Current Concepts of Periodontal Regeneration

“Current Concepts of Periodontal Regeneration” – New York State Dental Journal

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Current Concepts of Periodontal Regeneration
Stuart J. Froum, D.D.S.; Cynthia Gomez, D.DS, M.S.; Michael R. Breault, D.D.S.
Abstract
The purpose of this article is to provide a review of the various regenerative therapies and materials in use today, along with treatment and patient variables that may affect outcome predictability. Future direction in this ever-changing field is also discussed. Techniques currently in use are reviewed and evaluated. They include open flap debridement, the use of bone grafts and bone substitutes, guided tissue regeneration, combination techniques, root surface treatment and the use of biologics. Clinical and histological human studies employing the above-mentioned treatments are discussed. The advantages and disadvantages of each treatment modality are discussed, along with patient and local factors that have been shown to affect success rates.
THE GOALS OF PERIODONTAL THERAPY have long included arresting the disease process, preventing disease recurrence and regenerating periodontium lost as a result of periodontal disease. The latter implies reconstruction of lost tissues, including bone, cementum, and a functionally oriented periodontal ligament.1
Over the past three decades, great strides have been made in the field of periodontal regeneration. Reviews of the literature identify many surgical techniques and materials that have been used successfully to obtain new clinical and histological attachment.2-12 Although to date the goal of complete, predictable regeneration has not been attained, the literature has clearly demonstrated the clinical feasibility and histological possibility of periodontal regeneration with many of these procedures.
The purpose of this article is to provide a review of the various regenerative therapies and materials in use today, along with treatment and patient variables that may affect outcome predictability. Future direction in this ever-changing field will also be discussed. Whenever possible, this review will focus on human studies of the various regenerative procedures. Techniques currently in use include open flap debridement, the use of bone grafts and bone substitutes, guided tissue regeneration, combination techniques, root surface treatment, and the use of biologics.
Open Flap Debridement
The open flap debridement (OFD) procedure has previously been reviewed 2-4, 8, 13 As a regenerative technique, OFD is often used as a control comparison in assessing other modalities. 13 Results vary considerably from study to study, with the average gain in probing attachment level ranging from 1.1 mm to 1.5 mm (average 1.5 mm), and the average fill ranging from 0.5 mm to 3.1 mm (average 1.1 mm). 2-4, 8, 13 Bone fill, but not clinical attachment level gain (CAL), correlated significantly to the depth of defect. Research has also shown clinical hard and soft tissue results to be highly correlated to the degree of plaque control and professional maintenance frequency. 14-16
A greater recurrence of probing depth has been shown to occur with OFD when compared to osseous resective techniques. 17, 18 But a recent study comparing scaling and root planning, osseous surgery and Modified Widman therapy in the treatment of human infrabony defects concluded that, with good patient maintenance, excellent five-year results were achieved with all three treatment modalities. The authors concluded that all three treatment methods were effective in reducing probing depths, with slight changes in CAL. 19 However, results following OFD have been shown to be disappointing in treating furcation defects. 20-23
Bone Grafts
Comprehensive literature reviews have provided evidence that significant levels of new probing attachment and osseous fill can occur following techniques using autogenous and allogenic bone grafts. 2, 4, 8, 11 Autogenous graft material from the iliac crest has long been considered as having the greatest potential for osseous regeneration. A clinical study of 182 transplant sites resulted in an average fill of 3.33 mm. This included complete furcation fill in seven of eight sites, with a 4.5 mm mean increase in height of bone in the furcation. 24
Human histology of sites treated with fresh autogenous iliac bone grafts over a two- to eight-month period verified new bone and a functionally oriented periodontal ligament. 25 Limitations of techniques employing extraoral sources of bone (iliac crest) include an additional surgical site, the need for another doctor (usually a hematologist) to harvest the bone, the transporting and logistics of storing the material, varying amounts of morbidity at the donor site and root resorption with fresh iliac bone in a limited number of cases.
Moreover, two separate studies comparing intraoral bone and iliac grafts showed that, with the exception of furcations, both materials produced comparable results. 26,27 In fact, the former study Research has shown clinical hard and soft tissue results to be highly correlated to the degree of plaque control and professional maintenance frequency. showed a mean increase in bone height following intraoral autogenous grafting of 3.44 mm in measurements taken nine months to” seven years post surgery. The latter study compared OFD, intraoral bone grafts and iliac marrow grafts. The average osseous fill was 70.6% {2.98 mm) in intraoral grafted sites,60.7% (4.36 mm) defect fill in iliac crest-treated sites and 21.8% {0.66 mm) fill in the open debridement sites.
The disadvantage of techniques using intraoral autogenous sources includes limited donor material, the necessity of a second surgical site and possible compromise of an area requiring future implant placement.
