Introduction
Composite resins are fundaments of contemporary restorative dentistry.[1] Along with evolution of materials and application techniques, composite restorations
are capable of closely recreating both the physical and optical properties of natural
teeth. As a result, naturally looking, durable, and functional restorations can be
provided for both anterior and posterior dentition.[2]
[3]
[4]
Composite resins present viscous consistency which can impede proper anatomical contour
modeling or adaptation of the material to cavity walls.[5]
[6] To overcome sticking of the composite to hand instruments, lubrication of the instruments
with modeling resins, bonding agents, or alcohol became a common practice. Such method
deviates from the recommendations of most of the manufacturers. Due to possibility
of altering the characteristics of restorative material some authors advise against
this technique.[7] Incorporation of other substances into the modeled composite layer may disrupt its
composition and influence material properties.[8]
[9]
[10]
Instrument lubrication technique has not been officially described in the scientific
literature, thus lack of standardized research methods to analyze this topic can be
observed. Within available in vitro studies, authors investigated multiple materials and methods of their application
on mechanical and optical properties of restorative materials.[8]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
The study aims to summarize the currently available knowledge about influence of instrument
lubrication on properties of dental composites. Literature selection was conducted
within MEDLINE, SCOPUS, and EBSCO databases. Studies describing usage of resins as
a surface glaze after the finished composite polymerization were excluded.
Resin Lubricants
Widely used group of lubricants meant to facilitate material modeling include resins
existing either in clear form, as the so called unfilled resins, or being part of
the adhesive systems. They are composed of various methacrylate derivatives present
also in organic matrix of dental composites, that is, bisphenol A-glycidyl methacrylate
(Bis-GMA), urethane dimethacrylate (UDEMA), triethylene glycol dimethacrylate (TEGDMA),
and photoinitiators that allow light curing and in the case of the bonding agent,
also additional ingredients facilitating efficient application and adhesion to tooth
structure. Hydrophilic molecules present in adhesive systems, such as water, ethanol,
or acetone, might affect elements of the composite matrix.[28]
[29]
[30]
Physical Properties
Most of contemporarily used composite materials are based on Bis-GMA monomers and
comonomers present relatively lower viscosity and molecular weight.[31]
[32] Organic matrix composition influences handling and physical properties of final
product.[5]
[33]
[34] Incorporation of additional resin portions with a lubricated instrument raises concerns
over possible change in composition of applied composite, leading to a loss of its
optimal properties.[8]
[35] Studies describing influence of instrument lubrication with resins and bonding agents
on physical properties of composites are shown in [Table 1].
Table 1
Influence of adhesive systems and unfilled resins used as lubricants on the physical
properties of composites
|
Study (year)
|
Lubricant
|
Lubricant application method
|
Composite
|
Parameters tested
|
Results
|
|
Tjan and Glancy[15] (1988)
|
Command resin, Bondlite (used with Herculite)
HelioBond, Adhesit (used with Heliomolar)
|
Composite modeling instrument wetted with resin
|
Herculite
Heliomolar
|
Cohesive strength at the composite interfaces
|
Lubrication with adhesive decreased Heliomolar strength, no effect on Herculite specimen
No effect of lubrication with unfilled resins on cohesive strength of Herculite and
Heliomolar
|
|
Dunn and Strong[12] (2007)
|
Unfilled resin (name not mentioned)
|
Interproximal carver instrument dipped once into a single drop of resin
|
Filtek Z250
|
Flexural strength
