Tooth Retained Implant: No More an Oxymoron

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1 بنام خدا بنام خدا OPEN ACCESS Freely Available Online Original Hypothesis Tooth Retained Implant: No More an Oxymoron Divya Bhat a Abstract a Department of Periodontics, D.A.P.M.R.V. Dental College, Karnataka, India. Correspondence to: Divya Bhat 1232, 13th Cross, Girinagar, Bangalore , Karnataka, India. Tel: bhat.divya@gmail.com Received: August 30, 2010 Accepted: January 20, 2011 Published: January 28, 2011 Introduction: Periodontally affected teeth are treated in one of the two ways. (1) Tooth retention after periodontal surgery, in which the degree of regeneration achieved is unpredictable. (2) Tooth extraction and implant placement. Implants have an osseointegrated surface which does not provide adequate shock absorption. Regeneration can be achieved by resecting the crown of the affected tooth and submerging the root. This technique has not had a clinical application so far as the tooth becomes difficult to restore. Placing an implant within the root can make the retained root restorable. At the same time, as the implant is placed within the root surface it achieves a periodontal integration which dampens occlusal forces better than osseointegration. Therefore, such a tooth retained implant may serve as an additional treatment option with significant benefits over tooth retention and implant placement alone. The hypothesis: Implants placed within retained roots have shown cementum deposition and attachment of periodontal ligament fibers over their surface. This periodontal attachment may be able to dampen forces better than in an osseointegrated implant. Moreover, since an implant is being placed, the crown of the tooth can be resected and submerged. This prevents epithelial migration, allows for the periodontal ligament cells to populate the wound and favors regeneration. Evaluation of the hypothesis: The technique of placing implants within cavities prepared in the root and then submerging them are simple for any practitioner placing implants routinely. Key words: Tooth retention; Regeneration; Implant, Periodontal attachment; Submergence. Copyright: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. doi: /j.dehy

2 Introduction Periodontal disease and dental caries are the two most common conditions leading to the loss of teeth. Currently the best technique to replace missing teeth is by placing dental implants. These implants are connected to the jaw in a fashion similar to attachments seen in lower animals like reptiles, where teeth are ankylosed to bone. In mammals teeth are suspended in sockets by ligaments. This evolutionary change permits movement of mammalian teeth and the continual repositioning necessitated by jaw growth or tooth wear [1]. Thus, current dental implants need to evolve also and their mode of integration needs to change from osseointegration to periointegration. The osteointegration mode of tissue integration is limited in its capacity to dampen rapidly applied loads. Bone has limited viscoelastic capacity, offering only a small amount of protection against breakdown at the interface when substantial loads are applied [2]. A periodontal integration would serve better in dissipating the occlusal forces. In some studies titanium dental implants were placed in contact with retained root tips whose periodontal ligament served as a source of cells which could populate the implant surface during healing. Microscopic analysis revealed that a distinct layer of cementum with inserting collagen fibers had formed on the surfaces of these implants, and these fibers, often oriented perpendicularly to the surface, were embedded in the opposite bone [3]. Retaining the roots helps in establishing a periodontal ligament support for the implant. The question is if the tooth can be retained, then what is the role of the dental implant? Periodontal regeneration is difficult to achieve. Root submergence has shown a considerable amount of regeneration, but this technique requires resection of the crown of tooth structure making the tooth difficult to restore. This restoration is facilitated by implant placement within the root. Thus, using an implant over the retained root promises considerable benefits over currently available techniques in terms of regeneration around a periodontally affected tooth as well as in providing a periodontal ligament around an implant. This paper reviews the principles behind placing an implant within the retained root. The hypothesis There are two basic theories regarding the bone-implant interface; one is fibroosseous integration and the other is osseointegration [4]. When implants are exposed to the oral cavity during healing, they are sub- 32 Vol 2, No 1,

