Biomedical subjects

J S Rees

Publications and source records attributed to J S Rees.

At least 19 recordsLinked to original sources

PubMed2006

Surface and pulp chamber temperature rises during tooth bleaching using a diode laser: a study in vitro.

OBJECTIVE: To measure the surface and pulp chamber temperature increases in vitro on upper and lower anterior teeth during a tooth whitening procedure using a diode laser. METHOD: A thermocouple was used to measure the temperature increase on the surface of an extracted upper central incisor tooth. Pulp chamber temperature readings were made on upper and lower central incisors, lateral incisors and canines. A diode laser recommended for tooth bleaching was tested at three different power settings (1W, 2W, 3W). Temperature measurements were made with and without the bleaching agent present on the labial tooth surface. RESULTS: The increase in surface temperature readings ranged from 37 degrees C (1W) to 86.3 degrees C (3W) with no bleaching gel present. Pulp chamber temperature increases ranged from 4.3 degrees C (1W) to 16 degrees C (3W). The presence of the bleaching gel reduced temperature increases seen at the tooth surface and within the pulp. CONCLUSIONS: The increase in the pulp chamber temperature with the laser used at 1-2W was below the critical temperature increase of 5.5 degrees C thought to produce irreversible pulpal damage. However, a power setting of 3W produced a pulp chamber temperature increase above this threshold (16 degrees C) and caution is advised when using this setting.

Body Temperature↗

PubMed2006

The biomechanics of abfraction.

The role of occlusal loading in the development of non-carious cervical lesions is becoming increasingly prominent. It is suggested that high occlusal loads result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause disruption of the bonds between the hydroxyapatite crystals, eventually resulting in the loss of cervical enamel. This article reviews the evidence to support the thesis that occlusal loading can contribute to the process of non-carious cervical tooth loss or abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to non-carious cervical tooth loss.

Animals↗

PubMed2006

The effect of preparation height and taper on cement lute stress: a three-dimensional finite element analysis.

Three dimensional finite element models of an upper second premolar and molar with full veneer gold crown preparations were developed from extracted samples. The cement lute width was kept constant at 40 microm, but the height and preparation taper were varied. For both models the preparation height was either 1.5 mm (short preparation) or 3 mm (long preparation). The preparation taper was either 10 degree or 30 degree, giving a total of eight models. Each model was loaded with a 10 N horizontal load, a 10 N vertical load or a 10 N load distributed across the occlusal surface. The maximum shear stress and the maximum Von Mises' stress in the cement lute of each model were recorded. For the premolar, the maximum shear stresses ranged from 0.3-5.43 MPa and the maximum Von Mises' stress ranged from 1.44-14.98 MPa. For the molar, the maximum shear stresses ranged from 0.15-5.22 MPa and the maximum Von Mises' stress ranged from 0.3 7-15.02 MPa. The stress fields were consistently higher in the premolar with a 30 degree preparation taper compared to the 10 degree taper. The attainment of a cavity taper of 100 is still important to minimise stress in the cement lute and is particularly important in teeth with a lower preparation surface area such as a premolar

Bicuspid↗

PubMed2005

Surface and intra-pulpal temperature rises during tooth bleaching: an in vitro study.

OBJECTIVE: To measure the surface and intra-pulpal temperature increases in vitro on upper and lower anterior teeth during tooth whitening procedures. METHOD: A thermocouple was used to measure the temperature increase on the surface of an extracted upper central incisor tooth. Intra-pulpal temperature readings were made on upper and lower central incisors, lateral incisors and canines. Four lamps recommended for tooth bleaching were tested; a plasma arc lamp, a xenon-halogen lamp, a standard halogen lamp and a diode laser lamp. Temperature measurements were made with and without the bleaching agent present on the labial tooth surface. RESULTS: The increase in surface temperature readings ranged from 0.44 degrees C (luma arch) to 86.3 degrees C (laser) with no bleaching gel present. Intra-pulpal temperature increases ranged from 0.30 degrees C to 15.96 degrees C. The presence of the bleaching gel reduced temperature increases seen at the tooth surface and within the pulp. CONCLUSIONS: The increase in the intrapulpal temperature with most bleaching lamps was below the critical threshold of a 5.50 degrees C increase thought to produce irreversible pulpal damage. The only lamp that produced an intrapulpal temperature increase above this threshold was the laser-based lamp and caution is advised when using this equipment.

