Is hard tissue formation in the dental pulp after the death of the primary odontoblasts a regenerative or a reparative process?

OBJECTIVES: Conceptually, two types of tertiary dentine may be produced in response to caries and environmental irritations: "reactionary dentine" that is secreted by existing primary odontoblasts and "reparative dentine", formed after the death of the odontoblasts by proliferation and differentiation of progenitor cells into odontoblast-like cells. Because histologic evidence for tubular dentine generated by newly differentiated odontoblast-like cells is lacking in human teeth, the present study examined pulpal cellular changes associated with caries/restorations, in the presence or absence of pulpal exposures. METHODS: Ninety-six extracted human teeth were histologically processed and serial sectioned for light microscopy: 65 contained untreated enamel/dentine caries; 20 were heavily restored and 11 had carious exposures managed by direct pulp-capping. RESULTS: Sparsely distributed, irregularly arranged dentinal tubules were identified from the tertiary dentine formed in teeth with unexposed medium/deep caries and in restored teeth; those tubules were continuous with the tubules of secondary dentine; in some cases, tubules were absent. The palisade odontoblast layer was reduced to a single layer of flattened cells. In direct pulp-capping of pulp exposures, the defects were repaired by the deposition of an amorphous dystrophic calcified tissue that resembled pulp stones more than dentine, sometimes entrapping pulpal remnants. This atubular hard tissue was lined by fibroblasts and collagen fibrils. CONCLUSIONS: Histological evidence from the present study indicates that reparative dentinogenesis cannot be considered as a regenerative process since the so-formed hard tissue lacks tubular features characteristic of genuine dentine. Rather, this process represents a repair response that produces calcified scar tissues by pulpal fibroblasts. CLINICAL SIGNIFICANCE: Formation of hard tissue in the dental pulp after the death of the primary odontoblasts has often been regarded by clinicians as regeneration of dentine. If the objective of the clinical procedures involved is to induce healing, reduce dentine hypersensitivity, or minimise future bacteria exposure, such procedures may be regarded as clinical success. However, current clinical treatment procedures are not adept at regenerating physiological dentne because the tissues formed in the dental pulp are more likely the result of repair responses via the formation of calcified scar tissues.

A prospective cohort study of endodontic treatments of 1,369 root canals: results after 5 years.

OBJECTIVE: The purpose of this prospective study was: 1) to follow-up a large number of endodontic treatments performed by a single operator, periodically checked over a 5-year period; and 2) to correlate outcome to a number of clinical variables. STUDY DESIGN: This prospective study included all consecutive cases during the selected time period. All cases were followed regularly for a 5-year period. At the 5-year end point of the study, 470 patients with 816 treated teeth and with 1,369 treated root canals were available for evaluation. RESULTS: The overall rate of success among the 816 teeth/1,369 root canals available for evaluation was 88.6%/90.3%. The success rate for 435 teeth/793 root canals undergoing vital pulp therapy was 91.5%/93.1%. Teeth/root canals with necrotic pulp but without detectable periapical bone lesion were successfully treated in 89.5%/92.3%. If the pulp necrosis was complicated by apical periodontitis, the success rate fell to 82.7% for the teeth and 84.1% for the root canals (P = .037). Teeth with periapical lesion <5 mm had a success rate of 86.6%, and in cases where the lesion was ≥ 5 mm the rate of success was 78.2%. CONCLUSIONS: More severe disease conditions negatively affects outcome. An optimal working length was identified. Excess of root canal filling material decreases success. Infected pulp space should be treated with an effective intracanal dressing. The quality of the coronal restoration or the placement of intracanal post retentions does not affect treatment outcome.

Influence of a passive sonic irrigation system on the elimination of bacteria from root canal systems: a clinical study.

INTRODUCTION: The present investigation evaluated the ability of a new passive sonic irrigation (sonic group) system (EndoActivator) to eliminate cultivable bacteria from root canals in vivo and compared it with that of standard syringe irrigation (control group). METHODS: Data were obtained by using bacteriologic sampling of root canals treated by endodontic residents. Sampling results from 1 session of treatment were then compared with results obtained after intervisit calcium hydroxide disinfection and a second session of treatment. RESULTS: There was no significant difference in the ability of sonic group and control group to eliminate cultivable bacteria from root canals (P > .05). A second session and intervisit calcium hydroxide disinfection were able to eliminate cultivable bacteria from significantly more teeth than a single session of treatment (P < .05). CONCLUSIONS: These in vivo results strengthen the case for a multi-visit approach to the treatment of apical periodontitis.

