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Vol 13, No 1 (2025) 
ISSN 2167-8677 (online) 

DOI 10.5195/d3000/2025.1088 

 

	

	

http://dentistry3000.pitt.edu	

Effect of Different Surface Treatment on Hardness of Dental Alloys 
 
Evan Hussain Alwan1, Sara Abdulbast Turki2, Zaid Ezzat Abdul Majeed2 
 
1Medical Technical Ins.tute and 2College of Health and Medical Technology, Middle Technical University, Iraq 

Abstract 

Objec<ves: Inves<gate different surface treatments on hardness of specimens produced by 
CAD-CAM milling techniques and selec<ve laser mel<ng technique. Materials and Meth-
ods: Thirty disc-shaped specimens were put into three main groups. Each group has ten 
examples of Co-Cr metal that were made of different materials. There were three kinds of 
milling: hard, selec<ve laser mel<ng (3D printer), and soP. Everything was cut up into 15 
mm wide pieces that were 3 mm thick so that they could be used for more tests. The last 
step was to finish them off and make their surfaces smooth with a diamond grinder. A 
scanning electron microscope (SEM) was used to look at one example from each group and 
figure out how the surface of the metal frame was made. We tested how hard specimens 
were. We used the independent sample one-way ANOVA to determine differences. Re-
sults: Hardness tests for all test groups in the study showed that 3D prin<ng usually gave 
the best hardness in the control and sandblast groups. Hard cuXng gave the most hardness 
in the Laser group.  We used One- and Two-way ANOVA and Levene's test to look at the 
data sta<s<cally. All the tests had p-values of 0.001, which means that the hardness values 
for each milling type are very different from one another. Conclusion: 3D prin<ng generally 
resulted in the highest hardness values, and the control and sandblast groups hard milling 
showed superior hardness in the Laser group. 

Open Access 
Cita%on: Alwan EH et al. (2025) Effect of Different Sur-
face Treatment on Hardness of Dental Alloys. Den%stry 
3000. 1:a001 doi:10.5195/d3000.2025.1088 
Received: October 21, 2025  
Accepted: November 12, 2025 
Published: December 12, 2025 
Copyright: ©2025 Alwan EH et al. This is an open access 
ar%cle licensed under a Crea%ve Commons ASribu%on 
Work 4.0 United States License. 
Email: evan.hussain.alwan@gmail.com

	
	
Introduc)on 
Pre-treatment	of	different	CAD/CAM	materi-
als,	 such	 as	 ceramics,	 zirconia,	 resin-infil-
trated	ceramic,	and	resin-based	composites,	
is	 required	 and	 will	 show	 differences	 in	
roughness,	 surface	 energy,	 and	 imperfec-
tions	 [1].	 There	 is	 a	 need	 to	 establish	 best	
practices	for	obtaining	a	more	favorable	sur-
face	roughness	and	wear.	It	is	known	that	de-
pending	 on	 the	 material	 and	 the	 surface	
treatment,	 surface	 roughness,	 microhard-
ness,	 volumetric	 loss,	 and	 height	 loss	 of	
enamel,	are	affected	[2].	The	chemical	stabil-
ity	of	CAD/CAM	materials	is	also	affected	by	
surface	 treatment	 (glazed	 or	 polished)	 and	

unique	signatures	of	 ion	elution	can	be	de-
tected	[3].	The	goal	of	our	work	was	to	deter-
mine	what	 is	 the	best	approach	 to	pretreat	
surface	of	CAD/CAM	materials.	
 
Material and Methods 
Thirty	metal	specimens	of	15	mm	in	dimen-
sions	and	3	mm	thickness	were	used	in	this	
study.	Metal	 specimens	were	 fabricated	 by	
using	 CAD/CAM	 system	 and	 selective	 laser	
melting	(3Dprinting)	(Figure	1).	
	

	
Figure	1.	Specimens	used	in	the	study.	
	
