Linear measurements using virtual study models A systematic review

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1 Originl Article Liner mesurements using virtul study models A systemtic review Nghe S. Luu ; Liliy G. Nikolchev b ; Jen-Mrc Retrouvey c ; Crlos Flores-Mir d ; Trek El-Bily e ; Json P. Crey f ; Pul W. Mjor g ABSTRACT Objective: To perform systemtic review of the literture to ssess the relibility nd vlidity of liner mesurements using virtul vs plster study models. Mterils nd Methods: A serch strtegy ws developed for four online dtbses, nd references were further hnd serched for studies dditionl ppers. Three reserchers determined the eligibility of ppers by pplying specific selection criteri nd ultimtely selected 17 ppers. Grouped by virtul model cquisition type nd the number of lndmrks used in given mesurement, the dt were weighted by smple size nd nlyzed in terms of the relibility nd vlidity of liner mesurements. Results: The intrrter relibility ws high for two-lndmrk nd.two-lndmrk liner mesurements performed on lser-cquired models or cone-bem computed tomogrphy (CBCT) cquired models nd were similr to mesurements on plster models. Vlidity ws high for two-lndmrk nd.twolndmrk liner mesurements compring lser-cquired models or CBCT-cquired models to plster study models, nd the weighted men differences were cliniclly insignificnt. Agreement of mesurements ws excellent, with less vribility thn correltion. Acquisition type hd no perceived influences on relibility nd vlidity. More thn two-lndmrk mesures tended to hve higher men differences thn two-lndmrk mesures. Conclusions: Virtul study models re cliniclly cceptble compred with plster study models with regrd to intrrter relibility nd vlidity of selected liner mesurements. (Angle Orthod. 2012;82: ) KEY WORDS: Dentl models; Odontometry; Reproducibility of results; Imging; Threedimensionl Privte Prctice, Edmonton, Albert, nd former student, Orthodontic Grdute Progrm, School of Dentistry, Fculty of Medicine nd Dentistry, University of Albert, Edmonton, Albert, Cnd. b Privte prctice, Fredericton, New Brunswick, Cnd. c Director, Division of Orthodontics, Fculty of Dentistry, McGill University, Montrel, Quebec, Cnd. d Director, Orthodontic Grdute Progrm, School of Dentistry, Fculty of Medicine nd Dentistry, University of Albert, Edmonton, Albert, Cnd. e Associte Professor, Orthodontic Grdute Progrm, School of Dentistry, Fculty of Medicine nd Dentistry, University of Albert, Edmonton, Albert, Cnd. f Associte Professor, Mechnicl Engineering, University of Albert, Edmonton, Albert, Cnd. g Professor nd Chir, School of Dentistry, Fculty of Medicine nd Dentistry, University of Albert, Edmonton, Albert, Cnd. Corresponding uthor: Dr Pul W. Mjor, Fculty of Medicine nd Dentistry, Room 5-478, Edmonton Clinic Helth Acdemy, University of Albert, Avenue, Edmonton, Albert, Cnd, T6G 1C9 (e-mil: mjor@ulbert.c) Accepted: Mrch Submitted: November Published Online: April 24, 2012 G 2012 by The EH Angle Eduction nd Reserch Foundtion, Inc. INTRODUCTION A key process in dignosis nd tretment plnning in dentistry is the study model nlysis (SMA). In performing SMA, common dignostic prmeters re mesured on dentl models, such s overjet, intermolr width, nd rch perimeter. The current gold stndrd for SMA involves plster csts mesured with clipers. In recent decdes, threedimensionl (3D) virtul study models hve mde hedwy into dentistry. Avilble literture on 3D virtul dentl study models hs lrgely focused on those cquired by lser, 1 15 while others hve investigted hologrphic scnning, 16 stereophotogmmetry cpture, 17 nd, more recently, cone-bem computed tomogrphy (CBCT) Numerous studies hve investigted the vlidity nd relibility of liner mesurements mde on plster vs virtul study models, but systemtic review hs not been performed to collectively summrize their conclusions. To our knowledge, the only systemtic review on 1098 DOI: /

