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The proportion of elderly people in the population has increased throughout the course of the 20th century, particularly in developed countries. As might be expected, age is one of the most important factors in edentulousness. Although ageing itself does not cause tooth loss, the frequency of dental and general diseases and functional disabilities increase with advancing age, which may predispose older people to edentulousness. Therefore, total edentulism is a widespread, intraoral condition among the aged population; complete dentures are still the most common treatment offered to the edentulous patient worldwide[2, 3]. To ensure sufficient retention and stability, complete dentures must extend up to the soft palate in the maxilla and to retromolar tissues in the mandible[3-6]. Thus, the volume of the oral cavity may decrease and some crucial functions may be disturbed, such as speech production and chewing efficiency[7-9].
Respiration is one of the most vital functions, and it can be described as the exchange of gases between the living organism and the atmosphere to meet the metabolic demands of the body. In the course of oral respiration, oral tissues and existing dentures are the first contacting structures of the air passing through upper airways. It has been stated that edentulism produces a decrease in size and tone of the pharyngeal musculature[11, 12]. However, it was reported that sleeping without dentures(WOD) created an adverse effect on the Apnoea–Hypopnea Index, especially in edentulous patients with respiratory deformation during sleep support this idea. Furthermore, Bucca et al. advocated that edentulism had an adverse effect on spirometric measurement. Thus, on pulmonary function testing (PFTs), there has been some controversy about whether the edentulous subject should remove dentures during spirometric measurements or not[15, 16].
Pulmonary function tests are highly valuable tools for physiologic evaluation of the respiratory system, diagnosis of some pathologies, and clinical case management. PFTs include a large number of tests, ranging from simple non-invasive oximetry to sophisticated invasive blood gas analysis. Invasive tests display some implemental difficulties in physiologic studies, even though they provide precise results[18-20]. Although reference values, results, and interpretation may vary individually, spirometry is widely used throughout general medicine to assess the mechanical or bellows properties of the respiratory system by measurement of the dynamic or respired lung volumes and capacities[10, 18, 21]. Thus, spirometric test has been generally used for evaluating the respiratory disorders including chronic obstructive lung disease, pneumonia, and asthma. Compared with other pulmonary function tests, the spirometric test has some important advantages, including being non-invasive and ease of use[10, 21, 22].
The aim of this study was to determine the effects of complete dentures on spirometric values. The null hypothesis of the study was that wearing dentures in edentulous subjects do not produce significant changes in test results of spirometry.
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Sex, age distribution and body mass index (BMI) of participants are shown in Table 1. The mean, median, minimum, maximum and standard deviation values of spirometric parameters in four different oral conditions are presented in Table 2.
Table 1. Distribution of the participants according to sex, age and Body Mass Index (BMI)
| ||Number of participants||Age (Mean)||BMI (Mean)|
Table 2. The mean, maximum and minimum values of spirometric parameters obtained from 46 patients in four different oral conditions
|Oral status||Mean (SD)||Median (Min–Max)|
|WODs-FVC||3.05 (0.8)||3.18 (1.52–4.83)|
|WULDs-FVC||2.98 (0.9)||3.14 (1.39–4.8)|
|WLD-FVC||2.93 (0.89)||3 (1.3–4.62)|
|WUD-FVC||2.91 (0.93)||2.96 (1.49–4.61)|
|WODs-PEF||5.73 (2.38)||5.01 (1.27–11.78)|
|WULDs-PEF||5.51 (2.44)||4.9 (1.39–10.86)|
|WLD-PEF||5.36 (2.19)||4.76 (1.27–9.77)|
|WUD-PEF||5.41 (2.16)||5.02 (1.5–9.03)|
|WODs-FEV1||2.35 (0.82)||2.33 (0.95–4.02)|
|WULDs-FEV1||2.31 (0.81)||2.21 (0.98–3.9)|
|WLD-FEV1||2.29 (0.82)||2.16 (0.72–3.87)|
|WUD-FEV1||2.28 (0.82)||2.2 (1–3.91)|
|WODs-FEF25–75||2.7 (1.4)||2.44 (0.67–5.33)|
|WULDs-FEF25–75||2.56 (1.41)||2.14 (0.57–5.34)|
|WLD-FEF25–75||2.62 (1.47)||2.3 (0.6–6.3)|
|WUD-FEF25–75||2.6 (1.51)||2.2 (0.5–6.65)|
The highest mean value was found in the WODs condition for each spirometric parameter (Table 2). Moreover, the lowest mean value was seen in the WUD condition for FVC and FEV1. Furthermore, the lowest mean values were obtained in the WLD condition for PEF, and in the WULDs condition for FEF25–75 (Table 2).
