Experimental gingivitis: reproducibility of plaque accumulation and gingival inflammation parameters in selected populations during a repeat trial

Localized microbially induced inflammation influences distant healthy tissues in the human oral cavity

Variation in human immune response to the same bacterial or viral pathogen is well established in the literature. Variation in immune response to microbial challenge has also been observed within the human oral cavity. Our recent study focused on characterizing observed variations in microbially induced gingival inflammation-resulting in three distinct clinical Inflammatory Responder Types (IRTs): High-IRT, Low-IRT, and Slow-IRT. Here, we applied a high-resolution temporal multiomic analysis during microbially induced inflammation in order to characterize the effects of localized oral inflammation on distant healthy tissues in young healthy adults. Our results highlight a nonlocalized subclinical effect with alterations in proinflammatory host mediators and an ecological shift toward dysbiosis within the subgingival microbiome in an IRT-dependent manner-despite maintained oral hygiene. Our results provide mechanistic insight into how healthy tissues within humans are influenced by distant localized inflammation and may ultimately become susceptible to disease.

Free sugars and gingival inflammation: A systematic review and meta-analysis

AIM

Consumption of free sugars has been associated with chronic non-communicable diseases. The aim of the study was to investigate the effect of free-sugar consumption on gingival inflammation using a systematic review and meta-analysis based on the PICO question 'What impact does the restriction of free sugars have on the inflammation of gingival tissue?'

MATERIALS AND METHODS

Literature review and analyses were based on the Cochrane Handbook for Systematic Reviews of Interventions. Controlled clinical studies reporting on free-sugar interventions and gingival inflammation were included. Risk of bias was performed with ROBINS-I and ROB-2, and effect sizes were estimated with robust variance meta-regressions.

RESULTS

Of the 1777 primarily identified studies, 1768 were excluded, and 9 studies with 209 participants with gingival inflammation measures were included. Six of these studies reported on the dental plaque scores of 113 participants. Restriction of free sugars, when compared with no such restriction, was associated with statistically significantly improved gingival health scores (standard mean difference [SMD] = -0.92; 95% confidence interval [CI]: -1.43 to -0.42, p < .004; I2 [heterogeneity] = 46.8) and a trend towards lower dental plaque scores (SMD = -0.61; 95% CI: -1.28 to 0.05, p < .07; I2  = 41.3). The observed improvement of gingival inflammation scores with restricted consumption of free sugar was robust against various statistical imputations. No meta-regression models were feasible because of the limited number of studies. The median publication year was 1982. Risk-of-bias analysis showed a moderate risk in all studies.

CONCLUSION

Restriction of free sugar was shown to be associated with reduced gingival inflammation. The systematic review was registered at PROSPERO (CRD 42020157914).

Human Umbilical Cord Mesenchymal Stem Cells: Current Literature and Role in Periodontal Regeneration

Periodontal disease can cause irreversible damage to tooth-supporting tissues such as the root cementum, periodontal ligament, and alveolar bone, eventually leading to tooth loss. While standard periodontal treatments are usually helpful in reducing disease progression, they cannot repair or replace lost periodontal tissue. Periodontal regeneration has been demonstrated to be beneficial in treating intraosseous and furcation defects to varied degrees. Cell-based treatment for periodontal regeneration will become more efficient and predictable as tissue engineering and progenitor cell biology advance, surpassing the limitations of present therapeutic techniques. Stem cells are undifferentiated cells with the ability to self-renew and differentiate into several cell types when stimulated. Mesenchymal stem cells (MSCs) have been tested for periodontal regeneration in vitro and in humans, with promising results. Human umbilical cord mesenchymal stem cells (UC-MSCs) possess a great regenerative and therapeutic potential. Their added benefits comprise ease of collection, endless source of stem cells, less immunorejection, and affordability. Further, their collection does not include the concerns associated with human embryonic stem cells. The purpose of this review is to address the most recent findings about periodontal regenerative mechanisms, different stem cells accessible for periodontal regeneration, and UC-MSCs and their involvement in periodontal regeneration.

