Abstract
Purpose
This study aimed to evaluate the association between interdental cleaning and untreated root caries amongst middle-aged and older adults in the US.
Materials and methods
Data were obtained from the National Health and Nutrition Examination Survey (NHANES) (2015–2016 and 2017–2018). Adults aged ≥40 years who underwent full mouth examination and root caries assessment were included. Participants were classified based on their interdental cleaning frequency as none, 1–3 d/wk, and 4–7 d/wk. Associations between interdental cleaning and untreated root caries were assessed using a weighted multivariable logistic regression model adjusted for sociodemographics, general behaviour, general health condition, oral conditions, oral health behavior, and dietary factors. Subgroup analyses stratified by age and sex were performed after adjusting for covariates in the logistic regression models.
Results
The prevalence of untreated root caries was 15.3% amongst 6217 participants. Interdental cleaning for 4–7 d/wk was a significant risk factor (odds ratio, 0.67; 95% confidence interval, 0.52–0.85). It was associated with a 40% reduction in the risk of untreated root caries in participants aged 40 to 64 years and a 37% reduction in women. Untreated root caries was also significantly associated with age, family income, smoking status, root restoration, number of teeth, untreated coronal caries, and recent dental visit.
Conclusions
Interdental cleaning for 4–7 d/wk was associated with fewer untreated root caries amongst middle-aged adults and women in the US. The risk of root caries increases with age. Low family income was a risk indicator for root caries amongst middle-aged adults. Additionally, smoking, root restoration, number of teeth, untreated coronal caries, and recent dental visits were common risk factors for root caries in middle-aged and older people in the US.
Key words: Cross-sectional study, Interdental cleaning, National Health and Nutrition Examination Survey, Untreated root caries
Introduction
The emphasis on retaining and maintaining the natural dentition through preventing dental caries and attention on root caries is increasing.1 Root caries affect middle-aged and older adults,2,3 and the updated prevalence of untreated root caries was >10% amongst adults aged ≥40 years in the US between 2017 and 2020.4 Therefore, preventing and treating root caries in adults is important. The proportion of sites where root caries are detected have been previously reported, with lesions found on buccal (53%), distal (24.9%), lingual (12.3%), and mesial (9.8%) surfaces amongst 796 adults aged 20–65 years in the USA.5 Moreover, 47% of untreated root caries were observed on the distal surface and 28% on the mesial surface amongst 306 Hong Kong elders aged 62–92 years when root surface restorations were excluded.6
As a multifactorial disease, root caries is mainly associated with fermentable carbohydrates, cariogenic bacteria, and host-related factors.7,8 Cariogenic bacteria produce lactic acid–using carbohydrates, which demineralises root structures after root surface exposure.9 Several factors, including age, socioeconomic status, smoking, gingival recession, and oral hygiene, are also associated with root caries.10
Poor oral hygiene is a shared risk factor for root caries, coronal caries, and periodontitis.11 Root caries usually present as a soft decayed lesion in the dentine of the tooth root below the cementoenamel junction (CEJ),12 which can be attributed to loss of periodontal attachment following periodontitis.13 Oral health–related behaviours associated with gingival recession are also associated with root caries.14 Interdental cleaning is associated with lower levels of coronal and interproximal caries15,16 and reduces the risk of gingivitis and periodontitis.17,18 The central role of the microbial oral biofilm in caries development and periodontal disease is known19; however, direct evidence that interdental cleaning is associated with a lower incidence of periodontal disease and caries in adults is limited.20 Furthermore, few studies have investigated the relationship between interdental cleaning and root caries, with conflicting findings.21, 22, 23, 24 Therefore, we aimed to determine whether interdental cleaning is associated with untreated root caries amongst middle-aged and older adults in the US using a nationally representative sample. We hypothesised that interdental cleaning is associated with a lower risk of developing untreated root caries amongst adults.
