ceramic inlay review

8/6/2019 Ceramic Inlay Review

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manageable amounts of unrelated information, with theselection of relevant information requiring particularskills and knowledge. The best evidence of the clinicaleffectiveness of alternative interventions has been con-sidered to be in systematic reviews of randomised con-trolled trials [12]. Systematic reviews of published litera-ture, which use objective and reproducible methods toidentify eligible studies and abstract and analyse relevant

data, provide the most useful mechanism for assessingthe evidence presented by clinical trials. To make sys-tematic reviews reliable and unbiased, they must be car-ried out rigorously and adhere fully to an exacting meth-odology [11, 80]. Studies included in the reviews are se-lected by systematic application of a predetermined listof criteria. Results of the studies selected should be syn-thesised appropriately by means of powerful statisticalmethods. By employing explicitly defined methods, sys-tematic reviews are able to integrate existing informationeffectively and provide comprehensive summaries of allavailable evidence.

The purposes of the present review were to assess the

quality of published clinical trials on ceramic inlays andevaluate their clinical effectiveness using a systematicapproach. To evaluate clinical effectiveness, the follow-ing null hypotheses were tested: (1) there is no differ-ence in longevity between ceramic inlays and other pos-terior restorations, (2) there is no difference in postoper-ative discomfort between ceramic inlays and other poste-rior restorations, (3) there is no difference in the aesthet-ic qualities of ceramic inlays and other tooth-colouredposterior restorations.

Materials and methods

The Cochrane Collaboration guidelines are primarily in-tended for conducting systematic reviews of the effec-tiveness of intervention [11]. In the present review, weattempted to adopt those general principles to evaluatethe clinical effectiveness of ceramic inlays from pub-lished findings of clinical trials. Additionally, the qualityof the published papers on ceramic inlays was assessedby a systematic approach.

Selection criteria

Inclusion and exclusion criteria for the selection of pa-pers for review were established prior to the literaturesearch. The inclusion criteria consisted of written clini-cal studies (randomised controlled trials (RCTs), con-trolled clinical trials (CCTs), and case series) of class Iand class II ceramic inlay restorations in premolar andpermanent molar teeth. All types of ceramic inlays fired, milled-CAD/CAM and copy milled, cast, and heat-pressed were included. Excluded were studies involv-ing laminate veneers, ceramic onlays, and ceramiccrowns. A case report and a laboratory study were alsoexcluded.

Search strategy

A journal search, consisting of both electronic and handsearching, was undertaken to identify all relevant stud-ies, irrespective of language.

Electronic databases

Electronic searches included the following databasesfrom 1990 to 2001: MEDLINE, EMBASE, and theCochrane Controlled Trials Register. The subject searchused a combination of controlled vocabulary and free textbased on the search strategy for MEDLINE using the keywords ceramics, dental porcelain, and inlays.

Hand searching of databases

Hand searching of the following key journals from 1990to 2001 was undertaken: Acta Odontologica Scandina-

vica, British Dental Journal, International Dental Jour-nal, Journal of the American Dental Association, Journalof Dentistry, Journal of Dental Research, Japanese Jour-nal of Conservative Dentistry, Journal of Prosthetic Den-tistry, Operative Dentistry, and Quintessence Internation-al. These ten journals containing articles on restorativedentistry were identified according to experts advice.

The reference lists of all the relevant studies, existingreviews, and personal reprint collections of authors werescreened for additional relevant publications.

Selection of relevant publications

Each publication was initially assessed for relevance bytwo of the authors (MH and CAY) using data presentedin the abstract. When an abstract was not available orfailed to provide sufficient information, a reprint of thefull paper was obtained. When papers or abstracts report-ed different stages of clinical trial, only the longer-termstudy was included in the review. When both a full paperand an abstract were published based on data from thesame clinical trial, only the full paper was included.

