Sanjukta Deb

Novel hydroxyapatite-based dental composites

Newly designed composite resins for dental applications have been studied. The matrix phases were based on 2,2 bis-4(2-hydroxy-3-methacryloyloxypropoxy)phenyl propane and a urethane dimethacrylate. Tetrahydrofurfuryl methacrylate was added as a diluent to both dimethacrylates in a proportion of 30 wt%. Heat-cured composite resins were obtained with filler weight fractions of 60% and 67%. After surface treating hydroxyapatite powder with a silane coupling agent, filler contents of 60%, 67% and 80% were employed. These materials were then evaluated for Youngs modulus, flexural strength, diametral tensile strength and Vickers hardness. With the exception of Youngs modulus, all mechanical properties of the tested materials were significantly improved when a silanized hydroxyapatite filler had been used.

Neuroleptics in the treatment of aggressive challenging behaviour for people with intellectual disabilities: a randomised controlled trial (NACHBID)

OBJECTIVE(S) To assess the effects and cost-effectiveness of haloperidol, risperidone and placebo on aggressive challenging behaviour in adults with intellectual disability. DESIGN A double-blind randomised controlled trial of two drugs and placebo administered in flexible dosage, with full, independent assessments of aggressive and aberrant behaviour, global improvement, carer burden, quality of life and adverse drug effects at baseline, 4, 12 and 26 weeks, and comparison of total care costs in the 6 months before and after randomisation. At 12 weeks, patients were given the option of leaving the trial or continuing until 26 weeks. Assessments of observed aggression were also carried out with key workers at weekly intervals throughout the trial. SETTING Patients were recruited from all those being treated by intellectual disability services in eight sites in England, one in Wales and one in Queensland, Australia. PARTICIPANTS Patients from all severity levels of intellectual disability; recruitment was extended to include those who may have been treated with neuroleptic drugs in the past. EXCLUSION CRITERIA treatment with depot neuroleptics/another form of injected neuroleptic medication within the last 3 months; continuous oral neuroleptic medication within the last week; those under a section of the Mental Health Act 1983 or Queensland Mental Health Act 2000. INTERVENTIONS Randomisation to treatment with haloperidol (a typical neuroleptic drug), risperidone (an atypical neuroleptic drug) or placebo using a permuted blocks procedure. Dosages were: haloperidol 1.25-5.0 mg daily; risperidone 0.5-2.0 mg daily. MAIN OUTCOME MEASURES Primary: reduction in aggressive episodes between baseline and 4 weeks using Modified Overt Aggression Scale. Secondary: Aberrant Behaviour Checklist; Uplift/Burden Scale; 40-item Quality of Life Questionnaire; Udvalg for Kliniske Undersøgelser scale; Clinical Global Impressions scale. Economic costs recorded using a modified version of Client Service Receipt Inventory for 6 months before and after randomisation. RESULTS There were considerable difficulties in recruitment because of ethical and consent doubts. Twenty-two clinicians recruited a total of 86 patients. Mean daily dosages were 1.07 mg rising to 1.78 mg for risperidone and 2.54 mg rising to 2.94 mg for haloperidol. Aggression declined dramatically with all three treatments by 4 weeks, with placebo showing the greatest reduction (79%, versus 57% for combined drugs) (p = 0.06). Placebo-treated patients showed no evidence of inferior response in comparison to patients receiving neuroleptic drugs. An additional study found that clinicians who had not participated in clinical trials before were less likely to recruit. Mean total cost of accommodation, services, informal care and treatment over the 6 months of the trial was 16,336 pounds for placebo, 17,626 pounds for haloperidol and 18,954 pounds for risperidone. CONCLUSIONS There were no significant important benefits conferred by treatment with risperidone or haloperidol, and treatment with these drugs was not cost-effective. While neuroleptic drugs may be of value in the treatment of aggressive behaviour in some patients with intellectual disability, the underlying pathology needs to be evaluated before these are given. The specific diagnostic indications for such treatment require further investigation. Prescription of low doses of neuroleptic drugs in intellectual disability on the grounds of greater responsiveness and greater liability to adverse effects also needs to be re-examined.

