Original Article Comparison of Enamel Morphologic Characteristics

After Conditioning with Various Combinations of Acid Etchant and Er:YAG Laser in Bonding and Rebonding Procedures: A SEM Analysis

Authors:

  • Mohammad Sadegh Ahmad Akhoundi

  • Ardavan Etemadi

  • Maryam Nasiri

  • Elahe Soltanmohamadi Borujeni

Affiliations:

  1. Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran

  2. Assistant Professor, Laser Research Center of Dentistry, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Periodontics, Dental Branch, Islamic Azad University, Tehran, Iran

  3. Postgraduate Student, Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran

Abstract

Objectives:

  • Evaluation of re-etched enamel via Scanning Electron Microscopy (SEM).

  • Investigation of the effects of Er:YAG laser in primary and secondary bonding compared to standard acid etching concerning enamel surface changes.

  • Determining if primary and secondary enamel preparation methods influence enamel characteristics post-rebonding through SEM analysis.

Materials and Methods:

  • Sample Size: Twelve freshly extracted premolars

  • Group Division: Four groups based on conditioning method (acid etchant vs. Er:YAG laser) during primary and secondary bonding.

  • Sample Preparation: All samples conditioned with the designated methods, bonded with orthodontic brackets, debonded, and prepared for secondary conditioning. Additional controls were established using samples conditioned only once for comparison.

  • Evaluation Method: Buccal enamel surfaces assessed using SEM.

Results:

  • Acid-Etched Samples:

    • Exhibited distinct enamel etching patterns indicative of acid conditioning.

  • Er:YAG Laser Irradiated Samples:

    • Displayed amorphous and irregular surfaces without conventional etching patterns.

    • Notable deep gap present in one sample indicative of potential damage to underlying enamel layers and dentin.

Conclusions:

  • Er:YAG laser conditioning leads to irregular, less distinct morphological changes versus conventional acid etching.

  • Recommendation to employ caution when using Er:YAG laser to prevent permanent enamel damage.

Keywords:

  • Scanning Electron Microscopy

  • Orthodontics

  • Laser

Received: 10 January 2017

Accepted: 18 April 2017

INTRODUCTION

  • Direct bonding to enamel is critical in orthodontics.

  • Success in bonding correlates with the enamel preparation method; thus, knowledge of enamel characteristics is pivotal.

  • Current standard for enamel conditioning: use of 37% phosphoric acid.

Enamel Surface Changes Post-Acid Etching:

  1. Type 1: Honeycomb appearance; prism core material removed while prism peripheries remain intact.

  2. Type 2: Cobblestone effect; peripheral regions of prisms dissolved, retaining core integrity.

  3. Type 3: Hybrid areas combining both Type 1 and Type 2 characteristics.

Limitations of Acid Etching:

  • Potential removal of superficial enamel.

  • Variability in etching depth.

  • Enamel sensitivity to various contaminants (e.g., water, saliva).

Alternatives to Acid Etching:

  • LASER (Er:YAG) is seen as a less damaging alternative with minimal thermal side effects.

  • Need to evaluate LASER conditioning methods for enamel morphology and bond strength.

Conflicting Literature:

  • Some studies confirm Er:YAG as a suitable alternative to acid etching, while others reject it.

Literature Review:

  • Previous studies (Brauchli et al., Dunn et al., Sawan et al.) have compared laser treatment effects; showing discrepancies in etching efficacy and studies indicating critical subsurface fissuring post-LASER ablation.

MATERIALS AND METHODS

Study Design:

  • In-vitro analysis comparing two conditioning methods: 37% phosphoric acid versus Er:YAG laser.

  • Sample Size: Fourteen freshly extracted premolars, disinfected and stored appropriately.

Sample Preparation:

  • Cleaned sample surfaces and divided into four groups for conditioning based on treatment type:

    • Group 1: Acid-etched both sessions

    • Group 2: Acid-etched first session, Er:YAG second

    • Group 3: Er:YAG first, acid-etched second

    • Group 4: Er:YAG both sessions

  • Conditioning Procedure:

    • Acid etching protocol: 37% phosphoric acid for 15 seconds, followed by rinsing and air-drying.

    • Laser Specifications for Groups 3 and 4:

    • Power: 2W

    • Energy: 200mJ

    • Frequency: 10 Hz

    • Duration: 10 seconds

    • Water Spray: 70%, Air: 90%.

Bonding Procedure:

  • Bonding using premolar brackets with a special primer and adhesive, followed by curing processes.

  • Post-bonding, brackets were debonded; remaining adhesive was removed.

  • Teeth conditioned for secondary analysis with SEM.

  • One tooth from each conditioning group was solely conditioned once to analyze distinct changes in enamel morphology.

SEM Analysis:

  • Analyzed at varying magnification (500x to 10000x) to assess enamel surface changes post-conditioning and rebonding.

RESULTS

Observational Findings:

  • Initial intact enamel surface: Smooth surface with micro-cracks.

  • Acid-Etched Samples:

    • Typical etching patterns evidenced comparable to Type 1.

    • Micro-cracks were minimal and clinically insignificant.

  • Er:YAG Laser Samples:

    • Significant irregularity in structure with no coherent patterns, attributed to micro-explosions from laser energy.

    • Amorphous areas noted in several samples, differing from distinct etching seen in acid-etch samples.

  • Group 4 Sample:

    • Notable deep gap, potentially impacting underlying enamel and dentin layers.

    • Enamel characteristics favored standard acid etching over Er:YAG laser application.

DISCUSSION

Comparative Analysis:

  • Enamel morphology varied between acid-etch and Er:YAG laser conditioned samples.

  • Laser conditioning produced non-homogeneous, amorphous structures without observable etching patterns.

  • Lack of extensive literature on rebonding implications of these conditioning methods.

Findings in Context:

  • Micro-fissures and structural irregularities were observed post-laser application, raising concerns for adhesion quality.

  • Preliminary findings suggest that Er:YAG laser is not an equivalent alternative to acid etching due to damaging morphological changes.

CONCLUSION

  • Enamel conditioned solely with acid etchant exhibited more homogenous characteristics compared to laser-treated samples.

  • Damage induced by laser application during bonding phases can jeopardize rebonded outcomes and shear bond strength.

REFERENCES

  1. Brauchli LM et al.

  2. Silverstone LM et al.

  3. Bader C et al.

  4. Attrill DC et al.

  5. Lee BS et al.

  6. Basaran G et al.

  7. Walsh LJ et al.

  8. Ozer T et al.

  9. Türköz C et al.

  10. Von Fraunhofer JA et al.

  11. Üşümez S et al.

  12. Roberts-Harry DP.

  13. Martínez-Insua A et al.

  14. Dunn WJ et al.

  15. Sawan MN et al.

  16. Keller U et al.

  17. Hess JA.

  18. Sasaki LH et al.