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

Emissivity evaluation of human enamel and dentin

Background: Human enamel and dentin temperatures have been assessed with non-contact infrared imaging devices for safety and diagnostic capacity and require an emissivity parameter to enable absolute temperature measurements. Emissivity is a ratio of thermal energy emitted from an object of interest, compared to a perfect emitter at a given temperature and wavelength, being dependent on tissue composition, structure, and surface texture. Evaluating the emissivity of human enamel and dentin is varied in the literature and warrants review. The primary aim of this study was to evaluate the emissivity of the external and internal surface of human enamel and dentin, free from acquired or developmental defects, against a known reference point. The secondary aim was to assess the emissivity value of natural caries in enamel and dentin.

Method: Fourteen whole human molar teeth were paired within a thermally stable chamber at 30°C. Two additional teeth (one sound and one with natural occlusal caries–ICDAS caries score 4 and radiographic score RB4) were sliced and prepared as 1-mm-thick slices and placed on a hot plate at 30°C within the chamber. A 3M Scotch Super 33 + Black Vinyl Electrical Tape was used for the known emissivity reference-point of 0.96. All samples were allowed to reach thermal equilibrium, and a FLIR SC305 infrared camera recorded the warming sequence. Emissivity values were calculated using the Tape reference point and thermal camera software.

Results: The external enamel surface mean emissivity value was 0.96 (SD 0.01, 95% CI 0.96–0.97), whereas the internal enamel surface value was 0.97 (SD 0.01, 95% CI 0.96–0.98). The internal crown-dentin mean emissivity value was 0.94 (SD 0.02, 95% CI 0.92–0.95), whereas the internal root-dentin value was 0.93 (SD 0.02, 95% CI 0.91–0.94) and the surface root-dentin had a value of 0.84 (SD 0.04, 95% CI 0.77–0.91). The mean emissivity value of the internal enamel surface with caries was 0.82 (SD 0.05, 95% CI 0.38–1.25), and the value of the internal crown-dentin with caries was 0.73 (SD 0.08, 95% CI 0.54–0.92).

Conclusion: The emissivity values of sound enamel, both internal and external, were similar and higher than those of all sound dentin types in this study. Sound dentin emissivity values diminished from the crown to the root and root surface. The lowest emissivity values were recorded in caries lesions of both tissues. This methodology can improve emissivity acquisition for comparison of absolute temperatures between studies which evaluate thermal safety concerns during dental procedures and may offer a caries diagnostic aid.

Microbiological Aspects of Root Canal Infections and Disinfection Strategies: An Update Review on the Current Knowledge and Challenges

The oral cavity is the habitat of several hundreds of microbial taxa that have evolved to coexist in multispecies communities in this unique ecosystem. By contrast, the internal tissue of the tooth, i.e., the dental pulp, is a physiologically sterile connective tissue in which any microbial invasion is a pathological sign. It results in inflammation of the pulp tissue and eventually to pulp death and spread of inflammation/infection to the periradicular tissues. Over the past few decades, substantial emphasis has been placed on understanding the pathobiology of root canal infections, including the microbial composition, biofilm biology and host responses to infections. To develop clinically effective treatment regimens as well as preventive therapies, such extensive understanding is necessary. Rather surprisingly, despite the definitive realization that root canal infections are biofilm mediated, clinical strategies have been focused more on preparing canals to radiographically impeccable levels, while much is left desired on the debridement of these complex root canal systems. Hence, solely focusing on "canal shaping" largely misses the point of endodontic treatment as the current understanding of the microbial aetiopathogenesis of apical periodontitis calls for the emphasis to be placed on "canal cleaning" and chemo-mechanical disinfection. In this review, we dissect in great detail, the current knowledge on the root canal microbiome, both in terms of its composition and functional characteristics. We also describe the challenges in root canal disinfection and the novel strategies that attempt to address this challenge. Finally, we provide some critical pointers for areas of future research, which will serve as an important area for consideration in Frontiers in Oral Health.

