Preheating and "snow-plow" composite application technique affect double bond conversion but not bond strength to dentine

OBJECTIVE

To measure degree of conversion (DC) of a flowable composite, microtensile bond strength (MTBS) to dentine in the snow-plow technique with/without preheating and temperature in the preheated composite.

MATERIALS AND METHODS

For DC, snow-plow specimens of Filtek Ultimate Flowable (Flow) and Filtek Bulk Fill (Bulk) (3M) were prepared by light-curing composites simultaneously in standardized molds while in control groups light-curing was separate. DC of Flow was measured using micro-Raman spectroscopy. For MTBS, specimens were prepared on dentine of human extracted molars by simultaneous (snow-plow) or separate (control) light-curing. MTBS was measured using a universal testing machine after 24 h and 6 months. Data were analyzed using ANOVA with Tukey's post hoc (α = 0.05).

RESULTS

Increased curing time significantly increased DC in snow-plow from 13.4% ± 11.6% (10 s) to 31.8% ± 4.4% (40 s) albeit significantly lower than controls (p < 0.05). Preheated Bulk improved conversion in snow-plow (44.3% ± 1.7%) and control (50.5% ± 2.6%) (p < 0.05). No significant differences occurred in MTBS between groups (p > 0.05). MTBS values ranged between 66.7 ± 8.4 MPa (snow-plow group_21°C_baseline) and 54.1 ± 15.8 MPa (control_21°C_long-term). Temperature in the preheated Bulk dropped to ~38°C after 30 s.

CONCLUSIONS

Snow-plow technique, irrespective of preheating, resulted in lower DC of Flow than separate light-curing of composite increments. Snow-plow, irrespective of preheating, resulted in similar initial and long-term MTBS to dentine.

CLINICAL SIGNIFICANCE

Clinicians with preference for flowable composite liners in Class II restorations should be aware that the snow-plow technique of simultaneous light-curing of flowable and bulk-fill composite increments affects monomer-to-polymer conversion, albeit no effect on immediate, and long-term bonding to dentine was detected. Preheating sculptable bulk-fill composite improves conversion of the flowable liner in the snow-plow technique but has no detectable effect on bond strength to dentine.

Evaluation of Relative Dentin Abrasivity in Whitening Toothpastes Containing Acids

INTRODUCTION AND AIMS

This study aimed to evaluate the relative dentin abrasivity of whitening toothpastes containing acids using the Radioactive Dentin Abrasivity - Profilometry Equivalent (RDA-PE).

METHODS

A total of 100 bovine dentin specimens were prepared and assigned to the following groups (n = 10): 5 hydrogen peroxide (HP) whitening toothpastes (WTH1-WTH5) with or without acid (citric acid, ethylenedinitrilotetraacetic acid disodium, and phosphoric acid), 2 whitening toothpastes with silica and containing citric or phosphoric acid (WTS1 and WTS2), one conventional toothpaste (CT), and 2 reference slurries (RS). All specimens were brushed for 4,000 or 10,000 strokes using toothbrush and toothbrushing machine. The average dentin depth was measured using a noncontact profilometery, and the RDA-PE value was calculated based on the RS. The pH of the solution, average particle size, particle content, and particle hardness were measured. The RDA-PE data were analysed using one-way analysis of variance and Tukey's test, and the effects of the 4 measured factors on RDA-PE were investigated via multiple regression analysis.

RESULTS

The RDA-PE values of the HP whitening toothpastes (mean value: 19-46) were significantly lower, whereas those of the silica whitening toothpastes (80 or 111) were similar to those of the RS after 4,000 strokes (100). The RDA-PE values of all whitening toothpastes were significantly lower than the RS values after 10,000 strokes (242). The HP whitening toothpastes were slightly acidic (pH ≤6) compared to the other solutions. The HP (2.9%-3.7%) and silica (8.9% or 9.9%) whitening toothpastes had significantly lower particle content than RS (16.6%). The particle content significantly influenced the RDA-PE values by multiple regression results.

CONCLUSIONS

The RDA-PE values of whitening toothpastes varied. The particle content in the solution was a key factor affecting the RDA-PE value.

CLINICAL RELEVANCE

Whitening toothpastes containing acids did not cause significant dentin abrasion.

Hydroxyapatite-based dental inserts: Microstructure, mechanical properties, bonding efficiency and fracture resistance of molars with occlusal restorations

This study aimed to (1) comparatively analyze properties of Sr- and Mg-substituted hydroxyapatite (HAP)-based dental inserts; (2) evaluate insert bonding to restorative materials, and (3) evaluate the effect of doped HAP inserts on fracture resistance (FR) of human molars with large occlusal restorations. By ion-doping with Sr or Mg, 3 insert types were obtained and characterized using XRD, SEM, Vickers hardness and fracture toughness. Shear bond strength (SBS) was determined between acid etched or unetched inserts and following materials: Maxcem cement (Kerr); Filtek Z250 (3M) bonded with Single Bond Universal (SBU; 3M) or Clearfil Universal (Cf; Kuraray). Modified Class I cavities were prepared in 16 intact molars and restored using insert + composite or composite only (control) (n = 8/group). FR of restored molars was determined by static load until fracture upon thermal cycling. Fracture toughness was similar between Sr/Mg-doped inserts (0.94-1.04 MPam-1/2 p = .429). Mg-doped inserts showed greater hardness (range 4.78-5.15 GPa) than Sr6 inserts (3.74 ± 0.31 GPa; p < .05). SBS for SBU and Cf adhesives (range 7.19-15.93 MPa) was higher than for Maxcem (range 3.07-5.95 MPa) (p < .05). There was no significant difference in FR between molars restored with insert-containing and control restorations (3.00 ± 0.30 kN and 3.22 ± 0.42 kN, respectively; p > .05). HAP-based inserts doped with Mg/Sr had different composition and mechanical properties. Adhesive bonding to inserts resulted in greater bond strength than cementation, which may be improved by insert acid-etching. Ion-doped HAP inserts did not affect FR of restored molars. In conclusion, HAP-based dental inserts may potentially replace dentin in large cavities, without affecting fracture resistance of restored teeth.

Clinical longevity of direct and indirect posterior resin composite restorations: An updated systematic review and meta-analysis

OBJECTIVES

To answer the PICO(S) question: Is there a difference in clinical longevity between direct and indirect resin composite restorations placed on permanent posterior teeth?

DATA

Randomized controlled clinical trials (RCTs) investigating direct and indirect resin composite restorations in posterior permanent teeth were considered.

SOURCES

Several electronic databases were searched, with no language or date restrictions. The revised Cochrane Collaboration's tool for assessing risk of bias (RoB-2) was used to analyze the studies; meta-analyses were run and the certainty of evidence was assessed by the GRADE tool. A subgroup meta-analysis was performed for resin composite restorations placed on posterior worn dentition.

