Biomedical subjects

S H Wei

Publications and source records attributed to S H Wei.

At least 55 records · Page 3Linked to original sources

PubMed1996

Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free acetone-based, single-bottle primer/adhesives.

OBJECTIVES: The goal of this study was to illustrate and define the micromorphological spectrum which exists at the resin-dentin interface when two water-free, acetone-based, single-bottle primer/adhesive systems (One-Step, Bisco, and Prime & Bond, Dentsply/L.D. Caulk) were applied to acid-conditioned dentin under different dry and wet bonding conditions. METHODS: Forty-eight 1 mm dentin discs were each conditioned with 10% phosphoric acid and rinsed for 20 s. They were randomly divided into 4 groups based upon the status of the remaining surface moisture; Group I (30 s dry); Group II (3 s dry); Group III (blot dry) and Group IV (overwet). Bonded dentin disc pairs were then demineralized in EDTA and embedded in epoxy resin for transmission electron microscopic examination. RESULTS: The micromorphological spectra of the two bonding systems were essentially similar. Both were effected by even mild desiccation (3 s), resulting in incomplete intertubular resin infiltration. Optimal intertubular resin infiltration was achieved when the collagen network was kept moist and appeared relatively unaffected by the presence of excess surface moisture. On the other hand, intratubular resin infiltration was severely compromised in the presence of excess water within the dentinal tubules and at their openings in the dentin surface. The continuity of the resin layer deteriorated; blister-like spaces formed on the dentin surface and resin globules were found around the tubular orifices and on the surface of the hybrid layer. In addition, a complex phase separation pattern was observed in Prime & Bond that was characterized by phase inversion in the presence of surface moisture. SIGNIFICANCE: The "window of opportunity" for optimal interfacial integrity for both water-free systems appeared to depend upon keeping the demineralized collagen network moist, coupled with the complete evaporation of excess and "displaced" water from tissues prior to light-curing the prime/adhesives.

Acetone↗

PubMed1996

Cephalometric A point changes during and after maxillary protraction and expansion.

The purpose of this study was to analyze the treatment and posttreatment maxillary changes achieved with maxillary protraction therapy. The cephalometric records of 25 consecutively treated Chinese children with Class III malocclusions (mean age 8.4 years) were analyzed for cephalometric A point changes, which were then compared with an untreated, age and sex matched Class III control sample. A cephalometric maxillary superimposition technique was used to differentiate between the skeletal and the local contributions to the total A point change. Results showed that 6 months of maxillary protraction therapy produced a mean A point advancement of 2.4 mm compared with 0.2 mm in the control group. Of this advancement, 75% was found to be due to skeletal maxillary advancement and 25% was attributed to local remodeling. Significantly less downward movement of A point was found with treatment compared with the controls, which could be related to the direction of force application. No significant differences were found in the horizontal and the vertical movements of A point between the treatment and the control groups during the 12-month posttreatment period, indicating stability of early maxillary protraction in patients with Class III malocclusions.

Case-Control Studies↗

PubMed1996

Soft tissue and dentoskeletal profile changes associated with maxillary expansion and protraction headgear treatment.

