Study selection
There were 1,434 studies searched. References in selected papers were searched and no additional studies were located. After reading full texts, ten studies were finally selected. Process selection appears in Figure 1.
There were 495 duplicates in the 1,434 studies. 875 studies were ruled out after reading titles and abstracts. Another 43 studies were ruled out after reading the full text. There were 11 unavailable or awaiting classifications. Finally, 10 studies were included. Studies eventually included were from 2004 to 2015.
Study characteristics
All research included were RCTs. Follow-up periods were 3 and 6 months. Characteristics of articles selected for primary outcomes appear in Table 2. Characteristics of articles selected for secondary outcomes appear in Table 3. Reasons for study exclusion appear in Appendix 3.
Limited information of 11 studies could be obtained from the publication. Inclusion, or exclusion could not be decided because of unobtainable full texts and unknown specific conditions. These appear in Appendix 4.
Quality and risk of bias assessment
Bias analysis results for the studies appear in Appendix 5 and 6. Most studies did not have high bias risks. Funnel plots could not be done due to limited number of studies (<10).
Meta-analysis Results of Primary Outcomes
The follow-up period lengths of the studies varied. Most were 3 and 6 months. This allowed for grouping into 3- and 6-months and reduced heterogeneity.
Outcome 1:PPD (Fig.2)
(1) 3 months: (Fig. 2a)
- a) Initial PPD ≤4mm
Only one met the criteria, which reported no statistical differences between ultrasonic and manual subgingival scaling.[12]
- b) Initial PPD >4mm
When initial PPD was medium, differences between ultrasonic and manual subgingival scaling were statistically significant. PPD reduction after manual subgingival scaling was greater than ultrasonic instruments (MD 0.14,95% CI [0.02, 0.26], P=0.02). Heterogeneity was great (Tau² = 0.01; Chi² = 28.94, df = 3 (P < 0.00001); I² = 90%).[12-15]
When initial PPD was deep, heterogeneity was acceptable (Tau² = 0.01; Chi² = 4.24, df = 3 (P = 0.24); I² = 29%). PPD reduction after the two treatments were not statistically significant (MD 0.13, 95%CI [-0.02, 0.28], P=0.09).[12-14, 16]
(2) 6 months: (Fig. 2b)
- a) Initial PPD ≤4mm
Two studies[12, 17] met the criteria as they used baseline changes as outcomes and one baseline changes value of 0. A meta-analysis could not be done using the two studies. They both reported no statistical differences between ultrasonic and manual subgingival scaling.
- b) Initial PPD >4mm
When initial PPD was medium, differences between ultrasonic and manual subgingival scaling were not statistically significant (MD 0.19, 95%CI [0.11, 0.27], P=0.22). Heterogeneity was large (Tau² = 0.02; Chi² = 25.89, df = 3 (P < 0.0001); I² = 88%).[12, 15, 17, 18]
When initial PPD was deep, heterogeneity was also great (Tau² = 0.08; Chi² = 8.74, df = 3 (P = 0.03); I² = 66%). PPD reduction after manual subgingival scaling was greater than ultrasonic instruments with a statistically significant difference (MD 0.50, 95%CI [0.10, 0.89], P=0.01).[12, 16-18]
Outcome 2:CAL (Fig. 3)
(1) 3 months: (Fig.3a)
- a) Initial PPD ≤4mm
Only one met the criteria, reporting no statistically significant difference between the two methods.[12]
- b) Initial PPD >4mm
When initial PPD was medium, differences between ultrasonic and manual subgingival scaling were not statistically significant (MD -0.08,95%CI [-0.18, 0.03],P=0.14). Heterogeneity was great (Tau² = 0.01; Chi² = 10.92, df = 3 (P = 0.01); I² = 73%).[12-15]
When initial PPD was deep, difference between ultrasonic and manual subgingival scaling was not statistically significant (MD -0.06, 95%CI [-0.58, 0.46], P=0.81). Heterogeneity was also high (Tau² = 0.16; Chi² = 23.28, df = 3 (P < 0.0001); I² = 87%).[12-14, 16]
(2) 6 months: (Fig.3b)
- a) Initial PPD ≤4mm
The heterogeneity of the two studies was too large (Tau² = 0.10; Chi² = 10.55, df = 1 (P = 0.001); I² = 91%) for a meta-analysis to be performed. They both indicated no statistically significant differences between ultrasonic and manual instruments.[12, 17]
- b) Initial PPD >4mm
No statistically significant differences were found between the ultrasonic and manual subgingival scaling when initial PPD was medium (MD -0.06, 95%CI [-0.17, 0.06], P=0.33). Heterogeneity was slightly great (Tau² = 0.01; Chi² = 6.29, df = 3 (P = 0.10); I² = 52%).[12, 15, 17, 18]
At deep pocket depth, differences between the two were not statistically significant (MD 0.28, 95%CI [-0.20, 0.77], P=0.26). Heterogeneity was large (Tau² = 0.15; Chi² = 10.37, df = 3 (P = 0.02); I² = 71%).[12, 16-18]
Secondary outcome measures
(1) GR: Sculean et al.[18] indicated no statistical differences studying single or multiply-root teeth between ultrasonic and manual subgingival scaling at 6-months when initial PPD was deep. Kargas et al.[15] noted that, at medium depths, there were no statistical differences between ultrasonic and manual subgingival scaling at either 3 or 6-months.
