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A review assessing the quality ofreporting of risk factor research in

implant dentistry using smoking,

diabetes and periodontitis and

implant loss as an outcome:critical aspects in design andoutcome assessment

Rocchietta I, Nisand D. A review assessing the quality of reporting of risk factorresearch in implant dentistry using smoking, diabetes and periodontitis and implantloss as an outcome: Critical aspects in design and outcome assessment. J ClinPeriodontol 2012; 39 (Suppl. 12): 114121. doi: 10.1111/j.1600-051X.2011.01829.x

AbstractAim: To assess, using a structured review, the quality of reporting (design and

outcome assessment) of risk factor research using the STROBE statements. Theoutcome was implant loss, and the risk factors assessed were smoking, diabetesand periodontitis.

Materials and Methods: Literature search was performed individually for each ofthe risk factors and the outcome using three sets of database: (a) MEDLINE, (b)references derived from relevant reviews and (c) references derived from identifiedmanuscripts. Only casecontrol and cohort studies were included and assessed

using the STROBE statements.Results: A total of 104 papers were retrieved, three of which were found to becohort studies (one in the diabetes and two in the periodontitis review) and nonewas a casecontrol study. A total of 101 of 104 papers were case series or cross-sectional study.

Conclusions:Risk factor research in implant dentistry is mostly comprised of caseseries studies. These are used to generate hypotheses, but are the wrong tool to

test these hypotheses. In the near future, well-designed observational studies areneeded and should be reported according to the proposed checklist.

Isabella Rocchietta1 and David

Nisand2

1Foundation IRCCS CaGranda Maggiore

Policlinico Hospital, Department of

Reconstructive Surgery Science and

Diagnostics, University of Milan, School of

Dentistry, London, UK; 2Private practice,

Paris, France

Key words: casecontrol study; cohort study;

dental implants; diabetes; periodontitis;review; smoke

Accepted for publication 8 November 2011

Conflict of interest and source of funding statement

The author declares no personal conflict of interest. This workshop was financiallysupported by the European Federation of Periodontology and by unrestrictedgrants from Astra, Nobel Biocare, and Straumann.

2012 John Wiley & Sons A/S114

J Clin Periodontol 2012; 39 (Suppl. 12): 114121 doi: 10.1111/j.1600-051X.2011.01829.x


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Introduction

Risk factor research is a major topicin implant dentistry with numerousreports in the literature discussingpoorer outcomes in association witha variety of conditions. Implant lossis the most frequently assessed out-come within the implant dentistryfield. The most frequently andknown risk factors associated withthe outcome of implant loss are thefollowing exposures/diseases: diabe-tes, periodontitis and smoking hab-its. Unfortunately, most of theavailable data regarding risk factorsin implant dentistry are extractedfrom case series. The latter could bedefined as descriptive papers, wherea group of patients in which a cer-tain treatment has been carried out(for example, dental implant inser-

tion) are followed and observed fora certain period of time (these maybe retrospective or prospective).During this time, some parametersare assessed (usually through thepatients charts, for example, smok-ing habits) and evaluated withrespect to their influence on theoverall outcome (implant loss).While such study design helps ingenerating hypotheses, it could notbe used to test a hypothesis (Grimes& Schulz 2002a).

Observational studies have been

generated to conduct risk factorresearch. It employs three majordesigns: cross-sectional studies, casecontrol studies and cohort studies.These three designs are considered tohave different validity, with cross-sectional studies being at the highestrisk of bias and results of properlydesigned and executed casecontroland cohort studies being the mostauthoritative. Frequently, the threedesigns are used sequentially: cross-sectional studies are employedinitially to generate hypotheses.

Thereafter, case

control and cohortstudies are used to verify the hypoth-eses and assess causality (BradfordHill 1965).

