Endosseous Dental Implant System with accompanying Prosthetics

Related Application

This application is related to and takes priority from the Indian Provisional Application

201841004520 filed on 6th Feb 2018 and is incorporated herein in its entirety.

Field of invention

The present invention relates to novel endosseous dental implant system and its method of use thereof.

Background of the invention

A dental implant (also known as an endosseous implant or fixture) is a component that is surgically placed in the alveolar bone either in Mandible or Maxilla. This is fabricated out of material that integrates well with the bone. The placed implant is further held firmly upon osseointegration with the bone where it is placed, a process that takes place over time. Other superstructures such as abutments or multi-units are mounted on implants and fixed with locking screws. This helps in switching the platform to facilitate ease of providing different prosthetic solutions based on individual oral profile. The above components together form the total implant system. The implant system forms the anchor and acts as an interface between the bone structure and the dental prosthesis such as denture, bridge, crown etc, that are placed on the super structures of the implant system.

The implant design can influence several aspects of implant placement and loading. These include: a) Ease of surgical placement b) Primary stability during surgical placement of implant, c) Retention of implant in the bone structure during healing and osseointegration d)

Osseointegration with the bone e) Withstanding masticatory loads and transferring it to the surrounding bone f) Be compatible with varying bone density that differs within the Alveolar bone and between persons.

There are many external form designs of the implant that are known in the art. External form is that surface that comes in contact with the bone and which aids in fusion with bone and forms the major component of the design that supports primary and later secondary stability in conjunction with bone integration. External form that supports stabilization includes dimensions, taper, thread forms and surface characteristics of the implant.

US8038442 provides a system comprising two distinct dental components including a body, means to attach implant to bone and a recess. US8758012 claims a dental implant for supporting a dental prosthesis, the implant comprising a body comprising an outer surface, an apical end, a coronal end, a threaded portion and a longitudinal axis. US7806693 discloses a dental implant for supporting a dental prosthesis and a thread chamber positioned below the internal connection socket.

While there are many designs as recited above that exist which handle the necessary physical and functional requirements of the implants, there continues to be a need to improve the primary stability of the implant within the Alveolar bone and later to improve the implants' secondary stability through better osseointegration. Some aspects of the marketed implant that needs improvement are: a) thread form that takes into account smooth i nsertion and ease of torqueing b) a sealing surface at the implant/abutment interface, c) a locking screw that retains the abutment over a long duration of use d) range and flexibilities to accommodate a variety of prosthetic needs e) early or immediate loading of placed implants.

Summary of invention

The implant system that is the subject matter of this invention consists of the following components: (a) I mplant fixture (b) Abutment or multi-unit (c) Locking screw

The implant (Fig. 4) upon placing in the bone, need to be stable to withstand masticatory and lingual forces. It needs to be amenable for straight or angular emergence depending on the orientation of the jaw, available bone and the loading pattern. Stability is known to be of two types. The first is primary stability which is initial stability obtained upon placing the implant and engaging the bone. This is determined by the external form of the implant that is placed in the osteotomy site. The bone density which varies within the alveolar arch is classified into 4 different levels and also varies between persons. For example, anterior mandible is known to have higher density as compared to the posterior Maxilla. The stability needs to be maintained irrespective of bone types.

Progressively, bone remodels due to the stresses generated during osteotomy and implant placement leading to osteoblasts adhering to the implant surface. The initial drop in stability due to the remodeling and the later increase due to osseointegrations is termed secondary stability. The external topographical form of the implant surface with micro and nano pores generated through surface modification processes greatly enhance the "body in contact area".

Brief description of the drawings

Fig. 1 is an exploded view of the dental implant system with straight abutment.

Fig. 2 is an exploded view of the dental implant system with an angular abutment.

Fig. 3 is an exploded view of the dental implant system with a multiunit abutment system.

Fig. 4 is a sectional view of the implant body (fixture) of this invention.

Fig. 5 is a view of the straight abutment of the implant system.

Fig. 6 is a view of a variant of the straight abutment system.

Fig. 7 is a sectional view of an angled abutment system.

Fig. 8 is a sectional view of a multi unit abutment system.

Fig. 9 is a view of the locking screw of the implant body.

Fig. 10 is a view of impression coping.

Fig. 11 is a view of the locking screw for impression coping.

Fig. 12 is a view of implant analog.

