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Biomedical subjects

L K Cheung

Publications and source records attributed to L K Cheung.

At least 37 records · Page 2Linked to original sources
PubMed1998

The development of a new direct digital extra-oral radiographic system prototype using a thin-film transistor panel.

OBJECTIVE: To develop a new method of direct digital image acquisition for extra-oral radiography. METHODS: A selenium detector was combined with a thin-film transistor sensor and integrated with current technology for computed radiography in a system named Direct Radiography (DR). The effective image area of the prototype is 178 mm x 213.5 mm, and consists of a 1280 x 1536 pixel matrix with a pixel pitch of 139 microns x 139 microns. The electrical characteristics were evaluated and image quality was tested with a dried human mandible and half-skull phantom. The resultant images were subjectively reviewed by seven oral and maxillofacial radiologists. RESULTS: The prototype had a signal-to-noise ratio of 400:1 when the exposure was 250 x 10(-8) C/Kg. Spatial resolution was equal to the Nyquist frequency of 3.55 cycles/mm. The images of the phantoms were considered to be of equivalent quality to conventional screen-film images and demonstrated the normal anatomical structures used for clinical evaluation. Three to four images per minute were generated with this system. CONCLUSION: The DR system has an X-ray sensitivity comparable with a 400-speed film-screen system and appears suitable for clinical radiography. Further evaluation is therefore planned.

Humans↗
PubMed1998

Objective evaluation of oral and maxillofacial sensory nerves.

OBJECTIVE: The purpose of this article is to recommend a set of methods for the clinical objective evaluation of neurosensory nerves and to establish criteria for the clinical objective evaluation of oral and maxillofacial regions in a Chinese population. METHODS: Sensations in the oral and maxillofacial regions of 35 healthy subjects were objectively and quantitatively evaluated by means of two-point discrimination, static light touch, brush directional stroke, and thermal discrimination. RESULTS: Criteria for the clinical neurosensory evaluation were established for the sensations of the oral and maxillofacial regions of healthy Chinese. CONCLUSIONS: Two-point discrimination, static light touch, brush directional discrimination, and thermal discrimination can provide objective, quantitative information for the evaluation of sensory nerve impairment. These convenient methods represent the important tools in the diagnosis and treatment of sensory nerve impairment in oral and maxillofacial regions.

Adolescent↗
PubMed1998

A modified approach to the Le Fort II osteotomy.

A modified technique of Le Fort II osteotomy is described for the correction of naso-maxillary hypoplasia. The surgical access was via a combination of bicoronal flap and transoral sulcular incision. Any periorbital skin incision is avoided. This is made possible by having the medial orbital cut made through the lacrimal groove. The anterior limb of the medial canthal ligament is detached, but leaving the posterior and superior limbs intact. Following mobilization, the osteotomy segment is stabilized by miniplates without intermaxillary fixation. This method eliminates the need for facial incision and hence the residual scar. Patients' recovery and acceptability of this modified approach to Le Fort II osteotomy is much enhanced.

Humans↗
PubMed1997

A bone graft condensing syringe system for maxillofacial reconstructive surgery.

A new system of metallic syringes and pluggers specifically designed for delivery and condensation of particulate bone graft is reported, and the clinical application in maxillofacial reconstructive surgery is described. This bone graft condensing system has advantages over the conventional plastic injection syringes in enabling much better bone graft condensation as well as easier bone delivery and insertion of the syringe to the depth of the reconstruction crib.

Bone Transplantation↗
PubMed1997

Temporalis myofascial flap in maxillofacial reconstruction: clinical and histological studies of the oral healing process.

OBJECTIVES: To report our experience with temporalis myofascial flaps (TMF), describe the healing process of uncovered flaps in the mouth, and the histology of the repaired mucosa in the long term. DESIGN: Prospective clinical and histological study. SUBJECTS: 36 patients who received a TMF over a 6.5 year period for serial assessment of the oral healing, 24 patients whose scars over the reconstructed area were assessed clinically, and 11 whose repaired mucosa was assessed histologically. MAIN OUTCOME MEASURES: To follow the clinical process of oral healing of the TMF and describe the repaired mucosa healed over the flap. RESULTS: The uncovered TMF in the mouth healed gradually starting with an acute inflammatory phase, going through chronic inflammatory and proliferative phases with eventual epithelialisation of the oral mucosa. There were no major complications. The healed mucosa showed mild scarring in 70% of cases and the repaired mucosa had characteristic histological features that were distinct from the normal mucosa. CONCLUSION: The TMF is an extremely reliable and versatile flap for maxillofacial reconstruction which heals gradually with eventual coverage by mildly scarred repaired mucosa.

Adolescent↗
PubMed1997

Cephalometric parameters affecting severity of anterior open bite.