One of the goals of early treatment of Class III malocclusion with maxillary expansion and protraction headgear is to significantly improve the dentofacial profile. The objectives of the present study were to determine (1) the interrelationships of the soft tissue and dentoskeletal profiles after maxillary expansion and protraction headgear treatment and (2) which cephalometric variables could contribute to an accurate prediction of the protraction effect on the soft tissue profile. Lateral cephalometric radiographs of 20 consecutively treated Class III patients (10 males, 10 females) by protraction headgear were included in this study. Their ages at the start of protraction headgear treatment ranged from 6 to 11 years, with an average of 8.1 +/- 2.1 years. None of the patients had previous orthodontic treatment. For each patient, the first lateral cephalogram was taken 6 months before the initiation of headgear treatment (T0), and the second radiograph at the start of treatment (T1). Therefore (T1-T0) represented 6 months of growth with no treatment. A third radiograph was taken 6 months after start of treatment (T2). In this way, (T2-T1)-(T1-T0) represented the effect the result of appliance therapy alone and each subject served as his/her own control. A computerized cephalometric analysis was used including variables assessing sagittal and vertical relationships of skeletal and soft tissue profiles, incisal relationships, soft tissue thickness, and lip structure. Data were analyzed by means of paired t tests, Pearson's product-moment coefficient correlation, and multiple regression analyses. The results showed significant improvements in dentofacial profile after 6 months of maxillary protraction. The skeletal and soft tissue facial profiles were straightened and the posture of the lips was improved. The normal incisal relationship (overjet) that was achieved had a significant impact on the soft tissues overlying both upper and lower incisors resulting in better lip competence and posture. Significant correlations were found between changes in the sagittal relationships of skeletal and soft tissue profiles in both the maxilla and the mandible (p < 0.05). The forward movement of the maxilla was accompanied by a corresponding forward movement of the soft tissue profile at 50% to 79% of the hard tissue. In the mandible, the downward and backward movements of the soft tissues were equivalent to 71% to 81% of the corresponding hard tissues. The lack of high r square values in the multiple regression analyses reflected a low prediction value for the maxillary variables, but moderately high prediction value for the mandibular variables that could be used in preorthopedic treatment planning. This study showed that significant dentoskeletal changes and improvements in dentofacial profile resulted from 6 months of treatment with maxillary expansion and protraction.

Cephalometry↗

PubMed1996

Treatment response to maxillary expansion and protraction.

A prospective clinical trial was conducted to determine the skeletal and dental contributions to the correction of overjet and overbite in Class III patients. Thirty patients (12 males and 18 females with a mean age of 8.4 +/- 1.7 years) were treated consecutively with protraction headgear and fixed maxillary expansion appliances. For each patient, a lateral cephalogram was taken 6 months before treatment (T0); immediately before treatment (T1); and 6 months after treatment (T2). The time period (T1-T0) represented changes due to 6 months of growth without treatment; (T2-T1) represented 6 months of growth and treatment. Each patient served as his/her own control. Cephalometric analysis described by Björk (1947) and Pancherz (1982a,b) was used. Sagittal and vertical measurements were made along the occlusal plane (OLs) and the occlusal plane perpendicular (OLp), and superimposed on the mid-sagittal cranial structure. The results revealed the following: with 6 months of treatment, all subjects were treated to Class I or overcorrected to Class I or Class II dental arch relationships. Overjet and sagittal molar relationships improved by an average of 6.2 and 4.5 mm, respectively. This was a result of 1.8 mm of forward maxillary growth, a 2.5-mm of backward movement of the mandible, a 1.7-mm of labial movement of maxillary incisors, a 0.2-mm of lingual movement of mandibular incisors, and a 0.2-mm of greater mesial movement of maxillary than mandibular molars. The mean overbite reduction was 2.6 mm. Maxillary and mandibular molars were erupted occlusally by 0.9 and 1.4 mm, respectively. The mandibular plane angle was increased by 1.5 degrees and the lower facial height by 2.9 mm. Individual variations in response to maxillary protraction was large for most of the parameters tested. Significant differences in treatment changes between male and female subjects were found only in the vertical eruption of mandibular incisors and maxillary and mandibular molars. These results demonstrate that significant overjet and overbite corrections can be obtained with 6 months of maxillary protraction in combination with a fixed expansion appliance.

Cephalometry↗

PubMed1996

Resin permeation into acid-conditioned, moist, and dry dentin: a paradigm using water-free adhesive primers.

Preservation of the morphological integrity of demineralized dentin collagen in its hydrated state may account for the success observed in wet-bonding procedures. This study investigated the micromorphological differences between moist- and dry-bonding techniques with the use of: (a) Aelitebond, an alcohol-based, water-free, single-component dentin adhesive primer system; and (b) a water-free, acetone-based experimental primer similar to the acetone-based, water-containing All-Bond 2, a two-component primer system. In the wet groups, acid-conditioned dentin surfaces were blotted so that they remained visibly moist prior to bonding. In the dry groups, dentin surfaces were air-dried for 30 sec. Following the bonding procedures, dentin discs in each group were laminated together by means of a chemical-cure resin and processed for scanning electron microscope (SEM) and transmission electron microscope (TEM) examination. Conditioning with 10% H3PO4 for 20 sec. produced complete demineralization of the outer dentin. In the wet groups, banded collagen and interfibrillar spaces could be observed at the surface of the acid-conditioned dentin. Complete wetting of the loosely arranged collagen fibrils by the resin resulted in the formation of a hybrid layer. In the dry groups, only a very thin hybrid layer was observed on the dentin surface, along the walls of the tubules, and along the course of their lateral branches. The absence of banded collagen and interfibrillar spaces within these areas suggested the existence of a collapsed dentin matrix along various liquid-vapor boundaries that restricted resin permeation into the subsurface intertubular matrix, producing an incompletely infiltrated "hybridoid region".

