Denture Plaque Biofilm Visual Assessment Methods: A Systematic Review

Denture plaque, a biofilm that develops on denture surfaces, could contribute to many oral and systemic afflictions. Hence, a quantitative assessment of denture plaque is important to evaluate the denture hygiene of denture wearers, particularly to prevent plaque biofilm-associated diseases. The aim of this systematic review, therefore, was to review and summarize the visual denture hygiene assessment methods using denture plaque indices and with planimetries published in the literature. English language studies published up to March 2022 in four electronic databases, PubMed, Medline, Embase, and Cochrane Library, were searched, followed by a manual search of Google Scholar by two assessors. The review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) whenever possible. Details of the visual assessment methods, including the types of denture assessed, its materials and its surfaces, as well as the use of a disclosing agent, were the main outcomes. Of 492 screened studies, 74 were included per the inclusion and exclusion criteria. Of these, 60 studies utilized various denture plaque indices while 18 used planimetries. 43 out of 60 studies with indices and 17 out of 18 studies with planimetries used disclosing agents for visual evaluation of plaque. A total of 21 indices were described in the included studies, of which seven graded a divided denture surface, while the remainder graded entire denture surface. Of the 18 planimetric assessments, one study quantified squares of the disclosed plaques on denture images, 16 studies quantified such pixels with computer programs, and a single study quantified points, pixels, and contour of plaque areas. In summary, denture plaque indices appear to be popular in denture plaque assessment due to their simplicity. Computerized planimetric assessment, though more time-consuming, provides a more accurate assessment of plaque load as it is less prone to subjectivity and assessor errors.


Introduction
Dental prostheses such as removable partial and complete dentures are still widely used to replace missing teeth, particularly in the developed world, mainly due to the higher financial outlay of various dental implants.−4 Denture plaque is essentially a biofilm comprising a complex aggregate of micro-organisms and their metabolites that accumulate on denture surfaces. 2 positive correlation between the amount of denture plaque biofilm and the severity of denture stomatitis is well established. 5,6Furthermore, denture plaque aggregates particularly in debilitated hospitalized individuals are known to correlate well with potentially fatal systemic complications such as aspiration pneumonia. 1,7,8Meanwhile, most denture wearers, especially in developing countries, have poor knowledge of denture hygiene. 9Hence, over the years, many workers have attempted to either quantitatively or semiquantitatively assess denture hygiene to educate and motivate patients in a visually impressive manner and also to develop clinical correlates of plaque-related diseases. 10,11he presence and distribution of plaque biofilm on the denture surfaces could be assessed using either the naked eye with denture plaque assessment indices or the latter with planimetries. 12Those indices utilize a calibrated assessor for semi-quantitative grading of denture plaque biofilm.The assessor usually assesses the area of denture surfaces covered with plaque biofilm using a disclosing agent. 12More recently, however, planimetries have been employed to provide a better quantitative assessment of plaque biofilm-covered denture surfaces.Computer programs are usually used in planimetric analyses to provide a quantitative indication of the area with plaque deposition.In general, denture plaque indices are also helpful to motivate individual patients to improve their denture hygiene while the latter, more sensitive planimetric assessment methods can be used in research settings to compare the relative efficacy of denture cleansing agents and methods.
Over the last few decades, many indices and planimetries evaluating denture hygiene for clinical as well as research purposes have been used and these have been reviewed in an attempt to obtain a global oversight on denture plaque levels, 2 denture hygiene, 13 and denture hygiene practices. 14owever, to the best of our knowledge, there is no recent comprehensive review of the subject and the current review was undertaken to provide a contemporaneous, critical account of the visual denture hygiene assessment methods described in the literature.

Methods
The review question "Which visual assessment methods have been used to measure denture plaque biofilm in previous studies?"was specifically set using a Population, Intervention, Control, and Outcomes (PICO) model (Table 1).This review was registered on the PROSPERO international prospective register of systematic reviews (CRD42023390370).The review followed the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Literature Search
The literature in four electronic databases, PubMed, Medline, Embase, and Cochrane Library, was searched by two assessors (KMT and AWKY) independently using a defined search strategy (Table 1).Relevant references from the selected studies were retrieved and an additional hand-search via Google Scholar was performed by the same assessors to identify other potentially eligible studies.The most recent search was performed on March 31, 2022.Abovementioned two independent assessors initially screened through the titles and abstracts of retrieved studies.Duplicates of studies were removed.The shortlisted studies were then screened with full-text analysis.The inclusion criteria for this systematic review were as follows: English language studies; visual assessment of denture hygiene on removable partial or complete dentures; original clinical studies.Simulated in vitro studies, case reports and short communications, studies without statistical analysis as well as studies using assessment methods other than visual assessments were excluded.Disagreements between assessors were solved by discussion for a consensus.