|
No influence of lubricant on flexural strength
|
|
Barcellos et al[16] (2008)
|
Composite wetting resin
C&B liquid
Scotchbond MultiPurpose
Adper Single Bond
Prime & bond NT
|
Tip of the instrument painted with the moistured microbrush
|
Venus
|
Cohesive strength at the composite interfaces
|
SBMP lubrication increased cohesive strength, other lubricants had no effect on cohesive
strength
|
|
Barcellos et al[17] (2011)
|
Adper SE plus
Clearfil SE bond
Futurabond M
Optibond all-in-one
Futurabond NR
One up bond F
|
Tip of the instrument painted with the moistured microbrush
|
Venus
|
Cohesive strength at the composite interfaces
|
Lubrication reduced cohesive strength in all groups except Adper SE Plus
|
|
Tuncer et al[20] (2013)
|
Modeling resin
|
Round-ended plugger with a diameter of 2-mm dipped into the modeling resin
|
GrandioSO
Gradia direct posterior
Aelite LS Posterior
Filtek Silorane
Aelite all-purpose body
Filtek ultimate
Clearfil majesty esthetic
|
Microhardness
Surface roughness
|
Modeling with lubricant and polimerization under polyester strip decreased microhardness
and surface roughness
Modeling with lubricant with mechanical polishing decreased microhardness and surface
roughness of Grandioso
Increased surface roughness of Filtek Silorane and Aelite All Purpose
|
|
de Paula et al[21] (2016)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Brush coated with adhesive and the excess removed by stroking onto a glass plate
|
Filtek Z350 XT
Empress Direct
|
Degree of conversion
Cross-linking density
|
Both adhesives lowered DC and CLD of Empress Direct
No significant difference in DC of Filtek Z350 XT
SBMP lowered CLD of Filtek Z350 XT
|
|
Münchow et al[25] (2016)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Adhesive applied with disposable microbrush applicator
|
Filtek Z350 XT
|
Flexural strength
Flexural modulus
Microtensile cohesive strength
Surface analysis under SEM
Water sorption and solubility
|
ASB reduced flexural strength of composite.
Both lubricants:
• had no effect on cohesive strength
• Reduced loss of cohesive strength, flexural strength and flexural modulus after
6 months
• Reduced solubility and water sorption
No differences in specimen morphology were observed under the SEM examination
|
|
Patel et al[14] (2017)
|
Optibond FL
Optibond solo plus
Optibond all-in-one
|
Plugger dipped into lubricant for 1 second and left to drip/drain for 2 seconds prior
to use
|
Solitaire 2
|
Diametral tensile strength
Water sorption
|
All tested lubricants increased water sorption and reduced diametral tensile strength
of composite
|
|
Hamouda[26] (2017)
|
Tetric N-bond Universal
Tetric N-bond
|
Plugger dipped into lubricant for 1 second and left to drip/drain for 2 seconds prior
to use
|
Tetric N-ceram
|
Water sorption and solubility
|
Lubricants increased water sorption of composite
No effect on solubility in water
|
|
Melo et al[18] (2018)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Brush coated with adhesive and the excess removed by stroking onto a glass plate
|
Filtek Z350 XT
Empress direct
Esthet X HD
|
Degree of conversion
|
SBMP reduced DC of all tested composites
ASB reduced DC of Empress and increased DC of Esthet X A2
|
|
Kutuk et al[19] (2020)
|
Modeling liquid
G-premio bond
Optibond XTR primer
|
Humidified sable brush and microbrush applicator
|
Essentia Dark Enamel
|
Microhardness
Surface roughness
|
Optibond XTR lubrication lowered composite microhardness
No effect of lubrication on surface roughness
|
|
Bayraktar et al[27] (2021)
|
Modeling liquid
Composite primer
Modeling resin
|
Humidified sable brush with excessive material removed using a clean paper tissue
|
Charisma Smart
Estellite Asteria
Ceram-X one SphereTEC
Admira fusion
Filtek ultimate
Clearfil majesty ES-2
|
Microhardness
|
All of the lubricants reduced composite microhardness
|
Abbreviations: ASB, Adper Single Bond; CLD, cross-linking density; DC, degree of conversion;
SBMP, ScotchBond MultiPurpose; SEM, scanning electron microscope.