A casecontrol study is an obser-vational study that selects individu-als based on their disease or healthoutcome status (e.g. implant loss).It looks back through time atpotential exposures that both groups(cases and controls) may haveencountered (Schulz & Grimes2002). The statistic generated to

measure association is the oddsratio (OR), which is the ratio of theodds of exposure in the cases to theodds of exposure in the controls.OR greater than 1 indicate thatthose with the disease are morelikely to have been exposed,

whereas if it is close to 1, then theexposure and disease are not likelyto be associated. The advantage ofcasecontrol studies is that they arerelatively simple to conduct and lessexpensive than cohort studies.

A cohort study selects individualsbased on exposure status (e.g.tobacco, diabetes). The study sub-

jects should be at risk of the out-come under investigation at thebeginning of the cohort study; thisusually means that they should bedisease free (e.g. no implant loss)when the cohort study starts. Thecohort is followed through time toassess their later outcome status(Grimes & Schulz 2002b). The pointestimate generated is the RelativeRisk (RR), which is the probabilityof disease for a person in theexposed group, over the probabilityof disease for a person in the unex-posed group. RR greater than 1indicates association; in such anoccasion, the conclusion is that thosewith the exposure were more likelyto develop disease.

Along with a need for qualita-

tively high study designs to testhypotheses in the field of risk factorsresearch, there is also a great needto improve the quality of reportingof studies, as inadequate reportingof research may hamper the assess-ment of the strengths and weak-nesses of the studies reported in theliterature.

In 2007, the STROBE statementswas introduced to properly assessthe quality of reporting of observa-tional studies. The checklist standsfor Strengthening the Reporting of

Observational studies in Epidemio-logy (http://www.strobe_statement.org) and it is composed of 22 itemsby a group of international research-ers. It is mandatory to highlight thatthe checklist presented is not aninstrument to evaluate the quality ofobservational research. They serve asguidance on how to report thesestudies.

The aim of this review was toclearly identify all casecontrol andcohort studies published, evaluate

the quality of reporting and makepragmatic recommendations forfuture well-performed risk factorresearch.

Materials and Methods

A literature search was performedindividually for each of the risk fac-tors and the outcome using threesets of database; (a) MEDLINE, (b)references derived from relevantreviews published in the last 5 yearsand (c) references derived from ini-tially identified manuscripts. TheMEDLINE search was limited toclinical articles published in the Eng-lish language until May 2011.

In the first search, smoking wasdefined as the suspected risk forimplant loss. As such, the followingsearch terms were used: smokingOR smoking AND dental implants OR dental ANDimplants OR dental implants ORdental AND implant OR dentalimplant AND humans AND Eng-lish.

A second search was performedsetting periodontitis as the suspectedrisk. The search strategy includedthe following terms: periodontitisOR periodontitis AND dentalimplants OR dental ANDimplants OR dental implants ORdental AND implant OR dental

implant AND humans AND Eng-lish.

In the third search, diabetes wasconsidered as the suspected risk andthe following terms were used: dia-betes mellitus OR diabetes ANDmellitus OR diabetes mellitusOR diabetes OR diabetes insipi-dus OR diabetes AND insipidusOR diabetes insipidus AND dentalimplants OR dental ANDimplants OR dental implantsAND humans AND English.

Two examiners then reviewed

titles and abstracts individually. Atotal of 176 titles were identified(106 in the smoking group, 48 in theperiodontitis group and 22 in thediabetes group) of a total of 1200papers. The abstracts were read, andconsequently a total of 104 full textarticles were generated (71 in thesmoking group, 25 in the periodonti-tis group and 8 in the diabetesgroup). The articles were carefullyread by both authors and sorted bystudy design, and only casecontrol

2012 John Wiley & Sons A/S

Quality of reporting risk factor research studies 115


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and cohort studies were included tobe assessed using the STROBE state-ments to evaluate the quality ofreporting. (Figs 13).

Those articles designed as casecontrol or cohorts were scored usinga dichotomic scoring system on the

full 22 items of the STROBE state-ments to determine if certain itemswere properly addressed. Six of the22 items contained more than onecriterion, which are strongly con-nected to each other. Hence, if thepaper assessed failed one of the crite-

ria, the entire item was considered tobe not properly addressed.

