The effect of continuous long-term illumination with visible light in different spectral ranges on mammalian cells

One of the biggest challenges in tissue engineering and regenerative medicine is to ensure oxygen supply of cells in the (temporary) absence of vasculature. With the vision to exploit photosynthetic oxygen production by microalgae, co-cultivated in close vicinity to oxygen-consuming mammalian cells, we are searching for culture conditions that are compatible for both sides. Herein, we investigated the impact of long-term illumination on mammalian cells which is essential to enable photosynthesis by microalgae: four different cell types-primary human fibroblasts, dental pulp stem cells, and osteoblasts as well as the murine beta-cell line INS-1-were continuously exposed to warm white light, red or blue light over seven days. We observed that illumination with red light has no adverse effects on viability, metabolic activity and growth of the cells whereas exposure to white light has deleterious effects that can be attributed to its blue light portion. Quantification of intracellular glutathione did not reveal a clear correlation of this effect with an enhanced production of reactive oxygen species. Finally, our data indicate that the cytotoxic effect of short-wavelength light is predominantly a direct effect of cell illumination; photo-induced changes in the cell culture media play only a minor role.

Effect of Low-Level Diode Laser and Red Light-Emitting Diode on Survival and Osteogenic/Odontogenic Differentiation of Human Dental Pulp Stem Cells

Background: This investigation set out to compare the impacts of low-level diode laser (LLDL) and red light-emitting diode (LED) on the survival of human dental pulp stem cells (hDPSCs) and osteogenic/odontogenic differentiation. Methods and materials: In this ex vivo experimental study, the experimental groups underwent the irradiation of LLDL (4 J/cm2 energy density) and red LED in the osteogenic medium. Survival of hDPSCs was assessed after 24 and 48 h (n = 9) using the methyl thiazolyl tetrazolium (MTT) assay. The assessment of osteogenic/odontogenic differentiation was conducted using alizarin red staining (ARS; three repetitions). The investigation of osteogenic and odontogenic gene expression was performed at two time points, specifically 24 and 48 h (n = 12). This analysis was performed utilizing real-time reverse-transcription polymerase chain reaction (RT-PCR). The groups were compared at each time point using SPSS version 24. To analyze the data, the Mann-Whitney U test, analysis of variance, Tukey's test, and t-test were utilized. Results: The MTT assay showed that LLDL significantly decreased the survival of hDPSCs after 48 h, compared with other groups (p < 0.05). The qualitative results of ARS revealed that LLDL and red LED increased the osteogenic differentiation of hDPSCs. LLDL and red LED both upregulated the expression of osteogenic/odontogenic genes, including bone sialoprotein (BSP), alkaline phosphatase (ALP), dentin matrix protein 1 (DMP1), and dentin sialophosphoprotein (DSPP), in hDPSCs. The LLDL group exhibited a higher level of gene upregulation (p < 0.0001). Conclusions: The cell survival of hDPSCs was reduced, despite an increase in osteogenic/odontogenic activity. Clinical relevance: Introduction of noninvasive methods in regenerative endodontic treatments.

Influence of violet LED associated or not with peroxide gel on inflammation, mineralization, and collagen fiber maturation in dentin and pulp tissue

OBJECTIVES

To evaluate the influence of violet LED, associated or not with a 17.5% hydrogen peroxide (HP) bleaching gel, on inflammation, mineralization in pulp tissue, and collagen fiber maturation in dentin and pulp tissue.

MATERIALS AND METHODS

The maxillary molars of eighty Wistar rats were distributed into four groups (n = 10): CONT - without treatment; HP - 30-minute application of 17.5% HP; LED - 20-minute application of violet LED; and HP+LED - application of PH and violet LED. Rats were euthanized and jaws were processed for histologic and immunohistochemical evaluation (IL-17, IL-23, and osteocalcin) and picrosirius red immediately after (T0), and at 7 (T1), 15 (T2), and 30 days (T3) post-treatment, with Wilcoxon, Mann-Whitney, paired T-test, and T-test (α = 0.05).

RESULTS

HP and HP+LED presented necrosis and severe inflammatory infiltrate. When compared to CONT group, LED presented severe osteocalcin (OCN) immunostaining in T2 and less immature fibers in T2 and T3.

CONCLUSION

The violet LED caused no severe damage to the pulp tissue, increased IL-17 and IL-23 expression in T0 when associated with HP, and had no influence on pulp tissue mineralization, besides accelerating the maturation of collagen fibers of dentin.

CLINICAL RELEVANCE

Violet LED therapy induced no inflammation in the pulp tissue of rats and played no role in pulp tissue fibrosis, besides accelerating the maturation of dentin collagen fibers.

Inverse and reciprocal regulation of p53/p21 and Bmi-1 modulates vasculogenic differentiation of dental pulp stem cells

Dental pulp stem cells (DPSC) are capable of differentiating into vascular endothelial cells. Although the capacity of vascular endothelial growth factor (VEGF) to induce endothelial differentiation of stem cells is well established, mechanisms that maintain stemness and prevent vasculogenic differentiation remain unclear. Here, we tested the hypothesis that p53 signaling through p21 and Bmi-1 maintains stemness and inhibits vasculogenic differentiation. To address this hypothesis, we used primary human DPSC from permanent teeth and Stem cells from Human Exfoliated Deciduous (SHED) teeth as models of postnatal mesenchymal stem cells. DPSC seeded in biodegradable scaffolds and transplanted into immunodeficient mice generated mature human blood vessels invested with smooth muscle actin-positive mural cells. Knockdown of p53 was sufficient to induce vasculogenic differentiation of DPSC (without vasculogenic differentiation medium containing VEGF), as shown by increased expression of endothelial markers (VEGFR2, Tie-2, CD31, VE-cadherin), increased capillary sprouting in vitro; and increased DPSC-derived blood vessel density in vivo. Conversely, induction of p53 expression with small molecule inhibitors of the p53-MDM2 binding (MI-773, APG-115) was sufficient to inhibit VEGF-induced vasculogenic differentiation. Considering that p21 is a major downstream effector of p53, we knocked down p21 in DPSC and observed an increase in capillary sprouting that mimicked results observed when p53 was knocked down. Stabilization of ubiquitin activity was sufficient to induce p53 and p21 expression and reduce capillary sprouting. Interestingly, we observed an inverse and reciprocal correlation between p53/p21 and the expression of Bmi-1, a major regulator of stem cell self-renewal. Further, direct inhibition of Bmi-1 with PTC-209 resulted in blockade of capillary-like sprout formation. Collectively, these data demonstrate that p53/p21 functions through Bmi-1 to prevent the vasculogenic differentiation of DPSC.

Effects of diode laser irradiation on dental pulps in rats

OBJECTIVES

To evaluate the effects of different power densities of diode laser on dental pulps in rats.

BACKGROUND

In this study, we used the maxillary central incisors (n=80) of the 40 adult male Wistar albino rats.

METHODS

Rats were randomly divided into four groups according to power densities of diode laser (n=10). Histopathological changes in pulp and height of odontoblast layer were examined . All data were compared statistically using Mann‒Whitney U (Bonferroni) test, p<0.05.

RESULTS

G2 displayed slight histolopathologic alterations such as odontoblast cell disorganization and irregularities in cell extensions. Alterations were more prominent in the G3 than G2. Although the lowest odontoblast layer was measured in the G4, the difference in height of odontoblast layer among the groups was not found to be statistically significant.

