EVOLUTION OF THE CONCEPT OF ROOT PLANING IN THE TREATMENT OF PERIODONTAL POCKETS : CLARIFYING THE CONCEPT

Introduction

Mechanical periodontal debridement (or scaling and rooting planing : SRP) preceded by and combined with oral hygiene procedures have been the gold standard of periodontal treatments for decades (^{Cobb, 1996} ; ^{Lembariti et al., 1998}). Scaling involves the elimination of hard deposits that adhere to tooth surfaces while planing is defined as the elimination of the bacterial flora that is free floating or that adheres to the surfaces of periodontal pockets, the elimination of residual calculus, and the elimination of cementum and dentin that is contaminated by bacteria and bacterial products (^{O'Leary, 1986}). These treatments, which are technically difficult and time consuming to perform, are required to reduce gingival inflammation and pocket depth and improve attachment in most sites (^{Kaldahl et al., 1996}). After teaching good dental hygiene, root planing is the first option for practitioners and patients in the treatment of periodontal disease and, when correctly performed, is often sufficient. Classically, SRP uses both mechanical and manual instrumentation procedures.

A LITTLE HISTORY

Most practitioners currently accept that bacterial plaque organized into biofilms is the aetiological factor that triggers periodontal disease. However, at the beginning of the century, ^{Hartzell (1911)} thought that necrotic cementum was a root cause of periodontal disease and that diseased cementum had to be removed.

During the 1950s, it was accepted that calculus was the aetiological agent of periodontitis and that the disease « soft-drink » the cementum. The recommended approach involved removing part or all of the cementum (^{Schaller, 1956}). The clinical dogma that diseased cementum was softer than healthy cementum became the guiding force behind the perceived need for a hard surface (^{Riffle, 1956}).

It was not until the 1960s that the importance of plaque in the aetiology of periodontal disease came to the fore and that the goal of any treatment was to eliminate plaque and render the root surface smooth in order to prevent the accumulation of new plaque (^{Green et Ramfjord, 1966}).

In the 1970s, the focus largely shifted to bacterial toxins that supposedly penetrated and were fixed by the cementum (^{Nabers, 1970}). Treatments thus consisted of eliminating the layers of endotoxin-contaminated cementum (^{Jones et O'Leary, 1978}).

Based on these observations, clinicians developed the classic concept of root planing, which consisted of removing bacteria, bacterial products, and contaminated tissues (^{Daly et al., 1982}) by eliminating all contaminated cementum and dentin (^{O'Leary, 1986}).

During the 1980s, numerous articles reported that endotoxins were present on tooth surfaces but were only loosely attached to the cementum (^{Nakib et al., 1982}). In addition, while the elimination of large quantities of cementum and dentin did not necessarily remove all traces of endotoxin (^{Moore et al., 1986} ; ^{Hughes et Smales, 1986} ; ^{Nyman et al., 1986}) it did increase the risk of exposing dentin and lateral root and pulp canals in the interradicular space.

Based on these results, the elimination of a layer of cementum by curettage is neither necessary nor justified (^{Greenstein, 1992}).

ELIMINATING PLAQUE

We now know that plaque is organized into a biofilm that enables bacteria to adhere to tooth surfaces (^{Costerton et al., 1995}) and that protects pathogens from both host defense mechanisms and antimicrobial agents. This is why it is essential to disrupt this matrix (^{Darveau et al., 1997}) and why mechanical treatments play such an important role in treating all forms of periodontal disease. We also know that the bacteria in periodontal pockets accumulate near attachment zones (^{fig. 1}). The distance between the plaque border and the attachment system has been measured and the « bacteria-free zone » can vary from 0.2 to 1.1 mm (^{Waerhaug, 1976}). The most apically located bacteria are often anaerobes and are the most capable of causing severe damage to periodontal tissues (^{Slots, 1999}) which is why mechanical instrumentation must be used to eliminate them. ^{Dragoo (1992)} has described the average distance between the bottom of pockets and the lower limits of instrument accessibility as well as the average depth of deposit-free subgingival tissue for pockets with an average depth of 6.8 mm ^{table I} . ^{Dragoo (1992)} highlighted the superior effectiveness of mini-inserts with respect to conventional manual and ultrasonic instruments. Another study using other types of mini-inserts reported that bacterial deposits were left on only 5 % of furcation dome, a result that was superior to previously described methods (^{Gagnot et al., 1999}) Irrigation, micro-currents, and ultrasonic cavitation may also disrupt biofilms (^{Khambay and Walmsley, 1999} ; ^{Walmsley et al., 1990}) While all bacteria adhering to dental surfaces cannot be removed, decreasing the total bacterial load often allows host defenses to control the bacterial flora and repair mechanisms to function. Ultrasonic devices can also deliver antiseptics in situ, although the cogency of using such substances has not been proven (^{Greenstein, 2000}).

