UNIVERSIDADE ESTADUAL PAULISTA

“JÚLIO DE MESQUITA FILHO”

Instituto de Ciência e Tecnologia

Campus de São José dos Campos

ORIGINAL ARTICLE DOI: https://doi.org/10.4322/bds.2025.e4568

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in

any medium, provided the original work is properly cited.

Comparative study of conventional and 3D printed denture base

polymers: eﬀect of low-pressure plasma as a surface treatment

method

Estudo comparativo de polímeros para bases de próteses dentárias convencionais e impressas em 3D: efeito do plasma de

baixa pressão como método de tratamento de superfície

Ahmed Abdulraheem MEKI1 , Mohamed KHALAF2 , Hosam Muhammed ELSAYED3 , Fayez EL-HOSSARY2 ,

Mahmoud AMMAR4 , Emad Boriqaa Abd ELSALAM4 

1 - Sphinx University, Faculty of Dentistry, Department of Prosthodontics. Assiut, Egypt.

2 - Sohag University, Faculty of Science, Physics Department. Sohag, Egypt.

3 - Al Azhar University (Assiut Branch), Faculty of Oral and Dental Medicine, Dental Biomaterial Department. Assiut, Egypt.

4 - Al Azhar University (Assiut Branch), Faculty of Oral and Dental Medicine, Department of Prosthodontics. Assiut, Egypt.

How to cite: Meki AA, Khalaf M, Elsayed HM, El-Hossary F, Ammar M, Elsalam EBA. Comparative study of conventional and 3D printed

denture base polymers: effect of low-pressure plasma as a surface treatment method. Braz Dent Sci. 2025;28(1):e4568.

https://doi.org/10.4322/bds.2025.e4568

ABSTRACT

Objective: To compare exure strength (FS) and surface roughness properties of conventional heat polymerized

(CHP) and three-dimensionally printed (3DP) denture base resins and study the effect of plasma surface treatment

on these properties. Material and Methods: Rectangular resin samples (65 × 10 × 3.3 mm3) were fabricated

from two material groups: CHP and 3DP resins (N=24/material group). Each group was divided into control and

treated groups (n=12/subgroup) to study their exural strength and surface roughness properties. A comparative

evaluation of these properties was performed between the control groups at rst. Afterwards, treated groups were

exposed to low pressure atmospheric plasma treatment and were compared with control (untreated) samples

regarding changes in their properties both before and after plasma treatment. Results: The surface properties

of control CHP groups showed higher FS (p<0.0001) and lower surface roughness (p=0.0002) than the 3DP

group. Generally, when compared to the control group of each material, the plasma-treated CHP group and the

treated 3DP group showed signicant increase in FS (p<0.0001). Surface roughness signicantly increased in

treated group of CHP (p<0.0001) but had no signicant change in treated 3DP group (p=0.068). Conclusion:

Conventional heat polymerized denture base resins possess superior exural strength and lower surface roughness

compared to 3D printed resins. Plasma surface treatment is an effective method to strengthen both CHP and 3DP

denture base resins and roughen (micro-etch) CHP resin surfaces toward further chemical reactions.

KEYWORDS

Acrylic denture base; Plasma; Polymethyl methacrylate; Surface treatment; Three-dimensional printing.

Resumo:

Objetivo: Comparar a resistência à exão (RF) e as propriedades de rugosidade supercial de resinas para

bases de próteses dentárias polimerizadas por calor convencionais (CHP) e impressas em três dimensões (3DP)

e estudar o efeito do tratamento de superfície com plasma nessas propriedades. Material e Métodos: Amostras

de resina retangulares (65 × 10 × 3,3 mm3) foram fabricadas a partir de dois grupos de materiais: resinas CHP

e 3DP (N=24/grupo de material). Cada grupo foi dividido em grupos controle e tratados (n=12/subgrupo)

para estudar suas propriedades de resistência à exão e rugosidade supercial. Uma avaliação comparativa

dessas propriedades foi realizada entre os grupos controle inicialmente. Posteriormente, os grupos tratados

foram expostos ao tratamento com plasma atmosférico de baixa pressão e foram comparados com as amostras

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

INTRODUCTION

Polymethyl methacrylate (PMMA) has

become the dominant biomaterial for the

fabrication of prostheses in dental laboratories

and clinics due to their favorable mechanical

and aesthetic properties, simple processing

techniques, cost-efciency, and reduced toxicity.

