4 L.A. Casemiro et al.Table 2 Inhibition halos <strong>of</strong> the <strong>acrylic</strong> <strong>resins</strong> <strong>with</strong> incorporation <strong>of</strong> different percentages <strong>of</strong> Irgaguard B5000 silver–zinczeolite (values given in mean ± SD mms).Strains 0% 2.5% 5.0% 7.5% 10.0%Percentage <strong>of</strong> silver–zinc zeolite added to QC20C<strong>and</strong>ida albicans ATCC 28366 0.0 ± 0.0 12.3 ± 0.4 13.5 ± 0.7 15.49 ± 0.8 16.43 ± 0.7C<strong>and</strong>ida albicans (clinical isolate) 0.0 ± 0.0 11.6 ± 0.8 12.4 ± 0.4 14.74 ± 0.4 16.78 ± 0.2Streptococcus mutans ATCC 25175 0.0 ± 0.0 10.9 ± 0.3 11.7 ± 0.6 13.76 ± 0.8 15.65 ± 0.4Streptococcus mutans (clinical isolate) 0.0 ± 0.0 11.4 ± 0.8 14.1 ± 0.2 15.53 ± 0.7 16.03 ± 0.1Percentage <strong>of</strong> silver–zinc zeolite added to Lucitone 550C<strong>and</strong>ida albicans ATCC 28366 0.0 ± 0.0 11.5 ± 0.3 13.6 ± 0.4 14.3 ± 0.5 16.65 ± 0.9C<strong>and</strong>ida albicans (clinical isolate) 0.0 ± 0.0 10.7 ± 0.6 12.7 ± 0.3 14.8 ± 0.7 15.12 ± 0.1Streptococcus mutans ATCC 25175 0.0 ± 0.0 9.8 ± 0.8 10.3 ± 0.1 13.48 ± 0.4 15.76 ± 0.2Streptococcus mutans (clinical isolate) 0.0 ± 0.0 11.6 ± 0.4 13.5 ± 0.8 14.07 ± 0.3 16.32 ± 0.1Percentage <strong>of</strong> silver–zinc zeolite added to Onda-CrylC<strong>and</strong>ida albicans ATCC 28366 0.0 ± 0.0 9.12 ± 0.7 10.25 ± 0.5 12.52 ± 0.3 13.41 ± 0.7C<strong>and</strong>ida albicans (clinical isolate) 0.0 ± 0.0 10.44 ± 0.5 12.79 ± 0.6 13.21 ± 0.4 14.65 ± 0.6Streptococcus mutans ATCC 25175 0.0 ± 0.0 10.90 ± 0.9 11.28 ± 0.5 13.69 ± 0.1 15.97 ± 0.1Streptococcus mutans (clinical isolate) 0.0 ± 0.0 9.89 ± 0.2 11.69 ± 0.1 13.42 ± 0.2 15.70 ± 0.2Flexural strength (MPa)1251007550250QC20 Lucitone 550 Onda-CrylPercentage <strong>of</strong> Irgaguard B50000%2.5%5.0%7.50%10%Figure 1 Flexural strength test values <strong>of</strong> the <strong>acrylic</strong><strong>resins</strong> <strong>with</strong> incorporation <strong>of</strong> the different percentages <strong>of</strong>Irgaguard B5000 silver–zinc zeolite (values given inmean ± SD MPa).For QC20, the addition <strong>of</strong> zeolite in percentagesgreater than or equal to 2.5% resulted in decrease<strong>of</strong> flexural strength compared to the controlgroup (p < 0.05). No statistically significantdifferences (p > 0.05) were observed between thefollowing pairs <strong>of</strong> groups: 2.5% <strong>and</strong> 5%; 2.5%<strong>and</strong> 7.5%; 2.5% <strong>and</strong> 10%; 5% <strong>and</strong> 7.5%; 7.5%<strong>and</strong> 10%. For Lucitone 550 <strong>and</strong> QC20, theaddition <strong>of</strong> antimicrobial zeolite in any <strong>of</strong> thepercentages under study resulted in statisticallysignificant decrease <strong>of</strong> flexural strength(p < 0.05). Nevertheless, there were no significantdifferences (p > 0.05) between the groups <strong>with</strong>addition <strong>of</strong> 2.5% <strong>and</strong> 5% <strong>of</strong> zeolite or betweenthe groups <strong>with</strong> addition <strong>of</strong> 7.5% <strong>and</strong> 10% <strong>of</strong>zeolite. The incorporation <strong>of</strong> 2.5% <strong>of</strong> zeolite toOnda-Cryl did not yield statistically significantdecrease in flexural strength (p > 0.05). However,when a percentage <strong>of</strong> zeolite ‡5% was added tothe resin, there was decrease in flexural strengthwhen compared <strong>with</strong> the control group(p < 0.05). There was no significant differencebetween the groups to which 5% <strong>and</strong> 7.5% <strong>of</strong>zeolite had been added.Izod impact strengthImpact strength results are shown in Fig. 2. Comparedto the control groups, no statistically significantdifferences (p > 0.05) were observed betweenQC20 (0.4 ± 0.2 MPa) <strong>and</strong> Lucitone 550(0.4 ± 0.1 MPa). The other interactions [Lucitone550 X