Use of Blue and Blue-Violet Lasers in Dentistry: A Narrative Review

Introduction: Blue and blue-violet diode lasers (450 and 405 nm) seem to represent an interesting approach for several clinical treatments today. The aim of this narrative review is to describe and comment on the literature regarding the utilization of blue and blue-violet lasers in dentistry. Methods: A search for "blue laser AND dentistry" was conducted using the PubMed database, and all the papers referring to this topic, ranging from 1990 to April 2020, were analyzed in the review. All the original in vivo and in vitro studies using 450 nm or 405 nm lasers were included in this study. All the articles on the LED light, laser wavelengths other than 405 and 450 nm and using lasers in specialties other than dentistry, as well as case reports, guideline papers and reviews were excluded. Results: From a total of 519 results, 47 articles met the inclusion criteria and were divided into 8 groups based on their fields of application: disinfection (10), photobiomodulation (PBM) (4), bleaching (1), resin curing (20), surgery (7), periodontics (1), endodontics (1) and orthodontics (3). Conclusion: Blue and blue-violet diode lasers may represent new and effective devices to be used in a large number of applications in dentistry, even if further studies will be necessary to fully clarify the potentialities of these laser wavelengths.

Evaluation of temperature rises during the application of different power levels of potassium titanyl phosphate and neodymium-doped:yttrium aluminum garnet lasers to external primary root canals

Background/purpose

Nowadays, laser systems play crucial roles in endodontic treatments. Therefore, these systems should be investigated in terms of parameters that may prevent periodontal tissues damages during laser irradiation. In this context, the purpose of this study was to evaluate temperature rises during the application of different power levels of potassium titanyl phosphate (KTP) and neodymium-doped:yttrium aluminum garnet (Nd:YAG) lasers to external primary root canals.

Materials and methods

Sixty primary mandibular molars were selected and chemomechanical preparation was performed. KTP laser treatment was applied to 30 of these 60 samples and the remaining 30 received Nd:YAG laser treatment. The teeth samples received laser application (KTP or Nd:YAG) at three different power levels (1 W, 1.5 W, and 2 W, respectively, applied to 10 samples from each group). Nine holes were drilled (1 mm in diameter) through the level of the coronal, middle, and apical third of each tooth canal to provide entry for a Type L thermocouple wire, which was used to measure temperature changes. Data were assessed with two-way analysis of variance and the Tukey test.

Results

All power levels indicated statistically significant differences between Nd:YAG and KTP laser systems (P < 0.05). Moreover, the same regional (apical, middle, and coronal) comparisons performed between Nd:YAG and KTP laser systems showed statistically significant differences (P < 0.05).

Conclusion

All parameters of KTP laser indicated lower temperature rises than Nd:YAG laser. Therefore, KTP laser may be preferable to protect the periodontal tissues from harmful thermal effects during the endodontic treatment of primary root canals.

An in vitro evaluation of microtensile bond strength of resin-based sealer with dentin treated with diode and Nd:YAG laser

BACKGROUND

Smear layer is a negative factor which prevents adhesion of the filling material to the dentinal walls. Recent advances in dental research have incorporated lasers as a potential adjunct in root canal treatment by removing the smear layer before filling the root canal system, enhancing the adhesion of sealers to dentin and improving the sealing ability.

AIM

To evaluate the microtensile bond strength of AH-Plus resin-based sealer to dentin after treatment with 980 nm diode and 1,064 nm neodymium-doped:yttrium aluminum garnet (Nd:YAG) laser in vitro.

MATERIALS AND METHODS

Thirty specimens prepared for three groups namely group I (control), group II (980 nm diode-lased specimens) and group III (Nd:YAG-lased specimens). One tooth from each group was observed under scanning electron microscope for evaluation of intracanal root dentin morphology. Remaining specimens were used for making microsections by hard tissue microtome. Specimens for groups II and III were lased with 980 nm diode and 1,064 nm Nd:YAG laser. AH Plus sealer was applied onto specimens and mounted onto Instron universal testing machine for microtensile bond strength testing. Results were subjected to statistical analysis using one-way analysis of variance (ANOVA) and Tukey's test.

