Cervical Thirds Research Articles

The use of MTA/blood mixture to induce hard tissue healing in a root fractured maxillary central incisor. Case report and treatment considerations

To report the use of MTA/blood mixture for the induction of hard tissue healing of multiple horizontal root fractures in a maxillary incisor. An 18-year-old male patient was referred after suffering trauma to the anterior maxilla. Radiographic evaluation revealed multiple horizontal fractures in the middle and cervical third of his maxillary right central incisor. Clinical evaluation revealed third grade mobility of the coronal segment. The patient's accompanying radiographs revealed that root canal treatment of all segments had been previously initiated and both segments had been rendered pulpless. The coronal segment was repositioned and stabilized. A bi-antibiotic mixture, containing equal parts of ciprofloxacin and metronidazole, was used for the disinfection of the root canal segments. A blood clot was induced from the periapical area and MTA powder was mixed with the blood creating a bioceramic mixture covering all the fractures. Thick MTA was placed as a coronal barrier and the tooth was restored. Recall examination after 24months revealed healing of the horizontal fractures. The MTA mixed with the blood lost its radio-opacity over time. Tooth mobility returned to normal limits. A low range of 5-25% of all horizontally root fractured cases develop pulp necrosis, confined in the coronal segment, leaving the apical segment with vital tissue. In the unfortunate situation that the pulp of both segments becomes necrotic or the entire pulp tissue is removed, the use of MTA/blood mixture may be beneficial for the induction of hard tissue healing. MTA when mixed with blood seems to lose its radio-opacity over time.

Wear behaviour of monolithic zirconia crowns – clinical results

Purpose: (1) To compare the strains and the stresses values within the periodontal ligament (PDL) following the application of three types of loading regimes: pure intrusion (PI), buccal tipping (BT), and intrusion combined with buccal tipping (IT). (2) To verify the correlation between these results and the available clinical findings regarding root resorption (RR) occurrence. Methods and materials: A tridimensional finite element (FE) model was constructed with axisymmetric geometry to simulate the tooth root. The model includes root, cementum, PDL, cortical and trabecular bone. All materials were considered linear elastic, except the PDL that was modeled as a nonlinear hypo-elastic material. Based on the literature that evaluates the influence of force magnitude on the RR occurrence, the loading magnitude was defined: PI simulated by applying 25-g or 225-g of axial loading; BT by applying the same force magnitudes 90◦ to the long axis; IT combining PI and BT. The displacement of the root within the PDL was calculated as percentage of the original thickness of the PDL to verify the amount of PDL deformation. Strains and stresses at the nodes at the PDL–cementum interface at cervical, middle and apical thirds were also assessed. Results: For the PI movement, the root displaced vertically within the PDL uniformly (9% of the PDL total thickness for 25-g and 36% for 225-g). For the PI and BT, the maximum root displacement occurred at the cervical buccal third (8% and 13% for 25-g, and 33% and 57% for 225-g; respectively). Higher forces generated higher values of strains and stresses within the PDL. For the PI movement, the apical and middle thirds showed higher values of strains than the cervical third. For the BT, the apical and cervical thirds showed higher values of strains than the middle third. For the IT, the cervical and middle thirds at the buccal side showed the highest values of strain. The maximum stresses were seen at the cervical third for the PI, and at the cervical and buccal lingual sides for the BT and IT (tensile sides). Conclusion: As expected, higher orthodontic forces generated higher values of strains and stresseswithin the PDL. From clinical findings, it is possible to verify that the RR occurred mostly in areas under compression. Therefore, our results support that RR might be related with changes of the blood supply associated with the constriction of the PDL at the compression sides.

Orthodontic loading influence on root resorption susceptibility: Finite element analysis

