Journal of

Oral Rehabilitation

Journal of Oral Rehabilitation 2014 41; 564--572

Relationship between self-reported sleep bruxism and pain in patients with temporomandibular disorders A. BLANCO AGUILERA*, L. GONZALEZ LOPEZ†, E. BLANCO AGUILERA‡, J. L. DE LA HOZ AIZPURUA*, A. RODRIGUEZ TORRONTERAS§, R. SEGURA S A I N T - G E R O N S § & A . B L A N C O H U N G R
IA § *Master Program in Orofacial Pain and Temporomandibular Disorders, San Pablo CEU University, Madrid, †Private Practice, Cordoba, ‡Master Program in Oral Medicine, Oral Surgery and Implantology, University of Santiago de Compostela, Santiago de Compostela, and §Cordoba Health District, Andalusian Health Service, Cordoba, Spain

SUMMARY The aim of this study was to evaluate the association between self-reported sleep bruxism and the age, gender, clinical subtypes of temporomandibular disorders (TMD), pain intensity and grade of chronic pain in patients previously diagnosed with TMD. Thousand twohundred and twenty patients of the Andalusian Health Service were examined using the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) questionnaire. The inclusion and exclusion criteria were those included in the RDC/TMD criteria. The bruxism diagnosis was drawn from the question, ‘Have you been told, or do you notice that you grind your teeth or clench your jaw while sleeping at night?’ in the anamnestic portion of the questionnaire. A bivariate analysis was conducted, comparing the presence of perceived parafunctional activity with age (over age 60 and under age 60), gender, different subtypes of TMD, pain intensity, grade of chronic pain and presence of self-perceived locked

Introduction Bruxism has been defined by the American Academy of Orofacial Pain as a diurnal or nocturnal parafunctional activity that includes unconscious clenching, grinding or bracing of the teeth (1). Lobbezoo et al. (2) recently defined bruxism as a repetitive jawmuscle activity characterised by clenching or grinding of the teeth and/or by bracing or thrusting of the mandible. The importance of this type of activity lies © 2014 John Wiley & Sons Ltd

joints. The overall prevalence of self-reported sleep bruxism (SB) was 54
51%. A statistically significant association was found between the presence of SB and patients under age 60, women, greater pain intensity, greater pain interference with activities of daily living, and the axis-I groups affected by both muscular and articular pathology. There is a statistically significant association between selfreported sleep bruxism and women under age 60 who have painful symptoms of TMD. There is also a positive association between this parafunctional habit and the presence of chronic pain. However, more studies that cover larger samples and differentiate between sleep bruxism and awake bruxism are needed. KEYWORDS: sleep bruxism, gender, temporomandibular disorders, pain intensity, oral parafunction Accepted for publication 15 March 2014

in the fact that it has been related with TMD, although there are still many concepts to be clarified regarding the mechanisms causing TMD and the role that bruxism plays in the aetiology and pathophysiology of this disorder (3, 4). Some authors consider necessary to differentiate between Sleep Bruxism and Awake Bruxism as these two entities seem to have different pathophysiological mechanisms (5–7). One of the chief arguments is based on differences between the type of muscular doi: 10.1111/joor.12172

SELF-REPORTED SLEEP BRUXISM AND PAIN IN TMD PATIENTS activity exhibited in the two phases of the day. It has been found that while in sleep bruxism, approximately 90% of episodes are eccentric (grinding) (8), in awake bruxism more episodes tend to be centric (clenching). An exception is found in patients with neurological disorders, cerebral lesions or drug addictions, in whom grinding movements while awake are also regularly found (9). Various methods exist for diagnosing sleep bruxism. The foremost are polysomnography, electromyography, the use of questionnaires and the presence of tooth wear. Polysomnography and, to a lesser extent, electromyography have been considered the most effective (gold standard), but the high cost of the study, the difficulty of gaining access to them in the public health system and the long waiting times involved forestall their use in studies of large samples. Tooth wear is not regarded as a reliable basis for diagnosis, as it is influenced by many factors (e.g. age, gender, diet) (10, 11), being the real impact of bruxism very low, as Pergamalian (12) or Johansson pointed out (13). Accordingly, tooth wear is just an additional clinical finding in the diagnostic process (14, 15). As a result, many authors use questionnaires as an accessible method of diagnosis, because questionnaires are more suited to be used in large samples of population, which, in turn, allow a greater capacity for analysis and statistical evaluation in the estimation of the studies’ results. (16, 17). Our questionnaire-based study sought to assess the influence of sleep bruxism on clinical aspects of TMD, disease subtype (articular or muscular), the intensity of pain and the presence of locked joints.

