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. 2020 Apr 21;15(4):e0230809. doi: 10.1371/journal.pone.0230809

Tooth wear as an indicator of acculturation process in remote Amazonian populations

David Normando 1, Mayara Silva Barbosa 2, Paulo Mecenas 3, Cátia Quintão 2,*
Editor: J J Cray Jr4
PMCID: PMC7173625  PMID: 32315345

Abstract

Riverine populations are typical of the Amazon region that depend on nature for subsistence. These people are considered an intermediate population between the urban and indigenous, the original Amazon habitants. The aim of this cross-sectional study was to evaluate the relationship between tooth wear and age in a remote riverine population from the Amazon, located by the Tucumanduba River (n = 94), and to compare them to previous findings obtained from semi-isolated indigenous (n = 223) and urban populations (n = 40) from the Amazon region, which were examined using the same methodology. Using linear regression, tooth wear explained 54.5% of the variation in the ages of the riverine subjects (p<0.001). This coefficient is mid-way between those obtained in semi-isolated indigenous populations (65–86%) and urban subjects (12%) living in the Amazon. Our findings suggest that tooth wear, a direct evidence of what an individual ate in the past, may be an indicator of the acculturation process in remote populations.

Introduction

Several methods can be used to estimate chronological age in humans [1–5]. One of the most traditional is the analysis of the degree of mineralization and tooth eruption [1, 6–8]. However, this methodology cannot be used in estimating the chronological age of mature individuals, without a trace of growth, as once at this stage all teeth are already formed and in position. Thus, a measurement parameter that changes continuously over time, without any recovery or neoformation, would be ideal.

Dental wear can be an effective tool for estimating age in different populations [9–11]. As dental hard tissues undergo progressive loss due to mechanical and/or chemical wear and are not replaced [12, 13], quantifying dental wear to estimate chronological age is valid, especially, after development of the dentition and growth cessation. Though, factors such as diet, cultural habits, malocclusion severity and gastroesophageal reflux may modify the degree of wear and its relationship with age according to the investigated population [14, 15].

In the Amazon live the riverine people, a population that depends on the river network for their subsistence and transportation. The local economy consists of small-scale fishing and agriculture. The food is based on the consumption of regional roots, cassava flour, fruits, vegetables and meat from wild animals [16]. During daily tasks it is not uncommon for them to use their teeth as tools [17]. The presence of such habits reveals the cultural origin of these individuals that come from indigenous communities.

In a previous study conducted in the Amazon region, a high correlation was observed between dental wear and chronological age in semi-isolated indigenous communities, thus making it possible to predict the age of an individual through dental wear with relative reliability. Meanwhile, the association was low when a sample of an urban Amazonian population was evaluated [11]. Riverine communities are considered to be an intermediate population between indigenous and urban, not living as isolated as the indigenous populations, but, relatively distant from urban centers. Recently, however, with the increasing urbanization of the Amazon and financial assistance programs from the Brazilian government, there has been greater contact of the riverine people with urban centers [16, 18]. This increased the acculturation process, characterized by cultural changes derived from the contact between two distinct cultures, and assimilation and/or loss of traditional customs may occur [19–21].

Therefore, this study aims to investigate the correlation between tooth wear and age in a riverine population of the Amazon and compare with data previously obtained from indigenous and urban populations in the same region. The purpose of this comparison is to understand the effects of the acculturation process, especially the changes in eating habits, in the Amazon populations.

Materials and methods

Ethical considerations

This work was approved by the Research Ethics Committee of the Institute of Health Sciences of the Federal University of Pará under the protocol number 2.055.941, dated May 2017, S1 File. For inclusion in this study participants over 18 years or parents and/or guardians responsible for individuals under 18 years signed an informed consent form.

Study design

This is a cross-sectional study and conforms to the STROBE guidelines. [22]. The group studied belongs to the riverine community that inhabits the sides of the Tucumanduba River, in the municipality of Abaetetuba, Pará state, Amazonia, Brazil. This community lives in relative isolation, without basic sanitation and with limited access to urban centers. The participants' recruitment and data collection occurred from September 2017 to April 2018.

