Novel non-invasive reinforcement of MOD cavities on endodontically treated teeth

Stress Distribution of Endodontically Treated Tooth MOD Cavity Restored with Ribbon Fiber-Reinforced Composite (Wallpapering Technique) Using Finite Element Method

Purpose

This research aimed to describe the stress distribution of an endodontically treated tooth with a mesio-occluso-distal (MOD) cavity restored with direct composite reinforced with polyethylene and e-glass ribbon fiber.

Methods

This research was a descriptive study using the finite element method. A 3D model of the mandibular first molar solid after endodontic treatment with class II MOD preparation was prepared using Solidworks software. Finite element simulation was carried out using Abaqus software. In the first simulation, 180 N force was applied (vertically 90° perpendicular to the occlusal surface) at four points of loading: the tip of the mesiobuccal and distobuccal cusp, central fossa, and distal marginal ridge. For the second simulation, a 100 N force was applied at a 45° lateral angle to the occlusal surface at two loading points: the lingual slope of the mesiobuccal and distobuccal cusp.

Results

This study showed that the stress concentration was located in the occlusal pit and fissure, CEJ distal area, bifurcation in dentin, and the 1/3 cervical area of root dentin. The stress value generated after vertical and lateral force did not exceed the tooth and restoration's compressive and tensile strength value. The failure occurred at the interface of enamel and composite near the loading point area due to vertical load, both on polyethylene and e-glass fiber ribbon-reinforced composite restoration. Stress distribution of an endodontically treated tooth with a MOD cavity restored with ribbon fiber-reinforced composite using the finite element method showed that the highest stress concentration occurred on the surface close to the loading point, in narrow, concave, and sharp areas, and more apically for endodontically treated teeth.

Conclusion

Neither the tooth nor restoration failed after vertical and horizontal loads. The interface between enamel and composite on the occlusal surface failed.

Influence of the Fiber Post Length on the Fracture Strength of Endodontically Treated Teeth

Background and Objectives: Although fiber posts are widely used in the restoration of endodontically treated teeth (ETT), their ideal cementation depth into the root canal is still debated in literature. The aim of the present study was to evaluate whether the different intra-radicular insertion lengths of the fiber posts influence the fracture strength of ETT. Materials and Methods: A total of 10 permanent human lower incisors with straight roots of similar length and volume extracted for periodontal reason were sectioned 2 mm above the cement-enamel junction (CEJ) to a total length of 18 mm and endodontically treated in the same manner, then randomly divided into two groups of five each (Groups 1 and 2, n = 5). Two sound incisors, with no endodontic treatment, were used as the control group (Group 3, n = 2). After one week of storage in a humid environment, spaces for fiber post no. 1 (Reforpost, Angelus, Londrina, PR, Brazil) were prepared in the first two groups at a depth of 5 mm (Group 1) and 7 mm (Group 2), and the fiber posts were adhesively cemented using self-adhesive resin cement (Maxcem Elite, Kerr GmbH, Herzogenrath, Germany). After 7 days, the samples were vertically positioned and fixed in a self-curing transparent acrylic resin, up to 2 mm below the CEJ level, and mechanically tested in compression after another week of storage using a displacement-controlled testing machine up to each sample's fracture. The force-displacement curves were recorded for each sample, the means were calculated for each group and a statistical comparative analysis between groups was conducted. Results: Although no statistically significant differences between groups were observed, the highest mean fracture force (N) was recorded in Group 2 (1099.41 ± 481.89) in comparison to Group 1 (985.09 ± 330.28), even when compared to the sound, non-treated teeth (1045.69 ± 146.19). Conclusions: Within the limitations of this in vitro study, teeth where fiber posts were placed deeper into the root canal (7 mm) recorded slightly higher fracture forces in comparison with shorter lengths (5 mm). However, similar biomechanical performances obtained in the mechanical tests showed no statistical differences between the 7 mm and the 5 mm inserted posts.

Fatigue performance of endodontically treated molars reinforced with different fiber systems

OBJECTIVE

The aim was to investigate the fatigue performance of root canal-treated (RCT) molars restored with different direct restorations utilizing discontinuous and continuous fiber-reinforced composite (FRC) systems. The impact of direct cuspal coverage was also evaluated.

MATERIALS AND METHODS

One hundred and twenty intact third molars extracted for periodontal or orthodontic reasons were randomly divided into six groups (n=20). Standardized MOD, regular cavities for direct restorations were prepared in all specimens, and subsequently, root canal treatment and root canal obturation was carried out. After the endodontic treatment, the cavities were restored with different fiber-reinforced direct restorations as follows: SFC group (control), discontinuous short fiber-reinforced composite (SFC) without cuspal coverage (CC); SFC+CC group, SFC with cuspal coverage; PFRC group, transcoronal fixation with continuous polyethylene fibers without CC; PFRC+CC group, transcoronal fixation with continuous polyethylene fibers with CC; GFRC group, continuous glass FRC post without CC; and GFRC+CC, continuous glass FRC post with CC. All specimens underwent a fatigue survival test in a cyclic loading machine until fracture occurred or 40,000 cycles were completed. The Kaplan-Meier survival analysis was conducted, followed by pairwise log-rank post hoc comparisons between the individual groups (Mantel-Cox).