RESULTS

Group III Nd:YAG had maximum mean microtensile bond strength values (11.558 ± 0.869), followed by group II diode (9.073 ± 0.468) and group I control (6.05 ± 0.036). Statistically significant differences were seen among all the groups. SEM analysis shows removal of smear layer in both groups II and III.

CONCLUSION

Both Nd:YAG and diode laser were more effective than control group in improving the microtensile bond strength of AH Plus sealer to dentin.

CLINICAL SIGNIFICANCE

Lasers have the potential to increase the adhesiveness of root canal sealer to dentin surface, thereby improving the quality of root canal obturation.

Effects of CO2 laser irradiation of the gingiva during tooth movement

Patients often feel pain or discomfort in response to orthodontic force. It was hypothesized that CO(2) laser irradiation may reduce the early responses to nociceptive stimuli during tooth movement. The distribution of Fos-immunoreactive (Fos-IR) neurons in the medullary dorsal horn of rats was evaluated. Two hrs after tooth movement, Fos-IR neurons in the ipsilateral part of the medullary dorsal horn increased significantly. CO(2) laser irradiation to the gingiva just after tooth movement caused a significant decrease of Fos-IR neurons. PGP 9.5- and CGRP-positive nerve fibers were observed in the PDL of all study groups. The maximum temperature below the mucosa during CO(2) laser irradiation was less than 40 degrees C. It was suggested that CO(2) laser irradiation reduced the early responses to nociceptive stimuli during tooth movement and might not have adverse effects on periodontal tissue.

Clinical effect of CO(2) laser in reducing pain in orthodontics

OBJECTIVE

To test the hypothesis that there is no difference in the pain associated with orthodontic force application after the application of local CO(2) laser irradiation to the teeth involved.

MATERIALS AND METHODS

Separation modules were placed at the distal contacts of the maxillary first molars in 90 patients in this single-blinded study. In 60 of these patients (42 females and 18 males; mean age = 19.22 years) this was immediately followed by laser therapy. The other 30 patients (18 females and 12 males; mean age = 18.8 years) did not receive active laser irradiation. Patients were then instructed to rate their levels of pain on a visual analog scale over time, and the amount of tooth movement was analyzed.

RESULTS

Significant pain reductions were observed with laser treatment from immediately after insertion of separators through day 4, but no differences from the nonirradiated control side were noted thereafter. No significant difference was noted in the amount of tooth movement between the irradiated and nonirradiated group.

CONCLUSIONS

The hypothesis was rejected. The results suggest that local CO(2) laser irradiation will reduce pain associated with orthodontic force application without interfering with the tooth movement.

Surgical laser use in implantology and endodontics

The use of surgical lasers has been advocated to aid in the placement and second stage recovery of dental implants, together with soft tissue contouring. In addition, laser use has been suggested as an aid in decontamination of the implant surface in cases of peri-implantitis. In endodontics, the association of laser energy with dentine hypersensitivity, bacteriocidal action and pulp-capping, has led to a growing number of reports as to its beneficial use, together with claims of morphological changes in the canal wall, to enhance endodontic treatment success.

Increases in intrapulpal temperature during polymerization of composite resin

STATEMENT OF PROBLEM

The polymerization of dental composite resins can generate increases in intrapulpal temperature that may damage the pulp. The development of new polymerization devices such as the argon laser makes the assessment of these temperatures important.

PURPOSE

This study compared increases in temperature generated by argon laser and halogen light when polymerizing a bonding system and a composite resin, and also sought to determine whether both types of polymerization lights generate temperature increases below the safe limit of 5.5 degrees C.

