Effect of eugenol on respiration and division in human pulp, mouse fibroblasts, and liver cells in vitro

Eugenol depressed cell respiration in homogenates of human dental pulp and in mouse fibroblast monolayers. The depression was concentration-dependent, with a threshold at about 10(-4)M and a maximum at 10(-3)M in both preparations. Onset of the depression appeared to be rapid. The effects of variation in both duration and concentration of eugenol exposure on subsequent uptake of 3H-thymidine were examined in mouse fibroblast monolayers and human pulp explants. Fibroblasts survived short-term (up to 12 hr) exposure to 10(-3)M eugenol or less, but died after exposure to 10(-3)M for one day or more. The cells survived exposure to 10(-4)M for ten days, the longest period examined. Human pulp maintained in tissue culture medium showed similar eugenol susceptibility. Analysis of these data, when coupled with those of previous studies on eugenol release from ZOE and diffusion through dentin, gives strong support for the concepts that: the blandness of ZOE when applied to intact dentin is due to eugenol reaching the pulp in sub-toxic concentrations, and the irritant effect of ZOE when applied directly to soft tissue is due to the development of concentrations of eugenol in tissue adjacent to ZOE sufficient to inhibit respiration and thus kill cells.     

Influence of eugenol-containing temporary cement on efficacy of dentin-bonding systems

Zinc oxide-eugenol (ZOE) cements are widely used as temporary filling materials. However, eugenol has earlier been shown to have a detrimental effect on both resin composites and dentin-bonding systems. The aim of the present in vitro study was to examine whether ZOE cement would also reduce the efficacy of relatively new dentin-bonding systems. This was done by determination of gap formation around resin composite fillings in dentin cavities and of bond strength of resin composite to enamel and dentin. The tooth surfaces involved were either freshly cut, or had been exposed to a ZOE cement (IRM) or to a non-ZOE cement (Cavit) for 7 d before application of a dentin-bonding system (Gluma CPS or Scotchbond Multi-Purpose Plus) and a resin composite (Z100). Gap formation was assessed in a light microscope on 20-min-old fillings and expressed as wall-to-wall contraction (the width of the maximum marginal gap in % of the cavity diameter). Bond strength was measured in shear on 1-d-old specimens. The mean values of wall-to-wall contraction were 0.06-0.09% with Scotchbond Multi-Purpose Plus and 0.20-0.24% with Gluma CPS. The mean values of bond strength to enamel were 22-25 MPa for Scotchbond Multi-Purpose Plus and 20-23 MPa for Gluma CPS, and to dentin were 20-22 MPa for Scotchbond Multi-Purpose Plus and 13-14 MPa for Gluma CPS. The use of Scotchbond Multi-Purpose Plus resulted in higher bond strength to dentin and less wall-to-wall contraction than did Gluma CPS. No differences were found in either wall-to-wall contraction or in bond strength between the three groups for either dentin-bonding system. Thus, the ZOE cement did not influence the efficacy of two relatively new dentin-bonding systems.     

Glutaraldehyde collagen cross‐linking stabilizes resin–dentin interfaces and reduces bond degradation

This study evaluated the stability of resin–dentin interfaces treated with glutaraldehyde‐containing agents, and assessed collagen degradation in dentin matrices treated with Gluma. Microtensile bond strength (μTBS) was evaluated 24 h and 6 months after treatment with three desensitizers (Gluma Desensitizer, Gluma Desensitizer Power Gel, and MicroPrime G) and two etch‐and‐rinse adhesives (Comfort Bond & Desensitizer and iBond TE). Demineralized beams of human dentin were treated with water or Gluma, and the degradation of collagen in these beams was assessed by quantification of the dry mass loss and of the amount of hydroxyproline released from hydrolyzed specimens after 1 or 4 wk. All groups demonstrated significant reduction in μTBS after 6 months, except for Gluma Desensitizer and iBond TE groups, which showed decreases of 7.2% and 10.8%, respectively. The most prevalent failure mode was ‘mixed’. Significantly less hydroxyproline was released from Gluma‐treated beams than from control beams after 4 wk. Beams treated with Gluma yielded significantly less dry mass loss than did beams in the control group. Collagen cross‐linking with glutaraldehyde‐containing agents may assist in the stabilization of resin–dentin bonds by reducing the amount of collagen solubilized from dental matrices in the hybrid layer. In turn, this may contribute to the preservation of adhesive interfaces.     

