Two-dimensional changes and surface characteristics from an erbium laser used for root canal preparation.

BACKGROUND AND OBJECTIVE: Erbium lasers have been advocated for use in root canal because of their ability to ablate dentin and remove biologic debris in the root canal space. This study evaluated the ability of an Er:YAG laser to remove dentin predictably in the root canal system and its cleaning ability. STUDY DESIGN/MATERIALS AND METHODS: Twenty-eight single-rooted extracted teeth were assigned into two groups. The first group was cleaned and shaped using crown-down technique with GT rotary files (control). The second group used an Er:YAG laser with ceramic tip, above the dentin ablation threshold for root canal shaping. A separate group of three teeth was evaluated for cleanliness using an Er:YAG laser with spiral tips. Amount of dentin removed in the buccal-lingual and mesial-distal directions was measured, the data analyzed by ANOVA. Surface characteristics were qualitatively examined. RESULTS: The control group produced cleaner, better shaped root canals, faster than the Er:YAG group. The Er:YAG group removed more dentin in the coronal portion but less in the middle and apical thirds. The Er:YAG with spiral tip group left a dense smear layer in the middle and apical thirds. The Er:YAG group was subject to procedural errors more often than the control group. CONCLUSION: The Erbium laser studied was equivalent to rotary files in the coronal and middle thirds but not in the apical thirds of the root canal system.

Tissue pH and temperature regulate pulpal nociceptors.

The TRPV1 receptor acts as a sensor for environmental changes in pH and temperature. Since many nociceptors express TRPV1, it is possible that local tissue-cooling may inhibit nociceptor activity via reduction of TRPV1 activation. The present study used isolated superfused rat dental pulp to test the hypothesis that capsaicin receptors are activated in inflamed tissue, as measured by alterations in neuropeptide release. We tested the hypothesis that alterations in the tissue temperature and pH of isolated superfused rat dental pulp regulate capsaicin-induced release of calcitonin gene-related peptide (CGRP). Application of capsaicin with increased proton concentration (i.e., lowered pH) produced a nearly two-fold increase in peak immunoreactive CGRP release, as compared with capsaicin applied at a pH of 7.4. Reduction in tissue temperature from 37 degrees C to 26 degrees C completely blocked the capsaicin effect. The study indicates that environmental stimuli regulate the activity of capsaicin-sensitive neurons innervating dental pulp, and these factors may be significant clinically in the development and amelioration of dental pain.

Ultrastructure and nanomechanical properties of cementum dentin junction.

The attachment between cementum and dentin has been given several definitions and nomenclature, including: interzonal layer, intermediate cementum, collagen hiatus, Hopewell-Smith's hyaline layer, and more commonly, cementum-dentin junction (CDJ). Understanding the attachment of two structurally dissimilar hard tissues such as cementum and dentin defined by a junction may provide information necessary to engineer functionally graded materials that can be used for efficient tooth restorations in clinical dentistry and other bioengineering applications. Hence, in this study, as a first step toward understanding the CDJ using a biomechanical approach, it was hypothesized that the CDJ between cementum and dentin is a wide zone with mechanical properties significantly lower than the neighboring tissues. The structure of the CDJ was studied using an atomic force microscope (AFM), and site-specific mechanical response of the three regions; cementum, CDJ, and dentin were determined using an AFM-nanoindenter under dry and wet conditions. The AFM results of the CDJ demonstrated a valley under dry conditions and a peak under wet conditions. The magnitude of the depth of the valley was approximately the same as the height of the peak of the CDJ, ranging from 10 to 40 microm. The nanomechanical properties under dry conditions indicated no significant difference (p > 0.05) in elastic modulus and hardness of the CDJ (Er = 17.5 +/- 2.7 GPa, H = 0.6 +/- 0.1 GPa) and cementum (Er = 18.7 +/- 2.5 GPa, H = 0.6 +/- 0.1 GPa). The mechanical properties of the CDJ were significantly lower (p << 0.05) than dentin (Er = 19.9 +/- 2.9 GPa, H = 0.6 +/- 0.1 GPa) under dry conditions. However, under more relevant hydrated conditions, the mechanical properties of CDJ (Er 3.0 +/- 0.7 GPa, H = 0.1 +/- 0.0 GPa) were significantly lower (p << 0.05) than those of cementum (Er 6.8 +/- 1.9 GPa, H = 0.2 +/- 0.1 GPa) and dentin (Er 9.4 +/- 2.3 GPa, H = 0.3 +/- 0.1 GPa). Based on the results from this study, it can be concluded that the CDJ can be regarded as a wide zone containing large quantities of proteins including collagen that contribute to hydration and significantly reduce mechanical properties, compared with the adjacent hard tissues, cementum, and dentin. The lower mechanical properties of the CDJ may make it possible for it to redistribute occlusal loads to the alveolar bone.

