Postradiation Matrix Metalloproteinase-20 Expression and Its Impact on Dental Micromorphology and Radiation-Related Caries.

Recent evidence suggests that head-and-neck radiotherapy (HNRT) increases active forms of matrix metalloproteinase-20 (MMP-20) in human tooth crowns, degrading the dentin-enamel junction (DEJ) and leading to enamel delamination, which is a pivotal step in the formation of radiation-related caries (RRC). Additional participation of enzymatic degradation of organic matrix components in caries progression was attributed to MMP-20 in dentin. Therefore, the current study tested the hypothesis that MMP-20 is overexpressed in the DEJ, dentin-pulp complex components, and carious dentin of post-HNRT patients, leading to detectable micromorphological changes to the enamel and dentin. Thirty-six teeth were studied, including 19 post-HNRT specimens and 17 nonirradiated controls. Optical light microscopy was used to investigate the micromorphological components of the DEJ, dentin-pulp complex components, and carious dentin. The samples were divided into 2 subgroups: nondemineralized ground sections (n = 20) and demineralized histological sections (n = 16). In addition, immunohistochemical analysis using the immunoperoxidase technique was conducted to semiquantitatively assess MMP-20 expression in the DEJ, dentin-pulp complex components, and carious dentin. No apparent damage to the DEJ microstructure or other dentin-pulp complex components was observed and no statistically significant differences were detected in MMP-20 expression (p > 0.05) between the irradiated and control groups. This study rejected the hypothesis that MMP-20 is overexpressed in the DEJ, dentin-pulp complex components, and carious dentin of post-HNRT patients, leading to detectable micromorphological changes. Hence, direct effects of radiation may not be regarded as an independent factor to explain aggressive clinical patterns of RRC.

Effectiveness on oral pain of 808-nm diode laser used prior to composite restoration for symptomatic non-carious cervical lesions unresponsive to desensitizing agents.

This study compares sensitivity reduction after dental restoration with and without prior diode laser (DL) irradiation for cervical dentine hypersensitivity (CDH) from non-carious cervical lesions (NCCLs) unresponsive to desensitizing agents. Eighty-eight teeth of 28 subjects (21 females; age 23-64 years), with CDH from NCCL were included in this study. NCCLs of each oral quadrant were randomized in two groups (study group (SG)) to estimate the sensitivity reduction after dental restoration (SG-1) compared with the DL irradiation used prior to restoration placement (SG-2). The subjects were asked to rate the sensitivity experienced during air stimulation using a visual analog scale before (baseline), immediately after, and at 6 and 12 months from restoration. The outcomes showed a significant reduction of discomfort compared to baseline for NCCLs of SG-2 with the decrease of 78.5, 78.9, and 78.1 % immediately and at 6 and 12 months after restoration, respectively; in comparison with the decrease of 70.1, 67, and 65.3 % for NCCLs of SG-1 immediately and at 6 and 12 months after restoration, respectively; and compared to baseline. The DL irradiation prior to dental restoration can further improve the painful symptomatology of CDH from NCCL unresponsive to desensitizing agents.

The influence of different power settings of Nd:YAG laser irradiation, bioglass and combination to the occlusion of dentinal tubules.

OBJECTIVE: The purpose of this study was to investigate the influence of bioglass, Nd:YAG laser irradiation and their combination on dentinal tubuli occlusion as a potential dentinal hypersensitivity treatment for cervical dentinal hypersensitivity (CDH). BACKGROUND DATA: CDH affects 8-30% of adults and nearly 85% of perio-treated patients. Various treatment schemes have been applied for treating CDH, among them being fluoride application, laser irradiation, and, recently, bioglass (NovaMin(®)). In this in vitro study, we evaluated the efficacy of NovaMin(®) paste (NM) (Denshield, Sultan, USA), Nd:YAG laser irradiation (L) at various power settings, and their combination, on dentinal orifice occlusion (DOO) as potential treatments for CDH. METHODS: Forty-nine human dentin surfaces were organized into seven equal groups: groups A and B received NM followed by L (0.5 and 1 W, respectively); groups C and D received L (0.5 and 1 W, respectively) followed by NM; group E received NM; and groups F and G received L (0.5 and 1 W, respectively). Specimens were evaluated with regard to DOO under environmental scanning electron microscope. RESULTS: Treatment modality significantly affected DOO (p=0.012). Groups B and G scored higher DOO than the rest. By ordinal logistic regression (with boostrap standard errors), the combination of NM followed by 1 W Nd:YAG laser irradiation (group B) significantly (p<0.001) contributed to DOO, compared with groups A, C, D, E, and F. CONCLUSIONS: Under the limitations of this study, Nd:YAG laser irradiation at 1 W, alone or combined with NM, is a superior method for producing DOO, and may lead to an effective treatment modality for CDH.

