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Tratamiento periodóntico adyuvante para la infección gástrica por Helicobacter pylori

Appendices

Appendix 1. CENTRAL search strategy

  1. h‐pylori.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  2. h‐pylori infection.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  3. Helicobacter pylori.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  4. Helicobacter pylori infection.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  5. PPI.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  6. proton pump inhibitor.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  7. or/1‐6

  8. (clarithromycin or 6‐o‐methylerythromycin or abbott‐56268 or biaxin or clarith or klaricid or "te 031").mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  9. (amoxicillin or actimoxi or almodan or amix or amopen or amoram or amoxicot or amoxidin or amoxil or amoxymed or amrit or biomox or brl 2333 or clamoxyl or dispermox or flemoxin solutab or galenamox or larotid or moxatag or moxilin or p‐hydroxyampicillin or penamox or polymox or respillin or rimoxallin or senox or sumox or trimox or utimox or wymox or zoxycil).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  10. (2 methyl 5 nitroimidazole 1 ethanol or anabact or bayer 5360 or clont or danizol or edg dentalgel or elyzol or flagyl or gineflavir or metric or metro iv or metrocream or metrodzhil or metrogel or metrolotion or metrolyl or metronizole or metrotop or metrovex or metrozol or metryl or nidazol or noritate or norzol or nydamax or obagi or protostat or rozex or satric or trichopol or tricom or trivazol or vagilen or vaginyl or vandazole or vitazol or zadstat or zidoval).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  11. (chlorhexidine or acclean or acriflex or avagard or betasept or calgon vesta or chloraprep or chlorhexamed or chlorhexigard or chlorohex 2000 or chlorostat or corsodyl or curasept ads 220 or cx antiseptic dusting or denticare or dyna‐hex or eludril or excel or gibitan or habistat or hexidine or hibiclens or hibident or hibiscrub or hibisol or hibitane or mk 412a or novalsan or oris or oro clense or peridex or periochip or periogard or periosep or perisol or phiso‐med or pre‐scrub ii or rotersept or sebidin a or spectrum‐4 or sterexidine or steripod pink or tubulicid or unisept or uriflex c).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  12. (omeprazole or h 16868 losec or nexium or omesec or prilosec or rapinex or ulcergard or zegerid).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  13. (ranitidine or ah 19065 or azanplus or biotidin or gr 122311x or pylorid or raciran or raniberl or ranisen or rantec or sostril or taladine or tritec or wal‐zan or zaedoc or zantac).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  14. (tinidazole or bioshik or fasigin or fasigyne or tindamax or tricolam).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  15. or/8‐14

  16. (periodontal and (disease$ or therap$)).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  17. (oral hygiene or buccal cavity or dental hygiene).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  18. periodontal scaling.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  19. periodontal root planing.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  20. subgingival bacterial plaque.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  21. (gingival and (pocket$ or plaque$)).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  22. or/16‐21

  23. 7 and 15 and 22

Appendix 2. MEDLINE search strategy

  1. randomized controlled trial.pt.

  2. controlled clinical trial.pt.

  3. randomized.ab.

  4. placebo.ab.

  5. drug therapy.fs.

  6. randomly.ab.

  7. trial.ab.

  8. groups.ab.

  9. or/1‐8

  10. exp animals/ not humans.sh.

  11. 9 not 10

  12. helicobacter pylori.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  13. helicobacter.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  14. pylori.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  15. H‐pylori.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  16. or/12‐15

