Robert M. Love

Invasion of dentinal tubules by oral bacteria.

Bacterial invasion of dentinal tubules commonly occurs when dentin is exposed following a breach in the integrity of the overlying enamel or cementum. Bacterial products diffuse through the dentinal tubule toward the pulp and evoke inflammatory changes in the pulpo-dentin complex. These may eliminate the bacterial insult and block the route of infection. Unchecked, invasion results in pulpitis and pulp necrosis, infection of the root canal system, and periapical disease. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria is involved in the invasion of dentinal tubules and subsequent infection of the root canal space. Gram-positive organisms dominate the tubule microflora in both carious and non-carious dentin. The relatively high numbers of obligate anaerobes present-such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp.-suggest that the environment favors growth of these bacteria. Gram-negative obligate anaerobic rods, e.g., Porphyromonas spp., are less frequently recovered. Streptococci are among the most commonly identified bacteria that invade dentin. Recent evidence suggests that streptococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra-tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate the invasion of dentin by select bacterial groupings. An understanding the mechanisms involved in dentinal tubule invasion by bacteria should allow for the development of new control strategies, such as inhibitory compounds incorporated into oral health care products or dental materials, which would assist in the practice of endodontics.

Coinvasion of Dentinal Tubules by Porphyromonas gingivalis and Streptococcus gordonii Depends upon Binding Specificity of Streptococcal Antigen I/II Adhesin

ABSTRACT Cell wall-anchored polypeptides of the antigen I/II family are produced by many species of oral streptococci. These proteins mediate adhesion of streptococci to salivary glycoproteins and to other oral microorganisms and promote binding of cells to collagen type I and invasion of dentinal tubules. Since infections of the root canal system have a mixed anaerobic bacterial etiology, we investigated the hypothesis that coadhesion of anaerobic bacteria with streptococci may facilitate invasive endodontic disease. Porphyromonas gingivalis ATCC 33277 cells were able to invade dentinal tubules when cocultured with Streptococcus gordonii DL1 (Challis) but not when cocultured with Streptococcus mutans NG8. An isogenic noninvasive mutant of S. gordonii, with production of SspA and SspB (antigen I/II family) polypeptides abrogated, was deficient in binding to collagen and had a 40% reduced ability to support adhesion of P. gingivalis. Heterologous expression of the S. mutans SpaP (antigen I/II) protein in this mutant restored collagen binding and tubule invasion but not adhesion toP. gingivalis or the ability to promote P. gingivalis coinvasion of dentin. An isogenic afimbrial mutant ofP. gingivalis had 50% reduced binding to S. gordonii cells but was unaffected in the ability to coinvade dentinal tubules with S. gordonii wild-type cells. Expression of the S. gordonii SspA or SspB polypeptide on the surface of Lactococcus lactis cells endowed these bacteria with the abilities to bind P. gingivalis, penetrate dentinal tubules, and promote P. gingivaliscoinvasion of dentin. The results demonstrate that collagen-binding andP. gingivalis-binding properties of antigen I/II polypeptides are discrete functions. Specificity of antigen I/II polypeptide recognition accounts for the ability of P. gingivalis to coinvade dentinal tubules with S. gordonii but not with S. mutans. This provides evidence that the specificity of interbacterial coadhesion may influence directly the etiology of pulpal and periapical diseases.

A Micro CT study of the mesiobuccal root canal morphology of the maxillary first molar tooth

AIM To observe the morphology of the root canal system of the maxillary first molar mesiobuccal root using micro computed tomography and compare it to current canal classifications. METHODOLOGY Twenty mesiobuccal roots were resected from randomly selected extracted human maxillary first molar teeth and prepared for scanning using a SkyScan micro CT scanner (SkyScan 1172 X-ray microtomograph, Antwerp, Belgium) at a slice thickness of 11.6μm. Three-dimensional images were produced and analysed to record the number and configuration of the canals, the presence of accessory canals, connections between the canals and number of canal orifices and foramina. RESULTS The majority of roots had complex root canal systems with a second mesiobuccal canal present in 90% of the roots examined. Intercanal communications were observed in 55% of the roots. A single apical foramen was found in 15% of roots, two foramina were present in 20% and three or more foramina were present in 65%. In half of the roots, there were two orifices at the furcation level; 40% had one orifice and 10% had three orifices. Accessory canals were present in 85% of the roots. Only 60% of root canals could be classified using the classification of Weine et al. (1969) and 70% using the classification of Vertucci (1984). CONCLUSION Micro computed tomography offers an ability to examine root canal anatomy in fine detail and confirms that the morphology of the mesiobuccal root of the maxillary first molar teeth is complex and that present morphology classifications do not fully reflect the complexity.

