The effect of an additional application of sealer during continuous wave of condensation obturation

Background: Root canal fillings with a thin layer of sealer lining the dentine wall, a high percentage of core material that closely adapts to the dentine and sealer penetration into dentinal tubules is considered desirable. The continuous wave of condensation (CWC) is a warm obturation technique. It involves a down-pack of a master apical cone associated with the partial removal of the core material from the coronal segments of the root canal. Backfilling with a thermoplasticised core material is then carried out. It is unknown if a second application of sealer, following the down-pack, would be beneficial. Aim: To assess the effect of an additional sealer application during the CWC technique by measuring the distance between gutta-percha (GP) and canal wall, percentage of sealer and sealer penetration into the dentinal tubules. Materials and methods: Palatal roots of 105 extracted human maxillary molars were sectioned and prepared to a master apical file size 40, 0.06 taper with Vortex Blue® files. Roots were randomly assigned to seven groups (n = 15). Groups A (AH Plus™), B (Roth 801 Root Canal Cement) and C (Sealapex™) had a single application of sealer dyed with Sudan Black B before CWC obturation (Elements™ Free). Group D (negative control) was obturated without sealer. Groups E (AH Plus™), F (Roth 801 Root Canal Cement) and G (Sealapex™) received a second application of dyed sealer following the down-pack. Roots were sectioned at 2, 3, 4, 6, 7 and 8 mm from the root apex. The obturations were microphotographed (10 and 20x) and images measured with ImageJ. The distance from GP to canal wall, percentage of sealer and dentinal tubular penetration depth and direction was calculated at each level. The distance between the GP and canal wall were analysed using Mood’s median test and the chi-squared test of independence (p < 0.05). Results: At each ascending level, sealer percentage decreased for each experimental group while the number of outer third penetration depths increased when all groups were combined. Comparisons with Group D revealed all groups had significantly increased distance between the GP and canal wall at 2 - 4 levels (p = 0.00 – 0.05), increased sealer percentage at 4 – 6 levels (p = 0.00 – 0.03) and increased penetration depths. Comparison between a single and double application of sealer revealed Group E had increased distance between the GP and canal wall compared to Group A at the 4 and 6 mm levels (p = 0.01 – 0.05). Group F had increased distances compared with Group B at 6 mm (p = 0.03) and Group G was increased over Group C at 8 mm (p = 0.03). A double application of sealer increased the sealer percentage in Group A at the 2 mm level compared with Group E. No significant difference in sealer percentages were noted when groups B and F were compared or Groups C and G. Analysis of Groups A and E revealed that additional sealer increased outer third penetration depths for Group E, which was also evident for Group G when compared to Group C. Conclusions: An additional application of sealer slightly increased the distance between the GP and canal wall. It did not affect Roth’s and Sealapex™ sealers but decreased the sealer percentage of AH Plus™ to a minor degree. It increased the outer third penetration depths for AH Plus™ and Sealapex™ but not Roth’s sealer