Bonding to enamel using alternative Enamel Conditioner/etchants

Effect of experimental dentin etchants on dentin bond strength, metalloproteinase inhibition, and antibiofilm activity

OBJECTIVE

this study evaluated dentin microtensile bond strength (µTBS) and failure modes (at 24 h and one year), bonding interface regarding hybridization, surface morphology regarding demineralization, in situ metalloproteinase (MMP) activity, and antibacterial effect of three dentin etchants compared to 35% phosphoric acid (PA).

MATERIALS AND METHODS

The Adper Single Bond 2 adhesive (3 M Oral Care) was applied on moist dentin etched with PA (control) or on air-dried dentin etched with 3% aluminum nitrate + 2% oxalic acid (AN), 6.8% ferric oxalate + 10% citric acid (FO), or 10% citric acid (CA). The µTBS test used 40 human teeth (n = 10). Failure modes and surface morphology were analyzed by scanning electron microscopy (n = 3), while bonding interface morphology and MMP activity were evaluated by laser scanning confocal microscopy (n = 3). Antibacterial activity was evaluated against S. Mutans biofilm by means of viable cells count (CFU/mL).

RESULTS

PA presented the highest bond strengths regardless of aging time. PA, AN, and CA showed stable bond strengths after one year of storage. Adhesive and mixed failures were predominant in all groups. Thin hybrid layers with short resin tags were observed for the experimental etchants. The AN-based etchant was able to inhibit MMP activity. All tested etchants presented antibacterial activity against S. Mutans biofilm.

SIGNIFICANCE

This study suggests different dentin etchants capable of inhibiting MMP activity while also acting as cavity disinfectants.

Treatment of saliva contamination of resin core foundation before adhesive luting

This study aimed to evaluate the influence of surface pretreatment on the shear bond strength of resin luting cement to saliva-contaminated resin core foundation. The surface free energy (γS) of the adherent surfaces was examined. The two-way analysis of variance revealed that the surface pretreatment and storage conditions had a significant effect on the strength of the bond to resin core foundation. The γS values of the saliva-contaminated group were significantly lower than those of the other groups, and they tended to improve after surface pretreatment. The tendency of improvement in γS values differed depending on the type of pretreatment agents. Surface treatment with solutions containing functional monomers is effective in removing saliva contaminants from the resin core foundation surfaces and in creating an effective bonding surface for the resin luting cement.

Noninvasive diagnostic method using optical coherence tomography detected a vulnerable dentin enamel junction created by phosphoric acid etching

To investigate the influence of phosphoric acid etching on the dentin enamel junction (DEJ) using optical coherence tomography (OCT). Human teeth were assigned to four groups: 1. control, no additional treatment (CT); 2. The primer of "SE Bond2" was applied (SE), 3. "Enamel Conditioner" was applied (EC), 4. "K-etchant syringe" was applied (KE). After treatment, the DEJ was observed using a laser microscope (CLSM), OCT, and scanning electron microscopy (SEM). Additionally, an ultimate tensile strength (UTS) test at the DEJ was performed. No cracks were observed by CLSM. In contrast, cracks were observed all samples by SEM. Additionally, OCT revealed a white line along the DEJ in all KE specimens and some EC specimens. The UTS test showed a significant difference between CT and KE. This study found that phosphoric acid etching may cause excessive demineralization and weaken the DEJ. This fragility was observed using a non-invasive diagnostic method using OCT.

The Influence of a Novel, Crenelated Design of CAD-CAM Ceramic Veneers on the Debonding Strength

