Relationship between number of proximal contacts and survival of root canal treated teeth

AIM

The present study tested the hypothesis that having two proximal contacts (PCs) at access is associated with improved survival of root canal treated (RCT) teeth, controlling for important presenting conditions, endodontic variables and restorative factors.

METHODOLOGY

A treatment database at the University of Iowa College of Dentistry was used to identify permanent teeth undergoing obturation between 1 July 1985 and 31 December 1987. The list was restricted to teeth of patients with at least one dental visit in each two-year interval from 1985 to 1996, and a simple random sample of 280 patients (n = 400 teeth) was selected. Dental charts, radiographs, and computerized databases were examined to ascertain variables of interest and to verify study inclusion criteria. Kaplan-Meier survival estimates were generated for the 221 teeth satisfying study inclusion criteria. Multivariate Cox models were developed, with standard errors adjusted to account for clustering of teeth within patients.

RESULTS

The final Cox model showed that teeth with < or =1 PC at access were lost at a rate three times that of teeth with 2 PCs (hazard ratio = 3.1; 95% confidence interval = 1.9-5.1), controlling for tooth type, presence of radiographic caries at access, and presence of a crown before or after obturation.

CONCLUSIONS

Because RCT teeth with two PCs at access experienced substantially better survival than teeth with fewer than two PCs, the influence of PCs on prognosis should be recognized during treatment planning. Future research should employ prospective study designs, capture additional variables, and provide data to support endodontic treatment decisions.

In vitro longitudinal assessment of coronal discoloration from endodontic sealers

A major cause of tooth discoloration may be sealer remnants in the chamber. The objective of this study was to evaluate, longitudinally, coronal discoloration from four sealers. Extracted premolars were sectioned in the coronal third of the root. The chamber contents were removed and instrumentation was via the canal. The following sealers were bulk introduced into the chamber: AH26, Kerr Pulp Canal Sealer, Roths 801 (nonstaining), and Sealapex. The apical access was sealed with white sticky wax. Teeth were maintained in a moist environment at 37 degrees C. Initial (immediate pretreatment) digital images of the teeth were made for base line comparison. Subsequent images were at 1-, 3-, 9-, and 12-month intervals. Then images were mixed and descriptively evaluated blindly by trained evaluators. Discoloration was induced by the four sealers, with slight to moderate visible changes that increased through 12 months. There was slightly more discoloration with AH26 and Kerr Pulp Canal Sealer. In conclusion discoloration induced by the endodontic sealers produced slight to moderate and generally progressive discoloration over 12 months.

Apical terminus location of root canal treatment procedures

The apical termination of root canal treatment is considered an important factor in treatment success. The exact impact of termination is somewhat uncertain; most publications on outcomes are based on retrospective findings. After vital pulpectomy, the best success rate has been reported when the procedures terminated 2 to 3 mm short of the radiographic apex. With pulpal necrosis, bacteria and their byproducts, as well as infected dentinal debris may remain in the most apical portion of the canal; these irritants may jeopardize apical healing. In these cases, better success was achieved when the procedures terminated at or within 2 mm of the radiographic apex (0 to 2 mm). When the therapeutic procedures were shorter than 2 mm from or past the radiographic apex, the success rate for infected canals was approximately 20% lower than that when the procedures terminated at 0 to 2 mm. Clinical determination of apical canal anatomy is difficult. An apical constriction is often absent. Based on biologic and clinical principles, instrumentation and obturation should not extend beyond the apical foramen.

Scanning electron microscopy and histologic analysis of an apexification "cap": a case report

A maxillary permanent central incisor with a history of trauma, apexification, and internal thermocatalytic bleaching sustained a horizontal fracture at the cementoenamel junction, which necessitated extraction of the tooth. After removal, the root apex was examined histologically and by scanning electron microscopy. An apexification "cap" with unusual anatomic character and structure was observed.

Endodontic considerations in the geriatric patient

Endodontic needs of today's and tomorrow's growing older adult population present increasing challenges for dental care providers. Biologic and anatomic differences in the dental tissues between older and younger patients must be understood and considered in treatment planning and performance for appropriate endodontic procedures. These differences generally do not contraindicate treatment, which, when performed correctly, will be successful in the elderly patient.

