Ability of Freshman/Senior Students to Place Controlled Composite-Layer Thicknesses

Objectives: To compare in-vitro incremental composite thicknesses placed in a controlled-size Class I preparation by Freshman and Senior dental students.
Methods: Testing followed an approved, exempt protocol at Augusta University (910480-1). Dental student volunteers (1^st and 4^th year) were instructed to fill 3-D printed coronal portions of simulated teeth having a circular, Class I preparation (5 mm dia, 8 mm deep), using 3, 2-mm thick increments of alternating composite shades (B1/C4, Premise, Kerr). Participants placed and condensed the amount of composite they considered would provide a 2-mm thickness, photo-cured that portion (1^st increment), placed and photo-cured a composite of contrasting color as the next increment (2^nd), and then completed the task with the amount they considered appropriate as the last 2-mm thick increment (3^rd). No instruments were provided that gave any concept of linear measurement: only a standard, hand composite condenser. Thus, all increment thicknesses relied on operator subjective interpretation. Completed, filled specimens were ground in half, occluso-gingivally, polished, and digital images were recorded. Enhanced contrast was used to emphasize distinction between the alternating shades of composite layers. Thicknesses of individual increments were made along the center of each sectioned specimen using software (ToupView, ToupTek). N=15/test group. The effect of increment number and operator classification on composite thickness were compared using a 2-way ANOVA and Tukey’s post-hoc test at a pre-set alpha of 0.05.
Results: Table presents results. Student year (p=0.002), increment layer (p=0.005), as well as their interaction (p=0.045) all significantly contributed toward increment thickness. Only middle increments for both groups included the target value (2.0mm), with Seniors over-estimating first increment thickness. The Max-Min range was lower for Seniors within each increment than for Freshman.
Conclusions: Senior students showed less variability when estimating increment thickness. but only the middle increment for each group included the 2-mm thickness target value.