Claus Löst

The ability of root ZX apex locator to reduce the frequency of overestimated radiographic working length.

The aim of this in vitro study was to evaluate the ability of the Root ZX device to avoid instrumentation beyond the apical foramen in premolars after conventional working length radiography. Thirty extracted premolars with 43 root canals were subjected to radiographic and electronic working length determination. Radiographic working length determination resulted in overestimation in 51% of the root canals, although the measuring file tip was located to be 0 to 2 mm short of the radiographic apex. Electronic working length measurements with the Root ZX reduced the percentage of overestimation to 21%. In 6 root canals (14%), both radiographic and electronic working length measurements led to overestimation. It is concluded that complementing radiographic working length determination with electronic apex locator measurements may help to avoid overestimation beyond the apical foramen in premolars.

Efficiency of Hand and Rotary Instruments in Shaping Oval Root Canals

This study was designed to determine the efficiency of hand and rotary instruments in shaping oval root canals. Seventy-five oval canals were equally divided into three groups. The apical third was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars). The middle third with an oval cross-section was shaped with Hedström hand files using circumferential technique, with 6% taper rotary Hero files in a circumferential filing movement or with rotary LightSpeed instruments in a step-back technique. Instrumentation was performed under clinical conditions in a phantom head. The teeth were sectioned at two levels in the middle third of the root. An assembly technique allowed comparing the canal outline before and after instrumentation. The photographed root sections were superimposed and traced under a stereomicroscope. The ratio of prepared to unprepared canal outline was calculated for each section. The lowest values were observed in the LightSpeed group (mean: 0.42; 95% confidence interval (CI): 0.37; 0.47). Significantly higher values were recorded in the Hero group (mean: 0.58; 95% CI: 0.53; 0.64) and in the Hedström group (mean: 0.56; 95% CI: 0.49; 0.62). No instrumentation technique was capable of completely preparing dentin walls of oval root canals. Circumferential filing of the middle third of oval root canals with either 6% taper Hero files or conventional Hedström hand files gave comparable results.

Frequency of Overinstrumentation with an Acceptable Radiographic Working Length

The aim of this in vitro study was to determine how frequent a seemingly accurate working length ending radiographically 0 to 2 mm short of the radiographic apex resulted in an instrumentation beyond the apical foramen. Under simulated clinical conditions working lengths of 169 root canals were radiographically determined in 91 extracted teeth. In all cases the measuring files adjusted to the final working length (Iwork) were located 0 to 2 mm short of the radiographic apex. Iwork was subsequently compared with the actual reference length (Iref) representing the distance between the apical foramen and the coronal reference. Instrumentation beyond the apical foramen (Iwork > ref) occurred in premolars in 51% (95% confidence interval: 36%; 66%) of the cases, in molars in 22% (95% confidence interval: 14%; 30%), and in anterior teeth in no case. These results suggest that in premolars and molars a radiographically working length ending 0 to 2 mm short of the radiographic apex provides, more often than expected, a basis for unintentional overinstrumentation.

Healing of apical periodontitis in dogs after apicoectomy and retrofilling with various filling materials

OBJECTIVE To histologically assess the efficacy of various retrofilling materials in apical surgery. STUDY DESIGN The pulps of mandibular premolars in seven beagle dogs were infected; this resulted in periapical lesions. Apical surgery was performed without disinfection of the root canals. Super EBA (Harry J. Bosworth Co., Skokie, III.), two formulations of glass ionomer cement, amalgam with varnish, IRM,(Caulk Co., Ltd., Densply International, Milford, Del.) and a light-cured composite resin were the retrofilling materials used. Roots infected and apicoectomized without retrofilling were positive controls. After 6 months the dogs were killed. The experimental roots and surrounding apical tissues were prepared and histologically examined and relative percentages of bone and inflammation were calculated. RESULTS Super EBA was consistently the best. In overall periapical condition, Super EBA was statistically superior to all materials except IRM. IRM was superior to the glass ionomer cements but not the other materials. As to percentage of bone, Super EBA was the best overall; it was superior to glass ionomer, composite resin, and the positive control but not different from amalgam or IRM. When comparing remaining numbers of inflammatory cells, Super EBA was superior with the lowest number of inflammatory cells present. CONCLUSION Although not statistically different from IRM, Super EBA was consistently the best retrofilling material tested when compared with all retrofilling materials studied.

