Differential resin-dentin bonds created after caries removal with polymer burs

Polymer Mixtures for Experimental Self-Limited Dental Burs Development-A Preliminary Approach (Part 1)

Alternative techniques have been investigated for effectiveness in caries removal because conventional metallic dental burs can lead to an excessive loss of sound tissue. The aim of the present study is to realize a preliminary approach in obtaining effective polymer mixtures for polymeric bur development, capable of removing primary dental caries using combinations of polymers to ensure the requirements for such instruments, but also a greater compatibility with the teeth structure. This study assessed the main mechanical properties, water sorption, solubility and microscopic structure of four new polymer mixture recipes to provide essential features in obtaining experimental self-limited dental burs. Two mixtures have in their composition polymer mixtures of Bis-phenol A diglycidyl ether dimethacrylate/Triethylene glycol dimethacrylate/Urethane dimethacrylates (R1, R2), and two other mixtures have Bis-phenol A diglycidyl ether dimethacrylate/Polymethyl methacrylate/Methyl methacrylates (R3, R4). The incorporation of nanoparticles into the polymer matrix has become essential due to the need of polymer biocompatibility increasing along with teeth surface remineralization, so that the powder charge was added to four recipes, such as 5% glass with BaF2 and 0.5% graphene with silver particles. All data sets were analyzed using the One-Way ANOVA test. R3, R4 showed higher compressive strength and diametrical compression values; these values increased when glass and graphene were added. Moreover, the addition of glass particles lead to an increase in flexural strength. Regarding the sorption, sample R3 had the most significant differences between day 69 and the rest of the investigation days, while the solubility varied at different intervals. From the mechanical evaluation, we could conclude that the Bis-GMA/PMMA/MMA mixtures fit the mechanical characteristics supported by polymer burs, following future studies regarding their use on the affected dentin.

Biodentine or Mineral Trioxide Aggregate as Direct Pulp Capping Material in Mature Permanent Teeth with Carious Exposure? A Systematic Review and Meta-analysis

OBJECTIVE

To evaluate the success rate of direct pulp capping (DPC) with Biodentine in mature permanent teeth with carious vital pulp exposure compared to that of DPC with mineral trioxide aggregate (MTA) by means of a systematic review and meta-analysis.

DATA SOURCES

The two authors searched independently the literature published through July 31, 2020, in five electronic databases (PubMed, the Cochrane Central Register of Controlled Trials, Web of Science Core Collection, the Wiley Online Library, and the SCOPUS database).

STUDY SELECTION

The research protocol was previously registered in the PROSPERO database (CRD42020192511). Clinical studies that met the inclusion criteria were chosen and independently screened by the authors.

DATA EXTRACTION

A custom-designed spreadsheet was used to extract the data. The quality of each study was evaluated by means of the revised Cochrane risk of bias (ROB) tool or the ROB of nonrandomized studies of interventions tool.

DATA SYNTHESIS

Three randomized controlled trials and one retrospective study met the inclusion criteria. Only one study had a high risk of bias. The included studies reported data on a total of 95 participants with an age range of 8-51 years. No significant difference was observed in the overall treatment outcome when comparing Biodentine with MTA (Risk ratio=1.00, 95% confidence interval [0.93-1.07], p=1.00).

CONCLUSIONS

Biodentine had comparable clinical and radiographic success to that of MTA when used as a DPC agent in mature permanent teeth with carious vital pulp exposure. Additional high-quality studies are needed.

Is the presence of 10-MDP associated to higher bonding performance for self-etching adhesive systems? A meta-analysis of in vitro studies

OBJECTIVE

The purpose of this systematic review and meta-analysis was to analyze the literature on the bond strength of self-etching (SE) adhesives containing 10-MDP or other acidic functional monomers, comparing the bonding performance of both compositions.

METHODS

This study is registered in PROSPERO (CRD42020175715) and it followed the PRISMA Statement. The literature search was performed in PubMed, Web of Science, SciELO, Scopus, LILACS, IBECS, and BBO from the starting coverage date through 30 June 2021. Study eligibility criteria consisted of in vitro studies that evaluated the bond strength (microtensile, microshear, tensile or shear testing) to sound dentin/enamel of a minimum of two distinct SE systems, with at least one material containing 10-MDP and one other being comprised of a distinct acidic composition. Statistical analyses were carried out with RevMan 5.3.5 and using random-effects models with the significance level at p < 0.05. Also, Bayesian network meta-analysis (NMA) was conducted using MetaInsight V3 tool.

