Additional studies on the distribution of stresses during vertical compaction of gutta-percha in the root canal

Influence of obturating techniques on root dentin crack propagation: A micro-computed tomography assessment

Aim:

The aim is to assess and compare the microcrack formation in radicular dentin after obturating the root canals with cold lateral condensation (CLC), warm vertical condensation (WVC), and injectable gutta-percha (IGP) techniques using micro-computed tomography (CT).

Materials and Methods:

Human extracted mandibular premolar teeth (n = 60) were haphazardly assigned based on the obturation technique into three experimental groups (n = 20 each). Root canals are cleaned and shaped with M Two rotary files and 3% sodium hypochlorite irrigant. Cross-sectional images were taken with Micro-CT to record the baseline defects present on root samples. After root canal obturation either with CLC or WVC or injectable obturation techniques, micro-CT images were captured again to analyze the increase in the number and type of dentinal defects. Statistical analysis of data was performed using the Mann–Whitney U test and the Mcnemar test at 5% significance level.

Results:

An increase in the number of radicular micro-cracks was identified in samples obturated with lateral condensation technique (1.66%). No change in the percentage of micro-cracks was recorded after obturation with warm vertical or injectable guttapercha (IGP) techniques (P > 0.05). The three obturation techniques were not statistically different in the occurrence of micro-cracks after obturation.

Conclusion:

The three obturating techniques tested showed no significant increase in radicular dentin defects' occurrence or propagation.

Biomechanical influence of anchorages on orthodontic space closing mechanics by sliding method

This study aims to analyse the stress distributions and initial displacements of teeth during the space closing stage through a three-dimensional finite element method. Computed tomography images of a patient were used to reconstruct the detailed teeth and alveolar bone, and brackets with stainless steel archwire were modelled according to the orthodontic prescriptions. The second premolars and first molars were chosen as the anchorages in the model 6-force, with buccal tubes attached to the second molars in the model 6-force-7, and the second molars as additional anchorages in the model 7-force. The results indicated that a movement of lingual lateral inclination occurred on the incisors during the retraction, and the frictional force between the teeth and the archwire significantly reduced the stress on the teeth and periodontal structures. Graphical abstract Malocclusion is one of the most common issue in dentistry with high prevalence and orthodontic treatment need. The extraction of first premolar teeth was normally needed at the beginning of the treatment. And the straight wire appliance together with the sliding mechanics was used for space closure at the end of the treatment. However, side effects like root resorption also found after the surgery. Biomechanically, the stress distributions and initial displacements of teeth during space closing stage might be a crucial factor contributed to those undesirable side effects. And different selections of anchorages might alter the biomechanical environment during the treatment. Thus, the purpose of the current study was to analyse the stress distributions and initial displacements, with the different anchorage selections, of teeth during space closing stage through 3D finite element method.

Root Canal Filling: Fracture Strength of Fiber-Reinforced Composite-Restored Roots and Finite Element Analysis

The aims of this study were to evaluate the effect of root canal filling techniques on root fracture resistance and to analyze, by finite element analysis (FEA), the expansion of the endodontic sealer in two different root canal techniques. Thirty single-rooted human teeth were instrumented with rotary files to a standardized working length of 14 mm. The specimens were embedded in acrylic resin using plastic cylinders as molds, and allocated into 3 groups (n=10): G(lateral) - lateral condensation; G(single-cone) - single cone; G(tagger) - Tagger's hybrid technique. The root canals were prepared to a length of 11 mm with the #3 preparation bur of a tapered glass fiber-reinforced composite post system. All roots received glass fiber posts, which were adhesively cemented and a composite resin core was built. All groups were subjected to a fracture strength test (1 mm/min, 45°). Data were analyzed statistically by one-way ANOVA with a significance level of 5%. FEA was performed using two models: one simulated lateral condensation and Tagger's hybrid technique, and the other one simulated the single-cone technique. The second model was designed with an amount of gutta-percha two times smaller and a sealer layer two times thicker than the first model. The results were analyzed using von Mises stress criteria. One-way ANOVA indicated that the root canal filling technique affected the fracture strength (p=0.004). The G(lateral) and G(tagger) produced similar fracture strength values, while G(single-cone) showed the lowest values. The FEA showed that the single-cone model generated higher stress in the root canal walls. Sealer thickness seems to influence the fracture strength of restored endodontically treated teeth.

