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Biomedical subjects

M J Tyas

Publications and source records attributed to M J Tyas.

At least 19 recordsLinked to original sources
PubMed1992

Tunnel restorations: a review.

Conventional cavity designs are coming under increased scrutiny because of an increased emphasis on preservation of tooth substance. The tunnel restoration when used with glass ionomer, may overcome some of the disadvantages of conventional cavity preparations. Justification for the use of the tunnel restoration is from a limited number of short-term clinical observations and destructive laboratory testing of marginal ridge strength. The technique is not without shortcomings. Long-term clinical and nondestructive laboratory trials examining the strength of teeth with tunnel restorations should be undertaken prior to its acceptance as a replacement for techniques in which the marginal ridge is removed.

Cermet Cements↗
PubMed1992

An investigation of the composite resin/porcelain interface.

Failures at composite resin/porcelain interfaces under shear-like loading were examined. Porcelain surfaces were treated with hydrofluoric acid and/or one of two silane coupling agents, using two different composite resin cements. The results showed that after seven days storage, bond strengths of specimens which had undergone porcelain surface treatment were greater than the cohesive strength of the porcelain itself, resulting in brittle fracture of the porcelain. The diluted restorative composite resin performed as well as the commercial composite resin cement. Silane pretreatment of porcelain was important as the bond strength of etched/silane primed specimens was significantly higher than the etched only specimens. However, one primer appeared to be more efficient than the other in bond promotion. Some explanations for the differences in bond strengths are offered.

Acid Etching, Dental↗
PubMed1992

Colour stability of composite resins: a clinical comparison.

Ninety three Class III cavities were prepared in 66 patients, and restored with one of three resin-based restorative materials; a hybrid self-cure material, a microfine self-cure material, or a microfine light-cure material. Standard sets of clinical colour transparencies were used to evaluate colour match with the surrounding tooth and marginal discoloration over five years. After five years, all materials had become slightly darker, the microfine self-cure material significantly more so than the light-cure material. There was no significant development of marginal discoloration.

Acrylic Resins↗
PubMed1992

One-year clinical performance of PMDM-based dentine bonding agents.

Two PMDM-based dentine bonding agents and a microfilled composite were used to restore a total of forty non-undercut caries-free cervical abrasion lesions without enamel etching. Restorations were evaluated over one year and the loss rate calculated using a life table analysis. Marginal staining was assessed from colour photographs on a continuous linear rating scale. After one year, 5 per cent of Tenure bonded restorations were lost compared with 52 per cent of Mirage bonded restorations. Slight marginal staining was evident around Tenure bonded restorations after one year.

Adult↗
PubMed1992

Glass ionomer (polyalkenoate) cement restorations.

Glass ionomer cements are recognized for their properties of reliable adhesion to tooth structure and fluoride release. The introduction of light-cured base and liner glass ionomer cements has overcome some of the disadvantages of self-cured materials. During the review period, most papers deal with either fluoride release, microleakage, or adhesion. There were few clinical studies.

Dental Bonding↗
PubMed1991

Bond strength of restorative materials to human dentin: influence of post-extraction time.

This study was undertaken to determine if the time after which teeth are extracted influences the tensile bond strength of a glass ionomer (Fuji II: GC) and a dentin bonding agent (Scotchbond Self Cure; 3M) to dentin. Within 20 min of extraction, 14 teeth were bonded with glass ionomer and 13 teeth with Scotchbond Self Cure plus a composite material (Clearfil; Kuraray), by attachment of orthodontic brackets to prepared dentin surfaces. The bonds were fractured in tension, and yielded values of 3.7 MPa for glass ionomer and 1.08 MPa for Scotchbond Self Cure + Clearfil. These data were significantly different (P less than 0.002) from data previously obtained from the use of old teeth, from which values of 2.20 MPa and 1.82 MPa for glass ionomer and Clearfil + Scotchbond Self Cure, respectively, were obtained. It was concluded that the time after extraction can significantly change bond strengths to dentin, but that the direction and magnitude of these changes depend on the adhesive system used.

Composite Resins↗
PubMed1991

Dental materials science--the maintenance of standards.

Standards for dental materials are available for both biological and chemical/physical properties. In order to predict the clinical performance of a material by means of standard tests, both the test and the method used in the test should ideally simulate clinical usage. However, owing to lack of knowledge with regard to intra-oral failure modes, and technical considerations in the performance of tests, this ideal may not always be achieved.

Biocompatible Materials↗
PubMed1991

Three-year clinical evaluation of dentine bonding agents.

