Furcation involvements : surgical and prosthetic treatments by separation and root resections

Introduction

The position and the complex anatomy of multi-rooted teeth make oral hygiene in the posterior regions of the maxilla somewhat difficult by encouraging the adherence and growth of the bacterial biofilm. The susceptibility and the vulnerability of the molar regions to periodontal disease have been confirmed by epidemiological studies showing elevated morbidity rates of 18-30 %, or even 85 %, according to the social and ethnic groups under observation (^{Lindhe et al., 1989} ; ^{Papapanou et al., 1989}). The severity of furcation involvements increases with age and the presence of occlusal overload. The onset of tissue destruction has been revealed by ^{Svardström and Wennström (1996)}, who detected at least one lesion by 40 years of age. This rate doubles in smokers (^{Mullally and Linden, 1996}), and by the same amount in the presence of prostheses (^{Wang et al., 1994}).

In the present state of our knowledge, the only corrective treatments for interradicular lesions are surgical (resective) and endodontic, with or without orthodontic and prosthetic treatments. The quality with which these multidisciplinary treatments are carried out will optimise the long-term prognosis by modifying the tissue environment and by reducing risk factors. They will be influenced by a particular challenge : the treatment objectives desired by the patient.

Assessment of tissue destruction

Periodontal probing assesses the severity of destruction, but its real value is often debated. Indeed, clinical probing underestimates the depth of lesions (^{Zappa et al., 1993}) and good reproducibility of the measurements cannot be assured (^{Eickholz, 1995}). The diagnostic assessment of the lesion must not exclude the possibility of an endodontic lesion because anatomical factors (for example, accessory canals, dentinal tubules) and biologic factors (the similarity of the pathogenic flora in periodontal and pulpal disease) testify to strong perio-endo inter-relationships. However, ^{Trope et al. (1988)} differentiate between periodontal endodontic aetiologies of furcation involvements by the levels of spirochetes (30-60 % against 10 %). These lesions are classified according to the degree of horizontal penetration of a periodontal probe into the interradicular space (^{Goldman and Cohen, 1980} ; ^{Hamp and Nyman, 1989}). As a matter of interest, one can distinguish :

- class (or degree or grade) I : horizontal penetration of the bony support not exceeding one third of the bucco-lingual (or palatal) width of the tooth ;

- class (or degree or grade) II : horizontal penetration of the bony support greater than one third but not completely crossing the interradicular space ;

- class (or degree or grade) III : « through-and-through » penetration of the interradicular space.

^{Tarnow and Fletcher (1984)} and later ^{Hou and Tsai (1997)} improved this classification by defining subclasses that incorporate morphological variants of the defect (the vertical component), the type of root trunk and any associated bony lesions. These proposals are useful to establish a treatment plan and to assess prognosis.

Criteria for making treatment decisions

Effects of conventional treatments for interradicular lesions

The treatment of interradicular lesions affecting multi-rooted teeth represents a major challenge. Indeed, anatomical features such root morphology, the width of the interradicular space, the height of the cervical trunk, as well as the presence of accessory canals, or even anomalies of embryological origin, complicate the treatment of these lesions by the usual debridement procedures, with or without surgery. They constitute potential obstacles to the thorough instrumentation of the area, even if access flaps are raised. Only 12.5 % of the root surfaces associated with furcation lesions (probing depth 5-6 mm), treated by non-surgical debridement, have all calculus deposits removed. This rate rises to 25 % when access is gained surgically.

Recourse to rotary instrumentation increases the percentage of calculus-free surfaces to 38 %. The greater the depth of the lesion, the less effective the treatment (^{Matia et al., 1986} ; ^{Parashis et al., 1993}).

« Split mouth » studies comparing the clinical effects of non-surgical treatments (root planing) with surgical debridement of lesions (with or without bone resection) and observed over periods of 15 months to 8 years, give equivalent results in terms of reduction in probing depths and of bleeding, but the teeth affected by interradicular lesions show a loss of clinical attachment 2.5 times greater than those where the integrity of the interradicular space is preserved (^{Kalkwarf et al ., 1988} ; ^{Schroer et al., 1991} ; ^{Wang et al., 1994}).

