Stimulatory effect of laser irradiation on calcified nodule formation in human dental pulp fibroblasts

The application of lasers in vital pulp therapy: a review of histological effects

Vital pulp therapy (VPT) is primarily intended to preserve the vitality of pulp tissues, which have been exposed for any reason. Various materials and techniques have been proposed to improve treatment outcomes, including the use of lasers. This study aimed to review the histological results of different dental lasers including low-level lasers, carbon dioxide (CO2), erbium-doped yttrium aluminum garnet laser (Er:YAG), neodymium-doped yttrium aluminum garnet (Nd:YAG), erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers, and diode lasers for VPT. This focused review included a comprehensive electronic search of Scopus, MEDLINE, Web of Science, and Google Scholar databases from 2000 to 2022 by two independent investigators. Different combinations of keywords were used, and reference mining of related papers was done. The review included studies related to histologic evaluation of laser-assisted vital pulp therapy that stated the laser parameters that were used. Articles with radiographic or clinical assessments or articles lacking necessary data were excluded. Non-English articles were excluded unless their abstract was in English and encompassed the necessary data. Most studies indicated the efficacy of lasers for reduction of inflammation, acceleration of healing, and increasing the thickness of dentinal bridge. According to the evidence, lasers used in combination with pulp capping agents are beneficial to enhance the success rate of VPT.

Photobiomodulation Therapy and Pulp-Regenerative Endodontics: A Narrative Review

Regenerative endodontic procedures (REPs) were used to recover the dental pulp’s vitality in order to avoid the undesirable outcomes of conventional endodontic treatment and to promote dentinal formation, especially for immature permanent teeth. Photobiomodulation therapy (PBMT) exhibits photobiological and photochemical effects for improving the root canal’s environmental conditions by compensating for oxidative stress and increasing the blood supply to implanted stem cells and improving their survival. Basic research has revealed that PBMT can modulate human dental pulp stem cells’ (hDPSCs) differentiation, proliferation, and activity, and subsequent tissue activation. However, many unclear points still remain regarding the mechanisms of action induced by PBMT in REPs. Therefore, in this review, we present the applications of laser and PBMT irradiation to the procedures of REPs and in endodontics. In addition, the effects of PBMT on the regenerative processes of hDPSCs are reviewed from biochemical and cytological perspectives on the basis of the available literature. Furthermore, we consider the feasibility of treatment in which PBMT irradiation is applied to stem cells, including dental pulp stem cells, and we discuss research that has reported on its effect.

Efficacy of Mineral Trioxide Aggregate and Photobiomodulation on Pulp Capping of Dogs’ Teeth

AIM: The present study assessed the effect of mineral trioxide aggregate (MTA) and photobiomodulation (PBM) on pulp capping of exposed pulp of dogs’ teeth. METHODS: Forty-eight teeth in three mongrel dogs were randomly divided into two major study groups; Group I where MTA was used as a pulp capping agent and Group II in which both MTA+PBM were used. The groups were equally subdivided according to the observation period following completion of pulp capping into Subgroup (A) 1 week, Subgroup (B) 2, and Subgroup (C) 16 weeks. The teeth were examined for histological inflammatory response as well as dentine bridge formation. RESULTS: With regard to inflammatory response at 1 week significantly, less intense inflammation was observed in MTA+PBM (Group II) compared to the MTA (Group I) for the same time period with no significant difference for between Group I and Group II for other time intervals. As for dentin bridge formation, PBM+MTA groups showed statistically significant thicker dentine bridge formation at 16 weeks than MTA alone group for the same time period with no significant difference for between Group I and Group II for other time intervals. CONCLUSIONS: Under the conditions of this study, PBM appeared to be a beneficial adjunct in dental pulp capping procedures in which MTA was the pulp capping material.

Does the application of GaAlAs laser and platelet-rich plasma induce cell proliferation and increase alkaline phosphatase activity in human dental pulp stem cells?

