What type of filling? Best practice in dental restorations.
Explore the source record for details and available documents.
Cost-Benefit Analysis↗
Biomedical subjects
P M Dummer
Publications and source records attributed to P M Dummer.
Shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated root canals. Part 1.
The aim of this study was to determine the shaping ability of Mity Roto 360 degrees and Naviflex nickel-titanium rotary instruments in simulated root canals. In all, 80 canals consisting of four different shapes in terms of angle and position of curvature were prepared by Mity Roto 360 degrees and Naviflex instruments using the techniques recommended by the manufacturers. This study describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, change in canal length, and three-dimensional canal form. Overall, the mean preparation time for canals prepared using Mity instruments was 5.99 min and 5.81 min when using Naviflex instruments. Canal shape had no significant effect on the speed of preparation with either instrument. No instruments separated during the study; however, 14 Naviflex and 2 Mity instruments were deformed. Canal type did not influence significantly the tendency of either instrument to deform. None of the canals became blocked with debris during preparation. The majority of canals prepared by both instruments retained their original working length, and there was no significant difference between the canal shapes in terms of the mean loss of distance or category of distance change for either instrument. Apical stops as judged from intracanal impressions were present in 29 (72%) of the canals prepared with Mity instruments and in 33 (82%) of those prepared with Naviflex instruments. However, the majority were judged to be of poor quality. Significant differences (p < 0.05) were noted in the quality of apical stops between the canal types using Mity instruments. Canals prepared with Mity and Naviflex instruments were found to be smooth in the apical half of the canal in approximately one-half of the specimens and coronally in nearly all canals. Neither instrument produced horizontal or longitudinal grooves. Favorable flow characteristics were apparent in over one-half of the canals prepared with Mity Roto instruments; however, nearly all specimens had poor taper. Flow and taper were generally poor in the specimens prepared with Naviflex instruments. Under the conditions of this study, Mity Roto 360 degrees and Naviflex instruments prepared canals rapidly, with no separations, canal blockages, and with minimal change in working length. Although, flow was adequate using Mity Roto 360 degrees instruments, the taper characteristics were less than ideal compromising the three-dimensional form of the canals. Naviflex instruments, while creating better taper, produced poorer flow characteristics. The results suggest that when using Mity Roto 360 degrees or Naviflex instruments, the stepdown sequence should be modified to improve canal flow and taper. Alternatively, an instrument with increased taper should be used to complete preparation before obturation.
Dental Instruments↗
Shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated root canals. Part 2.
The aim of this study was to determine the shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated canals. Forty simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by both sets of instruments using a stepdown approach. This study describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation, and thus the overall postoperative shape. Pre- and postoperative images of the canals were taken using a videocamera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. Neither Mity Roto 360 degrees nor Naviflex instruments created any zips or elbows. Ledges were produced in 20 (50%) canals prepared with Mity instruments and in 29 (72%) canals prepared with Naviflex instruments. Statistically significant differences (p < 0.001) between canal shapes occurred in relation to the incidence of ledges with 40 degrees canals (35) associated with more aberrations than 20 degrees canals (14); the position of the beginning of the curve had no effect. The distance of ledges from the end point of preparation was also affected significantly (p < 0.01) by canal shape. Neither instrument created any perforations or danger zones. At specific positions along the canal length, canal shape had a significant influence on total width and the amount of material removed from the inner and outer aspects of the canal curve. The direction of canal transportation at the end point of preparation was most frequently toward the outer aspect of the curve in canals prepared with Naviflex instruments, whereas the Mity instruments produced a more balanced preparation. At the apex and beginning of the curve, transportation with both instruments was generally toward the outer aspect of the curve. Overall, mean absolute transportation was small and was below 0.1 mm at every position except the orifice. Under the conditions of this study, Mity Roto 360 degrees and Naviflex rotary instruments prepared canals with a high incidence of ledges. However, in the absence of other aberrations, both instruments would seem to be a valuable addition to the endodontic armamentarium.
