Faculty Bibliography

Purpose: To investigate the reliability and failure modes of indirect composites as single-unit implant crowns. Materials and Methods: Thirty-eight custom-milled titanium alloy locking-taper abutments were divided into two groups (n = 19 each), and crown build-up of a mandibular molar was accomplished using two indirect composite systems (Ceramage, Shofu, Kyoto, Japan; Diamond Crown, DRM, Branford, CT). Three crowns of each material were loaded until failure for determination of the step-stress profiles. Reliability testing started at a load 30% of the mean load to failure and used three profiles with increasing fatigue loading (step stress). Weibull curves with 300 N stress and 90% confidence intervals were calculated and plotted using a power-law relationship. Weibull modulus 'Beta' and characteristic strength 'Eta' were identified, and a contour plot was used (Beta vs. Eta) for examining differences between groups. Specimens were inspected in polarized light and scanning electron microscope for fracture analysis. Results: Use level Weibull probability showed fatigue being a damage factor only for the Ceramage group (beta= 3.39) but not for the Diamond Crown group (beta= 0.40). Overlap in the confidence bounds resulted in no statistical difference. Irrespective of composite system, fracture initiated in the region immediately below the contact between the indenter and the cusp, with the crack propagating toward the margins of cohesive failure. Conclusions: No significant differences were observed in life and Weibull probability calculations for Ceramage and Diamond Crown veneered onto Ti alloy abutments. Failure modes comprised composite veneer chippings

BACKGROUND: The authors analyzed the in vitro and in vivo performance of lithium disilicate glass-ceramic (LDGC) restorations and yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) (that is, zirconium oxide) restorations with regard to reliability, clinical performance and abrasion resistance. METHODS: In the in vitro study, four authors subjected samples of LDGC, Y-TZP and metal-ceramic crowns to step-stress fatigue testing. Four investigators assessed the in vivo clinical performance of LDGC and zirconium oxide-based restorations at four and seven years, respectively. In addition, one author conducted a randomized, controlled clinical trial to analyze the volumetric loss of enamel and ceramic antagonist surfaces. RESULTS: The LDGC crowns exhibited the highest fatigue load-to-failure values in the in vitro analysis. The results of the in vivo assessment showed that the clinical performance of the LDGC restorations at four years was comparable to that of the zirconium oxide-based crowns at seven years. The results of the in vivo, randomized, controlled clinical trial showed that LDGC crowns were not only resistant to wear, but also were wear friendly to enamel antagonist surfaces. CONCLUSIONS: The LDGC crowns in the in vitro and in vivo studies exhibited high durability, and they were wear friendly to opposing natural dentition. CLINICAL IMPLICATIONS: LDGC and zirconium oxide-based crowns are a clinically acceptable means of treating teeth that require full-coverage restorations. In addition, LDGC materials exhibit excellent clinical performance, as well as demonstrate acceptable abrasion compatibility with the opposing natural dentition

OBJECTIVE: This study tested the hypothesis that bond strength of total- and self-etching adhesive systems to dentine is not affected by the presence of remnants from either eugenol-containing (EC) or eugenol-free (EF) temporary cements after standardized cleaning procedures. METHODS: Thirty non-carious human third molars were polished flat to expose dentine surfaces. Provisional acrylic plates were fabricated and cemented either with EC, EF or no temporary cements. All specimens were incubated for 7 days in water at 37 degrees C. The restorations were then taken out and the remnants of temporary cements were mechanically removed with a dental instrument. The dentine surfaces were cleaned with pumice and treated with either total-etching (TE) or self-etching (SE) dental adhesive systems. Atomic force microscopy was used to examine the presence of remnants of temporary cements before and after dentine cleaning procedures. Composite resin build-ups were fabricated and cemented to the bonded dentine surfaces with a resin luting cement. The specimens were then sectioned to obtain 0.9mm(2) beams for microtensile bond strength testing. Fractographic analysis was performed by optical and scanning electron microscopy. RESULTS: ANOVA showed lower mean microtensile bond strength in groups of specimens treated with EC temporary cement than in groups treated with either no cement or an EF cement (p<0.05). Mean microtensile bond strength was lower in groups employing the SE rather than the TE adhesive system (p<0.001). SE samples were also more likely to fail during initial processing of the samples. There was no evidence of interaction between cement and adhesive system effects on tensile strength. Fractographic analysis indicated different primary failure modes for SE and TE bonding systems, at the dentine-adhesive interface and at the resin cement-resin composite interface, respectively. CONCLUSION: The use of eugenol-containing temporary cements prior to indirect bonding restorations reduce, to a statistically similar extent, the bond strength of both total- and self-etching adhesive systems to dentine

