Utilization of tooth filling services by people with disabilities in Taiwan

Background The oral condition of people with disabilities has considerable influence on their physical and mental health. However, nationwide surveys regarding this group have not been conducted. For this study, we used the National Health Insurance Research Database to explore the tooth filling utilization among people with disabilities. Methods Using the database of the Ministry of the Interior in 2008 which included people with disabilities registered, we merged with the medical claims database in 2008 of the Bureau of National Health Insurance to calculate the tooth filling utilization and to analyze relative factors. We recruited 993,487 people with disabilities as the research sample. Results The tooth filling utilization was 17.53 %. The multiple logistic regression result showed that the utilization rate of men was lower than that of women (OR = 0.78, 95 % CI = 0.77–0.79) and older people had lower utilization rates (aged over 75, OR = 0.22, 95 % CI = 0.22–0.23) compared to those under the age of 20. Other factors that significantly influenced the low tooth filling utilization included a low education level, living in less urbanized areas, low economic capacity, dementia, and severe disability. Conclusion We identified the factors that influence and decrease the tooth-filling service utilization rate: male sex, old age, low education level, being married, indigenous ethnicity, residing in a low urbanization area, low income, chronic circulatory system diseases, dementia, and severe disabilities. We suggest establishing proper medical care environments for high-risk groups to maintain their quality of life.


Background
Oral diseases are crucial health concerns for people with disabilities [1]. Because of their physical and mental limitations, the activities of daily living of people with disabilities are restricted. Moreover, people with disabilities have limited self-care abilities, relatively poor health conditions, and a low utilization of medical services [2][3][4]; hence, they generally have poor oral conditions and several periodontal diseases [5][6][7]. Oral health conditions generally influence various aspects of life, such as nutritional status, quality of life, and personal perceptions and feelings [8][9][10]. In addition, oral health is a critical factor influencing overall health. Therefore, the oral health and treatment of people with disabilities require further attention.
Regarding the number of decayed, missing, or filled teeth (i.e., the DMFT index), studies have indicated that the total DMFT score for people with disabilities is higher than that for people without disabilities [6]. Despite the high proportion of decayed or missing teeth, people with disabilities have a low rate of tooth fillings [11]. Tooth decay can induce pain and cause difficulty in food consumption and chewing; in severe cases, infection-caused sepsis can endanger patients' lives [12,13]. Missing teeth may alter teeth arrangement, affect chewing ability [14], and trigger periodontal diseases. Moreover, malocclusion caused by missing teeth can induce temporomandibular pain and affect the facial appearance [15].
According to dental early-treatment concepts, tooth fillings can prevent teeth from further decay, preserve the original tooth root, reduce the possibility of severe decay or cavities, and reduce the utilization of additional medical services. Therefore, the utilization of the toothfilling services is a major indicator of the oral healthcare status for people with disabilities. In addition, the utilization of preventive health services was associated with gender, marital status [16], educational level, age, income, health status, severity of disability, and urbanization level of residence area [17].
This study used a nationwide survey to investigate the tooth-filling service utilization rate among approximately 0.93 million Taiwanese people with disabilities and to explore the factors that influence tooth-filling utilization. Moreover, we present a population-based statistical analysis that could serve as a reference or foundation for future studies.

Data source and processing
We used the database of the Ministry of the Interior (

Description of variables
The independent variables were (a) personal characteristics, such as sex, age, education level, marital status, and indigenous ethnicity; (b) economic status, such as premiumbased monthly salary (seven levels based on income) and low-income households; (c) health condition, such as catastrophic injuries or illnesses, chronic diseases, disability categories, and disability degrees; and (d) environmental factors, such as the degree of urbanization (levels 1-7 for highly urbanized cities and townships, moderately urbanized cities and townships, emerging cities and townships, average cities and townships, aging cities and townships, agricultural cities and townships, and remote cities and townships, respectively).

Study participants
The study participants encompassed people with disabilities of all ages. Disabilities considered in this study were visual impairment, hearing impairment, speech impediment, limb impairment, mental illness, multiple impairments, major organ malfunction, facial disfigurement, dementia, autism, chromosomal abnormalities, congenital metabolic disorders, congenital defects, mental illness, impaired balance, refractory epilepsy, and disabilities caused by rare diseases. We excluded chronically unconscious patients because they are unsuitable for evaluating the tooth-filling service utilization rate.

