Complications and maintenance in prosthodontic care: removable partial dentures

Patients seeking prosthodontic treatment will have had a series of factors that have contributed to the loss of their tooth structure and so, often present with complex treatment needs for restoring function and aesthetics.¹ With increasing longevity, improved management of chronic diseases and associated comorbidities, there is an emphasis on patient-centred management and professionally directed recall and maintenance programmes.² Many types of restorations are used to address patients' needs, but all require careful and co-ordinated planning and a long-term partnership with the patient to maintain an enduring result.³ Thus, an appropriate patient recall regimen, professional maintenance, as well as at-home maintenance are all important.⁴ For patients with dental prostheses, maintenance protocols are crucial for minimizing the risk of failure of supporting teeth, and preventing caries, periodontal disease and prostheses failure.¹ It is also important to recognize that maintenance protocols will vary according to the health status of the patient.⁵ An understanding of the specific prognostic factors associated with different dental restorations, and their relative contribution to the duration of tooth survival will facilitate the development of prosthodontic treatment strategies and evidence-based predictions for the long-term prognosis of natural teeth.⁶ This review evaluates the scientific evidence available on the complications associated with removable partial dentures (RPDs) and on patient recall and maintenance regimens.

Complications

An individualized assessment of the risks and benefits when designing and providing dental prostheses for patients with tooth loss is important. Its impact on dental health must be considered carefully.¹

Abutment survival

In RPD treatment, identifying the specific prognostic factors that dictate the survival of abutments is crucial.¹ In a longitudinal retrospective study, Tada et al⁷ examined the survival rates of direct and indirect abutments (Figure 1) over 5 years and reported survival rates as:

• 86.6% for direct abutments;
• 93.1% for indirect abutments;
• 95.8% in non-abutment teeth.

These survival rates were significantly associated with:

• Crown-root ratio;
• Root canal treatment;
• Pocket depth;
• Type of abutment;
• Occlusal support.

During the observation period, periodontal maintenance was provided at least once a year.⁷ The decreased survival rate for direct abutments was possibly due to the continuous and repetitive mechanical stress with which these teeth are loaded.⁸ The use of retainers also contributes to deterioration in oral hygiene around abutment teeth.⁹

The results from a 28-year follow-up survey indicated that the number of residual teeth significantly influenced tooth loss, with fewer residual teeth at baseline tending to increase tooth loss.¹⁰ In another study, patients with free-end saddle type RPDs tended to experience more abutment loss, with more loss bilaterally than unilaterally.⁸ Both of these studies^8,10 indicated that a decrease in the number of residual teeth and, therefore, occlusal support area (Figure 2), had the potential to cause occlusal instability. This in turn leads to an increased occlusal load on the abutment teeth, with subsequent potential for damaging the underlying periodontal tissues.

Root canal-treated abutments also independently affected survival rates. The 5-year survival rate in one study was 51% for root canal-treated abutment teeth.¹¹ However, in this study the higher rate of failure could be due to the use of a post and conical double crown-retained rather than clasp-retained RPD. Another study showed a 71.5% 5-year survival rate for endodontically treated teeth with clasp-retained RPD.¹² The failure rate was double for RPDs compared with fixed partial denture and four times greater than that for single crowns.

Oral and denture hygiene

RPDs are susceptible to plaque accumulation and with poor oral and denture hygiene can have adverse effects on oral health (Figure 3). A Cochrane review¹³ was unable to identify the most effective way of removing plaque from dentures owing to the low-quality of evidence. In one study,¹⁴ it was reported that during the 10 year re-evaluation only 36% of the dentures were free of hygiene-related problems. This has been attributed to a lack of awareness and regular recall programmes for good denture and oral hygiene.

Caries

The use of an RPD can create a suitable environment for the growth of many micro-organisms, including cariogenic bacteria (Streptococcus mutans and sobrinus), and Candida albicans, and is considered a risk factor for several plaque-related oral diseases.¹

In a randomized clinical trial (RCT), Jepson et al¹⁵ assessed caries incidence between bilateral cantilever resin-bonded bridges and conventional RPD in lower shortened dental arches over 2 years. They reported that the incidence of new or recurrent carious lesions was 6.6% in the adhesive bridge group, and 32.7% in the denture group (Figure 4). Furthermore, there was little difference in caries incidence between non-abutment and abutment teeth in the bridge group. Whereas, in the denture group, caries incidence was 14% for non-abutment teeth and 60% for abutment teeth, with frequent manifestation of root caries. The relative risk of new caries was four times greater in the denture group compared to the bridge group.¹⁵

This raises interesting clinical questions about providing RPDs for elderly patients. In Jepson et al,¹⁵ a metal framework with a plate connector was used for the RPDs in the majority of the cases. The increased gingival coverage could explain the increased incidence of caries and associated plaque levels. However, in another similar study,¹⁶ RPDs with a metal framework and lingual bar were used. Caries incidence was reported six times more frequently for those with the RPD than for those with the fixed cantilever bridge over 5 years, despite annual recall. Oral hygiene and periodontal status were maintained in both groups. Based on these two studies, it is difficult to assess whether a denture designed to avoid gingival coverage influenced caries incidence as the duration of the studies was different.

