1Root-end filling materials

Chong & Pittford, Endodontic Topics, 2005 Vol 11, - Root-end filling materials: rationale and tissue responseThe requirements of an ideal root-end filling are reviewed, before the demise of amalgam is considered. The focus is on tissue response to newer alternative materials: zinc oxideeugenol cements, Mineral Trioxide Aggregate, glass ionomer cements, composite resins, compomers, and Diaket. The conflicting findings of in vitro and in vivo studies are analysed, as well as whether a root-end filling is necessary. The 'apical seal' is revisited with support for the concept of a 'double seal' that is physical and biological.Role of a Root-end Filling

Management of the resected root end during periradicular surgery is critical to a successful outcome (7). Gutmann & Pitt Ford, 1993 - Management of the resected root end: a clinical review

The portion of root apex that is inaccessible to instrumentation and, as a consequence, cannot be cleaned, shaped or filled, or is associated with extraradicular infection that is unresponsive to non-surgical treatment, is removed. A filling material is then placed into a prepared root-end cavity as a 'physical seal' to prevent the passage of microorganisms or their products from the root canal system into the adjacent periradicular tissues. The placement of a root-end filling is one of the key steps in managing the root end.

The ideal healing response after periradicular surgery is the re-establishment of an apical attachment apparatus and osseous repair (8, 9). Andreasen,1973 - Cementum repair after apicoectomy in humans. and

Craig & Harrison, 1993 - Wound healing following demineralization of resected root ends in periradicular surgery.

However, histological examination of biopsy specimens reveals three types of tissue response (10): Andreasen & Rud, 1972 - Modes of healing histologically after endodontic surgery in 70 cases.

1. healing with reformation of the periodontal ligament; 2. healing with fibrous tissue (scar); and 3. moderate-to-severe inflammation without scar tissue.

The deposition of cementum on the cut root face is considered a desired healing response and a pre-requisite for the reformation of a functional periodontal attachment (8). Andreasen,1973 - Cementum repair after apicoectomy in humans.

2Resection of the root end results in an exposed dentinal root face surrounded peripherally by cementum with a root canal in the middle.

Cementum deposition occurs from the circumference of the root end and proceeds centrally toward the resected root canal.

The cementum provides a 'biological seal,' in addition to the 'physical seal' of the root-end filling, thereby creating a 'double seal' (11). Regan, 2002 -.Comparison of Diaket and MTA when used as root-end filling materials to support regeneration of the periradicular tissues.

Requirements of an ideal root-end filling material

The requirements of an ideal root-end filling material are well documented (1214) (Table 1).

Table 1. The requirements of an ideal root-end filling material

After Gartner and Dorn (12), Kim et al. (13), Chong (14).Root-end filling materials should: Adhere or bond to tooth tissue and "seal" the root end three dimensionally Not promote, and preferably inhibit, the growth of pathogenic microorganisms Be dimensionally stable and unaffected by moisture in either the set or unset state Be well tolerated by periradicular tissues with no inflammatory reactions Stimulate the regeneration of normal periodontium Be nontoxic both locally and systemically Not corrode or be electrochemically active Not stain the tooth or the periradicular tissues Be easily distinguishable on radiographs Have a long shelf life, be easy to handle

Amalgam its demiseIt has become clearly recognized that there are many disadvantages with amalgam (12, 1822).

Corrosion and dimensional changes

3Amalgam corrodes at different rates depending on its composition. Electrochemical corrosion of amalgam was reported to be responsible for failures of amalgam root-end fillings (23).

Unsightly amalgam tattoosScattering of excess amalgam particles during placement of the root-end filling can lead to tissue disfigurement. 'Focal argyria' results when the implanted material corrodes causing unsightly tattoos (24).Biocompatibility and safety issues

The biocompatibility of amalgam is cited as a current issue of concern in dentistry (25).

Many in vivo usage studies in animals have reported unfavorable tissue response to amalgam (1821, 2630).

Furthermore, regardless of the time period, no root end filled with amalgam was free from inflammation (20, 21), as all were associated with moderate or severe inflammation.

The biological effects of amalgam are thought to be dependent on mode of manufacture and composition of the alloy (31)

.Zinc is known to be cytotoxic (32, 33) and its release from amalgam is considered a major cause of cytotoxicity (34, 35).

Therefore, zinc-free amalgams are less cytotoxic compared with zinc-containing amalgams (36, 37).