A recent literature review of 10 studies using 12 grafting materials (two autogenous, eight decalcified freeze-dried allograft bone [DFDBA], and two freeze-dried bone allograft [FDBA]) showed an average probing depth reduction of 2.7 mm, average fill of 2.2 mm, and average CAL gain of 2.1 mm. This represents a fill of approximately 60% of the original defect depth. Bone fill showed a stronger correlation to defect depth than with OFD alone. 11
The issue of safety when using allografts has been well established, thus minimizing that factor as a concern. 28,29 Controlled clinical trials have shown greater bone fill in DFDBA-treated sites than in nongrafted controls, with DFDBA reporting a mean bone fill of 2.6 mm (65% defect fill) compared to the nongrafted controls’ 1.3 mm (30%) defect fill.30
Comparison of freeze-dried bone allograft (FDBA) and DFDBA in 11 paired intraosseous defects showed no statistical differences in gain in attachment level or fill of defect.31 However, while there is no reported human histology of FDBA-treated sites, there is with DFDBA. 31 In fact, “histological evidence of regeneration following the use of DFDBA is the most extensive and conclusive in the periodontal literature.” 11
In 32 human histological sections, a mean bone fill of 5.4 mm was reported, which represents 79% fill of the original defect. 32 However, a lack of osteoinduction following use of DFDBA in human healing extraction sockets has caused at least one group of researchers to question the continued use of this material for bone grafts. 33,34 The differences in results may be explained in part by recent data that has shown that substantial differences exist in the osteoinductive ability of DFDBA from samples obtained from different bone banks. 35, 36
A recent review of the autograft and allograft periodontal literature concluded that “the amount of fill of the original defect (with both of these graft materials) is about 60% “and “the average gain of attachment is 2.68 mm. 37
Bone Replacement Grafts
Bone substitutes (alloplastic materials) are synthetic implant materials that are differentiated from grafts, which are defined as “any tissue or organ used for implantation or transplantation.”12 A variety of materials have been used to treat periodontal defects. Alloplasts may be divided into ceramic and non-ceramic categories. These may be further divided into absorbable and nonabsorbable materials.
Absorbable ceramics include tricalcium phosphate and absorbable hydroxyapatite. Nonresorbable ceramics include dense hydroxyapatite and porous hydroxyapatite. Non-ceramic absorbable materials include plaster of Paris. Non-ceramic, nonabsorbable materials include bioactive glass and a calcium-coated polymer consisting of polymethylmethacrylate and hydroxyethylmethacrylate.
Controlled clinical comparison studies have demonstrated greater gain in CAL and defect fill with both the absorbable and nonabsorbable allografts when compared to OFD.11 These implants, including porous and dense hydroxyapatite, calcium-coated polymer and tricalcium phosphate, have demonstrated comparable clinical results to autogenous and allogenic grafts.12 Moreover, five-year 38 and four-year evaluation of dense hydroxyapatite39 in intraosseous defects, and a six-year evaluation of the coated copolymer in furcation defects40 show continued clinical stability over time with these materials.
From a clinical standpoint, these materials appear to be biocompatible, non-toxic, nonallergenic, non-carcinogenic and non-inflammatory. However, a variety of histological studies on tricalcium phosphate, 41-43 nonporous hydroxyapatite, 44 porous hydroxyapatite45, 46 and a calcium-coated copolymer47 have demonstrated that these materials function as biocompatible defect fillers.
While many of these materials serve as scaffolds for new bone, to date, alloplasts have failed to demonstrate new cementum and a functionally oriented ligament.
An organic, bovine-derived hydroxyapatite matrix (ABM), a xenograft, has been used as a bone substitute in treatment of human periodontal defects. Three studies evaluated the performance of ABM combined with a cell-binding peptide (ABM/P-15).
The first study was a multicenter clinical evaluation of ABM/P-15 compared to OFD with and without DFDBA. Six-month re-entry results showed ABM/P-15 grafts had significantly better mean defect fill, 2.8 ± 1.2 (12.3%), compared to OFD, mean defect fill of 1.5 ± 1.3 mm (40.3%), and DFDBA-treated sites with mean defect fill of 2.0+ l.4mm(51.4%).48
In the second study, 33 patients with paired infrabony defects were treated with ABM or ABM/P-15. The patients were evaluated six months after treatment. ABM/P-15 had significantly greater mean defect fill (2.9 +/- 1.2 mm) than that obtained with ABM alone (2.2+/- 1.4 mm). 49
In a third study, a series of 25 cases were presented involving combination one-, two-, three-wall defects in patients who were originally treated with ABM/P-15 grafting, reentered and measured six months later. The three-year follow-up showed a mean gain in CAL from 5.4 mm, measured presurgically, to 3.8 mm three years following surgery. There was also a mean decrease in PD from 5.3 mm prior to surgery to 2.9mm after three years. 50 In a human histological study, ABM/P-15 was shown to result in regeneration of lost periodontium in two out of four block sections.51
Recently, in a comparative study of the treatment of intraosseous defects, a bioactive glass showed significant clinical superiority in gain of CAL (2.96 mm vs. 1.54 mm) and defect fill (3.28 mm vs. 1.45 mm) compared to OFD. 52 Another recent controlled six-month reentry study comparing bioactive glass and DFDBA for the treatment of osseous defects showed similar improvements with both materials. A comparison of bone fill (61.8% vs. 62.5%) and defect resolution (73.33% vs. 80.87%) with bioactive glass vs. DFDBA, respectively, demonstrated no significant differences in results. CAL gain was also similar with bioactive glass (2.27 mm) vs. DFDBA (1.93 mm). 53 A recent human histological study examined healing in infrabony defects in five teeth treated with bioactive glass ceramic six months after treatment. Histologic sections revealed a long junctional epithelium and new connective tissue attachment. The graft particles were biocompatible, but new bone formation was minimal and limited to the apical borders of the defects. 54
Guided Tissue Regeneration
In 1976, it was theorized that the type of tissue that predominates in the healing wound would determine whether the response is one of repair or regeneration. 1
This hypothesis stated that periodontal ligament (PDL) regeneration could only occur from cells derived from the PDL.1 It was thought that regeneration of lost bone and a functional PDL to new cementum could be attained by excluding connective tissue and functional epithelium from the healing wound. A more current theory by the same author included bone-derived cells as a source of regenerative tissue. 2 This concept led to the theory of selective cell repopulation, or guided tissue regeneration (GTR). Clinically, this was accomplished by placing an occlusive barrier between the flap and the tooth and its supporting alveolar bone.
