|Year : 2013 | Volume
| Issue : 3 | Page : 143-150
Tooth implant supported Prosthesis: A Literature review
Vidya Kamalaksh Shenoy1, Shobha J Rodrigue2, E Prashanti3, Sharon J. R. Saldanha2
1 Department of Prosthodontics, AJ Institute of Dental Sciences, Mangalore, Karnataka, India
2 Department of Prosthodontics, Manipal College of Dental Sciences, Mangalore, Karnataka, India
3 Department of Prosthodontics, Melaka Manipal Medical College, Melaka Manipal University, Karnataka, India
|Date of Web Publication||21-Apr-2014|
Shobha J Rodrigue
Department of Prosthodontics, Manipal College of Dental Sciences, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Implants are connected to the natural teeth in the management of partially edentulous patients. The use of this concept has been a subject of discussion as some authors have recommended it while others stress on the potential complications associated with splinting implants to natural teeth. Purpose: The purpose of this article was to systematically review the literature regarding the rationale, difference in the biomechanical behavior of the implant and the natural teeth, nature of connection, potential complications associated with splinting of implants and teeth, and guidelines to be followed. Materials and Methods: Various databases like PubMed, Ebscohost, Science Direct were searched between 1980 to December 2011 to retrieve articles regarding the implant natural teeth connection. A manual search for the references from the retrieved articles was also completed. The articles published only in English, randomized clinical trials, prospective and retrospective clinical studies, laboratory and computer generated research were included. Abstracts, opinion articles, technique articles and questionnaire based studies were excluded. Results: The biomechanical impact of mismatch in the mobility pattern of natural teeth and implants has been controversial. Various complications associated with tooth implant supported prosthesis has been reported with intrusion and implant overloading being the cause of concern. Marginal bone loss associated with overload around the implant has been reported and found to be within acceptable levels. The reports also suggested no significant differences between various types of connections utilized and to use the non rigid connections with caution. Conclusion: Whenever possible implant supported prostheses should be the treatment of choice. However, certain clinical situations demand connecting teeth to implants.
Clinical Relevance to Interdisciplinary Dentistry
- The difference in the biomechanical behaviour between osseointegrated implants and teeth and the efficacy of the different modes of connection that have been employed are explored.
- Evidence based decisions could be made concerning utility of connecting teeth to implants
Keywords: Tooth and implant connection, dental implants, intrusion, nonrigid attachment, partial edentulism
|How to cite this article:|
Shenoy VK, Rodrigue SJ, Prashanti E, Saldanha SJ. Tooth implant supported Prosthesis: A Literature review. J Interdiscip Dentistry 2013;3:143-50
|How to cite this URL:|
Shenoy VK, Rodrigue SJ, Prashanti E, Saldanha SJ. Tooth implant supported Prosthesis: A Literature review. J Interdiscip Dentistry [serial online] 2013 [cited 2019 Jun 16];3:143-50. Available from: http://www.jidonline.com/text.asp?2013/3/3/143/131198
| Introduction|| |
Various modalities of treatment are available to replace missing teeth depending on the number and condition of remaining teeth, space available, adequacy of bone support, cost, and patient desires. Implant supported fixed dental prosthesis has been proven as an efficient modality of treatment.  Implant is connected to remaining natural teeth sometimes when there is an anatomic limitation of space for implants or failure of an implant to osseointegrate. 
The advantages of tooth implant supported prosthesis include splinting of a natural tooth to an implant, increased mechanoreception, and additional support for the total load on the dentition. In addition, connecting teeth with implant broadens treatment possibilities for the restorative dentist, reduces the cost for teeth replacement, and avoids the use of cantilevers. , The disadvantages include higher need for maintenance and repair with such connections. ,,
The problem with the connection of implant-to-natural- tooth-supported prosthesis arises from the fact that the tooth and the osseointegrated implants have dissimilar mobility patterns and this may subject the implant to excessive stresses. Numerous studies have reported pronounced marginal bone loss or failure of implant to osseointegrate especially those closest to implants.  This led to the controversy of whether connecting implant to the natural teeth is a viable option. Various complications like, intrusion of the teeth, ,,, mechanical failure , caries and loss of occlusal contacts  have been reported in the literature associated with this treatment approach. In addition, there is no clear guideline on when and how implant to natural teeth connection should be achieved.