Human variation in gingival inflammation

Oral commensal bacteria actively participate with gingival tissue to maintain healthy neutrophil surveillance and normal tissue and bone turnover processes. Disruption of this homeostatic host-bacteria relationship occurs during experimental gingivitis studies where it has been clearly established that increases in the bacterial burden increase gingival inflammation. Here, we show that experimental gingivitis resulted in three unique clinical inflammatory phenotypes (high, low, and slow) and reveal that interleukin-1β, a reported major gingivitis-associated inflammatory mediator, was not associated with clinical gingival inflammation in the slow response group. In addition, significantly higher levels of Streptococcus spp. were also unique to this group. The low clinical response group was characterized by low concentrations of host mediators, despite similar bacterial accumulation and compositional characteristics as the high clinical response group. Neutrophil and bone activation modulators were down-regulated in all response groups, revealing novel tissue and bone protective responses during gingival inflammation. These alterations in chemokine and microbial composition responses during experimental gingivitis reveal a previously uncharacterized variation in the human host response to a disruption in gingival homeostasis. Understanding this human variation in gingival inflammation may facilitate the identification of periodontitis-susceptible individuals. Overall, this study underscores the variability in host responses in the human population arising from variations in host immune profiles (low responders) and microbial community maturation (slow responders) that may impact clinical outcomes in terms of destructive inflammation.

Sex differences in the association between obesity and gingivitis among 12-year-old South Brazilian schoolchildren

OBJECTIVE

To assess the association between weight status and gingivitis in a representative sample of 12-year-old schoolchildren from South Brazil.

BACKGROUND

An association between obesity and gingivitis in children and adolescents has been observed; however, the present evidence has major limitations.

METHODS

A cross-sectional study was conducted in Porto Alegre, South Brazil, from September 2009 to December 2010 and included a representative sample of 1528 12-year-old schoolchildren attending public and private schools. Data collection included the application of a questionnaire, recording of anthropometric measures (weight and height), and clinical examination (gingival bleeding index, recorded in four sites per tooth). The outcome of the study was the prevalence of gingivitis, defined as the proportion of schoolchildren presenting ≥52% of bleeding sites (based on the median). Weight status was categorized according to body mass index into normal, overweight, or obese. The association between predictor variables and gingivitis prevalence was assessed using Poisson regression models. Unadjusted and adjusted prevalence ratios (PR) and their 95% confidence intervals (95% CI) were estimated.

RESULTS

Gingivitis prevalence was 48.7% (95% IC = 33.8-63.6) and, on average, schoolchildren presented 51.8% (95% IC = 46.2-57.5) of bleeding sites. Obese individuals had 13% higher prevalence for presenting gingivitis than did normal-weight ones (PR = 1.13, 95% CI = 1.09-1.18, P < .001). The stratified analysis showed that this association was sex-specific: Obese girls presented a greater chance of having gingivitis (adjusted PR = 1.21, 95% CI = 1.09-1.34, P < .001), but such association was not observed among boys (PR = 1.07, 95% CI = 0.95-1.20, P = .29).

CONCLUSION

This study showed sex differences in the association between obesity and gingivitis among 12-year-old South Brazilian schoolchildren.

Experimental gingivitis in patients with and without altered passive eruption

BACKGROUND

Individuals with altered passive eruption (APE) are assumed to be more susceptible to periodontal diseases. To date, this hypothesis has not been sufficiently supported by scientific evidence. The aim of this study, using an experimental gingivitis model, was to examine the development and resolution of gingival inflammation in patients with APE when compared to patients with normal gingival anatomy.

METHODS

A localized experimental gingivitis was induced in 9 patients with APE (test group) and 9 patients without APE (control group) in the maxillary right quadrant. After 21 days, patients were instructed to resume proper home oral hygiene procedures. At baseline (day 0) and at days 7, 14, 21, 28, 35, and 42, plaque index (PlI), gingival index (GI), and gingival crevicular fluid volume (GCF) were evaluated for teeth 6 (canine), 7 (lateral incisor) and 8 (central incisor) of test and control groups.

