Dentin Exposure after Tooth Preparation for Laminate Veneers: A Microscopical Analysis to Evaluate the Influence of Operators' Expertise.

Background: To assess the quantity of dentin exposure detected by 3 operators with different clinical expertise for 2 designs of tooth preparation for laminate veneers: window (WI) and butt joint (BJ). Methods: 20 intact maxillary central incisors were collected and then prepared for laminate veneers to a depth of 0.6 mm, with a cervical mini-chamfer finish line of 0.3 mm. Each prepared tooth was analyzed by 3 operators with different expertise: undergraduate student (ST), general practitioner (GP), and prosthodontist (PR), at sight under magnification. Besides descriptive statistics (CI 95%), 2-way ANOVA and Games−Howell tests were used to analyze differences among groups (α = 0.05). Results: The means of percentage and area of detected dentin exposure were WI = 30.48%, 21.57 mm2; BJ = 30.99%, 21.97 mm2; ST/WI = 22.82%, 16.44 mm2; GP/WI = 58.05%, 40.64 mm2; PR/WI = 10.55%, 7.63 mm2; ST/BJ = 28.99%, 20.83 mm2; GP/BJ = 40.56%, 28.32 mm2; PR/BJ = 23.42%, 16.75 mm2. Significant differences were found between ST/WI vs. GP/WI (p = 0.005) and GP/WI vs. PR/WI (p < 0.001). Conclusions: There was no difference in detection of exposed dentin among operators with different expertise for BJ preparation, whereas differences were found between the general practitioner and the other 2 operators in WI. Moreover, the quantity of exposed dentin was not related to different tooth preparation designs.

Polyacrylic resins regulate transcriptional control of interleukin-6, gp80, and gp130 genes in human gingival fibroblasts.

Studies have failed to identify the molecular mechanisms that regulate the genotoxic and cytotoxic effects of methacrylate resins, which are important in the biocompatibility of dental materials. Interleukin (IL)-6 has a crucial role in the control of acute-phase protein response during inflammation. In humans, the synthesis and release of two major acute-phase proteins, C-reactive protein and serum amyloid A, are regulated by IL-6. This study focused on IL-6 and activation of its receptors gp80 and gp130 in human gingival fibroblasts in order to assess the effects of the commercial acid resins Jet Kit, Unifast, and Duralay on control of inflammation.

Evaluating residual dentin thickness following various mandibular anterior tooth preparations for zirconia full-coverage single crowns: an in vitro analysis.

The objective of this study was to evaluate the residual dentin thickness (RDT) after different tooth preparations. Ninety mandibular anterior teeth were divided into three groups: central incisors, lateral incisors, and canines. Specimens were prepared for single-crown coverage with shoulder, slight chamfer, and knife-edge finish lines. Specimens were sectioned and divided into four subgroups according to measurement areas: (1) buccal, (2) distal, (3) lingual, and (4) mesial. The RDT was analyzed statistically by means of one-way analysis of variance and Tukey post hoc test (P = .05). Significant differences were found for shoulder but not for slight chamfer and knife-edge finish lines. The interproximal areas wound up being critical due to thin RDT, potentially interfering with the structural and biologic integrity of teeth.

Proliferation and adhesion capability of human gingival fibroblasts onto zirconia, lithium disilicate and feldspathic veneering ceramic in vitro.

Human gingival fibroblasts (HGFs) were cultured onto CAD/CAM zirconia (Group A), CAD/CAM zirconia after polishing (Group B), CAD/CAM lithium disilicate after polishing (Group C), and feldspathic ceramic (Group D) to evaluate their proliferation and adhesion potential. After 3 h, HGF adhesion was similar in all groups. Later, HGFs closely adhered to surfaces, particularly onto groups B, C and D, acquiring an elongated shape. Proliferation assay showed no differences in cell viability among the groups after 24 h, while significant increase was shown after 72 h in Groups B and C. After 24 h, similar Collagen I levels were found in all groups, while after 72 h Groups B and C revealed a deep reduction in respect to the 24 h level. In vitro, HGF behavior may reflect variability in soft tissue response to different surface materials for prosthetic restorations, and support that polished zirconia is able to achieve a better integration in vivo in respect to the other materials.

Effect of fiber post length and bone level on the fracture resistance of endodontically treated teeth.