The first GTR study on a human with clinical and histologic evidence of regeneration was done in 1982. 3 In this case report, a millipore filter was used as the barrier. Today, expanded polytetrafluroethylene (ePTFE) is the nonabsorbable membrane with the most documented research.
Human studies over the past two decades of infrabony defects treated with ePTFE barriers showed definitive clinical gains in new attachment, with three-wall defects having the greatest improvement. 4 Average CAL gain in three-wall defects, when measured at nine-month reentry, ranged from 4-4.5 mm,5 or > 50% fill.6
In another study of three-wall defects, using ePTFE barriers, a 75% defect fill was reported. An average initial probing depth of 9.6 mm was reduced to 3.9 mm, three and one-half years after membrane placement. 7
In a series of three, 12-month studies of one-, two-and three-wall intrabony defects treated with ePTFE barriers, results showed a 93% fill of three-wall defects, 82% fill of two-wall defects and 39% fill of one-wall defects. 8, 9, 10
In 1986, using ePTFE membranes, 3.8 mm of new cementum was histologically demonstrated in four sites with intrabony defects. 11 In another histological study (1990), five human subjects with intrabony defects were treated with either Teflon or ePTFE barriers. The results demonstrated histological new attachment as early as five weeks with both membranes.12
The majority of the studies using ePTFE and other nonabsorbable membranes in intrabony defects showed positive results13, 14 Several demonstrated that GTR with ePTFE barriers in deep interproximal, intrabony defects produced greater gains in CAL and bone fill than what was obtained with OFD. 15, 16, 17, 18 However there is one study of 28 human subjects that conducted, after six months, ePTFE was equal to open flap debridement in very deep intrabony defects. 15
Guided tissue regeneration using nonabsorbable barriers has been studied in the treatment of Class II and III buccal furcations in both maxillary and mandibular molars. 19, 20
In a six-month evaluation of ePTFE-treated Class II furcation defects, a 4.1 mm gain in CAL gain was reported in both vertical and horizontal dimensions. 19 Two studies of Class III furcation treatment showed a 1.8 mm CAL gain 20 and a 2.4 mm CAL gain.21 However, one author concluded that ePTFE offered little advantage in treatment of maxillary Class II furcation involvements.22
Clinical closure (complete resolution) of Class U and Class III furcation involvements is not predictable, according to the literature. One study demonstrated 14 of 21 membrane-treated sites obtained complete clinical closure of Class II buccal furcation defects. 23 However, other research showed only 1 of 11 furcations clinically closed in six months. 24 Still another study had no clinical closures in the same observation period.25
Class III furcations have yet to be treated successfully in humans, as have Class II interproximal furcations in maxillary molars. 26 The greatest success in treatment of Class III furcations was reported in a six-month comparison study of 21 pairs of matched Class III mandibular furcation defects treated with either ePTFE membranes or OFD. The authors reported eight defects healing with complete closure, 10 showing partial closure and three still open. Not one of the 21 OFD-treated defects showed complete closure. 27
Absorbable Membranes
Absorbable membranes offer a distinct advantage over ePTFE in that there is no need for a second surgery to retrieve the membrane. 28 The second surgical procedure may in fact disrupt the healing and maturation of the tissue.29
There are two main variables with absorbable barriers. The first relates to absorption time of the membrane. Early resorption is not desirable because the regenerating tissues may still be immature. Research has demonstrated that the critical window for healing tissues is three to four weeks post-surgery. 30-32
The second variable relates to the breakdown products of the absorbable membranes. Most membranes break down by hydrolysis into acids or esters. 33
There are several prototypes of membranes available in the market. The major membranes are: PLA/PGA: polylactic/polyglyclic acid (Resolut-W.L Gore & Associates, Inc., 1500 N. 4th St., P.O. Box 2500, Flagstaff, AZ 86003); PLA: poly-DL lactide (Atrisorb-Atrix Lab. Inc., 2579 Midpoint Drive, Fort Collins, CO 80525); polygalactin 910: polymer of polyglycolic—acid not available at this time (Vicryl- Johnson & Johnson, Skillman, NJ); and polylactic acid and collagen (Biomend Merot Sulzer Calcitek, 2320 Faraday Ave., Carlsbad, CA 92008; Bio-Gide Osteohealth Co., One Luitpold Drive, Shirley, SY11967).