A laboratory study of coronal microleakage using four temporary restorative materials.

AIM: The aim of this study was to compare the sealing abilities of Fermin and Canseal with the more popular temporary coronal filling materials, Cavit and Caviton. METHODOLOGY: Standardized access cavities were prepared in 160 intact human permanent molar teeth. They were divided into five groups consisting of 32 samples. The teeth were restored using one of the temporary filling materials, namely: Fermin, Canseal at two powder to liquid ratios, Caviton and Cavit. Thermal cycling and/or load cycling were applied on the samples. Assessment of microleakage utilized methylene blue dye penetration. Grading of the microleakage pattern was from 1 to 3, with 3 providing the best seal. Results were analyzed using two-way anova and by Fisher's PLSD post hoc test (P < 0.05). RESULT: Microleakage along Fermin, Caviton and Cavit samples did not go beyond Leakage Grade 2. Dye penetration into these materials was noted. This was not observed in the two groups of Canseal tested. However, the two groups of Canseal exhibited total leakage notably after being subjected to thermal cycling. There was a statistically significant difference in the microleakage scores obtained between the materials and conditions tested (P < 0.0001). CONCLUSION: Fermin was found to exhibit the best seal amongst the four materials tested followed by Caviton, and Cavit. Thermal cycling influenced the seal of certain types of temporary filling materials more than load cycling.

Endodontic status in older U.S. adults. Report of a survey.

BACKGROUND: Aging people experience a number of changes in the root canal systems of teeth that, while they are normal, have the potential to compromise the pulp's response to injury. METHODS: To better understand the dental perspective on these changes, the authors mailed a questionnaire to diplomates of the American Board of Endodontics. The questions dealt with the respondents' experiences, ages of their patient population and their perception of root canal changes in aging patients. The authors analyzed the data in terms of number of diplomates providing a response and stratified them on the basis of the respondents' number of years in practice. RESULTS: Respondents indicated that the number of patients aged 65 years and older in their practices is increasing. Virtually all of the diplomates agreed that the root canal gets smaller with age, but that this diminution does not contribute to the failure of treatment of affected teeth. Most respondents indicated that aging patients' teeth are in poorer condition than those of younger patients. CONCLUSIONS: As the U.S. population ages, clinicians need to have a better understanding of the physiological changes occurring in older patients' teeth that may influence the treatment required to help patients retain their natural dentition. Further studies are needed to determine the impact of aging on dental disease and treatment modalities. CLINICAL IMPLICATIONS: Recognition of changes in the dentition of aging patients will lead to more successful treatment, retention of functional natural dentition and better maintenance of general health.

Prostaglandin E2 enhances bradykinin-evoked iCGRP release in bovine dental pulp.

Mediators produced during inflammation are responsible for hyperalgesia and expression of neurotransmitters and receptors in the nervous system. The production of bradykinin (BK) and the prostaglandins (PGs) may regulate initiation of pain. This study tested the hypothesis that BK and prostaglandin E2 (PGE2) have a positive interaction in evoking neurosecretion of immunoreactive calcitonin gene-related peptide (iCGRP). Bovine dental pulp was prepared and stimulated by the superfusion method with BK alone and in combination with PGE2. Kinin receptor antagonists to bradykinin-evoked release of iCGRP were also tested. Also tested was the hypothesis that dental pulp contains either the B1 or B2 or both BK receptors. Results showed that PGE2 enhanced BK-evoked iCGRP release by more than 50%. Western immunoblots revealed detectable B2 receptor protein with no detectable B1 receptor protein. We conclude that BK evokes iCGRP release from bovine dental pulp which is enhanced by a positive interaction with PGE2. Neurosecretion is evoked from isolated terminals of dental pulp fibers via the bradykinin B2 receptor-dependent mechanism.