(2) BOP: Christgau et al.[17] found that at 6-months, manual subgingival scaling showed greater BOP reduction at initial deep pocket depth compared to ultrasound.
(3) Residual dental calculus: Schwarz et al.[19] indicated that for single-root teeth at deep initial depth, ultrasonic subgingival device was superior to manual instruments in removing subgingival dental calculus. Yukna et al.[20] found no statistical differences in residual dental calculus rates between ultrasonic and manual subgingival scaling with initial PPD at 5-6mm, 7-8mm or > 9mm. Gellin et al.[21] found no statistical differences in dental calculus clearance rates between the two methods when initial PPD was 0-3mm, 4-5mm, or, 6-12mm. When ultrasonic subgingival scaling was combined with manual instruments, the effectiveness was superior to either ultrasonic or manual instruments individually.[21]
Sensitivity analysis
Outcome: PPD
At 3-months, at medium depth, heterogeneity was great (I2=90%, Fig.2a). After sensitivity analysis, four studies were found highly heterogeneous to each other and were unsuitable for meta-analysis. After a bias analysis, the heterogeneity source was thought to be: (1) small number of studies; (2) the fact that tissue healing took time and early probing disrupted attachment gains. At 3-months, PPD and CAL reductions were unstable, causing large heterogeneity.
At medium depth, 6-months, Kargas et al.[15] was found to have significant heterogeneity. After excluded, heterogeneity decreased to 0% (Tau² = 0.00; Chi² = 0.02, df = 2 (P = 0.99); I² = 0%). The results showed statistically significant differences between manual and ultrasound groups. PPD reduction after manual subgingival scaling was greater than ultrasonic subgingival scaling (MD 0.19,95%CI [0.11, 0.27], P<0.00001). Compared with the other three studies, only non-smokers were included in this study, which might be the reason for heterogeneity (Fig. 4a).
When initial PPD was deep at 6 months, D'Ercole[16] was a major origin of heterogeneity (Tau² = 0.03; Chi² = 3.86, df = 2 (P = 0.15); I² = 48%). After exclusion, heterogeneity decreased to 48% (Fig. 4a).
Outcome:CAL
When initial PPD was medium, at 3-months follow-up, the heterogeneity of CAL was high (Tau² = 0.01; Chi² = 10.92, df = 3 (P = 0.01); I² = 73%). According to a sensitivity analysis, four studies were highly heterogeneous with each other, making them unsuitable for meta-analysis (Fig. 4b). The heterogeneity source was also thought to be: (1) too few studies; (2) tissue healing took time and early intervening probing may damage attachment gain. When the follow-up period was only 3 months, CAL were unstable which caused great heterogeneity.
Heterogeneity was also large in the following three groups: 1) deep pocket, at 3-months follow-up; 2) medium pocket, at 6-months follow-up; 3) deep pocket, at 6-months follow-up. After excluding Ioannou 2009[12], heterogeneity decreased from: 87%; 52%; and 71%, to 24%; 0%; and, 0%. This study was the only one in which 50% of the patients were smokers, while other papers were unclear about the ratio of smokers or had a small number of smokers, which might be the reason for heterogeneity. After exclusion, at deep pocket depth of a 6-months follow-up, after manual subgingival scaling, CAL reduction was more than ultrasonic subgingival scaling and were statistically different. (MD 0.58, 95%CI [0.27, 0.89], P=0.0002) (Fig. 4b, Fig. 4c).