PLA/PGA is a polyglcolic/polylactic acid polymer used to form a cell occlusive film with open fibrous structure on both sides. It maintains integrity in vivo for four weeks. It does require suturing, 34
In a multi-center study evaluating the use of PLA/PGA in Class II furcations and intrabony defects, an average of 2.1 mm CAL gain and 2.5 mm probing pocket level reduction was reported after one year.35 Two separate studies used collagen gel as a membrane in combination type intrabony defects and found 50% or more fill in 93% of defects. 36, 37
In a multi-center study, collagen membranes used in Class il furcations showed positive results with averages of 50% bone fill in both vertical and horizontal directions when compared to OFD. 38 Another study using collagen membranes and OFD showed no defect closure of Class II furcation defects in either group in six to seven months.39 The performance of collagen barriers was compared to ePTFE in the treatment of mandibular buccal Class II furcation defects. 40 While the collagen membrane showed statistically better results, from a clinical standpoint, both membranes were equal in gaining new horizontal and vertical attachment. In a study of collagen barriers in the treatment of 52 adult matched periodontal defects, collagen barriers provided greater gain in CAL than OFD alone. 40
A meta-analysis of GTR articles published between 1994 to early 1996 showed that mean PD reduction and CAL gain with collagen membranes were 4.1 mm and 4.0 mm, respectively. 42
Collagen as a barrier offers several advantages. It is homeostatic, helps stabilize the blood clot and enhances fibrin linkage. It is also chemotactic to fibroblasts. It is a weak immunogen and, resorbs in six to seven weeks. It requires no sutures, and is pliable, so it conforms better to root trunks. 43, 44
The disadvantage of collagen is that it tends to collapse in large defects if a broad base is not provided and the membrane is not supported. 41, 45-47 A recent review of collagen membranes concluded that long-term clinical trials are still needed to evaluate the performance of collagen membranes in various types of periodontal defects. 46
Other studies reported that the absorbable barriers (PGA/PLA, PLA and collagen) were as effective as ePTFE for the treatment of Class II furcations and intrabony defects. 47-51The general consensus seems to be that furcation closure in a horizontal dimension is better with absorbable membranes. 49-55 The clinician must choose the appropriate barrier for the appropriate defect. When using nonabsorbable barriers, the need for a second procedure to remove the membrane may result in disruption of healing tissue.
Although GTR using nonabsorbable and absorbable membranes has revolutionized clinical practice, the technique is not as yet predictable. More research in regeneration of Class III furcations and maxillary Class II interproximal furcation defects is needed to make furcation closure a predictable goal.
Combination Techniques
The combination of various treatments—including composite bone grafts, the use of barrier membranes with root demineralization, bone grafts and coronal flap positioning, and variations of the above—have been documented in human clinical trials. In a field test combining the results of many practitioners, it was reported that the addition of autogenous bone to freeze-dried bone allografts (FDBA) significantly improved clinical results. Sixty-three percent of sites treated with FDBA alone had more than 50% bone regeneration. The composite of autogenous bone plus FDBA showed 80% of treated sites with more than 50% bone fill.1
Another study showed that a composite graft of tricalcium phosphate, plaster of Paris and Doxycycline resulted in significantly better results in the treatment of mandibular Class II furcations in both CAL gain (1.9 vs. 0.6) and horizontal defect fill (3.1 vs. 0.6) compared to OFD.2 However, the tatter study had no comparison of this composite with other graft materials in similar defects.
In a study of the treatment of mandibular Class II furcation defects with ePTFE membranes with and without the use of porous hydroxyapatite (HA) at six-month reentry, there was no difference in CAL gain but significant difference in defect fill (2.3 vs. 0.1) in favor of the sites treated with the HA and membrane. 3
Although acid root conditioning appears to have little effect on the clinical results of regenerative procedures in humans (see the section that follows, “Root Surface Treatment”), it has been included in many of the studies utilizing combination regenerative procedures. Several studies that included acid conditioning reported improved results when treating furcations with a combination of nonabsorbable membranes and bone grafts compared to either procedure alone. 4, 5 Two studies by the same authors reported a 72% vs. 31% closure of mandibular Class II and Class III furcations where grafts were used in combination with ePTFE membranes vs. the membrane alone. Moreover, long-term stability of CAL gain and defect fill was improved in the graft-membrane sites vs. the membrane- alone sites over a 53- to 70-month period. 5
Two six-month reentry studies, however, produced conflicting results when comparing the use of bone grafts plus membrane to membrane-alone treated sites using nonabsorbable membranes. One study showed significant improvement of Class II and Class III furcation fills utilizing DFDBA with ePTFE vs. ePTFE alone (85% vs. 50% defect fill). 6 The ePTFE plus DFDBA group also showed significant advantage over the ePTFE alone group in CAL gain (3.1 mm vs. 1.4 mm) vertical bone level gain (3.5 mm vs. 1.4 mm) and horizontal bone level gain (2.4 mm vs. 1.0 mm).
