Harvard School of Dental Medicine

Leveraging systems biology approaches, we illustrate how metabolically distinct species of Clostridia protect against or worsen Clostridioides difficile infection in mice by modulating the pathogen's colonization, growth, and virulence to impact host survival. Gnotobiotic mice colonized with the amino acid fermenter Paraclostridium bifermentans survive infection with reduced disease severity, while mice colonized with the butyrate-producer, Clostridium sardiniense, succumb more rapidly. Systematic in vivo analyses revealed how each commensal alters the gut-nutrient environment to modulate the pathogen's metabolism, gene regulatory networks, and toxin production. Oral administration of P. bifermentans rescues conventional, clindamycin-treated mice from lethal C. difficile infection in a manner similar to that of monocolonized animals, thereby supporting the therapeutic potential of this commensal species. Our findings lay the foundation for mechanistically informed therapies to counter C. difficile disease using systems biology approaches to define host-commensal-pathogen interactions in vivo.

Multidrug-resistant (MDR) infections have been identified globally among men who have sex with men (MSM). The highly drug-resistant phenotype often confounds initial antimicrobial therapy, placing patients at risk for adverse outcomes, the development of more drug-resistant strains, and additional treatment failures. New macrolide-resistant strains complicate treatment further as azithromycin is a next-in-line antibiotic for MDR strains, and an antibiotic-strain combination confounded by gaps in validated clinical breakpoints for clinical laboratories to interpret macrolide resistance in We present the first high-resolution genomic analyses of 2,097 U.S. isolates, including those from MDR outbreaks. A sentinel shigellosis case in an MSM patient revealed a strain carrying 12 plasmids, of which two carried known resistance genes, the pKSR100-related plasmid pMHMC-004 and spA-related plasmid pMHMC-012. Genomic-epidemiologic analyses of isolates revealed high carriage rates of pMHMC-004 predominantly in U.S. isolates from men and not in other demographic groups. Isolates genetically related to the sentinel case further harbored elevated numbers of unique replicons, showing the receptivity of this lineage to plasmid acquisition. Findings from integrated genomic-epidemiologic analyses were leveraged to direct targeted clinical actions to improve rapid diagnosis and patient care and for public health efforts to further reduce spread. Multidrug-resistant isolates with resistance to macrolides are an emerging public health threat. We define a plasmid/pathogen complex behind infections seen in the United States and globally in vulnerable patient populations and identify multiple outbreaks in the United States and evidence of intercontinental transmission. Using new tools and sequence information, we experimentally identify the drivers of antibiotic resistance that complicate patient treatment to facilitate improvements to clinical microbiologic testing for their detection. We illustrate the use of these methods to support multiagency efforts to combat multidrug-resistant using publicly available tools, existing genomic data, and resources in clinical microbiology and public health laboratories to inform credible actions to reduce spread.

Microplastics (MPs; mm) and nanoplastics (NPs; 1-1,000 nm) are pervasive environmental contaminants with growing implications for human health. MPs have been detected in multiple human biofluids and tissues, raising concerns about chronic exposure and potential downstream inflammatory and systemic effects. Orthodontic treatment relies heavily on polymer-based appliances (e.g., polyurethane, PETG, PMMA) worn for extended periods, yet the contribution of orthodontic appliances to microplastic exposure remains poorly characterized. This in vitro pilot study evaluated microplastic particles recovered after exposure of five commonly used maxillary orthodontic appliances to artificial saliva at 37°C under calibrated mechanical agitation intended to approximate clinically relevant wear patterns (nighttime wear-equivalent vs full-time wear-equivalent). Following exposure, a 1 ml aliquot of supernatant was analyzed using laser-directed infrared spectroscopy (LDIR) to quantify particle recovery, measure particle diameter and eccentricity, and assign polymer type. Because one appliance was tested per appliance type and control particle counts were very low, particle-count comparisons were interpreted descriptively and inferential statistics were limited to exploratory, polymer-stratified particle-characteristic comparisons between the two aligner systems at the full-time wear-equivalent condition. Controls contained few particles (Control_8: 1 PET particle; Control_20: 1 PET and 2 PTFE particles). In nighttime wear-equivalent conditions, particle recovery in the analyzed aliquot ranged from 11 to 16 particles across appliances (Essix PETG retainer: 16; Biocryl nightguard: 11; Hawley retainer: 16), with polymer composition varying by appliance. In full-time wear-equivalent conditions, the SmartTrack® and Zendura aligners yielded substantially higher particle recoveries and multiple polymer classifications. In polymer-stratified comparisons between SmartTrack® and Zendura at the full-time wear-equivalent condition, no differences in particle eccentricity or eccentricity-category distributions were detected after multiplicity correction; diameter differences were also not statistically significant after correction. These findings support that orthodontic appliances can contribute to microplastic particle recovery under simulated intraoral conditions while underscoring the need for replicated appliance-level studies and improved control characterization to estimate exposure and variability.

