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Discussion on choices of and
advances in dental materials
Summary
• Where have we come from?
• What do we currently have?
• Where could we be heading?
Where have we come from?
• Pre 1960
– Gold
– Amalgam
– Zinc phosphate / Zinc oxide & Eugenol
– Bowen’s resin (BIS-GMA) 1955
• 1960
– Adhesion to enamel
• 1980
– Glass ionomer chemistry
– Composite bonding to enamel
• 1990
– Dentine bonding
• 2000
– No etch bonding and the rise of the posterior composite
Cohesive gold
Restorations 60 years old
when photographed
Amalgam Zinc phosphate
Composite resin Composite resin
Zinc cement - glass
polyalkynoate spectrum
Glass Ionomer Cement
Zinc
oxide
Polyacrylic
acid
Alumino-
slilcate
glass
Phosphoric
acid
Zinc phosphateZinc phosphate
cementcement
Zinc polycarboxylate
cement
Glass Glass ionomerionomer
cementcement
Silicate cement
What do we currently have?
Amalgam
Do teeth with amalgam have a high
incidence of cuspal fracture?
• No
– 1.5% in 600 teeth after 5 years
– 1.8% in 1400 teeth after 10 years
– 5% in 1213 teeth after 15 years
• Bonded amalgams may fare even better
Whal Dental Update 2003;30:256-262
Do temperature changes in amalgam cause
cusp fracture
• No
– Coefficient of thermal expansion of resin is
greater than amalgam
– No prolonged contact with temperature extremes
before swallowing
– Of greater importance is tooth preparation and
parafunction
Do teeth with amalgam restorations have a
higher rate of recurrent decay?
• No
– 0% of 600 teeth at 5 years
– 1.1% of 1400 teeth at 10 years
– 0% of 35 teeth at 10 years
– <5% after 14 years (no nos.)
Do resin composite restorations usually
last as long as amalgam restorations?
• No
• 2001 study
– 12 yrs = median age 1827 failed amalgams
– 5 yrs = median age of 1548 failed composites
• 2000 study of 6761 teeth
– median age of replaced amalgam = 10 yrs
– and composite = 8 yrs
– amalgam lasting longer than composite in C I, II III IV and V restorations
• 1998 study
– median age of amalgam replacement = 15 yrs,
– composite = 8 yrs
Aren’t bonded restorations preferable to
amalgam restorations
• Yes
– Composite bonded to enamel and dentine creates
a monoblock whereas amalgam may create a
wedge
– Increasing numbers of dentists are bonding
amalgam restorations
– Some evidence of good bond strength of amalgam
to dentine
Amalgam is over 100 years old – doesn’t
that make it old fashioned?
• No
• So is radiography, nitrous oxide, gold and
rubber dam
• High copper formulations, factory measured
components, pre-capsulated amalgam
Has amalgam been banned in Sweden and
Germany?
• No
• Amalgam use in the EU is governed by
Medical Devices Directive 93/42/EEC.
• 1998 EU working group stated, “no scientific
evidence of systemic health problems or toxic
effects from dental amalgam.
Do amalgam restoration release a large
amount of mercury?
• No
– It is estimated that a patient would have to have
2740 amalgam restorations to reach the threshold
limit value of 82.20 microns per day considered
dangerous for occupational exposure in the USA
Does mercury from amalgam restorations
cause ill health?
• No – except rare cases of allergy (Eg Lichenoidreaction)– Sandborgh-Englund G, Nygren AT, Ekstrand J, Elinder C-G. No evidence of renal toxicity
from amalgam fillings. Am J Physiol 1996; 271: R941–945.
– Saxe SR, Wekstein MW, Kryscio RJ et al. Alzheimer’s disease, dental amalgam and mercury. J Am Dent Assoc 1999; 130: 191–199.
– Casetta I, Invernizzi M, Granieri E. Multiple sclerosis and dental amalgam: case-control study in Ferrara, Italy. Neuroepidemiology 2001; 20: 134–137.