Quality assessment

Quality assessment of the selected papers was undertak-en by two reviewers working independently, using themodified systematic assessment list consisting of 24items (Table 1). This list was developed according topublication guidelines [2, 6, 56] and previously pub-lished reviews [52, 69]. The calibration of quality assess-ment was carried out by two reviewers (MH and CAY)using a sample paper prior to the assessment. The sys-tematic assessment criteria were applied to each paper inturn.


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The two assessors initially evaluated all of the articlesindependently. The level of agreement between assessorswas evaluated using kappa statistics with a 95% confi-dence interval (CI). Disagreements between the asses-sors were identified and discussed, and a final score wasagreed for each paper.

To estimate intra-rater reliability, ten full papers wereselected at random and assessed by one reviewer twicewith a 1-month interval. The criteria were scored asyes or no or, when insufficient information was pro-vided, as unable to determine. The results were ex-pressed as percentages of the total attainable scores foreach of the items assessed.

Evaluation of clinical effectiveness

Study selection

To evaluate the clinical effectiveness of ceramic inlays,RCTs and CCTs in which other forms of posterior res-torations were used as control groups were selected bythe two independent reviewers according to the resultsof quality assessment. The author of each selectedstudy was contacted to provide detailed information onstudy design or to provide details with respect to miss-ing data. The study design of each of the selected pa-pers was assessed by a statistician involved in the re-view process. If a trial was excluded from evaluationbecause of the study design, the reasons for exclusionwere described.

Data extraction and synthesis

The following information was extracted from the papersselected for evaluation of the clinical effectiveness of ce-ramic inlays: date of the study, year of publication, set-ting and funding source of the trials, sample size, age

and gender of the participants, and the types of teeth andcavities restored. Differences among study participants,duration of study, interventions, outcomes, and informa-tion on adverse events or effects were also recorded.

Data were extracted by two reviewers independentlyusing specially designed data extraction forms. Theseforms were piloted on several papers and modified as re-quired before use. Data presented in graphs and figureswere extracted whenever possible. Such data were onlyincluded, however, if both reviewers independently ex-tracted the same result. Any disagreement was discussedand a third reviewer consulted as necessary.

The outcomes were evaluated in terms of failure rate,postoperative pain/discomfort, and aesthetic qualities.Restorations were considered to have failed when re-placement was indicated or endodontic problems oc-curred. In addition, restorations evaluated as clinicallyunacceptable using clinical criteria such as the UHPHS[9] or CDA [74] criteria were also considered failures.Postoperative pain/discomfort was evaluated as the pres-ence or absence of sensitivity to temperature or occlusalloading within 1 month after restoration.

Table 1 Intra- and inter-rater agreement on 24 items of quality assessment.N/A not calculable

Item Theme assessed Kappa values

Intra-rater Inter-rater

1 Is the hypothesis/aim/objective of the study clearly described? 1.00 0.602 Is the setting of the study or the source of the subjects studied described? 0.82 0.763 Is the distribution of the study population by age or gender described? 1.00 0.964 Are the inclusion criteria stated? 1.00 0.87

5 Are the exclusion criteria stated? 1.00 0.946 Are the treatments well described? 1.00 N/A7 Are the main outcomes to be measured clearly described in the Introduction or Methods section? 1.00 0.408 Is the sample size stated? 1.00 N/A9 Was the sample size justified? 1.00 1.00

10 Was the concurrent control group used? 0.62 0.8211 Was random allocation to treatment used? 1.00 1.0012 Was the method of random allocation given? 1.00 1.0013 Was blind assessment of the outcome carried out? 0.05 0.2314 Was there more than one examiner for outcome assessment? 0.78 0.8815 Was examiner calibration carried out? 0.80 0.8316 Are the statistical methods described? 1.00 0.7717 Is the participation/follow-up rate stated? 0.41 0.6918 Was the participation/follow-up rate greater than 80%? 0.44 0.5519 Are the nonparticipants/subjects lost to follow-up described? 0.42 0.6620 Are the main findings of the study clearly described? N/A N/A

21 Are results stated in absolute numbers when feasible (e.g., 10/20, not 50%)? 0.62 0.9322 Are confidence intervals given? 1.00 0.9023 Are any important adverse events reported? 1.00 1.0024 Are any conclusions stated? 1.00 0.58


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Statistical analysis

The Cochrane Oral Health Group statistical guideline[80] was followed to evaluate the clinical effectivenessof ceramic inlays.

