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Week of March 2, 2001

Title: The standardized-taper root canal preparation-Part 1. Concepts for variably tapered shaping instruments.

Author: Buchanan, L. S.

Journal: International Endodontic Journal 33(6): 516. November 2000.

Prepared by: G. Altenburg

Purpose: To introduce the concept of variable taper instruments for predictable and ergonomic root canal preparation, and demonstrate the design features of Greater Taper files.

The variably taped file concept and its advantages

• Perfectly adequate coronal enlargement
  Maximum flute diameter of 1 mm.

• Confirmed full deep shape
  Eliminates under-shaping of canals near the junction of the middle and apical thirds.

• Predictable apical resistance form
  If a file of greater taper is mistakenly taken 1 or even 2 mm beyond the root canal terminus, there is still linear, tapered resistance form present because even the most tapered file size has a 0.2 mm tip diameter. In fact, in cases with slightly larger terminal diameter (0.25-0.30 mm) the shaping strategy is to intentionally overextend these files, so that the segment of the file that is that diameter is taken to the terminus of the canal, ensuring a continuous apical taper-form.

• Standardized predefined tapers

• Enhanced cleaning efficacy

• Enhanced obturation efficacy

• GT flute geometry
  Standard and Accessory Series instruments come in hand and rotary (hand-piece driven) styles, the hand files having reverse-cut triangular flutes and the rotary files having clockwise U-blade flutes. Both types of GT files have variably pitched flute angles, which deliver several advantages over conventional fluting patterns. All these instruments are available in lengths of 17, 21, 25 and 30 mm.
  
  Most ground-flute files have blade angles that are relatively open (reamer-like) at their tips and are more closed (K-type) near their shanks. This is the easiest flute arrangement for CNC (computer numerically controlled) fluting machines to create. GT files (hand and rotary) have the opposite flute angulation (K-type) flute angles at their tips, and more open reamer-like flute angles at their shank ends.
  
  This design maximizes strength at the file tip, where it is weakest and where the less aggressive flute angles are acceptable since less dentine removal is needed. It also creates an open aggressive reamer blade at the fatter, shank end of the file where the diameter of the file adds strength and also where the canal needs the most aggressive dentinal cutting action. In the rotary version of the GT file, the grabbiness that is so common withother hand-piece-driven files is significantly lacking, another important advantage of this variable-pitch flute design. When the shank-end flutes are closed (K-type), they literally act like screw threads, pulling the files into the canal. Shank-end flute angles, which are more open, present less of an inclined plane to the canal wall being cut, and therefore are demonstrably less likely to thread into a canal. As an aside, limiting the maximum flute diameters also greatly contributes to the GT rotary files.

• Standard GT file features
  The standard set contains three taper sizes (0.06, 0.08, and 0.10 mm). All three files have the same tip diameters (0.20 mm), the same 1 mm maximum flute diameters (MFDs), and the same variable-pitch flute patterns. All of these files, hand or rotary, standard or accessory, are made of hyper-flexible nickel titanium, as stainless steel is not strong enough or flexible enough in these greater taper configurations.
  
  Because they vary by taper, but have the same tip diameters and MFDs, the flute lengths become shorter as the tapers increase. This results in canal shapes for large long roots that have dramatic, but relatively short, apical tapers (5-7 mm) and coronally parallel walls.
  
  In large long roots, this does require custom rolling of conventional nonstandardized gutta percha cones to make their shank ends parallel in diameter. Using the GT-tapered gutta percha cones, paper points, and condensation devices (Autofit by Analytic Endodontics, Orange, CA, USA) obviates the need for this irritating subroutine.
  
  The three files in the standard set each have the same tip diameter, a great departure from ISO-tapered files, which come in 21 tip sizes. These instruments will ideally shape 90% to 95% of the roots you will encounter in practice, because most root canal termini are 0.15-0.25 mm in diameter. Remarkably, it takes just one of the three files in the 0.12 GT Accessory Series to manage canals with large apical diameters.
  
  We only needed all of those ISO sizes because serial instrumentation requires file tip diameters stepping back through much of the canal. GT files, due to their tapers ranging between the common 0.2 mm tip diameters and their common 1.0 mm MFDs, contain 13 ISO file diameters along each of their lengths (or 26 if using half sizes). In fact, variably tapered files have an infinite number of diameters, between 0.2 and 1.0 mm, along their lengths.

