The results are shown in Fig.1and Table 1.
The achievement of pulpal anaesthesia at any time varied between treatments (Fig.1). Labial Infiltration achieved anaesthesia in 50% of teeth at some stage, 50%of teeth were anaesthetized after lingual Infiltration and 92% after combined labial and lingual Infiltration. No tooth was successfully anaesthetized after intraligamentary injections (w2 =20; P < 0.001).When comparing only the Infiltration techniques there was a significant difference in the achievement of pulpal anaesthesia (w2 =8.2, P < 0.05). The curve in Fig.1 for the combined labial and lingual technique shows a maximum of10 out of the12 teeth anaesthetized at any one stage, however,11teethwere successfully anaesthetized with this technique (one had lost anaesthesia at14m in and another achieved pulpal anaesthesia at 18 min). The areas under the curves shown in Fig. 1vary significantly between treatments (F=9.3, P < 0.001).When the three Infiltration techniques are compared there is a significant difference in the areas under the curves (F=3.9, P < 0.05). However, when only those teeth that were successfully anaesthetized are considered there was no difference in the duration of anaesthesia within the time-frame of this study (maximum duration 30 min). The mean (+-SD) duration of anaesthesia for the teeth successfully anaesthetized being as follows; for buccal Infiltration 22.3+-9.2 min (range 6=30 min); for lingual Infiltration 19.0+-8.4m in (range 6= 30 min); and for the combination 23.6 _7.6 min (range 6=30 min).
The individual visual analogue scores for the injections are shown in Table 1. The injections varied in the amount of discomfort produced (F=3.74; P < 0.05). The mean (+-1SD) VAS score for intraligamentary injections was 28+-12 mm, for buccal Infiltrations 17+-8 mm and for lingual Infiltrations 16+-16 mm. Intraligamentary injections were more uncomfortable than both buccal Infiltrations (t=3.7; P < 0.01) and lingual Infiltrations (t=2.67; P < 0.05). The infiltration techniques did not differ in the discomfort they produced (t=0.27; P=0.8). In pain trials, a score of 30 mm or more is considered to represent moderate discomfort (Collins et al. 1997). In this study, six volunteers considered the discomfort to be at least moderate in intensity for the intraligamentary injection compared to one subject for the labial Infiltration and two volunteers for the lingual Infiltration.
Table 1. Visual analogue scores for injection discomfort.
Figure 1. The survival of anaesthesia over time for the four different anaesthetic techniques. The time represents minutes after injection.
Labial: labial infiltration of1.0 mL 2% lidocaine with 1: 80 000 adrenaline;
Lingual: lingual infiltration of 1.0 mL 2% lidocainewith1: 80 000 adrenaline;
Both: the combination of 0.5 mL labial and 0.5 mL lingual infiltration of 2% lidocaine with 1: 80 000 adrenaline;
pdl: intraligamentary injection of 0.18 mL 2% lidocainewith1 : 80 000 adrenaline.