Materials and methods The sample included 1220 patients referred to the Orofacial Pain Unit of the Dental Medicine Section of the C
ordoba Health District by family physicians, neurologists, ENT specialists, maxillofacial surgeons and other dental surgeons during the period from January 2007 to March 2012. All subjects signed an informed consent form, and the study was approved by the ‘Hospital Reina Sofia’ Ethics Review Board. The inclusion and exclusion criteria used were those specified in the classification portion of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). © 2014 John Wiley & Sons Ltd

Inclusion criteria Age: ≥18 years (as RDC/TMD has been neither used nor validated for patients under age 18) presenting some of the following signs or symptoms: pain in the temporomandibular joint (TMJ) or the masticatory musculature, limitation or restriction during opening, closing or lateral movements or joint noise, with or without pain.

Exclusion criteria Systemic rheumatic disease (except for fibromyalgia or rheumatoid arthritis), neurological disease or autoimmune disease, TMJ surgery or radiation treatment in head and neck areas, head and neck trauma 2 months prior to the study, pregnancy, treatment with narcotics, muscle relaxants or corticoids that cannot be stopped 1 week prior to the study, ingestion of antidepressants and NSAIDs at least 3 days previously, drug dependence and refusal to sign informed consent. Patients’ clinical histories were taken, additional data were gathered from the patients, and the questionnaire was filled out by the patients. A comprehensive physical examination of the masticatory system was performed according to the RDC/TMD guidelines, using a translated version from the international consortium to ensure intra- and interexaminer reproducibility (18, 19). The questionnaire was not limited to socio-demographic, psychological and clinical variables; it also asked a series of questions related to an anamnesis of patients’ signs and symptoms according to the protocol. One of these questions refers to self-reported sleep bruxism, enquiring ‘Have you been told, or do you notice that you grind your teeth or clench your jaw while sleeping at night?’ (Question 15c on the RDC/TMD). The locked joint history variable was drawn from another of the questions in the anamnesis section defined by protocol. The question was, ‘Have you ever had your jaw lock or catch so that it won’t open all the way?’ (Question 14a on the RDC/TMD). Pain intensity (CPI) was found using the GPS scale and applying the following formula: CPI = (Q1 + Q2 + Q3)/3 9 10, where Q1 is the severity of the pain the individual feels at the present time, Q2 is the intensity of the worst pain the individual has felt in

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A . B L A N C O A G U I L E R A et al. the last 6 months, and Q3 is the average intensity of pain over the last 6 months. The scale of measurement runs from a minimum of 0 (no pain) to a maximum of 10 (worst possible pain). The sum of Q1, Q2 and Q3 is divided by the number of questions in the indicator, and the quotient is multiplied by 10. The result is a new variable whose value ranges from 0 (absolute absence of pain) to 10 (intense pain). The Graded Chronic Pain Scale (GCPS) was originally developed by Von Korff et al. (20, 21). The GCPS integrates intensity of pain with disability. Disability is in turn found using algorithms that combine days of disability and the sum, divided by 10, of the visual analogue pain scales (0 and 10) (which address disability to work, affective relationships and social relationships). The values are quantified from 0 to 4 (0 = No pain; 1 = Low intensity (50) and no disability; 3 = High disability and moderate limitation; 4 = High disability and high limitation). We conducted a descriptive analysis of the sociodemographic and clinical variables. The bivariate relationship between sleep bruxism and age, gender, pain intensity, grade of chronic pain, existence of locked joints and the different subtypes of TMD classified according to axis I was analysed. The axis-I data were used in their turn to create the ‘grade of muscle disease’ variable and thus to classify patients by the grade of association between muscle disease and the other categories on axis I. For this purpose, the sample was divided into the following groups: 0 = No muscle pain; 1 = Muscle pain only; 2 = Muscle pain and discopathy; 3 = Muscle pain and arthropathy; 4 = Muscle pain, discopathy and arthropathy. The objective of this adjustment or ‘recoding’ was to analyse the possible differences in the influence of bruxism depending on whether muscle pain was present alone, accompanied by arthropathy and/or discopathy, or was not present at all. The relationship between the grade of muscle disease and pain intensity was measured at the same time to assess the influence of pain intensity on the distribution of bruxism. Age was also recoded, to determine whether the presence of bruxism varied at all after age 60. Lastly, a multivariate model was built using a logistic regression, with sleep bruxism as a dependent variable and the socio-demographic and clinical variables mentioned above as independent variables (these were input into the model due to their theoretical