2 LINEAR MEASUREMENTS USING VIRTUAL STUDY MODELS 1099 virtul study models by Fleming et l. 21 summrized ssessments of vlidity but not relibility. Demonstrted relibility in repeted mesurements within virtul models nd plster seprtely re necessry before interpreting vlidity between the two modlities. The ims of this study were to perform systemtic review of the literture to ssess the vlidity nd relibility of liner mesurements using virtul vs plster dentl study models, grouping our nlysis by virtul model cquisition type nd the number of lndmrks used in given mesurement. MATERIALS AND METHODS The PICO 22 serch strtegy ws dopted for this study, nd the resulting serch string ws tilored for PubMed (from 1966 to My 16, 2010) nd dpted with no limits for the following online dtbses: OVID Medline, OVID All EBM Reviews, nd Lilcs. The PubMed serch ws lter updted to December 8, Eligibility of selected rticles ws determined in four phses. Selection of rticles t ech stge ws performed by three reserchers. Discrepncies between reserchers ssessment of eligibility were verblly discussed, nd finl selections were greed on by mjority vote. All non-english ppers selected t ech stge were ppropritely trnslted. In phse 1 of the selection process, from the electronic dtbse results, the titles nd bstrcts were screened with the following selection criterion: min focus on the ssessment of liner mesurements in 3D virtul models of the humn dentition. In phse 2 of the selection process, the full rticles from those studies selected in phse 1 were retrieved where possible, nd the following selection criteri were pplied: vlidity nd relibility mesures provided, gold stndrd mesurements tken from plster csts, nd the study with minimum smple size of 10. In phse 3 of the selection process, the reference lists from the selected rticles in phse 2 were screened with the sme selection criteri s phse 1. In phse 4 of the selection process, the retrievble rticles from phse 3 were ssessed with the sme selection criteri s phse 2. In this systemtic review, the importnt mesures were relibility nd vlidity. Relibility refers to the consistency with which mesurement cn be mde, nd this ws ssessed by reports of men difference, greement (intrclss correltion coefficient, [ICC]), nd correltion (Person s correltion coefficient [PCC]) of repeted mesures using virtul nd plster models. Vlidity refers to the bility to truly mesure wht is intended, nd this ws lso ssessed using mesures of men difference, greement (ICC), nd correltion (PCC) between virtul nd plster models. Relevnt dt were tbulted in spredsheet using Excel 2007 (Microsoft, Redmond, Wsh). For both vlidity nd relibility, the dt were weighted by smple size nd nlyzed by descriptive sttistics. Weighted mens llowed us to pool the results from studies tht hd reltively lower smple sizes while llowing those studies with higher smple sizes to contribute more to the findings of this systemtic review. In the clcultion of weighted men differences, s n exmple, individul men differences multiplied by their respective smple sizes, s reported in the study, were dded together nd then divided by the totl sum of the ssocited smple sizes. Weighted ICC nd weighted PCC were clculted in similr mnner. Of the selected rticles, interrter relibility 1,8,15,19 ws uncommonly reported, so only intrrter relibility 2,3,5,8,9,13,17 20 in terms of men differences, ICC, nd PCC were tbulted. Other reported mesures of relibility, 4,6,7,10 12,14,16 such s stndrd devitions, rndom error, or sttements confirming tests of repeted mesurements, were lso ccepted but not summrized. Furthermore, becuse relibility is lwys within single modlity (ie, within plster models or virtul models lone), weighted men differences were clculted by first converting reported differences into bsolute vlues. The prmeters summrized in this systemtic review were, by inspection, the most commonly reported of the selected rticles. The prmeters tht could not be ctegorized under one of the commonly reported liner prmeters, but were nonetheless reported in the literture, were noted but not summrized in this pper. In this systemtic review, we set cliniclly relevnt thresholds for men differences for two-lndmrk liner mesurements t 0.5 mm nd t 2.0 mm for liner mesurements bsed on more thn two lndmrks. 