Submitted Successfully!
To reward your contribution, here is a gift for you: A free trial for our video production service.
Thank you for your contribution! You can also upload a video entry or images related to this topic.
Version Summary Created by Modification Content Size Created at Operation
1
Andrea Scribante
 -- 1451 2023-05-27 12:28:09 |
2 format
Jason Zhu
 Meta information modification 1451 2023-05-29 03:36:37 |

Video Upload Options

Do you have a full video?
Send video materials Upload full video

Confirm

Are you sure to Delete?
Yes No
Cite
If you have any further questions, please contact Encyclopedia Editorial Office.
Butera, A.; Maiorani, C.; Morandini, A.; Trombini, J.; Simonini, M.; Ogliari, C.; Scribante, A. Periodontitis in Pregnant Women. Encyclopedia. Available online: https://encyclopedia.pub/entry/44914 (accessed on 19 April 2024).
Butera A, Maiorani C, Morandini A, Trombini J, Simonini M, Ogliari C, et al. Periodontitis in Pregnant Women. Encyclopedia. Available at: https://encyclopedia.pub/entry/44914. Accessed April 19, 2024.
Butera, Andrea, Carolina Maiorani, Annalaura Morandini, Julia Trombini, Manuela Simonini, Chiara Ogliari, Andrea Scribante. "Periodontitis in Pregnant Women" Encyclopedia, https://encyclopedia.pub/entry/44914 (accessed April 19, 2024).
Butera, A., Maiorani, C., Morandini, A., Trombini, J., Simonini, M., Ogliari, C., & Scribante, A. (2023, May 27). Periodontitis in Pregnant Women. In Encyclopedia. https://encyclopedia.pub/entry/44914
Butera, Andrea, et al. "Periodontitis in Pregnant Women." Encyclopedia. Web. 27 May, 2023.
Periodontitis in Pregnant Women
Edit
This entry is adapted from the peer-reviewed paper 10.3390/healthcare11101372

Periodontitis develops in 11% of pregnant women, and it is independently linked to severe complications during pregnancy such as preterm birth, low birth weight, and gestational diabetes. Periodontal disease appears to be associated with adverse events in pregnancy due to the transport of biofilm bacteria into the bloodstream and into placental tissue; what would cause adverse events is the body’s immune response to infection.

periodontitis pregnancy oral health adverse pregnancy outcomes

1. Introduction

Periodontal disease is a chronic and irreversible pathology of the supporting tissues of the tooth that affects between 20% and 50% of the world population; the distribution in adults differs significantly in low (28.7%), lower-middle (10%), upper-middle (42.5%), and high-income countries (43.7%) [1][2].
Periodontal disease is one of the risk factors for other systemic diseases, such as pneumonia, diabetes mellitus, arteriosclerosis, and coronary heart disease [3]. Numerous studies show that periodontitis sufferers have higher circulating neutrophil granulocyte values and higher systemic inflammatory parameters (such as reactive protein C) compared to healthy people. In particular, the latter parameter is an excellent predictor for the development of ischemic diseases, atherosclerosis, and the imperfect metabolic control of diabetes [4][5]. In addition, it seems to be one of the risk factors for complications during pregnancy [6].
About 14.2 to 54.8% of pregnant women suffer from periodontal disease, and 11% develop periodontitis, which can cause the destruction of periodontal tissue and the distribution of bacteria and other inflammatory mediators [7].
Periodontitis is independently linked to severe complications during pregnancy, such as preterm birth, low birth weight, and gestational diabetes. [7][8]: the reason could be linked to the translocation of pathogenic bacteria to the fetus-placenta unit or the effect of inflammatory mediators such as interleukin-1 (IL-1), IL-6, IL-8, tumor necrosis factor alpha (TNF alpha), or prostaglandin E2 (PGE2) on the fetus-placenta unit [9][10].
Bacteremia is the transient or continuous presence of viable bacteria in the bloodstream. In people with periodontal disease, subgingival microflora is contracted with the damaged inner epithelium of periodontal pockets, which allows bacteria to enter the bloodstream [11]. This would seem to be the mechanism for the association between periodontal disease and adverse events during pregnancy [12].
Two experimental hypotheses support the correlation between periodontitis and pregnancy-related negative events. The first is based on the possibility that women with periodontitis are subject to frequent bacteremia. Bacteria activate a cascade of inflammatory processes at the level of the placenta and the fetus, with the risk of pre-term delivery and/or birth of underweight children [13]. The second hypothesis is based on the fact that periodontitis can cause a generalized increase in cytokines, substances with pro-inflammatory activity that cause alterations to the placenta and the fetus [14]. The periodontal bacteria (in particular Porphyromonas Gingivalis) can in fact enter the bloodstream, reach the placenta, and generate toxins inside the amniotic fluid that result in inflammation, potentially causing premature birth [15]. In addition to premature birth, other related adverse events include reduced body weight gain of the unborn child and the development of premature uterine contractions, with the risk of pre-term delivery and/or the birth of underweight children [16].
The onset of periodontal disease appears to be linked to a change in the composition of sub-bacterial gingival flora with an increase in the relative amount of pathogenic periodontal anaerobic bacteria associated with increased circulating levels of estrogen and progesterone and these would be a factor promoting the growth of pathogenic periodontal anaerobes; alteration of the local immune response with increased susceptibility to gum inflammation and depression of the chemotactic and phagocytic response of neutrophil granulocytes and other cellular-immune functions mediated, which contributes to the stimulation of the production of prostaglandins induced by varicose veins; to the pro-inflammatory effects on the gums mainly on vascular proliferation, on the production of collagen, on epithelial keratinization and the fluid content of the connective tissue [17][18][19].