Participants and eligibility criteria

The sample of this study included ninety-four (94) riverine individuals from the community of Tucumanduba, between 13 and 61 years old, of both sexes. Personal information, including name, age, sex and address were recorded.

To be included in the study, individuals should have permanent dentition with all teeth erupted, excluding third molars, and no more than seven tooth losses, since a high number of missing teeth could influence the amount of dental wear found on the rest of the dentition.

This population was compared to the indigenous and urban populations evaluated in a previously published research article [11], following the same methodology, composed of 223 indigenous individuals from Middle Valley Xingu, Pará, Brazil, and 40 individuals residing in an urban center, Belém, Pará, Brazil.

Variables analyzed, data sources, and measurements

The variables considered in the sample were the amount of occlusal tooth wear and the participants’ chronological ages. To measure occlusal tooth wear, a previously described and widely applied index (the modified Mockers index) was used, [11, 23–25]. Occlusal faces of the second and first premolars and incisal faces of canines, lateral and central incisors in both dental arches were clinically examined, always using good quality lighting. Then scores were recorded for each tooth: 0 = no wear; 1 = enamel wear only; 2 = dentin wear, with the occlusal/incisal face showing more enamel than dentin; 3 = dentin wear, with the occlusal/incisal face showing more dentin than enamel; 4 = advanced wear stage, near or with pulp exposure (Fig 1). The dental examination was performed by one previously calibrated researcher with experience in this measurement. The reliability of the method was tested after evaluating 20% of the sample, to then examine the entire sample. The assessment was performed using natural daylight and a flashlight, with an assistant recording the measures.

Fig 1. Modified tooth wear measurement index.

Fig 1

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A—upper dental arch; B—lower dental arch; 0—absence of wear; 1—enamel wear only; 2—dentin wear, with the occlusal/incisal face showing more enamel than dentin; 3—dentin wear, with the occlusal/incisal face showing more dentin than enamel; 4—advanced wear stage, near or with pulp exposure.

Since a previous analysis of the tooth wear regression coefficient of the evaluated teeth (incisors, canines and premolars) found a weak to moderate association with chronological age, therefore, for each individual, an arithmetic mean of tooth wear was calculated, as described by Normando et al. [24, 25]. The birth dates of the participants were recorded according to birth records.

Statistical analysis

The determination of chronological age through tooth wear was statistically analyzed using simple linear regression using the MINITAB 17 Statistical Software package (Minitab Inc, State College, PA, USA). Intraclass correlation was used to test the reliability of the tooth wear evaluation. A significance level of 5% was used for all the analyses.

Results

Participants

Initially, 95 individuals were deemed to be eligible and were examined, however, the birth date of one participant could not be confirmed, so he was not included in the analysis. Thus, the sample analyzed in the Tucumanduba riverine community was composed of 94 individuals, 42 females (44.7%) and 52 males (55.3%), with a mean age of 24.7 years (13.1–61.9). No significant differences were observed between males and females regarding dental wear (p> 0,05), and for this reason the results were combined.

Outcome data

Means and ranges of tooth wear values for each population are described in Table 1. The intraclass correlation reveals excellent reproducibility for tooth wear measurements (r = 0.78–0.94, p<0.0001).

Table 1. Sample size (n), mean and range of tooth wear and age of riverine groups, indigenous (Assurini, Xicrin-Kaiapó and Arara) and urban (Belém, Pará).

Group n Mean of tooth wear (Min-Max) Age (years) (Min-Max)
Riverine 94 0.64 (0.0–2.6) 24.65 (13.1–61.9)
Assurini 46 0.82 (0.0–2.3) 19.16 (10.8–45.5)
Xicrin-Kaiapó 60 0.63 (0.0–2.3) 21.51 (10.8–49.3)
Arara 117 0.91 (0.0–2.9) 21.27 (10.3–48.1)
Belém 40 0.90 (0.2–1.6) 22.25 (13.1–42.4)
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In the riverine population, a significant association was observed between occlusal tooth wear and chronological age (R2 = 0.55, p< 0.001) (Fig 2). Wear measurement explained 55% of the age variability in these individuals. This coefficient of determination is intermediate between those found in semi-isolated indigenous populations (R2 = 0.86–0.65) and the urban population of the Amazon (R2 = 0.12).

