A.M. Fletcher

The nature of the interface between polymethyl methacrylate denture base materials and soft lining materials

Abstract Four of the commonly used resilient denture lining materials were investigated. They were of different chemical composition, physical forms and processing cycles. Scanning electron microscope examinations of the interface between the liners and the regular acrylic resin base material were carried out in an attempt to assess the bonding of these materials to the denture base, and to evaluate the reliability of their use. The physical and mechanical bonding properties of the resilient lining materials to acrylics were studied, which included tensile, shear, peel and compression tests to measure the efficacy of the joint between the acrylic and the lining materials and its resistance to various external damaging loads. The effect of water on the liner/denture base interface and on the liners bonding properties to acrylics was also investigated, and the validity of roughening the tissue surface of the denture base prior to processing the liner was assessed. The findings point to the advisability of using the acrylic type of soft liners whenever resilient liners are indicated. Roughening the fitting surface of the denture base to which the resilient lining materials are to be applied has a weakening effect on the bond between the lining and the denture base. Long-term exposure of the liners to water has a destructive effect. The infusion of the water into the material leads to swelling and stresses build up at the denture base interface and these tend to promote distortion and reduction in bonding.

The Level of Residual Monomer in Self-curing Denture-base Materials:

Because residual monomer may cause tissue irritation, we investigated two self-curing acrylic denture-base materials — one a compression type, and the other a pourable material — by means of gas-liquid chromatography, Both exhibited higher residual monomer levels than did heat-cured acrylics, with thick sections having lower values than did thin sections. The pourable material showed lower values than did the compression variety.

A method of improving the bonding between artificial teeth and PMMA

Abstract Specially designed tooth-heads were roughened prior to bonding to selected denture base resins. Shear and tensile tests, at varying cross-head speeds, were carried out on the specimens after immersion in water, de-ionized water or saliva substitute. The results show that the high strain rates, such as may be achieved in the mouth, are likely to be conducive to early bond failure. Roughening the bond interface promotes bonding and reduces the likelihood of premature failure.

Dental materials: 1982 literature review Part 1

Objectives: Leptin is a hormone-like protein produced by the adipose tissue. It plays an important role in protection of host against inflammation and infection. Some studies have reported changes in leptin levels in the gingival crevicular fluid (GCF), saliva and blood serum of patients with periodontal disease compared to healthy individuals. The aim of the present study was to compare the salivary leptin levels in patients with advanced periodontitis and healthy individuals. Materials and Methods: In this case-control study, the salivary samples of healthy individuals and patients with advanced periodontitis with clinical attachment loss >5mm were obtained using a standardized method and the leptin levels were measured in the salivary samples by means of ELISA. The effects of the periodontal status and sex on the salivary leptin levels of both groups were statistically analyzed by two-way ANOVA. Results: The means ± standard deviation (SD) of salivary leptin levels in healthy subjects and patients with advanced periodontitis were 34.27±6.88 and 17.87±5.89 pg/mL, respectively. Statistical analysis showed that the effect of sex on the salivary leptin levels was not significant (P=0.91), while the effect of advanced periodontitis on the salivary leptin levels was significant compared to healthy individuals (P<0.0001). Conclusions: In patients with advanced periodontitis, the salivary leptin levels were significantly lower compared to healthy individuals. Thus, assessment of salivary leptin can be done as a non-invasive and simple method to determine the susceptibility of patients to advanced periodontitis.This report, which is to be presented in two parts, reviews published papers on dental materials, based on literature for 1982. In this part the following topics are considered: metals, including dental amalgam and casting and wrought alloys; ceramics, implants and aspects of dental biomechanics.

Some mechanical properties including the repair strength of two self-curing acrylic resins

Abstract Self-curing acrylic resins have been used mainly in prosthetic dentistry for the construction of custom-built impression trays, occlusion registration bases and for repairing fractured dentures. Their major disadvantages when compared with heat-cured resins are their relatively poor mechanical properties and a high level of residual monomer. Recently, pour-type resins have been introduced for the fabrication of denture bases. The present study was undertaken to examine some of the mechanical properties of these materials and compare the results with those previously reported.