One hundred and four patients with anterior open bite (AOB) were subdivided by statistical means into three distinctly separate groups with AOB of different severity based on the extent of separation of the incisors in the vertical plane. Cephalometric evaluation of all subjects was completed using 24 skeletal and 12 dentoalveolar measurements, and the results were compared between the mild, moderate and severe groups of AOB. The findings suggest that the palatal plane, mandibular occlusal plane, upper anterior dental height and upper posterior dental height correlate significantly with the severity of AOB. In contrast, skeletal jaw relationship in the horizontal plane correlated only weakly with severity. This study further highlighted the steep mandibular occlusal plane as an important indicator of AOB severity in contrast to the maxillary occlusal plane.

Adolescent↗
PubMed1997

The epithelialization process in the healing temporalis myofascial flap in oral reconstruction.

The aim of this study was to investigate prospectively the epithelialization process in the healing temporalis myofascial flap (TMF). Eight cats underwent maxillectomy and immediate reconstruction with TMF. They were killed at the determined time and the reconstructed maxillae were processed for examination by light microscopy and scanning electron microscopy. Results revealed that epithelialization of the healing TMF was initiated by hyperplastic changes followed by active migration of epithelial cells deriving from the wound margins. The partial maxillectomy wound was completely covered by a smooth oral mucosa at postoperative week 24. The mucosa had histological and ultrastructural features different from normal palatal mucosa.

Animals↗
PubMed1997

[The vascular network in human temporalis muscle and its surgical application].

Despite the widespread clinical use of the temporalis muscle flap, understanding of the intramuscular vasculatures and its distribution remains poor. The paper aims to evaluate the vascular network in human temporalis muscle for surgical application. Materials consisted of 30 fresh human temporalis muscle specimens. Vascular infusion was by either solution of Indian ink, lead oxide or methylmethacrylate. The vascular anatomy was analysed by stereomicroscopy, radiography and scanning electron microscopy. The results showed that the vascular supply of human temporalis muscle was primarily derived from 3 sources. Double veins pairing an artery was a common feature. The capillaries formed a dense interlacing network with orientation along the muscle fibres. In the coronal plane, the vessels were concentrated on the lateral and medial aspects with a reduced vascular density in the intermediate.

Capillaries↗
PubMed1996

An animal model for maxillary reconstruction using a temporalis muscle flap.

PURPOSE: This article describes the feasibility of using the temporalis muscle flap to cover a defect after maxillectomy in cats and to evaluate the clinical healing process of this flap in the oral environment. MATERIALS AND METHODS: The material consisted of 30 cats of the Felis catus species. A standardized unilateral maxillectomy was performed and the resulting defect immediately closed with a pedicled temporalis flap. The healing of this flap was clinically assessed at determined intervals. RESULTS: Healing of the temporalis flap in the oral environment of cats progressed from an inflammatory to a proliferative phase, with eventual coverage by a smooth oral mucosa 18 to 24 weeks after surgery. CONCLUSIONS: The cat proved to be a useful model for this type of study.

Animals↗
PubMed1996

Blood loss and transfusion requirements in orthognatic surgery.

PURPOSE: This study quantified the blood loss and transfusion requirements in orthognathic surgery. PATIENTS AND METHODS: Three hundred sixty consecutive healthy orthognathic surgery patients were included in this retrospective study. The female:male ratio was 1.8:1, and the age range was 8 to 49 years (mean, 24). Estimated blood volume (EBV), estimated blood loss (EBL), and transfused blood were calculated. RESULTS: EBL ranged from 50 to 5,000 mL (mean, 600) representing up to 73% of EBV (mean, 16%). In total, 24% (84 patients) were transfused, 8.7% (6 patients) after single-jaw surgery and iliac bone harvest and 26.7% (78 patients) after bimaxillary osteotomies. Forty-seven patients received 1 unit of transfused blood, 25 patients had 2 units, and 12 patients had more than 2 units. Most transfused patients lost 11% to 40% of EBV. CONCLUSIONS: Transfusion is not necessary for single-jaw surgery unless a bicoronal flap or iliac bone harvest are required. Although only 27% of bimaxillary osteotomy patients required transfusion of 1 to 2 units, this group was not predictable based on the type of procedure involved, and a further subgroup (4% of the 291 patients) required a larger transfusion.

Adolescent↗
PubMed1996

The vascular anatomy of the human temporalis muscle: implications for surgical splitting techniques.

Despite the wide application of the temporalis muscle flap and its modifications, understanding of the vascular pattern and territories within the muscle remains poor. This study aimed to evaluate the vascular architecture in the human temporalis muscle for surgical application. The material comprised 15 fresh cadavers (30 muscle specimens), which were divided into three groups for vascular infusion by either Indian ink solution, lead oxide solution, or methylmethacrylate resin. The vascular network in the temporalis muscle was analyzed by stereomicroscopy, radiography, and scanning electron microscopy. The human temporalis muscle was found to have vascular supply from three primary arteries: the anterior deep temporal artery (ADTA), the posterior deep temporal artery (PDTA), and the middle temporal artery (MTA). Each primary artery branched into the secondary arterioles and then the terminal arterioles. The venous network accompanied the arteries, and double veins pairing one artery was a common finding. The capillaries formed a dense, interlacing network with orientation along the muscle fibres. Arteriovenous anastomosis was absent. In the coronal plane, the vessels were located mainly on the lateral and medial aspects of the muscle with a significantly lower vascular density in the midline. Morphometric analysis of the arterial network showed that the PDTA was larger in size at primary and secondary branching levels than the ADTA and the MTA, whereas no differences were present at the terminal arteriolar levels. The distribution of the arterial territories was as follows: the ADTA occupied 21% anteriorly, the PDTA occupied 41% in the middle region, and the MTA occupied 38% in the posterior region. This improved understanding of the vascular architecture within the temporalis muscle complements the anatomic basis of the flap-splitting technique and increases the safety of its application.