MATERIAL AND METHODS

Thermocouples linked to a temperature reading system were positioned in the pulp chamber of 10 extracted bovine incisors. Class V cavities were prepared, etched, and filled with a 1-bottle bonding system (Single Bond) and composite resin (Z-100). The test groups were as follows (n = 5 for all groups): halogen light for bonding system (HB); halogen light for composite resin (HC); argon laser for bonding system (LB), and argon laser for composite resin (LC). The polymerization parameters were halogen light operated at 600 mW/cm2 for 40 seconds, which served as control, and argon laser operated at 200 mW for 10 seconds. Data were analyzed by a 2-way (light versus material) analysis of variance (ANOVA) (alpha = .05).

RESULTS

The average temperature increases were 2.35 degrees C (HB), 2.69 degrees C (HC), 1.25 degrees C (LB), and 1.5 degrees C (LC). Significant differences between halogen light and argon laser (P = .002), but not between composite and bonding system, were demonstrated.

CONCLUSIONS

The argon laser produced significantly lower increases in pulpal temperature than the halogen light, independent of the thickness of the polymerized material.

Effects of Nd:YAG Laser Irradiation on Root Canal Dentin Wall: A Scanning Electron Microscopic Study

OBJECTIVE

The purpose of this study was to evaluate, by scanning electron microscopy (SEM), the effects of Nd:YAG laser irradiation applied perpendicular or parallel to the root canal dentin wall.

METHODS

Thirty human teeth were divided into two groups: Group A (20 roots), laser application with circular movements, parallel to the dentin root surface; and Group B (10 roots), roots cut longitudinally and laser applied perpendicular to the root surface. Group A was subdivided into A1 (10 roots), laser application with 100 mJ, 15 Hz and 1.5 W; and A2 (10 roots) with 160 mJ, 15 Hz, and 2.4 W. Group B was subdivided into B1 (10 hemisections) and B2 (10 hemi-sections) with parameters similar to A1 and A2. Four applications of 7-sec duration were performed, with a total exposure of 28 sec. SEM evaluations were made in the cervical, middle, and apical thirds, with 500x and 2000x magnifications. Morphological changes scores were attributed, and the results were submitted to Kruskal Wallis statistical test (5%).

RESULTS

Significant statistical differences were found between groups Aand B (p = 0.001). In groups A1 and A2, few areas of dentin melting were observed. In groups B1 and B2, areas of melting dentin covering dentin surface were observed.

CONCLUSIONS

It was concluded that intracanal laser application with circular movements (parallel to the surface) produces limited morphological changes in root canal dentin wall.

Temperature evolution on human teeth root surface after diode laser assisted endodontic treatment

The thermal rise threshold of an 810-nm semi-conductor diode laser on the root surface when used in root canals in vitro for laser assisted root canal treatment is investigated in this study. A total of 50 human single-rooted extracted teeth were included. For this study, the canals were enlarged up to an apical size of ISO#50 file. Laser irradiation was performed with six different settings. Specimens were irradiated at 0.6-1 W output power at the distal end of the fiber and about 1-1.5 W output power in the continuous mode (CW) as two groups. In the third group, 0.6-1 W output power, 10 ms pulse length (PL) and 10 ms interval duration (ID) were selected. In three other groups 1-1.5 W output power were used with different PL and ID as following: PL 10 and ID 10 ms, PL 10 and ID 20 ms and PL 20 and ID 20 ms. The total irradiation time was from 5 to 20 s per canal with a 200 mum in diameter and 25 mm long tip. After laser treatment, the temperature changes at the outer root surface were registered by means of NiCr-Ni measuring sensors and a T 202 thermometer. The safe temperature threshold for applying this diode laser in root canal is considered as 7 degrees C increase. To avoid increasing the temperature changes at the outer root surface related to this threshold, following total irradiation times were found: 0.6-1 W output power (10 ms PL/10 ms ID): 20 s (s), 1-1.5 W output power (10 ms/10 ms and 20 ms/20 ms): 15 s, 0.6-1 W output power CW and 1-1.5 W output power (20 ms PL/10 ms ID): 10 s and 1-1.5 W output power CW: 5 s. In the first three groups, 5 s irradiation and 5 s rest period avoided a temperature increase above the threshold of 7 degrees C).

