1090 Journal of Dental Education ■ Volume 71, Number 8

Tweezer Dexterity Aptitude of Dental StudentsWilliam P. Lundergan, D.D.S., M.A.; �liza�et�� �. Soderstrom, �.D.�., M.A.;�liza�et�� �. Soderstrom, �.D.�., M.A.; David W. C��am�ers, �d.M., M.B.A., P��.D.Abstract: The rationale for using the Perceptual Ability Test (PAT) as a component in admissions decisions for dental schools is that candidates vary in an underlying aptitude that is predictive of degree of success in technique course performance and perhaps in clinical performance. There have been periodic attempts to identify tests that more directly measure manual dexterity aptitude that would supplement the predictive power of admissions decisions. Previous research has demonstrated that a commercially available “speeded” tweezer dexterity test (Johnson O’Connor Test #32022) is not associated with performance in dental school or dental practice. Our research investigated both Test #32022 and Test #18 that measure both speed and accuracy as potential pre-dictors of dental school performance in technical and clinical courses. This article reports the results of a longitudinal, compara-tive study of tweezer dexterity scores for students at the University of the Pacific School of Dentistry during their first and last quarters in school. The goals of the study were to 1) evaluate the correlation between beginning students’ scores on two different types of tweezer dexterity tests; 2) compare dental students’ scores to normative data for the general population; 3) determine the effect of a dental curriculum on students’ performance on Test #18; and 4) evaluate the two tests as potential dental school admission screening instruments in comparison to the PAT. Fifty first-quarter students were tested from a class of 134. Forty-nine of these students were retested on Test #18 during their final quarter. The predictor value of the initial scores for the two dexterity tests was assessed for seven outcome measures reflecting student technique performance. Analysis showed a significant correla-tion (r=0.318, p<0.05) between the two dexterity tests. The difference between the norm mean (41.58) and the dental student mean for Test #18 (40.42) was not significant (p>0.05). The correlation between the first and final quarter administrations for Test #18 was r=0.517 (p<0.01). The predictive power of these tests for the seven educational outcomes measures was weak. Results suggest that dental student tweezer dexterity is no different from that of the general population and is not changed by completing a dental school curriculum. The ability for an applicant to perform successfully in dental school will not be reliably predicted by tweezer dexterity score.

Dr. Lundergan is Professor and Chair, Department of Periodontics; Ms. Soderstrom is Assistant Professor, Department of Periodontics; and Dr. Chambers is Professor and Associate Dean for Academic Affairs and Scholarship, Office of Academic Affairs—all at the University of the Pacific Arthur A. Dugoni School of Dentistry. Direct correspondence and requests for reprints to Dr. William P. Lundergan, University of the Pacific, Arthur A. Dugoni School of Dentistry, 2155 Webster Street, Suite 522, San Francisco, CA 94115; 415-929-6543 phone; 415-929-6654 fax; wlunderg@pacific.edu.

Key words: tweezer dexterity, aptitude, psychomotor skills, predictor value

Submitted for publication 7/17/06; accepted 3/22/07

Surgery and dentistry are two professions that are generally assumed to require a high degree of manual dexterity or psychomotor skill. The

literature is replete with studies that assess manual dexterity as an applicant screening instrument for these professions.1-13 Squire et al.7 used the Purdue Pegboard and the Minnesota Manual Dexterity tests to compare manual dexterity between medical and surgical residents. The authors found no significant difference in dexterity between the two groups and concluded that dexterity tests should not be used in assessing candidates for surgical residency training positions.

The Johnson O’Connor Research Foundation describes tweezer dexterity as an aptitude for work-ing with small tools and as an aptitude used in such delicate tasks as dentistry, surgery, nursing, mechani-cal drawing, watchmaking and repair, and miniature instrument assembly.14 Studies using tweezer dexter-

ity tests developed for aptitude testing by the Johnson O’Connor Research Foundation have not confirmed a high manual dexterity aptitude for dentists. A study by Weinstein et al.15 found a negative relationship for practicing dentists between high dexterity scores on the Johnson O’Connor Tweezer Dexterity Test #32022 (a pure speed test) and peer evaluations of restorative work quality. To explain this result, these authors hypothesized that dentists develop an inter-nalized standard emphasizing accuracy rather than speed. A report by Simon and Chambers16 described their search for a profile of aptitudes characterizing successful dentists. That study used the Johnson O’Connor Tweezer Dexterity Test #18, which is thought to assess both speed and accuracy. That study also failed to confirm the traditional viewpoint and reported a mean score on tweezer dexterity for dentists that was not significantly different from the norm mean for the general population.