Scanning electron microscope study comparing four root canal preparation techniques in small curved canals

Various instrumentation techniques have been proposed and examined with conflicting results. They include hand and ultrasonic techniques and combinations of the two. In the present study we assessed the effectiveness of four preparation methods for cleaning small, curved root canals, using backscattered-imaging scanning electron microscopy (SEM). The methods were: (i) step-back without initial coronal flaring; (ii) step-back with coronal flaring; (iii) step-back with initial coronal flaring and finished by ultrasonic irrigation; and (iv) ultrasonics only. Eighty freshly extracted maxillary and mandibular molars were randomly placed into four treatment groups of 20 teeth each. After preparation, roots were sectioned longitudinally and examined wet by SEM. Each canal was qualitatively evaluated and the groups compared for removal of debris and smear layer, both overall and at each level (apical, middle and coronal). There were no statistically significant differences between the techniques, either overall or within any of the regions. When comparing regions (regardless of technique) the middle level was cleaner than the apical or coronal levels. In conclusion, efficacy differed little among the techniques; none of them completely removed smear layer and all left debris.

Coronal leakage of mixed anaerobic bacteria after obturation and post space preparation

OBJECTIVES

The purpose of this study was to assess bacterial leakage of a mixed anaerobic community of organisms in obturated canals after post space preparation.

STUDY DESIGN

A mixed microbial community of strict anaerobic organisms (F. nucleatum, P. micros and C. rectus) was developed. With the use of an in vitro model system, coronal leakage was assessed in 40 anterior teeth after obturation and post space preparation. The specific leakage time in days for each organism to penetrate through the obturating material was determined. In addition, colonization of the apical canal space was assessed by scanning electron microscope after longitudinal splitting of randomly selected specimens.

RESULTS

Eighty percent of the teeth demonstrated coronal leakage of F. nucleatum and C. rectus by the 90 day interval. Bacterial penetration occurred from 48 days to 84 days. Scanning electron microscope examination showed a heterogeneous biofilm of coccal and bacillary species colonizing the apical portion of the canal wall.

CONCLUSIONS

This study demonstrated that coronal leakage phenomena do occur after loss of coronal seals. The model system developed using mixed, anaerobic bacterial cultures is more clinically relevant and may be used to assess bacterial penetration through gutta percha obturation.

Neonatal male circumcision after delisting in Ontario. Survey of new parents

OBJECTIVE

To determine the prevalence of neonatal circumcision immediately following delisting of the procedure in Ontario and to examine parents' knowledge, attitudes, and behaviours regarding circumcision.

DESIGN

Cross-sectional survey.

SETTING

Perinatal tertiary care centre in southwestern Ontario.

PARTICIPANTS

Of the 151 mothers approached, three were excluded because they did not speak English and two declined participation; 112 of 146 mothers of healthy male newborns responded for a response rate of 77%.

MAIN OUTCOME MEASURES

Circumcision status of infant and parents' knowledge, attitudes, and behaviour.

RESULTS

The circumcision rate before delisting had been 56.2%; in the months immediately after, the rate was 59.8% (95% confidence interval was 51%, 69%). Mothers of infants in the outcome groups did not differ significantly in any demographic feature other than education, where the group deciding against circumcision reported higher education levels (Wilcoxon nonparametic two-sample test: zeta = 2.29, P = 0.02). Mothers who chose circumcision listed medical (59%) and sociocultural considerations (40%) a most important to their decision. Father's circumcision status was strongly associated with the infant's (chi 2[df 1] = 25.13, P = 0.0001). Although 74% discussed circumcision with their family physicians, many parents were not well informed about risks or benefits. Anesthetic use during circumcision was reported by 29%, but 48% did not know whether any had been used.

CONCLUSIONS

The prevalence of neonatal circumcision did not change after delisting. Informed consent was often lacking. Sociocultural issues are important to some parents and need to be addressed in the consultation process.

Instrument deterioration with usage: nickel-titanium versus stainless steel

Nickel-titanium instruments purportedly resist deformation and loss of sharpness better than do stainless steel instruments but may be more susceptible to breakage. The processes of wear and breakage of nickel-titanium and stainless steel instruments were examined. Sixty files of five types (12 each) and three manufacturers were used. All were used repeatedly in curved canals until failure or for a maximum of 22 minutes. Each instrument was examined with scanning electron microscopy both new (control) and at spaced intervals for evidence of wear and fatigue. All new instruments were of good quality. Stainless steel instrument tended to wear the most rapidly, and next were nickel-titanium rotary instruments; the most resistant to wear were nickel-titanium hand instruments. There were few instrument separations. In general, nickel-titanium (particularly hand) instruments resisted deterioration better than did stainless steel. Nickel-titanium rotary instruments (2 of 12) had the most breakage.

Radiographic and histologic periapical findings of root canal treated teeth in cadaver

The success of root canal treatment can be subjectively evaluated both clinically and radiographically. Normally, the recall radiograph is the main factor in evaluating success or failure.

OBJECTIVES

This study evaluated periapical areas of root canal treated teeth by correlating radiographic and histologic findings.

