R.W. Billington

The in vivo perception of roughness of restorations.

Objective To determine a threshold of detection value for surface roughness of restorations by patients using their tongue.Method Samples of composite resin were finished with differing grades of abrasive. The surface roughness (Ra) was measured and representative scanning electro-micrographs taken. These were compared with labial enamel. Twenty-five volunteers were asked to rank them in order of perceived roughness using the tip of their tongue.Results These showed that the 60% of volunteers were able to rank the specimens correctly, and were able to distinguish differences in roughness values from between 0.25 and 0.50 μm. This range encompasses that of natural enamel.Conclusions The subjects were able to distinguish lower roughness values than have previously been reported. It is concluded that when finishing restorations the surface should have a maximum roughness 0.50 μm if it is not to be detected by the patient.

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties

OBJECTIVE The objective of this study was to enhance the mechanical strength of glass-ionomer cements, while preserving their unique clinical properties. METHODS Copolymers incorporating several different segments including N-vinylpyrrolidone (NVP) in different molar ratios were synthesized. The synthesized polymers were copolymers of acrylic acid and NVP with side chains containing itaconic acid. In addition, nano-hydroxyapatite and fluoroapatite were synthesized using an ethanol-based sol-gel technique. The synthesized polymers were used in glass-ionomer cement formulations (Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or fluoroapatite) were also incorporated into commercial glass-ionomer powder, respectively. The synthesized materials were characterized using FTIR and Raman spectroscopy and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. RESULTS After 24h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163-167 MPa), higher diametral tensile strength (DTS) (13-17 MPa) and much higher biaxial flexural strength (23-26 MPa) in comparison to Fuji II GIC (160 MPa in CS, 12MPa in DTS and 15 MPa in biaxial flexural strength). The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177-179 MPa), higher DTS (19-20 MPa) and much higher biaxial flexural strength (28-30 MPa) as compared to the control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184 MPa for CS, 22 MPa for DTS and 33 MPa for BFS) which were statistically higher than control group. CONCLUSION It was concluded that, both NVP modified and nano-HA/FA added glass-ionomer cements are promising restorative dental materials with improved mechanical properties.

A preliminary comparison of the mechanical properties of chemically cured and ultrasonically cured glass ionomer cements, using nano-indentation techniques.

There is a requirement for a dental cement with properties comparable or superior to conventional glass ionomer cements (GICs) but with the command set properties of the resin-modified GICs. The objective of this work was to show that the application of ultrasound to conventional Fuji IX commercial glass ionomer cement imparts a command set, whilst improving the short-term surface mechanical properties. Nano-indentation techniques were employed to highlight the improvements in hardness and creep resistance imparted to the cement through the application of ultrasound. The instant set imparted by the application of ultrasound provides improved surface hardness and creep, particularly within the first 24 h after setting. The surface hardness of the chemically cured Fuji IX (176 M Pa) increased by an order of magnitude when set ultrasonically (2620 M Pa), whilst creep reduced to a negligible amount. Rapid setting allows for shorter chair time and an improved clinical technique, making restorations more convenient for both the patient and clinician.

Variation in powder/liquid ratio of a restorative glass-ionomer cement used in dental practice

This study investigates the powder/liquid ratios of a glass-ionomer restorative (ChemFil II, Dentsply) mixed in clinical practice. Twenty-two dental surgery assistants (11 from general practice; 11 from a dental hospital) mixed this cement as they would for clinical use. Samples were taken of three mixes from each assistant and the powder/liquid ratios were derived from weight loss on dehydration. A wide range of ratios were obtained, but in no case was the manufacturers recommended ratio of 6.8:1 achieved. The consistency measured in accordance with BS 6039 showed the cement at 6.8:1 to be less fluid than the requirements of the standard and other glass-ionomer restoratives. When tested at the mean ratio used in practice, 5.0:1, the consistency complied with BS 6039, but the compressive and diametral strengths did not, being about half the values found at 6.8:1. It was concluded that this restorative was often mixed in practice at much lower powder/liquid ratios than that recommended by the manufacturer and that this would impair the cements mechanical properties

The comparative strengths of commercial glass-ionomer cements with and without metal additions

