Observations on cavity liners for composite resin restorations

Adhesion or surface roughness and discoloration at the interface between pulp-insulating materials and composite resins were taken as indications for interaction between the resins and the insulating materials. Some interaction occurred between all insulating materials and resins investigated. After separation of the restorative resins, the interaction of Dycal with the different composite resins varied considerably and decreased in the following sequence: Opotow, Natural, and Adaptic. The interactions of ZOE with Natural and with Adaptic were similar and more pronounced than the interaction at the Adaptic-Dycal interface but less pronounced than at the Dycal-Natural interface. A very thin film of Tubulitec was found to adhere to the composite resins in some areas.The adherence of liners containing calcium hydroxide to dentin was found to be generally stronger than the bond between these liners and composite resins. Separation of the composite resins caused tears in the varnishes and frequently in Hydroxyline. Almost completely intact layers of the varnish Copalite were observed on dentin, but Zahnlack apparently dissolved to a great extent in the resins.Among the liners containing calcium hydroxide, Dycal and Tubulitec were found to give rise to a high pH in samples of saliva, but Hydroxyline did not. Porosity and a folded surface were observed for Hydroxyline, indicating the entrapment of the solvent beneath a dry superficial layer.     

Adhesion of liners to dentin. In vivo experiments

Research was performed in vivo on 42 vital teeth. Cavities of I and V Class where made, than restored with glass ionomer liners and composites. The teeth were extracted, stained and sectioned. Optic microscope did not show any stain under the ionomer liner, even in cases where composites were infiltrated. Electron microscope did not show any gap between ionomer liner and dentin.     

Effect of the tenure dentin bonding system on leakage of light-activated liners

This study investigated the effect of the Tenure dentin bonding system on the sealing properties of four light-activated liners. Dentinal slot preparations were made in extracted human molars and "restored" with Cavalite, TimeLine, VLC Dycal, and Zionomer liners. Samples were immersed in 0.05 percent crystal violet solution for 2 hours, then embedded in clear casting resin, sectioned, and examined with an optical microscope. Our results indicated that the Tenure dentin bonding system reduced dye penetration around each of the light-activated liners tested. The Tenure/VLC Dycal system provided a more effective seal than the other liners.     

空气喷砂机对牙齿硬组织作用的实验研究

目的：研究空气喷砂机制洞对牙齿硬组织结构的改变。方法：空气喷砂机去龋并制备洞形后。利用扫描电镜观察牙齿硬组织的组织学变化。结果：空气喷砂机所制备的洞形不规则，有裂隙形成，硬化牙本质残留，有少量玷污层形成。结论：空气喷砂机所制备洞形可保留更多正常牙质，有利于复合树脂材料的充填。     

Using cavity liners with direct posterior composite restorations

Cavity liners have traditionally been used in direct and indirect restorations for purposes such as promoting reparative dentin and neutralizing acids. Today, liners are used when resin composites are used as the restorative materials on the posterior teeth, but for a different reason. Clinically, liners are considered to decrease sensitivity and wet the cavity better than restorative composites because of their flowability, adaptation to the dentinal surface, and adhesion. As bonding systems and composite materials continue to improve and become better understood, so do the techniques for placing composites. This has led to the reassessment of the clinical relevance and function of liners. Some clinicians don't use cavity liners, assuming they are a thing of the past; some use composite liners, and others use resin-modified glass ionomer liners. Additionally, there is not a clear agreement over the function of liners, such as when and why they should be used or what type of liner material would provide the best performance for a particular clinical situation. This article attempts to clarify some of the confusion surrounding the use of liners by reviewing the available literature on the subject and attempting to give evidence-based rationale for the use and protocol for the clinician.     

Parameters that affect in vitro bonding of glass-ionomer liners to dentin

The purpose of this study was to evaluate the effects of two concentrations of poly (acrylic acid) (10 and 25%), three treatments (untreated, passive conditioning, and active conditioning), and two storage conditions (24 hours in 37 degrees C water and thermal cycling) on the in vitro tensile bond strength of three commercial glass-ionomer liners to human dentin. Bond strengths to untreated dentin after storage for 24 hours ranged from 19.0 to 21.7 kg/cm2 for Glasionomer Base Cement, Cement/Liner, and Ketac-Bond, but dropped to a range of 4.9 to 9.7 kg/cm2 after thermal cycling. Active conditioning with 10% acid resulted in bond strengths after 24-hour storage that ranged from 23.5 to 44.0 kg/cm2, compared with values from 21.7 to 38.0 kg/cm2 with active conditioning using 25% acid. Active conditioning with 10% acid resulted in bond strengths after thermal cycling that were in the range of 15.8 to 27.4 kg/cm2 and were 80 to 320 percent higher than values resulting from passive conditioning under these conditions. Active conditioning with 10% acid for 30 seconds produced a bond strength for Glasionomer Base Cement of 44.0 kg/cm2, compared with a bond strength of 28.7 kg/cm2 for a 10-second active conditioning. Qualitative analysis of scanning electron photomicrographs showed that dentin tubules were opened to a greater extent by active conditioning with 25% acid than by passive conditioning with 10% acid.     

