[Root canal post for build-up restorations: necessary or redundant?] / Wortelstift bij funderingsrestauraties: noodzakelijk of overbodig?

The purpose of root canal posts is to obtain additional retention for build-up restorations of endodontically treated teeth so they can be functionally reconstructed. Due to developments in adhesive dentistry and a lack of clinical evidence, root canal posts are used less and less. Currently, the advice of the European Society of Endodontology is to use a root canal post only in front teeth and premolars in the absence of remaining coronal dentine walls. It is important to avoid additional preparation when placing a root canal post, because this causes (additional) weakness of the tooth. The loss of dental tissue due to preparation cannot be compensated for by placing a post.

[Build-up restorations after extensive loss of tooth tissue]. / Funderings restauraties bij uitgebreid weefselverlies van gebitselementen.

After (extensive) loss of tooth tissue, vital teeth can be built up completely with composite restoration material. Sometimes, the application of additional retentive preparations is indicated. In exceptional cases, a root canal treatment is indicated, following which a root canal post is applied if necessary. Endodontically treated multi-rooted teeth can be built up entirely with composite, utilizing the pulp chamber and root canal accesses for retention. However, in single-rooted teeth a root canal post is necessary, in which case a prefabricated root post is used. Traditionally, metal posts were used in combination with a cast, indirect build-up restoration. Subsequently, directly fabricated cores, combining metal posts with amalgam or, at the present time, composite restoration material, became customary. The present trend is to use prefabricated or individually fabricated fibre-reinforced posts. After restoring a tooth with a build-up restoration, a combined build-up restoration can be chosen, or a direct or indirect crown single tooth prosthesis.

Fracture resistance of reattached incisor fragments with mini fibre-reinforced composite anchors.

OBJECTIVES: Fractured coronal fragments of incisors can be adhered to the remaining tooth with resin composite, but are prone to failure. This study explores whether mini fibre-reinforced composite (FRC) anchors increase fracture resistance of reattached fragments. METHODS: Forty-five extracted incisors were randomly divided into three groups. In Groups A and B coronal fragments were reattached to the remaining tooth, with additionally two anchors placed in Group B. In Group C resin composite buildups were made. Specimens were statically loaded until failure occurred. Failure modes were characterized as intact remaining tooth substrate (adhesive or cohesive failure of coronal fragment) or fractured remaining tooth substrate (fracture limited to enamel or extending into dentin). RESULTS: Mean fracture loads were 255N (SD=108N) for Group A, 599N (SD=465N) for Group B and 786N (SD=197N) for Group C (values significantly different, all p values <0.05). Group A showed purely adhesive failures, while Groups B and C showed 73 and 53% fractures of remaining tooth substrate (p<0.05). CONCLUSIONS: Mini FRC anchors increase fracture resistance of reattached coronal fragments, but induce more remaining tooth substrate fractures.

Influence of test parameters on in vitro fracture resistance of post-endodontic restorations: a structured review.

A structured literature review aimed to elucidate test parameters for in vitro testing of post-endodontic restorations. The literature was digitally searched using MEDLINE, EMBASE, MedPilot and an additional hand search was performed. Two independent researchers assessed the articles in relation to the defined inclusion and exclusion criteria. The literature search revealed 125 abstracts. Sixty-nine studies were included. Fifty-seven per cent of the studies investigated maxillary incisors only. The restorative stage as complex of tooth, post, core, and crown and post-and-core restored specimens without crowns were used most frequently. Fifty-nine per cent of the studies used static loading. Only 15% of the studies performed thermocycling and mechanical loading (TCML). However, the number of thermo- and load cycles varied. The cross-head speed of linear loading after TCML ranged from 0.01 to 150 mm min(-1). The reviewed studies were heterogeneous in test design regarding the used test parameters. A methodological standardization of in vitro testing of post-endodontic restorations is recommended.

[In vitro fracture behaviour of composite crowns with and without posts]. / In vitro faalgedrag van composietkronen met en zonder stift.

The failure load and failure mode of severely damaged endodontically treated maxillary premolars were examined within a laboratory study. The premolars were divided into 4 groups. The first of which was restored with prefab metal posts, the second with prefab fibre posts and the third with custom-made fibre posts; all 3 receiving direct resin crowns. In a 4th (control) group no post-space preparation was performed and no posts were placed; a direct resin composite complete crown was made. After thermocycling, all specimens were statically loaded in a universal test machine until failure, under an angle of 30 degrees. There was no significant difference between the mean failure loads. Failure was merely due to unfavourable, non-repairable fractures (ending below the simulation of bone level). This study suggests that posts are not necessarily required to increase the failure load of direct resin composite crowns, however, clinical studies are necessary to confirm these findings.

Ex vivo fracture resistance of direct resin composite complete crowns with and without posts on maxillary premolars.

AIM: To investigate ex vivo the fracture resistance and failure mode of direct resin composite complete crowns with and without various root canal posts made on maxillary premolars. METHODOLOGY: The clinical crowns of 40 human extracted single-rooted maxillary premolars were sectioned at the cemento-enamel junction. The canals were prepared with Gates Glidden drills up to size 4. Thirty samples were provided with standardized post spaces in the palatal canal and all roots were embedded in acrylic. Minimal standardized preparations in the canal entrances were made. Groups of 10 samples were treated with (i) prefabricated metal posts, (ii) prefabricated glass fibre posts, (iii) custom-made glass fibre posts, and (iv) no posts (control). Posts were cemented with resin cement and resin composite complete crowns were made. All specimens were thermocycled (6000x, 5-55 degrees C). Static load until fracture was applied using a universal loading device (crosshead speed 5 mm min(-1)) at a loading angle of 30 degrees . Failure modes were categorized as favourable and unfavourable failures. RESULTS: No significant difference was observed between the mean failure loads (group 1: 1386 N, group 2: 1276 N, group 3: 1281 N, and group 4: 1717 N, P > 0.05), nor between frequencies of failure modes (P > 0.05). All failures were fractures of the resin composite crown in combination with tooth material (cohesive failures). CONCLUSIONS: Within the limits of this laboratory investigation it is concluded that severely damaged and root filled maxillary premolars, restored with direct resin composite complete crowns without posts have similar fracture resistances and failure modes compared to those with various posts, which suggest that posts are not necessarily required.

[The restoration of endodontically treated teeth: the minimally invasive (post-) core buildup?]. / Het restaureren van endodontisch behandelde gebitselementen: de weefselbesparende (stift)opbouw?

The rebuilding of endodontic treated teeth is a common situation in general dental practice. The final (post-) core buildup, with or without a crown, should protect the restoration as well as the tooth against fracture, should prevent debonding of the restoration, should not permit leakage and should provide an acceptable esthetic result. Several factors influencing these properties are described. The (post-) core buildup in relation to the concept of minimally invasive dentistry is discussed. In conclusion, there is no unambiguous guideline for restoring endodontically treated teeth. Standardised in vitro and in vivo studies are needed.

[A finite element model of a cusp-replacing adhesive restoration]. / Een eindige-elementenmodel van een knobbelvervangende adhesieve restauratie.

This article describes the development of a three-dimensional finite element model of a premolar, based on a micro-scale computed tomographic data-acquisition technique. Using the model shrinkage stresses were analysed during and after the polymerisation process of resin composite. The stress patterns generated were three-dimensional. The results of this study indicate that failure of the interface is more probable than failure of the composite material. The described procedure is a relatively easy method to produce a highly detailed 3-D finite element model of a premolar with an adhesive cups-replacing restoration.