Barriers in Access to Dental Services Hindering the Treatment of People with Disabilities: A Systematic Review

Background People with disabilities tend to have greater oral health problems compared to those without disabilities. This may be due to barriers they come across in accessing dental services. Objectives The objective of this systematic review was to provide a critical digest of the scientific literature concerning barriers and facilitators of access to oral health services for people with disabilities. Methods The electronic databases PubMed, Scopus, Web of Science, Latin American and Caribbean Health Sciences Literature (LILACS), and Brazilian Library of Dentistry (BBO) were searched using keywords relevant to the subject. The search was not restricted to specific languages or years of publication; all relevant studies were translated and reviewed. Results Sixteen studies including 14 articles, a doctoral thesis, and a monograph were selected, and their quality was analysed using the Downs and Black assessment tool. Barriers to dental services were divided into physical or nonphysical based on the dentist's perspective, as per the perception of parents/guardians or by the persons with disabilities. The barriers that emerged included the dentist's lack of preparation to assist people with disabilities, structural problems of access to dental offices, communication difficulties, and lack of awareness regarding the need for dental treatment for the disabled person. Conclusion It is concluded that people with disabilities continue to run into complex physical, behavioural, or multidimensional barriers in accessing dental services. Improved training of dentists for the care of this population is hereby emphasized. The legal framework enabling access to dental care for people with disabilities must also be respected in each country.


Introduction
e number of persons with disabilities worldwide is almost one billion [1]. e affected population is at a higher risk of caries and periodontal disease [2][3][4][5] compared to those without disabilities. Epidemiological profiles in oral health show a difference, for example, in the DMFT (decayed, missing, and filled teeth) of people with disabilities when compared to people without disabilities. ese differences may vary according to the country and the types of disabilities included in the survey. In South Korea, researchers evaluated comparable samples of people (a) with physical disabilities (DMFT � 7.3), (b) with mental disabilities (DMFT � 8. 3), and (c) with multiple disabilities (DMFT � 8.2) and people without disabilities (DMFT � 4.9) [6]. In another study carried out in Portugal, with institutionalized people with disabilities, a mean DMFT of 11.2 was found which was much higher than the general population of the same age group [7]. In Brazil, in a study carried out with people with Down syndrome, cerebral palsy, and intellectual deficit, the average DMFT was 11.0, also quite high when compared to the general population of the same age group [8].
is is partly due to the difficulties encountered in the care of the oral cavity, which include structural barriers and motor difficulties and those associated with communication with the caregiver regarding the need for oral health care [4], in addition to the degree of dependence on caregivers for hygiene and good eating practices [3].
is dependence observed in persons with disabilities can often make their oral care take a back seat for parents or caregivers, as their overall health becomes a priority [9,10].
When individuals with disabilities take initiative to access health services and gain access, they subsequently choose to continue care in services that have empathetic, compassionate, and responsible professionals [11]. Yet, access to care is deemed to be the first barrier to the initiation of a health service, wherein the patient's problem should be known and their therapeutic itinerary in the service network be traced so as to solve the health problem [12]. Access to health services by persons with disabilities should consider (but not exhaust themselves with) their most basic and specific health needs [5,13,14].
Knowledge of the main barriers that hinder oral health care in people with disabilities needs to be discussed. Access to care is determined by the geographical location of the patients and services, the convenience and ability to organize services in order to accommodate the individual, their adaptability to the service provided, and the reciprocal acceptability of professionals and end users [15]. Access is determined by the type of health system in each country and the local context. In order to enable access to health care, the health service must meet the needs of the user, be available, and be appropriate to the population.
us, universal access to health services comprise (i) a political aspect involving decision-making and agreement by the different levels of the government in a country, thereby prioritizing and programmatically arranging the services and the intervention devices in context; (ii) economic and social aspects that cover financing issues and mitigation or elimination of barriers encountered by the user; (iii) system organization starting from the user's entry into the service up till the resolution of their health problem; and (iv) technical-scientific training and cultural competence, through comprehensive actions and respect for individuals, understanding the healthdisease transitions, beliefs, values, and traditions [16].
Based on the above, the objective of this systematic review was to critically gather from the scientific literature the main barriers and facilitators of access to oral health services for people with disabilities.

