Glass ionomer cements
(GICs) are getting used for a good range of applications in dentistry, so as to
beat the poor mechanical properties of glass ionomers, several modifications
are introduced to the standard GICs. Nanotechnology involves the utilization of
systems, modifications or materials the dimensions of which is within the range
of 1–100 nm. Nano-modification of conventional GICs and resin modified GICs
(RMGICs) will be achieved by incorporation of nano-sized fillers to RMGICs,
reducing the dimensions of the glass particles, and introducing nano-sized
bioceramics to the glass powder. Studies suggest that the commercially
available nano-filled RMGIC doesn't hold any significant advantage over
conventional RMGICs as far because the mechanical and bonding properties are
concerned. Conversely, incorporation of nano-sized apatite crystals not only
increases the mechanical properties of conventional GICs, but can also enhance
fluoride release and bioactivity. By increasing the crystallinity of the set
matrix, apatites can make the set cement chemically more stable, insoluble, and
improve the bond strength with tooth structure. Increased fluoride release also
can reduce and arrest secondary caries. However, because of an absence of
long-term clinical studies, the utilization of nano-modified glass ionomers
continues to be limited in daily clinical dentistry. Additionally to the in
vitro and in vivo studies, more randomized clinical trials are required to
justify the utilization of those promising materials. The aim of this paper is
to review the modification performed in GIC-based materials to boost their
physicochemical properties.
Recent development
Expansion of the concept of incorporation of polymerization and polyelectrolyte
salt formation mechanisms within one molecule or a mixture of molecules has led
to a spectrum of materials which range from classical acid-base GIC to modified
polymer-ceramic (glass) composites with little polyelectrolyte character. The
objectives sought in these latter materials are to enhance the strength,
toughness and resistance to dissolution whilst retaining the basic attributes
of adhesion, fluoride release and biocompatibility related to the GIC system.
The requirement to produce adequate water within the system for polycarboxylate
reactions to occur, i.e. adequate hydrophilicity, has led to difficulties in
some materials in balancing this requirement against the hydrophobicity
required in resin cement systems.
As is well-known,
resin cement systems, even those containing monomers having potentially
functional polar groups like carboxylate or phosphate, lack intrinsic adhesion
to dentine unless a 'conditioning pretreatment to enhance surface penetration
is utilized. as an example, Leung and Morris have demonstrated by Raman
spectroscopy that 4-META during a methacrylate medium reacts too slowly with
enamel for salt formation and first bonding is more likely because of improved
wetting, enhanced surface penetration and micromechanical interlocking.
Further, Ruse and Smith have shown previously that aciddemineralized surfaces
of dentine contain little calcium or phosphorus thus reducing still further the
possibility of calcium salt formation on subsequent application of functional
resin bonding systems. Treatment of dentine by acidic primers containing
hydrophilic solvents or monomers is thus required to also enhance penetration
facilitating formation of the so-called 'hybrid layer' or 'resin diffusion
zone'. The performance of resin-modified GIC in terms of intrinsic adhesion
behavior to dentine is thus a sign of the contribution of polyelectrolyte
character and/or penetration enhancement with micromechanical interlocking to
their mechanistic behavior. Another aspect of resin-modified systems is
important shrinkage on setting arising from monomer polymerization.
The current status of
resin-modified glassionomer cements has been reviewed by Sidhu and Watson
including the vexed question of the generic name. Classification of those
materials is formed more confusing by the multiplicity and complexity of
current formulations. Thus Vitremer (3M) luting cement relies on the Vitrebond
(3M) copolymer developed by Mitra. The copolymer relies on an acrylic-itaconic
acid chain having amide-linked methacrylate groups. The formulation also
contains HEMA and tartaric acid and water. An acid-base reaction occurs on
mixing but is overtaken by a polymerization reaction, both light and chemically
initiated. Although there must be less -COOH and reduced chain mobility
compared to a conventional GIC, there's evidently enough interaction with tooth
tissue and enhanced penetration to produce adequate bonding without a
requirement for primer treatment. We have shown recently that this technique
interacts chemically with dentine but bonding is reduced by a delay between
application and light-curing.
Another current material, Fuji Duet (GC
Corp.), supported a polyacrylic acid-itaconic acid) copolymer is stated to be
'water based' and 'resin reinforced'. It contains hydroxy acid and HEMA. It
requires, however, the utilization of a 10/2 citric acid/ferric chloride
conditioner so as to understand its bonding potential thus suggesting a greater
proportion of non-ionic monomers and fewer polyelectrolyte character. (1)
Between these materials which lay emphasis on the GIC characteristics and
products that are essentially polymer composites containing F-containing
fillers like GIC glass are several hybrid materials that contain relatively
large amounts of acid monomers in polymerizable systems. These approaches are
discussed by Hammesfahr. Samples of these materials include
Advance(Dentsply-Caulk) Hybrid Ionomer Cement and Dyract(DentsplyCaulk).
