Quality of dental restorations. FDI Commission Pro... - ResearchGate

124ning the material, operator andpatient effects on restoration quality.One of the major issuesappears to be the statistical treatmentof data. It is difficult toconduct clinical studies, with theaim of establishing a numericalrelationship between one specificrisk factor and the technical excellence,restoration service period orreplacement reasons. The mainreason is that the clinical performanceof a restoration is dependenton many known and unknownclinical variables that are difficultto control or record. It is alsodifficult, if not impossible, toassure independence among manyclinical variables that affect restorationclinical performance. Currently,there do not appear to be anygenerally acceptable, valid statisticaltechniques for isolating theinfluence of a single variable;indeed, many of the variables maynot be independent. In full knowledgeof this situation, clinicalresearchers employ various strategieswhen designing trials aimingto clarify parameters of restorationquality (Figure 3).Restoration quality has beenaddressed in both prospective andretrospective longitudinal studies aswell as in cross-sectional studies.Data from prospective and retrospectivelongitudinal studies can beused for constructing survivalcurves, proportions of restorationswith varying technical excellence asa function of time and reasons forreplacement.Current restorative materialshave excellent physical and mechanicalproperties. Prospective clinicalstudies therefore need to beextended for many years and/orinclude large numbers of restorationsbefore any strong statisticalinferences can be made. Longobservation periods are associatedwith problems such as patient dropouts,patient representativity andchanges in the clinician’s diagnosticabilities or understanding of replacementcriteria. Finally, also ethicalreasons may occasionally restrict theFigure 3. Parameters of the quality of dental restorations. The horizontal axis representstime, while the vertical axis is the proportion of restorations remaining over time. The boldline represents the proportion of restorations remaining in situ (that is ‘survival’), and theseare in the category ‘excellent’ (for example ‘alpha’), ‘acceptable’ (‘beta’) or ‘defective’(‘charlie’). Replacements may be ‘true’ reasons, that is bulk fractures, secondary caries,marginal deficiencies, discolouration, etc, or because of faulty diagnosis, inclusion intolarger restorations, primary caries on other surfaces, etc. Arbitrarily lines depict theproportion of restorations/replacements that fall into the carious categories. The horizontalline at 50% marks the median survival time. The intersections between this line and the otherlines represent from left to right when 50% of the remaining restorations are: excellent,acceptable and remaining in situ.possibility of conducting prospectiveclinical studies.Retrospective studies are basedon analysing patient records or acombination of patient records andquality evaluation of restorations.A frequent problem with manyretrospective studies is that little orno information is available onpossible reasons for replacement.Several studies have revealed thatreplacements are not alwaysexplained by restoration failure 1 ,and even if they are, retrospectivedata give no indication regardingwhether the failures are relateddirectly to the restoration, to therestorative process or to externalfactors 72 .Cross-sectional clinical studieshave either been presented asreplacement studies or recordingsof data from patients’ records.Other data have been derived fromassessment of technical excellenceof restorations in situ or inextracted teeth, or from detailedstudies of failed restorations.Cross-sectional studies that focuson mean age of failed restorationsidentify the ‘geometric centre’ ofthe area above the survival curve inFigure 3, while studies that focuson the age of remaining restorationsidentify the centre below thiscurve.In replacement studies, theprevious history and age of therestorations is often unknown.Although the type of materialusually is recognised, specific tradenames or batch numbers areseldom recorded. A characteristicof the study method is that theevaluation criteria are not explicit,which leaves the diagnoses to theoperators involved in the study. Theresults do not indicate any causalrelationships, and they are probablyinfluenced by factors such associoeconomy, patient demographyand the dentist:patient ratio. Thesame arguments are applicablewhen interpreting results fromcross sectional studies. Although theevaluation criteria may often beaccurately described, the history andclinical parameters at the time ofrestoration placement remainsunknown.International Dental Journal (2001) Vol. 51/No.3