Carbon↗
PubMed1996

An unusual facial sinus.

An unusual presentation of a chronic suppurative granuloma on the alar base area originating from a maxillary lateral incisor is reported. Treatment involved adequate endodontic therapy with simultaneous apical surgery and excision of the granuloma and sinus tract. Awareness of the possible dental origin of facial sinuses, despite their unusual location, is emphasized.

Adult↗
PubMed1996

Use of flow cytometry in the analysis of stage III squamous cell carcinoma of the oesophagus and its association with MIB-1.

AIMS: To examine the prognostic and pathobiological importance of DNA content in oesophageal squamous cell carcinomas in Hong Kong Chinese subjects; to evaluate its association with the immunohistochemical proliferative marker MIB-1. METHODS: Paraffin wax embedded tumour tissue and adjacent normal tissue (control tissue) samples from 45 resected stage III oesophageal squamous cell carcinomas were studied using flow cytometric analysis. The DNA content and the clinicopathological data of these patients were analysed together with the MIB-1 labelling index. RESULTS: DNA aneuploidy was present in 14 (31%) of the 45 cases. However, the DNA content did not correlate significantly with the age, sex, or survival of the patients, nor the length, location, differentiation and MIB-1 labelling index of the oesophageal carcinomas. The synthetic (S) phase fraction of diploid tumours bore no relation to the patients' survival or MIB-1 score. CONCLUSIONS: Flow cytometry was not as useful as the MIB-1 labelling index in predicting the biological characteristics of the tumours and the prognosis of patients with oesophageal squamous cell carcinomas. This study does not support the routine use of DNA flow cytometric analysis in oesophageal cancers.

Aged↗
PubMed1996

The blood supply of the human temporalis muscle: a vascular corrosion cast study.

Knowledge as to the blood supply of the human temporalis muscle is limited to its extramuscular path and relations, little information existing about the intramuscular vascular architecture. To investigate the 3-dimensional vascular network in the human temporalis muscle, in 5 fresh cadavers an infusion of methylmethacrylate resin was made via the carotid vessels with subsequent removal of the organic tissues by a corrosion process. The vascular corrosion casts of the temporalis muscle were studied by stereomicroscopy and scanning electron microscopy. In 6 well perfused muscle specimens, the temporalis muscle was found to be consistently supplied by 3 arteries: the anterior and posterior deep temporal arteries, and the middle temporal artery. Each primary artery branched into the secondary arterioles and then terminal arterioles. The venous network accompanied the arteries, and double veins pairing a single artery was a common finding. Arteriovenous anastomosis was absent, whereas arterioarterial and venovenous anastomoses were common. The capillaries formed a dense interlacing network with an orientation along the muscle fibres. Understanding of the intramuscular angioarchitecture of the temporalis provides the vascular basis for surgical flap manipulation and splitting design.

Arterioles↗
PubMed1996

Variations in costochondral grafting of the mandibular ramus.

This paper reviews the indications for, and the biological basis of, costochondral grafting for mandibular condyle replacement in adults and children. Our approach to costochondral grafting is described and illustrated, and known variations in techniques are reviewed and discussed. Data from our clinical series of 28 grafts is summarized.

Adolescent↗
PubMed1996

Functional reconstruction of the jaws: new concepts.

This paper describes the surgical reconstruction of the maxilla and mandible after ablative surgery. The methods described are original and recently developed with illustrative clinical data presented. Presurgical planning of the occlusion, titanium mesh design supporting the bone graft, and implant-borne prostheses are integral elements of the concepts described to achieve functional reconstruction of the jaws.

Adolescent↗
PubMed1995

Titanium miniplate fixation for osteotomies in facial fibrous dysplasia--a histologic study of the screw/bone interface.

In four patients who had osteotomies of the jaws affected by fibrous dysplasia (FD), screws embedded in bone blocks were removed at a re-entry operation 20 months postoperatively. Morphometric measurement of the bone density and calculation of the bone contact percentage were performed. Both normal and dysplastic bone were found to have some direct bone contact with the titanium screws. Although the bone contact percentage was higher in the normal bone when compared with FD, statistics failed to show any significant difference (P < 0.05). The dysplastic bone healed well around the titanium screws without inflammatory reaction and direct dysplastic bone/screw contact was noted. Longer screws should be used in facial FD in order to compensate for the reduced bone contact percentage.

Adult↗