Fig 2. Association between tooth wear and age for the riverine population.

Fig 2

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Linear regression was statistically significant (p <0.001), explaining 55% of age variability in this group. *p<0.05.

Discussion

The results of this study revealed a significant association between dental wear and chronological age in a sample of Amazonian riverines. The measurement of wear explained 55% of the age variation in these individuals. This value is intermediate to that obtained in semi-isolated indigenous populations and urban populations [11].

The amount of tooth wear present in a person depends on many factors [15, 26–28]. Therefore, quantifying dental wear to predict chronological age requires specific prediction models for each population to control these confounding factors which may vary between different cultures. Thus, extrapolation of our results to other populations requires caution.

There are several well accepted indices in the literature to measure tooth wear, and to compare different population groups through different indices can lead to wrong conclusions [15]. For example, in Chinese Malaysian and Indian populations, a high correlation was found between tooth wear and age [9, 10], similar to that seen in Xingu indigenous populations. Nevertheless, another measurement index was used, in addition to different selection criteria. Thereby, assume that this proximity in prediction capacity is due to similar cultural habits is incorrect. In this study, the association between dental wear and age was compared for each population using the same measurement index, examiners and eligibility criteria.

Our results show an association between tooth wear and chronological age in riverine people intermediate to that found in indigenous groups and urban population. The strongest association between the variables was observed in the indigenous groups mainly due to the fact that they present customs that cause greater tooth abrasion, such as their diet based on abrasive and unrefined foods [15, 29, 30]. A national survey on health and nutrition of indigenous people in Brazil showed that the main sources of food for groups living in the north are the cultivation and/or raising animals, in addition to hunting and fishing, which was reported less frequently in other regions [31]. In addition, indigenous people often use their teeth as “tools,” serving as a third hand for holding, cutting and even breaking objects [24, 32]. In contrast, the people in the urban populations eat processed foods, which are less abrasive, and use their teeth primarily to eat [15, 33]. More pronounced dental wear in these people is often due to the presence of para-functional habits, dental erosion and, more rarely, to intrinsic factors such as gastroesophageal reflux and alcoholism [14, 15, 34]. This leads to greater variability of wear in relation to age, with individuals of different age groups presenting similar levels of wear [11]. This way, the association between age and tooth wear in this group is less.

In turn, riverine people have a diet and behavior similar to those of indigenous communities, such as the consumption of regional roots, cassava flour, local fruits and vegetables, fish or meat of wild animals [16, 34]. Cassava is obtained through slash and burn agriculture and is the most common crop planted both in the wetland and upland environments, mostly to be transformed into cassava flour. Most riverines families produce cassava flour only for their own consumption. In some cases, when families can work together, they may produce it in sufficient amounts to be sold in the nearby city [16, 35]. In general, fish is by far the main animal protein consumed, both in the rainy season and in the dry season, being present in approximately 60% of meals. Other sources of protein such as peccary (Tayassu pecari), tortoise (Chelonoidis spp.) and paca (Cuniculus paca) increase their participation in the diet during the dry season [35,36]. Meanwhile, the urban development of the region and government financial programs allowed to this population more access to urban centers and, consequently, increased the consumption of processed food beyond the acquisition of new habits [16, 18, 35]. Probably because of this, the association between tooth wear and chronological age observed in this group was less than that found in the indigenous and more than the urban population.

The process of cultural contact through which a person or group adopts values and practices from another culture, to a greater or lesser extent, is called acculturation. Ethnic minorities living with or in contact with multicultural societies face two key questions: maintain their ethnic identity or acquire behaviors from another culture [19–21]. As a result, there may be four situations: integration, assimilation, separation, or marginalization. Integration represents people who maintain their native culture but also adopt new culture habits. Assimilation refers to those who adopt the habits and behaviors of the new culture without maintaining their traditional customs. Separation occurs when individuals do not recognize or engage in new culture attitudes and behaviors and keep their original culture intact. And marginalization occurs when a group does not engage with another culture, but also fails to preserve its original [19–21, 37].