Clinical studies have demonstrated the general superiority of ultrasonic treatments over manual instrumentation. While there is no improvement in attachment, pocket depth reduction, or bleeding, there is a 25 % to 50 % reduction in the time required to achieve the same results (^{Baehni et al., 1992} ; ^{Drisko et Lewis, 1996}).

DETOXIFYING SURFACES

While bacterial lipopolysaccharides (LPS) have been detected on tooth surfaces, they do not seem to attach to the cementum of periodontally involved roots (^{Hughes et Smales, 1986}). It has also been shown that using an ultrasonic instrument (Cavitron^®) at very low pressure (between 10 g and 75 g) for very short periods (0.8 s/mm²) eliminates all endotoxins, even if some traces of calculus remain (^{Chiew et al., 1991}).

The cavitation effect and micro-currents produced by ultrasonic instruments have an additive effect in eliminating endotoxins (^{Khambay et Walmsley, 1999} ; ^{Walmsley et al., 1990}). Meticulous, gentle ultrasonic debridement treatments that avoid removing cementum and dentin have been shown to be superior to manual curettage in eliminating endotoxins, improving probing attachment, reducing pocket depth, and decreasing gingival inflammation (^{Smart et al., 1990} ; ^{Copulos et al., 1993}).

ELIMINATING CALCULUS

While subgingival calculus is associated with the progression of periodontal disease, it is more a consequence than a cause of periodontal disease (^{Anerud et al., 1991}). There is an apparent paradox between the fact that many authors have described the efficacy of nonsurgical root planing while others have reported that instrumentation, even surgical root planing, cannot eliminate all deposits from root canals (see ^{Corbet et al., 1993}, for review). ^{Listgarten and Ellegard (1973)} have shown by SEM observations that epithelial cells can adhere to calculus, which means that, within acceptable limits, the presence of residual deposits does not prevent healing. The notion that healing can occur over and around particles of residual calculus has been supported by an animal study conducted by ^Fujikawa and a study with humans by ^{Nyman Sherman} have described the difficulty in totally eliminating subgingival calculus and have also shown that short-term clinical results are not affected by the presence of the residual calculus they observed after tooth extraction (Sherman et al. ^{, 1990b}). Calculus is not in and of itself pathogenic since it can be detoxified by ultrasonic instrumentation. However, it does provide an ideal « nest » for bacteria ^{(Nyman et al., 1986)}.

Subgingival calculus adheres more strongly than supragingival calculus and, as such, more effort must be exerted to remove it during the initial treatment with the attendant risk of causing greater trauma to the cementum and gingival tissue. The risk of removing tissue with manual curettes is much higher when eliminating subgingival calculus because greater force is required and less control can be exerted ^{(White et al., 1996} Studies comparing the capacity to eliminate calculus have shown no differences in terms of type of instrumentation. However, it takes less time to achieve a clinically clean surface with a piezoelectric ultrasonic instrument (74 ± 27 s) than with a magnetorestrictive instrument (104 ± 25 s) or manual curettes (126 ± 38 s) ^{(Busslinger et al., 2001)}. It has also been shown that the new generation of inserts can reach into furcations and, while they cannot completely eliminate the calculus, they can remove bacteria from the surface ^{(Gagnot et al., 1999)} (^{fig. 2}).

The total elimination of calculus is not essential. Furthermore, it is impossible to remove all calculus, especially in deep pockets and in interradicular spaces because manual curettes cannot reach these areas (see ^{Drisko et Lewis, 1996}, for review).

It should also be remembered that the skill of the operator is an important factor in the efficacy of calculus removal (^{Fleischer et al., 1989}).

SURFACE TEXTURE

Cementum curettage

Root planing is defined as a treatment whose goal is to produce a hard, smooth surface by eliminating bacterial deposits and « soft » cementum contaminated by endotoxins and/or bacteria ^{(Lindhe et al., 1998)} Root planing, by its very definition, is in fact cementum curettage. The cementum layer is 20 to 200 µm thick and is thinnest in the cervical region where it is only 20 to 50 µm deep (^{Selvig, 1965}). The elimination of the cervical cementum layer would explain post-operatory hypersensitivity. ^Nyman have reported that the removal of cementum may cause damage to the pulp that patients and practitioners alike find disagreeable. In addition, continuing such treatments during highly recurrent maintenance procedures may lead to a fracture, necessitating extraction (^{fig. 3} and ⁴).

The elimination of cementum is proportional to the number of curette passages. With sharpened curettes, zones of exposed dentin appear after the second passage while the cementum is almost completely removed after seven passages ^{(Coldiron et al., 1990)} These results differ from those reported by ^Borghetti in that they do not take into consideration the instrument pressure exerted on the teeth. The elimination of tissue is also proportional to the pressure exerted on the teeth ^{(Ritz et al., 1991)}. Studies on dentin have shown that a 6.8 µm-thick layer is removed when a pressure of 3 N is exerted while a 20.6 µm-thick layer is removed when a pressure of 8.5 N is exerted ^{(Zappa et al., 1991)}; ^{(Rees et al., 1999}) have compared the efficacy of various instruments and report that manual curettes remove the most hard tissue (^{table II}).