STUDY DESIGN

Jaws were resected from cadavers and radiographed. Those teeth that had received root canal treatment were evaluated for success or failure based on radiographic criteria. Teeth and surrounding bone were then removed en bloc and prepared for light microscopy. Untreated teeth without periapical pathosis were examined as controls.

RESULTS

Root canal treated teeth classified as failures were found to consistently have inflammatory resorptive lesions at the periapices. In contrast, those treated teeth classified as radiographically successful showed varying reactions ranging from normal uninflamed to mildly inflamed.

CONCLUSIONS

Those classified as failure showed consistent inflammation. However, the majority of our examined treated teeth were radiographically normal and exhibited no periapical inflammation.

Canal debridement: effectiveness of sodium hypochlorite and calcium hydroxide as medicaments

The action of chemicals such as calcium hydroxide (Ca(OH)2) and sodium hypochlorite (NaOCl) that are used as tissue solvents may be enhanced by prolonged contact. The objective of this study was to determine if sealing Ca(OH)2 and NaOCl into the canal space would improve debridement of both the main canal and areas inaccessible to files. Mesial root canals of 75 freshly extracted mandibular molars were step-back hand-instrumented. Another six molars were controls. Either Ca(OH)2, NaOCl, or no medication was sealed in the canals for 1 or 7 days. Canals were finally irrigated with H2O and prepared for histological evaluation. The cleanliness of main canals and inaccessible areas (isthmi and fins) at the apical, middle, and coronal thirds was examined, scored, and compared by nonparametric statistical analysis. Results showed no significant differences among different groups in either the 1-day or 7-day time intervals in either the main canal or inaccessible areas. Instrumentation combined with NaOCl irrigation alone accounted for the removal of tissue in the main canal. In conclusion, in this system, prolonged contact with Ca(OH)2 and NaOCl was similarly ineffective; neither contributed significantly to canal debridement.

Induced hypoxia in rat pulp and periapex demonstrated by 3H-misonidazole retention

Cellular hypoxia may be a useful indication of tissue distress in the dental pulp that could be used to investigate the early stages of pulpal responses. Tritiated misonidazole (3H-MISO) is a marker which preferentially labels cells with decreased oxygen tension (hypoxia). The experiments reported here were carried out to determine whether this agent could distinguish between hypoxic and normoxic pulp and periapical tissues. Rats were injected intra-peritoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic, hypoxic, and control groups. Normoxic animals were maintained at ambient pressure. We induced hypoxia by maintaining animals in a hypobaric chamber at 0.5 atm for 24 hrs. 3H-MISO retention was assessed by quantitative analysis of tissue autoradiographs. 3H-MISO retention rates in normoxic animals showed little variation except for increased retention in mature ameloblasts and immature odontoblasts in the continually erupting incisor. In both incisor and molar pulps, hypobaric hypoxia significantly increased 3H-MISO retention when compared with normoxic controls. Hypobaric hypoxia also resulted in intense 3H-MISO retention in cellular cementum, periodontal ligament, osteocytes, and, occasionally, in molar pulp horn odontoblasts. This study demonstrated that, with standard autoradiographic techniques, 3H-MISO can label induced hypoxic disturbances in the pulp and surrounding periodontium.

Breakage of ultrasonic root-end preparation tips

Modified ultrasonic tips are used to prepare rootend cavities during endodontic surgery. The purpose of this study was to determine whether such tips are prone to breakage during use. Ten different tip designs were driven by an ultrasonic unit at maximum power. Multirooted teeth were instrumented, the apex removed, and the tooth was placed horizontally on a pan balance. The apex was instrumented by each ultrasonic tip in turn for 15 min, with the load being increased by 100 g every 5 min. Those tips with curvatures of 70 degrees or greater fractured within the first 5-min loading period. Breakage occurred approximately 2 to 3 mm from the end and always at a bend. Scanning electron microscopy revealed that the fractures were brittle in nature, with little change in the remaining section. Two tips bent: one isthmus preparation tip and one silver point removal tip. All the other designs were deemed satisfactory after experimentation. This study shows that fracture of ultrasonic tips can occur and is related to the degree of bending.

Penicillin as a supplement in resolving the localized acute apical abscess

PROBLEM

Antibiotics are often prescribed indiscriminately to treat endodontic emergencies.

OBJECTIVES

This study examined (1) the effect of penicillin supplementation on reduction of symptoms and (2) the course of recovery of localized acute apical abscess after emergency treatment.