2. Periodontitis

Several studies have shown the onset of periodontal problems during the second and third trimesters of pregnancy due to the change and increase in sex hormones and blood flow.
High levels of estrogen can cause gingival hypersensitivity to local factors, including bacterial plaque. This can lead to an increase in gingival volume, often associated with bleeding, or even the onset of periodontal disease, which usually regresses at the end of pregnancy; this is due to the growth of anaerobic bacteria, associated with increased circulating levels of estrogen but also progesterone [20][21].
Moreover, during gestation, the alteration of the vascular permeability of the gums can facilitate the transport of biofilm bacteria into the bloodstream until they reach the placental tissue [20].
In this tissue, the slow venous circulation and the invasive ability of microorganisms promote possible penetration into the fetus and into the amniotic fluid. Here, an immune response is triggered that could lead to the release of pro-inflammatory cytokines. If the body is able to fight the infection, there will be no consequence; otherwise, membrane rupture and premature birth may occur. These inflammatory compounds can negatively regulate the expression of genes essential for the growth of the fetus, causing a low birth weight, and generating structural damage to the placental circulation that increases the blood pressure of the mother [13][14][15][16].
Periodontal disease in pregnant women would appear to develop unexpected and adverse results, such as preterm birth [22][23][24][25][26][27][28][29], low birth weight [22][25][26][28][29][30][31][32], and pre-eclampsia [33]. The objective of the review was to research and highlight possible adverse events in pregnancy in women with periodontal disease. Preterm birth and low birth weight appear to be the most common events, at least according to this analysis. Preterm birth was found in 50% of the studies analysed, a result similar to that obtained by Manrique-Corredor et al. in a systematic and meta-analytical review, the authors evaluated 31 studies, and 60% of them saw an association between periodontal disease and preterm birth; Chambrone et al. also showed a positive association with preterm birth and low birth weight in 81.8% of the studies involved in the review [34][35].
The analyzed studies support these results: 50% of the studies showed an association between periodontal disease and preterm birth, and 50% had an association with low birth weight.
Periodontal diseases are associated with an increased risk of premature and/or underweight births [36]. Today, it is known that some acute inflammatory processes in the mother, even if localized far from the genitourinary tract, can play a secondary role in the appearance of pathological alterations in pregnancy [37]. Other studies, however, have not shown a clear association between periodontal disease and any adverse events [38][39][40][41].
However, although these events have often been associated, there is no clear evidence or correlation between periodontal disease and pregnancy. A predisposition can be affirmed due to the migration of bacteria present at the periodontal pockets through the bloodstream to the placenta and the fetus, which could cause muscular contractions of the uterus, cervical dilation, and premature rupture of the amniotic sac [42]. Numerous clinical studies would be needed to establish a positive association between periodontal disease and adverse events during pregnancy.
So, based on these considerations, pregnant women and women planning a pregnancy should be aware that there may be a link between their periodontal condition, general health, and possible complications of pregnancy. For this reason, periodontal treatment may be necessary, which in this case should be performed before conception; however, it could also be performed during pregnancy [43]. In addition, as negative pregnancy outcomes and periodontitis have in common some important risk factors (e.g., smoking), pregnant women should be aware of the importance of healthy habits and lifestyles [44]. It has been shown that periodontal treatment carried out in pregnancy is safe and helps to reduce the level of gingival inflammation, allowing oral health to be maintained in this delicate period. In addition, current scientific knowledge suggests that periodontal therapy before conception may reduce the risk of the related adverse effects mentioned above [8][43].
Unfortunately, very often treatments are carried out late; the ideal would be to start before pregnancy to obtain a positive outcome on the clinical result of gestation. In fact, non-surgical periodontal treatment in pregnant women would seem not to achieve an improvement of the unfavorable, probably also because the available studies are very heterogeneous. The result is mixed opinions [45][46][47][48][49][50].
However, action should be taken against dysbiosis caused by periodontal disease, perhaps by supplementing the use of probiotics in pregnant women, which seem to have positive effects on gum bleeding indices, together with the correct oral hygiene methods for the removal of bacterial biofilm [20][51][52].
The studies involved present some limitations. Although most of them have validated the association between periodontal disease and some adverse events in pregnancy, this statement cannot be generalized. The results of the individual studies are influenced by some variables such as ethnicity, socio-economic status, age, the period of pregnancy, and systemic pathologies related to the mother. It would be useful to standardize the sample taken from the studies, trying to eliminate any variable that could influence the results.

