A recent literature review has proposed that beyond esthetics, a series of alterations are associated with severe malocclusions as seen in DFD, including functional deviations, poor quality of life, painful symptoms, and disruption of tooth structure, besides OSA [24]. However, there are only a few pieces of evidence for the global sleep quality in individuals diagnosed with a DFD. The present study was designed to gain further insights regarding the impacts of DFD on sleep quality. We employed either objective or subjective measures for assessing the sleep profile of a small sample composed of males and females with DFD, in preparation for orthognathic surgery. Attempts have also been made to verify the connection between sleep disturbances and salivary biomarkers in these individuals.
The participants enrolled in this study had homogeneity regarding ethnicity and mean age. Accordingly, 15 out of 20 individuals seeking orthognathic surgery in our School were Caucasians. Irrespective of the wide age variation (from 17 to 46 years), the mean age did not show significant differences when comparing the males and females that composed the sample. Herein, most individuals had a diagnosis of class III skeletal deformity (65%), a feature that has been observed in a previous study by our group, with 76% of patients displaying a class III deformity [13].
Prior data demonstrated that cephalometric data can be predictive of sleep disorders, such as OSA [25]. Herein, there were no significant differences for throat or tongue length, or alar width regarding sex, whereas females presented a lower height of the facial inferior segment, compared with males. It is not clear whether facial patterns influence the volume of upper airways and global sleep quality, but it has been demonstrated that face height presents a positive correlation with the total airway dimensions [26], which might be relevant for interpreting our results.
An evaluation of anthropometric parameters showed that males had higher values of body weight and height, although the BMI was not significantly different between the sexes. Nonetheless, females showed inferior values for both neck and abdominal circumference, when compared with males. It is worth noting that only three males presented an oxygen desaturation index/h higher than 5, which is parallel with elevated age, BMI, and abdominal circumference, for individual comparisons. The severity of OSA has been positively correlated with sex, BMI, and Mallampati classification, as well as abdominal and neck circumference when analyzing a group of 205 patients with OSA diagnosis confirmed by polysomnography (PSG)[27]. However, most of the participants in our study (85%) did not show elevated oxygen desaturation rates, despite the DFD diagnosis. The present data contrasts somewhat with the notion that severe malocclusion, as seen in DFD patients, is a risk factor for OSA [24]. Based on our preliminary results, it is possible to infer that anthropometric features, besides sex and age, might greatly influence OSA detection in DFD patients. Herein, OSA has been assessed by HSAT, and not by classical PSG, which might represent a limitation of the current study. Moreover, it is not possible to exclude that DFD individuals present with asymptomatic OSA, without changes in the oxygen desaturation values.
In addition to the objective assessments, we have also employed subjective instruments to examine the sleep quality of individuals with DFD. Noteworthy, 17 out of 20 participants presented total PSQI scores higher than 5, allowing to suggest that DFD displays a negative impact on sleep quality, independent of sex. A previous study conducted with class III DFD females showed a positive relationship between PSQI scores and temporomandibular joint degeneration [28]. Another study enrolling class II and class III DFD patients, in preparation for orthognathic surgery, suggested that lower PSQI scores were associated with higher levels of satisfaction after the surgical procedure [29]. Thus, the low sleep quality in DFD patients undergoing orthognathic surgery might be related to either functional or psychological alterations. In the present study, the mean PSQI score was 8.2, with means of 7.4 and 9, for males and females, respectively. Contrasting somewhat with our data, a study carried out in Asia showed that controls and DFD individuals displayed mean PSQI global scores of 5.36 and 5.35, respectively [30]. Although our study did not include a control group, it is tempting to suggest that cultural aspects might account for sleep quality patterns in DFD patients.
As for the ESS, scores higher than 10 are indicative of diurnal somnolence. In the present study, only 30% of DFD individuals demonstrated ESS values superior to 10. The mean ESS scores were 8.7 and 8.9, for males and females, respectively. Supporting our results, class III DFD pre-surgery patients showed median ESS scores of 7.0 [31]. It is possible to propose that a DFD diagnosis is not associated with somnolence episodes during routine activities.
In this study, we also employed the FLSQ to assess sleep alterations in DFD individuals. In this case, we analyzed data regarding general sleep features, besides nocturnal apnea, snoring, and daytime sleepiness as part 1. For these parameters, there were no significant differences when comparing males and females. Nevertheless, for part 2 of the FLSQ, which considered the associated complaints, such as painful and cognitive aspects, the scores were significantly higher in females. When summing parts 1 and 2 of this questionnaire, there was also a tendency for higher scores in females. This difference might be associated with different factors, including the inferior volume of airways [26], as in our study the females presented shorter facial height values. This suggestion remains to be further explored by tomographic measures. Remarkably, 85% of individuals presented with FLSQ scores higher than 1, regardless of sex, reinforcing the notion that DFD greatly influences sleep efficiency. A previous study showed the impacts of anxiety on the temporomandibular disorder and sleep disturbance, this latter parameter being evaluated by the FLSQ [32].
Detectable levels of IL-1β and glutamate have been demonstrated before in the saliva of DFD individuals [13, 14]. The present study confirms and extends these results, showing detectable salivary levels of IL-1β and glutamate, besides serotonin, in DFD individuals, without differences between males and females (Supplementary Figure S1). A correlation analysis showed a significant negative correlation between serotonin levels and the FLSQ, while analyzed separately for parts 1 and 2 or considering the total scores. Corroborating our data, lower serum serotonin concentrations are likely associated with severe sleep bruxism and high BMI, as indicated by a study enrolling 105 patients [33]. Interestingly, the FSSQ has a sequence of questions concerning sleep apnea and snoring, which are relevant for assessing respiratory-related sleep alterations. Despite we did not detect OSA by HSAT, it was demonstrated that treatment of OSA by 3-month positive air pressure therapy (PAP) resulted in an enhancement of serum serotonin levels [34]. Considering the many roles of serotonin it is possible to conclude that low levels of serotonin might be linked with other changes seen in DFD patients besides sleep alterations, such as anxiety and depression.
The present study has some limitations that need to be considered. Firstly, the experimental N was limited to 20 patients, including 10 females and 10 males. Future studies with a greater sample size are required to gain further insights into the relationship between DFD and sleep disorders. In addition, the same parameters that had been evaluated before surgery in the present study should be also analyzed postoperatively in a long-term basis. As another relevant limitation, we have evaluated sleep alterations by questionnaires and by HSAT. Despite the drawbacks, all of the questionnaires are validated and they are widely used for sleep quality assessment [16–18]. Moreover, HSAT might be an advantageous approach considering the costs and feasibility, when compared to the gold standard polysomnography method [12]. Finally, although saliva represents a useful biological source for measuring oral and systemic biomarkers, that can be obtained in a noninvasive manner, both the collection procedures and sample processing remain to be standardized [12].
Our data bring preliminary evidence regarding sleep disturbances in males and females undergoing orthognathic surgery for DFD correction. Data showing a negative correlation between serotonin levels and the FLSQ scores shed new light on the biological mechanisms underlying sleep alterations under DFD, reinforcing the notion that the management of those patients must be focused on a holistic view. The low levels of serotonin might also be associated with well-recognized psychological ailments in DFD, such as anxiety and depression, opening new avenues for DFD patient care.