STUDY DESIGN

Patients with pulp necrosis and periapical pain and/or localized swelling were considered. Those eligible did not have any signs of spreading infections. Patients received appropriate local treatment, and a double-blind protocol was used to randomly assign them to one of three groups: penicillin VK group, placebo group, or neither medication group. All received ibuprofen 600 mg four times daily for 24 hours. Patients entered their pre- and postoperative pain and swelling experience on a visual analog scale for up to 72 hours.

RESULTS

Resolution was fairly rapid in most patients. Statistical analysis of the scores of 32 respondents revealed no significant differences (at p < 0.05) between the three groups in course of recovery or symptoms at any time period.

CONCLUSIONS

Patients with localized periapical pain or swelling generally recovered quickly with local treatment. The data did not show a demonstrable benefit from penicillin supplementation.

Effect of rubber-dam retainers on porcelain fused to metal

Metal ruber-dam retainers may damage tooth structure, restorations, and the porcelain surface of crowns. In this study, effects of metal versus plastic retainers on the surface of porcelain fused to metal (PFM) were compared, specifically: defects at point of beak contact, and porcelain fracturing. Evaluation was performed with scanning electron microscopy (SEM); micrographs were examined for porcelain defects. No damage was evident with metal or plastic retainer placement. In conclusion, neither metal nor plastic retainers consistently damaged PFM surfaces.

Cross-sectional configuration of endodontic files compared with manufacturers' design

The cross-sectional configuration of seven files at coronal and apical levels were compared with diagrams presented by manufacturers. The presence of cutting edges was also examined. Ground-twisted (K-file, K-Reamer, and K-flex) and machined files (Flex-R, Unifile, S-file, and Hedstrom) were included in #10, #25, and #40. Twelve files of each size and brand comprised the samples. Files were embedded in acrylic, which was then cut in cross-section in the apical and coronal parts of the flutes. These were photographed under a microscope. Six clinicians viewed the slides projected onto a screen for comparison with manufacturers' design and evaluation of visible cutting edges. The inconsistencies were primarily in machined files, smaller sizes, and apical sections of the instruments. Data showed that overall the cross-sections and presence of cutting edges compared well with the designs intended by the manufacturers.

Anaerobic tissue-dissolving abilities of calcium hydroxide and sodium hypochlorite

Closed root canals likely have an oxygen-free environment; most bacteria in canals are anaerobic. These bacteria and other debris are difficult to remove. Unknown is tissue dissolution with chemicals under these anaerobic conditions. This study evaluated and compared dissolving properties of calcium hydroxide (Ca(OH)2) and sodium hypochlorite (NaOCl) on bovine pulp tissue in aerobic and anaerobic environments. Sixty bovine pulp specimens were dried, then randomly divided into six groups. Groups A and B were immersed in Ca(OH)2 + water solution, whereas group C and D were in 2.5% NaOCl. Groups E and F (controls) specimens were placed in distilled water. Groups A, C, and E were incubated anaerobically, and groups B, D, and F were incubated under regular atmospheric conditions, all for 7 days. Percentages of weight loss were compared between groups. Results showed the following: (a) both chemicals partially dissolved pulp tissue, (b) anaerobic environment did not alter tissue-dissolving properties of Ca(OH)2 or NaOCl, and (c) Ca(OH)2 and NaOCl were equal and more effective than water.

Electrothermal debracketing: patient acceptance and effects on the dental pulp

Adhesives bond ceramic brackets so effectively that their removal by mechanical forces can fracture the brackets and may damage the tooth surface. Electrothermal debracketers have been developed to facilitate removal; whether the heat generated will damage the underlying pulp is unclear. In our experiment, a prototype device with a high heat tip was used to remove brackets from premolars in patients. The following parameters were evaluated: (1) time required for removal, (2) patient acceptance, and (3) histologic effect on the pulp. Forty-eight experimental teeth planned for orthodontic extraction were bonded by a filled Bis-GMA composite resin and a monocrystalline sapphire bracket. After the chemically cured composite set, debracketing was performed according to the manufacturer's recommendations. Seventeen premolars were not etched or bracketed and served as controls. The interval between heat application and removal of the bracket was timed. Patients were questioned as to sensations during debracketing. Teeth were extracted at 5 to 7 or 28 to 32 days and histologically prepared. Pulps were evaluated for alterations. Brackets were removed in an average of 2.1 seconds, usually at the bracket/composite interface. Patient acceptance was generally positive. Pulpal necrosis was not observed but, in a number of specimens, slight inflammation and odontoblastic disruption occurred at both observation periods.

Vertical root fracture in nonendodontically treated teeth

Vertical root fractures have been reported to occur primarily in endodontically treated teeth due to condensation forces and/or with post placement. This study describes 11 Chinese patients with 12 molars that developed vertical root fractures without endodontic or post procedures. These showed characteristics of a true vertical root fracture as confirmed after extraction. Fractured teeth showed a consistent pattern. The majority were severely attrited mandibular molars in males. All had clinically intact crowns with no or minimal restorations.