It has superseded previous denture base materials

due to its reduced volumetric shrinkage, better

mechanical and surface properties, reduced

residual monomers and surface porosity [1,2].

With the current technologies advancing at

a rapid pace and the integration of CAD-based

technology in dental elds, complete dentures

can be fabricated using computer-aided design/

computer-aided manufacturing (CAD/CAM)

technology, either by computerized milling

(subtraction) from a single block or three-

dimensional (3D) printing (addition) techniques

using raw liquid resin [3].

The additive manufacturing techniques

(AMT), also called rapid prototyping, were

introduced to dental elds to enhance the nal

product quality and eliminate some of the

drawbacks of the milling techniques regarding

nal waste products and the wear of cutting burs.

The fabrication process includes a distinct layered-

manufacturing method using unpolymerized

liquid resin in an accurate printing machine.

Afterward, a mandatory photo-polymerization

step is required to enhance mechanical properties

and avoid distortion [4].

This technique has gained popularity due

to its precision, reduced time, standardized

production, waste minimization, and lower

infrastructure costs along with producing

ner details (undercuts and better anatomy).

Still, in this processing method, incomplete

polymerization (residual monomers) may occur

before the photo-polymerization step causing

dimensional changes and affecting strength and

surface texture of the nal product [5].

Since it is very difcult to produce a material

that meets all ideal requirements alone, the

general attitude is to apply some improving

treatments to these materials to augment their

properties and utilize their full potential in

various elds. Among these treatment methods is

the use of plasma surface treatment. Low pressure

plasma is a well-introduced treatment method

for dry surfaces due to its simplicity, tunability

and solvent-free aspect. Also, its peerless ability

to modify polymer surfaces and modify the

surface energy of the denture base surface,

thereby improving bonding, biocompatibility,

mechanical properties, chemical stability and

surface texture [6] without affecting the main

bulk properties and its implementation of green

chemistry principles [7].

Plasma parameters are important for the

treatment process and they depend on principal

factors including type of gas used, operating

pressure, input power, location of the sample

from the plasma source [8]. In the eld of applied

plasma science, it is recommended to assess these

conditions before determining the most suitable

parameters for each treatment process.

Many different types of gas-plasmas have

been cited in the literature including oxygen,

ammonia, helium, and argon for modication

of polymer surfaces. The resulting effect on

the material mainly depends on the type of gas

controle (não tratadas) em relação às mudanças em suas propriedades antes e depois do tratamento com plasma.

Resultados: As propriedades de superfície dos grupos CHP controle mostraram maior RF (p<0,0001) e menor

rugosidade supercial (p=0,0002) do que o grupo 3DP. Geralmente, quando comparado com o grupo controle

de cada material, o grupo CHP tratado com plasma e o grupo 3DP tratado mostraram aumento signicativo na

RF (p<0,0001). A rugosidade supercial aumentou signicativamente no grupo tratado de CHP (p<0,0001),

mas não apresentou alteração signicativa no grupo 3DP tratado (p=0,068). Conclusão: As resinas para bases

de próteses dentárias polimerizadas por calor convencionais possuem resistência à exão superior e menor

rugosidade supercial em comparação com as resinas impressas em 3D. O tratamento de superfície com plasma

é um método ecaz para fortalecer as resinas para bases de próteses dentárias CHP e 3DP e tornar as superfícies

da resina CHP mais rugosas (micro-jateamento) para reações químicas adicionais.

Palavras-chave

Base de prótese acrílica; Plasma; Polimetilmetacrilato; Tratamento de superfície; Impressão tridimensional.

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

used [9]. Crosslinking of a polymer outer surface

can also be enhanced by gas plasma [10].

For an effective prosthetic care and patient

satisfaction, denture base material must possess

a sufcient exural strength (FS) to withstand

occlusal forces during mastication. A standard

method to measure the FS of denture bases

is the three-point bending test stated in ISO

standards [11]. Also, surface roughness is of

great importance in denture base materials and

should be kept within acceptable clinical values

to be used safely in the oral cavity [12].

