Temperature changes in a cemented mandibular endoprosthesis: in vitro and in vivo studies.

Using polymethylmethacrylate (PMMA) cement in cemented endoprostheses may cause heat necrosis and prosthesis failure due to the highly exothermic reaction. This study determined the magnitude and duration of temperature change during the cementation of a mandibular endoprosthesis in an in vitro and in vivo Macaca fasicularis model. In the in vivo study the median maximum temperature (T(max)) around the mandible-prosthesis unit (MPU) was 31.0°C with the peak T(max) at hole 1 (1mm from stem). The in vitro study recorded a lower T(max) and indicated a trend that increased spacing (groove) around the prosthesis results in a higher T(max). All the T(max) MPU measurements were lower than normal body temperature (38°C). In the in vivo study the median maximum temperature change (T(maxΔ)) was 1.8°C; in the vitro study, the T(maxΔ) of the 4mm groove width was significantly higher than all others. Temperature increases were transient, with the temperature returning to baseline a median of 6.0min after T(max). Histological analysis showed surrounding tissue at the cement-bone interface with mild inflammation. Within the parameters tested, there was minimal risk of thermal damage. The temperature changes were influenced by the quantity of cement used and the distance from the prosthesis stem.

Osteo-odonto-keratoprosthesis surgery: a combined ocular-oral procedure for ocular blindness.

The aim of this retrospective study was to describe the oral procedures used in osteo-odonto-keratoprosthesis (OOKP) surgery, and the demographics and oral findings of candidate patients in Singapore. The OOKP procedure utilizes an autologous tooth-bone complex to mount a poly-methylmethacrylate optical cylinder, as an artificial cornea, stabilized by an overlying autologous buccal mucosal graft. Consecutive patients referred over 3 years for dental evaluation prior to OOKP surgery were included. A total of 21 patients underwent oral clinical and radiographic evaluation. The aetiology of blindness included Stevens-Johnson's syndrome (11 cases), chemical burns (9 cases) and multiple failed corneal grafts (1 case). Evaluation revealed that 12 patients were suitable for OOKP surgery, 8 were at risk of complication or failure and 1 had no usable teeth. Fourteen patients have undergone unilateral OOKP Stage 1 surgery successfully. Complications included fracture of a tooth from its lingual bone necessitating the harvesting of a second tooth (1 case), oronasal perforation (1 case), exposure of adjacent roots (5 teeth), lower lip paresthesia (2 cases) and submucosal scar band formation in the buccal mucosal graft donor site (10 cases). Thirteen patients have completed Stage 2 surgery, with attainment of their best possible visual potential following OOKP surgery.

The effect of prior radiation therapy for treatment of nasopharyngeal cancer on wound healing following extractions: incidence of complications and risk factors.

This is a prospective study of wound healing after extractions in patients who had radiation therapy for nasopharyngeal cancer. From 40 patients who fulfilled all the study criteria were extracted a total of 155 teeth. The demographic data were analysed, checking for factors that might affect the healing process after extraction. Wound healing was divided into three groups: normal wound healing, delayed healing and osteoradionecrosis. Logistic regression was used to analyse possible relationships. There was a low complication rate: 5.8% and 1.9% of extractions showed delayed healing and osteoradionecrosis, respectively. The age of the patient at time of extraction was the only significant factor that influenced the occurrence of delayed healing. It was observed that localized radiation absorption was considerably different from the total radiation dose. In conclusion, postradiation extractions have a low risk of complications and the results point to age as a factor that may influence wound healing.

Effects of aging on repair of resin-modified glass-ionomer cements.

The effects of aging on the repair bond strengths of resin-modified glass-ionomer cements after different methods of surface conditioning were studied. Surface conditioning methods included the following: maleic acid; maleic acid with resin application; polyacrylic acid; polyacrylic acid with resin application. Shear bond testing between the aged and new material was carried out with an Instron Universal testing machine. Surface conditioning with maleic acid and resin application gave the highest repair bond strengths at 3 and 6 months. There was, however, no statistically significant difference in bond strengths between the different treatment groups after both 3 and 6 months storage. Intergroup comparisons revealed no significant difference in failure modes after both storage periods. For all treatment groups, no significant difference in repair bond strengths was noted between storage after 1 week, 3 and 6 months. There appears to be a general decrease in repair bond strengths for all treatment groups after 3 months storage. The clinical repair of resin-modified glass-ionomer cements after this period of time is therefore not recommended.

Effects of aging on repair bond strengths of a polyacid-modified composite resin.

The effect of age of a poly-acid-modified composite resin on repair bond strength after different methods of surface conditioning was studied. Surface conditioning methods included the following: maleic acid with resin application; polyacrylic acid with resin application; sand-blasting with resin application. Shear bond testing between the aged and new material was carried out with an Instron Universal Testing Machine. Although repair bonds strengths after all surface conditioning methods were significantly higher than the control group at 1 week, no statistically significant differences in bond strengths were noted after aging the material for 6 months. After all aging periods, surface conditioning with sand-blasting and resin application resulted in the highest repair bond for poly-acid-modified composite resins. Specimens with cohesive failure in the material gave significantly higher repair bond strengths than specimens with adhesive failure at the repaired interface.

Effects of finishing/polishing time on surface characteristics of tooth-coloured restoratives.

This study compared the effects of immediate and delayed finishing/polishing procedures on the surface characteristics (surface roughness and hardness) of tooth-coloured restoratives including a microfilled, a heavily filled and a polyacid-modified composite resin and a resin-modified glass-ionomer cement. Eighty-four specimen discs were made for each material; the first 12 were used as controls and the remaining 72 specimens were randomly divided into two equal groups. The first group was finished/polished immediately after light polymerization and stored for 1 week in distilled water at 37 degrees C while the second group was finished/polished after 1 week storage in distilled water at 37 degrees C. Finishing and polishing was carried out using the following systems: Enhance system, white stones with Vaseline and Super-snap disks system. The finished/polished surfaces were subjected to profilometric evaluation and microhardness testing. The effects of delayed finishing/polishing procedures on surface roughness and hardness appear to be both material and technique dependent. Delayed finishing/polishing of polyacid-modified composite resins and resin-modified glass-ionomer cements generally resulted in a smoother surface. The surface roughness of composite resins after finishing/polishing procedures were generally not influenced by the finishing/polishing time. For all materials, delayed finishing/polishing with the various techniques generally resulted in a surface of similar hardness to or harder than that obtained with immediate finishing/polishing and the control group.

Surface characteristics of tooth-colored restoratives polished utilizing different polishing systems.

The surface characteristics of different tooth-colored restoratives polished with the Enhance system, white stones, and the Super-snap system were evaluated using profilometry and microhardness testing. Surface characteristics of materials cured against a Mylar Uni-strip were used as a control. The results of this study show that the surface characteristics (roughness and hardness) following polishing with different systems are material dependent. The result may be attributed to the discrepancy between filler and matrix hardness of the restorative. Filler content, particle size, and the ability of the polishing system to abrade the filler may also contribute to the observed change in surface characteristics.