Characterization of induced pulpal hypoxia using 3H-misonidazole

Tritiated misonidazole (3H-MISO) is a bioreductively activated marker which preferentially binds to cells with decreased oxygen tension (hypoxia). Detection of hypoxia may be an important indicator of metabolic imbalance. For 3H-MISO to be functional as a marker, normal oxygen (normoxic) levels must be distinguishable from increased hypoxic retention. This investigation characterized retention of 3H-MISO in: (a) normoxic pulp, (b) induced hypoxic pulp, and (c) reoxygenated hypoxic pulp. Rats were injected intraperitoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic and hypoxic groups with appropriate controls. Normoxic animals were maintained at ambient pressure. Hypoxia was induced by placing animals in a hypobaric chamber at 0.5 atm. Pulps were then removed and prepared for liquid scintillation counting. Hypoxic pulps retained significantly more 3H-MISO than normoxic pulps (analysis of variance, p = 0.001). Hypoxic 3H-MISO retention was unaffected by subsequent, transient tissue reoxygenation. 3H-MISO detects changes in pulpal oxygen status that deviate from normal.

Extensive idiopathic apical root resorption. A case report

Multiple idiopathic external apical root resorption is an unusual phenomenon. A brief review of cases in the literature is presented as well as a report of a patient with severe resorption. No significant systemic, dental, or familial findings could be identified as a possible cause. Careful chronologic radiographic documentation showed that roots with normal length began to resorb several years earlier, and the resorption continued over a defined period of time, terminating spontaneously before tooth loss or obvious pulp damage. Because the pathogenesis is generally unknown, no specific treatment modalities exist at present.

Vasculature of the dental pulp of atherosclerotic monkeys: light and electron microscopic findings

Arteriosclerosis is a pathological condition in which there is a severe luminal narrowing of arterioles, resulting in tissue ischemia and necrosis. Arteriosclerosis has been reported in the dental pulp of normotensive persons as young as 40 yr of age. To date, no corroboration of these findings have been published. Our study examined pulp from atherosclerotic monkeys for such changes under controlled conditions. The lingual artery and canines from 11 nonatherosclerotic (control) and 11 atherosclerotic (experimental) cynolmolgus monkeys were histologically evaluated with light and transmission electron microscopy. Lingual arteries from controls did not exhibit atherosclerotic plaques, whereas those of the experimental monkeys did show fibro-foamy plaques. However, neither experimental nor control animals exhibited any arteriosclerotic alterations in the pulp. Our study concluded that, in this animal model, which did demonstrate atherosclerosis in the oral cavity, no similar alterations were found in the pulp.

Coronal leakage: bacterial penetration through obturated canals following post preparation

Coronal leakage of bacteria from saliva into root canal filling materials is a potential cause of failure. This problem may be more pronounced when only a small volume of obturating material remains in the canal, such as after post preparation. In this study, coronal leakage of bacteria through unsealed, apically obturated canals was investigated using a new in vitro model system.

Bacterial retention in canal walls in vitro: effect of smear layer

When dentin is planed by endodontic instruments, a smear layer forms. Whether this layer should be removed is unknown and controversial. This study was conducted to assess the effect of the smear layer on retention of bacteria using an in vitro root canal bacterial colonization model. Canals of 26 extracted human canines were step-back prepared using 2.5% NaOCl. Teeth were then randomly divided into two groups based on the type of high volume final flush: 1-20 ml of sterile saline (0.85% wt/vol) or (2-10 ml of 17% EDTA followed by 10 ml of 2.5% NaOCl which removes smear layer. Streptococcus anginosus (milleri) was cultured in trypticase soy broth supplemented with 0.5% yeast extract at 37 degrees C in 5% CO2. Cells were harvested by centrifugation and resuspended in fresh media. Serial dilutions were performed to achieve inocula of 10(6) colony-forming units in a 30-microliters volume. Teeth were inoculated and incubated for 2 h in 5% CO2 at 37 degrees C. Following incubation, teeth were split and processed for microbiological analysis. Numbers of colonizing bacteria were determined by a spiral-plating system. Enumeration of the numbers of bacteria revealed a reproducible, order of magnitude difference (p = 0.0002) between teeth with smear layer (10(4) colony-forming units) versus teeth without smear layer (10(5) colony-forming units). This suggests that smear layer produced during root canal therapy may inhibit bacterial colonization of root canals. One suggested mechanism is that smear layer may block bacterial entry into dentinal tubules.