Purpose: (1) To compare the strains and the stresses values within the periodontal ligament (PDL) following the application of three types of loading regimes: pure intrusion (PI), buccal tipping (BT), and intrusion combined with buccal tipping (IT). (2) To verify the correlation between these results and the available clinical findings regarding root resorption (RR) occurrence. Methods and materials: A tridimensional finite element (FE) model was constructed with axisymmetric geometry to simulate the tooth root. The model includes root, cementum, PDL, cortical and trabecular bone. All materials were considered linear elastic, except the PDL that was modeled as a nonlinear hypo-elastic material. Based on the literature that evaluates the influence of force magnitude on the RR occurrence, the loading magnitude was defined: PI simulated by applying 25-g or 225-g of axial loading; BT by applying the same force magnitudes 90◦ to the long axis; IT combining PI and BT. The displacement of the root within the PDL was calculated as percentage of the original thickness of the PDL to verify the amount of PDL deformation. Strains and stresses at the nodes at the PDL–cementum interface at cervical, middle and apical thirds were also assessed. Results: For the PI movement, the root displaced vertically within the PDL uniformly (9% of the PDL total thickness for 25-g and 36% for 225-g). For the PI and BT, the maximum root displacement occurred at the cervical buccal third (8% and 13% for 25-g, and 33% and 57% for 225-g; respectively). Higher forces generated higher values of strains and stresses within the PDL. For the PI movement, the apical and middle thirds showed higher values of strains than the cervical third. For the BT, the apical and cervical thirds showed higher values of strains than the middle third. For the IT, the cervical and middle thirds at the buccal side showed the highest values of strain. The maximum stresses were seen at the cervical third for the PI, and at the cervical and buccal lingual sides for the BT and IT (tensile sides). Conclusion: As expected, higher orthodontic forces generated higher values of strains and stresseswithin the PDL. From clinical findings, it is possible to verify that the RR occurred mostly in areas under compression. Therefore, our results support that RR might be related with changes of the blood supply associated with the constriction of the PDL at the compression sides.

Evaluation of the nanostructure of cervical third cementum in health and chronic periodontitis: An in vitro study.

Background:During the progression of periodontal disease, the cementum undergoes alterations in its structure and composition. Understanding the nanostructure of cementum, in terms of its mechanical properties, will provide an insight into the milieu that periodontal ligament cells encounter in health and chronic periodontitis. This study aims to analyze the nanomechanical properties of the cervical third of the cementum (transverse section) in health and chronic periodontitis.Materials and Methods:Twenty teeth (10 healthy and 10 periodontally diseased) were collected and the nanomechanical properties of the transverse section of the cervical third cementum were evaluated with depth-sensing nanoindentation technique under dry conditions. A total of 100 nanoindentations were performed to analyze the modulus of elasticity and hardness of cervical third of the cementum.Results:The nanomechanical properties of the healthy cervical third cementum sections were significantly higher (P < 0.05) (hardness: 0.720 ± 0.305 GPa; modulus: 15.420 ± 3.902 GPa) than the diseased cementum section (hardness: 0.422 ± 0.157 GPa; modulus: 11.056 ± 3.434 GPa).Conclusion:The results of our study indicate that the hardness and modulus of elasticity of the cervical third cementum decreases significantly in chronic periodontitis.

Effect of gutta-percha solvents on fiberglass post bond strength to root canal dentin.

The purpose of this study was to investigate the influence of gutta-percha solvents on the bond strength of fiberglass post to root canal dentin. Forty bovine incisors were decoronated, prepared, filled, and randomly distributed into four groups (n = 10) according to the gutta-percha solvent used: control, xylene, eucalyptol and orange oil. After root canal treatment, the posts were cemented into the prepared root canals using a resin-based cement. A micro push-out test was executed, and the patterns of failure were assessed with microscopy. The data were analyzed using two-way ANOVA followed by Tukey's test. The control group exhibited greater bond strength compared to the eucalyptol group in the cervical and middle thirds of the root (P < 0.05); however, it did not differ significantly from the xylene and orange oil groups (P > 0.05). No difference was observed in the values of the xylene, orange oil, and eucalyptol groups (P > 0.05). The cervical third had higher values than the apical third for all tested solvents (P < 0.05). Adhesive failure between resin cement and dentin was the most frequent type of failure. The use of xylene and orange oil as gutta-percha solvents did not influence the bond strength of fiberglass posts to root canal dentin.

Filling of simulated lateral canals with gutta percha or resilon when using thermomechanical compaction.