Composite Resistance
Materials used for replacing dental tissues must be characterized by high and universal
resistance to withstand constant occlusal forces.[36] Filler content and monomer types within the composite matrix affect its mechanical
properties.[35]
[37] Changes in precisely selected material composition caused by lubricant incorporation
during the application might disturb its internal structure and influence its durability.[3]
[38]
Dunn and Strong have not shown any significant differences in flexural strength between
composite samples layered with or without the use of modeling resin.[12] Münchow et al confirmed those observations regarding the use of ScotchBond MultiPurpose
(SBMP; 3M ESPE, St Paul, Minnesota, United States) dental adhesive, however, with
more hydrophilic bonding agent, Adper Single Bond (ASB; 3M ESPE, St. Paul, Minnesota,
United States), flexural strength decreased compared with control group after 24 hours
of water storage. Additionally, in presented study, the flexural strength test was
repeated after 6 months and the loss of flexural strength was lower than in the control
group. Authors explain this by reduction of microporosities on the composite surface;
however, scanning electron microscope (SEM) image analyses have not revealed any differences
in samples micromorphology.[25]
Negative outcome of instrument lubrication on composite resistance was observed by
Patel et al. Authors described higher diametral tensile strength (DTS) in control
group than in groups where IV-, V-, and VII-generation bonding agents were used as
lubricants.[14]
Composite Tensile Strength
Majority of clinical situations require composite layering because of limited depth
of curing light penetration through the material and need of polymerization shrinkage
reduction, as well as from esthetic reasons, to compose a restoration from materials
with different optical properties.[39]
[40] Instrument lubrication may lead to changes of material characteristics at the composite
layers interface and influence the tensile strength between the increments resulting
in lower durability of the restoration.[41]
[42]
Tjan and Glancy observed reduced resistance of Heliomolar (Ivoclar Vivadent, Schaan,
Liechtenstein) material lubricated with currently unused bonding system based on polyurethane,
Dentine Adhesit (Ivoclar Vivadent, Schaan, Liechtenstein).[15] Polyurethane setting reaction requires the presence of water which can explain obtained
low value of tensile strength.[43] Differences in tensile strength have not been noted regarding Heliomolar composite
layers applied with the use of Helioseal resin (Ivoclar Vivadent, Schaan, Liechtenstein)
which is a combination of Bis-GMA and TEGDMA, as well as within Bis-GMA based Herculite
(Kerr, Orange, California, United States).[15]
Barcellos et al study has shown reduction of tensile strength between composite layers
caused by instrument lubrication with all tested self-etch adhesive systems except
for Adper SE Plus Adhesive (3M ESPE, St Paul, Minnesota, United States), adhesive
resin from VI-generation system. According to the authors, this is due to fact that
ionization of acidic phosphate monomer (MHP) present in Adper SE Plus occurs only
in presence of hydrophilic radicals contained in the primer of this system.[17]
In earlier studies, the same authors proved that only one out of three tested total-etch
adhesive systems, ScotchBond MultiPurpose used during composite modeling caused the
increase of cohesive strength of layers in comparison to the control group. ASB, Prime
& Bond NT (Dentsply DeTrey, Konstanz, Germany) and modeling resins did not influence
this parameter. This relation has been explained by chemical similarity of SBMP and
compounds of tested composites, as well as by its lack of hydrophilic solvents.[16]
Positive effect of instrument lubrication with SBMP on composite tensile strength
was not confirmed during microtensile bond strength (µTBS) test, performed after 24 hours
of water storage. Similarly, as in case of flexural strength tests, lubrication with
ASB and SBMP decreased tensile strength loss after 6 months of water storage compared
with control group.[25]
Surface Characteristics
Surface quality and smoothness are some of the conditions providing clinical success
and durability of created restoration. High gloss of composite surface apart from
obvious patient's esthetical satisfaction guarantees also higher staining resistance
of the resin.[44] Instrument lubrication during composite application allows to obtain more even surface
of freshly placed composite; however superficial modified layer can behave differently
during mechanical finishing and polishing.[45]
No effect of instrument lubrication with universal bonding agents and modeling resin
on nanohybrid composite microhardness was observed by Kutuk et al. Microhardness reduction
was only obtained during lubrication with self-etch system primer. Both tested adhesive
systems and modeling resin had no effect on surface roughness of the composite.[19]
In the study, investigating instrument lubrication with modeling resin, Tuncer et
al proved reduction in composite surface microhardness in a group where superficial
layer was not mechanically finished. Samples modeled with lubricated instrument but
thereafter grinded with aluminum oxide discs have not shown statistically significant
difference in surface roughness compared with control for five out of seven examined
composites. The results observed were related to removal of resin-rich superficial