Metal reinforced glass-ionomer cements are said to possess superior mechanical properties when compared to non-metal reinforced glass-ionomer cements. However, the literature to date does not always support this view, owing to the variety of materials and test methods employed. In this study the mechanical properties of three reinforced and three standard materials were tested using the standard specification tests of compressive and diametral strength in addition to tensile strength using the four point bend test. The tensile strength was also measured using the shell test in order that this test, which on theoretical grounds is more suited to these materials, may be evaluated. Six specimens of each material were prepared for each of the test modalities resulting in the conclusion that the addition of metal to glass-ionomer cements can markedly increase the strength of the materials. However, the method of fusing the metal to the glass rather than by simple addition does not produce any advantages in strength. In this evaluation one reinforced material was significantly stronger than all other materials in all four test modalities. The compressive strength test which appears in most standards does not appear to be very discriminatory. Of the tensile tests, which have more clinical significance, the results of the diametral strength tests, which are included in some standards, appear to be at variance with the other two tensile tests, suggesting that the flexural or shell test would be more appropriate

The effect of the disc support system on biaxial tensile strength of a glass ionomer cement

OBJECTIVE This was to examine how varying the type of support, from a complete ring to a series of point supports, affected the biaxial tensile strength of one glass ionomer cement. METHOD Three support diameters from 11.5 to 28.6 mm were achieved using 3 mm ball bearings as point supports equidistantly spaced around the diameter. From 3-30 point supports were used depending on diameter. At the maximum number of point supports for each diameter the support points were 3 mm apart. After 24h storage in water at 37 degrees C the biaxial tensile strength of 1 mm thick glass ionomer restorative cement discs was measured using a loading rate of 1 mm min(-1). The load at break was converted to biaxial tensile strength using the Timoschenko and Woinowsky-Kreiger equation using a Poissons ratio value of 0.30. The mean strength of six specimens tested per support regime was calculated. RESULTS Comparison with the mean result obtained from using a continuous knife-edge support showed there to be no significant difference (unpaired t-test) between the different support systems except in two cases, both being when a four-point support was used. Neither the support diameter nor the number of point supports was crucial. SIGNIFICANCE Results from studies where different systems have been used to support brittle cement discs may be compared.

The effects of adding fluoride compounds to a fluoride-free glass ionomer cement on subsequent fluoride and sodium release.

Studies have shown that ions in a glass ionomer matrix are 1-10% of the amounts present in the original glass. To measure more precisely the release from a cement matrix, known amounts of ions were added to LG30 glass which was fluoride and sodium-free. Cement without additions acted as the control. 1.4-1.6% of each of sodium, calcium and aluminum fluorides were added to three portions of control blend. The sodium and fluoride release into deionised water from five discs of each cements blend was measured for 8 months. This represented complete release for sodium but not for fluoride. Traces of fluoride and sodium in the glass produced low but measurable amounts indicating about a third of the fluoride and substantially all sodium present in LG30 was released. The addition of calcium fluoride had no significant effect on sodium or fluoride release and aluminium fluoride minimal effects. Adding sodium fluoride significantly enhanced release of both ions although fluoride release was less than from a glass containing 5% fluoride. Only small proportions of the additions, 2-5% of the fluoride and 13% of sodium, were released. Sodium and fluoride appeared to be released independently. For LG30 cements additives were poor at supplying extra ions.

Effects of adding sodium and fluoride ions to glass ionomer on its interactions with sodium fluoride solution.

