Evaluation of subsurface defects created during the finishing of composites.

The objective of this study was to test the hypothesis that a degraded subsurface layer containing microcracks is produced in dental composites as a result of finishing procedures. Various composites in the form of rectangular bars were finished with a 12-fluted carbide bur or a fine diamond within minutes of light-curing, and were subsequently stained with silver nitrate. Microscopic evaluation revealed that significant penetration of stain occurred in the unfinished as well as in the finished surfaces. The extent of dye penetration that could be directly attributed to a damaged layer produced by the finishing procedure was less than 10 microns, being greatest for a microfill (Silux Plus) and a hybrid (P-50) composite. There was no difference between the effects of the finishing instruments. SEM analysis of the subsurface showed an absence of any cracks for the composites. However, occasional disruption of the interface between the pre-polymerized resin fillers and the matrix was apparent for the microfill material. The results showed that only a very limited subsurface damage may be created in certain composites during the initial contouring of a restoration.

Wear and marginal breakdown of composites with various degrees of cure.

Loss of anatomical form due to wear has been cited as one factor limiting the clinical use of posterior composites. The physical properties and possibly the wear resistance of composite are influenced by the extent to which it is cured. The aim of this study was to vary degree of conversion (DC) in composites to test the hypothesis that resistance to wear and marginal breakdown could be improved by enhanced curing. A light-cured hybrid composite containing a 50% Bis-GMA/50% TEGDMA resin and 62 vol% of strontium glass (1 to 2 microm) with microfill silica was formulated (Bisco). Composite was placed into two 2.5-mm-diameter cylindrical holes in Co-Cr teeth replacing first and second molars in the mandibular dentures of 50 edentulous patients. The composites were light-cured for different time periods (9 s, 12 s, 25 s, 40 s, and 40 s + 10 min at 120 degrees C) and then polished. The microfill Heliomolar was also tested. DC (%) was measured by FTIR and ranged between 55% for 9 s of light-curing and 67% for 40 s of light-curing followed by heat application. Impressions were evaluated at baseline, 6 mo, 1 yr, and 2 yrs. Stone casts were evaluated independently by three observers to determine the % of the total margin exhibiting breakdown. Epoxy replicas were measured with a profilometer for wear. Wear of the hybrid composite at 2 yrs ranged from a high of 144 microm with 9 s of light-curing to a low of 36 microm with 40 s of light-curing followed by heat. Heliomolar exhibited from 11 to 16 microm of wear at 2 yrs. There was a strong negative correlation (r2 = 0.91) between the degree of cure and the abrasive wear of the hybrid composites. Marginal breakdown was negligible for the hybrids, and was reduced for the microfill from 40% to 15% of the margin by heat treatment. This study showed that the resistance to abrasive wear of a dental composite could be improved by enhancement of its degree of conversion.

Testing sealing properties of restorative materials against moist dentin.

The objectives of this investigation were (1) to develop a sensitive laboratory system that simulates the physiological and clinical conditions of a prepared human tooth in order to facilitate the determination of the bonding and sealing efficacies of restorative dental materials and (2) to conduct experiments with two dentin bonding agents, two posterior composite resin restorative materials (hybrid and microfilled), and a glass-ionomer type II filling material. The system functioned well and provided data to indicate that, after margination, the two posterior composite resin restorative materials performed equally and both performed better than the glass-ionomer filling material; none of the materials provided a perfect seal immediately after insertion, although some restorations demonstrated perfect seals from 16 hours to 28 days after placement; the seal of the glass-ionomer material improved after 28 days of storage in buffer solution; each successive step in the respective composite resin procedures improved the seal except in one case for the microfilled resin.

Properties of posterior composite: results of round robin testing for a specification.

OBJECTIVES: Seven sites participated in the round robin testing of five dental composites in order to evaluate specific testing protocols for use in a specification for posterior composites. METHODS: The flexure strength, flexure modulus, solubility in water, and opacity after soaking in water and ethanol, were evaluated for five commercial dental composites at the seven different sites. Samples were either aged for one day or seven days before testing. RESULTS: Although they were not without problems, the results were supportive of including in a specification a test for solubility in water as well as one for flexural strength and flexural modulus. The specification would be similar to that described by ISO 4049, but based upon the results of this study, an increase in the acceptable values for two of these tests was suggested. The results of this study also demonstrated that despite following an identical protocol and using materials from identical batches, significant variations in absolute values were obtained among the Test sites. However, there was generally good agreement among the sites in the relative ranking of the materials. SIGNIFICANCE: These results provide a strong rationale for the inclusion of one or two standard materials in a specification designed to evaluate composites suggested for use in posterior teeth.

Effects of time after extraction and depth of dentin on resin dentin adhesives.

An adhesive shear test has proved to be reproducible and potentially usable for screening new systems. When evaluating current resin dentin adhesives, it appears that the length of time elapsed since extraction of the tooth has little effect on adhesion. Conversely, adhesion significantly decreases as the pulp is approached.

Cements for permanent luting: a summarizing review.

Three cement systems are favored for permanent luting of cast restorations. These include zinc phosphate, reinforced zinc oxide-eugenol, and polycarboxylate cements. Although others have been used in the past and new luting media are anticipated for the future, the status of currently used cement for luting is based mainly on the results of laboratory research and on clinical experience. Zinc phosphate cement, with an impressive 100-year history, currently holds the advantage. Future comprehensive clinical studies, correlated with results of physical and biological testing, may eventually direct the clinican's preference to another, newer material. It is hoped that properties and strength values that are clinically significant also will be identified, so that laboratory tests can be more predictive of clinical success.