Methods
Study population and design
The study used data from the National Health and Nutrition Examination Survey (NHANES) conducted in 2015–2016 and 2017–2018. NHANES is a comprehensive, cross-sectional survey that provides objective health information for the entire US population. A full description of the NHANES methodology and data collection procedure is available at www.cdc.gov/nchs/nhanes.htm.25 Data from 6217 adults aged ≥40 years who underwent a complete dental examination and root caries assessment in the database were included in the analysis (Figure). The National Center for Health Statistics Research Ethics Review Board approved the survey protocols, and all participants (or their proxy) provided written informed consent for data collection and analysis.
Fig.
Flowchart of the participants.
Study variables
Outcome variable: untreated root caries
The key outcome variable was the presence or absence of untreated root caries based on the NHANES examiners’ determination of any untreated root caries on all teeth, excluding the third molars. Licensed dentists assessed untreated root caries using a strict protocol. A surface-reflecting mirror and a #23 dental explorer were used for inspection, and all exposed portions of the tooth root surface were examined. Untreated root caries was defined as any decay occurring on the root surface apical to the CEJ, including active lesions that appear yellow or orange, yellowish-brown, or light brown or lesions in remission with or without cavitation or hardening and that are darker or almost black. The outcome-variable acquisition process is available at www.cdc.gov/nchs/nhanes.
The presence of untreated root caries was recorded as “yes” or “no.” The prevalence of untreated root caries was the percentage of participants with at least 1 untreated root caries.
Exposure variable: interdental cleaning
The main exposure variable was interdental cleaning. This survey used the question: “Aside from brushing your teeth with a toothbrush in the last 7 days, how many days did you use dental floss or any other device to clean between your teeth?” to assess interdental cleaning. The responses were categorised as none, 1–3 d/wk, or 4–7 d/wk.
Other independent variables
Based on previous studies,10,12 independent variables, including sociodemographic factors, general behaviour, general health condition, oral conditions, oral health behaviour, and dietary factors, were considered as covariates in our analysis.
-
1.
Sociodemographic factors: Age was a continuous variable. Sex was categorised as “male” or “female.” Race/ethnicity was categorised as “Hispanic,” “Caucasian,” “African American,” or “other races” (including multiracial). Education attainment was categorised as “< high school,” “high school,” or “> high school.” The family income-to-poverty ratio was used to calculate the family income level and was categorised as <1.3, 1.3–3.5, or ≥3.5.
-
2.
General behaviour: Smoking status was categorisd as “never smoked,” “current smoker,” or “former smoker.”
-
3.
General health condition: Diabetes mellitus was self-reported and categorised as “yes” or “no”.
-
4.
Oral conditions: Root restoration for the root caries was categorised as “yes” or “no.” The number of teeth was calculated from the remaining teeth (0–28, excluding the third molars). Untreated coronal caries was categorised as “yes” or “no.”
-
5.
Oral health behaviour: Recent dental visit was categorised as “within the past year” or “>1 year.”
-
6.
Dietary factors: Individual daily total carbohydrate and sugar intake in the first 24-hour dietary recall data were used. A 2-day average of total carbohydrate and sugar intake was used if participants responded to a second 24-hour dietary interview. Total carbohydrate and sugar intake were categorised based on tertiles as “low,” “middle,” and “high.” The covariate acquisition process is available at www.cdc.gov/nchs/nhanes/.
Statistical analysis
All statistical analyses were performed using Stata 15.0 (Stata Corp LLC). Associations are presented as odds ratios (ORs) with 95% confidence intervals (CIs). Statistical significance was set at P < .05. Survey procedures were used to account for the complex sampling design of the NHANES dataset. Sample weights were used to generate results on a national level. After adjusting for covariates, 3 weighted logistic regression models were developed to determine whether interdental cleaning was associated with untreated root caries. The unadjusted model was adjusted for none. The semi-adjusted model was adjusted for sociodemographic factors (including age, sex, race/ethnicity, education, and family income-to-poverty ratio). The fully adjusted model was further adjusted for smoking status, diabetes mellitus, root restoration, number of teeth, untreated coronal caries, recent dental visits, and total carbohydrate and sugar intake in addition to the covariates included in the semi-adjusted model. Subgroup analyses stratified by age and sex were performed after adjusting for the same covariates in the fully adjusted model. We created a separate category for covariates with missing observations and conducted regression analysis to account for missing observations and their potential effect on the outcome. We report the odds ratios for unadjusted, semi-adjusted, and fully-adjusted models.
