The impact of post preparation on the residual dentin thickness of maxillary molars

doi:10.1016/S0022-3913(11)60119-4

The Journal of Prosthetic Dentistry

Volume 106, Issue 3, September 2011, Pages 184-190

https://doi.org/10.1016/S0022-3913(11)60119-4 Get rights and content

Statement of problem

The oval-shaped palatal roots of maxillary molars usually have smaller cross-sectional diameter in the buccolingual direction. However, the effect of parallel-sided post preparation on the remaining dentin thickness of root canal walls is unknown.

Purpose

The purpose of this study was to investigate, in vitro, the residual dentin thickness (RDT) of palatal roots in maxillary molars after various intracanal procedures for post placement, and to determine the risk of root canal perforation or weakening on different root canal walls at 2 levels, coronal and apical.

Material and Methods

Fifteen extracted first maxillary molars exhibiting radiographic mesiodistal root canal widths ranging from 3.8 to 4.2 mm, measured at 5 mm from the apex, were selected from a pool of teeth. The teeth were horizontally sectioned at 2 levels, coronal and apical, after being embedded in acrylic resin with the aid of a metal index, allowing identical repositioning of the sectioned parts throughout the study. Each sectioned surface was photographed with a digital camera coupled to a microscope. The palatal roots were subsequently prepared for post placement as follows: endodontic preparation up to file K50, Largo 3 and 4 drills, and ParaPost 4.5 and 5.0. Cross-sections were rephotographed after each step. Image J software was used to measure the RDT of each root wall at both levels, and data were further analyzed with a 3-way ANOVA/General Linear Model (GLM) for repeated measures. The post-hoc Tukey's range test was used to calculate differences in RDT among the 4 root walls at each root level (α=.05).

Results

A significant difference was observed among the intracanal procedures (P<.001). At the apical level, RDT was significantly lower after ParaPost preparation than at the coronal level (P=.009). Buccal and palatal walls displayed significantly lower RDT than the mesial and distal walls at both levels (P=.004).

Conclusions

Intracanal preparation up to ParaPost 5.0 increased the risk of perforation or weakening of the buccal and palatal walls, especially at the apical level.

Section snippets

Material and Methods

This in vitro repeated-measure study, approved by the ethical committee at the University Center of Maranhão, included 15 teeth from a pool of 33 first maxillary molars, selected according to the radiographic mesiodistal thickness of the palatal root. A sequence of intracanal preparations was performed on the palatal root. After each preparation stage for post placement (before preparation, after hand instrumentation, after Largo reamer enlargement, and after ParaPost preparation) standardized

Results

Table I shows means and standard deviations for RDT on each post space wall and at sectioned levels after each stage of the preparation for post placement. The 3-way ANOVA (Table II) indicated a significant reduction in RDT after each stage of the post space preparation at both levels (P<.001). Comparing the levels, a significant difference in dentin reduction was detected only after the use of a ParaPost drill; here the reduction was significantly higher at the apical level than at the coronal

Discussion

A significant difference in the RDT of root canal walls at both levels was observed after post preparation with the ParaPost system. Thus the null hypothesis was rejected. A significant reduction in RDT after each stage of preparation for post placement at the palatal root of maxillary molars at both levels was observed (P<.001). This is consistent with previous studies that demonstrated a significant reduction in RDT after the subsequent stages for post preparation using the ParaPost System.5,

Conclusion

Within the limitations of this in vitro study, intracanal preparation up to a parallel-sided ParaPost 5.0 drill increased the risk of perforation or weakening of the root in the buccal and palatal aspects, especially at the apical level.

