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| REVIEW ARTICLE |
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| Year : 2013 | Volume
: 3
| Issue : 2 | Page : 142-147 |
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Tooth-implant connection: A critical review
N Aparna, S Rajesh
Department of Prosthodontics, Mahatma Gandhi Postgraduate Institute of Dental Sciences, Puducherry, India
| Date of Web Publication | 25-Sep-2013 |
Correspondence Address:
N Aparna
"AMRITHA", 34, Debassyn De Richmont Street, Puducherry - 605 001
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0974-6781.118853
 Abstract | | |
Background: Controversy regarding tooth-implant connection in implant dentistry has emerged due to the differences in the mobility pattern of tooth and implant causing increased stress on the implant leading to implant failure.
Purpose: The purpose of this review is to critically analyze the technical complications, the biological impact of tooth-implant connection and the treatment modalities that may be helpful in preventing intrusion.
Materials and Methods: A detailed search was carried out in the dental literature available in English language from 1989 to 2012 which included review articles and case reports. The search was carried out in PubMed database, Google search engine, Medline and Science Direct as well as manual search of peer reviewed literature using relevant key words.
Results: Literature search revealed studies involving complications and biomechanical interactions of tooth-implant connection and the survival rates of tooth-implant supported fixed prosthesis (TISP).
Conclusion: Thus tooth-implant connection has its own advantages, disadvantages, risks and complications, but what justifies its application is the risk-benefit evaluation with a special attention on patient requirements. Thus many longitudinal studies are necessary before this method is declared as the treatment of choice. Keywords: Biomechanics, implant supported, intrusion, literature review, splinting, tooth-implant connection
How to cite this article:
Aparna N, Rajesh S. Tooth-implant connection: A critical review. J Dent Implant 2013;3:142-7 |
| Introduction | |  |
Implant-supported fixed prostheses (ISP) is one of the treatment modalities for patients with missing teeth. But lack of space or failure of an implant to integrate may lead us to a tooth-implant connection. It was believed that a tooth-implant connection would cause great amount of bending stress to an implant, because of the changes in their mobility patterns. [1] But some authors concluded that it is indeed beneficial to use such connection in fixed prosthesis.
Thus the purpose of this article is to evaluate theoretical concepts, biomechanical complications and the clinical guidelines for splinting teeth to implants.
| Review of Literature | | |
The history of connecting implant to the natural teeth dates back to early 1980s, when there was no implant with anti-rotational feature. So connecting implant to teeth was done to prevent rotation of the restoration and its complications.
Per Ingvar Branemark [2] {1982} introduced implants with hex head for aligning during insertion, but its non-hex abutment surface necessitated connection of tooth to implants.
Core-vent (Zimmer) {1984} introduced the first anti-rotation implant abutment that had an ‛adjustable narrow neck'. [2] So to overcome this weak link, tooth-implant connection was made necessary.
In 1986, the first screw retained abutment without any anti-rotational feature was introduced, which necessitated tooth-implant connection.
Dr. John Beumer {1988} introduced the first screw retained abutment with anti-rotational feature, 'The UCLA Abutment'. [2],[3] With this invention, creation of free standing implants without the tooth- implant connection became feasible for the first time.
Akagawa et al. {1998} performed a comparative analysis of TISP and ISP in monkeys for 2 years and concluded that teeth connected to implants with rigid connectors performed well as bridge supported by natural teeth.
Gunne et al. [4] {1999} and Lindhe et al., [5] {2001} also reported that bone resorption around implants incorporated in a TISP was similar to the bone loss adjacent to the implant in an ISP when assessed within the same individual.
Hosny et al. [6] {2000} compared the free-standing and tooth-connected implants for a period of 14 years and found that the amount of marginal bone loss in either situation did not differ significantly. Thus stable bone levels around the implants suggest that excessive loads to implants did not occur when they were connected to teeth.
