The Application of Tissue Engineering to Regeneration of Pulp and Dentin in Endodontics
Misako Nakashima, PhD, DDS, and Akifumi Akamine, PhD, DDS
Caries, pulpitis, and apical periodontitis increase health care costs and attendant loss of economic productivity. They ultimately result in premature tooth loss and therefore diminishing the quality of life. Advances in vital pulp therapy with pulp stem/progenitor cells might give impetus to regenerate dentin-pulp complex without the removal of the whole pulp. Tissue engineering is the science of design and manufacture of new tissues to replace lost parts because of diseases including cancer and trauma. The three key ingredients for tissue engineering are signals for morphogenesis, stem cells for responding to morphogens and the scaffold of extracellular matrix. In preclinical studies cell therapy and gene therapy have been developed for many tissues and organs such as bone, heart, liver, and kidney as a means of delivering growth factors, cytokines, or morphogens with stem/progenitor cells in a scaffold to the sites of tissue injury to accelerate and/or induce a natural biological regeneration. The pulp tissue contains stem/progenitor cells that potentially differentiate into odontoblasts in response to bone morphogenetic proteins (BMPs). There are two strategies to regenerate dentin. First, is in vivo therapy, where BMP proteins or BMP genes are directly applied to the exposed or amputated pulp. Second is ex vivo therapy and consists of isolation of stem/progenitor cells from pulp tissue, differentiation into odontoblasts with recombinant BMPs or BMP genes and finally transplanted autogenously to regenerate dentin. This review is focused on the recent progress in this area and discusses the barriers and challenges for clinical utility in endodontics.
Dynamic Finite Element Analysis of the Human Maxillary Incisor Under Impact Loading in Various Directions
Haw-Ming Huang, MS, Keng-Liang Ou, PhD, Wei-Nang Wang, DDS, Wen-Ta Chiu, MD, PhD, Che-Tong Lin, DDS, PhD, and Sheng-Yang Lee, DDS, PhD
The aim of this study was to investigate fracture patterns occurring when a human upper central incisor is subjected to impact loadings at various angles. A two dimensional finite element (FE) model of the maxillary incisor and surrounding tissues was established. The structural damping factor for the tooth was then calculated and assigned to the model. Dynamic FE analysis was performed to stimulate the associated impacts. Time-dependent traumatic forces at 0°, 45°, and 90° labially to the long axis of the tooth were applied to the model. Von Mises’s equivalent stress contours within the FE models were calculated. Our results indicated that tooth damping lagged behind peak stress by 0.05 ms. In addition, we found that impact direction played an important role in terms of outcome for the fractured incisor. These results can, in part, explain the mechanisms underlying the alternative outcomes when upper incisors are subjected to impact.
Searching for Archaea in Infections of Endodontic Origin
J.F. Siqueira, Jr., DDS, PhD, I.N. Rôças, DDS, PhD, J.C. Baumgartner, DDS, PhD, and T. Xia, DDS
Archaeais a highly diverse group of prokaryotes, whose members have been traditionally recognized as extremophiles. Recently, some of these microorganisms have also been found to thrive in nonextreme environments, including the human body. Methanogenic archaea have been detected in samples from subgingival plaque associated with periodontal disease and a pathogenetic role is suspected. The purpose of this study was to survey samples taken from different types of endodontic infections for the presence of archaea. Samples were taken from untreated and treated root canals associated with asymptomatic chronic periradicular lesions as well as from cases diagnosed as acute periradicular abscesses. Overall, 96 samples were obtained. DNA from samples was extracted by using two different protocols and used as template for polymerase chain reaction amplification using oligonucleotide universal primers for the domains Archaea or Bacteria. Samples were also checked for the presence of spirochetes by making use of a group-specific primer. While bacteria were present in all samples, no case yielded archaeal DNA. Spirochetes occurred in a high number of cases. Our findings suggested that members of the Archaea domain are not members of the microbiota present in different types of endodontic infections and thereby may not be implicated in the etiology of apical periodontitis.
