Acid-etched Teeth Research Articles

Effects of Acid Etching on the Microstructure and Stiffness of Human Teeth

Abstract The mechanical properties of acid-etched enamel and dentin are important for understanding tooth erosion and developing innovative dental restorative materials. In this study, the microstructure and mechanical properties of both enamel and dentin were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to quantify the impact of acid etching. SEM images demonstrated that enamel rods have a diameter of approximately 5 μm, while dentinal tubules have a diameter of around 2 μm. After acid etching, the intertubular and peritubular regions were exposed, with the peritubular regions showing a thickness of approximately 1 μm. AFM measurements showed that the stiffness of enamel at the bottom, middle, and top layers is 26.28±4.24 GPa, 32.03±8.68 GPa, and 23.94±3.53 GPa, respectively. For dentin, the stiffness is 16.28±2.76 GPa at the bottom layer and 17.59±5.33 GPa at the middle layer. AFM morphology and stiffness maps illustrated the microstructures of enamel rod and sheaths, as well as dentin tubules in both unetched and acid-etched tooth sections. The stiffness of the acid-etched enamel rod and peritubular dentin decreased by 7-fold and 3.6-fold, respectively, compared to the unetched enamel rod and peritubular dentin.

Does Er,Cr:YSGG laser increase shear bond strength of fluoridated and non-fluoridated teeth compared to acid etching?

ABSTRACT Purpose Fluoride varnish can decrease shear bond strength (SBS) of orthodontic brackets to enamel. Recently, laser has been used as a method of enamel preparation for bracket bonding. The present study aimed to compare SBS of orthodontic brackets on fluoridated and non-fluoridated teeth prepared by acid and laser etching. Materials and methods In this in-vitro study, 84 human extracted maxillary first premolars were divided into 4 groups: (1) fluoride varnish + acid-etching (AF); (2) fluoride varnish + laser-preparation (LF); (3) acid-etching (A); (4) laser-preparation (L). AF and LF groups were exposed to fluoride varnish and after 6 hours were washed. Samples in AF and A groups were prepared with 37% phosphoric acids and LF and L groups were etched by Er,Cr:YSGG laser. Afterwards, brackets were bonded. The samples were assessed by universal testing machine for SBS. Adhesive remnant index (ARI) was assessed under magnification in stereomicroscope. Statistical analysis was done by ANOVA analysis. P-value was considered to be 0.05. Results Maximum and minimum SBS were observed in A (SBS = 18.77) and AF (SBS = 2.78) groups, respectively. SBS of fluoridated laser-etched teeth (LF) was more than fluoridated acid-etched teeth (A). SBS was less than acceptable clinical bond strength in AF group. ARI was similar between groups (P-value < 0.097). Conclusion Fluoride varnish decreased SBS of brackets to enamel. Laser caused more SBS in fluoridated teeth than acid etched teeth. Thus, enamel preparation by laser may be considered a successful method in fluoridated teeth. Randomized controlled trials are recommended for this issue.

Comparison of Shear Bond Strength, Adhesive Remnant Index and Enamel Cracks in Bonding and Rebonding of Stainless Steel Brackets to Enamel Surface Conditioned with Er:YAG Laser Versus Conventional Acid Etching

Objectives : The aim of the present study was to compare shear bond strength (SBS), adhesive remnant index and enamel cracks in bonding and rebonding of brackets to enamel, conditioned with erbium-doped yttrium aluminium garnet (Er:YAG) laser and conventional acid-etching. Material s and Methods: Fifty-two bovine lower incisors were randomly divided into four groups consisting of group 1 (acid-conditioning in both bondings), group 2 (acid-conditioning in first and laser-conditioning in second bonding), group 3 (laser-conditioning in first- and acid-conditioning in second bonding), and group 4 (laser-conditioning in both bondings). After bracket placement, the samples were thermocycled and tested for SBS in both bonding procedures. Adhesive remnant index scores and enamel cracks were also determined. Tukey's test and one-way analysis of variance was used for statistical analysis (P<0.05). Results: Mean SBS in the first bonding was 23.59MPa in groups 1 and 2, and 6.9MPa in groups 3 and 4. (P<0.001). The acid-etched teeth had a significantly lower SBS in rebonding, regardless of the reconditioning method (P<0.001). The SBS of the teeth conditioned with Er:YAG laser in the first bonding did not show significant changes in rebonding, although mean SBS was higher compared to the first bonding (P=0.675). Bonding most often failed at the enamel-adhesive interface and enamel cracks were observed in a few teeth. Conclusion: The method of primary enamel preparation can affect SBS in rebonding. Based on our results, the mean SBS of Er:YAG-conditioned groups was clinically acceptable in bonding and rebonding, although it was lower compared to the acid-etched samples.

