Scanning electron microscopic study of the apical dentine surfaces lased with ND:YAG laser following apicectomy and retrofill

Effects of laser modalities on shear bond strengths of composite superstructure to zirconia and PEEK infrastructures: an in vitro study

In the last decade, demand for metal-free esthetic restorations has grown considerably due to the development of materials to fulfill the need for an esthetic prosthesis. We examined the effects of erbium-doped yttrium aluminum garnet (Er:YAG), neodymium-doped yttrium aluminum garnet (Nd:YAG), and potassium titanyl phosphate (KTP) laser applications on the shear bond strength (SBS) of nanohybrid composite superstructures to zirconia and PEEK infrastructures. Zirconia and PEEK specimens were prepared with CAD/CAM technology in accordance with ISO 11405 standards. The disc-shaped samples were randomly separated into four groups (n = 8) according to applied laser type: no treatment and Er:YAG, Nd:YAG, and KTP lasers. Nanohybrid composite resin was applied as a veneering material to each infrastructure. After surface treatment of infrastructures by the lasers, the SBS test was carried out to determine the bonding of infrastructures, which were also examined with a stereomicroscope. The SBS were significantly higher in the PEEK specimens treated with the studied lasers. Nd:YAG laser was the most effective method, followed by Er:YAG laser and KTP laser. The lowest SBS value was obtained in the no-treatment group. Stereomicroscopically, the studied lasers produced different irregularities on the infrastructures. PEEK as a framework provides meaningfully higher bonding strength to composite resins compared to zirconia. Nd:YAG, Er:YAG, and KTP, in descending order, are efficacious in increasing the attachment of studied structures.

A comparative scanning electron microscopy evaluation of smear layer removal from teeth with different irrigation solutions and lasers

The aim of this study was to evaluate the efficacy of smear layer removal from teeth following root canals using lasers (Er:YAG and Nd:YAG), NaOCl, 17% EDTA, and MTAD by scanning electron microscopy (SEM). Root canals were irrigated with 3 mL of 5.25% NaOCl after each file. Teeth were randomly divided into five groups. In the final irrigation, canals were irrigated with 5.25% NaOCl (Group 1, control), 17% EDTA (Group 2), or BioPure MTAD (Group 3). Laser groups were irradiated with Er:YAG laser (1.8 W, 120 mJ, 15 Hz) (Group 4) or Nd:YAG laser (1 W, 100 mJ, 15 Hz) (Group 5). The smear layer at the apical, middle, and coronal thirds of each root canal was imaged using SEM. Smear layer removal by EDTA was the most effective in all regions. The difference between EDTA and MTAD was statistically significant in the coronal and middle (p < 0.05), but not the apical (p > 0.05), regions. The difference between the control and laser groups was not statistically significant (p > 0.05). In all regions, the difference between 17% EDTA-MTAD and the control-laser groups was statistically significant (p < 0.05). Although improvement was observed in removal of the smear layer using alternative materials and techniques, application of a combination of EDTA and NaOCl remains an effective technique.

Effect of Nd: YAG laser on the apical seal after root-end resection and MTA retrofill: a bacterial leakage study

Laser irradiation has been investigated in terms of preventing leakage in retrofilled root canals. The aim of the present study was to evaluate the effect of neodymium-doped yttrium aluminum garnet (Nd: YAG) laser on the bacterial leakage of mineral trioxide aggregate (MTA)-retrofilled roots. In this ex vivo experimental study, 90 single-rooted incisor teeth were filled with gutta-percha and AH26 sealer. The apical 3 mm of all the roots were resected and 3-mm retrocavities were prepared by an ultrasonic device. The specimens were randomly divided into two experimental (n = 25), one positive control (n = 10), and two negative control (n = 10) groups. In the laser + MTA group, the cavity walls were irradiated by Nd: YAG laser prior to MTA placement. In the MTA group, MTA was placed without laser irradiation. The root surfaces were covered with two layers of nail varnish except for the apical 2 mm. The specimens were then embedded in a bacterial leakage test system and examined daily for 90 days. Contamination periods were recorded. Data were analyzed by Kaplan-Meier and Mann-Whitney U tests (α = 0.05). Five teeth with and five teeth without laser irradiation underwent scanning electron microscopic evaluation. The specimens in the laser + MTA group were contaminated earlier than those in the MTA group (p < 0.05). Comparison of survival times between the two groups showed significant differences (p < 0.05). Nd: YAG laser irradiation can decrease the sealing capacity of MTA in comparison to the apical seal achieved by MTA without laser irradiation. Further studies are recommended to provide a better seal for the MTA-retrofilled teeth after laser irradiation.