The continued in vivo evaluation of the wear of restorative resins.

This study reports on the 3-year results of a method designed to measure the in vivo wear rates of resin systems in denture teeth. Adaptic and Profile showed the most amounts of wear, followed by Finesse, Miradapt, and Isopast. The least amounts of wear were seen with Isosit and Silar. The similarity to the magnitudes of wear reported in other studies suggests the appropriateness of using this technique.

Resin restoration. Factors affecting clinical performance.

This article reviewed the significant factors affecting clinical performance of resin restorations: cavity design and manipulation. The appropriate selection of the specific material should be based on the clinical situation, and the types and characteristics of resins available.

The use and abuse of aesthetic materials in posterior teeth.

This paper summarizes the clinically significant concerns surrounding the use of aesthetic restoratives in posterior teeth. Composite resins are far from ideal and possess some properties that should be of real concern to the dentist. They are not amalgam substitutes. On the other hand, they do have a place in the conservative cavity where aesthetics are desired. The suggested use of composite and porcelain inlays or onlays is an attempt to circumvent some of the concerns generated by the routine use of composites. However, the relative scarcity of clinical studies suggests a limited usage at this time.

Reduction in operatory mercury levels after contamination or amalgam removal.

The threshold limit value (TLV) for occupational exposure to mercury can be exceeded in the dental operatory after a contamination event or during certain dental procedures. The objective of this study was to determine the time required for the mercury vapor levels to return to baseline in both non-ventilated and ventilated operatories after they had been contaminated with mercury to the TLV of 0.050 mg/m3; and to evaluate the efficiency of an activated charcoal filtering device for removing mercury vapor. The results showed that even in a poorly ventilated operatory, the mercury vapor level returned to background within 20-30 minutes after a contamination, and within 10-20 minutes when the operatory was ventilated. The filtering device reduced the level of mercury vapor by approximately 25% during a continuous contamination event, but did not clear the operatory faster than normal settling after a limited source contamination. The filter caused a significant reduction in mercury in the breathing zones of the patient and dentist during and after amalgam removal, but did not eliminate the exposure. This study demonstrated the difficulty in contaminating an operatory with mercury vapor and confirmed the limited time mercury remains airborne, presumably due to its density and affinity for surfaces.

Marginal adaptation of the Concept inlay system.

PURPOSE: To evaluate the fit of the Concept inlay system in three clinically relevant cavity preparations (an occlusal, MO and MOD). MATERIALS AND METHODS: The processed inlays were adjusted as needed and seated on master dies. The greatest marginal discrepancy occurring along each margin was recorded and evaluated. RESULTS: The majority of the margins exhibited gaps in the range of 20-45 microns (statistically insignificant) with the exception of the distal margin of the MO which averaged approximately 80 microns and the buccal and lingual margins of the MOD which were approximately 70 microns (both statistically larger than the 20-45 microns range). This heat and pressure cured composite inlay system is capable of producing fairly closely fitting restorations.

Bonding of dentin adhesives in clinically-simulated occlusal resin composite restorations.

The purpose of this study was to measure the bond strength of resin dentin bonding agents under clinically-simulated conditions. Using extracted human teeth subjected to physiologic-pulpal fluid pressure, occlusal cavity preparations were restored with three dentin bonding agent/resin composite combinations. The teeth were sectioned to remove the occlusal enamel and upper part of the restoration. The force required to remove the remainder of the restoration was converted to a dentin bond strength value. The effect of incremental placement of the resin composite also was investigated. Scotchbond 2 showed better bonding than Gluma or Scotchbond Dual Cure, and Gluma showed better bonding than Scotchbond Dual Cure. Although all materials showed better bonding with the use of three increments of resin composite versus one, only in the case of Scotchbond 2 was there a statistically-verified difference.

Fluoride penetration into the hybrid layer from a dentin adhesive.

PURPOSE: To evaluate the in vitro microleakage of a new fluoride-containing dentin adhesive and to provide evidence for fluoride release from the adhesive and penetration into the dentin. MATERIALS AND METHODS: Class V preparations with margins in enamel and dentin were made in the buccal and lingual surfaces of six extracted human third molars. Six preparations were restored with Scotchbond Multipurpose (SBMP)/Z100 composite and six with a new fluoride containing dentin adhesive (FB)/Litefil composite. After aging for 30 days in water at 37 degrees C, the teeth were stained with silver nitrate, sectioned and graded by two observers for leakage at the enamel and dentin margins. Selected FB specimens were examined in the scanning electron microprobe using WDS for fluoride and EDS for calcium and phosphorous. Fluoride release into water from disks of FB adhesive was evaluated for up to 112 days using a specific ion electrode. RESULTS: Fluoride leached from the adhesive at a decreasing rate with time. The final rate over 112 days was 0.02 ppm/day (0.2 microgram/cm2/day). Leakage at the enamel and dentin margins was similar for both adhesives (Mann-Whitney U-test; P < or = 0.05). SEM evaluation showed the presence of a discontinuous hybrid layer of 2-3 microns. Fluoride was present within, but limited to, the hybrid layer for the FB adhesive. The penetration of fluoride could only be confirmed in areas where leakage had occurred.