Dental Instruments↗
Comparison of the performance of four files with rounded tips during shaping of simulated root canals.
A total of 160 simulated canals of various angles and positions of curvature were prepared by hand using either Mani Flexile Files, Mani SEC-O Files, Maillefer Flexofiles, or Zipperer Flexicut Files. After orifice enlargement, each file type was used to prepare 40 canals employing a balanced force motion and a modified double-flared technique. Pre- and postoperative images of the canals were taken with a videocamera, and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre- and postoperative views. Significant differences (p < 0.001) in preparation time were observed, with Flexile Files being quickest and SEC-O Files being slowest. Overall, Flexofiles and Flexicut Files deformed significantly more (p < 0.001) than Flexile and SEC-O Files. The incidence of canal blockage was not influenced by instrument type, but the incidence of apical extrusion was significantly greater (p < 0.001) with SEC-O Files. SEC-O Files created significantly fewer (p < 0.001) and significantly narrower (p < 0.001) zips, with significantly less (p < 0.001) removal of material from the outer aspect of the curve and thus significantly less (p < 0.001) transportation. Flexicut Files created the widest canals apically, with the greatest removal of material from the outer aspect of the curve and the most transportation. Flexofiles created significantly more (p < 0.001) perforations. Under the conditions of this study, obvious differences between instruments were highlighted with SEC-O Files preparing canals more safely and with least destruction. The unique rounded tip of the SEC-O Files may have had an influence on the outcome.
Analysis of Variance↗
Evaluating undergraduate preclinical operative skill; use of a glance and grade marking system.
OBJECTIVES: The purpose of the study was to evaluate the intra- and inter-examiner variability of a panel of examiners using a 'glance and grade' marking system when assessing Class II preparations. METHODS: The examination panel consisted of five university staff with varying clinical and teaching experience. The panel assessed 75 disto-occlusal preparations suitable for restoration with dental amalgam prepared in extracted human premolar teeth. The majority of the preparations were cut by undergraduates in their preclinical year of study and the remainder by an experienced staff member. The panel were blind to the identity of each operator. RESULTS: The study revealed a high degree of both intra- and inter-examiner variability, with some preparations being given a pass on one occasion and a fail on another and vice-versa. In addition, some of the panel, perhaps assuming that the practical exercise had been prepared entirely by undergraduates, were reluctant to award good grades. CONCLUSIONS: The study has highlighted the need for better staff training and a more comprehensive system of assessing preclinical skills.
Clinical Competence↗
Shaping ability of ProFile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 2.
The aim of this study was to determine the shaping ability of ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using the 'crown down' approach recommended by the manufacturer. Part 2 of this two-part report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and the overall post-operative shape. Out of 37 completed specimens 9 zips (24%) and one ledge (3%) were created, but no perforations or danger zones were found. There were significant differences (P < 0.01) between canal shapes for the incidence of zips and elbows but not for their distance from the end-point of preparation. At specific positions along the canal length there were significant differences between the canal types in terms of their mean total width; overall, at the end-point of preparation and along the curved portion of the canals those specimens with 40 degrees curves were widest. This trend continued for the width of material removed from the outer aspect of the canal curves, whereas along the inner aspect of curves more material was removed in the 20 degrees canals. Overall, transportation was towards the outer aspect of the curve at the end-point of preparation and along the curved portion of canals but more balanced along the straight coronal section. Absolute transportation was small and below 0.1 mm at every position including the zips. Under the conditions of this study, ProFile nickel-titanium rotary instruments with ISO sized tips produced a larger number of zips than expected; however, the degree of zipping was limited and relatively minor.
Dental Instruments↗
Shaping ability of Quantec Series 2000 rotary nickel-titanium instruments in simulated root canals: Part 1.
