Ibn Sina University

Behavior of human periodontal ligament cells on dentin surfaces ablated with an ultra-short pulsed laser

Abstract

This study aimed to evaluate the effects of an ultrashort pulsed laser (USPL) (1064 nm, 20 ps, 100 kHz) with different laser fluences (F, 4, 6, 8 J/cm2) and pulse overlaps (PO, 0, 50%) on human periodontal ligament cells (hPDLs) behavior. Dentin samples were ablated with USPL with different combinations of fluences and pulse overlaps; some samples were ablated with an Er:YAG laser (2940 nm, 150 µs, 100 mJ/pulse, 5 J/cm2) and some samples were ground with a carbide bur. Then hPDLs were grown on the samples after different treatments. Dentin morphology and cell adhesion were observed with SEM and gene expressions were measured by RT-PCR. The results showed dentin surfaces ablated with USPL when F = 4 J/cm2, PO = 0, and F = 6 J/cm2, PO = 0 were partially intact with obvious ridges and valleys and cells on these surfaces grew mostly along the valleys. USPL ablated surfaces in other groups were entirely ablated and cell cluster formation was observed. The RT-PCR results showed an upregulation of osteocalcin of cells grown on the dentin after some laser treatment. It can be concluded that USPL could improve the attachment and differentiation of hPDLs and thus potentially promote periodontal tissue regeneration.

Introduction

Apicoectomy is an endodontic surgical procedure which is usually performed when a conventional root canal therapy has failed and a retreatment was already unsuccessful or is not advised1. The most traditional way to remove the root-end in clinic is the use of burs, and the root surface after different types of burs may have various patterns on the resected root surface2. The most important goal of apicoectomy is to produce a resected root-end with optimal conditions for subsequent regeneration of the periodontal ligament (PDL) across the resected root-end3. Different root surfaces may have different effects on the cell behavior like attachment and orientation4. Previous studies have shown that cell behavior is significantly influenced by the surface properties, including surface roughness and morphology5,6. After apicoectomy, cells in adjacent tissue become activated; they proliferate, migrate to the wounded area and produce growth factors and new matrix components3, which lead to bone generation, cementum deposition and PDL tissue formation7.

In last years, lasers were widely used for different dental treatments8,9,10,11,12,13,14,15,16,17,18, including root end resection19,20. This technique shows some advantages compared to traditional grinding tools like low level of discomfort and vibration21. Using the Er:YAG laser for apicoectomy has shown promising results22. In 1990s, the USPL drew the attention of researchers because its superior results for ablating dental hard tissues compared to both traditional grinding instruments and long-pulse laser systems23. The USPL removed tissue at lower energy levels, exhibited precise ablation depth and minimal thermal damages, low level of pain and reduced noise. These advantages owe to a special plasma-mediated ablation mechanism24,25,26. Previous studies show that ablating dental hard tissues using an USPL with appropriate parameters results in low levels of carbonization, melting, resolidification and microcracks, and the dentinal tubules remain mostly open. Moreover, the boundaries of the ablation cavities are clear and fine defined, the walls are steep and smooth, the non-irradiated areas exhibit no heat effects, and the original morphology is unchanged25,27,28,29.

Regarding the outstanding dental hard tissue ablation capability of USPL, it is interesting to apply this laser also in apicoectomy. However, the resected root surfaces after treatment with burs, Er:YAG laser and USPL may have different effects on cell behavior. Therefore, the present in vitro study investigated the behavior of primary human periodontal ligament cells on USPL ablated dentin surfaces.

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