Management of the endodontically treated tooth. Part I: Concept for restorative designs

A cast post that is made with an unlined metal casting ring may exhibit anisotropic shrinkage which could result in distortion and consequently require more chair time for fitting in the root canal.

The purpose of this study was to investigate whether the presence of a ring liner and the burn-out temperature of the investment material affect the clinical time required to fit a cast post.

Sixty identical post patterns were fabricated from a customized stainless steel root form. They were divided into 3 groups (n=20) as follows: group LH used a cellulose ring liner and a final burn-out temperature of 815°C; group NH used no liner with the same temperature; group NL used no liner with a final burn-out temperature of 600°C. All groups were invested in stainless steel casting rings with the same phosphate-bonded investment (Hi Temp) and cast with same alloy (Protocol). Two blinded investigators, with different levels of experience, adjusted and placed the posts in the experimental root form until a subjective acceptable fit was achieved. Each investigator fit 10 cast posts for each group, and the time required to achieve a subjective acceptable fit was measured in seconds. Two-way ANOVA was used to test the significance of the investigator, group, and their interaction. One-way ANOVA and a post hoc Tukey HSD test were used to find significant differences among the groups (α=.05).

The 2-way ANOVA showed a significant effect of the investigator (P=.001) and group (P<.001), but not interaction (P=.15). The 1-way ANOVA showed significant differences among the 3 groups (P<.001), and the Tukey HSD test showed significant differences between the following pairs: LH and NH (P=.009), and LH and NL (P<.001). NH and NL did not demonstrate a significant difference.

Investing a post pattern without a ring liner and setting the final burn-out temperature at 600°C allow the fabrication of cast posts that require significantly less adjustment time for clinical placement than those invested with a ring liner and burned out at 815°C. (J Prosthet Dent 2009;102:224-228)

Dental fractures can occur in endodontically treated teeth restored with posts.

The purpose of this study was to evaluate the in vitro fracture resistance of roots with glass-fiber and metal posts of different lengths.

Sixty endodontically treated maxillary canines were embedded in acrylic resin, except for 4 mm of the cervical area, after removing the clinical crowns. The post spaces were opened with a cylindrical bur at low speed attached to a surveyor, resulting in preparations with lengths of 6 mm (group 6 mm), 8 mm (group 8 mm), or 10 mm (group 10 mm). Each group was divided into 2 subgroups according to the post material: cast post and core or glass-fiber post (n=30). The posts were luted with dual-polymerizing resin cement (Panavia F). Cast posts and cores of Co-Cr (Resilient Plus) crowns were made and cemented with zinc phosphate. Specimens were subjected to increasing compressive load (N) until fracture. Data were analyzed with 2-way ANOVA and the Tukey-Kramer test (α =.05).

The ANOVA analysis indicated significant differences (P<.05) among the groups, and the Tukey test revealed no significant difference among the metal posts of 6-mm length (26.5 N ±13.4), 8-mm length (25.2 N ±13.9), and 10-mm length (17.1 N ±5.2). Also, in the glass-fiber post group, there was no significant difference when posts of 8-mm length (13.4 N ±11.0) were compared with the 6-mm (6.9 N ±4.6) and 10-mm (31.7 N ±13.1) groups. The 10-mm-long post displayed superior fracture resistance, and the 6-mm-long post showed significantly lower mean values (P<.001).

Within the limitations of this study, it was concluded that the glass-fiber post represents a viable alternative to the cast metal post, increasing the resistance to fracture of endodontically treated canines. (J Prosthet Dent 2009;101:183–188)