Blood extracts containing platelet products are gaining popularity in promoting healing and pulp regeneration. This study was designed to evaluate the effect of platelet-rich plasma (PRP) and gallium-aluminum-arsenide (GaAlAs) laser on proliferation and differentiation of human dental pulp stem cells (hDPSCs). In this ex vivo study, hDPSCs isolated from impacted mandibular third molars were cultured in Dulbecco's Modified Eagle's medium )DMEM(with 10% fetal bovine serum (FBS). After reaching the desired confluence, the cells were distributed into 4 groups, namely, control, PRP, laser, and PRP+laser for MTT assay and alkaline phosphatase (ALP) test. In the PRP and PRP+laser groups, 10% PRP was added to each well on the plate. In the laser and PRP+laser groups, as for the proliferation test, laser irradiation was carried out for 45 s, while 135 s was designated for ALP test. After 1, 3, and 5 days, cell proliferation and ALP activity were assessed using MTT and ALP colorimetric assay, respectively. Two-way ANOVA was utilized to analyze data. In PRP and PRP+laser groups, cell proliferation and viability increased until day 3 but began to decline afterwards until the 5th day. In the laser group, the increase in proliferation and viability was observed till day 5 which was less than the control group. Laser and control groups exhibited significantly higher cell viability and proliferation than both PRP and PRP+laser groups. ALP activity was more pronounced in PRP+laser, PRP, and laser in descending order; however, all were less than that of the control group. Only in the control group did the ALP activity augment during the 5-day period. Laser irradiation could induce pulp cell proliferation and demonstrated a better performance than PRP in this regard.

Wound Healing and Cell Dynamics Including Mesenchymal and Dental Pulp Stem Cells Induced by Photobiomodulation Therapy: An Example of Socket-Preserving Effects after Tooth Extraction in Rats and a Literature Review

High-intensity laser therapy (HILT) and photobiomodulation therapy (PBMT) are two types of laser treatment. According to recent clinical reports, PBMT promotes wound healing after trauma or surgery. In addition, basic research has revealed that cell differentiation, proliferation, and activity and subsequent tissue activation and wound healing can be promoted. However, many points remain unclear regarding the mechanisms for wound healing induced by PBMT. Therefore, in this review, we present an example from our study of HILT and PBMT irradiation of tooth extraction wounds using two types of lasers with different characteristics (diode laser and carbon dioxide laser). Then, the effects of PBMT on the wound healing of bone tissues are reviewed from histological, biochemical, and cytological perspectives on the basis of our own study of the extraction socket as well as studies by other researchers. Furthermore, we consider the feasibility of treatment in which PBMT irradiation is applied to stem cells including dental pulp stem cells, the theme of this Special Issue, and we discuss research that has been reported on its effect.

Combination effects of diode laser and resin-modified tricalcium silicate on direct pulp capping treatment of caries exposures in permanent teeth: a randomized clinical trial

OBJECTIVE

The purpose of this randomized clinical trial was to evaluate efficiency of diode 808-nm (Picasso-AMD, USA) laser using power 1.5 W, continuous wave (CW), fiber diameter of 400 μm, non-initiated and in contact mode, tip angle set at 90°, beam divergence 16°, 2 s per an area with 1-mm diameter, power density 190.98 W/cm², energy density 381.97 J/cm², vertical and horizontal scanning movement on the exposure site, and laser irradiation combined with a resin-based tricalcium silicate material (TheraCal LC, Bisco, USA) in direct pulp capping in caries exposures of permanent teeth over a period of 6 months.

MATERIAL AND METHODS

In this randomized clinical trial, a total of 20 anterior and posterior vital teeth without symptoms and radiographic changes of 14 patients between the age group of 15-35 years, of which randomly 10 teeth were considered, each for TheraCal LC, the exposed area was sealed with TheraCal paste and TheraCal combined with diode laser; the treated area was sealed with TheraCal paste after diode 808-nm laser irradiation. At the 1-, 3-, and 6-month recall examinations, the loss of vitality, spontaneous pain, reactions to thermal stimuli and percussion, and radiographic changes were considered failure. The samples were randomly divided using runs test. Measurements on the digitized radiograph were performed at the recalls. The data were analyzed by repeated measurements ANOVA using SPSS 25.

RESULTS

Analysis had indicated that at the end of follow-ups, a statistically significant increase in dentin thickness with both groups (p value < 0.001) was found. Clinically, diode laser group has shown better results (p value < 0.001); however, radiographically, no significant difference was observed between groups (p value = 0.56). In both groups, the highest thickness of dentin formed was at the first month; 0.40 mm ± 0.19 mm (p value < 0.001).