(1) Background: Aesthetic dentistry has become one of the most dynamic fields in modern dental medicine. Ceramic veneers represent the most appropriate prosthetic restorations for smile enhancement, due to their minimal invasiveness and highly natural appearance. For long-term clinical success, accurate design of both tooth preparation and ceramic veneers is of paramount importance. The aims of this in vitro study were to assess the stress in anterior teeth restored with Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) ceramic veneers and compare the resistance to detachment and the fracture of ceramic veneers prepared using two different designs. (2) Methods: Sixteen lithium disilicate ceramic veneers were designed and milled using the CAD-CAM technology and divided into two groups according to the preparations (n = 8): Group 1, conventional (CO), with linear marginal contour and Group 2, crenelated (CR), the latter with our novel (patented) sinusoidal marginal design. All samples were bonded to anterior natural teeth. The mechanical resistance to detachment and fracture was investigated by applying bending forces on the incisal margin of the veneers in order to determine which type of preparation leads to better adhesion. An analytic method was employed, as well, and the results of the two approaches were compared. (3) Results: The mean values of the maximum force recorded at the veneer detachment were 78.82 ± 16.55 N for the CO group and 90.20 ± 29.81 N for the CR group. The relative increase, equal to 14.43%, demonstrated that the novel CR tooth preparation provided higher adhesive joints. In order to determine the stress distribution within the adhesive layer, a finite element analysis (FEA) was performed. The statistical t-test showed that the mean value of the maximum normal stresses is higher for the CR-type preparations. (4) Conclusions: The patented CR veneers represent a practical solution to augment the adhesion and mechanical properties of ceramic veneers. The obtained results demonstrated that CR adhesive joints triggered higher mechanical and adhesive forces, which subsequently led to a higher resistance to detachment and fracture.

Ceramic Bonding Interface under Shear-Compression Stress: Ultra-High-Speed Imaging Contribution

The aim of this study is to visualize and characterize by ultra-high-speed imaging (UHSI) the failure phenomena at the resin-ceramic bonding interface of lithium disilicate (LiSi2) samples bonded with gold-standard protocol (Monobond Plus [MB]) and the nontoxic one (Monobond Etch & Prime [MEP]) subjected to mechanical loading. Unprecedented frame rate, image resolution, and recording time were reached by using the most advanced UHSI camera. The finite element analysis (FEA) of the proposed mechanical test confirmed that the specific design of our samples enables a combined shear and compression stress state, prone to test the bonding interface while being close to physiological stresses. Ten LiSi2 samples were pretreated by gold standard (MB, n = 5) and self-etching primer (MEP, n = 5). Axial compression loading gradually increased until catastrophic failure was performed. As shown by the FEA, the angle between the bonding interface and load direction leads to shear-compression stresses at the resin-ceramic bonding interface. Failure was recorded by UHSI at 300,000 fps. All recorded images were analyzed to segregate events and isolate the origin of fracture. For the first time, thanks to the image recording setup, it was observed that debonding is the first event before breakage, highlighting that sample fracture occurs by interfacial rupture followed by slippage and cohesive failure of materials. Failure mode could be described as mixed. MEP and MB showed similar results and behavior.

Progress in Dental Adhesive Materials

There have been significant advances in adhesive dentistry in recent decades, with efforts being made to improve the mechanical and bonding properties of resin-based dental adhesive materials. Various attempts have been made to achieve versatility, introducing functional monomers and silanes into the materials' composition to enable the chemical reaction with tooth structure and restorative materials and a multimode use. The novel adhesive materials also tend to be simpler in terms of clinical use, requiring reduced number of steps, making them less technique sensitive. However, these materials must also be reliable and have a long-lasting bond with different substrates. In order to fulfill these arduous tasks, different chemical constituents and different techniques are continuously being developed and introduced into dental adhesive materials. This critical review aims to discuss the concepts behind novel monomers, bioactive molecules, and alternative techniques recently implemented in adhesive dentistry. Incorporating monomers that are more resistant to hydrolytic degradation and functional monomers that enhance the micromechanical retention and improve chemical interactions between adhesive resin materials and various substrates improved the performance of adhesive materials. The current trend is to blend bioactive molecules into adhesive materials to enhance the mechanical properties and prevent endogenous enzymatic degradation of the dental substrate, thus ensuring the longevity of resin-dentin bonds. Moreover, alternative etching materials and techniques have been developed to address the drawbacks of phosphoric acid dentin etching. Altogether, we are witnessing a dynamic era in adhesive dentistry, with advancements aiming to bring us closer to simple and reliable bonding. However, simplification and novelty should not be achieved at the expense of material properties.