Detailed description

The implant system (Fig. 1, 2) of the present invention consists basically 3 parts viz. Implant body (Fig. 4) or fixture, Abutment Part which is straight (fig. 5,6) or angular ( fig. 7) and a locking screw (Fig. 9). The invention also provides for a multi unit variant implant system (fig. 3) wherein, an additional multi-unit part (Fig. 8) with the required angle is provided between the implant body and a straight abutment. In one embodiment, the external form of the implant (Fig. 4) has a cylindrical shank (9) and a tapered region (8). The tapered region having an included angle in the range of 6 to 14 degrees, allows for easy placement into the osteotomy site and allows generating a desired compressive component in the jaw bone when occlusal forces are loaded. The tapered region (8) engages with the softer cancellous bone. The cylindrical region (9) engages with the harder cortical region, which along with the thread form that is described further helps in better distribution of stresses. The ratio of cylindrical length to tapered length is in the range of 0.8 to 2 and is determined depending upon the diameter and the length of the implant chosen for the specific site either in Mandible or Maxilla.

The invention is customized to have a thread form ( 7, Fig 4) that is arrived at after considering the nature of masticatory/occlusion forces exerted on the implant system and the ability of the bone structure to absorb these forces. It will be appreciated by the skilled person in the art that the thread form is a flexible component. Also the process of osseointegration is influenced to a great extent on the nature of forces applied to the interface between the implant and the bone. Compressive forces have the effect of increasing bone density and strength, while tensile and shear forces weaken the bone. Square threads are the strongest for pure compressive loads and V - shaped threads generate a higher shear forces than reverse buttress and square threads. Masticatory loads generate both compressive and shear loads due to moment loads. The present invention brings together a unique combination of all these thread forms and a major advantage of providing ease of insertion at the same time.

The thread forms may have a taper to the cylindrical axis, with the angle in the range of 3 to 10 degrees. This angle again supports the resolution of occlusal loads into compressive

components in the bone. The bone is known to handle the compressive loads better than shear and tensile forces, and as such, such a resolution is desired.

In another key embodiment, the thread flank has a face angle from the plane normal to thread longitudinal axis, to the apical side of the flank in the range of 3 to 15 degrees, which provides for a resolution of force to predominantly 'compressive' in nature. The face towards coronal region has an angle in the region of 25 to 50 degrees. Consequently, the coronal face would be larger than the apical face, which again provides for better resolution of biting forces. The advantage of the angle scheme of the present invention is that it provides the necessary strength for the thread flank and also the required body in contact for integration with the bone.

Another aspect of the pitch is that within the pitch of the thread, the root form has a linear base length that is larger than that covered by base length of thread flanks along the thread longitudinal axis. This feature has the advantage that it allows for more cross-sectional area for the bone which is weaker in strength as compared to the implant material, to bear the occlusal forces - compressive, shear and bending loads. Further, upon completion of the

osseointegration process, the secondary stability is also aided as osteoblasts reach this site and aid further bone growth in the recess.

In another aspect of the implant the tip thickness of the thread in the range of 0 to 0.2 mm is lower near the apical region as compared to the coronal region. The lower tip thickness allows for an efficient cutting at the contact between the osteotomy site and the implant body. As the screw progresses the thickness increases to a higher level within the range, which allows for the bone to provide a gradually increasing level of resistance. The increasing resistance results in a higher torque with the progress of implant body, and the stresses generated aid bone remodeling.

The depth of the thread that is in the range of 0 to 0.7mm is higher at the apical region as compared to the depth at the coronal region. The cancellous bone which is weaker would benefit from a higher area of engagement that can oppose masticatory forces. The higher depth towards the apical end will ensure is a good engagement of cancellous bone with the thread. On the same note, thread depth at the coronal end is shallower. This allows for a lower formation of the thread on the osteotomy site as the outer diameter of the implant body becomes progressively larger. This allows the implant body to cut through the harder cortical region during implant placement without raising the stress levels higher than the threshold levels at which cracks can appear on the bones thus weakening the bone and initiating bone resorption. The pitch of the outer threads is in the range of 0.5 to 1.5mm to facilitate an optimum level of resistance to the loads, secondary bone growth and for adequate ease of entry. The external form on the outside diameter has microthreads (10) having pitch in the range of 0.1 to 0.3mm towards the coronal end. The length of the micro thread is between 1 and 2 mm along the axis of the implant. This serves two objectives - one is to provide higher engagement area at a shallow depth in view of the harder cortical bone, thus providing sufficient body in contact for primary stability while keeping the implant placement stresses within the threshold levels and for osteoblasts' engagement to generate secondary stability and the other to serve as windy and a laborious path for microorganisms to go deeper into the osteotomy site, post loading. At the coronal end there is an unthreaded smooth region for a length of 0.3 mm to 1 mm, along the axis, to reduce the adherence of plaque to the surface, in case of bone loss. This region is either cylindrical or has radius or taper emerging towards outside or inside, depending upon the clinical requirement. The bottom of the implant has a form having radius or chamfer in the range of 2 to 5 mm or a single or dual chamfer ranging between included angle of 50 and 150 degrees to the axis, which serves as a healing area that helps in mildly compressing the bone chips that are accumulated from the osteotomy and the self-cutting process.