2,5,8 Dt for ll virtul study models were grouped to investigte ny differences between virtul model cquisition types. The collected dt were lso grouped to investigte differences between two-lndmrk nd.two-lndmrk liner mesurements. RESULTS A flow chrt of the selection process is illustrted in Figure 1. The initil serch strtegy reveled 278 potentil rticles from electronic dtbses, nd 59 rticles were chosen bsed on the titles nd bstrcts; subsequently, 20 were selected fter reding the entire rticles. From these 20 rticles, 238 unique references were identified, from which 62 retrievble rticles were screened, but ultimtely no dditionl rticles were selected from the hnd serches. Three rticles tht were ultimtely excluded 9,16,17 hd initilly stisfied the selection criteri t ech phse. One study ssessed

3 1100 LUU, NIKOLCHEVA, RETROUVEY, FLORES-MIR, EL-BIALY, CAREY, MAJOR Figure 1. Flow chrt of the selection process. virtul models of neontl cleft plte 9 ptients without ny erupted teeth. Another study investigted virtul models cquired by hologrphic scnning, 16 but the pper ws published two decdes go. Similrly, the study on models cquired by sterophotogmmetry 17 hs not been revisited for lmost decde. The updted PubMed serch of December 8, 2011, identified n dditionl three potentil bstrcts. Of these, one would be rejected becuse it did not fulfill the finl selection criteri, 23 nd two were in Chinese, nd lthough we ttempted to contct the uthors, we were not ble to obtin copies of these rticles. 24,25 A finl totl of 17 rticles were selected for this review. Intrrter relibility for both plster (Tble 1) nd lser-cquired (Tble 2) study models were reported for ll of the common two-lndmrk nd.two-lndmrk mesurements. All weighted men differences were less thn 0.5 for the two-lndmrk prmeters nd less thn 1.5 mm for the.two-lndmrk prmeters. For repeted mesurements in plster, ICC vlues were bout.85 for ll two-lndmrk prmeters nd greter thn.98 for crowding; similrly, PCC vlues were

4 LINEAR MEASUREMENTS USING VIRTUAL STUDY MODELS 1101 Tble 1. Intrrter, Plster Study Models: Men Difference, Agreement, nd Correltion Vlues Weighted by Smple Size With Stndrd Devitions (Where Possible to Clculte) Shown for Most Commonly Reported Prmeters Absolute Difference Agreement Correltion Prmeter n Men SD n ICC SD n PCC SD Plster, Liner mesurements, two lndmrks Overjet Overbite Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Mx_IMW Mx_ICW Mn_IMW Mn_ICW Plster, liner mesurements,.two lndmrks Mx_Perim Mx_Crowd Mn_Perim Mn_Crowd Bolton Bolton ICC indictes intrclss correltion coefficient; PCC, Person s correltion coefficient; Mx_, mxillry; Mn_, mndibulr; IMW, intermolr width; ICW, intercnine width; Perim, rch perimeter; Crowd, crowding if negtive; SD, stndrd devition; Bolton6/Bolton12, Bolton millimeter, positive when mndibulr excess. greter thn.91 for two-lndmrk prmeters nd greter thn.96 for rch perimeter. For repeted mesurements in lser-cquired models, ICC vlues were ner.99. Although the intrrter relibility dt for CBCT-cquired models will not be presented in tble becuse of insufficient comprtive dt, ICC vlues from two studies 19,20 were greter thn.80, nd PCC vlues from the third study 18 were well bove.90, which suggested good greement nd excellent correltion of repeted mesures. The vlidity of commonly reported liner prmeters subgrouped by two-lndmrk nd.two-lndmrk mesurements between plster nd specific cquisition types, lser cquired or CBCT cquired, re presented in Tbles 3 nd 4, respectively. For lser-cquired study models, the men differences compred with plster study models were well below 0.5 mm for two-lndmrk mesures nd less thn 1 mm for.two-lndmrk mesures. Most prmeters were reported in terms of ICC with weighted vlues tht tended to be greter thn.90. The virtul study models cquired by CBCT scnning hd men differences compred with plster study models of less thn 0.5 mm for two-lndmrk mesures. None of the rticles included in this systemtic review reported men differences for

