An initial search yielded 1,875 articles and further reduced to 801 after removing duplicates. In total, 43 articles were included after screening the title and the abstract following the eligibility criteria, and their full texts were read and screened. A further 27 articles were excluded, yielding a total of 16 studies (Supplementary Table 1).

Study characteristics

Most of the articles were published after 2000, with 12 published after 2010 and one published in 1980. All the articles were published from western countries, including Australia (n = 4), the United States (n = 4), the United Kingdom (n = 3), Sweden (n = 3), the Netherlands (n = 1) and Poland (n = 1). Most of the participants were dental patients, while one study explored the views of dental hygienists, and another explored dental teams' perspectives as part of the stakeholders. In total, 12 studies used a quantitative method, two studies a qualitative method, one a mixed method, and one was a review article.

Definitions of trust

Only four15,19,26,27 of 16 articles had some form of definition of trust. These were referenced to previous studies encompassing two definitions which focused on: i) patient's expectations for care; and ii) the acceptance of their personal vulnerability due to illness or unequal provider-patient relationship. Two studies26,27 defined trust as 'expectation for care' that would be met when trust was established or maintained. This definition underlined the pre-requisite for trust to be developed when a patient's expectation of care was met during their health care encounters. However, the other two studies defined trust as a potentially vulnerable situation of the patients that relies on health providers to act in patients' best interests.15,19 Although the definition has not been explored in-depth in dentistry, Armfield and co-authors have discussed the most pertinent components of trust, including reliability, competence, dependability, compassion, confidentiality and communication.19

Existing instruments to measure trust

In total, 12 articles19,26,27,28,29,30,31,32,33,34,35,36 used either various scales or single items to measure trust (Table 2). A limited number of scales were used more often, with three using the Dentist Trust Scale (DTS)19,29,30 and four applying the Dental Belief Survey (DBS).28,31,32,33

Table 2 A summary of trust measurementsDental Trust Scale

The DTS was adapted from the Physician Trust Scale with minor changes. The DTS covered four dimensions of trust, namely, fidelity, competence, honesty and global trust. Armfield et al.19 added two new items to explore: i) patient trust in the previous dentist they visited; and ii) reasons of changing dentist. These two items were designed to help identify reasons for poor trust in the dentists.

Dental Belief Survey

The original DBS initially had 15 items which aimed to measure the dentist-patient relationship exploring four dimensions, that is, communication, belittlement, lack of control and trust, with answers ranging from 1 = 'highly positive' to 5 = 'highly negative'.28 As part of the DBS, only two items were used to measure trust which focused on distrust rather than trust. These two items explored how sceptical and distrustful the patient felt about their dentist, that is: 'I am not sure I can believe what the dentist says' and 'dentists say things to try and fool me'. This, however, highlights a potential question of whether two items could measure a complex construct like trust.28 The DBS was then revised by adding 13 more items while retaining or slightly modifying the original 15 questions to cover three aspects: ethics (which replaced 'belittlement' and 'trust' in DBS), communication and control. The revised scale, DBS-R,32 was evaluated for its psychometric properties. The trust dimension was suggested to be reintroduced to improve the stability of the scale and reliability of this dimension. Trust dimension had six items when reintroduced. One item, however, was strongly loaded also on the ethics dimension, indicating the close relation between these two sub scales.32

2009 UK Adult dental health survey: measures of trust

Although both derived from the 2009 UK Adult dental health survey,37 Muirhead's work27 used a single item to measure patient feeling of 'confidence and trust' in dentists, whereas Yuan et al.34 explored more broadly the concept of trust through four items, in addition to the 'confidence and trust' item. The three additional items explored dentists' listening and explanation skills when discussing treatment, as well as whether patients were treated with respect.

Other instruments to measure trust

Although trust and mistrust should not be regarded as the opposite side of the concept, one study adopted three items from the measure of medical mistrust to test patient mistrust of dental providers.36 Groenstijn's work used a single item to test global trust by directly asking the patients how much they trust their dental care provider,38 whereas Reid et al. used a 32-item survey, developed based on health care ethics literature, to measure trust and therefore to assess the differences in patients' views of an ideal dentist and their dentists.35

Dental professionals' perception of patient trust

Only two qualitative studies39,40 were found to report dental professionals' views on patient trust. One study explored dental hygienists' perspectives on communication and interpersonal processes during the dental encounter.39 The dental hygienists admitted their responsibility and the importance of building trust with the patient. For them, trust could be established through creating a 'reliable relationship' and being responsive to patients' requirements. The hygienists also emphasised the importance of a first appointment in the building of trust, and how a negative attitude of the patient could affect the development of trust. Patient-centred communication was regarded as essential in building a trustful relationship and treatment success.

The other study explored dentists' perceived barriers and facilitators to preventing oral diseases in six European countries.40 Trust was seen as a key factor in the dentist-patient relationship. The dentists recognised the importance of patient-centred communication rather than using 'victim blaming' or 'lecture' approaches to communicating with the patient. Interestingly, dentists thought they were perceived negatively by patients.