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Cited by (22)

Microcomputed tomography analysis of the radicular residual dentin thickness in mandibular second molars after virtual fiber post placement: Identification of danger zones
2023, Journal of Prosthetic Dentistry
Mandibular second molars have variable root, pulp chamber floor, and radicular groove morphologies, potentially affecting residual dentin thickness and post placement suitability. However, an identification of the danger zones is lacking.
The purpose of this in vitro study was to investigate the residual dentin thickness in the danger zone of mandibular second molars after virtual fiber post placement by using a simulation method based on microcomputed tomography (μCT).
A total of 84 extracted mandibular second molars were scanned using μCT and classified according to root morphology (separate or fused) and pulp chamber floor morphologies (C-shaped, non-C-shaped, or no pulp chamber floor). Fused-root mandibular second molars were further classified based on the radicular groove type (V-, U-, or Ω-shaped). All specimens were accessed, instrumented, and rescanned with μCT. Two types of commercial fiber posts were also scanned. Clinical fiber post placement was simulated in all prepared canals by using a multifunctional software program. The minimum residual dentin thickness of each root canal was measured and analyzed by using nonparametric tests to identify the danger zone. Perforation rates were calculated and recorded.
Larger fiber posts decreased minimum residual dentin thickness (P<.05) and increased perforation rate. In regard to mandibular second molars with separate roots, the distal root canal exhibited a significantly higher minimum residual dentin thickness than the mesiobuccal and mesiolingual root canals (P<.05). However, no significant difference in minimum residual dentin thickness was found between the different canals in fused-root mandibular second molars with C-shaped pulp chamber floors (P<.05). Fused-root mandibular second molars with Ω-shaped radicular grooves had a lower minimum residual dentin thickness than those with V-shaped radicular grooves (P<.05) and demonstrated the highest perforation rate.
The morphologies of the root, pulp chamber floor, and radicular groove were correlated with residual dentin thickness distribution in mandibular second molars after fiber post placement. A comprehensive understanding of mandibular second molar morphology is essential for determining the suitability of post-and-core crown restorations after endodontic treatment.
Cone beam computed tomography analysis of residual dentin thickness after virtual post placement in the palatal roots of maxillary first molars
2022, Journal of Prosthetic Dentistry
Citation Excerpt :
The percentage of molars with inadequate or no RDT was approximately 85.7% when the largest post size (1.14 mm) was examined at 5 mm from the apex. These findings are consistent with those of a previous study when a larger post size (1.25 mm) was compared, although the sample size was smaller.24 In contrast with previous in vitro studies,5,22-24,27 the present investigation assessed the use of posts in palatal roots without using extracted teeth.
In endodontically treated maxillary first molars, post space preparations in the palatal roots can compromise the residual dentin thickness (RDT) and increase the risk of perforations or root fractures. This can be attributed to the direction of the buccopalatal curvature that cannot be viewed with conventional 2D imaging.
The purpose of this clinical study was to investigate the RDT of palatal roots following the placement of digital post analogs of different diameters positioned at various distances from the radiographic apex by using cone beam computed tomography (CBCT).
A total of 122 deidentified CBCT data sets containing both maxillary permanent first molars were randomly selected from a private radiology practice. Digital parallel-sided post analogs were superimposed onto the CBCT coronal images at distances of 3 mm, 4 mm, and 5 mm from the radiographic apex and at a depth equal to the height of the anatomic crown (1:1 crown/post ratio). Post analogs of 0.9 mm, 1.0 mm, and 1.14 mm in diameter were matched with safety zone analogs representing 1 mm of circumferential RDT. The minimum RDT for each analog was determined and grouped into 3 categories: RDT≤0 mm, 0 mm<RDT<1 mm, and RDT≥1 mm. The statistical significance between post diameters and post depth was analyzed with the Friedman test and Conover post hoc test (α=.05).
Significant differences in RDT were found at all tested depths and diameters of post analogs (P<.001). Generally, the amount of RDT increased as the post length was reduced. Most teeth (>50.0%) had inadequate or no RDT. The depth of the post (P<.001) had a greater impact on RDT than the post diameter (P>.017). No similarities were found in the RDT between contralateral molars in 86.9% of the images.