The aim of this study was to determine the shaping ability of Quantec Series 2000 nickel-titanium instruments in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by Quantec instruments using the technique recommended by the manufacturer. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, change in canal length and three-dimensional canal form. The time necessary for canal preparation was on average 5.7 min and was significantly influenced (P < 0.01) by canal shape. One instrument fractured and three size nine instruments deformed; however, canal shape did not influence significantly instrument failure. All of the canals remained patent, none became blocked with debris. The majority of the canals maintained working distance (26 out of 40), however the mean change in length differed significantly (P < 0.05) between canal types. Overall, canals with 40 degrees curves lost length whilst those with 20 degrees curves gained in length. Examination of intracanal impressions revealed that preparation with Quantec Series 2000 instruments produced canals with definite apical stops, smooth canal walls and good flow and taper. However, the quality of apical smoothness and flow was influenced significantly (P < 0.0001) by canal shape with specimens having 40 degrees canals displaying less desirable qualities. Under the conditions of this study, Quantec Series 2000 rotary nickel-titanium instruments prepared simulated canals rapidly, safely and with good three-dimensional form.
Dental Instruments↗
Shaping ability of Quantec Series 2000 rotary nickel-titanium instruments in simulated root canals: Part 2.
The aim of this laboratory based study was to determine the shaping ability of Quantec Series 2000 nickel-titanium rotary instruments in simulated root canals. A total of 40 canals with four different shapes in terms of angle and position of curve were prepared with Quantec Series 2000 instruments using the technique recommended by the manufacturer. Part 2 of this report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and overall post-operative shape. Pre- and post-operative images of the canals were taken using a video camera attached to a computer with image analysis software. The pre- and post-operative views were superimposed to highlight the amount and position of material removed during preparation. Twenty-one zips and elbows were created during preparation with a significant difference (P < 0.005) between canal shapes in terms of the incidence of aberrations. Four perforations were created, with significant differences (P < 0.005) between the canal shapes; three ledges were also created but no danger zones. Highly significant differences (P < 0.001) were apparent between the canal shapes in total canal width at specific points along the canal length and in the amount of resin removed from the inner and outer aspects of the curve. Canal transportation at the end-point of preparation was most frequently directed towards the outer aspect of the curve, and without exception in canals with 40 degrees curves. At the beginning of the curve, transportation became more evenly balanced between the inner and outer aspect of the curve, although predominated towards the outer. Transportation was generally directed towards the outer at the orifice, especially in canals with 40 degrees curves. Mean absolute transportation at the various measurement points was less than 0.11 mm; significant differences occurred between canal shapes at the end-point of preparation (P < 0.0001), at the zips (P < 0.005), at the apex (P < 0.0001) and beginning of the curve (P < 0.05) and at the orifice (P < 0.0001). Under the conditions of this study, Quantec Series 2000 rotary nickel-titanium instruments created a relatively large number of aberrations including four perforations. The aberrations were created by the larger instruments implying that these should be used with caution at the full working distance. Scanning electron micrographs of these instruments revealed sharp instrument tips which appeared likely to predispose to transportation and the creation of defects along the outer aspect of severely curved canals.
Dental Instruments↗
Shaping ability of Profile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 1.
The aim of this study was to determine the shaping ability of ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips in simulated canals. A total of 40 simulated root canal made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using the 'crown down' approach recommended by the manufacturer. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length and three-dimensional canal form. The time necessary for canal preparation was on average 5.2 min and was not influenced significantly by canal shape. Three instrument fractures occurred and a further 3 instruments deformed; size 35 instruments failed the most (4) followed by size 30 (2), four of the failures occurred in canals with 40 degrees curves. None of the canals became blocked with debris and change in working distance was minimal. Intra-canal impressions of canal form demonstrated that most canals had apical stops and smooth canal walls whereas all canals had good flow and taper. Under the conditions of this study, ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips prepared simulated canals rapidly and created good three-dimensional form.
Dental Instruments↗
Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 2.