In the context of advanced periodontitis or rapidly progressing periodontitis, our capacity to stabilise the clinical parameters by non-surgical debridement is limited. The loss of attachment always continues whether or not there is an associated bleeding on probing from the interradicular lesions, when compared with non-molar sites (^{Loos et al., 1988}).

If one attempts to quantify the therapeutic risk, bearing in mind the triad proposed by ^{Newman et al. (1994)} (i.e. the association between bleeding probing and presence of Pg/Pi, quantity of plaque and smoking), the non-specific failure rates for interradicular lesions vary from 44-50 %.

Effects of resective treatments for interradicular lesions

Resective techniques aim to remove the obstacles linked to anatomical factors and to create a clinical environment that is conducive to good oral hygiene in the interradicular space.

As there is no uniform terminology in the scientific literature, we will here resort to the one adopted by the ^{American Academy of Periodontology (1998)}. This specifies that root separation implies section of the root complex and the retention of the roots, in order to differentiate it from root resection which, they propose, is the removal of the root as well as the coronal part of the tooth.

These multidisciplinary techniques are demanding because they rely on the mastery of, and the rigour with which the various associated treatments are undertaken. The assessment of the survival of the resected teeth is not easy to establish because :

- in the scientific literature, the parameters used for assessment are not identical among the studies ;

- there is a variable degree of expertise of among the practitioners ;

- the factors influencing the decision to resect are variable (periodontal, endodontic, fractures, caries). ^{Buhler (1994)}, in a meta-analysis, evaluated a mean failure rate for root resections of 13 % over a short observation period (7 years). ^{Hamp et al . (1975)} reported more encouraging results on 310 multirooted teeth. Five years after treatment, there had been no tooth loss, 7 teeth had residual pockets of 4 to 6 mm and 1 tooth had a pocket greater than 6 mm. ^{Basten et al. (1996)} noted failure rates of 8 %, amongst 49 molars in subjects of 7 to 22 years-of-age. ^{Carnevale et al. (1991)}, in a randomised retrospective study of 3 to 11 year-old subjects, confirm high success rates of 90 % and attribute their failures to endodontic or caries factors. The duplication of these results is limited by the selection of patients (their degree of cooperation) and the very high technical quality of the work. Only ^{Blömlof et al. (1997)} noted failures (18 %) attributable to a progression of the periodontal disease rather than to the type and the constraints of treatment (endodontic, resectional). Most studies stress that even though the failures are not of periodontal origin but arise because of root fractures, caries or the impossibility of carrying out endodontic treatment, the health of the teeth deteriorate further, or are even lost. ^{Müller et al. (1995)} attempted to evaluate the decisional criteria from a retrospective survey of 1 100 interradicular lesions treated by two operators. The choice of the treatment depended on the severity of the disease and the type of the lesion. The decision to amputate a root of a first maxillary molar was much more likely than for a first mandibular molar. The resective technique used did not prejudice the future of multi-rooted teeth but smoking was found to be a risk factor (^{Blömlof et al., 1997} ; ^{Jaoui and Ouhayoun, 1999}).

Finally, it seems that the efficacy and the reliability of resective treatments depend on a multifactorial approach and they are in conflict with treatment by implants (endosseous) in the posterior zones (^{Bühler, 1994}). This approach to treatment must be remembered when the survival of the tooth depends on a therapeutic strategy (^{Caffesse, 1989}).

Indications and contra-indications of resective techniques

^{De Sanctis and Murphy (2000)} summarised the indications and contra-indications of resective treatments and singled out the factors to be considered in periodontal, endodontic and prosthetic assessments.

Periodontal indications

When bone loss affects one or several roots, a conservative approach by guided tissue regeneration may be rendered impossible. Class II and/or III interradicular lesions and dehiscences form the main groups where these techniques are indicated.

Endodontic and restorative indications

The inability to treat and to obturate a root canal, root fracture and/or perforation and/or severe root resorption sum up the difficulties of treatment that, within a conservative philosophy of treatment, only a surgical approach can hope to eliminate.

Prosthetic indications

Corrective surgery is indicated in cases where there is close proximity of a root and/or excessively reduced interproximal space, a fracture of the cervical trunk or caries that encroaches on the biologic space.

