (ANOVA, α=0.05).

RESULTS

Cell survival varied between 9.1+/-1.3% (alignment A2/post cure P2/material M2/wash system W2) and 58.5+/-5.9% (alignment A1/post cure P1/material M1/wash system W1). Univariate analysis of variance revealed significant differences between mean values for post cure (p = 0.000), wash system (p = 0.002) and materials (p = 0.000), but not for the alignment (p = 0.406). With standardised washing and adapted post cure, both tested materials provided lowest cytotoxicity even in all three printing alignments.

CONCLUSIONS

The selection of the material as well as the post-processing (post-polymerization, washing procedure) show influence on the in vitro cytotoxicity. Alignment during manufacturing does not affect toxicity.

CLINICAL RELEVANCE

Materials, washing and post-polymerization should be matched to reduce cytotoxic effects during additive manufacturing.

Dynamic fatigue of 3D-printed splint materials

OBJECTIVES

Printed splints may be an alternative treatment for functional disorders. In addition to the selection of materials, the influence of cleaning or polymerisation can affect the dynamic behaviour and fatigue limit of printed materials.

MATERIAL AND METHODS

96 discs (n = 6 per group, 16mmx2mm) were printed (P30+ DLP-printer, Straumann, CH; 100 μm layer) from splint materials (M1: Luxaprint OrthoPlus, DMG, G; M2: V-Print Splint, Voco, G). Specimens were either automatically cleaned (C1: Straumann P Wash, Straumann, CH) or manually cleaned (C2: Voco Pre-/Main-Clean protocol, Voco, G). Post polymerisation was performed with LED (P1: Cure, Straumann, CH) or Xenon light (P2: Otoflash N171, Ernst Hinrichs Dental, G). The flexural fatigue limit was determined under cyclic loading in terms of a staircase approach with a piston-on-3-ball-test according to ISO 6872 after 24 h or 60 days water storage (37 °C). Specimens were preloaded with 50N and dynamic force was applied for 10⁵ loadings per step (f = 3Hz; steps 1: 50N-100N, 2: 50N-150N, 3: 50N-200N, 4: 50N-250N; F1000, Prematec, G; water at 37 °C).

STATISTICS

Kaplan Maier Log Rank (Mantel-Cox) test, ANOVA, Pearson correlations, Levene-test (α = 0.05, SPSS 26.0, IBM, Armonk, NY, USA)).

RESULTS

Mean survival cycles after 24 h of storage varied between 40388 (M1C2P2) and 195140 (M2C2P1) cycles and after 60 d decreased to 14022 (M1C2P2) and 173237 (M2C1P1). Kaplan Maier Log Rank test revealed significant differences between the material combinations. For M1 cleaning (Pearson: 0.346, p = 0.016) and for M2 polymerisation (Pearson: 0.616, p = 0.000) significantly influenced the number of loading cycles. Intermediate effects were found for material (p = 0.026), cleaning (p = 0.024) and polymerisation (p = 0.000) as well as the combination of material and polymerisation (p = 0.008).

CONCLUSIONS

The results show that the number of possible loading cycles of additively manufactured splint specimens depends on the type of material, their cleaning and post-polymerisation.

CLINICAL SIGNIFICANCE

Materials, cleaning and post-polymerisation of additive manufacturing processes should be matched to improve dynamic loading performance of splint materials.

Insights into the relationship between structure and rheological properties of starch gels in hot-extrusion 3D printing

This work investigated the relationship between structure, rheological properties and 3D printability of starch. For this purpose, the structural evolution of various starch gels at different concentrations and printing temperatures was systematically studied. The mechanical strength (G', τ_y) and extrudability (τ_f) of CS and RS gels were used to determine its 3D printability. Furthermore, G', τ_y and τ_f were closely related to the structure of starch and starch gel network. Ascribing to compact and stable gel network, CS samples with 20% concentration at 70-75 °C printing temperature and RS samples with 15-20% concentration at 75-80 °C printing temperature displayed preferable printing values (G', τ_y and τ_f), indicating the suitability for HE-3DP. RS samples exhibited higher mechanical strength than CS samples and were more suitable to print owing to the formation of new crystal structure. Overall, this work provided important information for HE-3DP based foods with good printability.