Influence of different tooth etchants on bur-cut and uncut enamel

This study aimed to evaluate the effect of pre-etching for two-step self-etch adhesive bonding to bur-cut and uncut enamel. Bur-cut and uncut enamel surfaces were assigned to surface treatments of no etchant (CT), Enamel Conditioner (EC; Shofu, Kyoto, Japan), or K-etchant syringe (KE; Kuraray Noritake Dental, Tokyo, Japan). The bonded samples were thermal cycled and evaluated by microshear bond strength (μSBS). The adhesive interface after acid-base challenge and the conditioned enamel surfaces were morphologically analyzed using scanning electron microscopy (SEM). For bur-cut enamel, EC and KE pre-etching significantly improved μSBS. For uncut enamel, KE showed higher μSBS than EC. SEM observation revealed that only KE removed the prismless layer of the uncut enamel surface. EC could improve enamel bonding and appears to be a substitute for phosphoric acid, especially for bur-cut enamel. However, uncut enamel could not be effectively conditioned by EC with a lower bond strength than KE.

The influence of finishing lines and margin location on enamel and dentin removal for indirect partial restorations: A micro-CT quantitative evaluation

OBJECTIVES

This in vitro research aimed to quantitatively evaluate the enamel and dentin tissue removal and the residual adhesion surface area (RAS) after different margin designs and locations for indirect partial restorations (IPR).

METHODS

A human molar was scanned using a Micro-CT and the STL file obtained was used to 3D-print 50 resin-tooth replicas. IPR standardized preparations were performed. The specimens were randomly assigned to 5 groups (n = 10), according to preparation and margin location to the dental equator (DE): 1) Rounded shoulder above the DE (SA); 2) Hollow chamfer above the DE (CA); 3) Butt joint above the DE (BJ); 4) Rounded shoulder below the DE (SB); 5) Chamfer below the DE (CB). Then, the tooth replicas were scanned and each STL file was aligned and superimposed to the original STL model file. Data of enamel and dentin volume removal and RAS were assessed and statistically analyzed (one-way ANOVA and Kruskal-Wallis tests for the two dental substrates respectively). Significance was set at p<0.05.

RESULTS

Differences in dental tissue reductions were related to the margin location. Above the equator, SA, CA, and BJ performed comparably (p>0.05). Below the equator, CB was significantly more conservative in enamel reduction than SB (p<0.05) and showed the highest enamel adhesive surface exposure among the tested preparations (p<0.05).

CONCLUSIONS

When the preparation margin is placed above DE, BJ determines a greater exposure of dentin, reducing the adhesive surface in enamel. Below DE, SB seems to be more aggressive in terms of tissue removal compared to CB.

CLINICAL SIGNIFICANCE

The results of this in vitro study suggest that in teeth requiring partial restoration with the margin below the dental equator, a chamfer preparation would be more conservative than a shoulder preparation. When above the equator, preparations with flat designs would expose more dentine providing a worse substrate for adhesion.

Dentin conditioned with a metal salt-based conditioner

OBJECTIVES

Universal adhesives (UAs) can optionally be applied in either an etch-and-rinse (E&R) or self-etch (SE) bonding mode. As the preferred bonding mode differs for enamel versus dentin, a universal conditioner for both enamel and dentin in replacement of the relatively aggressive phosphoric-acid etchant remains desirable. This study aimed to test if a metal salt-based etchant (ZrO(NO₃)₂) provides as durable bonding to dentin as a classic E&R or SE bonding mode METHODS: Before applying the UA Adhese Universal ('AdU'; Ivoclar Vivadent) to bur-cut dentin of 24 teeth (n = 8), dentin was conditioned with either (1) an experimental metal salt-based conditioner ('ZON'; Ivoclar Vivadent) or (2) 37% phosphoric acid (Total Etch gel, Ivoclar Vivadent), representing a classic 'E&R' mode; (3) a third experimental group involved AdU applied in SE mode. Bonding effectiveness was determined in terms of immediate ('1w') and aged ('50k' TC) micro-tensile bond strength (μTBS) to bur-cut dentin. Adhesive-conditioned dentin interfacial interactions were characterized by S/TEM.