Body Temperature↗

PubMed2005

The bleaching depth of a 35% hydrogen peroxide based in-office product: a study in vitro.

OBJECTIVES: The aim of the present study was to quantify the penetration of 35% hydrogen peroxide into enamel and dentine and to relate this to the resultant shade change of the tooth. METHOD: The crowns of 24 caries and developmental defect free human maxillary incisors were stained internally with a standardised tea solution. Twelve specimens were power bleached with light activated 35% hydrogen peroxide and 12 placed in water; both exposure times were 30min. Three different shade assessment methods (Vita shade guide [SG], shade vision system [SVS] and a chromometer) were employed prior to, after tea staining and after power bleaching/water treatments. Twelve specimens each from the bleach group and the water control water group were sectioned mesio-distally. An additional 12 specimens from the bleach and the control group were sectioned labio-palatally. The stain area for each specimen was measured using image analysis software. RESULTS: With tea staining, the mean changes in Vita shade guide units (SGU) ranged from 3.66 to 8.33. With the SVS system changes of 3.66-9 units were seen. Chromometer readings showed that following bleaching the L* values moved in the direction of black (3.8-6.7) and a* and b* values were in the red (0.3) and yellow (1.5) direction, respectively. Samples bleached and sectioned mesio-distally showed stain coverage of 28.6-39.4%, while palatal sections showed stain coverage of 58-72%. Control samples, whether sectioned mesio-distally or labio-palatally, showed staining throughout the dentine (97-100% coverage). CONCLUSION: A 35% hydrogen peroxide in-office bleaching gel demonstrated bleaching into dentine of uniform depth.

Analysis of Variance↗

PubMed2004

The effect of hydrogen peroxide concentration on the outcome of tooth whitening: an in vitro study.

AIM: This in vitro study examined the effect that various concentration of hydrogen peroxide (5-35%) had on tooth whitening. METHOD: Extracted third molars were sectioned and stained using a standardised tea solution to Vita shade C4. These stained specimens were then bleached with a series of gels containing 5, 10, 15 or 25% w/w hydrogen peroxide. Each specimen was bleached for a number of sessions with one session being defined as 3 x 10 min exposure. RESULTS: The number of applications of the various concentrations of bleaching gel varied from 12 applications for the 5% gel to one application for the 35% gel. Plotting the number of applications against hydrogen peroxide concentration showed an exponential response curve. CONCLUSIONS: The concentration of hydrogen peroxide in a proprietary bleaching gel had a marked effect on the number of applications required to produce an optimal shade outcome.

Algorithms↗

PubMed2004

The laboratory assessment of enamel erosion: a review.

OBJECTIVES: To review the various methods and techniques available to assess enamel erosion in vitro. DATA: Peer reviewed scientific articles. SOURCES: Medline and Web of Science searches and manual searching. STUDY SELECTION: Laboratory based assessments only included. CONCLUSIONS: A number of macroscopic and microscopic techniques have been used to assess enamel erosion in vitro and in situ. This review examines techniques which are either well established or comparatively novel techniques that are being explored for their potential.

Dental Enamel↗

PubMed2004

A safety study in vitro for the effects of an in-office bleaching system on the integrity of enamel and dentine.

