The wearing of removable partial dentures can result in an increased risk of the occurrence of problems such as caries on the remaining dentition, principally because the dentures can hamper the  application of adequate oral hygiene procedures. This article reviews the potential problems associated with removable partial dentures, describes the various preventative actions that can be taken and highlights the importance of the patient being made aware of the need for adequate oral hygiene procedures.

By Dr C. van Loveren

Removable partial dentures may endanger the health of remaining dentition by, for example, increasing the risk of caries, of periodontal disease, of luxation by forces on the abutment teeth and of mucositis. It was found that 60% of non-crowned abutment teeth had to undergo re-treatment or extraction five years after the placement of a partial denture, with the figure rising to 80 % of abutment teeth needing to be re-treated or extracted after ten years [1]. The periodontal health of patients not wearing their removable partial dentures was better than that of patients who did wear them [2]. A frequently cited reason for the poor oral health of patients with removable partial dentures is the close contact between the connectors and the gingiva and teeth, which creates plaque retention areas. There are however also other frequently reported reasons for the failure of removable partial dentures. Yeung et al showed that 50% of the population they studied no longer wore their removable partial dentures. The most frequent complaints were discomfort, reduced chewing abilities, food impaction and poor esthetics [3].

Nevertheless it is possible to wear removable partial dentures without any negative complications for the oral health of the wearer [4]. Prerequisites for such positive outcomes are the initial diagnosis and elimination of existing risks of caries and periodontal disease, and the treatment and elimination of existing health problems. Other factors are a suitable preventive initial design of the denture and, if necessary, subsequent improvement of the fit of the dentures as well as focussed after care and checkups. The dentist should also always ascertain that the patients have an satisfactory oral health status while removable partial dentures are being worn [5]. In this article the prevention of plaque-related diseases connected with the wearing of removable partial dentures is discussed.

An open hygienic design prevents plaque accumulation
The results of a European consensus meeting of prosthetic dentists indicated that removable partial dentures should have an open accessible design, which avoids plaque retention sites, and close contact with remaining teeth and gingiva [6]. As a general rule, the design of removable partial dentures should be as simple as possible with denture bases, major connectors and minor connectors avoiding contact with the free gingiva and contacting the alveolar ridge or the palate at least 3 mm away from tooth surfaces [7]. Spiekermann and Gründler emphasised that clasps should be placed as far as possible from gingival margins and that the number of minor connectors should be kept to a minimum [8]. They suggested direct minor connectors approaching from the base areas, with open proximal spaces, instead of palatally- or lingually-approaching minor connectors. The also suggested that gingival relief could be further achieved by designing the first replacement tooth of a base as a pontic. Minor connectors should be designed around the lingual aspect of the abutment tooth and onto the next tooth, thus avoiding the need to cross the gingival margin [7].

Selfcare
The patient plays an important role in the success of removable partial dentures. A well-designed denture, which enables the patient to adequately clean the dentition with a fluoride toothpaste, often results in problems being avoided, but this is frequently quite difficult. For example, the reason that removable partial dentures were needed in the first place is often related to prior inadequate oral hygiene. Without a solution to this basic problem and without ensuring a subsequent adequate level of oral hygiene, removable partial dentures may even be contra-indicated. In addition, even if the status of oral hygiene is adequate at the time the denture is first used, the quality of the oral hygiene may deteriorate as the patient gets older [9]. The oral hygiene should therefore be checked regularly. Likewise, the patients should continuously be encouraged and motivated to maintain an adequate level of oral hygiene.

Additional selfcare
If further preventive measurements are indicated, daily topical use of fluoride by brushing or rinsing should be a first option. The choice between brushing and rinsing depends on likely compliance and cost-efficiency. Additional brushing may prevent caries and improve gingival health. If rinsing is indicated, a choice should be made between the use of fluoride for caries prevention or antimicrobials to improve gingival health or a combination of both. Antimicrobial rinses without fluoride do not contribute to caries prevention [10, 11]. In the case of removable partial dentures, an oral rinse to prevent both caries and gingival inflammation seems the logical choice. Ideally the oral rinse should contain approximately 250 ppm fluoride for caries prevention on crown and root surfaces as well as an effective antimicrobial [12]. One such product is Corsodyl Daily Defence that contains 228 ppm fluoride and 0,06% chlorhexidine. Alternative possibilities are products (both toothpastes and rinses) containing stannous fluoride or oral rinses with fluoride and essential oils [13, 14, 15]. Of course such products were not developed specifically for use with removable partial dentures and have not been tested in this particular context. It is thus not clear to what extent positive results from the use of such products may apply to patients wearing dentures. The dental professional should therefore check on an individual basis whether the products actually deliver the expected benefits. If no benefits are seen another strategy should be adopted.