Regional variation in root dentinal tubule infection by Streptococcus gordonii

The purpose of this study was to investigate the pattern of bacterial invasion of dentinal tubules at different regions in human roots. Specimens were obtained from single-rooted teeth that had their root canals prepared in a standard manner. Roots were then sectioned longitudinally through the canals and the resulting specimens chemically treated to remove the smear layers. Specimens were immersed in a suspension of Streptococcus gordonii for 3 weeks and then prepared for histological analysis. Sections from the cervical, midroot, and apical areas were examined. The pattern of bacterial infection of the cervical and midroot areas was similar, characterized as a heavy infection with bacteria penetrating as deep as 200 microns. Invasion of the apical dentin was significantly different, with a mild infection and maximum penetration of 60 microns.

Dental stem cells and their potential role in apexogenesis and apexification

Injury to an immature permanent tooth may result in cessation of dentine deposition and root maturation leaving an open root apex and thin dentinal walls that are prone to fracture. Endodontic treatment is often complicated and protracted with an uncertain prognosis frequently resulting in premature tooth loss. Postnatal stem cells, which are capable of self-renewal, proliferation and differentiation into multiple specialized cell lineages have been isolated and identified within the dental pulp, apical papilla and periodontal ligament. The ability of these cells to produce pulp-dentine and cementum-periodontal ligament complexes in vivo suggest potential applications involving stem cells, growth factors and scaffolds for apexification or apexogenesis. Similar protein expression amongst dental stem cells possibly implicates a common origin; however, the dominant cells to repopulate an open apex will be directed by local environmental cues. A greater understanding of the structure and function of cells within their environment is necessary to regulate and facilitate cellular differentiation along a certain developmental path with subsequent tissue regeneration. This review focuses on development of the apical tissues, dental stem cells and their possible involvement clinically in closing the open root apex. MEDLINE and EMBASE computer databases were searched up to January 2009. Abstracts of all potentially relevant articles were scanned and their contents identified before retrieval of full articles. A manual search of article reference lists as well as a forward search on selected authors of these articles was undertaken. It appears that dental stem cells have the potential for continued cell division and regeneration to replace dental tissues lost through trauma or disease. Clinical applications using these cells for apexogenesis and apexification will be dependent on a greater understanding of the environment at the immature root end and what stimulates dental stem cells to begin dividing and then express a certain phenotype.

Histopathological profile of surgically removed persistent periapical radiolucent lesions of endodontic origin

AIM To determine the types of periapical lesions associated with root filled teeth with persistent periapical pathosis that required surgical treatment based on specific inclusion and exclusion criteria. METHODOLOGY Periapical lesions from a consecutive clinical sample of 100 patients were examined histopathologically to determine a definitive diagnosis. RESULTS Females were more represented (n = 56), the average age was 46.5 years and there were no age differences between gender or lesion type. A diagnosis of periapical granuloma was the most common finding with a similar number present in females (n = 40) and males (n = 37). A cyst was present in 18% of the cases with a majority of females (n = 12) represented in the sample. Evidence of foreign material, with an appearance consistent with endodontic sealer materials, was seen in 25 periapical granulomas, two cysts and one scar. Two periapical scars were seen, one had a history of apicectomy and amalgam root-end filling while the other was associated with extruded root filling material. CONCLUSIONS By using defined clinical inclusion and exclusion criteria a predictable clinical diagnosis of a persistent periapical lesion due to endodontic origin can be reliably made. Periapical granulomas and cysts were the most common periapical lesions of endodontic origin associated with persistent periapical pathosis with the overall incidence of periapical cysts similar to previous studies. The presence of endodontic material in a high proportion of periapical lesions suggests a cause-effect association with the inference that clinicians should employ canal preparation techniques that limit apical extrusion of material.

