Electronic apex locators

Prior to root canal treatment at least one undistorted radiograph is required to assess canal morphology. The apical extent of instrumentation and the final root filling have a role in treatment success, and are primarily determined radiographically. Electronic apex locators reduce the number of radiographs required and assist where radiographic methods create difficulty. They may also indicate cases where the apical foramen is some distance from the radiographic apex. Other roles include the detection of root canal perforation. A review of the literature focussed first on the subject of electronic apex location. A second review used the names of apex location devices. From the combined searches, 113 pertinent articles in English were found. This paper reviews the development, action, use and types of electronic apex locators.

The fundamental operating principles of electronic root canal length measurement devices

It is generally accepted that root canal treatment procedures should be confined within the root canal system. To achieve this objective the canal terminus must be detected accurately during canal preparation and precise control of working length during the process must be maintained. Several techniques have been used for determining the apical canal terminus including electronic methods. However, the fundamental electronic operating principles and classification of the electronic devices used in this method are often unknown and a matter of controversy. The basic assumption with all electronic length measuring devices is that human tissues have certain characteristics that can be modelled by a combination of electrical components. Therefore, by measuring the electrical properties of the model, such as resistance and impedance, it should be possible to detect the canal terminus. The root canal system is surrounded by dentine and cementum that are insulators to electrical current. At the minor apical foramen, however, there is a small hole in which conductive materials within the canal space (tissue, fluid) are electrically connected to the periodontal ligament that is itself a conductor of electric current. Thus, dentine, along with tissue and fluid inside the canal, forms a resistor, the value of which depends on their dimensions, and their inherent resistivity. When an endodontic file penetrates inside the canal and approaches the minor apical foramen, the resistance between the endodontic file and the foramen decreases, because the effective length of the resistive material (dentine, tissue, fluid) decreases. As well as resistive properties, the structure of the tooth root has capacitive characteristics. Therefore, various electronic methods have been developed that use a variety of other principles to detect the canal terminus. Whilst the simplest devices measure resistance, other devices measure impedance using either high frequency, two frequencies, or multiple frequencies. In addition, some systems use low frequency oscillation and/or a voltage gradient method to detect the canal terminus. The aim of this review was to clarify the fundamental operating principles of the different types of electronic systems that claim to measure canal length.

New electronic canal measuring device based on the ratio method

The most striking disadvantage of most apex locators is that if there are electrolytes in the canal the meter shows a reading which is too short or sometimes the measurement itself becomes impossible. To overcome this drawback, a new concept for electrically measuring the root canal length has been developed. The device simultaneously measures two impedances of the canal using current sources with two different frequencies. Then the ratio between the two electric potentials proportional to each impedance is calculated. The quotient is shown on the device's meter and represents the position of a file tip in the canal. The present study found that the quotient was only negligibly influenced by the electrolyte present in the canal and decreased considerably as the file tip approached the apical foramen.

An in vivo evaluation of Root ZX electronic apex locator

The Root ZX has been introduced recently as a device capable of performing accurately in the presence of sodium hypochlorite, blood, water, local anesthetic, and pulpal tissues. The Root ZX was used to locate the apical foramen in 26 root canals of vital teeth. After extraction of the teeth, a stereomicroscope was used to confirm visually the relationship of the tip of the endodontic file to the apical foramen. The Root ZX located exactly the apical foramen in 17 canals (65.4%), was short in 1 canal (3.8%), and was overextended in 8 canals (30.8%). When a potential error of +/-0.5 mm from the foramen is accepted as a tolerable range for the clinical application of an electronic apex locator, the Root ZX was able to locate the foramen within this range in 25 teeth for a clinical accuracy rate of 96.2%.