In the case of Amazonian riverine people, integration best defines their relationship with the urban population, since the cultural base is maintained, though, the eating habits of the other culture were adopted. Dietary acculturation is characterized when members of a minority group adopt eating patterns/food choices from a greater group. This phenomenon can cause a transition in the nutrition pattern of the riverines, which may reflect in weakening of the association between tooth wear and chronological age [38]. This reflected in the weakening of the association between tooth wear and chronological age. Thus, it is possible to suggest that this relationship can indicate loss of cultural identity of traditional Amazonian populations since it is strong in semi-isolated communities and weakens with more contact with urban centers.

Thereby, dental wear can be used to estimate chronological age in Amazonian riverine residents, as a significant association was found between these variables. However, the reliability of this relationship decreases as a result of contact with the urban environment. Therefore, tooth wear, a strong evidence of the individual's eating habits in the past, may be an indicator of the acculturation process, and consequent cultural identity loss of traditional Amazonian populations.

Supporting information

S1 File. Approval of the Research Ethics Committee of the Health Sciences Institute of the Federal University of Pará.

(DOCX)

Click here for additional data file. (20.9KB, docx)

Acknowledgments

We thank Elma Vieira Takeuchi for her contribution to the conceptualization of the work.

Data Availability

All relevant data are within the manuscript and its figures and supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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Decision Letter 0

JJ Cray Jr

6 Jan 2020

PONE-D-19-25583

Tooth wear as an indicator of acculturation process in remote Amazonian populations

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Reviewers' comments:

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Comments to the Author

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Reviewer #1: Partly

Reviewer #2: Partly

Reviewer #3: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: I Don't Know

Reviewer #3: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This article is an analysis of the relationship between dental wear and age in an Amazonian Riverine population. The authors correlated the summed score of dental wear of the anterior teeth and premolars against personal age using a linear correlation. The resultant R squared value is intermediate between an urban population (very little relationship) and more isolated indigenous populations. The authors argue that tooth wear can be an indicator of the acculturation process, serving as a tool to assess the loss of cultural identity of traditional Amazonian populations.

There are a series of problems here - theoretical and methodological. Tooth wear is a product of the abrasiveness of food, patterns of occlusion, use of teeth as tools - as the authors point out. However, these are a relatively small part of any acculturation process. The authors use the four field model of acculturation: segregation etc etc. This model points out that there is no single trajectory in acculturation, that individual and group dimensions may vary (people may retain culturally significant values while participating in a broader economy for instance), and more recent work points out acculturation is a two way process between the groups involved. What the dental wear reflects is that as access to different types of food and technology changes so does the relationship between wear and age but this by itself is only part of acculturation and cannot used to assess the loss of cultural identity (as the authors argue in the last line of their article). Effectively the authors are asking a narrower question: does the relationship between age and dental wear alter as diet and technology change. Their data would suggest yes and this falls within the findings from a large series of other studies including extensive studies from the 1950s and 1960s at Yuendumu Central Australia.

However, in demonstrating this the authors need to consider the nature of their sample which includes people born between c2005 and 1957. In other words a population which has undergone extensive change - the younger people in their group have not experienced the same changes as the older individuals. The slope of the line is an artefact of the sample not proof that younger people will experience the same rate of dental wear as they age. In particular if the sample was divided by birth cohorts you will probably find different relationships since in figure 3 the slope for the very youngest individuals is flat. The authors need to look at the distribution of the residuals.

Furthermore their current sample includes older individuals than their comparative samples and in this instance it is the older individuals who seem to be pulling the slope so the R squared values are not strictly comparable given the structure of the sample. I recommend the authors think more carefully about the nature of the samples and the regressions.

The study is an interesting demonstration that the relationship between dental wear and age is population specific and reflects aspects of food availability and technology and that if that relationship is known for a specific population then it might be used as one way of assessing personal age of the unknown dead. However, using dental wear as a measure of acculturation is to ignore the work on acculturation and how it operates upon different dimensions.

Reviewer #2: This manuscript purports to investigate the correlation between tooth wear and chronological age in a riverine population of the Amazon. Valuable aspects of this research include its comparative aspect and the fact that urban and indigenous samples were studied by the same research team that studied the riverine group using the same methodology. This feature of the work enhances reliability and minimizes the possibility that results are impacted by differences in methodology or research protocol.