STUDY SELECTION

Twenty-three articles were included in qualitative synthesis, while 8 studies were used for meta-analyses. According to the RoB-2 tool, 5 studies were ranked as "low risk", 7 had "some concerns", while 11 papers were rated as "high risk" of bias. There were no statistically significant differences in short-term (p = 0.27; RR=1.54, 95% CI [0.72, 3.33]), medium-term (p = 0.27; RR=1.87, 95% CI [0.61, 5.72]) and long-term longevity (p = 0.86; RR=0.95, 95% CI [0.57, 1.59]). The choice of restorative technique had no influence on short-term survival of resin composite restorations placed on worn dentition (p = 0.13; RR=0.46, 95% CI [0.17, 1.25]). The certainty of evidence was rated as "very low".

CONCLUSIONS

Direct and indirect resin composite restorations may show similar clinical longevity in posterior region, regardless of the observation period or substrate (wear-affected and non-affected dentition). The very low quality of evidence suggests that more long-term RCTs are needed to confirm our results.

Effects of staining and artificial aging on optical properties of gingiva-colored resin-based restorative materials

Objectives

To evaluate CIEDE2000/CIELAB differences in color (ΔE₀₀/ΔE_ab), and translucency parameter (ΔTP₀₀/ΔTP_ab), and gloss of gingiva-colored resin-based restorative materials upon staining/aging.

Materials and methods

Disc-shaped, 10 mm in diameter, and 2-mm-thick samples (n = 5/group) were made from giomer (Beautifil II gingiva), oligomer-based (crea.lign GUM gel), CAD/CAM polymethyl-methacrylate-based (IvoBase CAD), PMMA-based (ProBase Hot), and dimethacrylate-based (SR Nexco Paste Gingiva). Color and gloss were recording using a benchtop spectrophotometer and gloss meter, respectively, at baseline (T0), and upon staining in coffee or red wine for 60 (T1) and 120 h (T2), or artificial aging of 150 kJ/m² (T1) and 300 kJ/m² (T2). Three-way analysis of variance (materials x staining conditions x time intervals), Tukey’s test (α = 0.05), and Pearson’s correlation test were used in analytical statistics.

Results

CIEDE2000 color differences ranged from 1.0 to 4.4 (coffee), 1.5 to 5.3 (wine), and 0.9 to 2.0 after artificial aging, with ΔE₀₀ values being significantly higher for Beautifil than other materials (p < 0.05). ΔTP₀₀ values ranged from 0.2 to 0.7 and were statistically higher upon staining in wine compared to artificial aging (p < 0.05). Gloss values at T0 were 76.7–87.0. Beautifil exhibited the lowest gloss retention (50.8–60.2%) after staining, compared to > 90% of other materials (p < 0.05). ΔE₀₀/ΔE_ab and ΔTP₀₀/ΔTP_ab were positively correlated (p < 0.0001).

Conclusions

Color, translucency, and gloss changes of gingiva-colored restorative materials were material- and staining/aging-dependent. Generally, wine caused greatest changes in color (with IvoBase CAD being the most color stable) and translucency parameter. All materials except Beautifil gingiva II exhibited staining- and aging-dependent gloss retention greater than 90% for all compared time intervals.

Clinical relevance

Optical properties of resin-based gingiva-colored restorative materials depend on material, staining/aging conditions, and exposure time. Certain materials should be avoided in individuals with high consumption of red wine and coffee.

Effects of bioflavonoid-containing mouth rinses on optical properties of tooth-coloured dental restorative materials

This study investigated differences in colour (ΔE₀₀) and translucency parameter (ΔTP₀₀) of nanofilled/microhybrid composites and a glass-ionomer cement following immersion in bioflavonoid (Citrox)- or chlorhexidine-based mouth rinses. Sixty disc-shaped specimens (N = 5/group) of Filtek Supreme (3M), Gradia Anterior (GC) and Fuji IX (GC) were exposed to Citrox/0.2%CHX (Perio+0.2, Curaprox), Citrox/0.09%CHX (Perio+0.09, Curaprox), 0.2%CHX (Savacol, Colgate-Palmolive) or distilled water by 2-min agitation daily for 28 days in an orbital shaker at 200 rpm at 37 °C. Colour recordings were performed using a clinical spectrophometer to obtain CIELab coordinates. General linear model, ANOVA, Tukey test (α = 0.05) and Pearson correlation test were used to analyse data. ΔE₀₀ ranged between 0.33 (Gradia_Savacol_T28) and 6.35 (Fuji_Savacol_T28) (p < 0.001). ΔTP₀₀ ranged between 0.36 (Fuji_ Perio+0.2) and 1.73 (Fuji_Savacol) (p < 0.05). Savacol resulted in higher ΔE₀₀ of Filtek and Fuji and ΔTP₀₀ of Filtek than Perio+0.09 and Perio+0.2 (p = 0.005). Perio+0.09 and Perio+0.2 resulted in higher ΔE₀₀ at T7 than T28 (p < 0.05). There was no correlation between ΔTP₀₀ and ΔE₀₀ (r = 0.445, p = 0.147). Generally, Perio+0.2 and Perio+0.09 mouth rinses produced similar or lower ΔE₀₀ and ΔTP₀₀ than Savacol. GIC Fuji showed higher ΔE₀₀ and similar or higher ΔTP₀₀ than composites Filtek and Gradia. ΔE₀₀ in all materials decreased in Perio+0.2 and Perio+0.09 over time.

Effects of non-thermal atmospheric plasma on dentin wetting and adhesive bonding efficiency: Systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis evaluated the effects of non-thermal atmospheric plasma (NTAP) treatment on dentin wetting and adhesive-dentin bond strength.

DATA/SOURCES

This report followed the PRISMA 2020 statement. Two reviewers conducted literature search of MEDLINE, Web of Science and Scopus databases up to the end of November 2020. Included in vitro studies compared the effect of NTAP on treated dentin of non-carious, intact, extracted human third molar teeth with different control groups. Studies with no adequate methods, missing data, lack of control group, or those using animal teeth were excluded. The random effects model was used to summarize the treatment effect with standardized mean difference (SMD) and 95% CI. Risk of bias was assessed using the custom Cochrane Collaboration's tool.

STUDY SELECTION/RESULTS

Seventeen studies met inclusion criteria. The effects on dentin wetting were reported in favor of NTAP (SMD -5.38; 95% CI [-6.97, -3.78]; p<0.00001; I2=81%). Regarding adhesive-dentin bond strength, statistically significant differences between the NTAP and control group were in favor of NTAP in the short-term (SMD 1.92; 95%CI [1.35, 2.50]; p<0.00001; I2=97%), and long-term (SMD 3.28; 95%CI [2.46, 4.09]; p<0.00001; I2=97%). A limitation of meta-analysis is moderate heterogeneity caused by methodological differences and lack of data, which was evaluated through risk of bias and sensitivity analysis.