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No studies have been reported that used the Johnson O’Connor Tweezer Dexterity Tests to es-tablish baseline aptitude scores for beginning dental students. This student population would be expected to differ from the practicing dentist population in that the emphasis on accuracy may not have been internal-ized as Weinstein et al. hypothesize. Furthermore, no study has evaluated the effect of a dental school cur-riculum on tweezer dexterity performance. If tweezer dexterity is a real aptitude, test scores should remain relatively stable because aptitudes are natural talents believed to be inherited.

The Perceptual Ability Test (PAT) is one of the four individual tests contained in the Dental Admission Test (DAT) battery. It consists of ninety two-dimensional and three-dimensional problems and involves factors such as angle discrimination in paper folding, block counting, form development, and object visualization. The PAT has shown a positive correlation with performance in preclinical technique courses, but at a low level of strength.1,17 The PAT is currently used by most dental schools as a component in the admissions decision process. Identification of a test with greater predictive power for dental school performance would be of value to most admissions committees.

This article reports the results of a longitudinal, comparative study of tweezer dexterity scores for students at the University of the Pacific Arthur A. Dugoni School of Dentistry during their initial and final quarters of instruction. The study had five goals: 1) estimate the correlation between two Johnson O’Connor Tweezer Dexterity Tests for this popula-tion group; 2) compare the students’ scores on the Johnson O’Connor Tweezer Dexterity Test #18 to national norm data; 3) compare the students’ scores on the Johnson O’Connor Tweezer Dexterity Test #32022 to national norm data for the general popula-tion; 4) determine the effect of a dental curriculum on students’ performance on the Johnson O’Connor Tweezer Dexterity Test #18; and 5) evaluate Test #18 and Test #32022 as potential screening instruments to identify dental school applicants capable of perform-ing well in dental school and compare the predictive value of these tests to the Perceptual Ability Test of the Dental Admission Test.

Materials and Met��odsThe Johnson O’Connor Research Foundation

has developed aptitude tests since 1922. Tweezer Test

#32022 is generally employed as a pure speed test. The test is in the public domain and is no longer used by the Johnson O’Connor Research Foundation in its aptitude testing. The test consists of a 5 7/8 inch by 11 7/8 inch board with a shallow reservoir holding one-inch long pins (lying flat) to be placed, using a tweezer, in the adjacent, non-tapered holes (Figure 1). The holes to be filled are in a 10-by-10 grid pat-tern. The score is the number of seconds elapsing between the placement of the first and last pins. The lower the score for Test #32022, the greater the tweezer dexterity.

A newer test (Test #18) is based on speed and accuracy, and is a proprietary test currently used by the Johnson O’Connor Research Foundation (Figure 2). The test taker moves ten rows of ten upright pins each from one side of a test board to a tapered hole on the other side. Each row is scored based on how fast the row is completed, minus penalty points for dropped pins. Time is measured to hundredths of a minute, and there is a 0.05 minute penalty for each dropped pin. The row time is then used to assign one to eight points for the row (Table 1). The total score is the sum of all the row scores, and scores can range from 10 to 80. The higher the score for Test #18, the greater the tweezer dexterity. It is possible to calculate an “accuracy only” score for Test #18 by removing the time penalty.

Norm data for Test #18 have been published internally by the Johnson O’Connor Research Foundation on over 5,000 subjects.18 These norms were constructed from their 1984 national database consisting of 8,452 cases (4,235 female and 4,217 male). Data from the 5,307 individuals who took Test #18 are summarized in Table 2.

For this study, fifty first-year students (rang-ing in age from twenty-one to thirty-eight) in their first quarter at the University of the Pacific Arthur A. Dugoni School of Dentistry were selected from a class of one hundred and thirty-four. All students enrolled in the class were assigned a number, and a random number table was used to select the fifty subjects. The group was blocked for gender so that twenty-five subjects were female and twenty-five subjects were male. Students repeating the first-year curriculum were not allowed to participate in the study. Participants signed an informed consent that was approved by our Institutional Review Board (Assurance No. M-1179). All students were tested in a quiet, comfortable, well-lighted room, free of distractions. Subjects performed the Test #18 first and then the Test #32022 following a brief rest.