Morphological assessment of dentine and cementum following apicectomy with Zekrya burs and Er:YAG laser associated with direct and indirect Nd:YAG laser irradiation

OBJECTIVES

This study aimed to assess the apical surface morphology of maxillary central incisors resected 3.0 mm from the tooth apex using Zekrya burs or Er:YAG laser, with or without subsequent direct Nd:YAG laser irradiation (apical and buccal surfaces) and indirect irradiation (palatal surface).

STUDY DESIGN

Forty maxillary central incisors were instrumented and obturated. The roots were divided into 4 groups according to the root resection method (Zekrya bur or Er:YAG laser - 1.8 W, 450 mJ, 4 Hz, 113 J/cm(2)) and further surface treatment (none or Nd:YAG laser - 2.0 W, 100 mJ, 20 Hz, 124 J/cm(2)). The teeth were prepared for SEM analysis. Scores ranging from 1 to 4 were attributed to cut quality and morphological changes. The data were analyzed by the Kruskal-Wallis test and by Dunn's test.

RESULTS

SEM images showed irregular surfaces on the apical portions resected with Zekrya burs, with smear layer and grooves in the resected dentine and slight gutta-percha displacement and plasticization. On the other hand, apicectomies carried out with Er:YAG laser showed morphological changes compatible with ablated dentine, with rough surfaces and craters. In spite of the presence of plasticized gutta-percha, with the presence of bubbles, an irregular adaptation of the filling material to the root walls was also observed. Direct Nd:YAG laser irradiation of the apical and buccal surfaces of the resected roots resulted in areas of resolidification and fusion in the dentine and cementum, with a vitrified aspect; indirect Nd:YAG laser irradiation of the palatal surfaces yielded a lower number of changes in the cementum, with irregular resolidification areas.

CONCLUSIONS

There were no differences in terms of cut quality between the use of burs and Er:YAG laser or between the 2 surfaces (apical and buccal) treated with Nd:YAG laser with direct irradiation. However, morphological changes were significantly less frequent on surfaces submitted to indirect irradiation (palatal) when compared with those directly irradiated.

Ultrasonic chemical vapor deposition-coated tip versus high- and low-speed carbide burs for apicoectomy: time required for resection and scanning electron microscopy analysis of the root-end surfaces

This study compared ultrasonic chemical vapor deposition (CVD)-coated tip (CVDentus #8.1117-1; Clorovale Diamantes Ind. e Com. Ltda Epp, São José dos Campos, SP, Brazil) versus high-speed (#FG700L) and low-speed (#699) carbide burs for apicoectomy, evaluating the time required for resection and analyzing the root-end surfaces by scanning electron microscopy. Thirty extracted human premolars had the canals instrumented and obturated and were randomly assigned to 3 groups (n = 10), according to the instrument used for root-end resection. The time required for resection of the apical 2 mm of each root was recorded. The resected apical segments were dried, sputter coated with gold, and examined with a scanning electron microscope at x350 magnification. A four-point (0-3) scoring system was used to evaluate the apical surface smoothness. The results were analyzed statistically by the Kruskal-Wallis test, and two-by-two comparisons analyses were performed using the Miller test. The significance level was set at 5%. Root-end resection with the high-speed bur was significantly faster (p < 0.05) compared with the low-speed bur and CVD tip. The carbide burs produced significantly smoother root-end surfaces than the CVD tip (p < 0.05). The low-speed bur produced the smoothest root-end surfaces, whereas the roughest and most irregular root ends (p < 0.05) were obtained with the CVD tip. However, no statistically significant difference (p > 0.05) was found between the high- and low-speed burs regarding the surface roughness of the resected root ends (p > 0.05). In conclusion, under the tested conditions, ultrasonic root-end resection took a longer time and resulted in rougher surfaces compared with the use of carbide burs at both high and low speed.

Evaluation of apical surface roughness after root resection: a scanning electron microscopic study

OBJECTIVES

The objective of this study was to compare, by scanning electron microscopy, the smoothness of the resected apical root surface after preparation with high-speed #699 bur, #699 bur plus Shofu finishing and Zekrya bur, and with an erbium:YAG laser.

STUDY DESIGN

Thirty-nine extracted human premolars were instrumented and obturated and their root apices were resected. The roots were divided into 4 groups according to the root resection method. The teeth were dried, metallized, and analyzed at x400 by scanning electron microscopy. Scores ranging from 0 to 3 were attributed to surface smoothness. The data were analyzed by the Kruskal-Wallis test for overall comparison, and by Dunn's test for individual comparisons.