Aims:To evaluate the filling of simulated lateral canals with gutta-percha or Resilon when using thermomechanical compaction.Setting and Design:Forty-five human single-rooted teeth were subjected to tooth decalcification and clearing.Materials and Methods:After root canal preparation, artificial lateral canals were made at 2, 5, and 8 mm from the working length (WL), corresponding to the apical, middle, and cervical thirds, respectively. The specimens were divided (n = 15) according to the filling material: Dentsply gutta-percha (GD), Odous gutta-percha (GO), and Resilon cones (RE). Root canals were obturated by thermomechanical compaction using a #45 compactor and no sealer. Lateral canals were analyzed by digital radiography and digital images after tooth decalcification and clearing using the Image Tool software.Statistical Analysis Used:Data were subjected to the Kruskal-Wallis and Dunn tests at 5% significance.Results:In the coronal third, RE and GO presented more filling ability than GD (P < 0.05). In the middle and apical thirds, RE presented the best results.Conclusions:Resilon demonstrated filling ability as material for root canal obturation by using thermomechanical compaction.

Microhardness of luting agents used for fiber post cementation submitted to thermo cycling

Aims and Objectives: The aim of this study was to analyze the microhardness of three resin cements used in cementing glass fiber posts in bovine incisor. The microhardness was analyzed in cervical, middle and apical thirds before and after thermocycling process. Materials and Methods: Bovine teeth were instrumented and divided into 3 groups composed of 10 teeth each. Then, the teeth were sectioned and obturated and had their canals prepared at a depth of 12mm. Once proceeded the desobturation, the roots and glass fiber posts were prepared for adhesive cementation. After cementation, the microhardness reading was carried out. After initial reading, the samples were placed in a thermocycler and subjected to 2,000 cycles and a new microhardness reading. The data collected were subjected to analysis of variance (ANOVA) and Turkey’s test. Results: It was observed a statistical difference among the microhardness of resin cements. However, the statistical difference of microhardness before and after thermocycling appeared only in group U-200. Conclusion: Thermocycling reduced microhardness values in all cements evaluated in this study. The autopolymerizing cement Multilink presented the most stable microhardness mean values after thermocycling in the coronal, middle and apical thirds.

Evaluation of osteoclasts’ distribution on the periodontal ligament of rabbits

Abstract Objective: assess the distribution and quantity of osteoclasts on periodontal ligament of rabbit’s molars in physiological conditions. Methodology: one hundred and seventy-six histological sections were analyzed, obtained through bone blocks removed from the first molar regions on both sides of the mandible of 44 rabbits. Sections were stained with TRAP technique. Results: osteoclasts were found in 53,98% of the slides and were absent in 46,02%. These cells were usually located on the cervical and median third. Nonparametric Friedman Exact test evidenced a statistically significant difference between the thirds, and Dunn’s a Posteriori test indicated such difference between apical and cervical thirds and apical and median thirds (p<0,05). Conclusion: physiological re-modeling of the alveolar bone occurs when stress generated is sufficient to induce monocytes differentiation in osteoclasts. These cells are more concentrated on the cervical and median thirds due to the direction of the dental movement. Keywords: Osteoclasts. Periodontal ligament. Bone Remodeling

Scanning Electron Microscopy Observations of Osseointegration Failures of Dental Implants that Support Mandibular Overdentures

: Investigating possible failure causes of mandibular implants after their immediate loading with an overdenture retained with bilateral bar attachments, using scanning electron microscope. Twenty edentulous male patients were included in the present study. Each patient had 2 fixtures inserted in the canine and the first molar areas on each side of the mandible. After abutments screwing, the 2 fixtures on the same side were splinted with a bar, and immediately loaded with an overdenture. Implants mobility was assessed on weekly basis. Failed implants were removed, and examined by scanning electron microscope. The failed implants, removed after 4 weeks of treatment, showed an intimate contact of mineralized and osteoid tissues with dense collagen-rich matrix in the apical third of implants. Furthermore, newly developed bone was observed at the same area in implants removed after 7 weeks. However, there was no evidence of such growth at the middle and/or cervical thirds in either case. Lack of osseointegration at the middle and cervical thirds of the root could be a possible cause of implant failure. Early loading by an overdenture retained with bilateral bars is considered a major contributing factor to incomplete osseointegration of the supporting implants.