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.

Microleakage assessment of pit and fissure sealant with and without the use of pumice prophylaxis

OBJECTIVES

This study evaluated the effect of pumice prophylaxis on the level of microleakage around and between the sealant and enamel.

MATERIALS AND METHODS

A total of 32 freshly extracted sound upper first premolars, assigned as suitable for sealant application, were chosen and divided randomly into two groups: (1) a test group, without prophylaxis; and (2) a control group, with prophylaxis. Sealant was applied to all teeth using the same conventional technique, with prophylaxis being omitted in the test group. The sealed teeth were thermocycled (120 x 30 s, 5 and 55 degrees C cycles) and then immersed in 2% Basic Fuchsin solution for 72 h. Each tooth was sectioned and examined for dye penetration under a stereomicroscope (x 60 magnification).

RESULTS

No dye penetration was seen in 19 (29.6%) of the teeth in the test group and 36 (56.2%) of the teeth in the control group. Dye had penetrated to the base of the fissure in 31 (48.4%) of the teeth in the test group and 23 (35.9%) of the teeth in the control group. Using a chi-square test for trend, the frequency of microleakage was significantly higher in the test group compared to the controls (P < 0.016).

CONCLUSION

Prophylaxis has a role in improving sealant retention. Removing this step may cause an increase in microleakage.

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.

Removal of gutta-percha from root canals using an Nd:YAG laser

AIM

To examine the use of an Nd:YAG laser in removing gutta-percha fillings from root canals when used in conjunction with eucalyptol, dimethylformamide (DMF) or no solvent.

METHODOLOGY

Root-canal fillings (sealer and gutta-percha) were removed with laser irradiation of 20 Hz/1.5 W from 30 roots randomly divided in three groups. In group 1, the solvent was eucalyptol; in group 2, the solvent was DMF; and in group 3, no solvent was used. Laser irradiation was performed until the temperature measured on the root surface increased by 4 degrees C over room temperature. The treatment was deemed complete when the apical foramen was reached with the optical fibre and a reamer. The samples were split longitudinally, and the area of remaining gutta-percha on the root-canal walls was determined with the aid of a computer program. The total number of laser pulses to achieve length and the highest temperature recorded was determined for each tooth. The results were statistically analysed using Student's t-test (P < 0.05) for independent samples.

RESULTS

The average temperature increase in group 1 was 9.17 +/- 0.56 degrees C; in group 2, 9.56 +/- 0.28 degrees C; and in group 3, 8.29 +/- 0.41 degrees C. The shortest time to achieve length was in group 3 (6.4 +/- 0.49 min), then in group 1 (6.7 +/- 0.85 min) and group 2 (7.05 +/- 0.79 min). The area of remaining gutta-percha was the largest in group 2 (6.13 +/- 5.76%), whilst the smallest was for group 3 (4.69 +/- 4.03%), but the difference was not statistically significant. The number of pulses was not statistically significant between the groups.

CONCLUSIONS

Use of an Nd:YAG laser alone is capable of softening gutta-percha. The addition of solvents did not improve the retreatment, either in terms of the time required for the procedure or in terms of the area of remaining gutta-percha on root-canal walls.

Ultrastructural changes of human dentin after irradiation by Nd:YAG laser

BACKGROUND AND OBJECTIVE

The use of Nd:YAG laser has been proposed for endodontic treatment. However, its ability to reduce dentin permeability, which is important for the success of root canal treatment, remains controversial.

STUDY DESIGN/MATERIALS AND METHODS

Nd:YAG laser irradiation was performed in pulsed mode on human dentin. The parameters were: pulse energy (100 mJ), rate (10 pps), and total irradiation time (4 seconds). The crystalline phases, electron diffraction patterns, morphology, and microstructure of specimens after laser irradiation were observed by dark-field emission transmission electron microscope (TEM).