The risk of insufficient RDT (<1 mm) after the placement of parallel-sided posts in the palatal roots of maxillary first molars is minimized if the post is inserted to a depth equaling the height of the crown compared with 3, 4, and 5 mm from the radiographic apex. The RDT of the palatal root of a maxillary first molar is not a reliable predictor of the contralateral palatal root RDT in the same patient.
Remaining dentinal thickness after simulated post space preparation and the fit of prefabricated posts to root canal preparation shapes
2021, Journal of the American Dental Association
Citation Excerpt :
Additional studies with other assumptions and their permutations are suggested in association with the assessment of progressive root morphology in other populations. We highlighted that, if posts are placed to 5 mm from the apical terminus, particular canals demonstrate higher levels of likelihood of violating the 1-mm rule, which can be interpreted as a proportionate risk of experiencing perforation or future root fracture, which is in agreement with other studies.27,28 Therefore, there is a higher risk of sustaining iatrogenic damage when preparing for a post in mandibular incisors and buccal and distal canals of molars.29
Post space preparation can increase the risk of experiencing perforation and root fracture. The authors assessed remaining dentin thickness after post space preparation and the fit of different prefabricated posts to root canal preparation systems in a theoretical model.
Ten datasets per type of tooth from cone-beam computed tomography were analyzed to determine the minimum root diameter from 5 through 13 mm from the apical foramen. The preparation shapes of 10 root canal preparation systems were calculated and compared with the root dimensions to determine the remaining dentin thickness. Eight post brands were compared with root dimensions to determine the areas where there was less than 1 mm dentin thickness.
The average root canal preparation shape produced canal diameters of 0.57 mm at 5 mm from the canal terminus and 0.94 mm at 13 mm from the canal terminus. The mean post size tip diameter was 1.03 mm, which is larger than the dimensions of the average canal preparation. Post preparation would result in less than 1 mm of dentin thickness remaining in premolars, smaller roots of molars, and mandibular incisors. The area with less than 1 mm of dentin thickness was around the post tip.
Endosequence Fiber Post (Brasseler USA), RelyX Fiber Post 3D (3M), and Rebilda (VOCO) were the better fitting posts with the root canal preparation shapes.
Many posts would result in less than 1 mm dentin thickness. Clinicians should use posts that fit their root canal preparations to minimize dentin removal.
Microcomputer tomography measurement of minimum residual dentin thickness in mandibular first molars after virtual fiber post placement
2020, Journal of Prosthetic Dentistry
Citation Excerpt :
In this study, the mean mRDT at the mesial side of distal roots was less than 1 mm (0.95 ±0.35 mm) after root canal preparation, and after post placement, the values were 0.76 ±0.34 mm for post #1, 0.63 ±0.35 mm for post #2, 0.52 ±0.35 mm for post #3, and 0.41 ±0.33 mm for post #4, which was acceptable for clinical application. Root anatomy is another important factor affecting RDT, which gradually decreases with the distance from the root canal orifice.6-8 The presence of oval roots with a buccolingual diameter much wider than the mesial-distal diameter is another factor affecting RDT.10,27,29,30
In endodontically treated teeth, the residual dentin thickness (RDT) after post space preparation plays a major role in preventing strip perforation and vertical root fracture.
The purpose of this in vitro study was to estimate and identify danger areas in mandibular first molars submitted to post space preparation by virtual fiber post placement and to determine a minimum RDT (mRDT) measurement by microcomputer tomography (μCT) combined with multifunctional software.
A total of 24 human mandibular first molars prepared with ProTaper instruments and commercial fiber posts (#1 to #4) were scanned by using a μCT system. A framework based on MeVisLab was used to simulate clinical post placement in 2 mesial and single distal root canals. The mRDTs were measured on 4 sides (buccal, lingual, mesial, and distal) at positions 1-, 3-, and 5-mm apically from the root canal orifice. The associations between mRDT and different characteristics were examined and analyzed by 4-way ANOVA (α=.05). For each level of each root canal, the least value from the mean mRDTs of 4 sides was selected, and the side related to the least value was identified and recorded. The perforation rate of each level in different root canals was also calculated.
Significant differences were detected among the different posts, root canals, levels, and sides (P<.001). The mean mRDT was higher in distal root canals than in mesiobuccal and mesiolingual root canals (P<.001). mRDTs of each level were mainly found on the mesial sides of distal roots and the distal sides of mesial roots. The perforation rate was higher when using #3 and #4 posts, and perforation mainly occurred at the distal side of mesial roots and at a level 5-mm apically from the canal orifice.