This investigates the effects of the addition of Na and F ions to a glass ionomer cement in which those ions are not inherently present on its interactions with dilute (0.2%) NaF solution. Both the effect of the solution on the cements surface morphology and the effect of the cement on the solution in terms of take up of Na+ and F- and of change in pH are to be investigated. These results are to be compared to previous results obtained with glasses which contained both, one, or neither of the ions as components of their glasses. NaF (1.3% by weight in the mixed cement) was added to the powder components of a glass ionomer based on LG30 glass (which contains Al, Si, Ca, P, and O only). Discs of cement were set in moulds at 37 degrees C for 1 h then stored in water at 37 degrees C for 3 days. Each test disc was then immersed in 10 ml 0.2% NaF solution whereas controls remained immersed in water (N = 3 for test and control). Test and control disc surfaces were assessed both qualitatively by electron microscopy and quantitatively by linear profilometry (Ra values). Potentiometry was used to measure solution pH and Na and F concentrations using a pH electrode and suitable ion selective electrodes both before and after cement immersion. The surface of test specimens was subject considerable disruption with the polysalt cement matrix being removed and residual glass particles being disclosed. The controls showed no such disruption. This effect was reflected in a significant difference of Ra. Such an effect was not shown by test and control surfaces of LG30 but a similar effect was to that shown by LG26 (which contains F as a glass component). Solution pH changed by 1 unit which was much more than the change shown by LG30 or LG26 but is similar to that of AH2 and MP4 cements which both contain Na. The Na and F uptake was much lower than for LG30 whereas that of LG26 was higher than LG30. The Na:F ratio was 0.29:1 compared to 1.26:1 for LG30 (LG26 = 1.01:1, AH2 = 1.02:1, MP4 = 1.04:1). Fluoride addition to a F-free glass ionomer renders it vulnerable to surface disruption by NaF solution showing that fluoride complexes produced in glass dissolution are not necessarily involved in this process. Sodium addition to a Na-free glass ionomer confirms the role of this cement in enhancing pH change in NaF solution. The level of uptake of F- from a NaF solution in much lower than that for the F-free glass ionomer which shows there is no direct relationship between F- uptake and surface disruption. The ratio of Na:F uptake is below 0.3:1, but the pH change is similar to cements where the ratio is close to unity which indicates that F-/OH- interchange is not a significant mechanism even when anion/cation uptake is not balanced.

Effect of monovalent ions in glass ionomer on their uptake and re-release

AIMS The study aims to directly measure uptake of Na and F ions by glass ionomer cement from dilute NaF solution and compare this with the subsequent re-release of these ions into water. In addition, the effect of the presence or absence of Na and/or F as a component of the glass is evaluated. MATERIALS AND METHODS The four glass ionomers used differed only in glass composition; AH2 contained both Na and F, LG26 contained F, MP4 contained Na and LG30 contained neither Na nor F. Discs of cement were set in moulds at 37 degrees C for 1 h and matured in water at 37 degrees C for 3 days. Test discs were immersed in 0.2% NaF solution for 24 h, control discs in water. Discs were subsequently immersed in water which was changed regularly. Ion-selective electrode measurements (F and Na) and atomic absorption spectrometry (Na) were used to determine uptake (change in immersion solution concentration) and re-release into water. RESULTS All cements took up large quantities of Na and F ions (range 95-336 mumol g-1). This resulted in internal ion concentrations from 16 to 56 times higher than the immersing solution. All re-release was complete within 97 days. No cement re-released more ion than taken up. Glass ionomers containing fluoride took up more Na and F than fluoride-free ones and then re-released a lower percentage of these ions. The cements all took up Na and F ions in equimolar proportions, but initially re-released more F than Na with F-free cement results tending to unity by 97 days. CONCLUSIONS Glass ionomer cements take up Na and F ions from NaF solution in large quantities and in equimolar proportion. This is re-released either wholly or in part in 97 days by which time the release does not differ from the controls. The presence or absence of F in the cement composition markedly influences both uptake and re-release. Fluoride/hydroxyl interchange does not appear to play an important role in uptake.

Effect of ultrasound on the setting characteristics of glass ionomer cements studied by Fourier Transform Infrared Spectroscopy

Objective To investigate the effect of ultrasound (US) application, US staring time and US duration on the setting of glass ionomer cement (GIC) by using Attenuated Total Reflectance Fourier Transform Infrared (ATR/FTIR) spectrometer. Methods Two conventional GICs, Fuji IX Fast and Ketac Molar were studied. US application was started at 30 s or 40 s after mixing and was applied for times between 15 and 55 s on samples of two different thicknesses. The samples were analysed using ATR/FTIR. Results US accelerated the curing process in both cements, US needed to be applied for more than 15 s. Both Fuji IX and Ketac Molar showed increased setting on increasing the US application duration from 15 s to 55 s. Increased setting of the GICs was produced when US application started 40 s after mixing rather than 30 s after mixing. Conclusions The significant findings of the study include that US application accelerated the setting processes, by accelerating the formation of the acid salts. The salt formation increased with increase time of US application. The effect of application of US to setting GICs is influenced by time of the start of application of the US. The effects appear to material specific, with Ketac Molar showing a greater effect than Fuji IX.