importance). The model’s conditions of validity and the collinearity of the independent variables were checked, the goodness of fit was confirmed using the Hosmer–Lemeshow test, and Nagelkerke’s coefficient of determination was calculated. SAS/STAT software, Version 9.2 of the SAS System for windows,* was used for the statistical analysis.

Results Descriptive univariate analysis Table 1 gives a description of the qualitative variables handled in the study. Of the 1220 patients examined, 1020 (84
4%) were women and 190 were men (15
6%). The age group most frequently represented in the sample was from 40 to 60 years old (38
6%), followed by from 18 to 29 years old (21
8%) and, very close behind, from 30 to 40 years old (21
5%). Six hundred sixty-five patients (54
5%) answered in the affirmative to the questions about the presence of bruxism, and 531 (43
5%) presented a history of locked joints. When the patients were distributed according to axis I, it was found that the most frequent diagnosis was combined muscle, joint and disc disease, with a total of 377 patients (30
9%), followed by muscle and joint disease, with 350 patients (28
7%). The most often-diagnosed chronic pain groups were group I with 24% and group II with 52
3%. The main pain intensity descriptors are presented in Table 2. Bivariate analysis The relationship between perceived bruxism and the variables of gender, age, axis I, regrouped axis I and locked joints can be seen in Table 3. The odds ratio (OR) of presenting perceived bruxism was 1
95 times higher in women than in men (95% CI, 1
42–2
67). In the age comparison, the OR proved to be 1
67 times lower in patients over age 60 than in the rest of the patients in the sample. Looked at in terms of the diagnostic axis (axis I), 61% of the Muscle + Discopathy + Arthropathy group presented perceived bruxism. In the Muscle + Arthropathy group, the bruxist percentage was 55
7, and in the Muscle + Discopathy

*SAS Institute Inc., Cary, NC, USA. © 2014 John Wiley & Sons Ltd

SELF-REPORTED SLEEP BRUXISM AND PAIN IN TMD PATIENTS Table 1. Description of qualitative variables

Variable Sex Male Female Age 18–29 years 30–40 years 41–60 years 61 years or more Missing values Sleep bruxism Yes No Locked joints Yes No Axis I No pathology Muscle disease Discopathy Arthropathy Muscle disease + Discopathy Muscle disease + Arthropathy Discopathy + Arthropathy Muscle disease + Discopathy + Arthropathy Chronic pain grade Grade 0 Grade I Grade II Grade III Grade IV Lost

Number of subjects

Percentage of subjects

190 1030

15
6 84
4

266 262 471 218 3

21
8 21
5 38
6 17
9 0
2

665 555

54
5 45
5

531 689

43
5 56
5

29 127 63 17 237 350 20 377

2
4 10
4 5
2 1
4 19
4 28
7 1
6 30
9

118 293 649 123 33 4

9
7 24
0 53
2 10
1 2
7 0
3

Sleep bruxism and pain intensity

Table 2. Description of pain intensity

Variable

Subjects

Minimum

Maximum

Average

Standard deviation

Pain intensity

1220

0

100

53
55

27
14

group, it was 53
2. The group with the lowest frequency of perceived bruxism was the No disease group (39
7%), followed by the group with Discopathy only (42
9%), the Discopathy + Arthropathy group (45%) and the group with Arthropathy only (52
9%). After axis I was regrouped, thus providing the group with no muscle disease with a larger sample size, it was found that, from the standpoint of statistical signifi© 2014 John Wiley & Sons Ltd

cance, the Muscle + Discopathy + Arthropathy group and the Muscle + Arthropathy group were the only ones to attain significance with respect to the group with the least perceived bruxism (the group with no muscle pain); they yielded an OR of 2
04 (95% CI, 1
36–3
06) and 1
64 (95% CI, 1
09–2
46). The Muscle + Discopathy group came very close to significance, with an OR of 1
48 (95% CI, 0
96–2
28). Locked joints were not associated with perceived bruxism, either, OR = 1
17 (95% CI, 0
93–1
47).