RESULTS

Three ultrastructural zones could be delineated in the dentin: (1) an outer zone with an ordered columnar structure composed of hydroxyapatite and beta-tricalcium phosphate, (2) an intermediate zone composed of an amorphous substance (about 40-70 nm in diameter), and (3) an inner zone of well-crystallized hydroxyapatite grains. These three zones were free of pores or voids.

CONCLUSIONS

Our study demonstrated that laser-irradiation might be used to reduce dentin permeability.

Enamel caries initiation and progression after argon laser irradiation: in vitro argon laser systems comparison

OBJECTIVE

The purpose of this in vitro laboratory study was to determine the effect of low-fluence argon laser (AL) irradiation delivered from two different argon laser systems on enamel caries-like lesion initiation and progression.

BACKGROUND DATA

Previous in vitro investigations and a recent in vivo pilot study have shown that AL irradiation of enamel provided a protective effect against in vitro and in vivo cariogenic challenges.

MATERIALS AND METHODS

Twenty extracted human molars were selected, and 10 teeth were assigned to the HGM argon laser group and 10 were assigned to the LaserMed argon laser group. The exposed buccal windows of sound enamel were exposed to low-fluence irradiation, while the lingual windows of enamel were not exposed to laser irradiation and served as the no-treatment (control) group. Enamel caries-like lesions were created using an acidified gel. Two longitudinal sections were taken per sample (n = 20 lesions per group) and evaluated by polarized light microscopy for body of the lesion depths after lesion initiation (8 weeks) and progression (12 weeks) periods.

RESULTS

After lesion initiation and progression, the body of lesion depths were similar for both argon-irradiated groups (p > 0.05). With the no-treatment (control) group, there were significant increases in lesion depth with a 61-78% increase for the lesion initiation period and a 50-69% increase for the lesion progression period when compared with the argon laser-treated groups.

CONCLUSION

Argon laser irradiation provides a certain degree of protection against in vitro enamel caries initiation and progression. Resistance to a continuous caries challenge was similar with either argon laser delivery systems (HGM and LaserMed). Argon laser irradiation may prove to be beneficial in reducing the caries susceptibility of sound enamel and white spot lesions in the clinical environment.

Changes in dentin after insertion of self-threading titanium pins with 3 methods: a scanning electron microscope pilot study

STATEMENT OF PROBLEM

Inserting a self-threading pin can cause dentinal cracks, but it is not known whether dentin bonding agents can penetrate these cracks.

PURPOSE

Part I of this in vitro pilot study was conducted to document the presence of dentinal cracks after the placement of self-threading pins with 3 methods. Part II was conducted to observe changes in dentin when a dentin bonding agent was applied before insertion of the self-threading pins.

MATERIAL AND METHODS

The crowns of 14 noncarious third molars were sectioned horizontally 2 mm above the cemento-enamel junction, and the occlusal portions were discarded. The teeth were put into a nontransparent bag and divided randomly into 2 groups. Group 1 consisted of 12 teeth. In each tooth, 4 pinholes were prepared with a handpiece at normal rotation speed (30,000 rpm). Self-threading pins were placed into 3 of the pinholes in each tooth: 1 manually, 1 by handpiece at 7000 rpm, and 1 by handpiece at 30,000 rpm. The fourth pinhole was left empty and served as the control. All group 1 teeth were sectioned vertically through the pins, dental hard tissue, and control pin holes. The examination surface of each specimen in group 1 was polished, and the smear layer was removed with Calcinase and NaOCl solutions. After dehydration in ascending grades of alcohol, specimens were coated with a 10- to 15-nm-thick layer of gold and examined with a scanning electron microscope. In the remaining 2 teeth (group 2), a dentin bonding agent was introduced into the pinholes prior to pin placement. Two pins were placed manually and 2 by handpiece at 30,000 rpm. After pin placement, sectioning, cleaning, and dehydration, the specimens were examined with a scanning electron microscope, and x-ray mapping was performed to determine the presence of titanium, silicon, and calcium.