Results
Baseline characteristics
Data for 6217 participants were obtained from the US NHANES dataset. The sample was representative of approximately 135.0 million institutionalised adults after adjusting for weighting. Table 1 summarises the characteristics of the study sample. The average age was 58.12 ± 0.20 years; 52.40% of participants were women. The prevalence of untreated root caries amongst adults was 15.30%, with the highest proportion found in those who did not perform interdental cleaning (27.15%), followed by those who performed interdental cleaning 1–3 d/wk (14.40%) and 4–7 d/wk (10.55%). Amongst the eligible participants, 22.88% did not perform interdental cleaning, whereas 52.39% performed it 4–7 d/wk. Participants with untreated root caries were more likely to be older, male, African American, and smokers. Further, they were more likely to have low education and income levels and have diabetes. These participants had root restoration, had fewer teeth, had untreated coronal caries, visited a dentist >1 year previously, did not perform interdental cleaning, and had higher carbohydrate and sugar intake.
Table 1.
Characteristics of participants (≥ 40 years of age) stratified by untreated root caries category (NHANES 2015–2018).
| Full sample | Untreated root caries |
|||
|---|---|---|---|---|
| Characteristic | No. (weighted %) or mean± SEs | No. (weighted %) or mean ± SEs |
||
| No | Yes | P value | ||
| 6217 | 5,040 (84.70) | 1177 (15.30) | <.001 | |
| Sociodemographic factors | ||||
| Age, y | 58.12 ± 0.20 | 57.84 ± 0.22 | 59.69 ± 0.45 | <.001 |
| Sex | <.001 | |||
| Female | 3190 (52.40) | 2697 (86.60) | 493 (13.40) | |
| Male | 3027 (47.60) | 2343 (82.62) | 684 (17.38) | |
| Race/ethnicity | <.001 | |||
| Hispanic | 1667 (12.69) | 1372 (85.02) | 295 (14.98) | |
| Caucasian | 2130 (68.06) | 1733 (85.82) | 397 (14.18) | |
| African American | 1392 (10.21) | 1051 (77.15) | 341 (22.85) | |
| Other races, including multiracial | 1028 (9.04) | 884 (84.39) | 144 (15.61) | |
| Educationa | <.001 | |||
| < High school | 1381 (11.75) | 1017 (73.33) | 364 (26.67) | |
| High school | 1369 (22.89) | 1053 (79.15) | 316 (20.85) | |
| > High school | 3457 (65.36) | 2963 (88.71) | 494 (11.29) | |
| Family PIRa | <.001 | |||
| <1.3 | 1473 (15.46) | 1043 (69.71) | 430 (30.29) | |
| ≥1.3, <3.5 | 2187 (34.29) | 1741 (80.37) | 446 (19.63) | |
| ≥3.5 | 1807 (50.25) | 1667 (92.95) | 140 (7.05) | |
| General behaviour | ||||
| Smoking statusa | <.001 | |||
| Never smoked | 3539 (55.96) | 3064 (90.11) | 475 (9.89) | |
| Currently smoking | 991 (14.43) | 626 (65.74) | 365 (34.26) | |
| Former smoker | 1683 (29.61) | 1348 (83.72) | 335 (16.28) | |
| General health condition | ||||
| Diabetes mellitusa | <.001 | |||
| Yes | 1251 (15.55) | 936 (78.54) | 315 (21.46) | |