Steele et al⁷ estimated the association between RPDs and the presence of root caries and concluded that wearing an RPD almost doubled the odds of having root caries (Figure 5). The authors stressed the need for preventive measures where possible. Infrequent toothbrushing was reported among the subjects, which could increase the risk of developing root caries owing to plaque accumulation. However, it was not mentioned in the study whether acrylic or metal frameworks were used for the partial dentures.

In another study,¹⁷ where acrylic partial dentures were most frequently used, there was higher root caries incidence in those wearing the acrylic partial dentures. Gingival recession also increases the risk of developing root caries.¹⁸ Studies comparing the incidence of caries between acrylic and metal-framework RPDs are, however, scarce, and a conclusion that one causes a greater or lesser incidence of caries cannot be drawn.

Periodontal diseases

Factors that compromise oral hygiene and encourage plaque retention can increase the risk of developing periodontal disease. RPDs can cause a high rate of tooth loss, with 26.4% of abutments being lost over 10 years due to periodontal disease.¹⁹ Higher plaque scores, greater gingival inflammation and loss of attachments at abutments compared with non-abutments have been reported, with further increases in values as the denture ages.²⁰

The use of RPDs was associated with an increased prevalence of gingival recession.²¹ In the study by Wright and Hellyer,²¹ both synthetic resin and metal framework RPDs were investigated, but there were no significant differences between them in terms of the extent of gingival recession. The majority of the designs in this study were, however, mucosa supported. Additionally, it is also difficult to randomly allocate individuals within a cohort who have different Kennedy classifications and for whom some tooth-supported designs cannot be applied.

In contrast to the above findings, increased levels of gingival inflammation were seen in areas covered by RPDs, but there was no direct evidence that the RPD caused dental or periodontal breakdown.²² Budtz-Jørgensen and Isidor¹⁶ reported that patients with RPDs had higher mean plaque and gingivitis scores than patients with cantilever bridges, but no changes in probing depth were recorded over 5 years. During this time patients were recalled every 6–12 months and received prophylaxis.

Studies have shown that sites that do not progress to attachment loss over time are characterized by less gingival inflammation, and those that do progress have persistently greater levels of gingival inflammation.²³ Therefore, gingivitis is a prerequisite and major risk factor for periodontitis, and its management and prevention should be key.²⁴

Denture stomatitis

In a systematic review,²⁵ the association of denture stomatitis (DS) with RPDs was evaluated. The prevalence of DS in RPD wearers ranged between 1.1% and 36.7%. The authors concluded that there is some evidence that the presence of DS is associated with RPD wearing (Figure 6), but no cause and effect relationship could be inferred because of the methodological limitations and the cross-sectional designs of the research studies included. A study also reported that RPD usage increases the frequency of oral mucosal lesions (OML) by 0.4 times as compared to non-RPD users.²⁶

Maintenance

It is important that patients adhere to the recommended oral hygiene regimens because they will play a fundamental role in the prevention of periodontal disease and tooth loss (Figure 7).²⁷

Recalls

Tada et al²⁸ investigated the impact of periodontal maintenance on tooth survival. Patients were divided into three groups based on the frequency of periodontal maintenance: every 3–6 months (3–6M); once a year (1Y); and those who refused or did not attend periodontal maintenance visits (NM). The survival rates of abutments (direct and indirect) were:

• 83.7% for 3–6M;
• 75.5% for 1Y; and
• 71.9% for NM.

Similarly, for non-abutment teeth survival rates were:

• 95.8% for 3–6M;
• 91.4% for 1Y; and
• 87.4% for NM.

In a follow up study,²⁹ professional biofilm control was performed every 3 months for 1 year after receiving the RPD, and was also performed before receiving RPD. There was, however, a significant increase in plaque index at follow-ups, and both direct and indirect abutments were more affected by gingival disease compared with non-abutments. This further confirms that RPD usage increases plaque scores, leading to gingival inflammation and, subsequently, periodontitis. If patients are not aware and motivated to maintain oral hygiene, they may be at higher risk of developing periodontal disease and caries. Although 3-monthly professional periodontal maintenance could limit the negative effects of RPD use, it could not completely remove them.