Influence of eugenol-containing temporary cement on bonding of self-etching adhesives to dentin

PURPOSE: To investigate the influence of eugenol-containing temporary cement on bonding of resin composite to dentin mediated by self-etching adhesives. MATERIALS AND METHODS: Flat dentin surfaces were produced by grinding of extracted human molars. The dentin surfaces were either used directly or after a one-week exposure to a zinc oxide-eugenol cement (IRM). A resin composite (Herculite XRV) was bonded to the dentin surfaces following treatment with 1 of 6 self-etching adhesives (AdheSE, Adper Prompt L-Pop, Clearfil SE Bond, iBond, OptiBond Solo Plus - Self-Etch Adhesive System, and Xeno III). An adhesive system containing 0.5 M EDTA as dentin conditioner (Gluma Classic) was included as negative control, and an etch-and-rinse adhesive system (OptiBond FL) was included as positive control. After storage in water at 37 degrees C for 1 week, the bonded specimens were fractured in shear (n = 8 in each group). RESULTS: Previous contact of dentin with zinc oxide-eugenol cement significantly decreased the bond strength mediated by the negative control and did not affect the bond strength mediated by the positive control. For the self-etching adhesives, no effect was found of previous contact with zinc oxide-eugenol cement. With and without previous contact with zinc oxide-eugenol cement, the etch-and-rinse adhesive system yielded a significantly higher bond strength than all other adhesive systems. CONCLUSION: Previous contact with zinc oxide-eugenol cement did not decrease the bond strength of resin composite to dentin mediated by self-etching adhesives. This finding suggests that eugenol-containing temporary cements may be safe to use in combination with self-etching adhesives.     

Effect of temporary cements on the microtensile bond strength of self-etching and self-adhesive resin cement

Objective. The aim of this study was to evaluate the microtensile bond strength (µTBS) of self-etching and self-adhesive resin cement systems to dentin affected by the presence of remnants of either eugenol-containing or eugenol-free temporary cements. Materials and methods. Thirty extracted teeth were obtained and a flat dentin surface was exposed on each tooth. Acrylic blocks were fabricated and cemented either with one of two temporary cements, one zinc oxide eugenol (ZOE) and one eugenol free (ZOE-free), or without cement (control). After cementation, specimens were stored in water at 37°C for 1 week. The restorations and remnants of temporary cements were removed and dentin surfaces were cleaned with pumice. Resin composite blocks were cemented to the bonded dentin surfaces with one of two resin cements, either self-etching (Panavia F 2.0) or self-adhesive (RelyX U-100). After 24 h, the specimens were sectioned to obtain beams for submission to µTBS. The fracture mode was evaluated under a stereoscopic loupe and a scanning electron microscope (SEM). Data from µTBS were submitted to two-way repeated-measure ANOVA and the Tukey test (alpha = 0.05). Results. The cross-product interaction was statistically significant (p < 0.0003). The presence of temporary cements reduced the bond strength to Panavia self-etching resin cements only (p < 0.05). Fracture occurred predominantly at the dentin–adhesive interface. Conclusions. The presence of eugenol-containing temporary cements did not interfere in the bond strength to dentin of self-adhesive resin cements.     

氧化锌丁香油对3种永久粘固剂剪切强度影响的研究

目的研究氧化锌丁香油对3种永久粘固剂与牙本质间粘结强度的影响。方法将因正畸需要拔除的60颗前磨牙制成试样块并用树脂包埋,一面暴露作为测试面,去除其釉质暴露浅层牙本质并用砂纸磨平。分为玻璃离子组(Ⅰ组)、树脂改性玻璃离子体组(Ⅱ组)、树脂粘结剂组(Ⅲ组),然后各组再分为对照组(A组),氧化锌丁香油组(B组),每组10个试样。在万能试验机上测试4 mm直径树脂块在A、B两种条件下用3种永久粘结剂粘固后的剪切强度。并用扫描显微镜观察剪切后试样表面形貌。结果 3组受氧化锌丁香油影响较大((3.22±1.47)MPa对比(1.22±0.35)MPa,P=0.001),1组、2组在A、B两种条件下剪切强度差异无统计学意义(P>0.05)。结论使用氧化锌丁香油粘固剂预处理牙本质表面,对树脂类粘固剂有不利影响,而对玻璃离子和树脂改性玻璃离子体无不利影响。     

An analysis of the release and the diffusion through dentin of eugenol from zinc oxide-eugenol mixtures

