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Biomedical subjects

L K Cheung

Publications and source records attributed to L K Cheung.

At least 19 recordsLinked to original sources
PubMed2000

Chemical cleaning of titanium tray for reconstructive surgery.

AIMS: To find out the extent of chemical contamination on the surface of titanium wrought mesh before and after swaging, and to assess the effectiveness of cleaning off these contaminants by various chemical methods. MATERIALS AND METHODS: Qualitative analysis of the surfaces of 6 wrought titanium meshes by scanning electron microscopy (EM) and radiological microanalyser. One of these meshes was subjected to experimental cleaning by different methods. Qualitative chemical analysis of 20 titanium trays fabricated for clinical use before and after acid cleansing. RESULTS: All 6 titanium meshes had surface contaminants, with silicon being the most common. The effective cleaning methods were chemical cleaning with Titaclean, mechanical trimming, or polishing with diamond paste. The 20 swaged titanium trays were effectively cleaned with either Titaclean or Chemi-Polish solution. CONCLUSION: Previously unknown surface contamination was common on wrought titanium mesh. Ultrasonic cleansing with Titaclean or Chemi-Polish effectively removed most of the contaminants on the titanium trays before they were implanted.

Aluminum↗
PubMed1999

Custom-made titanium mandibular reconstruction tray.

Reconstruction of the mandible after ablative surgery can be achieved by using preformed trays or trays formed from models produced by computer-assisted modelling systems. The former presents difficulty in matching the required facial contour, jaw relationship and condylar position; while the latter is expensive. This paper presents a simple and inexpensive method of fabricating a custom-made titanium bone grafting tray. The dimensions of the patient's mandible are obtained by clinical measurement. Such measurements are used to construct a mandibular replica. The region to be reconstructed is carved to produce the ideal shape and dimensions of an edentulous segment. The tray is made either by casting or by swaging. Twenty-one custom-made titanium bone grafting trays have been fitted in patients with encouraging results. This method of bone grafting tray construction is a simple, inexpensive technique for achieving excellent facial contour and functional reconstruction after mandibulectomy.

Bone Transplantation↗
PubMed1999

Microvascular network of the healing surface over the temporalis flap in maxillary reconstruction.

This study aims to describe and quantify the microvascular changes of the healing wound in a maxilla reconstructed by a temporalis myofascial flap (TMF). 24 cats underwent partial maxillectomies and reconstruction by TME Vascular infusion was performed immediately following sacrifice and then analyzed by radiography, light and SEM. Results showed that the superficial microvascular layer overlying the TMF underwent a similar transformation as in the histological healing sequence. The vascular density was highest during the initial 6 weeks, followed by reducing density at the chronic inflammatory phase, to normal at the proliferative and remodelling phases. The migrating epithelium brought on a microvascular sub-epithelial plexus, which eventually covered the TMF. The finding that the vascular source of this sub-epithelial plexus comes from the surrounding tissues rather than from the underlying TMF will have surgical implications for bony reconstruction of the maxilla.

Analysis of Variance↗
PubMed1998

Cephalometric characteristics of anterior open bite in a southern Chinese population.

The cephalometric characteristics of skeletal anterior open bite (AOB) in a southern Chinese population were evaluated in a group of 104 subjects with AOB and were compared with a control group of 40 subjects without AOB. The anteroposterior jaw relationship in the AOB group was Class I in 43%, Class II in 14%, and Class III in 43%. Cephalometric analysis of all subjects was completed by using 24 skeletal and 12 dentoalveolar measurements. Sexually dimorphic variables were identified and compared separately between groups with independent t tests. Two levels of significance were used, P < or = 0.05 and P < or = 0.001. Sexual dimorphism of cephalometric variables was present in both the test and the control groups, but affected more variables in the test group. Significant findings in AOB were shorter anterior cranial base, upward and forward rotation of the maxilla, increased gonial and mandibular plane angles, increased upper posterior dental height, and increased lower anterior facial height. These findings generally coincided with those for white subjects, however, there was no conclusive evidence in this study regarding the contribution of the upper anterior facial height or the posterior facial height to the AOB deformity.

Adolescent↗
PubMed1998

Functional reconstruction of the mandible: a modified titanium mesh system.

This paper describes a method for mandibular reconstruction utilizing autogenous cancellous bone in a titanium mesh. The mesh is designed preoperatively based on a duplicate of the patient's mandible which is modified to simulate an anatomically correct edentulous segment in the region to be reconstructed. The duplicate mandible is articulated with a maxillary dental cast, and a locating splint is fabricated for intraoperative use to aid the positioning of the mesh in relation to the upper teeth. The method facilitates future rehabilitation with dental implants and results in a symmetric and highly functional reconstruction of the mandible.

Adult↗
PubMed1998

Posterior maxillary anatomy: implications for Le Fort I osteotomy.

The most common site of haemorrhage in maxillary osteotomies is the posterior maxilla. Better understanding of the anatomy in this region may minimize possible vascular complications. The aim of the study was to study the osteology of the posterior maxillary region and establish clinical safety guidelines for the Le Fort I osteotomy Thirty human dry skulls were selected and assessed by a combination of direct inspection, computerized imaging and computed tomography (CT) scan analysis. Results showed that the presence of maxillary third molars influenced the transverse angulation of the posterior vertical cut. Synostosis of the pterygomaxillary junction was noted in 12% of samples. The mean length of the medial sinus wall from the piriform rim to the descending palatine canal at the Le Fort I level was 34 mm. The three-dimensional CT-reconstructed descending palatine canal ran at 60 degrees anteroinferiorly to the palatine plane and slightly medially to the exit through the greater palatine foramen.

Adult↗
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↗