Some issues discussed in the manuscript would benefit from further consideration include the description of subsistence, use of teeth as tools, and statistical analysis of intra- and inter-observer variation in observing and recording data on tooth wear.

I would like to see a more detailed account of subsistence methods. In the abstract we are informed that the riverine groups rely on nature for subsistence, which is quite general. Later the text states that subsistence includes small-scale fishing and agriculture, plus hunted wild meat. It would be informative for the reader to have estimates of what percent of the diet comes from farming / agriculture; fishing; and hunting. Do the riverine groups forage of collect food?, what kinds? Or does all the vegetarian portion of the diet come from agriculture? Can the type of agriculture be more precisely characterized? Is the farming horticultural? swidden? Are field left fallow? for how long? Please clarify. In the same regard, how similar or variable is the mode of subsistence in different study groups? This is important in understanding inter-group variation in diet and its impact on the degree of occlusal tooth wear.

In terms of methodology, especially the assessment of degree of tooth wear, were all subjects examined by one researcher? If so, was a statistical analysis of intra-observer reliability or repeatability of degree of dental wear conducted? If more than one researcher participated in the observation / scoring of dental wear, was a statistical assessment of concordance or of discordance between observers conducted? This is an important way in which the rigor in dental data collection can be assessed and should be routinely included in such studies.

Less important issues that need attention include redundancy, accuracy of wording, and issues with the references.

Wording & phrases that need reconsideration:

in the abstract and elsewhere the authors say that riverine populations inhabit river borders, this is redundant and should be revised.

p. 3, line 61, for example: is doubly redundant. “..living along the river borders, live the riverine people…” living populations…live; and river borders …riverine. Some revision of the text is required here.

p. 3, line 49: the authors state that mineralization and tooth eruption are inaccurate methods for mature individuals. I contend this should be changed to read that timing of mineralization and tooth eruption cannot be used in estimating the chronological age of mature individuals

p. 3, line 66 (and elsewhere, p. 10, line 207, for example) use of teeth as tools is mentioned, glancing at the references does not provide further information on How teeth are used as tools?

Please provide brief examples. In fact one of the references for use of teeth as tools appears to focus on dental caries prevalence, not tooth wear.

In several places in the References section extraneous information is provided in addition to the journal name. This is unnecessary and should be deleted.

p. 14, line 319: the official journal of the Human Biology Council.

p. 15, line 327: a journal of the Association for Psychological Science.

p. 16, line 346: official publication of the American Association of Orthodontists, its

constituent societies, and the American Board of Orthodontics.

p. 16, line 363: Bericht uber die biologisch-anthropologische Literatur.

additionally multiple references to electronic sources, such as doi, ePub, PubMed, PubMed Central and others are given for the same reference - this seem unnecessary and redundant, a single source for each publication should be sufficient.

p. 16, line 348 (for example): Epub 2016/11/23. doi: 10.1016/j.ajodo.2016.03.033. PubMed PMID: 27871711.

and line 352 (for another example) Epub 2011/09/14. doi: 10.1016/j.jdent.2011.08.014. PubMed PMID: 21911033.

Reviewer #3: Interesting sociological and anthropological article. The authors are quite experts in the field and have already published about these topics in different journals. I just believe that the discussion is a little bit too short concerning the acculturation process. The authors have just cited one (main) book dated from 2003 and one article. May be it could be more developped and put in perspective with other studies (if possible).

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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PLoS One. 2020 Apr 21;15(4):e0230809. doi: 10.1371/journal.pone.0230809.r002

Author response to Decision Letter 0

17 Feb 2020

Journal Requirements:

“Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming.

Authors: We adjusted the manuscript in accordance with PLOS ONE’s style.

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Authors: Thank you for your remark. We adjusted the manuscript providing details about the methodology used.

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Authors: Thank you for your remark. We have chosen to remove the Figure 1 from the manuscript.

Reviewers Requirements:

Reviewer #1:

“There are a series of problems here - theoretical and methodological. Tooth wear is a product of the abrasiveness of food, patterns of occlusion, use of teeth as tools - as the authors point out. However, these are a relatively small part of any acculturation process. The authors use the four field model of acculturation: segregation etc etc. This model points out that there is no single trajectory in acculturation, that individual and group dimensions may vary (people may retain culturally significant values while participating in a broader economy for instance), and more recent work points out acculturation is a two way process between the groups involved. What the dental wear reflects is that as access to different types of food and technology changes so does the relationship between wear and age but this by itself is only part of acculturation and cannot used to assess the loss of cultural identity (as the authors argue in the last line of their article).”

