Keywords Bioglass - hydroxyapatite - broad-spectrum antimicrobial - bioactive glass - sol-gel
technique
Introduction
Like wheels of time, dentistry too keeps evolving and innovating; one of such innovation
is Bioglass, developed by Hench in 1969. It comprises of calcium sodium phosphosilicate.
Bioglass precipitates hydroxyapatite crystal in aqueous solution, which has ability
to bond with soft and hard tissues of the body without rejection. The bioactivity
of Bioglass is due its reactions with tissue fluids, which initiates hydroxyapatite
crystal formation. The properties of bioactivity along with biocompatibility paved
way for Bioglass into modern dentistry for various purposes such as for repair of
voids and defects of facial bone, remodeling of dentoalveolar complex, etc.[1 ]
History
Bioglass was developed by Professor Larry Hench, of University of Florida, in 1969.
The idea of developing a material that could bond to bone struck him in a conversation
with a US army colonel who had just returned from war. The colonel suggested for a
material to be flourished that would be compatible with human body, since implants
then available were made of metals or polymers that were bioinert and caused fibrous
encapsulation in preference to a stable bond with tissue.[1 ]
The main discovery was of a glass with the composition 46.1 mol% silicon dioxide,
24.4 mol% sodium oxide (Na2 O), 26.9 mol% calcium oxide (CaO), and 2.6 mol% phosphorus pentoxide (P2 O5 ), later termed Bioglass 45S5, which forms firm bond with bone that could only be
detached on breaking the bone.[2 ]
The University of Florida used “Bioglass” as trade name for the original 45S5 composition.
Thus, the term Bioglass is used to refer to the 45S5 composition and is not a general
term for bioactive glass.[3 ]
Composition
Besides above content, it may also contain some of biocompatible and bioactive minerals
like:
Fluorapatite
Wollastonite
Diopside
Tricalcium phosphate ([Table 1 ])[4 ]
Table 1
Composition of Bioglass
Chemical compound
Content (%)
Silicon dioxide
45
Sodium oxide
24.5
Calcium oxide
24.5
Phosphorus pentoxide
6
Network modifiers, namely CaO, Na2 O, and P2 O5 , are generally used.[5 ] However, both CaO and Na2 O may be replaced with magnesium oxide and potassium oxide, which promote apatite
crystal formation. To alter the surface reactions and melting properties, aluminum
oxide and barium oxide may be added.[6 ] Ions may be added for modifying bioactivity and antimicrobial properties, viz. silicon
ions, phosphorus ions, strontium ions, silver ions, zinc ions, and fluoride ions.[7 ] More acid-resistant fluorapatite formation is initiated, rather than hydroxyapatite.
Augmented remineralization of dentin and reduced possibility of dentin-matrix degradation
is initiated by fluoride coupled with Bioglass. These attributes make fluoride vitally
important in dental applications of Bioglass.[8 ]
There are two variants of Bioglass available, type A and type B. The type A is alkali-free
Bioglass, especially sodium, with a composition of 70% diopside, 10% fluorapatite,
and 20% tricalcium phosphate, while the type B variant is bioinert with silica content
greater than 60% by weight.[9 ]
Method of Preparation
Conventionally, glasses were prepared using melt quenching above 1,300°C. Nevertheless,
this method had a few drawbacks such as:
Also, heat treatment of silicon-containing Bioglass results in release of stress from
glass, thereby affecting the mechanical properties.[11 ]
Another method of preparation of Bioglass used since 1970s is “sol-gel technique.”[1 ] This process involves hydrolysis and condensation followed by low-temperature heat
treatment. This approach has encouraged manufacturers to produce variety of glasses,
differing in content and structure, viz. fibers, coatings, scaffolds, and nanoparticles.
It has elevated porosity, apatite-formation ability, and more surface area in contrast
to melt quenching, which imparts higher mechanical properties.[12 ]
Mechanism of Action
When Bioglass is placed at the defect site, body fluids begin to hydrate glass surface
thereby initiating conversion reaction; soon, thin layer of hydroxyapatite crystal
is formed over glass surface that thickens over time thereby inducing other body cells
to take actions as per location followed by mineralization of the matrix ([Fig. 1 ]).[13 ]
Fig. 1 Schematic representation of mechanism of action of Bioglass.