• 0.12 accessory GT file features
  
  A set of three accessory GT files is available for those relatively unusual large root canals that have apical diameters of greater than 0.3 mm. These instruments have common tapers (0.12 mm mm-¹) and the same larger MFDs (1.5 mm), but they vary by their tip diameters (0.35, 0.5, and 0.7 mm). When used in canals with large apical diameters, they are typically able to complete the whole shape with just one file. More important, the resistance form created is of enough taper to really lock the master cone in tightly, to ensure apical control during obturation of these previously challenging cases.

Title: Apical Inflammatory Root Resorption: A Correlative Radiographic and Histological Assessment.

Author: Laux et al.

Journal: International Endodontic Journal 33(6): 483. November 2000.

Submitted by: Paul Slusarz, D.M.D.

Purpose: To investigate the reliability of routine single radiographs in detecting apical inflammatory root resorption by correlating the radiographic diagnosis to the histological findings.

Materials & Methods:

• 104 extracted teeth with attached apical periodontitis lesions were used for this study.
• The teeth and associated apical lesions were fixed and then the apical third of the roots were severed, decalcified, and embedded in Epon or HPMA.
• Serial or step serial sections were then prepared in the axial plane.
• Each of these teeth had a corresponding radiograph, 51% being PA’s and 49% were orthopantomograms (OPG).
• The histological sections of 104 specimens were analyzed by light microscopy and categorized into three groups: 
  
  Category 0: absence of unrepaired apical root resorption.
  Category +: surface resorption limited to the cementum only.
  Category ++: severe resorption of cementum and dentin.

• The radiographs were examined by a separate examiner and graded with a similar categorization:
  
  Category 0: no evidence of resorption.
  Category +: moderate resorption (presence of blurred irregularities on root contour)
  Category ++: severe resorption (presence of distinct radiolucent indentations or shortening of the root tip).

• During the third phase of the study, the encoded radiographs and histological specimens were decoded and compared.

Results:

• Radiographically, 90 specimens were diagnosed as having no apical root resorption, 11 with moderate resorption, and 10 with severe resorption.
• Histologically, 21 specimens showed no apical root resorption, 63 showed a moderate degree of resorption, and 30 specimens showed severe resorption.
• Overall, 19% of the teeth were radiographically diagnosed as having apical inflammatory root resorption, whereas histologically, 81% of the teeth revealed apical inflammatory root resorption.
• A correlative radiographic and histological assessment revealed a coincidence of diagnosis in 7% of the specimens and noncoincidence of diagnosis in 76% of the specimens.

Conclusions: The results indicate that routine single radiographs are not sufficiently accurate or sensitive to consistently diagnose apical root resorptive defects developing as a consequence of apical periodontitis.

Title: Periapical status and quality of root fillings and coronal restorations in a Danish population.

Author: Kirkevang LL, et al.

Journal: International Endo J 33 (6): 516. November 2000.

Reviewer: Mark Wang

Purpose: To investigate the quality of endodontic and coronal restorations and the association with periapical status in a Danish population.

Materials & Methods:

• A total of 614 randomly selected people (20-60 yr. old) had a full-mouth radiographic examination.
• The quality of endodontic and coronal restorations and the periapical status of endodontic treated teeth were assessed by radiographic criteria.
• Root fillings were categorized as ‘adequate’ or ‘inadequate’ with regard to root filling length & lateral seal.
• Coronal restorations were categorized into ‘adequate’ and ‘inadequate’, defined by the absence or presence of radiographic signs of overhang or open margins.
• Results were analyzed statistically using the chi-squared test.

Results:

• The total number of endodontic treated teeth was 773, 52.3% had apical periodontitis (AP).
• Root-filled teeth with an adequate lateral seal had a lower incidence of AP than teeth with an inadequate seal (44.3% vs. 57.8%).
• Teeth with an adequate root filling length were associated with a better periapical status than teeth with inadequate length of the root filling (42.0% vs. 67.6%).
• Similarly, adequate coronal restorations were associated with better periapical status than inadequate restorations (48.0% vs. 63.9%).
• When both root filling and coronal restoration quality were assessed, the incidence of AP ranged from 31.2% (optimal quality) to 78.3% (all parameters scored as inadequate).

Conclusion: Inadequate root canal and coronal restorations were associated with an increased incidence of AP.

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Week of March 9, 2001

Title:  The influence of sample dimensions on hydroxyl release from calcium hydroxide products

Journal: Endo and Dent Traumatol 16: 251-257, 2000

Author: Murray, PE et al.

Prepared by: Lance Isaac

Purpose: The purpose of this study was to investigate the effect of the product surface area surface area sample size on the rate of hydroxyl ion release from calcium hydroxide products.

