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© 2013 Dental Press Journal of Orthodontics Dental Press J Orthod. 2013 Nov-Dec;18(6):26-3026
original article
Surface morphology changes of acrylic resins during
finishing and polishing phases
Glaucio Serra1, Liliane Siqueira de Morais2, Carlos Nelson Elias3
How to cite this article: Serra G, Morais LS, Elias CN. Surface morphology
changes of acrylic resins during finishing and polishing phases. Dental Press J Or-
thod. 2013 Nov-Dec;18(6):26-30.
Submitted: August 09, 2010 - Revised and accepted: December 21, 2010
Contact address: Glaucio Serra Guimarães
Av. Nossa Senhora de Copacabana, 647, 1108 – Copacabana/RJ — Brazil
CEP: 22050-901 – E-mail: gserrag@hotmail.com
1
Adjunct professor, Fluminense Federal University.
2
Professor of Orthodontics, Gama Filho University.
3
Adjunct professor, Military Institute of Engineering (IME)
» The authors report no commercial, proprietary or nancial interest in the prod-
ucts or companies described in this article.
Introduction: The finishing and polishing phases are essential to improve smoothness and shining on the surface of acrylic
resins used to make removable orthodontic appliances. A good surface finishing reduces roughness, which facilitates hy-
giene, prevents staining and provides greater comfort to the patients. Objective: The aim of this paper was to analyze the
changes on surface morphology of acrylic resins during finishing and polishing phases.Methods: Thirty discs (10 mm in
diameter and 5 mm in length) were made with acrylic resin and randomly divided into ten groups. The control group did
not receive any treatment while the other groups received gradual finishing and polishing. The last group received the entire
finishing and polishing procedures. Surface morphology was qualitatively analyzed through scanning electron microscopy
and quantitatively analyzed through a laser profilometer test. Results: The acrylic resin surfaces without treatment showed
bubbles which were not observed in the subsequent phases. Wearing out with multilaminated burs, finishing with wood
sandpaper and finishing with water sandpaper resulted in surfaces with decreasing irregularities. The surfaces that were
polished with pumice and with low abrasive liquids showed high superficial smoothness. Conclusion: Highly smooth
acrylic resin surfaces can be obtained after mechanical finishing and polishing performed with multilaminated burs, wood
sandpaper, water sandpaper, pumice and low abrasive liquids.
Keywords:
Acrylic resins. Scanning electron microscopy. Surface properties.
Introdução: as etapas de acabamento e polimento são essenciais para a obtenção de lisura e brilho da superfície de resi-
nas acrílicas utilizadas na confecção de aparelhos ortodônticos. O bom acabamento da resina facilita a higiene, previne
o manchamento e propicia maior conforto ao paciente. Objetivo: o objetivo desse trabalho foi analisar as alterações na
morfologia superficial de resinas acrílicas (Clássico, São Paulo) durante as etapas do acabamento e polimento mecânico.
Métodos: foram confeccionados 30 discos (10mm de diâmetro e 5mm de altura) de resina acrílica autopolimerizável,
que foram divididos aleatoriamente em dez grupos. O grupo controle não recebeu nenhum tratamento. Os demais
grupos receberam acabamento e polimento graduais. O último grupo recebeu todo o tratamento de acabamento e
polimento. A morfologia superficial foi avaliada qualitativamente por microscopia eletrônica de varredura e quantita-
tivamente pela análise da rugosidade superficial. Resultados: as superfícies de resina acrílica sem tratamento apresen-
taram bolhas, as quais não foram observadas nas fases subsequentes. O desgaste com fresa multilaminada seguido de
acabamento com lixa de madeira e lixa d’água produziram superfícies com irregularidades decrescentes. As superfícies
polidas com branco de Espanha e líquido de baixa abrasividade (Kaol) apresentaram bom acabamento superficial.
Conclusão: é possível obter resina acrílica com alta lisura superficial após acabamento e polimento mecânico com
fresas, lixas de madeira, lixas d’água, branco de Espanha e líquidos de baixa abrasividade (Kaol).
Palavras-chave:
Resinas acrílicas. Microscopia eletrônica de varredura. Propriedades de superfície.