Search Strategy.
is systematic review was carried out according to the Cochrane Collaboration Guidelines Combined [17,18], Meta-analyses Of Observational Studies in Epidemiology (MOOSE) [19], and according to the model Preferred Reporting Items for Systematic reviews and Meta-Analysis guide (PRISMA) [20]. Prior to its initiation, the protocol for this review was registered at the PROSPERO database (protocol number: CRD42018107571). e guiding question of the review was defined as follows: How do people with disabilities access oral health services? e keywords were selected based on the study question and study population.
Online databases were consulted from August 24, 2018, to August 27, 2018, based on the date of online availability and included PubMed, Scopus, Web of Science, Latin American and Caribbean Health Sciences Literature (LILACS), and the Brazilian Library of Dentistry (BBO). In addition, the references cited in all the primary studies included were manually searched to add all the relevant publications that may not have been included in the main search. At this stage, the grey literature was also accessed through the ProQuest Dissertations and eses Full-Text databases, CAPES eses Periodicals, the Grey Literature Report, and Google Scholar. Abstracts from the annual conference of the International Association for Dental Research (IADR) and its regional divisions (1990-2018) were also searched. e search strategy was appropriately modified for each database; two reviewers (SVR and LCT) performed the search in order to identify eligible studies. Table 1 depicts the details of the search conducted with the search date and number of articles found in each database.

Eligibility Criteria.
ough observational studies (crosssectional, cohort, and case-control) were included, editorial letters, historical reviews, in vitro studies, controlled trials, case reports, comments, and qualitative studies were excluded from the present study. No language or publication date restrictions were imposed; all relevant studies were translated and revised.

Data Collection and Analysis Process.
After the exclusion of duplicates, using the ® Mendeley reference manager, studies were initially screened on the basis of titles and abstracts. Articles that appeared in more than one database were considered only once. e full-text versions of the articles were evaluated by a pair of reviewers (SVR and LCT) who determined study eligibility; disagreements were decided by a third reviewer (JSR). Each eligible article was assigned an identification code (first author/year) to facilitate its classification. Inter-rater reliability was calculated by Kappa statistic; a value of 0.87 was considered optimal. Relevant information on study design, participant characteristics, exposure, and outcomes was extracted through a customized pretested data extraction form ( Figure 1).

Bias Risk Assessment.
e quality of the articles was assessed by two independent reviewers (SVR and LCT) using the Downs and Black scale [21]. is instrument is used for quality assessment of observational studies and randomized clinical studies and comprises 27 items totalling up to 32 points (higher scores indicating superior quality). In this review, a modified version [22][23][24][25][26][27][28] of this instrument was used which consisted of 17 items (1-3, 5-7, 9-11, 16-18, 20-22, and 25-26), totalling up to a maximum of 17 points. e relevant domains for the instrument included description, external validity, and internal validity (confusion/ selection bias). Disagreements in the quality of the articles were resolved by a third reviewer (JSR).
For each aspect of quality assessment, the risk of bias was scored according to an adapted version of the Cochrane Collaboration tool [17], which included the top four domains from the Downs and Black quality assessment tool. Studies were considered to have a "low" risk of bias when the domains external validity, internal validity, and description attained their maximum scores. A single study presented a risk of "unclear" bias when the criterion description was not fulfilled and/or was unclear in the other key domains. A "high" risk of bias was considered when a study did not meet the criteria internal and external validity, and when more than two items reflected a high risk of bias in the domain description.
Kappa was also performed to measure inter-rater agreement and to analyse the risk of raters' classification bias. A Kappa value of 0.86 was attained, which is considered optimal as per the relevant literature.

Summary of Results.
Data were analysed using the extracted information which included the study title, author, year, country, sample size, study design, study results (barriers encountered in dental care, types of services accessed, type of dental procedures, and types of disabilities), and source of the study population. Because of the heterogeneity of the studies, a meta-analysis was not performed. e target audience of the questionnaires were people with disabilities; however, the dentist was interviewed. Also, the diversity among the studies was due to the age or the age groups of the target population, the difference in the health systems in the countries studied, and differences in the type of disability.
e studies originated in several countries and continents; six studies were from North America with four from the United States [70,72,74,77] and two from Canada [71,76]. ere were six studies from Brazil in South America [5,79,80,[82][83][84]. Two selected studies were from Europe, of which one was from England [73] and the other from the Netherlands [75]. A single article was selected from Malaysia [81] and another from Australia [78].
Only two studies were derived from a secondary database [72,74], and the other fourteen discussed data from primary sources that had a cross-sectional observational study design.

Bias Risk Assessment.
e results of the bias risk assessment are shown in Table 3. One study showed a low risk of bias for all the assessed items [74]. ough, three studies depicted an unclear risk of bias [70,72,84], seven of them showed a high risk of bias due to ambiguity in the description of confounding factors and their adjustment during the selection of the study participants [5,71,76,[79][80][81][82]. With respect to external validity, three articles presented a high risk of bias [70,82] and one presented an unclear risk [75]. At this stage, the extent to which the study conclusions could be extrapolated to the studied population was evaluated. On assessing internal validity (systematic error), only one article showed a high risk of bias, the main outcomes of which were not accurate and the Excluded articles (n = 43) Qualitative (7) Not just disabled people (4) About treatment (2) Does not talk about access, barriers/facilitators (6) Not specific to oral health (1) Speaks about a specific program (1) Not found in full (22)    data were only descriptively depicted [79]. In addition, on evaluating internal validity in terms of confusion and selection bias, only two studies showed low risk of bias due to control in sample selection, wherein data were collected from the same population and over the same time period [72,74] and one study showed unclear risk of bias [84].