1092 Journal of Dental Education ■ Volume 71, Number 8

Figure 1. �o��nson O’Connor �esearc�� Foundation Tweezer Dexterity Test #32022

Figure 2. �o��nson O’Connor �esearc�� Foundation Tweezer Dexterity Test #18

August 2007 ■ Journal of Dental Education 1093

Three calibrated observers scored the pin placement behavior. A secondary observer was used for over 20 percent of the observations (eleven of fifty subjects) to establish inter-observer reliability. Repeat reli-ability was estimated for Test #18 by scoring the first and second halves of the test separately. Forty-nine of these students were retested on Test #18 in their final quarter prior to graduation from dental school.

The predictor values of the two tweezer dexter-ity tests and the PAT were assessed for seven outcome measures reflecting student school performance in areas believed to involve manual dexterity. Grades in technique courses in the first year included Labo-ratory and Study Skills, Operative Dentistry, Fixed Prosthodontics, Dental Anatomy, and Endodontics. Two outcomes measures were recorded at the time of graduation: the cumulative GPA for all laboratory and clinic courses and the overall rank.

�esultsInter-observer reliability was assessed on

eleven of the fifty subjects for Test #18 and Test #32022. The correlation coefficients were 0.9977 and 0.9999, respectively. Repeat reliability was estimated by scoring the first and second halves of Test #18 separately. This method resulted in a repeat correla-tion coefficient of 0.7925. The Johnson O’Connor Research Foundation reports a reliability of 0.91 for Test #18.19

The mean score for the first-year dental stu-dents on the Tweezer Dexterity Test #18 was 40.42 (S.D.=19.1), as shown in Table 3. This is slightly above (suggesting greater dexterity) the mean score of 39.91 (S.D.=18.4) for the national norm data. Using a t-test, the difference between the normative mean and the first-year dental students’ mean was not found to be statistically significant (p>0.05). When the norm data are stratified for age, the dental students fall slightly below (suggesting less dexter-ity) the norm mean score of 41.58 (S.D.=18.84) for the eighteen to forty-one-year-old age group (all the dental students were in this age range). The difference between the norm mean for this age group and the dental student mean was not found to be statistically significant (p>0.05).

Gender stratification of the national norm data has indicated that males score slightly lower than females (mean score of 39.20 versus 40.61, respec-tively) on the Tweezer Dexterity Test #18. This gender difference was found to be statistically significant in

the Johnson O’Connor sample using a one-way analy-sis of variance (p<0.01).18 Our data also indicated that male dental students score lower than female dental students (37.80 versus 43.20, respectively). Using a t-test this gender difference was not found to be statistically significant (p>0.05).

Forty-nine students (twenty-five females and twenty-four males) retested for Test #18 during the final quarter of their senior year (Table 4). The mean score was 42.65 with a standard deviation of 19.14. A paired t-test showed no significant difference be-tween the initial and final quarter scores (p>0.05). A comparison of age-stratified national norm and dental student Test #18 scores can be seen in Figure 3.

Standard norm data are available for Test #32022, but the number of subjects tested and their demographics are not published. The median score for men is given as 360, and the median score for women is 342.20 Results of Test #32022 for first-year dental students are summarized in Table 5. Our study found the median score for male students was 327 and the median score for female students was 323. Mean scores for the male (330; S.D.=33.2) and female (330; S.D.=39.6) dental students were identical.

Ta�le 1. Tweezer Dexterity Test #18 scoring

Row Time Minus Penalty* Score

0.00 to 0.32 minutes 80.33 to 0.34 minutes 70.35 to 0.36 minutes 60.37 to 0.38 minutes 50.39 to 0.40 minutes 40.41 to 0.43 minutes 30.44 to 0.47 minutes 20.48 and up 1

*0.05 minutes are subtracted from the row time for each dropped pin.

Ta�le 2. Tweezer Dexterity Test #18 normative data

N Mean S.D.

Total 5,307 39.91 18.41Female ---* 40.61 18.85Male ---* 39.20 18.38Age (18-41) 3,744 41.58 18.84

*Number of subjects not published.Source: Johnson O’Connor Research Foundation Statistical Bulletin, 1985-37.

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A Pearson correlation analysis was completed to determine if a rela-tionship existed between the Tweezer Dexterity Test #18 and the Tweezer Dexterity Test #32022. The analysis showed that a significant correlation (r=0.318, p<.05) between the two dex-terity tests did exist for this population group. (The calculated correlation is actually negative because of the re-verse polarity of the scoring systems used on the two tests. Throughout this article we have reported correlations between tests that both report greater performance as positive correlations to avoid confusion.) The correlation be-tween the first-quarter and final quar-ter administrations of Test #18 was r=0.517 (p<0.01). The correlation, for first-quarter students, between the Test #18 total scores (speed adjusted for accuracy with a penalty for dropped pins) and the dropped pin penalty was r=0.490 (p<0.01). The “accuracy” component was approximately one quarter of the standard deviation of the combined test.

