Journal of Esthetic and Restorative Dentistry

This review examines the fundamental processes responsible for the aging mechanisms involved in the degradation of resin‐bonded interfaces, as well as some potential approaches to prevent and counteract this degradation. Current research in several research centers aims at increasing the resin–dentin bond durability. The hydrophilic and acidic characteristics of current dentin adhesives have made hybrid layers highly prone to water sorption. This, in turn, causes polymer degradation and results in decreased resin–dentin bond strength over time. These unstable polymers inside the hybrid layer may result in denuded collagen fibers, which become vulnerable to mechanical and hydrolytical fatigue, as well as degradation by host‐derived proteases with collagenolytic activity. These enzymes, such as matrix metalloproteinases and cysteine cathepsins, have a crucial role in the degradation of typeIcollagen, the organic component of the hybrid layer. This review will also describe several methods that have been recently advocated to silent the activity of these endogenous proteases.

The current challenge in adhesive dentistry is to develop dentin bonding systems that will reproducibly achieve high bond strengths similar to those obtained between resins and acid‐etched enamel. Some of the limitations of dentin as a bonding substrate are that it changes its structure as it is prepared deeper, it is difficult to dry, and its smear layer is weak. Further, it is difficult to avoid contaminating proximal boxes with blood. Such contamination lowers dentin bond strengths to very low values. Decontamination of such dentin must be done prior to resin placement. The forces of polymerization contraction depend, in part, on the shape of cavities and how they are filled. Bulk filling of class I cavities can lead to conditions in which the forces of polymerization contraction exceed dentin bond strength with some materials and locations. The future development of resin systems that do not shrink on polymerization would eliminate many current problems in adhesive dentistry.

Purpose: Since the introduction of densely sintered alumina ceramic material in prosthetic dentistry for the fabrication of all‐ceramic crowns, no scientific data have been presented on the color of these restorations in combination with different restorative materials. The purpose of this in vitro study was to evaluate the influence of five different restorative materials used for implant abutments or posts and cores on the color of veneered densely sintered alumina.

Materials and Methods: Sixty discs, 0.6 mm in thickness and 10 mm in diameter, were made out of densely sintered alumina ceramic material (Procera®, Nobel Biocare, Gothenburg, Sweden) and veneered using feldspathic porcelain (AllCeram®, Ducera, Rosbach, Germany) for a total thickness of 2 mm. Ten of the discs were evaluated colorimetrically using the CIE, L*, a*, b* system (control group). In addition, 50 discs, 3 mm in thickness and identical diameter, were fabricated using the following restorative materials (five different materials used on 10 specimens each): (1) high‐precious gold alloy, (2) aluminum‐oxide ceramic material, (3) titanium metal alloy, (4) yttrium‐stabilized zirconium dioxide ceramic material, and (5) glass‐ceramic material. The 50 veneered densely sintered alumina specimens were bonded to the 50 restorative specimens using an autopolymerizing luting composite. L*, a*, b* color coordinates were measured 10 times for each veneered densely sintered alumina specimen. Color differences were calculated using the equation ΔE = [(Δ*)²+ (Δa*)²+ (Δb*)²]®. ΔE values correspond to differences between the control group and each of the five materials groups.

Results: Mean color differences (ΔE) and SDs for each group were as follows: ΔE (1) = 1.42 ± 0.5, ΔE (2) = 1.53 ± 0.5, ΔE (3) = 1.55 ± 0.4, ΔE (4) = 1.95 ± 0.5, ΔE (5) = 1.23 ± 0.3. All restorative materials induced changes to the densely sintered alumina color relative to the original color. One‐way analysis of variance (ANOVA) tests showed statistically significant differences in ΔE between the groups; however, the Student‐Newman‐Keuls test revealed that the only statistically significant difference was between groups 4 and 5. Color differences between the groups were not visually perceivable (ΔE < 2).

CLINICAL SIGNIFICANCE

Within the limits of this in vitro study, veneered densely sintered alumina adhesively fixed with dentine‐like cement, successfully masks the shade of different metal or ceramic restorative materials.

Abstract: Older adults present special problems for the dentist trying to establish or reestablish esthetics. Periodontal diseases are of concern for this population since tooth loss from these widespread problems increases with age. In general, this loss occurs because of increased exposure time to pathogenic bacteria, not some change inherent in the body brought on by the aging process. The profession has begun to place more emphasis on systemic risk factors and their role in modifying periodontal inflammation. The current thinking is that bacteria are necessary to initiate and sustain periodontal diseases, but the clinical manifestation is dictated to a significant extent by systemic factors. Smoking, diabetes, and being positive for the interleukin‐1 genotype predispose the patient to developing more severe disease. For those older adults who lose teeth, dental implants have emerged as reliable replacements, and concerns about placing these devices in patients who have lost teeth as a result of periodontitis appear to be largely unfounded.