Naert et al. [7] {2001} conducted a 15-year clinical evaluation of TISP and found that more bone resorption occurred around rigid than around a non-rigid connector.
Lin CL et al. [8] {2006} studied the mechanical interaction of various systems of tooth-implant rigid and non-rigid connections using a non-linear 2D finite element analysis. He concluded that tooth-implant connection can be a treatment of choice in certain clinical situation. Rigid connection should be used with caution because though it reduces stress on the bone, it increases tension in implant and superstructure particularly with periodontal problems. He also reported micro-gap formation between implant abutments and fixtures under lateral occlusal forces.
| Materials and Methods | | |
PubMed, Medline, Science Direct and Google search engine were used to obtain the studies pertaining to tooth-implant connections. Literature search was performed from 1989 to 2012 issues. Key words used for the search were tooth-implant connection, tooth-implant supported FPD intrusion, splinting, biomechanics of tooth-implant supported prosthesis (TISP).
Exclusion criteria
- The papers which were not published in any of the reputed journals
- Studies without authentic results and conclusion
- Studies for which the abstracts were only available and the full article which was yet to be published.
| Results | | |
Concept of joining teeth to implants
Fabrication, fitting, maintenance and retrievability are all simplified if the implant is not connected with teeth. However, this is not always possible since:
- Teeth may be retained between implants
- It may be possible to place only one implant so that connecting an adjacent tooth is necessary to avoid cantilever
- A tooth may require stabilization by connecting to the rigid implant supported section.
Advantages of tooth-implant connection
- Tooth-implant connection broadens the treatment options:
- When anatomic structures restrict insertion of additional implants (e.g., maxillary sinus, mental foramen)
- If the patient is not willing for bone augmentation
- Lack of bone for implant placement
- Desire to splint a mobile tooth to implant
- Desire to use the proprioception of teeth which may limit the load applied to the teeth
- To avoid total load on the dentition
- More favorable bone reaction when the bridge is connected to both teeth and implants
- To avoid cantilever
- Reduction of the number of implants needed for a restoration
- To preserve the papilla adjacent to the tooth for esthetics or function
- Reduced cost due to reduction in the number of implants.
Disadvantages of tooth-implant connection
- Teeth incorporated between implants will be subjected to different stresses than the teeth at the end of the bridge spans
- Teeth may not be loaded sufficiently to provide proprioceptive feedback.
Technical complications of TISP
- Intrusion of tooth
- Intrusion of tooth with telescopic crown
- Implant fracture
- Abutment tooth fracture
- Abutment screw loosening
- Fracture of veneer
- Fracture of prosthesis
- Cement bond fracture.
Biologic complications of TISP
- Peri-implantitis
- Loss of implant
- Loss of abutment teeth
- Root fracture
- Caries
- Endodontic problem.
Intrusion theories
FPD flexure
When a tooth connected to an implant through keyway stress-breaker is loaded occlusally, the frictional resistance between the patrix and matrix attachments prevents the free movement of natural tooth. So with each application of apical loading force, the tooth is depressed slightly and is prevented from rebounding totally. [9],[10],[11],[12] This leads to intrusion.
Impaction of food particles
Micro-jamming of food particles at the bottom of the matrix will cause intrusion as impaction of debris will prevent tooth to its original position from rebounding.
Mandibular flexion (Average value: 0.9 mm)
Mandibular flexion was reported to generate forces that could cause tooth intrusion. [9],[13] However, intrusion has been reported both in maxillary and mandibular arches.
Differential energy dissipation
It is theorized that a natural tooth that supports an implant restoration receives an abnormally high level of mechanical stress, which activates the osteoclasts surrounding the root than the implant. [9],[10],[11],[12],[13],[14] This results in intrusion.
