Oral Biofilm Formation and Management on Dental Materials

Abstract

Oral biofilms readily form and grow on both natural and artificial surfaces in the mouth and are major contributors to dental caries, periodontal disease and prosthetic infections. Dental materials such as hydroxyapatite (HA), polymethyl methacrylate (PMMA) and stainless steel (SS), representing enamel, denture bases and orthodontic appliances respectively, are regularly exposed to microbial colonisation. Surface roughness and wettability affect microbial adhesion and biofilm formation; however, these influences are often masked in vivo due to the rapid formation of a salivary pellicle. Most previous studies have focussed on individual materials in isolation, often under simplified or non-comparable microbial conditions.
To address these limitations, this study conducted a direct comparison of biofilm formation on HA, PMMA and SS, using a saliva derived inoculum under pellicle free conditions. The absence of a salivary pellicle allowed evaluation of intrinsic material biofilm interactions without interference from biological surface modification. Biofilm development was assessed under two clinically relevant conditions, static anaerobic (non-shear) and dynamic aerobic conditions (shear), simulating both supragingival/appliance and subgingival/prosthetic niches.
Results showed that surface roughness had the strongest influence under shear stress with rough, hydrophilic HA (Ra = 2.99 μm) exhibiting the highest initial attachment and growth in dynamic conditions. PMMA, the most hydrophobic material, showed low initial attachment but the greatest biofilm increase in the static model. SS, the smoothest and intermediately wettable surface, supported moderate early growth and the highest final biomass under static conditions. Environmental conditions significantly modulated these trends; even smooth, hydrophilic SS supported biofilm accumulation under anaerobic conditions. Each material supported distinct microbial communities, suggesting that surface characteristics influence material specific colonisation.
In addition to differences in biofilm growth, microbial community analysis showed that biofilms on material surfaces exhibited lower alpha diversity than the bulk inoculum, reflecting selective pressures from surface roughness, wettability and chemical composition. HA supported higher alpha diversity than PMMA or SS, likely due to its rough, chemically favourable microtopography. Beta diversity (PCoA) revealed distinct microbial clustering by material. Taxonomically, HA surfaces promoted mid to late colonisers such as Fusobacterium, Pseudoramibacter and Megasphaera suggesting biofilm maturation. PMMA favoured anaerobes linked to denture plaque and stomatitis (Raoultella, Leptotrichia, Fusobacterium), while SS supported facultative anaerobes and
microaerophiles (Campylobacter, Citrobacter), likely driven by surface energy and oxygen diffusion dynamics.
Recognising the clinical challenge posed by these biofilm accumulations, particularly on denture surfaces exposed to limited salivary flow, the study then evaluated various biofilm removal strategies. Using high resolution X-ray computed tomography (XCT), the study quantitatively assessed and compared the effectiveness of manual brushing, chemical cleansers, ultrasonic cleaning and their combinations in removing Klebsiella pneumoniae biofilm from denture surfaces. The combination of ultrasonic bath and cleanser achieved the highest biofilm reduction (98.26%), outperforming other methods, especially in hard-to-reach areas.
These findings emphasise the importance of accounting both material properties and clinical environment when designing biofilm- resistant dental materials and highlight the value of integrated mechanical and chemical cleaning strategies for effective denture hygiene. The novel pellicle- free, multi- material model and advanced imaging approach presented here provide a strong foundation for future biomaterials research and clinical applications
Key words: Oral biofilms, dental materials, surface roughness, wettability, microbial diversity, X-ray computer tomography (XCT), biofilm removal, dynamic and static biofilm models

Date of Award	8 May 2026
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Marta Roldo (Supervisor) & Martino Pani (Supervisor)