Gerald W. Harrington

External resorption associated with bleaching of pulpless teeth

A number of cases observed in recent years have suggested that external resorption of cervical crown and root structure may be produced by bleaching the crowns of endodontically treated pulpless teeth. Although a direct cause and effect relationship of resorption to bleaching cannot be established with certainty, the clinical circumstances of the cases described in this report strongly suggest such a relationship.

A comparison of strains generated during placement of five endodontic posts

Twenty-five extracted human maxillary central incisors were randomly divided into five equal groups. Crowns were removed 1 mm incisal to the cementoenamel junction. Endodontic treatment was carried out and each tooth was affixed with two strain gauges. The strain gauge wires were connected to a Wheatstone Bridge circuit. Each group of five teeth was restored with either a Para-Post Plus (the control post), Flexi-Post, Vlock post, Kurer Fin Lock Anchor, or a Radix Anchor. Strains generated during post placement were recorded and compared for the five groups using a one-way analysis of variance. The maximum strains accompanying placement of the Kurer Fin Lock Anchor and the Radix Anchor were significantly higher than those induced by placement of the other posts. Also, when the threaded posts were allowed to contact the bottom of the prepared channel, high strains resulted.

Radiovisiography versus conventional radiography for detection of small instruments in endodontic length determination. Part 1. In vitro evaluation

Radiovisiography is a new intraoral radiographic imaging system. In this in vitro investigation, radiovisiography was compared with conventional radiographs viewed with x2 magnification. Twenty-five extracted maxillary molars were evaluated for clarity of size 8 and 10 endodontic file tips in relation to the radiographic apex. Five images of radiovisiography were compared with D-speed and E-speed radiographs: original, enhanced, negative-to-positive, standard zoom, and zoom in the negative-to-positive mode. D-speed radiographs were also compared with E-speed radiographs. Zoom in the negative-to-positive mode was statistically equivalent to D-speed radiographs (p = 0.264) and superior to E-speed radiographs (p < 0.001). The standard zoom was also superior to E-speed radiographs (p = 0.025). D-speed radiographs were statistically superior to E-speed radiographs; being judged better than E-speed 90% of the time. Accurate identification of the position of the tips of size 8 and 10 files was achieved on all D- and E-speed radiographs with the use of magnification.

The effect of immediate post preparation on apical seal

A total of 121 single-rooted teeth were tested in vitro to determine if post preparation by two methods had an effect on apical seal immediately after filling with gutta-percha. Prepared teeth were centrifuged in India ink, decalcified, and cleared. The degree of ink penetration was recorded and provided a measure of apical seal. The apical seal of teeth with post space prepared with warm pluggers and files was compared with the apical seal of control teeth, and no statistical difference in leakage was found. The use of Gates-Glidden drills to remove gutta-percha for preparation of post space immediately after filling the root canal resulted in statistically less leakage compared with gutta-percha filled controls.

Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems.

Thirty-six maxillary central incisors were endodontically treated and restored with a post and core and cast crown. Three different post and core systems were evaluated. Restored teeth were fatigue-loaded until preliminary failure of the casting occurred as detected by a strain gauge bonded across the lingual margin of the cast crown. After preliminary failure, fatigue loading was continued for 100,000 load cycles with the crown margin exposed to basic fuschin dye. Teeth were then immersed in dye for 24 h, sectioned, and evaluated for leakage. There was no significant difference in the number of load cycles required to cause preliminary failure among the three post and core systems. Leakage occurred in all three groups, with no significant difference between groups. The occurrence of preliminary failure is clinically undetectable, yet it allows leakage between the restoration and tooth that may extend down the prepared post space.

Evaluation of Fiber-Composite Laminate in the Restoration of Immature, Nonvital Maxillary Central Incisors

The purpose of this study was to evaluate the use of fiber-composite laminate, a reinforcement ribbon embedded throughout a composite restoration, to reinforce immature maxillary central incisors. Twenty-six mature maxillary central incisors were prepared a minimum of 3 mm below the facial cementoenamel junction to simulate immature nonvital teeth. They were separated into 3 groups: group 1 was unfilled and served as a control; group 2 was filled to the depth of the preparation with composite; and group 3 was filled with composite and Connect Reinforcement Ribbon. The specimens were subjected to class I loading in an Instron Testing Machine until catastrophic failure occurred. The results indicate a highly significant difference between the groups (p < or = 0.003). Group 1 fractured at an average load of 31.08 kg, group 2 at 51.00 kg, and group 3 at 37.93 kg. These findings suggest that composite alone increases fracture resistance of the immature tooth model more than composite with Reinforcement Ribbon.

Evaluation of the apical seal produced by the McSpadden Compactor and by lateral condensation with a chloroform-softened primary cone

One hundred seventy single-rooted teeth were tested in vitro to evaluate the apical seal produced by the McSpadden Compactor and lateral condensation with a chloroform-softened primary cone. The obturated teeth were centrifuged in India ink, decalcified, and cleared. The degree of ink penetration into the canal provided a measure of the apical seal. Teeth filled with gutta-percha and Grossmans sealer using the McSpadden Compactor had statistically less apical leakage than teeth filled with a chloroform-softened primary cone and sealer using lateral condensation (p

Replantation 2. The role of the periodontal ligament

Maxillary lateral incisors were extracted and then replanted in 24 Macaca fascicularis monkeys. In half the sample the periodontal ligament was removed prior to replantation. In half the teeth it remained intact. Forty-two teeth were observed. Root resorption was evaluated radiographically. Follow-up periods ranged from 16 to 39 months. Thirty-five teeth were still in situ at the longest follow-up period. In those teeth in which the periodontal ligament (PDL) was intact upon replantation, nine of 21 resisted or reversed resorption and were retained with an intact PDL space radiographically demonstrable at the conclusion of follow-up. In contrast, all but one of 21 teeth in which the PDL had been removed prior to replantation evidenced severe resorption.

Torsional properties of twisted and machined endodontic files

The torsional properties of conventionally twisted K-type endodontic files and recently developed machined K-type endodontic files were compared. File sizes 10 through 40 were subjected to torsional load in clockwise and counterclockwise directions independently. Results showed that a statistically significant reduction in clockwise rotation occurred at failure with all of the machined files except size 10. Counterclockwise rotation at failure was also significantly lower for the machined files in sizes 10 through 30. There was no difference in torsional strength between the file types regardless of rotation direction. Therefore, machined files exhibit less ductility than twisted files prior to fracture and may be more susceptible to torsional failure clinically.

A postreplantation evaluation of air-dried and saliva-stored avulsed teeth

The maxillary lateral incisors of five adult Macaca fascicularis monkeys were extracted as atraumatically as possible. One of each contralateral pair was allowed to air-dry for 90 minutes before replantation. The other tooth in each animal was stored in saliva in the animals buccal vestibule for 90 minutes before replantation. All teeth were splinted for two weeks. Endodontic treatment was performed at the time of splint removal. Clinical and radiographic examinations were performed at periods up to 22 to 27 months. All air-dried teeth demonstrated ankylosis and progressive replacement-type resorption. All saliva-stored teeth retained normal mobility and did not show radiographic evidence of significant root resorption through the duration of the study. In addition, all saliva-stored teeth showed radiographic evidence of reestablishment of an intact periodontal ligament (PDL) space. Histologic evaluation of one saliva-stored tooth at 25 months showed an intact PDL.