3 jected to forces which result in formation of fibrous connective tissues around the implant. This is called fibrointegration or osteopreservation. The pseudo-peri-implant membrane formed can neither withstand nor function under occlusal loads. The forces applied to this type of implant result in fibrous encapsulation, inflammatory reactions, and gradual bone resorption [4]. Osseointegration is achieved when the implant is not subjected to functional loads during healing. This type of integration can withstand forces but has a reduced capacity for shock absorption. The current modes of integration of implants have significant disadvantages when compared to periodontal support seen around the natural dentition. Thus, there is a need for new strategies to create a periodontal ligament around implants. The use of periodontal ligament cell sheets for peri-implant periodontal tissue reconstruction has been suggested. However, controlling the differentiation of the cell sheet to different functional periimplant periodontal tissues is very difficult [5]. A simpler and less expensive method for growing a functional periodontal ligament over the implant surface is by retention of the tooth root. The tooth retained implant can be considered to be a marriage between an endodontic stabilizer and a dental implant. The tooth retained implant is inserted in the root like the endodontic stabilizer and has a soft tissue interface similar to the dental implants. Steps suggested for placement of tooth retained implant are: 1. Endodontic therapy of the tooth in the first appointment. A cavity is prepared in the root, extending to the cementodentinal junction close to the root apex, to receive the implant. An impression of this cavity is made which is used to prepare the custom made implant. 2. In the second appointment, a flap is raised and the root surface is debrided. The crown is then resected and slits are made in the coronal aspect of the dentinal wall of the cavity. This is similar to the technique suggested by Parlar et al in 2005, where periodontal tissue invaded through the slits leading to cementum formation on the implant [3]. The custom made implant is cemented in place taking care not to displace cement into the periapical area. This is followed by placement of the cover screw and collagen barrier; and root submergence by close approximation of the flaps. 3. A second surgery is performed after about 4 months (third appointment) to expose the implant for restoration. Vol 2, No 1,

4 Capacity of reduced periodontium to regenerate One important consideration here is whether reduced periodontium can still replicate new tissue or not. This was shown in a study in which experimental periodontitis was produced around a maxillary central incisor in rhesus monkeys. Both the healthy and periodontally affected central incisors were extracted. The central incisor with the normal root surface was transplanted into the reduced periodontium and the diseased root in the normal periodontium. In the group in which the normal root had been autotransplanted into the reduced periodontium, the apical end of the sulcular epithelium approximated the level of the cementoenamel junction, indicating that connective tissue reattachment had occurred to the preexisting level on this normal root surface even though it had been transplanted into a reduced periodontium. Examination of the periodontitis-affected roots that had been autotransplanted into the normal peridontium showed that the epithelium that lined the sulcus extended in an apical direction along the cementum surface and terminated at a point considerably apical to the crest of the alveolar bone. This indicated that it was the exposed root surface, not the lack of a periodontium, which inhibited the potential for a new connective tissue attachment [6]. Therefore, even a reduced periodontium can regenerate. Concerns over tooth retention Over the years there has been a conflict over whether or not tooth retention leads to bone loss in adjacent teeth. Studies have been done comparing the long term effect of extracting or maintaining hopeless teeth on the alveolar bone height of the adjacent teeth. It was found that retention of hopeless teeth had no detrimental effects on adjacent teeth. Periodontal surgery inhibited further bone loss and resulted in slight radiographic bone gain for the hopeless teeth [7]. It is safe to say that periodontally affected teeth, following periodontal surgery, do not affect adjacent teeth and can be retained. Importance of native connective tissue The nature of regenerated connective tissue resembles that of the native tissue. This emphasizes the importance of retaining the tooth supporting tissues, which once removed cannot be replicated. The above was demonstrated by an experiment where root surface specimens were transcutaneously implanted into the backs of Sprague-Dawley rats into the dermal connective tissue (a connective tissue lacking periodontal progenitor cells). Scanning electron microscope observations revealed 34 Vol 2, No 1,