The	 specimens	were	 put	 into	 three	 groups	
based	on	the	three	different	ways:	



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

	http://dentistry3000.pitt.edu	
2	

Hard	 milling:	 10	 specimens	 made	 from	
metal	Kera-DISK	hard	milling	 (Eisenbacher	
DentalwarenED,GmbH).	
Soft	milling:	10	specimens	metal	made	from	
Kera-DISK	soft	milling	(Eisenbacher	Dental-
warenED,GmbH).	
Selective	 laser	 melting:	 10	 specimens	
made	 of	 metal	 (Riton	 D150Dental	 3D	
printer).	
After	printing,	a	carbide	cutting	bur	was	used	
to	Vinish	and	a	silicon	diamond	polisher	bur	
was	used	to	clean.	Last,	extra	care	was	taken	
to	clean	each	specimen	with	steam	to	get	rid	
of	 any	 metal	 oxide	 dust	 that	 was	 still	 on	
them.	
Scanning	 Electron	 Microscope	 (SEM)	 was	
used	to	study	the	metal	surface	topology	and	
details	of	all	groups	(Figures	2	to	10).	
Hardness	 test	was	done	with	 an	HV-1000Z	
Digital	Micro	Vickers	Hardness	Tester	from	
HST	 in	 China.	 Before	 and	 after	 the	 surface	
treatment,	a	9.8	N	force	for	20	seconds	was	
used	[4].	
Surface	was	treated	with	a	1,064	nm	Nd:YAG	
laser.	When	it	was	used	to	treat	the	surface,	
the	laser	was	set	to	these	settings:	each	spot	
has	a	1.30	KV	potential,	84.4	mJ	of	energy,	10	
waves,	and	a	1Hz	tone.	The	top	of	the	sample	
was	facing	the	laser	beam	in	the	opposite	di-
rection.	This	laser	beam	was	bent	by	some-
thing	with	a	focal	length	of	10	cm.	The	sam-
ple	was	put	10	cm	from	the	lens	with	the	help	
of	a	wheel	with	markings	on	it.	A	laser	spot	
was	 put	 on	 the	 scale	 every	 Vive	 degrees	 to	
make	a	straight	line	around	the	edge	of	the	
item	[5].	
We	used	an	aluminum	oxide	(Al2O3)	sand-
blaster	that	was	110	mm	long	and	0.25	MPa	
for	30	seconds	 to	make	 the	surface	of	each	
specimen	 rough.	 A	 10-minute	 ultrasonic	
bath	with	water	was	then	used	to	clean	the	
surface	[2].	
We	 used	 ANOVA,	 one-way,	 and	 two-way	
tests	 to	 compare	 hardness	 values	 for	 the	
groups.	
 
Results/Discussion 
The	control	group	showed	a	mean	hardness	
of	422.4	±	1.32	Hv.	The	laser-treated	group	
showed	 an	 increased	 mean	 hardness	 of	
548.7	±	1.59	Hv.	The	sandblast	group	exhib-
ited	 the	 highest	mean	 hardness	 of	 554.2	 ±	
1.51	Hv	(p=0.93).	
By	ANOVA,	we	found	that	the	mean	hardness	
(Hv)	was	significantly	different	between	the	
groups (F=25,352.6,	p=0.001).	Post	hoc	anal-
ysis	 using	 Tukey's	 HSD	 test	 demonstrated	
that	both	the	laser	and	sandblast	groups	had	
significantly	 higher	 mean	 hardness	 values	
compared	to	the	control	group	with	p-value	
of	0.001.	Specifically,	the	laser	group	showed	
a	mean	increase	of	126.37	Hv	over	the	con-
trol	 group,	 while	 the	 sandblast	 group	

