In vitro assessment of retention and resistance failure loads of complete coverage restorations made for anterior maxillary teeth restored with two different cast post and core designs.

BACKGROUND: The purpose of this in vitrostudy was to evaluate the retention and resistance form of complete coverage restorations supported by two different cast post and core designs. MATERIAL AND METHODS: Forty extracted maxillary central incisors were randomly divided into four groups of 10 specimens each (namely A, B, C and D). All specimens were endodontically treated and a uniform post space of 9mm was created. All prepared teeth had a 360o chamfer ferrule of 2mm in axial height measured 0.5mm coronally from the cementoenamel junction (CEJ) and an axial wall thickness of 1.5 mm. Specimens in groups A and C received cast post and cores with the standardized core design, where the core ended at the coronal part of the ferrule, while specimens in groups B and D received cores that were encircling the ferrule. Cemented complete coverage restorations in groups A and B underwent tensile load stress, while the restorations in groups C and D underwent compressive load stress until failure. RESULTS: Teeth in group A exhibited a mean failure load of 326.14±83.67 N under tension, while teeth in group B exhibited a mean failure load of 332.79±80.38 N (p=0.858). Teeth in group C recorded a mean failure load of 1042.81±205.07 N, and in group D a mean failure load of 875.15±167.64 N (p=0.061) under compression was registered. CONCLUSIONS: The standard cast post and core design with a 2 mm of ferrule height offers superior resistance, although not statistically significant (p=0.061), when compared to the core design encircling the axial wall ferrule. Both cast post and core designs offer equal retention. However, different failure modes of decementation were noted. Key words:Endodontically treated teeth, Post-and-core technique, Endodontic-post, Decementation, Root fracture, Ferrule effect.

In Vitro Assessment of Retention and Resistance Failure Loads of Teeth Restored with a Complete Coverage Restoration and Different Core Materials.

PURPOSE: To investigate in vitro the retention and the resistance form, as well as the failure modes of maxillary premolars restored with cast metal crowns and different core materials. MATERIALS AND METHODS: Sixty human extracted maxillary premolars were selected according to their size and were embedded in PMMA resin blocks. After removing a part of their clinical crowns, the teeth were randomly divided into 3 groups of 20 teeth and were either left unrestored, or they were restored with amalgam or composite resin. All teeth were prepared for a cast metal complete coverage restoration. The restorations were cemented on the prepared teeth with a resin-modified glass ionomer luting agent (GC Fuji Plus). All specimens were subjected to static loading at 1 mm/min by a universal testing machine, until failure. Half the specimens of each group were subjected to tensile loading along the long axis of the teeth. The other half were subjected to compressive loading at a 30° angle. Failure loads and failure modes for each tooth were recorded. The statistical analysis included descriptive statistics, one-way ANOVA, and Tukey's HSD test. RESULTS: One-way ANOVA revealed statistically significant differences among the 3 tested groups (p < 0.05) for both tests. The group of teeth with no core material presented the highest failure loads for both the tensile and the compressive loading tests, with mean loads of 381.02 Ν and 741.21 Ν, respectively. Mean tensile and compressive failure loads for the amalgam group were 277.34 Ν and 584.75 Ν, while the composite resin group presented the lowest tensile and compressive failure values, which were 250.77 Ν and 465.78 Ν, respectively. The compression loading test resulted in the same failure mode for all specimens, which included unfavorable fracture of the teeth in combination with detachment of the cast metal complete coverage restorations. The tensile loading test resulted in different failure modes between the groups that used a core material and the group with no core material. CONCLUSIONS: Teeth that lost more than half of their coronal structure presented better retention and resistance form if no core material was used, provided that a minimum of 2-mm axial wall height was present at the missing part. Teeth that have lost more than half of their coronal structure and were restored with amalgam core presented better retention and resistance form than those restored with composite resin. Catastrophic fractures, extending to the root, were associated with compression forces but not with tensile forces.

Comparative Assessment of a New Holistic-Oriented and an Old Specialty-Specific Undergraduate Curriculum in Removable Prosthodontics: A Study Based on Senior Students' Perceptions.

PURPOSE: A survey was conducted in the Dental School, Aristotle University, Thessaloniki, Greece, (i) to assess the perceptions and experiences of senior dental students, Classes of 2014 and 2015, toward the old, specialty-specific (OC) and new, holistic-oriented (NC) undergraduate curriculum, respectively, in removable prosthodontics and (ii) to identify areas of improvement in prosthodontic training. MATERIALS AND METHODS: Structural components of both curricula were collected, including the total number of (i) laboratory/lecture/clinical training hours, (ii) written examinations, (iii) mandatory clinical cases, and (iv) European Credit Transfer and Accumulation System (ECTS) credits. A 20-item closed-type questionnaire using a five-point Likert scale was distributed in two consecutive groups of seniors, Classes of 2014 (n = 54) and 2015 (n = 57); 54 OC and 57 NC senior students filled out the questionnaire. RESULTS: A greater percentage of NC students stated that (i) they felt less confident to carry out jaw relation recording and removable partial denture metal framework design and (ii) the time allocated for clinical training was less sufficient. Students of both curricula reported that the laboratory courses and lectures contributed little to their clinical performance. Implant restorations and prosthetic management of patients with craniomandibular disorders were the most popular treatment options that the respondents felt that should be incorporated in the undergraduate curriculum. CONCLUSIONS: As a general trend, students completing the revised curriculum reported more difficulties during their training and felt more insecure about their clinical competences. To enhance students' self-confidence in prosthodontics, more effective preclinical training methods, introduction of additional treatment options, and alternative educational methods should be considered.

In vitro assessment of retention and resistance failure loads of two preparation designs for maxillary anterior teeth.

STATEMENT OF PROBLEM: Parallel labiolingual walls and the preservation of the cingulum in anterior tooth preparations have been advocated. However, their contribution to retention and resistance form has not been evaluated. PURPOSE: The purpose of this in vitro study was to evaluate the retention and resistance failure loads of 2 preparation designs for maxillary anterior teeth. MATERIAL AND METHODS: Forty metal restorations were fabricated and paired with 40 cobalt-chromium prepared tooth analogs. Twenty of the specimens had parallel buccolingual walls at the cervical part (group PBLW; the control group), whereas the remaining 20 had converging buccolingual walls (group CBLW; the experimental group). The restorations were cemented to the tooth analogs with a resin-modified glass ionomer luting agent. Ten specimens from each group were subjected to tensile loading with a universal testing machine; the rest were subjected to compression loading until failure. Descriptive statistics and the independent t test (α=.05) were used to determine the effect of failure loads in the tested groups. RESULTS: The independent t test revealed statistically significant differences between the tested groups in tensile loading (P<.001) and in compressive loading (P<.001). The PBLW group presented a higher tensile failure load than the CBLW. On the contrary, the PBLW group presented a smaller compression failure load than the CBLW. CONCLUSIONS: Parallelism of the buccolingual axial walls in anterior maxillary teeth increased the retention form but decreased the resistance form.