CONCLUSION

Diode laser 808 nm under proper parameters combined with TheraCal LC can be recommended for direct pulp therapy in caries exposure of permanent teeth.

CLINICAL TRIAL REGISTRATION

This research was approved by Esfahan Medical University, Dental School, Azad Branch (KHUISF)) Esfahan, Iran [IR.IAU.KHUISF.REC.1397.261].

Combined effects of calcium hydroxide and photobiomodulation therapy on apexogenesis of immature permanent teeth in dogs

Treatment of high-risk traumatic immature teeth due to incomplete root development is challenging. Apexogenesis is currently the ideal treatment option that allows normal root development. The purpose of this study was to evaluate the apexogenesis process of immature permanent teeth of dogs when co-administered with calcium hydroxide and photobiomodulation therapy (PBMT). A total of 36 immature permanent anterior and premolar teeth were selected from three 4-6-month-old dogs of Iranian mixed generation. The teeth were categorized into two groups, calcium hydroxide with laser irradiation (CHL) and calcium hydroxide without laser irradiation (CH). All the selected teeth received calcium hydroxide pulpotomy. After restoring teeth with amalgam, the CHL group received gallium‑aluminum-arsenide (GaAlAs) diode laser (810 nm, 4.2 J/cm², 0.3 W, 9 s,CW) on apical one-third of both buccal and lingual roots. The irradiation was repeated every 48 h for fourteen days. Intravenous tetracycline was used to observe newly formed dentin in the first, third, seventh, and fourteenth days. The distance between tetracycline lines (DTL) was examined by Fluorescence microscopy. Generalized estimating equations (GEE) were used for data analysis. In all assessments, the mean DTL were greater in the CHL group. However, the two groups had no significant differences in the amount of deposited dentin between the first and third, third and seventh, and first and seventh lines. Meanwhile, there was a significant difference between the two groups in terms of the distances between lines 7 and 14, 1 and 14 and also 3 to 14 (P < .001). In other words, from the 7th day onwards, there was a significant difference between the two groups. Within the limitation of this study, the combination therapy of PBMT and pulpotomy with calcium hydroxide accelerated apexogenesis in immature permanent dogs' teeth.

Histopathological findings of an exposed human pulp carbonised by CO2 laser irradiation: A case report

This report shows the healing process of an exposed pulp carbonised by CO₂ laser irradiation prior to the application of a capping material. Six intact teeth from four volunteers were irradiated by CO₂ laser and randomly capped with either an adhesive resin (SE bond) (n = 3) or calcium hydroxide-based cement (Dycal) (n = 3). The laser was operated in super-pulsed mode (power output, 0.5 W) for an irradiation time of 30 s. All cavities were restored with composite resin. Each tooth was extracted at approximately 30, 50 or 260 days post treatment and prepared for histological evaluation. CO₂ laser irradiation controlled exudate and bleeding from each exposed pulp. Histological images revealed Dycal promoted complete dentine bridge formation at the carbonised pulp surface, and laser energy affected not only the pulp surface but also the deeper part of the pulp chamber.

Clinical and radiographic evaluation of diode laser pulpotomy on human primary teeth

Background and aims

The aim of this investigation was to evaluate clinical and radiographic effects of diode laser pulpotomy on young human primary molars.

Materials and methods

This double-blind, split-mouth randomized clinical trial was conducted on 14 children, aged 3-9 years. In total, 20 pairs of teeth were selected from those with pulpal exposure due to caries. Case selection was conducted based on clinical and radiographic criteria with similar teeth in each patient. One tooth was randomly assigned to diode laser pulpotomy as case and the other tooth was pulp-treated using formocresol as control. Diode laser at a 10-W power was applied on the remaining pulp tissue following coronal pulp amputation in the case group, while a cotton pellet with diluted formocresol was placed over the amputated pulp in the control group. Reinforced zinc oxide-eugenol paste was then placed over the pulp stump and the tooth was restored with stainless steel crown. A 6- and 12-month followed-up was conducted clinically and radiographically in order to assess the success rates. Data were analyzed with Fisher's exact test.