A SEM study of in vivo accuracy of the Root ZX electronic apex locator

Twenty-nine unprepared, vital teeth were used to evaluate the accuracy of the Root ZX in locating the root canal foramen. After extraction of the teeth, a scanning electron microscope analyzed the relation of the file tip to the foramen. The sample was divided into two groups (Group A and Group B) according to the presence of a normal apical foramen (along the root main axis) or of a lateral foramen (deviating from the root main axis). With a tolerance level of +/- 0.5 mm, a clinical accuracy rate of 82.75% was recorded in the total sample. With a +/- 1.0-mm tolerance level, an accuracy of 100% was found. The error in locating the apex was significantly smaller in cases with a normal apical foramen (Group A) than in cases with a lateral foramen (Group B) (p < 0.001). An accuracy of 100% at the +/- 0.5-mm tolerance level was registered in Group A.

An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals

The purpose of this study was to compare the canal length determined by an apex locator to the apical constriction in both vital and necrotic canals. Informed consent was obtained from patients waiting to have teeth extracted. The teeth were anesthetized, isolated, and accessed. The pulp was considered vital if bleeding was present in the pulp chamber. The Root ZX was used to measure the root canal length. The file was cemented into place, and the tooth was extracted. Twenty-nine teeth containing 34 cemented files were studied, and the distance from the apical constriction was measured. The Root ZX was 82.3% accurate to within 0.5 mm of the apical constriction. The mean distance from the apical constriction was 0.21 mm in vital cases versus 0.49 mm for necrotic cases. There was no statistical difference between the ability of the Root ZX to determine the apical constriction in vital canals versus necrotic canals.

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.

Accuracy of space analysis with emodels and plaster models

INTRODUCTION

The purposes of this study were to determine the accuracy and speed of measuring the overall arch length and the Bolton ratio, and the time to perform a Bolton analysis for each patient by using software (emodel, version 6.0, GeoDigm Corp, Chanhassen, Minn) compared with hand-held plaster models.

METHODS

Models from 30 patients selected from the files of the Department of Orthodontics at West Virginia University were included in this study. The mesiodistal width of each tooth from first molar to first molar was measured to the nearest 0.1 mm with digital calipers, and the Bolton ratio was calculated for each patient. The times required to make the measurements and to perform the analysis were recorded in seconds by using a stopwatch. This process was repeated to record the digital measurements with the software. To evaluate whether there was any magnification in the emodels, quarter-inch ball bearings were mounted on a modified study model. Measurements of the greatest diameter were taken on each ball bearing by using digital calipers and the emodel software. The difference between the 2 methods was calculated, and a paired t test was used to analyze the data.

RESULTS

There was no significant difference between the Bolton ratios calculated with the 2 methods. A significant difference in arch length calculations was found between the 2 methods, but it was within the range of error found in this study and was considered clinically insignificant. Significant differences were found in the time needed to make the measurements and the calculations between the 2 methods; the emodel software was an average of 65 seconds faster. The measurements on the ball-bearing mounted models were an average of .067 mm greater on the emodel software than direct measurements on the casts (range, 0 to -0.16 mm). The difference was significant (P <.0045).

CONCLUSIONS

These results suggest that, when performing a Bolton analysis, the emodel can be as accurate as, and significantly faster than, the traditional method of digital calipers and plaster models. A clinician who has switched to using emodel software can be confident in his or her diagnoses using it.

Ex vivo accuracy of three electronic apex locators: Root ZX, Elements Diagnostic Unit and Apex Locator and ProPex

AIM

To compare ex vivo the accuracy of three electronic apex locators (EALs): Root ZX, Elements Diagnostic Unit and Apex Locator and ProPex.

METHODOLOGY

Electronic working length determination was carried out in 40 extracted teeth using an ex vivo model. After access preparation, a first operator determined the reference length (AL) for each tooth under a 30x stereomicroscope using the apical constriction as the apical landmark. All teeth were then measured with each EAL and the results obtained were compared with the corresponding AL. The AL was subtracted from the electronically determined distance. The measurements exceeding the AL were recorded as positive (long) and the measurements short of the AL were recorded as negative. Data were analyzed using the Friedman Test and Tukey multiple range test for nonparametric correlation amongst groups. Statistical significance was considered at P < 0.05.