In vitro evaluation of dentin tubule occlusion by Denshield and Neodymium-doped yttrium-aluminum-garnet laser irradiation.

INTRODUCTION: This in vitro study evaluated the efficacy of bioglass (Denshield; Novamin Technology, Alachua, FL) and Neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser irradiation on dentinal tubuli orifice occlusion (DOO) by comparing samples examined under environmental scanning electron microscope (ESEM) after applying each desensitizing approach separately and in combination. METHODS: Forty-eight human molars were collected, randomly organized in 4 equal groups, and had their cervical dentin exposed. Additionally, in half of the specimens of each experimental group, the smear layer was removed (subgroups A1, B1, C1, and D1). Group A received NovaMin paste treatment for 5 minutes (NM) to the experimental surface. Group B received Nd:YAG laser irradiation (0.5 w, 10 Hz, and 50 mJ) (L). Group C received NM followed by L. Group D was treated with L followed by NM. All specimens were stored for 24 hours and evaluated for DOO under ESEM by 4 blinded observers. RESULTS: The presence of a smear layer significantly contributed to DOO regardless of the treatment modality (ordinal logistic regression, P < .001). Compared with group A, all other treatments delivered significantly more occluded dentin orifices (P < .001 for groups B and D and P < .05 for group C). A layer formation was observed in subgroups C2 and D2. CONCLUSIONS: Under these experimental conditions, a smear layer was essential for successful DOO. Laser irradiation alone and combined with NovaMin proved superior to NovaMin alone on DOO. This combined approach has the potential to improve the outcome of treatment for cervical dentin hypersensitivity. The biological significance of this newly formed layer needs to be elucidated.

Effect of desensitizing agents on the microtensile bond strength of a two-step self-etch adhesive to dentin.

The aim of this in vitro study was to evaluate the effect of cervical hypersensitivity treatments (neodymium yttrium aluminum garnet [Nd:YAG] laser and conventional techniques) on the microtensile bond strengths of adhesives to treated dentin. The buccal cervical enamel of 42 freshly extracted human mandibular third molars was ground flat to expose the cervical dentin. The dentin surfaces were polished with a series of silicon carbide papers, and the smear was removed with an ethylenediamine tetra-acetic acid solution. The teeth were randomly divided into six groups as follows: group 1, Vivasens; group 2, BisBlock; group 3, fluoride gel; group 4, Nd:YAG laser; group 5, Clearfil SE + Nd:YAG laser; and group 6, no treatment (control). The specimens were then restored with a two-step self-etch adhesive, with the exception of group 5. Five specimens from each group were restored with a nanohybrid composite resin. The adhesive interface of two specimens from each group was examined using scanning electron microscopy. The specimens were sectioned perpendicularly to the adhesive interface to produce beams (adhesive area 1 mm(2)). The beams were then attached to a microtensile tester and stressed to failure at 1 mm/min. The data were compared using one-way analysis of variance at a significance level of 0.05. The microtensile bond strengths of the control group were significantly higher than those found for group 1, group 2, group 3, and group 4 (p< 0.05). No significant difference was found between group 5 and the control group. Most of the premature failures were seen in group 2 (80%), and the fewest premature failures were seen in group 5 (13.3%). The SEM findings verified the microtensile test findings. In conclusion, desensitizing treatment procedures (with the exception of Clearfil SE + Nd:YAG laser) reduced the microtensile bond strength of a two-step self-etch adhesive to dentin.

