Journal of Dental Research

Historically, broad-spectrum antibiotics have represented a major component of the therapeutic armamentarium used to treat common oral diseases associated with a bacterial etiology. The fact that these diseases are due to the accumulation of multispecies biofilms composed of ever-increasing numbers of resistant organisms has dramatically affected the efficacy of many of these drugs. Furthermore, it is now appreciated that repeated use of broad-spectrum antibiotics also affects the composition of the host commensal microbiota, which can have both local and systemic implications. In recognition of the limitations of classical antibiotics, alternative chemical, physical, and mechanical strategies are either in use or development. These include novel narrow-spectrum antimicrobials such as antitoxins, bacteriophages, and antibody-conjugated drugs that can target specific microbes while minimizing the emergence of resistant organisms and preserving eubiotic microbes. Other approaches, such as new broad-spectrum non-antibiotic strategies and probiotics, are aimed at disrupting or altering the composition of oral biofilms and their extracellular matrices to facilitate the elimination of overt pathogens by the host response and/or adjunctive antimicrobials. This critical review describes the use and limitations of broad- and narrow-spectrum strategies currently being used to treat common bacterially induced oral diseases as well as alternative methods in development.

It has been questioned whether Streptococcus mutans can still be considered the major etiological agent for caries. The main argument is that most evidence has been based on single-species identification. The composition of the oral microbiome was not analyzed. This systemic review aims to assess the prevalence and abundance of S. mutans in caries-active (CA) and caries-free (CF) subjects based on clinical studies in which the microbiome was investigated. Three databases (PubMed, Cochrane, Embase) were searched until May 22, 2023, for eligible publications that included CA and CF subjects and reported the detection of both S. mutans and the oral microbial community, using DNA-based methods. The clinical and microbial outcomes were summarized and further analyzed using a random-effects model. Of 22 eligible studies, 3 were excluded due to the high risk of bias. In the remaining 19 studies, 16 reported the prevalence of S. mutans, 11 reported its relative abundance, and 8 reported both parameters. The prevalence of S. mutans in CA was either similar to (n = 4) or higher than (n = 12) the CF group. The reported relative abundance in CA was higher than CF in all 11 studies, although the values varied from 0.001% to 5%. Meta-analysis confirmed the significance of these findings. The summary of microbial community data did not reveal other caries-associated bacterial genera/species than S. mutans. In conclusion, the collected evidence based on microbiome studies suggests a strong association between the prevalence and abundance of S. mutans and caries experience. While the cariogenic role of S. mutans in the oral ecosystem should be recognized, its actual function warrants further exploration.

Understanding how dental attendance evolves throughout life can inform targeted preventive health care policies by identifying key moments when people are more or less likely to seek dental care. Trajectory modeling of age and time trajectories takes a life course approach to understanding dental attendance, offering insights into both developmental perspectives (e.g., life stages) and structural perspectives (e.g., social position and health care systems) throughout the life course. This study used group-based trajectory modeling to identify (1) the age trajectories of dental attendance among Australian adults from young adulthood to retirement age and (2) the distinct time trajectories of dental attendance among Australian working-age adults. Data from the Household, Income and Labour Dynamics in Australia (HILDA) study was used to fit 2 trajectory models (age and time based). Age trajectories were fitted for individuals aged 15 to 64 y using dental attendance data from 3 time points: 2009, 2013, and 2017. Time trajectories were fitted for working-age adults (24–54 y) using data from 2009 to 2017 and descriptively analyzed by social characteristics. Dental attendance was classified as frequent (less than 2 y since the last visit) or infrequent (2 y or longer). Two distinct age trajectories emerged among participants (N = 11,189): the mostly frequent (75.1%) and declining-infrequent group (24.9%). A sharp decline in the probability of being frequent attendees was observed between 15 and 20 y in a quarter of the population with no subsequent change. Four time trajectories were identified (n = 7,033): consistently frequent (37.8%), consistently infrequent (8.9%), increasing attendance (22.2%), and declining attendance (31%). Descriptive analysis showed that age and social inequalities were evident in the trajectories. The findings emphasize the need for preventive health care policies that account for life-stage dynamics and their impact on attendance behaviors, in addition to improving structural factors.