layer during finishing. Samples modeled with lubricant and polymerized under polyester
strip exhibited the lowest surface roughness. Among groups polished after polymerization,
instrument lubrication positively affected surface smoothness of Grandioso (VOCO,
Cuxhaven, Germany) composite but negatively influenced Filtek Silorane (3M ESPE, St
Paul, Minnesota, United States) and Aelite All Purpose Body (Bisco, Schaumburg, Illinois
United States) composites. The remaining restorative materials showed no difference
compared with the control group.[20]
In the research by Bayraktar et al, evaluating the effect of three different modeling
resins, composite microhardness reduction was observed for all of the tested composite
materials.[27]
Polymerization Quality
The achievement of desired performance by dental composite materials depends highly
on their correct polymerization.[46] Composite's degree of conversion is related to its composition and resin to filler
ratio.[47] Usage of higher inorganic filler content and monomers with high molecule weight
like Bis-GMA allowed to reduce the polymerization shrinkage of light-cured materials;
however, it also affected the reaction kinetics resulting in lower degree of monomer
to polymer conversion.[48]
[49]
[50]
[51] Lower degree of conversion has negative outcome on material properties leading to
reduced mechanical resistance and decreased color stability.[46] Moreover, high content of unreacted monomer facilitates its release to body environment,
limiting material biocompatibility and increasing cytotoxicity.[52]
[53]
In the study conducted by Melo et al, instrument lubrication with SBMP caused reduction
in the degree of conversion of all examined composites. Usage of ASB as a lubricant
also decreased the degree of conversion for Empress Direct (Ivoclar Vivadent, Schaan,
Liechtenstein) A2 and Bleach shades however increased it for Esthet X HD (Dentsply
Caulk, Milford, Delaware, United States) A2 shade.[18] De Paula et al during analysis of the same adhesives have not observed significant
effect of instrument lubrication on composites degree of conversion; however, lower
cross-linking density has been noted with SBMP as a lubricant.[21]
The amount of available studies verifying effect of instrument lubrication on polymerization
quality is limited. Results suggest possible incorporation of lubricant particles
into composite matrix and alterations in the polymerization reaction kinetics.
Scanning Electron Microscope Analysis
During cross-section surface analysis of freshly placed composite samples using SEM,
no changes in the micromorphology of interlayer interface have been observed.[23]
[25] Analysis performed after 12 months of wine storage revealed heterogenic structure
with evident connection layer in groups where instruments were lubricated with adhesives.[23]
Superficial composite layer examination after wine storage showed lower surface degradation
in the group modeled with adhesive system as a lubricant compared with the control
group. Authors connect that surface degradation with influence of the alcohol contained
in wine.[23] This hypothesis can be confirmed by lack of visible surface degradation of composite
modeled with lubricated instrument but stored in coffee solution observed in another
study.[19]
Water Sorption and Solubility
Composite restorations in the in vivo conditions are permanently interacting with
surrounding water solution: composite absorbs little amounts of water and also its
small particles get dissolved during the hydrolytic reaction.[54]
[55] Increased water sorption and solubility negatively affect mechanical properties
of composite material.[56] Those parameters rely mainly on composition and structure of composite organic matrix
phase,[57] therefore incorporation of additional monomers and hydrophilic substances during
modeling with lubricated instrument creates a possibility of significant changes in
terms of composite stability in mouth environment.[58]
The use of SBMP and ASB as instrument lubricants reduced composite solubility compared
with control group. Water sorption was reduced only with the use of SBMP.[25] In another study, no effect of modeling with V- and VI-generation adhesive systems
on composite solubility was also observed.[26]
Different outcome was obtained during measurements of water sorption, it has increased
in all tested groups. Additionally, the study has shown no linear relation between
number of layers modeled with lubricant and water sorption.[26] Higher water sorption was also confirmed for instrument lubrication with V- and
VII-generation bonding agents from another manufacturer and with adhesive resin from
VI-generation system.[14]
Optical Properties
Composite modeling with lubricated instruments or brushes is especially helpful during
work in the esthetic region. Replication of correct anatomical form and proper surface
texture already at the application stage allows clinician to save time needed for
contouring and finishing of the restoration. Qualitative and quantitative compositions
of organic matrix affect color, translucency, light refraction index of dental resins,
and also their staining susceptibility.[59]
[60]
[61] Changes within those parameters can determine failure in esthetic integration despite
the right restoration shape.[62]
Studies examining influence of instrument lubrication with modeling resins and adhesive
systems on composite optical properties are listed in [Table 2].