There is also growing concern among the general public over the use of amalgam in dentistry especially the introduction of mercury into the body (38). The question of amalgam's safety has been examined meticulously in a number of reviews (3944) and received attention from the World Health Organization (45).

Moreover, no significant elevation of blood mercury levels in humans following the placement of freshly mixed amalgam root-end fillings has been noted (46). Nevertheless, the dental profession has long realized that amalgam usage is more than an emotive issue.

Ineffective 'seal' from in vitro studiesMany in vitro leakage studies have demonstrated that amalgam does not provide an effective 'seal' (47). CONTD Although there are continuing questions on the validity and relevance of leakage studies (48, 49), they still have a place in providing an initial indication of a material's suitability.

Poor outcomes reported in clinical studiesMany clinical studies have reported poor outcomes with amalgam root-end fillings when the results were carefully reviewed and strict healing criteria applied (5053).

4Despite assertions that amalgam is still acceptable (54) or that there is not enough evidence to recommend alternative materials (55, 56), there is no shortage of opponents;

amalgam can no longer be considered the root-end filling material of choice (13, 14, 22, 5759). The use of amalgam as a root-end filling material can now be confined to history.

Newer root-end filling materials

Zinc oxideeugenol cements

Zinc oxide-eugenol (ZOE) cements are among the materials currently considered more effective than amalgam for root-end filling.

In an early report, Nicholls (60) expressed a preference for ZOE cements to amalgam for root-end fillings.

The material was considered easy to handle and reportedly gave good postoperative results. However, the original ZOE cements were weak and had a long setting time (61).

Another major disadvantage was their solubility. Indeed, the perceived view was that ZOE root-end fillings were likely to be absorbed over a period of time (62, 63)

and therefore unsuitable for long-term use. Consequently, the use of modified forms of ZOE cements was suggested (64, 65)

Two approaches were adopted to improve the physical properties of ZOE cements:

(i) The partial substitution of eugenol liquid with ethoxybenzoic acid (EBA) and the addition of fused quartz or aluminum oxide to the powder to give an EBA cement Stailine Super EBA cement (Staident International, Staines, Middx, UK).

(ii) The addition of polymeric substances to the powder. CONTD (a) polymethymethacrylate to the powder Intermediate Restorative Material (IRM) (De Trey, Dentsply, Konstanz, Germany)(b) polystyrene to the liquid Kalzinol (De Trey, Dentsply)

The biological properties of ZOE cements differ according to formulation and age of the material (37). Eugenol is the major cytotoxic component in ZOE cements (6669).

5Zinc released from these cements was suggested as being partly responsible for the prolonged cytotoxic effect (32).

The cytotoxicity of EBA is also because of eugenol; this was the only component in the cement to show a cytotoxic effect when the components were tested separately (75).

Over a period of time, the cytotoxicity of EBA gradually reduces to nil (76); the explanation being that EBA contained less eugenol at the start and it had all leached out.

Another explanation was that the generation of eugenol radicals, responsible for the cytotoxicity, may be suppressed by the EBA (77).

A reduction in cytotoxicity of EBA with time was also reported by Chong et al. (37)

Efforts were made to further improve the biocompatibility of reinforced ZOE cements by adding hydroxyapatite to IRM (80) and Type II collagen powder to EBA (81).

Of the reinforced ZOE cements, EBA is the strongest and least soluble of all the formulations (83, 84).

Hendra (64) recommended the use of EBA as a root-end filling material. EBA has a short setting time and because of its adhesive properties, an initial concern was difficulties in placing the material into the root-end cavity (85, 86).

Oynick & Oynick (65) reported that collagen fibres grew over EBA root-end fillings and claimed the material to be biocompatible.

Significant interest in reinforced ZOE cements as a root-end filling material was generated by the results of a retrospective study by (50). Dorn & Gartner, 1990 - Retrograde filling materials: a retrospective success-failure study of amalgam, EBA, and IRM

They examined the results of amalgam, IRM and EBA as root-end fillings. A total of 488 cases from two practices were reviewed, the recall period ranged from 6 months to 10 years. A successful outcome of 95% was found with EBA, 91% with IRM and 75% with amalgam; the difference between EBA and IRM was not statistically significant. CONTD

Good results were reported with EBA when periradicular surgery was performed with microsurgical techniques and with the aid of an operating microscope (1, 2). Rubinstein & Kim, 1999 - Short-term observation of the results of endodontic surgery with the use of a surgical operation microscope and Super-EBA as a root-end filling material. And

Rubinstein & Kim, 2002 - Long-term follow-up of cases considered healed one year after apical microsurgery.

