Joseph B. Dennison

Bio: Joseph B. Dennison is an academic researcher from University of Michigan. The author has contributed to research in topics: Dentin & Shrinkage. The author has an hindex of 35, co-authored 86 publications receiving 3699 citations. Previous affiliations of Joseph B. Dennison include University of Tehran.

Fracture resistance of endodontically treated teeth restored with composite posts.

Abstract: Statement of Problem. The most recent application of fiber-reinforced composites involves their use as post and core systems to restore endodontically treated teeth. Even though this last application has been advertised and used clinically by many dentists, there is very little information regarding the physical properties of these post systems. Purpose. The purpose of this study was to compare the effect of 3 fiber-reinforced composite post systems on the fracture resistance and mode of failure of endodontically treated teeth. Material and Methods. Ninety maxillary central incisors were divided into 8 experimental groups and 1 stainless steel (ParaPost) control group of 10 specimens each. Eighty teeth were assigned to 2 main experimental groups called "narrow" and "flared" canals. For the narrow canal group, post spaces were prepared with the corresponding reamer to restore the teeth with FibreKor, Luscent anchors, and Ribbond posts of 1.5 mm, 1.6 mm, and 2.0 mm in diameter, respectively. For the flared canals group thin-walled canals were simulated. Teeth for the flared canals were restored with the same posts but were cemented into tapered 2 mm wide canals created with a tapered diamond bur. Prefabricated posts (FibreKor and Luscent anchors) for narrow and flared canals were cemented with an autopolymerized resin cement and a flowable composite, respectively, whereas customized Ribbond posts were luted with a light-polymerized flowable composite for both canal types. An additional set of 20 Ribbond posts with coronal portions of variable size and shape referred to as "Ribbond nonstandardized" were also prepared and evaluated. Specimens were loaded to failure (kg) with a universal testing machine at a crosshead speed of 0.05 cm/min until failure occurred. Data were analyzed with analysis of variance and Student t tests ( P Results. Statistical analysis revealed no significant difference between flared and narrow canals in mean load to failure between the post systems except for the Ribbond posts ( P P Conclusion. Results from the study show that the load to failure of the stainless steel posts were significantly stronger than all the composite posts studied. However, the mode of failure or deflection of the fiber-reinforced composite posts is protective to the remaining tooth structure. (J Prosthet Dent 2003;89:360-7.)

Cytotoxic Interactive Effects of Dentin Bonding Components on Mouse Fibroblasts

Abstract: Previous studies have shown a wide range of pulpal reactions to dentin bonding systems and a poor correlation between in vitro and in vivo toxicity of dentin bonding agents. Because dentin bonding agents are composed of multiple components which may diffuse through dentin, we hypothesized that these components may cause cytotoxicity through interactive (synergistic) effects. We investigated the cytotoxicities of four dentin bonding components--HEMA, Bis-GMA, TEGDMA, and UDMA--and interactive effects for three binary combinations of the dentin bonding components--HEMA and Bis-GMA, Bis-GMA and TEGDMA, and TEGDMA and UDMA. Cytotoxicities to Balb/c 3T3 mouse fibroblasts were measured by the MTT assay. Concentrations which caused 50% toxicity compared with controls (TC50 values) were compared, and the interactive effects were determined by evaluation of the differences between observed and expected MTT activities of the cells. The ranks of toxicity of the dentin bonding components in terms of TC50 values were as follows: Bis-GMA > UDMA > TEGDMA >>> HEMA (least toxic) after 24- and 72-hour exposures. As binary combinations, the three combinations of dentin bonding components interacted in three ways--synergism, additivism, and antagonism--which were influenced by the concentrations of both components. The longer period of exposure resulted in a significant increase in the cytotoxicity of the dentin bonding components and combinations. The findings indicate that both exposure time and the interactions between the dentin bonding components may be important parameters in determining the cytotoxicity of dentin bonding agents in vivo.

A Clinical Evaluation of Chairside Lithium Disilicate CAD/CAM Crowns

Abstract: Background Developments in ceramic material science have led to improvements in the physical properties of modern ceramics, leading to a substantial increase in the clinical use of all-ceramic restorations. The authors evaluated the clinical performance of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent, Amherst, N.Y.) all-ceramic crowns. Methods The authors fabricated 62 lithium disilicate crowns with a chairside computer-aided design/computer-aided manufacturing (CAD/CAM) system (CEREC 3, Sirona Dental Systems, Charlotte, N.C.) and cemented them with two types of adhesive resin cements. Two examiners used modified U.S. Public Health Service criteria to evaluate the crowns at baseline, six months, one year and two years. Results There were no clinically identified cases of crown fracture or surface chipping. There was no reported sensitivity at one or two years with either cement. For margin discoloration, the percentage Alfa score was 86.9 percent for crowns cemented with a self-etching, dual-curing cement. All other percentage Alfa scores were greater than 92.0 percent, indicating no appreciable change in the crowns during the two-year study. Conclusions The results show that lithium disilicate crowns performed well after two years of clinical service. Clinical Implications Early results indicate that monolithic lithium disilicate CAD/CAM crowns may be an effective option for all-ceramic crowns.