Results

Clinical failure rate was almost zero when the cases were followed and examined clinically (100% success), with 95% and 90% of the cases in the case group (diode laser) being judged as successful in radiographic examination after 6 and 12 months, respectively. Cases in the control group (formocresol) had almost the same clinical success rate (100%) with no failure judged by radiographic evaluation at 6 and 12 months. These results did not show any significant differences when analyzed using Fisher's exact test (P > 0.05).

Conclusion

There was no significant difference between diode laser pulpotomy and formocresol pulpotomy of human primary teeth after 6 and 12 months. Only a fraction of cases (5%) had radiographic problems at their follow-up in the laser group.

Effect of concentrated growth factor on osteoblast cell response

OBJECTIVE

The purpose of this study was to assess the effect of concentrated growth factor (CGF) on osteoblast cell proliferation and differentiation.

METHODS

SaOS-2 osteoblast-like cells were cultured on titanium discs. The disc surfaces in the test group were treated with CGF serum, and those in the control group were left untreated. Cell counts, cell proliferation, and osteocalcin (OCN) levels were evaluated on days 1 and 3, and the alkaline phosphatase (ALP) activity was assessed on days 3, 7, and 14.

RESULTS

The proliferation values were significantly higher in the test group than in the control on days 1 and 3 (P<0.05). ALP activities increased gradually in both groups from day 3 to day 14, but the ALP values were significantly higher in the test group than in the control in all periods (P<0.05). The OCN level on day 1 was significantly higher (P<0.05) in the test group, and no statistically significant difference was found between the two groups on day 3 (P<0.05). A significant decrease was observed in OCN activity on day3 in comparison with day 1 in the control group (P<0.05).

DISCUSSION

The results suggest that CGF can efficiently stimulate the proliferation and differentiation of osteoblast cells, thereby improving the healing process around implants.

Effect of adhesive system application for cavities prepared with erbium, chromium: yttrium scandium gallium garnet laser on rat dental pulp tissue

We examined the effects of adhesive systems under study applied for a laser-cut cavity using an Er,Cr:YSGG laser on rat dental pulp at 24 h and 14 days postoperatively. Group 1, laser-cut cavities were treated with a self-etching-primer and bonding agent; group 2, pretreated with a phosphoric-acid, and then treated with a self-etching-primer and bonding agent; group 3, pretreated with a phosphoric-acid and sodium-hypochlorite, and then treated with a self-etching-primer and bonding agent; and group 4, treated with an all-in-one adhesive. A flowable resin composite was used as filling material for each cavity treated with each group. A glass-ionomer-cement was used as a control. The following items were evaluated: pulp-tissue-disorganization (PTD), inflammatory-cell-infiltration (ICI), tertiary-dentin-formation (TDF), and bacterial-penetration (BP). The results were statistically analyzed using the Kruskal-Wallis test and Mann-Whitney U test. No significant differences were observed among the experimental groups for all parameters after 24 h and 14 days (P > 0.05). The majority of the specimens showed PTD with edema formation after 24 h; however, all the specimens demonstrated pulpal healing with TDF after 14 days. On the parameter of TDF, all groups showed significant differences between the two postoperative periods (P < 0.01). On the parameter of ICI, a significant difference was found between the two postoperative periods in group 4 (P < 0.05). No specimens showed BP. The pretreatment on the cavity prepared with the laser using phosphoric-acid or sodium-hypochlorite did not affect the dental pulp healing of rat tooth.

[The application of stem cells, visible and infrared light in regenerative medicine. Part 1]

OBJECTIVE

The present article was designed to overview the experimental studies of visible and infrared light irradiation of human and animal stem cells (SC) in vitro and in vivo for the evaluation of its photobiomodulatory effects. The results will be used to elaborate substantiation for the choice of the parameters of SC light irradiation and to develop recommendations for the application of this method in regenerative medicine (RM).

BACKGROUND

The clinical application of light irradiation is a matter of contrsy, in the first place due to the difficulties encountered in the rational choice of irradiation parameters. The theoretical substantiation of such choice remains a stumbling block too despite the long history of photoghromotherapy. There is thus far no reliable theoretical basis for the adequate choice of such irradiation parameters as power density, radiation dose, and exposure time. The experiences with the light application for the purpose of regenerative medicine have never been summarized.