RESULTS

During the experimental gingivitis phase (days 0 to 21), the rate of change in gingival inflammation (GI) was dramatically different between the APE test group and the control group. On day 21, at the time of maximum plaque accumulation, the GI of the APE test group was a 109% greater than the GI of the test group (P ≤ 0.001) despite similar plaque levels (P = 0.436). During the resolution of inflammation phase (days 22 to 42), the APE test group continued to exhibit statistically higher GI scores than the control group (P = 0.029).

CONCLUSION

In the presence of similar amounts of plaque deposits and plaque accumulation rates, APE patients exhibited differences in the development and resolution of plaque-induced gingival inflammation when compared to controls.

Plaque-induced gingivitis: Case definition and diagnostic considerations

OBJECTIVE

Clinical gingival inflammation is a well-defined site-specific condition for which several measurement systems have been proposed and validated, and epidemiological studies consistently indicate its high prevalence globally. However, it is clear that defining and grading a gingival inflammatory condition at a site level (i.e. a "gingivitis site") is completely different from defining and grading a "gingivitis case" (GC) (i.e. a patient affected by gingivitis), and that a "gingivitis site" does not necessarily mean a "GC". The purpose of the present review is to summarize the evidence on clinical, biochemical, microbiologic, genetic markers as well as symptoms associated with plaque-induced gingivitis and to propose a set of criteria to define GC.

IMPORTANCE

A universally accepted case definition for gingivitis would provide the necessary information to enable oral health professionals to assess the effectiveness of their prevention strategies and treatment regimens; help set priorities for therapeutic actions/programs by health care providers; and undertake surveillance.

FINDINGS

Based on available methods to assess gingival inflammation, GC could be simply, objectively and accurately identified and graded using bleeding on probing score (BOP%) CONCLUSIONS: A patient with intact periodontium would be diagnosed as a GC according to a BOP score ≥ 10%, further classified as localized (BOP score ≥ 10% and ≤30%) or generalized (BOP score > 30%). The proposed classification may also apply to patients with a reduced periodontium, where a GC would characterize a patient with attachment loss and BOP score ≥ 10%, but without BOP in any site probing ≥4 mm in depth.

Regulation of PGLYRP1 and TREM-1 during Progression and Resolution of Gingival Inflammation

INTRODUCTION

The triggering receptor expressed on myeloid cells 1 (TREM-1) signaling pathway is stimulated by bacteria and, together with its putative ligand peptidoglycan recognition protein 1 (PGLYRP1), propagates proinflammatory responses.

OBJECTIVES

We aimed to evaluate the TREM-1/PGLYRP1/interleukin (IL)-1β regulation in response to biofilm accumulation and removal in an experimental human gingivitis model.

METHODS

The study (n = 42 participants, mean age: 23.8 ± 3.7 y) comprised a recruitment step (day -14) followed by experimentally induced biofilm formation (induction [I] phase, day 0 to +21) and a 2-wk resolution (R) phase (day +21 to +35). Plaque was recorded by the Modified Quigley and Hein Plaque Index (TQHPI), while records of gingival inflammation were based on the Modified Gingival Index (MGI). Unstimulated whole saliva supernatants (n = 210, 5 time points) were tested for TREM-1, PGLYRP1, and IL-1β by enzyme-linked immunosorbent assay.

RESULTS

During the I-phase, concentrations of all analytes showed a tendency for downregulation at day +7 compared to day 0. TREM-1 (P = 0.019) and PGLYRP1 (P = 0.007) increased significantly between day +7 and day +21. Although all analyte levels decreased during the R-phase, the difference was not significant except TREM-1 being at borderline significance (P = 0.058). Moreover, TREM-1, PGLYRP1, and IL-1β showed significant positive correlations (P < 0.0001) with each other. The study participants were grouped into "fast" and "slow" responders based on clinical gingival inflammation scores. At each time point, fast responders showed significantly higher concentrations of TREM-1 (P < 0.025), PGLYRP1 (P < 0.007), and IL-1β (P < 0.025) compared to slow responders. Mixed-effects multilevel regression analyses revealed that PGLYRP1 (P = 0.047) and IL-1β (P = 0.005) showed a significant positive association with the MGI scores.

