Ricardo Walter

Effects of natural cross-linkers on the stability of dentin collagen and the inhibition of root caries in vitro.

Purpose: To evaluate the effects of dentin collagen modifications induced by various cross-linkers on the stability of collagen matrix and the inhibition of root caries. Materials and Methods: The following cross-linkers were tested: 5% glutaraldehyde (GA), 0.5% proanthocyanidin (PA), 0.625% genipin (GE). In the first experiment, cross-linker-treated demineralized human root dentin was digested with bacterial collagenase, centrifuged, and the supernatants were subjected to amino acid analysis to determine collagen content. The residues were analyzed by SDS-PAGE and hydroxyproline analysis. In the second experiment, bovine root surfaces were conditioned with phosphoric acid, treated with the cross-linkers, incubated with Streptococcus mutans and Lactobacillus acidophilus for 1 week and the root caries inhibition was evaluated with confocal microscopy. Lastly, the ability of the bacteria to colonize the root surface was evaluated. In this experiment slabs of bovine root were treated with the cross-linkers and incubated in a suspension of S. mutans and L. acidophilus. The slabs were washed, resuspended in water, glucose was added, and the pH measured. Results: While all collagen was digested with collagenase in the control groups, only a small proportion was solubilized in the GA-, PA-, and GE-treated groups. The root caries was significantly inhibited by treatment with PA or GA. Drops in pH in the cross-linker-treated groups were essentially the same as in the untreated group. Conclusion: Naturally occurring cross-linkers, especially PA, could be used to modify root dentin collagen to efficiently stabilize collagen and to increase its resistance against caries.

Enamel and Dentin Bond Strengths of a New Self‐Etch Adhesive System

UNLABELLED statement of problem:  Self-etch adhesives typically are mildly acidic and therefore less effective than etch-and-rinse adhesives for bonding to enamel. PURPOSE   The purpose of this study was to evaluate the enamel and dentin shear bond strengths of a new two-step self-etch adhesive system, OptiBond XTR (Kerr Corporation, Orange, CA, USA). MATERIALS AND METHODS   The labial surfaces of 80 bovine teeth were ground to create flat, 600-grit enamel or dentin surfaces. Composite was bonded to enamel or dentin using the new two-step self-etch system or a three-step etch-and-rinse (OptiBond FL, Kerr), two-step self-etch (Clearfil SE Bond, Kuraray America, Houston, TX, USA), or one-step self-etch adhesive (Xeno IV, Dentsply Caulk, Milford, DE, USA). Following storage in water for 24 hours, shear bond strengths were determined using a universal testing machine. The enamel and dentin data sets were subjected to separate analysis of variance and Tukeys tests. Scanning electron microscopy was used to evaluate the effects of each system on enamel. RESULTS   Mean shear bond strengths to enamel ranged from 18.1 MPa for Xeno IV to 41.0 MPa for OptiBond FL. On dentin, the means ranged from 33.3 MPa for OptiBond FL to 47.1 MPa for Clearfil SE Bond. OptiBond XTR performed as well as Clearfil SE Bond on dentin and as well as OptiBond FL on enamel. Field emission scanning electron microscope revealed that OptiBond XTR produced an enamel etch pattern that was less defined than that of OptiBond FL (37.5% phosphoric acid) but more defined than that of Clearfil SE Bond or Xeno IV. CONCLUSION   The new two-step self-etch adhesive system formed excellent bonds to enamel and dentin in vitro. CLINICAL SIGNIFICANCE OptiBond XTR, a new two-step self-etch adhesive system, is a promising material for bonding to enamel as well as to dentin.

Antibacterial surface properties of fluoride-containing resin-based sealants.

OBJECTIVES The aim of the present study was to determine the antibacterial properties of three resin-based pit and fissure sealant products: Clinpro (3M ESPE), Embrace (Pulpdent), and UltraSeal XT plus (Ultradent). METHODS The antibacterial effects of the sealants were tested in both an agar diffusion assay and a planktonic growth inhibition assay using Streptococcus mutans and Lactobacillus acidophilus. The materials were applied to paper and enamel disks in the former and on the side walls of 96-well microtiter plates on the latter. RESULTS All materials showed either diffusible or contact antibacterial effects in the agar diffusion assays. The effect was diminished when enamel disks were used as substrate. In the planktonic growth inhibition assay, Clinpro had its effect reduced, but retained activity against both bacteria over time. L. acidophilus was more sensitive than S. mutans to UltraSeal. Embrace retained antibacterial activity against both bacteria over time. CONCLUSIONS Within the limitations of this in vitro study it can be concluded that all materials are capable of contact inhibition of L. acidophilus and S. mutans growth. Embrace has the longer lasting antibacterial activity when in solution, especially against S. mutans.