RESULTS

The present review encompasses 78 articles selected for the basic analysis that report the studies with the use of a variety of SC types. The analysis has demonstrated that clinical investigations into the influence of light on the stem cells are still in their infancy. It was shown that the irradiation parameters need to be chosen taking into consideration the type of the stem cells. Different authors report the achievement of the maximum SC proliferation and differentiation rates at energy densities as high as 50 mW/sq.cm, small radiation doses (around 1 J/sq.cm) and exposure time (on the order of seconds).

CONCLUSION

The general conclusion for Parts 1 and II of this communication will be presented in the next issue of this journal (number 2, 2015).

Photomodulation of proliferation and differentiation of stem cells by the visible and infrared light

OBJECTIVE

The aim of this article is to review experimental studies of visible and infrared light irradiation of human and animal stem cells (SCs) in vitro and in vivo to assess photobiomodulation effects on their proliferation and differentiation.

BACKGROUND DATA

The clinical application of light irradiation remains controversial, primarily because of the complexity of the rational choice of irradiation parameters. In laboratories, the theoretical justification underlying the choice of irradiation parameters also remains a challenge.

METHODS

A systematic review was completed of original research articles that investigated the effects of light irradiation on human and animal SCs in vitro and in vivo (to June 2014). Relevant articles were sourced from PubMed and MEDLINE(®). The search terms were laser (light) therapy (irradiation), stem cells, and phototherapy, stem cells.

RESULTS

The analysis revealed the importance of cell type when choosing the cell irradiation parameters. The influence of wavelength on the SC proliferation rate seemed to be nonsignificant. The high values of increased proliferation or differentiation were obtained using high power density, low energy density, and short exposure time. SC exposure to light without inducers did not lead to their differentiation. The maximum differentiation was achieved using irradiation parameters different from the ones needed to achieve the maximum proliferation of the same cells.

CONCLUSIONS

Increased power density and reduced energy density were needed to increase the SC response. Based on the analysis, we have presented a graph of the cell response to generalized photostimulus, and introduced the concepts of "photostress" and "photoshock" to describe the stages of this response.

GaAlAs laser irradiation induces active tertiary dentin formation after pulpal apoptosis and cell proliferation in rat molars

INTRODUCTION

This study aimed to clarify pulpal responses to gallium-aluminum-arsenide (GaAlAs) laser irradiation.

METHODS

Maxillary first molars of 8-week-old rats were irradiated at an output power of 0.5 or 1.5 W for 180 seconds, and the samples were collected at intervals of 0 to 14 days. The demineralized paraffin sections were processed for immunohistochemistry for heat-shock protein (HSP)-25 and nestin in addition to cell proliferation assay using bromodeoxyuridine (BrdU) labeling and apoptosis assay using deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL).

RESULTS

Intense HSP-25 and nestin immunoreactivities in the odontoblast layer were weakened immediately after 0.5-W irradiation and recovered on day 1, resulting in slight tertiary dentin formation by day 14. On the contrary, 1.5-W irradiation immediately induced the loss of HSP-25 and nestin-immunoreactivities in the odontoblast layer. On day 1, numerous TUNEL-positive cells appeared in a degenerative zone that was surrounded by intense HSP-25 immunoreactivity. BrdU-positive cells occurred within the intensely HSP-25-immunopositive areas during days 2 through 5, whereas TUNEL-positive cells gradually decreased in number by day 5. HSP-25- and nestin-positive odontoblast-like cells were arranged along the pulp-dentin border by day 7, resulting in remarkable tertiary dentin formation on day 14.

CONCLUSIONS

The output energy determined pulpal healing patterns after GaAlAs laser irradiation; the higher energy induced the apoptosis in the affected dental pulp including odontoblasts followed by active cell proliferation in the intense HSP-25-immunoreactive areas surrounding the degenerative tissue, resulting in abundant tertiary dentin formation. Thus, the optimal GaAlAs laser irradiation elicited intentional tertiary dentin formation in the dental pulp.