Statistical analyses
We used descriptive statistics to analyze the utilization of tooth-filling services by people with disabilities. By exploring tooth-filling service utilization rates and its correlation with several variables through a bivariate analysis, we summarized all variables as distinguishable-category data. Furthermore, we used SAS software, chi-square test, Fisher exact test, and univariate logistic regression to examine the correlation between variables and toothfilling service utilization rates. In addition, we used logistic regression to examine the potentially independent effect of demographic and clinical variables on utilization. We also performed the Likelihood Ratio Test to evaluate the validity of the adjusted logistic regression model. The value of -2LL (i.e., -2 times the log likelihood) was used to assess the significance of logistic regression model. The test was significant and implied the validity of the adjusted logistic regression model in our study.

Basic characteristics of people with disabilities
Males comprised 58.6 % (N = 547,017) of the participants. The average age of the participants was 49.98 years (SD = 18.97). The majority of the participants were either illiterate or possessed an elementary school level education (42.36 %, N = 395,409). The urbanization degree of nearly 80 % of the participants ranged from 1 to 4. The dependent-population (i.e., children and older adults) were the largest group when stratified by premium-based monthly salary (33.47 %, N = 312,480).
People with catastrophic injuries or diseases accounted for 31.17 % (N = 290,971). People with chronic diseases such as endocrine and congenital metabolic disorders, mental disorders, circulatory system diseases, digestive system diseases, and musculoskeletal system disorders and connective tissue diseases comprised the majority, with each disease accounting for approximately 30 % of the total. Limb impairment was the largest disability category (37.47 %, N = 349,790), followed by mental illness, major organ malfunction, and mental illness (approximately 10 % each). Regarding the disability degree, participants with mild and moderate disabilities accounted for 72.04 % (N = 672,409) of the study population (Table 1). Participants with chronic diseases demonstrated a higher tooth-filling service utilization rate compared participants without chronic diseases. Notably, participants with circulatory and urinary system diseases exhibited low utilization rates (p <0.001). When stratified by disability categories, participants with congenital metabolic disorders and autism had high utilization rates (36.33 % and 29.18 %, respectively), whereas participants with multiple impairments and dementia exhibited low utilization rates (13.35 % and 10.19 %, respectively) (p < 0.001). Regarding disability degree, participants with mild disabilities exhibited higher utilization rate (20.53 %) than did other participants (p < 0.001) ( Table 1).

Logistic regression models for tooth-filling service utilization among participants with disabilities
After adjustment for the variables, most correlating factors significant affected the utilization rate, except for (a) chronic diseases of the neural and urinary systems and blood and hematopoiesis diseases, and (b) the disability categories of facial disfigurement, congenital defects, impaired balance, and disabilities caused by rare diseases ( Table 2).
After controlling for other variables, the analysis revealed that males used tooth-filling services at 0.78 times the rate that females did (95 % CI [0.77, 0.79], p <0.001). Based on the reference group, which comprised participants <20 years, the adjusted odds ratio (OR) revealed a trend of declining tooth-filling service utilization rate with increasing age; participants ≥75 years exhibited a low utilization rate (0.22 times) compared with that of the reference group (95 % CI [0.22, 0.23], p <0.001). Utilization rate variation among the considered age groups was approximately 80 %.
The tooth-filling service utilization rate for participants from the least urbanized areas was lower (0.63 times) that that for participants from the most urbanized areas (95 % CI [0.61, 0.64], p <0.001). Furthermore, participants with a high premium-based monthly salary exhibited high tooth-filling service utilization rates. The tooth-filling service utilization rate for participants with the highest premium-based salary was higher (1.48 times; 95 % CI [1.43, 1.54], p <0.001) than that for the reference group comprised of participants with the lowest premiumbased monthly salary (NT$ ≤17,280).
Compared with participants with visual impairment, those with mental retardation, multiple impairments, dementia, and chromosomal abnormalities exhibited significantly lower tooth-filling service utilization rate; service utilization was the lowest among participants with dementia (OR = 0.75, 95 % CI [0.71, 0.79], p <0.001). Participants with other disabilities exhibited higher utilization rates than did participants with visual impairment. Participants with congenital metabolic disorders exhibited the highest utilization rates compared with other participants (OR = 1.64, 95 % CI [1.39, 1.94], p <0.05). Participants with more severe disability levels exhibited low utilization rates, and the utilization rate for participants with extremely severe disabilities was lower (0.57 times) than that for participants with mild disabilities (95 % CI [0.56, 0.59], p <0.001; Table 2).

