Our aim was to assess changes in the number of enamel microcracks (EMCs) after removing metal brackets in teeth with and without visible EMCs before the bonding procedure.
Before bonding, 13 patients having teeth with visible EMCs and 13 subjects whose teeth were free of EMCs were included in the study. All patients were asked to complete a questionnaire with a detailed medical history at the beginning of treatment and after removing metal brackets. The number of teeth with visible EMCs and the number of premolars without EMCs were recorded for each subject twice, that is, before bonding and after debonding, together with the tooth sensitivity assessments elicited by compressed air and cold testing.
The number of visible EMCs in premolars increased after removing metal brackets. EMCs were recorded in at least 25.0% of all evaluated teeth for the patients having teeth with and without visible EMCs at the beginning of treatment. However, the changes in the number of visible EMCs were not significantly different ( P = 0.619) between the groups. For the subjects with visible EMCs, tooth sensitivity caused by cold was registered nearly 3 times more often after removing brackets compared with the patients without EMCs prior bonding.
Formation of EMCs was noticed after debonding. Changes in the number appeared to be similar for the subjects with and without visible EMCs before bonding. Higher incidence of EMCs was associated with more frequent tooth sensitivity perceptions after removing brackets.
New enamel microcracks (EMCs) were noted after debonding in vivo.
There were similar changes in the number of EMCs for patients with and without previous EMCs.
There was a low prognostic value of EMCs’ visibility.
A higher incidence of EMCs was associated with more frequent teeth sensitivity.
Compared with in vitro, the tendency of a lower frequency of new EMCs in vivo.
A large number of published in vitro and in vivo studies have already demonstrated that the bracket removal leads to irreversible changes in the enamel irrespective of the debonding techniques and residual adhesive removal methods used. One way to describe the extent of enamel damage during orthodontic treatment with the fixed appliances is to qualitatively and quantitatively evaluate and measure the characteristics of enamel microcracks (EMCs). Over the last 2 decades, an increasing number of studies have been presented, analyzing topics ranging from distribution of frequency of cracks and their increased numbers and lengths, or changes in frequency and severity of EMCs to the evaluation of specific EMCs’ parameters (eg, number, direction, length, width). , Examining the teeth without EMCs before the bonding procedure, new EMCs were recorded in 23.3%-25.0% of teeth after removing metal brackets , and approximately 17.0%-34.0%—after debonding ceramic brackets. , , , EMCs, quite often visible with the naked eye both by the patients and the dentists, may compromise the integrity of the enamel, cause stain and plaque accumulation on the rough fractured surface, thus increasing susceptibility to carious lesions and damaging the appearance of the teeth. , In addition, the potential effect of EMCs on tooth sensitivity during the debonding procedure has already been assessed.
Current knowledge of changes in EMCs’ characteristics during the debonding procedure is based on in vitro studies. This is because, to date, no equipment has been developed allowing direct intraoral (ie, not through replication procedure) measurements of EMC parameters ensuring micrometer resolution (typical width, 1.81-13.04 μm; length, 2.67-12.42 mm) needed for the precise description of an individual EMC. So the question is, to what extent can the results of in vitro research be applied in clinical practice? It is known that in the oral environment, teeth are exposed to various physiological (eg, masticatory forces, oral humidity due to saliva, acid) and pathologic factors (eg, patient abuse). Study comparing in vivo and in vitro bond strength showed that although mean bond strength values in vivo were lower (approximately 40%), the changes followed the same pattern over time in both environments. Thus, it can be hypothesized that the debonding procedure in vivo could also lead to a lower frequency of new EMCs than the results of previously published in vitro studies. , , , Particular interest in pronounced EMCs (visible with the naked eye under normal room illumination), which can be observed directly (ie, without special equipment) during a routine intraoral examination. ,
The aims of this in vivo study were (1) to evaluate and compare the possible changes in the number of EMCs after removing metal brackets for patients having teeth with and without visible EMCs before the bonding procedure, and (2) to determine whether there is a probability of independence between the number of EMCs after removing metal brackets and medications taken, eating habits, dental treatment (other teeth than premolars), and tooth sensitivity (recorded in a questionnaire and induced by compressed air and cold stimuli) for the subjects with and without visible EMCs at the beginning of treatment.
