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Biomedical subjects

C C Youngson

Publications and source records attributed to C C Youngson.

36 records · Page 2Linked to original sources
PubMed1996

An in vitro study of the bond strength of light-cured glass ionomer cement in the bonding of orthodontic brackets.

The search to improve the properties of dental adhesives has lead to the development of light-cured glass ionomer cements. Using human teeth in vitro, the present study tested the shear/peel bond strengths of two light-cure materials ('Variglass VLC' and 'Fuji Lining LC') against a 'no-mix' composite orthodontic adhesive ('Right-On') and a chemically cured glass ionomer cement ('Ketac-Cem'). The light-cured materials were found to have an inferior bond strength compared with the two control adhesives. Based on the findings of this study, there is no evidence to support the use of the materials tested for the bonding of orthodontic brackets.

Acid Etching, Dental↗
PubMed1995

In vitro fracture fixation: adhesive systems compared with a conventional technique.

To find out whether adhesive techniques could have a role in bone fixation in selected cases an in vitro comparison between the current 'Champy' miniplate system and bonded stainless steel was undertaken using cyanoacrylate or dental composite cement. 33 bovine ribs were sectioned to simulate fracture separation, divided randomly into three groups, and immobilised by one of the three treatments. Distraction across the 'fracture' was produced using a universal testing apparatus, and forces at failure were recorded in Newtons (N). Image analysis enabled the contact area of the adhesive to be determined in mm2, so the bond strength in N/mm2 was derived. The Champy system failed at a significantly greater force (N) than the adhesives (p = 0.000). There was no significant difference in bond strength between either of the adhesive systems tested.

Analysis of Variance↗
PubMed1995

An in vitro assessment of tooth preparation for porcelain veneer restorations.

OBJECTIVES: This in vitro study aimed to examine the depth of preparation and incidence of dentine exposure resulting from the use of a 'freehand' technique to prepare maxillary central incisors for porcelain veneers. METHODS: Twenty-two maxillary central incisors were selected. Prior to preparation an index of the labial surface of each tooth was recorded and the tooth secured in a jig to permit accurate relocation. Two operators each prepared 11 teeth aiming to reduce the labial thickness evenly by 0.5 mm. Low viscosity silicone impression material was then placed on the index and the teeth relocated into the jig. Upon removal, this material was sectioned in the cervical, middle and incisal thirds of the tooth and its thickness measured using a toolmaker's microscope. The teeth were acid etched and also stained with a dentine dye to identify any area of dentine exposed during preparation. RESULTS: Significant differences (P < 0.001) in the depth of preparation at different sites, with least reduction in the mid-incisal region, were found. Greater reduction was found at the cervical and proximal margins with areas of dentine exposed at those sites in the majority of teeth. CONCLUSIONS: In view of the incidence and position of dentine exposure found in this study, the use of a dentine bonding system during the placement of porcelain veneers would appear essential when employing a 'freehand' preparation technique.

Dental Cavity Preparation↗
PubMed1995

In vitro radiographic representation of the extent of voids within obturated root canals.

The aim of this study was to determine whether radiographs provide an accurate representation of the degree of root canal obturation following a cold lateral condensation technique. A total of 40 extracted single-rooted lower premolar teeth were prepared using either a standardized step-back technique or an ultrasonic device by one of two operators. The four groups each of 10 teeth were obturated using lateral condensation by a third operator. To assess apical leakage the obturated teeth were coated with nail varnish to within 2 mm of the apex and immersed in methylene blue for 48 h. The teeth were then radiographed in bucco-lingual and mesio-distal planes prior to subsequent sectioning in a bucco-lingual plane. Sections and radiographs were analysed using an image analysis apparatus to determine the proportion of root canal occupied by gutta-percha, void and/or sealer. Mean percentages of void calculated from the bucco-lingual radiographs, mesiodistal radiographs and tooth sections were 4.14%, 5.98% and 4.98%, respectively. Statistical analysis showed no significant differences between the radiographic views and the tooth sections (P > 0.05). Both planes of radiograph accurately represented the proportion of void when compared with the tooth section.

