• G. Mark Richardson, Ph.D.• Senior Risk Assessment Specialist• Stantec Consulting Limited• Ottawa, ON

THE PERPLEXING DILEMMA OF FINDING THE PERFECT DENTAL RESTORATIVE MATERIAL –

A CHEMICAL RISK ASSESSMENT PERSPECTIVE

What is risk assessment?

–A qualitative or quantitative evaluation of chemical exposures and how those exposures compare to the ‘safe’ dose.

• Risk assessment is never black and white.

– All risks must be weighed relative to the benefits to be gained, and relative to the alternatives that can deliver the same benefits.

Is anything risk-free?• NO!

– Water is toxicCNN.com, Jan 13/07: SACRAMENTO, California (AP) -- A woman who competed in a radio station's contest to see how much water she could drink without going to the bathroom died of water intoxication, the coroner's office said Saturday.

– Oxygen is toxicWhy do you think that it’s important to consume anti-oxidants?

– Staying locked indoors in your home 24/7 is dangerous!

Two locations associated with most injuries and accidents: kitchen and bathroom

Can the (health) benefits outweigh the risks? Can risks outweigh the benefits?

Surgery

Medical/dental X-rays

Immunization

Penicillin

Chemotherapy drugs

Immunosupression drugs

Thallidamide

Humira or Remicade (arthritis drugs) linked to increase risk of cancer

Calcium channel blockers linked to cancer

Hormone replacement therapy (17-ß estradiol) linked to cancer

Amalgam is the most common dental restorative material in the US and Canada

181.1 million Americans of all ages carry a grand total of 3.68 billion restored tooth surfaces, which equates to 1.46 billion restored teeth. The vast majority of these are restored with dental amalgam.

A molar has 5 surfaces (lingual, buccal, mesial, distal, occlusal)Other teeth have 4 surfaces (no occlusal or chewing surface)

Numerous studies have demonstrated that Hg exposure increases with increasing amalgam load:

In exhaled and intra-oral air of persons with amalgam fillings

In saliva of persons with amalgam fillings

In blood of persons with amalgam fillings

In urine of persons with amalgam fillings

In feces of persons with amalgam fillings

In various organs and tissues of persons with amalgam fillings, including: kidney, pituitary gland, liver, and brain or parts thereof

In amniotic fluid, cord blood, placenta, and various foetal tissues in association with maternal amalgam load, including: liver, kidney and brain

In colostrum and breast milk in association with maternal amalgam load

Hg exposure in dental patients

From Dunn et al. 2008. NE Children’s Amalgam Trial

Number of amalgam surfaces

Large fillings cause more exposure than small fillings, but most researchers do not measure the size of the filling, just how many.

Dental amalgam 50% Hg0 by weight

Most significant single source of exposure to Hg for amalgam-bearing population (acknowledged by Health Canada)

The only material that is a recognized hazardous material before entering the mouth, a hazardous waste when removed from the mouth, but deemed ‘safe’ when in the mouth

Health Canada recommends avoiding placement in children, pregnant women, persons with other metallic dental work (such as braces), persons with kidney ailments

Now banned in Sweden and Norway.

Regulatory Hazard Rankings for Hg

EPA list of toxic pollutants (1978)

EPA list of Priority Pollutants (1982)

#3 on CERCLA Priority List of Hazardous Substances

Canadian List of Toxic Substances since 1988

Society of Toxicology (2009) – Hg only surpassed by concern for

tobacco use (smoking, chewing, second-hand smoke)

Superfund: Elemental Hg in 48.7% of 1,467 NPL sites (ATSDR

1999) (NPL = 1,689 sites in 2007)

Hazardous waste

UNEP international phase out initiative

Established RELs for Hg0

Agency orAuthor

Year Terminology REL(µg Hg0/m3)

REL-equivalent absorbed dose(µg Hg/kg-day)1

California EPA 2008 Chronic reference air concentration (RfC)