Data collection, extraction, and analysis
Data extraction was performed independently by the same assessors using a pre-defined data extraction template.Interassessor conflicts were discussed to reach a consensus.From the materials and methods section of each selected study, details of the denture hygiene assessment including the examined samples whether the actual denture or its images, complete or partial or both dentures, maxillary or mandibular or both dentures, types of denture materials, the use of a disclosing agent, and the assessed denture surfaces were extracted (Table 2 and 3).Furthermore, details of the denture plaque indices and planimetric assessment methods were also extracted (Table 4).Any missing information was secured as much as possible by emailing the corresponding author.The screening process and data extraction were performed using Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia).The methodological quality of selected studies was assessed by an assessor (KMT) using National Institutes of Health (NIH) Study Quality Assessment Tools for respective study types.

Discussion
In general, denture hygiene or denture plaque biofilm can be visually assessed using various indices and planimetries.Our review provides a contemporaneous account of these assessment methods described in the literature up to 2022.Clearly, the fact that there are so many methodologies in use to evaluate denture plaque biofilm implies that there is no single preferred method of assessment, and the data from the current review should facilitate decision-making by future investigators and clinicians embarking on similar studies on the optimal method of denture plaque evaluation.
In this review, most studies assessed acrylic complete dentures.Only a relatively small number of studies investigated metallic dentures and this may be related to imaging issues and poor contrast of disclosed metallic surfaces that may interfere with the computerized assessment of images.
Denture plaque biofilm usually develops unevenly on denture surfaces and more biofilm growth is seen on the fitting (intaglio) surface than on the polished (cameo) surfaces. 11,79his is because the intaglio surfaces are protected from the continuous, dynamic flushing action of saliva and the muscular movements of the tongue. 6Additionally, the intaglio surfaces, in comparison to cameo surfaces, are unpolished and may contain undercut regions, especially at the area around maxillary tuberosities and palatal rugae 19,30 which have limited access for a denture brush. 79This, together with the fact that the maxillary denture-bearing area is the main plaque-depository area, 12 and most affected by pathologies such as denture-associated stomatitis and related fungal infections. 87hese are the possible reasons why most workers have assessed the intaglio surfaces of maxillary dentures in comparison to cameo surfaces.Actually, indices that can effectively assess both maxillary and mandibular dentures should be preferable clinically as many patients have both maxillary and mandibular prostheses.Besides, the differences in plaque patterns between maxillary vs mandibular dentures were not clearly reported in reviewed studies.Moreover, there was no report of a significant difference in plaque score or plaque amount between maxillary and mandibular dentures.
Furthermore, because of different plaque growth on different denture surfaces, plaque assessment on divided areas enables assessment of localized areas of plaque deposition. 17f the indices used, the method of Augsburger and Elahi 84 where eight sub-divided areas were assessed is clearly less time-consuming 12 and preferable to the method of Paranhos et al. 29 where a total of 22 sub-divided areas were quantified.
Most denture plaque assessment indices were inexpensive and simple to use, being compatible with use in a clinic or community setting, thus permitting the study of a large number of subjects quickly and effectively. 88The ease and the rapidity of the assessment method are clearly important in communitylevel studies with large cohorts, as visual fatigue associated with prolonged assessment 36 could bias the outcome.Actually, assessment of actual dentures is quicker and simpler to grade for the entire surfaces, and also possible to use a blunt probe to physically detect the plaque 53,54,59 but assessors can easily confuse with any imaginary division of the denture surfaces in the assessment on divided denture-areas.Hence assessments of the denture images, captured by a camera, rather than on-site evaluation, have been suggested so that assessors evaluate the images at a later stage in a laboratory setting with no time constraints. 20,22Furthermore, denture images can be anonymized easily in this manner to reduce any potential evaluator bias.The use of such imaging also facilitates the testing and training of inter-and intra-assessor reproducibility as well as allows dividing denture surface into areas by computer.Thus the suggested imaging techniques are in general preferable to on-site naked-eye evaluations.
