Comparison of the left and right first molar root volume. Estimated mean percentage difference between the right and left first upper molar for total root volume and mesial root volume. All experimental groups showed a significant reduction in root volume (total root volume and mesial root volume) compared to the untouched left molar. Utilisation of a collagen membrane, with or without the incorporation of a growth factor, had a tendency to reduce root volume, although this was not statistically significant. Error bars represent the standard error of the mean difference. *P < 0.05 and **P < 0.01.