Bisphosphonate-Associated Osteonecrosis of the Jaws and Endodontic Treatment: Two Case Reports
Aaron P. Sarathy, DMD, Sidney L. Bourgeois, Jr., DDS, and Gary G. Goodell, DDS, MS, MA
Bisphosphonates are commonly used in the management of bone diseases, such as osteoporosis and Paget’s disease, and to prevent bone complications and to treat malignant hypercalcemia in certain types of cancer. Although this class of drugs has clear evidence of medical efficacy, there are an increasing number of reports of bisphosphonate-associated osteonecrosis of the jaws that have substantial implications for the patient and for the treating dentist. This case report reviews proposed possible mechanisms of bisphosphonate-associated osteonecrosis of the jaws and describes two case reports where nonsurgical and surgical root canal treatments were precipitating factors. Recommendations for prevention and treatment of the disease follow. Thorough history taking and timely consultation with the patient’s oral surgeon and oncologist are emphasized.
Cytotoxicity of Direct Current with Antibacterial Agents against Host Cells In Vitro
Yuko Nakamura, DDS, Keiso Takahashi, DDS, PhD, Akiko Shimetani, DDS,Hiroshi Sakagami, PhD, and Hirofumi Nishikawa, DDS, PhD
The purpose of this study was to investigate the cytotoxicity of iontophoresis treatment using direct current (DC) with or without antibacterial agents. The following antibacterial agents were used: diamine silver fluoride (AgF); sodium fluoride (NaF); and iodine zinc iodide (JJZ). The cytotoxic activity of DC with or without antibacterial agents against human polymorphonuclear cells (PMNs) was evaluated by the 3-[4, 5- dimethylthiazol- 2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. It was noted that DC (2 mA) killed PMNs in a time-dependent manner and the cytotoxicity was enhanced when DC was combined with antibacterial agents. The toxic effect of antibacterial agents was in the order: AgF > JJZ > NaF. The death of PMNs by DC was evaluated by flow cytometry using annexin V-FITC/ propidium iodide staining. DC appeared to induce necrosis rather than apoptosis of PMNs. These results suggest that iontophoresis treatment using DC and antibacterial agents may induce necrotic cytotoxicity in host cells around periapical lesions.
The Influence of Preparation Size on the Mechanical Efficacy of Root Canal Irrigation In Vitro
Kenneth W. Falk, DDS, and Christine M. Sedgley, PhD
This study tested the hypothesis that the mechanical efficacy of irrigation in reducing intracanal bacteria is dependent on canal preparation size. Root canals of 30 extracted permanent cuspids were prepared consecutively to sizes 36, 60, and 77 at working length (WL) using ProFile 0.04 taper Series-29 files. Smear layer was removed and teeth autoclaved following completion of each instrumentation sequence. Root canals were inoculated with a 15-_l suspension (1 × 106 cells) of Pseudomonas fluorescens 5RL, a salicylate-inducible bioluminescent reporter strain. Bioluminescence was measured before inoculation (background), after inoculation and after irrigation with 6 ml of irrigant delivered 1 mm from WL using a 28G safety-ended needle. The percentage of bacteria remaining following irrigation was 26.95 ± 9.71%, 10.46 ± 5.87%, and 10.64 ± 6.01% for sizes 36, 60, and 77, respectively (p < 0.001; repeated-measures ANOVA), with no difference between sizes 60 and 77 (p > 0.05; Tukeys). Irrigation 1 mm from WL was significantly less effective in canals prepared to size 36.
Structural Effects of Sodium Hypochlorite Solutions on Gutta-Percha Cones: Atomic Force Microscopy Study
Caroline R. A. Valois, MSc, Luciano P. Silva, PhD, and Ricardo B. Azevedo, PhD
Atomic force microscope (AFM) is a well-established methodology for structural characterization of materials. The purpose of this study was to investigate the effects of sodium hypochlorite (NaOCl) solutions on gutta-percha cone structure using AFM. Three standardized gutta-percha cones were cut 3 mm from the tip, attached to a glass base and immersed in 0.5, 2.5, or 5.25% NaOCl solutions. After 1 and 5 min the samples were positioned in the atomic force microscope. The analyses were performed on twelve different points ( n= 12) located between 1 and 2 mm from the tip after each period of immersion in NaOCl. Guttapercha cone without any NaOCl treatment were used as control. Root mean square (RMS) parameters for contact mode imaging and force modulation microscopy variations were measured. The differences between RMS values were tested by ANOVA with Fisher’s protected
LSD test for multiple comparisons (p < 0.05). Aggressive deteriorative effects on gutta-percha cone elasticity were observed for 5.25% NaOCl at 1 min when compared to the control (p < 0.05). In addition, 2.5% and 5.25% NaOCl solutions caused topographic changes after 5 min when compared to the control (p < 0.05). Conversely, 0.5% NaOCl solution did not cause any alteration on topography or elasticity of gutta-percha cone structure when compared to the control (p < 0.05). Thus, 0.5% NaOCl solution is a safe alternative for rapid decontamination of gutta-percha cones.