CONCLUSION

It was concluded that the use of diode laser caused changes at the cellular level in histological examination and may induce the formation of tertiary dentin by influencing the secretory activity of odontoblasts. As long as used in accordance with the recommended procedure, the diode laser can be safely used in dental hard tissues (Tab. 1, Fig. 4, Ref. 15).

Comparison of in vivo and in vitro models to evaluate pulp temperature rise during exposure to a Polywave® LED light curing unit

OBJECTIVES

To measure and compare in vivo and in vitro pulp temperature (PT) increase (ΔTEMP) over baseline, physiologic temperature using the same intact upper premolars exposed to the same Polywave® LED curing light.

METHODOLOGY

After local Ethics Committee approval (#255,945), local anesthesia, rubber dam isolation, small occlusal preparations/minute pulp exposure (n=15) were performed in teeth requiring extraction for orthodontic reasons. A sterile probe of a temperature measurement system (Temperature Data Acquisition, Physitemp) was placed within the pulp chamber and the buccal surface was sequentially exposed to a LED LCU (Bluephase 20i, Ivoclar Vivadent) using the following exposure modes: 10-s low or high, 5-s Turbo, and 60-s high. Afterwards, the teeth were extracted and K-type thermocouples were placed within the pulp chamber through the original access. The teeth were attached to an assembly simulating the in vivo environment, being similarly exposed while real-time temperature (°C) was recorded. ΔTEMP values and time for temperature to reach maximum (ΔTIME) were subjected to two-way ANOVA and Bonferroni's post-hoc tests (pre-set alpha 0.05).

RESULTS

Higher ΔTEMP was observed in vitro than in vivo. No significant difference in ΔTIME was observed between test conditions. A significant, positive relationship was observed between radiant exposure and ΔTEMP for both conditions (in vivo: r2=0.917; p<0.001; in vitro: r2=0.919; p<0.001).

CONCLUSION

Although the in vitro model overestimated in vivo PT increase, in vitro PT rise was close to in vivo values for clinically relevant exposure modes.

Effects of Er:YAG and Diode Laser Irradiation on Dental Pulp Cells and Tissues

Vital pulp therapy (VPT) is to preserve the nerve and maintain healthy dental pulp tissue. Laser irradiation (LI) is beneficial for VPT. Understanding how LI affects dental pulp cells and tissues is necessary to elucidate the mechanism of reparative dentin and dentin regeneration. Here, we show how Er:YAG-LI and diode-LI modulated cell proliferation, apoptosis, gene expression, protease activation, and mineralization induction in dental pulp cells and tissues using cell culture, immunohistochemical, genetic, and protein analysis techniques. Both LIs promoted proliferation in porcine dental pulp-derived cell lines (PPU-7), although the cell growth rate between the LIs was different. In addition to proliferation, both LIs also caused apoptosis; however, the apoptotic index for Er:YAG-LI was higher than that for diode-LI. The mRNA level of odontoblastic gene markers-two dentin sialophosphoprotein splicing variants and matrix metalloprotease (MMP)20 were enhanced by diode-LI, whereas MMP2 was increased by Er:YAG-LI. Both LIs enhanced alkaline phosphatase activity, suggesting that they may help induce PPU-7 differentiation into odontoblast-like cells. In terms of mineralization induction, the LIs were not significantly different, although their cell reactivity was likely different. Both LIs activated four MMPs in porcine dental pulp tissues. We helped elucidate how reparative dentin is formed during laser treatments.

Effect of Light Activation of Pulp-Capping Materials and Resin Composite on Dentin Deformation and the Pulp Temperature Change

OBJECTIVES

To analyze the effect of pulp-capping materials and resin composite light activation on strain and temperature development in the pulp and on the interfacial integrity at the pulpal floor/pulp-capping materials in large molar class II cavities.

METHODS

Forty extracted molars received large mesio-occlusal-distal (MOD) cavity bur preparation with 1.0 mm of dentin remaining at the pulp floor. Four pulp-capping materials (self-etching adhesive system, Clearfil SE Bond [CLE], Kuraray), two light-curing calcium hydroxide cements (BioCal [BIO], Biodinâmica, and Ultra-Blend Plus [ULT], Ultradent), and a resin-modified glass ionomer cement- (Vitrebond [VIT], 3M ESPE) were applied on the pulpal floor. The cavities were incrementally restored with resin composite (Filtek Z350 XT, 3M ESPE). Thermocouple (n=10) and strain gauge (n=10) were placed inside the pulp chamber in contact with the top of the pulpal floor to detect temperature changes and dentin strain during light curing of the pulp-capping materials and during resin composite restoration. Exotherm was calculated by subtracting postcure from polymerization temperature (n=10). Interface integrity at the pulpal floor was investigated using micro-CT (SkyScan 1272, Bruker). The degree of cure of capping materials was calculated using the Fourier transform infrared and attenuated total reflectance cell. Data were analyzed using one-way analysis of variance followed by the Tukey test (α=0.05).

RESULTS

Pulpal dentin strains (μs) during light curing of CLE were higher than for other pulp-capping materials ( p<0.001). During resin composite light activation, the pulpal dentin strain increased for ULT, VIT, and CLE and decreased for BIO. The pulpal dentin strain was significantly higher during pulp-capping light activation. The temperature inside the pulp chamber increased approximately 3.5°C after light curing the pulp-capping materials and approximately 2.1°C after final restoration. Pulp-capping material type had no influence temperature increase. The micro-CT showed perfect interfacial integrity after restoration for CLE and ULT; however, gaps were found between BIO and pulpal floor in all specimens. BIO had a significantly lower degree of conversion than ULT, VIT, and CLE.

CONCLUSIONS

Light curing of pulp-capping materials caused deformation of pulpal dentin and increased pulpal temperature in large MOD cavities. Shrinkage of the resin composite restoration caused debonding of BIO from the pulpal floor.

Osteogenic differentiation and gene expression of dental pulp stem cells under low-level laser irradiation: a good promise for tissue engineering

The effects of low-level laser therapy (LLLT) has been the focus of recent studies as being assumed responsible for promoting photostimulatory and photobiomodulatory effects in vivo and in vitro, increasing cell metabolism, improving cell regeneration and invoking an anti-inflammatory response. A positive effect of LLLT on the bone proliferation of some cell types has been observed, but little is known about its effect on dental pulp stem cells (DPSCs). Here, we accurately describe the technical procedure to isolate mesenchymal DPSCs, and assay their osteogenic capacity when irradiated with an LLLT source. These preliminary results show that LLLT irradiation influences the in vitro proliferation of DPSCs and increases the expression of essential proteins for bone formation, although it is necessary to carry out further experiments on other cell types and to uniform the methodological designs.

Laser-induced fluorescence in the diagnosis of pulp exposure and the influence of residual dentin thickness: An in vivo study

PURPOSE

To clinically (a) determine whether laser-induced fluorescence (LIF) was able to assess pulp tissue health or disease in situations of pulp exposure; (b) evaluate the influence of different pulp tissue conditions upon LIF through dentin thicknesses of ≤1 mm; and (c) explore possible differences between the diagnostic performance of quantitative (q) and qualitative (ql) LIF.

METHODS

98 healthy subjects were scheduled for the treatment of caries. Three groups were established according to pulp tissue condition: Group A (n=30 teeth) (deep caries with healthy pulp tissue); Group B (n=30 teeth) (pulp necrosis); and Group C (n=30 teeth) (irreversible symptomatic acute pulpitis). The carious lesions were eliminated, and q and ql LIF measurements were made at two levels: measurement in dentin at < 1 mm from the pulp (A-D); and direct pulp exposure measurement (A-LP). In healthy pulp tissue at level A-LP, eight teeth with accidental pulp exposure were used. The Kruskal-Wallis test was used to evaluate the statistical significance of the differences in LIF readings among the three groups. The diagnostic performance of q and ql LIF in application to pulp tissue health or disease was assessed by calculating the sensitivity and specificity of the two tests at level A-LP.