CONCLUSIONS

NTAP substantially improves dentin wetting and adhesive-dentin bond strength with 30 seconds exposure time and up to 10 mm tip-to-surface distances being sufficient for positive NTAP effects on bonding efficiency.

FUNDING

ON172207 and III41008 from the Ministry of Education, Science and Technological Development, Republic of Serbia. NP is funded by MESTD grant number 451-03-68/2020-14/200024.

CLINICAL SIGNIFICANCE

This systematic review and meta-analysis substantiate potential applicability of NTAP treatment of dentin in improving adhesive bonding clinically. Further research should be based on the optimized parameters such as time and distance with additional refinement of NTAP power.

Effects of whitening gels on color and surface properties of a microhybrid and nanohybrid composite

The aim of this study was to compare color changes, surface roughness and gloss of a microhybrid and nanohybrid composite whitened in a simulated in-office or at-home procedure using 40% hydrogen peroxide or 16% carbamide peroxide, respectively. CIELab coordinates were measured before, during and after treatment using VITA EasyShade V (VITA) and ∆E₀₀ calculated. Surface roughness was measured using a surface roughness tester (SJ210; Mitutoyo). Gloss was measured using a gloss checker (IG-331; Horiba). At-home whitening resulted in ∆E₀₀ of 1.23±0.49 (microhybrid) and 1.01±0.76 (nanohybrid). In-office exposure resulted in ∆E₀₀ of 0.69±0.38 (microhybrid) and 0.72±0.50 (nanohybrid). There were no significant differences in ∆E₀₀, surface roughness and gloss between whitening protocols (p>0.05). Color changes of a microhybrid and nanohybrid composite following simulated in-office or at-home whitening reached CIEDE2000 50:50% perceptibility but not acceptability threshold. Surface roughness and gloss of the microhybrid and nanohybrid composite were not affected by whitening.

Multifactorial analysis of optical properties, sorption, and solubility of sculptable universal composites for enamel layering upon staining in colored beverages

OBJECTIVE

To analyze the effects of factors 'composite,' 'medium,' and 'time' on color, translucency, and sorption/solubility of sculptable universal composites for enamel layering upon immersion in colored beverages.

MATERIALS AND METHODS

Disk-shaped specimens, 10 mm in diameter and 2 mm thick (n = 5/group), of ultrafine, hybrid composite Essentia (GC), microhybrid Gaenial Anterior (GC), nanofilled Filtek Ultimate Enamel and Body ( 3M ESPE) were immersed in red wine, coffee, or distilled water for 15 days. CIELab color coordinates were measured and CIEDE2000 (∆E₀₀ ) and Translucency Parameter differences (∆TP₀₀ ) were calculated. Sorption and solubility were determined according to ISO 4049:2009. Data were analyzed using the analyses of variance and Tukey's post-hoc test (α = 0.05).

RESULTS

Essentia and Gaenial exhibited the lowest and the highest staining-dependent color differences, with mean ∆E₀₀ range of 1.7-6.1 and 5.1-11.3, respectively (p < 0.05). ∆TP₀₀ was more pronounced in wine than in coffee (p < 0.05). Sorption and solubility varied between 9.8 and 15.3 μg/mm³ and -1.6 and -5.4 μg/mm³ , respectively, with positive correlation between ∆TP₀₀ and sorption (p = 0.005).

CONCLUSIONS

Total color and translucency differences of sculptable composites for enamel layering were material-, time- and medium-dependent. Translucency differences positively correlated with sorption. Overall, the ultrafine, hybrid composite exhibited the best results in terms of color stability, sorption and solubility.

CLINICAL SIGNIFICANCE

Clinicians should be aware of differences in color stability of sculptable composites for enamel layering as these are directly exposed to discoloration in the oral environment and are directly related to patients' long-term satisfaction and restoration longevity. Ultrafine, hybrid composite may be preferred due to better color stability, lower sorption and solubility compared to nanofilled and microhybrid composites evaluated in this study.

Immediate and Long-Term Porosity of Calcium Silicate-Based Sealers

INTRODUCTION

Open pores between endodontic sealer and root canal walls present potential niches for bacterial growth and migration pathways. The aim was to assess the internal and external porosity of calcium silicate-based sealers and to ascertain the long-term effect of storage in simulated body fluid on sealer porosity.

METHODS

Sixteen single-rooted teeth were filled with gutta-percha and 1 of 4 root canal sealers: BioRoot RCS, EndoSequence BC, MTA Fillapex, or AH Plus. Obturated roots, stored in Hank's balanced salt solution, were scanned after 7 days and after 6 months by using micro-computed tomography at an isotropic resolution of 9.9 μm. Total, open, and closed porosity were calculated in the coronal, middle, and apical thirds. Data were statistically analyzed by using general linear model and paired t test (α = 0.05).

RESULTS

Significantly higher percentage of open than closed porosity was found in all groups. Initially, significantly greater open and total porosity were found for MTA Fillapex than for AH Plus. After 6 months, the percentage of open and total porosity increased in BioRoot RCS and MTA Fillapex and decreased in AH Plus and EndoSequence BC. Both initially and after storage, coronal region of all sealers had significantly greater total porosity than middle and apical regions, which were comparable.

CONCLUSIONS

None of the root fillings were void-free, with predominant open porosity persisting after long-term storage.

Dissimilar sintered calcium phosphate dental inserts as dentine substitutes: Shear bond strength to restorative materials

The application of sintered calcium phosphate dental inserts in the central part of tooth cavities can reduce amount of embedded dental composite and polymerization shrinkage of final dental fillings. The aim of this study was to analyze comparatively physico-chemical and mechanical properties of dental inserts and shear bond strength (SBS) between three dissimilar hydroxyapatite-based dental inserts and different restorative materials, after application of different clinical protocols. Starting from two different hydroxyapatite nano powders and nanostructured stabilized zirconia (YSZ), monophasic two-step sintered dense HAp inserts (TSSHAp), biphasic single-step sintered controlled porous inserts (HAp/TCp), and single-step sintered reinforced HAp/YSZ inserts were processed and characterized. Obvious differences in the microstructure of inserts surface were visualized after etching with 37% phosphoric acid. Fracture toughness of sintered inserts was ranged between 1.01 and 1.85 MPam^1/2 (maximum value in the case of HAp/YSZ), while hardness values were in the range of 3.71-5.22 GPa (maximum value in the case of TSSHAp). Acid etching before application improved SBS between inserts and Maxcem compared to direct cement application. TSSHAp and HAP/TCp inserts showed comparable and relatively high SBS values, certainly higher compared to HAp/YSZ inserts. Slightly higher SBS values were measured in the case of TSSHAp insert group, and the highest mean SBS value of 18.51 MPa was determined between TSSHAp inserts and Filtek Z250_SBU following the "self-etch" protocol.