In Vitro Inhibition of Bacterial Growth Using Different Dental Adhesive Systems

OBJECTIVES This study evaluated the antibacterial potential of four different adhesive systems. METHODS & MATERIALS Gluma Comfort Bond + Desensitizer, Gluma Comfort Bond, iBond and One-Up Bond F were tested against Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus and Actinomyces viscosus. The inhibition of growth by calibrated preparations was quantified by the measurement of zones of inhibition on bacterial lawns. Bactericidal activity was determined as reductions in recoverable colony-forming units in bacterial suspensions exposed to test preparations. RESULTS All the preparations exhibited detectable zones of inhibition for all target bacteria through six months. When the bactericidal action was evaluated, all the materials were able to kill all the tested bacteria when tested immediately after polymerization. After one week of aging, iBond was the only material that continued to kill all of the test strains.

Fracture of layered zirconia restorations at 5 years: A dental laboratory survey

Statement of problem. The use of ceramic restorations has significantly increased in recent years because of their esthetic properties and the high cost of noble metals. However, given the lack of long‐term clinical trials and the limitations of in vitro studies, the durability of ceramic restorations is still questionable. Purpose. The purpose of this retrospective study was to determine the fracture rate of layered zirconia restorations at up to 5 years of clinical performance by using a dental laboratory survey model. Material and methods. Data up to 5 years were collected from 2 commercial dental laboratories. Layered zirconia restorations returned to the laboratory for remaking because of failure (fracture) were identified and included. Restorations were categorized as anterior or posterior. Each category was further divided into complete coverage single crowns (SCs) and multiple unit fixed dental prostheses (FDPs). Fracture rates were compared and analyzed using the chi‐square test (&agr;=.05). Results. A total of 31 594 restoration records were reviewed and included 13 419 anterior restorations (10 134 SCs and 3285 FDPs) and 18 175 posterior restorations (12 810 SCs and 5365 FDPs). The overall fracture rate up to 5 years for all restorations (anterior and posterior) was 3.31%. The fracture rates for anterior restorations were less than for posterior restorations. The fracture rates for anterior SCs were approximately half those of the posterior SC fracture rate, and the combined fracture rate (anterior and posterior) was 3.25%. For FDPs, anterior FDPs fractured at a rate similar to that of posterior FDPs. The combined fracture rate (anterior and posterior FDPs) was 3.47%. Conclusions. Layered zirconia restorations displayed relatively low fracture rates in the relatively short term of 5 years.

Bulk-Fill Flowable Composite Resins

Recent developed flowable composite resins have been marketed for bulk filling of preparations or replacement of dentin in a single increment. The obvious attraction of these materials-quicker placement of restorations-has rapidly made them very popular despite the limited in vitro data and lack of clinical studies. This Critical Appraisal will review some of the available in vitro literature on the topic and summarize the available knowledge in this new category of restorative materials.

Safety and efficacy of a high-adhesion whitening strip under extended wear regimen

OBJECTIVES This randomized, parallel group, single centre clinical trial was conducted to evaluate the safety and compare the whitening efficacy for an extended wear of an experimental 9.5% H₂O₂ high-adhesion whitening strip, relative to a marketed 10% H₂O₂ control strip. METHODS Twenty-nine eligible adult volunteers were randomly assigned to either a treatment series with an experimental 9.5% H₂O₂ high-adhesion whitening strip at home for 2h, once a day, for 8 days; or a marketed 10% H₂O₂ whitening strip for 30 min, on a similar daily regimen. Tooth color/whitening progression was recorded under standardized lighting conditions at baseline, day 3, day 5, and day 9, via digital imaging. Outcomes were reported using the CIELAB system. Usage safety was also assessed at each follow-up visit. Whitening efficacy for each group was investigated using a paired-difference t-test. The treatment groups were compared among each other using the analysis of covariance, with the baseline value and age as the covariates. RESULTS Both treatment groups demonstrated statistically significant mean color improvement from baseline for b* (yellow ness) and L* (lightness) at each post-baseline visit. In addition, the 2-h high-adhesion strips demonstrated significantly greater improvement in b* and L* relative to the 30-min strip group at each follow-up visit. CONCLUSIONS The 2-h regimen for the 9.5% H₂O₂ high-adhesion whitening strip was more efficient for tooth whitening than the 30-min regimen of 10% H₂O₂ whitening strip. Both treatments were well tolerated and the use of the test products during the study time frame was considered safe. CLINICAL RELEVANCE Extending the daily wear time of whitening strips can improve the efficacy of the treatment and ultimately shorten the length of the treatment without any significant adverse effects.