Modulated regeneration of acid-etched human tooth enamel by a functionalized dendrimer that is an analog of amelogenin

In the bioinspired repair process of tooth enamel, it is important to simultaneously mimic the organic-matrix-induced biomineralization and increase the binding strength at the remineralization interface. In this work, a fourth-generation polyamidoamine dendrimer (PAMAM) is modified by dimethyl phosphate to obtain phosphate-terminated dendrimer (PAMAM-PO3H2) since it has a similar dimensional scale and peripheral functionalities to that of amelogenin, which plays important role in the natural development process of enamel. Its phosphate group has stronger affinity for calcium ion than carboxyl group and can simultaneously provide strong hydroxyapatite (HA)-binding capability. The MTT assay demonstrates the low cytotoxicity of PAMAM-PO3H2. Adsorption tests indicate that PAMAM-PO3H2 can be tightly adsorbed on the human tooth enamel. Scanning electron microscopy and X-ray diffraction are used to analyze the remineralization process. After being incubated in artificial saliva for 3weeks, there is a newly generated HA layer of 11.23μm thickness on the acid-etched tooth enamel treated by PAMAM-PO3H2, while the thickness for the carboxyl-terminated one (PAMAM-COOH) is only 6.02μm. PAMAM-PO3H2 can regulate the remineralization process to form ordered new crystals oriented along the Z-axis and produce an enamel prism-like structure that is similar to that of natural tooth enamel. The animal experiment also demonstrates that PAMAM-PO3H2 can induce significant HA regeneration in the oral cavity of rats. Thus PAMAM-PO3H2 shows great potential as a biomimetic restorative material for human tooth enamel.

Orthodontic bonding to acid- or laser-etched prebleached enamel

ObjectiveBonding forces of brackets to enamel surfaces may be affected by the procedures used for bleaching and enamel etching. The aim of this study was to investigate the bonding strength of orthodontic brackets to laser-etched surfaces of bleached teeth.MethodsIn a nonbleached control group, acid etching (group A) or Er:YAG laser application (group B) was performed prior to bracket bonding (n = 13 in each group). Similar surface treatments were performed at 1 day (groups C and D; n = 13 in each subgroup) or at 3 weeks (groups E and F; n = 13 in each subgroup) after 38% hydrogen peroxide bleaching in another set of teeth. The specimens were debonded after thermocycling.ResultsLaser etching of bleached teeth resulted in clinically unacceptable low bonding strength. In the case of acid-etched teeth, waiting for 3 weeks before attachment of brackets to the bleached surfaces resulted in similar, but not identical, bond strength values as those obtained with nonbleached surfaces. However, in the laser-etched groups, the bonding strength after 3 weeks was the same as that for the nonbleached group.ConclusionsWhen teeth bleached with 38% hydrogen peroxide are meant to be bonded immediately, acid etching is preferable.

Determinants of enamel decalcification during simulated orthodontic treatment

To determine the relative effects that phosphoric acid etching, metal brackets, composite resin adhesives, and filled resin sealants have on enamel decalcification. One hundred and fifty teeth were randomly divided into six groups to test the effects of acid etching, brackets, and a composite resin adhesive. The right side of each tooth was sealed. The teeth were submitted to a simulated carious challenge by Streptococcus mutans in a nutritive media for 42 days. Scanning electron photomicrographs (SEMs) were used to qualitatively evaluate the tooth surfaces. DIAGNOdent laser fluorescence was used to quantify the decalcification changes that occurred. SEMs showed normal enamel on the control teeth, etching patterns on the acid-etched teeth, surface degradation on the teeth that had resin, and sealant tags on the sealed side. The untreated control group showed significantly less decalcification (P ≤ .05) than did all groups except the no etch+bracket group. The no etch+bracket group showed significantly less decalcification than did the etch+bracket, no etch+resin, and the etch+resin groups. Acid-etched teeth demonstrated significantly more decalcification (34%) than did those that were not etched. The teeth with resin showed significantly more decalcification (24%) than did those without resin. There was no significant difference between teeth that did and did not have brackets. The unsealed side of the teeth showed small amounts of--but significantly more--decalcification (5%) compared to the sealed side. Acid etching and composite resin adhesives increase enamel decalcification in vitro, while brackets do not. Filled resin sealants protect the teeth from decalcification.