| No | 4962 (84.45) | 4101 (85.85) | 861 (14.15) | |
| Oral conditions | ||||
| Root restoration | <.001 | |||
| Yes | 400 (6.71) | 259 (72.08) | 141 (27.92) | |
| No | 5817 (93.29) | 4781 (85.61) | 1036 (14.39) | |
| Mean number of teeth | 23.19 ± 0.11 | 24.14 ± 0.10 | 17.98 ± 0.30 | <.001 |
| Untreated coronal caries | <.001 | |||
| Yes | 1468 (18.71) | 737 (50.72) | 731 (49.28) | |
| No | 4749 (81.29) | 4303 (92.52) | 446 (7.48) | |
| Oral health behaviors | ||||
| Recent dental visita | <.001 | |||
| Within the past year | 3625 (66.14) | 3222 (91.04) | 403 (8.96) | |
| >1 year | 2575 (33.86) | 1808 (72.41) | 767 (27.59) | |
| Interdental cleaning | <.001 | |||
| None | 1733 (22.88) | 1181 (72.85) | 552 (27.15) | |
| 1–3 d/wk | 1401 (24.73) | 1167 (85.60) | 234 (14.40) | |
| 4–7 d/wk | 3083 (52.39) | 2692 (89.45) | 391 (10.55) | |
| Dietary factors | ||||
| Total carbohydrate intakea | .061 | |||
| Low | 1927 (32.54) | 1543 (84.42) | 384 (15.58) | |
| Middle | 1926 (32.15) | 1600 (86.29) | 326 (13.71) | |
| High | 1927 (35.31) | 1541 (83.61) | 386 (16.39) | |
| Total sugar intakea | <.001 | |||
| Low | 1926 (30.72) | 1568 (85.26) | 358 (14.74) | |
| Middle | 1927 (34.12) | 1610 (87.56) | 317 (12.44) | |
| High | 1927 (35.16) | 1506 (81.54) | 421 (18.46) | |
Continuous variables are expressed as mean ± SEs (standard errors). Categorical variables are expressed as percentages. Weighted chi-square tests (categorical variables) and a weighted linear regression model (continual variables) were conducted to calculate the differences amongst subgroups.
P < .05 represents a significant association.
Education categories had 10 missing observations; family PIR categories had 750 missing observations; smoking status categories had 4 missing observations; diabetes mellitus categories had 4 missing observations; recent dental visit categories had 17 missing observations; total carbohydrate intake had 437 missing observations; total sugar intake had 437 missing observations.
Family PIR, family income-to-poverty ratio.
Association of interdental cleaning with untreated root caries
Unadjusted and semi-adjusted results indicated that participants who performed interdental cleaning had a lower risk of having untreated root caries than those who did not (Table 2). The association of interdental cleaning for 4–7 d/wk with untreated root caries remained significant after full adjustment for covariates (Table 2). Participants who performed interdental cleaning 4–7 d/wk had 33% lower odds of having untreated root caries than those who did not (OR, 0.67; 95% CI, 0.52–0.85) (Table 2).
Table 2.
Weighted multivariate logistic regression analysis of interdental cleaning with untreated root caries amongst adults (≥ 40 years) in the US (NHANES 2015–2018).