RESULTS

From 740 relevant studies evaluated in full-text analysis, 210 were incorporated to the systematic review and 206 in meta-analysis. The majority of studies was classified as having medium risk of bias (56.7%), followed by low (35.2%) and high (8.1%) risk of bias. Data from a total of 64 adhesive systems were collected, which favored the 10-MDP-based group at both dentin (overall effect: 6.98; 95% CI: 5.61, 8.36; p < 0.00001) and enamel (overall effect: 2.79; 95% CI: 1.62, 3.96; p < 0.00001) substrates. Microtensile testing was more frequently used (73.4%) in the included studies. Adhesives based on 10-MDP showed greater bonding performance than adhesives comprised of monomers such as PENTA, 6-MHP, 4-META, 4-MET, pyrophosphate esters, mixed composition or monomers derived from sulfonic acid (p ≤ 0.01); whereas similar bond strength values were verified between 10-MDP-based materials and those containing PEM-F, acrylamide phosphates, 4-AET, MAC-10, or monomers derived from polyacrylic and phosphonic acids (p ≥ 0.05). Adhesives based on GPDM were the only ones that resulted in greater bonding potential than the 10-MDP-based group (p = 0.03). Dental bonds in dentin were favored with the application of 2-step 10-MDP-based adhesives; whereas in enamel the dental bonds were favored for both 2-steps versions of adhesives, regardless of the presence of 10-MDP. Indirect evidence from NMA revealed that 1-step 10-MDP-free and universal 10-MDP-free adhesives seemed to perform worst in dentin and enamel, respectively.

SIGNIFICANCE

Adhesives containing 10-MDP showed higher bonding performance than materials formulated with other acidic ingredients, although this result relied on the type of mechanical testing, type of the substrate, acidic composition of the adhesive, and the application category of the SE system. This review summarized the effects of the foregoing factors on the adhesion to dental substrates.

Histological determination of cariously altered collagen after dentin caries excavation with the polymer bur PolyBur P1 in comparison to a conventional bud bur

BACKGROUND

To compare the polymer bur PolyBur P1 (P1) with tungsten carbide bud bur H1 SE (H1) in removing cariously altered collagen during dentin caries excavation.

METHODS

Fifty extracted teeth were split in the center of a carious lesion. The 100 specimens were randomly divided into 5 groups. Five dentists were asked to excavate 10 teeth each: one half with P1 and the corresponding half with H1. The time needed for caries excavation was measured. Subsequently, histological specimens were produced and analyzed by light-microscope after Mallory-Azan-staining. The thickness of remaining cariously altered collagen was measured (< 1 mm or > 1 mm). The results were statistically evaluated.

RESULTS

The average time to excavate a cavity with P1 was 254 (± 148) sec and 202 (± 129) sec with H1. The difference in times was not statistically significant (p > 0.05). In the group P1 in 66.1% of the sections cariously altered collagen remained, whereas 33.9% showed sound collagen. In the group H1 45.7% sections had remaining cariously altered collagen and 54.3% showed sound collagen. The difference between P1 and H1 was statistically significant (p = 0.004). In the group P1 the layer of cariously altered collagen was significantly more often thicker than 1 mm than in the group H1 (p < 0.05). The variable "type of bur" had a statistically significant influence for the presence of cariously altered collagen (p = 0.003).

CONCLUSIONS

Conventional H1 bud burs were significantly more effective in removing cariously altered collagen during dentin caries excavation than the polymer bur P1.

Mechanical loading influences the viscoelastic performance of the resin-carious dentin complex