Since the regeneration of periodontal tissue is not reproducible, the treatment must be as conservative and as gentle as possible. Clinicians must only eliminate bacteria and bacterial products. Blunt instruments with as little pressure as possible (0.3-0.5 N) should be used ^{(Kocher et al., 2001)}.

Rough surface

Many authors have maintained that the goal of good planing is to obtain a root surface that is as smooth as possible ^{(Lindhe et al., 1998} ; ^{Schluger et al., 1990)}However, smooth surfaces are not always deposit-free ^{(Jones et al., 1972} ; ^{Rabbanni et al., 1981)}. ^Genco have also cast doubt on this notion. Our observations have shown that the smoother the surface the more dentin is exposed (^{fig. 5}). At x 50 magnification, cementum surfaces appear fairly granular and dappled, but never smooth, and the granular texture of the surface is often attenuated by the instrumentation treatment (^{fig. 6}). By comparing surface textures after treatment with different instruments, various authors have reported that the largest number of deep grooves are produced by manual curettes and sonic instruments while fewer alterations are caused by piezoelectric and magnetorestrictive ultrasonic instruments ^{(Jotikasthira et al., 1992} ; ^{Jacobson et al., 1994)}.

^Busslinger conducted a comparative study and reported that surfaces are rougher following piezoelectric ultrasonic treatments than manual curette and Cavitron^® treatments, with a roughness index of 2.00 ± 0.41 following the piezoelectric treatment and 1.4 ± 0.4 following the manual curette and Cavitron^® treatments. It should be noted, however, that they used a dentin not a cementum model.

The role of cementum is to act as the attachment point of large numbers of collagen fibers, which is why a « rough » surface is important in order to increase the possibility of attachment. However, if the periodontal ligament is destroyed directly or indirectly by the subgingival microflora, a rough surface becomes more of an inconvenience because it promotes bacterial adhesion. It is thus important to have a standard definition of a so-called smooth root surface at the bacterial cell level.

Root planing can eliminate a large amount of cementum. Cementum elimination is proportion to the number of curette passages and the pressure exerted by the operator. Manual curettes remove more cementum than sonic and ultrasonic instruments. Manual curettes and sonic instruments cause greater alterations in surface texture than ultrasonic instruments. It is not at all clear that a clinically smooth surface is less adhesive for bacteria. Root planing is incompatible with the notion of supportive treatments.

REDUCING POCKET DEPTH

^Oosterwaal and ^Mora have reported that there are no clinically significant differences between manual and ultrasonic treatments. They observed the same changes in 6 to 9 mm pockets 6 months post-treatment. Inflammation decreased between 82 % and 86 %. The reduction in pocket depth was proportional to initial pocket depth, i.e., 1.3 mm for an initial depth of 4.2 mm, 1.9 mm for an initial depth of 5.5 mm, and 2.7 mm for an initial depth of 8 mm (^{Badersten et al., 1981} et ¹⁹⁸⁴).

ATTACHMENT LOSS

Attachment loss may continue with the progression of the disease, but may also be caused by instrumentation of the pocket following root planing ^{(Lindhe et al., 1982)} despite the absence of any clinical signs. Measurements made before and after scaling have shown an average attachment loss of 0.5 mm, which can vary by 10-20 % in narrow pockets. One year post-treatment, ^Claffey reported that 2 % of sites had lost attachment due to instrumentation, which corresponds to half the sites that lost attachment during the one-year period. ^Vanooteghem reported similar results over a three-year observation period. It should be specified that ^Claffey used an ultrasonic instrument (Cavitron^®) at maximum power while ^Vanooteghem used a combination of ultrasonic instrument (Cavitron^®) and manual curettes. However, the use of ultrasonic instruments at low power is currently recommended to reduce tissue damage ^{(Gagnot et al., 1998} ; ^{Kocher et al., 2001)}.

Conclusion

When we examine the results obtained using mechanical treatments, it is clear that few differences have been observed between manual curettes and mechanically assisted instruments. However, since the appearance of new inserts (^{Holbrook and Low, 1991}), ultrasonic treatments have been shown to be superior in eliminating bacterial deposits in deep pockets and furcations. In addition, the time saved because there is no need to sharpen instruments, greater patient comfort, and less user-fatigue should result in practitioners increasingly turning to ultrasonic instruments. It is important to understand that associating ultrasonic treatments with the notion of supportive treatments must include an awareness of the primordial need to protect subjacent structures (cementum and gingival tissue) by using as gentle an approach as possible. With this in mind, the terms cementum curettage and root planing must be dropped and replaced by pocket debridement, which is more in line with reality and clinical requirements, as that was proposed by ^Smart .

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