For FVC and FEV1, WODs values were significantly higher than those of WDs, WLD and WUD values (p < 0.05). No significant difference was found between WODs and WULDs values for PEF. However, WODs values were significantly higher than those of WUD and WLD values (p < 0.05). In addition, WODs values were significantly higher than those of WUD and WLD for FEF25–75 (p < 0.005). There was no significant difference between WODs and WLD conditions (p > 0.05). Comparisons of spirometric values between WODs and three different oral conditions are presented in Table 3.
Table 3. Comparison of spirometric values between without dentures (WODs) and three different oral conditions (WULDs, WLD and WUD)
|Comparisons of spirometric values||p|
|WODs-FVC & WULDs-FVC||0.018a|
|WODs-FVC & WLD-FVC||0.001a|
|WODs-FVC & WUD-FVC||0.003a|
|WODs-PEF & WULDs-PEF||0.321b|
|WODs-PEF & WLD-PEF||0.003b|
|WODs-PEF & WUD-PEF||0.024b|
|WODs-FEV1 & WULDs-FEV1||0.042*|
|WODs-FEV1 & WLD-FEV1||0.009a|
|WODs-FEV1 & WUD-FEV1||0.001a|
|WODs-FEF25–75 & WULDs-FEF25–75||0.009b|
|WODs-FEF25–75 & WLD-FEF25–75||0.057b|
|WODs-FEF25–75 & WUD-FEF25–75||0.003b|
In all spirometric parameters, the most important significant difference was found between WODs-FVC and WLD-FVC (p < 0.001), and WODs-FEV1 and WUD-FEV1 (p < 0.001) (Table 3).
In all spirometric parameters, high correlation values were found between WODs and WULD, WLD and WUD (p < 0.001, r > 0.8). All correlative p values were lower than 0.001. Correlation values are given in Table 4.
Table 4. The correlations of the results obtained from spirometric measurements of edentulous patients without dentures (WODs) and three different oral conditions (WULDs, WLD and WUD) with dentures
| ||WDs r||WLD r||WUD r|
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According the findings from this study, spirometric values for pulmonary function testing were affected by wearing complete dentures. Therefore, the hypothesis was rejected. Indeed, previous studies[26-31] showed that there is a strict relationship between orofacial conditions and the upper airway. However, until the end of the 20th century, clinical findings were not used for the evaluation of respiratory functions in different dental conditions such as partial or total edentulism. The most significant clinical evidence about the relationship between oral conditions and respiratory functions emerged in the late 1990s.
Bucca et al. reported that Apnoea-Hypopnea Index (AHI) scores almost doubled during sleep WOD in a 44-year-old COPS and OSA patient who began to wear complete dentures because of total tooth loss after extractions. Cephalometric analysis of the patient revealed significant narrowing in the anteroposterior oropharyngeal distance from 1.5 to 0.6 cm. After these striking findings, they extended their study to six edentulous male OSA patients, and authors observed that removal of complete dentures significantly decreased retropharyngeal space and that sleeping WOD was associated with a decrease in mean and lowest arterial blood saturation while increasing AHI scores. The authors concluded that the removal of complete dentures significantly decreased the retropharyngeal distance in OSA patients during sleep, and they advised them to not remove their complete dentures while sleeping to avoid the risk of upper airway collapse[13, 32].
Likewise, in a study evaluating the effect of complete dentures on AHI scores carried out on 34 OSA patients, Arisaka et al. determined that wearing complete dentures decreased AHI scores in 19 patients while increasing the scores in eight patients during sleep. Interestingly, the improvement of AHI scores did not originate from the decrease in apnoea scores, but from the reduction in hypopnea scores. Moreover, there was no significant difference between different prosthetic conditions (with and WOD in the mouth) in regard to mean, the lowest SpO2 indexes and the desaturation index.
