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Biomaterials Focus Group -Research Highlight 1

Understanding dental composite wear behaviourthrough in-vitro analysis -

A study by Assoc Prof Adrian Yap,Assoc Prof Teoh Swee Hin and Prof Chew Chong Lin

For more than a century, dental amalgam (an alloy of up to

50% mercury mixed with silver, tin and copper) has been thechoice restorative material for posterior teeth. However, its

usage is declining due to the fear of mercury toxicity, thepotential hazardous environmental effects, and increased

aesthetic demands by patients. Dental composites are gaining

popularity as a "directly placed" alternative for amalgamrestorations. An optimal formulation for any dental composite

material must possess two key elements of marginaladaptation and wear behaviour. The wear process in the

mouth can be categorized into Occlusal Contact Area (OCA)and Contact Free Area (CFA) wear. OCA wear is a result of

sliding wear caused by direct tooth contact during involuntary

grinding of teeth and indirect tooth contact during eating. CFAwear is caused by the suspension of food and water duringeating and tooth brushing. OCA wear of composites may be

three to five times greater than CFA wear.

Figure 1: The compression-sliding wear instrumentation.The wear of commercial dental composites was studied by ateam comprising staff from the Department of Restorative

Dentistry and Centre for Biomedical Materials Applications and

http://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htm

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Technology (BIOMAT), Faculty of Engineering. By employing

an integrated biological and engineering approach, the

scientists have designed a CFA wear apparatus and an OCAwear instrument (Figure 1) that controls contact stress, wear

environment and the number of contact cycles. Theresearchers defined and evaluated the different variables that

could influence wear, and looked at their effects on severalcommercial composite restoratives, using a dental amalgam

for comparison. They found that increased contact stress andcyclic loading resulted in greater OCA wear. At low contact

stresses the composites generally showed abrasive wear and

filler dislodgement due to preferential loss of the resin matrix(Figure 2). At higher contact stresses, possible cohesive failure

(i.e., failure within the body of the composite) of the resin

matrix occurred subsequent to micro-crack formation as fillerstransmitted forces to the surrounding matrix. Conditioning andwear testing in water demonstrated the greatest wear. For all

materials, conditioning and wear testing in heptane (which

simulates butter, fatty meats and vegetable oils) resulted in

the least wear. The amalgam alloy and one mini-filledcomposite (average particle size from 0.1 to 1.0 micron)

exhibited fatigue wear mechanisms (Figure 3) with extendedwear testing. Although fatigue wear did not occur with themicro-filled composite (average particle size from 0.01 to 0.1

micron), extended wear testing resulted in deep and wide

micro-cracks (Figure 4) that may precipitate catastrophicfailure. The investigators did not observe a significantrelationship between the change in composite hardness and

OCA wear. Results of OCA wear were markedly different fromthose arising from CFA wear testing.

Figure 2 : Abrasive wear and filler dislodgement.

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Figure 3: Fatigue wear with deformed and delaminated layers.

Figure 4: Microcrack formation.The laboratory findings from this study on composite wear

gave an insight into the high data variance observed in many

previous clinical wear studies. This team of researchersbelieved that the standardization of variables for in-vivo wear

assessment will enable better data discrimination and avoidmisinterpretation.

[Previous|Main|Next]For any commments and suggestions, please feel free to emailA/Prof SB Keng

Faculty of DentistryNational University of Singapore

National University Hospital5 Lower Kent Ridge Road

Singapore 119074

Telephone : (65) 67724987Fascimile : (65) 67785742

http://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/FG2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/FG2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/FG2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/bfgrh2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/bfgrh2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/bfgrh2.htmmailto:rsdksb@nus.edu.sgmailto:rsdksb@nus.edu.sgmailto:rsdksb@nus.edu.sgmailto:rsdksb@nus.edu.sghttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/bfgrh2.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/rr2000_main.htmhttp://www.dentistry.nus.edu.sg/faculty/facpub/research%20report/FG2.htm