0.03 0.005

Richardson et al 2009 Chronic referenceexposure level (REL)

0.06 0.01

Lettmeier et al 2010 Chronic reference airconcentration (RfC)

0.07 0.011

US ATSDR 1999 Chronic minimal risklevel (MRL)

0.2 0.032

US EPA 1990 Chronic reference airconcentration (RfC)

0.3 0.048

1. REL-equivalent dose calculated as per US EPA (2004)

2. The USEPA REL for methyl Hg = 0.1 µg/kg-day (2 times greater than EPA REL for Hg0)3. The HC REL for methyl Hg = 0.2 µg/kg-day (20 times greater than HC REL for Hg0)

CalEPA

Richardson et al. & Lettmeier et al.

US ATSDR

US EPA

100%

97%

76%

59%

Total N = 82.5 million adults (21-60y)

Frequency Histogram - Adults

Exposure to Hg0: Dose versus REL

CalEPA

Richardson et al. & Lettmeier et al.

US ATSDR

US EPA

100%

100%

49%

29%

Total N = 7.7 million children (5-13y)

Frequency Histogram - Children

Results

TODDLERS CHILDREN TEENS ADULTS SENIORS Total pop > REL

Total pop with fillings 379,004 7,714,637 11,289,979 82,524,655 20,403,213 122,311,488

% > CalEPA REL 100 100 100 100 100 122,311,488

% > Richardson et al REL 100 100 97.2 98.0 97.9 119,908,745

% > Lettmeier et al REL 100 99.7 95.3 96.2 96.0 117,784,675

% > US ATSDR REL 60.0 48.8 49.4 75.7 77.3 87,852,641

% > US EPA REL 45.2 29.2 30.8 59.0 61.9 67,220,662

‘Safe’ Number of Amalgam-Filled Surfaces(N ≤ REL)

Age group REL sourceREL

(µg Hg/m3)REL-associateddose (ug/kg-d)

No. Surfaces≤ REL dose

Toddlers,children &young teens    

California EPA (2008) 0.03 0.005 0.6

Richardson et al (2009) 0.06 0.01 1.3

Lettmeier et al (2010) 0.07 0.011 1.4

US ATSDR (1999) 0.2 0.032 4

USEPA (1990) 0.3 0.048 6

Older teens,adults &seniors    

California EPA (2008) 0.03 0.005 0.8

Richardson et al (2009) 0.06 0.01 1.7

Lettmeier et al (2010) 0.07 0.011 1.8

USATSDR (1999) 0.2 0.032 5.3

USEPA (1990) 0.3 0.048 8

Published Estimates of Hg Exposure in Adults With Dental Amalgam

0 5 10 15

3.4; 0.15 - 11.6

Estimated adult Hg dose from amalgam (mg/day)

Richardson&Allan (1996) ARichardson&Allan (1996) B 3.7; 0.24 -11.5

1 - 12. 5

3 - 17

4.5; 0.3 - 13.9

CCEHRP (1993)

Halbach (1995) A

WHO (1991)

Halbach (1995) B 3.4; 0.1 - 11.8

Weiner & Nylander (1995) 9; 4 - 19

2.3; 0.5 - 4Olsson & Bergman, 1992

Vimy & Lorscheider , 1990Berglund , 1990 1.7; 0.4-4.4

Aronsson et al., 1989

Mackert , 1987 1.24; 0.51-1.83

7.7; 2.5 - 17.5Clarkson et al., 1988

Patterson et al., 1985

10 ; 4.0 – 14.7

Mackert , 1991 1.2

Mackert & Berglund , 1997 1 to 3

USEPA RfC for Hg

CalEPA RfC

for H

g

Mean: 4.9 – 10.1; Range: 0.44 – 45.6

Richardson et al (2011)

3.8 µg/day

0.38 µg/day

9.1 ; 1.5 – 21.5

6.5 ; 0 - 27

WHO (2003) 1 – 21.6

Recent interesting facts about amalgam use in Canada:

1. Canadian Mercury Imports for Use in Dentistry Appear to be Rising

1 2 30

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

YEAR

QUA

NTI

TY IM

PORT

ED (k

g)

1994 1999 2008

2130 kg

1642 kg

4700 kg

Recent interesting facts about amalgam use in Canada:

2. >985,000 amalgam fillings were placed into Canadian children’s baby teeth since 1996 (Statistics Canada, 2007 Canadian Health Measures Survey).