Correlations Between AFM and SEM Imaging of Acid-Etched Tooth Enamel

Enamel bond strength is an important factor in restorative dentistry and crucially depends on the enamel roughness. To increase roughness, different etching procedures are employed and profilometric estimations, with probe profilometers, including atomic force microscopy (AFM), have been made. However, no correlation between roughness and bond strength has been found. To search for a possible error source leading to the underestimation of enamel roughness when utilizing probe profilometers, the authors compared scanning electron microscopy and AFM images of acid-etched tooth enamel. The results showed that AFM imaging cannot correctly depict the acid-etched enamel surface, because of the high steepness of the enamel crystallites and the generation of convolute images. This leads to a large underestimation of the profilometric parameters measured with AFM, or other profilometers, on acid-etched tooth enamel surfaces.

Effect of light-emitting diode on bond strength of orthodontic brackets.

The aim of this study was to evaluate the effect of light-emitting diode (LED) light curing on shear bond strength (SBS) of orthodontic brackets bonded to teeth. Light exposure of 40 seconds from a conventional halogen-based light-curing unit was used as a control. Eighty human premolars were divided into four groups of 20 each. Brackets were bonded to acid-etched teeth with Transbond XT light-cured adhesive. In the first group, the adhesive was light cured for 40 seconds with a conventional halogen unit (XL3000, 3M). In the other three groups, adhesive was cured with a commercial LED unit (Elipar FreeLight, 3M ESPE) for 10, 20, or 40 seconds. SBS of brackets was measured on a universal testing machine and recorded in megapascals. Adhesive remnant index (ARI) scores were determined after failure of brackets. Data were analyzed using analysis of variance and chi-square tests. No statistically significant differences were found among the SBS values of halogen-based light-cured (13.1 +/- 3.1 MPa) and 20- and 40-second LED-cured (13.9 +/- 4.8 MPa and 12.7 +/- 5.1 MPa) specimens (P > .05). However, 10 seconds of LED curing yielded significantly lower SBS (P < .05). No statistically significant differences were found between the ARI scores among groups. The results of this study are promising for the orthodontic application of LED-curing units, but further compatibility and physical characteristic studies of various orthodontic adhesives and clinical trials should be performed before validation.

Non-Contact Surface Morphology Analysis of CO&lt;SUB&gt;2&lt;/SUB&gt; Laser-Irradiated Teeth by Scanning Electron Microscope and Confocal Laser Scanning Microscope

A newly developed scanning electron microscope (SEM) installed with a 3D analyzer and a confocal laser scanning microscope (CLSM) were used to evaluate the images and surface profiles of enamel and dentin after CO 2 laserirradiation. The surface roughness (Ra) was measured and the results were correlated with a stylus profilometer. Raman analysis was done and the laser irradiation effect after acid etching was also examined. Human intact extracted teeth were vertically sectioned. The laser was applied perpendicularly to non-etched and 35% phosphoric acid-etched teeth. The enamel resulted in a crater-like surface. The material was removed in the places where hydroxyapatite crystallites ran parallel to the irradiated surface. Non-etched dentin showed little change after irradiation, with some cracks mostly in the peritubular dentin; whereas in acid-etched dentin there was evaporation of collagen and melting of hydroxyapatite. The SEM and CLSM showed similar profiles and different image contrast. Ra levels obtained by the SEM and CLSM were similar to that obtained with the stylus profilometer. Raman analysis showed that bands of organic collagen matrix on dentin were lost and broad peaks due to carbon were observed. Both the SEM and CLSM provided non-contact evaluation of structural changes of teeth by laser irradiation through surface analysis in selected microareas, which was not possible using the stylus profilometer. Dentin showed more structural changes on the acid-etched surface by irradiation than on the non-etched one.

Laser etching of enamel for direct bonding with an Er,Cr:YSGG hydrokinetic laser system