| Unadjusted model | Semi-adjusted model | Fully adjusted model | |
|---|---|---|---|
| Characteristics | OR (95% CI) | OR (95% CI) | OR (95% CI) |
| Interdental cleaning | |||
| None | Ref | Ref | Ref |
| 1–3 d/wk | 0.45 (0.35–0.59)⁎⁎⁎ | 0.63 (0.48–0.83)⁎⁎ | 1.05 (0.75–1.45) |
| 4–7 d/wk | 0.32 (0.26–0.39)⁎⁎⁎ | 0.44 (0.35–0.55)⁎⁎⁎ | 0.67 (0.52–0.85)⁎⁎ |
| Sociodemographic factors | |||
| Age, y | 1.01 (1.01-1.02)⁎⁎ | 1.01 (1.01–1.02)* | |
| Sex | |||
| Female | Ref | Ref | |
| Male | 1.34 (1.10–1.62)⁎⁎ | 1.10 (0.90–1.36) | |
| Race/ethnicity | |||
| Hispanic | 0.61 (0.42–0.88)* | 0.79 (0.58–1.08) | |
| Caucasian | Ref | Ref | |
| African American | 1.24 (0.93–1.66) | 0.95 (0.68–1.35) | |
| Other races, including multiracial | 0.90 (0.64–1.28) | 1.07 (0.63–1.82) | |
| Education | |||
| < High school | 1.68 (1.27–2.23)⁎⁎ | 1.03 (0.75–1.41) | |
| High school | 1.49 (1.23–1.80)⁎⁎⁎ | 0.90 (0.71–1.13) | |
| > High school | Ref | Ref | |
| Family PIR | |||
| <1.3 | 4.55 (3.36–6.16)⁎⁎⁎ | 1.64 (1.06–2.55)* | |
| ≥1.3, <3.5 | 2.64 (1.81–3.83)⁎⁎⁎ | 1.42 (1.00–2.03) | |
| ≥3.5 | Ref | Ref | |
| General behavior | |||
| Smoking status | |||
| Never smoking | Ref | ||
| Current smoker | 2.02 (1.51–2.68)⁎⁎⁎ | ||
| Former smoking | 1.26 (1.03–1.54)* | ||
| General health condition | |||
| Diabetes mellitus | |||
| Yes | 1.16 (0.88–1.53) | ||
| No | Ref | ||
| Oral conditions | |||
| Root restoration | |||
| Yes | 2.25 (1.38–3.67)⁎⁎ | ||
| No | Ref | ||
| No. of teeth | 0.91 (0.89–0.92)⁎⁎⁎ | ||
| Untreated coronal caries | |||
| Yes | 8.41(6.30–11.23)⁎⁎⁎ | ||
| No | Ref | ||
| Oral health behaviour | |||
| Recent dental visit | |||
| Within the past year | Ref | ||
| >1 year | 1.71 (1.29–2.25)⁎⁎⁎ | ||
| Dietary factors | |||
| Total carbohydrate intake | |||
| Low | Ref | ||
| Middle | 0.83(0.59–1.15) | ||
| High | 0.86(0.51–1.43) | ||
| Total sugar intake | |||
| Low | Ref | ||
| Middle | 0.97(0.65–1.45) | ||
| High | 1.38(0.82–2.33) |
The unadjusted model was adjusted for none. The semi-adjusted model was adjusted for age, sex, race/ethnicity, education, and family PIR. The fully adjusted model was adjusted for age, sex, race/ethnicity, education, family PIR, smoking status, diabetes mellitus, root restoration, number of teeth, untreated coronal caries, recent dental visit, total carbohydrate intake, and total sugar intake.
Ref, reference; family PIR; family income-to-poverty ratio.
P < .05;
P < .01;
P < .001.
Association of covariates with untreated root caries
In the fully adjusted model, we observed that older people had higher odds of having untreated root caries. Sex was not associated with untreated root caries (Table 2). Individuals with the lowest family income had substantially higher odds (1.64 times) of having untreated root caries than those with the highest family income. Current and former smokers had higher odds of having untreated root caries than nonsmokers (Table 2). Furthermore, individuals with root restoration and fewer teeth had a higher risk of having untreated root caries, whereas those with untreated coronal caries had 8.41 times higher odds of having untreated root caries. Participants who visited a dentist >1 year previously had higher odds of having untreated root caries than those who visited a dentist within the last year (Table 2).
Subgroup analysis for determining the association of interdental cleaning with untreated root caries
Based on stratification by age and sex, an effect size was observed (Table 3 and Table 4). After adjusting for all covariates, compared with no interdental cleaning, interdental cleaning for 4–7 d/wk was associated with 40% lower odds of having untreated root caries amongst middle-aged (40–64 years; OR, 0.60; 95% CI, 0.43–0.83) and 37% lower odds amongst women (OR, 0.63; 95% CI, 0.43–0.91). However, no significant difference was observed between those who performed interdental cleaning and those who did not amongst the elderly (≥65 years) and men (Table 3 and Table 4).
Table 3.
