Effects of Hybrid Coat on shear bond strength of five cements: an in vitro study

PURPOSE: To evaluate the sealing performance of Hybrid Coat and its influence on the shear bond strength of five dentin surface cements. MATERIALS AND METHODS: Six premolars were pretreated to expose the dentin surface prior to the application of Hybrid Coat. The microscopic characteristics of the dentinal surfaces were examined with scanning electron microscopy (SEM). Then, 40 premolars were sectioned longitudinally, and 80 semi-sections were divided into a control group (untreated) and a study group (treated by Hybrid Coat). Alloy restoration was bonded to the teeth specimen using five different cements. Shear bond strength was measured by the universal testing machine. The fracture patterns and the adhesive interface were observed using astereomicroscope. RESULTS: SEM revealed that the lumens of dentinal tubules were completely occluded by Hybrid Coat. The Hybrid Coat significantly improved the shear bond strength of resin-modified glass ionomer cement (RMGIC) and resin cement (RC) but weakened the performance of zinc phosphate cement (ZPC), zinc polycarboxylate cement (ZPCC) and glass ionomer cement (GIC). CONCLUSION: Hybrid Coat is an effective dentinal tubule sealant, and therefore its combined use with resin or resin-modified glass ionomer cements can be applied for the prostheses attachment purpose.

The retractive effects of different gingival retraction agents / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the retractive effects of different gingival retraction agents.</p><p><b>METHODS</b>Thirty subjects with healthy gingival conditions were recruited to the trial, and the buccal gingival sulcus of the hibateral first max-illary premolars of each subject (n=60) were treated randomly with one of the six agents--Group A was tetrahydrozoline hydrochloride, Group B was oxymetazoline hydrochloride, Group C was epinephrine hydrochlorid, Group D was AlCl3, Group E was Fe2 (SO4)3, and Group F was normal saline as control. Both pre-treated and post-treated accurate impressions of buccal gingival sulcus of the experimental teeth were made, so were the anhydrite casts. The casts of experimental teeth were sectioned into 2 mm slices bucco-lingually at the buccal eminence. Then the width of the sulcus was measured as the distance from the tooth to the crest of the gingival under a low-power microscope to compare the effect of these gingival retraction agents.</p><p><b>RESULTS</b>The width of gingival sulcus became larger after the treatment in all groups (P < 0.05). Either Group A or Group B had greater gingival retraction effects than Group C and Group F (P < 0.05). Except Group F, both Group D and Group E had no significant differences from the other groups (P > 0.05). There was no statistically signification between Group D and Group E (P > 0.05), neither was there any statistically significance between Group A and Group B (P > 0.05).</p><p><b>CONCLUSION</b>Tetrahydrozoline manifested excellent effect of gingival retraction.</p>

The effects of post space preparation and post restoration on apical sealing ability / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the effects of post space preparation and post restoration on apical sealing ability.</p><p><b>METHODS</b>60 extracted mandibular premolars each with single canal were selected. All canals were prepared by manual ProTaper instrument using crown-down technique. The samples were the divided into 5 groups randomly. Group A: 20 samples, the immediate post space preparation group; group B: 20 samples, the delayed post space preparation group; group C: 10 samples, the intact group; group D: 5 samples, a positive control; group E: 5 samples, a negative control. There were two subsets in groups A and B which were restored by temporary materials (A1 and B1) or fiber post and cores (A2 and B2). Indian ink dye method was used to measure the apical leakage in stereomicoscope.</p><p><b>RESULTS</b>The mean length of dye penetration for group A1, A2, B1, B2 and C were (0.52 +/- 0.47), (0.49 +/- 0.44), (1.17 +/- 0.77), (1.12 +/- 0.54), and (0.23 +/- 0.40) mm, respectively. Positive group demonstrated maximum dye penetration, and negative group showed no dye penetration. There was no statistically significant difference between group A1, A2 and group C (P>0.05). However, there were statistically significant differences between group B and group A, C (P<0.05). The length of dye penetration for group B was longer than that for group A and C.</p><p><b>CONCLUSION</b>The sealing ability was decreased after delayed post space preparation when using the AH-Plus sealer.</p>

An experimental study on repairing horn-shaped root canal orifice by different materials / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the fracture resistance and the failure pattern of horn-shaped root canal orifice restored by different materials.</p><p><b>METHODS</b>Fifteen human maxillary central incisors were selected. After schedule root canal therapy, the residual dental roots with horn-shape root canal orifice were prepared. The specimens were assigned to three groups randomly. A group was rehabilitated by casting metal post-core crown. B group was rehabilitated by prefabricated fiber post and composite core crown. C group was rehabilitated by shapeable fiber-reinforced composite resin post and core crown. Loads were applied on the samples at 130 degree to the long axis of the root and measured with universal testing machine. The failing patterns were recorded.</p><p><b>RESULTS</b>There were no difference in fracture resistance among three groups (P>0.05). But the failing patterns were different. A group manifested root fracture and separation between cement and root dentin. B group mainly manifested separation between cement and post. C group manifested separation between cement and root dentin.</p><p><b>CONCLUSION</b>For restoration of residual dental root with horn-shaped orifice, fiber composite post-core crown has advantages in residual root protection and once more restoration.</p>