Fj Trevor Burke

Monomer conversion versus flexure strength of a novel dental composite

OBJECTIVES To quantify the monomer conversion and flexural strength of an experimental oxirane-based composite material (EXL596) compared with two, commercially available, dimethacrylate based restoratives (Z250 and Z100). METHODS Fourier-transform infra-red spectroscopy (FTIR) was utilised to evaluate the degree of conversion (DC) (n=5) and biaxial flexure strength (BFS) testing (n=20) was used to analyse flexural strength and associated Weibull moduli (m) of each material following 0.1, 0.5, 1, 4, 24 and 48 h immersion in a lightproof waterbath maintained at 37+/-1 degrees C. RESULTS The DC of Z250 and Z100 following 0.1, 0.5 and 1 h post-irradiation was significantly greater than the DC of EXL596 for the same immersion periods. This was manifested as a significant decrease in BFS and associated m of EXL596 compared with Z250 and Z100 for the 0.1, 0.5 and 1 h post-irradiation periods. The DC and BFS of EXL596 were significantly greater than Z250 and Z100 following 24 h immersion. CONCLUSIONS Assessment of FTIR spectra, BFS and associated m has provided a useful method in the quantitative analysis of resin-based composite conversion. Identification of the decreased DC of EXL596 compared with Z250 and Z100 was achieved using FTIR. However, decreased conversion rates within the first hour following irradiation of EXL596 may compromise flexural strength properties (associated with a decrease in BFS and m) which may be inadequate under masticatory loading.

The reliability in flexural strength testing of a novel dental composite

OBJECTIVES To investigate the reliability of bi-axial flexure and three-point flexure testing of an experimental, low-shrink oxirane-based dental composite, EXL596 compared with two conventional methacrylate based restoratives, Z250 and Z100. METHODS Specimens (n=20) of a novel oxirane-based composite and two commercially available methacrylate based composites were fabricated for flexural testing to evaluate mean bi-axial flexure strengths, three-point flexure strengths and the associated Weibull moduli (m) following 24 h immersion in a lightproof waterbath maintained at 37+/-1 degrees C. RESULTS Mean bi-axial flexure strengths and the associated m of EXL596, Z250 and Z100 were 168+/-11 MPa (m=16.2+/-4), 140+/-12 MPa (m=11.9+/-3) and 126+/-13 MPa (m=10.2+/-2), respectively. Three-point flexure strengths and the associated m of EXL596, Z250 and Z100 were 113+/-15 MPa (m=9.2+/-2), 92+/-10 MPa (m=8.5+/-2) and 79+/-16 MPa (m=6.3+/-1), respectively. CONCLUSIONS The present investigation suggests that bi-axial flexure strength testing of dental resin-based composites provides a more reliable testing method than three-point flexure. The increased reliability was considered in terms of the associated Weibull moduli following bi-axial flexure testing as a result of the elimination of the additional induced variability introduced during the curing regime of three-point flexure specimens.

Survival Rates for Porcelain Laminate Veneers with Special Reference to the Effect of Preparation in Dentin: A Literature Review

UNLABELLED The porcelain laminate veneer is an elective restoration, often placed in the absence of disease for purely esthetic reasons. As such, it would appear desirable that the success rate of the technique was 100%. It is therefore the purpose of this paper to review the literature on porcelain laminate veneer survival by searching dental databases containing clinical trials of porcelain veneer restorations. References of selected trials were also screened to identify relevant studies. Each paper that was included was examined to ascertain if preparation into dentin affected survival. A total of 24 papers were included in the review. It was concluded that survival rates of porcelain laminate veneers are rarely 100%, and there is reasonable evidence indicating that a veneer preparation into dentin adversely affects survival. CLINICAL RELEVANCE A review of the literature has indicated that porcelain laminate veneer survival is rarely 100%. Accordingly, patients should be made aware of this before embarking on this elective restorative technique. Clinicians should also be aware that the ideal preparation for porcelain veneers remains within enamel.