Dental Bonding↗

PubMed1996

Interinnominate motion and symmetry: comparison between gymnasts and nongymnasts.

Some clinical approaches to the treatment of low back pain evaluate and treat observed asymmetries of pelvic posture and motion. Scientific evidence suggests the motion available between the innominate bones is small and variable in nature. The purposes of this investigation were 1) to determine if interinnominate motion of subjects without low back pain was symmetrical in reciprocal test posture combinations, 2) to assess innominate bone symmetry in standing, and 3) to determine if a difference in the magnitude of interinnominate motion was present between a subject group which performs more frequent flexibility activities compared with a subject group representing the general population. Thirty-four subjects (eight male gymnasts, nine female gymnasts, eight male nongymnasts, and nine female nongymnasts) were evaluated in standing and three other reciprocal postures (modified standing, modified sitting, and half-kneeling). In each posture, the Metrecom Skeletal Analysis System was used to obtain coordinates for the anterior and posterior iliac spines. Projection angles were used to determine the relative positions of the right and left innominate bones. Results suggest that stand to right modified standing and stand to left modified standing oblique sagittal interinnominate composite motions were symmetrical, stand to right modified sitting and stand to left modified sitting oblique sagittal interinnominate composite motions were asymmetrical, and stand to right half-kneel and stand to left half-kneel oblique sagittal interinnominate composite motions' symmetrical properties were mixed depending on the group. Gymnasts as a group were found to have asymmetrically positioned innominate bones while nongymnasts as a group had symmetrically positioned innominate bones.

Adolescent↗

PubMed1996

A pilot study of the marginal adaptation and surface morphology of glass-cermet cements.

This study investigated changes in the marginal adaptation and surface morphology of Ketac-Silver and Chelon-Silver glass-current cements over time. Dispersalloy amalgam was used as a control. Contralateral pairs of carious primary molars were restored with the test materials and amalgam. Clinical evaluations were scheduled at 12, 18, and 24 months after placement. Gold-plated replicas of the restorations were observed with scanning electron microscopy. Fractures and cracks in the surface of the Dispersalloy and Chelon-Silver increased the surface roughness; however, the damage was superficial and self-limiting in the Dispersalloy restorations, while in Chelon-Silver the fractures caused the material to break down in layers. A substantial quantity of pores, usually smaller than 50 microns in diameter, were observed throughout the surface of the Chelon-Silver restorations. The pores in the surface of Ketac-Silver were fewer and smaller. The incidence of cavomarginal breakdown increased with time. Chelon-Silver restorations had a higher rate of cavomarginal breakdown than did Ketac-Silver and Dispersalloy restorations up to 18 months. However, there was no statistically significant difference in the marginal adaptation of the three groups at 24 months.

Cermet Cements↗

PubMed1996

Quantitative contribution of the collagen network in dentin hybridization.

