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.

The Antibiofilm Activity and Mechanism of Nanosilver- and Nanozinc-Incorporated Mesoporous Calcium-Silicate Nanoparticles.

BACKGROUND: Mesoporous calcium-silicate nanoparticles (MCSNs) have good prospects in the medical field due to their great physicochemical characteristics, antibacterial activity and drug delivery capacity. This study was to analyze the antibiofilm activity and mechanisms of silver (Ag) and zinc (Zn) incorporated MCSNs (Ag/Zn-MCSNs) with different percentages of Ag and Zn. METHODS: Ag/Zn(1:9, molar ratio)-MCSNs and Ag/Zn(9:1, molar ratio)-MCSNs were prepared and characterized. Endocytosis of nanoparticles by Enterococcus faecalis (E. faecalis) treated with Ag/Zn-MCSNs was observed using TEM to explore the antibacterial mechanisms. The antibiofilm activity of Ag/Zn-MCSNs with different ratios of Ag and Zn was tested by E. faecalis biofilm model in human roots. The human roots pretreated by different Ag/Zn-MCSNs were cultured with E. faecalis. Then, SEM and CLSM were used to observe the survival of E. faecalis on the root canal wall. Cytotoxicity of the nanoparticles was tested by CCK8 kits. RESULTS: The Ag/Zn-MCSNs release Ag+ and destroy the cell membranes to kill bacteria. The MCSNs containing Ag showed antibacterial activity against E. faecalis biofilms in different degrees, and they can adhere to dentin surfaces to get a continuous antibacterial effect. However, MTA, MCSNs and Zn-MCSNs could not disrupt the bacterial biofilms obviously. MCSNs, Ag/Zn(1:1, molar ratio)-MCSNs and Ag/Zn(1:9)-MCSNs showed no obvious cytotoxicity, while Ag-MCSNs and Ag/Zn(9:1)-MCSNs showed cytotoxicity. Zn-MCSNs can slightly promote cell proliferation. CONCLUSION: Ag/Zn-MCSNs have good antibiofilm activity. They might achieve an appropriate balance between the antibacterial activity and cytotoxicity by adjusting the ratio of Ag and Zn. Ag/Zn-MCSNs are expected to be a new type of root canal disinfectant or sealer for root canal treatment.

Effects of nanosilver and nanozinc incorporated mesoporous calcium-silicate nanoparticles on the mechanical properties of dentin.

Mesoporous calcium-silicate nanoparticles (MCSNs) are advanced biomaterials for drug delivery and mineralization induction. They can load silver and exhibit significantly antibacterial effects. However, the effects of MCSNs and silver-loaded MCSNs on dentin are unknown. The silver (Ag) and/or zinc (Zn) incorporated MCSNs (Ag-Zn-MCSNs) were prepared by a template method, and their characterizations were tested. Then the nanoparticles were filled into root canals and their effects on the dentin were investigated. Ag-Zn-MCSNs showed characteristics of mesoporous materials and sustained release of ions over time. Ag-Zn-MCSNs adhered well to the root canal walls and infiltrated into the dentinal tubules after ultrasound activation. Ag-Zn-MCSNs showed no significantly negative effects on either the flexural strength or the modulus of elasticity of dentin, while CH decreased the flexural strength of dentin significantly (P<0.05). These findings suggested that Ag and Zn can be incorporated into MCSNs using a template method, and the Ag-Zn-MCSNs may be developed into a new disinfectant for the root canal and dentinal tubules.

Root and canal morphology of maxillary second molars by cone-beam computed tomography in a native Chinese population.

Objective To evaluate the root and root canal morphology of the maxillary second molars (MSMs) in a native Chinese population by cone-beam computed tomography. Methods Cone-beam computed tomography images of 2412 MSMs from 1294 Chinese patients were analyzed to determine the number and morphology of the roots, the root canal morphology, the bilateral symmetry, and the correlations of these parameters with sex and age. Results The percentage of fused roots increased with age, while the percentage of fused roots in women was higher than that in men. The percentage of second mesiobuccal (MB2) canals in MSMs with three separate roots was higher in men than women. Patients aged 31 to 40 years showed a higher prevalence of MB2 canals, while those aged ≥51 years showed the lowest prevalence of MB2 canals among both men and women. There was a significant difference in bilateral symmetry of MSMs between men and women. Conclusion Root fusion of MSMs increased with age, while the root canal morphology was more complex in patients of intermediate ages.

Bilateral maxillary fused second and third molars: a rare occurrence.

This case report describes the diagnosis and endodontic therapy of maxillary fused second and third molars, using cone-beam computed tomography (CBCT). A 31-year-old Chinese male, with no contributory medical or family/social history, presented with throbbing pain in the maxillary right molar area following an unsuccessful attempted tooth extraction. Clinical examination revealed what appeared initially to be a damaged large extra cusp on the buccal aspect of the distobuccal cusp of the second molar. However, CBCT revealed that a third molar was fused to the second molar. Unexpectedly, the maxillary left third molar also was fused to the second molar, and the crown of an unerupted supernumerary fourth molar was possibly also fused to the apical root region of the second molar. Operative procedures should not be attempted without adequate radiographic investigation. CBCT allowed the precise location of the root canals of the right maxillary fused molar teeth to permit successful endodontic therapy, confirmed after 6 months.

[Diagnostic test study of dental operating microscope used for locating the second mesiobuccal canal orifice in maxillary first molars].

OBJECTIVE: To estimate the diagnostic potential of the dental operating microscope used for locating the second mesiobuccal canal (MB2) orifice in maxillary first molars. METHODS: 120 extracted maxillary first molars were used, all the access cavities were prepared and fixed on the dental study model. MB2 orifices were examined with naked eye and under a dental operating microscope (DOM). The examination was repeated by another dentist with the same methods. Then Indian ink was injected into the pulp chamber and all the teeth were treated to be transparent to determine if it had a real MB2. RESULTS: The sensitivity and accuracy of the DOM group were 0.78 and 0.76, higher than 0.61 and 0.65 of the naked eye group (P<0.05). The correspondency of Kappa index between observers by naked eye and DOM was 0.701 and 0.819, respectively. CONCLUSION: The use of DOM can increase the detection rate of MB2.

[Investigation of root canal curvature of human maxillary first premolar in buccolingual directions].

OBJECTIVE: To investigate root canal curvatures of human maxillary first premolars in buccolingual directions. METHODS: One hundred extracted permanent maxillary first premolars were used. After access preparation, a K-file was inserted into the canals and gently advanced until it reached the apical foramen. Then standardized periapical radiovisiography (RVG) images were taken from mesiodistal direction. The angle of curvature was determined according to the method described by Schneider. The radiu of curvature and length of the curved part of the root canal were calculated. RESULTS: 1) The total 50.00% (88/176) of root canal curves were in buccolingual directions, and 53 curves were showed in apical 1/3 of root region. 11.93% (21/176) of S-shaped canals were detected, and the first curves were mostly showed in middle 1/3 of root region, the secondary curves were totally showed in apical 1/3 of root region. 2) There was no difference of curvatures between buccal and lingual root canals, but the secondary curves of S-shaped canals were more complicated than other root canals. 3) There was no correlation between the angle of curvature and the radius of curvature (r=0.002, P>0.05), but significantly correlation between the angle of curvature and length of the curved part of the root canal (r=0.489, P<0.01). CONCLUSION: The occurrence of curved root canals in buccolingual directions may be high in human maxillary first premolars, and the curvatures of S-shaped canals were more complicated than others.