Antioxidant and pro-oxidant properties of chlorhexidine and its interaction with calcium hydroxide solutions

AIM

To evaluate the antioxidant and pro-oxidant properties of chlorhexidine (CHX).

METHODOLOGY

The scavenging and generation of reactive oxygen species (ROS) by CHX in the presence or absence of saturated Ca(OH)(2) solutions was evaluated. The reaction emitted chemiluminescence in the presence of lucigenin thus was determined by a luminometer to evaluate the levels of ROS production. Changes in DNA conformation were analysed by agarose gel electrophoresis. Paired Student's t-test was used to compare the difference between groups.

RESULTS

Chlorhexidine (0.00002-0.02%) effectively scavenged 56-88% of the superoxide radicals generated by the xanthine/xanthine oxidase reaction. Through analysis of PUC18 DNA conformation changes, CHX was shown to be a mild scavenger of hydroxyl radicals generated by H(2)O(2) plus FeCl(2). However, CHX (>0.083%) decreased the mobility of PUC18 plasmid DNA with potential production of DNA-DNA cross-link and severe DNA breaks (presence of DNA smear) at further higher concentrations. Furthermore, CHX induced ROS production including H(2)O(2) and superoxide radicals in 0.1N NaOH (pH = 12.76) or Ca(OH)(2) (pH = 12.5) solutions.

CONCLUSION

Chlorhexidine exhibited both antioxidant and pro-oxidant properties under different conditions. These events are possibly involved in the killing of root canal and periodontal microorganisms when CHX and Ca(OH)(2) were used in combination or separately. Potential genotoxicity and tissue damage when extruded into the periradicular tissue and at higher concentrations should be considered during periodontal and endodontic practice.

Persistent endodontic lesion due to complex cementodentinal tears in a maxillary central incisor—a case report

The cementodentinal tear is rarely detected by noninvasive procedures owing to its clinical picture simulating a root fracture or a periodontal or endodontic lesion. We present a case of complex cementodentinal tears in a 79-year-old woman who presented a repeated swelling at the labial mucosa of the left maxillary central incisor for 6 months. Periapical radiographs demonstrated a vertical radiolucent fracture line extending from the root apex along the mesial aspect of the root to near the middle portion of the root of the left maxillary central incisor. Because endodontic re-treatment failed to cure the disease, periapical surgery was performed, and 2 fractured U-shaped root fragments around the apical root surface were removed. Histologic examination showed that the 2 fractured root fragments were composed mainly of the dentin covered by a thin layer of the cementum and overlying periodontal ligament tissue, suggesting cementodentinal tears. A swelling recurred 8 months after the initial operation. Therefore, a second periapical surgery was performed. Although no obvious fracture line was observed around the root surface, the second surgery did not cure the disease, either. A persistent small swelling was noted at the alveolar mucosa of the affected tooth during the follow-up. We conclude that although a cementodentinal tear can be detected by a careful radiographic examination, its clinical outcome is not predictable by surgical removal only.

Cytotoxicity of DP-Bioglass Paste Used for Treatment of Dentin Hypersensitivity

DP-bioglass mixed with 30% phosphoric acid has been suggested to treat dentin hypersensitivity because the material is able to produce homogeneous occlusion of exposed dentinal tubules and is able to provide a sealing depth of up to 60 microm. The purpose of this study was to investigate the relative cytotoxic effect of the DP-bioglass paste, intermediate restorative material (IRM; DeTrey, Dentsply, Germany), and commercial desensitizing agent (Abmindent; Abmin Technologies Ltd, Turku, Finland) on human dental pulp cells by using a transwell insert model and a dentin-disc model. Cell viability was measured by means of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results of this study indicated that cell viability for the DP-bioglass paste did not differ significantly from those of the IRM or Abmindent in the transwell insert model. In addition, MTT results of DP-bioglass paste were similar to the control group in the dentin-disc model. The results indicated that DP-bioglass paste was a highly biocompatible material and could potentially serve as an effective material for treatment of dentin hypersensitivity.