RESULTS

Craze lines in dentin were associated with 54.5% of pins placed manually and 54.5% of pins placed with a handpiece at reduced speed (7000 rpm). Dentinal cracks were associated with 50% of pins placed with a handpiece at standard speed and with 16.7% of the control pinholes. X-ray mapping analysis revealed the presence of the dentin bonding agent between the pin and dentin wall. The dentin bonding agent was not found in the dentinal cracks except at the crack orifice.

SUMMARY

Within the limitations of this pilot study, the method of pin insertion had no direct bearing on the presence of dentinal cracks. The dentin bonding agent tested did not fill the entire space of dentinal cracks but did occlude their orifices and fill the spaces between pin surface and dentin walls in the pin preparation.

Microleakage and nanoleakage: influence of laser in cavity preparation and dentin pretreatment

OBJECTIVE

The purpose of this study was to verify if the application of the Nd:YAG laser following pretreatment of dentin with adhesive systems that were not light cured in class V cavities and were prepared with Er:YAG laser would promote better sealing of the gingival margins when compared to cavities prepared the conventional way.

BACKGROUND DATA

Previous studies had shown that the pretreatment of dentin with laser irradiation after the application of an adhesive system is efficient in achieving higher shear bond and tensile bond strength.

MATERIALS AND METHODS

Er:YAG laser (Kavo-Key, Germany) with 350 mJ, 4 Hz, and 116.7 J/cm2 was used for cavity preparation. The conventional preparation was made with diamond bur mounted in high-speed turbine. Dentin treatment was accomplished using an Nd:YAG laser (Pulse Master 1000, ADT. USA) at 60 mJ, 10 Hz, and 74.65/cm2 following application of the adhesive system. The cavities were stored with Single Bond/Z100 and Prime & Bond NT/TPH. Eighty bovine incisors were used, and class V preparations were done at buccal and lingual surfaces divided into eight groups: (1) Er:YAG preparation + Prime & Bond NT + TPH; (2) Er:YAG preparation + Single Bond + Z100; (3) Er:YAG preparation + Single Bond + Nd:YAG + Z100; (4) Er:YAG preparation + Prime & Bond NT + Nd:YAG + TPH; (5) conventional preparation + Prime & Bond NT + TPH; (6) conventional preparation + Single Bond + Z100; (7) conventional preparation + Single Bond + Nd:YAG + Z100; (8) conventional preparation + Prime & Bond NT + Nd:YAG + TPH. All specimens were thermocycled for 300 full cycles between 5 degrees C+/-2 degrees C and 55 degrees C+/-2 degrees C (dwell time of 30 sec), and stored in 50% silver nitrate solution for 24 h soaked in photodeveloping solution and exposed to fluorescent light for 6 h. After this procedure, the specimens were sectioned longitudinally in 3 portions and the extension of microleakage at the gingival wall was determined following a criteria ranging from 0 to 4 using scanning electron microscopy (SEM). The medium portion sectioned of each specimen was polished and prepared for nanoleakage avaliation by SEM.

RESULTS

Kruskall-Wallis and Miller statistical tests determined that group 3 presented less microleakage and nanoleakage.

CONCLUSION

Application of the Nd:YAG laser following pretreatment of dentin with adhesive Single Bond non-photocured Single Bond adhesive in cavities prepared with Er:YAG promote better sealing of the gingival margins.

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.

Morphological and atomic analytical changes of root canal wall dentin after treatment with thirty-eight percent Ag(NH3)2F solution and CO2 laser

OBJECTIVE

The morphological and atomic analytical changes of the root canal wall dentin, treated with 38% diamine silver fluoride [Ag(NH3)2F] solution and irradiated by carbon dioxide (CO2) laser at the continuous wave mode were evaluated in vitro.

SUMMARY BACKGROUND DATA

There has been no report on the morphological or atomic analytical changes of the effect of Ag(NH3)2F solution and CO2 laser on root canal walls.

