Journal of Pharmacy And Bioallied Sciences

: 2021  |  Volume : 13  |  Issue : 6  |  Page : 1106--1110

Evaluation of change in surface enamel microhardness in patients undergoing fixed orthodontic appliance therapy – A randomized control trial

Ramya Rajendran1, V Sudhakar1, R Sumanth Rangarajan1, Anandadevi Chinnasamy1, G Vasupradha2, J Sathiya Jeeva3,  
1 Department of Orthodontics, Adhiparasakthi Dental College and Hospital, Melmaruvathur, Tamil Nadu, India
2 Department of Oral Pathology, Adhiparasakthi Dental College and Hospital, Melmaruvathur, Tamil Nadu, India
3 Department of Dentistry, Annapoorana Medical College and Hospitals, Salem, Tamil Nadu, India

Correspondence Address:
Ramya Rajendran
Department of Orthodontics Adhiparasakthi Dental College and Hospital, Melmaruvathur - 603 319, Tamil Nadu


Aim: This study aims at determining the amount of enamel decalcification in terms of microhardness. Materials and Methods: Twenty patients requiring treatment by extraction method for Class I malocclusion with bimaxillary protrusion were selected for the study. Twenty patients were randomly divided into control group and experimental group. In the control group (n = 40), extraction of permanent first premolars was done on day 1 of bonding to assess the Vickers hardness number (VHN) of enamel surface, and in the experimental group (n = 40), extraction of the contralateral premolars was done on the 28th day after bonding to assess the VHN of enamel surface. The values are tabulated and analyzed by SPSS software. Results: There is significant surface enamel dissolution of enamel crystals in the experimental group compared to the control group, and a statistically significant difference in VHN is evident between the control and experimental groups. The surface enamel dissolution (VHN) is not significant difference noted between mandibular and maxillary premolars of the control and experimental groups. Conclusion: The present study has demonstrated a higher level of surface enamel dissolution in the experimental group. There is a marked difference in the VHN between the control and experimental groups, which is statistically significant. The scanning electron microscopy study also confirms the presence of surface enamel demineralization following orthodontic bonding.

How to cite this article:
Rajendran R, Sudhakar V, Rangarajan R S, Chinnasamy A, Vasupradha G, Jeeva J S. Evaluation of change in surface enamel microhardness in patients undergoing fixed orthodontic appliance therapy – A randomized control trial.J Pharm Bioall Sci 2021;13:1106-1110

How to cite this URL:
Rajendran R, Sudhakar V, Rangarajan R S, Chinnasamy A, Vasupradha G, Jeeva J S. Evaluation of change in surface enamel microhardness in patients undergoing fixed orthodontic appliance therapy – A randomized control trial. J Pharm Bioall Sci [serial online] 2021 [cited 2022 Aug 18 ];13:1106-1110
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The patient with fixed orthodontic appliance faces difficulties in maintaining proper oral hygiene. As a result, a lack of maintaining oral hygiene measures might lead to an increased risk of caries lesion. Enamel plays an essential role in protecting tooth structure against irreversible damages caused by acidic environment due to bacterial activity. The most common acidogenic bacteria are present in the plaque are Streptococcus mutans and lactobacilli. Dental caries often occurs due to the imbalance in the dynamic process of demineralization and remineralization of enamel. Subsequently, enamel can be re-established by adequate, stable minerals in the saliva or dental plaque. The intensity of dental caries can range from the development of opaque white-spot lesions (WSLs), or decalcification, to loss of surface integrity of enamel and further leads to cavitation.

Regardless of advances in orthodontic material and treatment mechanics, the fixed orthodontic appliances are closely associated with a rapid shift in the bacterial flora of dental plaque. Gorelick et al. conducted a study on WSL and reported that 49.6% of orthodontic patients presented with enamel opacities on at least one tooth after fixed orthodontic treatment.[1] Furthermore, Mizrahi compared the prevalence of WSL in both pretreatment group and posttreatment group and reported 85% in posttreatment and 72.3% in pretreatment.[2] The problems with enamel decalcification in orthodontic patients have been taken into consideration, and it caused clinicians to look solution for orthodontic-associated demineralization. Although there is no standard protocol for the prevention of decalcification, various preventive approaches have been generated to “counteract” demineralization of tooth structure for the patient undergoing orthodontic treatment. In general, preventive measures against these WSLs in the maintenance of good oral hygiene and fluoride toothpaste, oral mouthwashes, varnishes, and adhesives.[3] Recently, fluoridereleasing orthodontic adhesives, composites containing fluorides, and carbon dioxide laser are a few newer methods that have emerged to assist orthodontists in preventing the occurrence of WSL.[4],[5] From orthodontist point of view, the objective of treatment is to improve facial esthetics; the presence of unpleasant WSLs may influence advantageous effects of orthodontic treatment.

