Health Evidence Bulletins - Wales


The planning of publicly funded health care must be based on an understanding of the effectiveness of interventions. Such planning can only happen if information is readily available, reliable and comprehensible, to people who do not necessarily have a medical training.

The original Protocols for Investment in Health Gain were written in the early 1990s to suggest areas where the introduction, or more widespread use, of certain practices could lead to worthwhile improvements in health for the people of Wales. The documents also highlighted current practices which were of questionable value. This revision has been prepared by reviewing the earlier Protocol for Investment in Health Gain: Oral Health(1) to provide some clear, updated statements with a precise indication of the strength of the evidence and its sources for each statement; and to introduce new statements covering subjects of important current interest.

The statements represent a systematic summary of evidence found through a formal literature search across a wide range of sources(2). The evidence has been critically appraised using internationally accepted methods(2) compiled into this document under the direction of a consultant in dental public health, and reviewed by a multidisciplinary team who are directly involved in patient care(3). In addition to this document, the information will be available electronically, via the NHS Cymruweb. Information on the methodology adopted (including a copy of the documentation), the formats in which the document is issued and details of other publications in the series, is available on request(4).

The convention used in this document to indicate the type of evidence is(5):

‘Type I evidence’ - at least one good systematic review
(including at least one randomised controlled trial).
‘Type II evidence’ - at least one good randomised controlled trial
‘Type III evidence’ - well designed interventional studies without randomisation
‘Type IV evidence’ - well designed observational studies
‘Type V evidence’ - expert opinion; influential reports and studies


Many health issues do not lend themselves to investigation by randomised controlled trial. By valuing evidence from these trials more highly than observational studies there is a danger that interventions with limited effectiveness might be judged to be more worthy than those based on observation. Similarly, those observational studies which clearly prove effectiveness (and make a randomised trial unethical) might be undervalued. Randomised controlled trials are a reliable form of evidence and, when available, they are included. If not, high quality evidence has been sought within the other categories. Information assigned as type V evidence includes important reports or recommendations which should rightly be highly regarded.

The health gain notation (used to indicate the potential benefit to health) is(6):

‘beneficial’ - effectiveness clearly demonstrated (1)
‘likely to be beneficial’ - effectiveness not so firmly established (2)
‘trade-off between beneficial and adverse effects’ - effects weighed according to individual circumstances(3)
‘unknown’ - insufficient/inadequate for recommendation (4)
‘unlikely to be beneficial’ - ineffectiveness is not as clearly demonstrated as for 6 (5)
‘likely to be ineffective or harmful’ - ineffectiveness or harm clearly demonstrated (6)

It should be stressed that these gradings, while aiming to be impartial, represent only the best advice of the professionals involved in preparing the Bulletin. Although the statements are deliberately brief, statistically significant quantitative information has been provided where possible. This is usually given as % change, in keeping with the original source of the information. Cost-benefit issues are not considered.

In keeping with the original Protocols, these revised documents are designed to assist Health Authorities in developing local strategies, informing the development of health improvement programmes and in purchasing high quality health care. It is anticipated, however, that they will be of value to all health professionals in keeping abreast of the increasing body of dental literature and can provide an agenda for future action in a wide variety of settings. It should be stressed that the publications will act as a supplement to, not a substitute for, clinical skills and experience. We anticipate that some of the conclusions reached will be controversial. Every effort has been made to include the best evidence within a subject area. Readers who are aware of any important studies that have been overlooked are encouraged to contact the project team(7).


As in the original Protocol, diseases and disorders which compromise oral health have been grouped into subject areas. Eight subject areas were selected for the present exercise:

  1. Tooth decay
  2. Periodontal diseases
  3. Dentofacial anomalies
  4. Oral cancer
  5. Temporomandibular joint disorders and complex facial pain
  6. Tooth wear and hypersensitivity
  7. Dental injuries
  8. Inherited dental anomalies

Research retrieved via the Project Methodology is the basis of the new statements. Many of the original Protocol statements lacked evidence which met the defined criteria of the project. Where it was felt, by the expert review groups involved, that these statements are still valid and represent accepted good practice, they have been appended to each subject area as type V evidence, citing the original Protocol as the reference.  The source of evidence upon which each statement is based is thereby identified.

The project team does not claim to have discovered all existing evidence; if a reader can identify key evidence which has not been included the Internal Review Froup would welcome notification of such evidence. The document aims to be a framework on which to build and update evidence on oral health.

Much of dentistry carried out today is based on accepted good practice. For much of this practice, further research would be an inappropriate use of resources. However there remain areas where further research would be extremely well justified. Thus in addition to summarising the evidence for dentistry, this document aims to demonstrate the gaps in the evidence base and highlights opportunities and priorities for future research agendas.


This initiative is funded by the Wales Office of Research and Development for Health and Social Care.

March 1998

(1)  Welsh Health Planning Forum.  Cardiff: Welsh Office NHS Directorate, November 1992

(2) Contact Protocol Enhancement Project Office, Duthie Library, UWCM, Heath Park, Cardiff CF4 4XN.

(3)  See Contributors

(4)  Contact: Protocol Enhancement Project, Duthie Library, UWCM, Heath Park, Cardiff CF4 4XN.

(5)  This table is adapted from the Bandolier system (derived from the work at McMaster University, Canada) using the NHS Centre for Reviews and Dissemination criteria for a systematic review.  See ref. 3 or http://www.jr2.ox.ac.uk/Bandolier/band6/b5-6.html and the Database of Abstracts of Reviews of Effectiveness (DARE) in the Cochrane Library.

(6)  This Notation is modified from the tables used in Enkin M, Keirse MJNC, Renfrew M and Neilson J.  A guide to effective care in pregnancy and childbirth.  2nd ed.  Oxford: Oxford University Press, 1995 pp. 389-390

(7)  See 4


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Health Evidence Bulletins: Wales, Duthie Library, UWCM, Cardiff CF14 4XN. e-mail: weightmanal@cardiff.ac.uk