Pulpal responses to cooling tooth temperatures.

This investigation measured pulpal blood flow and sensitivity to electrical stimulation as tooth temperatures were lowered. Dark rubber dams were placed on test teeth before placement of the cooling device in an attempt to shield gingival microcirculation. Laser Doppler flowmetry was used to measure pulp blood flow, whereas sensory thresholds were recorded simultaneously using an electric pulp tester. As tooth temperatures were lowered, the teeth became less responsive. Pulp blood flow also slowed, but did not completely stop. Results indicated that sensory thresholds were altered, and in some subjects, abolished, without total cessation of pulpal blood flow.

Bradykinin levels in dental pulp by microdialysis.

Bradykinin is a potent mediator of pain and inflammation. To examine extracellular levels of bradykinin in human dental pulp, CMA/20 microdialysis probes were inserted into the pulp tissue of 22 teeth diagnosed with normal pulp or with irreversible pulpitis before their extraction or endodontic therapy. Probes were perfused with a modified Locke-Ringer's buffer and bradykinin levels in the dialysate evaluated using a radioimmunoassay. Mean extracellular levels of bradykinin within pulp tissue diagnosed with irreversible pulpitis were significantly higher (262.26 +/- 83.79 fmol/ml) than that found within normal pulp (19.41 +/- 6.47 fmol/ml). Highest levels of bradykinin were detected in pulp tissue diagnosed with irreversible pulpitis when the patient had reported pain in the past, compared with patients who were in pain just before their visit. These observations suggest that the bradykinin system is activated during pulpitis and may contribute to pain and inflammation.

Gingival microcirculation response to tooth brushing measured by laser Doppler flowmetry.

This study quantified changes in blood flow following tooth brushing, using laser Doppler flowmetry (LDF). Twenty subjects had polysiloxane stents fabricated with openings to permit placement of the LDF probe on the mesial papillae of 6 teeth. Probing depth, plaque index, and gingival index were recorded and subjects instructed in brushing. LDF initially recorded a 30 second baseline blood flow. The stent was removed and subjects brushed the site for either 3 or 10 seconds. The stent was repositioned and recordings again taken, followed by a control reading. The process was repeated 4 weeks later. Correlations between baseline and control readings were 0.585 (P < 0.001) at the first visit, and 0.654 (P < 0.001) at the return visit. The mean control blood flow was 156.4 perfusion units. The 3 and 10 second brushing increased the mean value 22.6 units and 21.2 units respectively (both P < 0.001). Tooth brushing for both 3 and 10 seconds significantly increased gingival blood flow in the papillary gingiva of healthy individuals.

In vitro study of the effects of Nd:YAG laser probe parameters on bovine oral soft tissue excision.

BACKGROUND AND OBJECTIVES: Lasers are now used for intraoral, soft tissue procedures. The effects of Nd:YAG probes on cutting efficiency and temperature rise were evaluated in vitro. STUDY DESIGN/MATERIALS AND METHODS: Three hundred twenty-micron 400-microns, 500-microns, and 600-microns probes were used to ablate bovine gingiva, mucosa, and tongue at various power and frequency settings. Thermocouples positioned under the subjacent cortical bone measured temperature rise. Tissue samples were evaluated histologically. RESULTS: Mean pooled temperature rise was 1 degree C at 3 W and 1.4 degrees C at 5 W. Excision width ranged from 0..63 mm to 0.79 mm at tested settings, cutting depths from 0.19 mm to 0.49 mm, lateral and deep coagulation from 0.27 mm to 0.62 mm. CONCLUSION: Temperature rise in bone was related to increased power. Cutting efficiency of laser probes was not significantly improved by increased power. Probes of 320 to 500 microns provided efficient cutting at 3 W and 5 W, thus reducing the potential for unacceptable temperature rise in bone.

Effects of Nd: and Ho:yttrium-aluminium-garnet lasers on human dentine fluid flow and dental pulp-chamber temperature in vitro.

Dentine specimens were prepared from freshly extracted third molars and initial permeability measured. Each specimen was subjected to Nd:yttrium-aluminium-garnet (YAG) (1.06 or 1.32 microns wavelength) or Ho:YAG (2.10 microns wavelength) laser energy while temperatures in the pulp chambers were recorded. Permeability was again measured and the surfaces examined by scanning electron microscopy. Six crown segments were used for each laser variable and eight permeability measurements were taken before and eight after laser exposure, while temperature was recorded during treatment. All wavelengths reduced permeability but temperature rises were high enough to have caused pulpal damage, indicating that shorter treatment times and lower power settings may be necessary if used in vivo.

