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Biomedical subjects

G S Cheung

Publications and source records attributed to G S Cheung.

16 recordsLinked to original sources
PubMed2001

Lay knowledge of physical education teachers about the emergency management of dental trauma in Hong Kong.

The purpose of this study was to investigate the knowledge of a group of physical education (PE) teachers about the emergency management of dental trauma in Hong Kong. A postal questionnaire was sent to PE teachers in 100 randomly selected secondary schools in Hong Kong. A total of 166 teachers from 65 schools responded. Results show that a majority of the respondents have received formal teaching training (98.8%). While all but one teacher had received formal first aid training, only eight of them recalled that they had received advice on the management of dental trauma. Concerning the management of tooth fracture, 118 respondents (71.1%) gave an appropriate answer. In contrast, only 29 teachers (17.5%) were able to indicate the appropriate management for an avulsed tooth. Over 60% (102) of the respondents indicated it was "very urgent" to seek professional assistance if a permanent tooth has been avulsed, but they had little knowledge of the correct procedures for replanting or transporting avulsed teeth. Only 15 respondents (9%) pointed out that milk was the medium of choice for transporting avulsed teeth. Finally, over 90% (157) of respondents indicated that they had never received advice on the emergency procedures for the management of dental avulsion. The present study showed that the level of lay knowledge of management of dental injuries in a selection of PE teachers in Hong Kong is inadequate and educational campaigns are necessary to improve their emergency management of dental injuries.

Adult↗
PubMed2001

Reversal of compromised bonding to oxidized etched dentin.

The mechanism responsible for hydrogen-peroxide- or sodium-hypochlorite-induced reductions in dentin bond strength is unknown. This in vitro study tested the hypothesis that these oxidizing agents were responsible by attempting to reverse the effect with sodium ascorbate, a reducing agent. Human dentin was treated with these oxidants before or after being acid-etched and with or without post-treatment with sodium ascorbate. They were bonded with either Single Bond or Excite. Hydrogen peroxide reduced the bond strengths of both adhesives, while sodium hypochlorite produced reduction in adhesion of only Single Bond (p < 0.05). Following treatment with sodium ascorbate, reductions in bond strength were reversed. Transmission and scanning electron microscopy showed partial removal of the demineralized collagen matrix only by sodium hypochlorite. The observed compromised bond strengths cannot be attributed to incomplete deproteinization and may be related to changes in the redox potential of the bonding substrates.

Acid Etching, Dental↗
PubMed1996

An in vitro comparison of the Excalibur handpiece and hand instrumentation in curved root canals.

Root canal preparation may be the most technique-sensitive and labor-intensive procedure in endodontic therapy. Many automatic handpieces and machine-driven devices have been marketed to expedite this procedure. Excalibur is one such handpiece. The purpose of this study was to compare the Excalibur hand piece with traditional K-files for their effectiveness in shaping curved root canals. A total of 24 standardized canals in extracted human mandibular molars were randomly divided into two groups. They were instrumented either with Excalibur according to the manufacturer's instructions or manually using the step-down technique. The cross-sectional shapes of the root canal at the apical, midroot, and coronal levels were digitized before and after instrumentation. Image analyzer software was used to compare the images. The results showed that the methods removed similar amount of dentin at all three levels. Although the Excalibur handpiece had a slight tendency to straighten the canal more than hand instrumentation, the difference was not significant. Strip-perforation occurred in three specimens in the Excalibur group, but none in the manual group. There was no separation of instrument throughout the experiment.

Dental High-Speed Equipment↗
PubMed1996

A comparison of stainless steel and nickel-titanium K-files in curved root canals.

The purpose of this study was to determine the effects of hand instrumentation using traditional stainless steel K-files and nickel-titanium K-files on the final shape of curved root canals. A total of 24 moderately curved canals in the mesial roots in extracted human mandibular first molars were randomly divided into two groups. These were instrumented manually using either stainless steel or nickel-titanium, K-files with the stepdown technique. The cross-sectional shape of each canal at three different horizontal levels were captured, before and after instrumentation, into a computer for comparison using image analyser software. Three parameters at each level were evaluated: (i) amount of dentine removed; (ii) least remaining dentine thicknesses on mesial and furcal aspects; and (iii) the amount and direction of canal transportation. The results showed that the two file types removed similar amounts of dentine at all three levels examined. The nickel-titanium files left a thicker layer of dentine on both the mesial and furcal aspects than stainless steel files. However, the difference was not significant (pooled T-test, P > 0.05). Both types of files transported the centre of the canals but the nickel-titanium instrument seemed to be safer because of the reduced amount of transportation towards the danger areas.