RESULTS

A significant correlation was observed between acute pulpitis and an increase in the q LIF values at level A-D (P= 0.004), but with no correlation to healthy pulp. Quantitative and qualitative LIF may be useful in diagnosing pulp tissue health or disease in situations of pulp exposure (A-LP).

Effects of Diode Laser Debonding of Ceramic Brackets on Enamel Surface and Pulpal Temperature

AIM

Debonding of ceramic brackets due to their high bond strength and low fracture toughness is one of the most challenging complications of orthodontic clinicians. Application of lasers might be effective in the debonding of ceramic brackets as they reduce bond strength of resins and, therefore, can eliminate the risk of enamel damage. However, the thermal effects of laser radiation on dental tissue can cause undesirable results. The aim of this study is to evaluate the enamel surface characteristics and pulpal temperature changes of teeth after debonding of ceramic brackets with or without laser light.

MATERIALS AND METHODS

Thirty polycrystalline brackets were bonded to 30 intact extracted premolars, and later debonded conventionally or through a diode laser (2.5 W, 980 nm). The laser was applied for 10 seconds with sweeping movement. After debonding, the adhesive remnant index (ARI), the lengths and frequency of enamel cracks were compared among the groups. The increase in intrapulpal temperature was also measured. The collected data were analyzed by Chi-squared test and paired t-test using Statistical Package for Social Sciences (SPSS) software.

RESULTS

There was no case of enamel fracture in none of the groups. Laser debonding caused a significant decrease in the frequency and lengths of enamel cracks, compared to conventional debonding. In laser debonding group, the increase in intrapulpal temperature (1.46°C) was significantly below the benchmark of 5.5°C for all the specimens. No significant difference was observed in ARI scores among the groups.

CONCLUSION

Laser-assisted debonding of ceramic brackets could reduce the risk of enamel damage, without causing thermal damage to the pulp. However, some increases in the length and frequency of enamel cracks should be expected with all debonding methods.

Intrapulpal temperature changes during root surface irradiation with dual-wavelength laser (2780 and 940 nm): in vitro study

This work reports that the ablation volume and rate of porcine skin changed significantly with the change of skin water content. Under the same laser irradiation conditions (532 nm Nd:YAG laser, pulse width = 11.5 ns, pulse energy = 1.54 J, beam radius = 0.54 mm), the ablation volume dropped by a factor of 4 as the skin water content decreased from 40 wt. % (native) to 19 wt. % with a change in the ablation rate below and above around 25 wt. %. Based on the ablation characteristics observed by in situ shadowgraph images and the calculated tissue temperatures, it is considered that an explosive rupture by rapid volumetric vaporization of water is responsible for the ablation of the high water content of skin, whereas thermal disintegration of directly irradiated surface layer is responsible for the low water content of skin.

The local anaesthetic effect of a dental laser prior to cavity preparation: a pilot volunteer study

OBJECTIVES

It has been suggested that laser preconditioning can produce dental anaesthesia. This study aimed to assess the response of the dental pulp to laser preconditioning.

METHODS

The effects of laser preconditioning, sham laser (negative control), and composite curing light (positive control) on the response of the dental pulp to electric pulp testing was investigated in this double-blind crossover trial with six volunteers. The Er,Cr:YSGG laser or curing light was shone on a premolar tooth in a sweeping motion for 30 seconds (in the sham treatment, the laser was not activated) in blindfolded volunteers subjected to a consistent aural stimulus. Treatment method at each visit was randomized and performed by a researcher not involved in pulp testing. Teeth were pulp tested twice initially by another member of the research team to get baseline readings, immediately following the treatment, and thereafter every two minutes for 10 minutes. Results were analyzed using analysis of variance and an independent-sample t-test.

RESULTS

There were no significant differences in pulpal response between treatments (p>0.05).

CONCLUSION

Laser preconditioning did not affect pulpal response as measured by an electronic pulp tester. Laser preconditioning did not result in any pain or noticeable symptoms for both teeth and soft tissues.

LED light attenuation through human dentin: a first step toward pulp photobiomodulation after cavity preparation

PURPOSE

To evaluate the transdentinal light attenuation of LED at three wavelengths through different dentin thicknesses, simulating cavity preparations of different depths.

METHODS

Forty-two dentin discs of three thicknesses (0.2, 0.5 and 1 mm; n = 14) were prepared from the coronal dentin of extracted sound human molars. The discs were illuminated with a LED light at three wavelengths (450+/-10 nm, 630 +/-10 nm and 850 +/-10 nm) to determine light attenuation. Light transmittance was also measured by spectrophotometry.

RESULTS

In terms of minimum (0.2 mm) and maximum (1.0 mm) dentin thicknesses, the percentage of light attenuation varied from 49.3% to 69.9% for blue light, 42.9% to 58.5% for red light and 39.3% to 46.8% for infrared. For transmittance values, an increase was observed for all thicknesses according to greater wavelengths, and the largest variation occurred for the 0.2 mm thickness. All three wavelengths were able to pass through the dentin barrier at different thicknesses. Furthermore, the LED power loss and transmittance showed wide variations, depending on dentin thickness and wavelength.

Short-term effect of low-intensity pulsed ultrasound on an ex-vivo 3-d tooth culture

We investigated the short-term effect of LIPUS on human dentin-pulp complex in vitro. We collected sixty-three premolars from patients who needed the extraction. The premolars were sectioned transversely into 600-μm-thick slices, and then divided into five groups according to LIPUS application time (control, 5, 10, 15 and 20 min). LIPUS transducer produced an incident intensity of 30 mW/cm(2). After 24 h, tissue was harvested for histomorphometrical analysis and RT-PCR (Genes of interest: Collagen I, DMP1, DSPP, TGF β1, RANKL and OPG). Histomorphometric analysis showed no significant difference among the five groups in the odontoblast count and predentin thickness. RT-PCR demonstrated no expression of TGF β1, low amounts of DSPP, a twofold increase in collagen I expression in the 5- and 10-minute LIPUS groups and a threefold increase in DMP1 expression in the 10-minute LIPUS group. LIPUS application was stimulatory to the dentin-pulp complex in vitro and increased the expression of collagen I and DMP1.

Heat generation caused by ablation of dental hard tissues with an ultrashort pulse laser (USPL) system

Heat generation during the removal of dental hard tissues may lead to a temperature increase and cause painful sensations or damage dental tissues. The aim of this study was to assess heat generation in dental hard tissues following laser ablation using an ultrashort pulse laser (USPL) system. A total of 85 specimens of dental hard tissues were used, comprising 45 specimens of human dentine evaluating a thickness of 1, 2, and 3 mm (15 samples each) and 40 specimens of human enamel with a thickness of 1 and 2 mm (20 samples each). Ablation was performed with an Nd:YVO4 laser at 1,064 nm, a pulse duration of 9 ps, and a repetition rate of 500 kHz with an average output power of 6 W. Specimens were irradiated for 0.8 s. Employing a scanner system, rectangular cavities of 1-mm edge length were generated. A temperature sensor was placed at the back of the specimens, recording the temperature during the ablation process. All measurements were made employing a heat-conductive paste without any additional cooling or spray. Heat generation during laser ablation depended on the dental hard tissue (enamel or dentine) and the thickness of the respective tissue (p < 0.05). Highest temperature increase could be observed in the 1-mm thickness group for enamel. Evaluating the 1-mm group for dentine, a significantly lower temperature increase could be measured (p < 0.05) with lowest values in the 3-mm group (p < 0.05). A time delay for temperature increase during the ablation process depending on the material thickness was observed for both hard tissues (p < 0.05). Employing the USPL system to remove dental hard tissues, heat generation has to be considered. Especially during laser ablation next to pulpal tissues, painful sensations and potential thermal injury of pulp tissue might occur.