Extrinsic energy sources affect hardness through depth during set of a glass-ionomer cement

OBJECTIVE To investigate the effect of various energy sources on the upper and lower surface hardness of a setting glass ionomer with various thicknesses. METHOD Cylindrical specimens (4 mm diameter by 1, 2 or 4 mm thickness) of a glass-ionomer cement were prepared with no applied energy source (control), by preheating GIC capsules in a waterbath prior to mixing, application of light with high irradiance or ultrasonic excitation with a scaler tip. The upper and lower surface hardness was measured 0.5 h, 4 h and 1 week following material mixing. The increase in temperature towards the lower surface of each specimen was monitored throughout the first 5 min of setting. RESULTS No significant differences in hardness between upper and lower surfaces or varying thicknesses were identified for control and preheated samples at any post-mix time (p>0.05). At 0.5 h post-mix, the upper surface hardness of preheated, light and ultrasonic treatments was significantly increased compared with that of the control groups. Following 4 h post-mix, the overall hardness of preheated samples was significantly greater (p<0.001) than other sample groups, which were not statistically different (p=0.684). No significant differences in hardness between test groups were identified following 1 week (p>0.05). CONCLUSIONS Preheating GIC capsules prior to mixing resulted in superior hardness values through depth up to and including 4 h post-mix compared with specimen surfaces treated with light irradiation or with an ultrasonic scaler tip.

Fracture resistance of teeth restored with dentin-bonded crowns constructed in a leucite-reinforced ceramic

OBJECTIVES Laboratory studies and preliminary clinical data have demonstrated satisfactory fracture resistance of all-ceramic crowns placed using a resin-composite luting material and a dentin-bonding system. This study investigates the fracture resistance of crowns constructed in a leucite-reinforced ceramic when placed using a dentin-bonding system and a dual-cure resin composite luting material and compares this with the fracture resistance of feldspathic porcelain crowns. METHOD Standardised preparations were carried out on 10 sound, unrestored, maxillary premolar teeth, the mean bucco-palatal width of which did not vary by more than 2.5%. Ceramic crowns (Fortress; Chameleon Dental, KS, US) were constructed using a standardised technique. Their fitting surface was etched with hydrofluoric acid. The crowns were placed using the dentin-bonding system Mirage ABC and the luting system Mirage FLC (Chameleon Dental, KS, US). The restored teeth were loaded in compression at 1 mm/min through a 4 mm steel bar placed along the midline fissure. RESULTS A mean fracture load of 0.88 kN was recorded. Results from previous work indicate a fracture resistance of 0.77 kN for feldspathic porcelain crowns placed using the same luting systems on similarly standardised preparations. Statistical analysis by one-way ANOVA and Tukeys multiple comparison procedure indicated that there was no significant difference in the mean fracture resistance of the teeth restored using the leucite reinforced ceramic and the teeth restored with feldspathic porcelain. SIGNIFICANCE Crowns constructed in a leucite-reinforced ceramic and placed using dentin-bonding and dual-cure resin composite luting materials may provide some increase in fracture resistance, but the results may not be significantly different from the feldspathic porcelain.

Introducing the Concept of Pragmatic Esthetics, with Special Reference to the Treatment of Tooth Wear

The impact of the so-called “cosmetic” dentistry, if assessed by the number of dental makeovers in television programs or in celebrity magazines, has increased substantially in recent years. This is likely to have increased the public’s awareness of their dental appearance,1 and in turn, may have increased the volume of porcelain laminate veneers that have been placed, although quantification of this is difficult. What is quantifiable, however, is that tooth wear (TW) alternatively known as tooth surface loss (TSL) is increasing in incidence,2 especially in younger people, and that the issues around treatment of this are, therefore, becoming increasingly relevant. In the past, treatment of TW was often by means of crowning affected teeth (Figures 1A–C), or by a “full oral rehabilitation.” This involved the crowning of many innocent or bystanding teeth, allegedly with the aim of protecting their surfaces from further TW. The irony, of course, was that the supposed “ideal” treatment plans resulted in either more massive destruction of the affected teeth than the causative factors themselves had produced, or even more curiously, caused significant destruction of other minimally affected teeth in the same arch, or the opposing arch. This could be considered by many people to be a strange way to treat teeth, which were already compromised by wear. More seriously affected cases were (and still are) offered overdentures, or