RESULTS

Smoother surfaces were observed for the groups treated with the #699 bur and the #699 bur plus Shofu point finishing, while rougher surfaces were obtained with the laser, which differed significantly from the other 2 methods (P < .05).

CONCLUSIONS

Treatment with the #699 bur plus Shofu finishing yielded better results in terms of surface smoothness, whereas the laser treatment produced more irregular and rougher surfaces after root resection.

Computer-assisted evaluation of microleakage after apical resection with laser and conventional techniques

The purpose of this in vitro study was to observe the morphological changes and apical dye penetration at apical dentin surfaces after apicoectomy with conventional techniques and laser beam. Sixty single-rooted extracted teeth were selected for the study. The crowns were resected below the cemento-enamel junction. Then, these teeth were treated endodontically and filled with gutta-percha using AH-26 root canal sealer. The teeth were randomly divided into four groups of 15 teeth in each. The roots were resected perpendicular to its long axis 3 mm from the apex using Er: yttrium-aluminium-garnet (YAG) laser irradiation in groups 1 and 2, and the resected root surfaces were lased with Nd:YAG laser in group 2. The apexes were resected by a high-speed handpiece in groups 3 and 4, and the resected root surfaces were lased with Nd:YAG laser in group 4. Ten teeth in each group were used for leakage studies, and the other five teeth were used for scanning electron microscopic examinations. Seven sections were obtained from each root to assess the microleakage, and the sections were analyzed in a computer-assisted manner. No statistically significant differences were observed between the leakage percentage of groups 1 and 3 and groups 2 and 4 (p>0.05). Morphological differences were observed between apical dentin surfaces resected with conventional techniques and laser beam.

Effects of Er:YAG laser and Nd:YAG laser treatment on the root canal dentin of human teeth: a SEM study

The objective of the study was to observe the morphological changes on root canal dentin after Er:YAG laser and Nd:YAG laser treatment. Twenty-one teeth biomechanically prepared were divided into three groups with seven teeth of each. Group A was unlased as a control. In group B, Er:YAG laser and in group C, Nd:YAG laser was applied to the root canal dentin. The roots were split longitudinally and examined using a scanning electron microscopy for the evaluation of debris, smear layer, and recrystallization. There was no statistically significant difference between the groups. This study indicates that laser beam is not effective in removing debris and smear layer.

Er:Yag laser irradiation of the microbiological apical biofilm

One problem in cases of healing-resistant periapical lesions is to eradicate the contamination at the periapical area. This contamination is due to the microbiological biofilm formed by microorganisms and their subproducts lodged in apical third of the root, on both cementum and dentin surface. Paraendodontic surgery consists of the mechanical removal of harmful agents to promote healing and periapical health. The purpose of this study was to assess the results of Er:YAG laser irradiation on the apical root third of newly extracted teeth to eliminate microbial contamination on root apex surface. Apical irradiation was performed with an Er:YAG laser device using an experimental contact tip, at 100 mJ, 10 Hz, 1 W, 39 J/cm(2), 3 times on the target area. SEM analysis showed the elimination of part of the irradiated cementum and the formation of small roughened without exposing the subjacent dentin. Vaporization of the remaining periodontal tissue and removal of microbiological apical biofilm (MAB) were also observed on the irradiated areas. Under the tested conditions and based on the findings of this study, Er:YAG laser may be considered effective for removal of microbiological apical biofilm.

Micromorphological Analysis of Dentinal Structure after Irradiation with Nd:YAG Laser and Immersion in Acidic Beverages

OBJECTIVE

The purpose of this study was to analyze dentinal surfaces that were exposed to acidic beverages, then treated with Nd:YAG laser and afterwards exposed to acidic beverages again.

BACKGROUND DATA

Dentin hypersensitivity can result from surface erosion caused by acidic beverages, which exposes and enlarges the dentinal tubules. Nd:YAG laser has been used as a treatment option.

METHODS

Sixty-eight dentin samples were prepared and assigned to five groups: G1, control (n = 4); G2, 3-h immersion (n = 16); G3, 3-h immersion + Nd:YAG; G4, 3-h immersion + Nd:YAG + 3-h immersion; and G5, 3-h immersion + Nd:YAG + 6-h immersion. Each group was divided into four subgroups, with different acid beverages: lemon (n = 4); passion fruit (n = 4); cola (n = 4); and wine (n = 4). Irradiation with the Nd:YAG was in contact mode, focused and perpendicular through a quartz fiber of 300 microm of diameter in scanning movements for 60 sec with a 10-sec interval and the paramenters 0.6 W, 10 Hz, 60 mJ, and 85 mJ/cm(2). Each subgroup was examined by scanning electron microscope.

