Methods of accessing a pulp chamber

Abstract

A method of accessing a pulp chamber of a tooth without puncturing the furcation of the tooth includes providing an endodontic instrument having an elongated shaft with an upper end and a lower end, a stop fixed to the shaft at a distance between 6-8 mm from the lower end, and a cutting head located along the shaft adjacent the lower end thereof, whereby the cutting head has a cutting surface. The method includes abutting the cutting head against a crown of the tooth, rotating the endodontic instrument while applying a force through the cutting head onto the crown of the tooth for cutting through the tooth to the pulp chamber and advancing the cutting head toward the pulp chamber until the stop contacts the crown of the tooth.

Description

BACKGROUND OF THE INVENTION

The present invention is generally related to endodontic instruments and is more particularly related to an endodontic instrument used to drill an access opening into a pulp chamber of a molar or bicuspid.

A molar includes a crown that projects above a gum line and a root that is secured within a jaw bone. The inside of the molar has a pulp chamber and root canal system through which blood vessels, nerves and connective tissue (hereinafter referred to as “pulp tissue”) extends. The pulp tissue extends from the crown of the tooth to the lower end of the roots where it connects to bone surrounding the root of the tooth. A bicuspid has a structure that is similar to that of a molar.

Frequently, the pulp chamber or root canal of a tooth becomes infected or inflamed. These problems may be caused by repeated dental procedures on the tooth, a crack in the tooth, blunt trauma to the tooth or tooth decay. The symptoms generally associated with an infected or inflamed pulp chamber include sensitivity to heat or cold, swelling and tenderness in the nearby gums, pain and/or discoloration of the tooth. Failure to treat an infected or inflamed pulp chamber may eventually lead to the formation of an abscess and/or cause severe pain.

An endodontic procedure is typically used to treat a tooth having an infected or inflamed pulp chamber. In endodontic therapy, commonly referred to as root canal, a dentist operates on a diseased pulp by removing the diseased pulp tissue and filling in the pulp chamber and the root canal with biocompatible material. Initially, the dentist must gain access to the pulp chamber using a cutting instrument for drilling into the crown of the tooth until the dental instrument reaches the pulp chamber. Once the pulp chamber has been reached, the dentist will remove the diseased pulp tissue from the pulp chamber so as to expose upper ends of the root canals. The dentist may then use a thin, elongated file adapted to fit into the relatively narrow root canals so as to remove all of the pulp tissue from the canals. Once the tissue has been removed from the canals, the dentist irrigates the canals to remove pulpal remnants. Finally, the dentist uses other elongated instruments to widen the root canals and remove irregularities in the canals so that a filling material can be introduced into the canals. Most root canal filling materials comprise biocompatible, thermoplastic material such as gutta purcha.

Unfortunately, perforations of the furcation of the tooth may occur when accessing the pulp chamber. Typically, a dentist relies on tactile sense when drilling into the pulp chamber. Generally, the level of resistance is greater when the dentist is drilling through the dentin, however, the level of resistance is reduced when the drill reaches the pulp chamber. This phenomenon occurs because the density of matter in the pulp chamber is less than the density of the dentin region of the tooth. Even though dentists are extremely focused on sensing when the drill transitions from the dentin to the pulp chamber, accidental perforation of the pulp chamber floor and the furcation occur on a regular basis. As is well know to those skilled in the art, a perforation of the furcation of a multi-rooted tooth is a serious complication.

There have been a number of efforts directed to limiting the depth of penetration of an endodontic instrument into a root canal. For example, U.S. Pat. No. 3,961,422 to Riitano discloses an endodontic file for opening a root canal including a stop for limiting the depth of penetration of the file into the root canal. The '422 patent discloses a bifurcated disk having a central instrument-receiving bore that is made of two disc halves. After the elongated file has been passed through the central bore of the disc, a resilient snap-ring is seated on a circumferential groove surrounding the bifurcated disc to secure the two disc halves of the stop together.

U.S. Pat. No. 6,390,814 to Gardiner discloses another endodontic file having a stop that limits insertion of the file into a root canal. U.S. Pat. No. 3,962,791 to Zdarsky discloses yet another endodontic file having a stop that limits how far the file can be inserted into the root canal of a tooth. The stop includes a two-part housing having a through-going passage and a compression spring positioned in the passage having an inner diameter that is normally smaller than the outer diameter of the shaft of the file. During assembly, the stop is slipped over the shaft of the root canal file, whereby the compression spring grasps the shaft for preventing sliding of the stop along the shaft. The stop may be slid along the shaft by first rotating the two parts of the housing relative to each other for loosening the spring from the shaft.

Although the prior art provides numerous endodontic files having stops for limiting penetration of the file into a root canal, the prior art provides no endodontic instruments used to access a pulp chamber of a tooth, such as a molar or bicuspid, whereby the instrument has a stop for preventing perforation of the floor of a pulp chamber or the furcation of a tooth. Thus, there is a need for an endodontic instrument used to drill an access opening into a pulp chamber of a tooth, whereby the instrument has a stop to prevent or limit insertion of the instrument into the tooth. These and other preferred embodiments of the present invention will be described in more detail below.

SUMMARY OF THE INVENTION

The present application is directed to an endodontic instrument used for drilling into the pulp chamber of a mandibular molar, a maxillary molar or a bicuspid, such as a maxillary furcated bicuspid. The endodontic instrument has preferably been designed to insure that the pulp chamber is reliably accessed without perforating the pulp chamber floor or the furcation of the molars and bicuspids. In other preferred embodiments, the endodontic instrument may be used to drill into the pulp chamber of any tooth having a furcation, such as a molar or a bicuspid.

In certain preferred embodiments of the present invention, an endodontic instrument includes an elongated shaft having an upper end and a lower end, and a stop fixed to the shaft at a distance between 6-8 mm from the lower end. The stop is preferably permanently fixed to the shaft of the instrument. The stop fixed to the shaft may be circular or have another geometric shape, such as a polygon. The endodontic instrument also preferably includes a cutting head located along the shaft adjacent the lower end thereof. In certain preferred embodiments, the cutting head preferably has an annular cutting surface extending about a first circumferential portion of the cutting head and a flat non-cutting surface extending about a second circumferential portion of the cutting head. The annular cutting surface preferably includes a spherical cutting surface having cutting edges provided thereon. In other preferred embodiments, the lower end of the shaft has a tip, such as a pointed tip. The tip desirably projects beyond a lower end of the cutting head.

As noted above, the stop prevents the endodontic instrument from being inserted too far into the molar or bicuspid, which could cause perforation of the pulp chamber floor or the furcation. Based upon an in vitro study measuring the critical morphology of molar and bicuspid pulp chambers, it has been determined that the pulp chamber ceiling in virtually all instances falls between a range of approximately 6-8 mm from the cusp tips of the molars and bicuspids. Thus, placing the stop at a distance of approximately 6-8 mm from the lower end of the endodontic instrument will reliably insure that the pulp chamber has been reached by the instrument without perforating the floor of the pulp chamber or the furcation of the molar or bicuspid. In other preferred embodiments, the stop is fixed to the shaft at a distance between 6.5-7.5 mm from the lower end of the shaft. In more preferred embodiments, the stop is fixed to the shaft at a distance of approximately 6.75-7.25 mm from the lower end of the shaft. In even more preferred embodiments of the present invention, the stop is fixed to the shaft at a distance of approximately 7 mm from the lower end of the shaft.

In certain preferred embodiments, the stop is rigid and is permanently fixed to the shaft. The shaft may also have an exterior surface including an annular groove whereby the stop is assembled with the shaft so that the stop is secured at least partially within the annular groove.

In certain preferred embodiments, the flat non-cutting surface of the cutting head preferably tapers inwardly between the upper and lower ends of the shaft. The flat non-cutting surface desirably tapers inwardly from the upper end of the shaft toward the lower end of the shaft at approximately 4-6 degrees. In more preferred embodiments, the flat non-cutting surface tapers inwardly at approximately 5 degrees. In still other preferred embodiments, the flat non-cutting surface may not taper at all. The cutting head has the annular cutting surface that extends about the first circumferential portion of the cutting head. The annular cutting surface desirably has cutting edges formed therein. In certain preferred embodiments, cutting edges are projections. In other preferred embodiments, the cutting edges have a helical pattern. The cutting head desirably has a cross-sectional diameter that is greater than a cross-sectional diameter of the section of the shaft located directly above the cutting head. As such, the outer perimeter of the cutting head preferably extends beyond the outer exterior surface of the section of the shaft located directly above the cutting head.

In other preferred embodiments of the present invention, an endodontic instrument for accessing the pulp chamber of mandibular molars, maxillary molars and maxillary furcated bicuspids includes an elongated shaft having an upper end and a lower end, a pointed tip provided at the lower end of the shaft and a rigid stop immovably fixed to the shaft at a distance between 6-8 mm from the pointed tip. The endodontic instrument also preferably includes a cutting head located along the shaft adjacent the pointed tip. The cutting head desirably has an annular cutting surface extending about a first circumferential portion of the cutting head and a flat non-cutting surface extending about a second circumferential portion of the cutting head.

During an endodontic procedure, the upper end of the endodontic instrument is preferably secured to a dental drill. In order to access the pulp chamber of a molar, the cutting head of the instrument is abutted against the crown of the molar. As the drill rotates the instrument at a high speed, a downward force is applied through the instrument and onto the crown of the molar so that the cutting head begins to cut through the enamel layer and dentin layer of the molar. As the cutting head cuts through the pulp chamber ceiling of the molar, the stop is adapted to abut against one or more cusp tips of the molar so as to prevent further advance of the cutting head. Based upon the results of the above-mentioned study measuring critical morphology of molar pulp chambers, the stop has been placed at a distance from the pointed tip that will prevent perforation of the pulp chamber floor and the furcation of the molar. Although the above description applies to accessing the pulp chamber of a molar, the instrument may be used in a similar fashion for accessing the pulp chamber of a bicuspid.

After the pulp chamber has been accessed using the endodontic instrument described above, a shaper bur is passed through the access opening for widening the interior axial walls of the opening. As the interior axial walls of the opening are widened, the upper ends of the root canals at the bottom of the pulp chamber are exposed. Thin, elongated files may then be used to remove pulp tissue from the root canals as part of a root canal procedure.

In other preferred embodiments of the present invention, a method of accessing a pulp chamber of a tooth, such as a molar or bicuspid, includes providing an endodontic instrument having an elongated shaft with an upper end and a lower end, a stop permanently fixed to the shaft at a distance between 6-8 mm from the lower end, and a cutting head located along the shaft adjacent the lower end thereof, wherein the cutting head has a cutting surface. The method preferably includes abutting the cutting head against a crown of the tooth, rotating the endodontic instrument while applying a force through the cutting head onto the crown of the tooth for cutting through the tooth to the pulp chamber, and advancing the cutting head toward the pulp chamber until the stop contacts the crown of the tooth.

In certain preferred embodiments, the cutting head may include a pointed tip and the abutting step preferably includes engaging the crown of the tooth with the pointed tip. The rotating step may include connecting a drill to the elongated shaft of the endodontic instrument and activating the drill for rotating the endodontic instrument. The advancing step ends when the stop contacts the crown of the tooth. After the advancing step, the cutting head is preferably withdrawn from the pulp chamber. A bur may then be inserted into the pulp chamber and used for widening the pulp chamber.

In another preferred embodiment of the present invention, a method of accessing a pulp chamber of a tooth without puncturing the furcation of the tooth includes providing an endodontic instrument having a shaft, a cutting head located at a lower end of the shaft, and a stop fixed to the shaft at a distance between 6-8 mm from the lower end of the shaft. The method also preferably includes abutting the cutting head against a crown of the tooth, rotating the endodontic instrument while applying a force through the cutting head onto the crown of the tooth for cutting through the tooth and advancing the cutting head toward the pulp chamber, and continuing to cut through the tooth while advancing the cutting head toward the pulp chamber until the stop contacts the crown of the tooth. Further advancement of the cutting head in the pulp chamber desirably ceases when the stop contacts the crown of the tooth.

These and other preferred embodiments of the present invention will be described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a mandibular molar.

FIG. 2 shows a cross-sectional view of a maxillary molar.

FIG. 3 shows a cross-sectional view of a maxillary bicuspid.

FIG. 4 shows a digital radiograph of a bicuspid.

FIGS. 5A and 5B show front elevational views of an endodontic instrument having a cutting head for accessing a pulp chamber, in accordance with certain preferred embodiments of the present invention.

FIG. 6 shows a cross-sectional view of the cutting head of the endodontic instrument of FIGS. 5A and 5B.

FIG. 7 shows a front elevational view of a shaper bur for shaping an inner wall of an opening formed in a tooth, in accordance with certain preferred embodiments of the present invention.

FIGS. 8A and 8B show a method of accessing a pulp chamber, in accordance with certain preferred embodiments of the present invention.

FIG. 9 shows a method of cleaning a pulp chamber, in accordance with certain preferred embodiments of the present invention.

FIG. 10A shows a stop for an endodontic instrument having a circular shape, in accordance with certain preferred embodiments of the present invention.

FIG. 10B shows a stop for an endodontic instrument having a square shape, in accordance with certain preferred embodiments of the present invention.

FIG. 10C shows a stop for an endodontic instrument having a triangular shape, in accordance with certain preferred embodiments of the present invention.

FIGS. 11A and 11B show a shaft for an endodontic instrument having a notch formed therein for engaging a stop, in accordance with certain preferred embodiments of the present invention.

DETAILED DESCRIPTION

A first study was conducted to measure key anatomical landmarks relating to pulp chamber morphology in mandibular and maxillary molars. One hundred human mandibular molars and one hundred human maxillary molars were randomly selected for the study. The randomly selected mandibular and maxillary molar samples were gathered from oral surgery and denture center practices. None of the teeth were crowned, however, some of the teeth contained caries and/or restorations. Teeth in which the caries and/or restorations violated the pulp chamber were rejected and not used in the study. The age, gender and systemic condition of the patients from which the molars were collected was unknown.

Before measurements were taken, each tooth was mounted using wax on a periodontal millimeter x-ray grid. The teeth were mounted perpendicular to the grid in a mesiodistal direction, which is the same x-ray orientation that is recorded in vivo. The x-rays were taken using a heliodent machine set on the molar setting with a numerical value of 25. Each x-ray was developed in an automatic developer sold by Air Techniques of Farmingdale, N.Y., and was examined using a stereoscopic microscope sold by Bausch & Lomb of Rochester, N.Y. The stereoscopic microscope used a magnification of lox. All measurements were made by the same individual and recorded to the nearest 0.5 mm.

FIG. 1 shows a typical mandibular molar analyzed in the study. The mandibular molar 20 includes a crown 22 having cusps 24 and a root 26. The molar 20 includes a pulp chamber 28 containing pulp tissue (not shown) and two or more root canals 30 extending through the root 26 thereof. The root canals 30 also include pulp tissue (not shown) that extends from a lower end of the root 26. Three direct measurements were taken of each mandibular molar. The measurement designated by the letter “A” represents the distance between the pulp chamber floor 34 and the closest point to the furcation 36. The measurement designated by the letter “B” represents the distance between the pulp chamber ceiling 32 to the closest point to the furcation 36. The measurement designated by the letter “C” represents the distance from the buccal cusp tip 24 of the molar 20 to the closest point to the furcation 36. The measurement designated by the letter “D” represents the distance from the buccal cusp tip 24 to the pulp chamber floor 34. The measurement designated by the letter “E” represents the distance from the buccal cusp tip 24 to the pulp chamber ceiling 32. The measurement designated by the letter “F” represents the distance between the pulp chamber ceiling 32 and the pulp chamber floor 34, i.e. the height of the pulp chamber. The x-ray analysis of the tooth also noted whether the pulp chamber ceiling 32 was located above, below or at the level of the Cemento-Enamel Junction (CEJ).

Referring to FIG. 2, direct measurements were also taken on each maxillary molar 20′. The measurement designated by the letter “A” represents the distance between the pulp chamber floor 34′ and the closest point to the furcation 36′. The measurement designated by the letter “B” represents the distance between the pulp chamber ceiling 32′ to the closest point to the furcation 36′. The measurement designated by the letter “C” represents the distance from the buccal cusp tip 24′ of the molar 20′ to the closest point to the furcation 36′. The measurement designated by the letter “D” represents the distance from the buccal cusp tip 24′ to the pulp chamber floor 34′. The measurement designated by the letter “E” represents the distance from the buccal cusp tip 24′ to the pulp chamber ceiling 32′. The measurement designated by the letter “F” represents the distance between the pulp chamber ceiling 32′ and the pulp chamber floor 34′. The x-ray analysis of the maxillary molars 20′ also noted whether the pulp chamber ceiling 32′ was located above, below or at the level of the Cemento-Enamel Junction (CEJ).

The results of the study are set forth in Tables I and II below. Table I shows the mean standard deviation and percentage variants for each measurement for maxillary molars. Table II shows the mean, standard deviation and percentage variants for mandibular molars.

TABLE I
Mean Measurements in mm for Maxillary Molars.
	N = 100
				D =	E =	F =
	A	B	C	(C − A)	(C − B)	(B − A)
Mean	3.05	4.91	11.15	8.08	6.24	1.88
SD	0.79	1.06	1.21	0.88	0.88	0.69
% Variance	25.8	21.6	10.9	10.9	14.11	36.5

TABLE II
Mean Measurements in mm for Mandibular Molars.
	N = 100
				D =	E =	F =
	A	B	C	(C − A)	(C − B)	(B − A)
Mean	2.96	4.57	10.9	7.95	6.36	1.57
SD	0.78	0.91	1.21	0.79	0.93	0.68
% Variance	26	20	11.1	9.94	14.6	43

As shown above in Tables I and II, despite the various sizes of molars, there appears to be a relatively uniform distance between the cusp tip of a molar and the pulp chamber ceiling. This cusp tip to pulp chamber ceiling height averages approximately 6 mm in distance. The distance between the pulp chamber floor and the furcation averages approximately 3 mm and the height of the pulp chambers average approximately 1.5 to 2.0 mm. Moreover, the pulp chamber ceiling and the Cemento-Enamel Junction were at the same level of the tooth in 98% of maxillary molars and 97% of mandibular molars.

A review of endodontic literature contains only a few studies related to measuring anatomical landmarks for pulp chambers of teeth. Due to large variants in the overall size of molars, those skilled in the art may have assumed that the morphology and arch position of the two and the dimensions of the pulp chamber would also show great variability, so that the measurements would be clinically useless. The first study, however, disclosed that the dimensions for both maxillary and mandibular molar teeth are very similar.

The results of the first study are supported by Sterrett J. B., Pelletier H., and Russell C. M., “Tooth Thickness at the Furcation Entrance of Lower Molars,” Journal of Clinical Peridontal 1996; 23: 621-7. Sterrett reported that the average distance from the pulp chamber to the furcation was 2.83 mm for mandibular first molars and 2.88 millimeter for mandibular second molars. Majzoub and Kon measured maxillary molars and found that the distance from the pulp chamber floor to the furcation was less than or equal to 3 mm in 86% of the teeth measured. Majzoub Z., Kon, S., “Tooth Morphology Following Root Resection Procedures in Maxillary First Molars,” Journal of Clinical Peridontal 1992; 63: 290-6. These earlier articles support the conclusions of the first study, which found that the distance between the pulp chamber floor to the furcation averages 3.05 mm for maxillary molars and 2.96 mm for mandibular molars.

A second study was conducted to measure key anatomical landmarks relating to pulp chamber morphology in human maxillary bicuspids. As part of the study, 107 human maxillary bicuspids were randomly selected. Each bicuspid was radiographed using the Trophy RVG digital imaging system and a Belmont Acuray X-ray at 70 kVp. Morphological measurements were made using the Digipan measuring mode of the Trophy system. As a control, the software measuring system was calibrated using measurements taken from X-rays of the first 30 teeth in the study. These radiographs were taken with a millimeter X-ray grid in place and then viewed and measured under a stereomicroscope as described by Deutsch and Musikant in J. Endod., vol. 30, pages 388-90, in an article entitled, “Morphological Measurements of Anatomic Landmarks in human Maxillary and Mandibular Molar Pulp chambers.” The measurements were then compared to the measurements taken with the Digipan measuring mode of the Trophy system. The experimental teeth were radiographed in a buccal-palatal view to show both cusp tips and the furcation in one radiograph. The buccal-palatal view allows for direct morphological measurements relating to the furcation.

The landmarks to be measured were chosen because of their ease of measurement and relevance to developing a technique of accessing the pulp chamber without perforation into the furcation. Three direct measurements were taken of each tooth. A drawing of the location of the measurements for furcated maxillary bicuspids can be seen in FIG. 3. Referring to FIG. 3, measurement “A” represents the distance from the pulp chamber floor 34″ to the closest point of the furcation 36″. Measurement “B” is the distance from the ceiling of the pulp chamber 32″ to the closest point of the furcation 36″. Measurement “C” is the distance from the mid point of a line 37″ connecting the two cusp tips 24″ and the closest point to the furcation 36″. Measurement “D” represents the distance from the mid point of the line 37″ connecting the two cusp tips 24″ to the pulp chamber ceiling 32″. Measurement “E” represents the height of the pulp chamber 28″.

Mean measurements were compared individually using one-way analysis of variance (ANOVA), where tooth type was the factor. The assumptions of normality and equality of variance were confirmed before application of ANOVA. Upon finding a significant difference with ANOVA, the Student-Newman-Keuls (SNK) multiple comparisons test was used to determine which types(s) of teeth were different from one another. All results were considered statistically significant if p<0.05. Summary statistics are given in terms of means and standard deviations.

FIG. 4 shows a digital radiograph of a furcated bicuspid. The measurements were calculated and shown on the screen with the Digipan measuring mode of the Trophy system. The direct radiographic measurement results of the control specimens did not differ significantly from the measurements using the Digipan measuring mode of the Trophy system.

The mean, standard deviation and percentage variance for each measurement is reported for maxillary bicuspids in Table III. Referring to FIG. 3, indirect measurements were calculated as follows: “D”=“C”−“B” represents the distance from the mid point of the line 37″ connecting the two cusp tips 24″ to the pulp chamber ceiling 32″. “E”=“B”−“A” represents the height of the pulp chamber 28″.

TABLE III
Mean Measurements in mm. for Maxillary Bicuspids.
	N = 107
				D =	E =
	A	B	C	(C − B)	(B − A)
	Mean	1.85	4.61	11.55	6.94	2.76
	SD	0.85	1.04	1.12	0.70	0.97
	% Variance	45.95	22.56	9.70	10.09	35.16

Table IV shows a comparison of the key measurements between molars and bicuspids. There were significant differences in mean dimension values across tooth type for dimensions “A” (p<0.0001), “C” (p<0.0012), “D” (p<0.0001), and “E” (p<0.0001).

TABLE IV
Comparison of mean measurements
for bicuspids and molars (mm).
Tooth	N	Measure	Mean	Std Dev	Min.	Max.
Bicuspid	107	A	1.85	0.85	0.60	5.50
		B	4.61	1.04	2.00	8.10
		C	11.55	1.12	9.20	14.30
		D	6.94	0.70	5.50	9.50
		E	2.76	0.97	0.00	5.70
Max. Molar	100	A	3.05	0.79	1.50	6.00
		B	4.91	1.06	3.00	9.00
		C	11.15	1.21	9.00	16.00
		D	6.25	0.88	4.00	8.00
		E	1.86	0.70	0.50	4.50
Mand. Molar	93	A	2.96	0.80	1.50	5.50
		B	4.59	0.90	3.00	7.50
		C	10.94	1.24	9.00	15.00
		D	6.35	0.96	4.00	8.50
		E	1.63	0.70	0.50	3.50

Further analysis using the SNK test revealed that for dimension “A”, the bicuspid mean was significantly lower than those for the two molar groups and the two molar groups did not differ from one another. For dimensions “C” and “D”, the bicuspid mean was significantly larger than those for the two molar groups and the two molar groups did not differ from one another. For dimension “E”, all three groups differed significantly from one another with bicuspids having the largest mean, maxillary molars the second largest and mandibular molars the smallest. These results can be seen in Tables V-IX.

TABLE V
For Measurement “A” means with the same
letter are not significantly different.
SNK Grouping	Mean	N	Tooth
A	3.0500	100	Max. Molar
A	2.9570	93	Mand. Molar
B	1.8542	107	Bicuspid

TABLE VI
For Measurement “B” means with the same
letter are not significantly different.
SNK Grouping	Mean	N	Tooth
A	4.9050	100	Max. Molar
A	4.5860	93	Mand. Molar
A	4.6121	107	Bicuspid

TABLE VII
For Measurement “C” means with the same
letter are not significantly different.
SNK Grouping	Mean	N	Tooth
A	11.1500	100	Max. Molar
A	10.9409	93	Mand. Molar
B	11.5505	107	Bicuspid

TABLE VIII
For Measurement “D” means with the same
letter are not significantly different.
SNK Grouping	Mean	N	Tooth
A	6.2450	100	Max. Molar
A	6.3548	93	Mand. Molar
B	6.9383	107	Bicuspid

TABLE IX
For Measurement “E” means with the same
letter are not significantly different.
SNK Grouping	Mean	N	Tooth
A	1.8550	100	Max. Molar
B	1.6290	93	Mand. Molar
C	2.7579	107	Bicuspid

A review of the endodontic literature does not contain any studies that measure anatomic landmarks relating to the pulp chamber of furcated bicuspids. Most studies are concerned with the number of canals in relation to the number of roots. See Vertucci, F., “Root Canal Morphology of the Maxillary First Premolar.” J. Am. Dent. Assoc. 1979, vol. 99, pages 194-98; Pecora et al., “Root form and Canal Anatomy of Maxillary First Premolars.” Braz. Dent. J., 1992, vol. 2, pages 87-94; Loh, H., “Root Morphology of the Maxillary First Premolar in Singaporeans.” Aust. Dent. J., 1998, vol. 43, lines 399-402; Kartal et al., “Root Canal Morphology of Maxillary Premolars.” J. Endod., 1998, vol. 24, pages 417-19. In addition, Oi et al. used micro-computed tomography (CT) to reconstruct the three-dimensional structure of pulp cavities of maxillary first premolar teeth. Oi et al., “Three-Dimensional Observation of Pulp Cavities in the Maxillary First Premolar Tooth Using Micro-CT.” Int. Endod. J., 2004, vol. 37, lines 46-51. Oi found that the mesial-distal widths and the heights of the pulp cavity decreased with age. The measurements they made were of the volume ratios of the pulp chamber and the diameter of the root canal orifices.

Krasner and Rankow described qualitative observations regarding anatomic patterns and relationships of the pulp chamber floor to the tooth and canals. Krasner et al., “Anatomy of the Pulp-Chamber Floor.” J. Endod., 2004, vol. 30, pages 5-16. They then reformulated these observations into general laws regarding the pulp chamber for use during access preparation.

Several different clinically useful methods for interpreting dental anatomy when performing endodontic therapy are reported in the dental literature. Chai and Thong measured the width of the buccal and lingual canal walls in “C” shaped molars in assessing risk of root perforations. Yoshioka at el. examined the accuracy of radiographic evaluation of root canal multiplicity in mandibular first premolars in vitro. Jerome and Hanlon reported a technique of file molding to detect complex root anatomy and multiplanar curvatures of the canal in a three-dimensional depiction. Lertchirakarn, Palamara, and Messer, did a finite-element analysis to relate stress patterns to fracture patterns observed in teeth subjected to clinical or experimental vertical root fracture. They examined factors potentially influencing the location and direction of root fracture including root canal shape, external root morphology and dentin thickness. Peters' literature review attempts to identify factors that influence shaping outcomes with nickel-titanium rotary instruments, such as preoperative root-canal anatomy and instrument tip design. Ponce and Fernandez histologically evaluated the localization of the cemento-dentino-canal junction and the diameters of the apical foramen and root canal at the cemento-dentio-canal junction, to achieve a better understanding of these structures. Using radiographs analyzed by a computerized digital imaging processing system, Schafer et al. evaluated 1163 canals to determine canal curvatures by measuring the angle and the radius of the curvatures and the length of the curved part of the canal.

There have been no known studies, however, directly concerning quantitative measurements of the pulp chamber. The variability of the bicuspid measurements fell into two groups. Measurements “A”, “B” and “E” showed high variability with 45.95%, 22.56% and 35.16% variability respectively. We suspect that the variability in these measurements is because of the fact that these measurements are related directly or indirectly to the height of the pulp chamber. Because calcification is a highly random event occurring over the lifetime of an individual, these measurements would be expected to vary as the individual ages.

Measurements “C” and “D” were much less variable with only 9.70% and 10.09% variability, respectively. This means that the distance from the cusp tips to the furcation and the ceiling of the pulp chamber was the least variable measurements for bicuspids. As stated above in the discussion of the first study for molars, the variability of these same measurements for molars were: cusp tip to furcation−maxillary molars=10.9% and mandibular molars=11.1%, cusp tip to chamber ceiling−maxillary molars=14.1% and mandibular molars=14.6% (3). It is interesting to note that in furcated teeth the measurements from the cusp tip to the furcation and various spots in the pulp chamber were the least variable of all the measurements. We noted and so did Krasner and Rankow that the CEJ was consistently at the level of the pulp chamber ceiling of molars (3,9). Although the present invention is not limited by any particular theory of operation, it is believed that the consistency of these measurements may be related to the interocclusal distance available for erupting teeth. Moreover, the consistency of the cusp to ceiling and furcation measurements is an especially important clinical finding for developing an access technique without perforation.

The measurements recorded in the second study provide a general guideline for a more quantitative approach to endodontic bicuspid access. The cusp tip to ceiling height is approximately 6.94 mm. The mean for the pulpal floor to furcation distance is 1.85 mm and the average height of a pulp chamber is 2.76 mm. When comparing these measurements to molars we find: The only measurement that is statistically the same across all three groups (mandibular molars, maxillary molars, and bicuspids) is measurement “B”, chamber ceiling to furcation. Therefore clinically, once you have reached the chamber ceiling (that is found at the level of the CEJ), you have approximately 4.5 mm before perforation. If you add this to the cusp tip to chamber ceiling measurement of approximately 6.5 mm for molars and bicuspids, you have approximately 11 mm. To reduce the possibility of perforation into the furcation, marking a bur at 11 mm will let the dentist know where they are in relation to the furcation.

The smallest percentage variance for molars and the second smallest for bicuspids is found in measurement “D”, the critical distance from the cusp tip to the pulp chamber ceiling. Measurement “D” for both mandibular and maxillary molars are statistically the same but different from furcated bicuspids. Numerically, the difference between molars and bicuspids is approximately 0.60 mm. Thus, in certain preferred embodiments of the present invention, affixing a stop on a bur at a distance of about 7 to 7.5 mm from the cutting tip will enable the dentist to drill into the middle of the pulp chamber of molars and bicuspids without fear of perforation. In calcified chambers, the 7.0 to 7.5 mm mark will enable the dentist to find where the middle of the pulp chamber used to be before calcification. Knowing this landmark will enable the dentist to more easily find the floor and the canals, with much less chance of perforation into the furcation.

Based upon the results of the two studies discussed above, an endodontic instrument has been invented that safely and reliably drills into the pulp chambers of mandibular molar, maxillary molars and bicuspids such as maxillary furcated bicuspids, without perforating the pulp chamber floor or the furcation of the tooth. FIGS. 3A and 3B show a preferred endodontic instrument 100 that is used to drill an access opening into the pulp chamber of mandibular molars, maxillary molars and bicuspids, such as maxillary bicuspids. The instrument 100 has an elongated shaft 102 with an upper end 104, a lower end 106 and a pointed tip 108 provided at the lower end 106 of the shaft 102. The endodontic instrument 100 also includes a stop 110 fixed thereto. In certain preferred embodiments, the stop 110 is made of a rigid material and is permanently fixed to an exterior surface of shaft 102. In other words, the stop is designed to permanently remain at a fixed distance from the pointed tip of the instrument.

The endodontic instrument 100 also preferably includes a cutting head 112 located along the shaft 102 adjacent the pointed tip 108. The cutting head 112 is preferably permanently affixed to the shaft and has a cross-sectional diameter that extends beyond the cross-sectional diameter of the shaft 102 in the vicinity of the lower end of the shaft. The cutting head may be integrally connected with the shaft 102 and may be made of the same material as the shaft. Referring to FIG. 4, in certain preferred embodiments the cutting head 112 has an annular cutting surface extending about a first circumferential portion 114 of the cutting head and a flat, non-cutting surface extending about a second circumferential portion 116 of the cutting head. The cutting head also includes cutting edges 118 provided on the annular cutting surface thereof. The cutting edges 118 may be in the form of helical threads. In certain preferred embodiments, the annular cutting surface includes a spherical cutting surface having cutting edges provided thereon.

Referring to FIG. 5A, the endodontic instrument 100 is preferably adapted for drilling access openings into the pulp chambers of maxillary and mandibular molars, and bicuspids. Based upon the above-mentioned study measuring critical morphology of pulp chambers, it has been determined that the average distance between the cusp tips and the pulp chamber ceiling of molars is approximately 6 mm. Moreover, it has been determined that the average height of a pulp chamber of a molar is approximately 2 mm. As a result, the endodontic instrument 100 (FIG. 5A) of the present application has been designed so that the fixed stop 110 is preferably at a distance “L” of approximately 6-8 mm from the pointed tip 108. In certain preferred embodiments, the flat non-cutting surface 116 tapers inwardly from the upper end toward the pointed lower end of the instrument 100. In more preferred embodiments, the flat non-cutting surface 116 tapers inwardly at approximately 4-6°. In even more preferred embodiments, the flat surface 116 tapers inwardly at about 5°. The above-described tool will also work effectively for accessing the pulp chambers of bicuspids, which have similar anatomical structures as molars.

FIG. 7 shows a shaper bur 130 including a shaft 132 having an upper end 134 and a lower end 136. The lower end of the shaper bur 130 has an exterior surface that is roughened. In highly preferred embodiments, the exterior surface includes a diamond material. As will be described in more detail below, after accessing the pulp chamber using the endodontic instrument shown in FIGS. 3A and 3B, the shaper bur is used to smooth out the interior axial wall of the access opening.

Referring to FIG. 8A, in certain preferred embodiments, a pulp chamber 28 of a molar 20 is accessed by using the endodontic instrument 100 shown and described above in FIGS. 5A and 5B. In preferred embodiments, this is accomplished by abutting the pointed tip 108 of endodontic instrument 100 against the crown of the molar 20. The pointed tip 108 provides an anchor point about which the endodontic instrument 100 may rotate. The upper end of the endodontic instrument is preferably connected to a drill for rapidly rotating the endodontic instrument. As the endodontic instrument 100 is rotated, a downward force is applied through the instrument and onto the crown of the tooth so that the cutting head 112 cuts through the dentin portion 25 of molar 20. Referring to FIG. 8B, the cutting head 112 continues to cut into the pulp chamber 28 until the bottom of stop 110 abuts against one or more cusp tips 24 at the top of crown 20. The stop 110 abutting against the one or more cusp tips 24 prevents further advance of the cutting head 112. In preferred embodiments, the stop is affixed approximately 6-8 mm from the pointed tip of the cutting instrument and is more preferably affixed approximately 7 mm from the tip of the endodontic instrument. Using the above-mentioned dimensions will enable a dentist to safely cut into the pulp chamber of molars without perforating the furcation 36.

Referring to FIG. 9, after access to the pulp chamber has been obtained, the shaping bur 130 is used to hollow out the access opening. The shaping bur preferably includes a roughened portion 136 that smoothes out the interior axial walls of the access opening for exposing and providing visual access to the upper ends of the root canals 30 of the molar. Once the root canals have been exposed, endodontic files may be used for cleaning out the root canals.

As noted above, the stop for the endodontic instrument of the present invention may have different geometric shapes. FIG. 10A shows a stop 210 having the cross-sectional shape of a circle. FIG. 10B shows a stop 210′ having the cross-sectional shape of a polygon which is a square. FIG. 10C shows a stop 210″ having a triangular shape. In other preferred embodiments, any geometric shape may be used for the stop. Preferably, the top and bottom faces of the stop are substantially parallel to one another.

Referring to FIG. 11A, in other preferred embodiments of the present invention, an endodontic instrument includes a shaft 302 having a notch or groove 340 formed therein. Referring to FIG. 11B, a stop 310 is fixed to shaft 302 with the stop 310 engaging the groove 340 of the shaft.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, the endodontic instrument of the present application can be preferably used to drill into the pulp chamber of any tooth having a furcation such as a bicuspid or a molar. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method of accessing a pulp chamber of a tooth comprising: providing an endodontic instrument having an elongated shaft with an upper end and a lower end, a stop permanently fixed to said shaft at a distance between 6-8 mm from said lower end, and a cutting head located along said shaft adjacent said lower end thereof, wherein said cutting head has a cutting surface; abutting said cutting head against a crown of said tooth; rotating said endodontic instrument while applying a force through said cutting head onto said crown of said tooth for cutting through said tooth to said pulp chamber; advancing said cutting head toward said pulp chamber until said stop contacts said crown of said tooth.

2. The method as claimed in claim 1, wherein said tooth is a molar or bicuspid.

3. The method as claimed in claim 1, wherein said cutting head includes a pointed tip and wherein the abutting step includes engaging said crown of said tooth with said pointed tip.

4. The method as claimed in claim 1, wherein the rotating step includes connecting a drill to said elongated shaft of said instrument and activating said drill for rotating said endodontic instrument.

5. The method as claimed in claim 1, wherein the advancing step ends when said stop contacts said crown of said tooth.

6. The method as claimed in claim 1, further comprising after the advancing step, withdrawing said cutting head from said pulp chamber.

7. The method as claimed in claim 6, further comprising inserting a bur into said pulp chamber and using said bur for widening said pulp chamber.

8. The method as claimed in claim 1, wherein said stop is fixed to said shaft at a distance between 6.5-7.5 mm from said lower end.

9. The method as claimed in claim 8, wherein said stop is fixed to said shaft at a distance between 6.75-7.25 mm from said lower end.

10. The method as claimed in claim 9, wherein said stop is fixed to said shaft at a distance of approximately 7 mm from said lower end.

11. The method as claimed in claim 1, further comprising providing a pointed tip at the lower end of said shaft.

12. The method as claimed in claim 1, wherein said stop is rigid.

13. The method as claimed in claim 1, wherein said stop is permanently fixed to said shaft.

14. The method as claimed in claim 1, wherein said shaft has an exterior surface including an annular groove and said stop is at least partially secured in the annular groove.

15. The method as claimed in claim 1, wherein said cutting head has a cutting surface extending about a first circumferential portion thereof and a flat non-cutting surface extending about a second circumferential portion thereof.

16. The method as claimed in claim 15, wherein the flat non-cutting surface of said cutting head tapers inwardly between the upper and lower ends of said shaft.

17. The method as claimed in claim 16, wherein the flat non-cutting surface tapers inwardly at approximately 4-6 degrees.

18. The method as claimed in claim 16, wherein the cutting surface of said cutting head has cutting edges formed therein.

19. The method as claimed in claim 15, wherein said cutting surface has an annular or spherical shape.

20. The method as claimed in claim 1, wherein said cutting head has a cross-sectional diameter that is greater than a cross-sectional diameter of said shaft located immediately above said cutting head.

21. The method as claimed in claim 1, wherein said stop has a shape selected from the group consisting of a circular shape and a polygon shape.

22. A method of accessing a pulp chamber of a tooth without puncturing the furcation of said tooth, the method comprising: providing an endodontic instrument having a shaft, a cutting head located at a lower end of said shaft, and a stop fixed to said shaft at a distance between 6-8 mm from the lower end of said shaft; abutting said cutting head against a crown of said tooth; rotating said endodontic instrument while applying a force through said cutting head onto said crown of said tooth for cutting through said tooth and advancing said cutting head toward said pulp chamber; continuing to cut through said tooth while advancing said cutting head toward said pulp chamber until said stop contacts said crown of said tooth.

23. The method as claimed in claim 22, wherein further advancement of said cutting head in said pulp chamber ceases when said stop contacts said crown of said tooth.

24. The method as claimed in claim 22, wherein said cutting head has an annular cutting surface extending about a first circumferential portion thereof and a flat non-cutting surface extending about a second circumferential portion thereof.

25. The method as claimed in claim 22, wherein said cutting head has a spherical cutting surface extending about a first circumferential portion thereof and a flat non-cutting surface extending about a second circumferential portion thereof.

26. The method as claimed in claim 22, wherein said shaft has an exterior surface including an annular groove and said stop is at least partially secured in the annular groove.