The aim of this laboratory based study was to determine the shaping ability of Lightspeed nickel-titanium rotary instruments in simulated root canals. A total of 40 canals with four different shapes in terms of angle and position of curve were prepared with Lightspeed instruments using the stepback technique recommended by the manufacturer. This report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation, and overall postoperative shape. Preoperative and postoperative images of the canals were taken using a video camera attached to a computer with image analysis software. The preoperative and postoperative views were superimposed to highlight the amount and position of material removed during preparation. Only one (2.5%) zip and one elbow were created, with no ledges, perforations, danger zones, or blockages being produced. At specific points along the canal length there were highly significant differences (p < 0.001) between the canal shapes in total canal width and in the amount of resin removed from the inner and outer aspects of the curve. The direction of canal transportation at the end point of preparation was most frequently toward the outer aspect of the curve; although in half of the canals, transportation was either directed toward the inner aspect or not observed. At the apex of the curve, the beginning of the curve, and halfway to the orifice, transportation was reversed with the majority of canals being transported toward the inner aspect of the curve. Mean absolute transportation was small and was below 0.06 mm at every position except the orifice. Overall, Lightspeed rotary instruments prepared canals well and would appear to be a valuable addition to the endodontic armamentarium.
Dental Alloys↗
Shaping ability of Lightspeed rotary nickel-titanium instruments in simulated root canals. Part 1.
The aim of this study was to determine the shaping ability of Lightspeed nickel-titanium rotary instruments in simulated canals. Forty canals consisting of four different shapes in terms of angle and position of curvature were prepared by Lightspeed instruments using the technique recommended by the manufacturer. This report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length, and three-dimensional canal form. Overall, the mean preparation time for all canals was 8.12 min with canal shape having no significant effect on the speed of preparation. No instruments deformed or separated during the study, and none of the canals became blocked with debris. Seventeen canals retained their original working length, but 16 gained in length and 7 lost length. There was no significant difference between the canal shapes in terms of the mean loss of distance or category of distance change. Apical stops as judged from intracanal impressions were present in 23 of the canals but they were all judged to be of poor quality. The canals were found to be smooth in the apical half of the canal in 36 specimens and in the coronal half of 24 specimens. All the canals had poor taper characteristics, and only 16 specimens showed good flow characteristics. Under the conditions of this study, Lightspeed instruments prepared canals rapidly, with no fractures, canal blockages, and with minimal change in working length. The three dimensional form of the canals was compromised as flow and taper were less than ideal, presumably as a result of an ineffective stepback procedure. The results imply that either the stepback sequence should be modified or another instrument with increased taper should be used to refine the canal walls before obturation.
Dental Alloys↗
Periapical radiographic techniques during endodontic diagnosis and treatment.
The objective of this article is to describe various radiographic projections which can be used during endodontic therapy. Changes to the angulation of the X-ray beam in relation to the teeth and film can help diagnosis and treatment by producing images which provide additional information not always visible on radiographs taken with standard angulations. For example, changes in angulation can be useful to determine the number and curvature of roots and canals, to identify superimposed roots and to distinguish between anatomical landmarks and apical pathology. Although use of such techniques increases the diagnostic yield of films, it must be appreciated that such views lead to images that are less distinct because of inherent image distortion. Nevertheless, use of the various techniques during endodontics can provide substantial benefit for clinicians in their daily practice.
Dental Pulp Cavity↗
Shaping ability of NT Engine and McXim rotary nickel-titanium instruments in simulated root canals. Part 1.