Tritium-labeled eugenol was released from mixtures of zinc oxide eugenol (ZOE) into aqueous solution at rates which declined exponentially with time, and which were directly proportional to the liquid-powder ratio. The release pattern was consistent with a model of progressive hydrolysis of zinc eugenolate in a limited-thickness ZOE surface layer. Intervening dentin had a profound effect on this pattern of release. In human teeth in vitro containing ZOE as a base or temporary filling, peak eugenol release at the pulpal surface of dentin was of the order of a thousand-fold less than that at the salivary surface. In such teeth, eugenol reached concentrations in excess of 10(-2) M in dentin just beneath ZOE, and 10(-4) M or less adjacent to the pulp space. Both pulpal outflow and dentin concentrations of eugenol remained relatively constant for more than a week, unlike release into aqueous solution. While these data were derived from studies on human teeth in vitro, they give a strong indication of probable events in vivo, and appear to provide a basis for the explanation of the paradox of the therapeutic and toxic actions of ZOE.     

A suitable base material for composite resin restorations: Zinc oxide eugenol

Objective

This in vitro study evaluated the effects of a zinc oxide eugenol (ZOE) base on the mechanical properties of a composite resin restoration.

Methods

Class I cavities were prepared on plastic teeth and filled with ZOE plus composite resin, following standard clinical procedures. The samples were sectioned sagittally and the ZOE–resin interface was exposed. After polishing, nanoindentation was performed on the region near the interface, and elastic modulus and hardness were plotted in the form of a color contour map. SEM was employed to observe the interface between composite resin and ZOE base.

Results

In the region close to the ZOE base, the elastic modulus and hardness of composite resin reduced to the values of 9.71 ± 0.54 and 0.51 ± 0.05 GPa, respectively. Eugenol from ZOE had detrimental effects on the composite resin only to a distance of less than 100 μm from the ZOE base.

Conclusion

Although eugenol suppresses polymerization slightly, by considering the biological advantages of ZOE, together with the results of the current investigation, ZOE may still be considered a suitable base material for composite resin. Bonding is essential for composite resin restorations over ZOE bases to avoid shrinkage detachment.     

Effect of Dentin Surface Modification on the Microtensile Bond Strength of Self‐Adhesive Resin Cements

Purpose: To explore the potential to modify human dentin surface as a means of improving the microtensile bond strength (μTBS) of resin cement to dentin. Materials and Methods: Sound human molars were collected, and their occlusal surfaces were ground flat to expose polished dentin. Indirect composite resin cylinders were cemented to the teeth with RelyX Unicem or G‐Cem self‐adhesive cements following dentin surface treatments: 6.5% grape‐seed extract, 5% glutaraldehyde, or 25% polyacrylic acid and control (no pretreatment). After 24 hours, the teeth were sectioned into beams to produce a cross‐sectional area of 1.0 mm². Specimens of each group (n = 25) were individually mounted on a jig and placed on a tensile testing machine. A tensile force was applied to failure at a 1 mm/min crosshead speed. Results: The use of polyacrylic acid on dentin prior to cementation with RelyX Unicem resulted in a statistically significant increase in μTBS compared to the control group (p= 0.0282). Polyacrylic acid (p= 0.0016) or glutaraldehyde (p= 0.0043) resulted in a statistically significant increase in μTBS of G‐Cem to dentin when compared to the control group. Treatment with grape‐seed extract did not result in a statistically significant increase in μTBS for either cement (p > 0.05). Conclusions: Priming dentin surfaces prior to the use of self‐adhesive resin cements may be a promising means of improving μTBS. In addition, it was concluded that the results of this study are material dependent as well as being dependent of the type of dentin primer.     

Effect of tin–chloride pretreatment on bond strength of two adhesive systems to dentin

Objectives

To determine the effect on resin composite-to-dentin bond strength of incorporation of an acidic tin–chloride pretreatment in two adhesive systems.