Results

Of the 104 articles that were read infull text, only three were found to be

cohort while none were categorizedas casecontrols, with the vastmajority of the papers being caseseries (Table 1).

The smoking risk factor researchretrieved a total of 71 papers. Ofthese full text articles, none was clas-sified as casecontrol study orcohort.

The diabetes risk factor researchcomprised of eight papers, of whichonly one was a cohort study. Therest were case series.

Lastly, a total of 25 full textpapers were assessed for the peri-odontitis risk factor research. Twowere cohort studies and none werecasecontrols.

Table 2 reports the scoring of thethree included cohort studies usingthe STROBE statements.

The cohort studies within theperiodontitis risk factor research ful-filled more criteria of the STROBEstatements compared with the diabe-tes risk factor paper.

All authors addressed focusedand pertinent questions that wereexplained in the papers. All three

papers addressed the issue of report-ing key results well.

The three cohort studies poorlyaddressed clear definitions of out-comes, exposures, predictors, poten-tial confounders and effect modifiers.Also, the potential sources of biaswere poorly reported. The statisticalmethods employed were found to bethe weakest points for all threecohorts, in particular; reporting onhandling of missing data, loss to fol-low-up and sensitivity analyses. Inaddition, the translation of relative

risk data into absolute risk wasabsent in all three papers.

Discussion

Only three papers in the English lit-erature were found to be cohortstudies, whereas none was judged tobe casecontrol studies when the dia-betes, periodontitis and smoking riskfactors were assessed for implantloss. The fact that no casecontrolstudies were found at all within the

Arcles Reviewed arcles

Key words

Smoking and dental implant 297 53

Limits

English, Human 261 45

Title selecon 106 matching with systemac review*

Abstract Selecon 71 (Full text arcles retrieved)

Case control study 0

Cohort study 0

155/261: Reason for exclusion: different topic,

case reports and review.

35/106: Reason for exclusion: incorrect

outcome assessment.

71/71: Reason for exclusion: case series or cross

seconal design.

Fig. 1. Search strategy for cigarette smoking. Heitz-Mayfield and Huynh-Ba 2009,Strietzel et al. 2007


Key words

Periodons and dental implant 1057 187

Limits



Abstract selecon 25 (Full text arcles retrieved)

Case-control study 0

Cohort study 2



23/48: Reason for exclusion: incorrect outcome

assessment.

23/25: Reason for exclusion: case series and

cross seconal design.

Fig. 2. Search strategy for periodontitis. Heitz-Mayfield et al. 2009, Safii et al. 2010and Ong et al. 2008


116 Rocchietta et al.


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extensive literature search made theauthors of the review look into thestrict characteristics of the studydesign to understand the reason forthis lack of information. A casecon-trol study requires a strict selectionof the control group. This wasclearly stated by Grimes & Schulz(2002a). The matching is fundamen-

tal either on an individual basis (in a1:1 ratio) or on a group basis, trans-lating this into a complex and chal-lenging methodology. Realistically,this may be accessible for an extre-mely large population from which toselect the appropriate controls. Inaddition, the authors of casecontrolstudies are required to clearly

describe the methodology of thematching process, specifying the con-founding factors that are taken intoaccount. All the confounding vari-ables that inevitably will not bematched or controlled need to beadjusted using appropriate statistical

methods. A case

control studyshould aim at minimizing the recallbias as well as the participation bias.Sample size calculation should beundertaken a priori to ensure thestudy has enough statistical power.In light of the relatively small samplesize of all the identified studies(ranging between 10 and 980), itremains unlikely that the authorscould have both matched case andcontrols and accounted for con-founding variables (Schulz & Grimes2002).

Three cohort studies were foundand assessed to extrapolate usefulinformation. The fact that very fewcohort studies were found highlightsthe complexity of performing suchstudy design when the incidence ofthe outcome assessed is rare. The 5-year failure rate of implant support-ing single crowns was reported to beonly 3.2% according to Jung et al.(2008). Moreover, it should be keptin mind that the main feature of acohort study is observation of a


Key words

Diabetes and dental implant 112 33

Limits



Abstract selecon 8 (Full text arcles retrieved)

Case-control study 0

Cohort study 1



14/22: Reason for exclusion: incorrect outcome

assessment.