Cytotoxicity of partial-stabilized cement

Partial-stabilized cement (PSC) is a kind of modified calcium silicate cement used for root-end surgery. Minor transition metal elements Co, Cr, and Zn were added for enhancing the setting property of to PSC. In our previous study, minor transition metal additions greatly improved the setting property of PSC. However, the concern of metal toxicity was raised, as the material would be used in the human body. In this study, we evaluated the cytotoxicity of PSC in comparison with mineral trioxide aggregate (MTA), which is one of the commercialized materials used for dental root-end filling. Primary osteoblast cell was used as the target cell. Cell proliferation, cytotoxicity, viability, function, and senescence were analyzed. The cytotoxicity of the PSC-Zn group (PSC with Zn addition) was similar to that of MTA. PSC-Zn is not only nontoxic at the cellular level but also has adequate mechanical property, which makes it a potential root-end filling material for apical surgery.

Microstructural changes of enamel, dentin-enamel junction, and dentin induced by irradiating outer enamel surfaces with CO2 laser

The microstructural changes of enamel, dentin-enamel junction (DEJ), and dentin after CO(2) laser irradiation were studied. Buccal enamel surfaces of human third molars about 2 mm from the DEJ were irradiated, and the laser tip was moved 5 mm in a mesiodistal direction with 5 s of irradiation time. The output powers were 2 to 10 W in a continuous mode, and the average doses were approximately from 250 to 1,250 J/cm(2). All specimens were examined by a scanning electron microscope, and heat-transfer simulation was also applied to calculate temperature distribution. Surface ablation of enamel and separation of enamel and dentin along the DEJ were observed when the laser power output exceeded 3 W. Heat-transfer simulation indicated that dentin was prone to store more thermal energy than enamel. In conclusion, operation parameters of the CO(2) laser should be carefully selected to avoid thermal damage to the DEJ.

Double-quantum filtered heteronuclear correlation spectroscopy under magic angle spinning

We present a simple experimental method to extract the van Vleck second moment of a multiple-spin system under high-resolution condition. The idea is to incorporate a double-quantum (DQ) filter into the pulse sequence of heteronuclear correlation spectroscopy so that a DQ excitation profile can be obtained by measuring a series of 2D spectra. The effects of spinning frequency and proton decoupling are demonstrated on the measurements of two model compounds, viz. hydroxyapatite and brushite. Based on the results obtained for the model compounds, the P-31 homonuclear second moment of the apatite component in rat dentin is characterized. The method is generally suited for the study of bone, enamel and dentin.

Application of Plasma Immersion Ion Implantation for Surface Modification of Nickel-titanium Rotary Instruments

By means of X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC), this study set out to investigate the application of plasma immersion ion implantation (PIII) for the surface modification of ProTaper NiTi rotary instruments. This study was undertaken because the PIII method was perceived to have the potential of developing into a standard surface modification technique that improves clinical quality and outcome. Specimens received nitrogen ion or nitrogen plus argon ion implantation. XPS analyses with and without argon ion etching were obtained for all specimens. In addition, DSC analysis was performed to investigate the phase transformation behavior of the bulk material. Results indicated that the surfaces of NiTi instruments were successfully modified by nitrogen PIII, whereby a light golden TiN layer was yielded. Moreover, the PIII technique did not alter the superelastic character of NiTi instruments because it was carried out at near-room temperature. We thus concluded that nitrogen PIII is a promising surface modification technique to improve the surface characteristics of NiTi rotary instruments.

In Vitro Study of Dentinal Tubule Occlusion with Sol-gel DP-bioglass for Treatment of Dentin Hypersensitivity

DP-bioglass paste has been demonstrated to produce 60 microm of sealing depth on exposed dentinal tubules. However, the occlusive effect depended on a continuous placement of DP-bioglass paste on dentinal surface for three days. In a bid to fabricate highly reactive DP-bioglass particles, a sol-gel method was used together with HNO3, NaOH, and H3PO4 as catalysts. As a result, the application time of DP-bioglass paste was significantly reduced to 10 minutes. Percentage of tubular occlusion with DP-bioglass was 53.2-65.4%, while One Coat Bond and Seal & Protect yielded 51.3% and 41.2% respectively. Further, the average depth of tubular occlusion with DP-bioglass was 55.8-62.7 microm, while One Coat Bond and Seal & Protect produced 40.8 microm and 32.5 microm respectively. In conclusion, the best sealing performance of tubular occlusion was rendered by DP-bioglass catalyzed with HNO3. Its performance was significantly better than Seal & Protect, and was considered to exhibit the greatest potential in treating dentin hypersensitivity.

