646 Compensation Method for Missing Wear Data in Long-term Clinical Trials

Friday, March 23, 2012: 8 a.m. - 9:30 a.m.
Presentation Type: Oral Session
S. BAYNE1, A. WILDER2, H. HEYMANN3, J. STURDEVANT2, and E. SWIFT JR.3, 1Dept. of Cariology, Restorative Sciences, and Endodontics, University of Michigan, Ann Arbor, MI, 2School of Dentistry, University of North Carolina, Chapel Hill, NC, 3Operative Dentistry, University of North Carolina, Chapel Hill, NC

Introduction:  In the few existing long-term clinical trials on posterior composites, patient attrition (typically 5-10% per year) substantially limits quantity and true quality of results.   Suspicions exist that many missing values underestimate actual changes. 

Objective:   Assess the impact of missing values using a novel estimation method for missing values in clinical trials of posterior composite wear over 10-years. 

Methods :  Two composites (1981-1991 FulFil [F70], conventional; 1998-2008, SureFil, packable; Dentsply-Caulk) were placed previously with conventional techniques, recalled (0.5-1-2-3-5-10y; 0.5-1-2-4-5-10y), and monitored with impressions for wear (Leinfelder method, baseline-subtracted, 3 highly-calibrated clinicians). Restorations were Class I and II in first or second molars with at least half of all possible wear values for inclusion.  Regression of occlusal wear for each restoration versus log time (y=m(ln(x)+b) was determined to calculate missing values.  Artificially completed data sets (W2) were compared to missing-value sets (W1) by one-way ANOVA (p≤0.05, Bonferroni). 

Results :  Means (X) and standard deviations (sd) are reported below with no significant differences (>0.05) between W1 and W2 for any recall for either composite. Surprisingly, increased values had little effect. While insignificant, the 10y W2 packable trend indicated a potential overestimate.


Wear (m)




Recall Period

W1 (missing values)

[n], Xsd

W2 (completed)

[n], Xsd

W1 (missing values)

[n], Xsd

W2 (completed)

[n], Xsd


[31], 8053a

[32], 7950a

[59] 1824a

[51] 1825a


[36], 13262a

[32], 13163a

[56], 1622a

[51], 1722a


[28], 15064a

[32], 15461a

[45], 2531a

[51], 3134a


[28], 17960a

[32], 18157a

[45], 6841a

[51], 6541a




[36], 5246a

[51], 4942a


[29], 20372a

[32], 19375a




[16], 22463a

[32], 22468a

[17], 14575a

[51], 9874a






W2 average r2 fit





Conclusion:   Added values from estimations for long-term trials did not affect results.

Acknowledgment: Supported indirectly by Dentsply-Caulk.


Keywords: Clinical trials, Composites and Wear