7/8: Reason for exclusion: case series design.

Fig. 3. Search strategy for diabetes. Salvi et al. (2008) and Javed and Romanos 2009

Table 1. References assessed as full text articles according to the risk factors

Risk factors

research

Number of

retrieved articles References

Smoking 71 Cavalcanti et al. 2011, Anner et al. 2010, Arisan et al. 2010, Garca-Bellosta et al. 2010, Gianserra

et al. 2010, Simonis et al. 2010, Vercruyssen et al. 2010, Aloufi et al. 2009, De Boever et al. 2009,Koldsland et al. 2009, Alsaadi et al. 2008a, b, Anitua et al. 2008, Balshe et al. 2008, Gatti et al.

2008, Huynh-Ba et al. 2008, Machtei et al. 2008, Sverzut et al. 2008, Aykent et al. 2007, Doyle

et al. 2007, Machtei et al. 2007, Sanna et al. 2007, Strietzel et al. 2007, Sa nchez-Pe rez et al. 2007,

Schwartz-Arad et al. 2007, DeLuca et al. 2006, Ellegaard et al. 2006, Mundt et al. 2006, Levinet al. 2006, Noguerol et al. 2006, Peleg et al. 2006, Roos-Jansaker et al. 2006, Wagenberg &

Froum. 2006, Jansson et al. 2005, Lemmerman & Lemmerman 2005, Moheng & Feryn 2005, Moyet al. 2005, Baelum & Ellegaard 2004, Kourtis et al. 2004, Ortorp & Jemt. 2004, van Steenberghe

et al. 2004, Karoussis et al. 2003, Rocci et al. 2003, Chuang et al. 2002, Kan et al. 2002,

Kumar A et al. 2002, Penarrocha et al. 2002, Schwartz-Arad et al. 2002, van Steenberghe et al.2002, Eckert et al. 2001, Kronstro m et al. 2001, Widmark et al. 2001, Berge & Grnningsaeter2000, Lambert et al. 2000, Schwartz-Arad et al. 2000, Wallace 2000, De Bruyn et al. 1999,

Grunder et al. 1999, Jones et al. 1999, Kan et al. 1999, Keller et al. 1999, Watson et al. 1999,

Wilson & Nunn1999, Minsk & Polson 1998, Watson et al. 1998, Bain 1996, Minsk et al. 1996,

Wang et al. 1996, De Bruyn & Collaert 1994, Gorman et al. 1994, Bain & Moy 1993.Periodontitis 25 Aglietta et al. 2011, Anner et al. 2010, Garca-Bellosta et al. 2010, Gianserra et al. 2010, Matarasso

et al. 2010, Roccuzzo et al. 2010, Simonis et al. 2010, De Boever et al. 2009, Koldsland et al.

2009, Fardal and Linden 2008, Gatti et al. 2008, Mengel et al. 2007, Roos-Jansa ker et al. 2006,Wagenberg & Froum 2006, Cordaro et al. 2005, Mengel & Flores-de-Jacoby 2005, Evian et al.

2004, Rosenberg et al. 2004, Karoussis et al. 2003, Hardt et al. 2002, Quirynen et al. 2001,

Brocard et al. 2000, Watson et al. 1999, Cune & de Putter C.A 1996, Rosenquist & Grenthe 1996

Di abetes 8 Anner et al . 201 0, Al saadi G et al . 20 08a, b, Tawi l et al. 2 008, Alsaa di et al. 2 007, Moy et al.2005, van Steenberghe et al. 2002, Morris et al. 2000




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Table2.