Evaluation of mandibular block using a standardized method

The purpose of this prospective randomized study was to investigate the manifestations and efficiency of mandibular block (MB) using a standardized method. In this study, 123 patients requiring MB were randomly assigned to receive MB using a repeated measures design. Mandibular block was administered in each patient by using 2.1 mL of 2% lidocaine with 1:100 000 epinephrine for the inferior alveolar nerve, lingual nerve, and/or buccal nerve. Clinical parameters including the electric pulp test and test for soft tissue sensation using a sharp dental explorer were assessed on both the operated side and contralateral side before and 5, 10, and 15 minutes after injection, and at the end of surgical procedure. Results of the test of the contralateral tooth served as the control group. No response to the electric pulp test at a maximum output (80 readings) was used as the criterion for pulpal anesthesia. Results obtained with electric pulp test and sharp explorer test were not significantly different during various intervals on the contralateral side, indicating the reliability of this standardized method for assessing MB. The MB technique achieved a high rate of subjective numbness (100%) according to the perception of the patients of overall numbness and lip numbness. Overall anesthetic success rates of pulpal anesthesia were 5.7% for the central incisor, 38.2% for the canine, 55.3% for the first premolar, and 90.2% for the first molar. No significant difference was found in the efficiency of anesthesia related to sex or age of the patients. A slower onset of pulpal anesthesia after MB was found for the anterior teeth than for the posterior teeth. This study suggests that the use of a standardized method might produce a clearer and more comprehensive evaluation of the efficiency and manifestations of MB.

Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface

OBJECTIVES

As the bond strength of composite resin to Er,Cr:YSGG laser-irradiated dentin has not yet been evaluated, the objectives of this study were to investigate the tensile bond strength and to analyze the resin-dentin interface among bur-cut/acid-etched, Er,Cr:YSGG laser-ablated/acid-etched and Er,Cr:YSGG laser-ablated human dentin.

METHODS

Crown dentin disks prepared from extracted human third permanent molars were used for the observation of surface morphological changes by scanning electron microscope (SEM). The laser energy parameters were 3.5 W and 20 Hz with water spray (air pressure level, 80%; water pressure level, maximum level). Another group of crown dentin disks were prepared for composite resin restoration and observation of resin-dentin bond interface after demineralization in 6N hydrochloric acid (HCl) for 1 min and deproteinization in 1% sodium hypochlorite solution (NaOCl) for 10 min. The tensile bond strengths of the three groups were measured by a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture types at the dentin-resin interface were analyzed using the digital stereoscopic microscope and fractured surfaces of the debonded specimens were examined by SEM.

RESULTS

All three groups showed that the treated surfaces were free of dentin debris and smear layer. The peritubular dentin protruded from the surrounding intertubular dentin after laser irradiation. The dentin-resin interface treated with Er,Cr:YSGG laser irradiation and acid etching demonstrated numerous resin tags converging into a bulge and then diverging again. The length of resin tags was greater than 100 microm. The tensile bond strengths of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were 5.37+/-1.51, 5.17+/-1.41 and 3.29+/-0.86 MPa, respectively. No statistical significance was found between the bur-cut/acid-etched and laser-ablated/acid-etched groups. The predominant fracture modes of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were Type 1 (50%), Type 2 (70%) and Type 1 (70%), respectively.

SIGNIFICANCE

Er,Cr:YSGG laser irradiation affects adversely adhesion of resin to dentin but acid etching following laser irradiation could increase the tensile bond strength as high as that of bur-cut/acid-etched human dentin.

Spectral editing based on selective excitation and Lee-Goldburg cross-polarization under magic angle spinning

We show that a Gaussian-shaped pulse can be used to excite selected 1H signals in hydroxyapatite, monetite and H-Y zeolite loaded with trimethylphosphine oxide (TMPO). This selective excitation method can be incorporated into Lee-Goldburg (LG) cross-polarization to obtain useful spectral editing opportunity. This new strategy has been applied to identify the Brønsted and the Lewis acid sites in H-Y zeolite using TMPO as the probe molecule.

Comparison of the Gow-Gates mandibular block and inferior alveolar nerve block using a standardized protocol

BACKGROUND

Although several previous studies have compared the efficacy of Gow-Gates mandibular block (GGMB) and inferior alveolar nerve block (IANB), the results remain controversial. This study used an objective, standardized and precise protocol to evaluate and compare the effectiveness and success rate of GGMB and IANB.