© 2013 Dental Press Journal of Orthodontics Dental Press J Orthod. 2013 Nov-Dec;18(6):26-3027
original article
Serra G, Morais LS, Elias CN
introduction
Orthodontic appliances are used on upper and lower
dental arches with the purpose of preventing, inter-
cepting, correcting or retaining orthodontic issues.
6,11
A wide variety of appliances are proposed, either xed
or removable, in accordance with the main purpose of
the treatment. As examples we can mention: expan-
sion appliances to correct crossbites,
6,4
facial masks to
correct maxillary retrognatism,
3
removable appliances
with Hawley clasp for retaining,
18
space retrievers and
space maintainers, xed inclined plane to correct dental
crossbite,
9
among others.
The rst step towards making a removable orth-
odontic appliance is the molding and production of
working casts, on which the retention claps are made.
The working casts are isolated with vaseline and acryl-
ization takes place. Self-curing acrylic resin is applied
to the casts by means of the Nealon technique (powder
and liquid) with thickness greater than the desired, en-
abling nishing and polishing procedures to take place
by means of wearing out procedures.
9
A wide variety of nishing and polishing techniques
have been proposed,
2,13
either by conventional mechan-
ical procedures or by chemical procedures which consist
in immersion in a monomer-based polishing liquid.
Chemically polishing acrylic resins produces a
smooth and shiny surface.
8
However, it reduces me-
chanical resistance when compared with mechanical
polishing, since it adversely aects resin resistance and
structure, increasing the chances of deformation.
11
In mechanical polishing, multilaminated burs are
used to remove excess acrylic, to give shape and to
smooth the surface. Finishing starts with 150, 180,
and 220 wood sandpaper, free of water, with the pur-
pose of obtaining a surface as flat as possible. After-
wards, 400, 600, and 1200 water sandpaper, under a
small flood of water, is used until a uniform surface
can be seen, without the marks left by wood sandpa-
per. Polishing is performed with a cotton wheel and a
mix of pumice and water. This phase is accomplished
when a flat, polished, and shiny surface is seen, with-
out the marks left by water sandpaper. To eliminate
the pumice, the appliance is cleaned and dried. The
final polishing of the appliance is performed with a
woolen wheel and low abrasive liquids for metal pol-
ishing (Brasso or Kaol). The appliance is cleaned with
soap and water, and dried with paper.
9
Polishing is important to facilitate the hygiene of
the appliance, to hinder the incorporation of pigments
or other substances originating from oral uids,
9
and
to improve appliance esthetics and longevity. Further-
more, surface smoothness provides comfort to the pa-
tient who is wearing the appliance. Inappropriate n-
ishing and polishing, polymeric surface and physico-
chemical properties of the material can inuence plaque
retention and staining, favoring the onset of periodontal
diseases and cavities.
13,15
Radford et al
12
assessed adhesion of fungus in rough
acrylic resins and found higher adhesion in rough surfaces
than in smooth surfaces. There is a correlation between
the number of fungus per unit of area and the wettability,
in other words, the more hydrophobic the surface is, the
less cellular adhesion it will have. Surfaces that promote
the development of dental plaque should be worked out
at the laboratory to produce polished surfaces. This will
reduce bacterial adhesion and colonization.
Materials used to make removable orthodontic ap-
pliances have their esthetic, physical, and mechanical
properties degraded aer remaining in the oral cavity.
Acrylic resins are prone to sorption, a process of absorp-
tion and adsorption of liquids, which depends on en-
vironmental conditions. The material stains with time
due to its contact with drinks, food and nicotine. Bev-
erages such as tea, coee, Coke, juices, and wine signi-
cantly promote the development of stains in dental ma-
terials, and so does nicotine. Keyf and Etikan
7
assessed
the changes on polished and unpolished resins in con-
tact with a wide variety of drinks and observed change
in brightness of all samples, with major changes being
observed in unpolished surfaces.
Reis et al
13
observed that the susceptibility of stain-
ing in acrylic resins is not only related to surface rough-
ness, but also to intrinsic factors (staining of the bulk
of resin) and extrinsic (adsorption and absorption of
pigment of exogenous sources). Low susceptibility to
staining is related to low range of water adsorption aer
nishing and polishing.
