Penetration of restorative resins into acid-etched human enamel

Effect of Extra Hydrophobic Resin Layer on Bonding of Universal Adhesive Systems to Enamel

OBJECTIVE

The objective of this study was to compare the effect of solvent in universal adhesives (UA) and the application of an extra layer of hydrophobic bonding resin on enamel shear bond strengths (SBS).

METHODS AND MATERIALS

Crowns of 224 bovine mandibular incisors were embedded in acrylic resin, wet-polished up to 600-grit silicon carbide paper and assigned to 3 UAs with different solvents (n=32): ethanol-based UA (ADU, AdheSE Universal, Ivoclar Vivadent); isopropanol-based UA (PBU, Prime&Bond Universal, Dentsply Sirona); and acetone-based UA (OPT, OptiBond Universal, Kerr Co). The same UAs were also applied with an extra layer of a hydrophobic bonding resin (HLB, Heliobond, Ivoclar Vivadent): ADU + HLB; PBU + HLB; and OPT + HLB. HLB alone was used as control. Enamel was etched with 37.5% H3PO4 (Kerr Gel Etchant, Kerr Co) for 15 seconds, rinsed with water, and air dried. UAs were applied according to the respective manufacturer's instructions. After adhesive application, composite cylinders (Filtek Z250, 3M Oral Care) were built up and light-cured (40 seconds/increment, 40 J/cm2) keeping the light tip in contact with the mold. Specimens were stored in water for 24 hours (24H) or for 6 months (6M). A knife-edged metallic rod (Ø=2.8-mm semicircular notch) loaded the composite cylinders until fracture. Mode of failure was analyzed with optical microscopy (40×). Statistics included twoway analysis of variance (ANOVA; adhesive strategy and water storage) and Tukey honestly significant difference (HSD) post hoc test (α=95%).

RESULTS

Mean enamel SBS ranged from 3.6 (±2.2) MPa (HLB/6M) to 24.7 (±7.1) MPa (ADU + HLB/6M). ANOVA revealed significant differences for adhesive strategy (p≤0.001) but no significant differences for water storage (p>0.05). All UAs resulted in similar mean enamel SBS with or without an extra layer of HLB at 24H. After 6M, only ADU resulted in higher enamel SBS when an extra layer of HLB was applied. All UAs resulted in higher mean enamel SBS than HLB (control). Most failures were adhesive exception for PBU/HLB/6M, which had mostly mixed failures.

CONCLUSIONS

UAs resulted in statistically higher enamel SBS than the nonsolvated hydrophobic bonding resin (control), regardless of the solvent in their composition. Application of an extra layer of hydrophobic bonding resin over UAs did not improve mean enamel SBS for isopropanol- and acetone-based UAs but did improve mean enamel SBS for the ethanol-based UA after 6M. Resin composite bonding to enamel using a hydrophobic bonding resin alone is not recommended.

On the method of revealing enamel structure by acid etching. Aspects of optimization and interpretation

The study aimed at finding an optimal combination of acid concentration and etching time when nitric acid is used as etchant for the study of the finer details of human dental enamel structure. Four hundred 2-3-mm-thick segments of facio-lingually sectioned human third molar crowns were assigned to 20 groups with 20 specimens in each group, each group differing with respect to acid concentration (0.1, 1, 2.5, and 5%) and etching time (15, 30, 45, 90, and 180 s). After etching and preparation, specimens were observed in the scanning electron microscope (SEM). Surface roughness/topography increased with increasing acid concentration and increasing etching time, but not in a linear fashion; generally, prisms tended to go from flat-surfaced to cone-shaped and prism sheaths from fissure-like to wedge-shaped. Intragroup variations and intergroup similarities were considerable. The two major enamel factors determining the etch effect are crystal orientation and prism sheath properties. Other factors, such as distribution of porosities and crystal quality, also contribute probably. Slight to moderate topography is best for observing the finer enamel structure, for example, etching with concentrations in the range 0.1-1% and with etching times in the range 15-90 s, the stronger the acid, the shorter the time. The depth effect of nitric acid is judged to be relatively small. Considerable variations in expression of prism cross-striations were observed. SEM observations of acid-etched enamel in carefully selected planes are a powerful method for the study of enamel structure, bearing in mind the artifactual aspects of the observed surface.

Influence of erbium, chromium-doped: Yttrium scandium-gallium-garnet laser etching and traditional etching systems on depth of resin penetration in enamel: A confocal laser scanning electron microscope study

OBJECTIVE

This study was performed to assess the resin tag length penetration in enamel surface after bonding of brackets to identify which system was most efficient.

