INTRODUCTION

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It is well known that edentulism produces a decrease in size and tone of the pharyngeal musculature (1). We recently observed that edentulism, by decreasing retropharyngeal space, favors the occurrence of obstructive sleep apneas (2). We wondered whether edentulism may influence spirometric measurements. To our knowledge, this problem has never been systematically investigated and we could not find any advice on this subject in American Thoracic Society (ATS) (3) or European Respiratory Society (ERS) (4) guidelines for spirometry. The subject is mentioned in a few books on pulmonary function testing, some recommending that edentulous subjects should remove dentures during spirometric measurements (5) and others advising that dentures should not be removed unless they are poorly fitting (6, 7). The aim of this study was to determine whether in edentulous subjects performing spirometry without dentures produces significant changes in lung volumes and airflow rates and whether such an effect, if any, is conditioned by preexistent lung function abnormalities.

	METHODS

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Spirometry was recorded with and without dentures in 36 asymptomatic healthy subjects (N) with spirometric values within the normal range (4), 22 patients with airway obstruction (FEV₁/vital capacity [VC] ranging from 32% to 63%) due to chronic obstructive pulmonary disease (COPD), and 18 patients with restrictive pattern (total lung capacity [TLC] ranging from 58% to 80% of predicted, and FEV₁/VC over 70%) due to interstitial lung disease (ILD). Subjects with a combined obstructive and restrictive pattern, with recent exacerbation of bronchopulmonary disease, with poor retention and stability of dentures (diagnosed by expert dentists), and who were not able to perform repeated respiratory efforts were excluded from the study. The study was approved by a local ethical committee and subjects gave their informed consent.

The subjects performed two consecutive sets of spirometric tests 15 min apart, one wearing dentures and the other without dentures, in randomized sequence. The measurements were performed following the ATS guidelines on spirometry (3). The subjects were in the seated posture, wearing nose clips, and were connected to a computerized water-sealed spirometer (BAIRES system, Biomedin, Padua, Italy), through a rubber mouthpiece with a gum shield that ensured an airtight fit. Cardboard tubes could not be used because most of the subjects had difficulty in sealing their lips around the mouthpiece without dentures. At the first set of measurements (with or without dentures, depending on randomization), not less than five maximal flow-volume loops were recorded, until three acceptable curves with FVC and FEV₁ reproducible to within 0.2 L were obtained. From the three acceptable curves selected with and without dentures, the largest FVC, FEV₁, and peak expiratory flow rate (PEFR) were calculated and used in the analysis. Forced expiratory flow (FEF_50%), forced inspiratory volume (FIV₁), and forced inspiratory flow (FIF_50%) were calculated from the "best test curve," that is the one with the highest sum of FVC and FEV₁ (3), obtained with and without dentures. A subgroup of subjects (five N, four ILD, and five COPD) underwent cephalometric assessment of retropharyngeal space with and without dentures (8).

Statistical Analysis

The comparisons of spirometric values with and without dentures within each group and the comparisons among groups were performed with repeated measures and ordinary ANOVA, using the Bonferroni multiple comparisons test for selected pairs of columns. Chi-square test was used for comparing prevalences among groups. For each test a p value below 0.05 was considered significant.

	RESULTS

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As shown in Table 1, the three groups differed in age (lowest in the ILD group), men prevalence (greatest in the COPD group), and spirometric values. In Table 2 are reported the mean values of the tests obtained with and without dentures in each group. Removing dentures produced a decrease in lung volumes and airflow rates both in the N and in the ILD groups, which was significant for PEFR, FEF_50%, and FIF_50% in the N group, and for PEFR and FEF_50% in the ILD group. By contrast, in the COPD group the values of spirometric tests with or without dentures were similar. The PEFR showed the greatest decrease, particularly in the N group. Although in all the groups FEV₁ was only slightly and not significantly lower without dentures, its decrease exceeded the reproducibility criterion of 5% in 18 normal subjects (50%), 6 ILD patients (33%), and only 1 COPD patient (comparison among the three groups ² = 12.8, p = 0.0017).

