Occlusal forces as a risk factor for periodontal disease

The essential role of Mkx in periodontal ligament on the metabolism of alveolar bone and cementum

Introduction

The periodontium is a connective tissue which consists of periodontal ligament, alveolar bone, cementum and gingiva. Periodontal ligament (PDL) is a specialized connective tissue that connects the cementum - coating the surface of the tooth - to the alveolar bone. Mohawk homeobox (Mkx) is a transcription factor that is expressed in PDL, that is known to play a vital role in the development and homeostasis of PDL. A detailed functional analysis of Mkx in the periodontal ligament for alveolar bone and cementum metabolism has not yet been conducted.

Materials and methods

Alveolar bone height, bone mineral density (BMD) and bone volume fractions (Bone volume/Total volume: BV/TV) were measured and analyzed using micro-computed tomography (Micro-CT) and 3DBon on 7-week-old male wild-type (WT) (Mkx+/+) (n = 10) and Mkx-knockout (Mkx-/-) (n = 6) rats. Hematoxylin and Eosin (H&E), tartrate-resistant acid phosphatase (TRAP), alkaline phosphatase (ALP) and Masson Trichrome staining were performed on 5, 6, and 7-week-old Mkx+/+ and Mkx-/- rats. Cementum surface area and the number of TRAP-positive osteoclasts/mm were quantified, measured, and compared for 5,6 and 7-week-old Mkx+/+ and Mkx-/- rats (n = 3 each).

Results

The level of alveolar bone height was significantly higher in Mkx-/- rats than in Mkx+/+ rats. On the other hand, there was significantly less BMD in Mkx-/- alveolar bone. A significant increase in cellular cementum could be observed as early as 5 weeks in Mkx-/- rats when compared with Mkx+/+ rats of the same age. More TRAP-positive osteoclasts were observed in Mkx-/- rats.

Conclusion

Our findings further reveal the essential roles of Mkx in the homeostasis of the periodontal tissue. Mkx was found to contribute to bone and cementum metabolism and may be essential to the prevention of diseases such as periodontitis, and could show potential in regenerative treatments.

Single Cell RNA Sequencing Reveals Critical Functions of Mkx in Periodontal Ligament Homeostasis

The periodontal ligament (PDL) comprises a fibrous tissue that connects teeth to alveolar bone and is essential for periodontal function. The transcription factor mohawk homeobox (Mkx) is expressed in the PDL where it plays an important role in the development and maintenance of the PDL. However, the precise and critical functions of Mkx in the cell populations comprising PDL have not yet been elucidated. The present study aimed to clarify the effects of a Mkx deficiency on PDL cellular heterogeneity and differences between gene expression in PDL tissues from wild-type (WT) (Mkx^+/+) and Mkx knockout (Mkx^−/−) rats using single-cell RNA sequencing. We identified 12 cell clusters comprising mesenchymal cells and macrophages. The expression of Mkx and scleraxis (Scx; another key transcription factor of PDL), was mutually exclusive, and partitioned mesenchymal cell clusters into Mkx and Scx types that dominantly expressed proteoglycans and elastic fibers, and type 1 and 3 collagen, respectively. Ossification-related genes were upregulated in mesenchymal cell and osteoblast clusters with more Mkx^−/− than Mkx^+/+ PDLs. Increased number of cells and inflammatory mediators were observed in macrophage clusters of Mkx^−/− PDL. These results suggested that Mkx plays an important role in maintaining PDL homeostasis by regulating specific cell populations and gene expression.

Tissue Engineering for Periodontal Ligament Regeneration: Biomechanical Specifications

The periodontal biomechanical environment is very difficult to investigate. By the complex geometry and composition of the periodontal ligament (PDL), its mechanical behavior is very dependent on the type of loading (compressive versus tensile loading; static versus cyclic loading; uniaxial versus multiaxial) and the location around the root (cervical, middle, or apical). These different aspects of the PDL make it difficult to develop a functional biomaterial to treat periodontal attachment due to periodontal diseases. This review aims to describe the structural and biomechanical properties of the PDL. Particular importance is placed in the close interrelationship that exists between structure and biomechanics: the PDL structural organization is specific to its biomechanical environment, and its biomechanical properties are specific to its structural arrangement. This balance between structure and biomechanics can be explained by a mechanosensitive periodontal cellular activity. These specifications have to be considered in the further tissue engineering strategies for the development of an efficient biomaterial for periodontal tissues regeneration.