5 1102 LUU, NIKOLCHEVA, RETROUVEY, FLORES-MIR, EL-BIALY, CAREY, MAJOR Tble 2. Intrrter, Lser-Acquired Virtul Models: Men Difference, Agreement, nd Correltion Vlues Weighted by Smple Size With Stndrd Devitions (Where Possible to Clculte) Shown for Most Commonly Reported Prmeters Absolute Difference Agreement Correltion Prmeter n Men SD n ICC SD n PCC SD Lser-cquired, liner mesurements, two lndmrks Overjet Overbite Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Mx_IMW Mx_ICW Mn_IMW Mn_ICW Lser-cquired, liner mesurements,.two lndmrks Mx_Perim Mx_Crowd Mn_Perim Mn_Crowd Bolton Bolton ICC indictes intrclss correltion coefficient; PCC, Person s correltion coefficient; Mx_, mxillry; Mn_, mndibulr; IMW, intermolr width; ICW, intercnine width; Perim, rch perimeter; Crowd, crowding if negtive; SD, stndrd devition; Bolton6/Bolton12, Bolton millimeter, positive when mndibulr excess..two-lndmrk mesures. Although none of the rticles reported ICC vlues, weighted PCC vlues from one study 18 rnged from.62 to.99. DISCUSSION Virtul study models cquired by lser scnning represented 14 of the 17 selected rticles, while those cquired by CBCT scnning were reported in the remining three. The number of good-qulity studies on lser-cquired study models is remrkble, but emerging pproches using CBCT show promise. However, two 19,20 of the selected studies using CBCT still required impressions, so errors my be replicted 1 s the process goes from the mouth to lginte impressions nd finlly to virtul models. The relibility nd vlidity of newer pproches tht generte virtul study models from direct CBCT scns of the ptient s mouth compred with the gold stndrd plster models hve yet to be reported. This systemtic review nd the one by Fleming et l. 21 selected 17 rticles ech. However, slight differences in our selection criteri resulted in our studies selecting only nine rticles 5 8,10,11,13,15,20 in common. We chose to focus on quntittive liner mesurements only; therefore, we hd rejected some of the rticles tht Fleming chose to include becuse they focused on PAR, 26 ABO, or ICON 30 scores, which

6 LINEAR MEASUREMENTS USING VIRTUAL STUDY MODELS 1103 Tble 3. Vlidity, Lser-Acquired vs Plster: Men Difference, Agreement, nd Correltion Vlues Weighted by Smple Size With Stndrd Devitions (Where Possible to Clculte) Shown for Most Commonly Reported Prmeters Difference, mm b Agreement Correltion Prmeter n Men SD n ICC SD n PCC SD Lser-cquired vs plster, liner mesurements, two lndmrks Overjet Overbite Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Mx_IMW Mx_ICW Mn_IMW Mn_ICW Lser-cquired vs plster, liner mesurements,.two lndmrks Mx_Perim Mx_Crowd Mn_Perim Mn_Crowd Bolton Bolton ICC indictes intrclss correltion coefficient; PCC, Person s correltion coefficient; Mx_, mxillry; Mn_, mndibulr; IMW, intermolr width; ICW, intercnine width; Perim, rch perimeter; Crowd, crowding if negtive; SD, stndrd devition; Bolton6/Bolton12, Bolton millimeter, positive when mndibulr excess. b Negtive men difference when mesurements from plster re lrger. re qulittive ordinl mesures. We lso rejected n rticle 31 tht Fleming ccepted becuse we found no reports on relibility of repeted mesurements. Of the rticles tht Fleming chose to exclude, we chose to ccept two studies tht used rtificil occlusl setups 1,14 since they re ssessments of liner mesurements nonetheless nd nother study tht plced mrking points on the csts in blck pen 2 since those points did not ffect the prmeters tht we chose to summrize. Finlly, our serch strtegy selected n dditionl five relevnt rticles 3,4,12,18,19 s of My 2010 tht were not mentioned by Fleming s systemtic review, three 4,12,19 of which were published by the time their serch ws conducted in Jnury By inspection, the most commonly reported twolndmrk liner prmeters were overjet; overbite; mxillry nd mndibulr mesiodistl tooth sizes from first molr to first molrs, inclusive; s well s mxillry nd mndibulr intermolr nd intercnine widths. The commonly reported.two-lndmrk liner prmeters were mxillry nd mndibulr rch perimeter nd crowding, s well s Bolton nterior nd Bolton overll discrepncies. A full study model nlysis should lso involve ctegoricl prmeters, such s Angle s clssifiction, but good-qulity studies incorporting these were infrequently reported. Future studies should investigte the relibility nd vlidity of ctegoricl prmeters.