Many studies have been conducted on demineralization and remineralization in the enamel surface for orthodontic patients, but studies related to the enamel surface microhardness for the patient undergoing orthodontic treatment are very minimal. Even though enamel plays a significant role in the process of decay, studies on alteration in the enamel surface holds great significance. As a result of dental caries, alteration in the enamel microstructure occurs where enamel hardness will be compromised in patients undergoing orthodontic treatment. The purpose of the current study is to evaluate the surface hardness of enamel in the patient undergoing orthodontic treatment.

 Materials and Methods

Patients who reported to the Department of Orthodontics, Adhiparasakthi Dental College and Hospital, who fulfilled the following criteria, were recruited for the study. Based on inclusion and exclusion of the study, a total of 20 patients were included in the study with a sample size of 40 in control and experimental [Table 1]. The study design and protocol were approved by the Ethical Committee of Adhiparasakthi Dental College and Hospital, Melmaruvathur. The subjects were explained about the purpose of the study, and informed consent was obtained from them. In the event of the subjects being <25 years of age, informed consent was also obtained from the respective parents. Subjects were clinically examined before the study.{Table 1}

The study sample consists of 80 permanent premolars scheduled for extraction due to orthodontic treatment from patients of Adhiparasakthi Dental College and Hospital. Before bracket bonding, surfaces of the premolars were polished with a rubber cup and rinsed and dried carefully.

The patients were bonded with fixed appliance (Mc Laughlin Bennett Trevisi (MBT) standard 0.022 slot brackets). Orthodontic brackets were bonded with Transbond XT (3M Unitek), a resin-based composite, and all the tooth surfaces including the control group are etched with 37% phosphoric acid gel. The excess adhesive was removed around the bracket and adhesive was light cured. On the day of bonding, the permanent first premolars (R) were extracted and kept as a control group and brackets are secured with modules. Patients were given regular oral hygiene instruction. After the 28th day of bonding, the (L) permanent premolars were extracted (experimental group) carefully to avoid accidental bracket removal and enamel damage. To eliminate bias, the control and experimental groups were segregated randomly.

The extracted premolars were stored in saliva (artificial) plastic container and maintained at 4°C, and Vickers hardness analysis was done on the same day. Teeth were cleaned with ethanol 60 s to remove organic substance and debris from enamel. The surface microhardness (SMH) of the samples was measured using a Vickers microhardness tester (HDNS KELLY INSTRUMENTS MVD 402 SHANGHAI) with a load Of 200 g for 10 s. All readings were performed by the same operator using the same calibrated machine. For each sample, indentation scores were taken 200 μm away from bracket surface cervically along the long axis of the tooth. Surface scanning electron microscopy (SEM) was done to confirm enamel demineralization [Figure 1] and [Figure 2]. A specimen was treated vapor coating of gold thickness about 30 nm. All specimens examined Quanta 250 FEG for optimization of surface damage. Magnification varied from 70 to 5000 nm. Each sample was scanned at low and higher magnifications in order to get an overall impression of enamel alteration.{Figure 1}{Figure 2}

Data were tabulated in an excel sheet and analyzed using SPSS statistical software, version 22, (Chennai, Tamil Nadu, India). The data were assessed for normality using paired t-test which revealed that the data were normal in distribution. Hence, parametric test (independent t-test) was employed to detect the significant difference between the control and experimental groups. The same test was employed to detect the significant difference in all quadrants in maxillary and mandibular.


The enamel microhardness was compared in the current study between the control group of immediate extraction without orthodontic bracket placement and the experimental group of extraction on the 24th day after orthodontic bracket placement. The mean enamel microhardness shows a statistically significant reduction of the experimental group (Mean 251.90±52.86) than the control group (Mean 293.18±53.83) [Table 2]. The mean enamel microhardness within the experimental group of first and second quadrant was 2.550 and 2.7623, respectively, and 2.3839 and 2.3742 in the third and fourth quadrants. Similarly, in the control group, the mean enamel microhardness was 3.1492 and 2.9924 in the first and second quadrants, and 2.7740 and 2.8200 in the third and fourth quadrants, respectively [Table 3]. Overall, statistically significant differences between the control and experimental groups (P = 0.05) suggest that the microhardness of bonded tooth was less than the control group [Table 4]. Nonetheless, only in the right upper quadrant shows statistically significant difference between the control and experimental group funds. In contrast, no significant differences were observed in other quadrants after 28 days in the experimental group.{Table 2}{Table 3}{Table 4}


This study was conducted at the Department of Orthodontics and Dentofacial Orthopedics, Adhiparasakthi Dental College and Hospital, in order to find an accurate value for the surface enamel microhardness of patients undergoing orthodontic treatment. Various retrospective studies have conducted between demineralization and remineralization of enamel surfaces in patient undergoing orthodontic treatment by various authors. The present study was conducted with an aim to arrive an exact Vickers hardness number (VHN) for the enamel surface dissolution following fixed orthodontic treatment. Numerous in vitro methods for SMH have been conducted, where there is a lack of standardization in values and difficulties in comparison of their results.

