WO2009102113A1

WO2009102113A1 - Dental implant fixture

Info

Publication number: WO2009102113A1
Application number: PCT/KR2008/007121
Authority: WO
Inventors: Tae Gwan Eom; Chan Kyoo Jang; In Ho Kim; Gwang Hoon Kim
Original assignee: Osstemimplant Co., Ltd.
Priority date: 2008-02-14
Filing date: 2008-12-03
Publication date: 2009-08-20
Also published as: KR100850637B1

Abstract

Provided is a dental implant fixture which rotates on a central axis to be inserted into an alveolar bone of a human body so as to form an artificial tooth. The dental implant fixture includes a body which includes an outer surface on which a first screw thread is formed, wherein the first screw thread includes first roots and first peaks which alternate with one another in the direction of the central axis; and a taper which is formed underneath the body to form a single body with the body, has a diameter which narrows downward, and includes an outer surface on which a second screw thread is formed, wherein the second screw thread includes second roots and second peaks which alternate with one another in the direction of the central axis, wherein a ratio between a height from one of the first peaks of the first screw thread to one of the first roots adjacent the one first peak and a length from the one first peak to the central axis is from 0.17:1 to 0.21:1.

Description

DENTAL IMPLANT FIXTURE

Technical Field

[1] The present invention relates to a dental implant fixture, and more particularly, to a dental implant fixture which prevents occurrence of bone absorption when implanted into a hard osseous tissue of a human body and also is prevented from moving inside a soft osseous tissue of a human body when implanted into the soft osseous tissue. Background Art

[2] A screw type dental fixture is inserted into an osseous tissue to form an artificial tooth root. When the screw type dental fixture is inserted into the osseous tissue to be integrated with a peripheral osseous tissue, an abutment is combined with the screw type dental fixture, and then a dental prosthesis, that is, an artificial tooth, is mounted on the abutment. In order to improve the integration with the peripheral osseous tissue, such a screw type fixture is made from titanium and includes a body having a screw thread formed from an upper end of an outer surface of the body to a lower end of the outer surface. Thus, the screw type fixture is used as a fixing unit to fix a dental or orthopedic prosthesis or the like into a bone. An osseous tissue into which a fixture is to be inserted and implanted consists of cortical and cancellous bones. The cancellous bone refers to a relatively soft osseous tissue of a bone, and the cortical bone refers to a relatively thin film which is harder than the cancellous bone and generally encloses the cancellous bone. When the fixture is implanted into the osseous tissue, a length of a part of the fixture contacting the cancellous bone is longer than a length of a part of the fixture contacting the cortical bone.

[3] Bone absorption is the greatest problem occurring when a general screw type fixture is used. The bone absorption refers to a phenomenon in which an amount of a peripheral tissue of an osseous tissue into which a fixture is implanted is reduced and thus degenerated. The bone absorption may attenuate a fixing force of the fixture, which may deteriorate the stability of a prosthesis and break down the prosthesis.

[4] In particular, if the fixture is used as a dental fixture, the bone absorption may lead to deposition of dental calculus, which causes an inflammation in a gingival tissue enclosing the fixture or may grow down the gingival tissue along an exposed end of the fixture. Thus, the bone absorption deteriorates the stability of the prosthesis and the esthetic of the gum.

[5] Biological factors causing the bone absorption have not been clearly identified.

However, over- stimulation and low-stimulation, which are caused by concentration of stress caused by the fixture on a part of an adjacent osseous tissue resulting from the unequal distribution of stress of the fixture in the adjacent osseous tissue, have been re- cognized as promoting bone absorption.

[6] If excessive pressure is applied onto the cortical and cancellous bones along a screw thread constituting an outer surface of the fixture during the implantation of the fixture, bone absorption occurs due to the excessive pressure.

[7] As shown in FIG. 1, a conventional dental implant fixture 100 includes a head 121, a body 120, and a taper 130. The head 110 has a central hole (not shown) into which a rotating tool is to be inserted. The body 20 is formed underneath the head 110 and has an outer surface on which a first screw thread 121 is formed. The taper 30 is formed underneath the body 10, and has an outer surface on which a second screw thread 131 is formed, and a diameter which is narrowed downward. As shown in FIG. 2, the taper 130 includes four self- taping parts 132.

[8] The first screw thread 121 includes first roots 123 and first peaks 124 which alternate with one another. As shown in FIG. 3, the first groove 123 positioned at an uppermost end of the body 120 is a distance 't' apart from the first groove 123 positioned under the groove 123 at the uppermost end of the body 120. Disclosure of Invention Technical Problem

[9] When such a conventional dental implant fixture is inserted into an alveolar bone of a human body, the conventional dental implant fixture has the following problems.

[10] In general, patients have osseous tissues of different hardnesses. In other words, some patients have fully hard osseous tissues, and other patients have fully soft osseous tissues.

[11] When the conventional dental implant fixture is implanted into an alveolar bone of a patient having a fully hard osseous tissue, a strong pressure is applied onto the alveolar bone of the patient, which may increase the possibility of bone absorption.

[12] Also, when the conventional dental implant fixture is implanted into a patient having a relatively soft osseous tissue, the possibility of bone absorption is low. However, since sufficient pressure is not applied onto an adjacent alveolar bone, the conventional dental implant fixture may move inside the relatively soft osseous bone.

[13] In order to solve these problems of the conventional dental implant fixture, various researches have been conducted; however, satisfactory outcomes have not been obtained. Technical Solution

[14] The present invention provides a dental implant fixture which reduces pressure applied onto a hard alveolar bone when implanted into the hard alveolar bone in order to prevent bone absorption and applies sufficient pressure onto a relatively soft alveolar bone when implanted into the relatively soft alveolar bone in order to not to move inside the relatively soft alveolar bone.

[15] According to an aspect of the present invention, there is provided a dental implant fixture which rotates on a central axis to be inserted into an alveolar bone of a human body so as to form an artificial tooth, including: a body which includes an outer surface on which a first screw thread is formed, wherein the first screw thread includes first roots and first peaks which alternate with one another in the direction of the central axis; and a taper which is formed underneath the body to form a single body with the body, has a diameter which narrows downward, and includes an outer surface on which a second screw thread is formed, wherein the second screw thread includes second roots and second peaks which alternate with one another in the direction of the central axis, wherein a ratio between a height from one of the first peaks of the first screw thread to one of the first roots adjacent the one first peak and a length from the one first peak to the central axis is from 0.17:1 to 0.21:1.

[16] The body may include first and second body parts, wherein the first body part has a diameter which increases upward, and the second body part is formed underneath the first body part to form a single body with the first body part and has a diameter which is uniformly maintained along the central axis.

[17] A ratio between a length from an upper end of the first body part to a lower end of the first body part and a length from an upper end of the body to a lower end of the taper may be from 0.3: 1 to 0.35: 1.

[18] A straight line connecting the first roots of the first body part, which are positioned adjacent to one another on a level passing the central axis, may be tapered at an angle from 0.2 ° to 0.7 ° with respect to the central axis.

[19] The first peaks of the first screw thread of the body may include flat surfaces, and a length from an upper end of each of the first peaks to a lower end of each of the first peaks may be from 0.05mm to 0.08mm.

[20] A ratio between a length from the upper end of the body to the lower end of the taper and a length from an upper end of the taper to the lower end of the taper may be from 0.39:1 to 0.51:1. Advantageous Effects

[21] If the dental implant fixture 1 of the present embodiment is inserted into an alveolar bone of a human body, the dental implant fixture 1 does not generate bone absorption and maintains a uniform fixing force regardless of whether the alveolar bone has a hard or soft osseous tissue. Description of Drawings

[22] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

[23] FIG. 1 is a front view of a conventional dental implant fixture;

[24] FIG. 2 is a rear view of the conventional dental implant fixture of FIG. 1 ;

[25] FIG. 3 illustrates a part of the conventional dental implant fixture of FIG. 1'

[26] FIG. 4 is a perspective view of a dental implant fixture according to an exemplary embodiment of the present invention;

[27] FIG. 5 is a front view of the dental implant fixture of FIG. 4;

[28] FIG. 6 is a rear view of the dental implant fixture of FIG. 4;

[29] FIG. 7 is a front view of a part of the dental implant fixture of FIG. 4;

[30] FIGS. 8 and 9 are graphs illustrating the results of comparison experiments performed in order to measure implant torques of the conventional dental implant fixture of FIG. 1 and the dental implant fixture of FIG. 4 with respect to implant depths of the dental implant fixtures of FIGS. 1 and 4; and

[31] FIG. 10 is a front view of a dental implant fixture according to another exemplary embodiment of the present invention. Best Mode

[32] Exemplary embodiments of the present invention will now be described in detail with reference to the attached drawings.

[33] A dental implant fixture 1 according to an exemplary embodiment of the present invention is inserted into an osseous tissue (not shown), which includes cortical and cancellous bones (not shown), in order to form an artificial tooth root. The dental implant fixture 1 has a cylindrical shape and an outer surface on which a screw thread is formed. When the dental implant fixture 1 rotates on a central axis 'C_L' thereof, the dental implant fixture 1 is inserted into an alveolar bone, which is formed of the cortical and cancellous bones, to form screw roots (not shown) in an inner surface of an implant hole which is formed in the alveolar bone using a drill, so as to be implanted into the alveolar bone. The dental implant fixture 1 may be formed of titanium which is generally used for dental implant fixtures, but may be formed of any type of metal material which is not rejected by the human body.

[34] The dental implant fixture 1 according to the present embodiment includes a head 10, a body 20, and a taper 30.

[35] The head 10 constitutes an upper part of the dental implant fixture 1 and has a central hole (not shown) which is formed in the center thereof. A rotating tool such as a driver or the like is inserted into the central hole. The head 10 has a diameter which gradually increases upward. The head 10 is not inserted into the alveolar bone but protrudes from the alveolar bone.

[36] The body 20 is disposed underneath the head 10 and forms a central part of the dental implant fixture 1. The body 20 has a cylindrical shape and an outer surface on which a first screw thread 23 is formed so as to include first roots 24 and first peaks 25 which alternate with one another in the direction of the central axis 'C_L.'

[37] The taper 30 is disposed underneath the body 20 which is disposed underneath the head 10 to form a single body with the head 10 as described above. The taper 20 has a diameter which narrows downward and an outer surface on which a second screw thread 31 is formed so as to include second roots and second peaks which alternate with one another in the direction of the central axis 'C_L.'

[38] A ratio between a height 'h_t2' from each of the first peaks 25 of the first screw thread

23 to each of the first roots 24 adjacent to the first peaks 25 and a length 'R₂' from the first peaks 25 to the central axis'C_L' may be from 0.17:1 to 0.21:1. Alternatively, the ratio may be from 0.18 : 1 to 0.20: 1. A height of a screw thread of the dental implant fixture 1 of the present embodiment is higher than a height of a screw thread of the conventional dental implant fixture 100 having the uniform diameter. In other words, the height of the screw thread of the conventional dental implant fixture 100 is short, but a length from each of the first roots 123 to the central axis is longer than in the present embodiment. Thus, when the conventional dental implant fixture 100 is implanted into an alveolar bone having a hard osseous tissue, a strong pressure may be applied onto the alveolar bone, which may cause bone absorption. When the conventional dental implant fixture 100 is implanted into an alveolar bone having a soft osseous tissue, the height of the screw thread is not high enough to be inserted into the alveolar bone. Thus, a contact area of the screw thread with the alveolar bone is narrow. As a result, it is difficult for the convention dental implant fixture 100 to be sufficiently fixed into the alveolar bone. However, the height of the screw thread of the dental implant fixture 1 of the present embodiment is high, and a length from each of the first roots 23 applying pressure onto the alveolar bone from the central axis 'C_L' is short. Thus, the dental implant fixture lof the present embodiment may prevent stress from being focused on the alveolar bone. As a result, there is a strong possibility that bone absorption will be prevented. Also, since the screw thread has high height, a contact area of the screw thread with an alveolar bone having a soft osseous tissue is wide when the dental implant fixture 1 is implanted into the alveolar bone. Thus, the dental implant fixture 1 is sufficiently fixed into the alveolar bone having the soft osseous tissue.

[39] If a height of the first screw thread 23 is higher than the ratio of 0.21 : 1 in the present embodiment, an amount of an osseous tissue, which is to be grown to be fixed with the dental implant fixture 1, is excessively increased. Thus, a recovery time of a patient is increased. Also, if the osseous tissue is not sufficiently grown, a fixing force of the dental implant fixture 1 may be weakened.

[40] The first screw thread 23 has a trapezoid shape and the first peaks 25 which have flat surfaces. A height 'h_c2' from an upper end of each of the first peaks 25 to a lower end of each of the first peaks 25 may be from 0.05mm to 0.08mm, most preferably, may be 0.07mm. A height from an upper end of each of the first peaks 124 of the screw thread of the conventional dental implant fixture 100 to a lower end of each of the first peaks 124 is 0.1mm. However, if the height is higher than 0.08mm, excessive pressure is applied onto the alveolar bone. If the height is lower than 0.05mm, the first peaks 124 may be excessively sharp. Thus, surfaces of the first peaks 124 may be broken down when the conventional dental implant fixture 100 is implanted into the alveolar bone. Also, excessively weak pressure may be applied onto the alveolar bone.

[41] All of the first roots 24 of the body 20 adjacent to the head 10 may be tapered on the same level, i.e., may slant at an angle from 0.2 ° to 0.7° with respect to the central axis 'C_L .' In detail, as shown in FIG. 7, the uppermost first groove 24 adjacent to the head 10 and the first groove 24 adjacent to the uppermost first groove 24 are disposed on the same straight line ¹I.' As shown in FIG. 3, the uppermost first groove 123 of the body 120 of the conventional dental implant fixture 100 protrudes by a distance 't' more than the first groove 123 positioned just under the uppermost first groove 123. The first roots 24 of the body 20 are tapered by removing a screw cutting bite from a lower end of the body 20 toward an upper end of the body 20 to form a screw thread at the body 20. In other words, the diameter of the body 20 is increased with the slow removal of the screw cutting bite from the body 20.

[42] If a diameter of an uppermost end of a dental implant fixture is increased as described above, an uppermost end of a body of the dental implant fixture may suddenly apply strong pressure onto an alveolar bone when the dental implant fixture is implanted into the alveolar bone, which may cause bone absorption of the alveolar bone. Since an uppermost groove has the same diameter as a groove positioned under the uppermost groove in the present embodiment, a rotation torque is not suddenly increased at the uppermost groove when the dental implant fixture of the present embodiment is implanted into an alveolar bone. As a result, the possibility that bone absorption will occur is low. For this purpose, a cutting bite (not shown) is rapidly removed from a body through an uppermost end of the body.

[43] The body 20 according to the present embodiment may be divided into first and second body parts 21 and 22.

[44] The first body part 21 has a groove diameter (or a diameter) which is increased upward and is adjacent to the head 10. The second body part 22 is disposed underneath the first body part 21 and has a uniform groove diameter. In other words, the first body part 21 has a diameter which is increased upward to be more distant from the central axis. Thus, a straight line connecting the first roots 24 of the first body part 21 adjacent to one another on a level passing the central axis 'C_L' may be tapered at an angle from 0.2 ° to 0.7 ° with respect to the central axis 'C_L.' In detail, as shown in FIG. 5, an angle 'θ' between a straight line ¹I₂₂' connecting one of the first roots 24 to the first groove 24 adjacent to the one first groove 24 and a straight line 'I₂₁' parallel with the central axis C _L may be from 0.2 ° to 0.7 °. Since diameters of the first roots 24 of the first body part 21 are increased upward, a pressure applied onto the alveolar bone is gradually increased when the dental implant fixture 1 is implanted into the alveolar bone, so as to firmly fix the dental implant fixture 1 into the alveolar bone. If the angle 'θ' is smaller than 0.2 °, an effect of the pressure may not be greatly expected. If the angle 'θ' is greater than 0.7 °, the alveolar bone is excessively pressed, which may cause bone absorption in the alveolar bone.

[45] A ratio between a length 'l_t2' from an upper end of the first body part 21 to a lower end of the first body part 21 and a length 'I₃₂' from the upper end of the first body part 21 to a lower end of the taper 30 may be from 0.3: 1 to 0.35: 1. If the length 'I₃₂' is smaller than the ratio of 0.3: 1, the pressure applied onto the alveolar bone is suddenly increased, and implant torque is lowered with a long implant length of the dental implant fixture 1. If the length 'l_a2' is greater than the ratio of 0.3: 1, a length of the first body part 21 may be excessively lengthened, and thus pressure may not be sufficiently applied onto the alveolar bone.

[46] A ratio between a length ¹Ii₂' from upper ends of the self-taping parts 32 (or the taper

30) to the lower end of the taper 30 and the length 'I₃₂' from the upper end of the body part 20 to the lower end of the taper 30 may be from 0.39: 1 to 0.51:1, more preferably, may be from 0.42:1 to 0.48:1.

[47] In the case of the conventional dental implant fixture 100 in which a length from upper ends of the self- tapping parts 132 (or the taper 130) to the lower end of the taper 130 is smaller than the ratio of 0.39:1, lengths of the self- tapping parts 132 (or the taper 130) are short. Thus, a pressure applied onto the alveolar bone may be suddenly increased when the conventional dental implant fixture 100 is initially implanted into the alveolar bone. In particular, when the conventional dental implant fixture 100 is inserted into an alveolar bone having a hard osseous tissue, bone absorption may easily occur. Also, since the length of the body 120 applying pressure onto the alveolar bone is excessively long (if the self- taping parts 132 or the taper 130 are short, the length of the body 120 is increased), the body 120 may apply excessive pressure onto the alveolar bone.

[48] If the length is greater than the ratio of 0.51:1, the lengths of the self-taping parts 132

(or the taper 130) are excessively long, and thus pressure applied onto the alveolar bone may be excessively reduced. In particular, if the conventional dental implant fixture 100 is inserted into an alveolar bone having a soft osseous tissue, the body 120 strongly pressing the alveolar bone may be excessively shortened. Thus, a fixing force of the conventional dental implant fixture 100 may be wholly weakened.

[49] As shown in FIG. 6, the taper 30 may include three self-taping parts 32.

[50] A process of implanting the dental implant fixture 1 of the present embodiment having the above-described structure into an alveolar bone of a human body will now be described.

[51] An implant hole (not shown) is formed in an alveolar bone (not shown) into which the dental implant fixture 1 is to be implanted, using a drill (not shown). The dental implant fixture 1 is rotated on the central axis 'C_L' by a predetermined tool so as to be inserted into the implant hole of the alveolar bone. The taper 30 of the dental implant fixture 1 is first inserted into the implant hole so as to form a female screw thread at an inner surface of the implant hole. Next, the body 20 is inserted into the implant hole to apply pressure on an outer surface of the alveolar bone so as to be implanted into the alveolar bone along the female screw thread formed by the taper 30. After a predetermined period of time elapses, tissues of cortical and cancellous bones are grown to be osseointegrated with the dental implant fixture 1 which has been implanted.

[52] Since the height of the first screw thread 23 of the body 20 of the dental implant fixture 1 of the present embodiment is optimized, the dental implant fixture 1 reduces the implant torque when inserted into an alveolar bone having a hard osseous tissue. Thus, the dental implant fixture 1 attenuates a pressure applied onto the alveolar bone. When the dental implant fixture 1 is inserted into an alveolar bone having a soft osseous tissue, the implant torque is increased with a long implant length due to the body 20 that is tapered. Also, the dental implant fixture 1 maximizes a contact area of with the alveolar bone in order to maximize the fixing force thereof.

[53] In addition, the first body part 21 is tapered, the length of the taper 30 is appropriately adjusted, and the height from the upper end of each of the first peaks 25 to the lower end of each of the first peaks 25 is optimized. Thus, the dental implant fixture 1 applies an appropriate pressure onto the alveolar bone so as to be inserted into the alveolar bone. Moreover, all of the first peaks 24 adjacent to the head 10 are disposed on the same level in order to prevent the implant torque from being suddenly increased around the head 10.

[54] An experiment was performed as described below to verify the effects of the dental implant fixture 1 of the present embodiment.

[55] <Comparison Experiment on Implant Torque during Implant>

[56] The present comparison experiment was performed in a similar environment to an osseous tissue of a human body in order to measure and compare implant torques of the dental implant fixture 1 of the present invention and the conventional dental implant fixture 100 of FIG. 1 so as to measure pressures of the dental implant fixtures 1 and 100 applied onto an alveolar bone. [57] In order to perform the present comparison experiment, an implant object (not shown), into which the dental implant fixtures 1 and 100 are to be implanted, and the dental implant fixtures 1 and 100 are prepared. A drill (not shown), which forms an implant hole in the implant object, a rotating tool, which rotates the dental implant fixtures 1 and 100, and a torque measurer (not shown), which measures the implant torques, are simultaneously prepared.

[58] The implant object is formed of first and second materials respectively having high and low bone mineral densities. The first material is to estimate a patient having a hard osseous tissue, and the second material is to estimate a patient having a relatively soft osseous tissue.

[59] Each of the first and second materials includes a hard upper part and a lower part positioned underneath the hard upper part so as to correspond to a cortical bone of a human body, in order to set an environment that is similar to an osseous tissue of the human body.

[60] Two types of dental implant fixtures are prepared. The first type is the dental implant fixture 1 of the present embodiment, and the second type is the conventional dental implant fixture 100 of FIG. 1.

[61] Conditions of parts of the dental implant fixture 1 of the present embodiment are shown below.

[62] - Diameter 'D₂' of Dental Implant Fixture: 5mm

[63] - Height 'h_t2' of First Screw Thread (Length from First Peak to First Groove): 0.45mm

[64] - Height 'h_c2' from Upper End of First Peak to Lower End of First Peak: 0.07mm

[65] - Length 'I₃₂' from Upper End of Body to Lower End of Taper: 15mm

[66] - Length 'I₁₂' from Upper Ends of Self-taping Part (or Taper) to Lower Ends of Self- taping Parts: 5.9mm

[67] - Length V of First Body Part: 5.25mm

[68] - Taper Angle 'θ': 0.273°

[69] Conditions of parts of the conventional dental implant fixture 100 of FIG. 1 are shown below.

[70] - Diameter 'D₁' of Dental Implant Fixture: 4.8mm

[71] - Height 'h_tl'of First Screw Thread (Length from Peak to Groove): 0.45mm

[72] - Height 'h_cl' from Upper End of First Peak to Lower End of First Peak: 0. lmm

[73] - Length 'l_al' from Upper End of Body to Lower End of Taper: 15mm

[74] - Length 'In' from Upper End of Taper to Lower End of Taper: 4.8mm

[75] - Uniform Diameter of Body (Taper Angle=0).

[76] FIGS. 8 and 9 are graphs for comparing measured implant torques of the dental implant fixtures 1 and 100 having the above-described conditions.

[77] FIG. 8 is a graph for comparing implant torques of the dental implant fixture 1 of the present embodiment and the conventional dental implant fixture 100 which are implanted into the first material. When the taper 30 of the dental implant fixture 1 is inserted into the first material to an implant depth from 3mm to 5mm, the implant torque is abruptly increased. When the implant depth exceeds 5mm, the implant torque is uniformly maintained within a range of 25Ncm. When the uppermost end of the body 20 is inserted into the first material to the implant depth of about 15mm, the implant torque is increased up to 30Nm.

[78] When the taper 130 of the conventional dental implant fixture 100 of FIG. 1 is inserted into the first material to an implant depth from 3mm to 4.5mm, the implant torque is abruptly increased. When the implant depth exceeds 4.5m, the implant torque is increased to a maximum of 30Ncm. Also, when the uppermost end of the body 120 of the conventional dental implant fixture 100 is inserted into the first material, the implant torque is increased up to 40Ncm.

[79] As described above, when the conventional dental implant fixture 100 of FIG. 1 is inserted into a hard osseous tissue, the conventional dental implant fixture 100 applies a strong pressure onto a peripheral part of an alveolar bone, which increases an effect of bone absorption. Also, when the uppermost end of the body 120 is inserted, the implant torque approximates 50Ncm, which may cause bone necrosis. However, the dental implant fixture 1 of the present invention maintains the implant torque within a range of 25Ncm or less. When the uppermost end of the body 20 is inserted, the implant torque is not abruptly increased.

[80] FIG. 9 is a graph illustrating implant torques of the dental implant fixture 1 of the present embodiment and the conventional dental implant fixture 100 which are implanted into the second material. When the dental implant fixture 1 is inserted into the second material to an implant depth from 3mm to 5mm, the implant torque is abruptly increased. When the implant depth exceeds 5mm, the implant torque is maintained within a range of lONcm or more. When the uppermost end of the body 20 is inserted, the implant torque is increased within a narrow range.

[81] When the conventional dental implant fixture 100 of FIG. 1 is implanted into the second material, the implant torque is maintained within a range of lONcm or less. When the uppermost end of the body 120 is inserted, the implant torque is slightly increased. The dental implant fixture 1 maintains the implant torque more satisfactorily than the conventional dental implant fixture 100 during the implantation into the second material

[82] As described with reference to FIGS. 8 and 9, when the conventional dental implant fixture 100 is inserted into the hard first material, the implant torque is entirely high, which increases the possibility of bone absorption. When the conventional dental implant fixture 100 is inserted into the soft second material, the implant torque is ex- cessively low. However, when the dental implant fixture 1 of the present embodiment is inserted into the hard first material, the implant torque is wholly low. When the dental implant fixture 1 is inserted into the soft second material, the implant torque is wholly high. Therefore, if the dental implant fixture 1 of the present embodiment is inserted into an alveolar bone of a human body, the dental implant fixture 1 does not generate bone absorption and maintains a uniform fixing force regardless of whether the alveolar bone has a hard or soft osseous tissue. Mode for Invention

[83] The dental implant fixture 1 of the present invention may be modified into another form as illustrated in FIG. 10. In the above-described embodiment, the head 110 into which the rotating tool is to be inserted is formed at the upper end of the body 20; however, a protrusion 11 may protrude from the upper end of the body 20 as shown in FIG. 10. The protrusion 11 has a size appropriate to be inserted into a rotating tool (not shown). The dental implant fixture 1 rotates when the rotating tool is inserted into the protrusion 11.

[84] In the above embodiments, one line screw thread is formed; however, two line screw threads or multi-line screw threads may be formed at an outer surface of a body.

[85] In the above embodiments, the screw thread having the same height is formed at the body; however, a screw thread having various heights may be formed at the outer surface of the body.

[86] In the above embodiments, the body includes first and second body parts; however, the body may include second and third body parts which form a single body. Here, the third body may be gradually tapered downward.

[87] As described above, a dental implant fixture according to the present invention is inserted into an alveolar bone having a hard osseous tissue without bone absorption. If the alveolar bone has a soft osseous tissue, the dental implant fixture is further firmly fixed into the alveolar bone.

[88] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

[1] A dental implant fixture which rotates on a central axis to be inserted into an alveolar bone of a human body so as to form an artificial tooth, comprising: a body which comprises an outer surface on which a first screw thread is formed, wherein the first screw thread comprises first roots and first peaks which alternate with one another in the direction of the central axis; and a taper which is formed underneath the body to form a single body with the body, has a diameter which narrows downward, and comprises an outer surface on which a second screw thread is formed, wherein the second screw thread comprises second roots and second peaks which alternate with one another in the direction of the central axis, wherein a ratio between a height from one of the first peaks of the first screw thread to one of the first roots adjacent the one first peak and a length from the one first peak to the central axis is from 0.17:1 to 0.21:1.

[2] The dental implant fixture of claim 1, wherein the body comprises first and second body parts, wherein the first body part has a diameter which increases upward, and the second body part is formed underneath the first body part to form a single body with the first body part and has a diameter which is uniformly maintained along the central axis.

[3] The dental implant fixture of claim 2, wherein a ratio between a length from an upper end of the first body part to a lower end of the first body part and a length from an upper end of the body to a lower end of the taper is from 0.3: 1 to 0.35: 1.

[4] The dental implant fixture of claim 2, wherein a straight line connecting the first roots of the first body part, which are positioned adjacent to one another on a level passing the central axis, is tapered at an angle from 0.2 ° to 0.7 ° with respect to the central axis.

[5] The dental implant fixture of claim 1, wherein the first peaks of the first screw thread of the body comprise flat surfaces, and a length from an upper end of each of the first peaks to a lower end of each of the first peaks is from 0.05mm to 0.08mm.

[6] The dental implant fixture of claim 1, wherein a ratio between a length from the upper end of the body to the lower end of the taper and a length from an upper end of the taper to the lower end of the taper is from 0.39: 1 to 0.51:1.

[7] The dental implant fixture of claim 1, further comprising a head which protrudes from the upper end of the body and comprises a central hole into which a rotating tool is to be inserted, wherein all of the first roots 24 adjacent to the head are disposed on the same level.

[8] The dental implant fixture of claim 1, further comprising a protrusion which protrudes from the upper end of the body so as to be inserted into a rotating tool, wherein all of the first roots adjacent to the protrusion are disposed on the same level.

[9] A dental implant fixture which rotates on a central axis to be inserted into an alveolar bone of a human body so as to form an artificial tooth, comprising: a body which comprises an outer surface on which a first screw thread is formed, wherein the first screw thread comprises first roots and first peaks which alternate with one another in the direction of the central axis; and a taper which is formed underneath the body to form a single body with the body, has a diameter which narrows downward, and comprises an outer surface on which a second screw thread is formed, wherein the second screw thread comprises second roots and second peaks which alternate with one another based in the direction of the central axis, wherein a ratio between a length from an upper end of the body to a lower end of the taper and a length from an upper end of the taper to the lower end of the taper is from 0.39:1 to 0.51:1.

[10] The dental implant fixture of claim 9, wherein a ratio between a length from each of the first peaks of the first screw thread to each of the first roots of the first screw thread and a length from each of the first peaks to the central axis is from 0.17:1 to 0.21:1.

[11] The dental implant fixture of claim 9, wherein the body comprises first and second body parts, wherein the first body part has a diameter which increases upward, and the second body part is formed underneath the first body part to form a single body with the first body part and has a diameter which is uniformly maintained along the central axis.

[12] The dental implant fixture of claim 11, wherein a ratio between a length from an upper end of the first body part to a lower end of the first body part and the length from the upper end of the body to the lower end of the taper is from 0.3: 1 to 0.35:1.

[13] The dental implant fixture of claim 11, wherein a straight line connecting the first roots of the first body part, which are positioned adjacent to one another on a level passing the central axis, is tapered at an angle from 0.2 ° to 0.7 ° with respect to the central axis.

[14] The dental implant fixture of claim 9, wherein the first peaks of the first screw thread of the body comprise flat surfaces, and a length from an upper end of each of the first peaks to a lower end of each of the first peaks is from 0.05mm to 0.08mm.

[15] The dental implant fixture of claim 9, wherein the ratio between the length from the upper end of the body to the lower end of the taper and the length from the upper end of the taper to the lower end of the taper is from 0.39 to 0.51 : 1.

[16] The dental implant fixture of claim 9, further comprising a head which protrudes from the upper end of the body and comprises a central hole into which a rotating tool is to be inserted, wherein all of the first roots 24 adjacent to the head are disposed on the same level.

[17] The dental implant fixture of claim 9, wherein further comprising a protrusion which protrudes from the upper end of the body to be inserted into a rotating tool, wherein all of the first roots adjacent to the protrusion are disposed on the same level.