OBJECTIVE: The aim of this study was to investigate safety concerns with bleaching procedures by studying the effects of a high concentration hydrogen peroxide (HP) in-surgery bleaching product on enamel and dentine. METHOD: Flat enamel and dentine samples embedded in epoxy resin were prepared from human third molar teeth. Erosion of enamel: groups of enamel samples were treated with 35% HP then citric acid (CA) or brushing with toothpaste or CA alone and water alone. Enamel Loss was measured using a profilometer. Abrasion/erosion of dentine: groups of dentine specimens were treated as follows: Group 1--brushed with water for 30 min. Group 2--brushed with 35% HP for 30 min. Group 3--power bleached for 30 min and then Group 4--brushed with toothpaste for 1 minute. Group 5--water soaked for 30 min followed by brushing with toothpaste for 1 min. Group 6--orange juice soaked for 30 min followed by brushing with toothpaste for 1 min. Treatment effects were measured using a profilometer. Hardness tests: enamel and dentine specimens were hardness tested using a Wallace indenter prior to and post bleaching. Scanning Electron Microscopy: enamel and dentine specimens were taped and the exposed tissue treated with 35% HP and then studied under scanning electronmicroscopy (SEM). RESULTS: Enamel erosion: bleaching enamel samples had no measurable effect on enamel. Pre-bleaching had no significant effect on subsequent CA erosion or brushing. Abrasion/erosion of dentine: no significant differences were found between treatments 1-5 with little change from baseline detected. Orange juice (Group 6) produced considerable and significantly more erosion than other treatments. Hardness tests: there were no significant changes in hardness values for enamel and dentine. SEM: there was no evidence of any topographical changes to either enamel or dentine. CONCLUSION: Using one of the highest concentrations of HP for tooth bleaching procedures and maximum likely peroxide exposure, there was no evidence of deleterious effects on enamel or dentine. It must be assumed that studies which reported adverse effects on enamel and or dentine of bleaches reflect not the bleach itself but the pH of the formulation used.

Beverages↗

PubMed2004

A reappraisal of the incremental packing technique for light cured composite resins.

The cuspal flexure caused by a direct placement composite resin was measured using a technique that did not interfere with cuspal movement. Twenty upper premolar teeth with mesial-occlusal-distal (MOD) cavity preparations were restored using a posterior composite resin. Ten teeth were restored using a bulk packing technique and 10 were restored using three 'U' shaped bucco-lingual increments. Total cuspal movement was measured 1 h following the initiation of curing. Bulk placement of the composite resin produced slightly more cuspal movement (12.5 microm) compared with the incremental placement of composite (11.3 microm). This difference was not statistically significant. The technique of incremental packing to reduce cuspal flexure is therefore questioned.

Bicuspid↗

PubMed2004

Undermining of enamel as a mechanism of abfraction lesion formation: a finite element study.

Many workers have suggested that abfraction lesion formation is caused by the physical overloading of enamel. However, an alternative mechanism, involving undermining of the cervical enamel along the amelodentinal junction (ADJ), may be a more realistic explanation. The aim of this study was to examine what effect undermining of the buccal cervical enamel would have on the stress distribution in upper teeth. Two-dimensional plain strain finite element meshes of an upper incisor, canine and first premolar and the supporting periodontal ligament and alveolar bone were developed. Each tooth was loaded with an oblique 100 N load, and the nodal maximum principal stresses (MPS) along a buccal horizontal sampling plane 1.1 mm above the amelo-cemental junction was measured. A discontinuity between the cervical enamel and dentine elements was then introduced (0.1 mm wide) using gap elements. The vertical extent of this defect varied from 0.1 to 0.5 mm. The value of the MPS varied from 1.8 to 209 Mpa, and the lowest values were found for the intact teeth (range 0.6-30.3 MPa). The discontinuity caused a dramatic increase in the numerical values of the MPS, and in many instances these exceeded the known failure stress for enamel.

Bicuspid↗

PubMed2004

A cross-sectional study of buccal cervical sensitivity in UK general dental practice and a summary review of prevalence studies.

AIM: The initial aim of this study was to establish the prevalence of dentine hypersensitivity (DH) in a cross-sectional study of patients visiting general dental practitioners in the UK over a period of one calendar month. METHODS: Eighteen dental practitioners examined 5,477 patients over a period of one calendar month, and patients who were diagnosed with DH were questioned further about their occupation and smoking habits. The amount of buccal gingival recession associated with the sensitive teeth was also recorded, as was the presence of periodontal disease. RESULTS: One hundred and fifty-two patients were diagnosed as having DH, giving a prevalence figure of 2.8%. The commonest teeth affected were the first molars and premolars, and the commonest initiating factor was cold drinks. A tendency for a greater number of DH teeth was also found for patients with periodontal disease who also smoked. There was also a tendency for the patients with DH teeth to come from higher social groups. CONCLUSION: At the time of conducting this study, the European Federation of Periodontology had not recommended that sensitive teeth associated with periodontal disease and treatment be termed root sensitivity (RS). The title of this paper was therefore chosen to reflect this decision, and the data represent teeth both within and between subjects with DH and RS.