Introduction: The purpose of the study was to assess the agreement between the Handicapping Labiolingual Deviation (HLD) Index and MassHealth orthodontic coverage decisions in order to discern whether discrepancies exist in the current screening process in the state of Massachusetts. Methods: This study consisted of a retrospective chart review including 57 patients at the Harvard School of Dental Medicine. Subjects were divided into two subgroups, those approved (n=31) for comprehensive orthodontic treatment and those denied (n=26) by MassHealth insurance. The HLD form submitted by the treating orthodontic resident was extracted from the MassHealth submission log. Using the iTero scan taken at the initial consultation, OrthoCAD software was then utilized to re-score the subjects according to the American Board of Orthodontics Discrepancy Index (DI). The DI score was then compared to the HLD score for each subject. In addition, the HLD score was compared to the ultimate approval or denial decision by MassHealth to assess agreement between the treating provider and the MassHealth reviewers. Results: To assess the agreement between HLD score and the MassHealth decision, a T-test was conducted. Approved cases had significantly higher HLD scores (mean=23.81, SD=7.00) than denied cases (mean=17.42, SD=7.11), with a mean difference of 6.38 points (p=0.001, 95% CI: 2.63–10.14). To compare the HLD Index and ABO Discrepancy Index, Pearson correlation was conducted, and normality of both variables was confirmed by the Shapiro-Wilk test. The two indices shared less than 9% of common variance (r².09), indicating very limited agreement. Among subjects submitted with an autoqualifier, the majority (77.8%) were approved (n=28), whereas only 22.2% were denied (n=8). The most commonly identified autoqualifier condition was an impinging overbite, observed in 14.04% (n=8) of cases. Both medical necessity letter submission (OR=10.20, 95% CI: 1.98-52.55, p=0.005) and HLD score (OR=1.20 per point, 95% CI: 1.07-1.34, p=0.002) were significant independent predictors of MassHealth approval. These associations remained significant in the multivariable model adjusting for malocclusion type, age group, and gender. Conclusion: Despite overall agreement between the HLD Index and MassHealth outcomes, the data reflects a discrepancy in cases that were submitted with an autoqualifier but ultimately denied comprehensive coverage for orthodontic treatment, suggesting that additional records (model composite, occlusogram) may serve as useful diagnostic aids, particularly in cases with deep impinging bite. Moreover, submitting a medical necessity letter was found to be a significant independent predictor of MassHealth approval, nearly doubling approval rates, and therefore treating providers should be encouraged to submit these on behalf of all patients.

The objective of this study was to evaluate preoperative, intraoperative, and postoperative factors influencing outcomes of primary root canal treatment (RCT) performed by postgraduate residents at Harvard School of Dental Medicine (HSDM) Advanced Graduate Education (AGE) Endodontics between 2018 and 2024.

Patient charts were reviewed from the axiUm electronic dental record system. 367 cases with both treatment and recall codes were identified, and 250 had confirmed recall visits with appropriate periapical radiographs. After excluding cases with less than six months of follow-up, 122 cases were included, comprising 89 retrospective and 33 prospective recalls. Periapical status was assessed using the Periapical Index by two blinded examiners, and cases were classified as success (healed/healing) or failure (non-healed) based on radiographic and clinical criteria. Univariable associations were evaluated using chi-square or Fisher’s exact tests and t-tests, and selected variables were analyzed in a Firth penalized logistic regression model. Time-to-failure was analyzed using Kaplan–Meier and Cox proportional hazards models.