RESULTS

The PFRC+CC group was characterized by significantly higher survival compared to all the groups (p < 0.05), except for the control group (p = 0.317). In contrast, the GFRC group showed significantly lower survival compared to all the groups (p < 0.05), except for the SFC+CC group (p = 0.118). The control group (SFC) showed statistically higher survival than the SFRC+CC group (p < 0.05) and GFRC group (p < 0.05), but it did not differ significantly from the rest of the groups in terms of survival.

CONCLUSIONS

Direct restorations utilizing continuous FRC systems (in the form of polyethylene fibers or FRC post) to restore RCT molar MOD cavities performed better in terms of fatigue resistance when CC was performed compared to the same FRC restorations without CC. On the contrary, teeth restored with SFC restorations performed better without CC compared to the ones where SFC was covered.

CLINICAL RELEVANCE

In the case of fiber-reinforced direct restorations for MOD cavities in RCT molars, direct CC is recommended when utilizing long continuous fibers for reinforcement, however, should be avoided when only SFC is used for their reinforcement.

Stress Concentration of Endodontically Treated Molars Restored with Transfixed Glass Fiber Post: 3D-Finite Element Analysis

The loss of dental structure caused by endodontic treatment is responsible for a decrease in tooth resistance, which increases susceptibility to fracture. Therefore, it is important that minimally invasive treatments be performed to preserve the dental structure and increase the resistance to fracture of endodontically treated posterior teeth. To evaluate under axial loads, using the finite element method, the stress distribution in endodontically treated molars restored with both transfixed or vertical glass fiber posts (GFP) and resin composite. An endodontically treated molar 3D-model was analyzed using finite element analyses under four different conditions, class II resin composite (G1, control model), vertical glass fiber post (G2), transfixed glass fiber posts (G3) and vertical and transfixed glass fiber posts (G4). Ideal contacts were considered between restoration/resin composite and resin composite/tooth. An axial load (300 N) was applied to the occlusal surface. The resulting tensile stresses were calculated for the enamel and dentin tissue from five different viewports (occlusal, buccal, palatal, mesial and distal views). According to the stress maps, similar stress trends were observed, regardless of the glass fiber post treatment. In addition, for the G1 model (without GFP), a high-stress magnitude can be noticed in the proximal faces of enamel (7.7 to 14 MPa) and dentin (2.1 to 3.3 MPa) tissue. The use of transfixed glass fiber post is not indicated to reduce the stresses, under axial loads, in both enamel and dentin tissue in endodontically treated molar with a class II cavity.

Fracture strength of non-invasively reinforced MOD cavities on endodontically treated teeth

The purpose of this in-vitro study was to evaluate the fracture resistance and failure mode of non-invasively reinforced endodontically treated mandibular molars. Sixty freshly extracted defect-free mandibular molars were divided into four experimental groups with extensive MOD cavities on endodontically treated teeth with different restoration types and one control group with intact teeth (n  = 12). The groups were as follows: “Normal”: direct resin composite; “Ring”: glass fiber-reinforced strip (Dentapreg) wrapped around buccal and lingual walls followed by direct resin composite; “Inlay”: indirect CAD/CAM resin composite inlay; “Onlay”: indirect CAD/CAM resin composite onlay; “Intact”: Intact teeth (Control). Tetric EvoCeram and Adhese Universal (Ivoclar Vivadent) were used for direct restorations and Tetric CAD (Ivoclar Vivadent) adhesively luted with Adhese Universal and Variolink Esthetic LC (Ivoclar Vivadent) were used for indirect restorations. All teeth were submitted to thermo-mechanical cyclic loading. All samples were then submitted to a compressive load until fracture. Fracture load was noted and teeth were analyzed to classify the failure mode as either catastrophic (C) or non-catastrophic (NC). No statistically significant difference was found between fracture strength of the five groups when all specimens were considered (p = 0.1461). Intact group showed the lowest percentage of catastrophic failures (41.67%). Ring group presents less catastrophic failures (75%) than Normal group (83.34%), and failures of indirect restorations—Inlay and Onlay—were almost all catastrophic (91.67% and 100%, respectively).

Estimation of stress distribution and risk of failure for maxillary premolar restored by occlusal veneer with different CAD/CAM materials and preparation designs

OBJECTIVES

To compare stress distribution and failure probability in maxillary premolars restored by simple occlusal veneer (SOV) and buccal-occlusal veneer (BOV) with 3 different CAD/CAM materials.