Incidence of dentinal defects after root canal filling procedures

AIM

To compare the incidence of dentinal defects (cracks and craze lines) after root canal preparation, lateral compaction and continuous wave compaction of gutta-percha and AH26 sealer.

METHODOLOGY

Two hundred mandibular premolar teeth were divided into four groups with similar average canal diameters (n=50). One group was left untreated and served as the control. The other three groups were prepared with ProTaper rotary instruments up to size F4. After preparation, one group was left unfilled while two groups were filled with gutta-percha and AH26 using either lateral compaction or the continuous wave technique. Roots were then sectioned at 3, 6 and 9 mm from the apex and inspected under a microscope. The appearance of dentinal defects was noted as well as the minimum and mean remaining dentine thickness. Chi-square tests were performed to compare the incidence of dentinal defects between the groups (α=0.05), and Pearson correlation test was performed to check the correlation between defects and root level or remaining dentine thickness.

RESULTS

The unprepared control group had no dentinal defects. The other groups exhibited significantly more defects than the unprepared group (P<0.05). There was no difference in the incidence of defects between the two filling techniques. There was no correlation between the appearance of defects and level of the root or remaining dentine thickness.

CONCLUSIONS

In extracted teeth, dentinal defects were observed in roots filled with gutta-percha and AH26 using the lateral compaction and continuous wave techniques.

Development of a Finite Element Analysis Model With Curved Canal and Stress Analysis

This study aimed to establish a model of a curved canal by finite element analysis (FEA). To develop a repeatable and comparable model, simulated curved canals with uniform shape were selected as prototype canals, and a suitable extracted single-root tooth was chosen as the outline. Subsequent combinations and modifications were performed by using the analysis program ABAQUS. By using a series of imitational occlusive forces loaded onto the incisive edge of the model, color plots and the maximal stresses at the apical region were analyzed. Stresses increased when the angle of the loads rose, and loads in the distal and mesial directions induced more stresses in the target region than did loads in the buccal and lingual directions. This study has established a standardized FEA model with a curved canal. Consequently, this model may be applied for future estimations in endodontic procedures for a curved canal.

Influence of instrument taper on the resistance to fracture of endodontically treated roots

OBJECTIVE

The aim was to compare the force required to fracture uninstrumented and instrumented canines and to investigate the root-reinforcing capability of AH Plus sealer.

STUDY DESIGN

In groups 1-3 (n = 24) canals were instrumented with either GT files, FlexMaster, or stainless steel hand instruments. Twelve teeth from each group were obturated with lateral compaction using gutta-percha and AH Plus. Group 4 (n = 12) acted as uninstrumented controls. The force required to fracture the roots was measured. ANOVA, Scheffé, and t test were used for statistical analysis.

RESULTS

The intact roots were significantly stronger than all groups with instrumented and unobturated roots (P < .05). Roots enlarged with GT files were significantly weaker (P < .05) than those instrumented with FlexMaster or hand instruments. Between the obturated and unobturated roots there were no significant differences (P > .05).

CONCLUSIONS

The roots were significantly weakened by the preparation with greater taper instruments. An obturation with AH Plus did not increase the fracture resistance.

Vertical root fracture in endodontically treated teeth: a review of 25 cases

OBJECTIVE

We sought to examine the clinical conditions under which 25 endodontically treated teeth underwent vertical root fracture (VRF) and to relate this condition to the time elapsed from endodontic treatment to fracture.

STUDY DESIGN

This was a retrospective study in which we reviewed 25 case histories of patients with postendodontic VRF and studied the effect of various pretreatment and posttreatment factors as they related to VRF.

RESULTS AND CONCLUSIONS

The mean time to VRF was 54 months; this was not significantly influenced by the presence or absence of prior restoration or by the presence or absence of a crown fitting. The use of a prefabricated, cylindrical, cemented intraradicular retainer increased the time between endodontics and VRF. Teeth restored with conventional amalgam took significantly longer to undergo VRF than those restored with composite or bonded amalgam. In contrast, amalgam-restored teeth suffered more coronal fractures before VRF than did teeth in the other 2 groups.