Conventional versus Storage Phosphor-Plate Digital Images to Visualize the Root Canal System Contrasted with a Radiopaque Medium

The pulp tissue was removed from 20 mandibular first molar teeth using 2.5% NaOCl irrigation and hand files. The dried canals were infused with radiopaque contrast medium. Standardized conventional and Digora digital images were obtained of each tooth positioned in a dried mandible at 0- and 30-degree horizontal angulations. Three evaluators rated the image clarity of the 0- and 30-degree original, enhanced, three-dimensional, zoom, and reverse digital image modes as superior, equal, or inferior to corresponding 0- and 30-degree conventional radiographs. The ratings were compared using the Wilcoxon signed rank test. The original, three-dimensional, zoom, or reverse digital images were inferior to the conventional radiographs for clarity of canal anatomy. The enhanced digital images were not always inferior to the conventional radiographs and were the only images superior to the original digital images. Overall, evaluators rated the image clarity of root canal anatomy on conventional radiographs better than on Digora images. However, factors in the experimental design may have contributed to this result.

Radiolucent inflammatory jaw lesions: a twenty-year analysis.

AIM To determine the range and demographic and clinical features of radiolucent inflammatory jaw lesions. METHODOLOGY Histopathology reports were reviewed to identify radiolucent jaw lesions. There were no clinical exclusive criteria, and the samples represented a wide range of clinical presentation and treatment history from multiple providers. Data were analysed using SPSS. To evaluate concordance of clinical and histological diagnoses, the clinicians provisional diagnosis was compared with the final histopathological diagnosis. RESULTS A total of 17 038 specimens were reviewed; of these, 4983 (29.2%) were radiolucent jaw lesions, of which inflammatory lesions accounted for 72.8% (n = 3626). Periapical granulomas (59.7%) were the largest group followed by radicular cysts (29.2%). The mean age was 44 years (range 2-100 years), men and women were equally represented and the anterior maxilla was the most common site for the biopsied lesions. A provisional diagnosis was correct for only 48.3% of periapical granulomas and 36% of radicular cysts. CONCLUSIONS This study included all presentations of periapical radiolucent lesions and showed that the incidence of cystic change in periapical lesions of endodontic origin is high at approximately 30% of all inflammatory lesions. Notwithstanding the relative frequencies, demographics and location of radiolucent inflammatory lesions presenting in the New Zealand population are comparable to that of other populations. No inflammatory radiolucent lesion can be reliably accurately diagnosed from clinical presentation and/or radiographic appearance alone.

Dental and maxillofacial skeletal injuries seen at the University of Otago School of Dentistry, New Zealand 2000-2004.

An epidemiological study of dental and facial trauma injuries was performed on patient presentations to the University of Otago School of Dentistry during the period 2000-2004. A total of 1287 patients were seen for dental injuries with 3473 tooth injuries. The mean age was 17.48 +/- 13.13 years (range: 2-86), the highest number of injuries occurred in the 16-25 year group with a male to female ratio of 2.01:1. Uncomplicated crown fractures were the most common injury that required treatment and the variables of age, gender, tooth type, type of injury, cause of injury, location where injury occurred were similar to other studies. Falls, accidental contact, assault and motor vehicle accidents attributed to >60% of the causes of trauma and to more serious injuries. Dental injuries sustained during sporting activities reflected the potential for high impact contact and the pattern of injury suggested that preventative measures had a positive outcome in limiting the number and degree of complexity of injuries. The emergence of skateboard injuries was a feature of this study. Non-sport causes attributed to the majority of facial fractures while rugby union was the most common sport associated with bone fractures. This study shows that dental and facial injury rates and patterns in a New Zealand region are similar to other populations.

Rigidity and retention of ceramic root canal posts.

Ceramic root-canal posts offer potential advantages over other types with respect to aesthetics and biocompatibility. Any post must be sufficiently rigid and retentive to withstand functional forces. Ceraposts (1.2 mm coronal diameter, ceramic, tapering, smooth posts) and Paraposts (1.25 mm, stainless-steel, parallel, serrated posts) were tested for rigidity by means of a three-point bending test. To test retention in roots, ceramic posts were cemented using one of three protocols: (1) glass-ionomer cement, (2) silane coupling agent and resin cement, or (3) sandblasted post surface, silane coupling agent, and resin cement. Stainless-steel posts were cemented with resin. The tensile force required to dislodge the posts, following four weeks of storage in water, was recorded. Data were compared using Students t-test and Mann-Whitney U analysis. Ceraposts were significantly more rigid than Paraposts (p < 0.001). Paraposts cemented with resin were significantly more strongly retained than Ceraposts following any cementation protocol (p < 0.001). Retention of the ceramic posts was significantly greater with a silane coupling agent and resin cement than with glass-ionomer cement (p < 0.001). Sandblasting the ceramic posts produced variable results and needs further investigation before it could be recommended.