References

  1. Nazir, M.; Al-Ansari, A.; Al-Khalifa, K.; Alhareky, M.; Gaffar, B.; Almas, K. Global Prevalence of Periodontal Disease and Lack of Its Surveillance. Sci. World J. 2020, 2020, 2146160.
  2. World Health Organization. Oral Health; World Health Organization: Geneva, Switzerland, 2018.
  3. Ameet, M.M.; Avneesh, H.T.; Babita, R.P.; Pramod, P.M. The relationship between periodontitis and systemic diseases—Hype or hope? J. Clin. Diagn. Res. 2013, 7, 758–762.
  4. Chaudhry, A.; Kassim, N.K.; Zainuddin, S.L.A.; Taib, H.; Ibrahim, H.A.; Ahmad, B.; Hanafi, M.H.; Adnan, A.S. Potential Effects of Non-Surgical Periodontal Therapy on Periodontal Parameters, Inflammatory Markers, and Kidney Function Indicators in Chronic Kidney Disease Patients with Chronic Periodontitis. Biomedicines 2022, 10, 2752.
  5. Jepsen, S.; Caton, J.G.; Albandar, J.M.; Bissada, N.F.; Bouchard, P.; Cortellini, P.; Demirel, K.; de Sanctis, M.; Ercoli, C.; Fan, J.; et al. Periodontal manifestations of systemic diseases and developmental and acquired conditions: Consensus report of workgroup 3 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions. J. Clin. Periodontol. 2018, 45, S219–S229.
  6. Benedetto, C.; Marozio, L.; Tavella, A.M.; Maulà, V.; Carmignani, D.; Curti, A. Response to activated protein C decreases throughout pregnancy. Acta Obstet. Gynecol. Scand. 2002, 81, 1028–1032.
  7. Le, Q.A.; Akhter, R.; Coulton, K.M.; Vo, N.T.N.; Duong, L.T.Y.; Nong, H.V.; Yaacoub, A.; Condous, G.; Eberhard, J.; Nanan, R. Periodontitis and Preeclampsia in Pregnancy: A Systematic Review and Meta-Analysis. Matern. Child Health J. 2022, 26, 2419–2443.
  8. Nannan, M.; Xiaoping, L.; Ying, J. Periodontal disease in pregnancy and adverse pregnancy outcomes: Progress in related mechanisms and management strategies. Front. Med. 2022, 9, 963956.
  9. Komine-Aizawa, S.; Aizawa, S.; Hayakawa, S. Periodontal diseases and adverse pregnancy outcomes. J. Obstet. Gynaecol. Res. 2019, 45, 5–12.
  10. Vesce, F.; Battisti, C.; Crudo, M. The Inflammatory Cytokine Imbalance for Miscarriage, Pregnancy Loss and COVID-19 Pneumonia. Front. Immunol. 2022, 13, 861245.
  11. Waghmare, A.S.; Vhanmane, P.B.; Savitha, B.; Chawla, R.L.; Bagde, H.S. Bacteremia following scaling and root planing: A clinico-microbiological study. J. Indian Soc. Periodontol. 2013, 17, 725–730.
  12. Starzyńska, A.; Wychowański, P.; Nowak, M.; Sobocki, B.K.; Jereczek-Fossa, B.A.; Słupecka-Ziemilska, M. Association between Maternal Periodontitis and Development of Systematic Diseases in Offspring. Int. J. Mol. Sci. 2022, 23, 2473.
  13. Minervini, G.; Basili, M.; Franco, R.; Bollero, P.; Mancini, M.; Gozzo, L.; Romano, G.L.; Marrapodi, M.M.; Gorassini, F.; D’Amico, C.; et al. Periodontal Disease and Pregnancy: Correlation with Underweight Birth. Eur. J. Dent. 2022.
