Forty freshly extracted maxillary premolars were used in this study. The teeth were collected from patients treated in the orthodontic department, Faculty of Dentistry, Alexandria University whose premolars were to be extracted for orthodontic purposes. The research protocol was approved by the Research Ethics Committee of Alexandria University Faculty of Dentistry (IRB No. 001056 – IORG 0008839) prior to any research-related activities. All research activities involving human specimens followed with the Declaration of Helsinki15 and the domestic laws 16. All specimens were deidentified and no potentially identifying patient information was collected in relation to the specimens.
A standard experimentation protocol for enamel surface roughness measurement after resin clean-up was followed in this study. 17 The teeth were scaled, polished with pumice and a rubber cup. Roots were sectioned, pulp remnants removed from the crown and subsequently disinfected in 70% ethanol.
The sectioned crowns were embedded in acrylic resin cylinders of 20 mm diameter x 10 mm height. The cylinders were coded for identification purposes. To standardize the area of surface analysis, four shallow indents were made with a carbide bur corresponding to the corners of an imaginary square centered in the middle third of the buccal surface of the crown.
The designated region of interest was subjected to profilometric analysis using a stylus profilometer (Mahrsurf PS10, Mahr, Germany) with the contact stylus perpendicular to the specimen surface. At each timepoint, two profilometric readings were recorded and the average of the two readings for each parameter was calculated.
The following roughness parameters were measured:
-
Ra – The average surface roughness which is defined as the arithmetic mean of absolutes distances from the center line within the measuring length.
-
Rp – Maximum profile peak height.
-
Rv – Maximum profile valley depth.
-
Rz - Average maximum peak to valley of five consecutive sampling lengths within the measuring length.
Following the baseline profilometric analysis, enamel surface was etched with 37% phosphoric acid for 30 sec, rinsed and dried with a two-way air water syringe. Modified edgewise metal brackets (Modern Orthodontics, Ludhiana, India) were bonded using a light cure orthodontic adhesive resin (Transbond XT, 3M Unitek, Manrovia, CA, USA) according to the manufacturer’s instructions. The specimens were stored in sterile water at 37° for one week prior to debonding. Brackets were debonded by a debonding plier by the same operator.
The specimens were randomly divided into two groups. The random sequence was generated in Microsoft Excel (Microsoft corporation, Washington, USA).18 The adhesive remnant was removed using a friction-grip12-fluted carbide bur Adhesive remover H22AGK, Komet dental, Brasseler GmbH, Lemgo, Germany). In the first group, an air-turbine high-speed handpiece (T3 Racer, Sirona, Bencheim, Germany) was used operating at 2.2 bar pressure to deliver 160,000 rpm. In the second group, an electric high-speed “red” contra-angle handpiece (XM-L0105, Westcode, Foshan Guangdong, China) on an electric motor (NL 400-1, Westcode, Foshan Guangdong, China) was used set at 120,000 rpm as per manufacturer’s instructions for both handpieces for the adhesive remover bur. A new bur was used for every 10 teeth. The resin cleanup was performed under the operatory light until no visible resin remnant was visible to the naked eye. The time needed for complete resin removal was determined by an investigator other than the operator blinded to the allocation of the specimens using a stopwatch.
The specimens were subsequently polished with a rubber cup and pumice using a slow speed handpiece (NSK, Nakanichi Inc, Tochigi, Japan) operating on an air-turbine at 1.5 bar pressure to deliver 3000–5000 rpm.
In addition to the baseline measurement, surface roughness parameters were recorded following resin-clean up and after polishing. All roughness parameters were measured by one investigator blinded to the allocation of the specimens.
Statistical analysis
The sample size estimation was conducted using G* power software version 3.1.9.6, (Universität Kiel, Germany), using a between-factor repeated measure ANOVA at α = 0.05 and power = 0.8. 19 An average of Ra for 2 groups over 3 time points were calculated from Eliades et al 17 yielding an effect size of f = 0.39 yielding a total sample size of 38 specimens with an actual power of 81.7%. The sample size was increased to 40 to allow for outliers or possible non-reads by the profilometer.
Parameters of surface roughness were compared between the groups using repeated measures ANOVA adjusted for baseline values followed by Bonferroni post hoc tests using Statistical Package for Social Sciences SPSS Version 21.0 (IBM Corp, Armonk, NY, USA). The time needed for resin cleanup was compared using independent samples t test. The level of significance was set at P ≤ 0.05.