Stimulatory Effects of CO(2) Laser, Er:YAG Laser and Ga-Al-As Laser on Exposed Dentinal Tubule Orifices

We investigated the effects of lasers irradiation on the exposed dentinal tubule. Human tooth specimens with exposed dentinal tubule orifices were used. Three types of lasers (CO₂ laser, Er:YAG laser and Ga-Al-As laser) were employed. The parameters were 1.0 W in continuous-wave mode with an irradiation time of 30 s for the CO₂ laser, 30 mJ in continuous-wave mode with an irradiation time of 60 s for the Er:YAG laser, and 1.0 W in continuous-wave mode with an irradiation time of 60 s for the Ga-Al-As laser. A non-irradiated group was used as a control. After laser irradiation, the dentinal surface of each sample was observed using SEM. Afterwards, all samples were immersed in methylene blue dye solution in order to evaluate the penetration of the dye solution and observe the change in dentinal permeability after laser irradiation. SEM observation showed that the control group had numerous exposed dentinal tubule orifices, whereas these orifices were closed in the laser-irradiated groups. There was consistent dye penetration into the pulp chamber in the control group, whereas no dye penetration was evident in the laser-irradiated groups. Therefore, laser appears to be a promising treatment for reducing permeation through exposed dentinal tubules.

Effect of CO₂ laser irradiation on wound healing of exposed rat pulp

This study examined the effects of direct pulp capping treatment using super-pulsed CO₂ laser preirradiation on the wound healing process of exposed rat pulp on days 1, 3, 7, 14, and 28 postoperatively. Group 1 was irradiated with a CO₂ laser and directly capped with a self-etching adhesive system. The laser was operated in super-pulse mode (pulse duration, 200 μs; interval, 5800 μs; 0.003 J/pulse). The irradiation conditions were a power output of 0.5 W, an irradiation time of 3 s, and repeat mode (10 ms of irradiation at 10-ms intervals for a total beam exposure time of 1.5 s), defocused beam diameter of 0.74 mm (approximately 20 mm from the exposed pulp surface), energy density of 0.698 J/cm² per pulse, total applied energy of 0.75 J, and an activated air-cooling system. Group 2 was capped with the self-etching adhesive system. Group 3 was capped with commercially available calcium hydroxide, and the self-etching adhesive system was applied to the cavity. The following parameters were evaluated: pulp tissue disorganization, inflammatory cell infiltration, reparative dentin formation, and bacterial penetration. The results were statistically analyzed using the Kruskal-Wallis test for differences among the groups at each observation period (P < 0.05). There were no significant differences among the experimental groups in any parameters at any postoperative period (P > 0.05). CO₂ laser irradiation was effective in arresting hemorrhaging but showed a tendency to delay reparative dentin formation compared with the application of calcium hydroxide.

Carbon dioxide laser irradiation stimulates mineralization in rat dental pulp cells

AIM

To examine the effect of carbon dioxide laser irradiation on mineralization in dental pulp cells.

METHODOLOGY

Rat dental pulp cells were irradiated with a carbon dioxide laser at 2 W output power for 20, 40 and 60 s, and were cultured in ascorbic acid and beta-glycerophosphate containing media. Cell viability was examined 24 h after laser irradiation by a modified MTT assay. Alizarin Red S staining was performed 10 days after laser irradiation. The amounts of secreted collagen from the cells after irradiation were quantified following Sirius Red staining. The expression levels of collagen type I and HSP47, collagen-binding stress protein, were analysed by real-time PCR. HSP47 protein expression was examined by Western blotting. Statistical analysis was performed using one-way analysis of variance (anova) followed by the Tukey's multiple comparison test.

RESULTS

The cell viability was not affected by laser irradiation at 2 W for up to 40 s. However, it was significantly decreased by 20% at 60 s (P < 0.05). The amount of mineralization after 10 days of irradiation at 2 W for 40 s was significantly increased in comparison to the other conditions (P < 0.05). The extracellular collagen production was significantly increased by 73% on day 2 and 38% on day 4 after laser irradiation (P < 0.05). Although collagen type I gene expression was not changed by laser irradiation, HSP47 gene and protein expression was induced within 12 and 24 h, respectively.

CONCLUSIONS

These results suggested that carbon dioxide laser irradiation stimulated mineralization in dental pulp cells. The laser irradiation also increased HSP47 expression but not collagen gene expression.

