The effect of instrument lubricant on the diametral tensile strength and water uptake of posterior composite restorative material: an in-vitro study.
Mr J Patel, Miss C Granger
Dental composite materials are widely used in dentistry with increasing popularity and improved mechanical properties and aesthetics1. Despite this they also possess many disadvantages including poor handling during placement, which may impact upon the long-term outcome of the restoration2, 3. This handling difficulty is well documented and many techniques have been suggested to ameliorate placement difficulties and minimise adhesion of dental composite material to instruments4, 5. Some clinicians advocate the use of various instrument lubricants, such as wiping the instrument with ethanol or coating it in dentine bonding agent5. Whilst this may help improve handling, it may conversely interfere with properties of the material. Thus one may question – in search of improved handling, does the clinician unwittingly modify the material by introducing contaminant into the composite, potentially affecting its properties?
This investigation assessed the effects of instrument lubricant on the diametral tensile strength (DTS) and water uptake of composite restorative material.
300 hybrid posterior composite cylinder specimens (Solitaire 2, Heraeus Kulzer, Frankfurt, Germany) in shade A1 were prepared in polytetrafluoroethylene moulds (5mm diameter x 8mm depth, with 4 x 2mm increments). 4 instrument lubricants were selected: ethanol; 3-step adhesive system (Kerr Optibond; bonding agent bottle); 2-step adhesive system (Kerr Solo-Plus; total-etch primer-adhesive bottle) and 1-step adhesive system (Kerr All-In-One; self-etch, primer, adhesive bottle). Bonding systems were brand standardised to eliminate inter-brand variability. 60 cylinders were prepared within each lubricant group and 60 cylinders were prepared as a control group without the use of instrument lubricant.
Protocol planning included pilot studies, power calculations and protocol refinement. Specimens were prepared by 2 operators, trained and calibrated for their prospective tasks. Following construction, specimens were randomly separated into three experimental groups (100 per group) (‘0-week/immediate’, ‘1-week’ and ‘12-week’) for longitudinal analysis following storage in phosphate buffered saline physiologic buffer (PBS) within individual sealed bottles at 37°C.
Water uptake was assessed gravimetrically with an electrical analytical balance at 1-week and 12-weeks. DTS was assessed at all three time-points on a Universal Testing Machine (Model HK5S, Instron Ltd, High Wycombe, UK), with their long axis perpendicular to the applied compressive load, with a 5KN load cell at a constant crosshead speed of 10mm/min, until the point of failure (machine set to peak hold).
Data were analysed with parametric analysis of variance (ANOVA) and Tukey’s HSD tests using the IBM SPSS statistics package.
Results identified statistically significant differences between specimen groups for both DTS and water uptake. Control specimens exhibited a significantly higher DTS and lower water uptake than all specimens placed with the use of an instrument lubricant (p<0.01). All experiment groups (including control) showed a reduction in DTS over time. Control samples matched evidence based values for DTS6, 7. They also exhibited a rapid early water uptake concordant with previous research literature.
Samples placed with ethanol as an instrument lubricant displayed distinctive banding (see figure 3). These sites commonly proved a weak-point for fracture (see figure 4) and further assessment is necessary here. Fracture patterns varied significantly suggesting a high tendency for catastrophic failure in ethanol and 1-step (self etch) groups (see figure 4). Further investigation of this is required and it is postulated that carbon and proton nuclear magnetic resonance (NMR) spectroscopy analysis may be useful here.
Diametral Tensile Strength