Color stability of bulk-fill and universal composite restorations with dissimilar dentin replacement materials

OBJECTIVE

To determine color changes in bulk-fill composite and universal composite restorations with dissimilar dentin replacement materials in extracted teeth after staining in red wine.

MATERIALS AND METHODS

Cylindrical, 4 mm deep, class I cavities were prepared in 140 human molars. Bottom 2 mm was restored with Biodentine (Septodont), everX posterior (GC) or experimental HAP inserts. Each dentin replacement material was covered with a 2-mm layer of a universal composite Filtek Z250 or Z550 (3M ESPE) or Gradia Posterior (GC). Groups combining top composite layer and the underlying dentin replacement were designated as "composite_dentin replacement." Filtek Bulk Fill (3M ESPE) and Tetric EvoCeram Bulk Fill (Ivoclar Vivadent) were placed as a single 4-mm layer. Color measurements were performed using Vita Easyshade 4.0 (Vita Zahnfabrik) initially and after 48-hours storage in red wine at 37°C.

RESULTS

Color differences (ΔE_oo ) ranged between 2.1 ± 0.7 (Z250_HAP) and 7.8 ± 1.1 (Z550_everX). EverX resulted in higher ΔE_oo of the overlying composite than HAP (P < .001) and Biodentine (P = .006). Generally, ΔE_oo was affected more by decreasing lightness (ΔL') than changes in chroma (ΔC').

CONCLUSIONS

EverX resulted in higher ΔE_oo of the restoration than Biodentine and experimental HAP after staining in red wine. No significant differences in ΔE_oo may be expected in different composites with the same underlying dentin replacement material. The same was generally true for bulk-fill and universal composites.

CLINICAL SIGNIFICANCE

Similar extent of color changes may be expected in bulk-fill and universal composites. Highly translucent everX might exhibit greater color differences irrespective of the capping composite than non-translucent materials. Clinicians have a wider choice of composite materials to cover a particular dentin replacement material, for example, everX or Biodentine, as similar color differences may be expected in various overlying composite brands.

Curing characteristics of flowable and sculptable bulk-fill composites

OBJECTIVES

The aim of this study was to determine and correlate the degree of conversion (DC) with Vickers hardness (VH) and translucency parameter (TP) with the depth of cure (DoC) of five bulk-fill composites.

MATERIALS AND METHODS

Six specimens per group, consisting of Tetric EvoCeram Bulk Fill ("TEC Bulk," Ivoclar Vivadent), SonicFill (Kerr), SDR Smart Dentin Replacement ("SDR," Dentsply), Xenius base ("Xenius," StickTech; commercialized as EverX Posterior, GC), Filtek Bulk Fill flowable ("Filtek Bulk," 3M ESPE), and Tetric EvoCeram ("TEC," control), were prepared for DC and VH: two 2-mm-thick layers, each light-cured for 10 s; one 4-mm bulk-fill, light-cured for 10 or 20 s; and one 6-mm bulk-fill, cured for 20 s. DC was measured using a Fourier-transform infrared spectrometer, VH using a Vickers hardness tester. DoC and TP were measured using an acetone-shaking test and a spectrophotometer, respectively. Data were analyzed using ANOVA and Pearson's correlation (α = 0.05).

RESULTS

DC and VH ranged between 40-70 % and 30-80 VHN, respectively. TEC Bulk, Xenius, and SonicFill, bulk-filled as 4-mm-thick specimens, showed bottom-to-top hardness ratios above 80 % after 20 s curing. A positive linear correlation was found for bottom DC and VH. An average DC ratio of 0.9 corresponded to a bottom-to-top VH ratio of 0.8.

CONCLUSIONS

Sculptable bulk-fills require 20 s, whereas 10 s curing time was sufficient for flowable bulk-fills using a high-intensity LED unit.

CLINICAL RELEVANCE

Clinicians should be aware that longer curing times may be required for sculptable than flowable bulk-fill composites in order to achieve optimal curing characteristics.

Refractive indices of unfilled resin mixtures and cured composites related to color and translucency of conventional and low-shrinkage composites

This study correlated the refractive indices (RIs) of unfilled resin mixtures and resin-based composites (RBCs) with color and translucency of conventional and low-shrinkage RBCs. Unfilled resin mixtures based on different ratios of conventional monomers Bisphenol A-glycidyl-methacrylate (BisGMA)/triethyleneglycol-dimethacrylate (TEGDMA) and urethane-dimethacrylate (UDMA)/TEGDMA and a low-shrinkage monomer FIT-852 (FIT, Esstech Inc.)/TEGDMA were used to prepare model RBCs, containing 30 wt % of the organic matrix and 70 wt % of silanated barium-glass fillers (n = 1.553, Esstech Inc.). The RIs of resins were measured on an ABBE refractometer, those of cured RBCs using the Becke-line method in immersion oils. Color and translucency were determined using an AvaSpec-2048 (Avantes BV) spectrometer. The RIs of unfilled resin mixtures decreased with increasing amounts of TEGDMA. Cured RBCs had higher RIs than their respective resin mixtures. BisGMA-based composites were more translucent with significantly lower L* values than FIT- and UDMA-based RBCs. The RIs of unfilled resins positively correlated with cured RBCs (p = 0.001), as did the RIs with translucency (p = 0.001) and color (p = 0.008). Resin mixtures and corresponding RBCs based on UDMA and its modified low-shrinkage version, FIT, showed similar optical properties. The RIs of unfilled resins appeared to be good predictors of the RIs of cured RBCs. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 7-13, 2017.

Accuracy of three electronic apex locators in determining the apical foramen in multi-rooted teeth: Randomised clinical and laboratory study

This study aimed to compare the accuracy of three electronic apex locators (EALs), Raypex 5, Apex NRG and ProPex II, in locating the apical foramen (AF) in vivo. Thirty multi-rooted teeth were included in the study. Distances from the file tip to the radiographic apex from the buccal (R1) and mesial (R2) aspect were measured after extraction. The distance from the file tip to the AF (L) was measured microscopically. Raypex 5, Apex NRG and ProPex II were accurate to within ± 0.5 mm in 84.6%, 78.6% and 66.7% of cases, respectively. R1, R2 and L measurements between the EALs were not statistically different (P > 0.05). R1 and L correlated positively (r(2) = 0.817; P < 0.001). There were no significant differences in all measurements between vital and non-vital root canals (P > 0.05). There was no statistically significant difference between the EALs. There was a positive correlation between electronic and radiographic measurements when locating the AF.