METHODS

Eighty extracted human single-rooted teeth were instrumented using a conventional technique and randomly divided into 8 groups of 10 teeth each. The teeth in group 1 were neither treated with Ag(NH3)2F solution nor lased. Groups 2, 3, and 4 were irradiated by laser at the parameters of 1, 2, and 3 W for 10 seconds, respectively. Group 5 was treated with Ag(NH3)2F solution only. The other 3 groups were treated with Ag(NH3)2F solution and then lased by the same method as groups 2, 3, and 4. After this treatment, 4 specimens each from group 1, 5, and 6 were analyzed by scanning electron microscope-energy dispersive x-ray spectroscopy (SEM-EDX) and other specimens in all groups were examined by scanning electron microscopy (SEM).

RESULTS

The smear layer and debris of the control and lased specimens were not completely removed, but the areas of carbonization of evaporation of smear layer and open dentinal tubules were observed on the specimens treated with Ag(NH3)2F and lased at 1 W (group 6). After laser irradiation, the amount of silver on the root canal surfaces was significantly reduced to approximately one-third level on the measurement of SEM-EDX (p < 0.01).

CONCLUSION

These results suggest that CO2 laser is an effective method to remove or melt smear layer of root canal walls after treatment with 38% Ag(NH3)2F solution if an appropriate parameter is selected.

Susceptibility of Nd:YAG laser-irradiated root surfaces in replanted teeth to external inflammatory resorption

Nd:YAG laser-induced modification of the root surface may inhibit development of external inflammatory resorption in replanted teeth. This study tested this hypothesis in vivo. The pulp chambers of six mandibular premolars in each of two dogs were accessed, inoculated with plaque, and sealed (Groups 1, 2). Two additional premolars in each dog were endodontically treated without inoculation (Groups 3, 4). After 2 weeks, teeth were hemisected and extracted. Each root had a 2 x 3 mm surface area denuded of cementum on the buccal and lingual surface. In Groups 1 (n = 12 roots) and 3 (n = 4), the denuded surfaces were wiped with 15% EDTA, coated with black ink, and irradiated with Nd:YAG laser (0.75 W, 15 pps, 300 microns tip, 20 s). In Groups 2 (n = 12) and 4 (n = 4), the surfaces were wiped with 15% EDTA, and rinsed with sterile saline for 20 s. Roots were replanted within 5 min. The dogs were perfusion-euthanised 10 weeks after replantation. Block specimens were removed, decalcified, embedded and horizontally sectioned (6 microns) at 180-microns intervals, resulting in 10 to 14 cross-sections of each root. From these, the middle five consecutive sections were stained with hematoxylin and eosin, and observed by light microscopy for occurrence of surface, inflammatory and replacement resorption on the denuded surfaces. No obvious differences were noted between the laser-irradiated and non-irradiated surfaces. Inflammatory resorption was frequent in Groups 1 and 2, and absent in Groups 3 and 4. Replacement resorption was minimal in Groups 1 and 2, and frequent in Groups 3 and 4. Differences between Groups 1 and 2, and between Groups 3 and 4 were not significant, whereas the differences between the two pairs of groups were statistically significant (chi-square and two-way ANOVA, P < 0.006). These results did not support the hypothesis, and questioned the clinical validity of the surface modification in Nd:YAG laser-irradiated dentin. Therefore, the clinical application of Nd:YAG laser to the root surfaces of replanted teeth is not warranted.

Scanning electron microscopic study of dentin lased with argon, CO2, and Nd:YAG laser

The purpose of this study was to compare morphological changes on the dentin surface induced by laser light delivered perpendicular or parallel to the dentin surface. The surface of the dentin slices and the root canal walls were lased with argon, CO2, and Nd:YAG lasers. When the laser beam was parallel to the dentin, the effects of the laser energy ranged from no effect to eroding and melting of the smear layer and dentin in the samples. When the laser beam was perpendicular to the surface, all three lasers produced well-shaped craters. From this, it was concluded that the angle of the laser beam in relation to the target surface can be a deciding factor of how much energy will be absorbed by the dentin and consequently of the morphological changes induced by the laser.