A comparative study of the properties of dental resin composites polymerized with plasma and halogen light

OBJECTIVES Newly developed curing units utilizing plasma arc methodology have been advocated for rapid curing of dental composites. This study was conducted to investigate the effect of plasma light using a 3 s and a step cure regime on the properties of four dental restorative materials and compare it with properties resulting from halogen light curing of the same materials. METHODS Composites Quadrant, Filtek and two polyacid modified composites (compomers) Dyract AP and Compoglass F were cured, using a conventional halogen light, a plasma light for 3 s (Apollo95E) and a plasma step cure (Apollo 95E) method. The parameters studied for characterization of the restorative materials were polymerization exotherm, surface hardness and their interactions with saline. RESULTS Irradiation with plasma light for 3 s or step cure produced an order of hardness: Filtek>Compoglass F>Dyract AP>Quadrant (p<0.001), however, halogen cure yielded an order of hardness: Filtek>Quadrant>Dyract AP>Compoglass F. No significant differences in hardness were observed on the exposed and non-exposed surfaces of the materials cured by plasma step cure whereas a 3 s cure yielded a significant difference in the cases of Quadrant, Compoglass F and Dyract AP (p<0.001). Mass losses were also found to be greater in the specimens cured by plasma light for 3 s in comparison with plasma step cure and halogen cure. SIGNIFICANCE Plasma step and halogen curing were found to yield composites with superior properties in comparison to a 3 s plasma cure, suggesting, that a step cure regime is a preferred method, when a plasma light unit is used. A 3 s curing with a plasma light may lead to less than optimum properties of the composite cements.

Radiopacity in bone cements using an organo-bismuth compound

In a joint replacement surgery it is vital for bone cement to be radiologically detectable. Consequently, heavy metal salts of barium and zirconia are incorporated as a contrast medium for this purpose. The addition of such particulate additives, however, can be detrimental to some of the physical, mechanical and biological properties. The present study reports the feasibility of using an organo-bismuth compound, namely. triphenyl bismuth (TPB) as a radiopaque agent for orthopaedic bone cements. TPB was incorporated in the bone cement matrix by two methods, (i) blending: TPB was added to the polymer phase of the bone cement and (ii) dissolution: by dissolving TPB in the monomer phase methylmethacrylate. The results showed that the inclusion of TPB at concentrations of 15% and 25% by weight of the polymer, in the bone cement matrix did not affect the polymerisation exotherm temperature and setting time. Furthermore, the addition of TPB via the dissolution method provided a statistically significant increase in the strain to failure in comparison to commercial acrylic cements containing barium sulphate, thus reducing the brittleness of the cement. The detrimental effects on the mechanical properties post conditioning in water, was also much less pronounced in the homogeneous TPB cements in comparison to barium sulphate containing cements. These observations can be attributed to the formation of a homogeneous and continuous matrix of the resultant bone cement with a much lower porosity.

Pre-warming of dental composites

OBJECTIVES Cavity lining with flowable composites have been proposed to improve initial marginal adaptation and minimize shrinkage stresses. The purpose of this study was to evaluate if prewarming of composites would influence the flow and enhance marginal adaptation thus the effect of pre-warming different types of composites on their properties are reported. METHODS Six different composites were used in this study including a flowable and a polyacid modified composite. Uncured composites were pressed between two glass plates with a known load and the film thickness was measured to determine flow. Polymerization shrinkage was measured by means of a one-dimension contacting transducer. Flexural strength was determined using a three-point bend test. Microleakage was determined in human lower third molars on both enamel and dentin restoration interfaces. Cytocompatibility was analyzed with an Alamar Blue redox cell proliferation assay. The flow properties, linear shrinkage, flexural strength, microleakage and cytocompatibility were evaluated at 22 °C and 60 °C. RESULTS The results indicated that the film thickness for each of the materials was significantly lower at 60 °C and the linear shrinkage was greater as a result of the higher degree of polymerization. The flexural strength of Spectrum TPH and Wave were found to be statistically significantly higher with pre-warming, however the other composites did not exhibit any differences. Microleakage studies showed that pre-warming had no significant bearing on the results and alamarBlue(®) results showed that the pre-heating did not have an effect on the cytotoxicity however the levels of cytotoxicity varied between the composites that can be attributed to the composition. SIGNIFICANCE Pre-warming of the composites studied enhanced flow as observed by measuring film thickness and did not significantly affect other properties.

The effect of strontium oxide in glass–ionomer cements

The reaction of strontium oxide powder with poly(acrylic acid) has been studied both alone and within glass–ionomer cements. Reaction was found to be slow and the strontium-carboxylate structure was found to be partially covalent in character, as determined by Fourier transform infrared spectroscopy (FTIR). These are similar to the structures formed by calcium in glass–ionomer cements, but are different from typical monomeric strontium carboxylates, which tend to be purely ionic. Strontium oxide powder introduced in two types of glass–ionomer cements, slowed down the setting reaction at both 21 °C and 37 °C, but at low levels (5 wt %), increased the compressive strength in both cement formulations studied. However, at higher levels, it was found to decrease the compressive strength. This study confirms the view that strontium is a cement-forming ion; but concludes that, except at very low levels, strontium oxide powder does not improve the properties of glass–ionomer cements.