For post placement in endodontically treated mandibular first molars, using a larger-sized post decreased the RDT and increased the perforation rate. Small fiber posts were safer and prevented perforation, with the distal root being the first choice. If more posts are required in a mesiobuccal and mesiolingual canal, the smallest appropriately sized post should be placed less than 3 mm from the root canal orifice. Combining virtual fiber post placement performed using a framework based on MeVisLab with μCT scanning is a convenient and accurate method of evaluating the risk of canal wall perforation.
Accuracy of Cone-beam Computed Tomography in Measuring Dentin Thickness and Its Potential of Predicting the Remaining Dentin Thickness after Removing Fractured Instruments
2017, Journal of Endodontics
The purpose of this study was to evaluate the accuracy of cone-beam computed tomographic (CBCT) to measure dentin thickness and its potential of predicting the remaining dentin thickness after the removal of fractured instrument fragments.
Twenty-three human mandibular molars were selected, and 4-mm portions of #25/.06 taper K3 files (SybronEndo, Orange, CA) were fractured in mesial canals. The teeth were then scanned using a micro–computed tomographic (micro-CT) system and a CBCT unit. Dentin thickness was measured and compared between both micro-CT and CBCT images to study the accuracy of CBCT readings. Then, the process of removing the fragments was simulated in CBCT images using the MeVisLab package (MeVis Research, Bremen, Germany); the predicted minimal remaining dentin thickness after removal was measured in different layers using VGStudio MAX software (Volume Graphics, Heidelberg, Germany). Data were compared with the actual minimal remaining dentin thickness acquired from micro-CT images, which were scanned after removing fractured instruments using the microtrepan technique. The results were analyzed statistically using intraclass correlation coefficients (ICCs) and a forecasting regression model analysis.
The ICC for the dentin thickness was 0.988. The forecasting regression model of CBCT imaging estimating dentin thickness was micro-CT imaging = 15.835 + 1.080*CBCT, R² = 0.963. The ICC for the remaining dentin thickness was 0.975 (P < .001). The forecasting regression model of CBCT imaging forecasting remaining dentin thickness was micro-CT imaging = 147.999 + 0.879*adjusted CBCT, R² = 0.906.
The study showed that CBCT imaging could measure dentin thickness accurately. Furthermore, using CBCT images, it is reliable and feasible to forecast the remaining dentin thickness after simulated instrument removal.
Influence of adhesive techniques on fracture resistance of endodontically treated premolars with various residual wall thicknesses
2013, Journal of Prosthetic Dentistry
The choice of restorative method is commonly based on the cavity configuration and the residual number of cavity walls. However, the residual wall thickness could be a valuable clinical parameter in the choice of restoration for endodontically treated teeth.
The fracture resistance of endodontically treated premolars was compared with different wall thicknesses restored with direct composite resin with and without cuspal coverage and with and without fiber post insertion.
This study included 104 intact human maxillary premolars extracted for periodontal or orthodontic reasons. Standardized mesio-occluso-distal cavities were prepared with different palatal wall thicknesses (1.5, 2, and 2.5 mm) and a buccal wall thickness of 2 mm. Teeth were restored with or without a fiber post and with or without cuspal coverage. Specimens were subjected to thermocycling (3000 cycles, 5 to 55°C) and embedded in polymerized acrylic resin. Teeth were submitted to cyclic fatigue followed by a static fatigue test with a universal testing machine; a compressive force was applied 30 degrees to the long axis of the teeth until fracture. The results were statistically analyzed by 3-way ANOVA (α=.05).
Residual wall thickness (P=.004), the type of adhesive restoration (P<.001), and fiber post insertion (P<.001) significantly influenced the fracture resistance of endodontically treated premolars.
In specimens with a cavity wall thickness >2 mm, direct intracuspal composite resin restorations supported by a fiber post achieved comparable fracture resistance. With a residual wall thickness <2 mm, only cuspal coverage with or without a fiber post provided satisfactory fracture resistance.

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: Presented at the International Association for Dental Research (IADR) annual meeting, Barcelona, Spain, July 2010.

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The impact of post preparation on the residual dentin thickness of maxillary molars

Statement of problem

Purpose

Material and Methods

Results

Conclusions

Section snippets

Material and Methods

Results

Discussion

Conclusion

J Prosthet Dent

J Endod

J Prosthet Dent

J Am Dent Assoc

J Endod

J Endod

J Endod

J Prosthet Dent

J Endod

J Am Dent Assoc

J Prosthet Dent