Cky Yiu

Collagen Degradation by Host-derived Enzymes during Aging

Incompletely infiltrated collagen fibrils in acid-etched dentin are susceptible to degradation. We hypothesize that degradation can occur in the absence of bacteria. Partially demineralized collagen matrices (DCMs) prepared from human dentin were stored in artificial saliva. Control specimens were stored in artificial saliva containing proteolytic enzyme inhibitors, or pure mineral oil. We retrieved them at 24 hrs, 90 and 250 days to examine the extent of degradation of DCM. In the 24-hour experimental and 90- and 250-day control specimens, we observed 5- to 6-μm-thick layers of DCM containing banded collagen fibrils. DCMs were almost completely destroyed in the 250-day experimental specimens, but not when incubated with enzyme inhibitors or mineral oil. Functional enzyme analysis of dentin powder revealed low levels of collagenolytic activity that was inhibited by protease inhibitors or 0.2% chlorhexidine. We hypothesize that collagen degradation occurred over time, via host-derived matrix metalloproteinases that are released slowly over time.

In vivo and in vitro Permeability of One-step Self-etch Adhesives

Adhesive dentistry should effectively restore the peripheral seal of dentin after enamel removal. We hypothesize that non-rinsing, simplified, one-step self-etch adhesives are effective for minimizing dentin permeability after tooth preparation procedures. Crown preparations in vital human teeth were sealed with Adper Prompt, Xeno III, iBond, or One-Up Bond F. Epoxy resin replicas were produced from polyvinyl siloxane impressions for SEM examination. Dentin surfaces from extracted human teeth were bonded with these adhesives and connected to a fluid-transport model for permeability measurements and TEM examination. Dentinal fluid droplets were observed from adhesive surfaces in resin replicas of in vivo specimens. In vitro fluid conductance of dentin bonded with one-step self-etch adhesives was either similar to or greater than that of smear-layer-covered dentin. TEM revealed water trees within the adhesives that facilitate water movement across the polymerized, highly permeable adhesives. Both in vitro and in vivo results did not support the proposed hypothesis.

The Effect of Chewing Gums Containing Calcium Phosphates on the Remineralization of Artificial Caries-Like Lesions in situ

Caries-Like Lesion Preparation Sound, extracted molars were cleansed of soft tissue debris and inspected for cracks, hypoplasia, and white spot lesions. The teeth were then coated with acid-resistant nail varnish (Lancester, Germany), leaving a narrow horizontal window, approximately 1 mm wide, on the buccal and lingual surfaces. Each tooth was immersed in 10 ml of a demineralizing solution [ten Cate and Duijsters, 1983] for 96 h to produce artifi cial caries lesions approximately 100–120 m deep. The teeth were sectioned with a Silverstone-Taylor hardtissue microtome buccolingually through the lesions, in an occlusalapical direction, to produce longitudinal sections approximately 100–150 m thick. One hundred and forty-four buccal or lingual sections were selected and randomly divided into three equal-sized groups, i.e. 48 sections per group. Every section was studied using polarized light microscopy and microradiography in order to record the depth and mineral content of the lesions before and after each of the three 21-day intra-oral periods. Prior to being attached to an intra-oral appliance, each section was carefully painted with acidresistant nail varnish, leaving only the lesion surface exposed to the oral environment. After the intra-oral test phase of the experiment, this nail varnish was removed by immersion in acetone for 10 s and by thorough rinsing with deionized water. All the sections were stored in an environment with 100% humidity until required for the experiment.

Evaluation of the Use of Topical Fluoride Gel

Professionally applied topical fluoride should be used judiciously and is indicated only in patients with moderate or high caries activity. While the anti-caries effectiveness of acidulated phosphate fluoride gels has been clinically documented, the 2% neutral NaF gel has not been adequately tested, and further clinical verification is needed. Daily use of a self-applied fluoride gel is recommended for patients undergoing orthodontic treatment or to those affected with xerostomia as a result of disease or head and neck radiation therapy. The dental profession and the public should be well informed on the proper use of clinically proven products to achieve optimum effectiveness and minimize the risk of fluoride ingestion.

Effect of silver diamine fluoride and potassium iodide on residual bacteria in dentinal tubules

BACKGROUND This study evaluated the antimicrobial effect of a silver diamine fluoride (SDF)/potassium iodide (KI) product (Riva Star) on the viability of intratubular bacteria. METHODS Forty-five dentine discs prepared from caries-free maxillary premolars were randomly divided into nine groups. Group 1 (negative control) contained non-infected sound dentine discs. The remaining discs were infected with Streptococcus mutans suspension and received dentine treatments as follows: Group 2 (positive control), discs were left untreated; Group 3 SDF/KI (Riva Star); Group 4 chlorhexidine (CHX); Group 5 CHX+SDF/KI; Group 6 Carisolv; Group 7 Carisolv+SDF/KI; Group 8 Papacarie, and Group 9 Papacarie+SDF/KI. The discs were then fractured into two halves, stained with fluorescent LIVE/DEAD stain and observed using confocal laser scanning microscopy. RESULTS SDF/KI exhibited a potent antibacterial effect, as represented by a significantly higher percentage of dead bacteria, in comparison with Carisolv and Papacarie (p<0.05). The application of SDF/KI following Carisolv and Papacarie chemomechanical caries removel gels significantly reduced the viability of intra-tubular bacteria in these groups. CONCLUSIONS The use of the silver diamine fluoride/potassium iodide product is effective in reducing the numbers of S. mutans in dentinal tubules infected with this organism.

A new method of evaluation of fracture patterns following microtensile bond strength testing using polarized light microscopy

PURPOSE This work describes a new method using polarized light microscopy to determine the failure modes of fractured beams following microtensile bond strength testing. The outcomes were validated using SEM and EDX elemental analysis. MATERIALS AND METHODS Resin adhesives and resin composites bonded to caries-free dentin samples as well as disks of adhesive and composite were observed with reflected polarized light microscopy (PLM) to obtain standard images. A set of beams fractured in the microtensile bond test were observed with PLM and compared with the standard images to determine failure mode through PLM color matching with the standard dentin, adhesive, or composite images. Samples were analyzed by EDX under SEM and compared with the PLM outcomes. RESULTS Reflected PLM images showed that the fractured surfaces covered with resin-based materials (adhesives or composite) appeared pink in color, in contrast to dentin surfaces, which appeared yellow. EDX mapping together with SEM observation confirmed the results obtained by PLM. CONCLUSION The results of EDX mapping and SEM observation showed that the use of polarized light microscopy is a simple, viable method for differentiation between the resin-covered dentin surfaces for determining fracture pattern analysis after bond testing.

Comparison of two radiographic methods for localization of bilateral supernumerary teeth

This journal suppl. entitled: Special Issue: Abstracts of the 2012 FDI Annual World Dental CongressThis journal supplement is the Special Issue: Abstracts of the 2012 FDI Annual World Dental Congress, September 2012This journal supplement is the Special Issue: Abstracts of the 2012 FDI Annual World Dental Congress

Wolf-Hirschhorn syndrome - novel and unreported oral findings

This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry, Seoul, Korea, 12-15 June, 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013

Reattachment of anterior teeth fragments after traumatic dental injury involving multiple crown fractures: a case report

This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry, Seoul, Korea, 12-15 June, 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013

Ectodermal dysplasia with anodontia: a case report

This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry, Seoul, Korea, 12-15 June, 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013This journal suppl. is the Special Issue: Abstracts of the 24th Congress of the International Association of Pediatric Dentistry ... 2013