STROBEstatementchecklis

tforcohortstudiesandscoringofthepapersincluded

Itemsno

Re

commendations

Cohortstudies

withperiodontitis

asariskfactors

Cohortstudywith

diabetesasriskfactor

Roccuzzo

etal.2010

DeBoever

etal.2009

Morris

etal.2000

Titlesandabstract

1

(a)Indicatethestudysdesignwithacommonlyusedterminthetitleortheabstra

ct

Y

Y

N

(b)Provideintheabstractaninformativeandbalancedsummaryofwhatwasdoneand

whatwasfound

Y

Y

Y

Introduction

Background/rationale

2

Explainthescientificbackgroundandra

tionalefortheinvestigationbeingreported

Y

Y

Y

Objectives

3

Statespecificobjectives,includinganypre-specifiedhypotheses

Y

Y

Y

Methods

Studydesign

4

Presentkeyelementsofstudydesignear

lyinthepaper

Y

Y

Y

Setting

5

Describethesetting,locations,andrelev

antdates,includingperiodsofrecruitment,

exposure,follow-upanddatacollection

Y

N

N

Participants

6

(a)Givetheeligibilitycriteriaandtheso

urcesandmethodsofselectionofparticipants.

Describemethodsoffollow-up

Y

N

N

(b)Formatchedstudies,givematchingcriteriaandthenumberofexposedandunexposed

Y

Y

Y

Variables

7

Clearlydefinealloutcomes,exposures,p

redictors,potentialconfoundersandeffect

modifiers.

Givediagnosticcriteria,ifapplicable

N

N

N

Datasources/measurement

8*

Foreachvariableofinterest,givesourcesofdataanddetailsofmethodsofassessm

ent

(measurement).Describecomparability

ofassessmentmethodsifthereismoretha

none

group

Y

Y

Y

Bias

9

Describeanyeffortstoaddresspotentialsourcesofbias

Y

N

N

Studysize

10

Explainhowthestudysizewasarrivedat

N

N

Y

Quantitativevariables

11

Explainhowquantitativevariableswere

handledintheanalyses.Ifapplicable,desc

ribe

whichgroupingswerechosenandwhy

Y

Y

N

Statisticalmethods

12

(a)Describeallstatisticalmethods,inclu

dingthoseusedtocontrolforconfounding

Y

Y

Y

(b)Describeanymethodsusedtoexaminesubgroupsandinteractions

N

Y

Y

(c)Explainhowmissingdatawereaddressed

N

N

N

(d)Ifapplicable,explainhowlosstofollow-upwasaddressed

N

N

N

(e)Describeanysensitivityanalyses

N

N

N

Results

Participants

13*

(a)Reportnumbersofindividualsateachstageofstudy

e.g.numberspotentially

eligible,

examinedforeligibility,confirmedeligible,includedinthestudy,completingfollow-upand

analysed

Y

Y

N

(b)Givereasonsfornon-participationateachstage

Y

Y

N

(c)Consideruseofaflowdiagram

Y

N

N

Descriptivedata

14*

(a)Givecharacteristicsofstudyparticipants(e.g.demographical,clinical,social)an

d

informationonexposuresandpotentialconfounders

Y

Y

Y

(b)Indicatenumberofparticipantswith

missingdataforeachvariableofinterest

N

N

N

(c)Summarizefollow-uptime(e.g.averageandtotalamount)

Y

Y

N

Outcomedate

15*

Reportnumbersofoutcomeeventsorsummarymeasuresovertime

Y

Y

Y

(continued)




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large sample that is representative ofa population over a long period oftime. Comparison is done on inci-dence rates in groups that differ inexposure levels. Finally, even if a ret-rospective design could theoreticallybe considered for a cohort study,

the latter would not be suitable inthe field of risk factors research, asthe measurements of the exposurewill be unreliable due to the natureof its acquirement post factum.