To the best of our knowledge, there have

been no studies on the impact of plasma surface

treatment on 3DP denture base materials. Since

printed denture bases have shown reduced FS

in previous studies [13] and plasma treatment

has been used to improve polymer surface

properties [9], this current study was conducted

to evaluate the impact of plasma treatment on FS

and surface roughness of CHP and 3DP denture

base material in the aim of improving 3DP resin

properties in denture bases.

The rst null hypothesis, regarding control

groups, was that CHP group would be superior in

both FS and surface roughness values. The second

null hypothesis was that plasma surface treatment

would signicantly affect surface roughness and

FS in both materials.

MATERIAL & METHODS

Specimen’s fabrication and grouping:

A total of 48 specimens from both materials

were fabricated and divided into control and

treated subgroups (gure 1). Six specimens were

used for each test.

Conventional heat-polymerized specimens

A total of 24 bar shaped samples were

prepared by investing modeling wax specimens

with the dimensions of (65 × 10 × 3.3 mm3) as per

ISO: 20795-1:2013 for three point bending testing

[11]. Investment was done and mold space was

prepared by dewaxing. Then, acrylic pink powder

and liquid (lot number 224008064, Acrostone

Dental & Medical Supplies, Cairo, Egypt) were

proportioned, mixed, packed, and polymerized

in a thermostatically controlled water bath,

complying with the manufacturer’s instructions,

and as described in previous studies [13]. After

polymerization using a long-curing cycle (74 ºC

for 8 hours) and slow bench cooling, deasking

was done and samples were retrieved and nished.

3D printed specimen fabrication

Designing software (MasterCAM® CNC

software v8.1) was used to virtually design

Figure 1 - Organizational chart illustrating the grouping of specimens and tests performed.

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

specimens with the same dimensions. The STL

design le was exported to the CAM software

(Chitubox Basic software v1.9.3) and positioned

at 0° on the platform with a 50 μm of layer

thickness complying with the manufacturer’s

instructions and similar to previous studies [14].

The STL le was copied, arranged, and sliced by

the same software and then exported to the 3D

printer (Phrozen shufe LCD Resin 3D Printer,

phrozen shuffle tech Co LTD, Taiwan) with

ultraviolet light source having a wavelength

ranging from 380 to 420 Nm. Pink liquid

resin (lot number WU082N02, Next Dent,

Denture 3D+, Vertex Dental, Netherlands) was

shaken and placed in resin tanks. After printing,

specimens were removed and cleaned using

two-step wash in Ethanol >90% (lot number

Eoo58111, OctoPharma, Ethyl alcohol, Egypt)

in an ultrasonic cleaner (CD-4820, Codyson,

China) for 4 minutes and then for another

one minute to remove any remaining uncured

resin [14]. Post-polymerization was done for

>20 minutes [15] using an ultraviolet curing

unit (Bre. Lux. Power Unit, Bredent, Germany)

in a temperature of >60°C, while submerged in

glycerin [16]. All samples’ dimensions in this

study were veried using digital calipers (Carbon-

ber composite digital caliper, Total Inc. China).

Plasma treatment:

Plasma used in this study is low pressure

plasma using a homemade reproducible

experimentally arranged system of direct current

(DC) glow discharge plasma system (Figure 2-3)

similar to another used in previous studies [17].

The vacuum cell consists of two parallel

moving electrodes surrounded at 2.5 cm by

a cylindrical tube made of Pyrex glass. Each

electrode is a brass disk with a diameter of 5 cm

and a thickness of 1.5 cm. A double-stage rotary

vacuum pump (Speedivac 2, Edwards High

Vacuum, Crawley, UK) was used to maintain

a base pressure of 4 × 10-2 bar. The vacuum

tube was connected to open air via a needle

valve (Edwards capsule dial gauge CG 16K)

by which the air gas flow can be controlled

to adjust the gas pressure inside the tube. A

vacuum gauge was connected to measure the

gas pressure inside the tube. To generate the

plasma, both electrodes were connected to a

DC power supply working up to 0.45 kV and a

variable load resistance controlled the current.

Specimens were positioned on the center of the

lower electrode, transversely in the direction of

gas ow. Samples were exposed to the generated

Figure 2 - A circuit representation of the device arrangement.

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

plasma (homogenous uniform glow) for 20 min.