  14. Loh, K.; Sivalingam, N. Urinary tract infections in pregnancy. Malays. Fam. Physician 2007, 2, 54–57.
  15. Rapone, B.; Ferrara, E.; Montemurro, N.; Converti, I.; Loverro, M.; Loverro, M.T.; Gnoni, A.; Scacco, S.; Siculella, L.; Corsalini, M.; et al. Oral Microbiome and Preterm Birth: Correlation or Coincidence? A Narrative Review. Open Access Maced. J. Med. Sci. 2020, 8, 123–132.
  16. Ren, H.; Du, M. Role of Maternal Periodontitis in Preterm Birth. Front. Immunol. 2017, 8, 139.
  17. Katz, J.; Chegini, N.; Shiverick, K.T.; Lamont, R.J. Localization of P. gingivalis in preterm delivery placenta. J. Dent. Res. 2009, 88, 575–578.
  18. Gallagher-Cobos, G.; Almerich-Torres, T.; Montiel-Company, J.M.; Iranzo-Cortés, J.E.; Bellot-Arcís, C.; Ortolá-Siscar, J.C.; Almerich-Silla, J.M. Relationship between Periodontal Condition of the Pregnant Woman with Preterm Birth and Low Birth Weight. J. Clin. Med. 2022, 11, 6857.
  19. Lin, W.; Jiang, W.; Hu, X.; Gao, L.; Ai, D.; Pan, H.; Niu, C.; Yuan, K.; Zhou, X.; Xu, C.; et al. Ecological Shifts of Supragingival Microbiota in Association with Pregnancy. Front. Cell. Infect. Microbiol. 2018, 8, 24.
  20. Mobeen, N.; Jehan, I.; Banday, N.; Moore, J.; McClure, E.M.; Pasha, O.; Wright, L.L.; Goldenberg, R.L. Periodontal disease and adverse birth outcomes: A study from Pakistan. Am. J. Obstet. Gynecol. 2008, 198, 514.e1–514.e8.
  21. López, R. Periodontal disease and adverse pregnancy outcomes. Evid. Based Dent. 2008, 9, 48.
  22. Yenen, Z.; Ataçağ, T. Oral care in pregnancy. J. Turk. Ger. Gynecol. Assoc. 2019, 20, 264–268.
  23. Saddki, N.; Bachok, N.; Hussain, N.H.; Zainudin, S.L.; Sosroseno, W. The association between maternal periodontitis and low birth weight infants among Malay women. Community Dent. Oral Epidemiol. 2008, 36, 296–304.
  24. Kumar, A.; Basra, M.; Begum, N.; Rani, V.; Prasad, S.; Lamba, A.K.; Verma, M.; Agarwal, S.; Sharma, S. Association of maternal periodontal health with adverse pregnancy outcome. J. Obstet. Gynaecol. Res. 2013, 39, 40–45.
  25. Marin, C.; Segura-Egea, J.J.; Martínez-Sahuquillo, A.; Bullón, P. Correlation between infant birth weight and mother’s periodontal status. J. Clin. Periodontol. 2005, 32, 299–304.
  26. Agueda, A.; Ramón, J.M.; Manau, C.; Guerrero, A.; Echeverría, J.J. Periodontal disease as a risk factor for adverse pregnancy outcomes: A prospective cohort study. J. Clin. Periodontol. 2008, 35, 16–22.
  27. Moore, S.; Ide, M.; Coward, P.Y.; Randhawa, M.; Borkowska, E.; Baylis, R.; Wilson, R.F. A prospective study to investigate the relationship between periodontal disease and adverse pregnancy outcome. Br. Dent. J. 2004, 197, 251–258.
  28. Ercan, E.; Eratalay, K.; Deren, O.; Gur, D.; Ozyuncu, O.; Altun, B.; Kanli, C.; Ozdemir, P.; Akincibay, H. Evaluation of periodontal pathogens in amniotic fluid and the role of periodontal disease in pre-term birth and low birth weight. Acta Odontol. Scand. 2013, 71, 553–559.