Endodontic filling removal procedure: an ex vivo comparative study between two rotary techniques

In this study, we compared the ex vivo removal capacity of two endodontic rotary techniques and determined whether there was a significant quantitative difference in residual material when comparing root thirds. Forty extracted molars were used. The palatal roots were selected, and the canals were prepared using a step-back technique and filled using a lateral condensation technique with gutta-percha points and Endofill sealer. After two weeks of storage in a 0.9% saline solution at 37 ºC in an oven, the specimens were divided into 2 groups of 20, with group 1 samples subjected to Gates-Glidden drills and group 2 samples subjected to the ProTaper retreatment System. Hedstroem files and eucalyptol solvent were used in both groups to complete the removal procedure. Then, the roots thirds were radiographed and the images were submitted to the NIH ImageJ program to measure the residual filling material in mm. Each root third was related to the total area of the root canals. The data were analyzed using Student's t test. There was a statistically significant difference between the two techniques as more filling material was removed by technique 2 (ProTaper) than technique 1 (Gates-Glidden drills, p < 0.05). The apical third had a greater amount of residual filling material than the cervical and middle thirds, and the difference was statistically significant (p < 0.05). None of the selected techniques removed all filling material, and the material was most difficult to remove from the apical third. The ProTaper files removed more material than the Gates-Glidden drills.

Evaluation of the interaction between sodium hypochlorite and several formulations containing chlorhexidine and its effect on the radicular dentin—SEM and push‐out bond strength analysis

The aim of the current study was to evaluate the presence of debris and smear layer after endodontic irrigation with different formulations of 2% chlorhexidine gluconate (CHX) and its effects on the push-out bond strength of an epoxy-based sealer on the radicular dentin. One hundred extracted human canines were prepared to F5 instrument and irrigated with 2.5% sodium hypochlorite and 17% ethylenediaminetetraacetic acid. Fifty teeth were divided into five groups (n = 10), according to the final irrigation protocol with different 2% CHX formulations: G1 (control, no final rinse irrigation), G2 (CHX solution), G3 (CHX gel), G4 (Concepsis), and G5 (CHX Plus). In sequence, the specimens were submitted to scanning electron microscopy (SEM) analysis, in the cervical-medium and medium-apical segments, to evaluate the presence of debris and smear layer. The other 50 teeth were treated equally to a SEM study, but with the root canals filled with an epoxy-based endodontic sealer and submitted to a push-out bond strength test, in the cervical, middle, and apical thirds. G2, G3, G4, and G5 provided higher precipitation of the debris and smear layer than G1 (P < 0.05), but these groups were similar to each other (P > 0.05), in both segments. The values obtained in the push out test did not differ between groups, independent of the radicular third (P > 0.05). The CHXs formulations caused precipitation of the debris and smear layer on the radicular dentin, but these residues did not interfere in the push-out bond strength of the epoxy-based sealer.

The presence and distribution of bacteria in dentinal tubules of root filled teeth

To investigate the distribution of bacteria within the dentine tubular network in a two-chamber model in order to determine a possible route of penetration. Root canals of teeth in the experimental group (n = 16) were instrumented and root filled using AH26 and gutta-percha. Canals in the teeth serving as positive (n = 1) and negative (n = 1) controls were instrumented, but not root filled. A two-chamber model was fabricated for each root - upper chambers were inoculated weekly with Streptococcus gordonii in brain-heart infusion broth over 90 days. Turbidity of the lower chamber was checked daily. Samples that showed turbidity during the experimental period and samples that showed no signs of turbidity at 90 days were fractured and prepared for SEM examination. SEM examination for the presence of bacteria within the dentinal tubules was performed in the cervical, middle and apical root thirds. In each root third, the depth of bacterial penetration was recorded as inner, middle or outer dentine. Bacteria were most commonly detected in the cervical third (14 of 30 areas). Irrespective of the root third examined, bacteria were most commonly detected in the inner dentine (i.e. adjacent to the root canal). Only two samples demonstrated bacterial penetration in the outer dentine. The dentine tubular network provides a potential pathway for bacteria to penetrate tooth roots in a two-chamber model.