RESULTS

All the acidic beverages contributed to exposure and increased diameter of the dentinal tubules.

CONCLUSIONS

Irradiation with Nd:YAG laser produced obliteration of and reduction in the number of dentinal tubules, thus modifying the original structure.

The sealing ability of an epoxy resin root canal sealer after Nd:YAG laser irradiation of the root canal

AIM

To evaluate ex vivo the effect of Nd:YAG laser irradiation with and without black ink on instrumented root canal walls, and the degree of both coronal and apical microleakage of filled root canals.

METHODOLOGY

Seventy-two single-rooted teeth were instrumented up to a size 40 K-file, and then divided into six groups of 10 teeth: groups 1 and 4 remained unlased and acted as control groups, groups 2 and 5 were treated with a Nd:YAG laser (Fidelis Plus, Herzele, Belgium), groups 3 and 6 were treated with a laser and black ink; the remaining 12 teeth served as positive and negative controls. The laser was operated at 1.5 W, 15 Hz, four times for 5 s with a 20-s interval. Groups 4-6 were filled using cold lateral condensation of gutta-percha and AH26. After storage in water for 48 h at 37 degrees C, through-and-through leakage (L in microL day-1) was measured for 48 h under a pressure of 1.2 atm using a fluid transport model and recorded as L=0 (L1), 0<L<or=10 (L2), L>10 (L3). After the assessment of leakage with the fluid transport model, the teeth were immersed in rhodamine B solution for 48 h at 37 degrees C. Apical and coronal dye leakage was scored after longitudinal splitting of these teeth. All teeth of groups 1-3 were split longitudinally and observed under SEM for evaluation of remaining smear layer.

RESULTS

Through-and-through leakage was only observed in the group lased with black ink (two samples-L2). Apical and coronal dye leakage was observed in all groups; there were no statistically significant differences amongst the three experimental groups. The through-and-through leakage, measured with the fluid transport model in two teeth of group 6, was confirmed in the dye leakage test (rhodamine B dye was observed along the total length of the root filling). There was evidence of melted and ablated root canal dentine in the laser-treated groups. These findings were more obvious in root canals lased in association with black ink. All apical foramina in the lased group remained patent.

CONCLUSIONS

Nd:YAG laser irradiation with black ink increased the amount of melted and ablated dentine areas compared with that without black ink. Nd:YAG lasing in association with black ink did not result in a reduction of either coronal or apical microleakage in root filled teeth.

Removal of Two Types of Root Canal Filling Material Using Pulsed Nd:YAG Laser Irradiation

OBJECTIVE

The aim of this study was to examine the usefulness of a pulsed Nd:YAG laser in removing two types of endodontic obturation material from the root canal in vitro.

BACKGROUND DATA

Recently, a fine flexible glass fiber made of quartz has been developed to transmit the laser beam more effectively and permit its concentration in a specific area. This has increased the potential usefulness of the Nd:YAG laser in root canal treatment.

METHODS

The time required for removing the root canal obturation material (Gutta-percha cones and, Sealapex or AH26) by means of either Nd:YAG laser irradiation or a conventional method (Gates Glidden drills and K files) was measured. Contact microradiography was used to assess the radiopacity of the root canals before and after the removal of obturation material. The surfaces of the root canal after removal of the obturation materials were also observed by scanning electron microscopy.

RESULTS

Although none of the methods used in this study resulted in complete removal of debris from the root canal wall, the time required for the removal of any of the root canal obturation materials using laser ablation was significantly shorter than that required using the conventional method (p < 0.05). It appeared that some orifices of the dentinal tubules were blocked with melted dentin following laser irradiation.

CONCLUSIONS

Nd:YAG laser irradiation is an effective tool for the removal of root canal obturation materials, and may offer advantages over the conventional method.

Scanning Electron Microscopy (SEM) and Optical Microscopy: Effects of Er:YAG and Nd:YAG Lasers on Apical Seals after Apicoectomy and Retrofill

OBJECTIVE

This study evaluated the dentinal and marginal permeability of the cut surface after apicoectomy, treatment and retrocavity preparation with Er:YAG and Nd:YAG lasers. Furthermore, scanning electron microscopy (SEM) analysed the morphological alteration of dentin caused by laser irradiation through an optical fiber.

BACKGROUND DATA

Numerous studies have shown the beneficial effects of laser treatment upon sealing dental apex, avoiding the changes of organic fluids, microorganisms and their by-products between the root canal system and periapex.