In 1996, Health Canada recommended that “non-mercury filling materials should be considered for restoring the primary teeth of children”.

Dental amalgam – Risks to Dentists - 1

• Sources of Hg vapour exposure in dentists– Vapour in office air

Hg leakage from stored capsulesHg leakage during triturationHg leakage by inappropriate disposal of spent capsules in operatory trashHg emission from contaminated amalgamatorsHg emission from heat sterilization of contaminated dental instrumentsHg emission from office dust (amalgam particles) on sills and other surfacesHg emission from chair-side saliva extractors/aspirators

– Vapour in dentist/patient breathing zone during removal of old amalgam fillings

– Amalgam particles in dentist/patient breathing zone during removal of old amalgam fillings

Dental amalgam – Risks to Dentists – 2Typical Hg vapour levels in dental ‘environments’

100

50

10

2500Breathing zone during removal - dry drilling

Breathing zoneduring removal - spray + aspiration

Average dental office air Hg level

Hg

air

co

nce

ntr

atio

n (

µg

/m3 )

25Occupational TLV = 25 µg/m3

Dental Amalgam – Risks to Dentists - 3

Cloud of amalgamparticulate

Equivalent Hg concentration:~85,000 µg/m3 during a

removal procedure

3 µm

What masks are designed to stop?> 3 µm

Dental amalgam – Risks to Dentists – 4

Are standard hygienic masks any help against particulate?

Average amalgam particle size = 2 µm

> 65% of amalgam particles < 1 µm

Is no dental health care preferable to or safer than no dental amalgam?

Risks to patients from composite resin materials• Bisphenol-a observed in saliva following placement of composite resin

fillings

• Bisphenol-a is an endocrine disruptor• mimics 17β-estradiol (but to what extent?)

Uncertainties with data and studies linking BPA to risk

BPA is between 1,000 times and 10,000 times less potent as an endocrine disruptor than 17β-estradiol

17β-estradiol is prescribed in Canada (and elsewhere) for hormone replacement therapy, birth control, treatment of severe acne, and local (topical) treatment of symptoms of menopause

Sources and Levels of Bisphenol-a Exposure(Richardson et al., 1997; 1999)

1.0 E-070.02

0.180.18

0.38

25.0 HC REL

50.0 US EPA REL

AIR

BEVERAGE

DENTALFOOD

TOTAL

Source

0.0

0.2

0.4

0.6

0.8

1.0

Est

imat

ed d

aily

dos

e (u

g/kg

-day

)

* * Assumes that all fillings are composite resin

Potential risks to dentists from composite resin materials

• Inhalation of plastic particles when old resin fillings drilled to remove– Not an issue if repair added on top of old resin filling

• Occupational dermatitis due to exposure to methylmethacrylate (component of BIS-GMA)

Is composite resin preferable to or superior to or safer than amalgam as a dental restorative material?

Risks posed by gold restorations• Gold is the noblest of metals

– i.e., supposedly the least reactive

• However, the reported rate of allergy to gold is similar to that reported for mercury– Gold = 20% to 45% depending on degree of sensitization– Mercury = 5% to 45% depending on degree of sensitization

• The levels of gold, platinum and palladium in blood or urine correlate with the number of tooth surfaces restored with gold alloys– Are there risks posed to dental patients by gold restorations?– Are there risks posed to dentists by working gold

restorations?

Is gold preferable to or superior to or safer than composite resin and amalgam as a dental restorative material?