Professional care and support
It is important that the dental professional ensures that the patient understands the risks associated with the wearing of a removable partial denture. The patient should be aware of food impaction, possible additional plaque retention and also the possibility of a change in plaque composition to one that is associated with disease [16]. It should be made clear to the patient that very few possibilities would remain if the denture fails. It must be clear that it is the patient’s responsibility to cope with increased risks associated with the dentures by the quality of the oral hygiene procedures used. The dental professional should check that the patient is able to carry out oral hygiene procedures at the necessary high standard. If this is not the case, it should be considered whether to withold the dentures. Any other preventive measurements that could be applied by the dental professional are less effective than a high standard of oral hygiene maintained by the patient himself. The importance of oral hygiene should always be emphasised during check-up visits to the dentist’s; such check-ups should be scheduled more frequently than for patients who do not have removable partial dentures. Patients should be advised not to wear the denture at night unless there are urgent reasons to do so. The denture should be cleaned with soap and a suitable brush

If the patient-applied oral hygiene procedures provide insufficient protection, additional preventive treatment administered by the dental professional should be considered. The approaches to the prevention of crown caries are essentially the same as those used for root caries since the etiology of the diseases is the same. However since dentine is much more vulnerable than enamel, the preventive measures aimed at protecting the dentine should be more intense.

Concentrated fluoride solutions, gel and varnishes
Although there is no study that specifically shows the efficacy of the topical application of concentrated fluoride solutions, gels or varnishes on cut surfaces, there are however, several arguments for their use. During drilling the outer fluoride-rich layer of enamel and dentine will be removed, so it seems logical to supplement the fluoride in the new outer layer. However, after application most of the fluoride will be present in a CaF2-like layer, that will initially provide caries prevention. However the layer will slowly dissolve and with it, the protective effect. Relatively little fluoride is incorporated into the enamel lattice and so only minimal protection is provided. Axelsson et al [17] showed a positive effect of fluoride-containing abrasive pastes after scaling and root planing. Unfortunately the design of this study did not involve a control group using a non fluoride-containing abrasive paste so no definitive conclusion can be drawn as to the fluoride effect.

For protection against crown caries one option is to only apply concentrated fluoride solutions, gels or varnishes whenever there are actual signs of caries activity.

Table 1 presents an overview of the studies carried out to evaluate the effect of topically applied fluoride on root caries. In a recent systematic review, only the study of Ravald and Birkhed [18] was judged to be of sufficient quality to merit detailed discussion [12]. In the Ravald and Birkhed study, three groups were compared. In group 1, Duraphat (2,3% F- as NaF) was applied 3 to 4 times a year, while group 2 received an application of 0,4% SnF2 gel three to four times a year. Group 3 had a daily rinse with a 250 ppm fluoride solution (as NaF). Although the differences between the groups were not statistically significant, the daily rinse seemed to be the regimen offering the highest protection. On average, group 1 developed 3.1 ± 0.75 new root caries lesions in two years, the 2nd group 2.3 ± 0.82 and the 3rd group 2.0 ± 0.6 root caries lesions. It was thus concluded that daily additional applications of fluoride were the most effective for the prevention of root caries [12].

Chlorhexidine
A protective effect against caries in tooth crowns has been demonstrated for EC40 (35 % chlorhexidine), 1% chlorhexidine gels and for Cervitec (1% chlorhexidine with 1% thymol) [19, 20, 21, 22, 23, 24]. The effect of EC40 and 1% chlorhexidine gel was only observed in children having ≥106 Streptococci mutans per mL of saliva and with high caries activity. A recent systematic review concluded however that the evidence for anti-caries efficiency of chlorhexidine varnishes was inconclusive in patients using fluoride daily [25]. Twetman [25] also concluded that there is no evidence that chlorhexidine protects against root caries in people with hyposalivation or with frail, elderly patients [25].

Dentin adhesives
The protective effect of dentine adhesives on root caries has only been evaluated in vitro and in situ. Grogono and Mayo applied Scotchbond Multi-Purpose on root surfaces and incubated the specimens in a demineralisation system [26]. After 70 days the root surfaces were still free of any signs of demineralisation. In situ studies showed some, but incomplete, protection against root demineralisation after the application of dentine adhesives [27]. The release of fluoride from such adhesives may only be short-lived and have only a very local effect and so seems clinically irrelevant. However there are only relatively few clinical studies that have been carried out on the protective effect of dentine adhesives on caries so it is impossible to provide firm advice on the subject.

Summary
The wearing of removable partial dentures may increase the risk of caries and periodontal disease in the remaining dentition. The risk is associated with insufficient oral hygiene which is hampered by the wearing of the removable partial denture. The design of the removable partial denture should be carried out according to the modern concepts of preventive dentistry: open and hygienic. Before placing a removable partial denture, the patient should be treated if necessary to ensure a healthy mouth. The patient should be instructed clearly on appropriate and adequate oral selfcare. Furthermore, patients should be made aware of their own responsibility for the cleaning of both the dentition and the denture. If adequate oral hygiene procedures twice a day are not satisfactory, the daily use of a fluoride-containing antimicrobial mouthrinse can be considered. Little effect can be expected from professionally applied fluoride or chlorhexidine solutions. The protective effect of dentine adhesives has been insufficiently explored.

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The author
Dr C. van Loveren,
Department of Cariology, Endodontology and Pedodontology,
Amsterdam University Dental Health Centre (ACTA).
e-mail: c.van.loveren@acta.nI