A preliminary report on the incidence of pre-existing pinhole defects in nitrile dental gloves

Introduction Examination gloves manufactured from natural latex have been the predominant glove choice to date in dental practice. However, concerns over hypersensitivity have resulted in the use of alternatives such as nitrile gloves. The aim of the current study was to assess the incidence of pre-existing pinhole defects in nitrile examination gloves.Methods Air inflation, followed by water submersion, was used to assess the incidence of pre-existing pinhole defects in five nitrile and two latex glove types. The gloves were filled with a constant volume of air and submerged in 3 litres of water for 10 seconds while being observed for air bubbles which would indicate pinhole defects. The position and number of pinholes were noted for 100 gloves of each type investigated.Results The incidence of pre-existing pinholes for latex gloves was 0% for the non-sterile surgical latex glove type and 3% for the powdered latex examination glove type, with pinholes located on the thumb, middle finger and ring finger. Of the nitrile gloves evaluated, three types were assessed to have no pre-existing pinhole defects. One type had a 2% incidence of pre-existing pinhole defects — one pinhole located on the thumb region of the glove and one on the ring finger portion of the glove. The fifth nitrile glove type had one pre-existing pinhole defect located on the middle finger.Significance All glove types examined met the European Standard (EN 455-1) and there was no statistically significant difference between glove types. However, the nitrile gloves generally exhibited less pre-existing pinhole defects than the latex examination gloves.

Relating aesthetics to clinical need: improved aesthetics of an ill-fitting crown and anterior toothwear

This case report presents a case in which a patient attended because of the poor appearance of an anterior crown, but she was unaware that she had a number of teeth affected by toothwear. Clinical relevance: The quest for aesthetic improvement may be a reason for a patient presenting for dental treatment.

Practice‐based PREP Panel handling evaluation of a new impression mixing device and the associated material

AIMS To evaluate the handling of a new impression mixing device and the associated impression material by general dental practitioner members of the PREP Panel. DESIGN By means of a questionnaire, the participating practitioners recorded their views on the mixing machine and impression materials, having used these for ten weeks. SETTING UK general dental practices. PARTICIPANTS General dental practitioner members of a UK practice-based research group. METHODS A questionnaire was designed to elicit views on the performance of the mixing device and impression material under test. This was distributed to the practitioners who had used the test materials for 10 weeks and the data thereby obtained collated and presented, principally in the form of VAS scales. OUTCOME MEASURES Rating of various parameters of the mixing device and impression materials on VAS scales. RESULTS The Pentamix 3 machine scored well for ease of initial use [4.8 on a visual analogue scale (VAS) where 1 = very difficult to use and 5 = very easy to use]. In a range of criteria (including cleanliness, easy handling, time to fill the tray and overall convenience) the Pentamix scored highly on VAS scales. A maximum score of 5 (on a VAS where 1 = very dissatisfied and 5 = very satisfied) was achieved for reproducible mixing quality. The appreciation of the Pentamix 3 mixing machine was demonstrated by the fact that 85% (n = 11) of evaluators stated that they would recommend it to colleagues. Regarding the impression material under evaluation, 85% (n = 11) of the evaluators stated that they would recommend Impregum Quick impression materials to their colleagues. CONCLUSIONS Within the limitations of this study, the Pentamix 3 automatic impression mixing device scored highly in this assessment, together with the impression materials assessed.

Retirement of Board Member

To celebrate the retirement of Editorial Board Member Professor Edwina Kidd from GKT (Guys Campus), a celebratory conference was held on Thursday, 2nd September 2004 at Guys. The speakers were eminent in the work for which Professor Kidd is world famous, namely, cariology. The day commenced with a presentation by Professor Ole Fejerskov from Denmark, in which he traced the history of cariology. A quote from him is applicable to all who practice dentistry: