[Evaluation of the effects of TF and S3 nickel-titanium instruments in severely curved molar root canal preparation].

PURSPOSE: To compare the shaping ability and dental cracks of Twisted File and S3 in severely curved molar root canal preparation. METHODS: Sixty extracted mandibular molars with mesiobuccal canals (canal curvature angles beyond 25°) were selected and divided randomly into 2 groups with 30 canals in each group. The canals were scanned by cone-beam CT(CBCT) before and after root canal preparation .The canal transportation was recorded at 3 points (3, 5, 7 mm to root tip). After root canal preparation，all the roots were horizontally sectioned 3，5 and 7mm from the apex. The slices were observed under optical stereomicroscope. SPSS 19.0 software package was used for statistical analysis. RESULTS: Transportations occurred in all groups. No significant difference was found between the two groups of canal transportation at the two points (5 mm and 7 mm to root tip) (P>0.05); at the point of 3 mm to the root tip,the transportation of canals prepared by S3 was obviously lesser than the canals prepared by TF. There was no significant difference in the incidence of dentinal cracks between the two groups (P>0.05). CONCLUSIONS: Under the conditions of severely curved molar root canal in extracted teeth, cracks were found in both groups, S3 was found to be better in maintaining original canal shape than TF system.

[Impact of particle size and morphology on zinc cation adsorption by hydroxyapatite and dentifrice containing hydroxyapatite].

OBJECTIVE: To study the influence of particle size and morphology on zinc cation adsorption by hydroxyapatite (HA) and dentifrice containing HA. METHODS: Four HAs with different particle sizes and morphologies, HA-containing dentifrice and blank dentifrice were prepared into suspensions of serial concentrations. Zinc ion solutions with an initial concentration of 10 mg/L was mixed with the suspensions and kept for 24 h for adsorption reaction. The zinc ion concentration in the supernatant was measured by inductively coupled plasma emission spectrometer and the sorption rate of zinc ion was calculated. RESULTS: HA and HA-containing dentifrice with various particle sizes and morphologies were all capable of absorbing zinc ions from simulated waste water, and the adsorption rate of HA-containing dentifrice was 3%-10% higher than that of HA. HA with a particle size of 12 µm and a spherical morphology showed the strongest adsorption ability, followed by short bar-shaped HA with a particle size of 30 µm. Both Langmuir and Freundlich equation could simulate the sorption processes of HA dentifrice, while only Langmuir equation could simulate the sorption processes of HA. CONCLUSION: Incorporation of HA in dentifrice can enhance zinc ion adsorption capacity of the material. The particle size and morphology of HA both affect the adsorption of zinc ions, and 12-µm HA particle with a spherical morphology has the best adsorption ability.

[Experimental study on pulp revitalization of Beagle dog's immature permanent teeth after pulpectomy].

OBJECTIVE: To observe the process of pulp revitalization of immature permanent teeth after pulpectomy. METHODS: Thirty-two single-rooted teeth with open apices from 4 Beagle dogs aged 4 months were included in the study. The pulpal tissues of 8 front teeth with single root of each dog were removed, and a blood clot was produced to the level of the cementoenamel junction followed by a double seal of mineral trioxide aggregate and composite resin. At day 7, 14, 21 and 28, respectively after operation, the dog was sacrificed, and then longitudinal paraffin sections were made for histologic investigation. RESULTS: After 7 days, about one thirth of the pulp chamber had an ingrowth of new tissue. After 14, 21, 28 days, there were more and more new tissue in the chamber. This new tissue consisted of well-organized and well-vascularized connective tissue. Hard tissue was too observed in the root canal. In some cases, the newly generated hard tissue even deposited against the canal dentinal walls. CONCLUSIONS: The pulp of immature permanent teeth can revitalize after removal of the original pulp tissue under suitable conditions.

[Nanoleakage at the resin-dental interface of four self-etching adhesives].

OBJECTIVE: To evaluate the nanoleakage and ultramorphology of four self-etching adhesives. METHODS: Sixteen freshly extracted, caries-free human third molars were selected. A flat dentin surface was exposed by removing occlusal enamel. All teeth were randomly divided into four groups acorrding to four different self-etch adhesive: Adper Prompt (A), iBond (B), Xeno III (C) and SE Bond (D). The dentin were bonded with dentin adhesive system according to manufacturer's directions. Composite layers were built up incrementally. The specimens were sectioned longitudinally across the resin-dentin interface into 4.0 mm×0.9 mm sticks and then traced with ammoniacal silver solution. Epoxy resin-embedded sections were prepared for transmission electron microscope (TEM) to observe nanoleakage. The images were qualitatively compared by NIH software, and data was analyzed by SPSS. RESULTS: Different thickness of hybrid layer and adhesives layer were observed for each adhesive. The hybrid layer of A, C was thicker than that of B, D, and adhesive layer of D was thicker than the others. The extent of nanoleakage varied among different adhesives: A (45.02 ± 9.49), B (43.97 ± 8.55), C (27.02 ± 10.86), D (12.94 ± 2.07). D presented significantly less silver deposition than any of the others did (P < 0.05). CONCLUSIONS: The thickness of hybrid layer and adhesive layer vary among the four adhesives. The shape and extent of nanoleakage of each adhesive are also different. Two-step system shows less nanoleakage than one-step systems do.