MATERIALS AND METHODS

Twenty-four extracted and endodontically treated teeth were divided into three groups: GI, apices were resected with Er:YAG laser (350 mJ; 4 Hz) treatment of cut dentinal surface and retrocavity were lased with this same laser (120 mJ; 4 Hz; bur 2051) using the optical fiber 50/10; GII, apicoectomy was performed similar to GI, however the cut dentinal surface was treated with Nd:YAG laser through optical fiber, as well as the retrocavity preparation (100 mJ; 15 Hz; 1.5 W); and GIII (control group), high speed burs were used.

RESULTS

Analysis of methylene blue dye penetration into dentin demonstrated that the specimens of the groups irradiated with laser showed to have lower infiltration indices than the control group. These results were compatible with structural and morphological injuries, evidenced by SEM.

CONCLUSION

Under the conditions of the present study, apicoectomy using Er:YAG laser, followed by dentinal surface irradiation and retrocavity preparation with Nd:YAG laser, showed to be an alternative clinical tool able to reduce the dentinal permeability.

Lasers in endodontics

With the rapid development of laser technology, new lasers with a wide range of characteristics are now available and being used in various fields of dentistry. In the past two decades, much experience and knowledge has been gained. This article provides an overview of the current and possible future clinical applications of lasers in endodontics, including their use in alleviating dentinal hypersensitivity, modification of the dentin structure, pulp diagnosis, pulp capping and pulpotomy, cleaning and shaping of the root canal system, and endodontic surgery. Endodontic procedures for which conventional treatments cannot provide comparable results or are less effective are emphasized.

Comparative Study of Dentine Permeability after Apicectomy and Surface Treatment with 9.6 µm TEA CO2and Er:YAG Laser Irradiation

Failure of apicectomies is generally attributed to dentine surface permeability as well as to the lack of an adequate marginal sealing of the retrofilling material, which allows the percolation of microorganisms and their products from the root canal system to the periodontal region, thus compromising periapical healing. The purpose of this study was to evaluate dentine and the marginal permeability after apicectomy and surface treatment with 9.6 micro m TEA CO(2) or Er:YAG 2.94 micro m laser irradiation. Sixty-five single rooted human endodontically treated teeth were divided into five experimental groups: group I (control), apicectomy with high speed bur; group II, similar procedure to that of group I, followed by dentinal surface treatment with 9.6 micro m CO(2) laser; group III, similar procedure to group I followed by dentinal surface treatment with Er:YAG laser 2.94 micro m; group IV, apicectomy and surface treatment with CO(2) 9.6 micro m laser; and group V, apicectomy and surface treatment with Er:YAG laser 2.94 micro m. The analysis of methylene blue dye infiltration through the dentinal surface and the retrofilling material demonstrated that the samples from the groups that were irradiated with the lasers showed significantly lower infiltration indexes than the ones from the control group. These results were compatible with the structural morphological changes evidenced through SEM analysis. Samples from groups II and IV (9.6 micro m CO(2)) showed clean smooth surfaces, fusion, and recrystallized dentine distributed homogeneously throughout the irradiated area sealing the dentinal tubules. Samples from groups III and V (Er:YAG 2.94 micro m) also presented clean surfaces, without smear layer, but roughly compatible to the ablationed dentine and without evidence of dentinal tubules. Through the conditions of this study, the Er:YAG 2.94 micro m and the 9.6 micro m CO(2) laser used for root canal resection and dentine surface treatment showed a reduction of permeability to methylene blue dye.

Influence of the EDTA, Nd:YAG laser and association of both on the filling of artificial lateral root canals

This study aimed at evaluating the influence of EDTA, Nd:YAG laser and the combination of both for filling of artificial lateral root canals. Forty-five human mandibular premolars were employed, on which three artificial lateral root canals were prepared by means of a reamer with a similar diameter to a K file #15. The teeth were instrumented through the stepback technique employing Gates Glidden burs at the middle and cervical thirds and manual files at the apical portion, and irrigation with 1% sodium hypochloride. The teeth were divided in three groups: Group 1 -EDTA for 5 minutes; Group 2 -application of Nd:YAG laser at 15 Hz, 100 mJ and 1.5 Watts; and Group 3 - association of both. Roots were filled through the Tagger's hybrid technique, radiographed and the radiographs were digitized. Scores were assigned to the filling of the lateral root canals. Statistical analysis revealed no significant differences between the entire groups and also on the analysis of each third.

In vitro study of the effects of Nd:YAG laser irradiation on the apical sealing of endodontic fillings performed with and without dentin plugs

OBJECTIVE

The aim of this study was to evaluate the effects of Nd:YAG laser irradiation on the apical sealing of root canal fillings with or without a dentin plug.

