Prosthodontics

Presentation of quantitative tooth wear datato ciinicians

Richard G. Chadwick, BDS, PhDVHarvey L, Mitchell, BSc, PhD"

Objective: The purpose of this study was to ascertain the ease of interpretation and usefuiness of differ-ent modes ot presenting quantitative tooth wear data to clinicians. Method and Materials: A question-naire that sought to ascertain both the ease of interpretation and usefuiness ot different modes of presen-tation tor monitoring tooth wear was distributed to 67 ciinicians. These modes (contour maps, surfacetopography and difference plots, and color-coded surface difference plots) were a product ot ongoing de-velopment that used a mathematic algorithm to detect and quantify wear of teeth with time. A toitow-upquestionnaire, based on a fusion of the desirable features of surface topography and color-coded surfacedifference piots, was distributed to 40 of the originai respondents to ascertain any improvement in clarityResults: in aii respects, contour maps were rated significantly more difficult to interpret and iess usefuithan the other techniques evaluated. No significant difference was detected between the other modaiities.The follow-up questionnaire demonstrated a significantly enhanced utility of the revised piot in informingthe dinician as to the worh sites and quantity of wear Conciusion: The combined mode of presentationseems an excellent way of presenting wearresuits to clinicians for ciinicai application (Quintessence Int1999;30:39î-398)

Keywords: algorithm, abrasion, attrition, erosion, tooth wear

CLINICAL RELEVANCE: The rate of tooth wear will dic-tate whether or nol to intervene operativeiy. Through com-bined surface topography and color-coded surface differ-ence plots, the resuits of mathematic surface-mappingprocedures may be communicated to ciinicians to assistin making treatment decisions.

•\TTithin the dental literature, a variety of techniquesVV have been proposed for assessing tooth wear.

Stich techniques may be classified as those intendedfor use in epidemiologic sttidies or methods designedto assess the need and outcome of treatments for indi-vidual patients.

The earliest indices designed to assess tooth wear'"'required a diagnosis of the etiology of the condition tobe made before their application. They were also oniyapplicable when 1 condition—erosion, abrasion, orattrition-was present. Often, however, these condi-tions may be present in a combination of permuta-

•Depardnenl ol Conservative Dentistry, University of Dundee, DentalSchool, Dundee, Scotland.

"Dspartment ol Civil, Surveying, and Environ m erial Engineering, Univer-sity of Newcastle. Newcastle. New South Wales. Australia.

Reprint requests: Dr R. G. Chadwick, Department of Consen/ative Den-tistry, University of Dundee, Dental Sctiool, Park Place, Dundee. DD1 4HNScotland. E-mail. rgchadwick@dental_school.dundee.ac.uk

tions in a single patient, thtis limiting the appiicationof such criteria.

Smith and Knight"' proposed a tooth wear indexthat eould be applied regardless oí the type of wearpresent. This was designed for use in both epidemio-iogic research and iong-term monitoring of an individ-ual's tooth wear. This index assigned a wear score toeach individual tooth surface, according to predeter-mined observationai criteria. It has been used in anumber of epidemiologic studies either aione'* or withslight modification.''^ It has not, however, beenadopted on a large scale for follow-up of individuai pa-tients, where the inspection of sequentiai dental studycasts is widely recommended.^'" Such an approach ishighly subjective and only detects relatively grosschanges in the surface topography of the teeth."

An aiternative approach, currently under develop-ment, is to obtain addition-cured silicone impressionsat different times, to enable the fabrication of electro-conductive replicas for mapping with a computer-controlled electrical probe." Through application of amathematie algorithm,'^ it is possible to compare themaps (dígita! terrain models) of the replicas of thesame tooth recorded at different time intervals andthereby determine quantitatively the amount of toothwear. Such data are inevitably mathematic and mustbe presented to the clinician in an easily comprehen-sible form. This article reports on an evaluation of 3potential methods of presenting such data.