In the present in vitro study, we evaluated the adhesion of an injectable platelet-rich fibrin (i-PRF) to laser-textured zirconia surfaces and their resultant friction behavior against bone tissue. Three types of zirconia surfaces were compared regarding the i-PRF coating effects: 1) grit blasted with 250-μm spherical alumina particles and acid etched with 20% hydrofluoric acid (ZLA), 2) laser textured with a random (RD) surface pattern, or 3) laser textured with a designed pattern based on 16 lines and 8 passages (L16N8). The coefficient of friction (COF) of the specimens was assessed on a reciprocating sliding pin-on-plate tribometer at 1-N normal load, 1 Hz, and a 2-mm stroke length. Sliding wear tests were carried out against bovine femoral bone tissue in 0.9% sodium chloride solution at room temperature. Surfaces were then assessed by scanning electron microscopy. COF mean values for test groups (0.35, ZLA; 0.45, L16N8) were lower when compared with the control groups (0.52, ZLA; 0.60, L16N8), with the exception of the RD group (0.47, test; 0.43, control). Results did not show significant differences in COF mean values between RD and L16N8 surfaces after coating with i-PRF. The 3-dimensional fibrin network embedded with leukocytes, platelets, and red blood cells was responsible for decreasing COF mean values over the zirconia surfaces, thus providing a lubricant effect. Also, the morphologic aspects of the laser-treated zirconia surfaces increased the adhesion of the platelet-rich fibrin, which could speed up the osseointegration process of zirconia implants.

Monolithic zirconia crowns fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) via subtractive manufacturing (SM) exhibit limited bonding properties compared with other ceramics. Traditional methods such as air abrasion can improve bonding but may negatively affect the mechanical stability of zirconia. Nanoparticle jetting (NPJ), an emerging 3-dimensional–printing technology for zirconia restorations, offers the potential to create intricate structures, such as porous surfaces, with high precision. This study aimed to demonstrate that NPJ-manufactured monolithic zirconia crowns with an intaglio porous design can enhance bonding properties while maintaining mechanical strength. Standard NPJ zirconia crowns and commercially available SM zirconia crowns (SZC) were used as control groups. The surface roughness, fracture load, 2-body wear, and shear bond strength (SBS) were evaluated. The NPJ intaglio porous crowns (NIPC) with an intaglio porous design exhibited satisfactory and comparable fracture strength to SZC (within 1-mm occlusal thickness). Although the NIPC retained a relatively high original surface roughness, it demonstrated similar occlusal surface roughness, 2-body wear, and aging resistance to SZC after thorough polishing. Furthermore, the NIPC showed significantly superior intaglio surface roughness and SBS compared with conventionally air-abraded zirconia. Overall, this study successfully demonstrated the potential of NIPC as a viable restorative option, offering robust bonding and reliable mechanical properties.

Polymer-infiltrated ceramic network (PICN) composites are recognized for their mechanical properties, closely resembling natural tooth enamel. However, the low fracture toughness of current PICN materials limits their broader use. This study draws inspiration from the natural enamel rod–sheath architecture to develop bionic PICN composites with an enamel-like structure, enhancing their fracture toughness for dental restorations. By simulating the morphology and arrangement of enamel rods, 3 types of zirconia ceramic scaffolds were designed and manufactured by digital light processing technology, which featured a straight-rod structure, a gnarled-rod structure, or a natural rod distribution structure. The scaffolds were surface treated and resin infiltrated to obtain enamel-structured PICN material, wherein the infiltrated resin formed a rod-sheath structure. With VITA Enamic (VE) as control, the enamel-like composites were characterized in detail for their microstructure, flexural strength, fracture toughness, flexural modulus, friction and wear properties, adhesive properties, and cell compatibility. Results show that the PICN with the natural rod distribution structure had the highest flexural strength and fracture toughness among the 3 PICN composites, but there was no significant difference in their moduli. Its strength and modulus were slightly lower than those of VE, but its toughness was 7.0 ± 0.6 MPa·m^1/2, around 7 times that of VE. The fracture mode in the ceramic phase was mainly transgranular, while ductile fracturing of the resin phase contributed to toughening. Furthermore, it exhibited superior wear resistance when compared with VE and bovine enamel. After sandblasting and priming, its bond strength to bovine dentin was comparable to that of VE after standardized treatment. Cytotoxicity assays confirmed high cell viability and healthy morphology. Overall, these results indicate that the newly developed PICN composites offer significant improvement over current dental materials, making them promising candidates for bonded prosthetic applications.