Figure 3. Tweezer dexterity comparison scores

Ta�le 3. Tweezer Dexterity Test #18 scores for first-year dental students

N Mean S.D. Score Range

Total 50 40.42 19.1 10-77Female 25 43.20 17.4 10-77Male 25 37.80 20.8 10-76

Ta�le 4. Tweezer Dexterity Test #18 scores for senior dental students

N Mean S.D. Score Range

Total 49 42.65 19.14 10-79Female 25 42.52 18.58 10-79Male 24 42.79 20.11 14-73

Ta�le 5. Tweezer Dexterity Test #32022 scores for first-year dental students

N Mean* Median* S.D. Score Range

Male 25 330 327 33.2 (281-406)Female 25 330 323 39.6 (284-476)

*Scores in seconds to complete tests.

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Results for the predictive potential as part of an admissions portfolio of the tweezer dexterity tests are shown in Table 6. Both versions of the dexterity tests are compared against the PAT, which is the cur-rent standard predictor contained in the DAT battery. Average PAT scores for students at the University of the Pacific generally are in the top quintile of U.S. dental schools. The analyses reported in this study were, however, for individual students, and a signifi-cant range of individual scores existed. The speeded Tweezer Dexterity Test #32022 is correlated with both Test #18 (r=0.318) and with the PAT (r=0.245). Test #32022 is also a weak predictor of first-year grades in Operative Dentistry, Fixed Prosthodontics, and Dental Anatomy courses and of overall, three-year grade performance in laboratory and clinical courses. The Tweezer Dexterity Test #18, which contains a correction for accuracy of performance, is not correlated with the PAT (r=0.045). Scores on this test during the first year of dental school do, however, predict first-year course grades in Fixed Prosthodontics and Endodontics technique courses. Test #18 performance is also weakly related to third-year laboratory and clinical GPA and to graduation class rank. The PAT score predicts all first-year technique course grades (except Endodontics) and overall, three-year laboratory and clinical GPA. The

test for differences between related correlations was performed on these results, and there were no statistically significant differences in the predictive power of any of the three predictors for the outcome measures used in this study.

On the premise that the PAT is a predictor already used by most dental schools, an analysis was performed to determine whether either of the tweezer dexterity tests adds new predictive power if the PAT scores are already known. The standard ap-proach is to perform partial correlations between the tweezer tests and course grades, holding PAT score constant by statistical means. The results of these tests are also reported in Table 6. Although several weak partial correlations were noted, the value for a tweezer dexterity test as a supplement to the PAT as a predictor of dental school course performance is not clear. (One tweezer test predicted performance in two of five first-year courses, but not clinical performance or overall rank. The other tweezer test predicted three of these possible seven outcomes.)

Test #18 was analyzed in such a fashion that the “accuracy” component could be extracted from the overall speed corrected for accuracy score. As shown in Table 6, accuracy on Test #18 was not correlated with the PAT and was not an effective predictor of the outcomes measures used in this study.

Ta�le 6. Comparison among Tweezer Dexterity Test #18, Test #32022, and Perceptual A�ility Test as predictor of various measures of dental sc��ool performance

Predictors First Year Final Year

#32022 #18 PAT SS OP FX DA EN Clin Rank

Test #32022 --- .318 .245 .431 .397 .285 .279Test #18 --- .045 .335 .329 .260 .242PAT --- .271 .308 .318 .447 .423

Tweezer tests adjusting for PAT

Test #32022 .386 .348Test #18 .339 .326 .266

Tweezer Test #18 corrected for speed (accuracy component only)

Test #18 .106

First-year outcomes measures are grades in courses with technique laboratories: Laboratory and Study Skills (SS), Operative Dentistry (OP), Fixed Prosthodontics (FX), Dental Anatomy (DA), and Endodontics (EN). Third-year outcomes measures are cumulative GPA for laboratory and clinic courses (Clin) and class rank. Only correlations that are significant at p<.05 are shown (the correlation between the PAT and Test #18 is insignificant but is shown here because it is part of the statistical test for dif-ferences between related correlations). Poles are reversed on rank and Test #32022 so that positive correlations represent high performance for all variables shown in this table.