Comparative Assessment of the Effects of Gates-Glidden, Largo, LA-Axxess, and New Brazilian Drill CPdrill on Coronal Pre-enlargement: Cone-beam Computed Tomographic Analysis

IntroductionThe removal of dentin interferences from the cervical third of root canals is essential for their correct cleaning and shaping and to facilitate access of endodontic instruments to the critical apical region. In mandibular molars, the concavity observed in the furcation area reduces dentin thickness, making this region more susceptible to perforation. The present ex vivo study used cone-beam computed tomographic imaging to compare 3 rotary burs with a new rotary bur recently launched in Brazil (ie, CPdrill; Helse Industry and Commerce Ltda, Santa Rosa, São Paulo, Brazil) regarding the amount of dentin removal from the distal wall of the mesial root of mandibular first molars. MethodsA total of 40 root canals were selected and randomly divided into 4 groups for cervical preparation: Gates-Glidden burs #2 and #3 (Dentsply Maillefer, Ballaigues, Switzerland), Largo burs #1 and #2 (Dentsply Maillefer), LA-Axxess burs #1 and #2 (SybronEndo, Glendora, CA), and CPdrill burs (1-size only). Dentin thickness in the distal wall of mesial canals at 2 mm from the furcation was measured using I-CATvision software before and after cervical preparation. ResultsThere was no statistically significant difference between groups regarding residual dentin thickness after instrumentation with the drills (P = .684). ConclusionsIt was concluded that CPdrill is safe for use in cervical preparation of the mesial root of mandibular first molars because it did not promote excessive dentin removal on distal walls.

Comparison of the changes of alveolar bone thickness in maxillary incisor area in extraction and non-extraction cases: computerized tomography evaluation

To compare, through computed tomography, alveolar bone thickness changes at the maxillary incisors area during orthodontic treatment with and without tooth extraction. Twelve patients were evaluated. They were divided into 2 groups: G1--6 patients treated with extraction of right and left maxillary first premolars, with mean initial age of 15.83 years and mean treatment length of 2.53 years; G2--6 patients treated without extraction, with mean initial age of 18.26 years and mean treatment length of 2.39 years. Computed tomographies, lateral cephalograms and periapical radiographs were used at the beginning of the treatment (T1) and 18 months after the treatment had started (T2). Extraction space closure occurred in the extraction cases. Intragroup and intergroup comparisons were performed by dependent and independent t test, respectively. In G1, the central incisor was retracted and uprighted, while in G2 this tooth showed vestibularization. Additionally, G1 presented a higher increase of labial alveolar bone thickness at the cervical third in comparison with G2. The incidence of root resorption did not present significant differences between groups. There were no changes in alveolar bone thickness when extraction and nonextraction cases were compared, except for the labial alveolar bone thickness at the cervical third of maxillary incisors.

Influence of diphenyliodonium hexafluorophosphate on the bond strength and mechanical properties of model resin cements

The influence of diphenyliodonium hexafluorophosphate (DPI) on the mechanical properties and bond strength of resin cement to the intraradicular dentin was evaluated. A model BisGMA/TEGDMA-based luting composite containing camphorquinone and ethyl 4-(dimethylamino)benzoate was modified by incorporating DPI at 0 (control), 0.5, 1, or 2mol%. Flexural strength (FS) and modulus (Ef) were evaluated by a 3-point bending test. The bond strength to dentin was evaluated by push-out testing of glass-fiber posts luted into bovine roots, which were sectioned into cervical, middle, and apical thirds. Polymerization stress (PS) was analyzed using photoelastic analysis. Data were statistically analyzed at p<0.05. No significant differences in FS were observed. The 2mol% group showed higher Ef than the control and 0.5mol% groups. The control group showed higher PS than the 1 and 2mol% groups. The control group showed higher bond strength in the cervical region than the other groups. The use of cements with DPI might be promising for the luting of fiber posts due to lower stress generation at the bonding interface.

Residents' journal review

Residents' journal review

Can the Cure Time of Endodontic Sealers Affect Bond Strength to Root Dentin?

The cure time of endodontic sealers may influence the bond strength of fiber posts to root dentin. Forty teeth were selected and endodontically filled using calcium hydroxide cement and then divided into 2 groups according to the time elapsed between endodontic filling and post luting (n = 20): Immediately - glass fiber post luting immediately after endodontic filling; and Delayed - post luting performed 7 days after endodontic filling. The roots were also subdivided according to resin cement used for post luting (RelyX ARC and RelyX Unicem). The specimens were stored at 37°C for 24 h and sectioned in six 1-mm-thick slices from cervical, middle and apical thirds. The slice specimens were submitted to a push-out test at a crosshead speed of 0.5 mm/min, and the bond strength values obtained (MPa) were submitted to two-way ANOVA in a split-plot arrangement and Tukey's test (α=0.05). For both RelyX ARC and Unicem, the bond strength was significantly higher when the posts were cemented 7 days after the endodontic treatment. RelyX Unicem showed significantly higher bond strength values than RelyX ARC for both cementation periods. It was concluded that post luting should be made after the complete setting of the root canal sealer. Self-adhesive resin cement should be preferred for fiber post luting.