Authors: We appreciated your suggestion and we agree. However, our intention was not to support the use of dental wear to quantify the loss of cultural identity, our aim is to provoke that it can be used as quantitative indicator of acculturation. The sentence in the last line of the article did not really pass that thought. We modified the discussion and conclusion to make our intention clearer.

“Effectively the authors are asking a narrower question: does the relationship between age and dental wear alter as diet and technology change.”

Authors: The influence of changing dietary habits and access to technology in the relationship between age and dental wear helps us to support the idea of this study, however we absolutely agree that this is not the main issue in our work. Our hypothesis is that interaction between the riverside population and the urban population changed habits of the former, which reflected in changes in the pattern of tooth wear and consequently in its relationship with age. This may suggest that the acculturation process, but we cannot really evaluate this process in general, since the relationship between dental wear and acculturation is only part of it, as you mentioned.

“Their data would suggest yes and this falls within the findings from a large series of other studies including extensive studies from the 1950s and 1960s at Yuendumu Central Australia.

However, in demonstrating this the authors need to consider the nature of their sample which includes people born between c2005 and 1957. In other words a population which has undergone extensive change - the younger people in their group have not experienced the same changes as the older individuals. The slope of the line is an artefact of the sample not proof that younger people will experience the same rate of dental wear as they age. In particular if the sample was divided by birth cohorts you will probably find different relationships since in figure 3 the slope for the very youngest individuals is flat. The authors need to look at the distribution of the residuals.”

Authors: Thank you for your suggestion. Indeed, it would be ideal to have a larger number of older people in the sample, however, according to our exclusion criteria, the individual could not have more than 7 missing teeth, which tends to exclude older participants. Note that the slope of the line for young people is caused by the concentration of wear scores between 0 and 1, reflecting the absence of wear or wear only in tooth enamel, which is “normal” for this age group. If we divide into birth cohorts, we can have a more accurate view, but more limited and with a lower power for comparison with the samples already evaluated.

“Furthermore their current sample includes older individuals than their comparative samples and in this instance it is the older individuals who seem to be pulling the slope so the R squared values are not strictly comparable given the structure of the sample. I recommend the authors think more carefully about the nature of the samples and the regressions.”

Authors: Thank you for your remark. Mean age is not much higher compared to comparative samples. The difference is approximately only 2 years for the urban population and 3 for the average indigenous population. Older individuals tend to pull the slope since they are prone to more dental wear, this inherent to the characteristic which we are evaluating. Interestingly, this was not observed in the urban population, probably due to factors besides diet which can lead to tooth wear in young people. Furthermore, we are not comparing mean difference of tooth wear only. Tooth wear is adjusted by age in the regression model.

“The study is an interesting demonstration that the relationship between dental wear and age is population specific and reflects aspects of food availability and technology and that if that relationship is known for a specific population then it might be used as one way of assessing personal age of the unknown dead. However, using dental wear as a measure of acculturation is to ignore the work on acculturation and how it operates upon different dimensions.”

Authors: We appreciate all your suggestions. We modified the text to make it clear that dental wear can be an indicator of acculturation and not a tool for measuring this process.

Reviewer #2:

“I would like to see a more detailed account of subsistence methods. In the abstract we are informed that the riverine groups rely on nature for subsistence, which is quite general. Later the text states that subsistence includes small-scale fishing and agriculture, plus hunted wild meat. It would be informative for the reader to have estimates of what percent of the diet comes from farming / agriculture; fishing; and hunting. Do the riverine groups forage of collect food?, what kinds? Or does all the vegetarian portion of the diet come from agriculture? Can the type of agriculture be more precisely characterized? Is the farming horticultural? swidden? Are field left fallow? for how long? Please clarify. In the same regard, how similar or variable is the mode of subsistence in different study groups? This is important in understanding inter-group variation in diet and its impact on the degree of occlusal tooth wear.”