6 A 96.8% successful outcome was seen in 94 out of the 128 cases treated when reviewed at 1 year (1). When the cases considered healed were reevaluated 57 years later, 54 out of the 59 roots (91.5%) recalled remained healed (2). In another study, when 120 teeth were followed-up for up to 3 years, a successful outcome of 92.5% with EBA was achieved when combined with modern periradicular surgery techniques (6).

In contrast, traditional surgical techniques and amalgam as a root-end filling material were reported to have a negative effect on outcomes (3).

Mineral Trioxide Aggregate (MTA)MTA was developed as a new root-end filling material at Loma Linda University, California, USA. A study on the physical and chemical properties of MTA investigated the composition, pH, radiopacity, setting time, compressive strength and solubility of the material compared with amalgam and reinforced ZOE cements (92).Torabinejad, 1995 -.Physical and chemical properties of a new root-end filling material.Unlike a number of dental materials that are not moisture-tolerant, MTA actually requires moisture to set. The MTA powder consists of fine hydrophilic particles. When mixed with sterile water, hydration of the MTA powder results in a colloidal gel that solidifies into a hard structure. It has a long setting time (2 h 45 min) so the material must be protected before it is fully set. The pH of MTA rises from 10.2 after mixing to 12.5 after 3 h, remaining unchanged afterwards. Likewise, the compressive strength of MTA increases with time, from 40.0 MPa after 24 h to 67.3 MPa after 21 days.The sealing ability of MTA was investigated using fluorescent dye and confocal microscopy (93), methylene blue dye (94), and bacterial marker (95); its marginal adaptation was assessed using scanning electron microscopy (96); the long-term seal was measured over a 12-week (97) and 12-month period (98) using different fluid transport methods. They all reported good results with MTA when ranked with other materials. This may be because of its moisture tolerance and long setting time. CONTD The biocompatibility assessment of MTA encompassed in vitro cell culture techniques using established cell lines, primary cell cultures or a combination(79, 105120). Apart from variations in sensitivity because of the cell type used, the results showed MTA to be biocompatible. Tissue response evaluated in vivo by intraosseous and subcutaneous implantation experiments (104, 121125) found MTA to be well tolerated. Although hard-tissue formation occurs early with MTA (129), there was no significant difference in the quantity of cementum or osseous healing associated with freshly placed or set MTA (130).

7The patterns of osteogenesis for intraosseous implants of MTA and EBA were similar at 15 and 30 days but interestingly, at 60 days, EBA exhibited greater osteogenesis than MTA (125). If the assessment period were longer, the difference may not have been significant.Investigations of why MTA appears to induce cementogenesis found that the material seemed to offer a biologically active substrate for osteoblasts, allowing good adherence of the bone cells to the material, while also stimulating the production of cytokines (106, 107). Cytokine release was not detected in another study on MTA (131) and the difference may be due to a number of factors including the cell types used with osteoblast-like cells (MG-63) used in the former studies (106, 107) and macrophages used in the latter (131).The effects of MTA on cementoblast growth and osteocalcin production were investigated in a tissue culture experiment (132). Results suggested that MTA permitted cementoblast attachment and growth, whilst the production of mineralized matrix gene and protein expression indicated that MTA could be considered cementoconductive.A study to elucidate the physicochemical basis of the biological properties of MTA concluded that calcium, the dominant ion released from MTA, reacts with tissue phosphates yielding hydroxyapatite, the matrix at the dentine-MTA interface (135). Sarkar 2005 -Physicochemical basis of the biologic properties of Mineral Trioxide Aggregate. J Endod 2005: The sealing ability, biocompatibility, and dentinogenic activity of MTA may be attributed to these physicochemical reactions.ProRoot MTA (Dentsply/Maillefer, Ballaigues, Switzerland) is the first commercially available version of MTA. Initially, ProRoot MTA was grey in color but because of aesthetic concerns (108), a white version is now available. Both products have similar composition but tetracalcium aluminoferrite is absent in white MTA (102). Principle differences in the constitution of the two versions of MTA were confirmed by X-ray energy dispersive analysis and X-ray diffraction analysis (136). CONTD The use of electron probe microanalysis of the elemental constituents indicated that the most significant differences between grey and white MTA were the measured concentrations of Al2O3, MgO and especially FeO (137). However, when two different osteoblast cell lines were evaluated morphologically to characterize their behavior when in contact with grey and white MTA (120), the MG-63 osteosarcoma cells adhered to white MTA for periods twice as long as primary osteoblasts. While there was no difference between cell lines in their adherence to grey MTA, primary cell cultures were considered more appropriate for in vitro testing of endodontic materials.The first randomized prospective clinical study on the use of MTA as a root-end filling material was published by. (5) Chong, 2003 - A prospective clinical study of Mineral Trioxide Aggregate and IRM when used as root-end filling materials in endodontic surgery. After 24 months, of the 108 patients reviewed (47 in IRM group, 61 in MTA group), the highest number of teeth with complete healing was observed with MTA. When the numbers of teeth with complete and incomplete (scar) healing were combined, the results for MTA were higher (92%) compared with IRM (87%). However, statistical analysis showed no significant difference in outcome between materials.