Analysis of Variance↗
PubMed1994

Influence of age on the extent of voids in root canals sealed using a cold lateral condensation technique.

The aim of this study was to examine whether it is more difficult to achieve complete obturation of the root canal in teeth from different age groups, using the measurement of voids within the obturated canal to determine the quality of endodontic therapy. One-hundred and fifty-two single-rooted premolar teeth extracted from patients of known age were collected. Following cleaning and storage the teeth were decoronated and radiographed. Forty selected teeth were allocated to one of four age-groups, (under 20, 20-35, 36-50, over 50 years) each consisting of 10 teeth. The working length was determined radiographically and preparation was carried out using the step-back technique. Each canal was obturated using cold lateral condensation with Tubliseal cement. The roots were then sectioned longitudinally and photographed. Sections and transparencies were subjected to image analysis to determine the total areas of root canal, sealer and voids respectively and statistical analysis of the differences between the various age groups was undertaken. There was a trend towards a reduction in the areas of sealer and sealer plus void with respect to increasing age group, although no significant differences existed. A significant relationship (P < 0.05) was found between the area of voids found in the youngest group when compared with all other groups, the greatest cumulative area of voids being found in the youngest teeth.

Adult↗
PubMed1994

Comparison of the quality of obturation following endosonic versus hand instrumentation.

This study was undertaken to compare the quality of root canal obturation following preparation by endosonic or hand instrumentation. Forty single-canal, extracted lower premolar teeth were selected. One group of 20 teeth was prepared using a standard step-back technique, the other 20 teeth were prepared with an ultrasonic machine. The groups were subdivided, with two operators preparing 10 teeth of each group. The teeth were obturated by a third operator using cold laterally condensed gutta percha. The root apices were then immersed in methylene blue dye for 48 h and the teeth sectioned longitudinally. Image analysis recorded the amount of sealer and void within the obturated canal. The linear distance of dye penetration was measured to provide an indication of apical seal. Examination of the root canal shape resulting from the different preparation techniques used was also undertaken. No significant difference was noted in the percentage of sealer and void present in the root canals obturated after endosonic or hand instrumentation. There was a slightly greater although not significant increase in the degree of linear penetration of dye in canals prepared endosonically. The endosonic technique used in this study appeared to produce a canal preparation of slightly less continuous taper than that obtained with hand preparation.

Analysis of Variance↗
PubMed1992

An in vitro comparative analysis: scanning electron microscopy of dentin/restoration interfaces.

One hundred maxillary premolar teeth were randomly allocated to ten groups. Each group was restored with one of ten different restorative techniques. The teeth were stored in deionized water for 7d prior to longitudinal sectioning in a mesio-distal plane. Following sectioning, ten specimens from each group were chosen at random from the 20 available sections. The sectioned surfaces were polished using 600-grit SiC abrasive paper and etched for 10 s with 50% phosphoric acid to remove the smear layer produced by sectioning. Five tooth sections from the dentin bonding resin groups were allowed to dry at 20 degrees C for 24h. The glass ionomer-based groups were reimmersed in deionized water during this period. The remaining five sections from each group were replicated using an addition-cure vinyl polysiloxane impression material and an epoxy resin. A comparison was made of the sections and the replicas. All tooth specimens were sputter-coated with gold for 4 min and examined using a scanning electron microscope. Replicas were gold-coated for 3 min. Different tooth/restoration interfaces, associated with different materials, were observed. A marked difference between the replicas and tooth sections was observed for glass ionomer-based restorations but not for resin-based bonding systems. Representative samples of replicas and specimens are shown, and the significance of the observed differences is discussed.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1992

A technique for three-dimensional microleakage assessment using tooth sections.