Material and methods
Before initiating orthodontic treatment, all the subjects (26 patients; age range, 14-34 years) included in the study were asked to complete a questionnaire with a detailed medical history ( Table I ). , The selection of the patients and the teeth for the research was on the basis of the primary and secondary selection criteria presented in Table II . , All eligible subjects were given verbal and written information about the study and the opportunity to ask further questions. Each participant provided informed consent.
|Date of bonding procedure:||Type of brackets:|
|1. Do you complain about teeth sensitivity? 0–Yes, 1–No|
|2. Do you currently receive or have you previously received professional desensitizing treatment? 0–Yes, 1–No|
|3. Have you used over-the-counter desensitizing products within the previous 6 wk (eg, special varnish or mouth rinse)? 0–Yes, 1–No|
|4. Have you used anti-inflammatory, analgesic, and/or psychotropic drugs within the previous 6 wk (eg, ibuprofen, antidepressants)? 0–Yes, 1–No|
|5. Are you pregnant or breast-feeding? 0–Yes, 1–No|
|6. Is your health good? 0–Yes, 1–No|
|7. Do you have eating disorders (eg, bulimia nervosa)? 0–Yes, 1–No|
|8. Do you suffer from digestive system or endocrine system diseases (eg, chronic acid regurgitation, diabetes)? 0–Yes, 1–No|
|9. Do you often (several times a wk) drink natural fruit juice, carbonated refreshments, and eat fruits (especially citrus fruits)? 0–Yes, 1–No|
|10. Have you had dental treatment (including teeth extractions) within the previous 3 mo? 0–Yes, 1–No|
|11. Have you had periodontal surgery within the previous 3 mo? 0–Yes, 1 – No|
|12. Have you previously whitened your teeth? 0–Yes, 1–No|
|Selection criteria for subjects|
|• Informed consent gained from patients and parents|
|• Orthodontic treatment: fixed orthodontic appliances on one or both dental arches, no preparation for the orthognatic surgery|
|• Duration of treatment up to 36 mo|
|• No current or previous professional desensitizing treatment and use of over-the-counter desensitizing products within the previous 6 wk|
|• No use of anti-inflammatory, analgesic, and psychotropic drugs within the previous 6 wk|
|• No pregnancy or breast-feeding|
|• No recorded eating disorders or excessive dietary or environmental exposure to acid|
|• No history of systemic conditions that may lead patients to dentin hypersensitivity (such as chronic acid regurgitation)|
|Selection criteria for teeth|
|Primary teeth selection criteria|
|• Maxillary and mandibular premolars having intact buccal enamel with no white spots, signs of dental fluorosis, enamel hypoplasia or erosion, and wedge-shaped defects|
|• No pretreatment with chemical agents (such as hydrogen peroxide)|
|• No previous orthodontic, endodontic, or restorative treatment|
|• No signs of gingival recession|
|Secondary teeth selection criteria|
|• Enamel microcracks visible on the buccal enamel surface|
The sample size was estimated using the formula on the basis of proportions for categorical (nominal) data, by which a minimum of 12 patients was required for each group at an α level of 0.05 and with a power of 80.0%. Considering the methodology and the possible withdrawal of subjects during the study period, we collected the baseline data from 32 patients. The final sample size consisted of 26 subjects: 13 had teeth with visible EMCs, and 13 did not have visible EMCs at the beginning of the orthodontic treatment.
The research was conducted in line with the protocol demonstrated in Figure 1 . Before the bonding procedure, the selected patients were divided into 2 groups of 13: group 1, subjects having teeth with visible EMCs (mean age, 20.38 ± 5.85 years) and group 2, patients whose teeth were free of visible EMCs (mean age, 19.00 ± 5.99 years). The presence of EMC that can be identified with the naked eye under normal room illumination was the main criterion for assigning patients to one of the 2 groups ( Fig 2 ). The number of teeth with visible EMCs and the number of premolars without EMCs were recorded for each patient.