Adolescent↗

PubMed2003

Development and evaluation of a method in vitro to study the effectiveness of tooth bleaching.

AIM: To develop and evaluate a reproducible intrinsic discolouration model in vitro, based on tea, which would allow the effectiveness of bleaching to be evaluated. METHOD: The crown portions of extracted human third molars were sectioned bucco-lingually in half. Colour assessments were made at baseline, post staining and post whitening using a standard clinical shade guide (SG), a shade vision clinical colorimeter system (SVS) and a reflectance chromometer. Internal staining employed a standard tea solution into which groups of five specimens were placed from 1 to 6 days. All assessments demonstrated maximum staining within one day. Groups of stained specimens were exposed to 1. Water (placebo control) 2. Enamel polished 3. Enamel polished and bleached through enamel 4. Bleached through enamel 5. Bleached through dentine 6. Bleached through enamel and dentine 7. Exposed to the bleach vehicle (minus active control). Control and bleach gel treatments were for 30 min. Comparisons of treatment effects were made using unpaired t-test on groups selected a priori for analysis. RESULTS: SG and SVS revealed that control and polish treatments had no or little effect respectively on tooth shade but all bleach treatments produced marked and statistically significant whitening effects and to a similar magnitude. Bleaching treatments returned the majority of specimens to the original shade or beyond representing a SG mean change of 13.8-15 shade guide units (SGU). Chromometer readings were consistent except that polishing alone increased tooth lightness slightly. CONCLUSIONS: Teeth were reproducibly stained internally, to provide a model in vitro by which to evaluate bleaching. The model, could be used to study many aspects of vital tooth bleaching, but has the limitation, without in vivo or in situ data, of cautiously extrapolating the effects in vitro to outcome clinically.

Colorimetry↗

PubMed2003

The prevalence of dentine hypersensitivity in a hospital clinic population in Hong Kong.

OBJECTIVES: Dentine hypersensitivity is a common clinical finding with a wide variation in prevalence values. The aim of this study was to establish the prevalence of dentine hypersensitivity and to examine some associated aetiological factors in a cross-sectional study of patients visiting the Periodontology and Oral Hygiene Clinic at Prince Phillip Dental Hospital, Hong Kong over a three-week period. METHODS: 226 patients were examined over a three-week period using a triple syringe to administer a blast of cold air to confirm the diagnosis of dentine hypersensitivity. Additional factors such as smoking habits, initiating stimuli, gingival recession and cervical tooth surface loss were noted. RESULTS: 153 patients were diagnosed as having dentine hypersensitivity, giving a prevalence figure of 67.7%. The commonest teeth affected were the lower incisors and the commonest initiating factor was cold drinks. CONCLUSIONS: The prevalence of dentine hypersensitivity in a hospital periodontology clinic population in Hong Kong was 67.7%.

Adolescent↗

PubMed2003

Abfraction lesion formation in maxillary incisors, canines and premolars: a finite element study.

Abfraction lesions are angular, wedge-shaped defects found at the cervical region of teeth and are caused by mechanical overloading initiated by cuspal flexure. Clinically, these lesions are more prevalent on the labial aspect of maxillary incisors. The aim of this study was to provide a biomechanical explanation for this clinical variation. Two-dimensional plane strain finite element models of an maxillary incisor, canine and first premolar were developed and the cervical stress profiles were examined along a horizontal plane 1.1 mm above the amelo-cemental junction. The local X (horizontal) stress on the labial/buccal side was 176.4 MPa for the incisor, 57.8 MPa for the premolar, and 3.4 MPa for the canine. Similarly, the maximum labial/buccal principal stress was 181.4 MPa for the incisor, 25.2 MPa for the premolar, and 66.8 MPa for the canine. The labial/buccal stress profile in the cervical region of an maxillary incisor was always greater than that found in an maxillary canine or premolar tooth. These findings provide a biomechanical explanation for the clinical variation seen in the prevalence of cervical abfraction lesions.

Bicuspid↗

PubMed2003

A comparison of the erosive susceptibility of cuspal and cervical enamel using an ultrasonic technique.