Microleakage is commonly assessed using restored teeth, sectioned through the midline of the restoration. It is impossible to determine if this is representative of the leakage throughout the whole tooth. This pilot study examined the feasibility of calculating areas and volumes of leakage using serial sections of restored teeth which had been subjected to dye immersion and image analysis. Using the sections, perspex models of the teeth were constructed to present the pattern of the dye leakage into dentine. This appears to be a viable technique for the three-dimensional assessment of microleakage.

Composite Resins↗
PubMed1992

Early in vitro marginal microleakage associated with different lining materials under Class II amalgam restorations.

The aim of this study was to determine which dental cavity lining material exhibited least microleakage when used under amalgam. Extracted premolar teeth, prepared with Class II cavities, had one of three lining materials (cavity varnish, zinc oxide-eugenol or light-cured glass-ionomer) placed. Following restoration the teeth were immersed in eosin and sectioned. Sections were subjected to image analysis measuring the linear leakage and area of spread into coronal dentine. Percentages in relation to restoration length and the area of crown dentine were calculated. Light-cured glass-ionomer cement liner significantly (P < 0.05) reduced all aspects of the microleakage parameters studied.

Analysis of Variance↗
PubMed1991

In vitro microleakage associated with posterior composite restorations used with different base/bonding system combinations.

The study aimed to determine the base/restoration combination which allowed the least microleakage in Class II cavities. One hundred premolar teeth were prepared with a standardized, minimal two-surface cavity and randomly ascribed to ten equal groups. The cavities were restored by use of one of ten different material/technique combinations. Restored teeth were sealed to within 1 mm of the restoration margins with nail varnish prior to the immersion of the crowns in 5% (buffered) eosin for 48 h. The teeth were then hemisected longitudinally, in a mesio-distal plane, through the midline of the restoration by means of a diamond disc with water coolant, and one half of each tooth was then photographed. The transparencies were examined by image analysis programmed to facilitate calculation of the percentage of the tooth/restoration interface and of the crown dentin exhibiting dye penetration. Light- and chemically-cured glass-ionomer-based restorations showed similar amounts of leakage when expressed as a percentage area of crown dentin. This was significantly (p less than 0.05) less than that shown by cavities both etched and bonded. Cavities restored without enamel etching or involving the use of a bonding system exhibited significantly (p less than 0.05) greatest leakage.

Acid Etching, Dental↗
PubMed1990

In vitro marginal microleakage: examination of measurements used in assessment.

Premolar teeth with Class II amalgam restorations placed after the application of cavity varnish (Group A), a light cured glass ionomer base (Group B) and 40 per cent polyacrylic acid as a pretreatment agent, followed by unset cermet cement (Group C) were examined for marginal leakage using dye penetration and image analysis. Including amongst the parameters examined were linear leakage length and leakage area, which were found to have no consistent correlation. Group A and C did not generally show significant differences in the parameters examined, whereas Group B exhibited significantly less linear leakage (P less than 0.001), and significantly less leakage area when the stained area was expressed as a percentage of available dentine (P less than 0.001). While allowing some linear leakage, it was found that the light cured glass ionomer base appeared to prevent the dye from entering the dentine. It is concluded that an assessment based solely on the leakage length is inadequate and that some measurement of penetration into dentine should be included in order to fully assess the microleakage potential of a material or technique.

Acid Etching, Dental↗
PubMed1990

In vitro marginal microleakage associated with five dentine bonding systems and associated composite restorations.