The sensitivity using compressed air (19°C-24°C, applied first) and cold stimuli (freshly melted ice water, 0°C) was also assessed for all the teeth included in the study both from groups 1 and 2 before orthodontic treatment. Detailed description of the thermal stimuli applications are presented in a previously published study. Discomfort or sensitivity induced by compressed air and cold stimulus were recorded with the help of a 100-mm long visual analog scale (VAS).
All the patients selected in the study were bonded with mechanically retained metal brackets (Mini Master; American Orthodontics, Sheboygan, Wis) with 0.22-in slots on one or both dental arches. The teeth were prepared in accordance with the standardized requirements for the bonding procedure: etching with 34.5% phosphoric acid gel (Vococid; Voco, Cuxhaven, Germany) for 30 seconds, rinsing with water for 20 seconds, drying with oil-free compressed air for 10 seconds, applying the primer (Contex Primer; Dentaurum, Ispringen, Germany) and curing it with light for 10 seconds. The bonding base of the bracket was applied with a resin adhesive (Transbond XT; 3M Unitek, Monrovia, Calif), the bracket was firmly positioned on the enamel surface, and the excess adhesive was removed from around the base of the bracket with an explorer. The light-cure adhesive was polymerized for 20 seconds (10 seconds from each proximal side) using a halogen light (Mini LED; Satelec, Cambridgeshire, United Kingdom). All the patients were treated using fixed orthodontic appliances on one or both dental arches (no additional devices such as miniscrews, fixed functional appliances were used) within 36 months.
At the end of the orthodontic treatment, the debonding procedure of metal brackets was carried out with the conventional utility Weingart pliers (Dentaurum) by hand. The mesiodistal edges of the bracket wings were squeezed gently until the bracket was removed. All visible residual adhesive was carefully removed from the surface of the teeth with a slow-speed handpiece and a carbide-finishing bur. The teeth were kept out of occlusion (biting on a cotton roll) during the debonding. In the weeks before removing metal brackets, the patients were in a passive phase of orthodontic treatment.
After the debonding procedure, all the subjects from groups 1 (average time of treatment, 26.69 months) and 2 (average time of treatment, 24.23 months) were asked to complete the same questionnaire as at the beginning of the orthodontic treatment ( Table I ). The number of teeth having visible with the naked eye EMCs and the number of premolars without those EMCs were registered. The sensitivity assessment was carried out immediately after removing metal brackets in the same manner as before bonding. The VAS scores of each subject (all examined teeth) from groups 1 and 2 were averaged to calculate the mean sensitivity intensity score for each group separately. The patients were blinded to the presence of visible EMCs. All the bonding and debonding procedures, EMCs’ visibility, and teeth sensitivity assessments were carried out by the same examiner (I.D).
Statistical analysis was performed using SPSS (version 17.0; SPSS Inc, Chicago, Ill). The number of teeth with EMCs that are visible and the number of teeth with EMCs that are invisible to the naked eye were reported as percentages of the total number of examined teeth in both groups. The number of patients with no change or an increase in the number of new EMCs after debonding were presented as percentages of the total number of subjects in each group, separately. A nonparametric Pearson chi-square test was used to evaluate any differences in the number of visible and invisible EMCs before and after debonding for group 1 (teeth with visible EMCs) and between groups 1 and 2 (teeth without visible EMCs). The chi-square test was used to study the probability of independence between the number of EMCs after removing metal brackets and medications taken, eating habits, dental treatment (other teeth than premolars), and tooth sensitivity. To visualize differences between 2 qualitative variables, we applied Mosaic plots using JMP statistical software (SAS Institute Inc, Cary, NC). Significance for all statistical tests was based on P values ( P = 0.05).
The distribution of visible EMCs among premolar teeth included in the study is shown in Table III . For most patients (53.8% before bonding and 61.5% after debonding) having teeth with EMCs at the beginning of the orthodontic treatment (group 1), more than 50.0% of all examined premolars demonstrated visible with the naked eye EMCs. After removing metal brackets, EMCs were recorded in at least 25.0% of all evaluated premolars either for the subjects having teeth with or without visible EMCs before bonding.