Effectiveness of an electronic apex locator used after preflaring of cervical and middle third

The electronic method has been studied and improved aiming to add precision, speed and reliability of the measurement technique to determine the exact location of the working length. Currently, the root canal preparation recommends prior to determine the tooth length and consequent perform instrumentation of the apical portion, a previous preflaring of the cervical and middle thirds in various techniques. This procedure may provide a reduction in system impedance, leading to read errors by the apex locators. Objective: Investigate the influence of preflaring of the cervical and middle thirds on the accuracy of measuring the working length by apex locators. Material and methods: Twenty-five mesial roots of molars were used and had their crowns cut at the cemento-enamel junction. The actual measure of each root canal was performed and then the samples were embedded into a mixture of alginate, used as a conducting medium, where electronic measurements were taken with apex locator before and after preflaring of the canals with Gates-Glidden drills in descending order (#4, #3, #2). Measurements obtained by electronic method were then compared with the actual measurement of the root canal. The results were tabulated and submitted to the Student t test Results: The results show that there was no statistical significance (p&lt;0.05) between the readings before and after preflaring. Readings closer to the foraminal ending occurred in the group after preflaring with Gates Glidden. Conclusion: It was concluded that preflaring with Gates Glidden drills were not able to influence significantly the accuracy of apex locator in determining the exact working length.

A foreign body in disguise

Young children habitually place objects in their mouths to discover and learn about the world and it is considered a normal stage of early childhood development. Ingestion and aspiration of foreign objects predominantly occurs in preschool toddlers with a peak incidence at age three years, and can have serious consequences. A 2-year-old boy presented to the Dublin Dental University Hospital with a tooth-coloured mass tightly adherent to a lower primary incisor. The lesion surrounded the cervical third of the crown on the lower right primary central incisor and extended subgingivally. The tooth was mobile but with minimal inflammation. The tooth was subsequently extracted under general anaesthesia to reveal that the mass was in fact a foreign body, although this was originally thought unlikely as a cause. The patient underwent an unremarkable recovery. The case of a foreign body disguised as a tooth-like abnormality was only identified under general anaesthesia, and even then it was impossible to prise the object from the tooth in situ. Misdiagnosis of impacted foreign bodies in young children presents complicated diagnostic problems.

Comparative study of retention of fiber-reinforced post at middle and cervical one thirds of root canal cemented by polycarboxylate and zinc phosphate cements measured at different storage times

Background: The purpose of this study was to compare regional bond strength at middle and cervical thirds of the root canal among glass fiber-reinforced composite (FRC) endodontic posts cemented with different cements, using the push-out test to compare the performance (retention) of two types of luting cements; polycarboxylate cement and Zinc phosphate cement used to cement translucent fiber post and to compare the result of the push-out test at different storage times;1 week ,1month and 2 months. Materials and methods: Ninety caries-free, recently extracted single-rooted human teeth with straight root canals was used in this study, The root canals were endodontically instrumented at a working length of 0.5 mm from the apex by means of conventional instruments for hand use (Dentsply, Switzerland) up to size 35.then root canal filling was performed followed by post space preparation up to 8mm including cervical and middle one third of root canal then the fiber post was cemented into canal post space then the root was sectioned to get cervical (4 mm in length) and middle (4 mm in length) thirds ,these thirds were examined by push out test to get values of retention of fiber post inside these canal thirds . Results and Conclusions: The results of this study has been showed that there was no significant differences between push out bond strength between fiber post and root at cervical third as compared with middle third when using polycarboxylate cement or Zinc phosphate cement to cement the fiber post to the canal walls and the results showed that there was no significant differences in push out bond strength for polycarboxylate or Zinc phosphate cement after one and two months but there was highly significantly increase in push out bond strength for resin cements used to cement the fiber post to the root canal after one and two months