Endodontically treated teeth are traditionally restored with a crown to prevent fracture. The aim of this study was to compare the fracture resistance and failure modes of endodontically treated maxillary premolars treated with or without a fiber post and restored with different types of crowns. Eighty human maxillary premolars were selected. After root canal treatment, the teeth were embedded in resin blocks and divided into four groups. Samples received MOD cavity preparations and were divided into two subgroups: with and without fiber posts and restored using porcelain fused to metal, lithium disilicate, fiber-reinforced composite, or zirconia crowns. The specimens were vertically loaded in the central fossa using a universal loading machine until failure, and the maximum breaking loads were recorded. Samples were perfused with Indian ink to highlight the fracture lines and the mode of failure that was classified as restorable or nonrestorable. Even without post, all crown designs resisted vertically applied forces beyond those that may be encountered in the mouth. Two-way analysis of variance revealed the use of a fiber post (p = 0.007) and the type of crown (p < 0.001) significantly affected the restorability of fractured teeth. The relationship between placing or not placing the post and the type of failure (restorable/nonrestorable) was found to be significant (χ² test, p = 0.002). Although post placement resulted in higher fracture resistance values, these were significant for Empress II crowns only. The results suggest that the posts could contribute to the reinforcement and strengthening of pulpless maxillary premolars. With respect to failure modes, placement of fiber posts improved the fracture from nonrestorable to restorable patterns. This study suggests that the placement of fiber posts is necessary to improve fracture resistance even under full-coverage crowns.

Statement of problem. Fracture of endodontically treated teeth has been of great interest because it is a common clinical occurrence.

Purpose of study. This research evaluated the fracture resistance of endodontically treated first maxillary premolars restored with different metal restorations and bonded with Panavia Ex resin.

Material and methods. Fifty teeth were randomly divided into five groups with MOD tooth preparation: (1) inlay with an isthmus width of one third the intercuspal distance for a silver amalgam restoration (negative control), (2) inlay with an isthmus width equal to that in group 1, (3) inlay with an isthmus width of half the intercuspal distance, (4) equal to group 3 with lingual and proximal preparation, and (5) onlay (positive control). The cast restorations of groups 2, 3, and 4 were bonded with Panavia Ex resin and those from group 5 cemented with zinc phosphate cement. Samples were restored and subjected to thermocycling, and the teeth were submitted to an axial compressive force.

Results. The cast inlay restorations that bonded with Panavia Ex resin significantly elevated the fracture resistance of endodontically treated maxillary premolars compared with the silver amalgam restorations. However, teeth restored with cast onlay restorations cemented with zinc phosphate cements recorded the best results.

Conclusion. The increase of fracture resistance by MOD inlay cast restoration bonded with Panavia Ex resin suggested valid clinical application within the conditions of this study. (J Prosthet Dent 1997;77:365-9.)

Objectives: Following endodontic therapy, the provision of a cast post and core restoration may be indicated. Many authors advocate retaining sound coronal dentine where possible, improving the resistance to fracture of the endodontically treated tooth. However, there is little conclusive experimental evidence to support this recommendation. This laboratory study was designed to investigate the effect of retained sound coronal dentine on the strength of a tooth restored with a cemented post and partial core restoration under direct loading.

Methods: Specimens with retained coronal dentine buccally, lingually, or buccally and lingually were restored with cast post and partial cores and tested to failure using an Instron Universal Testing Machine, Model 1195. Control post and full core restorations were also tested. The mode of failure for all specimens was recorded photographically.

Results: Teeth with retained buccal coronal dentine and post and partial cores were significantly less resistant to failure than controls with post and full cores (P < 0.01), failure occurring through crack initiation and propagation at the junction of the cast partial core and dentine core. There was no statistically significant difference in the strength of teeth with retained lingual coronal dentine or buccal and lingual dentine when compared to the control.

Conclusions: In conclusion, this in vitro model demonstrates that retained coronal dentine will not strengthen a tooth restored with a cast post and partial core. The clinical benefit of retaining buccal coronal dentine is brought into question when set against the increased technical effort and difficulty of producing the restoration in the dental technical laboratory and the possible overriding benefit of ferruling the crown margin onto a sound root structure.

This study compared three mechanical properties of two recently introduced core materials, a light-activated glass ionomer cement (VariGlass VLC) and a fluoride-release dual cure composite resin (FluoroCore), with those of a conventional silver-reinforced glass-ionomer cement (Miracle Mix). Seventy-two samples (eight per product for each property) were prepared for testing diametral tensile strength, flexural strength, and compressive strength. The specimens were cured, stored for 24 hours at 37 ° C in 100% humidity, and tested with the use of an Instron universal testing machine. The results of this study indicate that the diametral tensile strength, flexural strength, and compressive strength of the FluoroCore and VariGlass VLC materials were significantly higher than those of the conventional Miracle Mix. The values obtained with FluoroCore material were consistently higher than those obtained with VariGlass VLC material.