Few cohort studies were found,whereas none were casecontrols.This may be related to the fact thatcohort studies have many benefitsover casecontrol studies. The RR isa more powerful effect measure thanthe OR, as the OR is just an estima-tion of the RR, and because trueincidence cannot be calculated in acasecontrol study where subjectsare selected based on disease status.Temporality can be established in aprospective study as the cohort, andconfounders are more easily con-trolled for. Recall bias is less of aconcern than is the casecontrolstudy as confirmed by Grimes &Schulz (2002a). Nevertheless, theyare more costly, and there is agreater chance of losing subjects tofollow-up based on the long-timeperiod over which the cohort is fol-lowed.

The three cohort studies included

in our review fulfilled most of theSTROBE statements, with meticu-lous attention to clearly stating thescope of the study and reporting keyresults. However, they were lackingsome of the above mentioned criticalaspects. The statistical methodsemployed were found to be theweakest points for all three cohorts,in particular; reporting on handlingof missing data, loss to follow-upand sensitivity analyses . In addition,the translation of relative risk datainto absolute risk was absent in all

three papers. Likewise, Langan et al.(2010) have recently assessed thequality of reporting in observationalstudies in dermatology. The authorsselected casecontrol, cohort andcross-sectional studies publishedfrom 2005 to 2007 in the five majordermatology journals. The authorsassessed the quality of reporting ofthe studies using the STROBE state-ments. A total of 138 articles wereincluded and analysed, and theauthors reported that the qualityT

able2

(continued)

Itemsno

Re

commendations

Cohortstudies

withperiodontitis

asariskfactors

Cohortstudywith

diabetesasriskfactor

Roccuzzo

etal.2010

DeBoever

etal.2009

Morris

etal.2000

Mainresults

16

(a)Giveunadjustedestimatesand,ifapplicable,confounder-adjustedestimatesand

their

precision(e.g.95%

confidenceinterval).Makeclearwhichconfounderswereadjustedfor

andwhytheywereincluded

N

Y

Y

(b)Reportcategoryboundarieswhenco

ntinuousvariableswerecategorized

Y

Y

N

(c)Ifrelevant,considertranslatingestim

atesofrelativeriskintoabsoluteriskfora

meaningfultimeperiod

N

N

N

Otheranalyses

17

Reportotheranalysesdone

e.g.analysesofsubgroupsandinteractions,andsensitivity

analyses

Y

Y

Y

Discussion

Keyresults

18

Summarizekeyresultswithreferenceto

studyobjectives

Y

Y

Y

Limitations

19

Discusslimitationsofthestudy,takingintoaccountsourcesofpotentialbiasorim

precision.

Discussbothdirectionandmagnitudeofanypotentialbias

N

Y

Y

Interpretation

20

Giveacautiousoverallinterpretationof

resultsconsideringobjectives,limitations,

multiplicityofanalyses,resultsfromsimilarstudiesandotherrelevantevidence

Y

Y

Y

Generalisability

21

Discussthegeneralizability(externalvalidity)ofthestudyresults

Y

Y

Y

Otherinformation

Funding

22

Givethesourceoffundingandtherole

ofthefundersforthepresentstudyand,

ifapplicable,fortheoriginalstudyonwhichthepresentarticleisbased

N

Y

Y

Y,yes;N,no;*,informationshouldbegivenseparatelyforexposedandunexpo

sedgroups




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was very mixed. Key areas that wereinfrequently reported included sam-ple size calculations, missing data,losses to follow-up, and statisticalmethods. Only 13 studies (9%)explained the role of funders in theresearch. This was consistent with

the findings derived from this review.Smoking as a risk factor forimplant loss accounted for zero casecontrol studies or cohort studies.The most likely explanation for thisphenomenon is that in the vastmajority of these studies, smokingwas only a secondary outcome vari-able (Balshe et al. 2008), and thus,matching these patients becomesimpossible, hence precluding themfrom casecontrol studies. Also, theincidence of smoking in the popula-tion coupled with the low incidenceof implant loss would require acohort study of several thousandpatients over many years to haveenough statistical power to deter-mine the effect. None of the 71 stud-ies that were evaluated includedsample size greater than 980, whichthen accounts for the lack of cohortstudies on this issue.

