|Year : 2013 | Volume
| Issue : 2 | Page : 101-104
Shear bond strength of self-ligating orthodontic brackets on different types of porcelain crowns
Karamdeep Singh Ahluwalia1, Amit Gupta2, Isha Gaurav3, Nitul Jain4, Rakesh Garg5, Nidhi Gupta6
1 Department of Orthodontics and Dentofacial Orthopedics, Jaipur Dental College, Jaipur, Rajasthan, India
2 Department of Orthodontics, Jaipur Dental College, Jaipur, Rajasthan, India
3 Department of Oral Medicine and Radiology, Jaipur Dental College, Jaipur, Rajasthan, India
4 Department of Oral and Maxillofacial Pathology, Eklavya Dental College and Hospital, Kotputli, Rajasthan, India
5 Department of Periodontology, National Institute of Medical Sciences Dental College, Kotputli, Rajasthan, India
6 Department of Periodontics, Jaipur Dental College, Jaipur, Rajasthan, India
|Date of Web Publication||3-Jan-2014|
Karamdeep Singh Ahluwalia
Department of Orthodontics and Dentofacial Orthopedics, Jaipur Dental College, Jaipur, Rajasthan
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study is to compare shear bond strength (SBS) and adhesive remnant index (ARI) of self-ligating orthodontic brackets bonded to different porcelain crowns. Materials and Methods: Three groups of different types of porcelain crowns, each containing 12 crowns were fabricated by the same technician and allocated to one of the study groups as follows: Group I - IPS porcelain crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein), Group II - Porcelain fused to zirconia crowns (Zirkonzahn GmbH, Gais, Italy, Noritake Co., Tokyo, Japan) and Group III - Conventional porcelain fused to metal crowns (Ceramco3, Densply, PA, USA). The orthodontic brackets were bonded to these crowns using hydrofluoric acid (HFA) + silane etching protocol. After bonding, the SBS of the brackets were tested with a universal testing machine under standard test conditions. Results: Statistical evaluation using analysis of variance showed a significant difference between the groups (P < 0.001). The IPS group showed the highest SBS (11.58 ± 2.23 MPa) (P < 0.001). No significant difference was found between ceramo-zirconia and ceramo-metal groups (P > 0.05). Chi-square comparison revealed no significant difference in ARI scores between groups (P > 0.05). Conclusions: When HFA + silane etching protocol were used, IPS crowns showed the greatest SBS of orthodontic brackets. The ARI score was non-significant. Therefore, if there is a need to place crowns over teeth then these crowns can be used for restoration of teeth before orthodontic treatment.
Keywords: Porcelain, porcelain fused to metal, shear bond strength, self-ligating bracket
|How to cite this article:|
Ahluwalia KS, Gupta A, Gaurav I, Jain N, Garg R, Gupta N. Shear bond strength of self-ligating orthodontic brackets on different types of porcelain crowns. J Orofac Sci 2013;5:101-4
|How to cite this URL:|
Ahluwalia KS, Gupta A, Gaurav I, Jain N, Garg R, Gupta N. Shear bond strength of self-ligating orthodontic brackets on different types of porcelain crowns. J Orofac Sci [serial online] 2013 [cited 2020 Feb 23];5:101-4. Available from: http://www.jofs.in/text.asp?2013/5/2/101/124252
| Introduction|| |
Porcelain restorations are frequently used for various purposes such as damage caused by extensive decay, root canal treatment and tooth avulsion and for missing teeth in adult patients. Mainly two types of porcelain crowns are used in dentistry that is porcelain fused to metal (PFM) crowns and all-porcelain crowns. The demand for esthetic restorations has resulted in an increased use of all-ceramic restorations. Today, various types of all-ceramic crowns are in use such as zirconia crowns and glass-ceramics. 
As the number of adults seeking orthodontic treatment is increasing, clinicians often have to bond orthodontic brackets to teeth that have different types of porcelain restorations. As conventional bonding could not provide sufficient adhesion to porcelain to withstand orthodontic forces, a number of approaches have been attempted to alter the surface characteristics of porcelain to provide sufficient bond strength.  The approaches suggested can be classified into two groups; mechanical or chemical.
