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?