  29. Moreu, G.; Téllez, L.; González-Jaranay, M. Relationship between maternal periodontal disease and low-birth-weight pre-term infants. J. Clin. Periodontol. 2005, 32, 622–627.
  30. Sant’Ana, A.C.; Campos, M.R.; Passanezi, S.C.; Rezende, M.L.; Greghi, S.L.; Passanezi, E. Periodontal treatment during pregnancy decreases the rate of adverse pregnancy outcome: A controlled clinical trial. J. Appl. Oral Sci. 2011, 19, 130–136.
  31. Santa Cruz, I.; Herrera, D.; Martin, C.; Herrero, A.; Sanz, M. Association between periodontal status and pre-term and/or low-birth weight in Spain: Clinical and microbiological parameters. J. Periodontal. Res. 2013, 48, 443–451.
  32. Offenbacher, S.; Boggess, K.A.; Murtha, A.P.; Jared, H.L.; Lieff, S.; McKaig, R.G.; Mauriello, S.M.; Moss, K.L.; Beck, J.D. Progressive periodontal disease and risk of very preterm delivery. Obstet. Gynecol. 2006, 107, 29–36.
  33. Franzago, M.; Fraticelli, F.; Stuppia, L.; Vitacolonna, E. Nutrigenetics, epigenetics and gestational diabetes: Consequences in mother and child. Epigenetics 2019, 14, 215–235.
  34. Shub, A.; Swain, J.R.; Newnham, J.P. Periodontal disease and adverse pregnancy outcomes. J. Matern. Fetal Neonatal Med. 2006, 19, 521–528.
  35. Sacco, G.; Carmagnola, D.; Abati, S.; Luglio, P.F.; Ottolenghi, L.; Villa, A.; Maida, C.; Campus, G. Periodontal disease and preterm birth relationship: A review of the literature. Minerva Stomatol. 2008, 57, 233–250.
  36. Manrique-Corredor, E.J.; Orozco-Beltran, D.; Lopez-Pineda, A.; Quesada, J.A.; Gil-Guillen, V.F.; Carratala-Munuera, C. Maternal periodontitis and preterm birth: Systematic review and meta-analysis. Community Dent. Oral Epidemiol. 2019, 47, 243–251.
  37. Chambrone, L.; Guglielmetti, M.R.; Pannuti, C.M.; Chambrone, L.A. Evidence grade associating periodontitis to preterm birth and/or low birth weight: I. A systematic review of prospective cohort studies. J. Clin. Periodontol. 2011, 38, 795–808.
  38. Bianchi, S.; Macchiarelli, G.; Micara, G.; Aragona, C.; Maione, M.; Nottola, S.A. Ultrastructural and morphometric evaluation of aged cumulus-oocyte-complexes. Ital. J. Anat. Embriol. 2013, 118, 28.
  39. Boggess, K.A.; Beck, J.D.; Murtha, A.P.; Moss, K.; Offenbacher, S. Maternal periodontal disease in early pregnancy and risk for a small-for-gestational-age infant. Am. J. Obstet. Gynecol. 2006, 194, 1316–1322.
  40. Srinivas, S.K.; Sammel, M.D.; Stamilio, D.M.; Clothier, B.; Jeffcoat, M.K.; Parry, S.; Macones, G.A.; Elovitz, M.A.; Metlay, J. Periodontal disease and adverse pregnancy outcomes: Is there an association? Am. J. Obstet. Gynecol. 2009, 200, e1–e8.
  41. Rakoto-Alson, S.; Tenenbaum, H.; Davideau, J.L. Periodontal diseases, preterm births, and low birth weight: Findings from a homogeneous cohort of women in Madagascar. J. Periodontol. 2010, 81, 205–213.