Effect of CO₂ laser irradiation on hormesis induction in human pulp and periodontal ligament fibroblasts

BACKGROUND

We have recently reported that a low level of CO₂ laser irradiation induced growth stimulation (hormesis) of both human gingival fibroblast (HGF) and oral squamous cell carcinoma cell line (HSC-2), but the extent of hormetic response was much smaller than that previously reported for toxicants and radiation in other experimental systems. Here we investigated the extent of hormetic response induced by CO₂ laser irradiation in human pulp cells (HPCs) and periodontal ligament fibroblast (HPLF).

MATERIALS AND METHODS

HPC and HPLF cells were established from the periodontal tissues of the first premolar extracted tooth. Cells were cultured for 24, 48 or 72 hours after exposure to various irradiation powers, and the viable cell number was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method.

RESULTS

CO₂ laser irradiation induced biphasic effects on the growth of both HPC and HPLF cells. The maximum hormetic response was less than 50%. The hormetic response was found within the energy density of 7.98-79.77 J/cm², and cytotoxicity emerged at powers over 132.96 J/cm². Combining with our previous report, HPCs showed the highest hormetic response, followed by HPLFs and then HGFs. Both HPLFs and HGFs showed similar time-course of hormesis response, increasing response with incubation time.

CONCLUSION

The hormetic response may be the common survival mechanism by which cells escape from radiation-induced injury. Higher hormetic response of HPCs may reflect their potential for differentiation into one of the components in dentin.

Temperature rise during photo-polymerization for onlay luting

PURPOSES

(1) To measure the temperature rise during long-time irradiation needed to lute adhesive indirect restorations, with one halogen and five LED high-power lamps, in a simulated oral environment, and (2) to propose a technique to reduce heat.

METHODS

Temperature within the pulp chamber of an extracted human molar in a 35 degrees C water bath, before and after restoration with a ceramic onlay, was continuously recorded during 3 x 120 seconds of irradiation for different curing regimens, with and without cooling by compressed air, water and water spray. Temperature rise in a thermo-insulated well was also measured during 120 seconds of irradiation with LEDemetron II and TuTu.

RESULTS

Maximal temperature rise of 6.2 degrees C/7.7 degrees C on intact/onlay restored tooth was found after 3 x 120 seconds of irradiation. Compressed air application reduced the temperature by 4 degrees C for LEDemetron II, while water spray increased the temperature by 15.1 degrees C for TuTu. Temperature decreased with irradiation distance, except for LEDemetron II. Air was heated up to 65 degrees C after 120 seconds of irradiation in an insulated well with TuTu.

Laser application in tooth bleaching: an update review

Since the development of laser, a variety of potential applications for lasers in endodontics such as pulp diagnosis, disinfection of the root canal system, canal shaping, obturation of the root canal, apicoectomy, treatment of dentin hypersensitivity, and tooth bleaching have been proposed. The aim of this paper was to review the benefits and drawbacks of laser tooth bleaching.

Effects of intrapulpal temperature change induced by visible light units on the metabolism of odontoblast-like cells

PURPOSE

To investigate the effects of intrapulpal temperature changes induced by a quartz tungsten halogen (QTH) and a light emitting diode (LED) curing units on the metabolism of odontoblast-like cells.

METHODS

Thirty-six 0.5 mm-thick dentin discs obtained from sound human teeth were randomly assigned into three groups: QTH, LED and no light (control). After placement of the dentin discs in pulp chamber devices, a thermistor was attached to the pulpal surface of each disc and the light sources were applied on the occlusal surface. After registering the temperature change, odontoblast-like cells MDPC-23 were seeded on the pulpal side of the discs and the curing lights were again applied. Cell metabolism was evaluated by the MTT assay and cell morphology was assessed by SEM.

RESULTS

In groups QTH and LED the intrapulpal temperature increased by 6.4 degrees C and 3.4 degrees C, respectively. The difference between both groups was statistically significant (Mann-Whitney; P < 0.05). QTH and LED reduced the cell metabolism by 36.4% and 33.4%, respectively. Regarding the cell metabolism, no statistically significant difference was observed between both groups (Mann-Whitney; P > 0.05). However, when compared to the control, only QTH significantly reduced the cell metabolism (Mann-Whitney; P < 0.05). It was concluded that the irradiance of 0.5 mm-thick human dentin discs with a QTH in comparison to a LED curing unit promoted a higher temperature rise, which propagates through the dentin negatively affecting the metabolism of the underlying cultured pulp cells.

Changes in intrapulpal temperature after Er:YAG laser irradiation

OBJECTIVE

This study was performed to investigate the changes in temperature induced by an Er:YAG laser irradiation and to find the means to minimize potential thermal damage due to temperature rise after irradiation.

BACKGROUND DATA

Intrapulpal temperature rise was found to last after irradiation at times, although the addition of appropriate water spray during tooth ablation by Er:YAG laser produced efficient ablation with little thermal damage.

METHODS

To investigate intrapulpal temperature change, each extracted tooth specimen was embedded into a resin block and temperature-measuring probes were placed on the irradiated and the opposite pulpal walls. An Er:YAG laser irradiation was performed at 300 mJ/pulse and 20 Hz, with a water flow rate of 1.6 mL/min for 3 sec. Each lasing was followed by (1) no application of post-irradiation water spray, (2) post-irradiation water spray for 1 sec and (3) for 2 sec.

RESULTS

No significant temperature change was found on the irradiated pulpal wall during Er:YAG laser, while there existed significant temperature rise on the irradiated pulpal wall after irradiation. However, the addition of water spray for 1 or 2 sec after irradiation significantly decreased intrapulpal temperature compared to no application of post-irradiation water spray. There were no significant differences between the 1- and 2-sec groups.

CONCLUSION

It is suggested that the addition of water spray for 1 or more seconds after irradiation reduces post-irradiation temperature rise, possibly leading to thermal damage on the dental pulp tissue.

Effects of low-power red laser on dentine–pulp interface after cavity preparation. An ultrastructural study

OBJECTIVE

Studies on the influence of low-power red laser on the repair of dental structures are very scarce. This study investigated the effects of the laser therapy on the ultrastructure of the dentine-pulp interface after conservative class I cavity preparation.

DESIGN

Two female volunteers with 8 premolars indicated for extraction for orthodontic reasons were recruited. Class I cavities were prepared and the teeth were randomly divided into two groups. The first group received treatment with a GaA1As laser, lambda=660nm, power of 30mW and energy dose of 2J/cm(2), directly and perpendicularly into the cavity in a single visit. After the irradiation, the cavities were filled with composite resin. The second group received the same treatment, except by the laser therapy.

RESULTS

Twenty-eight days post-preparation, the teeth were extracted and processed for transmission electron microscopy analysis. Two sound teeth, without cavity preparation, were also studied. The irradiated group presented odontoblast process in higher contact with the extracellular matrix and the collagen fibrils appeared more aggregated and organised than those of control group. These results were also observed in the healthy teeth.