The aim of this study was to evaluate the changes in the mechanical behavior and bonding capability of Zn-doped resin-infiltrated caries-affected dentin interfaces. Dentin surfaces were treated with 37% phosphoric acid (PA) followed by application of a dentin adhesive, single bond (SB) (PA+SB) or by 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA+SB). ZnO microparticles of 10 wt. % or 2 wt. % ZnCl₂ was added into SB, resulting in the following groups: PA+SB, PA+SB-ZnO, PA+SB-ZnCl₂, EDTA+SB, EDTA+SB-ZnO, EDTA+SB-ZnCl₂. Bonded interfaces were stored for 24 h, and tested or submitted to mechanical loading. Microtensile bond strength was assessed. Debonded surfaces were evaluated by scanning electron microscopy and elemental analysis. The hybrid layer, bottom of the hybrid layer, and peritubular and intertubular dentin were evaluated using a nanoindenter. The load/displacement responses were used for the nanodynamic mechanical analysis III to estimate complex modulus, tan delta, loss modulus, and storage modulus. The modulus mapping was obtained by imposing a quasistatic force setpoint to which a sinusoidal force was superimposed. Atomic force microscopy imaging was performed. Load cycling decreased the tan delta at the PA+SB-ZnCl₂ and EDTA+SB-ZnO interfaces. Tan delta was also diminished at peritubular dentin when PA+SB-ZnO was used, hindering the dissipation of energy throughout these structures. Tan delta increased at the interface after using EDTA+SB-ZnCl₂, lowering the energy for recoil or failure. After load cycling, loss moduli at the interface decreased when using ZnCl₂ as doping agent, increasing the risk of fracture; but when using ZnO, loss moduli was dissimilarly affected if dentin was EDTA-treated. The border between intertubular and peritubular dentin attained the highest discrepancy in values of viscoelastic properties, meaning a risk for cracking and breakdown of the resin-dentin interface. PA used on dentin provoked differences in complex and storage modulus values at the intertubular and peritubular structures, and these differences were higher than when EDTA was employed. In these cases, the long-term performance of the restorative interface will be impaired.

Improved long-term bonding performance of an experimental all-in-one adhesive

The aim of this study was to determine the performance of an experimental all-in-one adhesive. The adhesive, named MTB-200 (Kuraray Medical), contained components to enhance both bond strength and hydrophobicity. The performance of the adhesive was compared with that of CLEARFIL TRI-S BOND (Kuraray Medical) and BeautiBond (SHOFU) using micro-tensile bond strength test and ultramicroscopic observations. The study revealed that the new adhesive had the highest tensile strength value among the three adhesives over time, although transmission electron microscopic images showed the phenomenon of filler de-bonding in the adhesive resin layer. In spite of modification in the experimental adhesive, the adhesive was suspected to degrade bond performance. However, revision of the composition of adhesives would be one of the solutions to enhance durability of interface.

Effectiveness of Different Mechanical Methods on Dentin Caries Removal: Micro-CT and Digital Image Evaluation

PURPOSE

To determine the caries removal effectiveness (CRE) and minimal invasive potential (MIP) of caries excavation methods using digital imaging and microtomography analyses.

METHODS

Twelve human molars with occlusal caries lesions in dentin were randomly divided into three groups (carbide bur, exacavator, and polymer bur). They were sectioned mesiodistally, and standardized digital and computed microtomography x-ray (micro-CT) images were taken from each section before and after caries excavation. On each image, initial carious dentin (IC), prepared cavity (PC), and residual caries (RC) were defined according to visual criteria using ImageJ software. CRE was determined based on the RC/IC ratio, whereas MIP was determined by the PC/IC ratio. Data were analyzed using one-way analysis of variance and Student t-test or with Kruskal-Wallis and Student-Newman-Keuls test. The level of significance was set at 0.05.

RESULTS

For both digital image and micro-CT analysis, the carbide bur showed higher CRE values than the excavator (p=0.0063 and p=0.0263, respectively) and the polymer bur (p=0.0028 and p=0.0005, respectively). The latter two presented similar results (p>0.05). Regarding MIP, for the digital image analysis, the polymer bur was different from the carbide bur (p=0.0030) but was not different from that of the excavator (p=0.1240). For micro-CT analysis, the MIP values of all the groups were significantly different, and the polymer bur was the most conservative method (p<0.05).

CONCLUSIONS

The carbide bur was the most effective method for caries removal but was not completely conservative. The polymer bur and excavator presented low invasive potential but were not able to remove all of the carious dentin.

A Zn-doped etch-and-rinse adhesive may improve the mechanical properties and the integrity at the bonded-dentin interface

OBJECTIVE

The objective of the study was to determine if zinc-doped etch-and-rinse dentin adhesive may induce therapeutic effects within the resin-dentin interface.