METHODS

The study group consisted of 162 patients (93 males and 69 females) who were randomly allocated to receive GGMB or IANB for extraction of third molars. Both methods used 2.7 mL of 2% xylocaine for each patient. Pulpal and gingival tissue anesthesia of mandibular central incisors, canines, first premolars and first molars were evaluated at 0, 5, 10, 15 and 60 minutes after injection of local anesthetic solution using both an electric pulp tester and a sharp explorer.

RESULTS

The success rates of pulpal anesthesia in the IANB group (central incisor, 6%; canine, 37%; first premolar, 54%; first molar, 88%) were not significantly different from the GGMB group (central incisor, 8.1%; canine, 37.1%; first premolar, 54.8%; first molar, 83.9%). All subjects achieved 100% lip numbness with both methods. At 60 minutes after injection, the success rates of gingival tissue anesthesia in canine buccal and lingual areas were higher in the IANB group (100% and 100%, respectively) than in the GGMB group (91.9% and 93.5%, respectively). In the molar buccal area, the success rates at 5 and 60 minutes after injection were higher in the IANB group (97% and 100%, respectively) than in the GGMB group (88.7% and 91.9%, respectively). Furthermore, the success rates in the molar lingual area at 10, 15 and 60 minutes after injection were higher in the IANB group (100%, 100% and 100%, respectively) than in the GGMB group (91.9%, 93.5% and 91.9%, respectively). Although IANB achieved higher success rates of gingival tissue anesthesia in some gingival areas, no significant difference between the two methods was found in overall efficacy.

CONCLUSION

This study demonstrated that the efficacy of pulpal and gingival tissue anesthesia are not significantly different between the GGMB and IANB methods.

Effects of simvastatin withdrawal on serum matrix metalloproteinases in hypercholesterolaemic patients

BACKGROUND

Serum matrix metalloproteinase (MMP) levels have been related to clinical outcomes in patients with coronary artery disease. Though statin treatment might reduce serum MMPs the change of levels after statin withdrawal remains obscure.

MATERIALS AND METHOD

Sixty-one consecutive hypercholesterolaemic patients whose lipid profiles had been well controlled by regular simvastatin (20 mg day(-1)) treatment for more than 6 months were enrolled. Statin was discontinued after their lipid profiles reached the treatment goal of the ATP-III guideline. The lipid profiles, serum MMP-2, MMP-3 and MMP-9, tissue inhibitor of MMP and highly sensitive C-reactive protein (hsCRP) levels were measured on the day of simvastatin withdrawal and 120 days later. A further 50 hyperlipidaemia patients who had never received statin treatment (positive control group) and 28 healthy patients with normal lipid profiles (negative control group) were also studied as control groups.

RESULTS

While the lipid profiles had been normalized, the levels of serum inflammatory markers were still higher in hypercholesterolaemic patients than in the healthy subjects. Up to 120 days after statin withdrawal there was no coronary event, but the lipid profiles and serum hsCRP levels had significantly rebounded in study patients. However, serum MMP-2 and MMP-9 levels remained unchanged and the MMP-3 level was even further reduced after statin withdrawal (115.04 +/- 84.54 vs. 92.71 +/- 66.71 ng mL(-1), P = 0.022). Moreover, the amplitudes of variation (%) of each parameter including MMPs, TIMP, hsCRP and lipid profiles after statin withdrawal were inversely correlated to their respective baseline levels before withdrawal (r = -0.702 to -0.284; P < 0.005).

CONCLUSIONS

The effects of short-term discontinuation of statin were different on serum hsCRP and MMPs levels in hypercholesterolaemic patients. While lipid profiles and serum hsCRP level had rebounded the serum MMPs levels were still unchanged, or even reduced, suggesting the prolonged effect of statin treatment, especially on serum MMP-3 level up to 120 days after simvastatin withdrawal. Further work is required to clarify the situation both in terms of these serum markers and clinical effects.

Bactericidal effects of diode laser onStreptococcus mutans after irradiation through different thickness of dentin

BACKGROUND AND OBJECTIVES

A reliable method to eradicate the bacteria of residual carious dentin has not yet been developed. The aim of this study was to evaluate the antibacterial effect of a diode laser on Streptococcus mutans through different thickness (500, 1,000, and 2,000 microm) of human dentin. The thermal effect of laser irradiation was also investigated.