Similarly, in another study,³⁰ no periodontal maintenance had been provided to RPD wearers, and periodontal conditions were examined at the time of insertion and 7 years later. Significantly increased values in gingival recession, periodontal depth and bleeding on probing were reported with increased incidence of caries for abutments compared with non-abutments. Most of the RPDs were tooth-supported (62.5%) and were planned using a surveyor. However, even an RPD with good technical quality does not eliminate biological complications. Yeung et al³¹ also reported a high prevalence of plaque, gingivitis and gingival recession, especially in dento-gingival surfaces in close proximity (within 3 mm) of the dentures. These findings were also seen in a systematic review,³² where the absence of good oral hygiene measures in RPD wearers led to accumulation of plaque, gingival inflammation and increased risk of caries, particularly root caries. Moreover, where possible, coverage of exposed root surfaces by RPD should be avoided in the denture design and topical fluoride should be regularly applied to exposed root surfaces to prevent caries.³³

Therefore, it is important to have an integrated prosthodontic maintenance programme with regular recall visits for both oral and denture hygiene and it should be adopted as a gold standard in general dental practice. Post-insertion follow-up will also ensure long-term continuous use of cobalt–chromium RPD.

Denture design

In an RCT³⁵ treating Kennedy class I and II with I-bar and circumferential design success rates of 76% and 71%, respectively, were reported, with no differences in periodontal status with either design over 5 years. Hence, a well-constructed RPD, supported by favourable abutments and accompanied by a regular recall programme can provide good treatment outcomes (Figure 8). RPD components also need to be considered from a hygienic viewpoint and the design should favour open/hygienic design principles (Figures 9 and 10) rather than biomechanical.³⁶ There is a need to focus on reducing the risks of oral tissue injury in RPD treatment and design.³⁶

In a retrospective study, Rehmann et al³⁷ investigated the long-term outcomes of clasp-retained, metal framework RPD designed according to hygienic principles. The mean observation time was 3 years and patients were put on yearly recall. Mean survival time was 8 years, and mandibular RPD showed better survival than maxillary. The mean time until the first repair was 4.6 years, and 30 of 65 RPDs needed at least one repair. The main reasons for repair were:

• Relining (n = 23);
• Clasp activation (n = 9);
• Clasp fracture (n = 6); and
• Only 5.8% of the abutment teeth were lost.

The authors concluded that the high survival and low extraction rates for the abutments may indicate that RPD designed according to hygienic principles met, or exceeded, results reported by similar studies.³⁷

In one RCT investigating oral health-related quality of life,³⁸ two different tooth replacement strategies for partially dentate older patients were applied, namely, a shortened dental arch approach, and conventional treatment using RPD. It was concluded that treatment based on the shortened dental arch achieved significantly better results than that based on RPD 12 months after treatment.

These findings highlight the importance of designing RPDs with a greater focus on hygienic principles to limit their associated complications. Regular recall can also improve RPD survival rate.

Oral hygiene and motivation

Ribeiro et al³⁹ examined the effect of oral hygiene education and motivation in RPD wearers. They reported that there was a higher frequency of plaque and gingival indexes at the preliminary visit than at follow-ups, and an illustrated denture instruction manual resulted in improvement in the plaque scores for the prostheses.

However, there is no certainty that increased knowledge and improved behavioural habits would remain stable over a longer period without periodic reinforcement.⁴⁰ Zaki and Bandt⁴¹ also observed that the use of self-educational materials and individual instruction by dental personnel could be effective in teaching oral hygiene measures to patients in dental practice. A systematic review concluded that a mechanical toothbrush, with the addition of professional oral prophylaxis, provided a significantly positive effect in reducing the incidence of gingivitis.⁴² Another systematic review concluded that power-driven toothbrushes had beneficial effects in reducing the levels of inflammation compared with manual toothbrushes.⁴³ A Cochrane systematic review⁴⁴ also found that powered toothbrushes reduce plaque and gingivitis more efficiently than manual toothbrushes in both the short and long term.

Morris et al⁴⁵ found that the mean proportion of plaque increased from 30% in the age group 25–34 years to 44% in those aged 65 years and above, which highlights the need for more professional care for the older patients.