After the exposure time, the tube was kept locked

to restore pressure and dissipate the heat for 10

minutes. The samples were handled carefully and

isolated in a dry place to minimize the effect of

surface aging [18]. A pilot study was performed

on a separate set of samples, with different

plasma exposure times to determine the best

plasma parameters for the required test without

affecting the specimen’s bulk.

Specimens Testing

Flexural properties (three-point bending test)

A total of 48 rectangular samples of the

four subgroups were tested using a universal

testing machine (Model 3345; Instron Industrial

Products, Norwood, USA) at room temperature,

as per ISO: 20795–1:2013 [11]. Each sample was

horizontally mounted in the loading xture (two

parallel supporting rods with span length of 50

mm) and connected to the testing machine and

a Bi-beveled chisel (2 mm width) with a 5 kN

of load force. Then, samples were compression

loaded until fractured by a crosshead at a steady

rate of displacement (1 mm/minute). Data was

recorded by computer software (Bluehill Lite

Software Instron® Instruments). The limiting

stress at which failure or instability is imminent

is represented by FS and its value for each sample

was calculated by the formula:

(FS =3FL/ 2wh

)

- where;

is the exural strength (MPa),

the load (N) at fracture,

is the span between

supporters (mm),

is the sample width (mm)

and

= sample height (mm).

Non-contact surface roughness testing:

Non-contact technique was done as

mentioned in the literature [19]. A digital

microscopic camera (U500x, Guangdong, China),

with a resolution of 3 Mega Pixels, was used

to capture the samples while connected with

compatible computer. The camera was placed

vertically at 2.5 cm away from the samples.

Light was obtained using an 8-LED lamp,

with a color index close to 95%. Images were

recorded at maximum resolutions and cropped to

350 × 400 pixels to standardize area of roughness

measurement. Analysis of the cropped images

was done using WSxM software for scanning

probe microscopy (SPM) on Windows. (Ver. 5,

Nanotec, Electronica, SL). System calibration was

made using a ruler. For each specimen, multiple

images were collected in the central and side

areas. Average heights (Ra) were calculated and

expressed in micrometers (μm).

Statistical analysis

Data were collected, tabulated, statistically

analyzed, presented as descriptive statistics,

and tested for normality using Shapiro-Wilk

tests. A two-tailed independent-sample

-test

was used to compare between control groups

and evaluate the difference between the control

and treated subgroups of the same material.

The condence interval was set at 95% and the

signicance level to 0.05. A

-value ≤ 0.05 was

considered statistically significant. Statistical

analysis was achieved using GraphPad Prism™

software (version 9.5 for Windows; GraphPad

Inc., California, USA).

Figure 3 - DC-glow discharge plasma system including DC power supply and Vacuum chamber.

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

RESULTS

Before plasma treatment, the mean FS of

control CHP groups (82.30 ±2.48) was higher

than control 3DP groups (66.14 ±2.6). Statistical

data analysis showed a highly signicant difference

in FS between the control groups (

<0.0001)

(Table I). The mean surface roughness of control

3DP groups (0.244±0.024) was higher than

control CHP group (0.14±0.037). The analysis

showed a highly signicant difference in roughness

between the control groups (

=0.0002) (Table II,

Figure 4).

After plasma treatment, when FS test

results were examined, the treated CHP group

(95.13±1.95) showed higher FS than control

group (82.30±2.48). The analysis showed a highly

signicant difference between treated and control

CHP groups (

<0.0001). Treated 3DP groups

(99.3 ±9.26) showed a signicantly higher FS

than control groups (66.14 ±2.6). The analysis

showed a highly signicant difference between

treated and control 3DP groups (p<0.0001)

(Figure 5-B).

Also, when surface roughness results were

examined, treated CHP group (0.28±0.016)

showed higher surface roughness than control

group (0.14±0.037). The analysis showed a

highly significant difference between treated

and control groups (

<0.0001). And treated

3DP groups (0.27±0.019) showed a higher FS

than control groups (0.24±0.024). Yet, statistical

analysis showed an insignificant difference

between treated and control groups (

=0.068)

(Figure 5A). A 3D surface analysis image scan of

control and treated groups is shown in gure (6).