RESULTS

Comparing the differences between measurements obtained with the three EALs and those obtained with the stereomicroscope, the percentage of measurements within +/-0.5 mm of the AL was 97.37% (84.22% within 0.5 mm short of AL) for the Root ZX, 94.28% (88.57% within 0.5 mm short of AL) for the Elements and 100% (35.9% within 0.5 mm short of AL) for the ProPex. The mean difference between the AL and the lengths measured by the Root ZX, the Elements and the ProPex were, respectively, -0.157 +/- 0.228, -0.103 +/- 0.359 and 0.307 +/- 0.271 mm.

CONCLUSIONS

The results of the present study confirm that the EALs determined the canal length within +/-0.5 mm from the apical constriction in the majority of cases. The majority of the ProPex readings were long.

Comparison of radiographic and electronic working lengths

The purpose of this study was to compare the ability of radiographic and electronic methods to determine reliably the location of the apical constriction. The working length of root canals in human cadaver teeth was determined by positioning an endodontic file at the apical termination point as indicated by an apex locator. These same teeth were radiographed at various angles with the file in place. The radiographs were evaluated by five examiners to determine a radiographic termination point for each canal. Teeth were extracted and examined histologically to determine the ideal termination point. The deviations of the two experimental termination points from the ideal termination point were compared. The mean of the absolute value of the deviations from the apical constriction for the apex locator was significantly less (p < 0.05) than that for the radiographic method. Thus, the method using the apex locator was slightly more reliable.

An in vivo comparison of two frequency-based electronic apex locators

The purpose of this study was to compare the accuracy of a two-frequency (Root ZX) and a five-frequency (Endo Analyzer Model 8005) electronic apex locator under clinical conditions. Thirty-two teeth planned for extraction were used. The coronal portion of each canal was flared using Gates Glidden drills and Orifice Shapers. The canals were irrigated with 2.6% sodium hypochlorite. A K-type file was used to determine a separate working length in each canal using the electronic apex locators. The teeth were extracted and the apical 4 mm of each root canal was exposed along the long axis of the tooth. Photographic slides of each canal were projected and the file position in relation to the minor diameter was determined by two investigators. The mean distance between the electronic apex locator working length and minor diameter was 1.03 mm for the Endo Analyzer and 0.19 mm for the Root ZX. A paired sample t test showed that the Endo Analyzer had significantly longer readings beyond the minor diameter than the Root ZX (p < 0.0001). The ability to locate the minor diameter (+/- 0.5 mm) was 90.7% for the Root ZX and 34.4% for the Endo Analyzer Model 8005.

An evaluation of root resorption incident to orthodontic intrusion

A new radiographic method was developed for measuring changes in root length. With this technique, orthodontic intrusion was investigated as a potential cause of apical root resorption of maxillary incisors. The experimental group consisted of 17 patients with excessive overbite who were treated with a Burstone-type intrusion arch, which delivered a low level of force (about 15 gm per tooth). A control group was made up of 17 patients in full-arch fixed appliances who were randomly selected. After a period of approximately 4 months, the intrusion group had only slightly more root resorption than the controls, 0.6 mm versus 0.2 mm (statistically significant difference). Intrusion measured at the center of resistance of the central incisor averaged 1.9 mm. The amount of resorption was not correlated with the amount of intrusion. A weak correlation, r = 0.45, was found between resorption and movement of the apex (i.e., in addition to intrusion, there was often palatal root movement). Results of this study seem to indicate that intrusion with low forces can be effective in reducing overbite while causing only a negligible amount of apical root resorption.

An in vitro evaluation of the accuracy of the root ZX in the presence of various irrigants

The purpose of this study was to evaluate the accuracy of the Root ZX in vitro in the presence of a variety of endodontic irrigants. The in vitro model, described by Donnelly, consisted of refrigerated gelatin made with 0.9% sodium chloride instead of water. The following irrigants were tested: 2% lidocaine with 1:100,000 epinephrine, 5.25% sodium hypochlorite, RC Prep, liquid EDTA, 3% hydrogen peroxide, and Peridex. A total of 30 extracted, single-rooted teeth were used. The experimental measurements in the presence of the various irrigants were compared with the actual canal lengths. The present data indicate that the Root ZX electronic apex locator reliably measured canal lengths to within 0.31 mm and that there was virtually no difference in the length determination as a function of the seven irrigants used. These results strongly support the concept that the Root ZX is a useful, versatile, and accurate device for the determination of canal lengths over a wide range of irrigants commonly used in the practice of endodontics.