Authors: Thank you for your remark. We added more information to the text regarding the dietary and subsistence habits of riverines and indigenous people in general, but some variability according to the community studied is quite common. Very specific information about the type of agriculture practiced, such as fallow time, was not added due to the literature scarcity and we have not collected it systematically.

“In terms of methodology, especially the assessment of degree of tooth wear, were all subjects examined by one researcher? If so, was a statistical analysis of intra-observer reliability or repeatability of degree of dental wear conducted? If more than one researcher participated in the observation / scoring of dental wear, was a statistical assessment of concordance or of discordance between observers conducted? This is an important way in which the rigor in dental data collection can be assessed and should be routinely included in such studies.”

Authors: Thank you for your observation. There was prior calibration of one researcher who obtained the measurements and, afterwards, the intraclass correlation test revealed excellent reproducibility for the measurements. This was added to the manuscript.

“Less important issues that need attention include redundancy, accuracy of wording, and issues with the references.

Wording & phrases that need reconsideration: in the abstract and elsewhere the authors say that riverine populations inhabit river borders, this is redundant and should be revised.

p. 3, line 61, for example: is doubly redundant. “..living along the river borders, live the riverine people…” living populations…live; and river borders …riverine. Some revision of the text is required here.

p. 3, line 49: the authors state that mineralization and tooth eruption are inaccurate methods for mature individuals. I contend this should be changed to read that timing of mineralization and tooth eruption cannot be used in estimating the chronological age of mature individuals.”

Authors: We removed redundant phrases from the manuscript, improved the accuracy of wording and adjusted the references. Thank you.

“p. 3, line 66 (and elsewhere, p. 10, line 207, for example) use of teeth as tools is mentioned, glancing at the references does not provide further information on How teeth are used as tools?

Please provide brief examples. In fact one of the references for use of teeth as tools appears to focus on dental caries prevalence, not tooth wear.”

Authors: Thank you for your remark. Teeth can be used as tools to cut food or fishing lines, to hold artifacts while fishing or even to break things. However, it is difficult to find a reference for the occurrence of these habits, as there are no studies that describe them. Thus, we decided to remove this sentence from the text.

“In several places in the References section extraneous information is provided in addition to the journal name. This is unnecessary and should be deleted.

p. 14, line 319: the official journal of the Human Biology Council.

p. 15, line 327: a journal of the Association for Psychological Science.

p. 16, line 346: official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics.

p. 16, line 363: Bericht uber die biologisch-anthropologische Literatur.

Additionally, multiple references to electronic sources, such as doi, ePub, PubMed, PubMed Central and others are given for the same reference - this seem unnecessary and redundant, a single source for each publication should be sufficient.

p. 16, line 348 (for example): Epub 2016/11/23. doi: 10.1016/j.ajodo.2016.03.033. PubMed PMID: 27871711.

and line 352 (for another example) Epub 2011/09/14. doi: 10.1016/j.jdent.2011.08.014. PubMed PMID: 21911033.”

Authors: Thank you for your remarks. We remove all unnecessary information.

Reviewer #3: Interesting sociological and anthropological article. The authors are quite experts in the field and have already published about these topics in different journals. I just believe that the discussion is a little bit too short concerning the acculturation process. The authors have just cited one (main) book dated from 2003 and one article. May be it could be more developped and put in perspective with other studies (if possible).

Authors: Thank you for all your suggestions. We improved the discussion concerning the acculturation process and added more references to describe this process. However, it is difficult to put other studies in perspective due to the scarcity of works on the acculturation process in riverines communities or similar populations.

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Decision Letter 1

JJ Cray Jr

10 Mar 2020

Tooth wear as an indicator of acculturation process in remote Amazonian populations

PONE-D-19-25583R1

Dear Dr. Mecenas,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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With kind regards,

JJ Cray Jr., Ph.D.

Academic Editor

PLOS ONE

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Reviewers' comments:

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Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #3: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #3: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #3: All the comments I made have been taken into consideration by the authors. I consider this paper acceptable for publication.

**********

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Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #3: No

Acceptance letter

JJ Cray Jr

20 Mar 2020

PONE-D-19-25583R1

Tooth wear as an indicator of acculturation process in remote Amazonian populations

Dear Dr. Mecenas:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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