  17. PPI.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  18. proton pump inhibitor.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  19. (amoxicillin or actimoxi or almodan or amix or amopen or amoram or amoxicot or amoxidin or amoxil or amoxymed or amrit or biomox or brl 2333 or clamoxyl or dispermox or flemoxin solutab or galenamox or larotid or moxatag or moxilin or p‐hydroxyampicillin or penamox or polymox or respillin or rimoxallin or senox or sumox or trimox or utimox or wymox or zoxycil).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  20. (clarithromycin or 6‐o‐methylerythromycin or abbott‐56268 or biaxin or clarith or klaricid or "te 031").mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  21. (2 methyl 5 nitroimidazole 1 ethanol or anabact or bayer 5360 or clont or danizol or edg dentalgel or elyzol or flagyl or gineflavir or metric or metro iv or metrocream or metrodzhil or metrogel or metrolotion or metrolyl or metronizole or metrotop or metrovex or metrozol or metryl or nidazol or noritate or norzol or nydamax or obagi or protostat or rozex or satric or trichopol or tricom or trivazol or vagilen or vaginyl or vandazole or vitazol or zadstat or zidoval).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  22. (chlorhexidine or acclean or acriflex or avagard or betasept or calgon vesta or chloraprep or chlorhexamed or chlorhexigard or chlorohex 2000 or chlorostat or corsodyl or curasept ads 220 or cx antiseptic dusting or denticare or dyna‐hex or eludril or excel or gibitan or habistat or hexidine or hibiclens or hibident or hibiscrub or hibisol or hibitane or mk 412a or novalsan or oris or oro clense or peridex or periochip or periogard or periosep or perisol or phiso‐med or pre‐scrub ii or rotersept or sebidin a or spectrum‐4 or sterexidine or steripod pink or tubulicid or unisept or uriflex c).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  23. (omeprazole or h 16868 losec or nexium or omesec or prilosec or rapinex or ulcergard or zegerid).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  24. (ranitidine or ah 19065 or azanplus or biotidin or gr 122311x or pylorid or raciran or raniberl or ranisen or rantec or sostril or taladine or tritec or wal‐zan or zaedoc or zantac).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  25. (tinidazole or bioshik or fasigin or fasigyne or tindamax or tricolam).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  26. or/17‐25

  27. periodontal therap$.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  28. oral hygiene.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  29. (buccal cavity or cavitas oris or mouth or oral cavity or dental hygiene).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  30. (periodontal and (disease$ or therap$)).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  31. periodontal scaling.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  32. periodontal root planing.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  33. ((subgingival or supragingival) adj5 bacterial plaque).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  34. (periodontal adj10 chemotherapeutic agent$).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  35. (irrigation adj10 periodontal pocket$).mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  36. gingival pocket.mp. [mp=title, original title, abstract, name of substance word, subject heading word, unique identifier]

  37. or/27‐36

  38. 11 and 16 and 26 and 37

Appendix 3. EMBASE search strategy

  1. Clinical trial.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  2. Randomized controlled trial.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  3. Randomization.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  4. Single‐blind method.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  5. Double‐blind method.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  6. Cross‐over studies.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  7. random allocation.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  8. placebo.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  9. randomi?ed controlled trial$.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  10. Rct.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  11. Random allocation.tw.

  12. randomly allocated.tw.

  13. allocated randomly.tw.

  14. (allocated adj2 random).tw.

  15. single blind$.tw.

  16. double blind$.tw.

  17. ((treble or triple) adj blind$).tw.

  18. placebo$.tw.

  19. prospective study.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  20. or/1‐19

  21. case study.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  22. case report.tw.

  23. abstract report/ or letter.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  24. or/21‐23

  25. 20 not 24

  26. H‐pylori.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  27. H‐pylori infection.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  28. Helicobacter pylori.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  29. helicobacter pylori infection.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  30. or/26‐29

  31. PPI.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  32. proton pump inhibitor$.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  33. (clarithromycin or 6‐o‐methylerythromycin or abbott‐56268 or biaxin or clarith or klaricid or "te 031").mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  34. (amoxicillin or actimoxi or almodan or amix or amopen or amoram or amoxicot or amoxidin or amoxil or amoxymed or amrit or biomox or brl 2333 or clamoxyl or dispermox or flemoxin solutab or galenamox or larotid or moxatag or moxilin or p‐hydroxyampicillin or penamox or polymox or respillin or rimoxallin or senox or sumox or trimox or utimox or wymox or zoxycil).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  35. (chlorhexidine or acclean or acriflex or avagard or betasept or calgon vesta or chloraprep or chlorhexamed or chlorhexigard or chlorohex 2000 or chlorostat or corsodyl or curasept ads 220 or cx antiseptic dusting or denticare or dyna‐hex or eludril or excel or gibitan or habistat or hexidine or hibiclens or hibident or hibiscrub or hibisol or hibitane or mk 412a or novalsan or oris or oro clense or peridex or periochip or periogard or periosep or perisol or phiso‐med or pre‐scrub ii or rotersept or sebidin a or spectrum‐4 or sterexidine or steripod pink or tubulicid or unisept or uriflex c).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  36. (omeprazole or h 16868 losec or nexium or omesec or prilosec or rapinex or ulcergard or zegerid).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  37. (ranitidine or ah 19065 or azanplus or biotidin or gr 122311x or pylorid or raciran or raniberl or ranisen or rantec or sostril or taladine or tritec or wal‐zan or zaedoc or zantac).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  38. (tinidazole or bioshik or fasigin or fasigyne or tindamax or tricolam).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  39. or/31‐38