Electronic apex locator

Locating the appropriate apical position always has been a challenge in clinical endodontics. The electronic apex locator (EAL) is used for working length determination as an important adjunct to radiography. The EAL helps to reduce the treatment time and the radiation dose, which may be higher with conventional radiographic measurements. According to recent publications, the accuracy of frequency-dependent EALs appears to be much higher compared with traditional-type EALs (simple resistance type or impedance type). This article reviews the history and the working mechanism of the currently available EALs, and suggests the correct usage of the apex locator for a better canal length measurement.

Accuracy of the Endex with variations in canal irrigants and foramen size

Several electronic apex locators (EALs) are currently available. The manufacturer of a new device, the Endex, claims that it is accurate regardless of canal conditions. This study compared the accuracy of the Endex with that of the Exact-a-pex, the Sono-Explorer Mark III, and the Neosono-D SE as to the effects of fluids in the canal and variation in foramen size. Sixty extracted single-canaled teeth were divided into two groups (narrow and wide foramina), depending on whether the apical foramina permitted the tip of a #30 K file to pass through. An in vitro model was used, in which teeth were fitted in test tubes with the roots immersed in 1% agar in phosphate-buffered saline. Root canal lengths were measured in dry canals, then with ethanol, Xylocaine, and sodium hypochlorite in the canals by each electronic apex locator. These lengths were compared with those of the actual root canal lengths. No significant differences were noted among the instruments in dry canals regardless of the foramen size. The endex was generally superior to the other instruments examined in canals containing conductive fluids, especially where the apical foramen was widened.

The accuracy of electronic working length determination

AIM

To determine in vivo the accuracy of two impedance quotient apex locators under clinical conditions.

METHODOLOGY

Electronic working length determination was carried out before extraction in 79 human teeth with 93 root canals. In 51 root canals, the determination was performed using the apex locator Justy II(R) (Hager & Werken, Duisburg, Germany); in 42 canals, the apex locator Endy 5000(R) (Loser, Leverkusen, Germany) was used. A root canal instrument was fixed at working length with composite material prior to extraction followed by the exposure of a radiograph. After histological preparation of the apical region, the teeth were examined under a light microscope. The distance of the file tips to the target intervals 'minor foramen - major foramen' and 'apical canal constriction' was determined. These values were compared with the calculated working lengths, determined by radiographic assessment. The data were statistically analysed by a paired t-test.

RESULTS

For both apex locators and both target intervals, no significant differences between the electronic and radiographical assessments were recorded. The probability of determining the area between minor and major foramen was 82.4% for Justy II and 81% for Endy 5000. However, accurate determination of the apical constriction was only successful in 51% (Justy II) and 64.3% (Endy 5000) of canals. Variation of the inaccurate measurements was higher for Endy 5000 than for Justy II.

CONCLUSIONS

Under clinical conditions, it is possible to determine the region between the minor and major apical foramen with electronic length measuring devices (ELD). However, use of these devices does not result in precise determination of the apical constriction.

Comparison of intermaxillary tooth size discrepancies among different malocclusion groups

The purpose of this study was to determine whether there is a prevalent tendency for intermaxillary tooth size discrepancies among different malocclusion groups. This study consisted of 60 subjects who served as the normal occlusion group and 300 patients divided into 5 malocclusion groups (ie, Class I with bimaxillary protrusion, Class II Division 1, Class II Division 2, Class III, and Class III surgery). Tooth size measurements were performed on the models of normal occlusion and pretreatment models of patients by the Three Dimension Measuring Machine. Moreover, tooth size ratios, analyzed as described by Bolton and the Student t test showed no sexual dimorphism for these ratios in each of 6 groups, so the sexes were combined for each group. Then these ratios were compared among different malocclusion groups. The results showed no significant difference between subcategories of malocclusion, so these groups were combined. There were now 120 cases in each of 3 categories: Class I, Class II, and Class III. A significant difference was found for all the ratios between the groups, the ratios showing that Class III > Class I > Class II. It demonstrated that intermaxillary tooth size discrepancy may be one of the important factors in the cause of malocclusions, especially in Class II and Class III malocclusions. Thus this study proved the fact that Bolton analysis should be taken into consideration during orthodontic diagnosis and therapy.

