Functional dentition and prosthodontic status in an Indigenous population from the South of Brazil

Aim: to analyze the prevalence of different definitions of functional dentition, prosthodontic status and associated factors, in an indigenous population from Brazil. Methods: a cross-sectional oral health survey was conducted with Indigenous adults aged 35-44 years. A single examiner collected clinical data through oral examinations and sociodemographic data using a structured questionnaire. Dentitions were classified according to four classification systems of functional dentition: FDWHO (> 20 teeth), FDGROUP2 (> 10 teeth in each arch), FDGROUP3 (all anterior teeth), and FDGROUP4 (> 10 teeth in each arch, all anterior teeth, and sufficient posterior region). Use and need of prosthodontics was also evaluated. Uni and multivariate analysis were conducted at the level of significance of 5%. Results: Indigenous adults presented considerably low frequencies of prosthodontic use and functional dentition, independently of the definition analyzed. Substantial differences of prevalence rates were observed among the four definitions of functional dentition, ranging from 48.62% to 11.93%. Age and municipality were associated with use of dental prosthesis and prosthodontic need, respectively. Significant discrepancies in functional dentition rates were observed regarding sex and time of the last dental appointment. Conclusions: Indigenous adults are severely affected by tooth loss and, consequently, by low frequencies of functional dentition. The scenario is worsened by the elevated need of the population for prosthodontics. The phenomenon was associated with age, sex, access to specialized dental care and time of the last dental visit.


Introduction
Oral health inequalities are particularly striking among Indigenous peoples from different nations 1 . Native populations constitute culturally different societies, with highly heterogeneous epidemiological profiles and treatment needs. Although it is not normally explored in studies with Indigenous, tooth loss might be an important parameter for assessing oral health status in different populations 2 . Tooth loss represents one of the most severe injuries to oral health due to its mutilating effects and the potential repercussions to the quality of life 3 . The resulting sequels reflect on a complex combination of epidemiological, socioeconomic, cultural, racial, and health-related factors [4][5][6] . Vulnerable groups and individuals belonging to lower social strata from different societies are most strongly affected by the problem, which implicates in identifying these injuries as a manifestation of oral health inequalities [6][7][8] .
The World Health Organization (WHO) defines the retention of a natural dentition of at least 20 teeth throughout life not requiring prosthetic replacement as the goal for oral health in adult populations 9 . This quantitative concept of Functional Dentition (FD) has been largely employed in dental research, although its appropriateness in assessing functionality has been challenged 8,10-12 . By questioning whether simply the number of teeth present is adequate to describe the functional status of dentitions, more comprehensive definitions of FD have emerged. According to Gotfredsen and Walls 13 (2007), oral functionality must encompass aspects of masticatory efficiency and ability, appearance, psychological and social comfort, tactile perception, speech ability, and taste. Thus, in accordance with more demanding notions of FD, new classificatory systems that consider teeth distribution, aesthetics, and occlusal units have been tested in different populations [14][15][16][17] .
Furthermore, the absence of a functional dentition is directly associated with the individual's prosthodontic status, since it constitutes a therapeutic approach to compensate functional and aesthetic implications of tooth loss. We hypothesize that more complex and qualitative concepts of functional dentition present greater implications to public health and oral rehabilitation of Indigenous populations than concepts that are essentially quantitative.
Studies assessing the oral health of Indigenous populations have essentially focused on the epidemiological analysis of dental caries. This context of epidemiological invisibility undermines the construction of scientific evidence needed to expose and reduce situations of health inequalities 18 . Thus, investigating functional dentition and prosthodontic status offers an original perspective to evaluate the extent and severity of edentulousness in vulnerable ethnic groups.