Cytotoxicity evaluation of endosequence root repair material.

OBJECTIVE: The purpose of this study was to evaluate the cytotoxicity of EndoSequence Root Repair Material (Brasseler USA, Savannah, GA) and compare it with gray and white MTA. STUDY DESIGN: Samples of 2 mg freshly mixed or set gray MTA (GMTA), white MTA (WMTA), EndoSequence Root Repair Material (ERRM), and AH26 were eluted with 300, 600, and 1,000 microL cell culture medium for 24 and 72 hours. L929 cells were seeded into 96-well plates at 3 x 10(4) cells/well and incubated with 100 microL elute from each elute group. Cells cultured only with culture medium served as negative control. AH26 was used as positive control. After 24 hours' incubation, cell cytotoxicity was evaluated by MTT assay. Cell viability was calculated as percentage of the control group. The results were analyzed with 1-way analysis of variance. RESULTS: For both set and fresh samples, there were no significant cell viability differences among GMTA, WMTA, and ERRM. Cell viability in the AH26 group was less than in all of the other 3 materials. CONCLUSION: This study suggests that ERRM may have cell viability similar to GMTA and WMTA in both set and fresh conditions.

Wound healing of apical tissues after root canal therapy: a long-term clinical, radiographic, and histopathologic observation study.

OBJECTIVE: The purpose of this study was to evaluate the pulp healing process and the dentin-cementum complex in 51 endodontically treated human teeth after long observation periods and to correlate histologic observations with conventional periapical radiographic findings. STUDY DESIGN: Specimens were obtained from the extraction of 77 treated teeth, which were deemed to be unrestorable, with no evidence of periapical bone lesion at the follow-up. After stringent evaluation of the radiographs, 51 cases that 3 independent evaluators assessed as having normal periapical conditions were selected. The specimens were histologically evaluated using serial sections. RESULTS: In the majority of the cases, complete healing was observed, with no signs of acute or chronic inflammatory processes in the remaining apical tissue or periodontal tissue fragments. Some cases showed moderate inflammation in the root canal tissue. Narrowing of the apical root canal by cementum was a common finding in most cases, but total closure was not observed. Debris intermixed with necrotic tissue and sealer particles was a common finding in the pulp stump. Bacteria were present in the coronal portion of the root in almost all cases, but in only 1 case could bacteria be demonstrated in the coronal and apical portions of the root. CONCLUSIONS: Apical tissue of properly treated teeth with no signs of periapical changes is only rarely significantly inflamed. When the tissue is inflamed, microbial causes can always be demonstrated. Despite the presence of microorganisms coronally in nearly all cases, apical tissue is seldom affected.

Chronologic comparison of root dentin moisture in extracted human teeth stored in formalin, sodium azide, and distilled water.

This study quantified in vitro the root dentin moisture when 10% formalin (group A), 3% sodium azide (group B), and distilled water (group C) were used as teeth storage media. The root dentin moisture of 66 extracted human mandibular single-rooted teeth was measured at baseline (day 0) and at 1, 3, 7, and 14 days using a digital grain moisture meter. The baseline dentin moisture value was used as covariate in the generalized estimating equation (GEE) analysis. The mean dentin moisture values (%) +/- SD on days 0, 1, 3, 7, and 14 were, respectively: 10.6 +/- 0.64, 14.3 +/- 0.71, 14.6 +/- 0.84, 14.4 +/- 0.64, and 14.7 +/- 0.75 in group A; 11.4 +/- 0.94, 14.6 +/- 0.95, 14.6 +/- 0.76, 14.6 +/- 0.93, and 14.8 +/- 0.81 in group B; and 10.2 +/- 0.95, 12.8 +/- 0.90, 13.3 +/- 0.95, 13.0 +/- 0.91, and 13.2 +/- 0.89 in group C. The dentin moisture increased in all 3 groups; however, there was no overall significant difference in moisture between the formalin and sodium azide groups.

Root dentin body moisture changes caused by ascorbic acid.