Accuracy of a new apex locator: an in vitro study

AIM

The purpose of this study was to test in an in vitro model the accuracy of a Bingo 1020 electronic apex locator, to compare the results to those of a well known apex locator, Root ZX, as well as to those of the radiographic method of tooth length determination.

METHODOLOGY

A total of 120 extracted teeth, preserved in Thymol solution and kept refrigerated, was used for the study. The experiment was performed on single-rooted teeth and on one-root canal, chosen randomly, in multirooted teeth. The teeth were randomly divided into 12 groups of 10 teeth each. After access preparation, the actual length (AL) was measured. The teeth were embedded in an alginate model specially developed for testing apex locators. Electronic tooth length measurements (EL) were carried out prior to root canal preparation using the two electronic apex locators (EAL) - Root ZX and Bingo 1020; three measurements were taken and an average computed. After the third measurement, the file was left in the root canal and a periapical radiograph was taken. The radiographic length (RL) was recorded by measuring the file length from the coronal reference point to the tip of the file. Each root canal was then prepared to a no. 40 K-file diameter using a standardized technique; saline was used for irrigation. Upon completion of the root canal preparation, EL measurements were taken by each EAL in dry conditions and with different irrigation solutions. Each measurement was repeated three times. The RL was recorded according to the last EL measurement. Results were subjected to statistical analysis.

RESULTS

In all parameters tested, a significant statistical difference was found between Bingo 1020 and the Root ZX. Measurements obtained using the Bingo 1020 were consistently closer to the AL (0.08 mm) than those obtained using the Root ZX. Both EALs measured the tooth length with great accuracy and a positive correlation of 0.76 (P = 0.00) existed between the two devices. No significant difference was found between the two apex locators when measurements were taken with the different irrigants (P = 0.34) and the content of the root canal did not affect the accuracy of the measurements. Lengths obtained by calculations from the radiographs were longer than the AL as well as the length obtained by both EALs (P = 0.00).

CONCLUSIONS

The Bingo 1020 proved to be as reliable as Root ZX and was user friendly. Under the experimental conditions, electronic measurements were more reliable than radiographs in the process of root length determination.

In vivo comparison of working length determination with two electronic apex locators

AIM

To compare the accuracy of two electronic apex locators (EALs) in the same teeth in vivo.

METHODOLOGY

The working lengths in 20 teeth with a single canal were determined with two different EALs (Root ZX; J. Morita Corporation, Tokyo, Japan and Raypex 5 VDW, Munich, Germany) before extraction. When the first EAL was used the files were advanced until the display indicated the 'apical constriction'. The files were then fixed in removable and replaceable light curing composite patterns. The procedure was repeated in the same tooth with the second EAL and a different file. The teeth were then extracted and the apical 4 mm of the root canals were exposed. After that the apical parts with the repositioned files in the canals were digitally photographed under a light microscope. On the images the minor diameter and the major foramen of each sample were marked and the respective distances of the file tips from these positions were measured with a computer program. Subsequently the values of the two groups of EALs were compared using a paired sample t-test.

RESULTS

The minor foramen was located within the limits of +/-0.5 mm in 75% of the cases with the Root ZX and in 80% of the cases with Raypex 5. The paired sample t-test showed no significant difference between the EALs regarding determination of the minor foramen.

CONCLUSION

The use of EALs is a reliable method for determining working length. The differences between the two EALs were not statistically significant.

