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.2024.e4564

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

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.

Evaluation the eﬀect ofglazing and the printing orientations on the

surface roughness and the microhardness of DLP dental zirconia:

an in vitro study

Avaliação do efeito da aplicação do glaze e das orientações de impressão na rugosidade de superfície e na microdureza de

zircônia odontológica DLP: um estudo in vitro

Nour I. DAWOOD1 , Zahraa Nazar ALWAHAB1 , Sahar Abdulrazzaq NAJI1 

1 - Middle Technical University, College of Health and Medical Techniques. Baghdad, Iraq.

How to cite: Dawood NI, Alwahab ZN, Naji SA. Evaluation the effect of glazing and the printing orientations on the surface roughness and the

microhardness of DLP dental zirconia: an in vitro study. Braz Dent Sci. 2025;27(4):e4564. https://doi.org/10.4322/bds.2024.e4564

ABSTRACT

Objective: To evaluate the effect of glazing and different printing angulations on the surface roughness and hardness

of 3D-printed zirconia specimens. Material and Methods: Forty-two cuboid-shaped specimens (10mm length, 10mm

width, 3mm thickness were constructed by ZIPRO printer (AON, South Korea) from a zirconia slurry. Three distinct

groups were established for the specimens based on the printing orientation angle (n = 14), Vertical (0°), Horizontal

(90°), and Diagonal (45°) orientations to the building direction. The diamond-impregnated system was used to

polish all specimens as the manufacturer’s recommendations. Two groupings were subsequently formed from the

specimens (n =7): polished groups (VP, HP, and DP), polished and then glazed with the diamond paste groups (VG,

HG, and DG). The surface roughness of each specimen was measured using a prolometer, and the microhardness

was determined using a Vicker microhardness tester. For assessing the specimens’ surface quality, the scanning

electron microscopy apparatus was employed. One-way ANOVA and Tukey’s HSD tests were used in analyzing the

study data, which had a signicant P-value (p < 0.05). Results: A signicant difference was observed between the

polishing and glazing groups for surface roughness and microhardness; however, no signicant differences were

identied in surface roughness between the polished and glazed groups in horizontal and diagonal orientations.

Conclusion: Glazing with diamond paste improved the zirconia surface qualitatively and quantitatively. Hardness

values were increased in the glazed groups compared to the polished groups in all three building orientations. The

optimal building angulation was the vertical orientation.

KEYWORDS

Additive manufacturing; Digital light processing zirconia; Glazed 3D-printed zirconia; Microhardness; Surface

roughness.

RESUMO

Objetivo: Avaliar o efeito da aplicação do glaze e de diferentes angulações de impressão na rugosidade de

superfície e na dureza de espécimes de zircônia impressos em 3D. Material e Métodos: Quarenta e dois espécimes

em formato cuboide (10 mm de comprimento, 10 mm de largura, 3 mm de espessura foram coneccionados

pela impressora ZIPRO (AON, Coreia do Sul) a partir de uma pasta de zircônia. Três grupos distintos foram

estabelecidos para os espécimes com base no ângulo de orientação de impressão (n = 14), orientações Vertical

(0°), Horizontal (90°) e Diagonal (45°) para a direção da impressão. O sistema impregnado com diamante foi

usado para polir todos os espécimes conforme as recomendações do fabricante. Dois grupos foram posteriormente

formados a partir dos espécimes (n = 7): grupos polidos (VP, HP e DP), grupos polidos e glazeados com pasta

de diamante (VG, HG e DG). A rugosidade da superfície de cada espécime foi medida usando um perlômetro,

e a microdureza foi determinada usando um aparelho de microdureza Vicker. Para avaliar a qualidade da

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

INTRODUCTION

Additive manufacturing (AM) has surpassed

traditional methods in manufacturing for its

fundamental shape-creation capabilities, design

flexibility, waste minimization, and capacity to

be customized. This technique employs a printing

process that builds upon itself, resulting in products

with long-lasting mechanical properties [1].