Spectroscopic changes in human dentine exposed to various storage solutions--short term.

OBJECTIVES: Tooth storage conditions in studies of dentine have not been standardized. The objective of this investigation was to determine the effects of storage solution and time on dentine, using spectroscopic methods. METHODS: Twenty-seven dentine disks (0.75 mm thick) were prepared from freshly extracted third molars with documented histories. The teeth were sectioned parallel to the occlusal plane using a diamond saw. Specimens were analysed non-destructively for surface chemical changes using specular reflectance infra-red Fourier transform spectroscopy (SRIFTS), and changes in optical properties were measured in the ultraviolet, visible and near-infra-red spectral ranges with an integrating sphere spectrophotometer (UV/VIS/NIR) before and after storage. A minimum of five specimens were stored in distilled water with 0.02% thymol, purified and filtered water, phosphate buffered saline with 0.02% thymol, 70% ethanol or 10% buffered formalin and evaluated at 0, 1, 2, 7, 14, 21 and 28 days. After each measurement, specimens were stored in fresh solutions. IR spectra were obtained from 4400 to 400 wave-numbers (cm-1). Optical properties of reflectance and transmittance were determined from 200 to 2500 nm, and absorbance was calculated. RESULTS: Analysis of the IR spectra indicated no significant differences in collagen or mineral peak positions for any solution at any time period. There were significant differences in peak intensities of dentine stored in distilled water, purified and filtered water and phosphate-buffered saline over time in the IR spectra. Furthermore, differences in optical properties of dentine disks were detected by UV/VIS/NIR. CONCLUSION: It was concluded that changes in surface chemistry and optical properties of dentine occur as a function of storage solution and time, which must be considered when studying dentine.

Sterilization of teeth by gamma radiation.

Clinical simulations and restorative materials research and development conducted in vitro require the use of large numbers of extracted teeth. The simultaneous need for infection control procedures and minimal alterations of structure and properties of the tissue prompted this study of gamma irradiation as a method to eliminate microbes associated with extracted teeth and their storage solutions. Evaluations of potential change in structure of dentin were conducted in terms of permeability, Fourier transform infrared spectroscopy (FTIR), and optical properties. The dose required for sterilization by gamma irradiation was established by means of a tooth model inoculated with Bacillus subtilis (10(8) organisms/mL). Sterilization occurred at a dose above 173 krad with use of a Cesium (Cs137) radiation source. Gamma irradiation did not affect permeability of crown segments of dentin. A comparative evaluation of the effects of four sterilization methods on dentin disks was based on FTIR and ultraviolet-visible-near infrared (UV/VIS/NIR) spectra before and after sterilization by (1) gamma irradiation; (2) ethylene oxide; (3) dry heat; and (4) autoclaving. No detectable changes were found with gamma irradiation, but all other methods introduced some detectable change in the spectra. This suggests that common methods of sterilization alter the structure of the dentin, but gamma irradiation shows promise as a method which both is effective and introduces no detectable changes as measured by FTIR, UV/VIS/NIR, or permeability.

Intrapulpal temperatures during pulsed Nd:YAG laser treatment of dentin, in vitro.

Lasers are being used for soft tissue removal, caries removal, and treatment of root surface sensitivity. One concern for laser safety is that the heat produced at the irradiated root surface may diffuse to the pulp causing irreversible pulpal damage. To test this heat diffusion, copper-constantan thermocouples were inserted into the radicular pulp canals of extracted teeth. Simulating direct exposure which might occur during gingival excision, superficial caries removal, and modification of the dentin surface for treatment of root surface sensitivity, a 2 mm2 area of the external root surface was uniformly irradiated with a pulsed Nd:YAG laser using a 320 microns diameter fiber optic contact probe. Power was varied from 0.3 to 3.0 W with frequencies of 10 and 20 Hz. Temperature changes during cavity preparations using a high speed handpiece with air coolant were also recorded. Repeated measures ANOVA (P < or = 0.05) indicated that intrapulpal temperatures increased as a function of power, frequency, and time. Intrapulpal temperatures decreased as remaining dentin thickness (0.2 to 2.0 mm) increased for each laser parameter. Irradiation of dentin using a Nd:YAG pulsed laser, within the treatment times, powers, and frequencies with adequate remaining dentin thickness, as outlined in this paper, should not cause devitalizing intrapulpal temperature rises.

