Citrate Improves Biomimetic Mineralization Induced by Polyelectrolyte-Cation Complexes Using PAsp-Ca&Mg Complexes.

Magnesium ions are highly enriched in early stage of biological mineralization of hard tissues. Paradoxically, hydroxyapatite (HAp) crystallization is inhibited significantly by high concentration of magnesium ions. The mechanism to regulate magnesium-doped biomimetic mineralization of collagen fibrils has never been fully elucidated. Herein, it is revealed that citrate can bioinspire the magnesium-stabilized mineral precursors to generate magnesium-doped biomimetic mineralization as follows: Citrate can enhance the electronegativity of collagen fibrils by its absorption to fibrils via hydrogen bonds. Afterward, electronegative collagen fibrils can attract highly concentrated electropositive polyaspartic acid-Ca&Mg (PAsp-Ca&Mg) complexes followed by phosphate solution via strong electrostatic attraction. Meanwhile, citrate adsorbed in/on fibrils can eliminate mineralization inhibitory effects of magnesium ions by breaking hydration layer surrounding magnesium ions and thus reduce dehydration energy barrier for rapid fulfillment of biomimetic mineralization. The remineralized demineralized dentin with magnesium-doped HAp possesses antibacterial ability, and the mineralization mediums possess excellent biocompatibility via cytotoxicity and oral mucosa irritation tests. This strategy shall shed light on cationic ions-doped biomimetic mineralization with antibacterial ability via modifying collagen fibrils and eliminating mineralization inhibitory effects of some cationic ions, as well as can excite attention to the neglected multiple regulations of small biomolecules, such as citrate, during biomineralization process.

Minimum residual root dentin thickness of mandibular premolars restored with a post: A finite element analysis study.

STATEMENT OF PROBLEM: Thin root dentin after post space preparation will increase the risk of root fracture. However, the minimum residual root dentin thickness to be preserved after post space preparation is unclear. PURPOSE: The purpose of this finite element analysis (FEA) study was to measure the residual root dentin thicknesses and analyze the stress distributions of post-restored mandibular premolars. MATERIAL AND METHODS: The cone beam computed tomography (CBCT) data of 90 first and second mandibular premolars from Chinese participants (44 men, 46 women; aged between 20 and 79 years) were analyzed. Cross-sections 5 to 9 mm from the radiologic apex were used to measure the buccolingual and mesiodistal root diameters. The probability that the residual thickness of the buccolingual and mesiodistal root walls would be no less than 0.5, 0.6, 0.7, 0.8, 0.9, and 1 mm after post space preparation with a #2 Peeso reamer was calculated. Six 3-dimensional finite element models of cast post-restored mandibular premolars with 0.5, 0.6, 0.7, 0.8, 0.9, and 1 mm mesial and distal root dentin thicknesses were established. A static force of 100 N was applied to the buccal cusp tip at 45, 60, 75, and 90 degrees to the long axis of the tooth, and the maximum tensile stress and von Mises stress were analyzed. The Bonferroni post hoc test (αcorrected=.003) was used for multiple comparisons. RESULTS: The buccolingual root diameter of mandibular premolars was wider than the mesiodistal root diameter. The probabilities that the mesiodistal residual root dentin thickness of mandibular first and second premolars at 5 mm from the apex would be no less than 1 mm after post space preparation with a #2 Peeso reamer were only 10% and 28%, respectively. The maximum tensile stress was at a minimum when the mesial and distal residual root dentin thickness was 0.6 mm in the external cervical dentin adjacent to the crestal bone and 1 mm in the apical dentin corresponding to the apex of the post. The maximum tensile stress of the mandibular premolar model with 0.6-mm mesial and distal residual root dentin thicknesses was lower than that with 0.9 mm and 1.0 mm thicknesses (Pcorrected<.001). CONCLUSIONS: Short posts or smaller instruments for post space preparation are recommended to obtain a 1-mm residual root dentin thickness in the mesiodistal direction of mandibular premolars. If a 1-mm thickness cannot be preserved, a minimum residual root dentin thickness of 0.6 to 0.9 mm in the mesiodistal direction should be retained.

Effect of an extrafibrillar dentin demineralization strategy on the durability of the resin-dentin bond.