CONCLUSION

These findings suggest that laser irradiation accelerates the recovery of the dental structures involved in the cavity preparation at the predentine region.

Assessment of Thermal Alteration during Class V Cavity Preparation Using the Er:YAG Laser

OBJECTIVE

The aim of this study was to evaluate in vitro the pulp thermal alterations during class V cavity preparations using the Er:YAG laser and high-speed water flow.

MATERIALS AND METHODS

Forty human teeth were selected and prepared for the thermocouple adaptation in the pulp chamber. The specimens were assigned to four groups: (1) laser 300 mJ/3 Hz, (2) laser 300 mJ/4 Hz, (3) high-speed 9 mL/min water flow, and (4) high-speed 100 mL/min water flow. The temperature was measured before the beginning and at the end of the preparation, as well as during the procedures. The groups were analyzed by scanning electron microscopy.

RESULT

Data analysis disclosed temperature reduction at high-speed drilling with the high-speed total water flow group, and these values were statistically different from the other groups. The results of the 9-mL/min water flow group were similar to those of the 300-mJ/3-Hz group and different from the 300-mJ/4-Hz laser group.

CONCLUSION

The laser promoted a greater increase in temperature only when compared with high-speed handpiece and water flow rate of 100 mL/min.

Effects of KTP Laser Irradiation, Diode Laser, and LED on Tooth Bleaching: A Comparative Study

OBJECTIVE

This in vitro study examines the whitening efficacy of a light-emitting diode (LED), a diode laser, and a KTP laser irradiation in dental bleaching by analyzing the change in color achieved from the treatment, the temperature increase induced in the pulpal cavity, as well as enamel microhardness measurement after treatment.

BACKGROUND DATA

Bleaching techniques achieved significant advances with the use of coherent or incoherent radiation sources to activate the bleaching agents.

METHODS

A hydrogen peroxide bleaching agent, Hi-Lite, was stimulated with an LED, a 980-nm diode laser at 0.8 W, or a 532-nm KTP laser at 1.0 W for 30 sec on 64 extracted human incisors. During irradiation, the temperature in the pulpal cavity was monitored. The color change was evaluated using the CIE L*a*b* color space measurement system, and Vikers enamel microhardness was tested after treatment.

RESULTS

A mean total color difference value (DeltaE*) greater than 5.0 was obtained in each group. KTP-laser-induced bleaching gave a significantly higher DeltaL* (8.35) after treatment (p < 0.01). Neither LED nor the two lasers produced significant differences in the enamel microhardness after treatment (p > 0.01). Mean maximal pulpal temperature rise was 2.95 degrees C for LED, 3.76 degrees C for KTP laser, and 7.72 degrees C for diode laser, respectively.

CONCLUSION

The results of this study suggest that KTP laser is effective at providing brighter teeth. According to the conditions used in this study, the LED and KTP laser induced a safer pulpal temperature increase when assisted with Hi-Lite bleaching gel.

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.

Temperature Response in the Pulpal Chamber of Primary Human Teeth Exposed to Nd:YAG Laser Using a Picosecond Pulsed Regime

OBJECTIVE

This study was conducted to analyze temperature variation in the pulpal chamber using the (Nd:YAG) picosecond-pulsed laser to promote ablation in enamel and dentin of primary teeth.

BACKGROUND DATA

Several previous studies reported the temperature rise in pulpal chamber during laser irradiation. Since there are no reports about pulp chamber temperature changes during irradiation with picosecond-pulsed laser, the purpose of our investigation is to quantify the intrapulpal temperature changes following picosecond-pulsed Nd:YAG laser irradiation of enamel and dentin of primary teeth.

METHODS

In this study, we used 10 intact primary exfoliated teeth: five molars and five incisors. We used a commercial neodymium:- yttrium-aluminum-garnet continuous-wave (CW)-pumped Q-switched and mode-locked Nd:YAG laser, with varying power levels (200, 300, and 350 mW) operating with 100-psec pulsed duration.

RESULTS

Typical plots show differences between heating and cooling of enamel and dentin of anterior and posterior teeth. Whereas for enamel the time evolution curves are dependent on power used for the investigated range (200-350 mW), for dentin the differences are not so evident. Observing temperature enhancement for each power, we were able to analyze operational conditions where temperature changes do not exceed 5.5 degrees C. Power-time-temperature (PTT) diagrams for clinical operations were determined based on varying power level and exposition time. Through the heating-cooling cycle, we could extract conventional heating and cooling times for enamel and dentin.

CONCLUSION

We have shown that the Nd:YAG picosecond-pulsed laser is a safe tool for ablation of primary teeth in a broad range of operational parameters.

Effect of Er,Cr:YSGG laser irradiation on eruption of rat mandibular incisor after disturbance of the enamel organ in the pulp

To investigate the efficacy of Er,Cr:YSGG (erbium,chromium:yttrium scandium gallium garnet) laser irradiation in root canal preparation and to evaluate its effect on eruption of rat incisors after disturbance of the enamel organ in the pulp, 20 canals of lower left incisor teeth were prepared by K-files followed by Er,Cr:YSGG laser irradiation, and 20 canals of right incisors were subjected to K-files only (control). At 1 week after irradiation, both sides of incisors erupted at the same level from the gingival margin. Histological findings showed that laser irradiation produced a slightly larger damage in the pulp than that of control. Scanning electron microscope observation revealed that laser-treated surface revealed a rough, irregular, and very clean surface; there was almost no evidence of debris or smear layer, and dentinal tubules were opened. Adequate power of Er,Cr:YSGG laser irradiation is effective in root canal preparation without disturbance of the eruption.

Mitogen-activated protein kinase/extracellular signal-regulated protein kinase activation of cultured human dental pulp cells by low-power gallium-aluminium-arsenic laser irradiation

AIM

To examine whether low-power laser irradiation (LPLI) promotes cellular proliferation of human dental pulp-derived fibroblast-like cells (dental pulp cells).

METHODOLOGY

Dental pulp cells were obtained by primary culture of human dental pulp tissues from extracted third molar teeth. The phosphorylation of the mitogen-activated protein kinase (MAPK) family after LPLI of these cells was investigated by Western blotting. By using a specific MAPK/ERK kinase (MEK) inhibitor (PD098059), the specific effect of LPLI on the MAPK pathway was also investigated by Western blotting as described above. The incorporation of [3H]thymidine into the cells after LPLI was determined, and statistical analysis was performed by Wilcoxon signed-ranks test.

RESULTS

Extracellular signal-regulated protein kinase (ERK) 1/2 was phosphorylated between 5 and 30 min after LPLI. Moreover, PD098059 inhibited LPLI-mediated ERK1/2 activation. LPLI did not affect p38 MAPK or c-Jun N-terminal kinase (JNK) phosphorylation. But LPLI did not stimulate [3H]thymidine incorporation into these cells.

CONCLUSIONS

These results indicated that LPLI activated MAPK/ERK, a signal for proliferation, differentiation and survival, but did not activate the stress signals p38 MAPK and JNK in human dental pulp cells.