Bruxism

Bruxism is a parafunctional activity of the masticatory system, which is characterized by clenching or scraping of teeth. This condition is often accompanied by a change in the shape and size of the teeth, as well as the function of the stomatognathic system. Bruxism can occur during sleep and in the waking state. The etiology is multifactorial and all causes can be divided into peripheral and central. The clinical signs and symptoms of bruxism are primarily characterized by temporomandibular disorders, the appearance of bruxofacets and changes in the hard dental tissues, supporting apparatus of the teeth and masticatory muscles, as well as headaches. The diagnosis of bruxism is made on the basis of anamnesis and clinical signs and symptoms, while electromyography and polysomnographic analysis are used in scientific researches. Therapy is aimed at controlling etiological factors and reducing symptoms. Occlusal splints are the most commonly used in the treatment of bruxism. Medications are used in situations when other methods, including psychotherapy, do not give positive results. Given the multifactorial etiology, the therapeutic approach must be multidisciplinary. The approach to the patient must be individual in order to treat as effectively as possible.

Gasdermin-d Played a Critical Role in the Cyclic Stretch-Induced Inflammatory Reaction in Human Periodontal Ligament Cells

It has been shown that cyclic stretch could induce inflammatory response such as pyroptosis and the release of IL-1β in human periodontal ligament cells, through activating inflammasome and related caspases. Though gasdermin-d (GSDMD) has been reported to be present in some inflammatory diseases and function as a crucial executioner of pyroptosis, the role of GSDMD in the stretch-induced inflammatory response in human periodontal ligament cells (HPDLCs) has not been well clarified. In this study, it was found that GSDMD was activated by cyclic stretch, and its activation affected the pyroptotic rate in HPDLCs, leading to the maturation and secretion of IL-1β and IL-18 ultimately. In addition, GSDMD was found to be regulated by caspase-1 directly. Nevertheless, the exact relationship between inflammasomes and GSDMD in the stretch-induced inflammatory response still needs to be further elucidated.

Orthodontic treatment in periodontitis-susceptible subjects: a systematic literature review

The aim is to evaluate the literature for clinical scientific data on possible effects of orthodontic treatment on periodontal status in periodontitis-susceptible subjects. A systematic literature review was performed on studies in English using PubMed, MEDLINE, and Cochrane Library central databases (1965-2014). By manually searching reference lists of selected studies, we identified additional articles; then we searched these publications: Journal of Periodontology, Periodontology 2000, Journal of Clinical Periodontology, American Journal of Orthodontics and Dentofacial Orthopedics, Angle Orthodontist, International Journal of Periodontics & Restorative Dentistry, and European Journal of Orthodontics. Search terms included randomized clinical trials, controlled clinical trials, prospective and retrospective clinical studies, case series >5 patients, periodontitis, orthodontics, alveolar bone loss, tooth migration, tooth movement, orthodontic extrusion, and orthodontic intrusion. Only studies on orthodontic treatment in periodontally compromised dentitions were included. One randomized controlled clinical trial, one controlled clinical trial, and 12 clinical studies were included. No evidence currently exists from controlled studies and randomized controlled clinical trials, which shows that orthodontic treatment improves or aggravates the status of periodontally compromised dentitions.

Rescue of a periodontally compromised tooth by non-surgical treatment: a case report

PURPOSE

This article describes a case of the successful non-surgical management of a periodontally compromised maxillary premolar.

METHODS

A combination therapy, including root planing, occlusal adjustment, and tooth splinting, was applied. Clinical and radiographic examinations were performed during the 16-month follow-up period.