Self-interrupted synthesis of sterically hindered aliphatic polyamide dendrimers

Significance Hydrolytically and enzymatically stable nanoscale synthetic constructs, with well-defined structures that exhibit antimicrobial activity, offer exciting possibilities for diverse applications in the emerging field of nanomedicine. Herein, we demonstrate that it is the core conformation, rather than periodicity, that ultimately controls the synthesis of sterically hindered aliphatic polyamide dendrimers. The latter self-interrupt at a predictable low generation number due to backfolding of their peripheral groups, which in turn leads to well-defined nanoarchitectures. 2,2-Bis(azidomethyl)propionic acid was prepared in four steps and 85% yield from the commercially available 2,2-bis(hydroxymethyl)propionic acid and used as the starting building block for the divergent, convergent, and double-stage convergent–divergent iterative methods for the synthesis of dendrimers and dendrons containing ethylenediamine (EDA), piperazine (PPZ), and methyl 2,2-bis(aminomethyl)propionate (COOMe) cores. These cores have the same multiplicity but different conformations. A diversity of synthetic methods were used for the synthesis of dendrimers and dendrons. Regardless of the method used, a self-interruption of the synthesis was observed at generation 4 for the dendrimer with an EDA core and at generation 5 for the one with a PPZ core, whereas for the COOMe core, self-interruption was observed at generation 6 dendron, which is equivalent to generation 5 dendrimer. Molecular modeling and molecular-dynamics simulations demonstrated that the observed self-interruption is determined by the backfolding of the azide groups at the periphery of the dendrimer. The latter conformation inhibits completely the heterogeneous hydrogenation of the azide groups catalyzed by 10% Pd/carbon as well as homogeneous hydrogenation by the Staudinger method. These self-terminated polyamide dendrimers are enzymatically and hydrolytically stable and also exhibit antimicrobial activity. Thus, these nanoscale constructs open avenues for biomedical applications.

Characterization of Genipin-Modified Dentin Collagen

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0–24 h). Changes in biochemical properties of NaB3H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (P < 0.05). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB3H4.

Six-year clinical performance of etch-and-rinse and self-etch adhesives

OBJECTIVE To evaluate the 6-year clinical performance of Xeno IV, Xeno III, and XP Bond adhesives in the restoration of non-carious cervical lesions (NCCLs). METHODS This was a randomized controlled clinical trial where 39 participants met the inclusion/exclusion criteria and were enrolled. Lesions restored were notch-shaped NCCLs. Prior to adhesive procedures, NCCLs were roughened. No enamel bevel was placed and no mechanical retention was created. Adhesive systems were applied following manufacturers instructions and the NCCLs were restored with composite resin (TPH(3)). Restorations were finished immediately after placement and scored with regard to retention, marginal discoloration, marginal adaptation, sensitivity, and secondary caries using modified USPHS criteria. Descriptive statistics were performed. Logistic regression models were performed for each outcome separately with compound symmetry correlation structure where teeth were clustered by participants. All analyses were conducted using SAS 9.2. RESULTS The 6-year recall rate was 77.5% of the restorations (76.9% of the participants). No statistical differences were found between adhesives for retention, marginal discoloration, and marginal adaptation. Restorations failed by loss of retention (16.7%, 27.6%, and 11.8% of Xeno IV, Xeno III, and XP Bond restorations, respectively) and marginal discoloration (7.4% of Xeno IV restorations). For every unit increase in restoration volume it was 1.31 (95%C.I. 1.05, 1.63, P=0.01) times more likely that the restoration retention would be maintained. SIGNIFICANCE The tested adhesive systems presented similar clinical performance after six years of service, with annual failure rates of 2.8%, 4.6%, and 2.0% for Xeno IV, Xeno III, and XP Bond, respectively.