The overall success rate was 80.3% (98/122), with a tooth survival rate of 99.2% (121/122). Inter-examiner agreement was high (κ = 0.85). In univariable analyses, satisfactory coronal restoration, apical extent of gutta-percha filling, absence of symptoms at first recall, and higher provider year were associated with success. In the multivariable Firth model, absence of symptoms at recall (OR 0.01; 95% CI 0.001–0.06; p 0.001) and satisfactory coronal restoration (OR 5.11; 95% CI 1.17–30.48; p = 0.029) remained significant predictors, whereas provider year was not independently associated with outcome. The model demonstrated excellent discrimination (AUC = 0.936). In the Cox model, satisfactory coronal restoration was associated with a 75% reduction in hazard of failure (HR 0.25; 95% CI 0.09–0.70; p = 0.01).

Within this postgraduate training setting, primary RCT demonstrated favorable outcomes. Coronal restoration quality and symptoms at first recall visit were the strongest predictors of success, highlighting the importance of achieving an adequate coronal seal and closely monitoring symptomatic patients. Longer-term, standardized follow-up is needed to better assess treatment durability and prognostic factors.

Background The bidirectional relationship between Metabolic Syndrome (MetS) and periodontal disease is well established. While periodontal therapy has been shown to improve certain MetS parameters, no studies to date have examined the impact of MetS on long-term periodontal treatment outcomes. This study investigated the effect of MetS and its individual components (hypertension, obesity, dyslipidemia, diabetes), as well as clinical and behavioral factors, on periodontal outcomes over five years. Methods In this retrospective longitudinal cohort study, 25,433 patient charts from the Harvard School of Dental Medicine were screened, and 320 met inclusion criteria. Patients were categorized into: Perio-Only (periodontitis without systemic comorbidities), Non-MetS (periodontitis with one or two systemic conditions), and MetS (periodontitis with ≥3 MetS components). Outcomes were evaluated at 6–8 weeks, and at 1, 3, and 5 years post-baseline. The primary outcome was number of residual sites with probing depth ≥5 mm. Results: At 1 year, patients with MetS had 4.75 more residual sites compared to those without MetS (p = 0.006). Differences were not statistically significant at 3 or 5 years, potentially reflecting reduced sample size at later follow-up time points. Dyslipidemia was associated with 3.41 additional residual sites at 1 year (p = 0.043), and obesity (BMI > 25) with 6.40 additional residual sites at 3 years (p = 0.01). Adherence to supportive periodontal therapy was strongly associated with improved outcomes, with compliant patients exhibiting 4.38, 16.62, and 13.66 fewer residual sites at 1, 3, and 5 years, respectively. Greater baseline disease severity was consistently associated with more residual sites over time. Conclusions: MetS and specific systemic components (dyslipidemia and obesity) negatively influence short- and mid-term periodontal treatment outcomes. Adherence to supportive care and baseline disease severity were also strong determinants of long-term results. These findings offer new clinically relevant insights into the oral–systemic connection and lay the groundwork for future prospective studies in this area.

Background: Traumatic dental injuries (TDIs) present a significant public health challenge in pediatric populations, with prevalence ranging from 20% to 30%. Diagnostic uncertainty complicates the management of permanent teeth following trauma. Transient denervation frequently renders traditional thermal sensibility testing unreliable during the initial months post-injury, while external inflammatory root resorption can progress rapidly before radiographic detection. There is a critical need for non-invasive predictive tools to identify teeth at high risk for delayed complications.

Objective: This prospective cohort pilot study aimed to determine if inflammatory cytokine and chemokine levels in the gingival crevicular fluid (GCF) of traumatized permanent teeth can serve as early biomarkers for adverse events, specifically pulp necrosis and external inflammatory root resorption.

Methods: This study recruited a cohort of 27 pediatric patients presenting to Boston Children’s Hospital with TDIs in their permanent dentition, resulting in a total of 64 traumatized teeth for analysis. GCF was collected non-invasively for proteomic analysis using the Olink Target 48 cytokine assay to quantify key inflammatory mediators. Clinical variables and trauma types were recorded to assess correlations with adverse endodontic outcomes. Statistical analysis in R used Fisher’s Exact Tests and Firth’s Logistic Regression to assess associations between clinical parameters and adverse outcomes, supplemented by Kaplan-Meier survival curves for event-free probability. GCF proteomic data were analyzed via Benjamini-Hochberg adjusted t-tests to compare protein levels across injury and outcome categories, with longitudinal trends plotted for a subset of cases.