CONCLUSION

The study demonstrated that TREM-1 and PGLYRP1 are regulated in response to biofilm accumulation and removal, and fast responders demonstrated higher levels of these analytes compared to slow responders.

KNOWLEDGE TRANSFER STATEMENT

The results of this study demonstrated the suitability of salivary TREM-1 and PGLYRP1 to reflect biofilm accumulation and removal and PGLYRP1 to monitor the progression and resolution of inflammation in gingivitis-susceptible individuals (fast responders). Combined with conventional risk factors, the molecular toolbox proposed here should be further validated in future studies to confirm whether it can be used for population-based monitoring and prevention of gingivitis.

The Influence of a Bifidobacterium animalis Probiotic on Gingival Health: A Randomized Controlled Clinical Trial

BACKGROUND

There is growing interest in the use of probiotics in periodontal therapy; however, until now, most research has focused on lactobacilli probiotics. The aim of this study is to evaluate the effect of 4-week use of yogurt supplemented with Bifidobacterium animalis subsp. lactis DN-173010 versus a placebo yogurt, followed by a 5-day non-brushing period.

METHODS

Individuals were included in this single-mask, randomized, controlled study if probing depth (PD) was ≤3 mm and attachment loss was ≤2 mm. After professional prophylaxis, they were randomized into two groups receiving yogurt containing either placebo or B. animalis for 28 days, followed by a 5-day non-brushing period. Outcome measures were plaque index (PI), gingival index (GI), bleeding on probing (BOP), PD, gingival crevicular fluid (GCF) volume, and total amount and concentration of interleukin (IL)-1β in GCF. These were measured at baseline, after 28 days of study product use, and subsequently after 5 days of plaque accumulation.

RESULTS

Fifty-one patients were analyzed. No intergroup differences could be detected before and after intake of study products. However, after plaque accumulation, significantly better results for all parameters were seen in the probiotic group compared with the control group (P <0.001): lower PI and GI, less BOP, less increase in GCF volume, and lower IL-1β total amount/concentration.

CONCLUSION

The use of a probiotic yogurt supplemented with B. animalis can have a positive effect on plaque accumulation and gingival inflammatory parameters after refraining from oral hygiene practices.

Periodontal diseases

Periodontal diseases comprise a wide range of inflammatory conditions that affect the supporting structures of the teeth (the gingiva, bone and periodontal ligament), which could lead to tooth loss and contribute to systemic inflammation. Chronic periodontitis predominantly affects adults, but aggressive periodontitis may occasionally occur in children. Periodontal disease initiation and propagation is through a dysbiosis of the commensal oral microbiota (dental plaque), which then interacts with the immune defences of the host, leading to inflammation and disease. This pathophysiological situation persists through bouts of activity and quiescence, until the affected tooth is extracted or the microbial biofilm is therapeutically removed and the inflammation subsides. The severity of the periodontal disease depends on environmental and host risk factors, both modifiable (for example, smoking) and non-modifiable (for example, genetic susceptibility). Prevention is achieved with daily self-performed oral hygiene and professional removal of the microbial biofilm on a quarterly or bi-annual basis. New treatment modalities that are actively explored include antimicrobial therapy, host modulation therapy, laser therapy and tissue engineering for tissue repair and regeneration.

Bleeding on probing around dental implants: a retrospective study of associated factors

AIM

To (i) identify factors associated with the probability of a peri-implant site to be positive to bleeding on probing (BoP+) and (ii) compare BoP+ probability around dental implants and contra-lateral teeth.

METHODS

In 112 patients, data related to 1725 peri-implant sites and 1020 contra-lateral dental sites were retrospectively obtained. To analyse the association between patient-, implant- and site-related factors and BoP+ probability, a logistic, three-level model was built with BoP as the binary outcome variable (+/-).

RESULTS

BoP+ probability for a peri-implant site with probing depth (PD) of 4 mm was 27%, and the odds ratio increased by 1.6 for each 1-mm increment in PD (p < 0.001). Also, BoP+ probability was higher in females compared to males (OR = 1.61; p = 0.048), and lower at posterior compared to anterior dental implants (OR = 0.55; p < 0.01). No significant difference in BoP+ probability was observed between peri-implant and contra-lateral dental sites when controlling for the difference in PD.