In Vitro Evaluation of the Cytotoxic Effects of Acid Solutions Used as Canal Irrigants
C. F. Malheiros, MDS, M. M. Marques, MDS, DDS, and G. Gavini, MDS, DDS
Solutions of EDTA and citric acid have been used as canal irrigants. These substances must be compatible with apical periodontal tissue. The aim of this study was to evaluate comparatively the cytotoxicity of a 17% EDTA solution and that of three solutions with different concentrations of citric acid (10, 15, and 25%) on cultured fibroblasts. The solutions were diluted to 0.1% and 0.5% in culture medium and then applied to NIH 3T3 cells. After 0, 6, 12, and 24 h (short-term assay; viability) and 1, 3, 5, and 7 days (long-term assay; survival), the cells were counted. The data were compared by ANOVA. In the short-term experiments, all solutions presented a percentage of cell viability similar to that of control cells, except for the 17% EDTA solution diluted to 0.5%. After the long-term assay, all groups presented a continuous and progressive cell growth except for the 17% EDTA solution and for the 25% citric acid solution at a 0.5% dilution. The citric acid solution did not impair cell growth and viability, proving to be noncytotoxic in vitro.
Susceptibility of a Polycaprolactone-Based Root Canal Filling Material to Degradation. II. Gravimetric Evaluation of Enzymatic Hydrolysis
Franklin R. Tay, BDSc (Hons), PhD, David H. Pashley, DMD, PhD, Cynthia K.Y. Yiu, BDS, MDS, Joyce Y.Y. Yau, BSc, MSc, Mak Yiu-fai, BDS, MDS, Robert J. Loushine, DDS, R. Norman Weller, DMD, MS, W. Frank Kimbrough, DDS, MS, and Nigel M. King, BDS, MSc, PhD
Polycaprolactone is susceptible to enzymatic biodegradation via ester bond cleavage. This study examined the susceptibility of Resilon, a polycaprolactone-based root filling material to enzymatic hydrolysis. Resilon, gutta-percha, and polycaprolactone disks, prepared by compression molding, were incubated in phosphatebuffered saline, lipase PS or cholesterol esterase at 37°C for 96 h. They were retrieved at different time intervals for gravimetric analysis and scanning electron microscopy. The materials exhibited slight weight gains when incubated in phosphate-buffered saline that can be attributed to water sorption. Gutta-percha showed similar weight gains in the two enzymes. Conversely, Resilon and polycaprolactone exhibited extensive surface thinning and weight losses after incubation in lipase PS and cholesterol esterase. Glass filler particles in Resilon were exposed following surface dissolution of the polymer matrix, creating rough surface topography. Biodegradation of Resilon by bacterial and salivary enzymes warrants further investigation of their activities using cultures of endodontically relevant microbes and human saliva extracts.