STUDY DESIGN/MATERIALS AND METHODS

Dentin specimens were inoculated with 2 microl of S. mutans on one side and irradiated by a diode laser on the other side with a power output ranging from 0.5 to 7 W. The laser tip was swept with the whole irradiation area of 7 mm x 3 mm at a speed of about 10 mm/second with a total irradiation time of 30 seconds. Cooling with distilled water (30 ml/minute) was applied simultaneously during laser irradiation. After laser irradiation, the bacteria was removed from the dentin surfaces and cultured for 48 hours at 37 degrees C anaerobically to assess the colony forming units (CFU) per ml. The morphology of the lased bacteria and the temperature rise during laser irradiation were observed by scanning electron microscope (SEM) and measured by thermocouple, respectively.

RESULTS

The results revealed that 7 W of laser power could kill 97.7% of CFU through 500 microm thickness of dentin. However, the bactericidal efficiency was significantly reduced as the dentin thickness was increased. The morphological changes of lased bacteria ranged from less affected such as loss of their wall bands and existence of minicells to more severely degenerated, such as disintegration and fusion of cells with pores on the cell wall. Only the dentin specimens with a thickness of 500 microm exhibited a temperature rise greater than 5.5 degrees C after receiving 5 or 7 W of laser irradiation.

CONCLUSIONS

A diode laser can eliminate the Streptococcus mutans of the residual carious dentin without inducing high pulpal temperature rise when the remaining dentin thickness is greater than 1 mm.

Application of Nondestructive Testing in Cyclic Fatigue Evaluation of Endodontic Ni-Ti Rotary Instruments

The purpose of this study was to investigate the application of nondestructive testing in cyclic fatigue evaluation of endodontic ProFile nickel-titanium (NiTi) rotary instruments. As-received ProFile instruments were made to rotate freely in sloped metal blocks by a contra-angle handpiece mounted on a testing machine. Rotation was interrupted periodically, and the instrument removed and engaged onto a device to monitor its stiffness by using two strain gauges in four different directions. This monitoring method has the potential to be developed into a convenient, nondestructive turnkey system that allows in situ assessment of the integrity of NiTi instruments in the clinic. Upon fracture, which was indicated by a change in instrument stiffness, the fractured surface would be examined under a scanning electron microscope. Microscopic evaluation indicated a small area of fatigue fracture with a large area of final ductile fracture, whereby the latter was the major cyclic failure mode. Based on the results of this study, we concluded that a potential nondestructive integrity assessment method for NiTi rotary instruments was developed.

Effects of various periodontal ligament elastic moduli on the stress distribution of a central incisor and surrounding alveolar bone

BACKGROUND AND PURPOSE

Previous studies investigating the effects of core or post on the fracture strength of teeth often omitted the periodontal ligament (PDL) because its physical properties are difficult to reliably quantify. This study investigated the effects of various PDL elastic moduli on the stress distribution around a central incisor and surrounding alveolar bone using 3-dimensional finite element stress analyses.

METHODS

Four 3-dimensional finite element models of an upper central incisor and the dento-alveolar complex were established. Five models were constructed, including: no PDL, as well as a PDL with elastic moduli of 6.9 MPa, 68.9 MPa, and 1750 MPa. Two loading conditions were simulated, one with protrusive force and one with intrusive force. Protrusive loading was generated using a point force of 200 N at 45 degrees inclination to the longitudinal axis of the incisor applied on the lingual side. Intrusive loading was generated using a point force of 200 N applied perpendicular to the incisal edge.

RESULTS

The absence of a PDL had detrimental effects on the surrounding bone, because the applied stress remained concentrated at the bone crest and cervical third of the root. A PDL with a lower elastic modulus, on the other hand, helped to alleviate the magnitude of stress throughout the surrounding bone and the bone crest, in particular, by distributing the stress deeper towards the apical region. The stress distribution at the crown was unaffected by variations in the PDL elastic modulus.

CONCLUSIONS

PDL with a lower elastic modulus can help protect the alveolar bone crest from stress concentration.

Plasma matrix metalloproteinase-3 level is an independent prognostic factor in stable coronary artery disease

BACKGROUND

Recent evidence suggests the important role of matrix metalloproteinases (MMPs) in the progression of atherosclerosis and development of clinical events. We assessed the prognostic value of different plasma MMPs in patients with stable coronary artery disease (CAD).

MATERIALS AND METHODS

A total of 165 consecutive nondiabetic patients with angiographically significant CAD (n = 150) or normal coronary angiograms despite exercise-induced myocardial ischemia (cardiac syndrome X, n = 15) and 17 normal subjects were evaluated. In each subject, plasma inflammatory markers including high sensitivity C-reactive protein (hsCRP) and MMP-2, 3 and 9 were measured. In CAD patients, major cardiovascular events including cardiac death, nonfatal myocardial infarction, unscheduled coronary revascularization and hospitalization as a result of unstable angina were prospectively followed up for more than 6 months.