OBJECTIVES: To quantify in vitro the root dentin moisture (DM) when soaked in 10% ascorbic acid solution (Group A) and distilled water (Group B) for up to 14 days. METHODS: Forty-four extracted human mandibular single-rooted teeth were sectioned perpendicular to the long axis at the CEJ to access the root dentin. The samples were divided into Groups A and B. Baseline (day 0) DM was measured using a digital grain moisture meter. One sample was placed in each tube, which was then filled with solution. All tubes were kept at 37 degrees C and 100% humidity. DM was measured after 1, 3, 7, and 14 days. The baseline DM value was used as a covariate in the generalized estimating equation (GEE) analysis to account for the difference in the baseline DM between the two groups. RESULTS: The mean DM (%) values+/-standard deviation on days 0, 1, 3, 7, and 14 were 11.4+/-1.08, 17.1+/-0.87, 18.2+/-0.76, 18.4+/-0.77, and 17.9+/-0.90 in Group A, and 10.2+/-0.95, 12.8+/-0.90, 13.3+/-0.95, 13.0+/-0.91, and 13.2+/-0.89 in Group B, respectively. Group A had significantly higher baseline DM than Group B (p=0.006). After adjusting for differences in the baseline, the GEE analysis indicated that, on average, Group A had a significantly higher increase in DM than Group B, with means+/-standard deviation of 4.35+/-0.26. CONCLUSIONS: The moisture increase in the ascorbic acid group was greater than that in the distilled water group. Soaking root dentin in the unreplenished ascorbic acid solution or distilled water beyond 3 days did not further increase DM.

A rapid nondestructive method for root dentin moisture measurements: in vitro pilot study.

Dentin moisture content is important in adhesive bonding and structural strength research; however, there is no rapid method available to assess dentin moisture without sample destruction. This study examined the use of a digital grain moisture meter to measure root dentin moisture in vitro. Extracted mandibular single-rooted teeth were sectioned at the CEJ. The moisture of the root dentin was measured at 6 measuring modes for different grains and repeated 5 times. Dentin weight changes before and after drying were measured to obtain control values. The control values were compared with machine readings. In conclusion, (1) each nondestructive measurement took less than 30 seconds, (2) 24 hours of storage at 37 degrees C and 100% humidity did not restore dentin moisture, and (3) 5 grain modes had a high validity and could be used for dentin moisture measurements.

Particle size and shape of calcium hydroxide.

The aim of this study was to examine the particle length, width, perimeter, and aspect ratio of calcium hydroxide powder using a flow particle image analyzer (FPIA). Five sample groups each with 10 mg of calcium hydroxide were mixed with 15 mL of alcohol and sonicated. Digital images of the particle samples were taken using the FPIA and analyzed with a one-way analysis of variance. The overall averages +/- standard deviation among the five groups for particle length (microm), width (microm), perimeter (microm), and aspect ratio were 2.255 +/- 1.994, 1.620 +/- 1.464, 6.699 +/- 5.598, and 0.737 +/- 0.149, respectively. No statistical significance was observed among the groups for all parameters. When the total of 46,818 particles from all five groups were classified into the five length categories of 0.5-microm increments, there were significant differences in width, perimeter, and aspect ratio (all p values <0.0001). In conclusion, calcium hydroxide particles have a size and shape that may allow direct penetration into open dentin tubules.

Stimulation of cytokines in osteoblasts cultured on enamel matrix derivative.

OBJECTIVE: The purpose of this study was to evaluate the influence of enamel matrix derivative (EMD) on the release of transforming growth factor beta 1 (TGF-beta1), interleukin-6 (IL-6), insulin-like growth factor I (IGF-I), bone morphogenetic protein 2 (BMP-2), and osteoprotegerin (OPG) in human and mouse osteoblasts. STUDY DESIGN: Human MG-63 and mouse MC3T3-E1 cells were seeded onto 6-well culture plates at an initial density of 5,000/cm(2) and grown in Dulbecco's eagle medium (DMEM) with 10% fetal bovine serum for 24 h. Then cells were cultured either with 100 microg/mL EMD added to DMEM or with DMEM only. After 2, 5, and 9 days' incubation the culture medium was collected and analyzed by enzyme-linked immunosorbent analysis. Data were analyzed using Student t test. RESULTS: The EMD treatment significantly increased the production of IL-6 and TGF-beta1 (P < .05) at all time points. The release of OPG was also increased in mouse osteoblasts (P < .05). IGF-I and BMP-2 were not detected in both control and EMD-treated groups. CONCLUSION: This study suggests that the stimulatory effects of EMD on tissue regeneration are mediated by the up-regulation of local mediators released by osteoblasts.

Particle size and shape analysis of MTA finer fractions using Portland cement.