exhibited	an	even	greater	mean	 increase	of	
131.84	Hv	over	 the	control	group.	Further-
more,	the	sandblast	group	displayed	a	mar-
ginally	higher	hardness	than	the	laser	group,	
with	a	mean	difference	of	5.47	Hv,	which	was	
also	 statistically	 significant	 (p=0.001)	 as	
shown	in	Table	1.	
For	 soft	 milling,	 the	 control	 group	 had	 a	
mean	hardness	of	447.3	±	0.35	Hv.	The	laser	
group	demonstrated	a	higher	mean	hardness	
of	452.1	±	0.45	Hv.	In	contrast,	lower	mean	
hardness	 value	 was	 observed	 in	 the	 sand-
blast	group	with	443.6	±	0.41	Hv	(p=0.7).	
The	 analysis	 of	 variance	 (ANOVA)	 for	 soft	
milling	 demonstrated	 a	 statistically	 signifi-
cant	 difference	 in	 mean	 hardness	 (Hv)	
among	the	three	groups	(p=0.001).	Post	hoc	
analysis	using	Tukey's	HSD	test	revealed	that	
the	 laser	 group	 had	 a	 significantly	 higher	
mean	 hardness	 compared	 to	 the	 control	
group,	with	a	mean	difference	of	-4.76	Hv	(p	
=	0.001).	In	contrast,	the	sandblast	group	ex-
hibited	a	significantly	lower	mean	hardness	
than	 the	control	group,	with	a	mean	differ-
ence	of	3.75	Hv	(p=0.001).	Additionally,	the	
laser	group	showed	the	highest	mean	hard-
ness	among	all	groups,	significantly	outper-
forming	the	sandblast	group	with	a	mean	dif-
ference	of	8.51	Hv	(p=0.001)	(Table	2).	
The	 control	 group	had	 a	mean	hardness	of	
596.3	±	0.16	Hv.	The	 laser	group	showed	a	
lower	 mean	 hardness	 of	 386.9	 ±	 0.39	 Hv.	
Conversely,	 the	 sandblast	 group	 exhibited	
the	highest	mean	hardness	of	 706.2	±	0.42	
Hv	(p=0.7).	
The	 analysis	 of	 variance	 (ANOVA)	 for	 3D	
printing	demonstrated	a	statistically	signifi-
cant	 difference	 in	 mean	 hardness	 (Hv)	
among	the	three	groups	(p=0.001).	Post	hoc	
analysis	using	Tukey's	HSD	test	revealed	that	
the	control	group	had	a	significantly	higher	
mean	hardness	compared	to	the	laser	group,	
with	 a	 mean	 difference	 of	 209.43	 Hv	
(p=0.001).	 However,	 the	 control	 group	 ex-
hibited	 significantly	 lower	 mean	 hardness	
than	the	sandblast	group,	with	a	mean	differ-
ence	 of	 -109.85	 Hv	 (p=0.001).	 Among	 the	
groups,	 the	 laser	 group	 demonstrated	 the	
lowest	mean	hardness,	in	comparison	to	the	
sandblast	group,	with	a	mean	difference	of	-
319.29	Hv	(p=0.001)	(Table	3).	
For	the	control	(Hv)	group,	the	mean	hard-
ness	values	for	hard	milling,	soft	milling,	and	
3D	 printing	 were	 422.41	 ±	 1.32,	 447.38	 ±	
0.35,	and	596.35	±	0.17,	respectively.	Among	
these,	 the	 3D	 printing	 group	 exhibited	 the	
highest	hardness	value.		
In	the	 laser	(Hv)	group,	the	mean	hardness	
values	for	hard	milling,	soft	milling,	and	3D	
printing	were	548.79	±	1.60,	452.15	±	0.45,	
and	 386.91	 ±	 0.39,	 respectively.	 Unlike	 the	
control	group,	hard	milling	had	 the	highest	
hardness	values,	while	the	3D	printing	group	