Finishing and polishing procedures aim at obtain-
ing a smooth and shiny surface for acrylic resins used
to make orthodontic appliances,
2
thus, facilitating hy-
giene, preventing staining and providing greater com-
fort to the patient. The purpose of this study was to ana-
lyze the surface morphology
19
of acrylic resins in each
step of mechanical nishing and polishing.
© 2013 Dental Press Journal of Orthodontics Dental Press J Orthod. 2013 Nov-Dec;18(6):26-3028
Surface morphology changes of acrylic resins during finishing and polishing phasesoriginal article
Material and Methods
Rings 10 mm in diameter and 5 mm in length were
made of stainless steel bands. The stainless steel rings
were placed over a glass plate isolated with solid vaseline.
Self-curing acrylic resin (powder and liquid) (Clássico,
Sao Paulo) was manipulated in the proportion described
by the manufacturer, poured into the rings where it re-
mained for 20 minutes until polymerization took place.
The resin discs were removed from the rings and ran-
domly divided into 10 groups of 3, totalizing 30 samples.
The upper face of each sample was treated as de-
scribed below. The control group did not receive any
treatment while the Kaol group received the entire n-
ishing and polishing treatment. The other groups were
submitted to subsequent steps of nishing and polish-
ing, as stated in Table 1.
The wearing out phase was performed with multi-
laminated burs, by which 1 mm of resin was removed.
Sanding was performed with up-and-down move-
ments, repeated 100 times, and the direction of sand-
ing was changed in 90 degrees every time a sandpaper
was replaced. Wood sandpaper polishing was performed
without water, while water paper polishing was per-
formed under refrigeration of a small ood of water.
At the end of each step, the samples were cleaned with
water to remove any particles of the sandpaper used in
the previous phase. Polishing performed with pumice
and water was carried out with a woolen wheel for 15
seconds. The discs were cleaned, dried and polished
with low abrasive liquids for metal polishing (Kaol) in
a woolen disc for 10 seconds. At the end of all steps, the
samples were washed with soap and dried with paper.
The supercial roughness of the samples was ana-
lyzed under the parameters Ra, Rq, and Rz in microm-
eters (µm). This scale translated the value of linear means
of all absolute distances of the roughness prole from
the central line (L) to the extension of measurement.
Aer that, the samples were metallized and the surface
morphology was analyzed through scanning electron
microscopy with secondary electrons image.
results
The untreated discs of acrylic resin showed surfaces with
bubbles (Fig. 1A) which were not observed aer the wear-
ing out phase performed with multilaminated burs (Fig 1B).
Finishing with wood sandpaper resulted in surfaces with ir-
regularities (Figs 1C, 1D and 1E) which remained the same,
but with low thickness, aer nishing with water sandpaper
(Figs 1F, 1G and 1H). The acrylic resin surfaces polished
with pumice and water had signicantly alterations in their
morphology, showing high surface smoothness (Fig 1I).
This characteristic was also observed, but in low magnitude,
aer polishing with low abrasive liquids (Kaol) (Fig 1J).
The alterations in surface roughness were compat-
ible with the quantitative assessment, hence, they sig-
nicantly decreased during nishing and polishing
procedures of acrylic resins (Table 2). The rst step of
nishing performed with multilaminated burs, resulted
in regular deformities, increasing the values of surface
roughness. The sequence of sandpapers and the pum-
ice gradually decreased the values of surface roughness.
Final polishing performed with low abrasive liquids
caused the surface to be even smoother, however, it is
considered less eective than the previous steps.
Group nFinishing and polishing phases
Control 3 No finishing/polishing
Burs 3 Wearing out with multilaminated burs
150 3 Finishing with wood sandpaper 150
180 3 Finishing with wood sandpaper 180
220 3 Finishing with wood sandpaper 220
400 3 Finishing with water sandpaper 400
600 3 Finishing with water sandpaper 600
1200 3 Finishing with water sandpaper 1200
Pumice 3 Polishing with pumice + water
Kaol 3 Polishing with Kaol
Table 1 - Treatments performed with each group. Table 2 - Surface roughness at finishing and polishing phases.