Effect of Evaporation on the Shelf Life of a Universal Adhesive

Objectives

The purpose of this study was to evaluate how evaporation affects the shelf life of a one-bottle universal adhesive.

Methods

Three different versions of Scotchbond Universal (SBU, 3M ESPE, Seefeld, Germany) were prepared using a weight-loss technique. SBU0 was left open to the air until maximal weight loss was obtained, whereas SBU50 was left open until 50% of evaporation occurred. In contrast, SBU100 was kept closed and was assumed to contain the maximum concentration of all ingredients. The degree of conversion (DC) was determined by using Fourier transform infrared spectroscopy on different substrates (on dentin or glass plate and mixed with dentin powder); ultimate microtensile strength and microtensile bond strength to dentin were measured as well.

Results

DC of the 100% solvent-containing adhesive (SBU100) was higher than that of the 50% (SBU50) and 0% (SBU0) solvent-containing adhesives for all substrates. DC of the adhesive applied onto glass and dehydrated dentin was higher than that applied onto dentin. Even though the ultimate microtensile strength of SBU0 was much higher than that of SBU50 and SBU100, its bond strength to dentin was significantly lower.

Conclusions

Evaporation of adhesive ingredients may jeopardize the shelf life of a one-bottle universal system by reducing the degree of conversion and impairing bond strength. However, negative effects only became evident after more than 50% evaporation.

Management in child and adolescent psychiatry: how does it look in the Balkans?

This paper examines the situation of child and adolescent psychiatry in the following Balkan countries: Greece, Serbia, Bulgaria, Romania, Bosnia and Herzegovina, FYROM, and Montenegro. With the exception of Greece, these countries are new democracies, with their mental health services in a transitional stage of organization. Overall, they have initiated programmes to move psychiatric care towards deinstitutionalization, developing outpatient infrastructures to handle psychiatric disorders. Child psychiatry as a specialization is still less developed than adult psychiatry at a significant, albeit different degree among these countries. The number of mental health services offered to children and adolescents is deemed insufficient, and the type of services limited and lacking. This situation is also reflected in the small number of child psychiatrists and other mental health specialists for children and adolescents, as well as in the complete lack (Montenegro) or deficiency of special programmes and actions for children and adolescents. The same also applies to mental health legislation. Greece is the exception in the development of the entire spectrum of services, the number of specialists, and the establishment of an adequate legislation framework reinforced by the incorporation of all international treaties on children's rights; although the recent economic crisis has affected the country negatively, threatening with regression to pre-reformational practices. Children and adolescents in need of mental health care have been increasing in all countries. The effect of violent and sudden changes taking place in most countries is a major factor for the emergence of increased and stress-related psychopathology and psychosocial problems in children and families. In all countries, there is a significant development of nongovernmental organizations undertaking a large part of reformation work. There is also the disconcerting phenomenon of professional exhaustion and the migration of experts from their countries. Finally, there is the common need to develop educational programmes and related clinical practices in all degrees of prevention, promoting interdisciplinary cooperation, the biopsychosocial approach to understanding and dealing with mental health issues, as well as the development of cooperation among all institutions concerning children (education, health, etc.). All this should be reflected in a national plan to promote child mental health as the foundation upon which the necessary cooperation among Balkan countries would be established in order to promote research, the exchange of experiences, common practices, mutual understanding, and common interests.

Analysis of local shrinkage patterns of self-adhering and flowable composites using 3D digital image correlation

OBJECTIVE

To analyze local shrinkage patterns in terms of surface shrinkage strains and z-axis displacements in a novel self-adhering composite and a conventional flowable composite using three-dimensional digital image correlation.

METHOD AND MATERIALS

Seven samples of each material were prepared in cylindrical Teflon molds 5 mm in diameter and 2 mm thick. The surface of the composites facing the cameras was sprayed with a fine layer of black paint. The unsprayed surface of each sample, opposite the one facing the cameras, was light cured for 40 seconds using a light-emitting diode unit. Digital images were taken immediately before and after light curing. Shrinkage was calculated as von Mises strains, and z-axis displacements were measured in microns. The data were statistically analyzed using two-way ANOVA at a = .05.

RESULTS

No significant difference in strain was observed between the two materials (P > .05). Strain distribution was nonhomogenous--the outer segments showed significantly higher strains than central parts in each material (P < .05). The opposite was observed for z-axis displacements-significantly greater displacements were found in central parts compared to the outer segments (P < .05).

CONCLUSION

Different shrinkage vectors across the surface of the tested flowable composites showed predominant in-plane shrinkage of the outer surface segments and out-of-plane shrinkage of the inner segments. These complex local deformation patterns in composite materials indicate zones of different types of forces exerted on the tooth-restoration interface in situ.

Psychotropic medication use in children and adolescents in an inpatient setting

Medication can be an effective part of treatment for several psychiatric disorders of childhood and adolescence but its use should be based on a comprehensive psychiatric evaluation and treatment plan. The aim of this study was to evaluate psychotropic medication use for children and adolescents treated as inpatients and to compare it with principles of rational pharmacotherapy, thus identifying possible downsides of current practices and pointing a way towards safer and more efficient practices. This is a descriptive study of prescribing trends at the Clinical Department for Children and Adolescents of the Institute of Mental Health in Belgrade, during the period from September 2009 to September 2010. Analyzed demographic data (age, gender) and the number of hospitalizations were obtained from medical histories, while diagnoses were obtained from discharge notes. Prescribed therapy was copied from medication charts. Drug dosages were analyzed as average daily doses prescribed during the hospitalization. Psychiatric diagnoses were classified according to The International Classification of Diseases and Related Health Problems, 10th Revision (ICD-10). During the examined time period, 264 patients were hospitalized (61.4% males), with an average age of 11.4±5.1 years. We have found that 66.3% of admitted patients were treated with pharmacotherapy in addition to other treatment modalities. There was a highly significant correlation between the age of patients and the prescribed dosage (Spearman's rho=0.360, p<0.001) as well as the number of prescribed drugs (Spearman's rho=0.405, p<0.001). The most commonly diagnosed psychiatric disorders were: autism spectrum disorders (20.8%), conduct disorders(19.7%), mixed developmental disorder (14.8%), adjustment disorder (7.2%), mental retardation (7.2%),acute psychosis (4.5%), and ADHD (2.3%). The most commonly prescribed medications were antipsychotics(45.9%), followed by antidepressants (17.2%), mood stabilizers (16.1%), benzodiazepines (14.4%), and other psychotropic drugs (6.4%). The most commonly prescribed antipsychotic was risperidone, used for more than 50% of the patients treated with antipsychotics. Taken together risperidone and chlorpromazine were more than 75% of all prescribed antipsychotics. 98.4% of prescribed antidepressants belonged to the SSRIs,with sertraline and fluoxetine accounting for almost 90% of them. All prescribed dosages were in accordance with the official guidelines. This is the first survey in Serbia to document the practice of prescribing psychotropic medication in the field of child and adolescent psychiatry. Current drug-prescribing practices at the Clinical Department for Children and Adolescents of the Institute of Mental Health in Belgrade are in accordance with current practices in the United States and Europe. Not every child with symptoms of mental health problems needs pharmacological treatment; when they do, the general rule of thumb should be "start low, go slow, and taper slowly". Follow-up studies are necessary to assess the change of trends, as well as studies in different patient populations and health centers, in order to globally evaluate psychotropic medication use in children and adolescents in Serbia.

