Supervisors info:
Σωτηρία Γκιζάνη, Αναπληρώτρια Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Μαργαρίτα Μάκου, Ομότιμη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Γεώργιος Βαδιάκας, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Summary:
Introduction
After orthodontic bracket debonding there are remnants of composite resin, left on the enamel surface which contribute to plaque accumulation and enamel staining. This may result in enamel demineralization and aesthetic concerns for the patient (Zarrinnia et al, 1995). Mechanical removal of the remaining resin has been associated with iatrogenic effects, including surface roughening (Ahrari et al, 2013; Karan, Kiircelli & Tasdelen, 2010; Eliades et al, 2004) and removal of the external rich in fluoride enamel layer (Al Shamsi et al, 2007; Banerjee et al, 2008; Ireland, Hosein & Sherriff, 2005; Janiszewska-Olszowska et al, 2015). Deep grooves created on the enamel surface after that removal are not eliminated over time (Zachrisson, 1979) with brushing or salivary flow. Furthermore, loss of the uppermost layer of the enamel surface may lead to exposure of the enamel prism endings to the oral environment and may in turn induce a decrease in the resistance of enamel to organic acids (Ogaard, 2001).
A variety of methods have been investigated for removal of orthodontic adhesive remnants such as hand instruments, polishing discs, burs, ultrasonic scalers, air abrasion systems and laser. Two of the most popular systems for enamel grinding and polishing after debonding are the Tungsten carbide bur and the Sof-Lex discs. The adverse effect of using these means on enamel morphology after bracket debonding is usually assessed by qualitative imaging methods like optical and electron microscopy. The introduction of 3D non-contact profilometric methods has greatly contributed to quantification of the surface topographical features employing a variety of roughness parameters (Ulusoy, 2009; Sharma et al, 2010) .
The aim of the present study was to evaluate the effect of two grinding and polishing methods (Tungsten carbide burs or Sof-Lex discs) for removal of resin remnants, on enamel surface roughness parameters, after bracket debonding.
Material and Methods
Intact premolars extracted for orthodontic reasons, free of coronal defects (cracks, fractures etc) were used for this study. The teeth were visually inspected using a magnifying glass, for the presence of coronal defects such as cracks, fractures. The teeth were washed in tap water and submerged in 0.1% thymol solution for no more than one month at room temperature.
On the buccal tooth surfaces an area (3x3mm) was designated for bracket bonding and the roughness of the central portion was measured by an optical profilometer (Wyko NT 1100, Veeco, S. Barbara, CA, USA) under the following conditions: Mirau lens, 20× magnification, vertical scanning imaging mode, 2 mm scanning length, 113.3×148.5 μm2 analysis area, 2% modulation and tilt correction with 0.1 nm (z-axis) and 0.2 μm (x-, y-axis) resolution. The surface roughness parameters measured were: i) the amplitude parameter Sa (the arithmetic average of the absolute values of the surface height deviations measured from the best fitting plane), ii) the amplitude parameter Sz (the 10 point height over the surface, representing the average difference between the 5 highest peaks and 5 lowest valleys), iii) the hybrid parameter Sdr (the developed area due to the surface texture versus an ideal plane area ratio), iv) the spatial parameter Sds (the sum peak density) and v) the functional parameter Sci (the ratio of the void volume of the unit sampling area at the 5-80% of the bearing ratio). On each specimen three measurements were performed and averaged, yielding the representative value. Then brackets (Bionic Stainless Steel Bracket System Category - Ortho Technology) were bonded on this area [Transbond XT adhesive and primer (3M Unitek, Monrovia, CA, USA), light curing for 30 seconds]. The teeth were stored in water (1 week/37oC) and then debonded by a plier. The debonded surfaces were randomly classified into two groups (A, B n=15/group). For group A, the resin remnants were removed by 12- and 30-fluted Tungsten Carbide burs (Komet Dental H390 314 018 and H390UF 314 018 respectively, Lemgo, Germany) used on the high-speed handpiece (n=15) and for group B by Sof-Lex discs (3M-ESPE – Coarse, Medium, Fine and Superfine – 13mm) used on the low-speed handpiece. Then the roughness of the central part of the designated region was measured again as above.
Statistical analysis
Normality assumptions were checked through Shapiro-Wilk tests and q-q plots. Due to the small sample size and the non- normal distribution of the data, non-parametric statistics were used. Descriptive statistics were used to present baseline and final values of roughness parameters (Sa, Sz, Sdr, Sds, Sci), by mode of resin removal (either carbide or soflex). Mann–Whitney U test was used to check baseline similarity of each one of the roughness parameters that were used as outcomes of interest (Sa, Sz, Sdr, Sds, Sci). Univariable and multivariable (adjusted for baseline values) linear regression with observed coefficients and 95% confidence Intervals (CIs) was used to assess the effect of mode of resin removal on final roughness parameter values. Standard errors (SE) were calculated using the bootstrap method with 500 replications (n=29).
The level of statistical significance was pre-specified at a=0.05. Statistical analyses were performed with STATA version 15.1 software (Stata Corporation, College Station, Tex, USA).
Results
No baseline value differences were detected among the intervention groups for all roughness parameters. The results of the multivariable analysis revealed a statistically significant difference in the final values of the following roughness parameters, after adjusting for baseline estimates: Sa, Sz, Sdr. Specifically, teeth treated with Sof-Lex (group A) revealed 0.48 μm lower final Sa values (95%CIs: -0.90, -0.05; p-value= 0.03), 3.73μm lower Sz values (95%CIs: -6.62, -0.84; p-value= 0.01) and 4.28μm lower Sdr values (95%CIs: -5.99, -2.57; p-value<0.001) than group B (Tungsten carbide burs. No differences were detected for the remaining two parameters (Sds, Sci) between the two intervention groups.
Conclusion
Sof-Lex discs resulted in lower final Sa, Sz and Sdr values in comparison to Tungsten carbide burs. These observations are in agreement with previous findings. No differences were detected for the Sds and Sci patameters between the two intervention groups.