Shear strength of core-veneer interface in bi-layered ceramics.

Abstract: Statement of problem Delamination of veneering porcelain from underlying ceramic substrates has been reported for all-ceramic restorations. Whether this phenomenon is an inherent weakness of the veneering porcelain due to a weak interface between the veneering and the core porcelains, or merely a fracture through the veneering porcelain itself, has not been explored. Purpose The purpose of this study was to investigate the strength of the substructure and veneering porcelain interface in all-ceramic systems. Methods The all-ceramic systems tested with their respective veneering porcelains were IPS-Empress2 with Eris (IE), Procera AllCeram with AllCeram (PA), Procera AllZircon with CZR (PZ), and DC-Zircon with Vita D (DC). The veneering porcelain recommended by the manufacturer for each material was fired to the ceramic core. A metal ceramic (MC) combination was tested as a control group. Sixty specimens, 12 for each system and control, were made from 1 master die. A cylinder of veneering porcelain 2.4 mm in diameter was applied using a specially designed aluminum split mold. After firing, the specimens were placed in a mounting jig and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (MPa) were analyzed with a 1-way analysis of variance and the Tukey test (α=.05). The failed specimens were examined microscopically at original magnification ×20 to classify the mode of failure as cohesive in the core, cohesive in the veneer, or adhesive at the interface. Results The mean shear strengths (±SD) in MPa were MC control 30.16 ± 5.88; IE bonded to Eris 30.86 ± 6.47; PZ bonded to CZR 28.03 ± 5.03; DC bonded to Vita D 27.90 ± 4.79; and PA bonded to AllCeram 22.40 ± 2.40. IE, PZ, and DC were not significantly different from the MC control. Microscopic examination showed that adhesive failure, or complete delamination, did not occur between the compatible ceramic core and veneering materials. Failure primarily occurred near the interface with residual veneering porcelain remaining on the core. IE with Eris exhibited cohesive failure in both the core and the veneer. Conclusion The bond strengths of 3 of the tested all-ceramic materials (IE, PZ, and DC) were not significantly different from the control (MC) group.

Polymerization Shrinkage and Depth of Cure of Bulk Fill Flowable Composite Resins

Abstract: Clinical Relevance Flowable composites had higher shrinkage than the nanohybrid restorative composite that was modified to have a flowable consistency during ultrasonic insertion. All materials tested had significantly less depth of cure than either manufacturers' claims or ISO 4049 scrape test results.

Resin-ceramic bonding: a review of the literature.

Abstract: Current ceramic materials offer preferred optical properties for highly esthetic restorations. The inherent brittleness of some ceramic materials, specific treatment modalities, and certain clinical situations require resin bonding of the completed ceramic restoration to the supporting tooth structures for long-term clinical success. This article presents a literature review on the resin bond to dental ceramics. A PubMed database search was conducted for in vitro studies pertaining to the resin bond to ceramic materials. The search was limited to peer-reviewed articles published in English between 1966 and 2001. Although the resin bond to silica-based ceramics is well researched and documented, few in vitro studies on the resin bond to high-strength ceramic materials were identified. Available data suggest that resin bonding to these materials is less predictable and requires substantially different bonding methods than to silica-based ceramics. Further in vitro studies, as well as controlled clinical trials, are needed.

Current ceramic materials and systems with clinical recommendations: A systematic review

Abstract: Statement of problem Developments in ceramic core materials such as lithium disilicate, aluminum oxide, and zirconium oxide have allowed more widespread application of all-ceramic restorations over the past 10 years. With a plethora of ceramic materials and systems currently available for use, an overview of the scientific literature on the efficacy of this treatment therapy is indicated. Purpose This article reviews the current literature covering all-ceramic materials and systems, with respect to survival, material properties, marginal and internal fit, cementation and bonding, and color and esthetics, and provides clinical recommendations for their use. Material and methods A comprehensive review of the literature was completed seeking evidence for the treatment of teeth with all-ceramic restorations. A search of English language peer-reviewed literature was undertaken using MEDLINE and PubMed with a focus on evidence-based research articles published between 1996 and 2006. A hand search of relevant dental journals was also completed. Randomized controlled trials, nonrandomized controlled studies, longitudinal experimental clinical studies, longitudinal prospective studies, and longitudinal retrospective studies were reviewed. The last search was conducted on June 12, 2007. Data supporting the clinical application of all-ceramic materials and systems was sought. Results The literature demonstrates that multiple all-ceramic materials and systems are currently available for clinical use, and there is not a single universal material or system for all clinical situations. The successful application is dependent upon the clinician to match the materials, manufacturing techniques, and cementation or bonding procedures, with the individual clinical situation. Conclusions Within the scope of this systematic review, there is no evidence to support the universal application of a single ceramic material and system for all clinical situations. Additional longitudinal clinical studies are required to advance the development of ceramic materials and systems.