Novel Antibacterial Resin Coating for Dental Provisional Crowns to Suppress Biofilms and Inhibit Secondary Caries

For wettability assessment (Figure 2; mean ± sd; n = 15), Commercial Control (70.5 ± 4.6°), Experimental Control (70 ± 6.8°), and UV+ 2.5% DMADDM (69.1 ± 7.6°) showed no significant differences among these three groups (p > 0.01). UV+ 5% DMADDM (54.7 ± 5.9°), UV+ 7.5% DMADDM (51.7 ± 7.6°), and UV+ 10% DMADDM (50.7 ± 8°) showed no significant differences among these three groups (p > 0.01), and there was a significant difference between the lower-concentration set and the higher-concentration set (p < 0.01).

In Figure 3 (mean ± sd; n = 15) the probe liquid is the uncured coating itself — a 3 µL droplet of each UV resin formulation placed on a TEMPSMART resin disk — so these values describe how the coating wets its substrate during application, not the wettability of a finished surface, and they are not comparable to the water contact angles above. The uncured resin droplets gave 26.84 ± 3.8° (Experimental Control), 26.48 ± 1.9° (UV+ 2.5% DMADDM), 26.70 ± 2.1° (UV+ 5% DMADDM), 27.95 ± 2.1° (UV+ 7.5% DMADDM) and 27.84 ± 1.5° (UV+ 10% DMADDM), with no significant difference between all groups (p > 0.01) — DMADDM loading does not change how the coating flows onto the crown.

Water contact angles are described as a qualitative measure of surface hydrophobicity, with an angle below 65° demonstrating a surface that is more hydrophilic.

The discussion states that while there was a significant difference in hydrophilicity between lower and higher concentrations of DMADDM, the overall hydrophilicity did not adversely impact the coating's performance, and the antibacterial properties of DMADDM "seem to outweigh" potential increases in bacterial adhesion due to hydrophilicity — that is, the authors treat the increased hydrophilicity as a potential liability that the chemistry overcame, not as a contributor to the antibacterial effect. They state the effect "can be confidently attributed to the intrinsic antibacterial properties of DMADDM, rather than to any variations in surface roughness". For uncured UV resin-based coatings, the paper states all coatings showed "excellent hydrophilicity," and that increased wetting ability allows for "faster and easier application" — a handling benefit during placement, which is the one performance claim the contact-angle data do support.

The three coatings with the lowest water contact angles — UV+ 5% (54.7 ± 5.9°), UV+ 7.5% (51.7 ± 7.6°) and UV+ 10% (50.7 ± 8°) — are exactly the three that suppressed biofilm most. On the common assumption that more hydrophobic surfaces resist adhesion, the direction here runs backwards, and the paper does not attempt to reconcile it statistically: no correlation between contact angle and CFU, MTT or lactic acid appears anywhere in it. The Discussion notes the prior literature is unresolved — some studies found bacteria favoured more hydrophilic surfaces, others found no reduced adhesion on more hydrophobic surfaces, and others "did not find any significant correlation between bacterial adhesion and the hydrophobicity of a material". The single sentence bridging to this study's own data is hedged and cited to prior work: S. mutans "was observed to have a high level of hydrophobicity, which may account for the reduced adhesion seen in the present study to the slightly hydrophilic resin-based coatings."

No significant difference in Ra was found between the commercial control and any DMADDM coating (p > 0.05), and the paper reports that "all specimens evaluated in this study had an average surface roughness (Ra) of 0.19 μm or less" — below the 0.2 μm literature threshold "beyond which biofilm adherence is much decreased and the surface is considered smooth". The coated groups reached that with fewer polishing steps than the commercial control. Roughness was measured by a Mitutoyo Surftest SJ-310 stylus profilometer, not by the Dropometer.

Water contact angles were measured via the sessile-drop technique in air using 5 µL DI water droplets evaluated over a 10 s timeframe, with 15 measurements taken.

The paper reports higher-DMADDM coating groups with lower water contact angles (UV+ 5%, 7.5%, and 10% DMADDM) compared with Commercial Control / Experimental Control / UV+ 2.5% DMADDM, with a significant difference between these sets (p < 0.01).

Uncured UV resin droplet contact angles were obtained from droplet images captured after 10 s. The paper's wording is: "The Droplet Lab's Sessile software (version 1.0.5.1) yielded the contact angle data by the utilization of the Young–Laplace equation."

The uncured UV resin droplet contact angles across Experimental Control and DMADDM-containing UV resin groups showed no significant difference between all groups (p > 0.01).

The paper notes that a water contact angle below 65° demonstrates a surface that is more hydrophilic, providing a criterion for qualitative interpretation of wettability. Two constraints travel with it: the criterion is defined for water and cannot be applied to the Figure 3 uncured-resin droplet values, and the paper itself calls contact angle "a qualitative measure of surface hydrophobicity" — a classification boundary, not a quantitative property.

Every contact angle in this study was taken on a freshly prepared, freshly polished specimen with no thermocycling, water storage or brush abrasion. The authors flag that gap themselves and identify wear resistance and long-term stability as the unanswered questions for clinical use. A lab replicating this protocol should measure contact angle at baseline and again after ageing, and should note the polishing asymmetry in the original design — the commercial control was polished through six grits to 2000, the coated groups through two grits to 1200.