Efficacy of rotary instruments with greater taper in preparing oval root canals

AIM To compare the preparation quality of two rotary systems and NiTi-hand files in oval root canals, and to evaluate the effect of canal dimensions on the preparation. METHODOLOGY Ninety roots with oval root canals were selected. The middle third was cross sectioned at two levels and photographed. The maximum and minimum diameters of the root and canal were recorded. Teeth were distributed in three groups (n = 30) using stratified randomization, and prepared under simulated clinical conditions with Mtwo, ProTaper, or NiTi-hand files. The pre- and post-preparation photographs were traced and superimposed, the thickness of dentine removed was measured and the ratio of prepared canal outline was calculated. The impact of preparation system and canal dimensions on the quality of the preparation was evaluated using regression analysis. RESULTS With regards to the ratio of prepared canal outline, no statistical significant difference was found between Mtwo (0.75 [95%CI: 0.69; 0.81]) and ProTaper (0.75 [95%CI: 0.69; 0.80]), but both systems performed significantly better than NiTi-hand files (0.65 [95%CI: 0.60; 0.71]). In six root canals in Mtwo-group (20%), and eight root canals in ProTaper-group (27%), the minimal thickness of dentine-wall after preparation was less than 0.5 mm. In contrast to the maximum diameter of the root canal, the minimum diameter influenced the quality of the preparation (P = 0.0006). CONCLUSIONS No instrumentation technique was able to circumferentially prepare the oval outline of root canals. Nevertheless, instruments with greater taper (ProTaper and Mtwo) were more efficient than NiTi- hand files, but this was, in some cases, at the expense of remaining dentine-wall thickness.

In vitro comparison of various types of sodium perborate used for intracoronal bleaching of discolored teeth

Fifty-eight extracted incisors were artificially stained to compare the efficacy of sodium perborate preparations used for intracoronal bleaching. All teeth were bleached for a 6-day period and the bleaching pastes replaced at days 1 and 3 (walking bleach technique). Sodium perborate-monohydrate, trihydrate, or tetrahydrate in conjunction with 30% H2O2 as well as tetrahydrate, either mixed with H2O or prepared as an experimental gel, were placed intracoronally at a level of 1-mm below the vestibular cementoenamel junction. Standardized slides were used to evaluate the color changes during bleaching. Success rates between 46 and 77% could be achieved, but no significant differences in final bleaching results between any of the sodium perborate types were observed. The use of the experimental gel resulted in comparable esthetic results (54%), although the portion of tetrahydrate in the gel was lower than that of the other preparations. In contrast to general recommendations that bleaching agents be left for 3 to 7 days in the access cavity before replacement, shorter bleaching intervals did not seem to affect the success.

Quantitative Radiographic Follow-up of Apical Surgery: A Radiometric and Histologic Correlation

The objective of this study was to establish an objective method for evaluating the treatment outcome of apical periodontitis (AP). AP was induced in the mandibular premolars of beagle dogs and apicoectomies were performed with retrofilling. Standardized periapical radiographs were taken immediately after completion of treatment and at 6 months. Ten pairs of standardized radiographs of 33 treated roots were analyzed. Radiographs were digitized and subtracted after warping and gamma correction. Areas of AP and adjacent normal areas (N) in digitized original and subtraction images were analyzed using eight radiometric computations. These computations were compared with subjective histologic evaluation and objective quantitative histomorphometry of the periapical condition at 6 months. The average gray value for AP on the subtraction images was found to have significant correlation with both objective (multiple regression p < 0.01) and subjective histology (logistic regression p < 0.01). Digital subtraction may be a useful tool in endodontic apical surgery assessment.