The intensity of acute pain was greater in the group  = 56
85; s.d. = 25
77) than with perceived bruxism (X  = 49
60, in the group without perceived bruxism (X s.d. = 28
12), with t-test = 4
68, df = 1218 and P < 0
0001 (Fig. 1). After the positive relationship was found between perceived bruxism and pain intensity, the average pain in each of the grades of muscle disease was analysed to ascertain whether the individuals who reported more sleep bruxism also felt the most intense pain. The result was positive. It was found that the only two groups whose relationship with bruxism was statistically significant were the groups reporting the greatest pain (df = 4, P < 0
001, Fig. 2). Sleep bruxism and pain interference with activities of daily living Perceived bruxism was more prevalent in the groups with a higher pain interference with activities of daily living. As can be seen in Table 4, the bruxism percentages rose gradually from 45% in the control group (Grade 0) to 72
2% in the Grade-IV group. The OR was more than three times higher in the Grade-IV group than in the Grade-0 group, practically twice as high in Grade III and 1
6 times higher in Grade II. In these three groups, the differences were statistically significant. The OR of Grade I with respect to Grade 0 was 1
18, which was not statistically significant. Binary logistic regression of the final model Lastly, a binary logistic regression was performed to analyse the influence of each of the theoretically important variables when the rest of the values remained stable. The variables analysed were gender,

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A . B L A N C O A G U I L E R A et al. Table 3. Relationship of bruxism with the qualitative variables handled in the study Bruxism

Sex Male Female Age >60 years 18–60 years Axis I No pathology Muscle pain (MP) Disk Displacement (DD) Arthropathy (Ar) Muscle pain + Discopathy Muscle pain + Arthropathy Discopathy + Arthropathy MP + DD + Ar Grade of muscle disease No muscle pain Muscle pain only Muscle pain + DD Muscle pain + Arthropathy Muscle pain +DD+Ar Locked joints Yes No

Yes

No

OR (95% CI)

77 (40
5%) 588 (57
1%)

113 (59
5%) 442 (42
9%)

Control 1
95 (1
42–2
67)

96 (44%) 569 (56
8%)

122 (56%) 433 (43
2%)

Control 1
67 (1
24–2
24)

11 58 27 9 126 195 9 230

(39
7%) (45
7%) (42
9%) (52
9%) (53
2%) (55
7%) (45%) (61%)

18 69 36 8 111 155 11 147

(62
1%) (54
3%) (57
1%) (47
1%) (46
8%) (44
3%) (55%) (39%)

Control 1
37 1
23 1
84 1
86 2
06 1
34 2
56

(0
60–3
14) (0
50–3
21) (0
55–6
20) (0
84–4
10) (0
94–4
49) (0
42–4
26) (1
18–5
58)

56 58 126 195 230

(43
4%) (45
7%) (53
2%) (55
7%) (61%)

73 69 111 155 147

(56
6%) (54
3%) (46
8%) (44
3%) (39%)

Control 1
1 1
48 1
64 2
04

(0
67–1
79) (0
96–2
28) (1
09–2
46) (1
36–3
06)

301 (56
7%) 364 (52
8%)

230 (43
4%) 325 (47
2%)

1
17 (0
93–1
47) Control

Fig. 1. Relationship of bruxism with the pain intensity.

Fig. 2. Relationship of bruxism with the grade of muscle disease.

age, presence of locked joints, grade of muscle disease and intensity of acute pain. The grade of chronic pain was not included in the regression, as it was the sum of disability plus pain intensity and was therefore collinear with pain intensity.

