Influence of thermal gradients on stress state of veneered restorations

Objectives

To assess transient and residual stresses within the porcelain of veneered restorations (zirconia and metal) as a result of cooling rate and porcelain thickness.

Methods

Porcelain-on-zirconia (PZ) and porcelain-fused-to-metal (PFM) crowns were fabricated with 1 or 2 mm of porcelain. Thermocouples were attached both internally and externally to the crowns to record transient temperatures. For fast cooling, the furnace was opened after the holding time and switched off. Slow cooling was accomplished by opening the furnace at 50 °C below the glass transition temperature (T_g) of the material. An axially symmetric FEA model simulated thermal stresses. Time-dependent temperature equations from thermocouple readings were set as boundary conditions. Framework materials and the porcelain below T_g were considered to behave elastically. Visco-elastic behavior was assumed for porcelain above the T_g modeling properties as dependent on cooling rate.

Results

Differences in residual stress were found for fast and slow cooled PZ and PFM crowns. Significant transient stress waves were observed within the porcelain when fast cooling through T_g. They are believed to be related to non-uniform volumetric changes originated from thermal gradients. Results were confirmed by modeling and physical testing of crowns containing a defect.

Significance

Residual stresses do not distinguish PZ from PFM. High magnitude transient stresses observed within the porcelain during fast cooling may explain clinical fractures involving internal defects. Stress waves may also originate internal micro-cracking which could grow under function. Therefore, slow cooling, especially for all-ceramic crowns with thick porcelain, is important to prevent thermal gradients and high-magnitude transient stresses.     

Cost comparison of genioplasty: when indicated,wire osteosynthesis is more cost effective than plate and screw fixation

Purpose

This retrospective study was conducted to determine the difference in the cost of genioplasty according to the osseous fixation technique used.

Patients and methods

A retrospective study among orthognathic surgery patients treated over a 54-month period ending in June 30, 2011 was conducted. Immediately post surgery, panoramic and cephalometric radiographs of these patients were assessed to determine the presence of genioplasty procedure and the type of fixation used. The cost of the actual fixation used by the surgeons was compared with that which the cost would have been had the surgeons used the criteria described in the hypotheses, for plate and screws fixation when genioplasty is performed.

Results

A review of 1,498 orthognathic surgery patients revealed that 473 of these patients underwent genioplasty. Out of 473 patients, 425 had genioplasty to either advance and-or superiorly reposition the chin. Of these, 230 had wire osteosynthesis and 243 had some form of rigid fixation. The unit cost of fixation for genioplasty when wire osteosynthesis is used is less than C$5.00. The mean unit cost estimate in our patient group when pre-bent plates are used was C$542.00. All 230 patients in whom wire osteosynthesis was used demonstrated stable fixation of the bony parts and no immediate postsurgical adjustment was required in any patient.

Conclusions

For patients requiring genioplasty to advance and-or superiorly reposition the chin, it is possible to use wire osteosynthesis to achieve accurate and stable fixation while reducing the fixation cost by more than C$500.00 per case. The surgeon should include cost considerations in the selection of treatment methods.     

Fine-needle aspiration of supraclavicular lymph nodes

Malignancies from many primary sites may metastasize to supraclavicular lymph nodes (SCLN). We reviewed 100 fine-needle aspirations (FNAs) of SCLNs. There were three major types of malignancy detected by this method: adenocarcinoma (n=40), squamous cell carcinoma (n=14), and other malignancies (n=29). Adenocarcinomas and other malignancies from all sites tended to metastasize to the left SCLN. Squamous cell carcinomas from all sites, however, tended to appear on the right side. For 61 patients, a previous diagnosis of malignancy had been made within 1 yr of the clinical appearance of the abnormal SCLN. For 20 patients, the primary diagnosis antedated SCLN metastasis by more than 1 yr, particularly patients with adenocarcinoma of the breast. prostate, or thyroid papillary carcinoma. Diagn Cytopathol 1996 14:216-220. © 1996 Wiley-Liss, Inc.     

Gemcitabine,paclitaxel, and oxaliplatin (GEMPOX) in the treatment of relapsed/refractory intracranial nongerminomatous germ cell tumors

Intracranial germ cell tumors (GCT) account for less than 5% of all central nervous system tumors in children in Western countries. Approximately 40% are nongerminomatous GCT (NGGCT). Despite correct treatment, 16% to 47% of the patients will relapse. There are no standard approaches in case of recurrence, and treatment in this situation remains a challenge. We report three patients diagnosed with relapsed intracranial NGGCT treated with gemcitabine, paclitaxel, and oxaliplatin, in whom the tumor showed a remarkable response with normalization of tumor markers.