Dental Instruments↗
PubMed1996

Endodontic failures--changing the approach.

The underlying reason for endodontic failures is almost invariably due to bacterial infection. The bacteria may be situated within a previously missed or uninstrumented portion of a root canal, infiltrate via a leaky coronal restoration and root filling, or cause contamination from an extra-radicular infection. Management of the failing root canal filling begins with the identification of the source of persistent infection. Should the infection be present within the root canal system, such as a missed canal, orthograde retreatment is the choice of treatment. This is also true for asymptomatic cases which had been inadequately obturated and which require the placement of a dowel into the canal for restorative reasons. Periapical surgery is best reserved for cases with no sign of healing after orthograde retreatment and those with extra-radicular infection. This paper discusses the relationship between endodontics and restorative dentistry, treatment planning for endodontic failures, and the reported rates of success with orthograde and surgical retreatments.

Bacterial Infections↗
PubMed1995

Incidence of post-operative sensitivity following indirect porcelain onlay restorations: preliminary results.

Indirect porcelain onlays have been used as cosmetic restoration of posterior teeth but there is little information on the incidence of post-operative sensitivity following their placement. An investigation on the incidence of post-operative sensitivity was carried out by bonding 27 onlays using Panavia and Flexo-Ceram cementing agents onto the posterior teeth of 12 patients aged 16 to 36 years. Analysis of the incidence revealed that 14 out of the 22 previously healthy teeth developed sensitivity symptoms; an incidence of 63.6 per cent. This preliminary investigation also showed that teeth lined with a glass ionomer material over the exposed dentine did not produce symptoms.

Adolescent↗
PubMed1994

Three-dimensional reconstruction of microleakage pattern using a sequential grinding technique.

Dye penetration tests are very commonly used to detect the absence of a fluid seal at the tooth-restoration interface. Airlocks in the marginal gap, leaching of water-soluble tracers during processing, and the failure of only a few sections to allow interpretation of the full pattern, limit these tests to low reproducibility and precision. The purpose of this present study was to generate high-resolution three-dimensional images of waterfast tracer patterns. Cylindrical class V (3 mm diameter, 2 mm deep) dentine-bonded resin composite restorations in buccal coronal dentine were thermally cycled (1000 x, 8 degrees C, 55 degrees C, 30 s dwell at each temperature) and then silver stained using an initial vacuum (100 mmHg pressure). Each restoration was sequentially abraded from the free surface on wet 180 grit silicon carbide paper, producing up to 30 parallel surfaces at approximately 0.15 mm separation through the restoration down to the pulp. Images of the ground surfaces were captured, and assembled by a computer image analyser program to give a three-dimensional model of the tracer pattern. The maximum depths of tracer penetration below the reference surfaces were 3.00 mm, 2.09 mm, 3.16 mm and > 2.29 mm for the four specimens. Projections of the models were viewed from several directions with sections in various locations to allow investigation of the full tracer pattern. This method allows the creation of high-resolution three-dimensional tracer patterns.

Composite Resins↗
PubMed1993

In vitro cleaning ability of root canal irrigants with and without endosonics.

A variety of methods have been used to evaluate the cleanliness of root canals after endodontic preparation and irrigation. Few irrigation agents other than sodium hypochlorite (NaOCl) have been tested in conjunction with endosonics. The purpose of this study was to examine the cleaning ability of water, NaOCl, Hibiscrub and a biological washing liquid when used as intracanal irrigants, with and without endosonics. Two methods of evaluation were employed to assess the root canal cleanliness after endodontic preparation. A total of 56 teeth, divided into eight groups, were prepared manually using the step-down technique. Each irrigating agent was used in two experimental groups, with and without endosonics. Two additional teeth which received neither instrumentation nor irrigation served as the controls. The teeth were split longitudinally and the state of cleanliness of the root canal was assessed by scoring the amount of stained organic debris and smear layer. It was demonstrated that the results of debris and smear layer scoring were significantly influenced by the type of irrigant and whether endosonics had been used. All agents exhibited similar cleaning ability when introduced manually. With endosonics, NaOCl yielded significantly less stainable debris (P < 0.05) than the other groups which showed no significant difference. The ability to remove the smear layer was enhanced, but at some distance short of the working length, by endosonics for all irrigants tested. None of the solutions tested was able to produce a canal wall that was free of smear layer.