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40,0030.00

30.00 -20,00

10.00 20.00 30.00

10.00 20.00 30.00 40.00

Fig 1 Contour maps, supenmposed on each other, of Ihe paiatalsurface of a rnaïiliary centrai incisor lollowmg a period in whichwear has tai<en piace.

RESULTS

The initial questionnaire return rate was 7OO/o. Table 1summarizes the mean scores and standard deviationsobtained for each presentation. A chi-square testrevealed that, in all respects, contour maps wererated significantly (P < 0.001) more difficult to inter-pret and less useful than the other techniques evalu-ated. No significant difference {P > 0,05) was de-tected, however, between surface difference plots andcolor-coded surface difference plots. The criticismsieveled against these last 2 methods related primariiyto difficulties in determining the tooth's outline andorientation.

The results of the follow-up questionnaire aregiven in Table 2, The questionnaire return rate was90%, Compared to the method with the lowestoverall mean score (highest utility) in the initial ques-tionnaire (surface topography plot), the revisedmethod of presentation performed significantly betterin informing tbe clinician as to botb the sites (P <0,01) and quantity of wear (P < 0.001). In addition,this method was considered to be potentially moreuseful (P < 0,01) than a surface topography with dif-ference plot.

METHOD AND MATERIALS

A series of digital terrain models of the palatal surfaceof an unrestored maxillary central incisor, held withinthe research unit as part of an ongoing project, were se-lected to generate the images used in this work. Theserepresented the tooth at baseline and 8 months later,when a degree of tooth surface loss had occurred,

A questionnaire was distributed to all 67 clinicianswithin the Dundee Dental School and Hospital, Thequestionnaire sought to ascertain both the ease of In-terpretation and usefulness of different modes of pre-sentation for monitoring tooth wear. The 3 modesevaluated were contour maps (Pig 1), surface topogra-phy and difference plots (Fig 2), and color-codedsurface difference plots (Fig 3), For each potentialmethod, the participants allocated a score of 1 (highutility) to 5 (low utility) based on their perception offts utility.

Following an analysis of the initial results, a follow-up questionnaire, based on a fusion of tbe desirablefeatures of presentation (Pig 4) elicited from the initialsurvey, was distributed to tbe 40 clinicians wboremained witbin the Dental Hospital since respondingto the initial survey.

DISCUSSION

For a diagnostic tool to become accepted and widelyused, it must be easy to apply and interpret. The studydescribed addressed this last aspect. Bebind surfacesbape matching and difference detection lie complexmathematic formulas'^ that lie outside the scope of thedental curriculum. It is important that the results ofsuch a process be conveyed to practicing clinicians ina readily understandable form,

Witb this point in mind, it is interesting to note thehigh levels of utility accorded to both color-codedsurface plots (2,73 [0,23]) and difference plots (2,65[0,141) compared to contour maps (4,19 [0,10]). Thiscould be due to the relative famiharity of the represen-tations of the tooth's surface, as afforded by the first 2modalities, wbicb clearly resemble tbe actual surfaceas seen by the dentist.

However, altbougb the plots gave meaningful infor-mation to some, the need for further improvement wasborne out by tbe lower overall mean score (1.80 [0,15])achieved when the desirable features of color-codedsurface and surface topography plots were combined.The high level of utility achieved by this method is par-ticularly pleasing because no training in the interpreta-tion of the plots was given. As a result, this mode ofpresentation seems an excellent way of presenting wearresults to clinicians for clinical apphcation.

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Fig 3 Color-coded surface difference plot of the palatal surface of a maxillary centralincisor following surface wear. The degree of wear is indicaled by the color coding, image gen-erated using Stanford Graphics (version 3,0C, Visual Numerics].

Tooth surface loss an

Degree of wear(Figs 3 and 4)

Yellow = no signilicartwear

Red= 100-200 pm

Green = 201-300 pm

Blue= 301^00 pm

Fig 4 Fusion of [he desirable features of surface topographic piots and color-coded surfacedifference plots for the palatai surlace of a maxillary central incisot following surface wear. Thedegree of wear is indicated by the color coding, and the outline of the tooth is shown in red.Image generated using Stanford Graphics.