PURPOSE: To determine the quantitative contribution of dentin hybridization to bonded assembly strength and demonstrate the micromorphology of the interface with and without collagen present. MATERIALS AND METHODS: Four groups of 10 molar teeth were finished to a 320 grit dentin smear layer. Two groups served as controls and two experimental groups were subjected to collagenase digestion of the collagen exposed by acid conditioning. All-Bond 2 and Amalgambond were used to bond Bisfil and Epic resin composite, respectively. Stored in water at 37 degrees C for 24 hours the assemblies were tested in a shear mode at a crosshead speed of 5 mm/minute. Means and standard deviations were subjected to analysis for statistical significance. Twenty four teeth in four groups were examined by scanning (SEM) and transmission electron microscopy (TEM) for the relationship between resin and conditioned dentin with and without the collagen network. RESULTS: All-Bond 2 and Amalgambond controls were 28.41 +/- 3.9 and 19.04 +/- 5.96 MPa, collagenase-treated groups scored 26.43 +/- 2.90 and 19.70 +/- 4.25 MPa respectively. No significant difference existed between the control and experimental groups. SEM showed an intertubular collagen network with patent tubules and a pronounced porous, irregular dentin topography following collagen digestion. A distinct hybrid zone and tubular penetration was observed but the collagenase-treated specimens showed only resin in the tubules and their lateral extensions. TEM confirmed the absence of a distinct hybrid zone in the collagenase groups with a tight, gap-free junction between the resin and the undemineralized dentin. An electron dense zone (< 50 nm) at the leading edge of conditioning was observed for All-Bond 2 and Amalgambond groups. It was concluded that the resin-reinforced or hybridized, collagenous network does not detract from, nor contribute any significant quantitative value per se to dentin bonding with the systems tested.

Acid Etching, Dental↗

PubMed1996

The overwet phenomenon: a transmission electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To identify ultrastructural features resulting from possible primer-water interaction when a two-bottle, acetone- and alcohol-based dentin adhesive (All-Bond 2) was applied to acid-conditioned dentin in the presence of excess water. MATERIALS AND METHODS: Three groups (3-second dry, visibly moist, overwet), each comprising eight dentin discs prepared from human third molars, were established and bonded with All-Bond 2 under different degrees of surface moisture. Variations in the ultrastructural appearance of the resin-dentin interface from laboratory demineralized and epoxy resin embedded disc pairs were examined either with en bloc ruthenium red pre-staining alone or further stained with uranyl acetate and lead citrate. RESULTS: Displacement of water by the volatile primer solvents resulted in the formation of a layer of resin-impregnated dentin in the three groups. Interaction of the primer with water following the evaporation of the volatile primer solvents resulted in phase separation of the primer components. Ultrastructural features observed within the previously water-filled blister-like spaces on the dentin surface in the visibly moist and overwet groups recapitulated what was observed within partially water-filled dentin tubules in the 3-second dry group. The overwet phenomenon appeared to be a result of emulsion polymerization, involving irreversible interaction of water-soluble bifunctional primer components with those that are water-immiscible, through the formation of micelles, resulting in the absence of total interfacial integrity.

Acid Etching, Dental↗

PubMed1996

The overwet phenomenon: a scanning electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To study with the scanning electron microscope the interfacial phenomenon that occurred in the presence of excessive surface moisture following the application of an acetone-based adhesive to acid-conditioned dentin. MATERIALS AND METHODS: Specimens consisted of flat dentin discs that were divided into three groups based upon the status of remaining surface moisture: (1) 3-second dry group, (2) blot-dry group, with the conditioned dentin surface remaining shiny as opposed to matte, and (3) overwet group: an additional 40 mL of distilled water spread thin on the dentin surface after blot-drying. Polished resin-dentin interfaces were brought into relief using plasma-etching and examined without further embedding. RESULTS: Although a hybrid layer was observed in all three groups, there was (1) a sequential deterioration of the bonded assembly along the hybrid layer-resin interface, and (2) loss of complete tubular seal as the quantity of surface moisture increased. Intratubular resin globules were observed beneath short resin plugs in the 3-second dry group. Small, isolated blister-like spaces, trapped within the resin layer, were observed along the surface of the hybrid layer in the blot-dry group, while similar, but larger spaces were found in the overwet group. The blister-like spaces, which were often continuous with incompletely sealed tubular orifices, were partially filled with extraneous resin globules dispersed within an amorphous matrix.