The purpose of this article was to review the literature regarding the rationale, difference in the biomechanical behavior of the implant and the natural teeth, nature of connection, potential complications associated and guidelines to be followed when connecting implants and natural teeth.
| Materials and Methods|| |
Various databases like PubMed, Ebscohost, Science Direct were searched between 1980 to December 2011 to retrieve articles regarding the implant natural teeth connection. The key words used were dental implants, implant tooth connection, intrusion, non-rigid connectors, partial edentulism and combination of these words. A manual search for the references from the retrieved articles was also completed. The articles published only in English, randomized clinical trials, prospective and retrospective clinical studies, laboratory and computer generated research were included. Abstracts, opinion articles, technique articles and questionnaire based studies were excluded.
The articles were analyzed for rationale of tooth implant supported prosthesis, mismatch in the tooth and implant movement, nature of connection utilized and the efficacy of the same, reasons for potential complications and also a comprehensive search for the guidelines for connecting implant to natural teeth was performed.
| Discussion|| |
There are various reasons for advocating the connection of implant to natural teeth. The common being local and systemic conditions which preclude the placement of additional implants, failed implants with some remaining implant, financial constraints for additional implant placement and bone augmentation procedures and anatomic limitations in the posterior areas where inadequate bone is present. , Other reasons include need for additional support where implants have to provide occlusal guidance and there is a need to share the load with the natural teeth to prevent over loading of the implant. Also in periodontally compromised teeth, implants can provide additional support to the remaining natural teeth. ,, Finally, restoring aesthetics in implant is more challenging than the natural teeth. Whenever possible it is better to preserve the natural teeth and connect it to the implant.
Mismatch in the tooth and implant movement
The natural teeth are attached to the alveolar bone by means of periodontal ligament fibers; whereas osseointegrated implant is rigidly anchored to the bone. This difference creates a potential biomechanical mismatch of the supporting units. The tooth exhibits normal physiological movement in vertical, horizontal and rotational direction. The primary factors influencing this movement include the health of periodontium, number, length, diameter, shape and position of the roots. Tooth movement may be divided into two phase pattern.  The first phase consists of rapid movement when the light force is applied and occurs as the periodontal ligament is compressed or stretched. The second phase consists of more linear movement that occurs as the alveolar socket is elastically deformed. Secondary movement is observed when a secondary force is applied and is directly proportional to the amount of force. This measures up to 40 μ under considerably greater forces [Figure 1].
Osseointegrated implants exhibit only linear movement during the entire loading cycle in proportion to the applied load without initial rapid movement due to lack of periodontal ligament. This movement is because of the viscoelastic nature of the bone.
A healthy natural tooth can move 200 μ in response to a 0.1 N force while an implant can be displaced 10 μ or less. , The ratio of the amount of movement of the tooth in a healthy periodontium to that of an implant has been estimated to be 10:1 and 100:1. 
Because of rapid initial movement, structure of the periodontium will allow a tooth to intrude about 50 μ under a force of less than 20 N whereas an implant under a load of 20 N will intrude only about 2 μ due to lack of initial movement. It has been suggested that physiologic movement of the natural tooth causes the prosthesis to act as a cantilever generating maximum resultant load up to two times the applied load on the implant. , The above observations indicate that implant would receive higher amount of loads in function and could lead to potential complications. Studies have also shown that teeth and implant share the occlusal load and all the forces are not transferred to the implant. , Resiliency of implant component, ,, cushioning effect of cement layer, and force deflection in superstructure , may contribute to this phenomenon. Therefore, biomechanical impact of mismatching of mobility pattern between the natural teeth and implant remains controversial.  When the applied load is concerned both magnitude and duration of the force has significant effect on the stress transferred to the bone around a tooth.  From a clinical standpoint this may be significant in patients with bruxism.
Types of connection
The type of connection used in tooth implant supported prosthesis is of three types:
- Rigid connection: The tooth is rigidly connected to the implant with a fixed dental prosthesis. ,
- Non rigid connection: The tooth is non-rigidly connected to the implant by means of precision attachments, non-precision attachments and telescopic restorations [Figure 2]. It acts as a stress breaking element.
- Resilient connection: It incorporates a flexible component that simulates the periodontal ligament. It acts as a stress absorbing element.