Table 2
Influence of adhesive systems and unfilled resins used as lubricants on the optical
properties of composite
|
First author
|
Lubricant
|
Lubricant application method
|
Composite
|
Parameters tested
|
Results
|
|
Tuncer et al[20] (2013)
|
Modeling resin
|
Round-ended plugger with a diameter of 2-mm dipped into the modeling resin
|
GrandioSO
Gradia direct posterior
Aelite LS posterior
Filtek Silorane
Aelite all-purpose body
Filtek Ultimate
Clearfil majesty esthetic
|
Color stability after thermocycling
|
Lubrication Increased color change of:
• Polished Filtek Silorane
• Filtek Ultimate and Filtek Silorane polymerized under polyester strip
• Lubrication reduced color change of:
- Polished Aelite all-purpose body and Aelite LS posterior
• Clearfill Majesty, Aelite All Purpose Body, Aelite LS Posterior polymerized under
polyester strip
|
|
Münchow et al[25] (2016)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Adhesive applied with disposable microbrush applicator
|
Filtek Z350 XT
|
Color stability
Transparency parameter
|
SBMP lubrication caused increased color change after 180 days of water storage but
lowered color change after 180 days of wine storage
ASB lubrication increased color change after 1 day of water storage
Lubrication with both adhesives increased translucency
|
|
Sedrez-Porto et al[23] (2016)
|
ScotchBond MultiPurpose
|
Instrument not mentioned
|
Filtek Z350 XT
|
Color stability
|
SBMP lubrication reduced color change after 6 and 12 months of wine storage for both
polished and unpolished specimen
|
|
Sedrez-Porto et al[24] (2017)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Adhesive applied with disposable microbrush applicator
|
Filtek Z350 XT
|
Color stability
Transparency parameter
|
SBMP lubrication reduced color change after 6 and 12 months of wine storage
Lubrication with both adhesives had no influence on translucency after 6 and 12 months
of water storage
|
|
Araujo et al[22] (2018)
|
ScotchBond MultiPurpose
Adper Universal
|
Brush covered with the adhesive
|
Filtek Z250
|
Color stability
Transparency parameter
|
Lubrication with Adper universal reduced color change during storage in staining solutions
Lubrication with both adhesives had no influence on translucency
|
|
Melo et al[18] (2018)
|
ScotchBond MultiPurpose
Adper Single Bond
|
Brush coated with adhesive and the excess removed by stroking onto a glass plate
|
Filtek Z350 XT
Empress direct
Esthet X HD (A2 and bleach shades)
|
Color stability
Transparency parameter
|
SBMP lubrication increased color change of Esthet X HD
Lubrication with both adhesives increased translucency of Filtek Z350 XT A2 shade
Lubrication with ASB decreased translucency of Esthet X HD bleach shade
|
Abbreviations: ASB, Adper Single Bond; SBMP, ScotchBond MultiPurpose.