RESULTS

Linear mixed-effects modeling revealed significantly higher immediate μTBS to dentin of ZON_AdU than E&R_AdU, while ZON_AdU performed not significantly different from SE_AdU. No significant differences were found between the three experimental groups after 50k TC (aged μTBS). S/TEM disclosed less exposure of dentinal collagen fibrils when AdU was bonded upon ZON etching than when applied in E&R mode. Moreover, ZON resulted in more hydroxyapatite (HAp) crystals remaining at the bottom of the hybrid layer, while dentinal tubule orifices remained nearly fully closed, by which hardly any resin tags were formed.

SIGNIFICANCE

The alternative metal salt-based conditioner revealed at dentin a more HAp-protected hybrid layer with less exposure of collagen fibrils, while a comparable bond strength was obtained to that with a phosphoric-acid E&R as well as with an SE (no conditioner) bonding mode. These findings confirm that the metal salt-based conditioner can be considered as a suitable alternative (enamel/)dentin conditioner to classic phosphoric acid employed in an E&R bonding mode.

Improved bond performances of self-etch adhesives to enamel through increased MDP-Ca salt formation via phosphoric acid pre-etching

OBJECTIVES

The chemical affinity between 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and hydroxyapatite (HAp) is an important factor in the enamel bonding provided by MDP-based self-etch (SE) adhesives, besides microinterlocking mechanisms. This study aimed to investigate how phosphoric acid pre-etching affects MDP-Ca salt formation in the application of MDP-based SE adhesives.

METHODS

Single Bond Universal (SBU), All Bond Universal (ABU), Clearfil Universal Bond Quick (CBQ), and a MDP-based all-in-one adhesive (EXP) were used in both SE and etch-and-rinse (ER) modes, along with Clearfil SE Bond and untreated enamel (UE) as controls. The MDP-Ca salts produced with or without etching were examined by nuclear magnetic resonance, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Zeta potential, contact angle, and scanning electron microscopy measurements were employed to elucidate the mechanism behind the changes in MDP/HAp chemical affinity upon pre-etching.

RESULTS

The percentage of MDP-Ca salt in EXP_ER (73.13%) was higher than that in EXP_SE (43.27%). Characteristic CH₂ (1130, 1441, 2853, and 2909 cm^-1), CC (1641 cm^-1), and CO (1718 cm^-1) bands were observed in the Raman spectra of EXP_ER. Pre-etching increased the negative zeta potential of the enamel surface compared to that of UE (P < 0.001). The contact angles of MDP-based adhesives applied to pre-etched enamel were significantly lower than those of the self-etched surface (P < 0.05).

SIGNIFICANCE

The increased MDP-Ca salt formation is a significant advantage of phosphoric acid pre-etching, improving the MDP/HAp chemical affinity in addition to increasing surface wettability.

Traditional Microscopic Techniques Employed in Dental Adhesion Research-Applications and Protocols of Specimen Preparation

Microscopy is a traditional method to perform ex vivo/in vitro dental research. Contemporary microscopic techniques offer the opportunity to observe dental tissues and materials up to nanoscale level. The aim of this paper was to perform a literature review on four microscopic methods, which are widely employed in dental studies concerning the evaluation of resin-dental adhesive interfaces-confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The literature search was performed using digital databases: PubMed, Web of Science and Scopus. On the basis of key words relevant to the topic and established eligibility criteria, finally 84 papers were included in the review. Presented microscopic techniques differ in their principle of operation and require specific protocols for specimen preparation. With regard to adhesion studies, microscopy assists in the description of several elements involved in adhesive bonding, as well as in the assessment of the condition of enamel surface and the most appropriate etching procedures. There are several factors determining the quality of the interaction between the substrates which could be recognized and a potential for further implementation of microscopic techniques in dental research could be recognized, especially when these techniques are used simultaneously or combined with spectroscopic methods. Through such microscopy techniques it is possible to provide clinically relevant conclusions and recommendations, which can be easily introduced for enamel-safe bonding and bonding protocols, as well as optimal pretreatments in dentine preparation.