Clinical reproducibility of three electronic apex locators

AIM

To compare the reproducibility of three electronic apex locators (EALs), Dentaport ZX, RomiApex A-15 and Raypex 5, under clinical conditions.

METHODOLOGY

Forty-eight root canals of incisors, canines and premolars with or without radiographically confirmed periapical lesions required root canal treatment in 42 patients. In each root canal, all three EALs were used to determine the working length (WL) that was defined as the zero reading and indicated by 'Apex', '0.0' or 'red square' markings on the EAL display. A new K-file of the same size was used for each measurement. The file length was fixed with a rubber stop and measured to an accuracy of 0.01 mm. Measurements were undertaken by two calibrated operators. Differences in zero readings between the three EALs in the same root canal were statistically analysed using paired t-tests with the Bonferroni correction, Bland-Altman plot and Linn's concordance correlation coefficients at α = 0.05.

RESULTS

Mean and standard deviation values measured by the three EALs showed no statistically significant differences. Identical readings by all three EALs were found in 10.4% of root canals. Forty-three per cent of readings differed by less than ± 0.5 mm and 31.3% exceeded a difference of ± 1 mm.

CONCLUSIONS

The clinical reproducibility of Dentaport ZX, RomiApex A-15 and Raypex 5 was confirmed with the majority of readings within the ± 1.0 mm range. However, the small number of identical zero readings suggests that EALs are not reliable as the sole means of WL determination under clinical conditions.

Micro-raman assessment of the ratio of carbon-carbon double bonds of two adhesive systems cured with LED or halogen light-curing units

PURPOSE

the purpose of the study was to compare the ratio of carbon-carbon double bonds (RDB) of two adhesive systems cured by five different light-curing units (LCUs) using micro-Raman spectroscopy. materials and methods: ten samples of an etch-and-rinse (Excite), a two-step self-etching adhesive system (AdheSE) - ie, primer and bond mixed - and AdheSE Bond only were prepared and cured with one of the following LEDs: Elipar Freelight2; Bluephase; SmartLite; Coltolux, each for 10 s; or a conventional halogen Prismetics Lite for 10 s or 20 s. Micro-Raman spectra were obtained from uncured and cured samples of all three groups to calculate the RDB. Data were statistically analyzed using ANOVA.

RESULTS

the mean RDB values were 62% to 76% (Excite), 36% to 50% (AdheSE Primer+Bond) and 58% to 63% (AdheSE Bond). At 20 s, Prismetics Lite produced significantly higher RDB in Excite than the other LCUs and Prismetics Lite at 10 s (p < 0.05). Prismetics Lite at 20 s and Elipar produced comparable RDB values of AdheSE Bond and AdheSE Primer+Bond (p > 0.05). Excite showed significantly higher RDB values than AdheSE (p < 0.05) whilst AdheSE Bond showed significantly higher RDB than AdheSE Primer+Bond (p < 0.05).

CONCLUSION

the etch-and-rinse adhesive cured with the halogen LCU for 20 s gave higher conversion than LED LCUs or halogen for 10 s curing time. The highest intensity LED [Elipar] produced higher or comparable conversion compared to the lower intensity LED LCUs for the same curing time. The etch-and-rinse adhesive showed higher RDB than the self-etching adhesive system. The presence of the primer in the self-etching adhesive compromised polymerisation.

Quantification of monomer elution and carbon-carbon double bonds in dental adhesive systems using HPLC and micro-Raman spectroscopy

OBJECTIVES

To quantify monomer elution from different adhesive systems using reverse-phase high-performance liquid chromatography (HPLC) and correlate this elution with the ratio of carbon-carbon double bonds from monomer to polymer (RDB) obtained using micro-Raman spectroscopy.

METHODS

Thirty dentine discs were cut from 30 human, intact, third molars and randomly allocated to five groups according to the adhesive applied: total-etch, Excite (Ivoclar Vivadent), two-bottle self-etch, Clearfil SE (Kuraray), one-bottle self-etch, Clearfil 3S (Kuraray), ormocer-based, Admira (Voco) and Filtek Silorane adhesive system (FS) (3M ESPE). Monomer elution was studied 1h, 6h, 24h, 96h and 7 days after immersion in 75% ethanol/water. The RDB was calculated immediately after light-curing and thereafter at 24h and 7 days. The data were statistically analysed using one-way ANOVA and Pearson's correlation coefficient (p<0.05).

RESULTS

More than 90% of the whole elution occurred during the first 1h, except for BisGMA in FS, with the highest absolute amount from Clearfil SE and the highest wt% from Admira. Initial RDB was in the ascending order FS<Admira<Excite<Clearfil SE<Clearfil 3S. In all groups, the RDB was significantly higher after 24h and 7 days than immediately after light-curing (p<0.05). Negative correlation was found only for the elution of HEMA and the RDB of Clearfil 3S.

CONCLUSIONS

Different adhesive systems showed different monomer elution kinetics. In all systems, the RDB increased after monomer elution. Overall, no direct correlation exists between the RDB of adhesives and the elution of unreacted monomers.

Temperature rise within the pulp chamber during composite resin polymerisation using three different light sources

The purpose of the study was to compare temperature rise during polymerisation of resin based composites (RBCs) with two LED light curing units (LCUs) compared to a halogen control light.

A study of temperature rise in the pulp chamber during composite polymerization with different light-curing units

AIM

The study compared pulp temperature rise during polymerization of resin-based composites (RBCs) using halogen and LED light-curing units (LCUs).

METHODS AND MATERIALS

A total of 32 teeth extracted from patients aged 11-18 years were used in the study. Thermocouples placed on the roof of the pulp chamber using a novel 'split-tooth' method. In Group 1 a halogen LCU with a light intensity of 450 mW cm(-2) was used and in Group 2, an LED LCU with a light intensity of 1100 mW cm(-2) was used. The teeth were placed in a water bath with the temperature regulated until both the pulp temperature and the ambient temperature were stable at 37 degrees C. Continuous temperature records were made via a data logger and computer. The increase in temperature from baseline to maximum was calculated for each specimen during the curing of both the bonding agent and the RBC.