Table I - Mean, standard deviations (SD), and signiﬁcance of FS in

PMMA groups

Groups

Mean ±SD (MPa)

-value*

Control Treated

CHP group 82.30 ±2.48 95.13 ±1.95 <0.0001*

3DP group 66.14 ±2.6 99.3 ±9.26 <0.0001*

-value* <0.0001*

*Signiﬁcant at (p≤0.05).

Figure 4 - Statistical analysis (Mean and standard deviation) of A) Flexural strength and B) Surface roughness between control groups.

Figure 5 - Statistical analysis (Mean and standard deviation) of (A) Surface roughnes and (B) Flexure strength between control and treated groups.

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

DISCUSSION

The first null hypothesis was partially

rejected as CHP control group showed lower

roughness values. The second null hypothesis

was partially rejected as plasma surface treatment

did not signicantly affect surface roughness of

3DP group.

Earlier studies of plasma treatment to

PMMA samples were done only to CHP resins.

Hence, this study included laboratory-based 3D

printed dental resin samples used for denture

base fabrication. In this study, control 3DP

samples demonstrated the lowest FS values and

yet, they were above the ISO recommendations

for minimum FS of polymers used for acrylic

denture bases (65 MPa) [11]; which supports the

manufacturer’s claim of its suitability as denture

base materials.

During the polymerization process, the

degree of double bond (terminal aliphatic C=C)

conversion into single covalent bonds between

carbon atoms (C-C) causes the change of material

from liquid to solid forms. Furthermore, the degree

of conversion (DOC) is an important indicator of

the mechanical and physical properties of the

resulting resin. Printed resins have incomplete

(lower) DOC in comparison with other types of

resins [20]. This indicates the presence of free

suspended monomers to the end-product with

possibility of leach-out and tissue irritation and

eventually affects the mechanical properties due

to the relatively weak bond between successive

printed layers [20].

In this study, control CHP group showed a

higher FS values when compared to 3DP control

group. This could be attributed to the high-

Figure 6 - showing 3D surface analysis image scan of control and treated groups A) CHP control group, B) CHP treated group, C) 3DP control

group, D) 3DP plasma treated group.

Table II - Mean, SD and signiﬁcance of surface roughness in PMMA

groups

Groups

Mean ±SD (µm)

-value*

Control Treated

CHP group 0.14±0.037 0.28±0.016 <0.0001*

3DP group 0.24±0.024 0.27±0.019 0.068

-value* 0.0002*

*Signiﬁcant at (p≤0.05).

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

temperature long-cycle polymerization process

used during fabrication of CHP samples [3]

which gives them a better chance of curing and

improves the fusion between cross-linking agents

and polymer chains. Consequently, this decreases

residual monomers, increases molecular weight,

and minimizes the chances of internal porosity,

crack propagation and material plasticity.

The decreased FS values of 3DP samples

could be due to the use of acrylic ester monomers

that have relatively low DOC [21] as the

abovementioned. Another explanation could be

the water-polymer bonds formed during layered

polymerization technique due to water sorption

properties [4]. When water molecules diffuse into

resin polymer, they form interpolymeric spaces

that force polymer chains away from each other

with water molecules in between them. This will

reduce adhesion forces between successive layers

and cause swelling of the denture base, hence

decreasing both strength and surface smoothness,

and increasing plasticizing effects [4].

This also has been veried by Gad et al. [21]

who found some voids using SEM at fracture

side of printed samples caused by evaporation

of water particles incorporated between layers of

printed samples. These voids decrease interfacial

bonding between layers and adversely affect

mechanical performance of printed samples and

initiate fractures.

This result agrees with earlier studies using

the same brand of liquid resin (NextDent Denture

3D+). Chhabra et al. [1], Fouda et al. [22] and

Gad et al. [21] reported similar results, and their

FS values were somewhat similar to our results

and in compliance with ISO recommendation.

Also, Al-Dwairi et al. [23] concluded the same

results which were slightly higher than the

recorded in our study. Al-Qarni and Gad [13]

showed similar results, but their exure values

of 3DP resins were lower than ISO requirements.

This difference can be explained by variations

in building parameters and post polymerization

process [5]. Prpić et al. [24] showed the same

results using another product of the same brand

(NextDent Base).