CONCLUSIONS

The probability of a peri-implant site to bleed upon probing is (i) associated with PD, implant position and gender, and (ii) similar to that observed at contra-lateral dental sites when controlling for the effect of PD.

Label-free quantitative proteomics reveals differentially regulated proteins in experimental gingivitis

We investigated the sequential protein expression in gingival crevicular fluid samples during the induction (I) and resolution (R) of experimental gingivitis. Periodontally and systemically healthy volunteers (n = 20) participated in a three-week experimental gingivitis protocol, followed by debridement and two weeks of regular plaque control. Gingival crevicular fluid (GCF) samples were collected at baseline, Day 7, 14, and 21 (induction; I-phase), and at Day 21, 25, 30, and 35 (resolution; R-phase). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) for label-free quantitative proteomics was applied. A total of 287 proteins were identified including 254 human, 14 bacterial, 12 fungal, and 7 yeast proteins. Ontology analysis revealed proteins primarily involved in cytoskeletal rearrangements, immune response, antimicrobial function, protein degradation, and DNA binding. There was considerable variation in the number of proteins identified, both among subjects and within subjects across time points. After pooling of samples between subjects at each time point, the levels of 59 proteins in the I-phase and 73 proteins in the R-phase were quantified longitudinally. Our data demonstrate that LC-MS/MS label-free quantitative proteomics is valuable in the assessment of the protein content of the GCF and can facilitate a better understanding of the molecular mechanisms involved in the induction and resolution of plaque-induced gingival inflammation in humans.

Gingival tissue transcriptomes in experimental gingivitis

AIMS

We investigated the sequential gene expression in the gingiva during the induction and resolution of experimental gingivitis.

MATERIAL AND METHODS

Twenty periodontally and systemically healthy non-smoking volunteers participated in a 3-week experimental gingivitis protocol, followed by debridement and 2-week regular plaque control. We recorded clinical indices and harvested gingival tissue samples from four interproximal palatal sites in half of the participants at baseline, Day 7, Day 14 and Day 21 (the "induction phase"), and at Day 21, Day 25, Day 30 and Day 35 in the other half (the "resolution phase"). RNA was extracted, amplified, reversed transcribed, amplified, labelled and hybridized using Affymetrix Human Genome U133Plus2.0 microarrays. Paired t-tests compared gene expression changes between consecutive time points. Gene ontology analyses summarized the expression patterns into biologically relevant categories.

RESULTS

The median gingival index was 0 at baseline, 2 at Day 21 and 1 at Day 35. Differential gene regulation peaked during the third week of induction and the first 4 days of resolution. Leucocyte transmigration, cell adhesion and antigen processing/presentation were the top differentially regulated pathways.

CONCLUSIONS

Transcriptomic studies enhance our understanding of the pathobiology of the reversible inflammatory gingival lesion and provide a detailed account of the dynamic tissue responses during the induction and resolution of experimental gingivitis.

Interleukin-1 beta levels in gingival crevicular fluid and serum under naturally occurring and experimentally induced gingivitis

AIMS

To evaluate the interleukin-1 beta (IL-1 beta) levels in gingival crevicular fluid (GCF) and serum in either naturally occurring (N-O) or experimentally induced (E-I) plaque-associated gingivitis.

MATERIAL AND METHODS

Thirty-seven periodontally healthy subjects were evaluated in real life conditions (N-O gingivitis) as well as after 21 days of experimental gingivitis trial (E-I gingivitis). During the experimental gingivitis trial, in one maxillary quadrant (test quadrant), gingival inflammation was induced by oral hygiene abstention, while in the contralateral (control) quadrant, oral hygiene was routinely continued. IL-1 beta concentrations in N-O and E-I gingivitis were investigated for IL-1B(+3954) and IL-1B(-511) gene polymorphisms.