METHODOLOGY

Our study was based on a more robust confocal microscopy for visualizing the resin tags in enamel. Totally, 100 extracted human first and second premolars have been selected for this study and were randomly divided into ten groups of 10 teeth each. In Group 1, the buccal enamel surface was etched with 37% phosphoric acid (3M ESPE), Group 2 with 37% phosphoric (Ultradent). In Groups 5, 6, and 7, erbium, chromium-doped: Yttrium scandium-gallium-garnet (Er, Cr: YSGG) laser (Biolase) was used for etching the using following specifications: Group 5 (1.5 W/20 Hz, 15 s), Group 6 (2 W/10 Hz, 15 s), and Group 7 (2 W/20 Hz, 15 s). In Groups 8, 9, and 10, Er, Cr: YSGG laser (Biolase) using same specifications and additional to this step, conventional etching on the buccal enamel surface was etched with 37% (3M ESPE) after laser etching. In Groups 1, 5, 6, 7, 8, 9, and 10 3M Unitek Transbond XT primer was mixed with Rhodamine B dye (Sigma-Aldrich, Germany) to etched surface and then cured for 20 s. In Group 2, Ultradents bonding agent was mixed with Rhodamine B. In Group 3, 3M Unitek Transbond PLUS, Monrovia, USA, which was mixed with Rhodamine B dye (Sigma-Aldrich, Germany). Group 4, with self-etching primer (Ultradent-Peak SE, USA) was mixed with Rhodamine B dye (Sigma-Aldrich, Germany). Later (3M Unitek, Transbond XT, Monrovia USA) [Figure 1] was used to bond the modified Begg brackets (T. P. Orthodontics) in Groups 1, 3, 5, 6, 7, 8, 9, and 10. In Groups 2, 4 Ultradent-Peak LC Bond was used to bond the modified brackets. After curing brackets were debonded, and enamel depth penetration was assessed using confocal laser scanning microscope.

RESULTS

Group J had a mean maximum depth of penetration of 100.876 μm, and Group D was the least having a maximum value of 44.254 μm.

CONCLUSIONS

Laser alone groups had comparable depths of penetration to that of self-etching groups but much lower than conventional acid etched groups.

Evaluation of penetration depth of a commercially available resin infiltrate into artificially created enamel lesions: An in vitro study

Background:

Early enamel lesions have a potential to re-mineralize and prevent caries progress.

Aim:

The aim of the following study is to determine the depth of penetration of low viscosity resin into artificially created enamel lesions.

Materials and Methods:

A sample of 20 sound premolars, indicated for orthodontic extraction, formed the study group. The teeth were coated with a nail varnish, leaving a window of 4 mm × 4 mm, on buccal surfaces of sound, intact enamel. Each tooth was subsequently immersed in demineralizing solution for 4 days to produce artificial enamel lesions. The demineralized area was then infiltrated with low viscosity resin (Icon Infiltrant, DMG, Hamburg, Germany) as per the manufacturer's instructions. All the restored teeth were then immersed in methylene blue dye for 24 h at 37°C. Teeth were then sectioned longitudinally through the lesion into two halves. The sections were observed under stereomicroscope at ×80 magnification and depth of penetration of the material was measured quantitatively using Motic software.

Results:

The maximum depth of penetration of the resin material was 6.06 ± 3.31 μm.

Conclusions:

Resin infiltration technique appears to be effective in sealing enamel lesions and has great potential for arresting white spot lesions.

Early versus delayed rebonding of orthodontic brackets

OBJECTIVES

There are controversial reports regarding the effect of repeated bonding on shear bond strength (SBS) of orthodontic attachments. The aim of this study was to evaluate the SBS of brackets following early and delayed rebonding, and after employing different methods of composite removal.

MATERIALS AND METHODS

Sixty eight premolars were randomly assigned into 4 groups. After initial debonding and recording the SBS, the adhesive remnants in the first group were removed by a round bur, in the second group by a green rubber wheel, and in the third and fourth groups by 12-fluted tungsten carbide burs, all of them connecting to a low speed handpiece. In the fourth group following adhesive removal, the teeth were kept in a simulated oral environment for one month. Then, rebonding was performed and the second SBS was measured. Two representative samples from each group were examined under a scanning electron microscope following adhesive removal. The data were analyzed by ANOVA, Paired sample t-test and Chi-Square test.

RESULTS

In the first group, the rebonding strength was decreased significantly (p<0.05), while composite removal with a tungsten carbide bur or a green rubber wheel did not affect SBS significantly (p>0.05). Late rebonding of brackets had no effect on the SBS (p>0.05).

CONCLUSIONS

Postponing rebonding to the next visit does not improve the SBS significantly. It is recommended to use a tungsten carbide bur or a green rubber wheel, and not a round bur for removing adhesive remnants following debonding of orthodontic brackets.