Argon laser oral safety parameters for teeth

Argon lasers have been reported to prevent or reduce demineralization of enamel in extracted teeth and to polymerize dental composites (using 25-100 J/cm2). Prior to clinical trials on caries prevention and curing composites, safety parameters for intraoral use of the argon laser need to be established. This study was conducted to determine the enamel damage, pulp temperature changes, and associated pulpal tissue damage following irradiation at various argon laser energy levels using 1.6-6.0 watts, approximately 1 and 2 mm diameter beam for 0.2-5.0 seconds. To evaluate pulpal damage, selected dogs' teeth were irradiated in vivo, extracted 7 days postlasing, fixed, decalcified, sectioned, stained, and read for pulpal damage. Pulp temperature and enamel damage tests utilized extracted dog and human teeth. Temperature probes were inserted in the pulp chambers and temperature changes recorded as enamel surface was lased. Enamel surface damage was evaluated by visual and microscope examination. Results showed that histologic pulpal damage occurred at > 600 J/cm2. Temperature changes were < 6 degrees F in human teeth with approximately 900 J/cm2. No enamel damage was observed at these energy densities. At energy densities needed for proposed uses, no apparent damage would be expected to pulp or enamel.

Pulsed Nd:YAG laser effect on eruption of rat mandibular incisors following disturbance of the enamel organ in the pulp

We investigated the effects of pulsed neodymium:yttrium-aluminium-garnet (Nd:YAG) laser irradiation time on the eruption of 56 mandibular incisors in 28 rats. Clinically, some incisors erupted and the others did not. The incisors were irradiated at 2 W, 20 pulses/s for the period of 3 s, 5 s, 7 s, and 10 s, and the regeneration process was monitored at 20 days after laser treatment. Incisors irradiated for 3-5 s continued their eruption; five incisors irradiated for 7 s and all incisors irradiated for 10 s did not erupt. In the incisors that continued to erupt, the inner epithelial cells differentiated into ameloblast and a part of the pulp cavity was occupied by osteodentin. In the teeth in which eruption had ceased, the inner epithelium cells did not differentiate into ameloblast, and most of the pulp cavity was occupied by osteodentin. The results indicate that a relatively short time duration of pulsed Nd:YAG laser irradiation in the pulp induced the reparative process without disturbing the eruption.

Pulpal safety of 9.6 microm TEA CO2 laser used for caries prevention

BACKGROUND AND OBJECTIVES

Lasers are used for several procedures involving hard and soft tissues of the oral cavity. A potential future application is the use of the CO2 laser to alter the surface structure of tooth enamel to render it more resistant to caries. A new 9.6 microm wavelength transverse excited atmospheric pressure (TEA) CO2 laser (Argus Photonics, Jupiter, FL) has been investigated as a device that can be used for this purpose without harming the dental pulp.

STUDY DESIGN/MATERIALS AND METHODS

Erupted caries- and restoration-free third molars (n = 24 participants; 74 teeth) were used in the study. Teeth were irradiated at an incident fluence of 1.5 J/cm2, a repetition rate of 10 Hz and a spot size 1 mm in diameter. At the low and high settings, 200-400 pulses at 5-8 microseconds pulse duration were delivered at 12 mJ per pulse for a total energy of 2.4 or 4.8 J delivered for 20 or 40 seconds, respectively. Other teeth were subjected to a sham dental procedure (positive control) or no procedure (negative control). Prior to testing, radiographs were taken of all teeth, and they were assessed pulpally using heat, cold, and electricity to determine vitality. The teeth were removed either immediately or at 1 week or 1 month after testing.

RESULTS

Teeth were bioprepared and examined histologically for signs of inflammation. Only one tooth developed symptoms of sensitivity to cold for 10 days following exposure to the high power level. The sensitivity was of fleeting duration and was judged to be reversible pulpitis. All teeth tested responded normally at pre-testing and pre-extraction time periods. Histological examination of all teeth disclosed no indication of an inflammatory response in the pulp tissue at any time point. All sections appeared normal with no changes seen in the normal pulpal morphology.

CONCLUSIONS

We conclude that the 9.6 microm wavelength laser causes no permanent/serious pulpal damage at the energy levels used and can be used safely for caries prevention treatments in humans.

Intrapulpal Temperature during Preparation with the Er:YAG Laser: Anin VitroStudy

OBJECTIVE

This investigation evaluated the variation of the intrapulpal temperature when dentine was irradiated by the Er:YAG laser.

BACKGROUND DATA

The effect of preparation with the Er:YAG laser on the intrapulpal temperature is probably the biggest problem in using the laser for preparation of dental hard tissue.

MATERIALS AND METHODS

Seventy-two bovine incisors were studied that had the enamel and dentine of the buccal surface polished to a thickness of 2.0 mm. The teeth were divided into three groups, according to the repetition rate used (Group I = 2 Hz, Group II = 4 Hz, and Group III = 6 Hz), and irradiated, with or without water cooling, using 250, 300, and 350 mJ of energy per pulse. Thermocouples were introduced inside the pulp chamber through the palatine opening of the samples and fixed to the vestibular wall of the pulp chamber using a thermal paste.

RESULTS

It was verified that there was a decrease of the intrapulpal temperature for all of the parameters in the Group I irradiated with water cooling and for the parameters of 350 mJ/4 Hz with water cooling. The other irradiations showed an increase of the intrapulpal temperature, varying from 0.03 degrees to 2.5 degrees C.

CONCLUSION

We conclude that the use of the Er:YAG laser promoted acceptable temperature increases inside the pulp chamber. However, we do not recommend this procedure without water cooling because macroscopic observations of the dentine irradiated without water cooling showed dark lesions, suggesting carbonization of this tissue.

Striatal Inhibition of Nociceptive Responses Evoked in Trigeminal Sensory Neurons by Tooth Pulp Stimulation

The noxious evoked response in trigeminal sensory neurons was studied to address the role of striatum in the control of nociceptive inputs. In urethane-anesthetized rats, the jaw opening reflex (JOR) was produced by suprathreshold stimulation of the tooth pulp and measured as electromyographic response in the digastric muscle, with simultaneous recording of noxious responses in single unit neurons of the spinal trigeminal nucleus pars caudalis (Sp5c). The microinjection of glutamate (80 ηmol/0.5 μl) into striatal JOR inhibitory sites significantly decreased the Aδ and C fiber–mediated–evoked response (53 ± 4.2 and 43.6 ± 6.4% of control value, P < 0.0001) in 92% (31/34) of nociceptive Sp5c neurons. The microinjection of the solvent was ineffective, as was microinjection of glutamate in sites out of the JOR inhibitory ones. In another series of experiments, simultaneous single unit recordings were performed in the motor trigeminal nucleus (Mo5) and the Sp5c nucleus. Microinjection of glutamate decreased the noxious-evoked response in Sp5c and Mo5 neurons in parallel with the JOR, without modifying spontaneous neuronal activity of trigeminal motoneurons ( n = 8 pairs). These results indicate that the striatum could be involved in the modulation of nociceptive inputs and confirm the role of the basal ganglia in the processing of nociceptive information.

Pulpal temperature rise during light-activated bleaching

The purpose of this study was to measure intrapulpal temperature rise induced by two kinds of bleaching gels when the tooth was exposed to a variety of light-curing units and a diode laser in vitro. The root portions of 80 extracted intact human maxillary central incisors were sectioned with a carborundum disk approximately 2 mm below the cementoenamel junction perpendicular to the long axis of the teeth. Two bleaching agents containing heat-enhancing colorant was applied to the labial surface. Light-curing units used were a conventional halogen (40 s), a high-intensity halogen (30 s), a light-emitting diode unit (40 s), and a diode laser (15 s). The temperature rise was measured in the pulpal chamber with a J-type thermocouple wire that was connected to a data logger. Ten specimens were used for each system and bleaching-agent combination. Differences between the starting temperature and highest temperature reading were taken and the calculated temperature changes were averaged to determine the mean value in temperature rise. Temperature rise values were compared using two-way analysis of variance (ANOVA) at a preset alpha of 0.05. Temperature rise varied significantly depending on curing unit and diode laser used. The diode laser induced significantly higher temperature increases than any other curing unit (11.7 degrees C). The light-emitting diode unit produced the lowest temperature changes (6.0 degrees C); however, there were no statistically significant differences among the curing units and there were no statistically significant differences between bleaching agents. Light activation of bleaching materials with diode laser caused higher temperature changes as compared to other curing units and the temperature rise detected was viewed as critical for pulpal health.