Stimulatory Effects of Hydroxyl Radical Generation by Ga-Al-As Laser Irradiation on Mineralization Ability of Human Dental Pulp Cells

The present study was conducted to investigate the effects of Ga-Al-As laser irradiation on the mineralization ability of human dental pulp (HDP) cells. HDP cells in vitro were irradiated once with a Ga-AL-As laser at 0.5 W for 500 s and at 1.0 W for 500 s in order to investigate free radicals as one mechanism for transmission of laser photochemical energy to cells. Production of the hydroxyl radical (*OH) was measured using the ESR spin-trapping method and was found to be increased by laser irradiation. The DMPO-OH was not detected in the presence of dimethyl sulfoxide (DMSO), a *OH scavenger. The formation of calcification nodule was also investigated by von Kossa staining. The number of calcified nodules was increased by 1.0 W-laser irradiation. Alkaline phosphatase (ALP) activity was higher in the 1.0 W-laser irradiation group. Expression of mRNAs for heat shock protein 27, bone morphogenetic proteins (BMPs) and ALP were greater in the 1.0 W-laser irradiation group. Expression of BMPs in the conditioned medium was also higher in the 1.0 W-laser irradiation group. In particular, DMSO decreased the number of calcified nodule produced by 1.0 W-laser irradiation. These results supposed that the mineralization of HDP cells is stimulated by laser irradiation, and that *OH generated by laser irradiation is a trigger for promotion of HDP cell mineralization.

Effect of GaAIAs laser on reactional dentinogenesis induction in human teeth

OBJECTIVE

This study investigated the biomodulatory effect of the gallium- aluminum-arsenate laser (GaAlAs) in pulp cells on reactional dentinogenesis, and on the expression of collagen type III (Col III), tenascin (TN), and fibronectin (FN) in irradiated dental tissues and controls (not irradiated).

BACKGROUND DATA

Several studies suggest a biomodulatory influence of low-intensity laser radiation in the inflammatory and reparative processes of biological tissues.

METHODS

Sixteen human premolar teeth were selected (after extraction due to orthodontal reasons) and divided into irradiated and control groups. Black class V cavity preparations were accomplished in both groups. For the irradiated group, GaAlAs laser (670 nm, 50 mW) with an energy density of 4 J/cm2 was used. Soon after, the cavities were restored with a glass ionomer and the extractions made after 14 and 42 days.

RESULTS

Histological changes were observed by light microscopy; less intense inflammatory reaction in the irradiated group was found when compared to the controls. Only the irradiated group of 42 days exhibited an area associated with reactional dentinogenesis. After immunohistochemical analysis by the streptoavidin-biotin complex (SABC) method, the expression of Col III, TN, and FN was greater in the irradiated groups.

CONCLUSION

Our results suggest that a GaAlAs laser with energy density of 4 J/cm2 and wavelength of 670 nm caused biomodulation in pulp cells and expression of collagen, but not collagen of the extracellular matrix, after preparation of a cavity.

Long-term effect of pulsed Nd:YAG laser irradiation on cultured human periodontal fibroblasts

BACKGROUND AND OBJECTIVES

The purpose of this study was to investigate the long-term effect of Nd:YAG laser irradiation on cultured human periodontal fibroblasts (hPF).

STUDY DESIGN/MATERIALS AND METHODS

The cultured hPF were irradiated by pulsed Nd:YAG laser. The power delivery was 50 mJ x 10 pps (pulse per second) with irradiation duration 60, 120, 180, or 240 seconds. The viability and collagen content of laser-irradiated hPF were assessed on day 5 after laser treatment. Light microscope and transmission electron microscope (TEM) were used to observe cytomorphological change. The irradiated hPF cultured in mineralizing medium for 28 days were examined by alizarin red S and Von Kossa stain.

RESULTS

The cellular viability and collagen content of hPF decreased after Nd:YAG laser irradiation. Cell damage was noted with retraction of cellular processes, loss of normal architecture, and lysis of some cells. However, survived hPF proliferated and migrated to the cell-debris-associated deposits. The electron-dense cytoplasm and amorphous organelles in laser-damaged cells was revealed by TEM. In vitro mineralization was demonstrated in the long-term laser-irradiated hPF cultured in mineralizing medium.

CONCLUSION

Nd:YAG laser irradiation induced partial loss of cellular viability and collagen content. The co-existence of viable cells and progressive degeneration of laser-damaged cells was associated with the in vitro mineralization of hPF.