Group Ra Rq Rz
Control 1.25 µm 1.57 µm 7.63 µm
Burs 1.52 µm 1.90 µm 8.99 µm
150 1.33 µm 1.72 µm 8.72 µm
180 1.03 µm 1.32 µm 6.31 µm
220 0.85 µm 1.44 µm 6.05 µm
400 0.60 µm 0.90 µm 4.10 µm
600 0.48 µm 0.65 µm 3.12 µm
1200 0.42 µm 0.53 µm 2.81 µm
Pumice 0.28 µm 0.36 µm 1.97 µm
Kaol 0.25 µm 0.34 µm 1.92 µm
© 2013 Dental Press Journal of Orthodontics Dental Press J Orthod. 2013 Nov-Dec;18(6):26-3029
original article
Serra G, Morais LS, Elias CN
Figure 1 - Surface morphology of acrylic resin discs analyzed through secondary electrons in scanning
electron microscopy: (A) No treatment; (B) Multilaminated burs; (C) Wood sandpaper 150; (D) Wood
sandpaper 180; (E) Wood sandpaper 220; (F) Water sandpaper 400; (G) Water sandpaper 600; (H) Water
sandpaper 1200; (I) Pumice; (J) Kaol.
discussion
According to Adams,
1
the heat-curing and self-cur-
ing acrylic resins are used to make removable orthodon-
tic appliances. With the use of self-curing acrylic resins
it is possible to easily repair and adjust orthodontic appli-
ances, however, these resins have low staining resistance.
On the other hand, making orthodontic appliances with
heat-cured acrylic resins in laboratory is complex and
time-consuming.
9
Staining and accumulation of dental
plaque are directly related to surface roughness.
12,13,16,20
Thus, a smooth and polished surface is desirable.
The results of this work showed that nishing and
polishing procedures resulted in roughness-free surfac-
es. These ndings corroborate those found by Chung
5
who analyzed the eects of nishing and polishing on
roughness of composite resins and concluded that these
procedures decreased surface roughness. The tenden-
cy in Orthodontics, as in other areas, is to simplify the
A
D
G
J
B
E
H
C
F
I
© 2013 Dental Press Journal of Orthodontics Dental Press J Orthod. 2013 Nov-Dec;18(6):26-3030
Surface morphology changes of acrylic resins during finishing and polishing phasesoriginal article
Aer that last step, the morphology of the acrylic sur-
face caused surface smoothness to increase.
It is worth noting that the methods of analysis
through scanning electron microscopy and laser pro-
lometer give useful information about the morphol-
ogy and roughness of the samples surfaces in a micro-
metrical scale. For further investigations carried out in
smaller scales, other tools such as atomic force micros-
copy, must be used.
17
Final considerations
Before an orthodontic appliance is placed into the
mouth, it should be highly polished. The rough sur-
face of the orthodontic appliance makes it uncomfort-
able, promotes dental plaque accumulation and biolm
formation, thus, reducing resin shining. Furthermore,
smooth and polished surfaces are less prone to bacterial
colonization, therefore, they are more desirable.
Highly smooth acrylic resin surfaces are obtained af-
ter mechanical nishing and polishing performed with
burs, wood sandpapers, water sandpapers, pumice, and
low abrasive liquids (Kaol).
technical procedures in a way that the aims are achieved
with least eort.
14
However, highly smooth acrylic res-
ins surfaces are obtained aer complete mechanical n-
ishing and polishing, only.
Multilaminated burs are used during mechanical pol-
ishing to remove excess acrylic, give shape and smooth
the surface of the appliance.
11
Aer this phase was com-
pleted, it could be observed that the surface of the resin
showed many irregularities. Finishing starts with wood
sandpaper used with the purpose of making the surface
as smooth as possible.
10
In this phase, the acrylic surface
is still irregular, with evident grooves. Aer that, wa-
ter sandpapers are used, until a uniform surface is seen,
without the marks le by the wood sandpaper.
10
This
procedure results in a surface with fewer irregularities
than the ones previously seen. Thenext step is polish-
ing with woolen discs and pumice until a smooth and
polished surface is seen, without the marks le by water
sandpaper.
10
The analysis of surface roughness associat-
ed with scanning electron microscopy met the aims af-
ter these steps were carried out. At last, nal polishing is
performed with woolen discs and low abrasive liquids.
10
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