The apical cuts (14, Fig. 4) that is at least one in number serves to provide a channel for bone chips collection in the cutting process and also for the bone growth during the osseointegration process and thus provide an anti-rotational lock. The body in contact for the osteoblasts during the secondary stabilization process is also effectively increased. This further greatly enhances the secondary stability of the implant.

As can be seen from the assembly (Fig. 1, 2) another component is mounted on the Implant body. This component serves to switch the platform from the Implant body to this unit

(abutment or multi-unit) on which the dental crown can be mounted. This component is commonly called as abutment which may be straight, angulated (Figs. 5 to 7) or multi-unit (Fig. 8). The switched platform is firmly seated on implant body through a connection. The seating between them needs to be with no gap and be firm at all loads in order not to allow any foreign body or plaque to get into and transfer the occlusal loads to the implant body. Abutments or multi-units are fixed on the implant body with the help of screws (Fig. 9).

Abutment (2, Fig. 1) has face that could include a tapered form (15, Fig. 5) having an included angle in the range of 15 to 45 degrees for mating with the implant body and extending to a cylindrical shape (16, Fig. 5) to provide the area for building the prosthesis on it is disclosed in this invention. In the design that has conical connection, the tapered portion (15, fig. 5) forms a connection with the corresponding feature (11, Fig. 4) of the Implant Body 1. This acts as a support for the dental prosthesis and the connection can be of any shape including 'conical' or 'flat' as per the loading requirement of the prosthesis. A further cylindrical or a conical portion (17, Fig. 5) provides a platform for building the crown based on the specific need and a counterbore (18, Fig. 5) or a countersink, to receive the locking screw (fig. 9).

In another embodiment, Fig. 5, the hexagonal portion (19) of the abutment (2, Fig. 1) serves to fit firmly with the matching recesses of the implant body. These matching portions of the implant body and abutment may also be shaped in different ways such as triangle, square, octagon or any other shape that has at least one flat surface.

The connection portion (16, Fig. 5) of the abutment is shaped to suit the individual patient. And the conical top portion (17, Fig. 5) of the abutment is configured by the dentist to receive the tooth crown suited to individual patient. This feature may also have a flat machined surface to facilitate right orientation of the crown.

The inner recess (18, Fig. 5) of the abutment is made to receive the locking screw (fig. 9) of the abutment to the implant body. The recess may have an internal thread region. The internal thread serves two purposes - one is to retain the locking screw after it is disengaged from the implant, second is to aid in the removal of the abutment from the implant in case of cold welding of the abutment after prolonged use. The abutment is also provided with internal threads (22, Fig. 5). This feature aids in disassembling the abutment from implant in the unfortunate event of a locking screw breakage and abutment is cold welded to implant after prolonged use.

As a variant, the invention also covers an abutment design having an elliptical collar (Fig. 6) (in place of circular collar in 16, Fig 5), an angled abutment (Fig. 7) and a multi-unit abutment (Fig. 8) to provide flexibility to cater to specific prosthetic requirements.

A locking screw (Fig. 9) to fix the abutment to the implant body is also covered in the invention. It has a hex profile (24, Fig. 9) for driving and a thread profile (23, Fig. 9). Portion (25, Fig. 9) of the screw (Fig. 9) is made to mate with the corresponding profile in the abutment (18, Fig. 5). The invention also covers other prosthetic accessories viz. Impression coping (fig. 10), locking screw for coping (Fig. 11) and Analogs (Fig. 12).

In order to improve the Osseointegration of the implant body with the bone, improve the secondary stability of the implant, it is a common practice in the field to change the surface morphology through various surface removal and surface additive methods including but not limited to abrasive blasting, shot/laser peening, acid etching, anodizing, plasma spraying, electrophoretic or sputter deposition, sol gel coating, pulsed laser deposition, biomimetic precipitation. The subject invention also covers any such modifications or variations achieved through one or more of the above methods or any other related forms of the disclosed invention.