However, another study noted no difference in closure of Class II furcations treated with membrane barriers with and without the addition of DFDBA grafts. 7 In the latter study, only 30% of furcations closed in each group.
Conflicting results have also been presented regarding the advantage of the addition of bone grafts to barrier techniques in the treatment of intraosseous defects. One long-term evaluation showed significant improvement in CAL gain and probing depth reduction following the use of ePTFE membranes with DFDBA and citric acid root conditioning. 5 Two other controlled human studies showed little clinical advantage between grafted and non-grafted controls when utilizing ePTFE membranes. 8, 9
Two studies utilizing absorbable collagen membranes with and without DFDBA grafts again show conflicting results. 10, 11 One study utilizing 6- to 12-month reentry of eight test and eight control defects showed no difference in CAL gain or defect fill between the two groups. 10 Another study of 15 test and 15 control defects with one-year reentry showed a significant improvement in collagen barrier plus DFDBA vs. collagen barrier-alone treated sites. Defect fill was 63% vs. 31% in favor of the collagen- and DFDBA treated sites. 11
Recent human histological data of four intrabony periodontal defects was presented. Two had received bovine bone (Bio-Oss Osteohealth Co., One Luitpold Drive, Shirley, NY 11967) alone and two were treated with the same bovine bone covered with a porcine collagen barrier (Bio-Guide Osteohealth Co., Shirley, NY). Both treatments, when evaluated in six- to nine-month specimens, resulted in new bone on the surface of the bovine particles, new cementum and inserting collagen fibers. The authors noted that the regenerative effect was more pronounced when the xenograft and barrier were used together (documenting 7 mm of new cementum and periodontal ligament). The membrane was only partially degraded by nine months. 12
Proof of principal was again demonstrated in human histological studies using a bovine bone covered with a porcine collagen barrier, resulting in three of four specimens showing regeneration. 13 In another study, use of an autogenous bone and bovine bone combination (1:1 ratio) covered with a collagen barrier also showed regeneration in lour human intrabony defects at nine months. 14
Studies utilizing citric acid root conditioning (CARC) and coronal flap placement (CFP) in the treatment of Class II mandibular furcations have shown similar improvements in defect fill and furcation closure with and without the inclusion of DFDBA to treat the defects. 15 Complete furcation closure was 6/14 with CARC and CFP and 7/16 with CARC, CFP and DFDBA. The use of duramater membranes with the above combinations produced poorer results. 16
Recently, a long-term (four to five years) evaluation of mandibular Class II furcation defects was published that showed complete closure following CFP and citric acid root treatment with and without DFDBA. Results showed that 12 out of 16 sites that had obtained complete closure of the furcation exhibited recurrent Class II furcation involvement. This study questions the long-term stability of CFP + CA with or without DFDBA. 17
Studies utilizing CFP in the treatment of mandibular Class III furcations showed that the addition of DFDBA18or DFDBA plus ePTFE membranes19 did not significantly improve the results with 3/11 furcations showing hard tissue closure when treated with CARC, DFDBA, ePTFE and CFP. (This compared to a closure of 1/11 Class III furcation with CARC, DFDBA and CFP.). 17
Recently, an uncontrolled case report study presented the results of the treatment of mesial and distal maxillary molar Class II furcation involvements. Treatment consisted of the use of DFDBA in combination with ePTFE or FDBA laminar bone strips. Two sites were treated with DFDBA alone, one site with DFDBA mixed with tetracychne, and one site with DFDBA plus calcium sulfate covered with an ePTFE membrane. Eight of twelve furcations (75%) demonstrated complete furca closure. 20
In summary, to date there is little in the way of controlled human studies to demonstrate significantly improved results utilizing combined procedures to treat intraosseous and Class III furcation defects. However, long-term case report data showing clinically improved results utilizing combined procedures (GTR and bone grafts) has been presented. 5 Clinical results in the treatment of Class II furcations appear to be improved when utilizing combination techniques, including barrier membranes and bone grafts. Moreover, human histological evidence in fact shows the possibility of suprabony osseous growth utilizing nonabsorbable barriers (ePTFE) with coronally anchored flaps. 21 More studies are necessary to define the variables involved for predictable regenerative results.
Root Surface Treatment
Animal studies have shown that contamination of the root surface by bacteria and endotoxin, and the changes in the exposed root surface mineral content (hypermineralization) will prevent connective tissue attachment and regeneration. 1-6 Consequently, all regenerative techniques include some form of root surface modification. The classic method of scaling and root planning, while effective in removing endotoxins from the root, 7 in most cases will not result in new connective tissue attachments but rather healing by long junctional epithelium. 8-10
Although citric acid applied to the root as an insitu demineralization solution has shown new connective tissue attachment to previously exposed root surfaces in human block sections, 11 clinical results have repeatedly shown no advantage compared to nonacid-treated controls.12 A recent review of GTR studies with and without the use of citric acid root conditioning showed no clinical advantage over the use of acid root conditioning. 13 In fact, comparison studies of root conditioning in combination with osseous grafts, 14 GTR techniques, 15, 16 and coronal flap positioning17 have consistently shown no additional clinical advantage to citric acid root condition.
