Award Date

December 2016

Degree Type


Degree Name

Master of Science (MS)


Dental Medicine

First Committee Member

Katherine Howard

Second Committee Member

Karl Kingsley

Third Committee Member

James Mah

Fourth Committee Member

Jennifer Pharr

Number of Pages



Retention is required in the majority of orthodontic patients throughout the remainder of their life. The traditional Hawley style retainer is still considered by many orthodontic professionals to be the gold standard in retention appliances. The orthodontic population, in general, is at a higher risk for caries due to plaque accumulation from poor diet, suboptimal oral hygiene, and often a lack of motivation. A Hawley retainer that reduces caries-causing oral microbes could improve oral health and be very beneficial to the post-orthodontic patient. Developing methods to safely include antibacterial products within the Hawley retainer’s base plate material could help effect these improvements and prove to be an additional incentive for continued, regular wear of orthodontic retainers.

The oral bacteria most commonly associated with caries formation, Streptococcus mutans, was chosen to study its biofilm formation on polymethyl methacrylate (PMMA) that is used in the fabrication of traditional Hawley retainers. Biofilm formation was evaluated using a drip flow reactor system followed by staining, scanning electron microscopy (SEM) and morphology analysis. Growth was assessed on four material types: PMMA, PMMA with silver, PMMA with a novel antibacterial agent, CZ-99, and PMMA with silver and CZ-99.

SEM images were analyzed using a combination of software products including Fiji (Image J), Matlab and MountainMaps 3D generating software (Digital Surf) to determine percentage area coverage and compared between samples. PMMA that contained silver prevented biofilm growth to the greatest degree. However, although biofilm formation was more pronounced on PMMA infused with CZ-99 a combination of CZ-99 and silver, it was found that this was likely due to poor cross-linkage of the polymer that allowed the antimicrobials to elute out fully.

In conclusion, results demonstrated significant reduction in biofilm formation in silver infused PMMA. Outcomes provided a compelling argument that the drip flow system and materials could be investigated further to determine if antibacterial PMMA can be used safely in the oral environment and explore their effectiveness in reducing biofilm formation. Future work with in vivo testing would be particularly beneficial.


Antibacterial; Hawley; Polymethyl methacrylate; Retainer; Silver; Streptococcus Mutans



File Format


Degree Grantor

University of Nevada, Las Vegas




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