Summary of the Main Barriers.
e barriers observed in this review were classified as physical or nonphysical or classified based on the perception of the person responsible for, or the caregiver of the disabled person involved in the study, and the perception of the dental surgeon attending to the disabled person. e results of the barriers detected are reported in Table 4.

Discussion
As this population needs specially organized health services and comprehensive preparation of professionals [85], it was observed that barriers to access were clearly pointed and appeared in all the included articles. However, there was no mention of the facilitators of access in any of the studies. e design of all included studies showed a cross-sectional framework allowing to simply estimate the prevalence of evaluated variables or at most their relationship. On the other hand, in addition to cross-sectional studies not being adequate to analyse causality, just association, another problem is the possibility of a low response rate of participants. erefore, the researcher needs to make use of sample contact strategies such as telephone and mail communication.
In the results of the studies included in this systematic review, the response rate of the questionnaires sent was reported in ten studies, not mentioning significant sample losses, suggesting that the response rate did not affect the results. For the others, for not having addressed this issue, it is unknown [70, 71, 74-78, 81, 83, 86]. It is emphasized that the sample selected for the study must be representative of the entire population studied, so that the results can be extrapolated. In addition to the risk of obtaining low responses, there is also a likelihood of biased responses [87].
Studies that were not found in their entirety and excluded from the final selection in this systematic review were mostly those reported during the period from the 1950s up to the 1980s. Not including these studies in the analysis of the results hampered the possibility of revealing old and persistent barriers to dental services.
is resulted in compromising the analysis due to a possible change in the nature of barriers over a longer time interval .
In the analysis of the study quality, the "report" item assessed whether the information provided by the study was sufficient for the reader to make an unbiased assessment of the conclusions derived from the study [21]. Examining this dimension, in this review, showed that six studies had a low risk of bias thereby implying that they addressed the requirements of the Downs and Black instrument which allows the reader to make an unbiased assessment [74, 76-78, 83, 86]. In contrast, seven studies did not meet these requirements [5,71,[79][80][81][82]84]. External validity determines the extent to which the study results can be extrapolated to the population studied; seven of the 16 studies had a low risk of bias [72][73][74][75][76][77][78]83], being reliable results for the sample of the studied population. With regard to internal validity (confusion and selection bias) only two studies reported a low risk of bias [72,74], thereby implying that the biases related to sample selection were addressed and the interventions quantified in the results. In this regard, thirteen studies showed high risk of bias [5,70,71,[75][76][77][78][79][80][81][82]84].
ese studies presented only the descriptive results pertaining to the data in the form of frequency of answers and percentages and did not perform statistical adjustments of the results.
Physical barriers reflect problems relating to accessibility that people with disabilities encounter to reach a dental care facility. Two articles reported physical barriers hindering 8 International Journal of Dentistry access to care facilities, such as surgeries being performed on the upper floors of buildings that did not have elevators and not remembering that dental extraction is a common requirement among people with disabilities [75,81]. Inadequate dental facilities are also barriers that affect access [70,76,80,84]. e compromised mobility of people with disabilities affecting their ability to reach the place of care is yet another critical barrier and has been reported in three studies included in this review [76,82,83]. Difficulties in access due to lack of adaptation to health care facilities and offices has been mentioned in four studies [76,77,79,81]. To overcome such barriers, dental offices and dental centres must follow and abide by accessibility laws as enforced in many countries such as Brazil, as access to dental care is a right of the disabled. Family involvement in access to care for people with disabilities is very essential, as family support and emotional bond play a fundamental role in their health. Expecting a child with disabilities can inflict emotional distress and guilt in parents, who are required to prepare appropriately and introject situations of difficulty that they may encounter, given the social, structural, and programmatic inequities that place a disabled person in a vulnerable situation [88]. e family of children with disabilities may be in denial upon identification of the condition, as they lack preparedness to care for a child with a disability. ey tend to adapt as they  ? , unclear risk; -, high risk. * Adapted from Cochrane Collaboration. * * Adapted from Downs and Black, scores from zero to 17 (higher scores indicate higher quality).
seek information in order to meet the care needs of their loved ones. Subsequently, they enter a phase of acceptance, when they establish an emotional bond with their child and understand their health care needs [89].
People with disabilities often have a number of associated health problems such that oral health care takes a back seat in the family [10].