MATERIALS AND METHODS

A maxillary premolar was digitized by a micro-CT scanner. Three-dimensional dynamic scan data were transformed, and finite element models of 2 different models (SOV and BOV restored teeth) were designed. Three different CAD/CAM materials, including lithium disilicate glass ceramic (LD) IPS e.max CAD, polymer-infiltrated ceramic-network (PICN) Vita Enamic, and resin nano-ceramic (RNC) Lava Ultimate, were designated to both veneers. Maximum principle stresses were determined by applying a 300-N axial load to the occlusal surface. Weibull analyses were performed to calculate the failure probability of the models.

RESULTS

LD-restored teeth showed the highest stress in the veneer, lowest stress in substrate teeth, and lowest failure probability for the overall system; RNC-restored teeth showed the lowest stress in the veneer, highest stress in substrate teeth, and highest failure probability. No significant differences were found in the cement layer among the different models. No significant differences of stress and failure probability existed between SOV and BOV preparations.

CONCLUSIONS

CAD/CAM composite resin occlusal veneers bear lower maximum stress than ceramic veneers. Teeth restored by composite veneers are more prone to failure than those restored by ceramic veneers. Additional reduction of the buccal surface did not increase the stress on the occlusal veneer under axial load.

CLINICAL RELEVANCE

Both occlusal veneers could be used under physiological masticatory force. CAD/CAM glass ceramic was safer than composite resins.

Fracture behavior of root-amputated teeth at different amount of periodontal support - a preliminary in vitro study

Background

The purpose of this study was to evaluate the effect of the amount of periodontal support on the fracture resistance of root-amputated maxillary molar teeth restored with either direct class. I. restorations or class II. mesio-occluso-distal (MOD) indirect overlay restorations with cuspal coverage.

Methods

Sixty sound maxillary first molars were collected and randomly divided into four groups. In Groups 1 and 2, MOD cavities were prepared and all cusps were reduced by 2 mm, whereas in Group 3 and 4, only a conservative Class I. cavity was prepared. Subsequently, root canal treatment was performed and the mesio-buccal roots were amputated. Groups 1 and 2 were restored with indirect composite overlay, while Groups 3 and 4 received direct composite fillings. After restoration, teeth were embedded as follows: Groups 1 and 3: normal bone level, Groups 2 and 4: furcation involvement. The specimens were submitted to static fracture resistance testing. Fracture thresholds and fracture patterns were measured and evaluated.

Results

Group 1 had the highest fracture resistance (2311,6 N) among the restored groups and showed statistically significant difference compared to Group 2 (p = 0.038) and Group 4 (p = 0.011). There was no statistically significant difference in terms of fracture resistance between the rest of the groups. In terms of the fracture patterns, Group 3 was characterized by the highest percentage (60%) of mostly favorable fractures, while the rest of the groups showed predominantly unfavorable ones.

Conclusions

The amount of periodontal support seems to influence the fracture resistance of root-amputated and restored maxillary molars.

Fracture behaviour of MOD restorations reinforced by various fibre-reinforced techniques - An in vitro study

PURPOSE

The aim was to evaluate the fracture resistance of various direct restorative techniques utilizing different fibre-reinforced materials for restoring deep class II. MOD cavities in molar teeth.

MATERIAL AND METHODS

Two hundred forty intact mandibular third molars were randomly divided into twelve groups (n = 20). Except for the control group (G12), deep mesio-occluso-distal (MOD) cavities were prepared all other groups. After adhesive treatment and rebuilding the missing interproximal walls with composite, the specimen were restored with different fibres and a final occlusal layer of composite as follows: composite only (G1), short fibre-reinforced composite (SFRC) (G2), glass fibre net (GFN) on the base of the cavity bucco-lingually (BL) and SFRC (G3), SFRC and GFN on top of it BL (G4), SFRC and occlusal splinting with GFN (G5), GFN circumferentially and SFRC (G6), polyethylene fibres (PF) on the base of the cavity BL and composite (G7), composite and PF on top of it BL (G8), composite and occlusal splinting with PF (G9), PF circumferentially and composite (G10), transcoronal splinting with PF (G11). Fracture-resistance for the restored teeth were tested using universal-testing machine. Fracture thresholds and fracture patterns were measured and evaluated.

RESULTS

The transcoronal splinting (G11) yielded the highest fracture resistance among the restored groups. Groups 1, 3 and 4 showed significantly lower fracture resistance values compared to intact teeth.

CONCLUSION

Incorporating polyethylene or a combination of short and bidirectional glass fibres in certain positions in direct restorations seems to be able to restore the fracture resistance of sound molar teeth.