Sex subgroup analysis for the association between interdental cleaning and untreated root caries amongst adults (≥40 years) in the US (NHANES 2015–2018).
| Male | Female | |
|---|---|---|
| No. (weighted %) | 3027 (47.60) | 3190 (52.40) |
| Characteristics | OR (95% CI) | OR (95% CI) |
| Interdental cleaning | ||
| None | Ref | Ref |
| 1–3 d/wk | 0.89 (0.60–1.32) | 1.14 (0.59–2.19) |
| 4–7 d/wk | 0.68 (0.41–1.12) | 0.63 (0.43–0.91)* |
We adjusted for age, race/ethnicity, education, family PIR, smoking status, diabetes mellitus, root restoration, number of teeth, untreated coronal caries, recent dental visits, and total carbohydrate and sugar intake.
Ref, reference; family PIR; family income-to-poverty ratio.
P < .05;
⁎⁎P < .01; ⁎⁎⁎P < .001.
Table 4.
Age subgroup analysis for the association between interdental cleaning and untreated root caries amongst adults (≥ 40 years of age) in the USA (NHANES 2015–2018).
| Middle-aged adults | Older adults | |
|---|---|---|
| No. (weighted %) | 4145 (70.13) | 2072 (29.87) |
| Characteristics | OR (95% CI) | OR (95% CI) |
| Interdental cleaning | ||
| None | Ref | Ref |
| 1–3 d/wk | 0.90 (0.61–1.34) | 1.40 (0.80–2.47) |
| 4–7 d/wk | 0.60 (0.43–0.83)⁎⁎ | 0.79 (0.55–1.14) |
| Sociodemographic factors | ||
| Age, y | 1.03 (1.00–1.06) | 1.03 (0.99–1.08) |
| Sex | ||
| Female | Ref | Ref |
| Male | 1.13 (0.80–1.60) | 1.12 (0.81–1.54) |
| Race/ethnicity | ||
| Hispanic | 0.74 (0.50–1.10) | 1.05 (0.66–1.68) |
| Caucasian | Ref | Ref |
| African American | 0.92 (0.58–1.47) | 1.08 (0.66–1.78) |
| Other races, including multiracial | 1.04 (0.48–2.22) | 1.24 (0.70–2.20) |
| Education | ||
| < High school | 1.08 (0.68–1.72) | 0.98 (0.63–1.54) |
| High school | 0.93 (0.68–1.27) | 0.77 (0.48–1.22) |
| >High school | Ref | Ref |
| Family PIR | ||
| <1.3 | 1.95 (1.01–3.80)* | 1.02 (0.60–1.73) |
| ≥1.3, <3.5 | 1.50 (0.87–2.59) | 1.25 (0.81–1.94) |
| ≥3.5 | Ref | Ref |
| General behaviour | ||
| Smoking status | ||
| Never smoked | Ref | Ref |
| Current smoker | 1.92 (1.47–2.51)⁎⁎⁎ | 1.94 (1.01–3.71)* |
| Former smoker | 1.49 (1.02–2.18)* | 1.03 (0.63–1.68) |
| General health condition | ||
| Diabetes mellitus | ||
| Yes | 0.98 (0.71–1.36) | 1.28 (0.89–1.84) |
| No | Ref | Ref |
| Oral conditions | ||
| Root restoration | ||
| Yes | 2.04 (1.03–4.03)* | 2.52 (1.41–4.52)⁎⁎ |
| No | Ref | Ref |
| No. of teeth | 0.89 (0.87–0.91)⁎⁎⁎ | 0.93 (0.91–0.95)⁎⁎⁎ |
| Untreated coronal caries | ||
| Yes | 9.33 (6.32–13.77)⁎⁎⁎ | 6.64 (4.17–10.56)⁎⁎⁎ |
| No | Ref | Ref |
| Oral health behaviour | ||
| Recent dental visits | ||
| Within the past year | Ref | Ref |
| >1 year | 1.78 (1.22–2.60)⁎⁎ | 1.67 (1.20–2.33)⁎⁎ |
| Dietary factors | ||
| Total carbohydrate intake | ||
| Low | Ref | Ref |
| Middle | 0.70 (0.47–1.03) | 0.95 (0.44–2.06) |
| High | 0.78 (0.37–1.62) | 0.86 (0.40–1.84) |
| Total sugar intake | ||
| Low | Ref | Ref |
| Middle | 0.96 (0.64–1.44) | 1.06 (0.48–2.34) |
| High | 1.33 (0.71–2.50) | 1.60 (0.74–3.47) |
We adjusted for age, sex, race/ethnicity, education, family PIR, smoking status, diabetes mellitus, root restoration, number of teeth, untreated coronal caries, recent dental visits, and total carbohydrate and sugar intake.