The Organization for Economic Cooperation and

Development (OECD) predicts that AM will

ultimately supersede Subtractive Manufacturing

(SM) shortly [2]. Zirconia restorations are

predominantly produced through milling utilizing a

CAD-CAM process. The introduction of lithography-

based ceramic manufacturing (LCM) occurred

a few years ago [3]. Zirconia ceramics provide

excellent mechanical properties, including strength,

hardness, fracture toughness, wear resistance,

corrosion resistance, and biocompatibility, while

facilitating machining by SM technology in the

pre-sintering phase [4]. Vat photopolymerization,

material jetting, sheet lamination, powder

bed fusion (PBF), material extrusion or fused

deposition modeling, binder jetting, and direct

energy deposition are the seven AM approaches

categorized by the American Society of Testing

and Materials [5,6]. Promising outcomes for

generating zirconia-based dental prostheses have

been established by stereolithographic techniques,

like Stereolithography (SLA) and Digital Light

Processing (DLP), thanks to the advent of AM

technology [7,8]. Recent investigations indicate

that vat photopolymerization when accompanied by

appropriate heat treatment techniques, can attain

a density and microstructure comparable to those

of conventional manufacture [9]. The mechanical

properties of the AM zirconia are close to those of

SM blocks, including high strength, hardness, and

fracture toughness, all of which are inuenced by

the powder combination [8,10]. One of the factors

that, when adjusted properly, decreases printing

duration and manufacturing cost while increasing

the dimensional precision of the nal product is the

printing orientation [11]. Yet, there are still problems

with 3D-printed ceramics’ performance, such as

the fact that different printing layer orientations

produce materials with varying characteristics.

According to previous investigations, zirconia

specimens printed with layers orientated vertically

to the tensile surface exhibited reduced exural

strength and elastic modulus in bending tests

compared to specimens printed with layers aligned

to the tensile surface [12,13]. So, to nd out what

printed materials are suitable for use and to design

the orientation of printed restorations for buildings,

it’s crucial to know how different printing layer

directions affect their mechanical characteristics

and longevity under fatigue. Surface quality is an

additional obstacle for 3D-printed dental ceramics

along with mechanical behavior as a result of the

step effect brought about by building in layers [14].

In its as-sintered state, 3D-printed zirconia displays

signicant surface roughness, especially on printing-

characterized surfaces [15]. Despite using the

same polishing procedures, mechanical properties

showed that surface roughness was the sole

distinguishing feature between the vertical and

horizontal specimens [16]. Prior research indicated

that construction direction can affect the surface

roughness of printed zirconia because of the

creation of tiny grooves at layer borders during

3D printing [17]. The profiles produced at low

print orientation angles are regular, with the peak

amplitude directly proportional to the height of

the layers. The width of the peaks widens with

steep print orientation angles, while the at area

or gap between successive peaks remains the

same. The experimental data demonstrate a more

superfície dos espécimes, o equipamento de microscopia eletrônica de varredura foi utilizado. Testes ANOVA

unidirecional e teste Tukey HSD foram utilizados na análise dos dados do estudo, que tiveram um valor P

signicativo (p < 0,05). Resultados: Foi observada uma diferença signicativa entre os grupos de polimento e

glaze na rugosidade da superfície e microdureza; no entanto, nenhuma diferença signicativa foi identicada na

rugosidade da superfície entre os grupos polido e glazeados nas orientações horizontal e diagonal. Conclusão:

A aplicação do glaze com pasta de diamante melhorou a superfície da zircônia qualitativa e quantitativamente.

Os valores de dureza foram aumentados nos grupos glazeados em comparação aos grupos polidos em todas as

três orientações. A angulação ideal da impressão foi a orientação vertical.

PALAVRAS-CHAVE

Manufatura aditiva; Zircônia de processamento por luz digital; Zircônia glazeada impressa em 3D; Microdureza;

Rugosidade de superfície.