Disclosing the plaque on the denture surfaces is demanding because plaque is usually colorless and cannot be visible easily. 89,90Disclosing agents are surrogate visual indicators 19 that are used in many denture plaque indices (15 out of 21) in this review to enhance the visibility of plaque biofilm.The dye in the disclosing agent diffuses into plaque, binds to plaque components such as proteins and polysaccharides, and is retained in the plaque. 91,92All but a single denture plaque index 85 in our review were entailing subjective judgments by the assessors and hence more prone to inter-and intra-assessor measurement errors.Moreover, these indices were in the ordinal scale, which is non-continuous and semi-quantitative, meaning that only low-power categorical statistical tests could be performed. 12An index that calculates the percentage of divided areas with plaque-deposited, is more objective and permits the use of powerful statistical tests, which is preferable in this context. 85lanimetric plaque assessment methods, as opposed to the traditional naked eye methods with indices, could be d e n t u r e p l a q u e b i o fi l m v i s u a l a s s e s s m e n t m e t h o d s considered as a relatively new development in denture plaque evaluation research. 29In principle, these methods are based on quantifying 10 either point counts or divided squares 68 of a projected image or tracing the contour of a disclosed plaque area using a digital planimeter. 10Then, the area with plaque deposition, in pixels, can be automatically measured using image analysis software.
As regards the surfaces studied in planimetric investigations most evaluated only the fitting surface while a few others assessed multiple surfaces such as both the intaglio and cameo surfaces, and left and right buccal surfaces. 12,71,79uch planimetric assessment of multiple denture surfaces is useful for evaluating the efficacy of denture cleansing procedures though it may lead to confusion as overlapping image surfaces in different images.
The other advantage of planimetries is that the results are provided in percentages (%), as a continuous numerical value i.e. ratio scale 93 that permits more powerful statistical analyses. 12The planimetric results also correlate well with other non-visual plaque assessment methods such as plaque weight and viable microbial counts. 94owever, there are some drawbacks associated with planimetries too.These include inherent artifacts due to reflected light or discoloration of the acrylic denture base.Additionally, image quality consequential to the standardization of the camera settings such as the resolution power, the exposure time, as well as background lighting are all factors that need to be considered. 12,22Other factors that affect the image quality are the angulation between the camera and the denture, 25,29,[69][70][71]76 and the denture position 25 and distance all of which should be standardized.
In conclusion, computerized planimetries provide a more objective assessment of denture plaque biofilm and do not require the calibration of assessors in comparison to naked eye visual assessment methods using denture plaque indices. 71,95Although time-consuming, 10,12,73 and requires additional equipment as well as effort for capturing and analyzing standard images, some have suggested that planimetries should be the method of choice for research on denture hygiene. 71,73On the contrary, the naked eye assessment using denture plaque indices are simple, and easy to interpret though subjective, 22 and perhaps more practical for those without access to imaging technology, providing acceptable results in a clinical setting.The latter, we believe, is more appropriate for community-level studies.Finally, very few plaque biofilm assessments of metallic denture bases have been conducted, and further work in this area is needed.

Figure 1 -
Figure 1 -PRISMA flowchart for search strategy together with the structure of this systematic review.(Four studies used both assessment methods and are hence mutually inclusive in both categories.)

Table 1 -
The search strategy and tools for risk of bias assessment used in the study

Table 2 -
32 )st of the 74 reviewed studies.(*studiesunder the same project of Zenthofer et al. 201434.#studies under the same project of Sloane et al.32 ) (continued on next page)

Table (
Continued) d e n t u r e p l a q u e b i o fi l m v i s u a l a s s e s s m e n t m e t h o d s

Table 3 -
A summary of the included visual assessment of denture hygiene studies.Four studies used both assessment methods and are hence mutually inclusive in both categories.

Table 4 -
Details about different denture plaque assessment indices and planimetric methods utilized to measure denture hygiene in the reviewed studies