Results: In this pediatric cohort (N=27), adverse events occurred in 17.2% of traumatized teeth (n=27). There was an average of 2.3 follow-ups per patient. While the majority of cases involved single trauma types, sustaining multiple simultaneous injuries significantly increased the risk of requiring treatment (OR = 4.65). GCF analysis revealed significantly elevated pro-inflammatory and resorptive biomarkers (adjusted p 0.05), including colony-stimulating factors, chemokines, and tissue degradation mediators. These molecular shifts correlated most strongly with crown fractures and minor displacements (). Exploratory analysis further identified a potential immunological transition based on complication type: isolated necrosis showed a trend toward acute pro-inflammatory signaling (IL-17C, IL-18, IL-15), whereas concurrent resorption was associated with elevated levels of the anti-inflammatory cytokine IL-27, suggesting a shift from an acute inflammation phase to a chronic phase.

Conclusion: Gingival crevicular fluid analysis identified a distinct profile of changes in biomarkers associated with differences in trauma type and the development of adverse outcomes in traumatized teeth. While the restricted sample size and overlapping injury profiles limited our ability to isolate specific clinical triggers or a definitive timeline for these shifts, these findings underscore the potential for non-invasive GCF profiling to predict delayed endodontic complications and inform future diagnostic thresholds.

Accurate diagnosis of pulpal disease remains a major challenge in endodontics, particularly when attempting to distinguish between reversible and irreversible pulpitis. While current clinical tests are effective in determining pulp vitality, they lack the specificity required to assess the true histological status of the tissue. This diagnostic limitation has become increasingly problematic with the advent of vital pulp therapies, which rely on the preservation of pulpal vitality and therefore require precise case selection. The aims of this study were to develop a reproducible murine model to define reversible and irreversible pulpitis based on histological criteria and to identify neurodegenerative biomarkers associated with pulpal injury that could serve as objective diagnostic tools. A total of twelve C57BL/6j mice were divided into four groups based on pulp exposure time: 0 hours, 24 hours, 72 hours, and 7 days. Following mechanical pulp exposure, teeth were left open to the oral environment for the designated period before being capped with Biodentine™ and allowed to heal for 14 days. Histological analyses were performed using Hematoxylin and Eosin staining to assess tissue structure and necrosis, immunohistochemistry targeting β-tubulin III to evaluate neuronal integrity, and fluorescence in situ hybridization to quantify bacterial invasion. Based on these analyses, the 0-hour and 24-hour exposure groups were identified as representative models of reversible and irreversible pulpitis, respectively. Quantitative histological assessment demonstrated a significant increase in necrotic pulpal tissue from 35% at 0 hours to 85% at 24 hours, confirming a clear threshold between reversible and irreversible injury. Immunohistochemical analysis revealed preservation of neuronal structure at 0 hours, while near-complete loss of β-tubulin III signal was observed at 24 hours, indicating extensive neuronal degeneration. Fluorescence in situ hybridization showed progressive bacterial invasion over time, although the extent of tissue damage appeared more closely associated with host inflammatory responses than with bacterial load alone. To explore the potential for objective, non-invasive diagnostics, gingival crevicular fluid, saliva, and pulp tissue samples were analyzed using the Olink Target 48 proteomic platform, focusing on neurodegenerative biomarkers. Results identified several proteins associated with neuronal injury and oxidative stress, including nerve growth factor (NGF), neurofilament light chain (NEFL), and glutaredoxin (GLRX). NGF was significantly upregulated in reversible pulpitis, while NEFL and GLRX showed increased expression in irreversible pulpitis, suggesting their potential utility as stage-specific biomarkers. Additional markers, including SYT1 and SCG2, were significantly downregulated in irreversible cases, reflecting loss of neuronal function. This study demonstrates that pulpal disease progression is closely associated with neuronal degeneration, supporting a neurodegenerative component to pulpitis. The murine model developed herein provides a reliable framework for studying pulpal pathology over time, while the identification of neuron-specific biomarkers highlights a promising avenue for improving diagnostic accuracy. Ultimately, the integration of biomarker-based diagnostics could enhance clinical decision-making, allowing for more predictable selection of vital pulp therapies and improved patient outcomes. Further research is warranted to validate these findings in human subjects and to explore their clinical applicability.

