Fracture strength and fracture patterns of root filled teeth restored with direct resin restorations.

OBJECTIVE: To compare fracture characteristics of root-filled teeth with variable cavity design and resin composite restoration. METHODS: 80 extracted intact maxillary premolars were divided randomly into eight groups; (1) intact teeth; (2) unrestored MOD cavity; (3) unrestored MOD cavity plus endodontic access through the occlusal floor; (4) unrestored MOD plus endodontic access with axial walls removed; (5) MOD restored with resin composite; (6) MOD plus endodontic access, resin composite; (7) MOD plus extensive endodontic access, resin composite; (8) MOD plus extensive endodontic access, GIC core and resin composite. A ramped oblique load was applied to the buccal cusp in a servohydraulic testing machine. Fracture load and fracture patterns were recorded. Fracture loads were compared statistically using 1-way ANOVA, with Dunnett test for multiple comparisons. RESULTS: Unrestored teeth became progressively weaker with more extensive preparations. Endodontic access confined within the occlusal floor did not significantly affect strength compared to an MOD cavity. Loss of axial walls weakened teeth considerably [292+80N vs 747+130N for intact teeth]. Restoration increased the strength of prepared teeth particularly in teeth without axial walls. Teeth with a GIC core were not significantly weaker than intact teeth [560+167N]. Failures were mostly adhesive at the buccal interface, with the fracture propagating from the buccal line angle of the occlusal floor (MOD and MOD plus access groups) or of the proximal box (axial wall removed). CONCLUSIONS: Direct restorations increased fracture resistance of root filled teeth with extensive endodontic access. Both restored and unrestored teeth showed similar fracture patterns.

Efficient 3D finite element analysis of dental restorative procedures using micro-CT data.

OBJECTIVES: This investigation describes a rapid method for the generation of finite element models of dental structures and restorations. METHODS: An intact mandibular molar was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different cavity preparations (MO/MOD preparations, endodontic access) and restorations (feldspathic porcelain and composite resin inlays). The different tooth parts were then imported in a finite element software package to create 3D solid models. The potential use of the model was demonstrated using nonlinear contact analysis to simulate occlusal loading. Cuspal deformation was measured at different restorative steps and correlated with existing experimental data for model validation and optimization. RESULTS: Five different models were validated by existing experimental data. Cuspal widening (between mesial cusps) at 100 N load ranged from 0.4 microm for the unrestored tooth, 9-12 microm for MO, MOD cavities, to 12-21 microm for endodontic access cavities. Placement of an MOD adhesive restoration in porcelain resulted in 100% cuspal stiffness recovery (0.4 microm of cuspal widening at 100 N) while the composite resin inlay allowed for a partial recuperation of cusp stabilization (1.3 microm of cuspal widening at 100 N). SIGNIFICANCE: The described method can generate detailed and valid three dimensional finite element models of a molar tooth with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications.

Effect of restorative procedures and occlusal loading on cuspal deflection.

This study examined the extent of cuspal flexure caused by progressively larger cavity preparations, including endodontic access, and progressive simulated occlusal loading with 50N, 100N and 150N. Ten intact extracted maxillary premolars were embedded in acrylic resin, and a small ball was attached to each cuspal tip as a reference point for intercuspal distance measurements. The teeth were subjected sequentially to the following procedures: conservative MO cavity preparation, extensive MO cavity preparation, endodontic access step and MOD cavity preparation. After each cavity preparation procedure, the specimens were subjected to increasing loads of 50, 100 and 150 N, and the intercuspal distance was recorded by means of a digital caliper. The extension of cavity preparation and the magnitude of occlusal load significantly influenced cuspal deflection. After 50 and 100 N loading, a similar cuspal deflection was exhibited by conservative and extensive MO preparations with or without the endodontic access step. With 150 N loading, the endodontic access step was related to a statistically larger cuspal deflection versus the deflection recorded for conservative and extensive MO preparations. The removal of both marginal ridges in MOD cavity preparation with endodontic access produced a dramatic increase in cuspal deflection for the three loads tested.

[Classification of premolars as a function of root anatomy and statistics]. / Classification des prémolaires en fonction de leur anatomie radiculaire et statistiques.

The frequent endodontic failures on premolar teeth can be partly attributed to their complicated root canal anatomy. Anatomical studies were initiated almost a century ago by W. Hess, resulting in the actual meticulous classification. Vertucci was the first to describe in an exhaustive way the scores of anatomical variations by assigning them to 9 types. The Wein model is just as complete but offers a more clinical approach. It will be used as reference in this article to weigh the various statistics appearing in the anatomical studies on premolars.

The outcome of endodontic retreatment: a 2-yr follow-up.

Retreatment is common in endodontics. The purpose of this article was to classify the different clinical situations encountered in retreatment cases and relate them to the outcome after an observation period of 24 months. A total of 425 patients (452 teeth) from 451 patients, consecutively admitted for root-canal retreatment, were monitored during a 24-month period. All teeth (254 molars, 107 premolars, and 91 single-root anterior teeth) were divided into two major categories: teeth with modified anatomy from previous endodontic treatment (root-canal-morphology altered) and teeth in which no significant anatomical changes were made by the former endodontic treatment (root-canal-morphology respected). Although the overall success was 69.03%, the success in the root-canal-morphology-respected group was 86.8% and in the root-canal-morphology-altered group 47% (Mann-Whitney U test p < 0.0001). The clinical success of an endodontic retreatment seems to depend on whether alterations in the natural course of the root canals were caused by previous root-canal treatment.

Effect of access cavity location and design on degree and distribution of instrumented root canal surface in maxillary anterior teeth.

AIM: The null hypothesis tested in this study was that in single-rooted anterior teeth with simple root canal anatomy, different access cavity designs ('lingual cingulum', 'lingual conventional', 'incisal straight-line') do not influence the ability of endodontic files to plane the walls of the root canals. METHODOLOGY: Thirty extracted human maxillary anterior teeth were divided randomly into three groups for each access cavity. The access cavities were prepared according to predefined criteria and the roots embedded in individual polyvinyl-siloxane putty matrices. The matrices allowed these teeth to be split into buccal and palatal halves and to be reassembled. The split teeth enabled removal of pulpal remnants from the root canal system and the walls to be stained with an even layer of permanent black ink. Once dried, the split roots were reassembled in the putty matrices and a step-back filing technique was used to prepare the canals with water irrigation. The canal walls were examined for residual ink staining and scored by three independent assessors using an index devised for the purpose. RESULTS: There was good agreement between the assessors. None of the access cavities allowed file contact with the entire root canal wall. The overall (palatal and buccal sections) scores showed significant differences (P < 0.01) between the access cavity groups in the extent to which the canal walls could be filed. The straight-line incisal access cavity had the greatest proportion of instrumented root canal surface. The lingual cingulum access cavity was the worst in this respect. The differences in residual ink scores between the access cavity types were significant for the buccal halves (P < 0.01) but not for the palatal halves (P > 0.05). CONCLUSIONS: The null hypothesis was proven. Regardless of access cavity design, mechanical preparation did not allow instrumentation of the entire root canal wall. Straight-line access allowed the greatest proportion of the root canal wall to be instrumented and the lingual cingulum access the least.