Cleaning of oval canals using ultrasonic or sonic instrumentation

This study investigated the effect of direction of file oscillation on the amount of debris and smear remaining within oval canals. Sixty-five lower premolars were allocated to six experimental groups (n = 10) and one control group (n = 5). Canals were prepared using Gates Glidden burs and hand instruments. Preparations were completed using either an ultrasonic size 15 K file or a sonic size 15 shaper file. Three preparation techniques were used: (a) file oscillation toward oval recesses within the canal, (b) file oscillation at right angles to the recesses, and (c) rotational movement of handpiece. Canals were examined under the scanning electron microscope and blindly scored for debris and smear layer. Log linear analysis revealed no significant difference (p > 0.05) between sonic or ultrasonic instrumentation as to debris or smear layer remaining. File oscillation directed toward oval recesses left the least amount of debris (p < 0.05). Smear layer remained unaffected by all techniques.

Prophylactic penicillin: effect on posttreatment symptoms following root canal treatment of asymptomatic periapical pathosis

It has been reported that administration of prophylactic penicillin may prevent flare-ups or other undesirable posttreatment sequelae following root canal treatment. To test this hypothesis in a prospective study, 80 patients with a diagnosis of pulp necrosis and chronic apical periodontitis were divided into three groups: group A (prophylactic penicillin, AHA recommendation), group B (placebo, same regimen), and group C (no medication). Medications and evaluations were double-blinded. Patients reported their posttreatment events including incidence of flare-ups, incidence and severity of pain/swelling, and occurrence of adverse side effects. Differences in the three groups were determined statistically using chi-square tests. The outcome showed no significant difference (p = 0.68) among the three groups. That is, administration/nonadministration of penicillin prophylactically was unrelated to posttreatment signs and symptoms following canal preparation. Incidence of flare-ups was very low (1 of 80). Occurrence of pain in the mild-moderate levels was fairly high (approximately 70% overall), but was primarily in the mild category. Overall incidence of side effects was also very low (2 of 80). Severe levels of pain/swelling and flare-up incidence were low with no difference between administration or nonadministration of antibiotics. Based on our data, using penicillin (a potentially dangerous drug) prophylactically to control posttreatment symptoms is not recommended in cases of pulp necrosis and asymptomatic periapical pathosis.

Healing of induced periapical lesions in ferret canines

A previous study showed that the ferret canine is an appropriate model for inducing periapical lesions. Ferret canines were used in this study to study changes in periapical lesions after root canal treatment (RCT). After periapical pathosis was induced in the maxillary and mandibular canines of six ferrets, RCT was performed on three of the four canines in each animal. Each ferret received periodic intraperitoneal injections of Procion red dye. Two animals were killed at each of 4, 8, and 12 wk after RCT. Apices and surrounding lesions were evaluated radiographically, histologically, and by fluorescent microscopy. Periapical radiolucencies increased in size during induction but showed no changes after RCT. Lesions in untreated teeth showed features of granulomatous inflammation, mainly the presence of macrophages and lymphocytes. After RCT, there was histological evidence of healing in the form of cementum deposition, increased vascularity, and increased fibroblastic and osteoblastic activity. Fluorescent staining showed cementum deposition of variable thickness in the treated specimens.

Adaptation of thermafil components to canal walls

The desired result of the Thermafil system is described as a centered carrier encased by gutta-percha in apposition to the canal walls. This study examined, in curved canals, the intracanal relationships of: (a) the metal carrier; (b) the surrounding gutta-percha; and (c) the sealer. Following the manufacturer's recommended techniques, 20 resin blocks that had canals prepared with conservative flaring were obturated. Cross-sections were made in the cervical, middle, and apical thirds and were evaluated with a stereomicroscope and scanning electron microscope to determine the location of the Thermafil components. In an additional 20 resin canal preparations obturated with the Thermafil system, the sealer was stained with dye to evaluate coating patterns. Then, these blocks were sectioned at the apex and examined under the stereomicroscope for adaptation at the apical extent of the preparation. In most preparations, the carrier abutted the canal wall in the cervical and middle sections but was usually surrounded by gutta-percha in the apical one third. The adaptation of components showed the most variability at the most apical extent of the preparation; complete encasement of the carrier did not occur in any specimen. Sealer distribution was variable throughout, usually being absent in the apical canal.