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

progressive decline starting at approximately

85 degrees, whereas the simulated roughness

would be zero at 90 degrees because the direction

of measurement coincides with the direction of the

printed layers [18]. Increased surface roughness

may contribute to more bacterial adhesion and

worse tooth/restoration deterioration, each of those

being undesirable for dental restorations [19]. Crack

propagation under cyclic loading can be initiated by

a surface defect, which in turn affects the fatigue

life and material strength [20]. Zirconia restorations

produced with AM technology are still in their

early stages of marketing, thus products have yet

to be widely used in the clinic [21]. Research has

shown that polishing ground zirconia can reduce

surface roughness just as well as glazing [22,23].

Meanwhile, some research has shown that glazing

is the most effective method for getting a smooth

surface [24,25]. To what extent would printing

layer orientation and glazing affect the topography,

surface roughness, and microhardness of 3D-printed

zirconia produced by a vat photopolymerization

DLP printer? That is what the study was primarily

meant to achieve. The study hypotheses were:

(1) the different printing orientations will not

significantly impact the surface roughness and

microhardness, and (2) glazing will signicantly

impact the surface roughness and hardness of the

DLP zirconia specimens.

MATERIAL AND METHODS

Specimen grouping

A cuboid-shaped specimen with 10 mm

length,10 mm width, and 3 mm [26] thickness

was designed by using an open-source specialized

3D modeling program (Exocad, Dental DB,

3.0 Galway, Darmstadt, Germany), and an STL

le was composed. Under the building angulation,

the specimens were categorized into three groups,

with fourteen specimens in each one:

• V Group: The first group consisted of 14

Vertical orientation specimens fabricated at 0º

angulation parallel to the building direction.

• H Group: The second group consisted of 14

Horizontal orientation specimens fabricated

at 90º angulation perpendicular to the

building direction.

• D Group: The third group consisted of 14

Diagonal orientation specimens fabricated

at 45º angulation to the building direction

as shown in Figure 1.

Based on the surface treatment, each was

split into two categories, with seven specimens

in each:

• (VP, HP, and DP) polished by a diamond

polishing system.

• (VG, HG, and DG) polished by a diamond

polishing system and then glazed with a

diamond paste.

Specimens’ fabrication

The STL le needs to be sliced by the dental

software program (ZIPROS slicing software AON

Co., Ltd), and support structures were added.

Forty-two specimens were printed in three building

directions (V, H, and D) by a DLP printer (ZIPRO,

AON Inc., Seoul, South Korea) from the zirconia

slurry (INNI-CERA BCM-W500/1000, ZIPRO

Dental, AON Inc., South Koria), with 50 μm layer

thickness, and 10000 μw /cm2 light intensity as the

recommendations of the manufacturers. Table I

shows the chemical composition of the zirconia

slurry used according to the manufacturer. After

Figure 1 - Specimens’ angulations

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

the printing procedure was complete, the printed

specimens’ support structures were carefully

removed during the green stage using a sharp

blade [27], and isopropanol (purity ≥ 99.5%)

was used for cleaning the specimens according

to the manufacturer’s instructions. Specimens

were then de-binded and sintered in a 3D-printed

zirconia sintering furnace (ZIRFUR, AON, South

Koria) at 1500 Cº for 21h and 45 min with a

heating rate of 0.2-10 Cº/h according to the

manufacturing instructions [3]. All specimens

were polished to a mirror shine to ensure the

surfaces were uniformly at. A cubic custom-

made self-cure acrylic holder (2 cm × 2 cm ×

3 cm) with a middle hole used for placing the

specimen and having two cross-shaped groves for

easy removal after completion. This holder was

made to facilitate the handling of the specimens

during treatment procedures. The holder contains

the specimen mounted in a dental flask as

shown in Figure 2A. The pre-polishing process

was performed using a diamond-impregnated

system DIACERA Figure 2E in one direction

for 60 s to the entire surfaces as in Figure 2B.

The polishing process was performed using

DIASYNT in two stages, rstly, by using green,

medium grit at a speed of 7000 to 12000 rpm in

one direction for 60 seconds to the entire surface.