The Guarani e Kaingang ethnic groups represent the second and third largest Indigenous peoples from Brazil, respectively. Yet, data regarding their health status remains scant. The Guarani people belong to the Tupi linguistic family and is present in eight states, from Pará to Rio Grande do Sul. The total Guarani population living in Brazil is estimated at 85,255 individuals. The Kaingang people belong to the Jê linguistic family and occupy approximately 30 territories distributed over São Paulo, Paraná, Santa Catarina e Rio Grande do Sul. The total Kaingang population is estimated at 45,620 individuals. Although Guarani and Kaingang peoples present different linguistic, cultural and historical trajectories, it is not unusual that these two groups co-inhabit the same territory 19 .
This study aimed to analyze the prevalence of different definitions of functional dentition, prosthodontic status and associated factors in an Indigenous population from Brazil.

Materials and methods
This exploratory, cross-sectional, population-based study was conducted from February and to August 2017, among the Kaingang and Guarani Indigenous peoples living on the Guarita Indigenous Reservation, Rio Grande do Sul State. The research project was previously presented to the local Indigenous leaders, who agreed to its realization. Human ethics research approval was granted by the Research Ethics Committee of the University of São Paulo Dentistry School, and the National Research Ethics Committee (process n. 1.756.066). This paper was prepared in accordance with the STROBE checklist for cross-sectional studies.
The Guarita Indigenous Reservation is located in the northwest region of the state of Rio Grande do Sul, southern region of Brazil, and is legally recognized as a land traditionally occupied by the Kaingang and Guarani peoples. The Indigenous population is distributed in 12 villages belonging to three different municipalities (Tenente Portela, Redentora, and Erval Seco). The infrastructure of all villages includes a public health care facility, electric energy network, and a public elementary school. Drinking water is extracted from the local drilled wells and does not receive fluoride addition. Access to all villages is carried out by land, and the distances to the Indigenous Health Office vary between 2 and 40 kilometers.
The total population of the Guarita Reservation is estimated by the Special Secretariat for Indigenous Health (SESAI) at 5867 individuals. Of those, the Guarani correspond to a small group of approximately 200 individuals concentrated in the most remote village. The number of inhabitants in each community varies from 181 to 744 people.
In order to obtain a representative sample, a census-based strategy was employed. Thus, all Indigenous adults from the Guarita Reservation who met the inclusion criteria were potentially eligible to be participants of the study. Inclusion criteria were individuals self-identified as Kaingang or Guarani and aged 35-44 years (age group specified by WHO to assess the oral health status of adults). All households from all villages were visited and individuals within the selected age group were invited to take part in the study by signing a written consent form. In addition to their native languages, all participants were Portuguese speakers.
Individuals unable to provide informed consent due to cognitive or physical impairment were excluded. The total number of adults aged 35-44 years is estimated by the SESAI at 300 individuals. Only 12 individuals actively refused to be included in the study. Number of losses was expressively affected by a seasonal outflow of Indigenous workers, mainly men, to another region of the state during the time of the study.
Oral examinations were performed by a single examiner (GHS) previously trained and calibrated, in open areas near the houses of the participants, under natural light, with the aid of sterilized clinical instruments (flat mouth mirror and classic-round periodontal probe) and individual protection equipment. Conditions of dental crowns, periodontal status, and use and need of prosthodontics were evaluated following the methodology recommended by the WHO to oral health surveys 20 . Dental crowns were classified according to the decayed, missing and filled (DFMT) index. Periodontal status was assessed by the Community Periodontal Index (CPI). Use of prosthodontics was assessed based on the presence of any type of removable dental prosthesis at the time of examination. Prosthodontic need was measured based on the extension, location, and number of edentulous areas in both dental arches. In case of prosthodontic users, dental prostheses were visually inspected, and their general condition was considered in the classification of prosthodontic need. Therefore, participants might be prosthodontic users and still present a prosthodontic need. Intra-examiner agreement was determined by re-examining 10 participants with an interval of 5 to 7 days between the two assessments. The Cohen's kappa coefficient showed substantial level of agreement (kappa=0.817).