RESULTS

The rise in pulp temperature was significantly higher with the LED LCU than with the halogen LCU for bonding and RBC curing (p<0.05). The major rise in temperature occurred during the curing of the bonding agent. During the curing of the RBC, rises were smaller.

CONCLUSIONS

Curing of bonding agents should be done with low intensity light and high intensity used only for curing RBC regardless of whether LED or halogen LCUs are used.

Changes in post-tetanic potentiation of A-fiber dorsal horn field potentials parallel the development and disappearance of neuropathic pain after sciatic nerve ligation in rats

Significant plastic changes in spinal nociceptive processing appear to accompany peripheral nerve injury or inflammation. Using a well-established model of neuropathic pain, we have recently reported that loose ligation of the sciatic nerve was accompanied by a long-lasting post-tetanic potentiation of sciatic-evoked A-fiber superficial dorsal horn field potentials. In the present study we demonstrate that the typical disappearance of thermal hyperalgesia as a behavioral sign of neuropathic pain several weeks after loose sciatic nerve ligation is accompanied by the loss of the long-lasting potentiation. These data suggest that a significant but reversible shift in the processing of sensory information in the spinal dorsal horn follows peripheral nerve injury, and lend further support to the notion that long-lasting synaptic plasticity may contribute to the development of neuropathic pain.

Contribution of GABA-A receptors to metaplasticity in the spinal dorsal horn

Metaplasticity is a higher-order form of synaptic plasticity that is induced by synaptic or cellular activity, which by itself may not produce changes in synaptic strength, but which modifies subsequent changes in synaptic efficacy. In this description of metaplasticity in the spinal dorsal horn, we report that a 50 Hz high-frequency tetanus, previously shown to elicit a potentiation of sciatic-evoked A-fiber spinal dorsal horn potentials, caused a depression when coupled with a more rapid rate of repetitive stimulation. This depression appeared to be dependent upon GABA(A) receptor activation because the 50 Hz tetanus elicited a persistent potentiation when the GABA(A) antagonist bicuculline was injected at 1 mg/kg (but not at 0.5 mg/kg) prior to tetanic stimulation. These data suggest the presence of strong inhibitory inputs in the spinal dorsal horn that are activated by an increased rate of primary afferent firing. The activation of these inputs may be necessary to prevent prolonged bursts of afferent activity from modifying synaptic strength because the latter may contribute to the development of persistent pain following peripheral nerve injury.

Increased spinal monoamine concentrations after chronic thoracic dorsal rhizotomy in goats

In goats, bilateral thoracic dorsal rhizotomy (TDR) causes severe ventilatory failure during exercise, followed by progressive functional recovery. We investigated spinal neurochemical changes associated with TDR and/or functional recovery by measuring spinal concentrations of the monoamines serotonin (5-HT), norepinephrine, and dopamine via HPLC. Changes in 5-HT and calcitonin gene-related peptide were visualized with immunohistochemistry. Goat spinal cords were compared 4-15 mo after TDR from T(2) to T(12) (n = 7) with sham-operated (n = 4) or unoperated controls (n = 4). TDR increased the concentration of cervical 5-HT (C(5)-C(6); 122% change), caudal thoracic norepinephrine (T(7)-T(11); 53% change), and rostral thoracic dopamine (T(3)-T(6); 234% change). TDR increased 5-HT-immunoreactive terminal density (dorsal and ventral horns) and nearly eliminated calcitonin gene-related peptide immunoreactivity in the superficial laminae of the dorsal horn in rostral thoracic segments; both effects became less pronounced in caudal thoracic segments. Thus TDR elevates monoamine concentrations in discrete spinal regions, including possible compensatory changes in descending serotonergic inputs to spinal segments not directly affected by TDR (i.e., cervical) but associated with functionally related motor nuclei (i.e., phrenic nucleus).

Differential effects of inorganic lead on hippocampal long-term potentiation in young rats in vivo

Tetanic stimulation at 50 Hz elicited long-term potentiation (LTP) in the hippocampal CA1 region of 28-day-old control animals. In contrast, no significant potentiation was seen following the same tetanus in animals chronically exposed to 1000 ppm of lead acetate during development. Gender differences were observed in animals exposed to 500 ppm of lead. In females, LTP was significantly attenuated, while in males the LTP was identical to that of controls.

Loose ligation of the rat sciatic nerve is accompanied by changes in the subcellular content of protein kinase C beta II and gamma in the spinal dorsal horn

This study examined whether loose ligation of the sciatic nerve was accompanied by specific changes in protein kinase C (PKC) betaII and gamma isozymes in the spinal dorsal horn. The isozyme staining pattern was visualized with immunocytochemistry. Their content in subcellular fractions was estimated from Western immunoblots. In control animals, PKC betaII immunoreactivity extended from lamina I into lamina III, while PKC gamma immunoreactivity was concentrated within laminae II and III. In ligated animals exhibiting thermal hyperalgesia, the content of both PKC betaII and gamma in the synaptosomal membrane fraction, but not crude cytosolic fraction, was significantly greater by an average of 40% from their respective controls. These data support suggestions that peripheral nerve injury engenders plastic changes in the dorsal horn to contribute to the development of persistent pain.

Long-term changes in sciatic-evoked A-fiber dorsal horn field potentials accompany loose ligation of the sciatic nerve in rats

The goal of the present study was to examine whether loose ligation of the sciatic nerve was associated with long-term changes in neuronal excitability in the spinal dorsal horn in urethane-anesthetized rats. The sciatic nerve was stimulated with 0. 1 ms long pulses at 1 stimulus/5 min, and the evoked dorsal horn field potentials remained stable in the absence of tetanic stimulation. In one set of control and ligated animals, high-frequency tetanic stimulation was applied to the nerve at 50 Hz (one 400 ms train of twenty 0.1 ms pulses), and the field potentials were recorded again (1 stimulus/5 min) for up to 4 h post-tetanus. In control animals, this protocol produced significant increases in field potential amplitudes at 15, 30 and 60 min post-tetanus. Interestingly, after this time the evoked field potentials began to decrease, and attained less than 50% of their pre-tetanic values at 240 min post-tetanus. In contrast, in ligated rats the pattern of post-tetanic potentiation was significantly different as the increases in amplitude persisted, and at 240 min post-tetanus the field potentials were almost twice their baseline values. In another set of control and ligated animals, low-frequency tetanic stimulation was applied at 5 Hz (one 400 ms train of two 0.1 ms pulses). Again a differential pattern of post-tetanic responses between control and ligated rats was seen. In control animals, a significant decrease in amplitude was evident within 30 min, and the depression became progressively more pronounced as the field potentials attained about a quarter of their baseline values at 180 min, and remained at these low levels at 240 min post-tetanus. On the other hand, in ligated animals, the depression was not significant, and at 240 min post-tetanus the field potentials were still at about 80% of their baseline values. These data demonstrate that long-term changes in spinal dorsal horn neuronal excitability accompany sciatic ligation to perhaps contribute to the development of neuropathic pain. These changes may result from a lessening of normally strong inhibitory processes in the spinal dorsal horn to generate conditions which favor post-tetanic potentiation over depression of dorsal horn neuronal responses.