Secondly, high-gloss polishing was carried out

using pink, fine grit at 4000 to 8000 rpm in

one direction for 60 s to the whole surface as in

Figure 2C and D. So, the high polish keeps the

Figure 2 - A: the custom-made holder contained the specimens mounted in adental ﬂask, B: thepre-polishing process by DYP-13 g bur, C and

D: the polishing process by H2DCmf bur, H2DC bur respectively, E: the diamond impregnated system.

Table I - Chemical composition of 3D printer zirconia specimens used in this study

Material Manufacturer Composition Lot. No.

Additive Manufacturing

(AM) DLP printer zirconia

Dental Zirconia Material,

INNI-CERA ZipPro Dental AON Co.,

Ltd. South Koria

The photoinitiator, Monomer,

Oligomer, additives, and 3mol%

yttria-partially stabilized tetragonal

zirconia polycrystals (3Y-TZP).

A1231013-003

BCM-W1000 slurry

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

antagonist from getting scratched up. A single bur

was used to polish every seven specimens. After

polishing, each specimen was measured using

an electronic digital caliper (INSIZE®, China)

to guarantee precision. The process is carried

out following the manufacturer’s requirements.

Seven specimens of each subgroup were glazed by

applying a uniform thickness of glazing diamond

paste (HeraCeram glaze universal 20g from

KULZER, Hanau, Germany). The glazing paste

was thoroughly mixed, and each specimen was

positioned on the holder and uniformly coated

with a fine zirconia brush (MPF BRUSH Co.,

Cyprus). The specimens were then sintered at

(850 Cº) in the ceramic sintering furnace (VITA

VACUMAT® 6000 M, Zahnfabrik, Germany) for

10 min according to the recommended firing

program.

Surface roughness (Ra) test

A portable roughness tester TR220 was

employed to quantitatively measure the surface

roughness of all specimens in micrometers (μm).

Each specimen had its mean roughness prole

(Ra) determined; so, the total surface roughness

could be described. The average values of each

specimen were determined by taking three

readings at different locations [28].

Vicker microhardness measurements

All specimens were measured using a Vickers

microhardness tester machine. The specimens are

placed on the horizontal stage of the tester and

subjected to a force of 9.8 N (1k) for 15 seconds

using a diamond Vickers indenter. The optimal

Vickers indenter is a perfectly polished, pointed,

square-based pyramidal diamond with face angles

of 136°. The specimen size is often a minimum of

0.50 mm and exceeds 10 times the indentation

depth (ASTM C1327-2015) [29]. The subsequent

expression computes the Vickers hardness:

HV = α P/d2 (1)

Where HV represents the Vickers hardness value

in kgf/mm2, P denotes the applied force in kg,

d represents the mean value of the indentation

diagonals in mm, and α is the indenter’s geometric

constant, equivalent to 1.8544 according to

(ASTM E384-22) [30]. The hardness value of

every sample can be automatically determined

through the tester devices.

Scanning Electron Microscopy (SEM) test

The SEM was utilized to assess the surface

topography, one specimen was randomly selected

from each group. After cleaning the specimens,

gold nanoparticles (24 carats) were applied to their

surface by using a Plasma Scattering Coater Device.

Then, they were clamped onto the SEM specimen

holder and placed in the scanning electron

microscope’s chamber. The SEM photomicrographs

were captured at 250 X magnication, having a

working distance of 400 μm, and an acceleration

voltage of 30.00 Kev [31].

Statistical analysis

The social science statistics package SPSS

version twenty-four was used to examine the

research data. The Shapiro-Wilk test was conducted

to assess normality. Levene’s test was employed to

evaluate the homogeneity of variances. There was

no violation of the homogeneity criteria, and the

data followed a normal distribution. A one-way

analysis of variance ANOVA with Tukey’s HSD test

was used for the statistical analysis. The recorded

surface roughness and microhardness were

averaged, and the standard deviations (SD)

and the standard error were computed for each

grouping. Considering statistical signicance, P

values less than 0.05 were considered.