RESULTS

(i) GCF IL-1 beta concentrations in E-I gingivitis were significantly higher compared with N-O gingivitis; (ii) an intra-individual correlation between GCF concentrations of IL-1 beta detected in N-O and E-I gingivitis was observed in control quadrants, but not in test quadrants; (iii) IL-1 beta concentration in GCF was associated with IL-1B(+3954) genotype only at test quadrants; (iv) IL-1 beta was detectable in serum only at low levels in a limited number of subjects, without difference between gingivitis conditions.

CONCLUSIONS

Aspects of the bacterial challenge to the gingival tissues, such as the amount of plaque deposits and plaque accumulation rate, appear to affect the IL-1 beta levels in GCF in subjects with a specific IL-1B genotype.

Gingival transcriptome patterns during induction and resolution of experimental gingivitis in humans

BACKGROUND

To our knowledge, changes in the patterns of whole-transcriptome gene expression that occur during the induction and resolution of experimental gingivitis in humans were not previously explored using bioinformatic tools.

METHODS

Gingival biopsy samples collected from 14 subjects during a 28-day stent-induced experimental gingivitis model, followed by treatment, and resolution at days 28 through 35 were analyzed using gene-expression arrays. Biopsy samples were collected at different sites within each subject at baseline (day 0), at the peak of gingivitis (day 28), and at resolution (day 35) and processed using whole-transcriptome gene-expression arrays. Gene-expression data were analyzed to identify biologic themes and pathways associated with changes in gene-expression profiles that occur during the induction and resolution of experimental gingivitis using bioinformatic tools.

RESULTS

During disease induction and resolution, the dominant expression pathway was the immune response, with 131 immune response genes significantly up- or downregulated during induction, during resolution, or during both at P <0.05. During induction, there was significant transient increase in the expression of inflammatory and oxidative stress mediators, including interleukin (IL)-1 alpha (IL1A), IL-1 beta (IL1B), IL8, RANTES, colony stimulating factor 3 (CSF3), and superoxide dismutase 2 (SOD2), and a decreased expression of IP10, interferon inducible T-cell alpha chemoattractant (ITAC), matrix metalloproteinase 10 (MMP10), and beta 4 defensin (DEFB4). These genes reversed expression patterns upon resolution in parallel with the reversal of gingival inflammation.

CONCLUSIONS

A relatively small subset (11.9%) of the immune response genes analyzed by array was transiently activated in response to biofilm overgrowth, suggesting a degree of specificity in the transcriptome-expression response. The fact that this same subset demonstrates a reversal in expression patterns during clinical resolution implicates these genes as being critical for maintaining tissue homeostasis at the biofilm-gingival interface. In addition to the immune response pathway as the dominant response theme, new candidate genes and pathways were identified as being selectively modulated in experimental gingivitis, including neural processes, epithelial defenses, angiogenesis, and wound healing.

Pro-inflammatory biomarkers during experimental gingivitis in patients with type 1 diabetes mellitus: a proof-of-concept study

AIM

To compare gingival crevicular fluid (GCF) biomarker levels and microbial distribution in plaque biofilm (SP) samples for subjects with type 1 diabetes (T1DM) versus healthy subjects without diabetes during experimental gingivitis (EG).

MATERIALS AND METHODS

A total of nine T1DM patients and nine healthy controls of age and gender similar to the T1DM patients were monitored for 35 days during EG. Hygiene practices were stopped for 3 weeks, and GCF, SP, plaque index (PI) and gingival index were determined. IL-1beta, IL-8, MMP-8 and MMP-9 were quantified by enzyme-linked immunosorbent assay, and SP samples were assessed by DNA-DNA hybridization for a panel of 40 subgingival microbial species.

RESULTS

IL-1beta levels in T1DM patients were elevated compared with healthy individuals, and showed differences between groups at 7-21 days while healthy patients showed IL-1beta increases from baseline to 14-21 days (p<0.05). Differences were observed in MMP-9 levels between patients with and without T1DM at 7-14 days (p<0.05). Orange complex species and PI measurements displayed a superior correlation with biomarker levels when compared with other complexes or clinical measurements during EG.

CONCLUSIONS

The mean GCF biomarker levels for IL-1beta and MMP-8 were most significantly elevated in T1DM subjects compared with healthy individuals during EG, not resulting from differences in the mean PI or microbial composition.