5 that the fiber attachment to experimental specimens differed morphologically from periodontal ligament fiber attachment to normal root surfaces. The numbers of fibers attached per unit length were fewer and the diameter was smaller than in normal periodontal ligament fiber attachment. The attachment to these experimental surfaces appears to have characteristics intrinsic to the connective tissue location [6]. Periodontal Integration around Implants A novel and unique experiment was carried out on dogs to show the ability of periodontal ligament cells to produce a new connective tissue attachment. After resection of the crowns of the canine teeth, the roots were hollowed-out to a depth of 5mm leaving a thin dentinal wall. Slits were then prepared in the cavity wall to create passages from this chamber to the surrounding periodontal ligament. A titanium implant was placed into the center of each chamber, and finally a collagen barrier was placed over the chamber before the roots were submerged. Histologic analysis after 4 months of healing revealed that a periodontal ligament, bone, and root cementum had formed beneath the implant and the dentinal wall of the chamber. Due to the invasion of periodontal tissue through slits into the chamber, cementum had formed on the implant as well as the dentinal wall, and a periodontal ligament was consistently interposed between the implant and the bone and between the bone and the dentinal wall [3]. From this we understand that it is possible to regenerate cementum and periodontal ligament on an implant surface if we retain the root with its supporting tissues. Rationale for implant placement Techniques for preventing epithelial migration into the wound area have provided limited success. One method which holds promise, but so far has had limited clinical application, is root submergence. The effect of excluding the epithelium by amputation of the crown of the tooth and covering the root with the flap, root submergence, has been analyzed in animals and humans. This experimental technique not only excludes the epithelium but also prevents microbial contamination of the wound during reparative stages. Successful repair of osseous lesions in the submerged environment was reported [8]. In order to promote regeneration, the crown is resected and the root submerged in the technique recommended by the author. These procedures make the restoration of the tooth difficult. An implant placed in the root alters this and makes the tooth restorable. Vol 2, No 1,

6 Table 1. Factors responsible for regenerating periodontium and the possibilities. Wound healing variables Manipulation of progenitor cell populations. Alteration of pathologically exposed root surfaces. Exclusion of gingival epithelium from the wound. Stabilization; and technical aspects dealing with the reduced periodontium, including grafting techniques. Evaluation of hypothesis Progenitor cells are maintained in the region by root retention. Exposed surfaces are cleaned during open flap debridement. Root submergence excludes the epithelium from the healing wound. In favorable defects, bone grafts may be included in the treatment protocol to act as scaffolds and promote osseous regeneration. Evaluation of the hypothesis Several variables decide the type of tissue that will occupy the periodontal space after healing. Table 1 describes the factors responsible for regenerating periodontium and the possibilities of the technique reviewed offers in achieving them. Therefore, the proposed technique may offers a possibility of regenerating periodontal tissues which helps retain the root and provide better integration for the implants. Conclusion The technique suggested by the author does not intend to substitute implants or other periodontal surgical procedures. In borderline cases where no current technique exists to save teeth with a questionable prognosis the suggested technique could prove to be of value. Longitudinal studies are necessary to validate our findings. However, in theory, the tooth retained implant seems to have an edge above the current techniques as it provides the advantages of both retaining teeth and placing implants. List of abbreviations There is no abbreviation. Conflicts of interests The authors are not associated with any company or financial position that constitutes a real or perceived conflict of interest. Acknowledgments This study was not financially supported by any institution and commercial sources. 36 Vol 2, No 1,

7 Authors' contributions Main idea: by DB. Literature search: by DB. Data interpretation: by DB. Manuscript preparation: by DB. Data collection: by DB. Funds Collection: N/A. References 1. Bhaskar SN. Orban s Oral Histology and Embryology, 11th Edition. Mosby, 1991: 205. Maryland: 2. Weiss CM, Weiss A. Principles and Practice of Implant Dentistry, 1st Edition. Maryland: Mosby, 2001: Karring T, Lindhe J. Concepts in Periodontal Tissue Regeneration. In: Lindhe J, Lang NP, Karring T, editors: Clinical Periodontology and Implant Dentistry, 5th Edition, Volume 1. Copenhagen: Blackwell Munksgaard, 2008: Hobo S, Ichida E, Garcia LT. Osseointegration and Occlusal Rehabilitation. Hanover Park: Quintessence Publishing Company 1996: Huang S, Zhang D. Periodontal ligament cell sheet engineering: A new possible strategy to promote periodontal regeneration of dental implants. Dent Hypotheses 2010; 1: Polson AM. Periodontal regeneration current status and directions. Rehabilitation. Hanover Park: Quintessence Publishing Company, 1994: Machtei EE, Hirsh I. Retention of hopeless teeth: effect on the adjacent proximal bone following periodontal surgery. J Periodontol 2007; 78: Newman MG, Takei HH, Kokkevold PR, Carranza FA. Carranza s Clinical Periodontology, 10th edition. Maryland: Saunders, 2006: 972. Make a new comment on this article via: Citation:. : No more an oxymoron. Dent Hypotheses 2011; 2: doi: /j.dehy This journal utilizes the LOCKSS system to create a distributed archiving system among participating libraries and permits those libraries to create permanent archives of the journal for purposes of preservation and restoration. Vol 2, No 1,