In the April 2017 issue of the AJO-DO , Meredith et al evaluated enamel topography after interproximal reduction under atomic force microscopy (AFM). As discussed in many previous studies, AFM uses several high-resolution scans for assessment of enamel topography and has been strongly recommended for this purpose. This tool has advantages such as the need for minimal preparation of the samples, taking 2-dimensional and 3-dimensional images simultaneously, and allowing reproducible assessment of samples. Using AFM was a strength of this study, but there is some uncertainty regarding the control group. The authors used dental blocks prepared of premolars extracted for orthodontic purposes. The exclusion criteria were staining, demineralization, decay, fluorosis, enamel cracks, defects, and restorations. The samples were divided into 8 equal groups. One was considered the control group. Selection of the control group as such is questionable because the surface roughness and the amount of primary wear of teeth are multifactorial and may be variable in different subjects and even in 1 person, and depend on many factors such as age, nutritional regimen, and oral hygiene. The fact that assessments were made under AFM in micrometer and nanometer scales further necessitates more careful selection of the control sample.

For instance, it has been demonstrated that routine use of beverages containing carbohydrates and electrolytes can result in dissolution of enamel and change its physical and chemical properties. Also, the pH of consumed foods and beverages can affect the microhardness and roughness of enamel surface. The teeth evaluated in the study were collected from different subjects and probably had different primary surface roughness values depending on each subject’s nutritional habits; this could not be determined with the naked eye. Considering the variations in surface topography of teeth, it is possible that the control group did not match the experimental groups in terms of primary surface roughness, and this might have caused bias in the results. Another possibility is that the primary surface roughness of a group could be higher or lower than that of the other groups; in this case, accurate comparisons of the groups would not be possible.

Since assessment of surface roughness by AFM requires no preparation of samples, this method appears to be the most suitable modality for determination of primary (baseline) surface roughness of teeth, and then the secondary surface roughness value can be compared with the primary (baseline) surface roughness of the same sample after applying different stripping tools. AFM enables highly accurate quantitative measurements. Thus, AFM can measure the precise value of surface roughness before and after the use of each stripping method. Another suggested method for intergroup comparison is that instead of comparing the preintervention and postintervention values in the same sample, the authors can measure the surface roughness of all samples in the groups before stripping; then, if the surface roughness values of the groups are not statistically significant, the authors could correctly compare the secondary surface roughness values of the groups after the application of different tools.