– Rodvall Y, Ahlbom A, Pershagen G et al. Dental radiography after age 25 years, amalgam fillings and tumours of the central nervous system. Oral Oncol 1998; 34: 265–269.
– Lindberg NE, Linberg E, Larsson G. Psychologic factors in the etiology of amalgam illness. Acta Odontol Scand 1994; 52: 219–228.
– Björkman L, Pedersen NL, Lichtenstein P. Physical and mental health related to dental amalgam fillings in Swedish twins. Community Dent Oral Epidemiol 1996; 24: 260–267
Lichenoid reaction Desquamative gingivitis
Is there credible scientific literature that
shows health problems due to mercury in
dental amalgam?
• No
• Independent analysis of data shows incorrect
conclusions often drawn
• Data extrapolating snail cells to human clinical
response
• Exposure to Hg levels x100 normal levels
Is mercury from dental amalgam
dangerous to dental staff?
• No– “the infants of dental workers actually had a lower
perinatal death rate than the rest of the infants” (Ericson A, KällénB. Pregnancy outcome in women working as dentists, dental assistants or dental technicians. IntArch Occup Environ Health 1989; 61: 329–333.)
– “In a study of 21 634 male dentists and 21 202 dental assistants there was no difference in the rate of spontaneous abortions or congenital abnormalities” (Brodsky
JB, Cohen EN, Whitcher C et al. Occupational exposure to mercury in dentistry and pregnancy outcome. J Am Dent Assoc 1985; 111: 779–780.)
– Of 1706 dentists screened at a 1991ADA meeting, only 29 (2%) had high urinary mercury levels. These high levels were correlated to poor mercury hygiene (the use of squeeze cloths). (Echeverria D, Heyer NJ, Martin MD et al. Behavioral effects of low-level
exposure to Hg among dentists. Neurotoxicol Teratol 1995; 17: 161–168.)
Are the ingredients of resin composite
non-toxic?
• No
• The ingredients of resin composite have been shown to be
– cytotoxic
– mutagenic
– To cause immunosuppresion or
– to inhibit DNA85 and RNA86 synthesis.
• Wataha et al. stated,
– ‘the components of resin composites are hazardous in that
they all cause significant toxicity in direct contact with fibroblasts.
Are the ingredients of resin composite
non-toxic?
• Composite restorations have been shown to leach
between 14 and 22 separate potentially hazardous
compounds, including
– DLcamphorquinone,
– 4-dimethylaminobenzoic
– acid ethy ester (DMABEE), drometrizole,
– 1,7,7-trimethylbicyclo[2,2,1]heptane, 2,2-
– dimethoxy[1,2] diphenyletanone (DMBZ),
– ethyleneglycol dimethacrylate (EGDMA),
– and triethyleneglycoldimethacrylate (TEGDMA)
Does amalgam in waste water cause
harmful environmental effects?
• Probably not
• Most amalgam from dental surgeries captured
by amalgam traps
• 3-4% of worldwide consumption of mercury is
for dental purposes
• Estimated that 0.3% of amalgam waste is
soluble
Is the death of amalgam imminent?
• Not yet………
– Sig. number of dentists still use amalgam
–Many patients prefer tooth coloured restorations
– Such patients do not tend to have health concerns
over amalgam
Amalgam when
• Strength
• Bulk
• Moisture control
“It may be prudent to
consider ‘phasing down’
instead of ‘phasing out’ of
dental amalgam at this
stage. A multi-pronged
approach should be
considered. Short-, medium-
and long-term strategies
should be developed.”
2009 meeting published2010
1. What is taught in UK dental schools
BDJ, 2010;209:129
Surveys
• 1989 – worldwide survey – 90% schools do NOT teach posterior composite
• 1998 – little change in American dental schools
• 1997 – paper, use of composite in load bearing posterior cavities should be, “‘limited
to the occlusal surfaces of premolars, and preferably those with limited occlusal
function”Wilson N H F, Setcos J C. J Dent 1989; 17: S29
Mjör I, Wilson N H F.. J Am Dent Assoc 1998;129: 1415.