Chi-Square Distribution↗
PubMed1993

An improved preparation for indirect porcelain veneers.

With a conventional preparation marginal microleakage is often observed at the cervical margin of porcelain laminate veneers. The leakage seems to be associated with the presence of cracks in the adjacent enamel layer. Removing the defective enamel by bevelling the cervical margin prior to cementation appears to be effective in controlling the microleakage. A modified veneer preparation which incorporates this additional short bevel is described in this paper.

Dental Cavity Preparation↗
PubMed1992

The use of role-play and psychodrama in the education of the dental undergraduate.

The delivery of effective information flow through self learning, critical thinking and problem solving is one of the objectives of current curriculum development within the Dental Faculty of the University of Hong Kong. These objectives reflect a desire to encourage skills related to 'comprehension learning' and 'meaning orientation' rather than 'rote' learning and 'surface' approaches. This paper explains the way in which role-play and psychodrama are used in an effort to achieve these objectives.

Cognition↗
PubMed1991

A preliminary investigation into the longevity and causes of failure of single unit extracoronal restorations.

Four types of single unit restoration, including porcelain jacket, full and partial veneer, and metal ceramic crowns provided at the Prince Philip Dental Hospital in Hong Kong were investigated for evidence of failure. Of the 4658 units of restoration provided between 1981 and 1989, 100 restorations of each type were selected at random by computer. The relevant patient were identified and invited to return for a review appointment. A total of 132 patients attended and 152 crowns were examined. The average length of service was 34 months at the date of examination. Using strict criteria, 21 (14 per cent) restorations were deemed to have failed. Technical failure was the most prevalent cause of failure, followed by aesthetic complaints and endodontic problems. The failure rates ranged from 2.4 to 7.8 per cent per year for the different crowns in order of: partial veneer less than full veneer less than metal ceramic less than porcelain jacket crowns. Fracture of restoration, which affected metal ceramic and porcelain jacket crowns, was the single most frequent cause of failure observed in this study.

Adult↗
PubMed1990

Reducing marginal leakage of posterior composite resin restorations: a review of clinical techniques.

It has been well established that composite resin restorations have leakage at the margins. The polymerization shrinkage of the material and its inadequate adhesion to the cavity walls are the primary causes. Unlike silver amalgam restorations, which are self-sealing with age, the gap at the composite-to-tooth interface tends to persist and invite postoperative sensitivity, adverse pulp reactions, and the development of recurrent caries. Many techniques or materials have been advocated to improve the clinical adaptation of this material and to reduce marginal leakage. They limit the effect of polymerization shrinkage and/or enhance the bonding of the composite material to the tooth structure. This article reviews the clinical techniques and materials that have been suggested and are presently available to improve the marginal quality of composite resins, with special reference to posterior restorations.

Acid Etching, Dental↗
PubMed1990

A clinical evaluation of conventional bridgework.

The present study evaluated the incidence and causes of failure of conventional bridgework provided in the Prince Philip Dental Hospital, Hong Kong. Any bridge that utilized resin-bonded (Maryland) retainers was excluded from this study. All patients with bridges fitted between 1981 and 1987 were recalled for review, and 143 patients attended, a response rate of 77%. A total of 169 bridges were examined, their mean length of service being 35 months. Thirty-five bridges were deemed to have failed. The most frequent cause was endodontic, followed by loss of retention, then persistent pain and sensitivity. Failures of endodontic origin affected mostly anterior bridges, which could be attributed to the over-sized pulp of anterior teeth and the amount of tooth reduction required for the ceramometal retainer. All of the bridges that failed because of endodontic problems had had ceramometal retainers. Taking posterior bridges alone, the failure rate was 4.4% per year. From the evidence of this study, the replacement of the maxillary canine with a cantilever bridge appears to be contra-indicated.

Adolescent↗
PubMedDate not supplied

An update on the use of resin-based dental adhesives.

The introduction of the acid-tech technique and the development of dentine bonding agents have been major steps forward in adhesive dentistry. However, the adhesion provided by the current dentine bonding resins is still inadequate to withstand many of the stresses encountered in clinical practice. The authors review the adhesive agents currently available, and the published evidence about their performance.

Composite Resins↗