In Figure 1 are given three representative examples of the changes in the shape of the flow-volume loop induced by removing dentures in each group. In normal subjects without dentures there was a marked decrease in both inspiratory and expiratory airflow rates, in the patients with ILD the decrease in airflow rates was milder, whereas in the patient with COPD the loop was even better without dentures. Cephalometric data, available in only 14 subjects, showed that removing dentures produced a significant decrease in retropharyngeal space, either in the overall subjects (from 1.52 ± 0.07 to 1.16 ± 0.09 cm, SEM, p < 0.0001) or within each group (N: from 1.47 ± 0.18 to 1.14 ± 0.24 cm, SEM, p = 0.032; COPD: from 1.64 ± 0.08 to 1.2 ± 0.08 cm, SEM, p = 0.0124; ILD: from 1.44 ± 0.05 to 1.12 ± 0.10 cm, SEM, p = 0.045). The mean values of the retropharyngeal spaces of the three groups were similar, either with or without dentures.

View larger version (13K): [in this window] [in a new window]   Figure 1.   Flow-volume loops with (dotted line) and without dentures, superimposed, representative of the group of normal subjects, of patients with ILD, and of patients with COPD.

	DISCUSSION

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The results of this study show that in edentulous subjects the use of dentures while performing spirometry produced a small but significant improvement in some airflow rates in both normal subjects and patients with ILD, whereas it caused no change in patients with COPD. The main effect of dentures use was manifested by improvement in PEFR, FEF_50%, and FIF_50% in normal subjects, and in PEFR and FEF_50% in patients with ILD. FVC and FEV₁ showed no significant change in any group. However, looking at individual values, the decrease in FEV₁ by removing dentures exceeded its reproducibility criterion of 5% in half of the normal subjects and in one-third of the patients with ILD.

Although the mechanism by which edentulism affects spirometry has to be investigated, we may suppose that it favors pharyngeal collapse (9) through a decrease in size and tone of the pharyngeal musculature (1). This hypothesis is sustained by the significant decrease in retropharyngeal space after removing dentures observed by cephalometry. The examples given in Figure 1 were obtained by superimposing the flow-volume loops with and without dentures in a representative case of each group. In normal subjects, removing dentures produced a marked decrease in PEFR and inspiratory airflow rates, consistent with a decrease in extrathoracic airway caliber (10, 11), whereas in patients with ILD all airflow rates were proportionally reduced. By contrast, in patients with COPD airflow rates were even better without dentures. Actually, patients with COPD as a group, despite a decrease in retropharyngeal space similar to that of N subjects and subjects with ILD, had no significant worsening of spirometric values after removing dentures. We may suppose that pharyngeal obstruction attenuated the dynamic compression of the airway wall due to increased intrathoracic airway resistance, in the same way as pursed-lip breathing. This explanation is in agreement with the observation of Higenbottam and Payne (12) that in patients with COPD the glottic width narrows with the progression of airflow obstruction, analogous to expiration through pursed lips.

According to the ATS guidelines for spirometry interpretation (13) the only measurements that should be used for interpretation of ventilatory defects are FVC, FEV₁, and FEV₁/VC. Because these variables did not change with or without the use of dentures, the classification of the ventilatory defect and the degree of severity of the ventilatory defect did not change. Therefore the use or nonuse of dentures in edentulous subjects during spirometric measurements does not have clinical relevance and will not likely impact patient management. However, because small albeit significant increases in some respiratory flows (PEFR, FEF_50%, and FIF_50%) in normal subjects and patients with ILD were observed with dentures on, the use of dentures, when properly fitted, should be recommended for the measurement of spirometry. This recommendation seems particularly relevant in the elderly, considering that edentulism troubles 18% of the subjects over 60 yr of age and that its prevalence will remain constant over the next 30 yr (14).