Shear bond strength of orthodontic brackets bonded with resin coating material

The purpose of this study was to determine whether a system using a resin coating material (PRG Barrier Coat) with anticariogenic ability can effectively bond orthodontic brackets to human teeth. Resin-modified glass-ionomer cement system (Fuji Ortho LC, group 1) and resin composite cement systems (BeautyOrtho Bond) combined with a self-etching primer (group 2), with the resin coating material (group 3), and with the resin coating material after an organic acid etching agent (group 4) were used for bracket bonding. The mean shear bond strength (SBS) was significantly higher in group 1 than in groups 2, 3 and 4. Groups 2 and 4 exhibited a significantly higher mean SBS than group 3. The resin composite cement system combined with the resin coating material after the organic acid etching agent can serve as an alternative for orthodontic bracket bonding.

Update on Enamel Bonding Strategies

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.

Effects of Phosphoric Acid Pre-Etching on Chemisorption between Enamel and MDP-Containing Universal Adhesives: Chemical and Morphological Characterization, and Evaluation of Its Potential

This study aimed to provide evidence that phosphoric acid pre-etching is necessary for the chemisorption between enamel and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing universal adhesives. Three MDP-containing universal adhesives: Single Bond Universal (SBU), All Bond Universal (ABU), and Clearfil Universal Bond Quick (CBQ), as well as an experimental MDP-containing adhesive (EX) were investigated. Clearfil SE Bond (CSE) was a control and untreated enamel (UE) was another control. Self-etch (SE) and etch-and-rinse (ER) bonding modes were employed for universal adhesives. The enamel surfaces with different treatments were observed with a scanning electron microscope (SEM). The chemical bonds in the enamel reactants were determined using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR). The charge changes with phosphoric acid pre-etching or without were characterized by ζ-potential. FTIR confirmed the chemisorption between enamel and MDP-containing adhesives. XPS and ³¹P NMR studies detected improved chemical affinity to the phosphoric acid etching + MDP-containing universal adhesives applied with enamel. The ζ-potential of MDP-containing universal adhesives absorbed with enamel, with or without etching became more negative compared with that of UE (P < 0.05). Furthermore, single etching created a negative ζ-potential with a higher absolute value (P = 0.009). Phosphoric acid pre-etching can increase the negative charge on the enamel surface and facilitate the chemical reactions of MDP and hydroxyapatite (HAp) to produce more calcium salts, thus improving the chemisorption between enamel and MDP-containing universal adhesives.

Bonding to dentin using an experimental zirconium oxynitrate etchant

OBJECTIVE

To investigate, by means of microtensile bond strength test (μTBS), nanoleakage expression analysis (NL), gelatin zymography and in situ zymography, the effects of an experimental metal salt-based zirconium oxynitrate etchant [ZrO(NO₃)₂,] - ZON with two simplified adhesives on long-term bond strength and endogenous enzymatic activities.

METHODS

Middle/deep coronal dentin surfaces (N = 32) were conditioned either with a traditional 37 % H₃PO₄ etchant (TE) or with ZON. Further, a single-component etch-and-rinse adhesive (EF) or a universal adhesive (AU) were applied and μTBS and NL tests were performed. Additional freshly extracted teeth were processed for gelatin zymography and in situ zymography evaluation. The tests were performed at baseline and (T0) and after 1-year-aging (T12). Bond strength and in situ zymography results were analyzed using analysis of variance (ANOVA) (three-way and one-way, respectively), while Chi-squared test was used for the NL results. Statistical significance was preset at α = 0.05.