Materials and methods

Human molars were ground to expose mid-coronal dentin. For microtensile bond strength (μTBS) testing, dentin was treated with Optibond FL or Clearfil SE according to one of six protocols (n?=?22/group). Group 1: Phosphoric acid etching, Optibond FL Prime, Optibond FL Adhesive (manufacturer’s instructions; control); Group 2: Tin–chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 3: Phosphoric acid etching, tin–chloride pretreatment, Optibond FL Prime, Optibond FL Adhesive; Group 4: Clearfil SE Primer, Clearfil SE Bond (manufacturer’s instructions; control); Group 5: Phosphoric acid etching, Clearfil SE Primer, Clearfil SE Bond; and Group 6: Tin–chloride pretreatment, Clearfil SE Primer, Clearfil SE Bond. The molars were then built up with resin composite (Clearfil Majesty Esthetic). After storage (1 week, 100  % humidity, 37 °C) the μTBS was measured and failure mode was determined. Additionally, pretreated dentin surfaces were evaluated using SEM and EDX. The μTBS results were analyzed statistically by a Welch Two Sample t-test and a Kruskal–Wallis test followed by exact Wilcoxon rank sum tests with Bonferroni–Holm adjustment for multiple testing (α?=?0.05).

Results

When Optibond FL was used, partial or total replacement of phosphoric acid with tin–chloride decreased μTBS significantly. In contrast, when Clearfil SE was used, inclusion of a tin–chloride pretreatment in the adhesive procedure increased μTBS significantly.

Conclusions

Tin–chloride pretreatment had a beneficial influence on the bond promoting capacity of the MDP-containing adhesive system Clearfil SE.     

Biologic properties of eugenol and zinc oxide-eugenol. A clinically oriented review.

Eugenol-containing dental materials are frequently used in clinical dentistry. When zinc oxide-eugenol (ZOE) is applied to a dentinal cavity, small quantities of eugenol diffuse through the dentin to the pulp. Low concentrations of eugenol exert anti-inflammatory and local anesthetic effects on the dental pulp. Thus use of ZOE temporary filling may facilitate pulpal healing; on the other hand, high eugenol concentrations are cytotoxic. Direct application of eugenol to pulp tissue may result in extensive tissue damage. The ability of ZOE-based endodontic sealers to influence periapical tissue healing is considered in view of eugenol's anti-inflammatory and toxic properties.     

The effect of a desensitizer and CO2 laser irradiation on bond performance between eroded dentin and resin composite

PURPOSE

This study was aimed to evaluate effect of the desensitizing pretreatments on the micro-tensile bond strengths (µTBS) to eroded dentin and sound dentin.

MATERIALS AND METHODS

Forty-two extracted molars were prepared to form a flat dentin surface, and then they were divided into two groups. Group I was stored in distilled water while group II was subjected to a pH cycling. Each group was then subdivided into three subgroups according to desensitizing pretreatment used: a) pretreatment with desensitizer (Gluma); b) pretreatment with CO₂ Laser (Ultra Dream Pluse); c) without any pretreatment. All prepared surfaces were bonded with Single Bond 2 and built up with resin composite (Filtek Z250). The micro-tensile bond test was performed. Fracture modes were evaluated by stereomicroscopy. Pretreated surfaces and bonded interfaces were characterized by scanning electron microscope (SEM). The data obtained was analyzed by two-way ANOVA (α=0.05).

RESULTS

For both sound and eroded dentin, samples treated with desensitizer showed the greatest µTBS, followed by samples without any treatment. And samples treated with CO₂ laser showed the lowest µTBS. SEM study indicated that teeth with eroded dentin appeared prone to debonding, as demonstrated by existence of large gaps between adhesive layers and dentin.

CONCLUSION

Pretreatment with Gluma increased the µTBS of Single Bond 2 for eroded and sound teeth. CO₂ laser irradiation weakened bond performance for sound teeth but had no effect on eroded teeth.     

丁香油酚对全酸蚀/自酸蚀牙本质粘接系统微拉伸强度的影响

目的:评价含丁香油酚的暂封剂氧化锌丁香油糊剂(zincoxide- eugenol ,ZOE)对全酸蚀/自酸蚀牙本质粘接系统微拉伸强度的影响。方法:选择因正畸拔除的完整、无龋前磨牙;两种全酸蚀牙本质粘接系统:AllBond 2和SingleBond ,两种自酸蚀牙本质粘接系统:ClearfilSEBond和iBond。实验组使用氧化锌丁香油糊剂;对照组牙本质表面不做任何处理;分别存储于3 7℃的蒸馏水中,一周后两组分别使用4种牙本质粘接系统,用微拉伸法测试粘接强度。在体视显微镜下观察断裂界面。结果:双因素方差分析使用ZOE对粘接强度有显著影响(P <0 .0 5 ) ,粘接剂的类型对粘接强度无显著性影响(P >0 .0 5 ) ,交互作用有统计学意义(P <0 .0 5 )。多重比较提示,AllBond 2和SingleBond的实验组和对照组无显著性差异,而ClearfilSEBond和iBond实验组的微拉伸强度明显低于对照组,有显著性差异。体视显微镜下观察断裂多发生在粘接剂内。结论:含丁香油酚的暂封剂氧化锌丁香油糊剂对全酸蚀系统的AllBond 2和SingleBond的粘接强度无影响,对自酸蚀系统的ClearfilSEBond和iBond有显著不利影响。     