Other dental materials needing assessment: Gold alloys

Au, Ag, Cu, Pd, Zn, Pt, In

Ceramics U, Cu, Pb, Zn

Glass ionomers and resin-modified ionomers Floride, Al, Sr, Zn, HEMA, polyacrylic acid, TEGDMA

Pit and fissure sealants used to prevent cavities in children Bis-GMA, TEGDMA, UDMA, HEMA, BPA, methacrylic acid, formaldehyde, SiO2,

Ti02

Base metal alloys used for bridges and partial dentures Ni, Cr, Co, Mo, Ti, W

Gallium alloys Ga, Ag, Sn, Cu, Pd, Zn, Pt

Take home messages Mercury exposure from dental amalgam is significant.

To reduce Hg exposure, reduce the number of amalgam fillings.

Even one amalgam filling will exceed the most stringent safe exposure limit for Hg vapour. For an average of 8 amalgam-filled teeth, Hg exposure is 20 Xs greater than the CalEPA REL.

Composite resin materials are safer; exposures more than 50 times lower than RELs

As a dental patient, exposure to Hg vapour and particulate occurs during removal of amalgam fillings. Does your dentist take measures to protect you from that exposure?

If you are a dentist and are removing old amalgam fillings, take suitable health and safety precautions to protect yourself and your staff from exposure to Hg vapour and particulate.

Dentists need more than a simple hygienic mask to protect themselves from those exposures. Vapour and particles will pass through a simple hygienic mask.

There is still more work to be done to assess risks posed by dental materials.

Some published reports & articles on dental materials by GM Richardson

• Mercury exposure and risks from dental amalgam in the US population, post-2000. Science of the Total Environment, 409: 4257-4268. 2011.

• Mercury Exposure and Risks from Dental Amalgam, Part 1: Updating Exposure, Re-examining Reference Exposure Levels, and Critically Evaluating Recent Studies. Report distributed by the US FDA to members of the FDA Expert Panel for Review of Dental Amalgam. Dated November 8, 2010.

• Mercury Exposure and Risks from Dental Amalgam, Part 2: Cumulative Risk Assessment and Joint Toxicity: Mercury Vapour, Methyl Mercury and Lead. Report distributed by the US FDA to members of the FDA Expert Panel for Review of Dental Amalgam. Dated November 11, 2010.

• Inhalation of mercury-contaminated particulate matter by dentists: an overlooked occupational risk. Human and Ecological Risk Assessment, 9(6): 1519-1531. 2003

• Waste mercury in dentistry: the need for management. Environmental Health Review, 47(2): 33-39. 2003

• Mercury Exposure From Dental Amalgam: Re-evaluation of the Richardson Model, Standardization by Body Surface Area, and Consideration of Recent Occupational Studies. In: Amalgam and Health - New Perspectives on Risks, Report 99:1, FRN, Sweden. 1999

• Dental Amalgam and Mercury Exposure: Potential Patient Risks and the Basis for Restrictions on Use. In: Amalgam and Health - New Perspectives on Risks, Report 99:1, FRN, Sweden. 1999

• Preliminary estimates of adult exposure to bisphenol-a from dental materials, food and ambient air. In: Henshel et al. (eds). Environmental Toxicology and Risk Assessment: Standardization of Biomarkers for Endocrine Disruption and Environmental Assessment. Eighth Volume, ASTM STP 1364, ASTM. 1999.

• An assessment of adult exposure and risks from components and degradation products of composite resin dental materials. Human and Ecological Risk Assessment, 3(4): 683-697. 1997

• A Monte Carlo Assessment of Mercury Exposure and Risks from Dental Amalgam. Human and Ecological Risk Assessment, vol. 2(no. 4): 709-761. 1996

– Assessment Of Mercury Exposure And Risks From Dental Amalgam. Health Canada, Bureau of Medical Devices. http://publications.gc.ca/collections/Collection/H46-1-36-1995E.pdf. 1995.