Irradiation of enamel with laser energy changes the physical and chemical characteristics of the enamel surface, and these alterations hold promise for the conditioning of enamel for bonding procedures. This laboratory study examined the influence of laser irradiation of enamel at 2 different power settings with an erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) hydrokinetic laser system (Millennium System, Biolase Technology, Inc; San Clemente, Calif) on the shear bond strength of orthodontic appliances and compared these with that of acid-etching. The prepared surfaces of 40 noncarious, intact, extracted premolars were exposed to laser energy: 20 teeth at 2-W setting (5.6 J/cm2) and 20 teeth at 1-W setting (2.7 J/cm2) of the commercial laser unit. Twenty teeth were etched with 37% orthophosphoric acid. Brackets were bonded with an orthodontic no-mix adhesive, and shear bond strength was determined with a universal testing machine. Data were analyzed with Kruskall-Wallis and Mann-Whitney U tests. Etched and restored surfaces of an acid-etched tooth and a 2-W laser-irradiated tooth were examined with scanning electron microscopy (SEM). Laser treatment under 2 W resulted in bond strengths of 7.11 ± 4.56 megapascals (MPa), which was not significantly different from that of acid etching (8.23 ± 2.30 MPa). Laser irradiation at 1 W resulted in bond strengths of 5.64 ± 3.19 MPa, which was significantly different from that of acid etching (P <.05). However, large SD and coefficient of variation values of both laser groups made reliability of this method as an enamel conditioner questionable. Scanning electron microscopy studies of the restored irradiated surfaces showed good surface characteristics, whereas the lased surface was still more irregular than the restored acid-etched sample. Although laser devices are effectively used in some other areas of dentistry, enamel conditioning with an Er,Cr:YSGG laser cannot be considered a successful alternative to the conventional methods of increasing bond strengths to enamel. (Am J Orthod Dentofacial Orthop 2002;122:649-56)

Sealant bond strengths of CO2 laser‐etched versus acid‐etched bovine enamel

Background and Objective The purpose of this study was to evaluate sealant shear bond strength on bovine enamel with standard acid etching compared with CO2 laser etching. Study Design/Materials and Methods Bovine enamel was prepared either by acid or laser etching and divided into four experimental groups, either acid or laser-etched teeth with or without a primer. A gelatin capsule was used to place the sealant on the prepared enamel surface and the bond tested in shear. Also surface roughness was evaluated by using a surface analyzer and an atomic force microscope. Results Shear bond strength results were the following: acid etch = 8.8 ± 3.8 MPa, acid etch with primer = 10.3 ± 5.5 MPa, laser etch = 4.0 ± 1.1 MPa, and laser etch with primer = 6.2 ± 2.3 MPa. Analysis of variance statistical analysis found no significant difference in bond strength between the acid-etched groups. However, the laser-etched groups had significantly lower bond strengths from the acid-etched teeth. In addition, a significant difference was observed between the laser-etched groups, where the use of the primer helped to increase the bond strength of the sealants. The surface roughness was significantly greater on the laser-etched teeth at the μm level (by using a surface analyzer) from the acid-etched and the control specimens. No difference in roughness (by using an atomic force microscope) was observed at the nanometer level between the laser and acid-etched teeth. Conclusion For these particular settings, the laser-etched teeth resulted in lower bond strengths to enamel and the use of a primer increased the bond strength for laser-etched teeth only. Lasers Surg. Med. 27:111–118, 2000. © 2000 Wiley-Liss, Inc.

Porcelain veneers bonded to tooth structure: an ultra-morphological FE-SEM examination of the adhesive interface

Objectives: The porcelain veneer technique bonds a thin porcelain shell to a minimally prepared tooth surface (enamel and/or dentin) with a luting composite in combination with an adhesive system. When complete, two adhesive interfaces are formed—resin to etched porcelain and resin to tooth structure. The purpose of this laboratory investigation is to analyze the ultra-structure of these two adhesive interfaces in order to find an explanation for some clinical phenomena and/or shortcomings of bonded porcelain veneers. Methods: The surfaces of four porcelain disks were treated successively by sandblasting, etching with hydrofluoric acid, ultrasonic cleaning, and silanizing. The effect of each step on the surface structure of the porcelain was evaluated by field-emission scanning electron microscopy (FE-SEM). In addition, the effect of acid etching the tooth surface of veneer preparations on seven extracted upper anterior teeth was similarly determined. Finally, pre-treated porcelain veneers were luted to veneer preparations on 12 extracted upper anterior teeth by means of a contemporary total-etch adhesive system and a photo-polymerizable luting composite. The tooth/luting composite and the luting composite/porcelain interface of the veneer complex were then evaluated ultra-morphologically by FE-SEM after the specimens had been etched with an argon-ion beam to enhance the surface relief. Results: FE-SEM imaging of the tooth/luting composite/porcelain interface showed strong micro-mechanical interlocking of the luting composite in the micro-retentive pits both of the acid-etched tooth surface and in the etch pits of the acid-etched porcelain surface. From this ultra-morphological perspective, the etched porcelain surface is more retentive than the etched tooth surface. At the tooth surface, cervical aprismatic enamel and exposed dentin showed the least resin-receptive surface texture. However, in these areas, no separation of the interface was observed when a multi-step total-etch adhesive system was used. Significance: The strong interlocking of the luting composite into the retentive etch pits of both the porcelain and tooth substrates contributes to strong adhesion of porcelain veneers with good retention. This study suggests that a modern multi-step total-etch adhesive system can produce adhesion even to the less retentive cervical enamel and exposed dentin. Further clinical research is necessary to evaluate the long-term retention of porcelain veneers and to correlate these in vitro observations with clinical performance.