Heterogeneity

The significance of the discrepancies in the estimates oftreatment effects from the different trials was assessedwith Cochrans test for heterogeneity [11]. If any signifi-cant heterogeneity (P0.61 (Table 2).

The mean difference between the two reviewers in theassessment of a paper was 7.9% (95% CI 6.1, 9.7). Thekappa values varied from 0.23 to 1.00, with a median of0.83 (Table 1), while 76% of the items presented goodagreement, with a high kappa value of >0.61 (Table 2).Complete agreement between the assessors was found ineight full papers and four other items assessed. Nearlyall of the disagreements were attributed to reading errorsor differences in interpretation of the published material.All disagreements between the two assessors were sub-sequently resolved through discussion.

Methodological quality

The results on the quality assessment of each paper arepresented in Table 3. In terms of study design, only fivepapers (10.9%) [24, 39, 60, 66, 85] were RCTs, 15(32.6%) [8, 33, 38, 41, 46, 48, 55, 71, 73, 88, 92, 93, 96,97, 99] were CCTs, and the remaining 26 (56.5%) [7, 10,

Table 2 Distribution of kappa values of intra- and inter-rateragreement

Kappa Strength of Distribution of kappa valuesvalue agreement

Intra-rater Inter-rateragreement (%) agreement (%)


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Table 3 Quality assessment of 46 studies on ceramic inlays. RCTrandomized controlled trial, CCTcontrolled clinical trial

Study Ref. Author, Publi- Items assesseda

design no. year cationstyle 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

RCT 66 Pallesen Full +b + + + + + + + + + + + + + + + +2000 paper

60 Molin 2000 + + + + + + + + + + + + + + + + +85 Sjogren 1998 + + + + + + + + + + + + + + + + +

24 Gladys 1995 + + + + + + + + + + + + + + +39 Isengerg 1992 + + + + + + + +

CCT 93 Thorodrup Full + + + + + + + + + + + + + +2001 paper

55 Manhart 2001 + + + + + + + + + + + + + +97 van Dijken + + + + + + + + + + + + + + + + +

199992 Thordrup + + + + + + + + + + + + + +

199996 van Dijken + + + + + + + + + + + + + + + +

199846 Katsube 1997 + + + + + + + + + + + + +41 Isidor 1995 + + + + + + + + + + + +38 Inaba 1995 + + + + + + + + + + + + + +88 Stenberg + + + + + + + + + + + + + + + +

199348 Klimm 1999 Ab- + + + + + + +8 Bodenheim stract + + + + + + + + + +

199733 Hein 1997 + + + + + + + + +99 Zuelling 1996 + + + + + + + +72 Roulet 1996 + + + + + + + + +71 Roulet 1995 + + + + + + + + + + +

Case 70 Reiss 2000 Full + + + + + + + + + +series 37 Iida 2000 paper + + + + + + + + + +

31 Hayashi 2000 + + + + + + + + + + +17 Frankenberger + + + + + + + + + + + + + +

200095 Torii 1999 + + + + + + + + + + +53 Malament + + + + + + + + + + + +

1999

22 Fizzi 1999 + + + + + + + + + + +81 Shearer 1998 + + + + + + + + + +14 Felden 1998 + + + + + + + + + + + + +18 Friedl 1997 + + + + + + + + + + + + + + +15 Fradeani 1997 + + + + + + + + + + + + + + +89 Studer 1996 + + + + + + + + + + + + + + + + + +68 Qualtrough + + + + + + + + + + + + + + + +