These findings show that patients need to be checked, re-motivated and re-instructed frequently, and by incorporating a preventive programme, it is possible to maintain a good standard of oral and denture hygiene in RPD wearers over a prolonged period of time. The use of powered toothbrushes should be considered as part of the regular oral hygiene armamentarium.⁴⁴

Denture repairs

In a retrospective study, Maeda et al⁴⁶ examined removable prostheses for clinical factors that influenced the frequency of relining procedures during maintenance periods at 3 monthly intervals for between 5 and 25 years. They reported a mean frequency of relining procedures at 27 months, with an interval of 20 months for those dentures with no occlusal support areas and 45 months for those dentures with up to four support areas. Also, as age increased, the interval between relining procedures increased. However, this study had several limitations, the main one of which being that the evaluation criteria for reline were not validated and may not be reproducible. In another study,⁴⁷ it was reported that 22.2% of the RPD of classes I and II (free-end saddles) required reline as compared to 12.3% of class III, IV and V (bounded saddle), showing a higher rate of relines for terminal edentulous areas.

In a retrospective study, Behr et al⁴⁸ examined the survival rate of 174 clasp-retained RPD. After denture insertion, all patients were advised to attend a follow-up appointment at least once a year, but not all patients followed this. The 5- and 10-year cumulative survival for all clasp-retained RPD was 96.4% and 89.9%, respectively. The 5- and 10-year event-free rate for caries was 58.4% and 39.6%, respectively. Complications encountered during this period were:

Related to prosthesis

• Clasp: 16.1%;
• Major connector: 5.1%;
• Minor connector: 3.4%.

Biological

• Caries on abutment: 31.6%;
• Inflammation of periodontal tissue around abutment teeth: 35.6%.

Most frequent

• Loss of abutment: 8.6%.

Post insertion problems

• Pressure areas of the mucosa: 30.5%;
• Mandible: 39.6%;
• Maxilla: 12.5%.

The importance of denture repair should be thoroughly discussed with the patient prior to initiating treatment, and with regular recalls and timely repairs, associated complications can be limited.

What the literature tells us

In successful prosthodontic treatment, responsibility is the key word. The dental responsibility is to use clinical judgement and expertise to decide when to restore a depleted dentition, with emphasis on minimizing any long-term detriment to the patient. The patient's responsibility is to understand that, in the vast majority of circumstances, the shortcomings of prosthodontic treatment can be minimized or magnified depending upon the patient's motivation to maintain the mouth in an impeccable state of hygiene. It is important to develop a prosthodontic treatment strategy based on an evidence-based prediction for the long-term prognosis of prosthodontic treatment care. A plaque-free prosthodontically treated mouth is one with an excellent prognosis.

The adverse effects for wearing an RPD on abutments and the periodontium could be minimized by regular dental biofilm control programmes, and with satisfactory hygienic denture design (Figure 11). Some tissue coverage is inevitable for direct abutment teeth; however, periodontal maintenance could moderate the impact of tissue coverage and further reduce the risk of tooth loss.

Oral and denture hygiene practices tend to deteriorate with time, despite patients receiving thorough instruction and being initially motivated. It is important to explain to patients that treatment does not end with denture placement, but with satisfactory oral hygiene maintenance, the negative effects of RPD use can be minimized, although not completely eliminated. Even thorough oral and denture hygiene practices tend to reduce over time, indicating a requirement for continual re-inforcement of oral hygiene instructions. The existence of a motivating force could produce a change in patients' behaviour, leading to alteration of habits and attitudes that could preserve oral health.

Clinical recommendations

Based on the literature, the following can be suggested:

• The number of residual teeth at baseline influences tooth loss, with fewer remaining teeth leading to increased tooth loss.
• With a free-end saddle, there is a greater risk of abutment loss, and greater need for relining procedures, especially in the mandible.
• There is a higher risk for abutment loss in root canal-treated teeth.
• There is a 4–6 times higher risk of caries, especially at root surfaces, for RPD wearers.
• The use of RPDs increases the risk of gingival recession and inflammation.
• Patients with 3–6-monthly professional maintenance recalls woud appear to have a lower risk of periodontal disease and abutment loss.
• RPD design should incorporate hygienic principles, rather than just biomechanical principles, as this also favours higher survival rates for abutments.
• Frequent recalls are important to remotivate and re-instruct RPD wearers to maintain a good standard of oral and denture hygiene. The use of a powered toothbrush, with the addition of professional oral prophylaxis can provide effective plaque control. The use of an illustrated denture instruction manual can help to achieve better plaque control.
• Topical fluoride should be regularly applied, especially on root surfaces, to prevent caries.
• The frequency of relining procedures is dependent on increasing age and the amount of occlusal support.
• Denture stomatitis is common for denture wearers, and therefore, frequent recalls, and optimum oral and denture hygiene, should be the gold standard for preventing complications with RPD use.