Materials and Methods: The rate of hydroxyl ion release from 4 Ca(OH)₂ products in solution was measured in vitro. These products were Hypocal, Calasept, Dycal and Life, all of which were mixed according to the manufacturer’s specifications, except for Calasept which was used as non-setting paste and was not light-activated. Two sizes of Teflon pellets were created, the first with an exposed surface area of 2.26mm² and a fixed volume of 2.26mm³, the second 1.005mm² and 2.26mm³ respectively. Each of the 1104 pellets was examined to ensure complete fill of test product and no material exposed but at the end of the pellets. They were then placed in 1mL of distilled water. Analysis of the rate of hydroxyl ion release was measured by titration with HCl using a pH indicator over time intervals of 1, 2, 3, 4, 6 and 8h, and each day for 14d at room t° . Prior to titration, the Ca(OH)₂ pellet was removed, and each analysis was replicated 10 or 12 times, and subjected to multivariate analysis.

Results: Over 14 days in solution, Dycal and Life setting products had a rate of hydroxyl ion release that could be as small as 1/3 of the rate of –OH release from the non-setting products Calasept and Hypocal. The mean rate of –OH release from the setting Ca(OH)₂ did not appear to change response to the alteration in surface area, and remained constant over the 14 days. The non-setting Ca(OH)₂ did release –OH at different rates with the 2 surface area dimensions.

Discussion/Conclusions:

1. Because measuring pH is open to the atmosphere, a reaction may occur between dissolved –OH and CO₂ from the air to make the solution more acidic, thus underestimating –OH solubilization. Direct measurement of –OH release via titration is preferable to indirect measurement with a pH meter.
2. The dimensions of the exposed sample surface area was found to be an important physical constraint to –OH release from non-setting Ca(OH)₂ products, which was not found to be the case with setting products.
3. The range of –OH activity in decreasing order was Hypocal, Calasept, Life and Dycal, with a range of 298% from first to last.

In cases where oral healing has been poor, the size and seal of prepared cavities could have negatively influenced the therapeutic release of hydroxyl ions from non-setting calcium hydroxide.

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Week of March 16, 2001

Title: Bacterial leakage in obturated root canals following the use of different intracanal medicaments

Journal: Endodontics & Dental Traumatology,16(6)282, Dec. 2000

Author: Barthel, C.R. and et al.

Reviewed by: Kimberly Pham, D.M.D.

Purpose:  To examine whether intracanal medication prior to root canal obturation has an effect on corono-apical penetration of bacteria.

Materials & Methods:

Ninety-three single rooted human extracted teeth with crown removed. The roots were instrumented to an ISO #60 file with irrigation of 2.5% sodium hypochlorite. Smear layer was removed with 5% EDTA.

The roots were divided into 4 test groups and several control groups. For 1 week they were dresses with different medicaments: The first group with a 5% CHX, the second with Ledermix, the third with a mix of Calcium hydroxide and water and the fourth without medication.

After obturation by lateral condensation technique, using AH26 sealer the roots were fixed between a top and a bottom chamber. The top chamber contained 3mL trypticase soy broth. With 10⁸ Staphylococcus epidermidis CFU’s/mL, whereas the bottom chamber contained sterile trypticase soy broth. For one years, the mounts were incubated at 37ºC. They were checked on regular basis for turbidity for in their bottom chambers indicating bacterial growth.

Ledermix is used in German dental practices because of its possible residual effect. It is shown to impair apical healing when applied as intracanal dressing in a study in dogs.

Results & Discussion:

• None of the test samples leaked for 3 months
• After 1 year, the calcium hydroxide group had only 6 leaking samples whereas the CHX group had 14, the Ledermix group 15, and the unmedicated group had 13 leaking samples.
• Calcium hydroxide may may have elevated the pH in the root canal thus prevented dissolution of hard tissues and leakage.
• Calcium hydroxide has a slow diffusion within the dentin because of high buffering capacity of the dentin, therefore elevated pH level remains for some time. This may explain the long-term antibacterial effect of calcium hydroxide.
• Ledermix did not perform better than no premedicatilon
• CHX was superior to Ledermix in the second third of the observation period

Conclusion: Under condition of this study, calcium hydroxide was the medicament of choice to avoid bacterial penetration of the root canal.

Title: The Sealing Ability of an Epoxy Resin Root Canal Sealer used with Five Gutta-Percha Obturation Techniques.

Author: De Moor et al.

Journal: International Endodontic Journal 33(6): 483. November 2000.

Submitted by: Paul Slusarz, D.M.D.

Purpose: To evaluate the apical sealing ability of an epoxy resin root canal sealer (AH-26) when used with different gutta-percha obturation techniques and with Thermafil and Soft-Core obturators.