Observations on pulpal response to carbon dioxide laser drilling of dentine in healthy human third molars

Preservation of pulpal health is the primary prerequisite for successful application of laser systems in the hard tissue management of vital teeth. The purpose of this study was to investigate the short and long-term pulpal effects to cavity preparations in healthy human teeth using carbon dioxide (CO2) laser. A total of seven, healthy, third molars that were scheduled to be removed due to space problems were used. After the laser drilling, the occlusal cavities were closed temporarily, and the teeth were extracted 7 days (n=5) and 3 months (n=2) after the operation. The specimens were fixed, decalcified, subdivided and processed for light and transmission electron microscopy. Seven days postoperatively all the five teeth that had been irradiated with the CO2 laser did not reveal any pathological changes in the pulpo-dentine complex. Three months postoperatively the two teeth that were prepared with the laser showed subtle but distinct apposition of tertiary dentine that was lined with intact odontoblasts. One of the specimens at 3 months revealed the presence of a mild, but very circumscribed, pulpal infiltration of chronic inflammatory cells subjacent to the cavity preparation. The latter is unlikely to be due to a direct effect of the laser irradiation but a possible consequence of microleakage of oral antigens and/or other tissue-irritating molecules through the temporary restoration and the remaining dentine thickness (RDT). Although these preliminary histological results suggest that the CO2 laser under investigation induced only minimal response of the dentine-pulp complex when used as a hard-tissue drilling tool, with specific energy settings, pulse duration within thermal relaxation time and emitting radiations at 9.6 microm of wavelength, larger clinical trials involving various types of teeth are necessary to reach definite conclusions for large-scale clinical application of the laser device.

Thermal Effect and Morphological Changes Induced by Er:YAG Laser with Two Kinds of Fiber Tips to Enlarge the Root Canals

OBJECTIVE

The aim of this study was to assess the application of Er:YAG laser root canal preparation using two fiber tip systems.

BACKGROUND DATA

Previous studies have not shown the thermal effect of Er:YAG laser using cone-shaped fiber tip.

MATERIALS AND METHODS

The ability of Er:YAG laser to enlarge root canals at a pulse energy set at 30 or 20 mJ and constant pulse rate of 10 pps (pulses per second) was tested. A cone-shaped (84 degrees top angle) or a flat fiber tip of Er:YAG laser was used for comparison. Four groups of 15 artificial root canals with fixed dimension were prepared from bovine teeth. Irradiation was accompanied by sterilized distilled water spray (2 mL/min). The temperature changes on the root surface were recorded with an infrared apparatus, and the thermal images were captured with a thermocamera. The morphological changes of irradiated root canals were examined by a scanning electron microscope (SEM).

RESULTS

The mean temperature rises were 9.4 degrees C and 7.1 degrees C with the cone-shaped fiber tip at a pulse energy of 30 and 20 mJ, respectively, and were 11.0 degrees C and 6.5 degrees C with flat fiber tip at a pulse energy of 30 and 20 mJ, respectively. Marked difference in temperature change between the cone-shaped and flat fiber tips was noted at pulse energy of 30 mJ, but not at 20 mJ. The thermal distribution using the cone-shaped fiber tip (in contrast to the flat tip) had an elliptical shape around the fiber tip and was limited to the apical end of the root canals. SEM observation found that irradiation with cone-shaped fiber tip (in comparison to the flat tip) produced a cleaner surface.

CONCLUSION

Our results suggest that the cone-shaped fiber tip of Er:YAG laser produced fewer thermal effects and morphological changes as compared to the other type of fiber tip.

Safety parameters for pulp temperature during selective ablation of caries by KTP laser in vitro

OBJECTIVE

To define the optimal parameters of KTP laser irradiation during a selective caries removal.

MATERIALS AND METHODS

Twelve decayed human teeth, recently extracted were used. Their root canals were prepared for insertion of a thermocouple probe into the pulp chamber. The demineralized tissues were colored by Acid Red 52 before proceeding to different conditions of irradiation.

RESULTS

Pulpal temperature increases (below 3 degrees C) were found under the following parameters with 15 sec of continuous lasing: 400 mWatts, 0.10-msec pulse width, PRR <50 Hz for efficient caries removal. A resting time average of 70 sec was necessary to allow pulp temperature to get back to its baseline.

CONCLUSION

KTP laser can be used safely and without any pulp over-heating under certain irradiation conditions.

Short-term histomorphological effects of Er:YAG laser irradiation to rat coronal dentin-pulp complex

OBJECTIVE

The objective of the study was to examine the morphological changes of neural elements in dentin-pulp complex ultrastructurally after Er:YAG laser irradiation and elucidate the mechanism of pain reduction in cavity ablation.

STUDY DESIGN

The Er:YAG laser was applied at occlusal surfaces of upper and lower first molar cusps of 6 rats, and shallow cavities were ablated. The dentin and pulps were examined with light and electron microscopes at 6 hours after the irradiation. Teeth, without laser irradiation, from three rats were used as controls.

RESULTS

Disruption of nerve terminals in the dentinal tubules, degeneration of nerve terminals between odontoblasts, and disruption of the myelin sheath in the pulp core were demonstrated with electron microscope.

CONCLUSION

Some Er:YAG laser beams could penetrate to deeper areas than ablated area, and damage of nerve fibers and terminals might be a mechanism of pain reduction in cavity ablation with Er:YAG laser.

Effects of low power Er:YAG laser on the tooth pulp-evoked jaw-opening reflex

BACKGROUND AND OBJECTIVES

Analgesic properties of laser irradiation have been of great interest in the field of dentistry. This study aimed at evaluating the analgesic effects of the Er:YAG laser system in rats during and after laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

A pulsed Er:YAG laser was applied to the oral mucosa of the mandibular incisor at an energy density of approximately 0.1 J/cm(2)/pulse for 10 minutes at 10 Hz, and the integrated digastric muscle electromyogram in tooth pulp-evoked jaw-opening reflex was used as an index of the nociceptive response.

RESULTS

Significant reflex suppression was observed 10 minutes after laser irradiation. The reflex amplitude started to return to its original level about 45 minutes after cessation of laser irradiation.

CONCLUSIONS

The Er:YAG laser used at low output levels presented inhibitory effects on the tooth pulp-evoked jaw-opening reflex, suggesting that this laser system may be of use for pain control during various dental treatments.

In vitro study of a neodynium:yttrium aluminum perovskite laser on human nonexposed pulp after cavity preparation

PURPOSE

The aim of this study was to investigate dental pulp reactions after a neodynium:yttrium aluminum perovskite laser pulse on the dentinal floor of occlusal cavities in an in vitro model.

METHODS

A Lokki dt laser was used at 30 Hz, 5 W, and 160 mJ for 0.5 s. The pulp reactions were analyzed in a previously described human tooth slice cultured model. The following markers were identified by immunohistochemistry: collagens I, III, and IV and HLA-DR-positive cells.