RESULTS

Surface roughness test

Table II presents the descriptive statistics

of the surface roughness values for polished and

glazed groups in three building orientations of the

specimens, including means, standard deviation,

standard error, and condence intervals for the

mean, minimum, and maximum values.

As in Table II, the (Ra) value of the polished

specimens was highest in the vertical orientation

group and lowest in the horizontal orientation

group. For the glazed groups, the (Ra) value was

the highest in the diagonal orientation group

and the lowest in the horizontal orientation

group. F-test by using one-way ANOVA was

done to identify if there had been a statistically

significant variation in the mean values when

comparing groups as in Table III. Tukey’s HSD test

was performed to determine the honest signicant

differences between groups as shown in Table IV.

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

Table II - Descriptive statistics of surface roughness (Ra) of polished and glazed zirconia specimens

N Mean Std. Devia-

tion Std. Error

95% Conﬁdence Interval

for Mean

Minimum Maximum

Lower

Bound

Upper

Bound

RA VP 7 3.4040 .35586 .13450 3.0749 3.7331 2.90 3.86

RA HP 7 1.5807 .05989 .02264 1.5253 1.6361 1.50 1.68

RA DP 7 3.0153 .15347 .05801 2.8734 3.1572 2.83 3.28

RA VG 7 1.3909 .02509 .00948 1.3677 1.4141 1.34 1.42

RA HG 7 1.5869 .05509 .02082 1.5359 1.6378 1.52 1.64

RA DG 7 3.0650 .31984 .12089 2.7692 3.3608 2.72 3.55

Table III - One-way ANOVA between all groups (surface roughness test).

Mean Square F P-value Sig

Between Groups 5.822 134.484 0.000 *HS

*P < 0.001 High signiﬁcant

Table IV – Tukey’s HSD test for surface roughness of all groups

(I)

(J) Groups

Mean Diﬀer-

ence Std. Error Sig.

95% Conﬁdence Interval

Groups (I-J) Lower Bound Upper Bound

RA VP RA HP 1.82329 .11577 .000 1.5039 2.1426

RA DP .38871 .11577 .013 .0694 .7081

RA HP RA DP -1.43457 .11577 .000 -1.7539 -1.1152

RA VG RA HG -.19600 .08720 .139 -.4366 .0446

RA DG -1.67414 .08720 .000 -1.9147 -1.4336

RA HG RA DG -1.47814 .08720 .000 -1.7187 -1.2376

The Vickers microhardness test

The descriptive statistics of the Vickers

microhardness measurement for polished and

glazed specimens in three building orientations

including means, standard deviation, standard

error, and confidence interval for the mean,

minimum, and maximum values were presented

in Table V. As in Table V, the microhardness value

of the polished specimens was the highest in the

vertical orientation group and the lowest in the

horizontal orientation. For the glazed group,

the microhardness value was the highest in the

vertical orientation group and the lowest in the

horizontal orientation group. Table VI presents the

results of the ANOVA test employed to ascertain

if the means of the groups exhibited signicant

differences. As demonstrated in Table VII, Tukey’s

HSD test was conducted to identify the signicant

differences among the groups.

SEM analysis

The representative images obtained from SEM

in Figure 3a showed that the vertical orientation

polished specimen had a layered strand pattern

with a at indentation across them, in a range of

178-191 nm. After glazing, the SEM image shows

a good glazing process occurred. However, dark

spots could result from gases escaping from the

micro gaps between the layers as in Figure 3d.

The SEM measurement of the horizontal

orientation specimens before glazing showed

that the surface was a single plate with a surface

containing depressions and elevations with a

diameter of 1.3-2.4 μm, all of which were on

one side as in Figure 3b. After glazing it was

shown that a good glazing occurred with very

few particles on the surface that did not exceed

2 μm in diameter as shown in Figure 3e.

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

Table V - Descriptive statistics of microhardness (VHN) zirconia polished and glazed groups in kgf/mm2

N Mean Std.

