Introduction
Patient-centered care has become increasingly important in orthodontics. As clinicians we aspire to achieve high-quality treatment outcomes and seek to do this in an evidence-based manner. Part 1 of this German cohort study dealt with orthodontic treatment effectiveness, showing that orthodontic treatments were mostly high-quality treatments and able to significantly improve malocclusions [
1]. Yet, within a modern healthcare system, the assessment of the quality of clinical care and its effectiveness should not only focus on occlusal measurements, but must involve patient-reported outcomes. Such patient-based evidence reveals important information about how patients function and feel with regard to their orthodontic treatment. As a multidimensional construct oral health-related quality of life (OHRQoL) can be assessed in order to elucidate patients’ physical and psychosocial well-being [
2]. OHRQoL seems to be linked to malocclusion, or to specific dentofacial traits that might impair physical and psychosocial well-being [
3]. Among other traits, excessive overjet with incompetent lip closure, a deviating overbite or crowding of anterior teeth have been discussed in this context [
4‐
9]. Correction of these specific malocclusions through orthodontic treatments has been shown to be able to reduce such impairment, leading to better OHRQoL [
10,
11]. However, active orthodontic treatment might temporarily reduce the level of OHRQoL, depending on the type of appliance used, the specific treatment stage and the initial malocclusion [
12]. Hence, OHRQoL and its relation to malocclusion and/or orthodontic treatment outcomes are crucial pillars of patient-centered, high-quality orthodontic care.
In general, there are several ways to measure OHRQoL of children and adults. Validated patient-reported outcome measures (PROMs) are the Oral Health Impact Profile (OHIP) [
13] and the Child Oral Health Impact Profile (COHIP) [
14‐
16]. Multiple items within several psychological, physical and social dimensions lead to a final score that stands for a rather impaired or unimpaired quality of life with regard to oral health. These PROMs have frequently been used in international research, thus, providing a good basis for comparisons between different study groups.
Besides OHRQoL, patient-reported outcomes like oral hygiene habits are of interest in the context of orthodontic treatment [
17,
18]. Research has shown that patients might change their oral hygiene habits in the course of orthodontic treatment and the concomitant need for more intense oral hygiene care [
19,
20]. The latter is essential in order to keep both soft and hard tissues healthy during treatment with fixed appliances [
21]. In addition, it might be important to learn more about patients’ dental awareness and locus of control [
22]. Whether one sees an external locus of control with regard to one’s oral condition or rather an internal one might uncover highly interesting factors of one’s sense of coherence or sense of self-efficacy, which consequently might influence orthodontic treatment with regard to adherence to treatment and quality of treatment [
23,
24].
Up to now, national research about the above-mentioned topic is sparse. Thus, part 2 of this multicenter cohort study aimed to explore patient-reported outcomes after orthodontic treatment and potential influencing factors within this German convenience sample. Yet, it has to be noted from the beginning on that due to the cross-sectional character of the study, pre-orthodontic PROMs are missing within this study population.
Discussion
This multicenter cohort study focused on the quality of orthodontic care in a German convenience sample. While part 1 addressed treatment effectiveness according to occlusal outcome measures [
1], the present part 2 dealt with cross-sectional data about patient-reported outcomes after orthodontic treatment. As a major part of these patient-reported outcomes, OHRQoL was evaluated using the German version of the COHIP and OHIP questionnaires through an iPad-based procedure. This process was not time-consuming for study participants, although the number of items per questionnaire was rather large. Mean levels of OHRQoL among study participants after orthodontic treatment were good and the average degree of impairment was low. Yet, because of the cross-sectional character of this study, pre-orthodontic patient-reported outcome values of study participants could not be obtained. This hindered the direct attribution of changes in OHRQoL to orthodontic interventions. Statements about the genuine effect of orthodontics on patient-reported outcomes cannot be made according to the present data. Nonetheless, taking the post-orthodontic OHIP-G 14 score of 3.09 in our study into account, it was comparably low with regard to national as well as international study populations [
4,
15,
16]. The 6th German Oral Health Study used the OHIP-G 5 version to evaluate OHRQoL and found a mean score of 1.3. For our data, the OHIP-G 5 score was comparably low, being 1.4. However, the cited study sample comprised youths who were 8–9 years old and not adolescents or adults older than 16 years after orthodontic treatment as in our ‘OHIP study group’ [
34].
The association between finished orthodontic treatments and OHRQoL is highly interesting and crucial to look at in the context of good quality of care. Silvola et al. conducted a large cohort study with 1885 Finnish adults and found that whenever study participants had been treated orthodontically, they reported better OHRQoL [
5]. Zheng et al. described significant changes in OHRQoL throughout orthodontic treatment—depending on the initial malocclusion and treatment stage—in their Chinese population of adolescents and young adults and found final mean OHIP-14 scores between 2.98 and 3.23. In addition, a cohort of adult study participants who had undergone combined orthodontic–orthognathic surgery showed a mean OHIP-14 score of 4.1 at the end of their treatment. Moreover, the Finnish authors found a correlation between high initial PAR scores and more impaired OHRQoL [
11]. In a systematic review, Mandava et al. came to the conclusion that fixed orthodontic treatment might improve OHRQoL and self-esteem in children as well as OHRQoL in adolescents and adults [
35]. A potentially beneficial effect of orthodontic treatments with regard to OHRQoL has been shown by other authors as well [
36‐
39].
To our knowledge, there is only very limited data available on COHIP scores
after orthodontic treatment, in contrast to evidence about such scores
prior to orthodontic treatment [
6,
7,
16,
40].