RESULTS

After 4 days of culture, under laser pulse, a concentration of type III collagen beneath the odontoblast layer, a higher level of vessels and an accumulation of HLA-DR-positive cells were routinely observed subjacent to the cavity.

CONCLUSION

This laser treatment leads to the first step of rapid pulp repair under culture conditions.

An immunocytochemical study of pulpal responses to cavity preparation by laser ablation in rat molars by using antibodies to heat shock protein (Hsp) 25 and class II MHC antigen

Initial responses of odontoblasts and immunocompetent cells to cavity preparation by laser ablation were investigated in rat molars. In untreated control teeth, intense heat shock protein (Hsp) 25 immunoreactivity was found in the cell bodies of odontoblasts, whereas cells immunopositive for the class II major histocompatibility complex (MHC) antigen were predominantly located beneath the odontoblast layer in the dental pulp. Cavity preparation caused the destruction of the odontoblast layer and the shift of most class-II-MHC-positive cells from the pulp-dentin border toward the pulp core at the affected site. Twelve hours after cavity preparation, numerous class-II-MHC-positive cells appeared along the pulp-dentin border and extended their processes deep into the exposed dentinal tubules, but subsequently disappeared from the pulp-dentin border together with Hsp-25-immunopositive cells by 24 h after the operation. By 3-5 days postoperation, distinct abscess formation consisting of polymorphonuclear leukocytes was found in the dental pulp. The penetration of masses of oral bacteria was recognizable in the dentinal tubules beneath the prepared cavity. These findings indicate that cavity preparation by laser ablation induces remarkable inflammation by continuous bacterial infections via dentinal tubules in this experimental model, thereby delaying pulpal regeneration.

The effect of direct and alternating electrical currents on the vessel walls of the tooth pulp -- TEM studies

Devices which operate on the basis of electrical charges are increasingly being used in stomatology, such as in cariology for the detection of invisible caries lesions or for the measurement of canal lengths during patient treatment. The majority of these devices now emit a current of alternating frequency. The aim of the work was to explain how the electrical devices of labile frequency commonly used in stomatology influence the vessels of the tooth pulp. Teeth extracted for orthodontic reasons were investigated with the use of a transmission electron microscope. The teeth were treated with current emitted by a specially constructed device. The control group comprised 4 teeth. No changes were found in the electron microscopic studies in the slides of the teeth treated with low charges of current. However, in the specimen treated with current charges of 9600 microC or more flattened endotheliocytes were found together with exudation in the vessel lumen. Cases are referred to in which the duration of the work was 2 or 3 times longer than normal and in which a current of constant intensity was emitted uninterruptedly.

Histopathological Changes in Dental Pulp Irradiated by Er:YAG Laser: A Preliminary Report on Laser Pulpotomy

OBJECTIVE

The effects of Er:YAG laser irradiation on the pulp tissue during a pulpotomy procedure were evaluated histopathologically.

BACKGROUND DATA

The effects on pulp tissue during laser pulpotomy using Er:YAG laser irradiation are not clear.

MATERIALS AND METHODS

Sixty mesial root canals of mandibular first molars in rats were divided into four groups. In three of these groups, root canals were irradiated using an Er:YAG laser at 2 Hz and 34, 68, and 102 mJ/pulse for 15 sec. Non-irradiated canals served as controls. The effects of laser irradiation on the remaining pulp tissue and periodontal tissues were evaluated at 0 days, 2 days, and 1 week after irradiation under light microscopy.

RESULTS

At 1 week after treatment, no inflammation or resorption was observed in any cases in the control or 34 mJ/pulse-irradiated groups. However, moderate to severe inflammation was observed in 9 of 10 cases (90%) in the 68 and 102 mJ/pulse-irradiated groups.

CONCLUSION

These results suggest that effects on pulp tissues during a pulpotomy procedure by Er:YAG laser irradiation are minimal, if appropriate parameters are selected, and this is a potential therapy for pulpotomy of human teeth.

Pulpal response to Er:YAG laser drilling of dentine in healthy human third molars

BACKGROUND AND OBJECTIVES

Maintenance of pulpal health is a critical prerequisite for successful application of light amplification by stimulated emission of radiations (lasers) in the hard tissue management of vital teeth. The purpose of this study was to investigate the short- and long-term pulpal effects to cavity-preparations in healthy human teeth using erbium-doped:yttrium, aluminum, and garnet (Er:YAG) laser.

MATERIALS AND METHODS

A total of seven healthy third molars that were to be removed due to space-problem were used. Following the laser excavation, the cavities in dentine were closed temporarily and the teeth were extracted after 7 days (n = 5) and 3 months (n = 2) post-operation. The specimens were fixed, decalcified, subdivided, and processed for light and transmission electron microscopy.

RESULTS

In the short-term group, four of the five laser-drilled teeth did not reveal any pathological changes in the pulp-dentine complex. One tooth showed mild disruption of odontoblasts (OB) and vascular dilatation subjacent to the deepest point of the cavity-preparation with a remaining dentine thickness (RDT) of less than 80 microm. The two teeth under long-term observation revealed distinct apposition of tertiary dentine (TD), lined predominantly with cuboidal cells on its pulpal aspect.

CONCLUSIONS

These results would allow a conclusion to be drawn that the Er:YAG laser under investigation is a pulp preserving hard-tissue drilling tool when used with the specific energy settings and emitting radiation at a wavelength of 2.94 microm.

Effect of ER:YAG and diode laser irradiation on the root surface: morphological and thermal analysis

BACKGROUND

The aim of the present study was to compare the effects of Er:YAG and diode laser treatments of the root surface on intrapulpal temperature after scaling and root planing with hand instruments.

METHODS

Fifteen extracted single-rooted teeth were scaled and root planed with hand instruments. The teeth were divided into 3 groups of 5 each and irradiated on their buccal and lingual surfaces: group A: Er:YAG laser, 2.94 microm/100 mJ/10 Hz/30 seconds; group B: diode laser, 810 nm/1.0 W/0.05 ms/30 seconds; group C: diode laser, 810 nm/1.4 W/0.05 ms/30 seconds. The temperature was monitored by means of a type T thermocouple (copper-constantan) positioned in the pulp chamber to assess pulpal temperature during and before irradiation. Afterwards, the specimens were longitudinally sectioned, and the buccal and lingual surfaces of each root were analyzed by scanning electron microscopy.

RESULTS

In the Er:YAG laser group, the thermal analysis revealed an average temperature of -2.2 +/- 1.5 degrees C, while in the diode laser groups, temperatures were 1.6 +/- 0.8 degrees C at 1.0 W and 3.3 +/- 1.0 degrees C at 1.4 W. Electronic micrographs revealed that there were no significant morphological changes, such as charring, melting, or fusion, in any group, although the specimens were found to be more irregular in the Er:YAG laser group.

CONCLUSIONS

The application of Er:YAG and diode lasers at the utilized parameters did not induce high pulpal temperatures. Root surface irregularities were more pronounced after irradiation with an Er:YAG laser than with a diode laser.

[Alternative methods for prevention and treatment of dental caries using laser and magnetic laser exposure]

Alternative methods for prevention and treatment of dental caries are presented, based on the use of laser and magnetic laser exposure (patent No. 2053818, in Russia) with a new generation laser device with Optodan microprocessor monitoring (patent No. 2014107, Russia). The methods are intended for wide clinical application in children and adolescents in pedodontic departments and outpatient centers and particularly for group and individual use in dental rooms at school.

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.