The aim of this study was to compare the erosive susceptibility of cuspal and cervical enamel from human premolar and molar teeth. Small blocks of cervical and cuspal enamel were immersed in either orange juice or Coca-Cola at 37 degrees C and the surface enamel loss was measured by surfometry at 1, 2, 3 and 4 h. Additionally, once-hourly enamel loss was measured, specimens were placed in an ultrasonic bath containing water and ultrasonicated for 5 s to determine the degree of surface demineralization. A further set of enamel specimens were prepared that had 100 microm of the enamel surface removed. This was done to remove the hypermineralized surface enamel layer. Surface enamel loss in orange juice at 4 h, following ultrasonication, ranged from 13.2 to 16.9 microm. The surface enamel loss in Coca-Cola at 4 h, following ultrasonication, ranged from 21.7 to 27.5 microm. Subsurface enamel loss in orange juice at 4 h, following ultrasonication, ranged from 10.7 to 16.1 microm. The subsurface enamel loss in Coca-Cola for 4 h, following ultrasonication, ranged from 36.8 to 37.2 microm. Overall, little difference was found in the erosive susceptibility of cervical and cuspal enamel to the effects of orange juice or Coca-Cola.

Bicuspid↗

PubMed2003

The effect of the addition of poly (methyl methacrylate) fibres on the transverse strength of repaired heat-cured acrylic resin.

The aim of the present study was to investigate the effect of addition of an experimental poly (methyl methacrylate) (PMMA) fibre in linear form, 0.75 mm in diameter on the transverse strength of repaired heat-cured poly (methyl methacrylate) denture base material. Specimens of heat-cured PMMA were repaired with an autopolymerizing acrylic resin and an autopolymerizing acrylic resin together with the addition of untreated and surface-treated PMMA fibres in different arrangements. The transverse bend test was carried out using a LIoyd's Instrument Material Testing Machine. From the results, it can be concluded that the box incorporated into the repair joint produced a significant decrease in the moduli of elasticity and rupture which may be due to stress concentration effects. The addition of one layer of untreated PMMA fibres significantly decreased the modulus of rupture. The addition of two layers of untreated fibres produced a slight but statistically non-significant increase in the modulus of rupture. The addition of surface-treated (with butadiene styrene latex emulsion) fibres into the repair complex gave no improvement compared with the addition of untreated fibres in terms of transverse strength. There was an insignificant decrease in the modulus of rupture compared with the untreated fibres.

Acrylic Resins↗

PubMed2003

Clinical evaluation of a carbon fibre reinforced carbon endodontic post.

This study reports a prospective clinical trial comparing a carbon fibre reinforced carbon (CFRC) endodontic post with a conventional prefabricated post. Twenty-seven single rooted maxillary anterior teeth in 18 patients (nine males and nine females; age range 18-60 years) were restored either with a CFRC post or a wrought precious alloy control. Cast type III gold alloy cores were used in conjunction with both post groups. The CRFC posts (n = 16) were cemented with a composite luting agent and the conventional posts (control) were cemented with zinc phosphate. Four failures were recorded in the CFRC post group at 24, 29, 56 and 87 months, compared with one failure in the control group at 84 months. These results suggest that post-retained crowns utilizing a CFRC material and a composite resin luting agent do not perform as well as conventional wrought precious alloy posts.

Adolescent↗

PubMed2003

Abfraction lesions: myth or reality?

UNLABELLED: Loss of tooth substance in the cervical region is usually attributed to toothbrush abrasion, erosion, or a combination of both factors. Recently the role of occlusal loading has become increasingly prominent. It is suggested that high occlusal loads cause large cervical stress concentrations, resulting in a disruption of the bonds between the hydroxyapatite crystals and the eventual loss of cervical enamel. This process has been called noncarious cervical tooth loss or abfraction. This article reviews the available evidence to support the thesis that occlusal loading can contribute to the process of abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to abfraction lesion formation. CLINICAL SIGNIFICANCE: It is important to recognize the potential role of occlusal loading in the loss of cervical tooth tissue so that management of the occlusion can be incorporated into a treatment plan for a patient with abfraction lesions.

Bite Force↗