The Influence of Interproximal Reduction on Enamel Roughness and Bacterial Adhesion

Introduction: Interproximal reduction (IPR), also known as enamel stripping, leaves many grooves and furrows on the enamel surface, which may increase the risk of caries. In this thesis, the influence of IPR on the morphology and roughness (Ra) of enamel surfaces and the bacterial adhesion to these surfaces were investigated. The specific aims of this thesis were to assess the roughness of enamel surfaces (both qualitatively and quantitatively) produced by the most commonly used IPR instruments, to investigate the adhesion of bacteria to these surfaces, and to evaluate the effect of polishing after IPR on the amount of bacterial adhesion. Materials and methods: Sixty-four human premolar teeth that were extracted for orthodontic treatment were collected. Enamel blocks were cut from the interproximal surfaces. Seven different IPR instruments were used for interproximal reduction (n = 8 in each group) and there was a control group (n = 8) consisting of untreated enamel blocks. The morphology and roughness of the sixty-four enamel surfaces were investigated qualitatively and quantitatively using atomic force microscopy. From the seven IPR-treated groups, the samples from the three instruments that yielded significantly different roughnesses, as well as the control group, were used for the adhesion experiments. Adhesion of Streptococcus sanguinis ATCC10556 to the enamel surfaces was assessed by counting the colony forming units that adhered to the roughened surfaces after 30 min exposure. Results: Generally, the larger grit IPR instruments created rougher enamel surfaces (Ra values for medium bur: 702.4 ± 134.4 nm; medium strip: 501.0 ± 115.3 nm; mesh disc: 307.1 ± 106.9 nm) and smoother surfaces were formed by use of the smaller grit instruments (Ra values for fine bur: 407.4 ± 94.8 nm; fine strip: 317.6 ± 49.6 nm; curved disc: 223.9 ± 64.7 nm). The differences in mean roughness within the groups of larger or smaller grit were significant (p < 0.001 and p < 0.05, respectively), and the differences in mean roughness between instruments of the same type but different grit (e.g. large grit bur compared to small grit bur) were all significant with p-values < 0.001 apart from surfaces prepared with different discs (p = 0.122). The smoothest surfaces were created by use of the entire series of Soflex polishing discs after the enamel reduction (Ra = 36.7 ± 13.7 nm), and these surfaces were significantly smoother than the control surfaces (Ra = 148.6 ± 38.5 nm)(p = 0.017). The rougher surfaces showed increased streptococcal adhesion. Greatest adherence was to the surface prepared with a medium diamond bur (Ra = 702.4 ± 134.4 nm); the CFUs bound were 12.3 x 105 ± 0.5 x 105, followed by the surface prepared by mesh disc (Ra = 307.1 ± 106.9 nm, CFU = 4.0 x 105 ± 0.5 x 105), followed by the control surface (Ra = 148.6 ± 38.5 nm, CFU = 1.2 x 105 ± 0.1 x 105)(p < 0.001). The least bacterial adhesion was to the smoothest surface - when Soflex polishing discs had been used following enamel reduction (Ra = 36.7 ± 13.7 nm, CFU = 0.3 ± 0.05 x 105). Conclusions: 1) Larger grit diamond instruments created rougher surfaces than did their smaller grit counterparts; 2) Diamond burs created the roughest enamel surfaces, followed by diamond strips, followed by diamond discs; 3) The Soflex polishing discs created the smoothest surfaces, even smoother than that of the untreated enamel; 4) There was a positive relationship between enamel surface roughness and the number of bacteria that adhered. Clinical significance: It is recommended that practitioners polish interproximal enamel after IPR to leave the enamel as smooth as possible to reduce possible bacterial adhesion