is barrier to oral health care was also detected by Nelson et al. [77]. Koneru and Sigal [76] also encountered a perceived lack of dental treatment in parents or caregivers. e dearth of time to take the affected child or the guardian to the dentist was reported by Nelson et al. [77] and Dantas Cardoso [82]. Cardoso et al. [80] cited instances in which as per the perception of the parents or caregivers, the child with disability did not need care. Instances depicted by Nelson et al. [77] reflect the lack of knowledge regarding the need for oral health care. ese included situations where the child was deemed to be too young to see a dentist, the father feared a visit to the dentist, or when the child had recently exfoliated his or her deciduous teeth. erefore, access to information and health education for parents and caregivers of people with disabilities can overcome these barriers [90]. e studies selected belonged to various parts of the world, with representation from the United States [70,72,74,77], Canada [71,76], Netherlands [73], Malaysia [81], Australia [78], England [73], and Brazil [5,79,80,[82][83][84]. Although these countries have diverse health systems, barriers to care reported in these studies were similar. One of the most common barriers was the lack of preparation and experience of the professional for dental care of disabled persons [5,70,75,[77][78][79][80]84]. Knowledge is fundamental for good dental practice, and innovation and the use of instruments that can facilitate the time of care can always help in the treatment of people with disabilities when we do not have a collaboration during the consultation [91].
is is a significant finding, which reflects upon the training received by the dentist or even the dental curriculum, which does not consistently cover the theme of dental care for people with disabilities [92]. In such situations, continuing health education programs can aid dental professionals to keep abreast of the techniques to meet the needs of people with disabilities.
Permanent health education allows professionals to refresh their knowledge and practices through latest evidence and the best treatment approach available, thereby enabling the enhancement of technical skills, scientific knowledge, and ethical development of the processes and also building relationships between the teams involved. e appropriate distribution of professionals and services to the proximity of the population in need, irrespective of their location with an aim to improve access to care and to enable continuing health education, is a complex task, as there is a noticeable concentration of specialized professionals in large centres [93].
is imposes alternatives such as the virtualization of learning through nonpresent or semipresent modules.
Most of the studies included in the review were centred primarily in countries such as Brazil, the United States, and Canada. Brazil has a universal Unified Health System (SUS) enshrined in its federal constitution of 1988. It is a free system accessible to all Brazilian citizens, including people with disabilities. It has doctrinal principles: universality, equity, and comprehensiveness [94,95]. Primary care is the gateway to the SUS; there are family health teams (FHS) which aim at comprehensive multidisciplinary care of the people [96]. In the year 2000, dentists were included in this team with the objective of oral health actions and services as a part of primary care [96]. Among the barriers observed in the studies conducted in Brazil, the lack of trained professionals for the dental care of people with disabilities was prominent, given that these surveys were conducted among people who attended the SUS [5,79,80,[82][83][84].
In the United States, the most frequent barrier was the lack of experience among dentists and the cost of treatment [70,72,74,77]. e latter reflected the characteristic of the country's health system, whereby there was no universal system followed, and one had to pay for health insurance or use Medicare and Medicaid, which are subsidized by the government for vulnerable groups of patients [97]. In Canada, the health system is provincial with variations in each province; however, access to oral health services is mostly not covered by this system [98]. e type of health system in a country is therefore a crucial determinant of the physical barriers and the cost of treatment [71,76]. e difficulty to provide dental care and the lack of trained professionals to care for people with disabilities has a direct influence on their oral health. e procedures that need to be performed are most often on patients requiring urgent care where they are already in pain, mandating tooth extraction due to decay or prophylaxis due to bacterial biofilm accumulation. Procedures such as restorations and preventive treatments can be performed in order to prevent tooth mutilation. e use of prostheses can also restore the well-being and quality of life of people with disabilities [70,71,74,[76][77][78][80][81][82][83]. e compilation of the barriers observed was derived from studies using quantitative methods which in turn may be a limitation of this systematic review, considering that qualitative studies may approach barriers differently. For example, qualitative studies are ideally not limited to structured questions with closed options, and one's view of access to services can be further explored, thus opening horizons for another systematic review (metasynthesis) for qualitative studies. Another limitation to be considered was the inclusion of only cross-sectional studies. Finally, it is alarming that facilitators of access to dental services for people with disabilities have not been discussed or reported in these revised studies, which paves way for further studies in this field, aiming at solving the barriers that hinder access to dental services.

Conclusion
People with disabilities continue to encounter various physical, structural, geographical, professional, or behavioural barriers that hinder their access to dental services. Furthermore, there is a need to improve the training rendered to dentists pertaining to care for this population in various national and regional contexts. It would be ideal to enforce and implement accessibility laws in every country. erefore, a lot remains to be achieved by the society with   Data Availability e data file of this study is available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no financial affiliation (e.g., employment, direct payment, stock holdings, retainers, consultantships, patent licensing arrangements, or honoraria) or involvement with any commercial organization with direct financial interest in the subject or materials discussed in this manuscript or any such arrangements existed in the past five years. No potential conflicts of interest relevant to the present article were reported.