Primary surface measurement reported
The study reports water contact angle measurements on resin disk specimens and contact angle measurements of uncured UV resin-based coating droplets to evaluate hydrophilicity/wettability.
Client Citation Analysis
Novel Antibacterial Resin Coating for Dental Provisional Crowns to Suppress Biofilms and Inhibit Secondary Caries
This study develops a DMADDM-modified UV resin coating for provisional crown composites and uses Dropometer-based sessile-drop contact angle testing to assess hydrophilicity of resin disk specimens and wetting behavior of uncured coating droplets.
At-a-Glance Summary
How the paper credits the instrument
"Using the contact angle measurement apparatus (Dropometer, Droplet Lab, Markham, ON, Canada), the water contact angle was measured via the sessile-drop technique in air." / "The Droplet Lab's Sessile software (version 1.0.5.1) yielded the contact angle data by the utilization of the Young–Laplace equation." — Section 2.3, Contact Angle Assays.
How the contact-angle data were used in the study
Water contact angle results are used for wettability assessment across the Commercial Control, Experimental Control, and UV resin-coated groups with different DMADDM concentrations (Figure 2). Contact angle results for uncured UV resin-based samples are used to compare the hydrophilicity of uncured coating droplets across the experimental UV resin groups (Figure 3).
Replication / reliability statement
The paper states "A total of 15 measurements were taken." for the water contact angle assay, and reports n = 15 for the uncured coating measurements. It does not state how many specimens those 15 measurements were spread across, and gives no measurement temperature or relative humidity for either assay. Values are reported as mean ± sd.
What the Dropometer did and did not do here
The Dropometer measured water contact angle on cured coated disks (Figure 2) and the contact angle of uncured resin droplets on a TEMPSMART substrate (Figure 3), which are 2 of the paper's 9 figures. It was not the primary measurement instrument. The study's principal outcomes were measured by other equipment: colony-forming-unit plate counts, a SpectraMax M5 microplate reader (metabolic activity and lactic acid), a BioTek Cytation 5 fluorescence microscope (live/dead staining), an FEI Quanta 200 SEM (biofilm morphology and coating thickness) and a Mitutoyo Surftest SJ-310 profilometer (surface roughness). The paper does not report a correlation analysis between contact angle and the biofilm outcomes.
Paper Details
Title
Novel Antibacterial Resin Coating for Dental Provisional Crowns to Suppress Biofilms and Inhibit Secondary Caries
Authors
Ibrahim Ba-Armah; Mohammad Alenizy; Nader Almutairi; Heba Alqarni; Abdullah Alhussein; Radi Masri; Gary D. Hack; Thomas W. Oates; Jirun Sun; Michael D. Weir; Hockin H. K. Xu
Journal
Coatings
Year
2024
Volume
14
Pages / Article
1370
License
Creative Commons Attribution (CC BY) license
Funding & interests
Supported in part by NIH 1R01DE033442-01A1 (Sun, Xu). Authors are at the University of Maryland School of Dentistry and School of Medicine, the ADA Forsyth Institute, and Imam Abdulrahman Bin Faisal, Hail, Prince Sattam bin Abdulaziz, King Khalid and King Saud universities; four authors held Saudi Arabian Cultural Mission scholarships. The paper states: "The authors declare no conflicts of interest." Droplet Lab is not named in the funding statement, acknowledgements or author affiliations; the Dropometer is named in the Methods (Section 2.3).
Data availability
"The data presented in this study are available upon request from the corresponding authors." No open repository deposit.
Study type
In vitro laboratory study on disk specimens. Single-species 48 h Streptococcus mutans biofilms under static conditions; no in vivo, animal or clinical work. The Institutional Review Board statement is "Not applicable."