Other studies of different brands showed oppo-

site results. Interestingly, Temizci et al. [3] con-

cluded in their study that FS in the 3DP group was

higher than milled group and HP group. In addi-

tion, Di Fiore et al. [25] reported in their study an

insignicant difference in FS values between CHP

and 3DP samples; with a slight increase in exure

values in 3DP samples. These unusual results

could be explained by the difference in material

brands used during each study, the difference in

build orientation, layer thickness and\or printer

used during sample processing [5].

Surface roughness test results showed higher

roughness values of the control 3DP group than

the control CHP groups. This high roughness

value could be a result of the voids formed by

water sorption properties of printed samples [21]

and/or a natural sequel to the layered building

of objects that forms micro-stepping surface, also

known as layer lines [5]. Although this surface

topography is inevitable, printing parameters

such as building orientations and layer thickness

were taken into consideration in this study.

It has been proven in the literature that,

during printing, the lower the layer thickness,

the higher the DOC, hence the lower residual

(uncured) monomers in the nal product. Also,

a zero degree of build orientation results in fewer

layers per specimen and improves their object’s

details (surface smoothness) [26] and FS as much

as possible when the printed layers are subjected

to vertical loads [21]. Another issue in additive

printing techniques that could be a source of

surface roughness is the possibility of forming

partially cured particles when inadequate post-

polymerization step is not properly achieved.

These particles may dislodge from the surface

and form microscopic porosities [5].

The results of the current study agree with

previous similar studies; Both Poker et al. [14]

and Gad et al. [21] concluded similar results using

the same product by a non-contact prolometer

scan. Additionally, Meirowitz et al. [27] in their

study of Candida albicans adhesion to denture

base fabrication methods, they reported that the

3DP samples showed higher surface roughness

than both CHP and milled samples. Furthermore,

using a contact prolometer, Falahchai et al. [28],

Di Fiore et al. [25] and Helal et al. [12] reported

similar results despite the difference of building

parameters. On the contrast to our findings,

Al-Dwairi et al. [23] reported an insignicant

increase in surface roughness in the CHP group

in comparison to the 3DP group of the same

resin brand.

Low-pressure plasma treatment causes free

radicals that result in four chemical modifying

effects on the polymer surface micro-environment,

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

these are (1) surface cleaning (removal of organic

contamination), (2) micro-etching (degradation/

ablation), (3) surface activation (modication of

the surface functional groups) and (4) cohesive

strengthening of the surface by cross-linking

(branching of polymer chains) in near surface

molecules that stabilize the surface mechanically [8].

The longer treatment time in the current

study was benecial to slow down the ageing

process of the polymers in the air, increase stability

of plasma polymer lms (PPFs) and maintain

their gained properties for a longer time. This

is achieved by enhancing surface cross-linking

and preventing interface enthalpy (polar group

reorientation and surface restructuring) [29]. This

is in agreement with a previous study by Vesel

and Mozetic [18] reporting that longer plasma

treatment times increase surface crystallinity,

and sequentially slow the ageing process due to

the limited surface mobility of chains at polymer

surfaces.

Among the factors affecting the strength of

polymers is the cross-linking of polymeric chains,

as it has a crucial impact on the deformation

behavior (strain hardening) of the polymer

resulted by restricting the motion of polymer

chains, hence giving strength to the polymer [30].

Another factor is the crystallinity degree, as

the crystalline phase enhances intermolecular

bonding leading to regularly aligned chains

(lamellae), leading to higher strength and

hardness features [31].

Studies show that plasma treatment of

polymers improves cross-linking by branching

of near surface molecules, along with the degree

of surface crystallinity, and increasing surface

roughness (etching). when they are exposed

to appropriate plasma density [32]. Similarly,

Yun et al. [33] reported an increase in polymer

cross linked structure and degree of crystallinity

upon exposure to plasma within the PPFs which

restricts chain mobility and increases mechanical

properties of the polymers. Motaal et al. [17]

revealed that plasma treatment increased the

exural strength of repaired CHP resins with auto

polymerized resins.

In contrast, Pan et al. [34] and Jassim [35]

reported a decreased strength of polymer after

plasma surface treatment. This might be related

to different types of plasma parameters used and/

or different brands of polymers.

The application of plasma on polymers

removes low molecular weight polymers by

breaking primary chemical bonds (chain cleavage)

by ion bombardment and transforming them

into high molecular weight surface polymers by

cross-linking reactions between remaining chains

and formation of PPFs on the outer surface,

which enhances surface stability in comparison

to conventional polymer coatings [29]. Cross-

linking of polymers can improve mechanical

properties, bond strength at the surface and their

ability to resist the heat by forming a very thin

cohesive layer [10].