Acid Etching, Dental↗

PubMed1996

The overwet phenomenon: an optical, micromorphological study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To evaluate the morphological effect of different degrees of surface wetness on "wet bonding" upon the acid-conditioned, resin-dentin interface using an acetone-containing adhesive system (All-Bond 2). MATERIALS AND METHODS: Dentin surfaces were conditioned with 10% phosphoric acid (20 seconds), washed and air dried (3 seconds) or blot dried. RESULTS: The surfaces were characterized by the formation of an intact layer of resin impregnated dentin. Dentin tubules were sealed with solid cores of primers commonly below which were intratubular primer globules. Excess moisture on the dentin surface resulted in the creation of blister-like spaces at the primer-dentin interface. A layer of resin-impregnated intertubular dentin was present and below such spaces were incompletely sealed tubules. Primer globules were also observed on the dentin surface. The presence of microscopic voids at the primer-dentin interface may offer a morphological explanation for the published decrease in bond strength when this system was applied in the presence of excessive surface moisture.

Acid Etching, Dental↗

PubMed1996

Innovative aspects of the 5th year BDS curriculum in Hong Kong.

In 1990, partially in response to the UK's proposal of a one-year vocational training, the BDS course in Hong Kong was extended from four years and one term in duration to a full five-years. The 5th year curriculum was intended to be as close to vocational training in nature as possible. The Board of Multidisciplinary Studies in the BDS 5-Year Curriculum was set up one year prior to the implementation of the course. The course was enthusiastically received by both students and teaching staff. The most successful and innovative aspects of the course included the new Family Practice Clinic, the elective programme where all students visited overseas dental institutions and the documentation of cases using log books in the final comprehensive examination. A post examination questionnaire validated the success of the programme.

Clinical Clerkship↗

PubMed1996

Analysis of fluoride ion concentrations and in vitro fluoride uptake from different commercial dentifrices.

The effectiveness of fluoride (F) dentifrices in reducing dental caries is well documented. However, not all F dentifrices are equally effective. The objective of this study was to compare fluoride uptake from Thai, Chinese and Indian dentifrices which are widely used in these respective countries. A non-fluoride dentifrice was included as a control. Dentifrices were analysed for fluoride concentrations using the 'acid-etch biopsy technique'. This study suggests that, when compared to 'multinational dentifrices', the Thai, Chinese and Indian dentifrices manufactured locally failed to show the F availability and/or F uptake efficacy even though they claimed to contain varying levels of F.

Acid Etching, Dental↗

PubMed1995

Sacroiliac kinematics for reciprocal straddle positions.

STUDY DESIGN: A descriptive and correlation approach was used to assess joint motion. OBJECTIVES: Magnitudes and directions of sacroiliac motion were examined from three different upright postural conditions. SUMMARY OF BACKGROUND DATA: Evidence and clinical views suggest that sacroiliac motion available in the normal case is extremely small to nonexistent. METHODS: Systems for standardizing the three postures and the Metrecom skeletal analysis system (Metrecom, Faro Technologies, Inc., Lake Mary, FL) for acquiring coordinate data for selected skeletal landmarks. RESULTS: The complete sacroiliac oblique-sagittal motion that occurred between the right forward and left forward stride positions was 9 degrees (SD 6.5). The composite oblique-transverse motion was 5 degrees (SD 3.9). The motions in each plane were significantly different from zero. A joint mobility relationship existed between the hip and sacroiliac joints. CONCLUSION: The results demonstrate that substantial angular motion is possible at the sacroiliac joints.

Adult↗

PubMed1995

Comparison of three methods of critical evaluation of microleakage along restorative interfaces.

This in vitro study compared microleakage along the dentin-restorative interface by use of a conventional single-surface and two stereoscopical protocols. The extent of microleakage in class V cylindric cavities that were restored with Scotchbond 2/P-50 was assessed after thermocycling and silver staining were performed. Specimens were randomized into three groups of 10 teeth for the three different protocols to be investigated. The categories were group 1, a single longitudinal section through the midline of the restoration, group 2, a multiple-surface protocol based on computer reconstruction of digitized images from multiple serial abrasions, and group 3, a clearing protocol based on immersion of demineralized specimens in methyl salicylate. The severity of microleakage for all groups was recorded on an ordinal scale and based on linear leakage length. The median leakage score for groups 1 through 3 was 2, 4, and 4, respectively. When comparisons were performed with nonparametric statistical analysis, both the clearing and the multiple-surface protocols recorded significantly more severe leakage than those detected from a conventional, single longitudinal, midline sectioning technique, (x2 = 8.595, p < 0.02). Furthermore microleakage patterns generated from the two stereoscopical protocols revealed extensive microleakage that advanced unilaterally or bilaterally through the dentin-restorative interface along the embrasure regions into the axial wall of the restorations. No significant difference was noted between the two stereoscopical protocols (Q = 0.260, p > 0.05), which suggested that the clearing protocol, which is less labor-intensive than the multiple-surface protocol, may be recommended for future comparative microleakage studies that involve the dentin-restorative interface.