199658 Molin 1996 + + + + + + + + + + + +34 Heymann + + + + + + + + + + +

199665 Oka 1995 + + + + + + + + + + + + +47 Kawai 1995 + + + + + + + + + +83 Sjoren 1992 + + + + + + + + + + +61 Mormann + + + + + + + +

1992

51 Krejci 1992 + + + + + + + + + + +7 Bessing 1990 + + + + + + + + + + +78 Schulte 1998 Ab- + + + + + + +63 Neo 1998 stract + + + + + + + + + +10 Cerutty 1998 + + + + + + + + + + +64 Noack 1994 + + + + + + + + + + + +25 Goetsch 1991 + + + + + +

a The 24 items assessed refer to Table 1b Items received yes in quality assessment


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14, 15, 17, 20, 22, 25, 31, 34, 37, 47, 51, 53, 58, 61, 63,64, 65, 67, 70, 78, 81, 83, 89, 95] were longitudinal clin-ical trials without control groups. Amongst these RCTsand CCTs, two trials [38, 88] had parallel design and six[60, 66, 85, 96, 97, 99] had split-mouth design. The de-signs for the 12 remaining studies [8, 24, 33, 39, 41, 46,

48, 55, 71, 73, 92, 93] were not explicitly stated, inap-propriate, or unable to be determined due to insufficientinformation.

The results on quality assessment for each item aresummarised in Table 4. Overall, aim/objectives, treat-ments, sample size, main findings, and conclu-sions were described in almost all of the studies. In con-trast, none of them mentioned justification of samplesize, method of random allocation, or important ad-verse events.

More than half of the studies (54%) described the set-ting of the study or the source of the subjects. Sixteenstudies recruited subjects from dental school patients[14, 17, 24, 31, 37, 38, 46, 47, 60, 64, 65, 67, 78, 89, 95,97]. Five involved patients who attended private practice[15, 22, 33, 41, 53], while another four [58, 83, 85, 96]recruited participants from dental school patients, privatepractices, and community health centers.

Less than half of the studies (44%) provided inclusioncriteria for the recruitment of participants. Exclusion cri-teria were stated in only 23%. The extent of the detailson the inclusion and exclusion criteria varied from studyto study. For inclusion, primary caries, replacement ofrestorations, Class II restoration, good oral hygiene,sound periodontal condition, and aesthetic demands were

considered. For the exclusion criteria, poor oral hygiene,active periodontitis, high levels of caries progression,bruxism or clenching, malocclusion, and occlusal para-function were considered.

None of the RCTs stated methods of randomisationsuch as the generation and concealment of random allo-

cation. Furthermore, although almost half of the studies(48%) employed more than one examiner in clinicalevaluation, calibration of the examiners was carried outin only 28% of the trials, and blind assessment was un-dertaken in only 4%.

The recall rates of participants were recorded in 29papers (63%). A total of 13 investigations (28%) [10, 15,20, 24, 46, 60, 61, 64, 66, 67, 85, 88, 92] achieved 100%recall rates over periods of 1.5 to 8 years. Only five pa-pers [65, 89, 96, 97, 99] (11%) reported the numbers andreasons for patients lost from the trials.

Most studies (87%) defined the main outcome in theirIntroduction or Materials and methods sections, prior tothe trial description. However, none of the studies esti-mated the sample size expected to detect possible signif-icant differences for the anticipated outcomes.

To evaluate the clinical performance of ceramic in-lays, 30 studies (65%) [8, 10, 14, 15, 17, 20, 22, 25, 31,34, 37, 38, 39, 46, 47, 48, 51, 55, 61, 63, 64, 65, 66, 70,71, 88, 89, 95, 96, 97] used the USPHS criteria, and sev-en (15%) [7, 58, 60, 83 85, 92, 93] followed the CDAcriteria. Other than patient dropout, none of the papersaddressed the subject of deviation from the protocol.

