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 »  Home  »  Endodontic Articles 11  »  Micro-tensile bond strengths of bonding agents to pulpal floor dentine
Micro-tensile bond strengths of bonding agents to pulpal floor dentine
Discussion - References.

Composite resin is recommended as a core build-up material in root filled teeth when adequate tooth structure remains. The advantage of Bonding properties coupled with a composite core buildup can achieve satisfactory form for resistance and retention (Morgano & Brackett 1999) as well as adequate mechanical properties (Levartovsky et al.1996). In the case of FluoroCore, fluoride release may be of value in preventing demineralization of adjacent tooth structure (Triolo et al.1991).
The micromechanical retention to tooth structure occurs when resin completely infiltrates dentinal surfaces and creates a hybrid or resin-reinforced dentine layer (Nakabayashi et al.1982). The one-bottle adhesive systems have been introduced to simplify the Bonding procedures and decrease the time needed for application. Whilst these materials have been evaluated for Bonding to the cut surface of coronal dentine, the intact pulpal floor dentine may behave differently as a Bonding substrate. The micro-tensile bond strength to superficial occlusal dentine of predominantly third molars was 36.0 _8.1MPa for Clearl Liner Bond 2 V and 29.9 _ 6.1MPa for Prime and Bond NT/NRC (Tanumiharja et al.2000) whichwas similar to the results of Schreiner et al. (1998).The bond strengths of two systems to pulpal floor dentine in this study were 22.49 _7.08 MPa for Clearl SE Bond and 15.58 _4.24 MPa for Prime and Bond NT which were lower than coronal dentine, as previously reported (Schreiner et al. 1998, Tanumiharja et al.2000).Thus, the Bonding mechanisms may be affected by the dentine location and changes in the properties in different parts of a tooth structure. This result is in accordance with a previous report by Belli et al. (2001).
The SEM study demonstrated the presence of numerous calcospherites on the surface of pulpal floor dentine (Fig.1). When acid etching was applied to the pulpal floor dentine, the superficial dentine was demineralized to expose the collagen fibers of the dentinal matrix (Fig. 2). The penetration of primer and adhesive resin in the conditioned dentine surface is to provide micromechanical interlocking between the dentine collagen and resin (Nakabayashi et al. 1982, Van Meerbeek et al. 1992). However, the use of strong phosphoric acid (Fig. 2) could remove inorganic material more aggressively than the acidic primer (Fig. 3), especially since the surface was not covered by a smear layer initially. This finding leads to the different characteristics of conditioned dentine surfaces, which may also affect the different bond strengths of the two systems (Wakabayashi et al.1994, Vargas et al.1997).
Accessory canals, which have been reported to occur frequently on the pulpal floor of molars (Vertucci & Anthony1986), may also assist in mechanical retention. In this study, we observed only one accessory canal in the pulpal floor of eight teeth. Accessory canals may not occur frequently enough to influence bond strength. However, the tubule density of dentine at pulpal floor area was less than in coronal dentine and this factor may influence bonding. Hence, the net influence of pulpal floor features on bond strength is difficult to predict.
The mean micro-tensile bond strength of the self-etching- priming system (Clearl SE Bond) was significantly greater than that of the one-bottle system (Prime &Bond NT) (P < 0.05) in this study. The acid conditioning of primer in Clearl SE Bond appeared sufficient to demineralize the dentine and envelop the collagen fibres and hydroxyapatite crystals. The use of strong 34%phosphoric acid with Prime & Bond NT, according to the manufacturer’s instructions, may be excessive in the absence of a smear layer and smear plugs, possibly causing ‘over etching’ and subsequent collapse of the collagen network. This situation may inhibit the penetration of adhesive resin and result in a weak hybrid layer (Phrukkanon et al.1999).
From this study, the SEM observation of debonded specimens from the Prime & Bond NT system mostly showed partial cohesive failure within Bonding resin/ composite, whereas those of the Clearl SE Bond system mostly showed partial cohesive failure within dentine. This finding may demonstrate that either the self-etching- priming system had a good Bonding to pulpal floor dentine or was more compatible with composite resin than the one-bottle system. The pretreatment of the pulp chamber with NaOCl, as occurs in routine biomechanical preparation, merits further study. One report mentioned that without pretreatment with NaOCl, irregular shapes of broken resin tags were observed (Belli et al.2001).
Bonding restorative material to the floor of the pulp chamber and the remaining tooth structure should eliminate any gaps and thus would promote a better quality of coronal seal (Davalou et al.1999). Good adhesion between the restorative materials and dentine is a crucial factor in increasing the opportunity for good marginal sealing, reduced microleakage, and longer life of the restoration (Nakabayashi & Pashley 1998). Thus, the use of composite resin and a dentine Bonding system has become widely accepted for restorative treatment of nonvital teeth.


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