Dental materials: 1982 literature review Part 2

Abstract This paper, which is presented in two parts, reviews the work on dental materials published in 1980 Included in Part 2 are sections on dental biomechanics, amalgam, corrosion, casting alloys, soldering, electroplating, magnetic materials, metals and alloys for orthodontic use. Part 1 included sections on composite filling materials, fissure sealants, microleakage, dental ceramics, acrylic resins, impression materials, dental cements, adhesion, endodontic materials, model, die, mould and investment materials.

Dental materials: 1974 literature review Part II

Abstract This paper, which is presented in two parts, reviews the work on dental materials published in 1977. Included in Part I were sections on amalgam, casting alloys, denture base polymers, composite filling materials, tissue conditioners and soft lining materials and fissure sealants. A review of the literature relating to impression materials, dental ceramics, model and die materials, cements, dental implants and dental biomechanics is presented in Part II.

Dental materials: 1988 literature review

This review of the published literature on dental materials during 1988 has been compiled by the members of the Dental Materials Panel of the United Kingdom. The editor would like to extend his grateful thanks to all the contributors who continue year after year to provide their views and critical assessment of what in their opinion have been the main contributions to their area of research. The field of dental materials is still growing apace and these regular reviews allow the reader to keep abreast of the main advances, a task which proves more and more difficult even within a particular speciality. Although the format of the review is well established this is by no means written in tablets of stone. Hence the editor would like to invite the readers to provide comments or criticisms of the review. Is the review sufficiently comprehensive? Is there too much or too little? Are there any topics which are not included and should be? Any suggestions from the readers of the Journal of Dentistry would be very helpful, as we are continually seeking to improve the review. Whatever your views, we would like to hear from you.

Dental materials: 1989 literature review

This review of the published literature on Dental Materials during 1989 has been compiled by the members of the Dental Materials Panel of the United Kingdom. The editor would like to extend his grateful thanks to all the contributors who provide their views and critical assessment of what in their opinion have been the main contributions to the area of research they have reviewed. The editor appreciates that the views expressed by the contributors may sometimes appear controversial to the reader. The reader is invited, indeed encouraged, to submit a letter to the editor, which will be forwarded to the author(s) who will be asked to comment. Both the original letter and the author’s response will be published simultaneously in a later issue of the Journal, if the views expressed add to the scientific argument.

Dental materials: 1987 literature review

Statement of the Problem: In the sandwich technique, the undesirable bond between the composite resin and glass-ionomer cement (GIc) is one of the most important factors which lead to the failure of restoration. Total-etch and self-etch adhesives may improve the bond strength based on their pH. Purpose: The purpose of this study was to evaluate the shear bond strength between the nanofilled composite resin and GIc using different adhesives. Materials and Method: In this experimental study, 40 specimens (6×6mm) in 4 groups (n=10) were prepared in acrylic mold. Each specimen contained conventional GI ChemFil Superior with a height of 3mm, bonded to Z350 composite resin with a height measured 3mm. In order to bond the composite to the GI, the following adhesives were used, respectively: A: mild Clearfil SE Bond self-etch (pH=2), B: intermediate OptiBond self-etch (pH=1.4), C: strong Adper Prompt L-Pop (pH=1), and D: Adper Single Bond 2 total-etch (pH=7.2). The shear bond strength was measured by using universal testing machine with a crosshead speed of 1mm/min. One-way ANOVA and Tukey’s test were used to analyze the data ( p < 0.05). Results: The shear bond strength in group A was significantly higher than group B ( p = 0.002), C ( p < 0.001), and D ( p < 0.001). Moreover, the shear bond strength of groups A and B (self-etch) was significantly different from group D (total-etch) ( p < 0.001); and C (self-etch) with D ( p = 0.024). Conclusion: The results of this study showed that applying the mild self-etch adhesive between the composite and the GIc results in stronger shear bond strength compared to intermediate and strong self-etch adhesives. Moreover, the self-etch adhesive increased the shear bond strength between composite resin and GIc more significantly than total-etch adhesive. Key Words: Self-etch Adhesive; Total-etch Adhesive; Nanofilled Composite; Shear Bond Strength; Conventional Glass-ionomer Cement