In another study, Bucca et al. performed spirometric tests on 76 edentulous patients [36 asymptomatic patients, 22 chronic obstructive pulmonary disease (COPD) patients, and 18 interstitial lung disease (ILD) patients] to determine the effect of complete dentures on respiratory functions. In addition, they reported that in asymptomatic and ILD patients, the pulmonary performance slightly improved when complete dentures were in the mouth. The authors added that no significant difference was found in COPD patients with or without wearing complete dentures. According to Bucca et al., PEFR, FIF50 and FEF50 values increased in asymptomatic patients and PEFR and FEF50 values increased in ILD patients. No significant difference was determined for FVC and FEV1 values in any patient groups.
Contrarily to the previous studies, Almeida et al. performed polysomnographic evaluation on 23 edentulous patients with OSA. They observed that wearing complete dentures during sleep was significantly increased AHI scores in mild cases. The result of this study was in accordance with that of Almeida et al. Nevertheless, if it is compared with spirometric test, it should be considered that subjects have different sleeping positions during polysomnography contrary to sitting at upright position of the standard spirometry.
Complete dentures are large devices and may cause narrowing of the oral cavity. Furthermore, the thickness of the complete denture (with artificial teeth) may shift the tongue posteriorly, causing collapse of the pharyngeal airway space. Indeed, the results of this study may be interpreted as the oropharyngeal airflow being unfavourably affected by the large coverage of complete dentures. In this regard, findings of our study are not in accordance with those of Bucca et al. In this study, the highest mean value for all spirometric parameters was obtained in the WODs condition. This difference may be due to different methodological approaches.
One of the most important differences in terms of methodology is the selection of subject type. Contrary to Bucca et al., only healthy subjects with a Malampatti Class 1 soft palate–tongue–pharynx relationship and no systemic disorders were selected for this study. Hence, such a standardisation of subjects provided a homogenous experimental population with a larger oropharyngeal volume with least airway difficulty. Another difference between two studies was the evaluation criteria of the existing dentures. In this study, the complete dentures of the subjects were carefully examined by two experienced prosthodontists in accordance with Nevalainen criteria, being aware that any fabrication error that could lead to the renewal of the dentures may affect the test results. Subjects using their dentures without any complaint, with an accurate occlusion, articulation and vertical dimension, and with a satisfying retention and stability were included in the tests. Owing to the fact that complete dentures must be renewed within periods of 5 years, only 4-year wearers were included in this study. Therefore, more coherent test results were obtained. As is apparent in Tables 3 and 4, this coherence manifested in strong positive correlations between the results obtained in four different oral conditions. This may be interpreted as appropriate completion of spirometric tests by the subjects.
Although the WOD group had the highest spirometric values, an idea that oropharyngeal airway volume was reduced when dentures were not in the mouth was generally accepted in the literature. Spirometric test values can optionally be varied at the same patients during test. Therefore, we are aware that confirmation of the results of this study by using polysomnography evaluation is needed. Invasive respiratory function tests can also be used as a confirmation method.
The inherent difficulty of determining the effects of taking the spirometry mouth-piece into the mouth is another disadvantage of the spirometry test. It was also impossible to determine the effect on test values of personal talent for taking the spirometry mouth-piece into the mouth. We think that patients with dentures took the spirometry mouth-piece into the mouth better than patients WOD. Furthermore, it is observed that patients' compliance for spirometry was different in all prosthetic conditions from the condition without prostheses, especially during the expiration phase of the test, since they were anxious if their dentures would remove from their mouths when they were performing test. This observation is supported by the best determination parameters of the expiration, since WOD-FEV1 values were significantly higher than WLD-FEV1, WUD-FEV1 and WULD -FEV1 values.
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Within the limitations of this clinical study, it is observed that complete denture wearing in edentulous subjects with a Mallampati Class I soft palate–tongue relationship may affect FVC, PEF, FEV1 and FEF25–75 spirometric parameters. Although the many advantages of spirometric test, reference values, results, and also the interpretations of the test may vary, the results of this study regarding the effects of complete dentures on the respiratory performance should be verified with the other advanced tests. So, this study may lead prosthodontists to make new researches on the effect of dentures on respiratory functions and parameters.