For the statistical analysis, only data regarding number of teeth present, and use and need of dental prosthesis were considered. The total number of teeth was determined by the sum of dental elements present in the mouth, except third molars. All missing teeth due to caries or other reasons were considered as dental losses. Posterior occluding pairs (POPs) were defined as the presence of two opposing teeth. Sociodemographic data were collected using a structured questionnaire.
Participants were classified dichotomously in relation to the use of upper and lower dentures at the moment of the examination and need of some kind of upper and lower prosthesis.
The outcomes related to the presence of functional dentition were classified according to four different concepts: This set of concepts was adapted from a classification system previously tested in the Brazilian population by Chalub et al. 21 .
Participants were classified according to sex, age, years of study, monthly household income, time of the last dental appointment, presence of periodontal pocket, and municipality. Age was the only continuous variable analyzed. Education was classified as up to 4 years of formal education or more than 4 years of education. Regarding monthly household income, the amount corresponding to half of the Brazilian minimum wage in 2017 (US$147.00) was adopted as a cutoff point. It was primarily determined in the Brazilian currency and converted to the US dollars (mean exchange rate in August 2017: R$3.15 = US$1.00). Time of last dental appointment was categorized either as within the previous 2 years, or in 3 or more years. Considering the cultural, linguistic, and geographic barriers that Kaingang and Guarani peoples face to access regular dental treatment, we find reasonable to use a 2-year period to classify time of the last dental appointment, rather than adopting the normative recommendation of annual dental check-ups. Periodontal status was classified as the presence of at least one periodontal pocket (probing depth ≥4mm), or its absence. Municipality was classified as Tenente Portela or others. This division is due to the fact that the municipality of Tenente Portela provides a Dental Specialties Center (CEO -Centro de Especialidades Odontológicas) in the public health care network. On the other hand, individuals living in the villages located in Redentora and Erval Seco are referred for specialized dental treatment in a municipality located 116 km away from the Indigenous Reservation.
Initially, descriptive analyses were carried out in order to describe the sample. Prevalence of FD and respective 95% confidence interval were calculated for each of the four definitions used. Association between the dependent and independent variables was verified through Poisson regression with robust variance and presented through prevalence ratio (PR) and confidence interval (95% CI). For the multivariate analysis, FD definitions were incorporated separately into the Poisson regression models created. Associations were considered statistically significant at the 5% probability level (p≤0.05). Analysis was performed using STATA 12.0 software (StataCorp, College Station, Texas, USA).

Results
Of the 109 individuals examined, only 2 participants were from the ethnic group Guarani. Mean age was 39.4 (SD 3.3). The majority of the participants was female, with a monthly household income of less than US$147.00, and living in the villages situated in the municipalities of Redentora and Erval Seco (Table 1).
There were no participants fully edentulous, and only 3.7% presented complete dentition. Mean number of present teeth was 18.6 (SD 6.1; Min 2; Max 28). Nearly all dentures were inadequate due to cracks, fractures, or ill-fitting, requiring to be replaced. About 30% of the participants presented complete anterior dentition. Prevalence rates of the different definitions of FD ranged from 48.62% to 11.93% (Table 2). Table 3 displays the univariate and multivariate analyses for the associations between prosthodontic status and independent variables. Age presented a statistically significant association with the use of upper (PR = 1.09, CI = 1.03-1.16) and lower dentures (PR = 1.27, CI = 1.06-1.53). Indigenous adults living in the villages located in Tenente Portela presented a significant difference regarding the need of upper dental prosthesis when compared to individuals from the other municipalities (RP = 0.74, CI = 0.55-0.99). Need for a lower dental prosthesis was not associated with any independent variable.
Associations between the four FD outcomes and independent variables are shown in Table 4. After adjustments for the other variables, the prevalence of FD WHO in the final model was 67% (95% CI 1.04-2.69) greater among men in comparison to women. When considering FD GROUP2 , prevalence of FD was twofold greater among men (PR 2.06; 95% CI 1.16-3.65). Indigenous adults who visited a dentist in the previous 2 years presented a significantly lower prevalence of FD GROUP4 (PR 0.27; 95% CI 0.08-0.91). There was no statistically significant association between the presence of a complete anterior dentition (FD GROUP3 ) and independent variables.

