Reduced saliva, dry mouth, can be caused by a number of factors including age, medications, auto-immune diseases such as Sjogren’s syndrome, and cancer treatment. This can be incredibly debilitating, affecting quality of life as the simple act of salivary lubrication allows us to speak and eat comfortably.
Take these away and our normal social interactions are inhibited. Saliva is critical for buffering of pH, promoting remineralisation and stabilising the oral microbiome. Disruption of healthy quality and quantities of saliva changes the niche oral microbiomes, which can lead to “dysbiosis” with impacts on teeth, gingiva, oral mucosa and an increased potential for opportunistic infection such as candidiasis or acute bacterial sialadenitis with swelling in the salivary glands.
Intraorally, the tongue can have a beefy red appearance with loss of papillae or deep fissures. The mucosa can appear erythematous and the lips may be dried and sore with angular cheilitis. Clinically, this means dental procedures can be uncomfortable and challenging, increasing the compromise of dental health. Therefore, creating a positive oral environment is crucial to long term management of our patients where all aspects of dental therapy are affected by hyposalivation.
What are the dental considerations when we treat someone with reduced saliva?
Microbiome, biofilm and tissue susceptibility, dental caries, restorative management, minimally invasive dentistry, salivary stimulants and substitutes. Choice of materials for caries, denture care, implant care, periodontal considerations.
Microbiome, biofilm and tissue susceptibility:
If we look at our historic literature, we often characterise dental plaque as an evil to be eradicated. However, it is a natural microbial biofilm and the microorganism composition remains relatively stable due to the balance of our host immune defenses and the commensal microbial interactions.
This microbiome is protective of the underlying hard and soft tissues but hyposalivation and a diet containing sugar will compromise the homeostasis leading to dysbiosis and disease. Studies have shown that with reduced saliva there is a shift in the microbial composition of supragingival plaque, with a marked increase in Lactobacillus and Candida albicans in irradiated head and neck cancer patients and increased Streptococcus mutans in Sjogren’s patients.
This means the pH of the plaque changes, favouring a more cariogenic biofilm of plaque on teeth. As roots become exposed this provides a different niche for microbiome colonization. In root caries the predominant aciduric bacteria were found to be Actinomycetes, Lactobacillus and Candida species. On the tongue and mucous membranes there was also an increase of Candida albicans, Staphlococcus aureus, enterics and enterocci. This can therefore lead to commonly noted signs of inflammation, soreness and halitosis.
However, in studies of patients with hyposalivation there were not found to be an increase in the common periodontal pathogens. In subgingival niches, species of non-oral bacteria were at a higher level than in healthy subjects. An understanding that our mouth requires a healthy microbiome, mycobiome and virome is important in our holistic approach to treating our patients. Simply wiping out all organisms is not sustainable and promoting our core commensals is crucial for prevention of caries, opportunistic infections and probably periodontal health too.
Dental caries and dry mouth:
Reduced saliva can lead to caries on smooth surfaces of teeth that are not usually susceptible. Since the demographic of patients affected by dry mouth are usually over 50 years old, they may have suffered from gingival recession, and it is not surprising that tooth-loss in this group is twice that of individuals with normal salivary rates. The rapid spread of root caries makes restorative dentistry particularly challenging with a patchwork of restorations common leading to secondary caries and subsequent “tooth death spiral” with extractions as a result.
Secondary caries is more common on root surfaces, whether that be around amalgam, glass ionomer or composite, as the pH level that caries begins in dentine (pH 6.5) is higher than on enamel (pH 5.5). Improving the buffering capacity of the oral environment and remineralisation potential is key to caries prevention and maintaining teeth. This concept is captured in the ecological plaque hypothesis that allows us to visualise ways to reverse the cycle of caries and clinically leads the minimal invasive dentistry concept.
Restorative management for dry mouth:
Minimally invasive dentistry:
The prevention key steps are plaque removal, excellent oral hygiene, dietary advice, ﬂuoride applications, salivary stimulants (if there is residual salivary capacity) or salivary replacements and rehydration if not. Fluoride leads to deposition of calcium ﬂuoride on the enamel surface and this reservoir of ﬂuoride aids remineralisation in low pH conditions. It also modiﬁes plaque metabolism reducing acid production and thereby acidophilic bacteria in plaque. High dose ﬂuoride and varnishes are recommended. Sipping water is often preferred by many patients to overcome the symptoms of hyposalivation. This can be augmented with chewing gum or sugar free lozenges.
Some find they cannot drink large amounts of water as this can complicate other medical conditions or cause discomfort with frequent trips to the toilet. In these people salivary substitutes can be recommended, but there is no strong clinical evidence for the efficacy of saliva substitutes or their superiority over water and in studies most preferred chewing gum to artificial saliva. These products are oft en found as sprays, mouthwash, or gels but some care is needed in recommending them as some have low pH or sugar as ingredients – not ideal for anyone who still has their natural dentition!