Contra-indications can be summarised as those relating to periodontal surgery (systemic factors, poor oral hygiene), to the local anatomy (fused roots, unfavourable tissue architecture), problems associated with endodontic treatment (untreatable roots, over-instrumentation, increased depth of the floor of the pulp chamber), the impossibility of carrying out restorative treatment (internal root resorption, perforation in the interradicular area by a pin) and to considerations of the overall treatment strategy.

Surgical treatment by root separation and resection

A coherent prosthetic treatment plan is essential because there is no doubt that « treatment by resection is a very sensitive technique and its indiscriminate use, without proper indication, in the absence of good oral hygiene on behalf of the patient, and efficient expertise on behalf of the restorative practitioner, must be avoided » (^{Carnevale et al., 1991}). There are three stages to be considered.

Endodontic phase

If possible, root canal therapy should always be considered as the first line of treatment followed by root resection. This first stage of treatment is completed by the fitting of a temporary restoration. Conservation of tooth tissue must be the rule not only at the stage of cutting the access cavity but also during the preparation of the root canal, ensuring the smooth transition between the two. Where there has been a substantial loss of substance, the use of adhesive materials should be considered.

There are three possibilities concerning the timing of the procedures. Endodontic treatment can be envisaged :

- after root amputation of a vital tooth following periodontal surgery. A calcium hydroxide dressing should be applied to the exposed pulp for a period of 2 weeks, following which the definitive endodontic treatment can be undertaken ;

- before periodontal surgery, if the need to amputate the root is known and decided upon in advance ;

- before periodontal surgery, if endodontic pathology is suspected. It will be necessary to perform root canal therapy in all root canals and to wait for at least 2 months before intervening surgically.

Surgical phase

Root separation

Root separation widens the interradicular space by dividing the crown of the tooth into two portions that will each support « half » crowns on each of the retained roots. This technique opens the interradicular space at the expense of tooth substance and not of its bone support. Certain anatomical conditions must be present, notably a short cervical trunk, together with very divergent and roots of adequate volume.

Root resection

Because of the need to elevate a flap, two possible protocols of root resection should be considered :

- to remove the root as a first stage, without the bone being affected (any involvement is supra-bony or juxta-bony). Two to three months later, when closure of the socket has occurred, it is possible to raise a flap in order to perform osteoplasty, root planing and any necessary debridement ;

- by preference, raise a flap, section the root, remove any bony spicules and possibly undertake a light ostectomy in order to achieve a positive architecture, prior to replacing the flap (^{fig. 1}, ², ³, ⁴, ⁵ and ⁶ .

What are the options ?

Section of the tooth and odontoplasty should always to be considered before replacing a flap but this can only be foreseen if the interradicular lesion is evident before the surgery. If an access flap is necessary in order to expose the interradicular lesion, root amputation will avoid leaving a sharp edge in the interradicular area that would constitute a zone vulnerable to recurrent disease. If there is significant bone loss, removal of the root is facilitated, amputation being effected in the root area with preservation of the coronal part of the tooth. If the extraction of the root is undertaken carefully, the crown-root section will facilitate the removal of the root in an occlusal direction. The type of section to be used will depend in the morphology of the bone defect and the subsequent treatment that is proposed (fixed prosthesis, etc.). Bone reshaping is often necessary around the adjacent roots. This will precede the repositioning of the flaps that are held in place with interrupted sutures. When root resections are being undertaken, it is necessary to avoid causing any damage to the vault of the furcation or to the remaining bone tissue. Also to be avoided are perforations in the areas of the root canal foramina, any projecting angles, and there should be sufficient space between the remaining roots in order to facilitate hygiene. It is necessary to remove any angular projections and to smooth out any excessively concave areas in order to eliminate any residual tissue irregularities that are responsible for the majority of failures in the maxilla.

Ultimately, root separation and amputation represent convenient surgical procedures for the elimination of pockets and of bony lesions. The quest of the best compromise between tissue preservation, reducing the risk of fracture and the pursuit smooth surfaces to facilitate the plaque control, constitutes the therapeutic objective that is to be sought-after.

The approach to prosthetic treatment

Prosthetic reconstructions complete the cycle of the care following surgery that involves root separation and/or resection. They should meet the major restorative principles whilst maintaining careful attention especially to the volume of available tissue and root morphology.

