The assessment of dental anxiety is becoming increasingly relevant with the stronger emphasis on evidence based methods for improving patient oral health care [1, 2]. In particular, recording self-reported dental anxiety in those patients who report psychological difficulties in receiving dental treatment enables planners of dental services to make informed decisions about suitable interventions [1, 3]. This is especially important in countries like China that are experiencing rapid economic development. China's health services are receiving close attention as its population is drawn into utilizing a mix of traditional and western influenced primary care provision. Dental services are expanding and little evidence is currently available on the factors responsible for uptake, of which dental anxiety is a likely candidate for explaining utilisation.
Issues that govern the choice and the use of dental anxiety measures in clinical practice and epidemiological surveys are: number of question items, complexity, validity and useability . There are a number of self-reported measures of dental anxiety that vary in length, theoretical background and psychometric evidence . Some scales are available in a variety of languages e.g. [6–8]. A popular measure of dental anxiety was the four item Corah's dental anxiety scale , however this scale omits assessing respondents' views to dental anaesthesia and has a complex answering scheme. The 5 item modified dental anxiety scale (MDAS) was constructed to satisfy both problems by introducing a new item about local anaesthesia and simplifying the response format . Conversion tables are available . A clinical cut-off score of 19 and above has been determined to identify highly dentally anxious individuals who require specialist care (e.g. behavioural management and/or anaesthesia) . A diagnostic classification for dental phobia has been devised based upon international criteria .
There are issues of usability that concern, first, how long the questionnaire takes to complete and, second the effect of instrumentation. An example of the first issue is the 36 item questionnaire (Dental Anxiety Inventory, DAI) designed to assess 3 'facets' of dental anxiety . Although highly reliable it was found to be impractical in clinical settings because of the relatively long completion time . A shorter 8 item version has been devised . The second issue of instrumentation has received little interest hitherto. There is some evidence that dental personnel are concerned about the possibility of raising dental anxiety by inviting patients to report their feelings associated with a dental visit . The design and subsequent development work with the Modified Dental Anxiety Scale has attempted to address this concern. The MDAS is brief and requires just 2–3 minutes to complete . Moreover, and crucially, the scale does not raise anxiety in respondents, regardless of their initial level of dental anxiety [17, 18] and rather than be detrimental its completion can be beneficial to patients when incorporated into managed care procedures within a practice setting .
The MDAS has been validated in the UK [10, 20, 21] and a number of other countries with native translations: Finnish, Arabic, Hindi  Turkish [22, 23], Norwegian , German, Portuguese and Rumanian . A previous report has demonstrated the validity of the Mandarin version of the short DAI , however the scale consists of 8 items and for clinical purposes, and inclusion in large epidemiological surveys, the shorter MDAS may be considered more suitable. The current study was motivated to develop the Chinese version of the MDAS that would be reliable and valid. Reliability was to be tested employing methods that reduce the number of assumptions used by traditional tests (explained below), and the scale's construct validity was checked by reference to the predicted relationships of the scale with a number of demographic and behavioural variables, and some tests of the structural relationships with other related constructs including general anxiety.
To date most dental anxiety scales have received limited attention to their theoretical underpinnings. Dental anxiety is not unitary and has been typically conceived under three connected approaches: behavioral, cognitive and physiological. Self-report methods primarily assess the cognitive component which can be split into at least two valid constructs  'exogenous and endogenous, with respect to the source of their anxiety'. The former describes dental anxiety as a conditioned response whereas the latter refers to a constitutional vulnerability to anxiety disorders. A dental anxiety measure that could feasibly capture some aspects of these two constructs would improve our understanding and hence treatment planning.
The MDAS although designed as a general screening instrument of dental anxiety requires further investigation to ascertain whether it is unitary. On inspection of the item content it can be hypothesised that the first two items constitute anticipatory dental anxiety (ADA) whereas the final three items tap emotions raised by the thought of having various dental treatments, that could be termed treatment dental anxiety (TDA). The separation of the scale into these two components may assist researchers and clinicians in understanding patient reaction to a dental visit. This proposed two factor model can be tested by adopting confirmatory factor analysis. This approach is particularly helpful for the researcher when a clear measurement structure is proposed [28, 29]. Various indexes of fit can be inspected to assess the proximity of the raw item responses to the hypothesised model . Not only can the measurement model be tested with the total sample collected but also comparisons can be made across important groups within the sample. It was expected that the Chinese MDAS would show higher levels of dental anxiety with females than males supporting previous findings [31, 23, 32] and lending support to the construct validity of the scale. In addition, older people and regular dental attenders are known to be less dentally anxious than their younger and irregular dental attending counterparts, respectively . These effects were predicted with the Chinese MDAS measure.
It is curious, that there is a high frequency of researchers demonstrating a sex difference in dental anxiety level, although no previous report has investigated the structure of responses to self report dental anxiety measures across gender. To maintain clarity of interpretation of the total scale score it would be an important feature of an assessment to show consistency of the measurement structure across gender.
The term dental anxiety was first conceptualised as a theoretical construct to understand the relationship between previous and frightening dental treatment experiences with the affect experienced when attending for dental treatment . This allowed dental anxiety to be formulated in terms of anticipatory anxiety to explain how anxious patients relived the original frightening experience when attending the dentist for treatment in the present [34, 35]. Furthermore, it was postulated that dental anxiety was related to an individual's general anxiety [36, 37]. Previous work with general anxiety scales, such as the HADS (from a large non-clinical sample: n = 2547) has shown that the anxiety subscale consists of two constructs: namely, negative affectivity (NA, items 1,5,7) and autonomic anxiety (AA, items 3,9,13) . Autonomic anxiety (AA) refers to high levels of autonomic arousal characterised by somatic symptoms such as shakiness, trembling and feelings of panic  whereas negative affectivity (NA) has been described as a 'temperamental sensitivity to negative stimuli'  or general distress . We posited that the AA subscale would be strongly associated with the anticipatory dental anxiety (ADA) items of the MDAS as individuals who tend to be 'physiological reactors'  will score highly on items that indicate imminent future exposure to the dental situation. Whereas individuals who suffer high levels of negative affectivity (NA) may be particularly likely to respond negatively to a wide variety of specific dental procedures (i.e. indiscriminate response across situations  page 466) and therefore accumulate high levels of Treatment Dental Anxiety (TDA). Such a pattern of relationships, if found in observed data, would help to confirm the construct validity of the MDAS. The generalisability of this structural model would be reflected if these relationships were found in more than one sample. We considered performing a strict test of this model with two samples from very different cultures (Chinese and English). If equivalence of relationships between the two cultural groups were found then this would aid our understanding of how dental anxiety was conceived by the two groups of respondents as well as support the validity of the measure. A similar approach has been reported previously, but without employing methodology to formally test for equivalence . There is some evidence that Chinese people remember past events in a different way to people from western cultures . Caucasians tend to reflect on single significant personal incidents, whereas Chinese will concentrate on situations that have greater societal importance and reduce the emphasis on individual past experiences .
Hence the overall aim of the present study was to assess the factorial structure and construct validity for the Chinese version of the Modified Dental Anxiety Scale (MDAS). The specific objectives were to:
To test the factorial structure of the Chinese version of the MDAS and confirm its integrity across an important demographic categorisation, namely: gender.
To investigate further the psychometric properties of this version of the MDAS by assessing first its reliability, second its construct validity through predicted relationships with demographic, behavioral and psychological constructs and thirdly, the consistency of the relationships of general and dental anxiety across cultures (Chinese and North-west of England).