RESULTS

Plasma levels of MMPs were significantly higher in CAD patients than in those with cardiac syndrome X and in normal subjects (MMP-2: 914.76 +/- 13.20 vs. 830.79 +/- 31.95 vs. 783.08 +/- 28.40 ng mL(-1), P = 0.002; MMP-3: 129.59 +/- 4.21 vs. 116.86 +/- 8.09 vs. 91.71 +/- 9.55 ng mL(-1), P = 0.011; MMP-9: 31.42 +/- 2.84 vs. 11.40 +/- 5.49 vs. 6.71 +/- 2.89 ng mL(-1), P = 0.006). In CAD patients, there were 48 major cardiovascular events during a mean follow-up period of 17.74 +/- 0.85 months. The numbers of diseased vessels (HR = 2.19, 95% CI 1.20-1.02, P = 0.011), plasma hsCRP (HR = 2.21, 95% CI 1.18-4.11, P = 0.013) and MMP-3 level (HR = 2.46, 95% CI = 1.15-5.28, P = 0.021) were associated with the development of cardiovascular events. However, only the plasma MMP-3 level was an independent predictor of the adverse events in CAD patients (HR = 2.47, 95% CI 1.10-5.54, P = 0.028).

CONCLUSIONS

Plasma MMP levels were increased in CAD patients. Plasma MMP-3 level, rather than hsCRP, was an independent prognostic marker for future cardiovascular events, suggesting its potential role in risk stratification and clinical management of stable CAD.

In vitro study of dentin hypersensitivity treated by Nd:YAP laser and bioglass

OBJECTIVES

An ideal material has yet to be discovered that can completely treat dentin hypersensitivity. However, if a highly biocompatible material such as bioglass, could be melted by laser irradiation to achieve better sealing depth for dentinal tubules, it may subsequently bond to dentin structures under a physiological environment and offer a prolonged therapeutic effect.

METHODS

The authors used four types of energy parameters to melt the composition-modified bioglass. These four types were 30 Hz, 330 mJ/pulse (G+ mode), 30 Hz, 160 mJ/pulse (G- mode), 10 Hz, 400 mJ/pulse (D+ mode), and 10 Hz, 200 mJ/pulse (D- mode). The temperature elevation, occlusive depth of bioglass, and phase changes in the bioglass after laser irradiation were evaluated by means of scanning electron microscope (SEM), thermometer, and X-ray diffractometer (XRD).

RESULTS

The occlusive depths of 2 and 10 microm in the dentinal tubules were achieved when the bioglass underwent 30 Hz, 160 mJ/pulse (G- mode) and 30 Hz, 330 mJ/pulse (G+ mode) of laser treatments, respectively. The bioglass experienced a temperature increase of less than 600 degrees C, and no phase transformation was observed after Nd:YAP laser irradiation.

SIGNIFICANCE

The melting point of a composition-modified bioglass could be reduced and its use plus Nd:YAP laser have the potential in clinical use to treat dentin hypersensitivity.

[Selective RPE laser treatment with a scanned cw laser beam in rabbits]

BACKGROUND

Selective RPE laser therapy with sparing of the neurosensory layer is possible by applying repetitive microsecond laser pulses. Macular diseases such as diabetic maculopathy, soft confluent drusen due to age-related macular degeneration or central serous chorioretinopathy were shown to be treated successfully-without concurrent laser scotoma-by this technique. It was the goal of this study to show, if selectivity could also be achieved using a conventional green cw-laser by scanning the beam across the retina during irradiation.

MATERIAL AND METHODS

A cw-laser beam at 532 nm was coupled to a slitlamp via a single mode optical fiber. The spot (18 microm) was scanned across the retina of Dutch-belted rabbits through a contact lens using a two-dimensional acusto-optical deflector. The scan-field was 300 microm x 300 microm in size and consisted of six separate scan lines. The scanning speed was adjusted so as to produce 5 micros exposure at each absorber in the center of the scan line. The entire scan pattern was applied 100 times at each site at a frame rate of 100 Hz. Dose response curve was measured by variation of the laser power. ED(50)-thresholds for RPE damage were calculated by fluorescein angiographic leakage in irradiated areas after exposure to different laser intensities. The extent of selectivity was examined by light microscopy.