  42. Iheozor-Ejiofor, Z.; Middleton, P.; Esposito, M.; Glenny, A.M. Treating periodontal disease for preventing adverse birth outcomes in pregnant women. Cochrane Database Syst. Rev. 2017, 6, CD005297.
  43. Wimmer, G.; Pihlstrom, B.L. A critical assessment of adverse pregnancy outcome and periodontal disease. J. Clin. Periodontol. 2008, 35, 380–397.
  44. Parihar, A.S.; Katoch, V.; Rajguru, S.A.; Rajpoot, N.; Singh, P.; Wakhle, S. Periodontal Disease: A Possible Risk-Factor for Adverse Pregnancy Outcome. J. Int. Oral Health 2015, 7, 137–142.
  45. Vogt, M.; Sallum, A.W.; Cecatti, J.G.; Morais, S.S. Periodontal disease and some adverse perinatal outcomes in a cohort of low risk pregnant women. Reprod. Health 2010, 7, 29.
  46. Da Silva, H.E.C.; Stefani, C.M.; de Santos Melo, N.; de Almeida de Lima, A.; Rösing, C.K.; Porporatti, A.L.; Canto, G.L. Effect of intra-pregnancy nonsurgical periodontal therapy on inflammatory biomarkers and adverse pregnancy outcomes: A systematic review with meta-analysis. Syst. Rev. 2017, 6, 197.
  47. Caneiro-Queija, L.; López-Carral, J.; Martin-Lancharro, P.; Limeres-Posse, J.; Diz-Dios, P.; Blanco-Carrion, J. Non-Surgical Treatment of Periodontal Disease in a Pregnant Caucasian Women Population: Adverse Pregnancy Outcomes of a Randomized Clinical Trial. Int. J. Environ. Res. Public Health 2019, 16, 3638.
  48. Tarannum, F.; Faizuddin, M. Effect of periodontal therapy on pregnancy outcome in women affected by periodontitis. J. Periodontol. 2007, 78, 2095–2103.
  49. Macek, M.D. Non-surgical periodontal therapy may reduce adverse pregnancy outcomes. J. Evid. Based Dent. Pract. 2008, 8, 236–237.
  50. Michalowicz, B.S.; Hodges, J.S.; DiAngelis, A.J.; Lupo, V.R.; Novak, M.J.; Ferguson, J.E.; Buchanan, W.; Bofill, J.; Papapanou, P.N.; Mitchell, D.A.; et al. Treatment of periodontal disease and the risk of preterm birth. N. Engl. J. Med. 2006, 355, 1885–1894.
  51. Butera, A.; Gallo, S.; Pascadopoli, M.; Maiorani, C.; Milone, A.; Alovisi, M.; Scribante, A. Paraprobiotics in Non-Surgical Periodontal Therapy: Clinical and Microbiological Aspects in a 6-Month Follow-Up Domiciliary Protocol for Oral Hygiene. Microorganisms 2022, 10, 337.
  52. Butera, A.; Gallo, S.; Maiorani, C.; Molino, D.; Chiesa, A.; Preda, C.; Esposito, F.; Scribante, A. Probiotic Alternative to Chlorhexidine in Periodontal Therapy: Evaluation of Clinical and Microbiological Parameters. Microorganisms 2020, 9, 69.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.
Upload a video for this entry
Information
Subjects: Dentistry, Oral Surgery & Medicine
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Andrea Butera
,
Carolina Maiorani
,
Annalaura Morandini
,
Julia Trombini
,
Manuela Simonini
,
Chiara Ogliari
,
Andrea Scribante
View Times: 180
Revisions: 2 times (View History)
Update Date: 29 May 2023
Table of Contents
    1000/1000
    Hot Most Recent
    Feedback