The drive for development of new and novel oral biomaterials has never been more important with many people using oral biomaterials today and seeing their benefits in restoring and improving their oral health for a more enjoyable lifestyle. The unique properties of biomaterials such as titanium (Ti), zirconia (ZrO2) and various polymeric materials have made them materials of choice in oral health: dental implants, oral and maxillofacial surgery, and even regenerative medicine. Oral biomaterials research today is an exciting and intensive multidisciplinary area that encompasses contributions from a wide range of fields from professional dentistry to biology, chemistry, physics, material science, and engineering.
Materials in Oral Health is a FREE 4-week course open to all interested learners. In the course, you will learn about the special properties and benefits of biomaterials including, titanium and titanium alloys, zirconia and other alloys, ceramics, and modern composites. You will gain insights of the practical use of these biomaterials in different aspects of dentistry and clinical implications. You will realize how contemporary dentistry is about unifying synthetic materials to living tooth and bone tissues. You will get in touch with the crucial roles of digital dentistry and learn about CAD/CAM technology in crown fabrication, 3D printing and digital orthodontics. And lastly, you will be introduced to procedures and testing methods used to test significant mechanical properties of biomaterials in the research laboratory.
We cordially invite those of you who wish to make a difference in tomorrow’s dental materials and oral health development to join us in the 4-week journey in Materials in Oral Health.
You can get recognition for completion of the course by obtaining a Course Certificate. You can refer to details on: https://learner.coursera.help/hc/en-us/articles/208280196
Professor in Dental Materials Science, Head of Unit Faculty of Dentistry, The University of Hong Kong
James Kit Hon Tsoi
Assistant Professor in Dental Materials Science, Assistant Dean of Electives and Experiential Learning Faculty of Dentistry, The University of Hong Kong
Resin dental adhesives are broadly classified
into an etch-and-rinse system, or self-etch system.
An etch-and-rinse adhesive system
requires a separate acid etching procedure,
which is usually done using 32% to 37% phosphoric acid.
A self-etch adhesive system does not require
a separate acid etching procedure
as it contains acidic resin monomer
that can etch and bond simultaneously.
An etch-and rinse dental adhesive system
can be a 3-step system or a 2-step system.
A 3-step etch-and-rinse system
consists of primer and bonding resin
that comes in two separate bottles.
Therefore, in clinical application
one has to perform three steps,
etching, priming and bonding of adhesive resin.
A 2-step etch-and-rinse system
consists of self-priming resin
that comes in a single bottle.
Therefore, in clinical application
one has to perform two steps,
etching and bonding of adhesive resin.
The 2-step etch-and-rinse system
is also popularly known as
one-bottle dental adhesive system.
An etch-and-rinse dental adhesive system
consists of resin monomers, solvents,
photoinitiator, inhibitors and filler.
Resin monomers in dental adhesive systems
are dimethacrylates.
The most common dimethacrylic monomer resin
that is incorporated in any etch-and-rise
dental adhesive system is Bis-GMA
which is Bisphenol-A glycidyl methacrylate.
The other dimethacrylate includes TEGDMA
which is Triethylene glycol dimethacrylate
and HEMA which is 2-Hydroxyethyl methacrylate.
Bis-GMA is also known as Bowen-resin.
It is a hydrophobic resin
and used in composites too.
It is highly viscous and has superior mechanical properties.
Additionally, it exhibits lower polymerization shrinkage
and rapid hardening.
In terms of water sorption,
Bis-GMA ranks inferior to TEGDMA.
TEGDMA is a less viscous resin monomer
and usually added as a diluent.
It is inferior to Bis-GMA in mechanical properties.
A resin mixture of Bis-GMA and TEGDMA
has an improved conversion rate.
HEMA is a hydrophilic monomer
that helps in priming the demineralized dentin,
it is also inferior to Bis-GMA in physical properties.
It is prone to hydrolysis.
Solvents are important ingredient
in any resin-based dental adhesive system.
It helps in carrying resin monomer
to the bond surfaces and subsequently
volatizes by which it also removes water
from the bonded surfaces.
The most commonly used solvents
in resin dental adhesive system
are water, ethanol and acetone.
Acetone has high vapour pressure
and low hydrogen bonding capacity.
In contrast, water has low vapour pressure
and high hydrogen bonding capacity.
Photoinitiator is essential for light-cured polymerization
of resin monomers in the dental adhesives.
Camphor quinone with a co-initiator system
is most commonly incorporated agent.
Camphor quinone absorbs over a wide spectrum of wavelength from 360 to 510 nm,
with peak absorbance around 460 nm
which lies in the blue light.
Inhibitors are added to dental resins
to scavenge free radicals originating from
prematurely reacted initiator.
Mostly useful in extreme storage conditions
such as high temperatures.
The most frequently used inhibitors in adhesives
are butylated hydroxytoluene.
A self-etch dental adhesive system
can be a two-step or a single-step system.
A two-step self-etch system
consists of self-etching primer
and bonding resin that comes in two separate bottles.
However, being a self-etch system,
in clinical applications, one has to perform only two steps,
application of self-etching primer
followed by application of adhesive resin.
A single-step self-etch system consists of
self-etch primer and bonding agent
that either comes in two bottles, or a single bottle.
In either forms, in clinical applications
one has to perform a single step.
Therefore, when it comes in two separate bottles
an operator should dispense equal amount
of required content from both the bottles and mix together
followed by its application.
A self-etch dental adhesive system
consists of resin monomers, solvents,
photoinitiator, inhibitors and filler.
The resin monomers in self-etch dental adhesive system
consists of acidic functional monomers
for dentine demineralization,
hydrophilic monomer for water solubility
and bi- or multi-functional monomers to provide strength.
The common acidic functional monomers are
10-MDP and 4-MET.
10-MDP is very hydrophobic and forms
a strong chemical bonding to hydroxyapatite of enamel and dentine.
It has been patented by Kuraray from Japan.
In recent years, 10-MDP is also introduced to
ceramic primers especially for
segmentation of zirconia restorations.
4-MET is an acidic monomer
frequently used together with methylmethacrylate.
It forms a weak bond with calcium in hydroxyapatite
when compared to 10-MDP.
Phenyl p is another acidic monomer
and was used as one of the first acidic monomers
in self-etching primers.
Phenyl p has only very little chemical bonding capacity
to hydroxyapatite.
This acidic monomer is not frequently used anymore