Influence of application parameters on bond strength of an “all in one” water-based self-etching primer/adhesive after 6 and 12 months of water aging

Our aim was to evaluate the influence of different application parameters on microtensile bond strength (μTBS) of an “all in one” water-based self-etching primer/adhesive to dentin. Extracted human third molars had their crowns transversally sectioned next to the dentinoenamel junction. Prompt-L-Pop adhesive was applied using five modes: (1) following the manufacturer’s instructions (MI); (2) after 36% H₃PO₄ etching (15 s) (AG); (3) after H₃PO₄ etching and 5% NaOCl (2 min) with constant agitation (HG); (4) as a double layer (DL); and (5) for double the application time (DT). Resin build-ups were constructed with Tetric Ceram. After storage for 24 h, 6 months, or 12 months in water at 37°C, the specimens were vertically sectioned into beams (cross-sectional areas, 1 mm²). Each beam was tested in an Instron Machine at 0.5 mm/min. Analysis of variance and Student-Newman-Keuls were used (P < 0.05). Bonded interfaces were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The highest μTBS values were obtained when AG was used, and the lowest when MI was employed. The HG, DL, and DT modes resulted in similar μTBS values. Water storage reduced μTBS in all groups except the MI group. SEM and TEM revealed hybrid layer and resin tag formation in all groups. Applied after AG, HG, DL, and DT, Prompt L-Pop adhesive provided adequate bond strength to dentin after 24 h of water storage. Bond strength decreased when specimens were stored in distilled water for 6 or 12 months.     

Use of polyphenols as a strategy to prevent bond degradation in the dentin–resin interface

This study evaluated the effect of dentin pretreatment with the polyphenols quercetin and resveratrol on the resin‐dentin microtensile bonding strength (μTBS) and collagen fibrils stability of the adhesive interface. Different concentrations (100, 250, 500, or 1,000 μg ml^?1) of quercetin or resveratrol, or a mixture of quercetin and resveratrol (3:1, 1:1, 1:3; vol:vol), as well as distilled water or 2% chlorhexidine digluconate, were applied to etched dentin. Then, a two‐step etch‐and‐rinse adhesive was applied followed by composite restoration. Measurements of resin–dentin μTBS were made after 1 and 120 d. The stability of collagen fibrils in the hybrid layer was evaluated using transmission electron microscopy. The Student's t‐test and two‐way factorial anova with Tukey's test were used to analyze the effects of dentin pretreatment and storage time on μTBS values. Comparisons between μTBS measurements made on 1 and 120 d showed that resveratrol had the best performance, with significantly higher μTBS values after 120 d for all concentrations of resveratrol tested. Quercetin pretreatment resulted in a significant rise of μTBS when used at concentrations of 100 and 500 μg ml^?1. Quercetin + resveratrol at the ratio of 1:1 performed better than when used at ratios of either 3:1 or 1:3. Resveratrol might represent a potential approach to achieve desirable bonding stability and reduce the frequent replacement of composite restorations.     

三种脱敏剂对全酸蚀粘结剂牙本质粘结强度和界面形态的影响

目的:研究、比较三种脱敏剂对全酸蚀粘结剂牙本质粘结强度及其粘结界面形态的影响。方法:选择12个无龋损离体人磨牙,磨除牙合面釉质,用600目碳化硅砂纸在流水下预备出有统一玷污层的牙本质粘结面后,随机分为4组,分别用去离子水(对照组)和3种脱敏剂(Hybrid Coat、Gluma、极固宁)进行脱敏处理后,应用Single Bond 2在面粘结4 mm树脂。然后将每个牙垂直于粘结面切割出12个1.0 mm×1.0 mm×4.0 mm的粘结试件,分别在SEM下观察其粘结界面微观形态并进行微拉伸强度(μTBS)测试。结果:HybridCoat组粘结强度最高((14.81±3.87)MPa,随后依次为去离子水组(13.39±4.67)MPa、Gluma组(12.76±2.96)MPa和极固宁组(10.48±4.32)MPa,各组间两两比较,极固宁组明显低于其他3组(P﹤0.05),其他3组间相比均无显著性差异(P﹥0.05);Hybrid Coat组形成的树脂突大部分>35μm,长而密集;Gluma组形成的树脂突长7～35μm;极固宁组形成的树脂突长20～35μm,较稀疏。结论:Hybrid Coat和Gluma对全酸蚀粘结剂牙本质粘结强度无明显影响,而极固宁则明显降低其粘结强度。     