Scanning electron microscopic examination of intracanal wall dentin: hand versus laser treatment.

Conventional cleaning and shaping of root canal spaces involves the use of hand and rotary instruments with irrigation. The procedure results in the formation of a smear layer consisting of dentin shavings, organic tissue remnants and microorganisms. The laser has been suggested as an aid in root canal preparation. In this study, pulsed and continuous wave 1.06 microns wavelength Nd:YAG lasers were used to compare their abilities to clean and shape root canal spaces to conventional methods. After preparation, the test teeth were sectioned longitudinally and examined by scanning electron microscopy. The results demonstrated that the laser was capable of removing the smear layer in its entirety and could occasionally alter dentin walls.

Effects of pulsed Nd:YAG laser energy on human teeth: a three-year follow-up study.

This study of laser use on dental hard tissues evaluated restorations and tooth vitality in teeth treated three years earlier. All teeth remained vital and asymptomatic. Restorations placed after caries removal were intact and clinically serviceable.

The effect of glass ionomer liners in lowering pulp temperatures during composite placement, in vitro.

New restorative systems allow for more esthetic restorations, but may cause adverse pulp tissue reactions due to either physical or chemical effects. This study evaluated the effect of glass ionomer liners in limiting temperature rise during composite placement with visible light-cure lamps. Neither chemical or light-cured glass ionomer liners limited the amount of pulp chamber temperature rise. Exposure time of the light-cure lamps played the greatest role in pulpal temperature rise regardless of glass ionomer liner of composite. Visible light-cure lamps varied in the amount of heat emitted.

Storage effects on dentin permeability and shear bond strengths.

The effects of duration of storage and selection of storage solution upon dentin permeability and bond strength were studied over a period of 8 days to 6 mon. Teeth were stored immediately after extraction in one of five commonly used solutions: 70% ethanol (E); 10% formalin (F); distilled water (W); distilled water with thymol (WT); or phosphate-buffered saline with thymol (ST). Permeability and lap shear bond strength measurements were evaluated in a repeated measures design (n = 20) after 8 days, 15 days and 6 mon. Dentin permeability varied with solution type and duration of storage as demonstrated by ANOVA, increasing F, E and the water-based solutions, respectively. Saline storage resulted in large significant decreases in permeability after prolonged storage, suggesting changes in dentin. Bond strengths were unaffected by duration of storage or by solution type, except for saline. Thus, permeability and bond strength values may be affected by storage conditions. The results of this study indicate that saline, the most commonly used solution in dental materials research, may be unsuitable for use as a result of its effect on dentin permeability and bond strength.

Identification of the physical modification threshold of dentin induced by neodymium and holmium YAG lasers using scanning electron microscopy.

Laser application to dentin has been advocated to modify the dentin substrate for restorative procedures. We examined the minimum energy density required to physically modify the dentin surface using 1.06 microns and 1.32 microns Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) and 2.10 microns Holmium-YAG (Ho:YAG) lasers. Three millimeter thick dentin sections from the middle occlusal third of crowns of third molars were used. To determine the effect of surface preparation, the sections were ground to 240, 320, 400, 600 grit or polished to 0.5 micron. Smear layer was removed using 0.5 M EDTA for 2 minutes. Five single pulse repetitions at each laser parameter were performed. Power (W) and energy per pulse (mJ/p) were increased for each wavelength until a physical modification occurred. The energy density (J/cm2) was then held constant and the threshold was confirmed using 200, 320 and 550 microns diameter quartz contact probes. Scanning electron microscopy (SEM) was used to verify the physical modification of the dentin. The physical threshold remained constant for ground and polished surfaces. Similar surface modifications were found for the three wavelengths tested. The threshold modifications occurred at 207, 165, and 83 J/cm2 for the 1.06 microns, 1.32 microns and 2.10 microns lasers, respectively. For all emission wavelengths tested the physical threshold modification occurred at relatively low energy densities. These lasers show promise for surface modification of dentin.