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TABLE 1 Results of the initial questionnaire

Aspect evaluated

It is clear at which sitesot the tooth surfacewear has occurred.

It is olear how muchoverall wear hasoccurred.

It is clear how muchwear has occurred atspeoific sites.

The graphicrepresentation is easyto interpret within theiimitations of thisscenario.This is a potentiallyuseful way otpresenting surfacewear data to clinicians.Overall mean score (SD)

Color ooäedsurfaee plot

2.85(1.46)-[1 = 11;2 = 143 = 0;4 = 15;

3.04(1.32)[1 =6; 2 = 14;3 = 7; 4 = 12;5 = 8]2.62 (1.38)[1 = 12; 2 = 153 = 5; 4 = 9;5 = 6]2.75 (1.39)[1 =10;2 = 163 = 4; 4 = 10;5 = 71

2.37(1.11)[1 = 10; 2 = 203 = 7; 4 = 7:5 = 2]2.73 (0.23)

'Mean score (SD| obtained lor eacli aspect evaluE'Number ot persons respcnding at the 5 levels [1utility].

Surface topographyand ditference plot

2.70(1.34)[1 =9; 2 = 18:3 = 4; 4 = 10:5 = 612.62(1.25)|1 =8; 2 = 20:3 = 6:4 = 8;5 = 5]2.87(1.35)[1 =6,2 = 19;3 = 6; 4 = 7;5 = 9]2.61 (1.26)|1 =9:2=18;3 = 5:4=10:5 = 4]

2,45(1.11)[1 = 9; 2 = 20;3 = 8; 4 = 8;5 = 2]2.65 (0.14)

ted^ strongly agree, higti utility; 5 =

Contour map

4.11 (0.93)|1 =0;2 = 4:3 = 6;4 = 18:5= 19]4.31 (0.61)|1 = 1;3 = 1:3 = 1:4 = 22;5 = 20]4.16(0-82)[1 = 0; 2 = 3;3 = 3; 4 = 22;5 = 16]4.28 (0.76)[1 =0:2 = 2:3 = 3: 4 = 22:5 = 20]

4.09 (0.87)[1 = 1;2 = 1;3 = 6: 4 = 22;5 = 15]4.19(010)

strongly disagree, IcniV

TABLE 2 Results of the follow-up questionnaire and comparison to the bestmode ot presentation in the initial survey

Aspect evaluated

It is ciear at which sites of fhefooth surface wear has occurred.

It is clear how much overallwear has ooourred.

It is clear how much wear hasocourred at specific sifes.

The graphic represenfationis easy to intrepref withm fhelimitafions of this scenarioThis is a pofentially useful wayof presenting sutiace wear datafo clinicians.Overail mean soore (SD)

Fusion mefhod

1.64(0.71)-[1 = 17;2 = 16;3 = 2:4 = 1;5 = 0t]1 94 (0.72)|1 =9; 2 = 20;3 = 5:4 = 1:5 = 0]1.64(0 71)|1 = 17;2 = 16;3 = 2;4 = 1;5 = 0]2.00 (0.85)[1 = 10:2 = 19;3 = 4; 4 = 3; 5 = 0]1.76(0.61)(1 = 10; 2 = 22;3 = 0;4 = 1;5 = 0]1.80(0.15)

•Mean score (SD) obtained tor eacli aspect evaluated.

Surface topographyand difference plot

2.70(1.34)[1 =9; 2 = 18;3 = 4; 4= 10; 5 = 6]2.62 (1.25)[1 = 8; 2 = 20;3 = 6; 4 = 8; 5 = 5]2.87(1.35)¡1 =6; 2 = 19;3 = 6, 4 = 7; 5 = 9]2 61 (1.26)|1 =9;2 = 18;3 = 5; 4= 10:5 = 4]245(1.11)(1 =9; 2 = 20:3 = 8: 4 = 8; 5 = 2]2.65 (0.14)

'Number ol persons responding at Ihe 5 levels {1 = strongly agree, high ulilify; 5 ^ strongly aisagree, iowJtllify).