In this study, the twenty patients were randomly divided into two groups, control group and experimental group. In the control group (n = 40), extraction of permanent first premolars was done on the day of bonding to assess the VHN of enamel surface, and in the experimental group (n = 40), extraction of the contralateral premolars was done on the 28th day after bonding for the purpose to assess the VHN of enamel surface. The splitmouth technique is used because it removes interindividual variability from the estimates of the treatment effect. The amount of demineralization can be observed after 28-day experimental period.[1],[6] In order to avoid any problems associated with standardization, the MBT prescription (0.022) was chosen in both brackets types. Due to progression of patient age, perikymata and enamel rods will wear away; as a result, the younger age group of 15–25 years was selected for this study. The enamel surface should be devoid of surface enamel changes such as cracks and hypocalcified areas. Cleaning of tooth surface with pumice would remove plaque and the organic pellicle as stated by Aboush et al. (1991); therefore, a thorough oral prophylaxis and polishing of the teeth were done using plain pumice slurry and a bristle brush as it cleaned more effectively. Thompson and Way conducted a study to determine the amount of enamel lost during oral prophylaxis; they concluded that the amount of enamel loss with the bristle brush was 14.38 μm exceeding the loss of 6.9 μm with the usage of rubber cup.[7]

Hermsen and Vrijhoef compared the effect of phosphoric acid and maleic acid on the enamel surface during acid etching, and they concluded that 10% maleic acid removed considerably less enamel in contrast with 35% phosphoric acid.[8] Pascotto et al. conducted in vivo study regarding the microhardness of the enamel under brackets bonded with two groups, Fuji Ortho LC or Concise, respectively. As a result, it shows that demineralization and surface dissolution were not occurred due to acid etching. In accordance with that, we did a pilot study and confirmed the above finding that enamel dissolution is related to plaque accumulation and not due to acid etching.[9]

Julien et al. identified risk factors for WSL as treatment time exceeding 36 months, teeth lacking fluorosis, patients with poor oral hygiene declining during treatment, and preexisting WSLs.[10] As far as our knowledge, none of the studies explained about the amount of enamel dissolution in numerical values. Consequently, this enamel dissolution value will set up a basis for further remineralization and demineralization.

Hardness is one of the mechanical properties which can be attributed to the degree of mineralization of the tooth. It directly depends on the mineral content and the crystalline arrangement of the prism. Hardness testing together with the intraoral models holds greater significance in demineralization and remineralization experiments. The microhardness of enamel was evaluated by two methods, Knoop hardness number and Vickers (VHN) hardness methods, and they concluded that Vickers indenter is more practical than Knoop because a square shape has to be preserved which is close to the outer surface and the error in the hardness of the enamel and dentin is easily detected due to small elongation of the diagonals of the indentation in the region of Dentino Enamel Junction (EDJ).[11] On the contrary, Meredith et al.[12] concluded that Knoop indentation is more popular because it is longer and shallower which is simple to interpret than the short diagonal of the Vickers.[12] The current study was conducted with the aim of quantifying the amount of dissolution on 4 weeks after bonding. The value for the surface hardness obtained in the present study for the control group on day 1 is 293.180 ± 40.324. The VHN is significantly decreased in the experimental group that is 251.897 ± 41.509. The mean difference of the experimental and control groups is 41.28 ± 5.36, which is statistically significant.

In this study, we have compared and analyzed quadrant-wise VHN in the control and experimental groups. There is a definitive pattern in the VHN in the control and experimental groups with respect to quadrants to dental arch. The VHN is increased in the left-side permanent premolar of a patient, i.e., second and third quadrants compared to the first and fourth quadrant permanent premolars. The familiar reason behind this finding is that all our patients are right handed and hence their oral hygiene is comparatively good in the left side compared to the right side. We extended our study to compare surface enamel dissolution between maxillary and mandibular premolars which is not statistically significant. SEM is one of the most excellent ways to study and understand the surface enamel changes following initial dissolution of enamel crystals. In our study, SEM study of the control and experimental groups was done under ×5000 magnification. There is a significant disturbance in the prisms, rods, and perikymata; orientation is evidenced in the experimental group which shows the signs of surface enamel dissolution. Prism peripheries were removed preferentially in the control group, leaving the prism cores projecting toward the enamel surface, whereas SEM of an enamel surface in the experimental group revealed prism separate prism cores with a gap between them corresponding to prism peripheries. In this study, the value of surface enamel dissolution has been derived, and initial enamel demineralization is evident after orthodontic bonding. Consequently, orthodontist responsibility is to evaluate the oral status of an individual and educate oral hygiene measures in an initial stage, which helps to promote oral health and disease prevention.


There is a significant difference in VHN in the control and experimental groupsThe VHN of the control group is 293.180 ± 40.324, while that of the experimental group is 251.897 ± 41.509, and the mean value of enamel dissolution surface is 41.28 ± 5.36Enamel microhardness value reduced significantly on the 28th day after orthodontic bondingVHN of fourth quadrant premolars is least followed by the first, second, and third quadrants, respectivelyThere is no significant change in VHN between maxillary and mandibular archesScanning electron microscopic study revealed the surface pattern changes in enamel prisms and perikymata indicating surface demineralization.

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Conflicts of interest

There are no conflicts of interest.


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