Objective: To investigate the influence of powder/liquid ratio of two glass ionomer cements using two different bore diameter delivery tubes, on the porosity of injectable glass ionomer pastes.
Method: Two commercial cements, FUJI IX (GC Dental) [FIX] and Amalgomer (Advanced Healthcare)[AM] were prepared as follows: AM powder was mixed with water as (P+A)/W ratio of 3.575/1 and 2.146/1. FIX liquid contains 50% of water and two combinations of liquid and powder were used as P/A/W= 7.2/1/2.29 [(P+A)/W=3.575/1] and P/A/W=2.575/1/1 [(P+A)/W=3.575/1]. P=glass powder, A= Acid, W= water. The first combination (COM 1) of FIX is the same as AM and the second combination (COM 2) contained more acid. After hand mixing, the pastes were immediately loaded into a 1 ml plastic syringe connected to a narrow bore needle with either a 1.29mm or 0.89mm diameter. The paste was injected into an epoxy mould containing a spherical cavity of about 3mm diameter. The density of the cements and epoxy moulds was measured using Archimedes Principle. This allowed the theoretical amount of cement required to fill each bubble to be determined. Having determined the true weight of the mould and injected cement the volume of air incorporated within the cement was determined by subtraction. 5 samples for each variant were measured.
Results: The mean percentage of the air volume was recorded [Table 1].
| AM L P/L=3.575/1 | AM S P/L=3.575/1 | AM L P/L=2.146/1 | AM S P/L= 2.146/1 | FIX COM 1 | FIX COM 2 |
AIR VOLUME (%) | 3.29 [sd=1.35] | 5.05 [sd=1.14] | 3.03 [sd=0.68] | 3.9 [sd=1.6] | 2.64 [sd=2.6] | 7.81 [sd=7.8] |
L= 1.29mm needle, S= 0.89mm needle, COM 1= combination 1, COM 2 =combination 2 | ||||||
Statistical analysis was carried out using student"t"Test. There was a significantly greater air void volume when using the smaller bore needle for AM samples [p=0.019] and more acid for FIX samples [p=0.003]
Conclusion: The internal bore of the needle significantly affects the porosity of the glass ionomer pastes. The smaller the needle bore the greater the air void volume. The effect was reduced as the P/L of the paste was reduced. Acid percentage could also affect the porosity of the cement.