Deviation Std. Error

95% Conﬁdence Interval

for Mean

Minimum Maximum

Lower

Bound

Upper

Bound

VHN VP 7 1.7114 .00660 .00250 1.7053 1.7175 1.70 1.72

VHN HP 7 1.4619 .00558 .00211 1.4567 1.4670 1.46 1.47

VHN DP 7 1.6054 .01652 .00624 1.5901 1.6207 1.58 1.62

VHN VG 7 2.5911 .06473 .02447 2.5313 2.6510 2.49 2.69

VHN HG 7 1.9990 .04930 .01863 1.9534 2.0446 1.95 2.10

VHN DG 7 2.0647 .12755 .04821 1.9468 2.1827 1.90 2.20

Table VI - One-way ANOVA test between all groups (microhardness test)

Mean Square F P-value Sig

Between Groups 1.160 299.572 0.000 *HS

*P < 0.001 High signiﬁcant

Table VII - Tukey’s HSD test for microhardness of all groups

(I) (J) Mean Diﬀer-

ence (I-J) Std. Error Sig.

95% Conﬁdence Interval

Groups Groups Lower Bound Upper Bound

VHN VP VHN HP .24957 .00510 .000 .2355 .2636

VHN DP .10600 .00510 .000 .0919 .1201

VHN HP VHN DP -.14357 .00510 .000 -.1576 -.1295

VHN VG VHN HG .59214 .04442 .000 .4696 .7147

VHN DG .52643 .04442 .000 .4039 .6490

VHN HG VHN DG -.06571 .04442 .465 -.1882 .0568

Figure 3 - SEM of 3D-printed zirconia showing (a) vertically polished, (b) horizontally polished, (c) diagonally polished, (d) vertically glazed, (e)

horizontally glazed, (f) diagonal glazed specimens.

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

The SEM analysis of the diagonal orientation

revealed the existence of plate-like structures in

three different dimensions as in Figure 3c. After

the glazing process, Figure 3f shows that a regular

glazing process occurred with some light areas

appearing on the surface which are attributed to

the surface structure containing several plates

with different heights.

DISCUSSION

This study examined the surface roughness

and the microhardness of 3D-printed zirconia

processed by a DLP printer in three building

orientations during polishing and after the glazing

process. The results of the recent study suggested

the complete rejection of the first hypothesis

because of highly signicant differences in surface

roughness and microhardness values between the

different orientations of the AM zirconia specimens.

The second hypothesis was partially rejected

because the horizontal and diagonal orientations

were not signicantly affected by the glazing.

The accepted surface roughness for the dental

restoration threshold is 0.2 μm, so an unpolished

surface with a value higher than this may increase

the propensity for bacterial adhesion and oral

biofilm development [17]. The appropriate

surface polishing protocols were performed in

this study to improve the surface quality [17].

Mirror polishing using appropriate equipment

and supplies that contain ne diamond particles

is currently the suggested approach for zirconia

surface nishing [32].

When comparing P specimens, the recent

study revealed that the highest surface roughness

value was in group RA VP, and the lowest was in

group RA HP. These ndings are in agreement

with the study of Abualsaud et al. [33], they

demonstrated that, in contrast to horizontal

specimens, those with a vertical or diagonal

orientation had a higher surface roughness due

to differences in the orientation of roughness

measurement concerning layer direction and

the existence of steps between successive layers.

These results are in harmony with the study of

Schiltz et al. [16], they attributed the increase

in surface roughness of the vertical orientation

group to the surface topography of these two

orientations (the vertical and the horizontal).

Also, the results of this study concurred with

the study of Xing et al. [34], they studied the effect

of printing orientations of 3D-printed zirconia

on the horizontal and the vertical surfaces of the

same specimen in different printing angulations,

they found that the surface roughness value of

the horizontal surface was lower than that of

the vertical surface. When zirconia restorations

are glazed, they create a uniform surface that

is smooth and uniform in shape, protecting

the antagonist tooth enamel and reducing the

accumulation of plaque on the restoration [32].