OBJECTIVES: This study aimed to evaluate the potential of the extrafibrillar dentin demineralization strategy on the long-term dentin bond strength of an etch-and-rinse adhesive. METHODS: A water-soluble glycol chitosan-EDTA (GCE), a chelating conditioner, was synthesized and subjected to size-exclusion dialysis to obtain molecules >40 kDa. The conjugation of EDTA to glycol chitosan was analyzed by Fourier transform infrared (FTIR) spectroscopy. Mid-coronal dentin surfaces of 80 teeth were either acid-etched with 35% phosphoric acid or conditioned with 25 mg/mL GCE (n = 40) and thoroughly water-sprayed before applying the etch-and-rinse adhesive Adper Single Bond Plus and placing Z250 composite resin (3 M Oral Care; St Paul, MN, USA). Resin-bonded specimens were prepared into beams with a cross-sectional area of about 0.9 mm2 vertically through the resin-dentin interfaces before the microtensile bond strengths (MTBS) were determined immediately or after 3, 6, or 12 months of water storage. The resin-dentin interfaces were analyzed using transmission electron microscopy (TEM). The MTBS data were analyzed using two-way ANOVA followed by the LSD post-hoc multiple comparisons (P < 0.05). RESULTS: FTIR spectra showed that EDTA was successfully conjugated to glycol chitosan. The phosphoric acid-etching group and GCE-conditioning group showed similar bond strength values after 24 h of water storage. The bond strength of the phosphoric acid-etching group after 12-month water aging was significantly reduced from 51.61 ± 3.30 MPa to 38.57 ± 4.81 MPa, while the bond strength of the GCE-conditioning group was not significantly reduced from 50.28 ± 3.62 MPa to 46.40 ± 4.71 MPa.The degradation of the hybrid layer could be detected in the phosphoric acid-etching group after 12 months of water aging, but not in the GCE-conditioning group. CONCLUSION: The extrafibrillar dentin demineralization strategy using GCE conditioner could defy the hybrid layer degradation of the dentin bond after 12 months of water aging and enhance the dentin bond durability of the etch-and-rinse adhesive Adper Single Bond Plus.

Separated root tip formation associated with a fractured tubercle of dens evaginatus: A case report.

BACKGROUND: Several previous studies have reported an unusual root formation in which a fractured apical fragment of an immature root continued to develop independent of the main root after trauma to an immature tooth. To date, there have been only rare reports of the continuing apical formation of the fractured root associated with dens evaginatus (DE). This paper presents a case of a separated root tip formation associated with a fractured tubercle of DE. CASE SUMMARY: An 11-year-old boy was referred for gingival sinus on the buccal side of the right mandibular second premolar (tooth # 45). Clinically, tooth # 45 was free of caries, but there was a sign of a fractured tubercle of DE on the occlusal surface. Radiography showed that the root canal of tooth # 45 was widely radiolucent. A separated root apex was found apically under the main root and was nearly completely formed with an apical orifice at the apical tip. Tooth # 45 was diagnosed as tubular fracture of DE with chronic apical periodontitis. A revascularization technique was recommended to treat the tooth. At 3-mo and 1-yr follow-up, the patient remained asymptomatic. Periapical radiography revealed that the separated root tip distally drifted with closure of the apex. However, the root length and thickness of the main root did not increased. CONCLUSION: Clinicians should be aware that even if tubercle of DE is fractured in an immature tooth, the root tip may be separated from the main root and completely formed.

Conservative endodontic management using a calcium silicate bioceramic sealer for delayed root fracture: A case report and review of the literature.

BACKGROUND: The success rate of conservative endodontic management for root fracture varies greatly based on different methods used. It has been rarely reported that calcium silicate-based materials are applied in root fracture treatment. CASE SUMMARY: A 38-year-old male patient presented with spontaneous pain from the upper left anterior teeth for 1 wk. The spontaneous pain was subsequently relieved, but pain on mastication persisted for 3 d. The patient had a dental trauma from a boxing match 15 years ago. Cone beam computed tomography showed that the maxillary left central incisor had oblique fracture lines and a radiolucent lesion around the fracture line. The tooth was diagnosed with an oblique root fracture with no healing and symptomatic apical periodontitis. In the following conservative endodontic management, the coronal and apical fragments of the canal both were chemo-mechanically prepared and obturated using a single cone gutta-percha with iRoot SP (Innovative BioCreamix Inc, Vancouver, Canada), a new calcium silicate-based bioceramic root canal sealer. At follow-ups at 1, 6, 12, and 24 mo, the patient was asymptomatic and the radiolucency around the fracture line was healing radiographically. CONCLUSION: Conservative root canal treatment is an alternative treatment in some cases of oblique root fracture with no healing. The application of bioceramic sealers and single core obturation techniques may also be essential to obtain an excellent outcome.

Defying ageing: An expectation for dentine bonding with universal adhesives?