Impaired rebound memory/Ratchet effect
A constant excessive force on a tooth causes its periodontal ligament to loosen its elastic memory and to remodel to a new less traumatic position. This new position of the tooth acquired is apical to its original position. The tooth will continue to move farther apically until no compressive force is placed on the periodontal ligament. [9],[14],[15]
Telescopic connections
Two theories have been presented to describe intrusion phenomenon with telescopic connections where no occlusal force is applied to the teeth:
- Disuse atrophy of periodontal ligament due to the lack of stimulation results in intrusion
- Transfer of shock waves to the underlying restoration with resulting natural tooth intrusion.
Micro-bonding of superstructure
Micro-bonding of superstructure to the underlying telescopic copings as a result of flexure of the prosthesis, implants and/or mandible will result in intrusion. [16]
Lack of passivity
Lack of passivity of implant restoration will result in tooth intrusion.
Factors to be considered when splinting teeth to implants
Simplicity of construction
Construction is simplified if the implant is independent of the teeth. This connection requires passivity of fit not only between the superstructure and the implants but also between the superstructure and teeth. [17]
Retrievability
Splinting implants to teeth complicates the design and clinical procedures associated with easy retrievability.
Distance of tooth from implants
The farther the tooth is from the implant, lesser is the flexure required for the implant abutment to accommodate for tooth mobility. The closer the tooth is from the implant, the implant abutment has to flex more to accommodate for tooth mobility.
Periodontal condition
If a periodontally weaker tooth is connected to an implant, the abutment has to flex more for the tooth to be loaded.
Reduction of lateral forces
When connecting tooth to an implant, the lateral forces have to be reduced by providing posterior disclusion.
Pier abutment
It is unlikely that the tooth which serves as a pier abutment between implants is subjected to functional loading unless it is considerably remote from the implants.
Mandibular flexion
Since the mandible flexes, posterior mandibular implants or teeth should not be connected to the teeth on the opposite side of the mandible. [17] If a joint is required, an attachment should be used to allow some movement to occur.
Clinical guidelines of tooth-implant connection
i. Avoid splinting natural teeth to implants
Some authors have advocated that tooth-implant connection is beneficial assuming that it provided the necessary proprioception. But the availability of evidence suggests that in a stand-alone design, the use of multiple wider implants will serve the purpose [18] .
ii. Splint implants to natural teeth only when the teeth need support
Fully integrated implants stabilize periodontally weak teeth whereas teeth do not stabilize implants. When a periodontally weak tooth is to be included as an abutment, the method of connecting tooth to dental implant should be decided. This is because the teeth and implant move at different rate and distance. So it is not wise to connect them in one-piece fixed prosthesis. Therefore, an interface attachment is required between a tooth and an implant.
There are three options:
Key-way type of stress-breakers
Key-way stress-breakers are commonly used with conventional fixed partial dentures (FPD) for separating splinted units and to connect the retainers. It is a good way to connect more than four units of FPD. Intrusion is a common complication of this connection. So to overcome this problem, double abutting the natural teeth is advocated though it may not totally eliminate the occurrence.
Precision, screw-retained tube-locks
This tube-locks offer a more rigid connection than a key-way. Screw-retained tube-locks are expensive, lab-intensive and tend to complicate the prosthesis design to accommodate minute screws. Maintenance can be compromised if the screw is lost, because intrusion is likely to occur without the screw and many a times the patient is unaware of the missing screw. This design is indicated when there is insufficient number of implant abutments to support the prosthesis (possibly as a result of implant loss or non-integration of an implant) and the Prosthodontist is then forced to connect implants to natural teeth for prosthesis retention.
A-splint connections
A-splint connections are semi-rigid connections between prosthetic components made by the modification of the original technique by casting a part of the connector with the abutment casting or using a U-shaped wire. The U-shaped wire is placed into the two receptacle boxes in adjacent castings to connect the two prostheses.
Parts are assembled in the mouth and U-wire placed, then A-splint is covered with composite. When splinting, more than four units of implant-supported prosthesis is deemed necessary or when implants are not parallel and connection is needed, then two methods of connecting the prosthetic parts are advocated:
- Key-way stress-breaker
- A-splint connections
Keyway attachments work so well to connect one-piece implant-supported fixed prosthesis that exceed four units than A-splints. But esthetics is very good with A-splints as they are completely covered by composite with no metal display.
