Table 3 Reasons for excluding studies

[24,25,26,27,28,29,30,31,32]

No UD-to-SRP comparisons.

[35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54]

Different PPD categories present in the same study or experimental group.

[56]

UD-SRP comparisons present and different PPD categories in the same study or experimental group.

[57, 58]

An in vitro study.

[10, 59]

Uncertain sample size.

[60, 61]

Study results were diagrams with unclear data.

[5]

There were treatments after the initial treatments during a follow-up period.

[62]

Follow-up was 24 months which is a long enough period for tissue changes affected factors other than the interventions. The injured tissue may have completely recovered spontaneously.

[63]

At each reassessment, study data was measured using different categories of PPD making it impossible to determine PPD change.