OBJECTIVES: The present study evaluated the long-term dentine bonding effectiveness of five universal adhesives in etch-and-rinse or self-etch mode after 12 months of water-ageing. METHODS: The adhesives evaluated included All-Bond Universal, Clearfil Universal Bond, Futurabond U Prime&Bond Elect and Scotchbond Universal. Microtensile bond strength and transmission electron microscopy of the resin-dentine interfaces created in human coronal dentine were examined after 24h or 12 months. RESULTS: Microtensile bond strength were significantly affected by bonding strategy (etch-and-rinse vs self-etch) and ageing (24h vs 12 months). All subgroups showed significantly decreased bond strength after ageing except for Prime&Bond Elect and Scotchbond Universal used in self-etch mode. All five adhesives employed in etch-and-rinse mode exhibited ultrastructural features characteristic of collagen degradation and resin hydrolysis. A previously-unobserved inside-out collagen degradation pattern was identified in hybrid layers created by 10-MDP containing adhesives (All-Bond Universal, Scotchbond Universal and Clearfil Universal Bond) in the etch-and-rinse mode, producing partially degraded collagen fibrils with intact periphery and a hollow core. In the self-etch mode, all adhesives except for Prime&Bond Elect exhibited degradation of the collagen fibrils along the thin hybrid layers. The three 10-MDP containing universal adhesives did not protect surface collagen fibrils from degradation when bonding was performed in the self-etch mode. CONCLUSIONS: Despite the adjunctive conclusion that bonds created by universal adhesives in the self-etch bonding mode are more resistant to decline in bond strength when compared with those bonds created using the etch-and-rinse mode, bonds created by universal adhesives are generally incapable of defying ageing.

Improvement of enamel bond strengths for conventional and resin-modified glass ionomers: acid-etching vs. conditioning.

OBJECTIVE: This study deals with the effect of phosphoric acid etching and conditioning on enamel micro-tensile bond strengths (µTBSs) of conventional and resin-modified glass ionomer cements (GICs/RMGICs). METHODS: Forty-eight bovine incisors were prepared into rectangular blocks. Highly-polished labial enamel surfaces were either acid-etched, conditioned with liquids of cements, or not further treated (control). Subsequently, two matching pre-treated enamel surfaces were cemented together with one of four cements [two GICs: Fuji I (GC), Ketac Cem Easymix (3M ESPE); two RMGICs: Fuji Plus (GC), RelyX Luting (3M ESPE)] in preparation for µTBS tests. Pre-treated enamel surfaces and cement-enamel interfaces were analyzed by scanning electron microscopy (SEM). RESULTS: Phosphoric acid etching significantly increased the enamel µTBS of GICs/RMGICs. Conditioning with the liquids of the cements produced significantly weaker or equivalent enamel µTBS compared to the control. Regardless of etching, RMGICs yielded stronger enamel µTBS than GICs. A visible hybrid layer was found at certain enamel-cement interfaces of the etched enamels. CONCLUSIONS: Phosphoric acid etching significantly increased the enamel µTBSs of GICs/RMGICs. Phosphoric acid etching should be recommended to etch the enamel margins before the cementation of the prostheses such as inlays and onlays, using GICs/RMGICs to improve the bond strengths. RMGICs provided stronger enamel bond strength than GICs and conditioning did not increase enamel bond strength.

[Effect of self-etching primers on microleakage of resin composites in class V restorations]

OBJECTIVE: To evaluate in vitro microleakage of class V restorations using two self-etching primers with a flowable resin or hybrid resins. METHODS: Forty human molars were divided into 3 groups according to axial surfaces. Each group was randomly assigned to 2 subgroups (n=20) with either butt-joint or the beveled preparations. Class V preparations were cut in cemento-enamel junction. Groups A, B, C were respectively restored with CLB2/Clearfil AP-X, APMB/FHC-Merz or APMB/Liquicoat. Half specimens of each subgroup were thermocycled 2 500 times. After staining, dye penetration was evaluated in the ordinal scale at 40Xmagnifications for occlusal and the gingival margins. The wall adaptation of the randomly selected specimens was analyzed with a SEM on replicas of the sectioned teeth. RESULTS: None of bond systems in this study prevented the microleakge. The restorations with the bur-beveled preparations leaked the same as those with the butt joint preparations (P>0.05). The thermocycled specimens and the non-thermocycled specimens leaked similarly (P>0.05). The flowable resin-liqucoat leaked significantly more than hybrid resin in dentinal margins (P<0.05). CONCLUSION: The self-etching primers can not reduce the microleakge in the dentin-restoration interfaces. The flowable resin leak more than the hybrid resin in dentin-restoration interfaces. The bur- beveled preparations do not significantly reduce the microleakage in class V resin restorations bonded with self-etching primers.