Periodontitis and peri-implantitis are chronic inflammatory diseases in which dysregulated host-microbial homeostasis compromises the oral mucosal barrier and leads to progressive soft-tissue destruction and bone loss. Although epithelial and stromal compartments are positioned to regulate barrier integrity and immune infiltration, how these non-immune cells differentially mediate inflammation in periodontitis versus peri-implantitis remains incompletely understood. The present study tested the hypothesis that distinct inflammatory profiles in periodontitis and peri-implantitis are associated with condition-specific changes in epithelial and stromal cellular states and their interactions with immune cells. Soft-tissue biopsies were collected from adults with periodontal health (n = 5 sites), periodontitis (n = 7 sites), and peri-implantitis (n = 8 sites). Single-nucleus RNA sequencing generated a cell-resolved atlas across epithelial, stromal, and immune compartments. Differential abundance, gene set enrichment, and pseudotime analyses assessed condition-specific shifts in cell proportions, biological pathways, and epithelial differentiation trajectories. Spatial transcriptomics and multiplexed immunofluorescence were used to validate candidate epithelial and endothelial niches and to visualize proximity-based interactions in situ. An in vitro endothelial assay tested cytokine inducibility of MHC class II under pro-inflammatory stimulation. The epithelial compartment resolved into seven differentiation states spanning a pseudotemporal continuum from basal repair-associated cells to suprabasal barrier-forming cells. Periodontitis was characterized by expansion of least differentiated, repair-skewed epithelial states and loss of suprabasal barrier-forming states. Peri-implantitis retained suprabasal differentiation programs but showed enrichment of stress keratins (KRT6A/B/C and KRT16). CXCL14 expression localized predominantly to suprabasal epithelial cells and showed the strongest spatial association with immune proximity in periodontitis. In the stromal compartment, a rare HLA-DR/MHC II-positive endothelial subset was enriched in disease and localized adjacent to T cells. This phenotype was recapitulated in cultured human endothelial cells under pro-inflammatory stimulation. These results support a model in which epithelial differentiation state and endothelial immune adaptation contribute in distinct ways to inflammatory niche organization in periodontitis and peri-implantitis. By integrating high-resolution single-cell and spatial data, this work delineates cellular niches and regulatory signatures that distinguish these diseases and identifies barrier-associated and vascular programs relevant to future host-modulatory strategies.

Statement of the Problem The interfacial bond between 3D-printed provisional resins and conventional polymethyl methacrylate (PMMA) reline materials is a critical determinant of clinical performance in modern prosthetic dentistry. Current strategies to enhance this bond rely primarily on post-fabrication surface treatments. Although these techniques can improve adhesion, they are often technique-sensitive and may introduce variability or unintended surface damage, potentially compromising clinical outcomes. Purpose
This in vitro study evaluated whether incorporation of a CAD/CAM-designed honeycomb macro-geometry into the surface of 3D-printed provisional resin could improve adhesion to conventional PMMA reline material when compared with commonly used mechanical and chemical surface treatment protocols. Materials and Methods
A total of 72 specimens (n=12 per group) were fabricated using a 3D-printed provisional resin and allocated to six surface modification groups: untreated control (C), sandblast (S), monomer application (M), CAD/CAM honeycomb geometry (H), combined sandblast–monomer treatment (SM), and combined honeycomb–sandblast modification (HS). For the honeycomb groups, a macro-geometric hexagonal pattern was incorporated into the “intaglio” treatment surface during the digital design phase prior to fabrication. All specimens were luted to an autopolymerizing PMMA resin. Mechanical testing was performed using a universal testing machine (UTM) at a crosshead speed of 0.5mm/min. Outcome measures included shear bond strength (MPa), peak load (N), and energy to yield (N·mm). Statistical analysis was conducted using one-way analysis of variance (ANOVA) followed by Tukey post hoc comparisons, with a significance level of α=.05. Results Statistically significant differences were observed among surface modification groups for shear bond strength and peak load (F(5,66)=22.01, P.001) as well as for energy to yield (F(5,66)=8.53, P.001). H demonstrated the highest mean shear bond strength (40.20 ± 7.28 MPa) and peak load (505.20 ± 91.43 N), corresponding to approximately a 2.7-fold increase in shear bond strength compared with C (15.00 ± 6.01 MPa). H also exhibited the greatest energy to yield (264.37 ± 194.94 N·mm), indicating increased energy absorption prior to failure. Conventional surface treatments improved bond strength, however, no modification protocol outperformed H. Conclusion Surface modification with honeycomb geometry significantly improves PMMA adhesion to printed provisional resin without compromising structural integrity and decreasing laboratory steps.