D.J. Lamb

The effects of process variables on levels of residual monomer in autopolymerizing dental acrylic resin.

Abstract Relationships have been established between process variables and the concentration of residual monomer in an autopolymerizing dental acrylic resin. It has been shown that long-lived polymer radicals are present in greater concentration after an initial cure at 22° than after cure at 55°. Assay of monomer concentrations by infrared spectroscopy showed residual monomer to be reduced by higher powder/liquid ratios, low temperature of initial cure, storage at elevated temperature and the exclusion of air (oxygen).

In vitro interaction between primary bone organ cultures, glass-ionomer cements and hydroxyapatite/tricalcium phosphate ceramics.

Primary organ cultures derived from neonate rat calvaria were maintained for 2 wk and used to study in vitro response of osteoblast and periosteal cells to the component and composite forms of three different glass-ionomer (polyalkenoic) cements, comparing them to densely sintered hydroxyapatite and tricalcium phosphate ceramics. Qualitative analysis by scanning and transmission electron microscopy revealed that osteoblasts colonized all the solid test materials, although there was a less favourable response to materials with a rough surface topography and to unset and fluoride-containing glasses. On solid materials migrated cells maintained their tessellated morphology and exhibited numerous micro-appendages anchoring them to the surface of the test materials. A collagen-containing extracellular matrix was elaborated on to the ceramics and set glass-ionomer cements, except for one (AquaCem). Mineralization of the extracellular matrix was seen adjacent to hydroxyapatite and tricalcium phosphate ceramics, that adjacent to the latter morphologically resembling bone.

The composition and rheology of denture adhesives

Abstract Ten brands of denture adhesive on sale in the United Kingdom have had their active constituents identified by infrared spectroscopy. Six contained Karaya gum, an acidic substance which in aqueous solution could cause decalcification of enamel. The viscosity of the denture adhesives studied was of the order of 106 poise. After mixing with water all showed an increase in viscosity, some showing a subsequent fall as further dilution with water took place.

Initial in-vivo evaluation of glass-ionomer cements for use as alveolar bone substitutes.

The response of rat femora to implantation of four glass-ionomer (polyalkenoic) cements (GIC) compared to that seen following implantation of densely sintered hydroxyapatite (Ha) ceramic was evaluated for periods up to 12 weeks. Light and transmission electron microscopic analysis of the GIC/bone interface revealed direct bonding of the GIC G338 and Ketac Cem (both based on fluoro-alumino-silicate) glasses to bone, with a mineralized collagen-containing extra-cellular matrix deposited on the surface of the GIC. AquaCem and the fluoride-free GIC based on MP4 glass showed incomplete osseointegration.

A study of the composition and diffusion characteristics of a soft liner

Abstract The composition of Coe-Soft, a soft liner, has been determined. The polymer powder is essentially polyethyl methacrylate and the liquid is a mixture of dibutyl phthalate, benzyl salicylate and ethanol. The diffusion of ethanol out of Coe-Soft into air proceeds by two processes and their rates have been measured. On immersion in water the ethanol diffuses out by the faster process at the same rate as into air. Subsequently water is absorbed without limit and equilibrium is not attained even after 131 days (4·68 months).

Efficacy of two alcohol-free cetylpyridinium chloride mouthwashes - a randomized double-blind crossover study.

AIM (1) To determine the plaque inhibition properties of two formulations of alcohol-free mouthwash [0.1% w/w cetylpyridinium chloride (CPC) (B) and 0.05% w/w CPC (A)] versus a placebo mouthwash (C). (2) To compare the plaque-inhibiting activity between these two new CPC mouthwashes. MATERIAL AND METHODS A double-blind, crossover study with three 1-week periods was used. Subjects were randomly assigned to one of the following groups. Group 1 (n=10) received the mouthwashes A, C and B in the periods 1, 2 and 3, respectively, group 2 (n=11) received the mouthwashes in the order B, A, C, while group 3 (n=11) received the mouthwashes in the order C, B, A. Mean plaque areas and Quigley & Hein plaque index scores were analysed using anova (analysis of variance). Measurements were made at the start of each period (baseline) and at 16, 24 and 40 h. RESULTS Mean plaque scores were similar across the groups at baseline. At all time points thereafter, volunteers using mouthwash A or B had significantly lower plaque areas and plaque index scores than those using mouthwash C (p<0.05), but there were no significant differences between the test formulations. At 16 h, the reduction in plaque area relative to mouthwash C was 22% for mouthwash A and 18% for mouthwash B; at 24 h, 11% for mouthwash A and 15% for mouthwash B; and at 40 h, 15% for mouthwash A and 16% for mouthwash B. CONCLUSIONS The use of both CPC mouthwashes resulted in less plaque accumulation compared with the control. There was no statistically significant difference in plaque accumulation between the two CPC mouthwashes.

Treatment of denture stomatitis by a sustained drug-delivery device: a preliminary study

Abstract Ten patients with diffuse denture stomatitis associated with the presence of candida species, but which had resisted previous antifungal therapy, were treated by means of a sustained drug-delivery device releasing miconazole. Over a period of 3 months candida was eliminated from the mouths of five patients. The prognosis appeared to be influenced by the initial level of candida infection and the presence of a systemic predisposing factor.

A scanning electron microscope study of CoCr partial dentures fractured in service

Abstract The fracture surfaces of 12 CoCr partial denture bases, broken in service, were examined by S.E.M. A technical cause of fracture could be identified in five of the samples. The remainder showed no obvious cause apart from interdentritic microporosity due to shrinkage. The presence of this phenomenon could explain past difficulties when attempting to improve the mechanical properties of cast CoCr alloys, and effort should be directed to the elimination of this defect.

Two-stage combined vestibuloplasty and partial mandibular ridge augmentation with hydroxyapatite

The preliminary results of a new two-stage technique for partial augmentation of the edentulous mandibular ridge with hydroxyapatite are reported. The technique, which has been applied to five patients, can be performed under local analgesia, and involves initial placement of temporary silicone spacers, together with submucous vestibuloplasty to preserve sulcus depth. The spacers are later replaced by dense particulate hydroxyapatite, and the connective tissue capsules that remain after removal of the spacers allow control of particle migration and minimize the amount of hydroxyapatite required.

The effect of miconazole on palatal candidosis induced in the Wistar rat

Abstract Autopolymerizing acrylic resin supplemented with 10 per cent miconazole nitrate was tested as a treatment for palatal candidosis as induced by Shakir et al. (1981) in the Wistar rat It was found that by fitting rats with appliances supplemented with 10 per cent( w w ) miconazole in the polymer powder, palatal candidosis could be prevented, and previously infected animals were cured after therapy for one month Rats fitted with supplemented appliances showed no adverse side-effects and tended to gain weight more rapidly than animals with unsupplemented appliances.