Properties of Bioglass
Bioglass is biocompatible, nontoxic, and chemically stable in biological environment.
It has antimicrobial property as well, since it elevates the pH and osmolarity locally,
thereby creating unfavorable environment for bacterial growth.[14 ]
[15 ]
Bioglass differs highly from conventional glass in its dissolution. Bioglass requires
a particular dissolution for its activation, which is accomplished by addition of
network modifiers like CaO or Na2 O, which makes both the surface and silica reactive.[14 ]
Alkali-free Bioglass coupled with zinc oxide and strontium oxide imparts antimicrobial
property against Staphylococcus aureus and Escherichia coli. These features make Bioglass a classic bone alternative in remedy for osteomyelitis,
peri-implant infection, sinus augmentation, and repairing orbital floor flaws.[15 ]
[16 ]
As Bioglass can be incorporated into hydrophilic and hydrophobic conditions, it may
be used along with dental implants as coating.[17 ] Also, particle size influences the antimicrobial properties; smaller-sized particles
provide larger surface area, thus increasing the antimicrobial effects.[18 ]
Advantages and Disadvantages of Bioglass
Advantages and Disadvantages of Bioglass
The chief advantage of Bioglass, which makes it a noteworthy innovation, is the high
surface speed reaction that facilitates forming of rapid networks to the tissues.
Its bioactive nature, broad-spectrum antimicrobial properties, and biocompatibility
are few other advantages. However, every material has some disadvantages; the main
disadvantage of Bioglass is its low mechanical strength.[19 ]
Clinical Application
As a result of its broad-spectrum antimicrobial property and bioactive property, Bioglass
has been a topic of keen interest for researchers. Bioglass has made its various clinical
implementations in fields of dentistry, spinal implants, tissue engineering, and various
other medical aspects.[17 ]
[20 ] In the discipline of dentistry, it was initially used in practice as bone replacements
in periodontal regeneration, dentoalveolar and maxillofacial reconstruction, and implants.[21 ] Other contributions of Bioglass in dentistry include its use as restorative material,
in intracanal medicament used for pulp capping, as dental adhesives, for enamel regeneration,
and to treat dental hypersensitivity and air abrasion ([Fig. 2 ]).
Fig. 2 Clinical applications of Bioglass in dentistry.
Bioglass in Oral Maxillofacial Surgery
Bioglass in Oral Maxillofacial Surgery
Bioglass induces superiority in quality and magnitude of bone generation and at a
faster rate in contrast to calcium phosphate-based compound.[22 ]
Biogran (Biomet 3i, Palm Beach Gardens, Florida, United States) is commercially available
for maxillofacial applications. It is widely used for repair or rehabilitation of
maxillofacial faults. Biogran (Biomet 3i, Palm Beach Gardens, Florida, United States)
differs from PerioGlass (NovaBone Products LLC, Alachua, Florida, United States) in
their particle size.[23 ]
NovaBone (NovaBone Products LLC) is commercially available, which may be employed
to make putty using blood from site of defect.[24 ]
Strontium oxide containing Bioglass has demonstrated to reduce bone resorption.[25 ] The alkali-free Bioglass is more biocompatible, resorbs bone at a slow rate, and
has higher osteoconductive property, which makes it more suitable for dental and oral
maxillofacial usages.[26 ]
Bioglass As Restorative Material
Bioglass As Restorative Material
Almost all of the restorative materials available are biomimetic but not bioactive.
Also, they undergo some degree of polymerization contraction leading to formation
of microgap, thus leading to microleakage, which affects the mechanical properties
of both tooth and the restoration. This microgap is often beyond the reach of routine
dental hygiene practice, thereby creating favorable environment for microorganisms'
growth, thus leading to secondary caries and restoration failures.[27 ]
Bioglass as restorative material induces remineralization, as it seals marginal interfaces
with hydroxyapatite crystal precipitates.[28 ] Fluoride-containing Bioglass causes remineralization of dentin. It also reduces
enzyme-mediated collagen network degradation of dentin. Resin composite with Bioglass
filler exhibits antimicrobial and bioactive properties, which prevent secondary caries.[29 ]
Resin-modified glass ionomer cement (GIC)-containing bioactive glass has higher remineralization
property. Also, it exhibits active antimicrobial property against Candida albicans and Streptococcus mutants .[30 ] This is the potential reason behind the effectiveness of resin-modified GIC-containing
Bioglass in prevention of secondary caries.[31 ] However, integration of Bioglass with resin-modified GIC weakens its strength and
mechanical properties thereby limiting its uses as liners and for cavities where occlusal
forces are not so strong.[32 ]
Bioglass as Intracanal Medicament
Bioglass as Intracanal Medicament
The main interfering determinants in the periapical repair process are bacteria and
its derivatives as they play a crucial role in periradicular diseases development
and its advancement.[33 ]
[34 ] Disinfection of the complicated root canal structure is vital as C. albicans and Enterococcus faecalis are the enduring root canal microorganisms that lead to root canal treatment failure.
This disinfection also imparts longevity to the treatment.[35 ] Suitable intracanal medicament in between treatment sessions provide effectives
antimicrobial effect. A broad-spectrum antimicrobial property is the ideal requirement
for an intracanal medicament, since it is more suitable with periapical tissue and
induces hard tissue repair, also reducing inflammation at the same time.[36 ]
[37 ]
As discussed earlier, Bioglass has antimicrobial and anti-inflammatory effects along
with osteoconductive properties that aid in repair of bone faults.[38 ] The broad-spectrum antimicrobial effects account for the use of Bioglass as intracanal
medicament.[39 ]
[40 ]
Recent researches show that Bioglass has higher antimicrobial effect in contrast to
calcium hydroxide, which is due to the fact that calcium hydroxide is affected by
buffering actions of dentin, whereas Bioglass is less responsive to the same.[41 ]
Clinical outcome: A recent research was conducted to study the effectiveness of chlorhexidine
gluconate-1% gel and bioactive glass S53P4 as intracanal medicaments. Method used
in the study was polymerase chain reaction. The result showed that both medicaments
caused a considerable reduction in amount of bacterial growth. Bioglass S53P4 caused
much more reduction than chlorhexidine gluconate-1% gel. Hence, to conclude, we can
say that Bioglass S53P4 has better antibacterial property as compared with chlorhexidine
gluconate-1% gel.[42 ]
To Treat Dentin Hypersensitivity
To Treat Dentin Hypersensitivity
An intense and momentary dental ache due to a physical, chemical, osmotic, evaporative,
or thermal cause is termed as dentin hypersensitivity. Most accepted dentin hypersensitivity
theory is the hydrodynamic theory.[43 ] Commercially available Sensodyne (GlaxoSmithKline) toothpaste has Novamin to deliver
relief by blocking the dentinal tubules and precipitating hydroxyapatite crystal.
The use of Bioglass instead of silica in toothpaste provides resilience against pH
rinse and helps cleaning off the blocked tubules. Recent experimental studies show
that Bioglass biosilicate dispersion in distilled water provides remedy for a follow-up
period of 6 months against dentin hypersensitivity.[44 ] The major advantage of using Bioglass in dentifrices is that it induces hydroxyapatite
formation, which in turn has following advantages:
It induces remineralization.
It is used for treatment of dentine hypersensitivity.
Hydroxyapatite can bind to microorganisms by interacting with the bacterial adhesin
thus agglutinating the microorganism.[45 ]
Fluoride Bioglass may be recommended for treatment of dentin hypersensitivity. It
can be used daily by individuals with a compromised periodontal status and individuals
with a compromised enamel surface.[46 ]
Dental Adhesives
Dental adhesives make adherence, or bonding, of a compound or material, like composites
used in dentistry or orthodontic brackets, to natural tooth tissue achievable. The
adhesive functions to link two substances.[26 ]
With use of orthodontic brackets, cases of white spot lesion are common. A favorable
condition for microbial flora growth is initiated, since the orthodontic bracket adheres
to the tooth surface. Prevention of white spot lesion incurs additional costs as regular
tooth brushing and use of fluoride dentifrices, mouthwash, or varnishes become vital.
