Circuit 2, station 1

In the UK, nearly one in five adults wear dentures, and this prevalence increases with age.

Dentures consist of two main components: the denture base and denture teeth. Various materials are used for the denture base, including acrylic (polymethylmethacrylate [PMMA]), metal alloys like cobalt-chromium, and polymers such as nylon-based thermoplastic resins, polyether ether ketone, and aryl ketone polymer. Among these, heat-cured PMMA is the most commonly employed denture base material. However, it is porous, non-shedding, and tends to accumulate denture plaque. 

Denture teeth can be fabricated from acrylic, composite resin, or porcelain, providing smoother surfaces. Nonetheless, denture plaque can accumulate at the ‘tooth-gingivae’ interface, which represents the junction between denture teeth and the pink resin of the denture, simulating gingival tissue.

Denture plaque harbours pathogenic microorganisms, including Candida albicans (associated with denture stomatitis) and Streptococcus mutans (linked to caries development). Methicillin-resistant Staphylococcus aureus has been isolated from denture patients, raising concerns about cross-contamination or infection during denture handling. Poor denture hygiene is prevalent due to inadequate knowledge of proper cleaning techniques and a lack of standardised denture hygiene assessments by dentists. This leads to increased risks of dental caries, periodontal disease, denture stomatitis, and halitosis.

Improper denture care can negatively affect clinical longevity and promote denture plaque buildup. For instance, incorrect brushing techniques, such as using a hard brush, can lead to microbial growth, while inappropriate denture cleaner use may permanently damage the denture. Educating patients about denture base/tooth materials and proper cleaning methods can enhance denture hygiene. The dental team is well-suited to provide this education.

This paper offers insights into key legislation, current and future denture care and hygiene methods, and their compatibility with existing denture materials. It also provides recommendations based on denture material types. The Denture Cleanliness Index (DCI) enables a quick evaluation of denture hygiene, grading severity semi-quantitatively based on staining on the denture’s fitting surface. Dentists and dental care professionals can use DCI scores, which range from 0 (best) to 4 (worst) and follow specific criteria.

To use the DCI, the patient’s denture is first rinsed gently under cold water to remove loose debris. Then, a liquid plaque disclosing dye is applied to the entire denture fit surface. After 30 seconds, excess dye is rinsed off, and the fitting surface is visually inspected to assign a DCI score. For patients with both maxillary and mandibular dentures, individual DCI scores are recorded, and the worst score becomes the overall DCI score for the patient.

Regarding denture hygiene, there are two primary methods: mechanical and chemical. It is recommended that patients utilise a combination of both for optimal denture plaque removal.

Mechanical methods include the use of manual brushing or vibrational-based cleaning aids, such as ultrasonic or sonic baths. Regular toothbrushes with soap and water are commonly used for manual cleaning, but proprietary denture brushes and mechanical cleaning adjuncts are preferable to reduce the risk of scratching, which can lead to biofilm accumulation and reduce denture longevity. While normal handwashing or dishwashing soap is popular for use with a denture or toothbrush, they may lack antimicrobial properties found in specially formulated denture cleaning agents. There are also adjuncts like pastes, gels, foams, or powders designed to enhance manual cleaning methods.

The choice between using a denture brush or a regular soft-bristled toothbrush should be made based on individual patient considerations, including factors like manual dexterity, ease of use, and accessibility for cleaning their specific denture.

Vibration-based cleaning baths are categorised into two types based on the frequency of vibrations: ultrasonic and sonic. These cleaning baths can be used with a specialised chemical cleaner provided by the manufacturer or with distilled or tap water.

Ultrasonic cleaning bath: Ultrasonic cleaning systems operate within a frequency range of 20-60 kHz. The vibrational energy generated induces cavitation, where bubbles form, collide, and implode on the denture surface, dislodging debris. Ultrasonic baths exhibit superior debris removal capabilities and are compatible with most denture material types. However, their relatively high cost may limit their widespread use by patients.

Sonic cleaning bath: Sonic cleaning baths operate at a lower frequency range, typically below 10 KHz, often around 6.5 KHz. They produce bubbles similar to ultrasonic baths but are less effective in cleaning dentures due to their lower vibrational energy output. While these units are more cost-effective, there may still be some cost implications due to battery usage.

Chemical methods involve the use of denture cleaning chemicals specifically formulated for disinfecting oral prostheses. It is crucial to emphasise that these chemicals must only be used outside the patient’s mouth to prevent harm. These chemicals can be categorised based on their chemistry and mode of action:

1. Bleach-based denture cleaners: These cleaners contain sodium hypochlorite at concentrations of 1.5% or 2% w/v and/or sodium hydroxide at 1.7% w/v. They offer broad-spectrum antimicrobial capabilities. The action of sodium hypochlorite is attributed to the dissociation of hydroxyl (OH-) and chloride (Cl-) ions in water, leading to the dissolution of microbial cell walls, mucins, lipid degradation, and enzymatic inactivation. These cleaners can be used for short durations (typically 10-20 minutes) or for overnight disinfection, as per the manufacturer’s instructions. The risk of acrylic discoloration and degradation of metal-based components is associated with these cleaners, depending on concentration and immersion duration.
2. Effervescent-type denture cleaners: Effervescent tablets contain oxidants like sodium bicarbonate, sodium percarbonate, and sodium persulphate, which release carbon dioxide bubbles when dissolved in water. Hydrogen peroxide-containing cleaners release oxygen. Sodium lauryl-sulphate, a commonly added detergent, aids in biofilm disruption and cleaning efficacy. These cleaners are less effective against microbes compared to bleach-based cleaners but are safe for metallic dentures. However, they should be avoided with dentures containing chairside or laboratory-fabricated acrylic reline materials, as they can degrade these lining materials over time.
3. Mineral acid-based denture cleaners: These cleaners, containing hydrochloric or phosphoric acids, are used infrequently in the UK but are more popular internationally. They dissolve calcified biofilm deposits and microbial cell membranes in organic biofilms. However, they are contraindicated for metal alloy-based dentures, as they cause tarnishing and corrosion of metallic components.
4. Enzyme-based denture cleaners: These cleaners are rarely used in the UK and are similar in composition to effervescent-type cleaners but also contain enzymes like lipases, amylases, and proteases. They are designed to degrade fats, glycoproteins, and proteinaceous organic matter, contributing to their antimicrobial activity. They are primarily used with dentures that have soft reline materials and have shown limited adverse effects on common denture reline materials.
5. Oral rinses: Oral rinses encompass mouthwash products such as 0.2% chlorhexidine gluconate, 0.05% salicylate solution, and phenolic-based mouthwashes like Listerine. While they are marketed for use as mouthwashes, they are also employed for denture cleaning. However, their antimicrobial properties vary widely. Chlorhexidine-based mouthwashes are commonly used and recommended for oncology patients with oral prostheses, with various concentrations demonstrating significant antimicrobial activity. Prolonged use of chlorhexidine solutions can stain dentures similar to natural teeth.
6. Flexible denture cleaners: Flexible dentures are made from thermoplastic polyamide resins, like nylon, and offer enhanced patient comfort and metal-free construction compared to traditional denture materials. Manufacturers of these dentures provide specific cleaning systems, including a specialised denture brush and chemical cleaning agent. The use of alternative denture cleaners may void the manufacturer’s warranty. Most flexible dentures are cleaned using effervescent-type denture cleaners, which are formulated similarly to other effervescent cleaners. It’s essential to follow the manufacturer’s instructions for cleaning these dentures.

Polymer-based dentures: There is limited research on the compatibility of conventional denture cleaning methods with new polymer denture materials (aryl ketone polymer-based dentures). Manufacturers have reported that these materials are compatible with existing denture care products and methods, but it is advised to follow the manufacturer’s instructions when using them.

Resilient denture-reline materials and tissue conditioners: Resilient denture liners can be either plasticised acrylic resin-based or silicone elastomer-based. Their compatibility with denture cleaners varies. Plasticised acrylic resin-based liners may harden after shorter immersion periods in bleach-based and effervescent-type cleaners compared to silicone elastomer-based liners. Silicone elastomer-based liners are more compatible with these cleaners. However, the instructions provided by the manufacturer should always be followed to ensure compatibility.

Alternative approaches to denture cleaning and disinfection: There are other methods of denture cleaning worth considering, particularly for patients who may have limitations with mechanical or chemical cleaning methods as described earlier.

Microwave Irradiation: Microwave irradiation for disinfecting dentures was initially proposed in 1985 by Rohrer and Bulard. This technique involves placing a denture in a bowl of tap water and heating it using a standard domestic microwave oven. However, there is currently no agreed-upon or standardised methodology for using this method to clean dentures. Various approaches have been reported, such as immersing dentures in tap water before microwaving or microwaving dry dentures. Microwave irradiation has demonstrated the ability to eliminate microorganisms on the surface of denture acrylic, including Candida albicans and Pseudomonas aeruginosa. Nevertheless, the use of microwave irradiation for denture disinfection remains a topic of debate and should not be recommended as a primary cleaning method over more established and reliable techniques.

Antibacterial Denture Wipes: These innovative denture cleaning wipes are infused with antibacterial cleaning solutions. They are designed for discreet denture cleaning when standard mechanical and chemical methods are impractical or unavailable. They complement traditional denture cleaning methods and have been well-tolerated by users, with no reported oral or skin reactions. Users have reported improvements in their quality of life and social confidence when using denture wipes. While studies have not yet compared the antimicrobial efficacy of these wipes to standard chemical cleaning methods like bleach-based or effervescent solutions, it is known that they offer superior antimicrobial activity compared to simply wiping with a dry tissue.

Impact of Inadequate Denture Hygiene: There is a significant relationship between patients’ knowledge of denture care and the quality of their denture hygiene. Studies have shown that patients who did not receive information on denture hygiene and care demonstrated good denture care in only 16% of cases.

In partial denture wearers, the quality of denture cleaning is proportionally related to the frequency of cleaning remaining natural teeth. Research has indicated that 92% of individuals with poor denture hygiene also exhibit equally poor levels of oral hygiene. Wearing removable partial dentures does not increase the risk of periodontal diseases, provided that pre-prosthetic periodontal health was optimal, and proper oral and denture hygiene habits are maintained. Therefore, in partially dentate individuals, there is an elevated incidence of dental caries and gingival diseases among those with poor denture and oral hygiene. In both complete and partial denture wearers, there is an increased risk of denture-related stomatitis, particularly in those with inadequate denture hygiene.

Denture-related stomatitis is characterised by chronic inflammation of the oral mucosa with a multifactorial aetiology, including poor denture hygiene, reduced salivary flow, and ill-fitting prostheses. The presence of Candida albicans on the denture surface and in contact with the oral mucosa, plays a pivotal role in its development. Denture stomatitis has a significant clinical impact and can negatively affect the quality of life of denture wearers, manifesting with clinical signs like redness and swelling of the palatal mucosa and self-reported symptoms such as altered taste and a burning sensation. However, in patients with optimal denture hygiene, the incidence and recurrence of denture stomatitis are significantly reduced.