It is important to note that studies that associate factors related to adherence of adolescents to dental treatment are scarce in the literature. Existing studies assessing adherence are restricted to therapeutic treatment and follow-up of recommendations by health care professionals, especially in relation to chronic diseases [21, 22].
Adherence is a process in which many factors have influences and different value loads, such as the nature of the disease, individual's personality, their social environment, relationship quality of the therapeutic team and the patient, health service conditions, and factors arising from the treatment itself .
When managing health services one of the great challenges is to enable adherence of adolescents to dental treatment, considering individual characteristics related mainly to life context and the adolescents' family.
Special attention should be given to adolescents of greater social vulnerability, considered "underprivileged", because social, political and economic inequality influence directly in family dynamics and, therefore, increased personal and social risk situation experienced by this individual. Additionally, adolescents, in their capacity as "developing people", have an intrinsic condition of vulnerability, lacking physical, mental and moral care, that is, a comprehensive understanding at their needs .
In this study, adolescents coming from neighborhoods with the worst social exclusion rates in the city of Piracicaba (State of São Paulo), that is, considered underprivileged, were reexamined. Among the subjects evaluated, 50.5% adhered to the dental treatment and 49.5% did not. Non-adherence has important clinical and social consequences. The most direct consequence is the dental treatment failure, which may result in oral diseases complications, and consequently, worsening the diagnosis and delay in the control and cure of these diseases. Moreover, no treatment of the disease may lead to deterioration of oral health and, consequently, increase the demand for specialized services and budget expenditures of the public sector.
In the results of this study, individuals who did not adhere to dental treatment were those from the lower income neighborhood families (0.5 to 1 minimum wage), corroborating with Carvalho , who associated non-adherence to antiretroviral treatment to the income of the surveyed families. Another study evaluated the level of adherence to treatment with antimicrobials and found that subjects with monthly family income above six minimum wages showed 8.3 times greater adherence than those with an income of five or less wages. Thus, income can be related to adherence mainly in extreme cases of poverty, since this condition brings difficult to adhere to treatment .
Family income directly influences the way of living of people, since greater purchasing power can help in maintaining health, treatment and prevention of diseases. At the same time, low wages negatively act on the acquisition of healthy behaviors by the population. Housing conditions are also identified as risk factors, and home should be evaluated when setting up a social exclusion situation  .
The variables related to family status and socioeconomic levels are very important in determining low adherence to treatment. Therefore, the results of this study showed that these variables have had greater effect on adherence than those arising from the diseases characteristics, the treatment or the adolescents.
In this sense, the prevalence and factors associated with adherence of children on antiretroviral therapy were evaluated in a previously study . It was found that the profile of children who do not have good adhesion was extremely related to the profile of their caregivers as well as income below the minimum wage and variables related to the family environment (presence of many children in the family and high degree of poverty).
In the present study larger number of people in the family (crowding) was associated with lower adherence to treatment. This variable was also found in studies on adherence to drug treatment , and adolescent adherence to psychiatric treatment . Some recent international publications indicate crowding as a risk factor for hospital admissions of children . However, there are no studies relating crowding with adherence to dental treatment.
With this variety of factors, the health team must know the determinants that may interfere with adhesion; it is imperative to recognize the specifics of their particular population. The understanding of the sociocultural factors that guide the adherence may help to define what to recommend to the patient, the communication between the patient and the professional and further following the proposed treatment .
Thus, the literature points out that adherence should be built and, in its presence, the individual appropriates the treatment, that is, there is a commitment resulting from understanding the effectiveness and meaning. Thus, non-adherence is a phenomenon that should be working with the patient, developing actions that promote effective work of professionals and an incorporation of the treatment by the patient.
The results of this study point out to a greater possibility of non-adherence by adolescents from crowding families. In addition, it must also consider that the family is an important means of dissemination of ideas and behaviors. Therefore, focusing numerous and low-income families is, mainly, a health education action with far-reaching potential.
Thus, developing communication strategies and team relationship with the patient and family is essential. These include the need to strengthen the link, enhance creativity and promote dialogue between the team, adolescents and their families, aiming to increase adherence. It is also important to empower the professional to handle this situation by implementing the ongoing assessment, discussion of team cases, in addition to maximizing the resources of health service actions in health awareness and promotion of health aimed at young people.
The relevance of this study is due to the lack of studies on adherence to treatment in health. Perhaps this is one of the first studies to discuss this topic in oral health. In addition, the longitudinal nature of the study (18-month evaluation) may be an important point to be raised. Furthermore, studies on adherence are essential for the prevention and control of complications of untreated oral diseases, and generate benefits that extend to patients, families, health systems and the economy.
It is important to note that the data was analyzed using multilevel analysis model, whose relevance has been pointed out by many researchers. This type of model is known by providing a more accurate assessment of the relationship between the environment and people. Probably, to date, this study is one of the first to use this technique to study factors that influence adherence to dental treatment of underprivileged adolescents.
However, we can mention a few limitation. The main limitation, of course, is related to the non-response rate, since we had difficulty locating important part of the sample of adolescents, although they have been sought in schools where they studied, in the Family Health Units, and also in their homes. Furthermore, qualitative studies could be suggested to complement the present results thus offering a better understanding of the factors impacting the adherence of adolescents in dental treatment.