The effects of therapeutic x-ray doses on mechanical, chemical and physical properties of poly methyl methacrylate

A simple and low-cost technic for immobilization of mandible during head and heck radiotherapy: a technical note

Immobilization protocols for head and neck radiotherapy (HNR) are needed to reduce radiation dispersion in non-tumoral tissues and to reduce damage to noble structures; however, involuntary mandibular movements require additional adaptations of thermoplastic masks.

PURPOSE

Our objective was to describe an easy and low-cost disposition to help thermoplastic masks immobilize the mandible during HNR.

MATERIALS AND METHODS

We created Styrofoam models to stabilize the mandible which was used to make adaptation to the thermoplastic masks. The Styrofoam model was inserted into alginate to construct a mold and a self-curing acrylic resin was added into the mold. After the acrylic resin hardened, the dispositive mandibular immobilizer was removed from the alginate mold and adjusted with Maxicut and Minicut or other drills and sandpaper. The alginate mold can be used on the same day to create backup devices.

RESULTS AND CONCLUSIONS

Our device was made in a simple way, has a low cost, and helps the thermoplastic masks to immobilize the mandible, leading to a more precise individualization of head and neck immobilization that can reduce unanticipated radiation scatter and improve radiation distribution.

Effects of boron on the mechanical properties of polymethylmethacrylate denture base material

Purpose:

The objective of this study was to determine whether the addition of different types of boron (Borax, Boric Acid and Colemanite) to polymethyl methacrylate denture base resin would improve flexural and impact strengths, and surface hardness of polymethyl methacrylate.

Materials and methods:

Borax, Boric acid, Colemanite were added to heat polymerized polymethyl methacrylate specimens were prepared for flexural strength (65x10x2.5 mm), impact strength (50x6x4 mm), and hardness (20x6x4 mm) tests according to the manufacturers’ instructions (n=10). To determine flexural strength of the specimens, they were loaded until failure on a universal testing machine using a three point bending test. Specimens were subjected to the Charpy impact test machine. Hardness of the specimens was measured with an analog shoremeter Shore D. The data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α=0.05).

Results:

The highest mean flexural strength value was seen in 3% Borax group and followed by 1% Colemanite group. In addition, the highest mean impact strength value was recorded in 1% Colemanite group, and differences between 1% Colemanite group and control group were found to be statistically significant (p=0,001). Furthermore, there was significant difference in hardness between control group and all other groups (p<0.001).

Conclusion:

The addition of 1% Colemanite to polymethyl methacrylate improved the mechanical properties of PMMA.

Influence of External Beam Radiotherapy on the Properties of Polymethyl Methacrylate-Versus Silicone-Induced Membranes in a Bilateral Segmental Bone Defect in Rats

INTRODUCTION

Standard care for malignant tumors arising next to a bone structure is surgical removal with safety margins, followed by external beam radiotherapy (EBRT). Complete tumor removal can result in large bone defects. A two-step bone reconstruction technique using the induced membrane (IM) technique has proven its efficacy to bridge gap nonunion. During the first step, a spacer is placed in the bone gap. The spacer then is removed and the IM around it is filled with autologous cancellous bone graft. However, the feasibility of this technique with the addition of adjuvant EBRT between the two reconstruction steps has not yet been studied. Polymethyl methacrylate (PMMA) used to be the standard spacer material for the first step. Silicone spacers could replace them owing to their good behavior when submitted to EBRT and their easier removal from the surgical site during the second step. The aim of this study was to evaluate the influence of EBRT on the histological and biochemical properties of IM induced using PMMA or silicone as spacer.

MATERIALS AND METHODS

The analyses were performed on PMMA- or silicone-IM with and without EBRT in a 6-mm bilateral femoral defect in 32 rats. Thickness and vessel content were measured in both groups. Bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factor (VEGF) content in lysates of the crushed membranes were measured by enzyme immunoassay. Finally, alkaline phosphatase activity was analyzed in human bone marrow stromal cell cultures in contact with the same lysates.

RESULTS

EBRT did not change the histological structure of the cellular internal layer or the fibrous outer layer. The nature of the spacer only influenced IM thickness, PMMA-IM with external radiotherapy being significantly thicker. EBRT decreased the vascular density of IM but was less effective on VEGF/BMP2 production. In vitro, IM could have an osteoinductive potential on human bone marrow stem cells.

CONCLUSION

EBRT did not modify the histological properties of IMs but decreased their vascular density. VEGF and BMP2 production within IMs was not affected by EBRT. Silicone spacers are able to induce membranes with similar histological characteristics to PMMA-IM.