The results of the regression showed high statistical significance for gender, age and pain intensity. The presence of muscle and joint disease together was found to be insignificant at a constant pain intensity; however, when subjected to bivariate analysis, it © 2014 John Wiley & Sons Ltd

SELF-REPORTED SLEEP BRUXISM AND PAIN IN TMD PATIENTS Table 4. Relationship of bruxism with the Graded Chronic Pain Scale Bruxism Yes Graded chronic pain scale Grade 0 53 (44
9%) Grade 1 144 (49
1%) Grade 2 369 (56
9%) Grade 3 75 (61%) Grade 4 24 (72
7%)

No

65 149 280 48 9

OR (95% CI)

(55
1%) (50
9%) (43
1%) (39%) (27
3%)

Control 1
18 1
61 1
91 3
30

(0
77–1
82) (1
09–2
40) (1
15–3
20) (1
40–7
63)

became significant. This revealed the great importance of pain in the presence of diseases of this type (Table 5).

Discussion The prevalence of bruxism was very similar to the prevalence reported in other papers that, like ours, used questionnaires to diagnose bruxism in a population with TMD, that is, approximately 60% (16). The type of research is important, because, as Lobbezoo et al. (22, 23) note, the prevalence of bruxism may vary according to the diagnostic methodology (less prevalence in diagnosis by electromyography or polysomnography), sample type (with an approximate prevalence of 8% in the general population) or bruxism activity type (grinding or clenching). It is especially important in relation to the sample type. While studies examining the presence of bruxism in general population show percentages of this parafunctional

habit lower than 10% (24), those studies made in TMD samples obtain higher frequencies (approximately 60%) (16). There is still no widespread agreement on the relationship between bruxism and gender in the literature. There are papers that defend a greater prevalence in men (25, 26), others that find a greater prevalence in women (27, 28) and still others who find no differences between the two genders (26). In our results, it was women who more frequently displayed the parafunctional activity of bruxism. This is especially to be noted, as it is women who, generally speaking, report a higher pain intensity (29). Another point of note was the severe imbalance between men and women in our sample; the fact that the female sex accounted for 84% of our total sample could have influenced the results to some measure. Several papers find data similar to ours in terms of age, with sharp drops in the presence of bruxism after age 65 (27, 28). The results of our study concerning the association between bruxism and TMD are in line with those of most of the papers that use patient self-perception measured through questionnaires as the diagnostic method for bruxism with the same object as ours, to assess the association between the two entities. That is to say, other studies confirm the presence of an association between the bruxist habit and the presence of pain. This is clear in the results of our research as well: it is only in the diseases that cause greater severity of pain, such as myalgia accompanied by arthralgia, where a statistically significant association is found. No

Table 5. Binary logistic regression of the final model

Gender Age (60 years) Pain intensity Grade of muscle disease No muscle pain Muscle pain only Muscle pain + Disk Displacement (DD) Muscle pain + Arthropathy (AR) Muscle pain + DA + DD History of locked joints Constant DD, disk displacement; AR, arthropathy. © 2014 John Wiley & Sons Ltd

Coefficient (B)

Standard Error

Wald (x2)