Still, and perhaps because clinical and histological data show no disadvantage, many clinicians include root conditioning as part of their combination procedures for periodontal regeneration.
Biologics and Devices
Wound healing is a complex, well-orchestrated sequence of events. In studying the dynamics of cell-to-cell and cell-to-tissue interaction, scientists discovered the presence of growth factors. Attempts have been made to harness and duplicate the mechanisms of act ion of these factors to enhance repair and regeneration.
Growth factors are naturally occurring polypeptides that act as biologic mediators, regulating cell proliferation, connective tissue differentiation and matrix synthesis. Platelets activated at the wound margins release PDGF (platelet-derived growth factors) and TGF-B (transforming growth factor) as well as other mediators.1 Plasma exudate is a source of IGF (insulin-like growth factor). 2 Macrophages, the scavenger cells, are also a source of PDGF, TGF-L and TGF-B. 3 BMPs (the bone morphogenetic proteins) are found within the bone.
This review will only discuss the abovementioned growth factors, as these have been the focus of a bulk of the studies on periodontal regeneration.
PDGF are derived from platelets and activated macrophages, osteoblasts and some tumor cell lines. PDGF, therefore, affects both hard and soft tissue healing. It activates the mesenchymal cells needed in the proliferative phase of healing (including endothelial cells), and it stimulates secretion of collagenase and extra-cellular matrix by fibroblasts in the remodeling phase. 4
Platelet-derived growth factor has been studied extensively for its ability to stimulate bone in the jaws, 5-10 cranium11 and long bone defects. 12-14 The synergistic effects of PDGF and IGF-I have been shown to promote osteoblast, PDL fibroblast and cementoblast DNA synthesis and matrix production. 15-17 Therefore, application of PDGF has been used in conjunction with IGF-I for periodontal tissue regeneration in several periodontal disease models. 18
The short-term application of PDGF-B/IGF-I growth factor in a gel carrier promotes new bone, cementum, and periodontal ligament formation in naturally occurring periodontal alveolar bone defects in beagle dogs. 7 The clearance studies revealed that the half-life of the factors at the site of application was three hours for IGF-I and four and one-half hours for PDGF-BB. In addition, PDGF and IGF-I promote rapid bone formation around endosseous oral implants. 6, 19
A phase I/ll human clinical trial was carried out to test the safety and efficacy of PDGF-B/IGF-I in the treatment of severe periodontal bone defects in humans. 20 The results revealed that no local or systemic adverse effects were found following administration of these GFs in periodontal patients. Significant bone defect till (>40%) was detected at 9 months following treatment with 150 0g/ml each of PDGF B/IGF-l. The standard surgical treatment gave only minimal bone fill of less than 20%. Also, the furcation lesions responded more favorably to the GFs with nearly 3 mm of horizontal bone fill.
Collectively, the animal and human studies suggest that PDGF or PDGF combined with IGF-I strongly stimulate periodontal tissue regeneration. The long-term delivery of PDGF by gene transfer stimulates gingival fibroblast, PDL cell and cementoblast mitogenesis and proliferation above that of continuous PDGF application. 21, 22 Therefore, alternative delivery approaches may achieve greater bioavailability of PDGF to various tissues.
IGF (insulin-like growth factor) is a product of fibroblasts, hepatic cells and fetal rat calvarial cells. By itself, it has minimal effects on wound healing. If combined with PDGF, it can enhance the rate and quality of wound healing. 6
Animal studies conducted utilizing PDGF-BB and IGF-1 showed substantial amounts of new bone, cementum and PDL in two to four weeks compared to controls. 23 Beagle dogs with naturally occurring periodontal disease treated with PDGF-BB and IGF-1 had 65% bone regeneration. 23 Monkeys with ligature-induced periodontitis treated with the same combination had 22% bone regeneration.
When PDGF-BB was used with citric acid and ePTFE in surgically induced Class III furcation defects in beagle dogs, by 8 and 11 weeks, there was complete regeneration of the defect. 10 When ePTFE was not used, significant ankylosis was present at the treated sites that regenerated. 24
Bone morphogenetic proteins (BMP) are non-collagenous proteins found in bone collagen. 25 To date, there have been nine BMPs isolated. 26 Of the nine BMPs, BMP-2 through BMP-9 are structurally related to one another. Due to their amino acid sequence, BMP-2 to BMP-9 are classified as belonging to the TGF B super family. 27
BMP is considered to be a morphogen. Morphogens are substances that initiate the development of tissues and organ systems by stimulating undifferentiated cells to phenotypically convert. 26 BMPs directly affect differentiation of cells into the chondrocytic and osteoblastic phenotype. Both primary cell types and lines are derived from different anatomic sources, and both respond to BMP. 28 BMPs are the only known molecule capable of forming bone and cartilage in ectopic sites. 26
Considering the properties of BMP, it is not difficult to see the interest it has generated among scientists and clinicians. In surgically induced defects in a baboon model, BMP-2 was used and found to produce two and one-half-times more bone and cementum in sites treated with the factor when compared to control sites. 29 Acute defects were induced and then submerged during closure in beagle dogs, with ePTFE, and when BMP-2 was used.30 Four-times more bone and cementum were found when compared to controls.