Ref, reference; family PIR; family income-to-poverty ratio.
P < .05;
P < .01;
P < .001.
Association of covariates with untreated root caries amongst the middle-aged and elderly
After adjusting for all established covariates, our study discovered that the risk factors for untreated root caries in US middle-aged (40–64 years) and elderly (≥65 years) adults were similar, except for interdental cleaning, family income, and former smoking. Moreover, age was not associated with higher odds of having root caries in either subgroup (Table 4).
Discussion
Few studies have explored the effect of interdental cleaning on root caries; a study discovered that daily flossing or more frequent flossing was significantly associated with a lower prevalence of new root decay.21 Conversely, some studies did not identify interdental cleaning as a risk factor for root caries.22, 23, 24 Here, participants who performed interdental cleaning 4–7 d/wk had a significantly lower prevalence of untreated root caries than those who did not amongst adults aged ≥40 years.
The protective effect of interdental cleaning on untreated root caries may be explained by the following reasons. First, interdental cleaning mechanically removes plaque from adjacent tooth surfaces that are often difficult to access via a conventional toothbrush,26 thereby reducing the risk of root caries. Second, interdental cleaning may reduce periodontal disease by removing plaque,18 and the buccal and lingual periodontal tissues may benefit from less interproximal periodontal disease. This decreases the risk of root surface exposure and the subsequent development of root caries.
Our study discovered no significant difference in the prevalence of root caries between individuals who performed interdental cleaning at a low frequency and those who did not perform interdental cleaning after adjusting for all covariates. These results suggest that low frequency is ineffective, and frequency is more important than the interdental cleaning method. For instance, low-frequency cleaners (1–3 d/wk) are more likely to have severe periodontal disease than high-frequency cleaners (4–7 d/wk). Therefore, increasing the frequency of interdental cleaning may benefit individuals with severe periodontal disease.15 High-frequency interdental cleaning (4–7 d/wk) was significantly associated with lower odds of untreated root caries in American adults. However, the association was inconsistent across different population groups; the association was not significant in older adults aged ≥65 years and men.
Generally, age has been identified as a risk factor for root caries.22 Our study demonstrated that the effect of age on the prevalence of root caries is low. Some health risk factors for the elderly, such as comorbidities, functional disabilities, or cognitive impairments, may pose barriers to accessing dental care, thereby affecting oral health.27 Periodontitis is most common amongst adults aged ≥65 years in the US.28 The extent of gingival recession increases with age.13 Furthermore, the ability of older adults to care for themselves declines with age, resulting in deterioration of oral hygiene. These factors contribute to a higher risk of root caries in older adults, reducing the marginal effect of interdental cleaning.
Regarding sex differences in oral health, men smoke at higher rates than women,29 have a higher prevalence of periodontal diseases,30 and are more likely to brush harder, which may result in gingival recession, contributing to root caries development.31 Men also have fewer dental visits, a poorer perception of their gum and tooth health, and poorer flossing habits,32 which may lead to a poorer interdental cleaning effect and contribute to root caries development.
Other sociodemographic factors were also related to root decay. Disparities in oral health based on race/ethnicity have been documented.33 African Americans have higher odds of developing coronal caries than Caucasians.34 Here, Hispanics had lower odds of having untreated root caries than Caucasians in the semi-adjusted model. This racial disparity was attenuated and rendered insignificant in the fully adjusted model. A significant association between higher income and lower prevalence of root caries has been reported.22 However, our results suggest that family income may not be a risk factor for untreated root caries in older adults. One possible explanation may be that the effect of income on oral health diminishes in older age groups or other factors, such as regular dental visits, self-oral health care ability, or cognitive impairment, become more prominent.