Fifty sound premolar teeth, extracted for orthodontic purposes and stored at room temperature in physiological saline since extraction, were prepared with a standardized minimal two-surface Class II cavity. The teeth were then ascribed randomly to five groups, each of ten teeth. Each of four groups was restored using a different dentine bonding system and the associated posterior composite resin according to the manufacturer's instructions. The fifth group was restored with Superbond C & B dentine bonding system and Occlusin composite. After immersion in de-ionized water for at least 7 days, the teeth were sealed with nail varnish to within 1 mm of the margin of the restoration. The teeth were then immersed in 5 per cent buffered Eosin for 48 h. Following mesiodistal sectioning the sections were photographed and subjected to image analysis to establish the length of dye penetration at the tooth/restoration interface and the amount of dye penetration into the crown dentine. Tripton/Occlusin and XR Bond/Herculite XR groups showed a significantly (P less than 0.05) smaller amount of leakage than Gluma/Lumifor or Scotchbond 2/P50 combinations when assessed as a percentage of the tooth/restoration interface exhibiting leakage. When the percentage of crown dentine showing dye penetration was considered, the Tripton/Occlusin group showed less leakage than the other material combinations. It is concluded that Tripton, when used with the recommended composite, will allow significantly less microleakage than Gluma/Lumifor, Scotchbond 2/P50 or Superbond C & B/Occlusin combinations and a similar amount to XR Bond/Herculite XR in vitro.

Acid Etching, Dental↗
PubMed1989

Speed variability of air-driven motors in the self-threading pin technique.

Effective pin placement is dependent upon correct preparation of the dentine channel. Various factors contribute to the success or otherwise of this channel preparation. One such factor is the rotational speed of the twist drill. It is widely recommended that the twist drill be operated within the 500-800 rpm speed range, in order to prevent a temperature rise in the pulp during the cutting process. This paper examines the ability of air-driven dental motors, when coupled to two speed-reduction handpieces with differing reducing ratios, to operate within this range. The results reveal a wide variation in the speed ranges of the motors tested. Of the two types of handpiece examined, it appears that a 10:1 speed reduction is appropriate for the majority of motors.

Dental Pins↗
PubMed1989

Current status of the cast metal inlay: a survey of dental schools in the UK and Hong Kong.

This study reports on the current status of the gold inlay in the undergraduate curriculum of Dental Schools in the UK and at the Prince Philip Dental Hospital, Hong Kong, to determine if the decline in the use of the cast gold inlay over the past 20 years is reflected in teaching at undergraduate level. A questionnaire, which was mailed to all the heads of departments of conservative dentistry in the UK, was designed to determine current teaching in respect of cast inlays. The results show that although the majority of UK dental schools continue to teach direct and indirect inlay techniques, a minority (4 and 5 respectively) no longer incorporate a practical exercise in this teaching. Reasons cited for the discontinuation of the technique are varied but the availability of simpler, more conservative techniques is emphasized. Examination of the treatment records at the Prince Philip Dental Hospital, Hong Kong, where the Class II inlay technique is taught both theoretically and practically, shows that only a small proportion of all posterior cast restorations fitted between May 1983 and April 1988 were inlays (4.6 per cent).

Dental Records↗
PubMed1989

A fluoride-containing composite resin--an in vitro study of a new material for orthodontic bonding.

The shear/peel bond strength of a new material, a 'hybrid' of a composite resin and a glass ionomer cement, was compared in vitro with the bond strengths of a composite resin and of a glass ionomer cement. The new material had a significantly greater bond strength than the other materials tested and its properties were very similar to the composite resin. Unlike the glass ionomer cement, etching of the enamel before applying the adhesive is required. The clinical indications for using this new cement are discussed.

Adhesiveness↗
PubMed1988

An in vitro study of the bond strength of a glass ionomer cement in the direct bonding of orthodontic brackets.

The shear/peel bond strength of a 'no-mix' composite orthodontic bonding resin was compared in vitro with that of a glass ionomer cement. The effect of pre-treatment of the enamel, with either phosphoric acid or polyacrylic acid, prior to using the glass ionomer cement was also assessed. The composite resin had a significantly higher bond strength than the glass ionomer cement. Simple prophylaxis and drying of the enamel achieved the best results when using the glass ionomer cement, whilst etching the tooth surface with phosphoric acid produced a significantly poorer bond to the enamel. Investigation of the site of failure showed the composite resin bonded very well to the tooth and less well to the bracket, whilst the glass ionomer adhered significantly better to the bracket base than to the tooth surface.

Acid Etching, Dental↗