7 1104 LUU, NIKOLCHEVA, RETROUVEY, FLORES-MIR, EL-BIALY, CAREY, MAJOR Tble 4. Vlidity, CBCT-Acquired vs Plster: Men Difference, Agreement, nd Correltion Vlues Weighted by Smple Size With Stndrd Devitions (Where Possible to Clculte) Shown for Most Commonly Reported Prmeters Difference, mm b Agreement Correltion Prmeter n Men SD n ICC SD n PCC SD CBCT impression cquired vs plster, liner mesurements, two lndmrks Overjet Overbite Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Tooth Mx_IMW Mx_ICW Mn_IMW Mn_ICW CBCT impression cquired vs plster, liner mesurements,.two lndmrks Mx_Perim Mx_Crowd Mn_Perim Mn_Crowd Bolton6 Bolton12 CBCT indictes cone-bem computed tomogrphy; ICC, intrclss correltion coefficient; PCC, Person s correltion coefficient; Mx_, mxillry; Mn_, mndibulr; IMW, intermolr width; ICW, intercnine width; Perim, rch perimeter; Crowd, crowding if negtive; SD, stndrd devition; Bolton6/Bolton12, Bolton millimeter, positive when mndibulr excess. b Negtive men difference when mesurements from plster re lrger. Relibility Intrrter relibility of repeted mesures on plster study models s well s virtul study models for twolndmrk mesures showed cliniclly insignificnt men differences t the 0.5-mm threshold, while both greement nd correltion were good to excellent for the prmeters tht were reported. For.two-lndmrk mesures, men differences were below the 2-mm threshold, indicting cliniclly insignificnt differences in repeted mesures s well s excellent greement nd correltion. Intrrter relibility, then, ws good to excellent for virtul study models, nd the sme cn be sid for plster s the differences in repeted mesurements of both two-lndmrk nd.two-lndmrk liner prmeters were judged to be cliniclly insignificnt. Vlidity The vlidity of virtul compred with plster study models for ll two-lndmrk nd.two-lndmrk liner prmeters showed cliniclly insignificnt men differences. This grees with the findings of Fleming et l., 21 who reported tht virtul models offer high degree of vlidity when compred with direct mesurement on plster models. Compred with plster, for twolndmrk prmeters, there ws excellent greement

8 LINEAR MEASUREMENTS USING VIRTUAL STUDY MODELS 1105 using lser-cquired models, while correltion using CBCT-cquired models rnged from poor to excellent. In contrst, Fleming did not summrize greement in terms of ICC or PCC vlues. Overjet, overbite, nd ll tooth width mesurements from first molr to first molr using lser-cquired study models were cliniclly insignificnt compred with plster, but the negtive weighted men differences suggested tendency towrd lrger mesurements on plster models. Intermolr nd intercnine distnces on lser-cquired models, however, hd tendency towrd smller mesurements on plster, but gin, the weighted men differences were cliniclly insignificnt. Similrly, differences in rch perimeter, crowding, nd Bolton mesurements were cliniclly insignificnt. Agreement for ll two-lndmrk mesures nd rch crowding were excellent. Compred with the compiled dt from rticles on lser-cquired study models, which hd combined smple sizes tht rnged from 100 to 204 per prmeter, the dt on CBCT-cquired study models hd reltively smller smple sizes tht rnged from 15 to 40. As observed with lser-cquired study models, the weighted men differences were ll negtive, indicting tendency towrd lrger mesurements on plster, but this finding hd no clinicl relevnce. Correltion of CBCT-cquired study models compred with plster ws poor for