Choice of restorative materials for caries with dry mouth:
Hyposalivation patients are susceptible to caries. When minimally invasive remineralisation approaches are not viable and smoothing and recontouring is not possible then restoration becomes necessary. The extent and position of the lesion will drive the restoration choice. Because of the harsh challenges of the oral environment many of these restorations will break down due to secondary caries, with over half of all restorative therapies being replacement restorations. The most common region for secondary caries to occur is on dentine, at the gingival margin, irrespective of the restorative material.
An excellent study of 71 hyposalivation patients published this year from multiple clinical practices in Finland found composite restorations survived longer than glass ionomer restorations, whereas in control healthy patients the survival of the two materials were similar. However, composite restorations were twice as likely to fail in hyposalivation patients compared to healthy patients, which demonstrates
the challenges that lack of saliva creates.
Composite bonded restorations and dry mouth:
With composite bonded restorations failure is more likely on the dentine surface due to the reduced bond strength of adhesives to dentine compared with enamel. Over time composite age with shrinkage and microleakage, particularly under repeated loading. Monomer release has been shown to attract Streptococcus mutans rich bioﬁlm. The composite can become roughened under acidic bioﬁlms, increasing the potential for further plaque retention and secondary caries. Composite bonding agents have excellent early bond strengths, however over time this decreases. Acids from bacteria or from phosphoric acid in the total etch technique on the dentine as well as the enamel surface can activate enzymes (proteases) that diminish the dentine bond strength. This degradation of the bond is so concerning that techniques and modifications to the adhesives have been trialed to inhibit the enzymes that breakdown dentine collagen (MMP inhibitors).
Fluoride, chlorhexidine and a specific part of the green tea extract (EGCG) have been shown to inhibit the enzymes that breakdown dentine collagen. In patients that suffer from bulimia there has been a demonstrated increase in proteases in their saliva that can be linked to greater tooth erosion. Inhibition of these enzymes with chlorhexidine or green tea extract have been shown to decrease dentine loss by 30 to 40 per cent in erosion challenges and maintenance of dentine structure improves the potential to remineralise dentine and prevent breakdown of the adhesive bond of composite to dentine surfaces.
Recognition of early failure of complex restorations in patients that suffer from hyposalivation was the inspiration for Dr Heff’s Remarkable Mints. This sugar-free lozenge is recommended for use throughout the day and tips the balance towards a favourable oral microbiome by diminishing Streptococcus mutans, neutralising acids and improving remineralisation with stimulation of saliva by the simple combination of ingredients: xylitol, green tea extract and calcium phosphate. The Remarkable Mints have been shown to improve remineralisation of carious dentine as it contains EGCG green tea extract, and this is likely due to the inhibition of proteases as well as the remineralising potential of the calcium phosphate and the anti-caries effects of xylitol.
Resin modified glass ionomer:
Resin modified glass ionomer has superior physical properties to glass ionomer cement, which has a greater tendency to deteriorate in acidic conditions. Both release fluoride, and the fluoride reservoirs can be “recharged” with high dose fluoride toothpastes and varnishes inhibiting S. mutans and Lactobacillus, however this effect is questioned and maybe limited by the thickness of biofilm on the surface in a clinical setting.
Compared with composite, glass ionomer restorations tend to be less aesthetic and have poorer success rates in clinical practice in hyposalivation patients, however, this might be due to a bias to choose glass ionomer over composite when a tooth is less easy to restore with subgingival margins and compromised moisture control.
Amalgam and dry mouth:
In patients with large cavities and poor oral hygiene, amalgam has a better longevity than composite, with composite failing through secondary caries. However, amalgam does not bond to the tooth and requires physical undercuts to retain, making it potentially more destructive to tooth substance. Restored amalgam shows lower colonization with S. mutans than composite but the biofilm can cause a drop in pH, and this leads to increased corrosion products being produced in the form of metal ions of mercury, copper, silver and zinc. These metal ions have antimicrobial properties; however, it is debatable whether patients would appreciate the release of some of these ions as an antimicrobial benefit!
Clinical recommendations for restorative materials:
Preparation of both enamel and dentine removes the biofilm and this can help bonding strengths. Etching the enamel with phosphoric acid has been shown to be very effective at creating long term successful composite restorations. However, dentine is more susceptible to acids, which can initiate enzymes that degrade dentine and compromise dentine bonding of adhesives. Therefore, avoiding acids on dentine during bonding is preferrable, including sclerotic dentine. For all materials surface roughness allows greater accumumlation of biofilm that further damages the surface in a vicious circle. So, polishing a restorative material to a smooth finish is really key to limiting the impacts of thick biofilm accumulation. Nanoparticle-sized composites appear to be more resistant to degradation by biofilms.