A high degree of patient cooperation is necessity to achieve adequate results. A key
interest of the researchers in this filed is to improvise fluoride-releasing sealants,
primers, and adhesives to achieve continuous fluoride release throughout orthodontic
treatment, so as to prevent occurring of white spot lesions caused due to use of orthodontic
brackets. However, addition of fluoride decreases the mechanical properties of the
resin-based adhesives, though fluoride release is reduced or is exhausted over time.[26 ] Bioglass has a bonding system that reduces micropermeability by inducing remineralization
of mineral-deficient areas while showing increase in modulus of elasticity at same
time. This property makes Bioglass suitable as dental adhesives. A bioactive glass
ceramic is Biosilicate, which when applied before application enhances the bond strength
system in both mineralized and unmineralized dentins.[47 ]
In Periodontics
Periodontitis is chronic inflammation of the periodontium, which is marked by formation
of pockets in gingiva, resorption of alveolar bone, loss of attachment, and thus leading
to loss of tooth structure if not treated.[48 ]
Bioglass in form of PerioGlass (NovaBone Products LLC, Alachua, Florida, United States)
is widely used to repair periodontal defects as it is an excellent grafting material.
It also found its uses in periodontal surgical practices to activate bone regeneration,
to be specific, in interproximal bone faults; this effectiveness is a result of its
hemostatic effect on trabecular bone.[49 ]
In Implant Dentistry
Dental implants are artificial screw-shaped tools that are inserted into alveolar
socket or periosteum, to hold replacement or bridge. Dental implant finds its uses
in prosthodontic constructions to improve its action and aesthetics.[50 ] Uninterrupted contact between the implant surface and bone tissue is vital to accomplish
adequate retention in bone, or osseointegration.[51 ] Titanium-based alloys are extensively employed materials for dental implants; these
are biocompatible and osteoconductive materials, but are bioinert. This bioinert nature
is overcome by addition of Bioglass. Titanium-based alloy implant, along with Bioglass,
provides active bonding and antimicrobial properties, thus reducing overall treatment
time.[52 ]
Clinical outcome: A study was undertaken to examine the clinical outcomes of hydroxyapatite-,
Bioglass-, and Ti6Al4V-coated dental implants ([Table 2 ]).
Table 2
Clinical outcome of study conducted on hydroxyapatite-, Bioglass-, and Ti6Al4V-coated
implants
Hydroxyapatite coated
Bioglass coated
Ti6Al4V coated
Total
41
45
40
Failed prosthetic attachment
23
21
20
Abnormal motility in perpendicular direction was observed with pus formation; along
with this, resorption of almost the entire area of hydroxyapatite coating was observed
in hydroxyapatite-coated failure implants. However, Bioglass-coated implants were
devoid of any such complications, as horizontal mobility and partial resorption of
coating were observed with failed Bioglass-coated implant.[53 ]
Enamel Remineralization
Primary carious lesions that have not cavitated, for example white spot lesion, may
be prevented from further spreading and remineralization. Through routine plaque removal
and fluoride deposition, operative procedures may be avoided. Fluoride has extensive
applications in toothpaste, varnishes, and mouth rinse due to its anticariogenic property,
and also because it enhances remineralization.[54 ]
Fluoride doped with Bioglass exhibits potential usage in dental utilization, for example,
as dentifrices and restorative materials.[55 ] A Bioglass coupled with fluoride and increased phosphate content is commercially
available as BiominF, which results in the formation of fluorapatite, in contrast
to calcium fluorite. The significantly higher phosphate content provides a source
for vital ions of fluorapatite.[56 ]
Conclusion
Hence, in conclusion we can say that Bioglass is a recent innovation that is not only
beneficial in various aspects of dentistry but also in orthopaedics and spinal implants.
The properties that make Bioglass a diverse material to be used in dentistry are:
Despite Bioglass having a higher bone regeneration capacity than bioceramics, it lags
behind other bioceramics in terms of commercial success, which may be due to its low
strength. Bioglass may have not yet reached its utmost usage, but research activity
is growing.