Freitas AC Jr, Bonfante EA, Rocha EP, Silva NRFA, Marotta L, Coelho PG. Effect of implant connection and restoration design (screwed vs. cemented) in reliability and failure modes of anterior crowns. Eur J Oral Sci 2011; 119: 323-330. (c) 2011 Eur J Oral Sci The mechanical performance of cemented or screw-retained implant-supported crowns with an internal or external configuration is yet to be understood. This in vitro study evaluated the effect of screw-retained and cement-retained prostheses on internal and external implant-abutment connections. Thereby, the reliability and failure modes of crowns were investigated. Eighty-four implants (Emfils; Colosso Evolution system) were divided into four groups (n=21 each): screw-retained and internal connection (Si), screw-retained and external connection (Se), cement-retained and internal connection (Ci), and cement-retained and external connection (Ce). Ti-6Al-4V abutments were torqued (30 Ncm) to the implants, and maxillary central incisor metal crowns were torqued (30 Ncm) or cemented (Rely X Unicem; 3M-ESPE) and subjected to accelerated life-testing in water. Use-level probability Weibull curves and reliability for 50,000 cycles at 150 N were calculated. The beta values for Si (1.72), Se (1.50), Ci (1.34), and Ce (1.77) groups indicated that fatigue/damage accumulation accelerated their failure. The Ci group presented the highest reliability, the Se group presented the lowest reliability, and Si and Ce groups presented intermediate reliability. Screw-retained restorations presented mainly abutment fracture. Cement-retained restorations resulted in failures of the screw in the Ce group, but implant/screw fracture in the Ci group

Several all-ceramic systems have been developed in dentistry to meet the increased expectations of patients and dentists for highly aesthetic, biocompatible, and long-lasting restorations. However, early bulk fractures or chippings have led the research community to investigate the mechanical performance of the all-ceramic systems. This overview explores the current knowledge of monolithic and bilayer dental all-ceramic systems, addressing composition and processing mechanisms, laboratory and clinical performance, and possible future trends for all-ceramic materials

The reliability and failure modes of molar crowns supported by three different implant-supported designs were tested according to the following groups: group 1, one standard-diameter implant (3.75 mm); group 2, one narrow-diameter implant (3 mm); and group 3, two narrow-diameter implants (3 mm). Loads were applied as mouth-motion cycles using a step-stress accelerated life-testing method. ? values for groups 1 and 3 (1.57 and 2.48, respectively) indicated that fatigue accelerated the failure of both groups, but not for group 2 (0.39). Abutment screw failure was the chief failure mode. Strength and reliability were significantly higher for groups 1 and 3 compared to group 2

Cancers often cause excruciating pain and rapid weight loss, severely reducing quality of life in cancer patients. Cancer-induced pain and cachexia are often studied and treated independently, although both symptoms are strongly linked with chronic inflammation and sustained production of proinflammatory cytokines. Because nerve growth factor (NGF) plays a cardinal role in inflammation and pain, and because it interacts with multiple proinflammatory cytokines, we hypothesized that NGF acts as a key endogenous molecule involved in the orchestration of cancer-related inflammation. NGF might be a molecule common to the mechanisms responsible for clinically distinctive cancer symptoms such as pain and cachexia as well as cancer progression. Here we reported that NGF was highly elevated in human oral squamous cell carcinoma tumors and cell cultures. Using two validated mouse cancer models, we further showed that NGF blockade decreased tumor proliferation, nociception, and weight loss by orchestrating proinflammatory cytokines and leptin production. NGF blockade also decreased expression levels of nociceptive receptors TRPV1, TRPA1, and PAR-2. Together, these results identified NGF as a common link among proliferation, pain, and cachexia in oral cancer. Anti-NGF could be an important mechanism-based therapy for oral cancer and its related symptoms