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Biomedical subjects

C Strydom

Publications and source records attributed to C Strydom.

10 recordsLinked to original sources
PubMed2006

Handling protocol of posterior composites--part 3: matrix systems.

Two of the major clinical problems related to direct posterior composite restorations are the clinician's inability to establish an ideal proximal contour and interproximal contact, which, in turn, can lead to continual food impaction and periodontal disease. The reason for this is that composites provide little internal force to counteract the force from the matrix. Therefore, unlike amalgams, which possess a very high resistance to deformation, composites are easily forced back into their original position by a tight circumferential matrix band. Thus, although tight contacts in small-moderate sized cavities may be possible for posterior composites using circumferential matrices, special matrix systems and wedging techniques are being required to establish a proper contact, especially when cavities with a wide buccolingual width are being restored.

Acrylic Resins↗
PubMed2005

Self-etching adhesives: review of adhesion to tooth structure part II.

UNLABELLED: Self-etching adhesives are steadily increasing in popularity among dental practitioners with their easy handling technique and their promise of no post-op sensitivity. As with any new bonding material, in vitro and in vivo investigations are required to assess the clinical efficacy of these systems. OBJECTIVES: The current literature was reviewed to provide information on these systems, including the influence of their acidity and permeability on the quality of the bond, the role of water in long-term degradation of the bond in in vivo and in vitro studies, and the clinical efficacy of the self-etching adhesives in clinical research studies. DATA SOURCES: Published abstracts, reviews, laboratory reports and clinical research papers in the dental literature. CONCLUSIONS: Very little information is available on self-etching systems pertaining to the long-term in vitro and in vivo durability of their bond and their medium- to long-term clinical outcome. Although post-op sensitivity seems to be something of the past, short-term clinical studies show that some self-etching adhesives do not perform as well as total-etch systems.

Acid Etching, Dental↗
PubMed2005

Polymerization and polymerization shrinkage stress: fast cure versus conventional cure.

Dentists nowadays have a choice of conventional halogen lights, halogen lights with more sophisticated curing cycles (step-cure, rapid-cure, ramp-cure & pulse-cure), fast halogen lights, laser lights, plasma arc lights (PAC) and, lately, LED lights. While the manufacturers of some of the curing units try to improve on the operational reliability of their lights with a slower initial rate of cure, other manufacturers simply wish to offer as fast a curing time as possible. The conventional approach to cure accepts that sufficient light intensity of at least 400 mW/cm2 at a wavelength of 400-500 nm, and an exposure time of at least 40 seconds is needed to cure a 2-mm layer of composite. When a halogen light with higher or very high intensity is used, alternative curing strategies provide for an initial slower cure to allow flow, and after that a higher-intensity cure to improve the degree of cure. In contrast, in the fast-cure or rapid-cure approach it is suggested that a layer of composite can be cured for only 5- 10 seconds at >2000 mW/cm2. Some go so far as to say that an exposure time of 3 seconds per layer may be enough. This contradictory approach is compounded by the fact that this support for fast cure does not seem to consider the negative consequences. Therefore, to address these concerns, this review discusses the possible effects of a fast cure approach compared to a more conventional approach in polymerization and polymerization shrinkage, and the consequences there-off. Other factors that play an influencing role in polymerization shrinkage stress are also included in the discussion.

Composite Resins↗
PubMed2005

Prerequisites for proper curing.

The prerequisites for proper curing include: 1) sufficient light intensity at 2) a certain wavelength, for 3) a certain time interval. This review discusses the radial output by halogen, PAC and LED lights, and the adaption of this output to meet the wavelength prerequisites for optimum polymerisation. Some basic terminology relating to the power of the light and intensity is explained and calculations are used to illustrate to the reader how the size of the light guide increases or reduces the intensity of the light beam.

Composite Resins↗
PubMed2005

Handling protocol of posterior composites Rubber Dam.

Although it can never provide perfect isolation, rubber dam greatly facilitates adhesive procedures by keeping the operating field dry throughout operative procedures. Research has shown time and again that the modern dentin bonding agents cannot cope with blood- or saliva contamination. In spite of this very few dentists use rubber dam routinely. Once experienced in its use, it should not take up much more clinical time than 2 minutes.

Humans↗
PubMed2004

Self-etching adhesives: review of adhesion to tooth structure part I.

UNLABELLED: Self-etching adhesives with their easy handling technique and promise of no post-op sensitivity are increasingly popular among dental practitioners. As with any new bonding material, in vitro and in vivo investigations are required to assess the clinical efficacy of these systems. OBJECTIVES: The current literature was reviewed to provide information about these systems in terms of: etching of and adhesion to prepared and unprepared enamel, primary enamel and sclerotic or caries-affected dentine. DATA SOURCES: Published abstracts and research papers on laboratory studies, as well as reviews available in the dental literature. CONCLUSIONS: Although the etching aggressiveness of self-etching systems can be used to predict the depth of demineralisation of tooth structure and the ultra-structure and thickness of the hybrid layer, it cannot be correlated to the bond strengths obtained on enamel and dentine. A certain mild two-step self-etching system, for example, consistently provides similar or higher bond strengths than more aggressive self-etching systems in laboratory studies. Where either intact enamel or sclerotic or caries-affected dentine is involved, self-etching systems generally provide lower bond strengths than total-etch systems; therefore coarsening of tooth structure, extra etching time or an extra application of the primer is recommended.