Materials & Methods:

• 237 extracted human straight single-rooted teeth with mature apices were used in this study.
• The crowns were removed 2mm above the CEJ and then prepared using a crown-down/step-back technique to an ISO #35 to #45 depending on the root.
• The roots were randomly divided into five experimental groups of 45 roots each, along with 6 positive and 6 negative controls.
• Group 1: Cold lateral gutta-percha condensation.
• Group 2: Warm vertical gutta-percha condensation.
• Group 3 Hybrid gutta-percha condensation.
• Group 4: Thermafil obturation.
• Group 5: Soft-Core obturation.
• Controls: 6 positive control teeth were filled with a loosely fitted gutta-percha cone only. 6 negative control teeth remained untreated.

Results:

• Mean extent of dye penetration in millimeters

Time	+ Control	- Control	Group 1	Group 2	Group 3	Group 4	Group 5
1 day	9.3	0	0.07	0.08	0.07	0.40	0.68
1 week	9.8	0	0.13	0.23	0.07	0.17	0.83
4 months	10.2	0	0.33	0.32	0.25	0.60	1.28
Maximum	11.2	0	1.55	2.45	1.53	3.24	4.23

• From this table it is clear that root fillings with Soft-Core obturators and AH26 leaked more than when AH26 was combined with the other 4 obturation techniques.
• Significant differences were found in leakage of the the various obturation techniques after 7 days, but no significant differences were found after 1 day and 4 months between the obturation techniques.

Conclusions: It was demonstrated that leakage occurred over time in all obturation techniques combined with AH26, and that leakage increased over time. The amount of apical leakage and the number of leaking teeth in the Soft-Core obturator groups was significantly higher than all other 4 gutta-percha obturation techniques combined with AH26. It was also demonstrated that the hybrid gutta-percha condensation technique turned out to be superior to the four other condensation techniques.

Title: Bone-like tissue growth in the root canal of immature permanent teeth after traumatic injuries

Author: Heling I, et al.

Journal: Endo & Dental Traumatology, 16(6) 298, December 2000.

Reviewer: Mark Wang

Introduction: Following a severe traumatic incident to permanent immature teeth, the growth of calcified tissue in the pulp space may occasionally occur. This calcified tissue may be diffuse or in intimate contact with the dentine. It has been suggested that a wide open apex, severe damage to the root sheath, and the absence of infection are only some of the predisposing factors leading to this metaplasia of pulp tissue into bone-like tissue. Five cases are described.

Case 1:

A 8 yr. old boy suffered trauma to the anterior segment, causing intrusion to tooth #8. Tooth #8 infraoccluded with a bone-like tissue within the root canal space, surrounded by a continuous PDL-like structure. There is invasive external lateral resorption on the distal of the crown.

Case 2:

An 11 yr. old boy suffered trauma 2 yr. ago on tooth #7, #8. The #8 had a complicated fracture with pulp exposure. An apexification procedure with Calxyl was started and sealed the orifice with amalgam. Bone-like tissue was identified beyond the remnants of the Ca(OH)₂ within root canal. 12 yr. follow-up of teeth #7, #8 showed continuous PDL in both teeth.

Case 3:

A 7 yr. old girl injured her upper incisors (#9) and was diagnosed as suffering from an acute-dento-alveolar abscess. Antibiotic was given. The tooth were treated with a partial filling of the root canal space with Calxyl & sealed with IRM. 2 month later bone-like tissue fills the apical part of the canal. The teeth then filled with MTA above the bone-like tissue. Apical closure is present 6 month after initiation of treatment.

Case 4:

A 9 yr. old boy presented for orthodontic treatment for non-erupted upper front teeth. He suffered trauma to his upper deciduous teeth when he was 2 yr. old. The x-ray showed high position of four incisors at the level of the floor of the nose. On tooth #9, there is a complete absence of root development. The tooth also had an open apex, but the wide pulp chambers was seen to be largely filled with a cone-like radiopaque material of similar opacity to the surrounding dentine.

Case 5:

A 15 yr. old girl had previously surgically repositioned tooth #29. The tooth was infraocclusion. Calcified tissue inside the root canal space was with intimate contact with the pulp chamber dentine. The scanning electron microscope (SEM) revealed adherence of a bone-like tissue to the dentine. The calcified tissue also contained blood vessel, calcified collagen fibers and globular structures.

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Created: September 20, 2000 Revised: URL:

Roy H. Stevens, DDS, MS; Wanda Gordon, D.M.D. - Comments to author:	wgordon@dental.temple.edu
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