Effect of precurving endosonic files on the amount of debris and smear layer remaining in curved root canals

Endosonic files are prone to constraint; this reduces their efficiency, particularly in the apical third and in curved root canals. Precurving the file may reduce constraint, thereby improving the file's ability to debride. This investigation was undertaken to compare both straight and precurved endosonic files as to debris and smear layer removal. Thirty-six curved root canals were randomly allocated into six groups. Each group was prepared using a step-down technique, then instrumented with either a straight or precurved endosonic file of size 15, 20, or 25. The tooth roots were split and examined under the scanning electron microscope. Blind examinations were made for debris and smear layer removal and evaluation scores were analyzed using a log linear approach. The root canals instrumented with the precurved files had a significantly lower debris score than those prepared with straight files. Precurving did not affect smear layer removal. In conclusion, precurving of files decreased the amount of debris but did not affect smear layer removal.

Tooth discoloration resulting from long-term tetracycline therapy: a case report

Administration of tetracycline to children or pregnant women is known to adversely affect the color of developing teeth. This case report suggests the possibility that discoloration from tetracycline may not be limited to tooth development in the child, but may also affect the adult dentition. When given over long periods of time in adults, the tetracycline molecule is incorporated into the continuously forming secondary dentin. It is possible that chronic sun exposure of the incorporated tetracycline may cause the formation of a reddish-purple oxidation product, resulting in discoloration of the permanent teeth.

Canal Master files: scanning electron microscopic evaluation of new instruments and their wear with clinical usage

Canal Master instruments have a short, fluted cutting area and a small flexible shaft; they may be predisposed to rapid wear and breakage. This study examined new and used files as to tip, flute, and shaft design when new and with increasing time of canal preparation. One hundred files prepared 140 curved canals. Sizes #20, #40, and #60 files were examined unused and after 1, 3, 5, and 7 min of use. Evaluation was for uniformity when new and for deterioration and breakage with usage. The smaller sizes (#20 and #40) had some inconsistencies when new and were most predisposed to wear and breakage with time. Findings suggest that smaller files could have had improved quality control by the manufacturer. Also, they should be used with caution and discarded after short times of use in small, curved canals. This should minimize instrument separation and maximize cutting efficiency.

Histologic evaluation of three endodontic instrument/preparation techniques

33 curved canals were prepared to quantify both the increase in canal area and predentin removal in the apical region. Compared were three different file designs/instrumentation techniques, that is "stepback" with K-flex file, "balanced force" with Flex-R file, and the Canal Master system. Following canal preparation and histological processing, cross-sections at 1 and 3 mm levels were examined using the Bioquant image analysis system. Results showed that, at the 3 mm leve, the mean increase in canal area and predentin removal showed no statistically significant difference (p > 0.05) between the techniques. At 1 mm, the step-back technique (with K-flex files) resulted in a significant increase in canal area and greater predentin removal than did the "balanced forces" (with Flex-R files) or the Canal Master system. However, although there were statistical differences, the actual differences were small; these may not translate to clinically significant differences in the 3 techniques.

Managing local anesthesia problems in the endodontic patient

Root canal therapy has a poor public image related to occasional and sometimes severe pain, and to dentists' inability to obtain profound anesthesia. Patients' apprehension, in combination with tissue inflammation, significantly lowers the pain threshold, which decreases the anesthetic's effectiveness. The best and also the first approach to achieving anesthesia is to administer a conventional block or infiltration. If profound anesthesia does not occur after this attempt, use a supplemental technique such as lingual infiltrations, PDL or intrapulpal injections. Because infiltrations are generally not effective, PDL and intrapulpal injections are preferred. The PDL is better than the intrapulpal injection because it is non-painful, safe and usually effective. The intrapulpal injection is limited and may be uncomfortable. Administer both the PDL and intrapulpal injections under back-pressure to achieve effective, but short-lived anesthesia. Special injection devices (for example, pressure syringes for the PDL) are not required for either technique. Two anesthetic types are useful. Administer 2 percent lidocaine with epinephrine for conventional and supplemental injections. For emergencies and long procedures, administer 0.5 percent bupivacaine with epinephrine to provide effective, long-lasting anesthesia and analgesia.

Histological evaluation of the presence of bacteria in induced periapical lesions in monkeys

In endodontic periapical lesions, both presence and location of bacteria are controversial. Various experimental techniques have produced differing results perhaps related to potential artifacts such as contamination during specimen recovery. Our objective was to examine for bacteria in uncontaminated, undisturbed periapical lesions in an animal model. Pulp necrosis was induced by exposing molars in nonhuman primates and closing the exposure after 1 week with amalgam. Lesions developed at 18 apices. After 7 months, block sections including tooth and surrounding tissues were removed, processed histologically, and Gram stained. Bacteria, primarily Gram positive, were consistently identified in necrotic tissue in canals. Two canals demonstrated bacterial masses to the apical foramen. No bacterial colonies, only intracellular microorganisms, were seen periapically. Inflammatory lesions seemed to resist the spread of bacteria, confining them to the canal space. Bacterial masses at the apical foramen could contaminate periapical tissues during surgery or extraction and give a false positive upon microbiological sampling.