RESULTS

Clinically the selective laser-induced RPE defect was demonstrated by fluorescein angiographic leakage and concurrent absence of ophthalmoscopic visibility. The angiographic ED(50)-damage threshold was 161 mJ/cm(2) (66 mW). Ophthalmoscopic visibility was not noticed even with the maximum available radiant exposure of 438 mJ/cm(2) (180 mW). Thus the safety range between angiographic and ophthalmoscopic thresholds had a factor of at least 2.7. First histological examinations revealed selective RPE destruction with intact photoreceptors for irradiation at laser power levels 2 times above angiographic threshold.

CONCLUSION

Selective RPE targeting is feasible with a conventional green cw-laser when scanning the focused laser beam across the fundus with a speed such that every point in exposed RPE is irradiated for duration of 5 micros.

Effects of root-end filling materials and eugenol on mitochondrial dehydrogenase activity and cytotoxicity to human periodontal ligament fibroblasts

Various root-end filling materials have been used to prevent the entry of root-canal pathogens into periapical regions. Five root-end filling materials were compared regarding the cytotoxicity, apoptosis, and mitochondrial dehydrogenase (MDH) activities of human periodontal ligament (PDL) fibroblasts, with the use of a novel transwell culture system. Exposure to IRM (a ZnO eugenol-based intermediate restorative material), a 2-ethoxybenzoic acid cement (Super EBA), and amalgam for 3 days inhibited the MDH activity of PDL fibroblasts as indicated by decrease in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction by 97%, 95%, and 51%, respectively. Evident suppression of MTT reduction by amalgam and glass ionomer cement (GIC) was noted after 5 days of exposure, with 73% and 46% of inhibition, respectively. Mineral trioxide aggregates (MTA) showed little effect on MDH activity. IRM and Super EBA were cytotoxic to PDL fibroblasts as indicated by a trypan blue dye exclusion technique. GIC and amalgam showed mild cytotoxicity. IRM, GIC, and amalgam further induced apoptosis of PDL cells, as revealed by the presence of sub-G0/G1 DNA content in flow cytometric histogram. Twenty-four-hour exposure to IRM and Super EBA elevated the MDH activities to 156% and 117%, correspondingly, of that of control. Eugenol, a phenolic ingredient in Super EBA and IRM, also increases MDH activity of PDL fibroblasts by 45% and 51%, at concentrations of 0.5 and 1 mM. However, at concentrations higher than 0.5 mM, eugenol decreased the number of viable PDL fibroblasts. These results suggest that MTA is a biocompatible root-end filling material, followed by self-curing Fuji II GIC and amalgam. IRM and Super EBA ingredients induced marked cytotoxicity and transiently stimulate MDH activities, which is possibly due to their content of eugenol and induction of cellular adaptive response.

In Vitro Study of DP-bioglass Paste for Treatment of Dentin Hypersensitivity

Sealing of exposed dentinal tubules is generally considered the most effective strategy to treat dentin hypersensitivity. On this account, we fabricated a DP-bioglass paste that created a homogeneous blockage on open dentinal tubules and formed a deep precipitate within dentinal tubules. DP-bioglass paste was prepared by mixing 20% to 60% phosphoric acid and DP-bioglass to treat dentin surfaces. CO2 laser irradiation was used to melt the DP-bioglass paste. The results demonstrated that 30% phosphoric acid was the optimum concentration to produce homogeneous occlusion on exposed dentinal tubules and 60 microm of sealing depth. CO2 laser irradiation could melt the DP-bioglass paste and create about 10 microm of sealing depth. Moreover, temperature rise during CO2 laser irradiation was only 4.86 +/- 0.47 degrees C. The results presented in this work suggested that DP-bioglass paste could produce considerable sealing depth in dentinal tubules with the potential of prolonging the therapeutic effect efficaciously.