Chalmers et al. (2011) conducted a survey in 2005 and
reported that approximately 60 % of people with intellectual and developmental disabilities visit dentists. In addition, people aged 22-64 years exhibited high toothfilling service utilization rates (approximately 64 %), and people ≥65 years exhibited the lowest utilization rate (45 %) compared with the other age groups [18]. However, studies have revealed that older people demonstrate a high rate of missing teeth and untreated decay or cavities [19], high total DMFT scores, and low tooth-filling rates [20,21]. These results are consistent with our finding that older peoples' tooth-filling service utilization rate is low.
We demonstrated that patients with dementia had the lowest tooth-filling service utilization rate. Dementia progressively increases in severity, gradually impairing cognitive function [22]. People with a low cognitive function score have a four-fold higher tendency of not regularly availing dental services [23].
Because people with extreme disabilities have physical or mental limitations, they face difficulty in availing medical care [24], thus developing poor oral health conditions [4,25]. Participants with extreme disabilities in this study demonstrated a tooth-filling service utilization rate 43 % lower than that of patients with mild disabilities.
Sex, residential area, and economic status influence the medical services utilization rate. Kung, Tsai, and Li (2012) indicated that females utilize more preventive health services than do males. A study conducted in the United Kingdom [26] reported that females more readily seek consultation for illness. In the present study, we demonstrated that 19.20 % of the female participants used tooth-filling services, which is significantly higher  A high urbanization degree is indicative of denser population and higher government expenditures, higher density of hospitals and medical institutes, more media broadcasts of health information, and higher access to disease treatment and prevention resources [27,28]. We revealed that the tooth-filling service utilization rate significantly increased with the degree of urbanization; by contrast, participants living in the least urbanized areas exhibited 40 % lower utilization rates. Furthermore, economic status influenced people's medical assistanceseeking attitudes and behavior [29]. Participants with a low premium-based salary and those from low-income households demonstrated low tooth-filling service utilization rates.
The overall tooth-filling service utilization rate for participants in this study was only 17.53 %, whereas that for the general population is 54.7 % [30]. People with disabilities exhibit high tooth damage because of poor oral health conditions and oral hygiene compared with people without disabilities [31,32]. However, the number of people with disabilities seeking dental services or undergoing early treatments is relatively low [3], worsening the tooth conditions until they visited a dentist. Thus, the probability of tooth extraction was higher than that for tooth filling. Similar results were reported in Rodriguez Vazquez et al. (2002), suggesting that when people with mental illnesses experience tooth decay or cavities, they receive destructive therapies, such as tooth extraction, instead of reforming the tooth appearance and function; this phenomenon causes a high rate of missing teeth among people with disabilities [33].
In this study, we focused only on tooth-filling service utilization in 2008 by people with disabilities. Because doctor visit rates, decay and cavity prevalence, other dental treatment conditions, and personal health behavior were not considered in out analyses, we could not determine the actual proportion of people who required tooth fillings, nor could we compare other risk factors; this is the primary limitation of our study. However, people with disabilities have exhibited a higher incidence rate of untreated tooth decay or cavities compared with those without disabilities [11,34]. Therefore, our analysis of nationwide data substantially supports future research and additional investigations for identifying the risk factors, thus serving as a foundation for cohort studies. Moreover, this study was a population-based study with a substantial sample size. Because we recruited participants who cannot easily be recruited, such as people with extreme disabilities and communication impediments, our results are not biased by the presence of groups with superior functions.
Since this study had a large population-based sample, it had a high statistical power and might cause some weak-association factors to reach significant level (p < 0.05). Thus, we suggest readers to focus on the factors with bigger odds ratios and to interpret the factors with a borderline odds ratio in a more conservative way. We advise to use confidence intervals (CIs) instead of p values in terms of practical importance.

Conclusion
In this nationwide study, we investigated the tooth-filling service utilization rate among people with disabilities. We identified the factors that influence and decrease the tooth-filling service utilization rate: male sex, old age, low education level, being married, indigenous ethnicity, residing in a low urbanization area, low income, chronic circulatory system diseases, dementia, and severe disabilities.
The association between tooth-filling service utilization and maintenance of oral health among people with disabilities is extremely crucial. We should focus on and provide more assistance to people with disabilities. Moreover, we should establish appropriate welfare policies for protecting the health of people with disabilities, for example, improving accessible environment for dental care, or proving dentists with financial incentives for dental care giving to people with disabilities.

Competing interests
The authors declare that they have no competing interests.

Authors' contributions
Conception and design was done by WCT, MCC, PTK, SMY, HPS; collection and assembly of data was conducted by WCT, MCC, PTK, LTC; data analysis and interpretation was performed by WCT, MCC, SMY, PTK, HPS, LTC;