The types of suggested mechanical surface conditioning techniques include, roughening the porcelain surface with a diamond drill or sandpaper discs , or sandblasting with aluminum oxide particles , Against this, chemical surface-conditioning techniques includes, chemical preparation with hydrofluoric acid (HFA) ,,,, or use of silanes (gamma-methacryloxypropyltrimethoxysilane). ,,,,,
In the literature, shear bond strengths (SBS) of various types of commercially available porcelain crowns  and temporary polycarbonate crowns  were measured. However, it was found that two of the most commonly used crowns such as IPS and zirconia were not used in any of the previous studies. Therefore, the aim of this study was to compare SBS of orthodontic brackets bonded to different kinds of porcelain crowns.
| Materials and Methods|| |
The study group consisted of total 36 porcelain crowns divided into three groups. Each group contained 12 crowns fabricated using different materials under suitable conditions and as per recommendations given by manufacturers by the same technician and at the same dental lab. These three groups and their material of fabrication were, namely:
- Group I: IPS porcelain crowns (Ivoclar Vivadent AG, Schaan, Liechtenstein).
- Group II: Porcelain fused to zirconia crowns (Zirkonzahn GmbH, Gais, Italy).
- Group III: Conventional PFM crowns (Ceramco3, Densply, PA, USA).
After 12 samples of each group were fabricated, the porcelain surfaces of each crown were etched with 9.6% HFA (Pulpdent, Watertown, Massachusetts, USA) for 2 min, followed by rinsing with water/spray combination for 30 s and then dried suitably before application of the silane. Silane primer (Ormco Porcelain Primer, Glendora, California, USA) was applied to the etched porcelain surface with a microbrush and allowed to dry for 5 min. A standard pre-adjusted edgewise (MBT 022" slot, Gemini Series, 3M Unitek, USA) bracket suitable for usage on maxillary central incisor were bonded with a light cured composite resin (Light Bond, Reliance Orthodontic Products Inc. Itasca, Illinois, USA) on the crown samples. A thin uniform layer of sealant was applied on the etched porcelain surface with a microbrush and cured for 30 s. A thin coat of sealant was also painted on the bracket base and cured for 15 s before applying the paste. Using a syringe tip, the paste was applied to the bracket base. The bracket was then positioned on the porcelain tab and pressed lightly. Excess adhesive was removed with a sharp scaler. Specimens were cured with soft start mode light-emitting diode (MiniLED™, Satelec, France) for 40 s (20 s on the mesial and 20 s on the distal surface of the brackets).
All specimens were stored in distilled water at 37°C for 24 h and thermo-cycled for 500 cycles between 5°C and 55°C using a dwell time of 30 s. Each specimen was loaded into a universal testing machine (Instron Universal Testing Machine, UK) using NexGen software (Nexjen Systems, Charlotte, North Carolina, USA) for testing, with the long axis of the specimen perpendicular to the direction of the applied force. A standard knife-edge was positioned to make contact with the bonded specimen.
Bond strength was determined in shear mode at a crosshead speed of 0.5 mm/min until fracture occurred. Values of failure loads (N) were recorded and converted into megapascals by dividing the failure load (N) by the surface area of the bracket base (9.63 mm 2 ). After debonding, all teeth and brackets in the test groups were examined under ×10 magnifications. Any adhesive remained after debonding was assessed and scored according to the modified adhesive remnant index (ARI). 
The scoring criteria of the index were as follows:
- The entire composite, with an impression of the bracket base, remained on the tooth.
- More than 90% of the composite remained on the tooth.
- More than 10% but less than 90% of the composite remained on the tooth.
- Lesser than 10% of composite remained on the tooth.
- No composite remained on the tooth.
Descriptive statistics, including the mean, median, standard deviation and quartiles were calculated for each of the groups tested. One-way analysis of variance (ANOVA) and Tukey's test were used to compare the SBS of the groups. The Chi-square test was used to determine significant differences in the ARI scores among groups. Significance for all statistical tests was predetermined at P < 0.05. All analyses were performed with the Statistical Package for Social Sciences version 17.0.0 (SPSS Inc., Chicago, Illinois, USA).
| Results|| |
The descriptive statistics on the SBS (MPa) for the groups are presented in [Figure 1]. ANOVA showed a significant difference between the groups (P < 0.001) [Table 1]. Group I showed the highest SBS (11.58 ± 2.23 MPa) (P < 0.001). No significant difference was found between Group II and Group III (P > 0.05).