In Advance (Dentsply-Caulk)
a GIC glass is mixed
with a liquid containing polymerizable carboxylic acids, water and diluent
monomer. The material sets by interaction between the glass and therefore the
monomeric acid monomers within the liquid and by a chemically initiated
("self-curing') reaction. Thus this approach aims to create the polyacid
structure in place. The novel acid monomer employed is termed OEMA monomer. The
system as supplied is alleged to produce bond strength to dentine at conventional
GIC levels but higher bond strength requires use of the Probond
(Dentsply-Caulk) acid phosphate primer suggesting limited tooth interaction
before setting of the composition. The degree of interaction with the glass is
before setting and therefore the effect of setting contraction because of
polymerization of the monomer component furthermore as changes in structure and
cross-linking within the cement over time don't seem to be clear at the moment.
Sufficient interaction occurs, however, to produce significant fluoride
release.
Newer advances of
Glass ionomer Cement
Conventional GIC lacks
in sufficient strength and toughness, which has attracted focused research so
as to enhance the mechanical properties of conventional GIC, Resinmodified
glass-ionomers(RMGI) were introduced, which contains hydrophilic monomers and
polymers like HEMA and that they have higher flexural strength compared to
traditional GIC." Recently, a replacement restorative concept is marketed,
a system application consisting of a posterior restorative GIC combined with a
unique nanofilled coating material, the compounded nanofillers protect against
the abrasive wear and therefore the coating acts as a glaze, enhancing its
esthetic properties.9.10 Hybridization of GIC and Composites using prereacted
glass ionomer technology, 'Giomer' was developed by Shofu. Newer bioreactive
material "HAINOMER was developed using hydroxyappatite with glass powder
and have shown a promising future during initial clinical trials as retrograde
filling material. More recently, Zirconia containing GIC, Proline containing
GIC, CPP-ACP GIC are synthetically manufactured to reinforce the
remineralization potential and aimed toward improving the strength."
Resin-Modified
GlassIonomer Cement as a Restorative Material
Resin-modified
glassionomer cements are compatible as luting cements and tooth adhesives where
thin layers are often photo-cured to polymerize the HEMA present within the
cement. In deep cavities, the chance of unpolymerized HEMA at the floor of the
cavity may end up in absorption of fluid from the tooth into the restoration or
permeation of free HEMA into the dentine and pulp where postoperative
sensitivity may develop (Watson1997 ). The scientific use of resin-modified
glassionomer cements as a restorative fabric should be restrained to shallow
cervical restorations where excessive aesthetics are required and center
build-ups in non-vital enamel where there's adequate remaining teeth structure.
Resin-modified glassionomer cements are well acceptable as dental adhesives,
thin hollow space lining materials and luting of translucent ceramic
restorations.(1)
Bioactive glass (BAG)
The first Bioglass was
invented by Larry Hench etal10 at the Universidad Florida It considers the.
indisputable fact that on Their acid dissolution is that the formation of a
layer rich in glass Ca+ and PO4 + ions round the glass, a glass like which will
Forms close bioactive connections with the bone cells and is fully Inbuilt with
bone.2 Osteo-conductivity, thanks to its good bioavailability BAG has been used
as a restorative, and biodegradability over a decade of material, and its
degradation Products stimulate protein development, Cell proliferation and Gen
Expression Activation Osteoblasts, also help to treat hypersensitivity to
dentine And promoting remineralisation of enamel.
The BAG formed a
stable bond or interface with biological tissues through the formation of an
apatite layer. The primary commercially available BAG had a composition of 46.1
mol % silica (SiO 2 ), 24.4 mol aflaxen oxide (Na 2 O), 2.6 mol % phosphorus
pentoxide (P 2 O 5 ), and 26.9 mol Nalfon oxide (CaO). This material was
labeled as 45S5 or Bioglass. 12 supported the composition of BAG added to GIC,
the modified GICs are shown to exhibit antimicrobial properties. It's said that
a substance is bioactive if it gives an adequate biological response and ends
up in Bonding of substance and tissue. (4) What's more, remineralisation. BAG
has antibacterial effect, because it increases the pH Solutions Aqueous. Mixture
of bioactive nano silica improves its biocompatibility with dental cement,
which is helpful in overcoming small differences that are an enormous downside
to several dental cements.
Clinical Applications
of Bioactive Glasses in Dentistry
The compositional
similarity to the bone and tooth structure combined with the bioactive
properties and apparent antimicrobial properties inspired the research of
baggage in clinical application in dentistry and were first used as bone
substitutes in dentoalveolar and maxillofacial reconstruction, periodontal
regeneration, and implants.
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