The Role of Endothelial Nitric Oxide in the Substance P Induced Vasodilation in Bovine Dental Pulp
Bekir Karabucak, DMD, MS, Helmut Walsch, DDS, MS, Yi-Tai Jou, DDS, DMD, Shlomoh Simchon, PhD, and Syngcuk Kim, DDS, PhD
Vasodilation, an important response in neurogenic inflammation, involves release of Substance P (SP) from the sensory nerve endings. It is now well known that SP causes edema formation and vascular relaxation in nondental tissues, however, the SP vasodilatory mechanism in the dental pulp is not completely understood. Endothelium-dependent relaxation is mediated by nitric oxide (NO) release with consecutive intracellular cyclic-GMP elevation in many vascular preparations. Recently, it has been shown in different vascular systems that SP-induced vasodilation is mediated by cyclic-GMP production through different pathways involving endothelial NO or direct endothelial-independent pathways. In the present study, the role of endothelial NO in SP induced vasodilation in the dental pulp was investigated to better understand the inflammatory mechanisms. Freshly extracted bovine dental pulp was used to measure NO production. Sodium nitroprusside (SNP), L-NAME and SP were utilized to induce and to inhibit NO production in endothelial cells. Released NO byproducts were measured with chemiluminescence assay technique. The present data demonstrate that SP induces NO production by activating NOsynthase (NOS) in endothelial cells. The NOS inhibitor L-NAME blocks NO production completely. In conclusion, in the bovine dental pulp, SP-induced vascular relaxation can be mediated by inducing NOS, and subsequently NO production in endothelial cells.
C-Reactive Protein and Serum Amyloid A in a Canine Model of Chronic Apical Periodontitis
Thomas M. Buttke, PhD, DDS, Guy Shipper, BDS, MDent, MS, E. Olutayo Delano, DDS, MS, and Martin Trope, DMD
Increased levels of systemic inflammatory markers have been observed in patients with chronic dental diseases, such as marginal periodontitis. A canine model was used to determine if a systemic inflammatory response was evident during chronic apical periodontitis (CAP). Dental pulps in 10 dogs were exposed and infected with dental plaque to induce CAP. Blood samples were drawn preoperatively and postinfection when CAP was seen radiographically. In three of the 10 dogs, an intravenous challenge of Porphyromonas gingivalis A7436 was given subsequent to the development of CAP. An ELISA assay was used to measure the levels of C-reactive protein (CRP) and serum amyloid A (SAA) as markers of systemic inflammation. During CAP the levels of CRP and SAA were not statistically different from the preoperative values as determined by the Friedman test (p < 0.05). One dog, which had an unplanned trauma-induced laceration of the paw 2 days before blood sampling, showed a 40-fold increase in CRP. The 3 dogs challenged by intravenous P. gingivalis A7436 showed elevated levels of CRP, consistent with an acute phase response. These data demonstrate that the canine model provides a useful means for studying the systemic effects of apical periodontitis, and show that CAP is not associated with elevated CRP or SAA.
Comparison of Apical Leakage Between Immediate Versus Delayed Post Space Preparation Using AH Plus Sealer
Fernando Solano, DDS, Gary Hartwell, DDS, MS, and Craig Appelstein, DMD
The purpose of this study was to compare the effect of immediate versus delayed post space preparation on the apical seal using AH Plus sealer. Forty-six single rooted anterior extracted teeth were instrumented and divided into four groups. Twenty teeth in groups 1 and 2 and three teeth in groups 3 and 4. In groups 1 and 2, each canal was obturated using warm vertical compaction and AH Plus sealer. In group 1 the post space was made immediately at the time of obturation and in group 2 the post space was made after placing the teeth in saline at 37°C for 1 wk. Group 3 and 4 represented positive and negative control groups, respectively. The teeth were placed in India ink for 72 h. The teeth were sectioned and the amount of apical dye migration was measured. Significant differences were
found between teeth whose post spaces are prepared at the time of obturation versus 1 wk later using warm vertical condensation and AH Plus sealer.
Inferior Alveolar Nerve Caused by a Radicular Cyst
Yoshiki Hamada, DDS, PhD, Hiroyuki Yamada, DDS, Akiko Hamada, DDS, Toshirou Kondoh, DMD, PhD, Mami Suzuki, DDS, Kazuhide Noguchi, DDS, Ko Ito, DDS, and Kanichi Seto, DDS, PhD
The inferior alveolar nerve is sometimes affected by periapical pathoses and mandibular cysts. However, mandibular intraosseous lesions have not been reported to disturb the lingual nerve. A case of simultaneous paresthesia of the right lingual nerve and the right inferior alveolar nerve is presented. The possible mechanisms of this extremely uncommon condition are discussed.