  40. (periodontal and (therap$ or disease$)).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  41. (oral hygiene or buccal cavity or dental hygiene).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  42. periodontal scaling.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  43. oral cavity.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  44. dental plaque$.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  45. gingival pocket$.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  46. periodontal root planing.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  47. periodontitis.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  48. preventive dentistry.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  49. mouth hygiene.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  50. oral hygiene.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  51. subgingival bacterial plaque.mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  52. (tooth adj4 (calculus or plaque)).mp. [mp=title, abstract, subject headings, heading word, drug trade name, original title, device manufacturer, drug manufacturer]

  53. or/40‐52

  54. 25 and 30 and 39 and 53

Search flow diagram
Figures and Tables -
Figure 1

Search flow diagram

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.
Figures and Tables -
Figure 2

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.
Figures and Tables -
Figure 3

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Comparison 1 Eradication therapy combined with periodontal therapy versus eradication therapy alone, Outcome 1 Eradication rate of gastricH.pylori.
Figures and Tables -
Analysis 1.1

Comparison 1 Eradication therapy combined with periodontal therapy versus eradication therapy alone, Outcome 1 Eradication rate of gastricH.pylori.

Comparison 1 Eradication therapy combined with periodontal therapy versus eradication therapy alone, Outcome 2 Non‐recurrence rate of gastric H.pylori.
Figures and Tables -
Analysis 1.2

Comparison 1 Eradication therapy combined with periodontal therapy versus eradication therapy alone, Outcome 2 Non‐recurrence rate of gastric H.pylori.

Comparison 2 Subgroup analysis: Stratified by different oral H.pylori status, Outcome 1 Eradication rate of gastricH.pylori.
Figures and Tables -
Analysis 2.1

Comparison 2 Subgroup analysis: Stratified by different oral H.pylori status, Outcome 1 Eradication rate of gastricH.pylori.

Comparison 3 Subgroup analysis: Stratified by different durations of periodontal therapy, Outcome 1 Eradication rate of gastricH.pylori.
Figures and Tables -
Analysis 3.1

Comparison 3 Subgroup analysis: Stratified by different durations of periodontal therapy, Outcome 1 Eradication rate of gastricH.pylori.

Comparison 3 Subgroup analysis: Stratified by different durations of periodontal therapy, Outcome 2 Non‐recurrence rate of gastricH.pylori.
Figures and Tables -
Analysis 3.2

Comparison 3 Subgroup analysis: Stratified by different durations of periodontal therapy, Outcome 2 Non‐recurrence rate of gastricH.pylori.

Comparison 4 Subgroup analysis: After removing low‐quality studies, Outcome 1 Eradication rate of gastric H.pylori.
Figures and Tables -
Analysis 4.1

Comparison 4 Subgroup analysis: After removing low‐quality studies, Outcome 1 Eradication rate of gastric H.pylori.

Summary of findings for the main comparison. Eradication therapy combined with periodontal therapy versus eradication therapy alone for gastric Helicobacter pylori infection

Eradication therapy combined with periodontal therapy versus eradication therapy alone for gastric Helicobacter pylori infection

Patient or population: patients with gastric Helicobacter pylori infection
Settings: outpatient clinic
Intervention: eradication therapy combined with periodontal therapy versus eradication therapy alone

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of participants
(studies)

Quality of the evidence
(GRADE)

Assumed risk

Corresponding risk

Eradication therapy alone

Eradication therapy combined with periodontal therapy

Eradication rate of gastric H. pylori

60 per 100

76 per 100
(69 to 82)

OR 2.15
(1.47 to 3.14)

543
(6 studies)

⊕⊕⊕⊝
moderatea

Non‐recurrence rate of gastric H. pylori

29 per 100

60 per 100
(47 to 72)

OR 3.60
(2.11 to 6.15)

299
(3 studies)

⊕⊕⊝⊝
lowb,c,d

*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; OR: Odds ratio.