BACKGROUND DATA

Previous studies have shown that Nd:YAG laser irradiation of root canal wall dentin promotes its melting, recrystallization, and therefore a less permeable surface.

MATERIALS AND METHODS

Thirty extracted and endodontically treated teeth were divided into three groups. Eight specimens of each group were evaluated by means of quantitative analysis, measuring the marginal apical dye leakage. The remaining two specimens were evaluated by means of qualitative analysis, using the scanning electron microscopy (SEM). For the quantitative analysis, the samples of group I were obturated. In group II, the apical third of the samples were irradiated by the Nd:YAG laser at four exposures of 100 mJ/pulse, 1 W, 10 Hz, 3 sec, and obturated. In group III, an apical dentin plug was condensed and lased using the same parameters of group II, and the root canals were obturated. The samples evaluated by SEM were prepared as those analyzed quantitatively; however, their root canals were not filled.

RESULTS

There were statistically significant differences among the groups regarding dye leakage. Group II showed the minor leakage average, followed, in order, by groups I and III. SEM analysis revealed open dentinal tubules in group I; melting and recrystallizing of the apical root dentin in group II; and melting and recrystallizing of a portion of the dentin plug in group III.

CONCLUSION

The Nd:YAG laser irradiation of the root canal apical third without the presence of dentin plug significantly improved the quality of the apical sealing under the experimental conditions tested.

A comparison of the morphological changes after Nd-YAG and CO2 laser irradiation of dentin surfaces

The purpose of this study was to compare the morphological changes after Nd-YAG and CO2 laser irradiation on dentin surfaces with or without the smear layer. Eighty-one 3-mm-thick dentin specimens collected from the middle third of molar crowns were used. The dentin surfaces were ground to #320, #400, and #600 grit in series to create a smear layer. Half of the specimens were treated with 14% EDTA for 2 min to remove the smear layers. The lasers were applied on each specimen perpendicularly with 1-mm focus distance to the dentin surface for 4 s. The parameters for the Nd-YAG laser were 50 mJ, 100 mJ, and 150 mJ at 10 pps, 20 pps, and 30 pps, and for the CO2 laser were 2 W, 3 W, and 4 W at 5 ms x 20 pps, 10 ms x 10 pps, 20 ms x 20 pps, 50 ms x 2 pps, 100 ms x 2 pps, and 200 ms x 2 pps. The results showed that the Nd-YAG laser caused crater and melting of the dentin surface, especially in dentin specimens with smear layers. The CO2 laser produced extensive cracking lines on dentin surfaces with a smear layer, whereas surface erosion and crater formation were found on specimens without a smear layer. In conclusion, both the laser types and smear layer have a significant influence on the morphological changes of dentin surfaces irradiated by lasers.

Lasers in endodontics: a review

Since the development of the ruby laser by Maiman in 1960 and the application of the laser for endodontics by Weichman in 1971, a variety of papers on potential applications for lasers in endodontics have been published. The purpose of this paper is to summarize laser applications in endodontics, including their use in pulp diagnosis, dentinal hypersensitivity, pulp capping and pulpotomy, sterilization of root canals, root canal shaping and obturation and apicectomy. The effects of laser on root canal walls and periodontal tissues are also reviewed. The essential question is whether a laser can provide equal or improved treatment over conventional care. Secondary issues include treatment duration and cost/benefit ratio. This article reviews the role of lasers in endodontics since the early 1970s, summarizes many research reports from the last decade, and surmises what the future may hold for lasers in endodontics. With the potential availability of many new laser wavelengths and modes, much interest is developing in this promising field.

Ultrastructural properties of laser-irradiated and heat-treated dentin

Previous studies using scanning electron microscopy and infrared absorption spectroscopy reported that laser irradiation causes compositional changes in enamel. The purpose of this study was to evaluate the ultrastructural and compositional changes in dentin caused by irradiation with a short-pulse laser (Q-switched Nd:YAG). The irradiated and non-irradiated areas of the lased dentin samples were investigated by scanning (SEM) and transmission electron microscopy (TEM), micro-micro electron diffraction, and electron microprobe analysis of dispersive energy (EDX). Heat-treated dentin was similarly investigated. This study demonstrated that laser irradiation resulted in the recrystallization of dentin apatite and in the formation of additional calcium phosphate phases consisting of magnesium-substituted beta-tricalcium phosphate, beta-TCMP, beta-(Ca,Mg)3(PO4)2, and tetracalcium phosphate, TetCP, Ca4(PO4)O. TEM analyses of the modified and unmodified zones of the irradiated areas showed two types of crystal populations: much larger crystals from the modified zone and crystals with size and morphology similar to those of dentin apatite in the unmodified zone. The morphology of crystals in the modified zones in the irradiated dentin resembled those of dentin sintered at 800 or 950 degrees C. In the irradiated areas (modified and unmodified zones), the Ca/P ratio was lower compared with that in the non-irradiated dentin. The Mg/Ca ratio in the modified zones was higher than that in the unmodified zones and in the non-irradiated dentin. In sintered dentin, the Mg/Ca ratio increased as a function of sintering temperature. The ultrastructural and compositional changes observed in laser-irradiated dentin may be attributed to high temperature and high pressure induced by microplasma during laser irradiation. These changes may alter the solubility of the irradiated dentin, making it less susceptible to acid dissolution or to the caries process.