The recent study results demonstrated a

notable reduction in surface roughness of the

horizontal orientation group that occurred after

glazing. The highest surface roughness value was

in the RA DG group, and the lowest was in the

RA VG. Table III showed signicant differences

between the vertical orientation specimen P

and PG groups (P < 0.001). Whereas, other

orientation groups did not show any signicant

differences between the P and PG specimens.

The SEM analysis images validated these ndings

on the surface roughness (Figure 3 d, e, f).

This improvement in surface topography after

applying the diamond paste is consistent with

Branco et al. [35] they demonstrate that the

glaze covering makes the surface smooth and

drastically reduces the surface roughness.

Hardness is the resistance to surface

indentation and scratching, which is a crucial

clinical quality for maintaining surface smoothness

and avoiding plaque accumulation, soft tissue

irritation, wearing of the antagonist dentition,

and resistance to discoloration [36]. In the current

study for P specimens, the highest hardness

mean value was in the VHN VP group, and the

lowest was in the VHN HP group. The results

agreed with the literature of Mei et al. [8], they

demonstrated that 3D-printed zirconia, when

constructed horizontally, frequently has pores

concentrated close to its surface. These surface

imperfections, being on the tensile side, would

readily generate sites of stress concentration

when subjected to a load.

Applying the glazed coating on the specimens

resulted in an increase in microhardness

values in all groups. As in Table VI, there were

highly signicant differences in microhardness

between P and PG groups. In contrast, the

study of Branco et al. [35] claimed that the

hardness value of the glazed specimens was

lower than that of unglazed ones because the

underlying zirconia substrates have a hardness

Braz Dent Sci 2025 Oct/Dec;27 (4): e4564

Dawood NI et al.

Evaluation the effect of glazing and the printing orientations on the surface roughness and the microhardness of DLP dental zirconia: an in vitro study

Dawood NI et al. Evaluation the eﬀect of glazing and the printing orientations

on the surface roughness and the microhardness of DLP dental

zirconia: an in vitro study

that is 3–3.5 times higher than the glaze layer.

According to the author’s knowledge, no other

previous studies examined the effect of glazing

on the surface roughness and microhardness

of 3D-printed zirconia specimens in different

printing orientations.

However, the limited number of specimens,

materials, and equipment employed in this

investigation, along with the small number of

published articles addressing various orientations,

reect several limitations. Consequently, future

research should examine additional 3D-printed

zirconia brands, and incorporate other mechanical

properties with various printing orientations.

Moreover, evaluate specimens with color and

translucency attributes.

CONCLUSION

The subsequent conclusions can be obtained

through the recent investigation, taking into

account its limitations:

1. The surface roughness and hardness values

of AM zirconia were influenced by the

construction angle.

2. The vertical orientation was the optimal

printing direction compared to the horizontal

and diagonal orientations in the surface

roughness and microhardness values.

3. Glazing the 3D-printed zirconia specimens

with diamond paste decreases the surface

roughness of all zirconia groups except for

the Diagonal orientation.

4. Glazing the 3D-printed zirconia specimens

with diamond paste increased the

microhardness values of all zirconia groups.

Acknowledgements

None

Author’s Contributions

NID: conceptualization. NID, ZNAW, SAN:

data curation. NID, SAN: formal analysis. NID:

funding acquisition. NID: investigation. NID, ZNAW:

methodology. NID, ZNAW: project administration.

NID: resources. NID: software. ZNAW: supervision.

ZNAW, NID: validation. ZNAW, NID: visualization.

NID, ZNAW: writing – original draft preparation.

NID, ZNAW: writing – review & editing.

Conict of Interest

The authors have no conicts of interest to

declare.

Funding

This research did not receive any funding

support.

Regulatory Statement

None.

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Zahraa Nazar Alwahab

(Corresponding address)

Middle Technical University, College of Health and Medical Techniques,

Baghdad, Iraq.

Email: zahraanalwshab@mtu.edu.iq

Date submitted: 2024 Oct 30

Accept submission: 2024 Dec 21