1096 Journal of Dental Education ■ Volume 71, Number 8

DiscussionOur analysis indicates a significant correlation

(r=0.318, p<0.05) between the two tweezer dexterity test scores for the dental student group when both tests were taken by students during their first quar-ter of dental school. Both tests require the skill of transferring pins using tweezers. Test #18 scores are dependent on speed and accuracy while Test #32022 scores only measure speed. Test #18 requires that pins be grasped from an upright position, while Test #32022 uses pins lying flat in a reservoir. Board hole designs also differ, as Test #18 presents a tapered en-try and Test #32022 does not. These tweezer dexterity tests are clearly not assessing identical behavior.

Our results for Test #18 are in contrast to the traditional viewpoint that a high innate degree of motor dexterity is required for success in dental school. Our findings using the Johnson O’Connor Research Foundation aptitude test battery suggest that first-year dental students are not significantly different in their tweezer dexterity from the general population. The same lack of significant difference was found when the norm data were stratified for age and gender. These results seem to support the find-ings of Simon and Chambers,16 who demonstrated that the mean Tweezer Dexterity Test #18 scores of successful dentists were not significantly different from mean normative scores. As these authors sug-gest, fine hand-eye coordination, such as is needed for practicing dentistry, may be trainable in the vast majority of dental school applicants.

Our study also suggests that tweezer dexterity is an aptitude that is not significantly influenced by completing a dental school curriculum. First-year students and those same students as seniors in their final quarter did not differ significantly in tweezer dexterity. This would be expected for a true aptitude. Aptitudes are different from knowledge or skill in that they are natural talents believed to be inherited. Knowledge and skill can be acquired by studying hard, practicing, or working in a particular occupa-tion. Aptitudes should not change, and aptitude test scores should remain relatively stable over time. Weinstein et al.15 hypothesized that dentists develop an internalized standard emphasizing accuracy rather than speed and use this to explain their finding that performance on Test #32022 (pure speed test) was negatively correlated with restorative work quality. Our finding that Test #18 scores (speed and accuracy test) do not differ significantly from the first quarter

of dental school to the final quarter suggests that internalization of a standard emphasizing accuracy does not occur during dental school.

The need to develop a measure providing meaningful data for psychomotor aptitude is appar-ent. Unlike an academic record, applicants cannot submit transcripts quantifying the quality of their fine motor skills. The predictive measures of choice used by admissions committees continue to empha-size predental grade point average (GPA) and DAT scores. Studies correlating admissions data to dental school performance show no positive correlation between pre-professional GPA and the students’ abilities in dental techniques.21,22 Studies addressing the relationship of PAT scores to summary measures of performance in preclinical technique courses have shown a positive correlation, but at a low level of power.1,17

Extensive research directed at dexterity evalu-ation, primarily with regard to predicting success in dental school, appears in the dental literature.1-3,5,6,8,9 Most of these studies have found limited predictive value for dexterity testing as it relates to dental school performance. Our results show that both tweezer dexterity tests and the PAT are weak predictors for various dental school performance outcome mea-sures. Test #32022 had a greater correlation with preclinical Operative Dentistry and preclinical Fixed Prosthodontics than did the PAT or Tweezer Dexterity Test #18. The PAT had the highest correlation of the three predictor variables with Dental Anatomy and cumulative GPA for laboratory and clinic. Test #18 had the highest correlation with preclinical Endodon-tics and final class rank. No statistically significant differences were found in the predictive power of any of these three predictors for the seven outcomes measures used. When the two tweezer dexterity tests were adjusted for the PAT score, some weak corre-lations were identified, but the pattern of additional predictive power is not clear.

We also analyzed the Tweezer Dexterity Test #18 data to extract the accuracy component from the test. As with the complete Test #18, accuracy on Test #18 was also not an effective predictor of the outcomes measures used in the study.

