Decoronation as an option for ridge preservation prior to implant placement

Abstract Decoronation is a surgical procedure based on idea of sectioning tooth crown and maintaining the root in situ with intention to preclude occurrence of severe deformities of bone and soft tissue which may aggravate later rehabilitation of patient. The aim of this report is to present the use of decoronation in a young adult patient as a solution in order to preserve sufficient amount of bone for delayed implant placement and decrease volume of grafting material to a minimum. Obtained results showed this procedure may greatly improve anatomical conditions for implant placement while reducing invasiveness and required financial means.


INTRODUCTION
Decoronation was firstly introduced by Malmgren et al. more than 30 years ago [1]. However, up to date there is scarce literature data concerning this concept. Basic idea of this method is removing the crown and maintaining the root of a tooth [2]. Originally proposed as a treatment protocol for ankylosed incisors in children after traumatic avulsion, this method revolutionized therapeutic approach to ankylosed teeth and improved conditions for an implant therapy after skeletal growth is finished.
Although this method often leads to root resorption and its replacement with bone, the width of alveolar ridge maintains unaffected [3,4]. Further, due to alveolar ridge preservation implant surgery may be minimized to a great extent [5]. This impact is explained by the following two mechanisms. Initially, after removing crown 1 -2 mm below cervical bone clot organization is inevitable and consequently bone forming cells and growth factors lead to biologic bone development. Secondly, by sectioning tooth below the level of the osseous crest interdental and circumferential periodontal fibers are detached allowing for adjacent teeth to erupt. As this eruption of the adjacent teeth progresses bone apposition on the top of interdental septum occurs [2].
On the other hand, alveolar socket and ridge preservation using various grafting materials is well known method used to compensate for bone resorption and provide adequate bone volume for an implant placement [6]. Nevertheless, economic aspects or willingness to avoid additional surgical trauma required for earning autologous bone are sometimes the main reasons that motivate patient to opt for a low -budget prosthodontic solution after tooth failure.
The aim of this report was to present tooth decoronation in a young adult patient as a solution for preserving sufficient amount of bone for delayed implant placement and decrease volume of grafting material to a minimum. The second objective was to increase the volume of (keratinized) soft tissue thus minimizing surgical trauma.

CASE REPORT
A 20 years old female patient was clinically and radiologically examined at the Department of Oral Surgery, School of Dental Medicine University of Belgrade. Having found non-salvageable maxillary left first premolar indicated for extraction patient was advised to undergo implant therapy due to intact canine and good condition of the second premolar ( Figure 1). However, due to financial reasons, patient was not able to do either immediate extraction and implant placement or alveolar socket preservation. Besides, patient was not psychologically prepared for surgical procedure. Therefore, decoronation was proposed as a temporary socket preservation method in order to help patient by avoiding usage of bone substitute and collagen membrane during this phase and lowering the costs. Decoronation was done using diamond bur under copious saline irrigation in accordance with recommendation from the literature [1]. Technique was modified by omitting horizontal incision and flap rising (Figure 2).
After a period of five months patient decided to proceed with implant therapy. Owing to excellent healing of soft tissue ( Figure 3A) crestal incision was made including mesial and distal papilla and flap was raised without releasing incisions. What was surprising is an outstanding amount of bone that had to be removed to access submerged roots ( Figure 3B). Minimally traumatic extraction of roots was done using periotomes ( Figure 4A-C). In line with standard drilling protocol standard diameter bone    With the intention of providing long term stability of bone and soft tissue support buccal alveolar socket was filled with bone substitute of low resorption rate and covered with absorbable membrane. Flap was repositioned and sutured with 5-0 nylon sutures. After six months implant was uncovered and definite prosthetic crown was delivered ( Figure 6A-C).

DISCUSSION
Regardless of obvious clinical advantages decoronation is not widely accepted amongst practitioners even 3 decades after its introduction. Presumably, the main reason may be a limited number of evidence based research data addressing success rate of this procedure as well as constant pressure induced by medical companies in favor of use varied materials.
When it comes to bone preservation a variety of different grafting materials have been used for decades. More recently enamel matrix derivate (EMD) has been found to promote complete periodontal tissue regeneration and therefore it is recommended for the treatment of avulsed teeth [7]. However, more artificial materials is used, it is higher the cost. On the other hand, it has been shown that not only bone preservation but also bone gain is to be expected after decoronation [1,3,8,9,10]. It is essential to highlight that effects on bone preservation and formation are time dependent. Namely, during pubertal growth spurt this procedure can greatly contribute to normal alveolar ridge development and after the growth peak is reached (by the age of 16) limited amounts of bone may be gained. Additionally, if decoronation was done before the occurrence of severe alveolar ridge deformation, tilting of the adjacent teeth could be reduced and accept- able soft tissue appearance could be established before implant placement. Our finding is consistent with those confirming bone and soft tissue gain. Moreover, when favorable gingival phenotype and bony socket walls are present acceptable healing by secondary intention will occur as a rule. By this approach mobilizing flap was avoided and mucogingival junction was left undisturbed which was crucial as its position may play an important role in long term implant stability regarding both function and aesthetics. Besides, it has been known for long time that every elevation of mucoperiosteal flap leads to the loss of crestal alveolar bone height irrespective of using partial or full thickness flap [11]. Hence, in those cases where anatomical conditions are encouraging more conservative approach is recommended.
On the contrary, Lin et al. showed that preservation of ridge width after decoronation was not 100% successful [4]. In this study a mean of 1.67 mm decrease in width was found with tendency to further decrease during time. Likewise, Tsukiboshi et al. concluded that decoronation procedure showed lack of bone preservation efficiency and related it to the loss of tooth dependent bone volume (TDBV) which is not genetically determined but based on vitality of periodontal fibers [12]. Nonetheless, based on existing literature data it can be emphasized that bone alterations after decoronation are similar to those found after using other preservation methods [13,14,15].
While grafting procedure at the time of implant placement cannot be excluded by decoronation it can help to preserve sufficient bone volume for implant insertion and additional grafting is only used for long term implant stability [16]. Correspondingly, Filippi et al. reported slight decrease in width after two weeks following decoronation procedure that remained constant after 9 months follow up [17].

CONCLUSION
Along with literature evidences it can be concluded that decoronation might be a beneficial alternative regarding bone preservation prior to implant placement. This surgical procedure is a simple and conservative technique to avoid bone loss, aesthetic disturbances and excessively invasive treatments. In order to achieve best results careful diagnosis and right indication assessment are mandatory.