Stickiness and Stringiness of Uncured Nano- and Nano-hybrid Composites

Objectives:   This study measured the stickiness of selected uncured resin-composites, comparing one nano-composite (NC) to four nano-hybrids (NH).  The tendency to string while handled was also examined.  This study also sought to obtain a correlation between measured stickiness parameters and the composite's tendency to string.

Methods:   Stickiness was analyzed utilizing a texture analyzer.  A stainless steel probe was pushed into composite at constant force for a given contact time, and withdrawn at a given rate.  During withdrawal, the maximum tensile force (Fmax) exerted on the probe and the Work (area under the force-distance curve) were measured.  Data (n=4/group) was collected at 37°C and two combinations of contact time and removal speed (1s and 8mm/s, or 20s and 1 mm/s).

Stringiness was assessed by handling each composite with a dental instrument, ranking them on a scale of 1 (least stringy) to 4 (most stringy).

Estelite^® Sigma Quick (ESQ), Filtek™ Supreme Ultra (FSU), Gradia Direct X (GDX), Paradigm™ Nano Hybrid (PNH), and TPH^®3 (TPH3) were examined.

Results:  

	Fmax(N) 1s, 8mm/s	Fmax(N) 20s, 1mm/s	Work(N·mm) 1s, 8mm/s	Work(N·mm) 20s, 1mm/s	Composite Type	Instrument Stringiness
FSU	1.6±0.3	1.1±0.2	0.8±0.2	0.7±0.2	NC	1
ESQ	6.49±0.08a	5.13±0.2b	14±2c	7.8±0.2d	NH	3
GDX	5.3±0.6a	3.0±0.3b	6.3±0.6c	3.1±0.6d	NH	3
PNH	2.1±0.4	1.36±0.06	1.2±0.3	1.15±0.15d	NH	2
TPH3	4.9±1.3a	4.1±0.5b	30±7c	8.4±0.2d	NH	4

Superscript indicates samples that were statistically different from FSU using the 2-sample t-test and p<0.05.

Work and Fmax were evaluated by linear regression for their correlation with instrument stringiness rating at either condition.  Work correlated best with stringiness, R²=71% for 1s and 8mm/s and R²=73% for 20s and 1mm/s.

Conclusions:   The texture analyzer measurement of Fmax and Work indicated that FSU was less than or equal to in stickiness for all composites examined.  This work aids the dental practitioner by quantifying composite stickiness.