Discussion
This study presents the first evaluation of FD in an Indigenous population. The employment of such measures represents an important shift in the paradigm of dental research from a disease-focused approach to positive outcomes of health. For instance, it was presented herein the mean number of teeth present rather than number of losses, which is a modest yet significant modification. This change is particularly relevant for the scientific literature covering the oral health of Indigenous peoples, which is typically restricted to the epidemiological analysis of dental caries Findings of this study might be useful for clinicians when deciding which criteria of functionality are suitable to guide prosthodontic rehabilitation. For vulnerable populations with high prosthodontic need, this information could lead to more appropriate therapeutic decisions and reduction of oral health inequalities. For instance, employing purely quantitative criteria (e.g., number of missing teeth) for prosthodontic treatment in an Indigenous population may reify existing inequalities by not identifying a significant proportion of individuals in need of oral rehabilitation. Understanding the burden of tooth loss for the aesthetics and functionality in a population is essential in order to plan effective and adequate oral health programs.
The employment of traditional sampling strategies to conduct research among hard-to-reach populations such as Indigenous peoples imposes important methodological challenges. It is likely that the high dispersion of the studied population throughout the territory and the difficulty to locate eligible participants prevented the accomplishment of a greater sample size. Missing data for household monthly income was substantial due to the number of participants who did not know or declined to provide this information (19,3%). The comparison of results between Kaingang and Guarani individuals was not possible due to the low number of participants of the latter. This study also presented limitations inherent to the cross-sectional design regarding the impossibility of establishing causal conclusions. Cultural and social characteristics of Indigenous peoples prevent the generalizability to other native communities and might be explored in further studies. Subjective perception of functionality was not assessed.
In this study, prevalence rates of FD ranged considerably according to the definition assessed. Nevertheless, our findings contrast with national data, suggesting that disparities between Indigenous and non-Indigenous adults persist regardless of the definition investigated. Data from the 2010 National Oral Health Survey (NOHS) for Brazilians in the age group of 35-44 years present prevalence rates of FD WHO , FD GROUP2 and FD GROUP4 of 77.9%; 72.9%; and 42,6%, respectively 21 . Frequencies of FD among Vietnamese and Chinese non-indigenous populations are similarly high and contrast with the findings reported in this study 14,22 . Such differences are most likely resulting from health inequalities related to ethnicity and structural determinants of health. A study with Indigenous peoples from the Xingu Park found that tooth losses accounted for 80% of the DMFT score of mother in the 35-44 age bracket 23 .
Lack of access to fluoridated water seems to be an important explanatory factor to the FD prevalence rates observed in this study as it has been associated with lower frequencies of FD WHO , FD GROUP2 , and FD GROUP4 10,21 .
In the final model, age was statistically associated with use of upper and lower prosthodontics. Greater prevalence of dental replacements among individuals of higher age was also described in a study with Chinese adults 22 . Although it is likely to be a result of the cumulative effect of dental caries and periodontal disease over time, such association in a well-delimited age group might indicate a trend of rapid and premature deterioration of the oral status. The lower need of upper dental prosthesis among Indigenous adults from the villages of Tenente Portela (PR: 0.74; CI: 0.55-0.99) seems to be an effect of the dental specialties offered in the local secondary care system. Indigenous residents of the other municipalities might experience financial restraints related to the costs of travelling to a distant location in order to receive the same level of health care.
Substantial differences in relation to sex were observed for FD WHO and FD GROUP2 , with higher prevalence rates among men. Similar results were previously described for FD GROUP4 in Brazilian adults 21 . A study with Sudanese tribes found that women were twice as likely to present less than 20 teeth when compared to men 24 . Greater risks of dental caries, tooth loss, and oral health impairment have also been reported for Indigenous women of Brazil and Australia [25][26][27] . This phenomenon may possibly be explained by the social positions attributed to gender as well as biological markers.