Onda-Cryl (0.3 ± 0.1 MPa) <strong>and</strong> QC20 XOnda-Cryl differed significantly (p < 0.05).The addition <strong>of</strong> 5%, 7.5% <strong>and</strong> 10% zeolite toQC20 decreased its impact strength (p < 0.05).There was no statistically significant difference(p > 0.05) between the control <strong>and</strong> the 2.5%Impact strength (MPa)0.50.40.30.20.10.0QC20 Lucitone 550 Onda-CrylPercentage <strong>of</strong> Irgaguard B50000%2.5%5.0%7.5%10.0%Figure 2 Impact strength values <strong>of</strong> the <strong>acrylic</strong> <strong>resins</strong><strong>with</strong> incorporation <strong>of</strong> the different percentages forIrgaguard V5000 silver–zinc zeolite (values given inmean ± SD MPa).Ó 2008 The Gerodontology Association <strong>and</strong> Blackwell Munksgaard Ltd, Gerodontology 2008; doi:10.1111/j.1741-2358.2007.00198.x
<strong>Antimicrobial</strong> <strong>acrylic</strong> <strong>resins</strong> 5group. Interactions among the groups that hadan addition <strong>of</strong> 2.5–10% <strong>of</strong> antimicrobial zeoliteshowed statistically significant differences (p 0.05). Onda-Cryl had its impact strengthdecreased <strong>with</strong> the addition <strong>of</strong> zeolite at percentages‡5% (p < 0.05). The control <strong>and</strong> 2.5% groupsdid not differ significantly (p > 0.05). The addition<strong>of</strong> zeolite in percentages from 2.5% to 10%resulted in no statistically significant difference inthe material strength.DiscussionThe addition <strong>of</strong> silver <strong>and</strong> zinc zeolites to heatpolymerised<strong>acrylic</strong> <strong>resins</strong> is consistent <strong>with</strong> thecurrent trend <strong>of</strong> incorporating antimicrobials intodental materials 8,10–20 . However, its feasibility isrelated to either maintenance or improvement <strong>of</strong>the material’s physical, <strong>mechanical</strong> <strong>and</strong> biological<strong>properties</strong>. This paper presents the results <strong>of</strong> antimicrobialactivity, flexural strength <strong>and</strong> impactstrength assays performed <strong>with</strong> heat-polymerised<strong>and</strong> micro-wave polymerised <strong>acrylic</strong> <strong>resins</strong> containingdifferent amounts <strong>of</strong> a silver–zinc zeolite.The impact strength <strong>and</strong> the flexural <strong>properties</strong> <strong>of</strong>denture base materials are <strong>of</strong> importance for predictingtheir clinical performance upon loading 49–51 .Other assays (sorption, solubility <strong>and</strong> elution <strong>of</strong>silver <strong>and</strong> zinc, assessment <strong>of</strong> the conversion degree<strong>and</strong> biocompatibility) are currently being conductedin our laboratory <strong>and</strong> will be submitted later forpublication.The control specimens (fabricated <strong>with</strong> noincorporation <strong>of</strong> zeolite), did not have antimicrobialactivity, which agrees <strong>with</strong> the results <strong>of</strong> previousstudies that report little or no antimicrobialactivity <strong>of</strong> the tested materials. The addition <strong>of</strong>2.5% <strong>of</strong> Irgaguard B5000 to QC20, Lucitone 550<strong>and</strong> Onda-Cryl <strong>resins</strong> was enough provide antimicrobialactivity against the test strains. The higherthe percentage <strong>of</strong> zeolite, the greater the antimicrobialactivity. The smallest inhibition halowere observed for the Onda-Cryl resin <strong>with</strong> 2.5%<strong>of</strong> zeolite against C. albicans ATCC (9.12 ± 0.7 mm),while the largest inhibition halos were observed forQC20 <strong>with</strong> 10% <strong>of</strong> zeolite against C. albicans clinicalisolate (16.78 ± 0.2 mm). These results may beattributed to silver <strong>and</strong> zinc (active elements <strong>of</strong>Irgaguard B5000), which leach out from the <strong>resins</strong>.Silver <strong>and</strong> zinc possess strong antibacterial <strong>and</strong>antifungal activity 13,14,20–26,29–35,39,42–45 . Thesefindings are similar to those reported by previousstudies that assessed the incorporation <strong>of</strong> zeolites<strong>and</strong> other antimicrobials into the tissue conditioners8,10–15,19 . Nevertheless, the antimicrobial activity<strong>of</strong> zeolites against other microorganisms involvedin denture stomatitis, a common condition amongdenture wearers 1–5 , should be investigated. Moreover,this study evaluated the short-term (7 days)antimicrobial activity <strong>of</strong> the materials <strong>and</strong> hencetheir long-term action should also be assessed.It is important to evaluate the <strong>mechanical</strong> <strong>properties</strong><strong>of</strong> <strong>acrylic</strong> <strong>resins</strong> containing zeolites becauseremovable <strong>and</strong> complete dentures are subjected torepeated flexural forces. Midline fractures are relatedto the flexural strength <strong>of</strong> the <strong>resins</strong>, <strong>and</strong> thisproperty is challenged every time the dentureundergoes cyclic functional deformation 49 . On theother h<strong>and</strong>, higher impact strength <strong>of</strong> the base<strong>resins</strong> reduces the possibility <strong>of</strong> fracturing when theprosthesis is dropped onto a hard surface 50,51 .Therefore, if the addition <strong>of</strong> zeolite results in asignificant decrease in the flexural <strong>and</strong> impactstrengths <strong>of</strong> <strong>acrylic</strong> <strong>resins</strong>, this may increase thepossibility <strong>of</strong> a fracture occurring inside or outsidethe oral cavity.Among the specimens fabricated <strong>with</strong> no addition<strong>of</strong> zeolite, Lucitone 550 controls showed thehighest flexural strength values while Onda-Crylcontrols showed the lowest but these were notsignificant. This may be attributed to the <strong>resins</strong>’compositions <strong>and</strong> polymerisation cycles, whichhave a direct influence on the <strong>mechanical</strong> <strong>properties</strong>51 . Short cycles, as for QC20, may result inincomplete polymerisation <strong>and</strong> the presence <strong>of</strong>residual monomer. The resulting plasticising effectreduces the molecular binding forces <strong>and</strong> allowsgreater deformation upon flexion 50,52 . The fact thatthe microwave-polymerised <strong>acrylic</strong> resin (Onda-Cryl) showed lower flexural strength than thewater-bath-polymerised <strong>resins</strong> (QC20 <strong>and</strong> Lucitone550) is consistent <strong>with</strong> those <strong>of</strong> previous studies 51 .A significant decrease <strong>of</strong> flexural strength incomparison to the control groups, was observed<strong>with</strong> the addition <strong>of</strong> 2.5% <strong>of</strong> zeolite to QC20 <strong>and</strong>Lucitone 550, as well as the addition <strong>of</strong> 5% <strong>of</strong>zeolite to Onda-Cryl (p < 0.05). The decrease <strong>of</strong>flexural strength values is in agreement <strong>with</strong> theresults <strong>of</strong> Addy <strong>and</strong> H<strong>and</strong>lery 53 , who reported thatthe addition <strong>of</strong> a similar agent to methacrylatesnegatively affected their <strong>mechanical</strong> <strong>properties</strong>.However, it is important to realise that the flexuralstrength values obtained for those samples wherethe percentage was 5% or below were in accordanceto ISO 1567, that is 65MPa.Ó 2008 The Gerodontology Association <strong>and</strong> Blackwell Munksgaard Ltd, Gerodontology 2008; doi:10.1111/j.1741-2358.2007.00198.x
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