What type of restoration?

If, prior to the surgical treatment, there a satisfactory volume of tooth tissue, the cavity can be filled with a plastic material such as composite or amalgam.

If there has been breakdown of the crown or a substantial amount of tissue has had to be sacrificed, the restoration must be retained by some form of root anchorage. However, curvature of the cervical third of the root can contraindicate the use of this means of retention for such restorative materials because they provide no reinforcement of the root being treated (^{Moyen and Armand, 1999} ; ^{Déjou and Laborde, 2001}).

If the root is isolated and potentially fragile, the preferred choice moves towards crown-root reconstructions that incorporate carbon fibres thanks to the similarity of its modulus of elasticity to that of the root dentine. Carbon fibre posts and adhesive composites assist the absorption of applied forces (^{Brouillet and Koubi, 2001}). In situations where adhesion is contraindicated (subgingival areas that do not permit a dry operative field), the crown-root reconstruction of choice moves toward a cast metal technique (inlay core) that is cemented into place. An impression is taken of the post hole and the posts fabricated to an « anatomical » shape (^{Geoffrion et al., 1986}). Gold alloys are preferred for these cast metal cores because of their ability to reduce the forces transmitted to the dentine (^{Ko et al., 1992}). Where the clinical situation favours adhesive techniques (where isolation is possible) and where the practitioner opts for an inlay core restoration, it is preferable to improve the resistance to root fracture by cementing the metallic restoration in place with an intrinsically adhesive product (^{Mendoza et al., 1997}).

Whatever the clinical situation, the crown or crown-root reconstruction must be placed as quickly as possible in order to ensure that the network of root canals remains sealed (^{Southard, 1999} ; ^{Pertot and Machtou, 2001}). However, it can only be done after the surgical phase in order to avoid any contamination of the surgical site at the time of the root separation and/or resection. The maintenance of the seal between the endodontic and surgical phases of treatment can be assured by using a dressing of the IRM^® type.

Provisional prosthesis

The function of the provisional restoration no longer has to be demonstrated, especially during the period of periodontal healing (^{Marin et al., 1994}). It seems worthwhile to integrate this stage into a logical position in the strategy of treatment. A provisional prosthesis should be envisaged :

- before the periodontal surgical intervention in cases of teeth presenting with coronal breakdown, in order to re-establish crown morphology and satisfactory occlusal contacts. In the context of root resections in the mandible, the construction of a temporary bridge supported by the remaining root and an adjacent tooth must be anticipated before the intervention. Particular attention should be paid to the emergence profile of the shoulder and to the polishing of the cervical margins, in order to assist periodontal healing. It is recommended that recourse is made to highly polished temporary prostheses constructed of cured resin in order to discourage the retention of bacterial plaque ;

- after periodontal healing for teeth presenting with a satisfactory crown morphology before the surgery where root resection has been undertaken in the maxilla or root separation in mandible. It seems preferable to fit the temporary restoration between 15 and 21 days after the surgery and to provide for the passage of oral hygiene aids into the interradicular and interproximal areas.

Whatever approach to treatment is adopted, the provisional prosthesis should be readjusted to the new periodontal clinical situation. One must assume that there is a consequent risk of toxicity to the healing periodontal tissues from the monomers contained in the resins during the rebasing procedures and an irritation from unpolymerised monomer (^{Fleiter and Renault, 1992} ; ^{Morenas et al., 1998}). Therefore, immediate rebasing is not desirable, especially after resective surgery. It is better define the cervical margins according to the new location of the gingival margin.

Construction of the definitive restoration

In the special situation of restoration of resected teeth, the objectives of treatment must, as a priority, take into account the need for prevention and the care of the periodontium by ensuring that the margins of restorations are supragingival. If retention proves to be inadequate, other devices (such as a box or groove) will reduce subgingival extension of the restoration. However, according to ^{Carnevale et al. (1990)}, the clinical parameters do not seem to be affected by the position of the margin of the restoration (supragingival or slightly subgingival). With a reduced amount of tooth tissue available, the preparation must be the least mutilating as possible. The choice of the positions of the margins should reflect the need for tissue preservation and will incline towards a shallow concave bevel (of 0.4 to 0.6 mm) or a simple chamfer. With this in mind, at the time of the surgery, it is necessary to eliminate overhangs or significant root concavities in order to achieve a straight emergence of the root (^{Fleiter and Renault, 1992}). Any persistent grooves or gutters must be identified on the preparation in order to allow the laboratory technician to construct the prosthesis without any over contouring. A thickness of at least 3 mm of dentine will be kept, especially in the area of the vault of the furcation, so that « biological space or volume » of the region is respected. Failure to respect this biologic space is responsible for 86 % of the failures after molar root resection (^{Majzoub and Kon, 1992}).