RESULTS

All periodontal parameters were improved. There were dramatic decreases (3-6 mm) in the probing pocket depth, tooth mobility, and marginal bone loss. Interestingly, gradual resolution of the periapical radiolucency and alveolar bone regeneration were observed in the radiographs, and the periodontal condition was maintained during the follow-up period.

CONCLUSIONS

Within the limits of this study, these results demonstrate the importance of natural tooth preservation through proper periodontal treatment and occlusal adjustment of the periodontally compromised tooth, which is typically targeted for tooth extraction and dental implantation.

The Impact of the Crown-Root Ratio on Survival of Abutment Teeth for Dentures

Crown-root ratio (CRR) is commonly recorded when planning prosthodontic procedures. However, there is a lack of longitudinal clinical data evaluating the association between CRR and tooth survival. The aim of this longitudinal practice-based study was to assess the impact of CRR on the survival of abutment teeth for removable partial dentures (RPDs). Data were collected from 147 patients provided with RPDs at a dental hospital in Japan. In total, 236 clasp-retained RPDs and 856 abutment teeth were analyzed. Survival of abutment teeth was assessed using Kaplan-Meier methods and Cox's proportional hazard (PH) regression. The Cox PH regression was used to assess the prognostic significance of initial CRR value with adjustments for clinically relevant factors, including age, sex, frequency of periodontal maintenance programs, occlusal support area, type of abutment tooth, status of endodontic treatment, and probing pocket depth. Abutment teeth were divided into 1 of 5 risk groups according to CRR: A (≤0.75), B (0.76-1.00), C (1.01-1.25), D (1.26-1.50) and E (≥1.51). The 7-year survival rate was 89.1% for group A, 85.9% for group B, 86.5% for group C, 76.9% for group D, and 46.7% for group E. The survival curves of groups A, B, and C were illustrated to be quite similar and favorable. The multivariable analysis treating CRR as a continuous variable allowed estimation of the hazard ratio at any specific CRR value. When CRR = 0.80 was set as a reference, the estimated hazard ratio was 0.58 for CRR = 0.50 (95% confidence interval [CI], 0.36-0.91), 1.13 for CRR = 1.00 (95% CI, 0.93-1.37), 1.35 for CRR = 1.25 (95% CI, 1.02-1.80), 1.53 for CRR = 1.50 (95% CI, 1.15-2.08), or 1.95 for CRR = 2.00 (95% CI, 1.44-2.65). These practice-based longitudinal data provide information to improve the evidence-based prognosis of teeth in providing prosthodontic procedures.

Cytological Kinetics of Periodontal Ligament in an Experimental Occlusal Trauma Model

Using a model of experimental occlusal trauma in mice, we investigated cytological kinetics of periodontal ligament by means of histopathological, immunohistochemical, and photographical analysis methods. Periodontal ligament cells at furcation areas of molar teeth in the experimental group on day 4 showed a proliferation tendency of periodontal ligament cells. The cells with a round-shaped nucleus deeply stained the hematoxylin and increased within the day 4 specimens. Ki67 positive nuclei showed a prominent increase in the group on days 4 and 7. Green Fluorescent Protein (GFP) positivity also revealed cell movement but was slightly slow compared to Ki67. It indicated that restoration of mechanism seemed conspicuous by osteoclasts and macrophages from bone-marrow-derived cells for the periodontal ligament at the furcation area. It was suggested that the remodeling of periodontal ligament with cell acceleration was evoked from the experiment for the group on day 4 and after day 7. Periodontal ligament at the furcation area of the molar teeth in this experimental model recovered using the cells in situ and the bone-marrow-derived cells.

Bruxism is unlikely to cause damage to the periodontium: findings from a systematic literature assessment

BACKGROUND

This paper systematically reviews the MEDLINE and SCOPUS literature to answer the following question: Is there any evidence that bruxism may cause periodontal damage per se?

METHODS

Clinical studies on humans, assessing the potential relationship between bruxism and periodontal lesions (i.e., decreased attachment level, bone loss, tooth mobility/migration, altered periodontal perception) were eligible. Methodologic shortcomings were identified by the adoption of the Critical Appraisal Skills Program quality assessment, mainly concerning the internal validity of findings according to an unspecific bruxism diagnosis.

