Evaluating the relationship between tooth color and enamel thickness, using twin flash photography, cross-polarization photography, and spectrophotometer.

OBJECTIVES: To understand (a) the effects of labial enamel on tooth color (b) relationship of color data taken by nonpolarized (NP), cross-polarization photography (CP), and spectrophotometry (SP). MATERIALS AND METHODS: Fifty extracted human maxillary incisors were coated with resin on their palatal surfaces. Their color was measured with NP, CP, and SP and their dimensions were scanned by an intraoral scanner. The labial enamel was removed using a modified selective enamel demineralization technique. Tooth dimensions and color were recorded again. The differences in the labial enamel thickness (ΔT) and color (∆E*00 and ∆L*, ∆a*, ∆b*) were statistically analyzed with the Pearson correlation coefficient and simple linear regression. RESULTS: In CP and SP methods, ΔT and ∆E*00 were weakly to moderately positively correlated (r = .38 and .27). In NP, CP, and SP methods, ∆T and ∆b* are weakly positively correlated (r = .27, .27 and .29). The color data of three measuring methods were highly positively correlated (r > .8). A linear relationship between ∆E*00 and ∆T were found (CP and SP groups). CONCLUSIONS: (a) Thicker labial enamel has a greater impact on tooth color. (b) Reducing labial enamel thickness shifts the tooth color toward yellow. (c) Tooth color measured from the three methods were highly correlated. CLINICAL SIGNIFICANCE: Knowing the relationship between enamel thickness and tooth color, a clinician can better predict the stump shade before tooth preparation. Due to the highly correlated measuring outcomes, it is reasonable to combine these three methods during shade matching.

Comparing the bond strength of fiber post cementation in the root canal using pre- and co-curing procedures with the same self-etching bonding system.

Background/purpose: Self-etching bonding systems are widely used in fiber post cementation. However, no clear guidelines are established for choosing pre- or co-curing procedures. We investigated the bond strength of fiber post cementation using pre-/co-curing methods in self-etching bonding systems and compared them with those of a self-adhesive system. Materials and methods: Post spaces were prepared in 30 single-rooted premolars/canines, and the fiber posts were cemented in three ways (10 specimens per group): using a self-etching bonding system with either a pre-curing or simultaneous co-curing procedure (RelyX™ Ultimate; groups SE-pre and SE-co, respectively) and using a self-adhesive system (RelyX™ Unicem 2, group SA). Each specimen was embedded and sliced perpendicularly to the long axis into three 2.5-mm-thick sections. Microphotographs of the coronal and apical surfaces of each section were acquired, and push-out tests (1 mm/min) were performed. One-way analysis of variance was conducted on the data, followed by Tukey's honestly significant difference post hoc test. Results: The bond strength in the whole root was not significantly different among the three groups. When independently evaluating each portion, group SE-co exhibited significantly lower coronal bond strength. The bond strength varied among root regions only in group SE-pre; the apical region had a significantly lower value. Conclusion: No cementation method is superior in all portions. Regarding pre-curing methods, clinicians must caution the fit between the post and post space, which may be affected by the pre-polymerized bond layer. The co-curing method used in a larger coronal cement space contributes to the poor bond strength.

Impacts of 3 Different Endodontic Access Cavity Designs on Dentin Removal and Point of Entry in 3-dimensional Digital Models.

INTRODUCTION: The purpose of this study was to evaluate the tooth structure theoretically required to be removed in the coronal and cervical regions to accomplish 3 different endodontic access preparations in a novel digital model. The deviation of the center of access cavity from the central fossa will also be measured and compared among the 3 endodontic cavity designs, which in turn may serve as suggested points of entry for different access openings. METHODS: Twenty-one maxillary molars and 15 mandibular molars were selected and 3-dimensionally imaged with cone-beam computed tomographic imaging. Three-dimensional (3D) volume reconstructions were made and converted into stereolithography files. Digital access cavity preparation was performed on each 3D reconstruction model with the 3 most commonly used endodontic access preparations: minimally invasive (MI), modified straight-line (MS), and traditional straight-line (TS) techniques. After the access cavity outlines were determined, digital sectioning of each reconstructed 3D tooth model was performed orthogonal to the long axis of the tooth at 3 levels: (1) passing through the central fossa, (2) 1.5 mm apical to the central fossa, and (3) 2 mm apical to the cementoenamel junction. The linear distance from the centroid of the access opening to the central fossa was measured to calculate the point of entry, and the amount of tooth structure removal at the pericervical area was measured to calculate the theoretically minimum amount of linear dentin removal required. Two-way repeated measures analysis of variance was performed for the interactions between different access designs and the amount of cervical dentin removal. Other data were statistically analyzed with 1-way repeated measures analysis of variance. The Tukey post hoc test was used for multiple comparisons. Significance was set at .05. RESULTS: The amount of deviation of the center of the access cavity from the central fossa in all test groups was less than 1 mm. The dimensions of access openings differed significantly among the 3 access forms (TS > MS > MI, P < .0001). The amount of required cervical dentin removal was the greatest in the TS method followed by the MS and MI methods (P < .0001). CONCLUSIONS: The central fossa could serve as good starting points in all access preparations in both maxillary and mandibular molars. Dentin removal in the coronal and cervical regions was the greatest in the TS design followed by the MS and MI designs. When comparing different canals in the same access form, less cervical dentin was sacrificed in the palatal canals of maxillary molars and the distal canals of mandibular molars.