Example:

The implant system of the present invention was subjected to analysis and tests to substantiate the functionality of the system. The implant system was compared to other implants commercially available in the market having custom external forms (Ex: Nobel Biocare,

Dentium) and the implant bodies with standard thread forms such as V and buttress forms. The comparative analysis was carried out using the methods as provided below

a) Stress on implant- abutment interfaces, microstrains on implant - bone interfaces: Compared between subject implant and some standards forms as provided above, using Finite element analysis ( FEA) method.

b) Measure of ease of entry - as measured by torque values, for a given osteotomy size - carried out through physical testing on Bone substitutes: Compared between subject implant body and some implants having custom forms (Ex: Nobel Biocare, Dentium)

c) Bone implant volume (bone volume within implant macro form envelope) - carried out through computer aided design ( CAD) models: Compared between subject implants, implants from market and standard thread forms and also custom forms of implants in market indicated earlier.

Finite element analysis is a computer based numerical technique that is used to model a physical system on a computer and view, compare and resolve structural issues if any through simulation of the loading conditions on the model (Ref: US20110117522). The system can be used to study the stress levels, displacements, strains, mechanical and fatigue performance of the modeled system. This study when used on the dental implant system in simulated loading conditions can be used to validate the design under conditions of load when in use in the mouth.

A detailed FEA study with appropriate mathematical modeling of the material and the bone, under various loads that are within the physiologic limits was carried out to validate the design. The external macro form of the Implant body of the present invention was compared to some of the standard forms, such as V form and the buttress thread forms commonly available on the implants in the market.

For the purpose of study, FEA was done under a standard load of 300N at 30 degree to vertical axis applied on the implant system uniformly through the abutment, evaluated on a

commonised pitch, at diameter 3.5mm and length 11.5 mm.

On the parameter of stress, the subject invention has shown 17 to 73% lesser stress on implant- abutment interface and has shown 20 to 73% lower microstrains in bone - implant interface, as modelled in a simulated set up within the Jaw bone and evaluated by FEA methods, when compared with standard forms of threads such as V and Buttress threads.

For ease of entry evaluation, a 3.5mm diameter implant per subject invention claim, and implants from other manufacturers well versed with the art, were placed in bone substitutes that are equivalent to bones of different densities found amongst people. Bone density in Mandible and Maxilla vary from person to person, within the jaw structure and across age spectrum. The classification based on "Hounsfield" number classifies the bone of Maxilla and Mandible, from D1 to D5. Bones with densities between D1 and D4 are usually implanted upon. The bone substitutes used in the trials corresponded to different densities of bone from D1 to D4 on osteotomies created for placement of implants. For an implant to be placed an osteotomy of a required size is created by sequentially drilling a hole into the bone in increasing sizes. The hole size allows the implant to be screwed into the bone. Lower osteotomy size allows for lesser effort in drilling. However, the torque levels are higher when the osteotomy size is lower. A placement torque value of higher than 60 N-cm is not desired since higher than this torque could lead to micro strains that would damage the bone. While at the same time, a placement torque of less than 30 N-cm, would make the implant unstable, will lead to micro strains that are lower than the minimum threshold levels required for bone remodeling and thus affecting the secondary stability of the implant. A desired goal of implant design then is to get a placement torque within the limits, with the least osteotomy size that can save on the number of drilling steps req uired. When this placement torque trial was done on bone substitutes representing different densities, the implant of subject invention showed results requiring osteotomy sizes that are about 3% to 16% less than the representative implants offerings in the market from companies such as Nobel Biocare, Dentium. For the purpose of trial a common diameter 3.5 mm of 10.5 mm length was used. Higher the diameter, the improvement percentages are expected to be higher, since more implant area would come in contact with bone. This is an example supporting the applicant's claim of ease of entry. Bone implant Volume (BIV) assessment is an indicator of stability. This assessment was made by drawing an envelope of the external macro form of the implant and calculating the bone volume within the implant external envelope. The BIV was compared with standard thread forms used in the market (such as V, buttress, reverse buttress and Square) and with some of the custom thread forms of implant manufacturers available in the market (Ex: Nobel Biocare, Dentium) well versed with the art and well received in the market. This was evaluated with computer aided design (CAD) tools. When compared to the implant of the present invention, other forms as detailed abovehad BIV about 26 to 41% lower. Higher BIV is an indicator of better primary stability of the implant, which in turn is an indicator of better resolution of occlusal forces.