Wilson N H F, Dunne S M, Gainsford I D. Int Dent J 1997; 47: 185.
Surveys
• 2004 – 2005. 30% of posterior restorations
placed by dental students are composite
Lynch C D, McConnell R J, Wilson N H F. Eur J Dent Educ 2006; 10: 38-43.
Lynch C D, McConnell R J, Wilson N H F. J Am Dent Assoc 2006; 137: 619-625.
Lynch C D, McConnell R J, Wilson N H F. J Can Dent Assoc 2006; 72: 321.
Lynch C D, McConnell R J, Wilson N H F. J Dent Educ 2007; 71: 430-434.
Guidelines
• 2007 , British Association of Teachers of
Conservative Dentistry (BATCD) published a
consensus document which recommended
that
– composite should be taught to dental students as
the ‘material of choice’ when restoring posterior
teeth, in particular when managing teeth with an
initial lesion of caries
Conclusions
• 2005 -2010 has seen great increase in use of posterior composite in dental schools
• Many schools now place more posterior composite than amalgam
• General Dental Practice surveys show more amalgams than posterior composites
• Some concern over teaching methods not considered best practice– Transparent matrices and transparent wedges
– Bevelling cavity margins
Types of Resin Composites
• All contain
– Resin
• Susceptible to shrinkage upon polymerisation
– May be modified methacrylate/acrylate
– OR a chemical that upon setting expands due to a ring
opening mechanism eg Oxirane
» This expansion in resin volumes offsets to a degree the
polymerisation shrinkage
» Still however a net shrinkage
Types of Resin Composites
• All contain
– Resin
• Susceptible to shrinkage upon polymerisation
– May be modified methacrylate/acrylate
– OR a chemical that upon setting expands due to a ring opening mechanism eg Oxirane
» This expansion in resin volumes offsets to a degree the polymerisation shrinkage
» Still however a net shrinkage
– Filler
• Type, concentration, particle size & particle size distribution control properties
Types of Resin Composites
• Resin and Filler alone useless without
effective coupling
• “The coupling agent transfers the stresses
generated under loading from the rigid and
brittle filler to the more flexible and ductile
polymer matrix”
• Matrix may be regarded as a “shock absorber”
Types of Resin Composites
• Classification
–Method of Activation
• Chemical/light
Types of Resin Composites
• Classification
–Method of Activation
• Chemical/light
– Filler particle size and distribution
Types of Resin Composites
Conventional (1) 1 – 50 µm 60 – 80 % by weight
Microfilled (2) 0.01 – 0.1 µm
Mean = 0.04 µm
30-60 % by weight
Hybrid Blend of (1) & (2) (1) 75%, (2) 8 %
Total 83 – 90 % by weight.
Nanocomposites Uses particles less than 1
µm diameter
(really like (2))
Types of Resin Composites
• Classification
– Handling Characteristics
• Packable
– Highly viscous
– Presents packaging challenges to manufacturers
• Flowable
– More fluid
– Less filler
Types of Resin Composites
• Classification
– Intended clinical application
• ISO 4049
– Type 1 – restoration of cavities involving occlusal surfaces
– Type 2 – All other polymer based filling and restorative
materials
Where could we be heading?
Amalgam
• Likely to be phased down then out
• Dictated by NHS SDR
• Informed by dental/therapy school teaching
policies
– Eg All direct occlusal restorations in composite
• Advantages
– Strength, colour and moisture tolerance
Composite
• Will grow in popularity
– Patient desire
• Placement techniques will improve
• Shrinkage reduction will make for less post-operative pain
• Wider applications
– Splinting
– Core build-up
– Occlusal rehabilitation
And far ahead……..?
• Restorations that inhibit caries and
periodontal disease
– Fluoride release
– CaPO4 release
– Slow release CHx
• Restorations that indicate when they are
failing
– Colour change?