In 78% of the studies, the main findings were de-scribed in absolute numbers rather than as percentages.

Table 4 Quality asessment of46 full papers and abstracts Item Themes assessed Numbers of

yes answers in46 papers (%)

1 Is the hypothesis/aim/objective of the study clearly described? 42 (91)2 Is the setting of the study or the source of the subjects described? 25 (54)3 Is the distribution of the study population by age or gender described? 28 (61)4 Are the inclusion criteria stated? 20 (44)5 Are the exclusion criteria stated? 11 (23)

6 Are the treatments well described? 46 (100)7 Are the main outcomes to be measured clearly described 40 (87)in the introduction or Methods section?

8 Is the sample size stated? 46 (100)9 Was the sample size justified? 0 (0)

10 Was the concurrent control group used? 20 (44)11 Was random allocation to treatment used? 5 (11)12 Was the method of random allocation given? 0 (0)13 Was blind assessment of the outcome carried out? 2 (4)14 Was there more than one examiner for outcome assessment? 22 (48)15 Was examiner calibration carried out? 13 (28)16 Are the statistical methods described? 29 (63)17 Is the participation /follow-up rate stated? 29 (63)18 Was the participation /follow-up rate greater than 80%? 25 (54)19 Are nonparticipants/subjects lost to follow-up described? 23 (50)20 Are the main findings of the study clearly described? 46 (100)21 Are results stated in absolute numbers when feasible 36 (78)

(e.g., 10/20, not 50%)?22 Are confidence intervals given? 6 (13)23 Are any important adverse events reported? 0 (0)24 Are any conclusions stated? 44 (96)


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While 63% used statistical treatments, only 13% ex-pressed their results in statistical analysis with confi-dence intervals.

Randomised controlled trials

The literature search yielded five randomised controlled

trials presented as full papers [24, 39, 60, 66, 85]. Twostudies [24, 60] used different types of posterior restora-tions such as gold inlays and composite resin inlays ascontrol groups. Another two [39, 66] compared ceramicinlays made from different ceramic blocks, and the re-mainder [85] compared ceramic inlays placed with dif-ferent types of cement. In the four RCTs [24, 60, 66, 85],trial outcomes were evaluated by more than one examin-er and 100% recall was achieved.

Controlled clinical trials

The literature search yielded 15 controlled clinical trialsconsisting of nine full papers and six abstracts with a va-riety of types of control. Six studies [33, 38, 48, 55, 88,93] used control groups of different types of posteriorrestorations: composite resin inlays in two [55, 93], goldinlays in one [38], amalgams in one [88], both compositeresin inlays and direct composites in one [48], and com-posite resin inlays, direct composites, and amalgam inthe remainder [33]. The clinical performance was com-pared between different types of ceramic inlay systemsin one study [92], between different ceramic materials inone [46], and between different luting cements in seven[8, 41, 71, 73, 96, 97, 99]. All of the nine studies pub-

lished in full papers achieved recall rates of >80%.

Study selection for evaluation of clinical effectiveness

To evaluate the clinical effectiveness of ceramic inlays,studies in which other posterior restorations were used ascontrol groups were identified. A total of eight papers[24, 33, 38, 48, 55, 60, 88, 93] , consisting of two RCTs[24, 60] and six CCTs [33, 38, 48, 55, 88, 93], wereidentified. The designs of these studies are summarised

in Table 5 and Table 6.As a consequence of study design assessment, three[38, 60, 88] of the eight papers were included in theevaluation of clinical effectiveness, while the remainingfive [24, 33, 48, 55, 93] were excluded. The reasons forexclusion are described in Table 6. One RCT [24] didnot clearly describe the study design (parallel or split-mouth design), and the numbers and types of restorationsper patient could not be determined. Two abstracts [33,48] did not state the numbers of restorations at baseline,making it impossible to determine recall rates. Althoughthe authors of these studies were contacted for more de-tailed information on study design, none replied. These

three studies were therefore excluded from the statisticaltreatment.In one CCT [55], the restorations were allocated ac-

cording to cavity size. When the width of a restored cav-ity was more than two thirds the occlusal width, it wasrestored with ceramic inlays. When the width was lessthan two thirds, a composite was used. As this allocationsequence was considered to affect the prognosis of resto-rations [98], the data from this paper were not used.