Induced periapical lesions in ferret canines: histologic and radiographic evaluation

Ferrets have been utilized in endodontic research to study periapical responses. However, various aspects of induction and healing of periapical pathosis in ferrets are unclear. This study evaluated the radiographic and histopathologic features of induced periapical lesions. Periapical pathosis was consistently produced in 8 canines of 2 ferrets by extirpating the pulp, leaving the cavities open for a week, then sealing for 12 weeks. The resulting lesions were evaluated radiographically every two weeks. The animals were then killed and the induced lesions evaluated histologically and histobacteriologically. Four untreated canines from 2 other ferrets were used as controls. Results showed that periapical rarefactions were visible in all teeth in the experimental group within 4 weeks. Histologically, the induced lesions consisted principally of a mononuclear inflammatory infiltrate, dominated by macrophages but with numerous lymphocytes. With Brown & Brenn staining, bacteria were demonstrated in the pulp space of teeth in which the lesions were induced and in the apical arborization of the canal system. Only one specimen had bacteria within the periapical lesion.

Pulp response to bases and cavity depths

In cavities of ferret canines, preparation depth and bases were compared as to their effect on odontoblasts and to rate of dentin formation. These were measured by injecting 3H-proline at 0, 20 and 40 days post-preparation. Odontoblast activity was determined by label density in each band; inter-band distances indicated the amount of dentin formed. Correlations were by Pearson's coefficient. The following were determined: 1) cavity depth (remaining dentin thickness) was the major factor in odontoblast response and in dentin formation; deeper cavities suppressed odontoblasts with less subsequent dentin formation at all time periods; 2) basing materials had little effect on odontoblast activity or on the rate of dentin formation. An exception was in deep cavities, with Ca(OH)2 showing more label; this activity was temporary with no increased dentin formation; 3) there was no evidence of a "rebound" response.

Current concepts of canal preparation

Canal preparation is a complex procedure, performed with inadequate instruments and chemicals in a restricted environment. With these limitations, it is surprising that the success rate for root canal treatment is good, although not as high as is commonly reported. The preparation of the canal is divided into two actions, cleaning and shaping. Both are quite different and require different criteria for evaluation. Specifically, cleaning is debridement, whereas shaping is preparing the canal for obturation. Cleaning (debridement) depends on straight-line access, and requires the action of both intracanal instruments and irrigants. Files should contact and plane as many walls as possible to loosen debris. This is followed by irrigation, which has the primary function of flushing debris from the canal space. The chemical action of the irrigant is less important, but is an aid in total debridement. Shaping of the canal depends on the obturating material and the condensing instruments. Because gutta-percha is the preferred material, and lateral condensation the most common technique (although not necessarily superior), preparations should be flared. It has been shown that the taper should be sufficient to permit deep penetration of the spreader or plugger alongside the gutta-percha during lateral condensation. Hand instrumentation remains the preferred approach for canal preparation. There are variations including standardized and flaring, with the flaring (or step-back) the most commonly taught and used. The step-back approach encourages a small apical preparation with larger instruments used at successively decreasing lengths to create a taper. An advantage is that this method tends to minimize procedural errors such as transportation, ledging, and apical perforation. Automated techniques continue to be of interest as the dentist searches for easier, faster, and generally more efficient techniques. Ultrasonic and sonic devices have generated considerable interest. Research has not demonstrated these instruments to be as effective as hand techniques unless employed in a special manner. Other types of engine-driven instruments are generally not indicated and may in fact be dangerous.

Vertical root fracture and relative deformation during obturation and post cementation

There are several speculated etiologies of vertical root fractures such as pressure exerted during post placement and excessive forces during lateral condensation. However, there are no reports comparing these two forces by use of the same measurement system. This study determined and compared on single-rooted teeth (1) the amount of strain to the root that occurs during obturation and post cementation and (2) the incidence of incomplete and complete vertical root fractures occurring during the aforementioned procedures. Canals of 32 extracted maxillary central incisors were step-back prepared. Teeth were randomly divided into negative and positive controls and experimental groups. The amount of root distortion was recorded with a strain gauge during each of the following procedures: (1) lateral condensation, and (2) lateral condensation plus cementation of a cast gold post. Relative deformations were compared statistically. Teeth were examined by transillumination and stereomicroscopy for incomplete and complete fractures and compared among groups. Data showed significantly more relative deformation with placement of a post and loading than with obturation alone. The accumulation of strain from both procedures did not significantly increase incidence of vertical root fractures. The results indicate that stresses from cementation of posts is more likely to cause relative deformation of roots.