mesiodistl mesurements of teeth 1-5 nd 4-1, moderte for teeth 1-4, 1-6, 2-5, 3-1, 3-3, 3-4, 4-3, nd good or better for ll remining two-lndmrk nd rch perimeter mesures. There ws no obvious explntion for this vrition in correltion. Influence of Acquisition Type on Relibility nd Vlidity There were no perceived differences in intrrter relibility nd vlidity cross the vrious cquisition types. The vrition in correltion for two-lndmrk mesures from CBCT-cquired models ws the only inconsistent finding, but further independent studies re required to confirm this. Aside from this possibly nomlous finding, overll the men differences were cliniclly insignificnt, nd the correltion nd greement were good to excellent. These findings were consistent cross lser-cquired nd CBCT-cquired virtul models compred with plster. Influence of the Number of Lndmrks in Mesurement on Vlidity nd Relibility In mgnitude, there ws tendency for the relibility nd vlidity of two-lndmrk mesures to hve smller men differences thn.two-lndmrk mesures, regrdless of cquisition type. For exmple, for the two-lndmrk prmeters, repeted tooth width mesurements in plster showed less thn 0.1-mm bsolute difference, while overjet, overbite, nd intermolr nd intercnine distnces hd double the bsolute differences but less thn 0.2 mm. For.twolndmrk prmeters, differences in rch perimeter, crowding, nd Bolton discrepncies rnged higher thn 0.2 mm, up to 0.7 mm. Although these findings were not cliniclly significnt, this pttern for incresing bsolute difference reltive to the number of lndmrks could be detected by inspection for repeted mesurements in lser-cquired models s well. CONCLUSIONS N The intrrter relibility ws high for two-lndmrk nd.two-lndmrk liner mesurements performed on lser-cquired models or CBCT-cquired models nd similr to mesurements on plster models. N The vlidity ws high for two-lndmrk nd.twolndmrk liner mesurements compring lsercquired models or CBCT-cquired models to plster study models, nd the weighted men differences were cliniclly insignificnt. N Agreement of mesurements ws excellent with less vribility thn correltion. N Acquisition type hd no perceived influences on relibility nd vlidity. N.Two-lndmrk mesures tended to hve higher men differences thn two-lndmrk mesures. N Virtul study models re cliniclly cceptble compred with plster study models with regrd to intrrter relibility nd vlidity of selected liner mesurements. REFERENCES 1. Alcn T, Ceylnoğlu C, Bysl B. The reltionship between digitl model ccurcy nd time-dependent deformtion of lginte impressions. Angle Orthod. 2009;79: Asquith J, Gillgrss T, Mossey P. Three-dimensionl imging of orthodontic models: pilot study. Eur J Orthod. 2007;29: Bootvong K, Liu Z, McGrth C, et l. Virtul model nlysis s n lterntive pproch to plster model nlysis: relibility nd vlidity. Eur J Orthod. 2010;32: Ch BK, Choi JI, Jost-Brinkmnn PG, Jeong YM. Applictions of three-dimensionlly scnned models in orthodontics. Int J Comput Dent. 2007;10: Goonewrdene RW, Goonewrdene MS, Rzz JM, Murry K. Accurcy nd vlidity of spce nlysis nd irregulrity index mesurements using digitl models. Aust Orthod J. 2008;24: Horton HM, Miller JR, Gillrd PR, Lrson BE. Technique comprison for efficient orthodontic tooth mesurements using digitl models. Angle Orthod. 2009;80: Keting AP, Knox J, Bibb R, Zhurov AI. A comprison of plster, digitl nd reconstructed study model ccurcy. J Orthod. 2008;35:

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