Dentin hypersensitivity has been widely recognized to be caused by patent dentinal tubules (DTs). A polyaspartic acid–calcium and magnesium (PAsp-Ca&Mg) complex process has been demonstrated to induce biomimetic mineralization of collagen fibrils. This study investigated the in vitro and in vivo occlusion of the DTs by a PAsp-Ca&Mg complex process. Dentin disks were treated by citric acid to open the DTs and randomly divided into 4 groups. Two experimental groups (n = 18) were applied with PAsp-Ca&Mg suspension and phosphate solution or phosphate-fluoride solution in sequence for 10 min. Two positive control groups (n = 18) were treated with Gluma or Duraphat. All the dentin disks were incubated in artificial saliva for 24 h. DT occlusion was characterized by scanning electron microscopy, and dentin permeability measurement was conducted regardless of being subject to abrasive or ultrasonic and acidic challenge. The incisors of 3 New Zealand rabbits were used to verify the in vivo occlusion of the DTs. In vitro and in vivo results demonstrated in-depth occlusion of the DTs to ~100 μm by the PAsp-Ca&Mg complex process. When compared with control groups, the PAsp-Ca&Mg complex process could significantly reduce dentin permeability (P < 0.05) irrespective of abrasive or ultrasonic and acidic challenge. The PAsp-Ca&Mg complex process not only deeply occluded patent DTs but also significantly decreased dentin permeability and provided a paradigm for ion-doped DT occlusion. This provides a promising strategy for managing dentin hypersensitivity.

Pyroptosis, a gasdermin-mediated immunogenic cell death, has been shown to elicit adaptive antitumor immune responses, thereby augmenting the response to cancer immunotherapy when pyroptosis is therapeutically activated. However, despite increased gasdermin E (GSDME) expression, significant pyroptosis remains elusive in certain tumor types, and the underlying regulatory mechanisms are poorly understood. In this study, we observed high signal regulatory protein α1 (SIRPA) expression in head and neck squamous cell carcinoma (HNSCC) cells, a target in cancer immunotherapy. Intriguingly, SIRPA inhibition markedly augmented pyroptosis activity in tumor tissues and modulated tumor growth in a HNSCC mouse model. Subsequent investigations revealed that SIRPA knockout upregulated GSDME expression and potentiated cisplatin-induced pyroptosis in cancer cells. Integrative transcriptomics and metabolomics analysis suggested that the SIRPA knockout profoundly altered protein ubiquitination and augmented argininosuccinic acid levels in cancer cells. Specifically, we demonstrated that ubiquitin-specific peptidase 18 (USP18), a deubiquitinating enzyme, targets GSDME for deubiquitination and that USP18 knockdown suppressed cisplatin-induced pyroptosis. Notably, we found that succinylation of GSDME, which is mediated by succinyl-CoA, promotes GSDME cleavage without affecting caspase-3 activation. Further experiments indicated that SIRPA expression in tumor cells can decrease the antitumor efficacy of chemotherapy and immunotherapy in HNSCC mouse models. In summary, our findings reveal a novel mechanism of pyroptosis evasion in HNSCC, whereby tumor-intrinsic SIRPA enhances GSDME ubiquitylation and inhibits its succinylation. These insights suggest that inhibiting SIRPA expression may improve the efficacy of immunotherapy for HNSCC by inducing pyroptosis.

Odontoblasts are terminally differentiated cells that exhibit mechanosensitivity and mineralization capacity. Mechanosensitive ion channels such as Piezo1 are present in odontoblasts and are associated with their physiological functions via Ca²⁺ signaling. Both Ca²⁺ signals via Ca²⁺ influx from mechanosensitive ion channels and Ca²⁺ release from Ca²⁺ stores function as secondary messenger systems for various biological phenomena. The endoplasmic reticulum (ER) serves as an intracellular Ca²⁺ store that mobilizes intracellular Ca²⁺. Changes in Ca²⁺ concentration inside the ER are among the factors that cause ER stress. Perivascular cells are located around odontoblasts in the dental pulp. Although such formation indicates that perivascular cells interact with odontoblasts, their detailed profiles under developmental and pathological conditions remain unclear. In this study, we revealed that pericyte marker, neural/glial antigen 2 (NG2)–positive cells, in cell-rich zones (CZs) can differentiate into Piezo1-positive odontoblasts following genetic odontoblast depletion in mice, and modeled as odontoblast death after severe dentin injury and as reparative dentin formation. NG2-positive pericytes differentiated into odontoblasts faster than glial cells. To determine how NG2-positive cells differentiate into Piezo1-positive odontoblasts, we focused on the ER-stress sensor protein, activating transcription factor 6a (ATF6a). After genetic odontoblast depletion, NG2-positive cells regenerated in the odontoblast layer and were capable of acting as functional odontoblasts. In the presence of extracellular Ca²⁺, the application of a sarco/ER Ca²⁺-ATPase (SERCA) inhibitor, thapsigargin, known as an ER-stress inducer, increased the intracellular Ca²⁺ concentration in the odontoblast lineage cells (OLCs). The increase was significantly inhibited by the application of a pharmacologic Piezo1 inhibitor, indicating that ER stress by SERCA inhibition augmented Piezo1-induced responses in odontoblast progenitor cells. However, the physiological activation of G_q-coupled receptors by adenosine diphosphate did not induce Piezo1 activation. Gene silencing of ATF6a and/or NG2 impaired the mineralization of OLCs. Overall, ATF6a orchestrates the differentiation of NG2-positive pericytes into functional odontoblasts that act as sensory receptor cells and dentin-forming cells.