COMPARING THE TENSILE STRENGTH OF BRACKETS ADHERED TO LASER-ETCHED ENAMEL VS. ACID-ETCHED ENAMEL

This study compared the tensile bond strength of brackets adhered to laser-etched enamel with that of brackets adhered to acid-etched enamel. Forty extracted, intact bovine teeth were treated with either 37 percent phosphoric acid for 15 seconds or neodymium:yttrium-aluminumgarnet laser on black-ink-coated enamel. After thermocycling, tensile stress was applied to the bonded specimens at a 0.1 millimeter/minute orosshead speed. A t-test comparison of means showed a significant difference between the laser-etched and acid-etched teeth, with the acid-etched teeth demonstrating significantly more tensile bond strength at a 95 percent level of significance.

A modified direct technique versus conventional direct placement of brackets: In vitro bond strength comparison

Bond strength and failure location were evaluated in vitro for two methods of direct bracket bonding. Sixty human premolars were divided into two groups of 30 each. In group I the brackets were bonded with a two-paste adhesive by using the conventional direct method. In group II brackets were bonded with a newly developed modified direct technique. During the modified direct technique, unfilled resin catalyst liquid was applied to a bracket, which had a coating of hardened composite cured against a dental anatomic matrix (tooth). After the acid-etched tooth was coated with unfilled resin base liquid, the bracket was placed. Mixed unfilled resin liquid (sealant) was then placed at the periphery of the bracket/tooth interface. Thus the major modification of the direct technique would entail fabrication by the manufacturer of a bracket with prehardened bis-GMA composite resin on its backing. Bond strengths were 155.2 (SD = 35.7) and 140.6 (SD = 30.1) kg/cm2 for conventional and modified techniques, respectively. With the conventional method, failure occurred mainly at the tooth/composite interface. Failure seen with the modified technique was mixed, but the major mode was composite/bracket. Therefore this modified bonding method promises similar bond strengths and some advantages over the conventional method including, elimination of composite flash from around the brackets, ample working time, consistent adhesive thickness, and reduction of porosity.

Recovery of Fluoride Orally on the Acid-etched Tooth Surface

Recovery of Fluoride Orally on the Acid-etched Tooth Surface

Tooth-colored inlays and onlays

Today's dental patient concerned about attractive restorations is looking for a dentist who incorporates the newest and best techniques into practice. This article discusses a newer concept that pleases both the patient and dentist: restorations that are bonded into acid-etched tooth preparations with composite resin cement--tooth-colored inlays and onlays. Basic questions asked by practitioners about these esthetic restorations are addressed; characteristics, performance expectations, comparisons with cast gold inlays and onlays, and comparisons with amalgam are presented, in addition to other relevant information for today's dental practitioner.

Microleakage around preventive composite fillings in occlusal fissures

The purpose of this study was to evaluated the microleakage around preventive composite fillings used in occlusal fissures with incipient caries, and to assess the influence of the consistency of the composite resin upon the leakage. The fissure enamel of 30 extracted maxillary premolars were partially removed using a small round bur (Ash No. 1/2). Dentin was not exposed. The cavities were etched with phosphoric acid and filled with undiluted composite (Adaptic) or composite diluted with different amounts of liquid resin (Adaptic Bonding Agent). Five teeth were not etched before filling, and served as a control group. The teeth were cycled thermally between two dye solutions and the marginal penetration of dye was evaluated by examining sections of the crowns in a dissection microscope. Marginal leakage occurred in all the control teeth and in none of the acid-etched teeth. It may be concluded that the preventive composite filling therapy provides good sealing of pits and fissures with incipient caries, and that the consistency of the composite used is not of primary importance.

Adhesive taglike extensions into acid-etched tooth enamel.

Adhesive tag like extensions into acid-etched tooth enamel can be directly observed in great detail by means of a modified scanning electron microscope technique. No taglike extensions of the adhesive were observed in tooth enamel that was not acid-etched before bonding of the adhesive.