Some restorative materials have been created with the idea of releasing antimicrobial or other agents to repair teeth. However, this effect typically diminishes over time and previous attempts often show compromised clinical properties. Therefore, correcting/improving the oral environment is probably a more predictable solution than trying to have a restoration that continues to irradicate microbes. The ability of dentin bonding agents to provide a good seal and stable adhesion to tooth substrates is one of the primary requirements for the durability of tooth-coloured restorations (Reis et al., 2008). Formation of a resin-infiltrated hybrid layer composed of collagen fibrils embedded by methacrylate-based resins contributes to adhesion (Breschi et al., 2010a). However, despite successful immediate bonding, longevity of the adhesive interface remains questionable because of physical and chemical factors challenging the adhesive interface (Breschiet al., 2010b). Universal adhesives represent the last generation of adhesives in the market.
Although they are designed under the all-in-one concept of existing one-step self-etch adhesives, it is possible to use them in the etch-and-rinse mode. In theory, degradation of the adhesive–dentin interface should not occur when water within the intra- and interﬁbrillar compartments of a collagen matrix is completely replaced by resin (Sadek et al., 2010). However, the hydrophilic nature of self-etch systems and the poor inﬁltration capacity of etch-and-rinse resins into collagen can impair the covering step. Collagen ﬁbrils poorly encapsulated by resin can be slowly hydrolysed by endogenous matrix metalloproteinases (MMPs) (Mazzoni et al., 2006).
Unfortunately, patients with hyposalivation are twice as likely to suffer tooth loss and need dentures. Tooth-loss and reduced saliva complicate denture retention affecting mastication, speech and self-image. Patients’ mucosa can become sore and irritated with candidiasis infection in up to 70 percent of denture wearers as well as increased S. mutans in partially dentate. Candida on dentures have been linked with systemic Candida infections in immunocompromised patients and possible reservoir for respiratory infections or MRSA. Candida starts off as budding yeast cells which begin to ﬁlament after four hours and form hyphae after eight hours. The formation of hyphae increases the adhesion and survival of more Candida species on dentures, becoming more resistant to bioﬁlm removal. Rough denture surfaces increased the adherence and accumulation of Candida albicans. The release of monomers from the surface also encourages the buildup of high bioﬁlm formation.
All patients should remove the dentures at night and mechanical cleaning of the denture is important to disturb the bioﬁlm and remove Candida albicans. Chemical cleaning is also possible with peroxides, hypochlorites and chlorhexidine. However, there is a risk of discolouration and different denture materials react differently to chemical agents, so it is important for individual guidance on denture care dependent on the materials used. Some patients can be overly diligent and excessive scrubbing, including abrasive cleaners, will roughen the surface favouring further bioﬁlm formation. Denture wearers do not often get on so well with chewing gum, so hyposalivation patients might be recommended salivary stimulants and substitutes that contain green tea extract as the lozenge can be sucked rather than chewed. Green tea extract has been shown to decrease S. mutans and Candida albicans improving the oral environment.
Implant care for dry mouth:
Implant retained prostheses have been recommended to overcome the issues of conventional dentures and susceptibility to caries in hyposalivation patients. They are shown to be successful and well accepted in Sjogren’s syndrome patients. (1) However, implants are not without concern too. Failure rates of implants in the edentulous maxilla have been reported to be greater than in the mandible, with a reported higher failure rate of osseointegration (about 16 per cent) in the eight edentulous Sjogren’s syndrome patients included in the study. They cautioned against attributing this to Sjogren’s since the study population was small. (15) Therefore, restoration of the teeth in a minimally invasive approach is appropriate rather than early extraction of teeth in favour of implants.
Periodontal disease and dry mouth:
Hyposalivation patients include a large group of causes including the side effects of polypharmacy, autoimmune conditions and as a consequence of cancer therapy, therefore risks of periodontal disease may be more from the patient’s genetic background and lifestyle choices such as smoking tobacco.
The greater loss of teeth found in Sjogren’s patients appear to be largely due to the susceptibility to caries rather than an increased risk of periodontal disease. However, the impacts of decreased saliva are likely to change the periodontal health and it is possible that the lack of deﬁnitive studies to show a greater risk of periodontal disease in Sjogren’s syndrome is only due to the small number and sample size of studies. In one case control study of Sjogren’s and healthy controls it was reported that Sjogrens patients were 2.2 times more likely to have higher bone loss with greater plaque scores and gingival recession despite carrying out more oral hygiene than the healthy controls.
Given that 45 per cent of the adult UK population suffers from periodontal disease, then greater management in the hyposalivation demographic will be inevitable. Plaque control remains essential and removal of plaque traps (which are more likely because of the patched restorations) are simple clinical recommendations.
Regular and frequent reviews are required for patients suffering from hyposalivation. Reviews should monitor oral hygiene and reinforce dietary advice, fluoride and xylitol compliance. Maintaining teeth is recommended, if possible, as they provide greater proprioception than implants and dentures. Implant success rates are likely to be lower in hyposalivation patients where the alternative of complete dentures is poorly tolerated.
References on request.
Original article was published in Dental Therapy Update, Vol 14, Issue 4, 2021.
Michael Heffernan is a Specialist Prosthodontist and co-founder of Dr. Heff’s Remarkable Mints.