One other CCT [93] described using a split-mouth de-sign. However, half of the patients received only one res-toration. Furthermore, the numbers of failed patients foreach type of restoration could not be determined. This

study was therefore also excluded.As a result of the assessment of the selected papers,one RCT [60] and two CCTs [38, 88] remained for the

Table 5 Studies included in the evaluation of clinical effectiveness of ceramic inlays. RCTrandomized controlled trial, CCTcontrolledclinical trial

Author Method Participants Interventions Outcomes Note

Molin 2000 RCT, split-mouth A total of 80 teeth restored Treatment groups: Longevity (failure) University-[60] design, four test (20 resotrations for each CAD/CAM (Cerec), CDA clinical criteria based

groups, 5-year treatment group), sintered (Mirage),duration all restorations followed-up, or heat-pressed (Empress)

nine males and 11females ceramic inlays control

2356 years of age group: gold inlay

Inaba 1995 CCT, parallel design, 24 out of 26 ceramic inlays Treatment group: sintered USPHS clinical University-[38] two test groups, and 18 of 19 amalgam ceramic inlay criteria based

1-year duration completing (Clapearl/Optec)control group: gold inlay

Stenberg 1993 CCT, parallel design, 25 ceramic inlays Treatment group: Castable USPHS clinical[88] two test groups, in 20 individuals and 25 ceramic inlay (Dicor) criteria

2-year duration amalgam fillings in 19 control group: amalgamindividuals completing,all restorations followed,1519 years of age


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evaluation of clinical effectiveness. Two [38, 60] of themwere comparisons between ceramic inlays and metal in-lays, and the other [88] used amalgam as a control group.Since they all used metallic materials as a control restor-ative, the aesthetic qualities of ceramic inlays could notbe considered in the present review.

Analyses of longevity

The selected RCT compared the failure rates between 60ceramic and 20 metallic inlays over 5 years [60]. Threeceramic inlays and one gold inlay had failed at 1-year re-view, one more ceramic inlay had failed at 3-year re-view, and three more ceramic and one more gold inlayhad failed at 5-year review. Each failure was found in adifferent patient, except one in whom two ceramic inlaysfailed.

In the present review, the three types of ceramic inlaywere combined to form a ceramic group. A conditionallogistic regression model was applied taking the cluster-ing of restorations within a patient into account. As therewas no patient with failures of both gold and ceramicrestorations, in order to fit the model, an extra patientwas added with one failure for gold and one for ceramic.There was no significant difference in failure rates be-tween ceramic and gold inlays, with an odds ratio of 1.12(SE 1.48; 95% CI 0.08, 15.0; P=0.98).

In one of the selected CCTs, 26 ceramic and 19 metal-lic inlays were placed at baseline and 24 ceramic and 18metallic restorations were reviewed [38]. No failures

were reported 1 year later, and there was no significantdifference in failure rates between the ceramic and me-tallic inlays.

The other CCT [88] compared the numbers of failuresbetween 25 ceramic inlays and 25 amalgams in 20 and19 individuals, respectively. All of the restorations were

followed for 2 years. One ceramic inlay failed at 1 yearand a second at 2 years due to fracture, while two amal-gams in the same patient needed repair due to caries atthe 2-year review. Statistical treatment could not be car-ried out due to small sample sizes. However, no signifi-cant difference was found between the failure rates ofceramic inlays and amalgam.