Several types of recombinant BMPs, including BMP-2,3 and 7, delivered by several carrier systems, have been used to regenerate periodontal tissue in animal models. Several groups have demonstrated the potent induction of cementogenesis and osteogenesis in animal models of periodontal disease using either BMP-231-33 or BMP-7/OP-1. 34, 35 These BMPs have also demonstrated predictability in stimulating bone around endosseous dental implants36-38 and in sinus augmentation procedures. 39
Recent studies also show the potential in oral reconstruction in human patients for both dental implants40, 41 and sinus elevations. 42,43 Taken together, several animal and human studies have shown that BMP-2,3, and 7, incorporated with the resorbable carrier systems, have profound effects on promoting regeneration of periodontal tissue. New approaches for BMP gene delivery to mandibular osteotomy44 and periodontal45 defects suggest that gene therapy may be another mode of BMP application.
There are several problems that have to be addressed before growth factors become part of the clinical periodontal armamentarium. The proper vehicle or delivery system for specific factors has not yet been identified. The amplification or suppressive synergy with other growth factors is not completely understood. There are still questions concerning the degree of concentration of growth factors when used by themselves or in combination with other factors. The variability of growth factor responses locally and systemically is still unknown. Growth factors may have potential for clinical use in the future.
Recent clinical trials have been performed utilizing porcine enamel matrix in a propylene glycol alginate (PGA) vehicle in an attempt to regenerate lost periodontal support. 46, 47The theory behind the use of this formulation was based on the findings that enamel matrix proteins from the epithelial root sheath are involved in the formation of acellular cementum. 48, 49 A review of the studies that explore the relationship between enamel-related proteins and the formation of cementum has been presented. 50
A random, placebo-controlled multicenter trial compared the long-term effect of the modified widman flap (MWF) plus the enamel matrix protein (EMP) to the MWF plus placebo. Thirty-three subjects with 34 paired lest and control sites were tested. Two interproximal sites in the same jaw with probing pocket depths > 6mm and intrabony defects > 4mm in height and > 2 mm in width were treated with test or placebo treatment following MWF. Gain in attachment level favored the test over control sites at eight months post surgery (2.1 mm vs. 1.5 mm), 16 months post surgery (2.3 mm vs. 1.7mm) and at 36 months post surgery (2.2 mm vs. 1.7 mm), respectively. A statistically significant bone gain (as determined by radiographs) at 36 months post surgery measured 2.6 mm at EMP-treated sites. This corresponded to a 66% defect fill.
At 36 months post surgery, the MWF plus placebo treated sites showed no gain of the initial bone loss, while the MWF plus EMP showed a 36% gain of the initial bone loss. 46
A recent controlled, human, 12-month reentry study compared 53 defects treated with MWF plus EMP with 31 defects treated with MWF alone. In all categories, the EMD (test) was superior to the treatment without EMD (control). Average probing depth reduction was 2.7 mm greater in the EMD group. Average gains in CAL level were 1.5 mm greater, and average fill of osseous defect 2.4 mm greater in the EMD group compared to the controls. Average defect fill was more than three-times greater in the EMD group versus control treated sites (74% defect fill vs. 23 % fill). 51
A recent review of biological principles necessary for successful regeneration proposed a clinical decision tree to support the use of EMD alone or combined with an autogenous graft with and without membrane barrier coverage. 52
Recent use of the enamel matrix protein was studied on created Class HI furcation defects in dogs. 53 Use of resorbable barriers with and without the EMP revealed that while both test and control groups showed clinical furcation closure, only the barrier-EMP group showed acellular cementum in the apical portion of the furcation. This acellular cementum reproduces the original cementum-periodontal ligament bone attachment apparatus that constitutes a true regenerated periodontal support. More human clinical and histological data are necessary to ascertain the effect of EMP in combination regenerative techniques utilizing bone replacement grafts and/or barrier membranes.