This study evaluated the combined influence of horizontal bone loss and post length on the fracture resistance of endodontically treated teeth (ETT). Twenty premolars were endodontically treated and divided into four groups of two different post insertion depths (5 and 7 mm) and two alveolar bone levels from cement-enamel junction (2 and 5 mm). After posts (RelyX Fiber Post) were cemented using a self-adhesive resin cement (RelyX Unicem Aplicap) and cores were built up (Filtek Supreme XT Universal Restorative, 3M ESPE, USA), cobalt-chrome copings were luted to each prepared tooth. All specimens were subjected to thermocycling and mechanical loading until fracture occurred. Mean fracture loads (N) were 1,445±342.2 (2 mm bone level/5 mm depth), 1,516±413.4 (2 mm bone level/7 mm depth), 1,736.4±1113.8 (5 mm bone level/5 mm depth), 1,038.6±600.2 (5 mm bone level/7 mm depth). No significant differences were found. Therefore, bone level and post length did not seem to influence the fracture resistance of ETT.

In vitro analysis of residual tooth structure of maxillary anterior teeth after different prosthetic finish line preparations for full-coverage single crowns.

To evaluate residual dentin thickness (RDT) after different tooth preparations, 90 sound maxillary anterior teeth were selected and divided into 3 groups according to tooth type (n = 30), namely, maxillary central incisors, maxillary lateral incisors, and maxillary canines. In each group, specimens were randomly divided and prepared for single-crown coverage with shoulder (SHO, n = 10, control), slight chamfer (CHA, n = 10), and knife-edge (KNE, n = 10) finish lines. After tooth preparation, specimens were sectioned and divided into 4 subgroups (buccal, distal, palatal, and mesial) according to measurement area. RDT values were compared by using one-way ANOVA and Tukey's post hoc test (P = 0.05). Significant differences were found between SHO and the other two groups (P < 0.05) but not between CHA and KNE (P > 0.05). SHO was significantly more aggressive than CHA and KNE, which were comparable. Interproximal areas became critical due to thin RDT, which could potentially compromise the structural and biological integrity of teeth. The choice of finish line should be guided by careful clinical evaluation.

SEM evaluation of human gingival fibroblasts growth onto CAD/CAM zirconia and veneering ceramic for zirconia.

AIM: To evaluate the growth of Human Gingival Fibroblasts (HGFs) cultured onto sample discs of CAD/CAM zirconia and veneering ceramic for zirconia by means of Scanning Electron Microscope (SEM) analysis at different experimental times. METHODS: A total of 26 experimental discs, divided into 2 groups, were used: Group A) CAD/CAM zirconia (3Y-TZP) discs (n=13); Group B) veneering ceramic for zirconia discs (n=13). HGFs were obtained from human gingival biopsies, isolated and placed in culture plates. Subsequently, cells were seeded on experimental discs at 7,5×10(3)/cm(2) concentration and cultured for a total of 7 days. Discs were processed for SEM observation at 3h, 24h, 72h and 7 days. RESULTS: In Group A, after 3h, HGFs were adherent to the surface and showed a flattened profile. The disc surface covered by HGFs resulted to be wider in Group A than in Group B samples. At SEM observation, after 24h and 72h, differences in cell attachment were slightly noticeable between the groups, with an evident flattening of HGFs on both surfaces. All differences between Group A and group B became less significant after 7 days of culture in vitro. CONCLUSIONS: SEM analysis of HGFs showed differences in terms of cell adhesion and proliferation, especially in the early hours of culture. Results showed a better adhesion and cell growth in Group A than in Group B, especially up to 72h in vitro. Differences decreased after 7 days, probably because of the rougher surface of CAD/CAM zirconia, promoting better cell adhesion, compared to the smoother surface of veneering ceramic.

Effect of the length of glass fiber posts on the fracture resistance of restored maxillary central incisors.

PURPOSE: To evaluate the influence of post length insertion on the fracture resistance of directly restored endodontically treated teeth. METHODS: 30 maxillary central incisors were restored with glass fiber posts and composite cores to produce groups with post lengths of (1) 5 mm, (2) 7 mm, and (3) 9 m. Specimens were loaded at 130 degrees (Instron). Fracture strengths were analyzed with the Kolmogorov-Smirnov Test to verify the normality of the data distribution and with ANOVA and Tukey's post hoc test at P < 0.05. Fracture patterns (restorable or unrestorable) were analyzed (Pearson's Chi-square test). RESULTS: The average fracture resistance was: Group 1 = 366.4 N, Group 2 = 507.4 N and Group 3 = 509.9 N. No significant difference was found among the three groups for fracture resistance or for failure mode. The insertion length did not influence the fracture pattern; more restorable fractures were detected.