Studying the effect of cigarettesmoking in health science has manydrawbacks. Inaccuracy of assessmentof exposure was found in all theretrieved case series. All the papersdivided the patient population into

smokers or non-smokers accordingto self-reported questionnaires or byreviewing the patients charts. Not asingle study reported on biochemicalmarkers, which indeed is a realisticand pragmatic measurement of thelevels of nicotine. Patrick et al.(1994) performed a meta-analysis toidentify circumstances in which bio-chemical assessments of smokingproduce systematically higher orlower estimates of smoking thanself-reports. They reported sensitivityvalues that ranged from 6% to

100% and specificity data that ran-ged from 33% to 100%. The authorssuggested to improve accuracy, andbiochemical assessment, preferablywith plasma cotinine, should be con-sidered in intervention studies. Inaddition, Curtis et al. (1993) stated,problems of validity arise whenstudy techniques do not representaccurately actual behaviours. This isparticularly likely when the behav-iour being investigated is sociallysensitive. Curtis et al. (1993) further

added, in addition to the problemof validity, the variability of behav-iours causes difficulties in investiga-tions designed to identifyassociations between behaviours andhealth. McKay (1999) criticallyevaluated the methodologies to study

relapse in substance abusers. Theyconcluded that retrospective reportscan perhaps provide the mostdetailed accounts of circumstancesand experiences, but are also morelikely to be inaccurate due to thelimitations of memory.

The vast majority of the paperswhen risk factors are associated toimplant loss are represented by caseseries. The results of these studiesshow how many people develop adisease or condition over time (e.g.implant loss), describe the character-istics of the disease and thoseaffected and generate hypothesesabout the cause of the disease. Animportant caveat (often forgotten orintentionally ignored) is that descrip-tive studies, which do not have acomparison group, do not allowassessment of associations. Onlycomparative studies (both analyticaland experimental) enable assessmentof possible causal associations(Grimes & Schulz 2002a). These maystill be informative depending on thestudy objective. If it was not for thecase series of Bra nemark et al.

(1983) and the Adell et al. (1981), itmight be very much that implantdentistry would have not come ofage and be a useful armamentariumin dentistry as it is today.

Most of the papers that claimedto be a casecontrol or cohort studystated the study design in the title orabstract. Nevertheless, these werefound to be case series. On the otherhand, if the study fulfils the correctguidelines and recommendations, thestudy design should be reportedclearly in the title or abstract. Ubri-

ani et al. (2007) reported the per-centages of papers in three majordermatology journals, where thestudy design was cited in the titlesand/or in the abstracts. They con-cluded that most articles in the three

journals did not report the studydesign used in the title or abstract.A consistent and clear indication ofthe design used in studies may betterenable editors, reviewers and readersto assess critically articles publishedin scientific journals.

With the above in mind, carefulplanning of future studies is likely toresult in much more casecontroland cohort studies. For the design ofcasecontrol studies, matchingshould be in the heart of its design.Every effort should be made to

match for the most important non-confounding factors. Adequatestatistical compensation should beexecuted solely for the confoundingfactors that are impossible to match.

For the future design of cohortstudies, a special emphasis should beplaced on the prospective design,and on the correct measurement ofthe exposure over a large group ofpatients representative of a samplepopulation and assessed over a longperiod of time. All things considered,such studies that account for thevarious confounding variables andthe relative rarity of the outcomewill probably require thousands andeven tens of thousands of partici-pants. Thus, such an undertakingcould only be accomplished by a

joint effort from many centres andeven a global mission.

In conclusion, the extremely lownumber of risk factor comparativeresearch studies found in this reviewdoes not allow drawing any definiteconclusions. However, these haveserved as a basis to highlight thecritical issues to be addressed for

future recommendations in designingcasecontrol and cohort studies. Thiswill not only improve the researchoverall, but it will give the clinicianreliable tools to extract data fromand treat patients with evidence-based therapies.

Acknowledgement

The authors acknowledge Prof. E.E.Machtei for his outstanding adviceduring the manuscript preparation.

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