Bond strength and morphology of resin materials applied to the occlusal surface of primary molars

International Journal of Paediatric Dentistry 2012; 22: 435–441 Background. Hydrophilic adhesives may be used as pit and fissure sealants (sealants), but there is concern about the ability of self‐etching adhesives to bond sealants to enamel. Aim. To study the bond strength (BS) and morphology of adhesive systems used as sealants. Design. OptiBond FL, OptiBond All‐in‐One, combined OptiBond All‐in‐One + OptiBond FL adhesive, and Fluroshield were applied to the occlusal surfaces of 16 primary molars (n = 4). Teeth were stored in distilled water (24 h at 37°C) and sectioned through the interface to obtain sticks (0.8 mm²) tested under a tensile load (0.5 mm/min). Failure modes were observed. Data were analysed by ANOVA and Tukey’s tests (α = 5%). The morphology of 12 primary molars was examined in terms of the etching pattern and resin reproduction. Results. Differences in the BS were found (P = 0.001), with OptiBond FL showing the highest (36.84 ± 5.7 MPa), Fluroshield (24.26 ± 2.13 MPa) and OptiBond All‐in‐One (17.12 ± 4.97 MPa) similar, and OptiBond All‐in‐One + OptiBond FL adhesive the lowest (9.8 ± 2.94 MPA). OptiBond FL showed the best results in terms of morphology. Conclusion. Under the conditions of this study, OptiBond FL was the best material to be used for sealing.     

Does tin pre-treatment enhance the bond strength of adhesive systems to enamel?

Objectives

The study investigated the modification of composite-to-enamel bond strength by pre-treatment of enamel with a concentrated, acidic SnCl₂-solution.

Methods

Six groups of flat human enamel specimens (n = 44 per group) were treated as follows: OB-H: H₃PO₄ etching, Optibond FL application (primer + adhesive; manufacturer's instructions); OB-S: SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); OB-HS: H₃PO₄ etching + SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); CF-N: Clearfil SE application (primer + bond; manufacturer's instructions); CF-H: H₃PO₄ etching, Clearfil SE application (primer + bond); CF-S: SnCl₂ pre-treatment, Clearfil SE application (primer + bond). Enamel specimens were then built up with resin composite (Clearfil Majesty Esthetic) and stored (100% humidity, 37 °C, 1 week). μTBS-measurement and failure mode analysis of one-half of the specimens were performed immediately after storage, while the other half was analysed after a thermocycling procedure (8500 cycles; 5 °C and 55 °C; dwell time 30 s). Additional specimens were prepared for SEM- and EDX-analysis.

Results

Highest values were measured for OB-H before and after thermocycling, lowest values for CF-N. Compared to OB-H treatment, OB-S treatment reduced μTBS before/after thermocycling by 23%/28% and OB-HS treatment by 8%/24% (except for OB-SH before (n.s.), all p ≤ 0.001 compared to OB-H). In the Clearfil SE treated groups pre-treatment increased μTBS significantly compared to CF-N (before/after: CF-H: +46%/+70%; CF-S: +51%/42%; all p ≤ 0.001).

Conclusion

Pre-treatment with H₃PO₄ or SnCl₂ markedly increased the μTBS of Clearfil SE to enamel. However, thermocycling partly reduced the gain in μTBS obtained by SnCl₂ pre-treatment.

Clinical significance

The application of an acidic and highly concentrated SnCl₂ solution is a good option to increase the μTBS between enamel and a resin composite mediated by an adhesive system containing the multifunctional monomer MDP.     