In vitro measurement accuracy of an electronic apex locator in teeth with simulated apical root resorption

The purpose of this in vitro study was to evaluate the accuracy of Root ZX apex locator to determine the working length in teeth with simulated apical root resorption. Fifty extracted, single-rooted, human teeth with mature apices were used in this study. An irregular cavity defect was drilled at the apex of each tooth simulating an apical root resorption. Three operators used the Root ZX to measure the working lengths, comparing the electronic readings with the direct visual measurements. The Root ZX was 62.7%, 94.0%, and 100.0% accurate to within 0.5 mm, 1 mm, and 1.5 mm of the direct visual measurements, respectively. Statistically significant differences were observed between operator A and B and A and C (p < 0.01), but no significant differences were detected between operator B and C (p > 0.01).

Crown-to-implant ratios of single tooth implant-supported restorations

STATEMENT OF PROBLEM

The crown-root ratio guidelines used to establish a prognosis for teeth serving as abutments are commonly applied to a dental implant-supported restoration or potential implant site. These guidelines are generally empirical and therefore lack scientific validation.

PURPOSE

The purpose of this study was to first determine the crown-implant ratios of single tooth implant-supported restorations, and then to compare the crown-implant ratios to the guidelines established for the crown-root ratios of natural teeth.

MATERIAL AND METHODS

A retrospective cohort study design was used. The cohort was composed of subjects (n=294) having 1 or more single tooth implants (Bicon) placed between May 1992 and April 2004. A chart review was conducted to obtain radiographs in which the entire crown and implant were visible. The length of the crown and implant were measured directly from the radiographs using magnification to calculate the crown-to-implant ratio. The length of the crown was divided by the length of the implant to determine the crown-implant ratio. Calculations were made to within 0.1 mm. Implant failure was recorded and defined as removal of the implant for any reason. Data were analyzed with descriptive statistics.

RESULTS

A total of 889 single tooth implants from 294 patients were measured and included in the study. The mean (SD) follow-up time was 2.3 (1.7) years, with a range of 0.1 to 7.4 years. Sixteen failures were recorded for a survival rate of 98.2%. The crown-implant ratios ranged from 0.5:1 to 3:1. The mean (SD) crown-implant ratio of implants in function was 1.3:1 (0.34). The mean crown-to-implant ratio of failed implants was 1.4:1 (2.5).

CONCLUSIONS

The results of this study suggest that the crown-to-root ratio guidelines associated with natural teeth should not be applied to a potential implant site or existing implant restoration. The crown-to-implant ratios of those implants that were in function were similar to those implants that failed.

Image quality of direct digital intraoral x-ray sensors in assessing root canal length. The RadioVisioGraphy, Visualix/VIXA, Sens-A-Ray, and Flash Dent systems compared with Ektaspeed films

The Trophy RadioVisioGraphy model 32000 system in Normal Mode, the Trophy RVG-PC in Normal and Archive Mode, the Gendex VIXA/Visualix, the Regam Sens-A-Ray, and the Villa Flash Dent in High-Resolution Mode and Normal Mode were compared with respect to the visibility of endodontic files. Kodak Ektaspeed film served as the reference. An acrylic embedded human skull was prepared for taking radiographs with endodontic files (Kerr files size 10 and size 15) on full root length and 1.5 mm short in upper and lower premolars and molars. Possibilities for enhancement of the digital images were not studied. Receiver operating characteristics curves were derived and the areas under the curves were averaged and compared using Student's t test statistic (p < 0.05). Kodak Ektaspeed film gave acceptable results for both file sizes. Both Trophy RVG units in Normal Mode and the Regam Sens-A-Ray system gave results above the areas under the curves equals 0.95 for the size 15 files. For the size 10 files the values of the areas under the curves of all sensors systems were below this threshold. It is concluded that both RVG units in Normal Mode and the Sens-A-Ray system render a comparable result with conventional radiography in determining root canal length with the use of a size 15 files. All sensor systems were unacceptably inferior to film images when size 10 files were used.