The effect of cross-linking agents on acrylic bone cements containing radiopacifiers

Poly(methylmethacrylate) PMMA, based cements are the most widely used bone cements in joint replacement surgery. Although, there are some disadvantages in the use of these cements, the clinical success rate is fairly high. Intrinsic radiopacity is difficult to achieve in these cements due to the constituent elements of the PMMA polymer. As radiopacity is an essential requirement, PMMA bone cements have been rendered radiopaque by blending heavy metal ion salts, which tend to adversely affect the mechanical and biological properties of the bone cement. In this study, dimethacrylate cross-linking agents were added to the monomer phase in order to generate a cross-linked matrix, with barium sulphate as a radiopaque agent. The results suggest that the mechanical properties can be improved or retained with the addition of such cross-linking agents.

Tissue engineering technology and its possible applications in oral and maxillofacial surgery

Tissue engineering is a rapidly advancing discipline that combines the attributes of biochemical and biomaterial engineering with cell transplantation to create bio-artificial tissues and organs. For the oral and maxillofacial surgeon, the reconstruction of maxillofacial defects in hard and soft tissues is an ongoing challenge. While autologous grafts and vascularised free flaps are the current gold standard, they are not without complications at both the donor and reconstructed sites. Tissue engineering, which aims to create tissue-matched, prefabricated, prevascularised bony or soft tissue composite grafts, or both, therefore has the potential to revolutionise practice in maxillofacial surgery. We review the technology of tissue engineering and its current and future applications within the specialty, and discuss contemporary obstacles yet to be overcome.

A novel method of forming micro- and macroporous monetite cements

Second to autologous bone grafts are the calcium phosphate cements (CPCs) used as synthetic bone substitutes due to their chemical similarity to the mineral component of bone. Their ability to conform to complex bone defects and excellent osteoconductivity also render them excellent scaffolds for bone tissue engineering, although they do have their own limitations. Calcium phosphates can be divided into two main categories, namely apatite and brushite. Apatites exhibit low solubility, whereas, calcium phosphates that set to form brushite, are metastable, which degrade rapidly, but do subsequently form hydroxyapatite that retards the rate. In contrast dicalcium phosphate anhydrous (monetite) has a higher solubility than octacalcium phosphate and does not transform to an apatite; thus, it is able to continue to degrade with time. Herein, a new method was used via the addition of sodium chloride to β-tricalcium phosphate and monocalcium phosphate monohydrate to form micro- and macroporous monetite (DCPA). The X-ray diffraction and FTIR spectra confirmed the formation of monetite in the presence of both, 6.2 M NaCl solution or 60% of solid sodium chloride. The maximum compressive strength (σc = 12.3 ± 1.8 MPa) and the Youngs modulus (E = 1.0 ± 0.1 GPa) of the monetite cements obtained were comparable to the upper limits of the values reported for cancellous bone and also higher than that reported by other routes used to form monetite. The porous cements analysed by microCT revealed an interconnected porosity with the preliminary in vitro biological evaluation indicating favourable osteoblast cell attachment and growth.

Effect of crosslinking agents on poly(ethylmethacrylate) bone cements

Asceptic loosening of cemented joint prostheses in many cases is related to the mechanical failure of the acrylic bone cement. Poly(methylmethacrylate) bone cements are widely used in orthopaedic surgery although there are well-known disadvantages. A lower modulus bone cement based on poly(ethylmethacrylate)–n-butylmethacrylate with a lower polymerization exotherm, and a low monomer extractibility, is a promising alternative. The effect of incorporating crosslinking agents in order to improve the mechanical performance of the PEMA bone cement is reported. Three different bifunctional dimethacrylate crosslinking agents with different chain lengths and degrees of flexibility were incorporated in the monomer phase, and cements formulated. The setting time was found to decrease in the presence of the cross-linking agents and the polymerization exotherm decreased in the presence of triethylene glycol dimethacrylate and polyethylene glycol dimethacrylate, n=400. Incorporation of triethylene glycol dimethacrylate showed an increase in the tensile strength and modulus with a decrease in the strain at maximum stress. However, polyethylene glycol dimethacrylate, n=400, did not improve the mechanical properties appreciably which may be attributed to the low crosslinking density and higher flexibility of the spacer group in the crosslinking agent.