The lower stress levels, micro strains observed on FEAs are predictors of better implant stability and favorable bone remodeling. Higher bone in volume aids in better primary stability and the bone in contact aids in larger surface area of bone available for osseointegration, thus aiding the secondary stability. These are indicators of longer implant life. Moreover, the lower osteotomy size allows obtaining the desired placement torque in a shorter time, as the hole sizes are progressively enlarged after placing the least drill size initially. This is an indicator of lower placement time and easier placement. Thus, the implant of the present invention shows the following functional features that are highly improved than the other implants known in the art: a) better resolution of masticatory forces

b) is easier to place, and

c) has higher BIV

Advantages of the Invention

The present invention helps in bringing in the necessary primary stability through an external form design comprising a combination of cylindrical and tapered surface, thread form that is effectively different in the apical region where it comes in contact with cancellous bone when compared to the form in the coronal area where it comes in contact with the harder cortical bone. The thread form allows a self-cutting process which supports in easier insertion to begin with and provides the required resistance necessary to cause minimum stresses that is needed for bone remodeling, along the path of insertion. Apart from aiding optimum insertion, the thread form is also designed to absorb and transfer multi component masticatory forces, the main component of which is compressive in nature. Thus, the varying thread form provides a cutting edge at the apical end and the strength needed at the crest of the impla nt. This optimizes between ease of insertion, providing resistance for bone remodeling, along with the capability to withstand biting forces. The thread design form also ensures transfer of compressive occlusal forces to the bone structure, which the bone physiology can accept naturally.

The micro threads at the coronal end have multiple roles. They reduce resistance on the tougher cortical bone and reduce microfractures. They increase surface area for greater osteoblast adherence and better bone remodeling, forming a tight bone seal for the implant bone interface. They restrict the path for peri-implantitis causing residual micro-organisms from the gingiva to the bone.

The jaw bone on which the implant is placed has predominantly two regions - cortical on the outer and cancellous on the inner. The cortical bone is very hard, and the cancellous bone is soft. Also, the densities of these bones vary in the alveolar arch. For the purpose of classification within the jawbone that are amenable for implant placement, bone densities are classified between D1 and D4, with D1 being the highest and D4 being the lowest. The implant must traverse cortical bone to reach cancellous and then engage both during fixation as well as integration. Therefore, implant body design needs to factor these varying densities and have a single design that can fit the varying density requirements, besides reducing inventory.

Another aspect of the design is to ensure accurate seating of the prosthetic components such as abutment, which forms the base for the artificial tooth crown. The abutment - implant interface should show no gap between them and should be fixed to the implant in a rigid manner to transfer loads to the implant body efficiently. The abutment design is dependent on emergence angle from the implant, as well as the functional and aesthetic needs of the patient. Post loading maintenance of peri-implant health is also a challenge with currently available designs. The distance from the interdental bone to the proximal contact of the crown cannot be maintained with current abutment designs, which also permit food and plaque accumulation below the crown. This area is difficult to clean for the patient.

The drawbacks of an implant supported prosthodontic procedure include long treatment duration from the time of implantation, process of osseointegration till tooth restoration, involving multiple appointments. The endeavor of implant related research is to reduce total duration of the treatment. Therefore, implant design must strive to facilitate immediate placement, ease of placement and early or immediate loading.

The current invention addresses the above mentioned challenges of a) ease of insertion b) optimum occlusal force resolution across bone densities c) effective sealing d) good primary stability to facilitate early to immediate loading e) adequate development of secondary stability f) maintenance of peri-implant health g) range of prosthetics options to suit the various jaw profiles and interdental spaces and further the art form of implantology by incorporating various novel features in the design of implants.

Abutments (Fig. 5 to 7) are designed in different forms and angulations to suit the varying anatomical angulations seen in the Maxilla and Mandible and transfer forces to bone optimally. The abutment consists of a bottom region that has hex external profile that engages with implant hex socket (19) , a conical or a flat region that transfers from the abutment to the implant ( 15), a collar region in the middle (16) that houses the locking screw internally and atop region (17) to enable mounting of dental crown prosthetic. Typically, the collar (16)

embodiment is circular in profile externally. The subject invention also has an embodiment where the collar is elliptical in form externally (Fig 6). The elliptical collar profile will aid in better emergence profile when the gap between the teeth is wider on mesio-distal axis than on the facio-lingual axis. This simulates the actual anatomy of the tooth in the cervical region, thereby helping in better peri implant health maintenance for the patient. A multi-unit type abutment system (Fig. 8) is designed to offer flexibility of angulation when multiple implants are needed to be used together, or when greater flexibility is required by the doctor for prosthesis mounting. A locking screw (Fig 9) to fix the abutment to the implant body is also covered in the invention. Further, to aid various needs of Prosthesis, parts like implant coping (Fig. 10), analogs (Fig. 12) and screw for coping (Fig. 11) have been designed as a part of this invention.