Translucency Change
Increased translucency of Filtek XT Z350 (3M ESPE, St Paul, Minnesota, United States)
and Filtek Z250 (3M ESPE, St Paul, Minnesota, United States) was described in the
literature while using the instrument lubrication technique with bonding agents from
the same manufacturer, ScotchBond MultiPurpose and ASB.[18]
[22]
[24]
[25] In the research conducted by Melo et al, composites from other producers were also
included, Empress Direct and Esthet X HD. Their translucency got decreased or was
not affected by modeling with lubricated instrument.[18]
Color Change
Color stability is one of the requirements for restorative materials. Pigments contained
in daily diet can cause external and internal discoloration both within the dental
tissue and in the composite.[63]
Tuncer et al examined effect of instrument lubrication with Modeling Resin (Bisco,
Schaumburg, Illinois, United States) on color change of composites. Higher color change
range was observed after thermocycling Filtek Ultimate (3M ESPE, St Paul, Minnesota,
United States) and Filtek Silorane samples; however, only for the latter change was
greater than estimated acceptation threshold.[64] Clearfill Majesty (Kuraray Medical Inc., Tokyo, Japan), Aelite LS posterior (Bisco,
Schaumburg, Illinois United States), and Aelite All-Purpose Body composites have shown
lower color change compared with control group. Instrument lubrication with SBMP and
ASB adhesives caused higher color change after water storage.[24]
[25] Melo et al observed increased color change only for one out of three tested composites.[18]
Instrument lubrication with SBMP, ASB and Adper Universal (3M ESPE, St Paul, Minnesota,
United States) resulted in lower composite color change after storage in strongly
staining solutions.[22]
[23]
[25]
Alcohol Lubricants
Usage of alcohol as a substance preventing sticking of the chemically cured composite
to plastic modeling instruments was for the first time described already over 40 years
ago. Instruments moistened in alcohol did not affect material adaptation to cavity
walls and composite resistance.[65] However, it has also been proven that too large contamination of composite resin
with alcohol drastically worsens its mechanical properties.[66] Research results regarding instrument lubrication with alcohol are listed in [Table 3].
Table 3
Influence of alcohol used as a lubricant on composite properties
|
First author
|
Lubricant
|
Lubricant application method
|
Composite
|
Parameters tested
|
Results
|
|
Tjan and Glancy[15] (1988)
|
70% ethanol
70% isopropanol
|
Modeling instrument moistured with alcohol
|
Herculite
Heliomolar
|
Cohesive strength at the composite interfaces
|
Lubrication with alcohols decreased Heliomolar cohesive strength, no effect on Herculite
specimen
|
|
Patel et al[14] (2017)
|
Ethanol
|
Ball burnisher dipped in alcohol for 1 second and left to drip for 2 seconds
|
Solitaire 2
|
Diametral tensile strength
Water sorption
|
Lubricant decreased diametral tensile strength and
increased water sorption
|
|
Dunn and Strong[12] (2007)
|
70% isopropanol
|
Interproximal carver instrument wiped with an alcohol saturated gauze
|
Filtek Z250
|
Flexural strength
|
Lubricant had no influence on flexural strength
|
|
De Paula et al[21] (2016)
|
70% ethanol
100% ethanol
|
Spatula left for 3 seconds on a gauze with dispensed alcohol
|
Filtek z350 XT
Empress Direct
|
Degree of conversion (DC)
Cross-linking density (CLD)
|
Reduced DC of Empress Direct in 70% ethanol group
No effect of 100% ethanol on DC
No effect of 70% and 100% ethanol on CLD
|
Tjan and Glancy have shown negative influence of instrument lubrication with alcohol
during layering of UDEMA-based composite on tensile strength. Such relation was not
observed for composite based on Bis-GMA, where samples during the tests sustained
mostly cohesive fractures. Different behavior of those two materials can be explained
by different vulnerability to degradation by hydroxyl ions contained in alcohol.[28] During fracture site analysis, the presence of white spots on layer's connection
surface was observed in samples treated with ethanol. Authors suggest that this can
be an effect of precipitation of filler particles after dissolution of resin matrix.[15] This phenomenon was also observed later in another study.[14]
Negative influence of instrument lubrication with alcohols on physical properties
of layered composite was described by other researchers. Patel et al demonstrated
composite resistance decrease in diametral tensile strength test for samples applicable
with the use of 70% ethanol and also their increased water sorption compared with
control group.[14] Different outcome was shown by Dunn et al, suggesting no effect of instrument lubrication
with the same ethanol concentration on resin's flexural strength.[12] Conflicting results can be explained by differences in lubricant application methods.