P value

Odds Ratio

95% CI

0
551 0
501 0
011

0
167 0
159 0
005

10
920 9
937 5
100

0
001 0
002 0
024

1
735 1
650 1
011

1
25–2
41 1
21–2
25 1
00–1
02

0
339 0
488 0
617 0
766 0
010 1
031

0
805 0
796 0
791 0
791 0
121 0
282

5
708 0
178 0
376 0
609 0
938 0
007 13
400

0
222 0
673 0
540 0
435 0
333 0
934 0
000

1
40 1
63 1
85 2
15 1
01 0
36

0
29–6
81 0
34–7
75 0
39–8
73 0
46–10
14 0
80–1
28

569

570

A . B L A N C O A G U I L E R A et al. such association is found for disk displacement. However, the main limitation of our study was not to analyse the presence of self-reported awake bruxism. It would be interesting to analyse in future research the differences between these two clinical entities (awake and sleep bruxism) with respect to the presence of TMD symptoms. One example of a study that found similar results is that of Casanova-Rosado et al. (30). After examination using RDC/TMD and questionnaires to assess parafunctional habits, it was found that one of the most significant variables related with the symptoms of TMD was bruxism. Other studies whose results resemble those of Casanova-Rosado et al. are Johansson (27), Unell (28), Osterberg (31), Mundt (32) and Gesch (33). When weighing the validity of the diagnostic method, it is important to bear in mind that, while the method is easily accessible, it does afford room for strong bias, as Manfredini et al. point out. The foremost bias concerns patients’ difficulty in differentiating between awake bruxism and sleep bruxism (16). Some patients come to the study with the preconceived notion that their jaw pain on waking is associated with sleep bruxism, and thus, they mark sleep bruxism. There are studies that even posit a stronger association between morning pain and awake bruxism, although the majority-held belief is that morning pain is more strongly associated with sleep bruxism (34). The studies that used other methods to diagnose bruxism, such as polysomnography and electromyography, did not find a significant association between bruxism and the painful symptoms of TMD (35, 36), and some even demonstrated a negative association, that is, that the patients with the highest grade of pain had a much lower number of sleep bruxism episodes (37–39). However, some studies did find an association between eccentric bruxist episodes in sleep and the presence of joint clicking (25). One especially remarkable study is that of Raphael et al. A TMD group and a control group were examined during two nights in a sleep laboratory. Despite the TMD group reported more sleep bruxism than the control group, they did not find any significant difference between both groups related to polysomnographic dates. They even found that grinding noises very common in both groups (more than 55 per cent) (40). Another relevant study at this respect is that of Rompr
e et al. A bruxist group and a control group

were analysed by means of polysomnography, and questionnaires were used to assess the pain and selfreporting of bruxism. It was then observed that the patients with greater bruxist activity during sleep felt less intensity of pain than did the patients with less parafunctional activity (41). However, it is important to stress that most of the activities found in the polysomnography were of the eccentric or grinding type. The percentage of centric or clenching activities was very low. So, it would be interesting to analyse the differences between both types of bruxism activity, because most of the awake activities tend to be centric (clenching) (9), and approximately 90% of sleep bruxism activities are eccentric (grinding) (8). With respect to the distribution of bruxism between the different clinical subtypes of TMD, according to our study’s findings, bruxism is more closely related with muscle disease associated with other groups than with discopathy alone, arthropathy alone or even muscle disease alone. Our results can be compared with those of Manfredini, Winocur et al. (26), who found data resembling ours in the Israeli population but different data in the Italian population, where a greater distribution of bruxism among all subtypes was found. This could be due to various causes. Firstly, the answer might be the less-frequent use of imaging as a supplementary diagnostic test in the Israeli sample (10%) and in our sample (5%) than in the Italian sample (80%). Secondly, another possible explanation is the different general characteristics of the samples: the Italian sample was made up primarily of patients referred for joint diseases, while both the Israeli sample and ours featured a wider spectrum of oro-facial pain (26). Many patients interpret morning pain as being due to sleep bruxism when in reality it might be more closely related with awake bruxism. In addition, polysomnographs show no positive association between eccentric bruxism or grinding and the presence of painful symptoms, although they do show such an association with disk displacements. These two facts together suggest the hypothesis that it is awake bruxism or clenching that is related with the painful joint and muscle symptoms, and that sleep bruxism or grinding is more closely related to disk displacements, and it could even be diminished as a defence mechanism in patients with painful disease. However, more © 2014 John Wiley & Sons Ltd

SELF-REPORTED SLEEP BRUXISM AND PAIN IN TMD PATIENTS studies with statistically significant samples are needed to analyse the influence of sleep bruxism on TMD. Studies that can address the influence of awake and sleep bruxism with different diagnostic methods are also necessary.

Conclusions There is a strong association between reports of sleep bruxism and the presence of painful symptoms of TMD, especially muscle disease accompanied by arthralgia. The prevalence of this parafunctional activity is much greater in women and in patients under age 60. No significant association has been found, however, between the presence of disk displacements and self-perception of bruxism. Despite these results, it is necessary to highlight the importance of differentiating between sleep bruxism and awake bruxism in future studies. The two types of bruxism may be associated differently with the range of symptoms and signs of TMD.

Disclosures The study protocol was approved by the local ethical committee. The authors declare they received no funding for this investigation. The authors declare they have no conflict of interests.

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Correspondence: Antonio Blanco Aguilera, Master Program in Orofacial Pain and Temporomandibular Disorders, San Pablo CEU University, Avenida de Am
erica No 7. 1°1, 14008 C
ordoba, Spain. E-mail: [email protected]

© 2014 John Wiley & Sons Ltd