Systemic and Local Factors
Much of the recent data has documented a direct influence of diabetes mellitus, smoking, human immunodeficiency virus, Down’s syndrome and aging on the incidence and/or progression of periodontal disease. However, information on the effect of systemic factors on regenerative outcomes is more limited. For example, there is no evidence to suggest that age will affect clinical results. In fact, following GTR surgery, there were no reported differences in results in the various age groups.1 Moreover, diabetics were reported to respond as well as control groups to periodontal surgery, provided proper maintenance and excellent plaque control are present.2 A recent review concluded, “the relationship between systemic factors and periodontal regeneration remains to be studied.”3
There is more evidence available when evaluating local factors and their effect on regenerative procedures. Evidence suggests that smoking has a negative impact on regenerative therapies. This is particularly true in cases of GTR, where in one study, smokers recorded <50% of the gain in CAL shown by nonsmokers4 Another study indicated that the majority of patient failures (80%) occurred in patients who smoked. 5
Plaque control and frequency of professional maintenance have been shown to be highly correlated to the CAL gain and osseous fill following open flap debridement (OFD). 6, 7, 8 In fact, OFD surgery performed on patients with poor plaque control actually resulted in loss of attachment. 7
Studies following GTR procedures with barrier membranes have also shown attachment level gains and osseous defect fill to be significantly correlated to the levels of plaque control. 9, 10 Moreover, long-term stability of the clinical gains achieved with GTR was again found to be associated with good oral hygiene and patient compliance in a supportive periodontal care program. 11, 12
In the treatment of Class II furcation defects with GTR, four-year gains in attachment level were found to be stable and to even improve slightly in patients with good oral hygiene and frequent recall visits. On the other hand, sites with poor plaque control exhibited a loss in attachment levels over the four-year post-surgical period. 1, 13
Similar findings in Class II furcations treated with GTR have been published, demonstrating failure in patients with high plaque scores14 and excellent clinical results in patients with good plaque control. 15
There is a paucity of literature concerning the effect of the use of antibiotics on regenerative outcomes in humans. One study utilizing FDBA alone or in combination with autogenous bone showed that the use of antibiotics resulted in greater graft success. 16 This same one-year reentry study showed graft success was also correlated to wound closure. 16
The importance of antibiotics has also been demonstrated in cases of GTR using membrane barriers. Two studies demonstrated that metronidazole-treated sites, in conjunction with GTR procedures, showed 92% defect resolution compared to non-metronidazole-treated sites, which showed 50% defect resolution. 17, 18
The advantage of using antibiotics, however, is not unequivocal. One series of studies showed antibiotic use did not improve clinical outcomes at one year. 19, 20 However, another study showed 15% more defect resolution when antibiotics were utilized with GTR procedures. 21
Tooth mobility has also been shown to affect regenerative results. Less clinical attachment level gains were shown in mobile vs. nonmobile teeth following periodontal treatment. 32 These results are supported by a study that showed teeth treated with occlusal adjustment prior to surgery had greater attachment level gains than non-treated controls. 23
Defect morphology has been shown to affect surgical responses. One study analyzing the factors that influence healing of intraosseous defects found that gain in CAL and decrease in probing depths were related to the initial overall depth of the defect and the depth of the three-wall defect component. The number of remaining bony walls surrounding the defect did not influence the results. 24,25
Similar positive correlations were found (when treating intraosseous defects with GTR procedures) between the depth of the three-wall part of the defect and gain of CAL, bone fill, and probing depth reduction. 26 In both GTR and non-membrane surgery there was no correlation of these clinical parameters to the defect circumference, number of tooth surfaces involved or predominant osseous walls, although the one-wall portion of the combination intrabony lesion showed the least tendency to fill. 25,27 Although in the latter study, defect morphology (number of walls) did not correlate to clinical results, the width of the presurgical defect angle (as determined by radiographs) negatively correlated with gain of CAL and bone fill: The wider this angle, the poorer the results. Moreover, at one-year reentry, the amount of newly formed granulation tissue under the membrane and the ability to cover this with the flap did correlate to gain of CAL and defect fill. 27
Morphology of furcation defects has also been shown to affect clinical outcomes. The deeper the initial defect, the greater the improvement when treating Class II mandibular furcations with GTR. 28 Location of the maxillary furcation also affects results. Maxillary Class II furcations have been shown to respond to GTR procedures when the furcation is only on the buccal, with little or no response when treating mesial or distal furcation defects.
The size of the furcation defect in Class III furcations treated with GTR procedures has been shown to influence clinical outcomes, with furcation closure more likely when the furcation opening did not exceed 3 mm. In general, Class III furcation detects treated with GTR procedures have been shown to give a less favorable response than mandibular29 or maxillary30 Class II buccal furcation defects.
Animal studies have demonstrated the importance of wound stability of the fibrin clot in the early stages of surgical healing. 31, 32 These results have been extrapolated to the human healing response. 33-36 The potential for suprabony healing has been seen histologically in human sections when the flap margin and wound is stabilized as part of the regenerative procedure. 37 This concept of wound stability and space maintenance under a GTR membrane has been shown to positively correlate to the success of clinical outcomes. 38
Finally, a number of studies have demonstrated a correlation between levels of membrane contamination and reduced gains in CAL. 39-41 One recent study cited similar clinical results when membranes became exposed and when they are not exposed, but remarked that all patients had meticulous oral hygiene and used chlorhexidine rinses until the membranes were removed six weeks post surgery. 42  It is evident that plaque control when using membrane barriers is essential for optimum clinical results.
In conclusion, there is human clinical evidence (albeit limited) that the endodontic status of the involved tooth, use of antibiotics, tooth mobility, defect characteristics, furcation defect type (Class II or Class III), and location and size of the defect may affect clinical outcomes in regenerative therapy. There is stronger evidence for smoking, plaque control and maintenance compliance affecting the results of regenerative procedures. •
References
Copies of the extensive references that accompanied this feature are available upon request to the Managing Editor, The New York State Dental Journal, 121 State St., Albany, NY 12207