Diabetes may increase the incidence of dental caries in adults, as poor glycaemic control increases the risk of caries in people with diabetes.35 However, a prospective population-based study found no difference in the odds of caries in participants with well-controlled diabetes compared with those without diabetes. Participants with diabetes had significantly higher rates of missing teeth than those without diabetes.36 Here, diabetes was not significantly associated with the prevalence of root caries amongst middle-aged and elderly participants after adjusting for all covariates. One potential explanation is that middle-aged and older people with diabetes may pay more attention to controlling their blood sugar, such as reducing their caries-causing food intake, or they may have fewer teeth, which could decrease the prevalence of root caries.
Smoking was identified as a significant risk factor for predicting root caries in middle-aged and elderly populations, which is consistent with previous findings.11,22 We used root restoration as a baseline variable for root caries experience to evaluate the incidence of untreated root caries. Middle-aged and elderly participants with root restoration were respectively 2.04 and 2.52 times more likely to have untreated root caries than those without root restoration, consistent with previous findings.21,37 Furthermore, previous studies have reported caries as the major reason for tooth loss,38 which agrees with our finding that the number of teeth is negatively correlated to the prevalence of root caries. Our study found a positive association between coronal caries and root caries, consistent with a previous report.39 Regular attendees to a dentist may be able to prevent root caries, and individuals who visit a dentist within a year pay more attention to their oral hygiene, resulting in relatively lower odds of having untreated root caries.
Fermentable carbohydrates, such as sugars and starches, are necessary for the occurrence and development of dental caries.40 Dietary sugar and carbohydrate intake were significantly associated with tooth decay in Australian adults.41 Here, the intake of carbohydrates and sugar did not significantly modify the association between interdental cleaning and root caries. Furthermore, after adjusting for all confounding factors, higher carbohydrate or sugar intake was not associated with higher odds of root caries. Possible explanations may include the flushing function of saliva, the prevention of caries through fluoride application, and the low carbohydrate dependence of cariogenic species involved in root caries—because they can utilise the nutrients from degraded collagen in dentin tubules.42
This study has some limitations. First, the cross-sectional design restricted us from determining a causal relationship between interdental cleaning and root caries. Second, data on brushing or fluoride use in adults in the NHANES dataset were unavailable; hence, we could not explore their effects on the prevalence of root caries. Third, the benefits of interdental cleaning depend on how effectively it is implemented43; however, data on the effectiveness of interdental cleaning were unavailable. Finally, the NHANES dataset did not include information on the number of root caries and the proportion of root surface affected by caries. Therefore, we could not evaluate the exact effect of interdental cleaning.
However, the NHANES clinical data on dental caries measurements were of high quality and reliability.44 The validity of our findings was strengthened because we used a large-scale, nationally representative sample. Notably, interdental cleaning for 4–7 d/wk was a significant factor in reducing untreated root caries amongst American middle-aged adults and women after accounting for other confounding factors. Our study provides insight into the relationship between risk factors and untreated root caries amongst middle-aged and older people in the US.
In conclusion, we found that interdental cleaning (4–7 d/wk) is associated with fewer untreated root caries amongst middle-aged adults and women in the US, thereby confirming our hypothesis. The risk of root caries increases with age, and low family income is a risk indicator for root caries amongst middle-aged adults in the US. American middle-aged and older people share common risk factors for root caries, including smoking, root restoration, number of teeth, untreated coronal caries, and recent dental visits.
Acknowledgements
We would like to thank Editage (www.editage.cn) for English language editing.
Author contributtions
LFS and ZXZ contributed to data collection, analysis, and manuscript writing. QQT contributed to the study design. LBH contributed to the study design and manuscript writing.
Conflict of interest
None disclosed.
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