Rigid versus non rigid versus resilient connection
The subject of mechanism of connection is very controversial. Rigid connection has been considered as an acceptable procedure by many authors who reported survival of restoration with the rigid connectors on account of the decreased rate of mechanical failure. ,
Subsequently, the use of stress absorbing and stress breaking element was advocated because of the assumption that a rigid connection between the tooth and implant results in additional strain on the implant on account of the mismatch in mobility patterns of tooth and implant. ,
The effect of intramobile element (IME) on providing vertical and rotational flexibility of the prosthesis in tooth implant supported prosthesis has been contradictory. , Some authors ,, claim that IME provides enough flexibility of the prosthesis on the implant to compensate for the prosthesis movement on the natural tooth, while others  concluded that IME does not compensate for the mismatch of the mobility pattern of implant and natural tooth. According to McGlumpy et al., it is the bending of the titanium superstructure screw that provides the required flexibility and thereby ensures even load distribution. 
Different types of non rigid connectors are described with most common being key and key way [Figure 3]. The placement of the key way on the natural teeth seems to be beneficial as it would allow for physiological tooth movement under function. Biomechanical studies demonstrate that a shift of force distribution from the superstructure to the supporting teeth occurs when non-rigid connectors are used ,,,, and tooth intrusion was considered as potential complication of non-rigid ,,,, connection with frequent emergency appointments. 
Contrary to this equivocal reports of incidence of intrusion with both rigid ,, and non-rigid connectors. ,, exist in the literature.
Most clinical observations reveal non-significant differences in function between rigid and non-rigid connections in tooth implant supported prosthesis. ,, These studies evaluating bone loss around implants in tooth implant supported prosthesis using long term radiographic follow up indicate more bone loss with rigid connection compared with non-rigid connection.  Although several non-rigid connectors have been proposed to compensate dissimilar mobility pattern between the implant and tooth, some authors have advocated rigid connection because the prosthesis and implant possess an internal flexibility to accommodate the difference in movement pattern. ,,,, Rangert et al., reported that flexibility in the screw joint of the implant matches the mobility of the periodontal ligament of a tooth and allowed sharing of occlusal load forces to occur. , Laboratory studies have demonstrated insignificant differences in the magnitude and pattern of stress generation with rigid and non-rigid connectors. Therefore, the choice of non-rigid connector will be limited to a desire for retrievability of the implant segment. It has been also reported that non-rigid connectors should be used with caution as it increases unfavorable stresses on the abutment. 
Becker et al., suggested to splint implant to two teeth when non-rigid connectors are considered.  Lin et al., investigated the biomechanical interaction in tooth implant supported FPD under several loading conditions with different number of teeth and connector types. They concluded that stress values were more for tooth implant supported prosthesis irrespective of connector type compared to free standing implant supported prosthesis in simulated axial and oblique function. Interesting point to note was loading condition is primary factor affecting stress distribution in implant than connector type and number of splinted teeth. However, finite element analysis (FEA) is based on theoretical assumptions under average conditions which may have affected the accuracy of the results obtained. Also bending movement of mandible during mastication is not considered in this study. 
In a three dimensional FEM  analysis, load duration appears to have a greater influence than load intensity on the stress distribution in the bone around an implant and a rigidly connected tooth. Static load is compatible with masticatory load intensity and duration that are reported in the literature with bruxism. , and transitional load represents a transitory biting event. This study also suggested that viscoelastic properties of the periodontal ligament plays a key role in good long term performance of tooth implant connected fixed bridge.
Most in vitro studies on rigid and non-rigid connections are based on FEM. These studies are based on theoretical assumptions. They assume that the presence of periodontal ligament provides a certain dental mobility, tooth to implant connection may cause a large portion of the load to be transferred to the implant as it is rigidly fixed to the bone. This stress concentration is proportional to the natural tooth mobility and length of the prosthesis. The findings of the biomechanical studies cannot be applied to a clinical situation.
Rangert et al., , claimed that a tooth when rigidly connected to an implant shares load support with implant and as the load increases the tooth is increasingly involved. This raises the question on the role of viscoelastic properties of periodontal ligament on load transfer.
The degree of overloading depends on the occlusal factors, tooth mobility and the existing number of implants. In other words, in a case with mobile teeth number of implants necessary to enable the implant to support the forces is important than the teeth. As there is little risk to the tooth, overloading of the implant can lead to screw loosening, screw fracture, implant fracture or loss of implant through bone resorption.