In experiment by Patel et al, the instrument was dipped in alcohol solution while
in the study by Dunn et al, the instrument was only wiped with alcohol moistened gauze.
Rapid ethanol evaporation from the instrument surface in room temperature could be
the reason why it had no effect on composite material during modeling. Similar doubts
about presence of lubricant on the instrument using absolute ethanol were described
by de Paula et al. The authors observed reduction in degree of conversion of the Empress
Direct composite while using 70% ethanol but no effect on that parameter with use
of absolute ethanol. Additionally, there was no effect of instrument lubrication with
70 and 100% ethanol on conversion degree of Filtek XT 350 composite and on the polymer
cross-linking density of both tested composites.[21]
Research results differ according to the application method used and composite type.
The amount of alcohol present on the instrument during the modeling can be significantly
different in mentioned studies. Furthermore negative effect of instrument lubrication
with alcohol seems connected with its quantity introduced into composite portion,
what is consistent with the observations of Sneed and Draughn.[66]
Discussion
The quoted results present current knowledge about influence of instrument lubrication
with resins, bonding agents, and alcohol on properties of dental composites.
From all tested lubricants the least negative effects on mechanical properties of
composites could be observed for resin with composition similar to composite organic
matrix, as well as in case of alcohols, presence of hydrophilic particles in adhesive
systems can more affect the composite properties compared with bonding agents with
more hydrophobic composition and unfilled resins.[29] Negative influence of instrument lubrication with methacrylate-based resins on mechanical
behavior of Filtek Silorane composite which is based on silorane matrix can additionally
suggest the importance of chemical compatibility between used lubricant and composite
material.
Changes in conversion degrees and microhardness values of superficial composite layers
indicate incorporation of lubricant particles into the composite structure and consequently
creation of external resin-rich layer.[49] That layer is probably thin enough to be completely eliminated during standard finishing
and polishing, which are inherent steps of each restorative procedure. As a result,
the possible influence of that layer on finished composite surface properties can
be most likely omitted.[20]
Most often examined resin was ScotchBond MultiPurpose adhesive, consisting mostly
of Bis-GMA and hydroxyethyl methacrylate (HEMA). Viscosity of monomer mixture has
a direct effect on degree of conversion and polymerization shrinkage of composites.[47] Modifications in Bis-GMA percentage influence resin polymerization parameters.[47]
[67]
[68] HEMA as a light molecular weight and low viscosity monomer promotes increase in
conversion degree due to higher particle mobility during polymerization process.[69] At the same time, HEMA is binding only in linear positions, not creating cross-chains
which results in higher susceptibility to hydrolysis.[54]
Instrument lubrication does not seem to have a noticeable effect on base color of
methacrylate composites when both the material and the lubricant present similar monomer
composition. The increase in staining resistance of composites after modeling with
resin lubricated instrument is an interesting relationship. This positive outcome
might be mainly connected to improved composite adaptation and reduction of surface
microdefects. As a result, a material sealing effect is obtained, similarly to surface
glaze application on already cured composite.[70] It is worth mentioning that studies regarding optical properties did not include
parameters, such as light refraction index or fluorescence, the properties of high
clinical significance that allow to achieve natural esthetics and metamerism of composite
restorations.[4]
[71]
The use of ethanol and isopropanol carries high risk of damaging composite resin matrix
elements which can cause decrease in tensile strength between the layers and surface
degradation. Observed lack of effect of ethanol on composite properties might be a
consequence of a full evaporation of that substance from the modeling instrument.
As a result, it cannot be equated to instrument lubrication but rather just instrument
cleaning and degreasing.