Influence of Apical Constriction Diameter on Root ZX Apex Locator Precision

Small-diameter hand files are systematically used to determine the initial working length and to establish patency of the root canal. In wide canals, electronic apex locator accuracy might be influenced by file size. This article reports on a study to assess the influence of apical constriction diameter on the precision of the Root ZX apex locator by using files of varying diameter on teeth with 3 different degrees of apical widening: 0.37, 0.62, and 1.02 mm. Ten extracted single-root teeth, stored in saline solution at 37 degrees C, were sectioned at the enamel-cement junction and embedded in an alginate mold. Initial working length (L0) was determined with a #10 Kerr file, and canals were irrigated with either 50% citric acid or 5.25% sodium hypochlorite. To assess the ability of the locator to identify the narrowest area of the root canal as constriction diameter increased, the canal was progressively widened by insertion of files of increasing diameter (10-100) at a point L0+1 mm. After each enlargement, the working length (L) was redetermined, with files from #10 (L10) up to the file used for widening. Comparison of statistical results was based on the difference between final working length and initial length (L10) for each apical width. Statistical analysis was carried out with analysis of variance test for comparison of means. Results showed that at apical constriction widths of 0.37 and 0.62 mm, there was no significant difference between initial working lengths as determined by a Kerr #10 file and final working lengths after widening with files of up to #60. In those teeth whose apical width had been increased to 1.02 mm, there was no statistically significant difference between initial and final working lengths as measured by files from #10-#25; however, significant differences were apparent between #10 and #30, #35, or #40 (P<.05), and the degree of significance increased considerably (P<.001) for files #45 or greater. These results suggest that Root ZX apex locator precision varies as a function of apical constriction diameter.

Electronic length measurement using small and large files in enlarged canals

Electronic apex locators are frequently used attached to a small size endodontic file; however, the effect on the measurement of the relative diameters of the file and the root canal has not been clarified. In this study, the length of enlarged canals was measured using small size files and files matching the canal diameter to observe a possible discrepancy. The accuracy of electronic length control during canal preparation with rotary files was also assessed. The root canals in 21 extracted, single rooted teeth were accessed, and their actual length (AL) established by passing a size 10 file just through the minor apical foramen. The teeth were then embedded in an alginate mold. The initial canal length (IL) was measured with the Root ZX apex locator by negotiating a size 10 file to the apical constriction. The canal was enlarged to size 60 with rotary files while the length was continuously controlled with the apex locator. Then, the final length measurements were obtained with a size 10 file and a size 60 file (FL-10 and FL-60, respectively). The average values of IL, FL-10 and FL-60 were calculated and compared using Repeated Measures Analysis of Variance followed by Tukey's Studentized Range test (P < 0.05). Using composite resin, the size 60 files were secured at the FL-60 length, the teeth were removed from the alginate mold, stained with Picroformal DI Buoin stain and the position of the file tip was observed histomorphometrically after the apical 4 mm of the canal was exposed by grinding the buccal aspect of the root. The IL was 0.45 mm shorter than AL (P < 0.05). The differences between FL-10, FL-60 and IL were not statistically significant. Histomorphometrically, the apical constriction was absent in all the teeth, but the file tips were confined within the root. This study concluded that the Root ZX indicated the location of an apical constriction even when the anatomic constriction was eliminated. In the enlarged canals, length measurements obtained with small and large size files were comparable.

Clinical evaluation of the measuring accuracy of ROOT ZX in primary teeth

OBJECTIVE

The aim of this study was to assess the accuracy of an electronic device (Root ZX; Morita, Tokyo, Japan) for measuring the root canal length in primary teeth.

STUDY DESIGN

The pulp tissue was removed from 71 nonrestorable teeth scheduled to be extracted under general anesthesia, and the root canals (n = 105) were irrigated (H(2)O(2), 3%; NaOCl, 1%). Subsequently, the length was determined clinically with the electronic device prior to extraction. Treatments were performed by 2 dentists (42 and 63 root canals). After extraction, the real length was recorded and the 2 measurements were compared.

RESULTS

Measurements were affected significantly by the dentists (P < .01; chi(2)). However, regression analysis revealed sufficient accuracy of the device, with a tendency to estimate the root canal length just short (x = -0.98 +/- 1.75 mm) of the apex. These results were not influenced by tooth type, root canal type, status of the periapex, or clinical condition (P > .05; chi(2)).

CONCLUSION

Root ZX can be strongly recommended for clinical implementation of endodontics in primary teeth, particularly when treating fidgety children.