Complications associated with tooth implant supported prosthesis
Complications associated with tooth implant prosthesis have been broadly categorized into biological and technical complications.
Biological complications include gradual bone resorption around the implant neck, ,,,,, bone fracture,  loss of osseointegration, ,, peri-implantitis, endodontic problems, caries after cement dissolution and root fracture.  Marginal bone loss is estimated to be threefold with rigid connection compared with free standing implant restorations and non-rigid tooth to implant prosthesis. However, it was within acceptable standards. ,,, From the above, it can be concluded that excessive loads to the implant may not have been transferred when they were connected to teeth. Contrary to this reports of similar amounts of bone loss with both rigid and non-rigid connectors exist in the literature. ,,
Technical complications are caused by mechanical damage to the teeth or implant and includes fatigue induced implant fracture, ,, fracture of abutment screw,  loosening of abutment screw, ,, loss of prosthesis cement bond ,,, to tooth or abutment, abutment fracture, teeth or root fracture,  tooth intrusion and fatigue induced prosthesis fracture. 
Naert et al., , reported complication rate of 5-10% for tooth implant supported prosthesis. The problems included 3.5% periapical lesion, 0.6% tooth fracture, extraction because of caries or periodontitis 1%, crown cement failure 8%, and framework fracture in three patients compared to only two abutment screw fracture in implant supported prosthesis group. Short term follow up studies reported that up to 5 years tooth implant supported prosthesis did not have a higher risk of technical or biological failure than implant supported prosthesis. However, after 10 years tooth implant supported prosthesis (TISP) had more failure than ISP (Implant supported prosthesis). ,, However, no statistical analysis substantiates the finding of this study.
Contrary to this reports of minor or no technical complications also exists in the literature with the tooth implant supported prosthesis, ,,,
The wide spectrum of findings seen may be due to the fact that over a period of time incidence of intrusion and complications increase and therefore short term clinical trials show better outcome.
Intrusion phenomena associated with tooth implant supported prosthesis
Intrusion is a major complication associated with tooth implant supported prosthesis whether rigid or non-rigid connectors are used and have been extensively debated in literature. The phenomenon of intrusion is troublesome for the patient and on the other hand a challenge for the clinician.
Incidence of intrusion
A prospective evaluation revealed an incidence of intrusion of 66% in the non-rigid group vs. 44% in the rigid group over 5 years.  These numbers are significantly higher than those reported in other studies possibly because the study design would have allowed evaluation of even minor levels of intrusion. In the same study tooth loss due to root fracture was reported with the use of both rigid and non rigid connectors. An overall higher rate of complication was reported in the non-rigid group.
Ericson et al., reported on 10 patients with tooth implant supported prosthesis followed up for 6-30 months. One case of natural tooth intrusion was reported after 3 months of follow up. They concluded that at least during the initial time after treatment there was satisfactory outcome in the use of implant and teeth in the same FPD. 
An alternative means to connect teeth to implants is the use of telescopic copings and superstructure. The incidence of intrusion has also been documented with telescopic crowns both in the maxillary and mandibular arches. ,,, When intrusion occurs debris and microorganism get impacted between the primary coping and telescopic superstructure. This will in turn lead to a vicious cycle, preventing the tooth from rebounding to its original position which potentially leads to progressive intrusion.  Flexion of the mandible and flexure of the FPD framework could also generate forces which causes intrusion of the teeth. In a clinical report on use of telescopic restoration to connect tooth with implant in the aesthetic zone no intrusion or other complication was reported after 3 year follow up. 
A retrospective multicenter analyses of 133 implants in 38 patients were observed for 3-36 months. A total of 53 prosthesis were inserted, 31 of which were combination implant natural tooth supported. No case of intrusion, periodontal or mechanical complications were observed.  Astrand et al., also reported that the tooth implant supported prosthesis did not cause any biological and technical complications. They followed 23 patients for 5 years with implant supported prosthesis and implant tooth supported prosthesis in the same patient for 5 years. ,, Pyeart et al., reported on 34 partially edentulous patients with 41 prosthesis in a follow up period of at least 6 months to a maximum of 49 months. 13 among them were tooth implant supported prosthesis, 1 implant had an implant fracture in the posterior mandibular region of tooth implant supported prosthesis. No incidence of intrusion was reported. 