Permeability and wetting properties of four cavity liners.

Four commercially available cavity liners were evaluated as to their permeability characteristics. The contact angle measurement of each liner also was calculated. S. S. White liner was found to have the lowest contact angle and permeability values with a better wetting property. Copalite, on the other hand, was found to have the highest contact angle and permeability values with a poor wetting property. Caulk varnish and Polyvar had values lying between the two materials. Copalite is the preferred material in decreasing marginal leakage because of its high contact angle, whereas the S. S. White liner is preferred in pulpal and axial surface protection because of its good wetting properties.     

Antibacterial effects of light-cured liners

Light-cured liners and glass ionomers have recently been introduced and it has not been established if they are antimicrobial. This study determined the effectiveness of several light-cured liners against Streptococcus mutans #6715. Fluoride release and pH determination tests were performed to define their antibacterial activity. After evaluation with agar diffusion methodology, two of the light-cured glass ionomers were considered inhibitory. These two liners released fluoride into the agar in excess of the minimum inhibitory value of 20 ppm. The other four materials released fluoride below reported inhibitory values, failed to lower the pH below 4.0 and were ineffective against Streptococcus mutans. The findings suggested that light-cured glass ionomers react similarly to conventionally-cured glass ionomers regarding antibacterial activity against Streptococcus mutans. It also indicated that antibacterial activity was dependent upon a lower pH. Fluoride release may not be as important to the mechanism of action; however, it cannot be ruled out.     

Shear bond strengths to dentin and fluoride release from fluoride-containing liners

The purpose of this study was to determine the shear bond strengths of five commercially available fluoride-containing restorative systems to dentin and to evaluate the fluoride release from them. The five systems evaluated were: (A) Vitrabond/Silux; (B) Zionomer Powder Liquid/Perfection; (C) Zionomer Paste Paste/Perfection; (D) TimeLine/Prisma-Fil; and (E) GC Dental Cement/Fuji II. Eighteen test specimens were prepared on the dentin surfaces of extracted human permanent first and second molars ground on 600 grit SiC paper with each system. The bonded cylinders were removed from the assembly apparatus 15 minutes after cure, stored in physiological saline at 37 degrees C for 24 hours and subjected to a shear load at 0.5 mm/min. Five cylindrical specimens were prepared for each system, the discs were suspended in 25 microL glass distilled water and the fluoride release (microgram F/mm2) determined at daily intervals for 15 days and then after 30 and 90 days. The data were analyzed by a one-way analysis of variance and Duncan's multiple range test. The following shear bond strengths (Mean +/- SD) were recorded (MPa): A: 8.86 +/- 1.49; B: 4.24 +/- 1.23; C: 4.41 +/- 1.39; D: 3.85 +/- 1.60; E: 4.81 +/- 1.21. With all the systems, the fluoride release dropped sharply during the first 7 days and then remained constant. The shear bond strength and the fluoride release from Vitrabond/Silux were significantly greater than that of the other systems.     

Marginal adaptation of commercial compomers in dentin cavity

The dentin cavity adaptation and setting characteristics of four commercial compomers were evaluated by measuring the wall-to-wall contraction gap width in the cylindrical dentin cavity and measuring the compressive strength for a maximum of 14 days after setting. The dentin cavity wall was pretreated by the dentin adhesives according to each manufacturer's instructions or the experimental contraction gap-free dentin bonding system. Complete marginal integrity was obtained in only one compomer and two resin composites which were combined with the experimental dentin bonding system. The compressive strength of two resin composites and two compomers ten minutes after setting was comparable to that after 14 days which indicated that the compomers exhibited setting characteristics as rapidly as the resin composite. It was concluded that a high efficacy dentin bonding system is required for commercial compomers to prevent gap formation during irradiation caused by the rapid setting shrinkage.