RESULTS

The six included articles covered a high variability of topics, without multiple papers on the same argument. Findings showed that the only effect of bruxism on periodontal structures was an increase in periodontal sensation, whereas a relationship with periodontal lesions was absent. Based on the analysis of Hill criteria, the validity of causation conclusions was limited, mainly owing to the absence of a longitudinal evaluation of the temporal relationship and dose-response effects between bruxism and periodontal lesions.

CONCLUSIONS

Despite the scarce quantity and quality of the literature that prevents sound conclusions on the causal link between bruxism and the periodontal problems assessed in this review, it seems reasonable to suggest that bruxism cannot cause periodontal damage per se. It is also important to emphasize, however, that because of methodologic problems, particularly regarding sleep bruxism assessment, more high-quality studies (e.g., randomized controlled trials) are needed to further clarify this issue.

Occlusal adjustment associated with periodontal therapy--a systematic review

OBJECTIVES

Occlusal adjustment as part of periodontal therapy has been controversial for years, mostly because the literature does not provide enough evidence regarding the influence of trauma from occlusion (TfO) on periodontitis. The need for occlusal adjustment in periodontal therapy is considered uncertain and requires investigation. The aim of this systematic review was to identify and analyse those studies that investigated the effects of occlusal adjustment, associated with periodontal therapy, on periodontal parameters.

DATA

A protocol was developed that included all aspects of a systematic review: search strategy, selection criteria, selection methods, data collection and data extraction.

SOURCES

A literature search was conducted using MEDLINE via PubMed, the Cochrane Central Register of Controlled Trials, and EMBASE.

STUDY SELECTION

Three reviewers screened the titles and abstracts of articles according to the established criteria. Every article that indicated a possible match, or could not be excluded based on the information given in the title or abstract, was considered and evaluated. On final selection, four articles were included.

CONCLUSIONS

Although the selected studies suggest an association between occlusal adjustment and an improvement in periodontal parameters, their methodological issues (explored in this review) suggest the need for new trials of a higher quality. There is insufficient evidence at present to presume that occlusal adjustment is necessary to reduce the progression of periodontal disease.

CLINICAL SIGNIFICANCE

Although it is still not possible to determine the role of occlusal adjustment in periodontal treatment, adverse effects have not been related to occlusal adjustment. This means that the decision made by clinicians whether or not to use occlusal adjustment in conjunction with periodontal therapy hinges upon clinical evaluation, patient comfort, and tooth function.

Correlation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of therapy

AIM

The association between periodontal status and biting force is unclear. The aim of this study was to investigate the relation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of periodontal treatment.

MATERIAL AND METHODS

A total of 198 patients, who had entered a periodontal maintenance programme, were examined for the presence of restorations on the occlusal surface, probing pocket depth, clinical attachment loss (CAL), bleeding on probing, and mobility of teeth. Quantitative analysis of total biting force, occlusal contact area and biting pressure (defined by biting force per 1 mm(2) of occlusal contact area) was performed using microcapsular pressure-sensitive sheets.

RESULTS

A multiple stepwise regression analysis showed that total biting force and occlusal contact area were positively associated with the number of present teeth and negatively associated with female gender, mean CAL and mean probing pocket depth. Biting pressure was positively associated with CAL.

CONCLUSIONS

Reduced periodontal support was found to be associated with decreased total biting force and with increased biting pressure (defined as force per 1 mm(2) of occlusal contact area).