A clinical study on the effects of pulsed Nd:YAG laser irradiation at root canals immediately after pulpectomy and shaping

OBJECTIVE

The effects of pulsed Nd:YAG laser irradiation for the treatment of root canals immediately after pulpectomy and shaping with regard to improvement of symptoms were evaluated clinically.

SUMMARY BACKGROUND DATA

The effects of pulsed Nd:YAG laser irradiation for the treatment of root canals were experimentally investigated using an animal model, but not under clinical conditions.

MATERIALS AND METHODS

Thirty-eight teeth from 29 patients were diagnosed as normal or irreversible pulpitis were used. After extirpation of pulp and shaping using a step-back technique and cleansing with 5% sodium hypochlorite (NaOCl) and 3% hydrogen peroxide (H2O2), laser irradiation was applied at 1 W and 15 pps for 1 second in 23 teeth (laser-treated group). Root canals were then obturated with gutta-percha points and sealer by the lateral condensation method. The condition of the obturations was confirmed radiographically. The control teeth were treated in the same way, but without laser irradiation. Occurrence of spontaneous pain was recorded 1 day after treatment and occurrence of percussion pain was recorded 1, 2, and 3 weeks after treatment.

RESULTS

Effective ratio, which was the ratio of the number of "none" teeth to total teeth number in the laser-treated group, was higher than that in the control group, but there was no significant difference between 2 groups with regard to spontaneous and percussion pain (p > 0.05).

CONCLUSION

These results suggest that the clinical application of pulsed Nd:YAG laser might be advantageous for the one-visit treatment of root canals immediately after pulpectomy shaping and to reduce postoperative pain.

Post-operative symptoms and healing after endodontic treatment of infected teeth using pulsed Nd:YAG laser

Forty-four teeth in 38 patients, diagnosed with chronic apical periodontitis, were endodontically treated. Root canals were shaped using a step-back technique with 5% NaOCl and 3% H2O2 as irrigants. In half of the teeth the canal terminus was irradiated with pulsed Nd:YAG laser (1 W, 15 pps, 1 s). All canals were then obturated with laterally condensed gutta-percha points and sealer, and final radiographs were obtained. Occurrence of spontaneous pain was recorded 1 day after treatment. Percussion pain was recorded after 1 week, and then at 3 and 6 months after treatment. Radiographic follow-up was performed at 3 and 6 months. Percussion pain was significantly less (P < 0.05) in the laser-treated group than in the control group, both 1 week and 3 months after treatment. Other differences between the groups were not significant. These results suggested that the clinical application of pulsed Nd:YAG laser might be advantageous for the treatment of infected root canals.

The carbon dioxide laser as an aid in apicoectomy: an in vitro study

OBJECTIVE

To achieve the required goal of optimally sealing the apical section and the root-canal when performing an apicoectomy, the authors decided to use the CO2 laser as an additional aid.

SUMMARY BACKGROUND DATA

The CO2 laser has previously shown to have an excellent sealing effect on dentin surfaces.

METHODS

In this in vitro study, the authors examined the effects of CO2 laser application in apicoectomies with the help of color penetration tests and scanning electron microscopic (SEM) examinations. Sections and root canals were irradiated with low power (0.5 W) in continuous wave mode for totally 20 sec. The thermal stress for the adjacent tissues attaching thereto is moderate as shown by infrared-spectroscopy.

RESULTS

A comparison with nonirradiated samples revealed that CO2 laser irradiation reduced color penetration at the section to a minimum. Also, irradiation of the root-canal wall resulted in satisfactory sealing of the surface. These findings were supported by the results of the SEM examinations.

CONCLUSIONS

CO2 laser treatment optimally prepares the tooth for final intraoperative filling because of sealing of the dentinal tubules, the resultant elimination of niches for bacteria and the sterilizing effect of the laser.