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

aDowngraded one level due to risk of bias (only Zaric 2009 described methods of randomization).
bDowngraded one level due to risk of bias (all patients in Jia 2009a were successfully treated for gastric H. pylori after triple eradication therapy).
cAlthough OR value was 3.60, we decided not to upgrade the quality of evidence because all patients in Jia 2009a were successfully treated for gastric H. pylori after triple eradication therapy.
dDowngraded one level due to imprecision (less than 400 total participants).

Figures and Tables -
Summary of findings for the main comparison. Eradication therapy combined with periodontal therapy versus eradication therapy alone for gastric Helicobacter pylori infection
Comparison 1. Eradication therapy combined with periodontal therapy versus eradication therapy alone

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Eradication rate of gastricH.pylori Show forest plot

6

543

Odds Ratio (M‐H, Fixed, 95% CI)

2.15 [1.47, 3.14]

2 Non‐recurrence rate of gastric H.pylori Show forest plot

3

299

Odds Ratio (M‐H, Fixed, 95% CI)

3.60 [2.11, 6.15]

Figures and Tables -
Comparison 1. Eradication therapy combined with periodontal therapy versus eradication therapy alone
Comparison 2. Subgroup analysis: Stratified by different oral H.pylori status

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Eradication rate of gastricH.pylori Show forest plot

6

543

Odds Ratio (M‐H, Fixed, 95% CI)

2.15 [1.47, 3.14]

1.1 Patients with defined oral H.pylori

3

327

Odds Ratio (M‐H, Fixed, 95% CI)

2.42 [1.52, 3.87]

1.2 Patients who were not tested for oral H.pylori

3

216

Odds Ratio (M‐H, Fixed, 95% CI)

1.70 [0.88, 3.26]

Figures and Tables -
Comparison 2. Subgroup analysis: Stratified by different oral H.pylori status
Comparison 3. Subgroup analysis: Stratified by different durations of periodontal therapy

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Eradication rate of gastricH.pylori Show forest plot

6

543

Odds Ratio (M‐H, Fixed, 95% CI)

2.15 [1.47, 3.14]

1.1 Periodontal therapy during eradication therapy

2

108

Odds Ratio (M‐H, Fixed, 95% CI)

2.72 [1.20, 6.14]

1.2 Periodontal therapy continued until testing the result of eradication therapy

4

435

Odds Ratio (M‐H, Fixed, 95% CI)

2.02 [1.31, 3.10]

1.3 Periodontal therapy continued for longer

0

0

Odds Ratio (M‐H, Fixed, 95% CI)

0.0 [0.0, 0.0]

2 Non‐recurrence rate of gastricH.pylori Show forest plot

3

299

Odds Ratio (M‐H, Fixed, 95% CI)

3.60 [2.11, 6.15]

2.1 Periodontal therapy during eradication therapy

0

0

Odds Ratio (M‐H, Fixed, 95% CI)

0.0 [0.0, 0.0]

2.2 Periodontal therapy continued until testing the result of eradication therapy

2

151

Odds Ratio (M‐H, Fixed, 95% CI)

3.13 [1.60, 6.10]

2.3 Periodontal therapy continued for longer

1

148

Odds Ratio (M‐H, Fixed, 95% CI)

4.49 [1.83, 11.04]

Figures and Tables -
Comparison 3. Subgroup analysis: Stratified by different durations of periodontal therapy
Comparison 4. Subgroup analysis: After removing low‐quality studies

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1 Eradication rate of gastric H.pylori Show forest plot

2

175

Odds Ratio (M‐H, Fixed, 95% CI)

3.18 [1.60, 6.33]

Figures and Tables -
Comparison 4. Subgroup analysis: After removing low‐quality studies