8The good results with both materials may be due to the strict entry requirements and stringent, established criteria for assessing treatment outcome. Similar results were reported by Lindeboom et al. (138) Lindeboom, 2005 - A comparative prospective randomized clinical study of MTA and IRM as root-end filling materials in single-rooted teeth in endodontic surgery, in a clinical study consisting of 100 single-rooted teeth; there were no statistically significant differences between MTA (92%) and IRM (86%) after 1 year.

Is a root-end filling always necessary?There has long been a debate on whether a root-end filling should always be placed and also whether a better 'apical seal' can be achieved by its placement especially when the root canal is already well filled (16, 54).Friedman (16) argued that a root-end filling should be placed routinely. A tooth lacking a root canal filling will need it and even if the root canal looks apparently well filled, it may still contain infection so a root-end filling should be placed. In cases of extraradicular infection, theoretically, a root-end filling is not necessary but clinically, the possible co-existence of intraradicular infection cannot be excluded so again a root-end filling is essential. CONTD However, these assertions need to be modified and should be better qualified. Numerous studies have inferred that the lack of a good root canal filling will or is likely to compromise the surgical outcome (157, 171, 192).In addition, a number of clinical studies on healing after periradicular surgery have confirmed the benefit of placing a good root canal filling prior to surgery (5, 53, 193195). Therefore, surgery should never be performed if a root canal filling is absent and a good quality root filling could be placed beforehand. Even if a root filling is present but the quality is questionable, then it would be better to replace it.The need for a root-end filling should be decided at the time of surgery, after root-end resection, when there is opportunity to examine the quality of the exposed root canal filling with magnification. If the portion of root apex that is inaccessible to instrumentation and consequently a source of infection is removed, provided the exposed root filling is of a good quality and there are no additional canals or canal extensions, a root-end filling is not necessary,

Does an ideal root-end filling material exist and which to choose?Currently, there does not appear to be an 'ideal' root-end filling material (13, 17, 200) as none fulfils all the desired requirements. Although there is insufficient evidence to specify a single material for root-end filling, the evidence points to ZOE cements, MTA, Diaket and Retroplast as being acceptable. The material to choose will depend on prevailing clinical conditions (151).

9The elusive 'apical seal'The 'apical seal' has long been considered paramount to the success of periradicular surgery (201). Over the years, numerous research and clinical studies involving a plethora of materials were conducted to identify the ideal apical sealing material. Interestingly, osseous wound healing was reported to be independent of the type, and presence or absence, of a root-end filling (202). Regan et al. (11) commented that the evidence collected during their histological study on Diaket suggested that formation of a complete cemental coverage over both the root end and the root-end filling material was possible, although not predictable. CONTD

It is feasible to promote, at least in theory, the formation of 'a double seal' following periradicular surgery, incorporating both a physical and biological covering over the resected root end (11). However, no current root-end filling material can provide a perfect 'physical seal.' Yet surgical endodontic management of the root end can result in successful outcomes, suggesting that an impenetrable 'apical seal' may not be an absolute pre-requisite. There may be other factors apart from sealing ability that may influence the outcome of periradicular surgery. In addition, differences between individuals in terms of their ability to fight infection, tolerance of surgery and rate of healing will have an effect on the outcome of periradicular surgery.