Depth of resin penetration into enamel with 3 types of enamel conditioning methods: a confocal microscopic study

INTRODUCTION

The clinical efficiency of a bonding material relies on its bond strength and debonding characteristics; the depth of resin penetration into enamel affects both of these factors. The depth of resin penetration has been previously studied by researchers using laborious, indirect methods, including the scanning electron microscope and the optical microscope.

METHODS

We used a more direct method, confocal microscopy, to visualize the resin tags in enamel. Thirty maxillary first premolars were selected and divided into 3 groups. In group A, the buccal enamel surfaces were conditioned with 37% phosphoric acid; in group B, a self-etching primer was used; and group C was treated with air abrasion. Transbond XT adhesive (3M Unitek, Monrovia, Calif) was used to bond a modified bracket. Transbond XT primer (3M Unitek) mixed with rhodamine B fluorescent dye (Chennai Chemicals, Chennai, India) was applied in groups A and C. In group B, rhodamine was mixed with self-etching primer. After curing, the brackets were debonded, and the teeth were visualized under the fluorescent channel of the confocal microscope.

RESULTS

Maximal resin penetration of 53.9 μm was observed in group A, followed by group B at 40.5 μm and group C at 39.9 μm.

CONCLUSIONS

Confocal microscope evaluation showed that enamel conditioning with 37% phosphoric acid produced greater depths of resin penetration than did self-etching primer or air abrasion.

The use of flowable composites as filled adhesives

OBJECTIVE

The effect of filled adhesives on bonding resin composites to dentin has not been fully understood. Due to their filler content, filled adhesives may act as stress breakers. The aim of this in vitro study was to evaluate the use of flowable composites of different viscosities on bonding to enamel and dentin without the use of an intermediate bonding resin.

MATERIALS AND METHODS

Enamel and dentin bond strengths of OptiBond FL, Syntac Classic, and EBS Multi combined either with their proprietary bonding agent or a flowable resin composite (Ultraseal XT Plus or Revolution) were measured. The tests were carried out with a microtensile device at a crosshead speed of 1mm/min after 24h of storage at 37 degrees C in water. Mean bond strengths were analyzed using the Wilcoxon test and multiple comparisons according to the Mann-Whitney U-test. The micro-morphology of corresponding resin-dentin interfaces of the same teeth were analyzed using SEM and TEM.

RESULTS

The control groups with adhesive systems used as per manufacturers' protocol showed bond strengths of 38.9-41.1 MPa to enamel and 28.8-33.4 MPa to dentin. With respect to bond strength to etched enamel, only Ultraseal XT Plus as bonding resin reached the level of the control groups. When used as bonding agents on dentin, both flowable composites produced lower microtensile bond strengths to etched and primed dentin than did the control groups. Micro-morphological analysis using SEM and TEM resulted in hybrid layer formation for both control and experimental groups. However, many areas of the resin-dentin interface showed insufficient penetration of the flowable composites at the top of the hybrid layer as well as numerous tubules obstructed by filler particles.

CONCLUSIONS

The flowable composites tested in this study should not be used to replace bonding agents. Flowable composites of thinner viscosity, such as Ultraseal XT Plus, may bond to enamel adequately without the requirement of an intermediate bonding resin.

Effect of varying etching times on the bond strength of ceramic brackets

Damage to the enamel surface when debonding orthodontic ceramic brackets has been a clinical concern. Ideally, bond failure at the bracket-adhesive interface should occur without damaging the enamel surface. The purpose of this study was to determine the shear bond strength and debonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time interval of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid. Ceramic orthodontic brackets were bonded to each etched tooth by using the same orthodontic bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The results of the analysis of variance indicated that there were significant differences in bond strengths between the various etching times (p=0.0001). The Duncan multiple range test revealed that the 5-second and no etch group exhibited significantly lower bond strengths. The results of the Chi square test evaluating the residual adhesives on the enamel surface also revealed significant differences (p=0.0001). However, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p=0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect either bond strength or the site of bond failure.

Shear bond strength of a resin composite to enamel etched with maleic or phosphoric acid

The purpose of this study was to evaluate the effect of 10 per cent maleic and 37 per cent phosphoric acid on the shear bond strength of Z100 composite resin with Scotchbond Multi-Purpose adhesive to primary and permanent tooth enamel. Four groups of 20 teeth each were established: 1, permanent teeth, 10 per cent maleic acid etched for 15 seconds; 2, permanent teeth, 10 per cent maleic acid etched for 30 seconds; 3, permanent teeth, 37 per cent phosphoric acid etched for 15 seconds; 4, primary teeth, 10 per cent maleic acid etched for 15 seconds. Five teeth from each group were randomly assigned for SEM examination of the etched enamel surface. Scotchbond Multi-Purpose primer and adhesive were applied to the etched enamel surface of the remaining 15 teeth and cured following the manufacturer's instructions. Z100 composite resin was placed in a nylon cylinder and cured for two 40 second intervals. Following thermocycling, the specimens were sheared on an universal testing machine and debonded areas were examined visually with a stereo microscope and with SEM. The mean shear bond strengths in MPa were: 1, 17.00; 2, 14.58; 3, 14.66; 4, 11.18. ANOVA and Student-Newman-Keuls analyses revealed no statistically significant difference among the groups. SEM examination showed the majority of specimens fractured at the adhesive-resin interface.