5.4
Scopus metrics (Elsevier / Scopus rating 2024)
Scopus metrics (Elsevier / Scopus rating 2024)
CiteScore subject ranks (CiteScore 2024)
- Q2 - Surfaces, Coatings and Films (45/132)
2.8
Journal Impact Factor (Clarivate JCR)
3.0
Journal Impact Factor (Clarivate JCR)
Journal Impact Factor (Clarivate JCR)
JCR category rank
- Q2 - Physics, Applied
- Q3 - Materials Science, Multidisciplinary
- Q3 - Materials Science, Coatings and Films
What Was Measured
Primary surface / interfacial measurement
Contact angle (degrees) was measured to assess hydrophilicity in two different configurations: (1) water contact angle — 5 µL deionised water on cured resin disk specimens, the configuration comparable to the water contact angle literature; and (2) resin-on-resin contact angle — a 3 µL droplet of the uncured UV coating itself placed on a TEMPSMART resin disk. The probe liquid in (2) is the coating, not water, so the Figure 3 values are a wetting test of the applied coating and are not comparable to water contact angles or to the Figure 2 values.
Supporting measurements
These measurements, made without the Dropometer, carry the paper's main conclusions. They comprise surface roughness (Ra) by stylus profilometry, SEM assessment of coating thickness, S. mutans biofilm colony-forming-unit counts, MTT metabolic activity, lactic acid production, live/dead fluorescence staining, SEM biofilm imaging, and human gingival fibroblast cytotoxicity by CCK-8 absorbance. Seven of the paper's nine figures report these.
Contact angle
contact angle measurement apparatus (Dropometer, Droplet Lab, Markham, ON, Canada); Droplet Lab’s Sessile software (version 1.0.5.1)
Surface roughness (Ra)
surface roughness analyzer (Surftest SJ-310; Mitutoyo America, Aurora, IL, USA)
Light curing
Labolight DUO (GC America, Alsip, IL, USA)
Coating thickness (SEM)
scanning electron microscope (Quanta 200, FEI Company, Hillsboro, OR, USA)
Inoculum density (OD600)
spectrophotometer (Genesys 10S, ThermoScientific, Waltham, MA, USA)
Absorbance / optical density (biofilm assays)
microplate reader (SpectraMax M5, Molecular Devices, Sunnyvale, CA, USA)
Biofilm imaging (live/dead)
Fluorescent microscope (BioTek Cytation 5, Agilent Technologies, Santa Clara, CA, USA)
Biofilm morphology (SEM)
scanning electron microscope (Quanta 200, FEI Company, Hillsboro, OR, USA)
Role of the Droplet Lab instrument
The Dropometer is used as a contact angle measurement apparatus to quantify surface hydrophilicity via sessile-drop testing in air. Water contact angle measurements were made by applying 5 µL deionized (DI) water droplets onto resin disks and evaluating the contact angle during a 10 s timeframe (15 measurements). For uncured UV resin-based coatings, a standard 3 µL droplet of each experimental UV resin group was applied onto the surface of the TEMPSMART resin disk and imaged after 10 s; contact angle values were obtained using Droplet Lab’s Sessile software (version 1.0.5.1) via the Young–Laplace equation.
In the study, the contact angle outputs are used to compare wettability/hydrophilicity between control and DMADDM-modified coating groups (cured disks) and to compare wetting behavior across uncured UV resin formulations.
The paper does not report a statistical analysis linking contact angle to the biofilm outcomes (CFU count, metabolic activity or lactic acid production). In the Discussion, the authors write that "the antibacterial properties of DMADDM seem to outweigh any potential increase in bacterial adhesion due to hydrophilicity", and, citing prior work on S. mutans, that its high hydrophobicity "may account for the reduced adhesion seen in the present study to the slightly hydrophilic resin-based coatings."
Bring This Measurement Into Your Lab
If you need water contact angle on dental resins, or how an uncured coating wets its substrate, we can show you a sessile drop workflow.
Key Findings
Water contact angle decreases at higher DMADDM concentrations (cured disks)
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).
Uncured UV resin droplet contact angles are similar across experimental groups
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).
The paper frames contact angle as a qualitative hydrophobicity/hydrophilicity indicator
Water contact angles are described as a qualitative measure of surface hydrophobicity, with an angle below 65° demonstrating a surface that is more hydrophilic.
Hydrophilicity did not compromise performance
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. 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".