Experimental two-step universal adhesives bond durably in a challenging high C-factor cavity model

ObjectivesTo determine the bonding effectiveness of experimental 2-step universal adhesives (UAs) to high C-factor class-I cavity-bottom dentin and to assess the potential bond-strength contribution of an additional flowable composite layer.MethodsThree experimental 2-step UA formulations, involving the application of a 10-MDP-based primer followed by a hydrophobic adhesive resin with a 15-to-20-µm film thickness and differing only for filler, referred to as BZF-21 (silica and bioglass filler), BZF-29 (silica filler) and BZF-29_hv (higher silica-filler loading resulting in a higher viscosity), all prepared by GC, along with three representative commercial adhesives, Clearfil SE Bond 2 (C-SE2, Kuraray Noritake), G-Premio Bond (G-PrB, GC) and OptiBond FL (Opti-FL, Kerr), were comparatively investigated for their ‘immediate’ and ‘aged’ (50,000 thermocycles) micro-tensile bond strength (μTBS), when applied either in etch-and-rinse (E&R) or self-etch (SE) mode, to high C-factor class-I cavity-bottom dentin (n = 10; 10 experimental groups). Four additional experimental groups involved the extra application of the flowable composite G-ænial Universal Flo (GC), employed as an intermediate liner in combination with the adhesives BZF-29 and G-PrB and again applied both in E&R or SE mode. Statistical analysis was performed using linear mixed-effects (LME) modelling and linear regression analysis (p < 0.05).ResultsAll 2-step UAs performed similarly when compared to the gold-standard E&R Opti-FL and SE C-SE2 adhesives, except for the aged μTBS of BZF-29_hv applied in E&R mode, and significantly outperformed the 1-step UA G-PrB. Significant reduction in μTBS upon aging was only recorded for 2-step UAs applied in E&R mode. The extra flowable composite layer significantly improved G-PrB’s μTBS.SignificanceThe experimental 2-step UAs revealed favorable bonding performance in the challenging high C-factor class-I cavity model, comparable to that of the multi-step gold-standard E&R and SE adhesives and superior to that of the 1-step UA investigated. An additionally applied flowable composite layer compensated for the lower bonding effectiveness of the 1-step UA in the high C-factor cavity model.     

Immediate dentin sealing of onlay preparations: thickness of pre-cured Dentin Bonding Agent and effect of surface cleaning

This study evaluated the thickness of Dentin Bonding Agent (DBA) used for "immediate dentin sealing" of onlay preparations prior to final impression making for indirect restorations. In addition, the amount of DBA that is removed when the adhesive surface is cleaned with polishing or air abrasion prior to final cementation was evaluated. For this purpose, a standardized onlay preparation was prepared in 12 extracted molars, and either OptiBond FL (Kerr) or Syntac Classic (Vivadent) was applied to half of the teeth and cured in the absence of oxygen (air blocking). Each tooth was bisected in a bucco-lingual direction into two sections, and the thickness of the DBA was measured under SEM on gold sputtered epoxy resin replicas at 11 positions. The DBA layer of each half tooth was treated with either air abrasion or polishing. The thickness of the DBAs was then re-measured on the replicas at the same positions. The results were statistically analyzed with non-parametric statistics (Mann-Whitney U test and Kruskal-Wallis test) at a confidence level of 95% (p=0.05). The film thickness of the DBA was not uniform across the adhesive interface (121.13 +/- 107.64 microm), and a great range of values was recorded (0 to 500 microm). Statistically significant differences (p<0.05) were noted, which were both material (OptiBond FL or Syntac Classic) and position (1 to 11) dependent. Syntac Classic presented a higher thickness of DBA (142.34 +/- 125.10 microm) than OptiBond FL (87.99 +/- 73.76 microm). The higher film thickness of both DBAs was at the deepest part of the isthmus (the most concave part of the preparation), while the lowest was at the line angles of the dentinal crest (the most convex part of the preparation). OptiBond FL presented a more uniform thickness around the dentinal crest of preparation; Syntac Classic pooled at the lower parts of the preparation. The amount of DBA that was removed with air abrasion or polishing was not uniform (11.94 +/- 16.46 microm), and a great range of values was recorded (0 to 145 microm). No statistically significant differences (p<0.05) were found either between different DBAs (OptiBond FL or Syntac Classic) or between different treatments (air abrasion or polishing). As far as the effect of different treatments at different positions, polishing removed more DBA from the top of the dentinal crest, but the difference was not statistically significant. Air abrasion removed less DBA from the corners of the dentinal crest (Positions 4 and 6) than the outer buccal part of the preparation (Positions 1 and 2). Neither air abrasion nor polishing removed the entire layer thickness of the DBA in the majority of the cases.