As all three studies showed no significant differencesin failure rates between ceramic inlays and other restora-tions, the data were unable to be synthesised by meta-analysis.

Analyses of postoperative sensitivity

In the selected RCT [60], no ceramic inlays were associ-ated with postoperative sensitivity, while one gold inlaywas found to give rise to symptoms 1 week after place-ment.

In one CCT [38], postoperative sensitivity was foundin 11 of the 26 ceramic inlays and nine of the 19 metallicinlays 2 weeks after placement. In this study, no signifi-cant difference was detected in the incidence of postop-erative sensitivity between ceramic and metallic inlays,with an odds ratio of 0.81 (95% CI 0.25, 2.68; P=0.70).

Table 6 Studies excluded from the evaluation of clinical effectiveness of ceramic inlays. RCT randomized controlled trial, CCTcon-trolled clinical trial

Author, year, ref., Method Interventions Reasons for exclusionduration

Thordrop 2001 [93] CCT Treatment group: Sort of split-mouth design, however, some patients only received5 years ceramic inlay one treatment. We were unable to use the data

control group:composite resin inlay

Manhart 2001 [55] CCT Treatment group: Allocation sequence is considered to lead to bias. The restorations2 years ceramic inlay were allocated to teeth treated according to cavity size. When the

control group: width of the cavity restored was more than 23

of the occlusal width,composite resin inlay the the cavity was restored with ceramic inlays; when less than 2

3,

composite was used

Klimm 1999 [48] CCT Treatment group: Numbers of restorations at baseline were unclear, therefore we2 years ceramic inlay were unable to calculate the recall rate

control groups: compositeresin inlay, composite resin

Hein 1997 [33] CCT Treatment group: Numbers of restorations at baseline were unclear, therefore weceramic inlay control were unable to calculate the recall rategroups: composite resininlay, composite resin,amalgam

Gladys 1995 [24] RCT Treatment group: Study design (parallel or split-mouth) was not clear. We were3 years ceramic inlay unable to clarify numbers and types of restorations placed per patient

control group: compositeresin inlay


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Importance of randomised controlled trials

Well-designed, properly executed RCTs have beenknown to provide strong evidence of the effectiveness ofhealth care interventions [3, 45, 56, 86]. However, only5% of the 46 clinical trials retrieved in the present re-view were RCTs. Further clinical research on ceramic in-lays should satisfy the essential requirements of mean-

ingful RCTs.In theory, bias should be minimised if randomisationis strictly and appropriately applied [13]. Successful ran-domisation is an essential requirement for maintainingthe quality of clinical trials. Such randomisation dependson two interrelated aspects: the generation of an unpre-dictable allocation sequence and the concealment of thissequence from investigators enrolling participants [56].Recent studies indicate that trials in which the allocationsequence had been inadequately concealed yielded largerestimates of treatment effects than trials reporting ade-quate allocation concealment [44, 79]. Careful attentionto randomisation is therefore required when conducting

and reporting clinical trials.Despite the importance of the random allocation se-quence, none of the RCTs published on ceramic inlaysdescribed the methods of randomisation. Researchersconducting clinical trials should be fully aware of theimportance of a rigorous randomisation sequence and itsapplication.

Recall rate

The occurrence of dropped participants is unavoidable inclinical trials involving representative samples of pa-

tients, as is the associated uncertainty as to the fate oftheir restorations. In the present review, 54% of the 46papers retrieved presented recall rates of over 80% overperiods of 1 to 8 years. Among these, 28% achieved100% recall rates over 1.5 to 8 years. Careful consider-ation of dropped restorations is required when consider-ing outcome, given that actual failure rates can only bedetermined if a 100% recall is achieved.

In the present review, 46% of the papers included re-ported


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Double-blind assessment

In clinical trials, the term blinding refers to keepingstudy participants, clinicians, and sometimes those col-lecting and analysing the clinical data unaware of the as-signed intervention. The blinding of patients, cliniciansand other persons involved in evaluating outcomes alsominimises the risk of detection bias. This type of bias

arises if the knowledge of a patients assignment influ-ences the process of outcome assessment. Blinding ofdata analysts can also prevent bias, as knowledge of theinterventions received may influence the choice of ana-lytical strategies and methods used.