Eighty Class V non-undercut cervical abrasion lesions were restored using four dentine bonding agents and composite resin. The restorations were examined over a three-year period, and the cumulative loss rate calculated each year. Marginal staining at each year was assessed using a standardized photographic method. The loss rate of restorations increased generally over the three-year period, reaching 30 to 60 per cent for the four products. Marginal staining also increased for all four products over the three-year period.

Adhesives↗
PubMed1991

Clinical evaluation of four composite resins in posterior teeth. Five-year results.

Four different composite resins (three small particle and one microfill) were placed in 106 posterior teeth and followed over a five-year period. Colour and marginal discoloration characteristics were assessed from standard photographs, and wear evaluated by standardized measurement of cavity wall exposure and scanning electron microscopy of replicas. The colour of the materials changed, but not to an unacceptable degree, over the five-year period, and marginal discoloration increased slightly. The wear rate of the four materials was similar, and appeared to decrease after about 2-4 years. Some materials exhibited surface damage, and some of the microfill restorations failed catastrophically.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1991

Cariostatic effect of glass ionomer cement: a five-year clinical study.

Composite resin and glass ionomer cement were used to restore 67 and 65 Class V carious lesions, respectively. The restorations were assessed each year for recurrent caries and marginal staining. After five years, 1 per cent of glass ionomer and 6 per cent of composite restorations had become carious, and there was approximately twice as much marginal staining around the composite as around the glass ionomers. There appear to be significant benefits in using glass ionomer to restore Class V carious lesions.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1990

Correlation between fracture properties and clinical performance of composite resins in Class IV cavities.

One hundred and two Class IV cavities were restored randomly with four composite resins. The restorations were assessed at six months, one year, two years and three years for surface chipping, bulk fracture and incisal wear. The data were correlated with various mechanical properties of the materials. A significant correlation was found between surface chipping/bulk fracture and fracture toughness (P = 0.002), elastic modulus (P = 0.006) and tensile strength (P = 0.045). There was a trend towards an association between incisal wear and both elastic modulus and inherent flaw size. Fracture toughness may be a useful indicator of the clinical performance of composites in Class IV cavities.

Color↗
PubMed1990

Determination of adhesive bond strength to dentine. A new method.

Specimens for the determination of adhesive bond strength to dentine were prepared using suitable surfaces of freshly extracted teeth from 15 patients who were having immediate dentures fitted. As soon as possible after extraction, shallow cavities were cut into the dentine to a depth of 1 mm using a high-speed round bur (diameter 4.2 mm) under water coolant. The cavities were restored using dentine bonding agents and single increments of light activated composite resin. The restored teeth were cut down to approximately 5 mm in diameter and 3 mm thick and were either placed in previously prepared sites in the buccal or occlusal surfaces of their respective dentures or in containers of tap water. Patients were instructed to remove their dentures only for cleaning with a soft nylon brush and toilet soap, while the laboratory specimens were stored at ambient temperature. After one week, the tensile force needed to dislodge each restoration from its cavity was determined using a universal testing machine. Previously reported laboratory methods for bond strength determination have usually employed a flat dentine surface. However, this study more closely resembled the clinical situation in that the smear layer was produced by a rotary cutting instrument, and the effects of polymerization shrinkage when curing the composite resin were simulated. Furthermore, it was easier to confine the bonding agent to the desired dentine surface.

Adhesives↗
PubMed1990

Clinical performance of dentine bonding agents in the enamel-etched Class V abrasion lesion.

Ninety-three non-undercut cervical abrasion lesions were restored with one of five dentine bonding agents and composite resin, using enamel etching to supplement retention. The restorations were reviewed at approximately one, six, 12 and 24 months. The loss rate at one year ranged from zero to 50 per cent, and marginal staining became apparent over the one-year period. It is evident that even with enamel etching, some dentine bonding agents are not effective enough to reliably retain composite in Class V abrasion lesions.

Acid Etching, Dental↗
PubMed1990

Cracked tooth syndrome: diagnosis, treatment and correlation between symptoms and post-extraction findings.

Although the cracked tooth syndrome has been known for over twenty years, it frequently remains undiagnosed because the condition is not sufficiently well recognized. Cracked tooth syndrome has been defined as an incomplete fracture of the dentine in a vital posterior tooth, and must be distinguished from a split tooth. A diagnosis can often be made by means of the history, and must be confirmed by reproducing the patient's symptoms. The ideal treatment consists of applying a stainless steel band to the tooth, with cessation of symptoms confirming the diagnosis, followed by a full coverage restoration. Case histories illustrating the syndrome are presented, and a further case is reported where a diagnosis of cracked tooth syndrome was made, and the tooth extracted, sectioned and stained to show the nature of the cracks and their relationship to the pulp.

Adult↗