demonstrated	the	lowest	values	in	this	cate-
gory.		
For	the	sandblast	(Hv)	group,	the	mean	hard-
ness	values	for	hard	milling,	soft	milling,	and	
3D	 printing	 were	 554.26	 ±	 1.51,	 443.64	 ±	
0.42,	 and	 706.21	 ±	 0.42,	 respectively.	 Like	
the	control	group,	3D	printing	demonstrated	
the	highest	hardness	values,	while	soft	mill-
ing	showed	the	lowest.	
The	analysis	 indicates	a	statistically	signiVi-
cant	 differences	 in	 hardness	 values	 across	
the	milling	types	with	p-value	is	0.001,	sug-
gesting	a	statistically	signiVicant	difference	in	
hardness	 among	 hard	 milling,	 soft	 milling,	
and	3D	printing.		
When	you	use	the	Bonferroni	post	hoc	test,	
these	gaps	get	even	bigger.	A	big	difference	
(p=0.001)	was	 found	between	hard	milling	
and	soft	milling.	There	was	also	a	difference	
between	 hard	milling	 and	 3D	 printing	 and	
soft	 milling	 and	 3D	 printing.	 There's	 no	
doubt	that	these	two	steps	are	different.	
The	 p-value	 analysis	 for	 speciVic	 group	dif-
ferences	conVirms	statistically	signiVicant	dif-
ferences	 in	 hardness	 across	 milling	 types	
within	each	group.		
In	 the	 control	 (Hv)	 group,	 all	 comparisons	
yielded	p-values	of	0.001,	indicating	signiVi-
cant	differences	in	hardness	values.	The	dif-
ference	between	hard	milling	and	soft	mill-
ing	 was	 -24.97	 (p=0.001),	 suggesting	 that	
soft	milling	resulted	in	slightly	higher	hard-
ness.		
The	 difference	 between	 hard	 milling	 and	
3Dprinting	was	-173.93	(p=0.001),	showing	
that	3D	printing	signiVicantly	increased	hard-
ness.	 Similarly,	 soft	 milling	 vs.	 3D	 printing	
exhibited	a	difference	of	-148.95	(p=0.001),	
conVirming	that	3D	printing	had	the	highest	
hardness	values.	
In	the	laser	(Hv)	group,	the	hard	milling	vs.	
soft	milling	comparison	showed	a	difference	
of	96.63	(p=0.001),	indicating	that	hard	mill-
ing	resulted	in	signiVicantly	higher	hardness	
than	 soft	 milling.	 The	 difference	 between	
hard	 milling	 and	 3D	 printing	 was	 161.87	
(p=0.001),	 conVirming	 that	3D	printing	had	
the	 lowest	 hardness	 values.	 Similarly,	 soft	
milling	 vs.	 3D	 printing	 had	 a	 difference	 of	
65.23	 (p=0.001),	 further	 supporting	 the	
trend	that	3D	printing	resulted	in	the	lowest	
hardness	in	this	group.	
In	 the	sandblast	(Hv)	group,	signiVicant	dif-
ferences	were	also	observed,	with	hard	mill-
ing	 vs.	 soft	milling	 showing	 a	 difference	 of	
110.61	 (p	 =	 0.001),	 conVirming	 that	 hard	
milling	resulted	in	signiVicantly	higher	hard-
ness.	 The	 difference	 between	 Hard	 milling	
and	3D	printing	was	-151.95	(p	=	0.001),	in-
dicating	 that	 3D	 printing	 exhibited	 signiVi-
cantly	 higher	 hardness	 than	 hard	 milling.	
The	largest	difference	was	seen	between	soft	
milling	 and	 3D	 printing,	 at	 -262.56	 (p	 =	



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

	http://dentistry3000.pitt.edu	
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0.001),	highlighting	a	substantial	increase	in	
hardness	with	3D	printing.	
Overall,	the	p-values	of	0.001	across	all	com-
parisons	 conVirm	 highly	 signiVicant	 differ-
ences	 in	 hardness	 values	 between	 milling	
types	within	each	group.	The	 Vindings	rein-
force	 that	3D	printing	generally	 resulted	 in	
the	highest	hardness	in	the	control	and	sand-
blast	groups,	whereas	Hard	milling	showed	
superior	hardness	in	the	laser	group	(Figure	
11).	
When	orthodontic	brackets	had	their	surface	
treated	with	laser	[6],	they	showed	the	high-
est	shear	bond	strength	when	compared	to	
sandblasting.	 On	 the	 other	 hand,	 bond	
strength	of	posts	to	dentin	used	in	endodon-
tic	treatment	was	affected	by	the	type	of	ma-
terial	 but	 not	 by	 the	 surface	 treatment	 [7].	
Laser	surface	treatment	of	composites	used	
to	 repair	 bond	 strength	 of	 CAD/CAM	 resin	
nanoceramic	showed	improved	micro-shear	
bond	 strength	 values,	 particularly	 short-
pulse	lasers	[8].	
Like	 our	 results,	 previous	work	 has	 shown	
that	 surface	 treatment	 by	 sandblasting	 fol-
lowed	 by	 acid	 etching	 was	 more	 effective	
that	 their	 individual	 applications	 and	 laser	
irradiation	 in	 terms	 of	 resin	 CAD/CAM	 ce-
ramics	retention	[9].	However,	combining	la-
ser	and	sandblasting	for	surface	treatment	of	
zirconia	and	metal	resulted	rougher	surfaces	
than	sandblasting	alone,	especially	for	metal	
[10].	
3D	printing	can	produce	very	strong	dental	
alloys	with	 high	 durability.	 Alloys	 like	 tita-
nium	and	cobalt-chrome	are	commonly	used	
for	3D	printing	and	offer	excellent	strength	
for	 dental	 prosthetics.	 Certain	 3D	 printed	
metals	can	be	even	stronger	than	their	con-
ventionally	manufactured	counterparts.	The	
final	 hardness	 of	 the	 printed	 alloy	 is	 influ-
enced	by	the	base	metal,	the	energy	input	of	
the	 printing	 process,	 and	 any	 subsequent	
heat	treatments	[11-13].	
 