Interactions of acinar cells on biomaterials with various surface properties

The purpose of this study is to evaluate the interactions of rat parotid acinar cells on biomaterials with different surface properties. The biomaterials used in this study included polyvinyl alcohol (PVA), chitosan, poly (ethylene-co-vinyl alcohol) (EVAL), and polyvinylidene fluoride (PVDF). Cell morphology was observed by photomicroscope. Cell growth and differentiated characteristic function were separately assayed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction activity and amylase activity. Results indicated that behaviors of acinar cells on materials might differ to a great extent depending on the surface hydrophilicity and morphology of the materials. On the relatively hydrophobic materials, the abilities of acinar cells to adhere and proliferate increased simultaneously. In addition, porous PVDF had higher cell growth compared with dense PVDF. Therefore, the hydrophobic PVDF with a porous structure was the best substrate for culturing acinar cells. According to our findings, a tubular PVDF scaffold with dense outer surface to prevent saliva leakage and with porous inner surface for the cell growth was proposed to serve as an artificial salivary gland for future use in the treatment of patients with salivary hypofunction.

Structural Changes of Er:YAG Laser–Irradiated Human Dentin

OBJECTIVE

The aim of this study was to investigate the phase, compositional, and morphological changes of Er:YAG laser-irradiated dentin.

BACKGROUND DATA

To date, nothing comprehensive has been reported about the phase and compositional changes of human dentin after Er:YAG laser irradiation.

METHODS

The human dentin was irradiated by Er:YAG laser with irradiation energies from 300 mJ/pulse-10 pps-10 sec to 700 mJ/pulse-10 pps-10 sec with and without water spray. After irradiation, the specimens were analyzed by means of x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

RESULTS

After exposure to Er:YAG laser, dentin showed no phase changes on the x-ray diffractometer. In Fourier transform infrared analysis, two absorption bands at 2200 and 2015 cm(-1) could be traced on dentin treated by Er:YAG laser with irradiation energies beyond 300 mJ/pulse-10 pps-10 sec and without water spray. The OH(-) band disappeared at 1630 cm(-1). Scanning electron micrographs revealed that laser energy of 500 mJ/pulse-10 pps-10 sec was sufficient to prompt melting and recrystallization of dentin crystals.

CONCLUSIONS

Our study demonstrated that Er:YAG laser irradiation on dentin with water spray would not significantly change the structure and composition. Therefore, water cooling is important for reducing the thermal effect of Er:YAG laser.

Morphologic study of Nd:YAG laser usage in treatment of dentinal hypersensitivity

Our previous in vitro study indicated that Nd:YAG laser irradiation on dentin could melt normal dentin surface and close the exposed dentinal tubule orifices without creating surface cracks. This study evaluated the morphologic changes of hypersensitive dentin after Nd:YAG laser irradiation. Thirty patients with clinically diagnosed cervical dentin hypersensitive teeth were treated with a Nd:YAG laser of 30 mJ intensity at 10 pulses per second for 2 min. An impression of the sensitive area was taken before and after laser treatment and then examined with a scanning electron microscope. The impression of the dentin surface after Nd:YAG laser treatment showed no protrusive rods, in contrast with the presence of numerous rods before laser irradiation. Because protrusive rods are a measure of open dentinal tubules, we interpret these data to support the hypothesis that Nd:YAG laser irradiation at specifications of 30 mJ, 10 pulses per second, and 2 min can be used to seal the exposed dentinal tubules.

The role of organic tissue on the punch shear strength of human dentin

OBJECTIVES

The tendency to fracture of human teeth has been attributed to numerous reasons, including pulpless tooth dehydration, tooth structure degeneration, and excessive spreader loading. To date, however, no consistent data has been gathered to ascertain the effect of organic tissue on the biomechanical properties of human dentin. This study explored the influences of organic tissue removal on the morphological changes and punch shear strength by means of low vacuum wet scanning electron microscope (Wet-SEM) and punch shear apparatus.

METHODS

The crown dentin slices with a thickness of 0.45-0.50 mm were prepared from extracted human molars. These specimens were immersed in 5% NaOCl for 1, 3, and 6 h to remove the organic tissue. The dynamic morphological changes of these dentin slices after immersion were observed using Wet-SEM. In addition, the punch shear strength and stiffness of specimens were measured.

RESULTS

The removal of organic tissue by 5% sodium hypochlorite treatment caused many cracks on the specimen surfaces. Intertubular and peritubular dentin were also affected, causing an abnormal configuration of dentinal tubule orifices. The 5% sodium hypochlorite treatment for 1, 3, and 6 h significantly reduced the punch shear strength of dentin. As the immersion time increased, the values of punch shear strength also diminished.

CONCLUSIONS

The organic tissue loss of human dentin would affect the structure of intertubular and peritubular dentin and cause many cracks on the dentin surface. The punch shear strength of human dentin also reduced after removal of organic tissue.