This type of periphery enables the construction of a restoration with a metallic margin and with a straight emergence profile (^{Estrabaud, 1994}). It is possible to achieve a good aesthetic result with this metallic periphery by making a concave chamfer that will accommodate cosmetic material. The embrasures must be preserved in order to facilitate access for interdental cleaning aids for good plaque control and for the formation of keratinised epithelium in the area of the gingival col. This feature must be checked when the framework of the prosthesis is tried in by using the appropriate cleaning aids, and the embrasures adjusted if necessary (^{fig. 7}, ⁸, ⁹, ¹⁰, ¹¹ and ¹² . The prosthesis should present a reduced occlusal dimension in the bucco-lingual direction with a shape that will direct forces along the axes of the remaining roots (^{Ache et al., 1991}). The occlusal contacts should be checked and adjusted throughout the whole range of masticatory positions so that all interferences that could be harmful to the periodontium can be eliminated (^{fig. 13}, ¹⁴, ¹⁵ and ¹⁶ .

The retention of one root of a tooth, especially in the mandible, will inevitably involve its attachment to the adjacent teeth. The shape of the pontic will be that of a premolar and will reduce the occlusal forces in the bucco-lingual direction (^{fig. 17} and ¹⁸).

In the case of root separation, it is necessary to be able to create sufficient space between the roots in order to achieve a satisfactory bony environment. It is sometimes necessary to undertake orthodontic treatment to achieve a controlled increase in the space between the roots. The shape of the prosthesis is that of two joined premolars with embrasures that facilitate plaque control (^{fig. 19}, ²⁰, ²¹ and ²² .

Long-term results of treatments for interradicular lesions (table 1)

Survival rates (or of failure!)

In connection with good plaque control, low sensitivity on behalf of the host explains the encouraging, even flattering, agreement of long-term results (^{Ross and Thompson, 1978} ; ^{Hirschfeld and Wasserman, 1978} ; ^{Mc Fall, 1982} ; ^{Goldman et al., 1986} ; ^{Wood et al., 1989} ; ^{Basten et al., 1996}). But, if one compares the survival rates of single-rooted and multi-rooted teeth, there would be 5 times greater risk of losing a molar or a premolar with furcation involvement than a molar without furcation involvement and/or a single-rooted tooth. It is from this data that leads us to treat interradicular Class III lesions by eliminating bony lesions by resective surgery, i.e. separation and/or amputation.

Implant treatment

For ^{Mc Guire and Nunn (1996)}, it is difficult to predict failure or complications. In a 5-year longitudinal assessment, teeth that present with interradicular lesions, increased mobility and parafunction have a limited survival rate unless there is a high level of oral hygiene. An implant solution can be debated, especially for advanced interradicular lesions, on the basis of an increased risk of bone loss. To undertake early extraction would, under this hypothesis, optimise the bone volume for the insertion of implants.

^{Etienne et al. (1997)} specified the parameters that play a part in the decisions leading to conservation or the placement of implants (the level of oral hygiene, the bony environment, complicated and/or uncertain multidisciplinary treatments).

Conclusion

The wide range of successes and failures reported in the scientific literature reflects the view that the resective treatments for interradicular lesions are procedures that depend on the technical expertise of the operators. Great care must be taken at every stage, from the selection of the case, the integration of the endodontic, periodontal and restorative treatments, to the subsequent maintenance periodontal treatment (^{Mattout and Mattout, 1986} ; ^{Carnevale et al., 1995} ; ^{Basten et al., 1996}). A critical reappraisal before the prosthetic restoration as well as the strict surveillance of a maintenance program increases the therapeutic challenge to the periodontist for the treatment of these particular lesions.

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