The increased exural strength values in

the CHP group in this study can be elucidated

based on the abovementioned cross-linking

phenomenon of plasma and its effect on polymer

degree of crystallinity, thus, increasing mechanical

properties of polymers by hindering their

molecular chains movement [31]. Yet, this result

disagrees with a previous study by Jassim [35]

reporting a decreased exural strength of CHP

acrylic after plasma treatment. The probable

cause of this difference is the use of argon plasma

in the previous study [35].

From a physical point of view, plasma

treatments increase roughness values (etching)

in polymers as a result of ion bombardment

into the polymer surface, which consequently

forms minute peaks and valleys in micro surface

levels (figure 6), hence increasing surface

roughness [36]. Also, this can be ascribed to the

fact that oxygen containing plasma treatment

is considered an effective etching technique to

polymeric surfaces that creates roughness by

preferential ablation of the amorphous residues

between the crystal domains effect [9,31].

The increase in roughness of CHP samples

after O2 containing plasma treatment agrees with

a previous study by Masood and Mahamed [9]

reporting similar roughness results due to the

formation of carbon-containing groups (C-O-C,

C=O, C=C) on the surface which was analyzed

using FTIR spectrum. Resulting in activating the

treated surface toward further chemical reactions

(surface etching) [9]. Yildirim et al. [6] also

reported similar roughness results using argon

plasma. However, this disagrees with Jassim

[35] who reported in a previous study a decrease

in roughness of CHP acrylic after argon plasma

treatment. Chytrosz-Wrobel et al. [31] reported

Braz Dent Sci 2025 Jan/Mar;28 (1): e4568

Meki AA et al.

Comparative study of conventional and 3D printed denture base polymers: effect of low-pressure plasma as a surface treatment method

Meki AA et al. Comparative study of conventional and 3D printed denture

base polymers: eﬀect of low-pressure plasma as a surface

treatment method

similar roughness results on other medically

relevant polymers after O2 plasma treatment.

This difference in surface topography can

improve mechanical interlocking and the increase

surface area available for molecular or chemical

reactions. Clearly, the rough geometry of the

interface provides an increased adhesion strength

using mechanical and chemical mechanisms [37].

Another observation of the results is that treated

3DP samples showed no significant effect on

roughness property in comparison to control

group. The author attributed this to the existing

inherent roughness resulting from the layered

manufacturing process used [14].

CONCLUSION

The current study indicated that 3DP resins

possess lower FS properties and higher surface

roughness than CHP resins. Plasma surface

treatment signicantly increased FS and surface

roughness in the treated CHP group. Plasma

treated groups of 3DP resins showed a high

increase in FS almost comparable to CHP resins,

without affecting their surface roughness when

compared to control groups.

Author’s Contributions

AAM: Conceptualization, Methodology,

Software, Validation, Formal Analysis,

Investigation, Resources, Data Curation, Writing

– Original Draft Preparation. MK: Resources, Data

Curation, Writing – Original Draft Preparation,

Writing – Review & Editing. HME: Resources,

Data Curation, Writing – Review & Editing.

FEH: Writing – Review & Editing, Visualization,

Supervision. MA: Writing – Review & Editing,

Visualization, Supervision. EBAE: Writing –

Review & Editing, Visualization, Supervision.

Conict of Interest

The authors have no conicts of interest to

declare.

Funding

This research did not receive any specic

grant from funding agencies in the public,

commercial, or not-for-prot sectors.

Regulatory Statement

This study was designed as an experimental

in-vitro controlled study without using any living

tissues. Hence, no ethical approval was necessary.

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Comparative study of conventional and 3D printed denture

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Meki AA et al.

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Meki AA et al. Comparative study of conventional and 3D printed denture

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treatment method

Date submitted: 2024 Nov 01

Accept submission: 2025 Jan 22

Ahmed Abdulraheem Meki

(Corresponding address)

Sphinx University, Faculty of Dentistry, Department of Prosthodontics, Assiut,

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E-mail: ahmedmeki95@gmail.com; Ahmed.abdelreheem@sphinx.edu.eg

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