Analyzing our data regarding potential influencing factors of OHRQoL after orthodontic treatment, the results showed a nonsignificant trend towards lower mean OHIP-G 49 and OHIP-G 14 scores for study participants whose treatments classified for the PAR category “greatly improved” (i.e., PAR score change of at least 22 points). While a variety of authors agree that higher initial levels of OHRQoL are associated with specific initial malocclusion traits like a compromised overjet [
7,
40‐
42] or severe initial malocclusion in general [
4,
43,
44], evidence is scarce about the correlation of patients’ OHRQoL after orthodontics and the degree of malocclusion changes throughout treatment [
10,
45]. Further and longitudinal research is needed in order to fully understand this crucial association.
Looking for other influencing factors of OHRQoL after orthodontics, there seemed to be sex-related differences. Of the patients who filled out the COHIP questionnaire, i.e., study participants younger than 16 years, girls showed more impairment of oral health-related quality of life compared to boys after orthodontic treatment. Especially the dimensions of social and emotional well-being might be more impaired in girls than in boys during puberty, a time span of major life changes [
44]. Sun et al. found similar results in their group of 15-year-old study participants. Yet, they emphasized that OHRQoL should be seen as a dynamic construct with numerous potential influencing factors that might change over the years [
46]. For adult patients, several researchers reported such gender-dependent differences for OHRQoL, namely a tendency to a more impaired well-being for females than for males [
4,
5]. Contrary to this, our study participants who were older than 16 years and who filled out the OHIP-based questionnaire, showed a reverse sex-related influence after orthodontic treatment: males reported slightly higher impact of their OHRQoL than females. The reasons for this outcome could not be fully identified. On average, orthodontic treatments lasted longer for males than females which might have caused perceived impairment [
47].
Within our study population, OHRQoL was more impaired for smokers. Smoking is harmful—not only for general health, but also for oral health in particular. Oral cancer, periodontal disease, tooth loss or staining might be oral conditions resulting from excessive tobacco use [
48,
49]. However, research on the association between OHRQoL and smoking is scarce [
50‐
52]. Results of this multicenter study highlight the correlation between an impaired OHRQoL—the self-perceived impact of oral conditions—and smoking. The dimension ‘functional limitations’ within the OHIP-G 49 construct proved to be significantly compromised for orthodontically treated smokers. The respective dimension contains questions about the self-perception of tooth staining, bad breath or taste impairments. It is not surprising that these aspects of oral health showed significantly more impairment for smokers. Yet, because ‘smoking’ is not a topic of great interest within orthodontic research or within orthodontic treatments and the accompanying consultation sessions as such, it should be kept in mind while advising our patients about oral health-promoting ways of life, especially when treating adults.
Patients’ BMI had no influence on OHRQoL within the current study population. Due to incomplete data, the effect of patients’ socioeconomic status could not be analyzed, implicating a potential for bias.
Patient-reported oral hygiene behavior as well as the reported self-efficacy and dental awareness were good, especially compared to national cohorts [
34,
53]. After orthodontic treatment, study participants brushed their teeth frequently and with adequate tools—according to their own reports. Almost 90% of the patients who filled out the OHIP-based questionnaire believed that they were in charge of their oral health. Apparently, they exhibited an internal control orientation. Interestingly, these patients showed a lower OHIP score compared to the patients who did not feel responsible for their oral health. According to the locus of control theory, people with an internal locus of control believe that they are responsible for their destinies [
54]. In dentistry and specifically in orthodontics, this locus of control theory has been thought to help determine and enhance patients’ adherence. Yet, a linear correlation between an internal locus of control and patients’ ability to adjust to specific situations (like the insertion of orthodontic appliances) has been hard to prove in relevant literature [
22‐
24]. Furthermore, almost 60% of the participants reported to visit their general dentist regularly. Up to 91% of all study participants found their oral condition either ‘very good’ or ‘good’ after orthodontics. These results from our national cohort highlight that orthodontically treated patients seem to be aware of their oral health and the possibilities to promote it.
There are several limitations of this multicenter study. A major drawback is the missing longitudinal patient-reported data. Thus, one can only judge the current,
post-orthodontic state and cannot directly relate this to the malocclusion
prior to orthodontics and/or the orthodontic treatment. Nevertheless, careful associations between the psychological and physical well-being of orthodontically treated patients and specific patient- and treatment-related factors might be highlighted and compared to existing longitudinal and cross-sectional study results as it has been done within this manuscript [
55]. Yet, it has to be stressed that the cross-sectional study design does not allow any robust statement about potential effects of orthodontic treatment and generalizability is limited. Selection and nonresponder bias could not be completely ruled out. Although a strict screening of all potential study participants was mandatory as mentioned above, the study center selection as such had not been random. Thus, this sample can be seen as a German convenience sample and might not be representative for every orthodontic practice or department in Germany. External validity is compromised. In addition, another limitation of this study is that neither an a priori sample size calculation based on OHRQoL nor an alpha adjustment because of multiple testing was performed. The PAR score and its dynamics throughout treatment were the primary endpoints and sample size considerations were based on part 1 [
1], while OHRQoL was a secondary outcome. Nonetheless, with regards to data from relevant literature, the current sample size seemed to be large enough to depict potential aspects about patient-reported outcomes in relation to PAR score dynamics within this cohort. In addition and already mentioned above, not all potentially confounding factors, for example, socioeconomic status have been taken into account in the present analyses.
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