The effect of a 980 nm diode laser with different parameters of irradiation on the bond strength of fiberglass posts.

The aim of this study was to assess bond strength of fiberglass posts to root canal dentin irradiated with a 980 nm diode laser at different parameters of power and frequency. Fifty human maxillary canines were separated into five groups (n = 10) according to the following parameters of laser power and frequency: Group 1 (1.5 W/100 Hz), Group 2 (1.5 W/continuous wave [CW]), Group 3 (3.0 W/100 Hz), Group 4 (3.0 W/CW), and Group 5 (no irradiation). Following post cementation, samples underwent a push-out test (0.5 mm/min); next, fracture analysis was performed with a light microscope at 50x and 100x magnification. All of the irradiated groups had increased bond strength values compared to the nonirradiated group. Groups 1 and 2 demonstrated the highest bond strength values; however, statistically significant differences were observed for only the cervical third of Group 4 and the cervical/apical thirds of Group 5. Fracture analysis showed a predominance of mixed failures for Groups 1 and 2 and adhesive failures between dentin and cement for the other groups.

Relationship between laser fluorescence and enamel hypomineralisation.

OBJECTIVES: To study the relation between the mechanical properties of hypomineralised enamel, and its laser fluorescence (LF). METHODS: Five extracted teeth with molar-incisor hypomineralisation (MIH) were sectioned longitudinally through the defects and polished to prepare the hypomineralised enamel for testing. Hardness (H) and elastic modulus (E) of enamel were measured using nanoindentation. Measurement recording started from the cervicoenamel junction and proceeded occlusally in increments of 200 microm. Laser fluorescence readings were taken along the same line and at the same sites using a DIAGNOdent pen. RESULTS: H, E, and LF readings from cervical enamel were within the expected range for normal sound enamel. After log transformation of the H and E measurements to allow for linear correlation analysis, there was a significant and moderately strong inverse correlation between LF and H or E samples (r (between specimens)=0.59, r (between specimens)=0.39, respectively; p<0.001). CONCLUSIONS: This study shows that, in the absence of dental caries, increased DIAGNOdent readings can indicate enamel hypomineralisation. While the increased LF readings in carious enamel are thought to be related to the presence of caries bacterial metabolites, the increased readings in hypomineralised enamel may be related to proteins in the hypomineralised enamel and/or light scattering by the inhomogeneous enamel.

Temperature variation at the external root surface during 980-nm diode laser irradiation in the root canal.

OBJECTIVE: To assess the temperature variation in the cervical, middle and apical thirds of root external wall, caused by 980-nm diode laser irradiation with different parameters. METHODS: The roots of 90 canines, had their canals instrumented and were randomly distributed into 3 groups (n=30) according to the laser potency (1.5 W, 3.0 W and 5.0 W). Each group was subdivided into 3 (n=10) according to the frequency (CM, 100 Hz and 1000 Hz), and each subgroup divided into 2 (n=5): dried canal or filled with distilled water. The maximum temperature values were collected by 3 thermocouples located at each third of the root external wall and recorded by digital thermometers. RESULTS: The groups irradiated in the continuous mode (CM) presented the highest values (11.82+/-5.78), regardless of the canals were dry or not, which were statistically different (p<0.01) from those obtained with 100 Hz (6.22+/-3.64) and 1000 Hz (6.00+/-3.36), which presented no statistical difference between them (p>0.01). The groups irradiated with 5.0 W presented the greatest temperature variation (12.15+/-5.14), followed by 3.0 W (7.88+/-3.92) and 1.5 W (4.02+/-2.16), differing between them (p<0.01). The cervical third of the root presented the highest temperature rises (9.68+/-5.80), followed by the middle (7.66+/-4.87) and apical (6.70+/-4.23), with statistical difference among them (p<0.01). After 30s from the end of irradiation, all the specimens presented temperature variation lower than 10 degrees C. CONCLUSIONS: Application of 980-nm diode laser in the root, at 1.5 W in all operating modes, and 3.0 W, in the pulsed mode, for 20s, can safely be used in endodontic treatment, irrespective of the presence of humidity.