Frequency distribution of the ARI scores is presented in [Table 2]. Chi-square comparison revealed no significant difference between groups (P > 0.05). There was a higher frequency of ARI scores of 3 and 4 in all groups, which indicated that failures were mainly in the adhesive-porcelain interface.
|Table 2: Frequency distribution of ARI scores and Chi-square comparison of the groups|
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| Discussion|| |
When a tooth presents clinically with a fracture or a carious lesion that is extending subgingivally and impinges on the biologic width, needed for restoration, then, depending upon the speciﬁc clinical situation the tooth may need surgical crown lengthening or forced orthodontic root eruption or both.
The disadvantage of crown lengthening is that it may alter the gingival level of the tooth when compared with that of the adjacent and contralateral teeth, which can lead to esthetic problems for the patient. The advantage of orthodontic extrusion combined with ﬁberotomy and root planning is that it enables the clinician to maintain the gingival level of the tooth relative to the adjacent/contralateral teeth.
Prior to orthodontic extrusion, however, multidisciplinary treatment procedures are required. These may include endodontic therapy to devitalize the tooth and render it free of pain and infection, restoration of the lost coronal tooth structure with a core retained by a post and a provisional restoration. In such a clinical situation, there are multiple interfaces between the remaining tooth structure and the orthodontic wire that ultimately exerts the force on the tooth in order to appropriately reposition it. These interfaces include, among others, dentin-luting (bonding) agent-provisional crown materials (PCM) and PCM-adhesive-bracket.
The mechanical characteristics of the interface between dentin and luting agents have been extensively studied and the mean SBS values in this respect have reached in excess of 35 MPa. The SBS values for orthodontic brackets attached to tooth enamel with resin composites or glass ionomer-type adhesives have been reported to be in the range of 4-26 MPa. ,,,
The selection of the premolar brackets was not preferred and instead maxillary central incisor brackets were used in this study. Because the curvature of the bracket against the ﬂat surface probably may have resulted in SBS values that were lower than those obtained with central incisor brackets with smaller curvature.
In this study, SBS of the brackets bonded to different porcelain surfaces were compared. Although there are many suggested bonding techniques, the combination of surface treatment with HFA and a silane coupling agent was used in this study, which produced the highest bond strength in bonding orthodontic brackets to porcelain crowns in a recent study. 
There are distinct differences in constituents, particle size and crystalline structure of the commercially available porcelains but have usually similar chemical formula. Therefore, different results are expected regarding bonding orthodontic brackets to porcelain. 
Minimum bond strength to be adequate for orthodontic bonding was 6 MPa,  the results of this study showed that the SBS for the two of the three porcelain groups were above and one of them was just below 6 MPa. In the present study, the conventional ceramo-metal and the ceramo-zirconia crowns had comparable SBS, which was lower than that of IPS e.max. Abu Alhaija and Al-Wahadni compared conventional ceramo-metal crowns and IPS empress 2 (earlier version of IPS e.max) and found higher SBS in ceramo-metal porcelain. This may be related to structural differences between empress 2 and e.max. The amount of adhesive remaining on the tooth was recorded using the ARI.  ARI scores are used to define the site of bond failure between the enamel-porcelain, the adhesive and the bracket base.
Bond failures within the adhesive or at the bracket-adhesive interface is preferred because it decreases the shear force stress at the crown surface and increases the probability of maintaining an undamaged crown surface. This type of failure in the adhesive-crown interface shows that the chemical and mechanical bonding was not equal to or exceeded the mechanical retention provided by the bracket base and the bond strength to the porcelain surface was lower than the cohesive strength of the adhesive.
The limitation of this study was that the study was performed in vitro. Therefore, SBS obtained in this study may not correspond well with clinical success. Further in vivo studies are still needed to substantiate the results obtained in this study.
| Conclusion|| |
After evaluating the SBS of an orthodontic bracket on different types of crowns, the following conclusions can be drawn. When HFA + silane etching protocol were used, IPS crowns showed the greatest SBS of orthodontic brackets. The ARI score associated with different types of crowns was non-significant. Therefore, if there is a need to place crowns over teeth then these crowns can be used for restoration of teeth before orthodontic treatment.
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[Table 1], [Table 2]