The aim of this study was to determine the shaping ability of NT Engine and McXim nickel-titanium rotary instruments in simulated root canals. In all, 40 canals consisting of four different shapes in terms of angle and position of curvature were prepared by a combination of NT Engine and McXim instruments using the technique recommended by the manufacturer. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length and three-dimensional canal form. Overall, the mean preparation time for all canals was 6.01 min, with canal shape having a significant effect (P < 0.01) on the speed of preparation. One instrument fractured and only four instruments deformed, with most of the failures occurring in canals with curves which began 12 mm from the orifice, that is, in short acute curves. None of the canals became blocked with debris. Following preparation, 20 canals retained their original working length but 19 lost length and one gained in length; there were significant differences (P < 0.05) between the canal shapes in terms of mean loss of distance and in the category of distance change. Apical stops as determined from intracanal impressions were present in 37 of the canals; 16 were judged to be of good quality and 21 of poor quality. The canals were found to be smooth in the apical half of the canal in 33 specimens and in the coronal half of 39 specimens. All canals had good taper characteristics and 35 had good flow characteristics. Under the conditions of this study, NT Engine and McXim instruments prepared canals rapidly, with few deformations, no canal blockages and with minimal change in working length. The three-dimensional form of the canals demonstrated good flow and taper characteristics.
Dental Alloys↗
Shaping ability of NT Engine and McXim rotary nickel-titanium instruments in simulated root canals. Part 2.
The aim of this laboratory-based study was to determine the shaping ability of NT Engine and McXim nickel-titanium rotary instruments in simulated root canals. A total of 40 canals with four different shapes in terms of angle and position of curve were prepared with NT Engine and McXim instruments, using the technique recommended by the manufacturer. Part 2 of this report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and overall postoperative shape. Pre- and postoperative images of the canals were taken using a video camera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. No zips, elbows, perforations or danger zones were created during preparation. Forty-two per cent of canals had ledges on the outer aspect of the curve, the majority of which (16 out of 17) occurred in canals with short acute curves. There were significant differences (P < 0.001) between canal shapes in terms of the incidence of ledges. There were highly significant differences (P < 0.001) between the canal shapes in total canal width at specific points along the canal length and in the amount or resin removed from the inner and outer aspects of the curve. The direction of canal transportation at the end-point of preparation was most frequently towards the outer aspect of the curve, especially in canals with 40 degrees curves. At the beginning of the curve, transportation in the majority of canals was towards the inner aspect of the curve. Mean absolute transportation was less than 0.03 mm throughout the curve and towards the end-point, with significant differences between canal shapes occurring at the apex (P < 0.05) and at the beginning of the curve (P < 0.001). Under the conditions of this study, NT Engine and McXim rotary nickel-titanium instruments created no aberrations other than ledges and produced only minimal transportation. The overall shape of canals was good.
Dental Alloys↗
Undergraduate endodontic teaching in the United Kingdom: an update.
Anecdotal evidence and scientific surveys suggest that the quality of root canal treatment within the General Dental Services is often less than ideal. Six years ago, it was reported that endodontic teaching in the United Kingdom was given a low priority and that the time devoted to the laboratory practice of root canal treatment should be increased. In the following year, the European Endodontic Society (ESE) published guidelines for the teaching of Endodontology and made recommendations as to what should be included in the undergraduate curriculum. Shortly afterwards, the ESE published quality guidelines for endodontic treatment. The aim of this project was to determine the current pattern of undergraduate endodontic teaching within the dental schools of the UK. Data were gathered by questionnaire from all 14 undergraduate dental schools and supplemented with further detailed enquiries where necessary. The results were compared with that reported following an identical survey carried out previously. Although the ESE curriculum guidelines for endodontic teaching provide an overall framework for teaching, the results of this study confirmed that a number of topics were either not included or were covered only briefly. However, the average time devoted to the preclinical instruction of root canal treatment in the first clinical year had increased from 14 to 24 h, with additional time provided in subsequent years by the majority of schools. In most instances, staff teaching endodontology in the UK have no specialist training.
Curriculum↗
Shaping ability of ProFile.04 Taper Series 29 rotary nickel-titanium instruments in simulated root canals. Part 2.
The aim of this study was to determine the shaping ability of ProFile.04 Taper Series 29 rotary nickel-titanium instruments in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using a step-down approach. Part 2 of this two-part report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and the overall postoperative shape. No zips, perforations or danger zones were created although 24 specimens (60%) had ledges on the outer wall of the canal. The incidence of ledges differed significantly (P < 0.001) between the canal shapes. At specific points along the canal length there were highly significant differences (P < 0.001) in total canal width and in the amount of material removed from the inner and outer aspects of the curve between the various canal shapes. Overall, 40 degrees canals were wider than 20 degrees canals and canals with curves which began 8 mm from the orifice were wider than 12 mm canals. The direction of canal transportation at the end-point of preparation was balanced between inner and outer in the 8 mm canals, but more often towards the outer in the 12 mm canals. At the apex of the curve, transportation was invariably towards the outer aspect of the curvature. At the beginning of the curve, transportation was more balanced between inner and outer. Mean absolute transportation, ignoring direction, was generally greater in 40 degrees canals and in those with the curve beginning 8 mm from the orifice. Of particular importance was the finding that excessive resin was removed from the outer aspect of the canal at the apex of the curve which was often associated with irregular widened areas or ledges. This is in contrast to the pattern of tissue removal found with stainless steel hand instruments where more resin is removed from the inner aspect of the canal at the apex, to create a danger zone.
Dental Alloys↗
Shaping ability of ProFile.04 Taper Series 29 rotary nickel-titanium instruments in simulated root canals. Part 1.
The aim of this study was to determine the shaping ability of ProFile.04 Taper Series 29 nickel-titanium instruments in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using a step-down approach. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, loss of canal length and three-dimensional canal form. The time necessary for canal preparation was not influenced significantly by canal shape. No instrument fractures occurred but a total of 52 instruments deformed. Size 6 instruments deformed the most followed by sizes 5, 3 and 4. Canal shape did not influence significantly instrument deformation. None of the canals became blocked with debris and loss of working distance was on average 0.5 mm or less. Intracanal impressions of canal form demonstrated that most canals had definite apical stops, smooth canal walls and good flow and taper. Under the conditions of this study, ProFile.04 Taper Series 29 rotary nickel-titanium instruments prepared simulated canals rapidly and created good three-dimensional form. A substantial number of instruments deformed but it was not possible to determine whether this phenomenon occurred because of the nature of the experimental model or through an inherent design weakness in the instruments.
Dental Alloys↗
Shaping ability of the M4 handpiece and Safety Hedstrom files in simulated root canals.
The aim of this study was to assess the shaping ability of the M4 reciprocating handpiece and Safety Hedstrom files in simulated canals. A total of 40 simulated canals of various angles and positions of curvature were prepared with an M4 handpiece using Safety Hedstrom files oriented with the ground, flattened surface towards the inner aspect of the curve. A standard regimen was adopted throughout. Pre- and post-operative longitudinal images of the canals were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount and location of resin material removed as a result of preparation were determined from composite images of superimposed pre- and post-operative views. Preparation time varied significantly (P < 0.001) between the canal types; overall, 20 degrees canals were prepared more quickly than 40 degrees canals. Zips and elbows were observed in 16 out of the 40 canals with most (11) being created in 40 degrees specimens. Ledges were found in 19 canals and perforations in only 1. There were no significant differences between canal shapes for these aberrations. Excessive removal of material from the inner aspect of the canal at the curve to create a danger zone was found in 20 canals, but only in those with 40 degrees curves. Significant differences in total canal width between the canal types were seen at the zips (P < 0.05), elbows (P < 0.05) and danger zones (P < 0.001). Transportation at the danger zones varied significantly (P < 0.001) between canal types. Under the conditions of this study, the M4 handpiece and Safety Hedstrom files created hour-glass preparations in a substantial proportion of canals. In reality, the Safety Hedstrom file with its one flattened surface was ineffective at reducing removal of material along the inner aspect of canal curves in severely curved specimens and clearly has the potential to create strip perforations in teeth.
Analysis of Variance↗