Evaluation of the sealant in orthodontic bonding

In the two-paste self-polymerizing orthodontic bonding systems, sealants are routinely used to protect enamel, to decrease marginal leakage, to enhance bond strength, and to increase interfacial permeability for the etched enamel, the bonding resin, and the bracket base. However, some studies have questioned the need for the sealant. Bond strengths with and without sealants in orthodontic bonding were compared in this study. The results indicated no statistical differences between the tensile bond strengths of the two evaluated groups. The distributions of debonding interface between groups were similar and also had no statistical difference. This study therefore indicated that use of the sealant in the two-paste orthodontic bonding system for enhanced strength is unnecessary. However, the use of a sealant may offer extra protection to the enamel during debonding procedures.

Evaluation of insertion methods for composite resin restorations

Laboratory studies were carried out to determine if there was one superior method to achieve the most intimate contact of a composite resin with its cavity walls. Three dentists restored 48 teeth by eight different techniques with two different composite resins. Photomicrographs showed very little difference in the size of the gap between tooth and composite resin regardless of which method was employed. The gap was smallest in the cavosurface area and greatest at the axio-occlusal line angle.

Effect of composite resin bond agent on microleakage and bond strength

A study was conducted to evaluate the efficacy of the bonding agents supplied with three composite resins in improving the sealing ability of the materials to tooth structure and the bond of the resins to enamel. When the enamel was not etched prior to insertion of the resin, the use of the bonding agents did not improve marginal seal. Little or no marginal leakage was detected when the restorations were placed by means of the acid etch technique, either with or without use of the respective bonding agents. A slight improvement in the bond of the resins to unetched enamel was secured by use of the bonding agents; however, this advantage was lost when the specimens were thermal cycled. Acid etching of the enamel significantly improved the bond of the strength of all three resins, both when the specimens were thermal-cycled and when stored at a constant temperature. Only one of the commercial bond agents enhanced the bond of its respective composite resin to etched enamel subjected to cycling.

A 5-year evaluation of semipermanent composite resin crowns

The use of composite resin crowns in the restoration of traumatized and hypoplastic permanent incisors has proved to be of great clinical and aesthetic value for the pedodontic practice. Due to the composite resin materials and the acid etch technique, an easy method of making and retaining the restorations is at hand. The present study deals with long-term observations of composite resin crowns in restoring Ellis Class II and Class III coronal fractures of traumatized permanent incisors. In all, 253 composite resin crowns were controlled every year for a minimum of 5 years. In no case was an intermediate resin layer applied on etched enamel before the restoration material was placed. Surface, marginal and "body" discoloration, marginal leakage, marginal caries, abrasion, and fractures were controlled. The study demonstrated that discoloration of the surface of the restorations, and a discoloration of the restorative material not restricted to its surface ("body" discoloration) were the most frequent causes for considering the crowns as semipermanent restorations. The other factors seemed to be of minor clinical significance.

Hardness testing of some fissure-sealing materials

The mechanical properties of fissure-sealing materials are of significant importance for their durability, i.e. their wear resistance. One of the methods of evaluating a material's resistance to attrition is to apply a hardness test. In the present investigation, the surface hardness of some fissure-sealing materials was tested. Sealants made from diluted composite materials and with inclusion of inorganic filler particles appeared to have a considerable higher surface hardness than the other sealing materials tested.

Penetration of restorative resins into acid etched enamel. II. Dissolution of entrapped air in restorative resin monomers

Viscosity, surface tension and contact angle are factors that influence the penetration of restorative resins into acid etched enamel. Furthermore, as the resin is drawn by the capillary forces into the pores of the etched enamel the pressure of the entrapped air will increase. The increased pressure has the effect that air will dissolve in a resin that is saturated with air at one atmosphere. The purpose of the present work was 1) to investigate the rate of dissolution of included air bubbles at increased pressure, 2) to use the results to calculate the depth of penetration by means of a cylindrical model of the capillary pores, and 3) to check the results of the calculations by measurements of the tag lengths of restorative resins placed on acid etched enamel. The rate of dissolution was measured in monomers of varying viscosity in a glass syringe by means of a stereo microscope. The calculations showed that the depth of penetration decreases only slightly with viscosity. Thin sections of restorative resins placed on acid etched enamel were prepared whereafter the enamel was dissolved in hydrochloric acid. Tag lengths of 50 micron or more were observed with composite as well as non-composite resins.