There is a difficulty in conducting double-blind as-sessment in dental interventions as found in the presentreview. Double-blind assessment is, for example, impos-sible in the evaluation of ceramic and gold inlays, giventhat the materials can be readily distinguished. Only incomparisons between tooth-coloured restorations is theblinding to assessors and patients possible, but in mostcases, the restorative materials can be distinguished. Re-

flecting this characteristic, quality scores with blind as-sessment ought to be low. This should be taken into ac-count when evaluating the quality of papers and utilisingthe results of quality assessment for further analyses.

Justification of sample size

Though all of the studies retrieved stated the sample siz-es of the trials, none of them justified the sample size, letalone calculated the number of participants required pri-or to commencing the trial. For scientific and ethical rea-sons, sample size needs to be planned prior to recruiting

participants, balancing clinical and statistical consider-ations. Ideally, a study should be sufficiently large tohave a high probability of detecting statistical signifi-cance between the materials to be compared.

It should be noted that reports of studies with smallsample sizes frequently include the erroneous conclusionthat the intervention groups do not differ, although toofew patients were studied to make such a claim [4]. Thisimportant issue should be addressed, since few authorsin clinical investigations reported the sample size [3, 94],as found in the present review.

Clinical effectiveness of ceramic inlays

Since the best evidence of the clinical effectiveness ofinterventions is considered to be provided by systematicreviews of randomised controlled trials, an attempt wasmade to adopt a systematic approach to investigating theclinical effectiveness of ceramic inlays. The assessmentof relevant studies in terms of study design yielded,however, only three clinical trials of appropriate quality.The clinical effectiveness of ceramic inlays can not bedetermined from such a limited number of single-centretrials, all of which included relatively small numbers of

participants (in the range of 20 to 25) with relativelyshort-term follow-up assessments over periods of one to5 years.

A comprehensive approach to evaluating the clinicaleffectiveness of ceramic inlays had been planned to in-clude longevity, postoperative pain, aesthetic qualities,and cost effectiveness. This evaluation could not be car-ried out due to the lack of sufficient information. A vari-

ety of statistical approaches were planned, such as meta-analysis, subgroup analysis, sensitivity analysis, and as-sessment of publication bias. We were unable to carryout such analyses in the present review due to the smallnumber of well-designed clinical trials reported. Such astatistical approach, if possible, could have clarified theclinical effectiveness and longevity of ceramic inlays.

Well-designed clinical trials of ceramic inlays, fol-lowing the CONSORT requirements [56], would be ofvalue and facilitate future systematic reviews of suchrestorations. Such work, however, would not addressquestions on the efficacy of ceramic inlays in everydayclinical practice. To find such answers, large practice-

based studies with sophisticated design would be re-quired to include consideration of cost benefits and con-sequences in terms of preserving teeth for life.

Conclusion

Based on the results of the literature search, critical ap-praisal, and the statistical analysis of clinical data, it isconcluded that no significant differences existed in lon-gevity or postoperative sensitivity between ceramic andother posterior restorations over assessment periods ofup to 1 year. Greater attention to the design and reporting

of studies is required to improve the quality of clinicaltrials of ceramic inlays. The best evidence is obtainedfrom well-designed randomised controlled trials withsufficient numbers of participants and restorations as-sessed over extended periods of time.

Acknowledgements The authors would like to thank Mrs. SylviaBickley and Ms. Anne-Marie Glenny at the Cochrane Oral HealthGroup for their help with the literature search and developing thequality assessment criteria. This study was supported in part by aGrant-in-Aid for Scientific Research (no. 14571812) from the Ja-pan Society for the Promotion of Science.

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