Effect of various types of sodium perborate on the pH of bleaching agents

Time-dependent changes in the pH value of various types of sodium perborate solutions used as bleaching agents were evaluated. Sodium perborate-monohydrate (MH), sodium perborate-trihydrate (TRH), and sodium perborate-tetrahydrate are available. Each perborate was mixed with 10%, 15%, or 30% fresh hydrogen peroxide or with bidistilled water in a powder to liquid ratio of 2 g:1 ml, respectively. The pH values were recorded at baseline and after 1h, 1 day, 3 days, and 7 days, respectively. At baseline the pH values of MH, TRH, and tetrahydrate in conjunction with 30% H2O2 were 8.7, 7.0, and 7.5, respectively. The pH increased significantly with decreasing concentrations of H2O2. For TRH, MH, and tetrahydrate mixed with bidistilled water more alkaline values were measured at baseline and after 1 h. Due to solidification of the samples, the pH could not be determined for MH starting day 1 and for TRH starting day 3. In conclusion, the pH of bleaching pastes depends on the content of water of crystallization in sodium perborate, H2O2 concentration, and time of measurement. The bulk of the mixtures recorded reached alkaline pH values of 10 to 11. It is recommended that the pH of the mixture being used be checked to avoid potential postbleaching root resorption.

Influence of cusp coverage on the fracture resistance of premolars with endodontic access cavities

AIM To assess the influence of cusp reduction and coverage with composite resin on the fracture resistance of premolars with prepared access cavities. METHODOLOGY Endodontic access cavities were prepared in 60 premolar teeth that were divided into four test groups: R1, R2, R3 and NR (n=15). In all test groups, MOD cavities were prepared and extended towards one of the cusps. The remaining cusp-wall thickness was: 1-1.5 mm in R1, 1.5-2 mm in R2 and 2-3 mm in both R3 and NR groups. In addition, in group R1, R2 and R3 the same cusp was reduced in height to 3.5 mm. Cuspal coverage and MOD restorations were performed using composite resin. Ten intact premolars served as positive controls and another ten MOD-prepared unrestored premolars as negative controls. Teeth were submitted to cyclic fatigue of 1.2 million cycles. A compressive load was applied 30° to the long axis of the teeth until fracture. Fracture loads were recorded and the means and the Confidence Intervals were compared. RESULTS The mean fracture resistance of each of the cusp-reduced groups R1, R2 and R3 (603, 712 and 697 N, respectively) was significantly higher than the non-reduced cusp group (305 N) and was comparable to the intact-premolar group (653 N). CONCLUSIONS Cusp reduction and coverage with composite resin significantly increased the fracture resistance of premolar teeth with MOD and endodontic access cavities.

Increased Apical Enlargement Contributes to Excessive Dentin Removal in Curved Root Canals: A Stepwise Microcomputed Tomography Study

INTRODUCTION To determine whether increased apical enlargement would result in a complete preparation of curved canals and to progressively assess shaping quality using multiple microcomputed tomography (MCT) scans. METHODS Ninety root canals with a curvature of 25° to 50° were selected. Five MCT scans, 1 preoperative and 4 postoperative, were acquired from each canal. Canal preparation was performed up to size 50 using 3 techniques, nickel-titanium (NiTi) hand files, Mtwo (VDW, Munich, Germany), and ProTaper (Maillefer, Ballaigue, Switzerland), by experienced operators in a dental mannequin so as to simulate the clinical conditions. At a level of 1 mm short of the working length, 2 parameters were evaluated in each of the 4 postoperative acquisitions: the percentage of the prepared outline and the amount of dentin removed (the prepared area). RESULTS Statistically, there was no significant difference between the 3 systems used regarding the prepared outline. The maximum prepared outline was achieved by the use of NiTi hand files (63%; confidence interval [CI], 54%-73%), whereas Mtwo and ProTaper amounted to 58% (CI, 50%-66%) and 60% (CI, 51%-70%), respectively. In contrast, the dentin area removed by ProTaper was significantly higher than that of Mtwo and NiTi hand files. CONCLUSIONS Increased apical enlargement of curved canals did not result in a complete apical preparation, whereas it did lead to the unnecessary removal of dentin.