Erbium:YAG and holmium:YAG laser root resection of extracted human teeth

Root resection of extracted human teeth was performed using the erbium:YAG (Er:YAG) and holmium:YAG (Ho:YAG) laser to investigate the clinical application of lasers on hard tissue. The CO2 laser and the mechanical drill were also used for comparison. After resection using these technologies, the morphological changes of the cut surface were investigated by optical and scanning electron microscope. Er:YAG laser irradiation produced smooth, clean resected surfaces without signs of thermal damages. Complete obturation of the root canal was maintained after Er:YAG laser irradiation. Ho:YAG laser irradiation, however, produced some signs of thermal damage. Relatively large voids between the gutta-percha and the canal walls were revealed after Ho:YAG laser irradiation. The sealing of the dentinal tubules was not completely attained as stipulated by original conditions of this study.

Connective tissue response to root surfaces resected with Nd:YAG laser or burs

PROBLEM

The Nd:YAG laser beam may be used for root resection, but the tissue compatibility of the resulting root surface has not been confirmed.

OBJECTIVE

This study assessed the connective tissue response over time to implanted root segments with Nd:YAG laser-cut or bur-cut surfaces.

STUDY DESIGN

Endodontically treated roots of 25 extracted human teeth were cross sectioned to form 3.5 mm thick disks by alternating a water-cooled Nd:YAG laser with a high-speed water-cooled tungsten fissure bur. A total of 63 disks were implanted into the dorsal subcutaneous tissue of 16 rats, then recovered with the surrounding tissue after periods of 3, 7, 14, 28, 60, and 90 days, and processed for light microscopic examination. Tissue against the cut surfaces was assessed for intensity and extent of inflammation and fibrous capsule thickness.

RESULTS

A two-factor analysis of variation showed statistically significant (p < 0.05) differences between the laser-cut and bur-cut surfaces.

CONCLUSION

Tissue repair about the root surfaces resected with Nd:YAG laser was delayed when compared with those resected with a bur.

Dentin ablation with three infrared lasers

BACKGROUND AND OBJECTIVE

Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics.

STUDY DESIGN/MATERIALS AND METHODS

Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns.

RESULTS

The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system.

CONCLUSION

Possible explanation for these observations is given in terms of plasma characteristics.

Dentin ablation with three infrared lasers

BACKGROUND AND OBJECTIVE

Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics.

STUDY DESIGN/MATERIALS AND METHODS

Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns.

RESULTS

The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system.

CONCLUSION

Possible explanation for these observations is given in terms of plasma characteristics.

Permeability, morphologic and temperature changes of canal dentine walls induced by Nd: YAG, CO2 and argon lasers

The permeability, temperature and morphologic changes of the wall of the root canal induced by Nd:YAG, CO2 and argon lasers were studied. The changes were evaluated according to the presence or absence of a smear layer. Root canals of 140 human single-rooted teeth were enlarged using a step-back technique. Permeability was evaluated by the extent of methylene blue dye penetration into the tubules. Temperature changes were measured using a thermovision system, and morphological changes were evaluated by scanning electron microscopy. Laser energy was delivered into the canal by means of a flexible optical fibre or metal tip. There were statistically significant differences in permeability between lased groups with and without a smear layer in the cervical third of the root canal following lasing. In the middle third of the root canal, all three laser types induced permeability increases in groups with a smear layer. In the apical third, statistically significantly decreases in permeability were observed among CO2 laser and Nd:YAG compared with control group (P < 0.01). Rises in temperature ranged from a minimum of +10.1 degrees C (CO2 laser) to a maximum of +54.8 degrees C (argon laser). All three laser devices appeared capable of producing a glazed-like surface and craters.

A comparison of the effects of Nd:YAG and Ho:YAG laser irradiation on dentine and enamel

This preliminary study was undertaken to investigate the effects of Nd:YAG and Ho:YAG lasers on enamel and dentine of extracted teeth. The Ho:YAG laser (spot size 250 microns, energy density 4160 J/cm2) produced a cleaner puncture in dentine with less melting of the surrounding tissue than did the Nd:YAG laser (spot size 20 microns), energy density 50,000 J/cm2), which produced considerable melting and recrystallization of dentine and was more difficult to control. It was possible to cut enamel and dentine with both lasers, but considerable melted and recrystallized enamel was produced. From the limited observations of this study it appears that the Ho:YAG laser is more suitable for cutting both enamel and dentine than the Nd:YAG laser. More work needs to be done to ascertain the effect on enamel and dentine of modification of the parameters of both lasers.