The aim of this study was to observe particle length, width, perimeter, and aspect ratio of mineral trioxide aggregate finer fractions using Portland cement. The High Power Field mode of the flow particle image analyzer was used for analysis. Images of particle samples were automatically collected by the analyzer along with analysis parameters. Mean, standard deviation, and the number of particles were calculated in each group. Parameters of length, width, and perimeter did not show a statistical significance when groups were compared. Examining the parameter of aspect ratio, there was evidence of a statistical significance seen (p<0.05). The cumulative percentage of particles that were between 0.5 and 3 microm in size was 88%. Fine particles may penetrate dentin tubules. The average aspect ratio was 0.744 (SD=0.155). It can be speculated that a dentin tubule occlusion pattern is dependent on the aspect ratio.

Application of small interfering RNA for inhibition of lipopolysaccharide-induced osteoclast formation and cytokine stimulation.

RNA interference (RNAi) is a unique and powerful tool used for the study of gene function by suppressing its expression. Nuclear factor of activated T cells (NFATc1) is the most strongly induced transcription factor mediated by receptor activator for nuclear factor kappa B ligand stimulation and has shown to be a key regulator of osteoclastogenesis. To determine the application of small interfering RNA (siRNA) for inhibition of lipopolysaccharide (LPS)-induced cytokine stimulation and osteoclast formation, murine monocyte, RAW 264.7 cells as well as differentiated osteoclasts were transfected with NFATc1-specific siRNA and then stimulated with 100 ng/mL LPS. By using real-time polymerase chain reaction analysis and enzyme-linked immunosorbent assay, we confirmed that monocytes whose NFATc1 protein expression was silenced by using RNAi produced lower levels of inflammatory cytokines, fewer numbers evolved into mature osteoclasts, and osteoclasts expressed lower levels of osteoclast-specific gene markers such as tartrate-resistant acid phosphatase and cathepsin K. These results suggested that RNAi could be used to modulate the effects of LPS stimulation.

Comparative analysis of the particle size and shape of commercially available mineral trioxide aggregates and Portland cement: a study with a flow particle image analyzer.

The aim of this study is to characterize the particle size distribution and circularity of various Mineral Trioxide Aggregates (MTA) (ProRoot MTA/ MTA Angelus/Gray and White) and Portland cements with effective size ranges of 1.5-160 microm using a flow particle analyzer (Sysmex FPIA-3000, Kobe, Japan). Cumulative percentage of particles between 6 and 10 microm were, 65, 73, 48, 53, and 70 %, for Gray ProRoot MTA, White ProRoot MTA, Gray MTA Angelus, White MTA Angelus, and Portland cement, respectively. ProRoot MTA contains fewer large particles than MTA Angelus. MTA Angelus contains a higher number of small particles than ProRoot MTA. White MTA contains smaller particles with a narrower range of size distribution than Gray MTA. MTA Angelus particles have relatively low circularity and wide size distribution and are less homogeneous than ProRoot MTA.

Endodontic treatment outcome: effect of the permanent restoration.

OBJECTIVE: To investigate the relationship between the presence of the coronal restoration and endodontic treatment success or failure. METHODS: This study comprised 200 endodontically treated teeth with 441 roots. Follow-up examination was conducted 4 +/- 0.5 years after completion of endodontic treatment. Outcome criteria were modified from Strindberg. RESULTS: Teeth/roots restored with permanent coronal restoration (casting or filling) had a higher success rate (80%) than teeth/roots not restored (60%; P < .01) in the analysis of aggregate data. However, the results of stratified analysis on key confounding factor (preoperative periapical diagnosis) showed that there is no significant association between the presence of permanent restoration and endodontic outcome. Teeth with preoperative apical periodontitis were less likely to be restored with a crown (23.9%) than teeth without apical periodontitis (76.1%; P < .01). Anterior teeth were more likely to be restored with a filling and sooner than the posterior teeth. These associations suggest a treatment selection bias. CONCLUSIONS: Stratified analysis on the key confounding factor reveals that endodontic outcome is driven by the presence of preoperative root canal infection (apical periodontitis). Lack of stratification on key confounding factors inaccurately suggests that presence of permanent restoration contributes to the success of endodontic treatment in the aggregate analysis of grouped data. The choice to restore the tooth as well as the choice and timing of permanent restoration may be the result of a bias in treatment selection. Stratified analysis on key confounding factors is the key to valid analysis and accurate results.