Analog-Digital Conversion↗

PubMed1995

Functional regions of the mouse interleukin-10 receptor cytoplasmic domain.

The functions of wild-type and mutant mouse interleukin-10 receptors (mIL-10R) expressed in murine Ba/F3 cells were studied. As observed previously, IL-10 stimulates proliferation of IL-10R-expressing Ba/F3 cells. Accumulation of viable cells in the proliferation assay is to a significant extent balanced by concomitant cell death. Moreover, growth in IL-10 also induces a previously unrecognized response, differentiation of the cells, as evidenced both by formation of large clusters of cells in cultures with IL-10 and by induction or enhancement of expression of several cell surface antigens, including CD32/16, CD2, LECAM-1 (v-selectin), and heat-stable antigen. Two distinct functional regions near the C terminus of the mIL-10R cytoplasmic domain which mediate proliferation were identified; one of these regions also mediates the differentiation response. A third region proximal to the transmembrane domain was identified; removal of this region renders the cell 10- to 100-fold more sensitive to IL-10 in the proliferation assay. In cells expressing both wild-type and mutant IL-10R, stimulation with IL-10 leads to tyrosine phosphorylation of the kinases JAK1 and TYK2 but not JAK2 or JAK3 under the conditions tested.

Animals↗

PubMed1995

Variability in microleakage observed in a total-etch wet-bonding technique under different handling conditions.

Using a stereoscopic clearing protocol and scanning electron microscopy, we investigated the extent and nature of microleakage in a total-etch, current-generation dentin adhesive by a wet-bonding technique under different handling conditions. The hypotheses were that inadequate light curing of the primer or incomplete drying of the primer solvent might adversely affect the sealing ability of an acetone-containing adhesive system. The study consisted of three experimental groups: (I) a control group with an adequate light source and with the primer solvent completely dried; (II) an "inadequate-light" group; and (III) an "incomplete evaporation of primer solvent" group. The extent of microleakage after silver staining and clearing of the specimens was scored based on a modified five-point scale. Nonparametric statistical analysis (Kruskal-Wallis ANOVA) followed by a multiple comparison test (Dunn test) indicated significant differences among the three groups (p < 0.05). SEM examination of the restorative interface revealed that microleakage appeared to be initiated from the bonding resin-hybrid layer interface in all three groups, representing the weak link in the adhesive system. In addition, microleakage was characterized by 5 zones, each delineating a stage in a continuous array of progressively deleterious microleakage patterns variously distributed among the three groups. It was suggested that, while the bonding resin-hybrid layer interface represented the intrinsic weakness in an already much improved dentin adhesive, extrinsic factors such as the adequacy of the curing light and, more importantly, complete removal of the primer solvents can and should be avoided to preserve the structural integrity of the marginal seal.

Acid Etching, Dental↗

PubMed1995

Strategies for application of scientific findings in prevention.

Dental research in the last 50 years has accomplished numerous significant advances in preventive dentistry, particularly in the area of research in fluorides, periodontal diseases, restorative dentistry, and dental materials, as well as craniofacial development and molecular biology. The transfer of scientific knowledge to clinical practitioners requires additional effort. It is the responsibility of the scientific communities to transfer the fruits of their findings to society through publications, conferences, media, and the press. Specific programs that the International Association for Dental Research (IADR) has developed to transmit science to the profession and the public have included science transfer seminars, the Visiting Lecture Program, and hands-on workshops. The IADR Strategic Plan also has a major outreach goal. In addition, the Federation Dentaire Internationale (FDI) and the World Health Organization (WHO) have initiated plans to celebrate World Health Day and the Year of Oral Health in 1994. These are important strategies for the application of scientific findings in prevention.

Dental Research↗