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the head and neck; however, the efficacy of existing treatment is limited and new effective strategies need to be explored. Our previous work demonstrates that isoguanosine (isoG) is a promising nucleoside molecule with superior self-assembly capability and significant anti-OSCC potential. However, the antitumor mechanism of isoG remains unclear. In this study, we reveal that the antiproliferative effect of isoG is mediated by its cellular metabolite, isoguanosine 5′-monophosphate (isoGMP), which induces excessive endoplasmic reticulum (ER) stress and cell death through adenosine monophosphate–activated protein kinase (AMPK) activation. IsoG activates AMPK and induces ER stress at low concentrations, with minimal impact on cell viability at these concentrations. To further explore the therapeutic potential of isoG, we investigated its role in modulating chemosensitivity. Our findings show that AMPK activation enhances the sensitivity of OSCC cells to 5-fluorouracil (5-FU), and the combination of isoG and 5-FU exhibits a synergistic anticancer effect. Building on the self-assembly characteristics of isoG, we developed an innovative treatment platform by introducing dynamic borate ester bonds to form an isoguanosine-phenylenediboronic acid-isoguanosine (isoGPBisoG) structure. When combined with 5-FU, this platform achieved remarkable therapeutic efficacy in 2 OSCC cell-derived xenograft models, with tumor inhibition rates of 71.0% and 56.6%, respectively, compared with control. These findings establish isoG as a potent enhancer of chemotherapeutic efficacy in OSCC via AMPK activation. More importantly, the isoGPBisoG and 5-FU combination represents a significant paradigm of a synergistic therapy platform. This novel approach offers a promising direction for the development of more effective OSCC treatments.

Oral squamous cell carcinoma (OSCC) is one of the most prevalent types of malignancies in the oral cavity, with a high incidence of lymph node (LN) metastasis. While previous studies have explored the mechanisms of lymphatic metastasis, little is known about the cellular architecture within the premetastatic niche of LNs. In this study, we established mouse models of premetastatic LNs, which demonstrated an immunosuppressive premetastatic environment in tumor-draining LNs prior to metastasis. We performed single-cell RNA sequencing on LNs from patients with OSCC, including premetastatic tumor-draining LNs and paired contralateral LNs. Our analysis identified a subset of CD4+ T cells that exclusively expressed MIR155HG, characterized by a preexhausted state and active immune exhaustion signaling with myeloid cells (henceforth, CD4+ Tex-pre cells). In silico analyses and in vivo experiments revealed a higher abundance of CD4+ Tex-pre cells in tumor-draining premetastatic LNs when compared with contralateral LNs, with their numbers increasing as LN metastasis progressed. Moreover, adoptive transfer of CD4+ Tex-pre cells aggravated immune suppression in tumor-draining premetastatic LNs and promoted LN metastasis. The presence of CD4+ Tex-pre cells was further validated by integrating external data sets and conducting in situ RNAscope staining. Finally, using bulk RNA sequencing data sets, we found that CD4+ Tex-pre infiltration was associated with lymphatic metastasis and that CD4+ Tex-pre scores could inform treatment decisions for low-grade cases without clinical nodal involvement. Overall, our study provides a comprehensive view of the single-cell landscape in the premetastatic niche of OSCC LNs and highlights the role of CD4+ Tex-pre cells in shaping the premetastatic niche.