Long-term effects of CO2 laser irradiation on treatment of hypersensitive dental necks: results of an in Vivo study.

OBJECTIVE: The present in vivo study was performed to examine the long-term effects of combined CO2 laser treatment and fluoridation on hypersensitive dental necks. SUMMARY BACKGROUND DATA: Attempts have been made to treat dental hypersensitivity by sealing exposed dentinal tubules, primarily using fluoride preparations, strontium chloride, and hydroxyapatite. However, these treatment methods have the disadvantage that the preparation is effective only for a limited period of time and must be applied repeatedly, at short intervals. The CO2 laser has been shown to have an excellent sealing effect on hypersensitive dentinal surfaces. METHODS: Test subjects suffering from dentinal hypersensitivity were recruited from the patients of the Department of Conservative Dentistry, School of Dentistry of the University of Vienna, Austria and treated with combined laser irradiation and fluoridation with stannous fluoride gel. The patients were followed up for a period of 18 months. In vivo examinations were supplemented by atomic absorption spectroscopy (AAS) of tiny dentin samples obtained from the dental necks 6 weeks and 18 months after laser treatment and by scanning electron microscopy (SEM). RESULTS: Compared to conventional fluoridation, combined laser irradiation and fluoridation was shown to be effective in the treatment of hypersensitive dental necks. When success was defined as complete freedom from pain, the success rate in the laser group was 96.5%. Furthermore, examinations of irradiated teeth under the scanning electron microscope still revealed complete closure of the dentinal tubules four and six months after laser treatment. AAS showed that tin was present in the samples, which indicates that combined laser treatment and fluoridation result in permanent integration of fluoride in the dentin surface. CONCLUSIONS: Based on these results, the CO2 laser can be recommended as an ideal tool for desensitization of dental necks.

Irradiation effects on microhardness of fluoridated and non-fluoridated bovine dentin.

The objective of this study was to evaluate the effects of irradiation on microhardness of dentin. Dentin blocks from the cervical region of bovine incisors were treated as follows: (1) no irradiation; (2) irradiation of specimens up to 60 Gy (2 Gy/day, 5 days/week); (3) no irradiation, but fluoridation of specimens for 5 min/d; (4) irradiation of specimens and daily fluoridation. Knoop hardness number (KHN) of the control specimens was 62.63+/-14.75 (mean+/-SD). This was significantly different from the irradiated dentin samples (8.74+/-2.59 KHN). Hardness of the fluoridated dentin specimens was 11.19+/-1.95 KHN in the non-irradiated group and 10.03+/-2.76 KHN in the irradiated groups, respectively. Within the limitations of an in vitro study, it is concluded that dentin is severely affected by irradiation. This could be an explanation for the frequently observed side-effects of irradiation like loss of enamel, gap formation at the amelodentinal junction, and caries of the cervical region. Fluoridation with acidic gels decreases microhardness of dentin surface, and does not prevent softening due to radiation, when saliva is absent.

Influence of laser enamel and dentine etching on marginal integrity of porcelain laminate veneers.

This investigation evaluated the effect of laser etching and acid etching techniques on the marginal leakage Vitadur N porcelain laminate veneers bonded either entirely on enamel, or with cervical margin located on root dentine of prepared extracted maxillary central incisors. Two different composite resin luting systems (light cured, or light and chemical cured) were used and compared. The bonded specimens were thermocycled and by employing the Standard dye penetration technique the leakage was scored from cervical and incisal margins. The least marginal leakage was observed beneath laminate veneers bonded entirely on enamel. Laser etching improved the sealing qualities of veneers with cervical margins on root dentine below the CEJ. Statistically insignificant differences were observed with the use of the two different composite resin luting systems.