Analgesic effects of butorphanol and buprenorphine in conscious African grey parrots (Psittacus erithacus erithacus and Psittacus erithacus timneh)

OBJECTIVE

To evaluate effects of butorphanol tartrate and buprenorphine hydrochloride on withdrawal threshold to a noxious stimulus in conscious African grey parrots.

ANIMALS

29 African grey parrots (Psittacus erithacus erithacus and Psittacus erithacus timneh).

PROCEDURE

Birds were fitted with an electrode on the medial metatarsal region of the right leg, placed into a test box, and allowed to acclimate. An electrical stimulus (range, 0.0 to 1.46 mA) was delivered to each bird's foot through an aluminum perch. A withdrawal response was recorded when the bird lifted its foot from the perch or vigorously flinched its wings. Baseline threshold to a noxious electrical stimulus was determined. Birds then were randomly assigned to receive an i.m. injection of saline (0.9% NaCl) solution, butorphanol (1.0 mg/kg of body weight), or buprenorphine (0.1 mg/kg), and threshold values were determined again.

RESULTS

Butorphanol significantly increased threshold value, but saline solution or buprenorphine did not significantly change threshold values.

CONCLUSIONS AND CLINICAL RELEVANCE

Butorphanol had an analgesic effect, significantly increasing the threshold to electrical stimuli in African grey parrots. Buprenorphine at the dosage used did not change the threshold to electrical stimulus. Butorphanol provided an analgesic response in half of the birds tested. Butorphanol would be expected to provide analgesia to African grey parrots in a clinical setting.

A technique for evaluating analgesia in conscious perching birds

OBJECTIVE

To develop a technique for objective assessment of modulation of nociperception in conscious perching birds.

ANIMALS

31 adult African grey parrots.

PROCEDURE

Birds were randomly assigned to receive saline (0.9% NaCl) solution (n = 10), butorphanol tartrate (11), or buprenorphine hydrochloride (10), i.m. Birds were fitted with a surface electrode on the medial metatarsus of 1 leg. An electrical stimulus was delivered to the bird's foot through an aluminum surface on half of the perch. The alternate side of the perch delivered a noxious thermal stimulus. A withdrawal response to either stimulus was recorded when the bird lifted its foot or vigorously flinched its wings.

RESULTS

Responses to thermal stimuli were extremely variable during baseline testing and after administration of drugs. Thus, significant differences were not detected after drug injection. In contrast, responses to an electrical stimulus were predictable with much less variation.

CONCLUSIONS AND CLINICAL RELEVANCE

This method and device allowed for the reliable determination of withdrawal threshold in perching birds. Use of this technique for objective assessment of modulation of nociperception in conscious perching birds will enable assessment of analgesic drugs.

Chronic exposure to lead acetate affects the development of protein kinase C activity and the distribution of the PKCgamma isozyme in the rat hippocampus

This study has examined the effect of chronic inorganic lead exposure on phospholipid-dependent protein kinase C (PKC) activity, and the distribution of its alpha (alpha), beta II (betaII), gamma (gamma), and zeta (zeta) isozymes in subcellular fractions of the developing rat hippocampus. Dams were exposed to either 0 or 1000 ppm lead acetate in their drinking water for one week and mated. Offspring were exposed to lead in utero, via lactation, and directly in the drinking water after weaning. The offspring were sacrificed at postnatal days 1 (P1), 8 (P8), 15 (P15), and 29 (P29). PKC activity was determined in the post-synaptosomal supernatant (PSS) and synaptosomal (P-2) membrane fractions by an in vitro assay using histone as the phosphate acceptor. The selected PKC isozymes were detected by immunoblotting techniques. In control animals, PKC activity (pmole/min/mg total protein) in both subcellular fractions substantially increased between P1 and P8. In chronically exposed rats exhibiting clinically relevant blood lead concentrations, this marked increase in PKC activity on P8 was significantly attenuated in both subcellular fractions. On this postnatal day, the amount of immunodetectable PKC gamma was significantly higher in the synaptosomal membrane fraction of lead-exposed rats. Other isozymes were unaffected. These results imply that in lead-exposed animals the PKC gamma isozyme was inactive even though it was associated with the membrane. These results also suggest that prolonged exposure to the heavy metal attenuated PKC activity at an important developmental time to potentially adversely affect normal hippocampal function.

Symposium overview: chemical modulation of neuroreceptors and channels via intracellular components

Whereas the roles of G proteins and protein kinases in various neuroreceptors and ion channels have been studied extensively, their roles in the actions of drugs and toxicants on these receptors and channels remain to be elucidated. Almost all drugs and toxicants exert multiple actions on multiple target sites, and there is no reason to assume that a chemical modulates a receptor/channel via a single mechanism. In fact, experimental evidence is slowly but steadily being accumulated to indicate that certain drugs and toxicants modulate neuroreceptor/channel functions through interactions with intracellular components such as G proteins and protein kinases. Multiple actions of a toxicant on various receptors/channels may be explained on the basis of its interaction with the G protein/kinase system that is a common denominator of the target sites. This is a virgin field that promises a quantum leap in the coming years. Each presentation and discussion will focus on expected future developments and potential significance in the field of neurotoxicology.

Diminished blocking effect of acute lead exposure on high-threshold voltage-gated calcium currents in PC12 cells chronically exposed to the heavy metal

Rat pheochromocytoma (PC12) cells were grown in 0, 10, 25, or 50 microM lead-containing growth media for up to twelve weeks. High-threshold whole-cell calcium currents from these PC12 cells were recorded in lead-free recording media (control), then in 1 microM lead-containing recording media (acute challenge), and finally again in lead-free recording media (wash). The acute lead challenge decreased calcium currents in all treatment groups (including 0 microM lead). However, this blocking effect of acute lead application diminished with prolonged chronic exposure to 25 and 50 microM lead. Although the acute lead challenge mainly caused a decrease in calcium currents, in some chronically exposed PC12 cells increased calcium currents were recorded during the application of 1 microM lead acetate. In other chronically exposed PC12 cells, the acute lead challenge caused the peak of the current-voltage curve to shift from +10 mV to 0 mV. The number of cells exhibiting either an increase in calcium current or a shift in the current-voltage relationship following acute lead challenge increased with prolonged chronic exposure to the heavy metal. The time-dependent increase in calcium influx may be responsible for at least one manifestation of lead neurotoxicity.