A rationale for not connecting implants to natural teeth
When restoring partially edentulous arches with implants, some clinicians believe that it is occasionally beneficial to connect implants to natural teeth. This connection is performed to gain support from the natural tooth and implant, to prevent rotation of the restoration or just merely to retain the natural tooth.
Connecting teeth to osseointegrated implants presents a biomechanical challenge. This is due to the implant being rigidly fixed to the bone with a periodontal ligament. This contributes to a greater mobility of teeth than osseointegrated implants. In this type of restoration, because of the physiological movement of natural tooth, some amount of movement is expected from within the implant system. One solution to this problem is the incorporation of an ‛intra-mobile element' which provides flexibility to implant to compensate for the mobility of the tooth. This intra-mobile element did not contribute to the flexibility of the system, rather it resulted in bending forces that were transmitted to the retaining screw of the implant. [19],[20]
If the implant components are subjected to repeated bending, this could result in screw loosening, metal fatigue and eventual fracture of an implant component. In addition, the amount of support offered by a natural tooth will also be altered. To reduce these torquing forces on the implant, different attachment mechanisms have been proposed by various authors. These methods include:
- Key and key-way type attachments (semi-rigid) [19],[21]
- Rigidly connected implant and tooth-supported segments
- Telescopic attachments.
| Conclusion | | |
Despite the fact that the potential mobility between a tooth and an implant are different and the precise etiology of intrusion is unknown, it is reasonable to rigidly connect a tooth to dental implant. This is particularly true if the anatomy or economic concern precludes the placement of an additional implant. This inference is made from almost every study that addressed this issue and found the survival rates were similar when TISPs and ISPs were compared.
The most common complication of splinting teeth to implants is intrusion. The literature supports the idea that a rigid connection between a tooth and an implant usually precludes intrusion. The literature supports the idea that a rigid connection between a tooth and an implant usually precludes intrusion of teeth. [22]
The following inferences were made from the various studies that dealt with the TISPs which can help us to prevent tooth intrusion and to enhance patient care when fabricating a TISP.
- Select periodontally healthy tooth surrounded by dense bone [23]
- Rigidly connect the tooth and implant by employing large solder joints or one piece castings (with no stressbreakers) [24],[25]
- Use of a non-rigid connector may be efficient in terms of compensation for dissimilar mobility between the tooth and implant under axial loading forces. [26],[27] However, it should be used with caution as it breaks the stress transfer and increases the unfavorable stress values in the prosthesis
- Avoid telescopic crowns
- Use permanent cementation
- Bridge span should be short. Place one pontic between two abutments. [28],[29],[30],[31] However, with additional tooth or implant support or cross-arch stabilization, additional pontics can be used [32],[33]
- Occlusal forces should be meticulously directed to the opposing arch
- Avoid TISPs in patients with parafunctional habits. [34] If TISP has to be used in such patients, over engineer the case by maximizing the number of implants and splinting
- Cantilever extensions should be used cautiously i.e. when a tooth or implant support is adequate. For example, Cantilever - implant - implant - pontics - tooth - tooth
- Avoid TISP in a case with endodontically treated tooth (either a core or a post and core)
- Tooth-implant supported prostheses suffer higher failure rate and complications with more trouble for both patient and clinician and less durability
- More longitudinal studies are needed for TISP before this type of treatment can be recommended on a first choice. The connection of implant-implant remains the safest option although depending on the particular clinical situation and the other case characteristics as well as the individual patient, it can be a visible alternative with an acceptable success rate
- Complete arch-fixed prosthesis supported by implants and teeth may be associated with tooth intrusion when non-rigid connectors are used. However, fixed partial dentures supported by implants and teeth with reduced periodontal support were not associated with tooth intrusion regardless of the type of connectors used [31],[35]
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