RESULTS

All the investigated factors (adhesive system, dentin conditioner and aging) significantly influenced μTBS, with the AU and ZON performing better compared to EF and TE, respectively, and with lower bond strength values after aging (p < 0.05). Incremented silver nitrate deposits were observed at the adhesive interfaces after aging, especially for the TE groups (p < 0.05). Further, the experimental groups treated with ZON had significantly lower levels of enzymatic activity compared to TE, as shown by gelatin and in situ zymography (p < 0.05).

CONCLUSIONS

The experimental etchant demonstrated promising results in hybrid-layer preservation over time when used with simplified bonding systems, and could therefore be recommended in the clinical practice.

Li-doped bioglass® 45S5 for potential treatment of prevalent oral diseases

OBJECTIVES

Despite the excellent properties of both pure bioglasses (BG) and BG doped with therapeutic ions (such as Li) in hard tissue applications, there is not enough information about their role in the remineralization and bacterial-growth in oral diseases. The aim of this contribution is to evaluate the effect of both pure BG and BG doped with 5-wt% of Li (BGLi) on both the remineralization of in vitro demineralized human-teeth and the antimicrobial behavior against strains from caries and periodontitis.

METHODS

Bioglass® 45S5 (BG) and BGLi were synthesized by the sol-gel method. The remineralization tests were carried out using in vitro demineralized enamel teeth and evaluated by Electron Microscopy (SEM) and Vickers micro-hardness (HV). The antimicrobial behavior of the particles was evaluated against S. mutans, A. actinomycetemcomitans, and P. gingivalis, representing pathogens from caries and periodontitis.

RESULTS

Enamel lesion was partially remineralized when both bioglasses (BG and BGLi) were applied on its surface with micro-hardness recoveries around 45 %. They further inhibited the growth of S. mutans and P. gingivalis, at 50 and 200 mg/mL, respectively. BGLi presented a higher toxicity against A. actinomycetemcomitans than BG, with inhibition concentrations of 20 mg/mL and 100 mg/mL, respectively.

CONCLUSIONS

Bioglasses could be used in the treatment of two of the most prevalent oral diseases: caries and periodontitis, promoting the remineralization of the teeth and killing the main pathogens. The presence of Li did not affect the bioactivity of the bioglass and improved the antibacterial effect over A. actinomycetemcomitans strain.

Zinc-Calcium-Fluoride Bioglass-Based Innovative Multifunctional Dental Adhesive with Thick Adhesive Resin Film Thickness

Apart from producing high bond strength to tooth enamel and dentin, a dental adhesive with biotherapeutic potential is clinically desirable, aiming to further improve tooth restoration longevity. In this laboratory study, an experimental two-step universal adhesive, referred to as Exp_2UA, applicable in both the etch-and-rinse (E&R) and self-etch (SE) modes and combining a primer, containing 10-methacryloyloxydecyldihydrogen phosphate as a functional monomer with chemical binding potential to hydroxyapatite, with a bioglass-containing hydrophobic adhesive resin, was multifactorially investigated. In addition to primary property assessment, including measurement of bond strength, water sorption, solubility, and polymerization efficiency, the resultant adhesive-dentin interface was characterized by transmission electron microscopy (TEM), the filler composition was analyzed by energy-dispersive X-ray spectroscopy, and the bioactive potential of the adhesive was estimated by measuring the long-term ion release and assessing its antienzymatic and antibacterial potential. Four representative commercial adhesives were used as reference/controls. Application in both the E&R and SE modes resulted in a durable bonding performance to dentin, as evidenced by favorable 1 year aged bond strength data and a tight interfacial ultrastructure that, as examined by TEM, remained ultramorphologically unaltered upon 1 year of water storage aging. TEM revealed a 20 μm thick hydrophobic adhesive layer with a homogeneous bioglass filler distribution. Adequate polymerization conversion resulted in extremely low water sorption and solubility. In situ zymography revealed reduced endogenous proteolytic activity, while Streptococcus mutans biofilm formation was inhibited. In conclusion, the three-/two-step E&R/SE Exp_2UA combines the high bonding potential and bond degradation resistance with long-term ion release, rendering the adhesive antienzymatic and antibacterial potential.