Many reports on more incidence of intrusion with non-rigid connectors as compared to rigid connectors exist in literature. ,, Some reported no intrusion with rigid connectors. ,,,,,,,,,
Clarke et al., suggested guidelines to overcome the intrusion which include proper patient selection, use of rigid connectors, avoidance of telescopic crowns on natural teeth, proper abutment preparation to maximize retention and resistance form and permanent cementation. 
Technique for partial reversal of intrusion has been described in clinical reports ,, and longevity of such attempts has not been established.
Etiology of intrusion
The cause for intrusion is unknown and several theories have been proposed. The cause may be multifactorial depending on the clinical situation and includes disuse atrophy, mechanical bending and impaired rebound memory.
Clinical reports on intrusion with non-rigid connectors invariably contain the portion of the key way on the natural teeth. Probable reason for this may be to allow for retrievability of the implant crown and to allow for apical differential movement of the tooth. However, friction between matrix and patrix of the attachment where occlusal forces depress the tooth and can prevent complete rebounding of the natural tooth after an occlusal load. Repetition of this process could create orthodontic forces leading to intrusion of the tooth. 
Guideline 1: Splint implants to natural teeth only when the teeth need support: Teeth do not stabilize implants.
Appropriate case selection and executing a proper treatment plan are paramount to address the biomechanical challenge associated with connection of implant to natural teeth. Natural teeth must have adequate periodontal support with good long term prognosis. Decreased periodontal support increases forces on the remaining bone and on the implant.  However, when a decision is made to include weakened natural teeth with an implant-supported prosthesis, the method and placement of attachment for the natural abutment to the implant supported abutments must be decided. Becker et al., suggested to splint implant to two teeth when non-rigid connectors are considered.  When a keyway attachment is used for connection of natural teeth to implants, there should be a minimum of two natural teeth connected (double abutted). The process of double abutting the natural teeth greatly reduces the chance for intrusion but may not totally eliminate the occurrence. As regards the placement of the attachment, the key is using a stress breaker with the female part on the implant crown and the male end on the pontic to eliminate the risk of intrusion and allow the tooth to move without overloading the implant. The one problem with this arrangement is loss of retrievability.
Guideline 2: Do not end the fixed prosthesis on the weakest splinted abutment.
Natural abutments connected to rigidly fixated implant should not exhibit clinical mobility or poor retentive form. A weak tooth does not offer additional support and further burdens healthier abutments.
Guideline 3: Regardless of the connection teeth must be cemented using definitive cement
Tooth pushes 28 microns but rebounds only to about 8 microns. The fixed prosthesis rebounds and pulls on the tooth. The cement eventually breaks, causing a space to develop. The prosthesis acts as a orthodontic appliance and pushes in the vertical direction. When a natural tooth acts as a pier abutment it must be considered as a pontic as it does not contribute to the support of the prosthetic load.
Guideline 4: For a natural pier abutment between two implants a stress breaker is not indicated
A living pontic decreases the interaction of forces found during function on account of the proprioceptive aspect of the periodontal complex. 
Guideline 5: Avoid telescopic attachments whenever possible
Intrusion has also been observed in tooth implant supported prosthesis with rigid connectors primarily in patients treated with telescopic attachments. ,, The reason may be due to disuse atrophy of the periodontal ligament. ,, When intrusion occurs debris and microorganism get impacted between the primary coping and telescopic superstructure. This will in turn lead to a vicious cycle, preventing the tooth from rebounding to its original position which potentially leads to progressive intrusion. Other possible causes of intrusion include microbonding of the superstructure against the telescopic copings during flexure of the prosthesis.
Design of the prosthesis should allow minimal movement in a buccolingual direction. Selective grinding procedures must be employed to reduce the cantilever effect and redistribute stress in maximum intercuspation or lateral working position for a tooth implant supported prosthesis. 
| Conclusion|| |
It is evident from the above review that connecting implant to natural teeth is accompanied by various adverse sequelae. Nevertheless, when the situation indicates, the implantologist can and should consider the option of connecting natural teeth to implant. It is paramount to formulate a treatment plan for predictable treatment outcome. A risk benefit analysis and anticipated complications should be presented to the patient and appropriate consent obtained before the treatment plan is finalized. The main focus should be to reduce the risk of intrusion of the tooth and of overloading the implant.
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[Figure 1], [Figure 2], [Figure 3]