Forty-nine of the fifty students successfully completed dental school and posted tweezer dex-terity scores for Test #18 ranging from the lowest possible (10) to nearly the highest possible (80). It seems reasonable to suggest that the tweezer dexterity tests evaluated have little significant predictive value for the complex skills needed for successful dental

August 2007 ■ Journal of Dental Education 1097

school performance. The degree of rapid arm/hand movement used during these tests may distract from the finer dexterity procedure executed at tweezer’s end. As Spratley states, it is not clear exactly which manual skills are required for a dentist, and the bal-ance needed between manual and intellectual skills remains uncertain.5

ConclusionA significant correlation (r=0.318, p<0.05)

between the Johnson O’Connor Tweezer Dexter-ity Test #18 scores and the Tweezer Dexterity Test #32022 scores was demonstrated for the dental stu-dent group. First-year dental students were shown to have no significantly different tweezer dexterity from members of the general population who take the Johnson O’Connor Research Foundation test battery. Finally, the findings suggest that tweezer dexterity is not changed significantly by completing a dental curriculum, and the ability for an applicant to perform successfully in dental school will not be reliably predicted by tweezer dexterity scores.

AcknowledgmentsThe authors wish to thank the Johnson

O’Connor Research Foundation and especially David Schroeder for sharing norm data and the use of the tweezer dexterity boards. We also wish to recognize Dr. Jim Simon for his assistance.

REFERENCES1. Gansky SA, Pitchard H, Kahl E, Mendoza D, Bird W,

Miller AJ, Graham D. Reliability and validity of a manual dexterity test to predict preclinical grades. J Dent Educ 2004;68(9):985-94.

2. deAndres AG, Sanchez E, Hidalgo JJ, Diaz MJ. AppraisalAppraisal of psychomotor skills of dental students at University Complutense of Madrid. Eur J Dent Educ 2004;8(1): 24-30.

3. Oudshoorn WC. The utility of Canadian DAT Perceptual Ability and Carving Dexterity scores as predictors of psychomotor performance in first-year operative dentistry. J Dent Educ 2003;67(11):1201-8.

4. Luck O, Reitemeier B, Scheuch K. Testing of fine mo-tor skills in dental students. Eur J Dent Educ 2000;4(1): 10-4.

5. Spratley MH. Regression analysis of dexterity tests and dental students’ practical examination results. Aust Dent J 1992;37(6):461-6.

6. Kao EC, Ngan PW, Wilson S, Kunovich R. Wire bending test as a predictor of preclinical performance by dental students. Percept Mot Skills 1990;71(2):667-73.

7. Squire D, Giachino AA, Profitt AW, Heaney C. Objec-tive comparison of manual dexterity in physicians and surgeons. Can J Surg 1989;32(6):467-70.

8. Boyle AM, Santelli JC. Assessing psychomotor skills: the role of the Crawford Small Parts Dexterity Test as a screening instrument. J Dent Educ 1986;50:176-9.

9. Walcott AM, Knight WG, Charlick RE. Waxing tests as predictors of students’ performance in preclinical den-tistry. J Dent Educ 1986;50:716-21.

10. Potter RHY, McDonald RE. Use and application of struc-tural models in dental education research. J Dent Educ 1985;49:145-53.

11. Peterson S. The ADA chalk carving test. J Dent Educ 1974;38:11-5.

12. Thompson CE. Motor and mechanical abilities in profes-sional schools. J Appl Psychol 1942;26:24-37.

13. Harris AJ. The relative significance of measures of me-chanical aptitude, intelligence, and previous scholarship for predicting achievement in dental school. J Appl Psy-chol 1937;21:513-21.

14. Inventory of aptitudes and knowledge. Boston: Johnson O’Connor Research Foundation Human Engineering Laboratory, 1988:9.

15. Weinstein P, Kiyak HA, Milgrom P, Ratener P, Morrison K. Manual dexterity as a predictor of quality of care among dental practitioners. J Dent Educ 1979;43(3):165-9.

16. Simon JF, Chambers DW. The search for a profile of aptitudes that characterize dentists. J Dent Educ 1992;56(5):317-21.

17. Kramer GA. Predictive validity of the Dental Admission Test. J Dent Educ 1986;50:526-31.

18. Bethscheider J. Comparison of tweezer dexterity. Statisti-cal Bulletin 1995-5, Johnson O’Connor Research Founda-tion, 1995:1-11.

19. Windle M. Norms for tweezer dexterity. Statistical Bul-letin 1985-37, Johnson O’Connor Research Foundation Human Engineering Laboratory, 1985:1-2.

20. Instructions for the 32022 O’Connor Tweezer Dexterity Test, Johnson O’Connor Research Foundation, 1986:1-5.

21. Ross NM. Dental aptitude test results and college grades as predictors of success in a school of dentistry. J Dent Educ 1967;31:84-8.

22. Fernández-Pabón JJ. Prediction of success in dental school on the basis of dental aptitude test scores and other vari-ables. J Dent Educ 1968;32:261-5.