Epidemiological evaluation of the multifactorial aetiology of abfractions

The purpose of this study was to determine risk indicators for the aetiology of abfractions (cervical wedge-shaped defects) on teeth using dental and medical variables obtained in a population-based sample of the cross-sectional epidemiological 'Study of Health in Pomerania' (SHIP). Medical history, dental, and sociodemographic parameters of 2707 representatively selected subjects 20-59 years of age with more than four natural teeth were checked for associations with the occurrence of abfractions using a two-level logistic regression model on a tooth and a subject level. The estimated prevalence of developing abfractions generally increased with age. The following independent variables were associated with the occurrence of abfractions: buccal recession of the gingiva, odds ratio (OR) = 6.7; occlusal wear facets of scores 1, 2 and 3, OR = 1.5, 1.9, 1.9; tilted teeth, OR = 1.4; inlays, OR = 1.6; toothbrushing behaviour, OR = 1.9 to 2.0 (two and three times a day versus once a day). First premolars had the highest estimated risk for developing abfractions, followed by the second premolars. Maxillary and mandibular teeth behaved similarly in terms of abfractions, with the exception of mandibular canines, which had a much lower estimated risk of incurring abfractions than did maxillary canines. The results of this analysis indicated that abfractions are associated with occlusal factors, like occlusal wear, inlay restorations, altered tooth position and tooth brushing behaviour. This study delivers further evidence for a multifactorial aetiology of abfractions.

The Influence of Dynamic Occlusal Interferences on Probing Depth and Attachment Level: Results of the Study of Health in Pomerania (SHIP)

BACKGROUND

The purpose of this study was to investigate potential associations between dynamic occlusal interferences and signs of periodontal disease in posterior teeth based on dental and medical measurements obtained from a population-based sample in the cross-sectional epidemiological study entitled, "Study of Health in Pomerania" (SHIP).

METHODS

Medical history and dental and sociodemographic parameters of 2,980 representatively selected dentate subjects, 20 to 79 years of age, were collected. The analysis was performed on posterior teeth only using a mixed linear model that considers the clustered structure of the data. The model also was adjusted with respect to known risk factors for periodontal disease.

RESULTS

The presence of non-working side contacts only was significantly related to probing depth (P<0.0001) and attachment loss (P=0.001). The presence of non-working side contacts and working side contacts on the same tooth was significantly related to increased probing depth (P=0.004) but not attachment level. The effect magnitude was a mean increase of 0.13 mm for probing depth and 0.14 mm in attachment loss. Known risk factors for periodontal disease that also showed significant associations with probing depth and attachment loss included male gender, age, smoking, education, and plaque score. Other factors significantly related to probing depth and/or attachment loss were tilted teeth, restored occlusal surfaces versus sound surfaces, elongated teeth, and tooth type (molar versus premolar).

CONCLUSION

The effect of non-working contacts on periodontal disease status was discernible, but weak in terms of magnitude and specificity.

Investigation of periodontal ligament reaction upon excessive occlusal load - osteopontin induction among periodontal ligament cells

OBJECTIVE

The purpose of the present study was to investigate the reaction of the periodontal ligament to excessive occlusal loading by observing the histological changes and osteopontin induction. The possibility of ligand for receptor activator of nuclear factor kappaB (RANKL) participation in osteopontin induction was also discussed.

BACKGROUND

The precise mechanism of periodontal ligament breakdown by excessive occlusal loading remains unclear. We established an experimental model for excessive occlusal loading in vivo. Osteopontin is known to be produced upon mechanical loading and is considered to induce the migration of osteoclasts to the resorption site. RANKL is one of the essential factors for osteoclast maturation and induces the constitutive induction of intracellular osteopontin in vitro.

METHODS

The occlusal surface of the upper left first molars of rats was raised by steel wire bonding in order to induce occlusal trauma. The destruction of the periodontal ligament was observed and the production of osteopontin and RANKL by periodontal ligament cells was detected via immunohistochemistry.

RESULTS

Our model produced wide-ranging destruction of the periodontal ligament. From day 3 to day 7, prominent compression of the periodontal ligament and osteoclast migration were observed at the apical interradicular septum. Osteopontin was detected in some osteoclasts, surrounding fibroblasts, and osteoblasts adjacent to the compression area. RANKL was observed from day 1 to day 7 around the osteoblasts and osteoclasts.

CONCLUSIONS

Our model was useful for the detailed investigation of periodontal ligament breakdown during excessive occlusal loading. Although intracellular osteopontin was produced in osteoclasts with intermittent occlusal loading, the role of this protein in the cells was not clear. No correlation between RANKL distribution and osteopontin production in osteoclasts could be found.