METHODS

Human acid-etched dentin was infiltrated with Adper™ Single Bond Plus (SB, 3M ESPE, St. Paul, MN, USA), SB doped with 10wt.% ZnO nanoparticles (ZnO-SB) or SB doped with 2wt.% ZnCl2 (ZnCl2-SB). AFM/nanoindentation analysis was performed on fully hydrated specimens to evaluate the nanomechanical properties (Hi: hardness; Ei: modulus of elasticity) across the resin-dentin interface after different SBF storage periods (24h, 1m, 3m). Confocal laser microscopy (CLSM) was used to evaluate the ultramorphology and micropermeability at 24h and 3m of SBF storage.

RESULTS

SB control specimens exhibited a decrease in Hi in the hybrid layer (HL) and bottom of the hybrid layer (BHL) and a decrease in Ei in the HL after 3m of SBF storage, indicating that severe degradation occurred in the control interface. ZnO-SB bonded specimens preserved the initial Hi and Ei at the HL and BHL subsequent SBF storage; ZnCl2-SB bonded specimens showed a decrease in Ei, in the HL over time. CLSM analysis confirmed that both Zn-doped adhesives were able to preserve the integrity of the HL.

SIGNIFICANCE

Specific formulation of Zn-doped etch-and-rinse adhesives may offer the possibility to maintain the nano-mechanical properties along the dentin-bonded interface by inhibiting dentin MMPs and by protective mineral crystals formation within the resin-dentin interface. Clinical advantages may be expected by preserving and improving the integrity of the hybrid layer when Zn-doped adhesives are employed.

Digital image analysis method to assess the performance of conventional and self-limiting concepts in dentine caries removal

OBJECTIVE

To assess dentine caries removal effectiveness (CRE) and minimal invasiveness potential (MIP) of carbide and polymer burs.

METHODS

Sectioned carious molars were photographed. Digital images were taken, before and after caries removal, using a Digital Single Lens Reflex camera. The following regions of interest were measured using visual criteria: Residual Infected Dentine (RI), Residual Affected Dentine (RA), Removal Sound Dentine (RA), Prepared Cavity (PC) and Removed Sound Dentine (RS). CRE was determined on basis of: relative residual infected dentine (RI/II), relative residual carious-affected dentine (RA/IA) and total relative residual dentine (RI+RA/II-IA). MIP was determined on basis of: infected dentine cavity size (PC/II), total relative cavity size (PC/II+IA), and corrected relative cavity size (PC-RS/II+IA).

RESULTS

The polymer bur showed the highest preservation of carious-affected dentine after excavation, when the RA/IA ratio was studied. Both kind of burs showed similar values after assessing the RI/II and RI+RA/II-IA ratios. The infected dentine relative cavity size (PC/II) was higher when the carbide bur was used. Both burs attained similar PC/II+IA and PC-RS/II+IA ratios.

CONCLUSIONS

Polymer burs accomplished the concept of minimal-invasive dentistry, showing its self-limiting ability. The minimal-invasiveness potential showed that carbide burs resulted in the worst compromise between effective and selective infected-caries removal.

Resistance to degradation of resin-dentin bonds produced by one-step self-etch adhesives

The objective of this article is to evaluate the resistance to degradation of resin-dentin bonds formed with three one-step adhesives. Flat, mid-coronal dentin surfaces were bonded with the self-etching adhesives [Tokuyama Bond Force (TBF), One Up Bond F Plus (OUB), and G-Bond (GB)]. The bonded teeth were subjected to fatigue loading, chemical degradation, and stored in distilled water for four time periods (up to 12 months). Specimens were tested for microtensile bond strength and microleakage. Fractographic analysis was performed by scanning electron microscopy. Bonded interfaces were examined by light microscopy using Masson's trichrome staining. An atomic force microscope was employed to analyze phase separation and surface nanoroughness (Ra) at the polymers. Vickers microhardness and the degree of the conversion (DC) were also determined. ANOVA and multiple comparisons tests were performed. Bond strength significantly decreased after the chemical challenge, but not after load cycling. Aging decreased bond strength after 6 months in TBF and GB, in OUB after 12 months. An increase of the nonresin protected collagen zone occurred in all groups, after storing. TBF showed the highest roughness, microhardness, and DC values, and GB showed the lowest. Mild self-etch one-step adhesives (TBF/OUB) showed a higher degree of cure, lower hydrophilicity, and major resistance to degradation of resin-dentin bonds when compared to highly acidic self-etching adhesive (GB).