The paper discusses, but does not test, a link between wettability and biofilm results
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 also the three that showed significant reductions in CFU, metabolic activity and lactic acid production. The paper does not report a correlation analysis between contact angle and these outcomes. The Discussion notes that prior literature is mixed: some studies found bacteria favoured more hydrophilic surfaces, others did not report decreased adhesion on more hydrophobic surfaces, and others "did not find any significant correlation between bacterial adhesion and the hydrophobicity of a material". Citing prior work, the authors note that 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."
Surface roughness was unchanged across all groups (Mitutoyo Surftest SJ-310)
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.
Figures & Visuals
What it shows
Shows representative water droplet images on samples and statistical comparisons of water contact angle (mean ± sd; n = 15) across Commercial Control, Experimental Control, and DMADDM-containing coating groups.
What it shows
Shows representative images (panel a) and statistical analysis (panel b; mean ± sd; n = 15) of uncured resin coating droplet contact angles across the experimental UV resin groups. The droplet imaged here is the uncured UV coating, placed on a TEMPSMART resin disk — not a water droplet.
Why It Matters
The paper's third hypothesis was that the surface characteristics of the DMADDM coatings would be comparable to those of the commercial control, and it assessed surface roughness and water contact angle for this. Roughness did not differ across groups, which the authors use to attribute the biofilm reduction to "the intrinsic antibacterial properties of DMADDM, rather than to any variations in surface roughness". For hydrophilicity, they report a significant difference between lower and higher DMADDM concentrations and state that the overall hydrophilicity did not adversely impact the coating's performance.
Within that context, the Dropometer-generated contact angle data support the paper’s interpretation of how DMADDM concentration changes wettability of cured coated disks, and how uncured coating droplets wet the TEMPSMART resin disk surface in a way the authors describe as favorable for application.
The authors list the study's limitations. Only a single bacterial species was examined, and the contact angles were reported at a single time point. The authors write: "It is yet to be established how easily the coating can be dislodged from the provisional crown material through ordinary toothbrushing and whether the hydrophilicity of the coating impacts hydrolytic degradation and leaching of the antimicrobial agent over time." They name wear resistance and long-term stability as the open questions, and call for multi-species biofilms and in vivo work. For a coating intended to sit on a provisional crown for up to two years, the wettability measured here is a baseline, not a service-life property.
Expert Perspective
Practical Takeaways
Dropometer workflow used for cured-surface wettability
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.
DMADDM concentration linked to lower water contact angle on cured disks
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 coating droplet wetting assessed with Young–Laplace analysis
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."
Uncured droplet contact angles were statistically similar across formulations
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).
A hydrophilicity interpretation threshold is provided in the discussion
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.
Durability of wettability is an open question the authors raise
The paper reports contact angles at a single time point and does not describe ageing, thermocycling or brushing before measurement. The authors identify wear resistance and long-term stability as key factors for clinical performance, and note that it is yet to be established whether the hydrophilicity of the coating affects hydrolytic degradation and leaching of the antimicrobial agent over time.
Frequently Asked Questions
What did the Dropometer measure in this study?
The authors used the Dropometer for sessile drop measurements in air: water contact angle with 5 µL deionized water drops on cured resin disks (Figure 2), and the contact angle of 3 µL droplets of each uncured UV resin coating on a TEMPSMART resin disk (Figure 3), with n = 15 for each. For the uncured coatings, the paper states that Droplet Lab's Sessile software (version 1.0.5.1) gave the contact angles using the Young–Laplace equation.
What contact angles were reported?
Water contact angles were 70.5 ± 4.6° (Commercial Control), 70 ± 6.8° (Experimental Control) and 69.1 ± 7.6° (UV+ 2.5% DMADDM), versus 54.7 ± 5.9°, 51.7 ± 7.6° and 50.7 ± 8° for UV+ 5%, 7.5% and 10% DMADDM, with a significant difference between the two sets (p < 0.01). The uncured coating droplets measured between 26.48° and 27.95°, with no significant difference between groups.
What do the authors conclude from the contact angle results?
The authors report a significant difference in hydrophilicity between lower and higher DMADDM concentrations, but state that the overall hydrophilicity did not adversely impact the coating's performance. They describe the uncured coatings as showing excellent hydrophilicity, which they relate to faster and easier application on provisional crowns.