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Certainly within the United Kingdom there is aneed for such a technique, because the 1993 NationalSurvey of Child Dental Health^ revealed a high preva-lence of tooth surface loss caused by erosion. Suchtissue loss can result in sensitivity or pain as well as anunesthetic appearance. iVlany patients with this condi-tion do not report a deterioration in appearance untilthere has been sufficient loss of tooth tissue, particu-larly on the palatal surfaces of maxillary incisors, forthe thinned incisai edges to fraeturc.'^

Restoration of lost enamel and/or dentin ean be adifficult and expensive process, requiring intensivemaintenance care as well as continual monitoring.''The dentist thus faces a dilemma in deciding when toobserve and when to treat. At present, such assess-ment is based on visual comparison of the dentitionwith previous study casts. Although ail UK Consul-tants in Restorative Dentistry universaliy apply thismethod, none believe it to be sufficientiy sensitive todetect small increments of wear that cumulatively maybe of great significance.'-' All agree that there is a needfor a sensitive method of monitoring this type of wearthat is appiicable in minimum chairside time.''

The technique described offers the potentiai for thedentist to record itnpressions of teeth exhibiting ero-sion at different times at chairside and, having hadthese mapped and anaiyzed by a laboratory, to receivethe results in the form reported so that an informeddecision on the clinical management of the patientcan be reached. This represents a vast improvementon the universally applied cast-comparison system ofmonitoring.

ACKNOWLEDGMENTS

The authors arc grateful both to all those who so willingly partici-pated in the study and to the medical charity, Teriovus. Utr providingiuppon (project no. T96/16).

REFERENCES

Kilchin PC. The prevalence of tooth root exposure to thedegree of abrasioti m different age classes. ] Dent Res 1941;20:565-581,Restarki JS, Gortner RA, McCay GM. Effect of acid bever-ages containing fluoride upon the teeth of rats and puppies.J Am Dent Assoc 1945;32:668-675.Ecc:les |D, Jenkins WG. Dental erosion and diet. ] Deht1974;2:153-159.Stnith BGN, linight JK. An index for tneasuring the wear ofteeth. Br Dent J 1984;156:435-438.Poyntcr ME, Wright PS. Tooth wear and sotne factors influ-encing its severity. Rest Dent 1990;68-ll.Donachie MA, Walls AWG. Assessment of tooth wear in anageing population J Dent 1995;23:157-164.O'Briati M. Children's Dcnta! Health in the United King-dotn, 1993. Office of Population Censuses and Surveys.London: Her Majesty's Stationari' Office, 1994.Hinds K, Gregory JR. National Diet and Nutrition Survey:Children Aged 1 1/2 to 4 1/2 years, vol 2. Report of theDental Survey, 1994. Office of Populatiort Censuses andSurveys. London: Her Majesty's Stationary Office, 1995.Winstanley RB. The treatineiit of severe attrition. DentUpdate 1984;ll:629-643.

Smith BGN. Toothwear. Aeliology and Diagnosis. DentUpdate 1989:16:204-212.Chadwick RG, Mitchell HL, Catneron I, Hunter B, TulleyM. Development of a novel system for assessing tooth andrestoration wear. I Dent 1997;25:41-47.Mitchell HL, Chadwick RG. Mathematical shape tnatchingas a tool in tooth wear assessment: Development and con-duct. J Oral Rehabii 1998 ;25:921-928.Nunn JH. Prevalence of dental erosion and Ihe implicationsfor orai health. EurJ Oral Sei 1996,104:156-161.Chadwick RG. Toothwear-Towards the third dirtiension.Bull R Coll Phys Surg Glasgow 1998:27:31-32,

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