Proliferation of dental pulp fibroblasts in response to thrombin involves mitogen-activated protein kinase signalling

AIM

To examine the involvement of mitogen-activated protein kinases (MAPK) signalling on thrombin-stimulated human dental pulp fibroblasts (DPF).

METHODOLOGY

Dental pulp fibroblasts were isolated from dental pulp connective tissue of third molars and expanded in vitro. Expression of thrombin receptors was analysed by RT-PCR, and cell proliferation was measured by 3[H]-thymidine incorporation assay. Phosphorylation levels of MAPK were determined by Western blot analysis, and alkaline phosphatase activity was measured to serve as a marker for odontogenic differentiation. Statistical analysis was performed by Student's t-test.

RESULTS

Dental pulp fibroblasts express the thrombin receptors protease-activated receptor-1 (PAR-1), PAR-3 and PAR-4. Measurement of 3[H]-thymidine incorporation revealed a dose-dependent increase of DNA synthesis in response to thrombin treatment. The thrombin-induced mitogenic activity was decreased by the extracellular signal-regulated protein kinase (ERK) signalling inhibitor PD98059 (P < 0.05), and by SB203580 (P < 0.05), a p38 MAPK inhibitor. Western blot analysis demonstrated increased phosphorylation of ERK in DPF following stimulation with thrombin, while p38 MAPK and c-Jun NH2-terminal kinase (JNK) were not activated. Alkaline phosphatase activity of DPF remained unchanged upon incubation with thrombin.

CONCLUSIONS

These results suggest that signalling via MAPK mediates the mitogenic activity of thrombin on DPF and may thus play a role during the early stages of pulp repair.

A histochemical study of the regeneration process after injury by pulsed Nd:YAG laser irradiation of root canals

Histological changes of rat dental pulp cells were followed after injury. The regeneration process after 3, 6 and 10 days was monitored. Mandibular incisors were irradiated with a pulsed Nd:YAG laser at 2 W and 20 pulses per sec (pps) for 5 sec and the pulp was examined histologically and immunohistochemically for TGF-beta1. Eruption of the developing tooth was disturbed for a short period only. Rapid formation of osteodentin was observed. After 3 days, a zone of fibrodentin matrix as well as newly formed vessels were found. Afterwards, regenerative dentin formation was observed accompanied by the formation of a layer of odontoblast-like cells in the damaged area. Immunohistochemical staining of TGF-beta1 showed that positivity was present in small tissue areas beneath the mantle dentin, the zone of fibrodentin matrix and odontoblast-like cells. These results indicate that pulsed Nd:YAG laser irradiation of rat incisor pulp induces formation of osteodentin, and TGF-beta1 plays a role during regeneration.

Immunohistochemical study on pulpal response in rat molars after cavity preparation by Er:YAG laser

While Er:YAG laser systems are in extensive use for caries removal and cavity preparation, the effects of such treatment on pulp tissue remain unclear. This study evaluates these systems using immunohistochemical methods and compares the results with information gained from treatment using conventional burs. Cervical cavities were prepared in the upper first molars of rats, using either an Er:YAG laser or a conventional tungsten-carbide bur. At intervals of 5 min, 6 h, 12 h, 1 d, 3 d and 7 d after cavity preparation, the teeth were processed for immunohistochemical analyses of tissue non-specific alkaline phosphatase, OX6-positive major histocompatibility complex class II antigen-expressing cells and PGP 9.5-immunoreactive nerve fibers. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Tissue non-specific alkaline phosphatase was observed mainly in the subodontoblastic layer under the cavity lesion, from 5 min, in both groups. The immunoreactivity was more pronounced in the laser group, but by 7 d no significant differences were recognizable. At 12 h, TUNEL-positive cells were detected around the odontoblastic layer in both groups. From 3 d to 7 d, a limited number of positive cells were still visible in the group that underwent standard treatment. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5-immunoreactive nerve fibers were also noted. From 12 h to 1 d, OX6-positive cells accumulated along the pulp-dentin border, extending their processes into the dentinal tubules. Numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer at 7 d. These results demonstrated that there was no appreciable difference in the manner in which pulp tissue responded to treatment with either Er:YAG laser or a conventional drill. This would seem to indicate the usefulness of the Er:YAG laser system in the removal of caries and cavity preparation.