Acid Etching, Dental↗
PubMed2002

Curing lights--the effects of clinical factors on intensity and polymerisation.

Curing lights are used to cure light-sensitive dental materials in clinical situations that range from small, easily accessible restorations to larger ones that are more difficult to access. The degree to which these materials cure depends on the intensity and quality of light to which they are exposed and the curing time. Once the light has left the curing unit, factors such as composite type, composite shade, thickness of resin increment or overlying tooth structure, the distance and orientation of the light tip, and the diameter of the light tip may reduce intensity and provide a lower degree of polymerisation. The only way to overcome this reduction is to increase exposure time. However, surveys have shown that dentists tend to cure for periods that are too short. Reasons for this may be that the dentist is unaware of the importance of adequate light intensity, as well as the influence of all the factors mentioned above that reduce intensity and lower the degree of polymerisation. This paper reviews the clinical factors that may reduce light transmission during polymerisation of composite restorations, and suggests several clinical recommendations to provide general practitioners with information on how to optimise the degree of cure obtained in their surgery.

Air↗
PubMed2002

Dental curing lights--maintenance of visible light curing units.

Successful curing depends directly on many factors of which the most important is the correct functioning of the curing unit to emit light of sufficient intensity and quality. If the contribution of any of these factors is at a less than adequate level, the light-sensitive materials will not polymerise completely, which in the long term may be responsible for secondary caries and decreased longevity of the restoration. Factors which may reduce the light output include ageing of the bulb and filter, damage of the light guide or fibre optics, deposits on the light tip due to composite build-up or autoclave scale, erosion of light tip surface due to immersion sterilisation, and line voltage fluctuations. Recent studies carried out to investigate the effectiveness of curing lights in clinical use show that most practitioners are unaware of the importance of routine monitoring, care and maintenance of curing lights. This paper reviews some of the available literature on the monitoring, care and maintenance of curing lights, including information on the influence that some of these may have on the intensity emitted by the curing light.

Dental Materials↗
PubMed1995

Laboratory evaluation of the Gluma 3-step bonding system.

PURPOSE: To determine in vitro (1) the shear bond strengths (SBS) of the modified Gluma system to enamel and dentin; (2) the qualitative and the quantitative microleakage (ML) of Class V preparations on the cemento-enamel junction (CEJ) and in dentin, respectively, restored with the Gluma system; and (3) the effect of the system's components on enamel and dentin by scanning electron microscopy. MATERIALS AND METHODS: Seventy-five extracted human maxillary permanent central incisors and 75 permanent first and second molars were embedded in brass tooth cups with cold-cure acrylic resin. The facial surfaces of the anterior and the occlusal surfaces of the molar teeth were ground wet on 180- followed by 600-grit silicon carbide paper. Demarcated sites on the surfaces were treated according to the manufacturer's instructions and Pekafill composite was bonded to the treated surfaces. Fifteen specimens prepared on enamel were removed 1 minute after cure (A) and the SBS determined. The remaining specimens were removed 15 minutes after final cure, stored in saline at 37 degrees C for 24 hours (B), for 1 week without (C) and with temperature cycling (D), and for 4 weeks (E). Similar regimens were used for dentin, groups F, G, H, I and J. The SBS were determined and expressed in MPa. The data were analyzed by ANOVA, Student-Newman-Keuls and t-tests. For the qualitative ML evaluation, Class V cavities were prepared on the CEJ of 30 human premolars and restored with Gluma/Pekafill. After thermocycling in 0.5% basic fuchsin, the teeth were sectioned and ranked according to the degree of microleakage. Class V cavities were prepared on the facial root surfaces of 15 human premolars and restored. The ML was determined quantitatively by a spectrophotometric dye-recovery method and expressed as microgram dye/restoration. RESULTS: The mean +/- SD of the SBS in MPa were: A: 14.6 +/- 2.2; B: 21.2 +/- 1.6; C: 20.5 +/- 1.4; D: 24.2 +/- 2.0; E: 22.8 +/- 3.7; F: 7.0 +/- 2.0; G: 16.1 +/- 4.0; H: 15.6 +/- 3.7; I: 10.9 +/- 3.3; J: 14.4 +/- 3.3. The quantitative ML was 1.00 +/- 0.39 microgram dye/restoration. The lowest SBS were obtained on specimens tested after 1 minute. Temperature cycling had a significantly adverse effect on the SBS to dentin (P = 0.0003). Etch patterns conducive to bonding were produced on the enamel. The resin system penetrated into the dentin tubules.

Analysis of Variance↗