Researchers have incorporated periodontal status as an additional level in the classificatory system of functional dentition, even though it did not seem to significantly affect the results 14,15 . In this study, periodontal status was included as an independent variable and was not statistically associated with functional dentition nor prosthodontic status. Additionally, income and years of education have been reported as associated factors for FD in Brazilian adults 10,21 . It is likely that these associations have not been observed in this study due to the similar socioeconomic characteristics of the participants and the modest sample size.
Time of the last dental visit was the only factor associated with FD GROUP4 . Indigenous adults who had not seen a dentist for an interval higher than 2 years presented better outcomes of FD in comparison to those who had a recent dental appointment. Sudanese adults who visited a dentist more frequently presented significantly fewer teeth than those who did not visit a dentist at all 24 . On the other hand, higher prevalence rates of FD WHO and FD GROUP2 have been reported to Brazilian individuals who attended a dental appointment in the previous 12 months 21 . Dental care may affect tooth loss in opposing directions according to the type of service offered. Restrictive and mutilating dental practices have historically promoted edentulousness as a health practice in the field of oral health in Brazil 7 . Dental health teams in both developed and developing countries seem to operate mainly by reinforcing the curative praxis of care, and often perform clinical practices that are biased by characteristics such as ethnicity and social class 4,28 .
Health inequities resulting from this complex interplay of social determinants tend to be expressed as extremely high demands for health treatments among Indigenous groups. Nearly all individuals observed in this study presented need for prosthodontic rehabilitation. The scant frequency of denture users and the general unsuitable conditions of the prostheses worn seem to aggravate the situation. Meanwhile, approxi-mately 69% of Brazilian adults in the same age group present need for some type of dental prosthesis 29 .
A strategic goal set by the WHO stipulates that 96% of all adults aged 35-44 years should present a FD comprising at least 20 teeth 30. While Brazilian and Vietnamese adults have not reached so far the goal for FD set by the WHO 12,14 , the situation of Indigenous from the Guarita Reservation is far worse. In fact, the prevalence of FD WHO observed in this study is similar to the frequency reported to the Brazilian adult population in 2003 (54%) 31 . Improvements in the oral health status of Brazilian adults, with a significant reduction in the number of missing teeth, resulted in a 44% increase in the prevalence rate of FD WHO in the 2010 NOHS 15,32 . Longitudinal data regarding Indigenous oral health is needed in order to assess whether the gap between Indigenous and non-Indigenous is narrowing or widening.
Nevertheless, the WHO's classification of FD might not guarantee a sufficient number of occlusal contacts for adequate functionality due to the multiple possible configurations of the teeth 14 . Chalub et al. 21 (2016) questions whether aiming at a FD based purely on quantitative criteria without considering teeth distribution and condition might lead to increasing oral health inequities. Conversely, the classification proposed by Nguyen et al. 14 (2011) (here referred as FD GROUP4 ) offers a qualitative system that is more compatible with functional and perceived demands 21,33 .
The low prevalence of FD GROUP3 indicates the magnitude of the aesthetic impairment affecting this population. Exploring subjective perceptions related to the low frequency of intact anterior dentition might provide a better understanding of its implications to social life. Despite limitations of the FD WHO definition, it may still represent an important instrument for comparison across populations and for the establishment of health goals. On the other hand, more demanding concepts such as FD GROUP4 might be appropriate to both planning of individualized treatments and formulation of public policies 34 .
The findings of this study suggest that tooth loss is an eloquent marker of social and health inequalities between Indigenous and non-Indigenous populations. Public policies targeting the health of Indigenous populations should address structural factors through viable measures, such as considering local fluoridation water systems, and improving the health care network of referrals to a closer Dental Specialties Center in order to facilitate the access to oral rehabilitation.