Conclusions 
Hardness	 values	 varied.	 3D	printing	 gener-
ally	resulted	in	the	highest	hardness	values	
in	the	control	and	sandblast	groups,	whereas	
hard	 milling	 showed	 superior	 hardness	 in	
the	laser	group.	
 
References	
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  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

	http://dentistry3000.pitt.edu	
4	

Table	1.	Summary	of	comparisons	for	hard	milling	specimens.	

	 Mean	 SD	 Std.	Error	 "95%	
Confidence	 Interval	for	
Mean"	

F-test	 P-	
value	

Lower	
Bound	

Upper	
Bound	

Hard	milling	Control	(Hv)	 422.4	 1.32	 0.41	 421.46	 423.36	 25352	 0.001	
Laser	(Hv)	 548.7	 1.59	 0.50	 547.64	 549.92	
Sand	blast	(Hv)	 554.2	 1.51	 0.47	 553.17	 555.33	
Total	 508.4	 61.9	 11.31	 485.34	 531.62	

Post	hoc	analysis	(Tukey	HSD)	
	 Mean	Difference	 P-value	
Control	(Hv)	 Laser	(Hv)	 -126.37364	 0.001	

Sand	blast	(Hv)	 -131.84160	 0.001	
Laser	(Hv)	 Sand	blast	(Hv)	 -5.46797	 0.001	
	
Table	2.	Summary	of	comparisons	for	soft	milling	specimens.	
	 Mean	 SD	 Std.	Error	 "95%	Confidence	Interval	

for	Mean"	
F-test	 P-	

value	

Lower	
Bound	

Upper	
Bound	

Soft	milling	 Control	(Hv)	 447.3	 0.35	 0.11	 447.1	 447.6	 1086	 0.001	
Laser	(Hv)	 452.1	 0.45	 0.14	 451.8	 452.4	
Sand	blast	(Hv)	 443.6	 0.41	 0.13	 443.3	 443.9	
Total	 447.7	 3.56	 0.65	 446.3	 449.0	

Post	hoc	analysis	(Tukey	HSD)	
	 Mean	Difference	 P-value	
Control	(Hv)	 Laser	(Hv)	 -4.76252	 0.001	

Sand	blast	(Hv)	 3.74538	 0.001	
Laser	(Hv)	 Sand	blast	(Hv)	 8.50789	 0.001	
	
Table	3.	Summary	of	comparisons	for	Laser	treatment. 
	 Mean	 SD	 Std.	

Error	
"95%	Confidence	Interval	
for	Mean"	

F-test	 P-	
value	

Lower	
Bound	

Upper	
Bound	

3D	
printer	

Control	(Hv)	 596.3	 0.16	 0.05	 596.2	 596.4	 21958	 0.001	
Laser	(Hv)	 386.9	 0.39	 0.12	 386.6	 387.1	
Sand	blast	(Hv)	 706.2	 0.42	 0.13	 705.9	 706.5	
Total	 563.1	 134.7	 24.5	 512.8	 613.4	

Post	hoc	analysis	(Tukey	HSD)	
	 Mean	Difference	 P-value	
Control	(Hv)	 Laser	(Hv)	 209.43	 0.001	

Sand	blast	(Hv)	 -109.85	 0.001	
Laser	(Hv)	 Sand	blast	(Hv)	 -319.29	 0.001	
	



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

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Figure 2. The scanning electron microscope (SEM) of 3D printer before surface treatment. 
 

 
Figure 3. The scanning electron microscope (SEM) of soft metal before surface treatment. 

 

 
Figure 4. The scanning electron microscope (SEM) of hard metal before surface treatment. 

 



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

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Figure 5. The scanning electron microscope (SEM) of soft metal after surface treatment sandblast. 

 

Figure 6. The scanning electron microscope (SEM) of soft metal after surface treatment laser. 
 

 

Figure 7. The scanning electron microscope (SEM) of (3Dprinter metal) after surface treatment sandblast. 



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

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Figure 8. The scanning electron microscope (SEM) of (3Dprinter metal) after laser surface treatment. 
 
 

 
 
Figure 9. The scanning electron microscope (SEM) of (hard metal) after sandblast surface treatment. 
 
 
 



  Effect of Different Surface Treatment on Hardness of Dental Alloys 

Vol 13, No 1 (2025)    DOI 10.5195/d3000/2025.1088 

	

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Figure 10. The scanning electron microscope (SEM) of (hard metal) after laser surface treatment. 
 
 
 

	
Figure	11.	Hardness	comparisons	for	the	study.