PEEK High Performance Polymers: A Review of Properties and Clinical Applications in Prosthodontics and Restorative Dentistry.

Various materials have been used over time in prosthetic dentistry. However, due to the evolution of science and knowledge, new materials are being brought to the forefront. Polyether ether ketone (PEEK) is a polymer with many potential applications in dentistry. The use of PEEK has become increasingly more common in dental practice; its favorable properties have made it a compelling alternative biomaterial in restorative dentistry. The current trend is moving towards the use of metal-free restorations and biomaterials which exhibit advanced properties in the complex oral environment. This review paper presents and summarizes clinical applications of PEEK in contemporary dentistry.

Presurgical planning in implant restorations: correct interpretation of cone-beam computed tomography for improved imaging.

Contemporary implant dentistry is a primarily prosthetically driven treatment. The implant position is defined during the diagnostic phase, and the radiographic guide (template) indicates accurately the area of concern on the cone-beam computed tomography (CBCT). CBCT is an essential diagnostic key to a successful treatment plan in many cases. The aim of this paper was to underline the importance of proper alignment of the scanning levels in CBCT in order to avoid distorted cross-sectional images. As demonstrated with two clinical cases in this preliminary study, the initial scanning images of the CBCT must be drawn parallel to the occlusal plane, as defined by the diagnostic wax-up of the final restoration. The radiographic template offers valuable information about the planned location and inclination of the implant and the restoration. Proper image reconstruction following the dental scan can contribute significantly to accurate cross-sectional images and detailed presurgical planning.

Formation of angiotensin II and other angiotensin peptides from des-leu 10-angiotensin I in rat lung and kidney.

The formation of AII from a metabolite of AI, des-leu10-angiotensin I [A(1-9)] has been studied in centrifugal fractions of rat lung and kidney using gradient elution HPLC to monitor the formation of peptide products. AII-forming activity was present in kidney S2 (22.3 nmol/mg protein/min) but not in kidney P2 centrifugal fractions. Lung S2 fractions showed relatively weak AII-forming activity (0.34 nmole/mg protein/min) whilst no activity was observed in lung P2. Carboxypeptidase N-like activity measured using both Hipp-Arg and Hipp-Lys as synthetic substrates did not parallel AII-forming activity, since this activity was highest in the P2 fractions of both lung and kidney, as were ACE and aminopeptidase activities. Whilst the major peptide produced in kidney S2 was AII (71%) significant amounts of both AIII (23%) and A(2-9) (6%) were also observed. In lung the amounts of these peptides produced as a percentage of the A(1-9) degrading activity were 2.9%, 2.4% and 21% respectively. The AII-forming activity in kidney S2 was not inhibited by enalaprilat, bestatin, amastatin, phosphoramidon or Pro-Phe but was inhibited (31%) by 1 mM cobalt (II). 1,10-Phenanthroline, iodoacetic acid, EDTA and puromycin significantly enhanced the formation of AII and increased the rate of degradation of the substrate, A(1-9). These results support the concept of a sequential carboxypeptidase pathway operating, particularly in kidney, to produce AII from AI. These results provide further evidence of an alternative metabolic pathway for the formation of AII not involving angiotensin converting enzyme.

Effect of chronic enalapril treatment on enzymes responsible for the catabolism of angiotensin I and formation of angiotensin II.

We have investigated the effect of chronic administration of enalapril on the carboxypeptidases responsible for the formation of angiotensin II from angiotensin I and other peptidases known to recognize angiotensin I as a substrate in the rat. These studies have shown an increase in activity in rate of formation of des-Leu-angiotensin I in both kidney S2 and P2 centrifugal fractions as well as a decrease in the rate of degradation of angiotensin I substrate. Similar increases in the formation of A(1-8) have been observed in kidney using A(1-9) as substrate. These two enzyme activities have been named carboxypeptidase K1 and K2, respectively to reflect their presence in rat kidney. These changes were accompanied by significant decreases in the activity of an amastatin-sensitive aminopeptidase and endopeptidase 24.11 in the kidney P2 fraction. These data suggest that chronic treatment with ACE inhibitors may differentially affect the activity of other enzymes capable of degrading angiotensin causing a substantial re-direction of angiotensin metabolism.

Radioimmunoassay for immunoreactive [des-Leu10]-angiotensin I.

A specific radioimmunoassay for the angiotensin-derived peptide [des-Leu10]-angiotensin I (AI-dL) is described. Antisera obtained from rabbits injected with immunogen prepared by coupling bovine beta-thyroglobulin to the peptide with carbodiimide were specific to this peptide and did not recognise related angiotensin peptides such as AI, AII, AIII, nor did they recognise other peptides such as bradykinin, substance P, bombesin or dynorphin(1-8). Immunoreactive AI-dL was detected for the first time in the plasma of rats and humans following purification by HPLC at concentrations of 78 and 40 pg/ml, respectively. Concentrations of AI-dL are increased following chronic administration of captopril to rats.

Bradykinin-potentiating activity of captopril disulphide dimer (SQ 14,551).

The ability of captopril and one of its metabolites, the disulphide dimer have been studied for their ability to affect angiotensin I and bradykinin responses. Captopril disulphide dimer (i.v.) potentiated the vasodilatory effects of bradykinin in urethane-anaesthetized rats, at doses of 0.1 and 0.3 mg/kg but did not inhibit the angiotensin I-mediated pressor response at these same concentrations. This activity of captopril disulphide dimer in vivo was not seen with bradykinin responses in isolated guinea pig ileum except at bath concentrations much higher than for captopril (10(-5) M). However captopril and captopril disulphide dimer at oral doses of 10 mg/kg both lowered systolic and diastolic blood pressures in spontaneously hypertensive rats. These studies are consistent with an in vivo bradykinin-potentiating activity of captopril disulphide dimer and suggest a possible antihypertensive activity of disulphide metabolites of captopril.

Capillary gas chromatographic drug screen for use in forensic toxicology.

A screening method is presented involving the use of capillary gas chromatography using a BP-5 column and nitrogen-phosphorous detection. This method is a quick yet reliable procedure for a large range of neutral and basic drugs and uses 1 mL or less of blood. Running standards that contain a number of commonly observed drugs with each batch of cases allows for more accurate tentative identifications of likely drugs in unknown cases and also provides a measure of quality assurance. This method is suitable for postmortem and clinical blood samples as well as plasma and serum.

Bond strengths of resin-to-metal bonding systems.

STATEMENT OF PROBLEM: Resinous materials for the veneers of fixed prostheses commonly require mechanical retention on metal substructures because there is no chemical adhesion. However, mechanical retention does not restrict creation of a marginal gap at the resin-metal interface, which can cause discoloration or detachment of resinous material. The development of a chemical resin-to-metal bonding could resolve this problem and also reduce the need for mechanical retention (pearls, wires) on metal frameworks. PURPOSE: This study evaluated six current methods with the use of various storage conditions to predict clinical efficacy. MATERIAL AND METHODS: Six resin-to-metal bonding systems were tested: Silicoater, Silicoater MD, Rocatec, OVS, Sebond, and Spectra-Link. All specimens were examined in bending tests after 24 hours of dry storage (category A), after 24 hours of water storage and thermocycling (category B), and after 2 months of water storage and thermocycling (category C). Tensional tests were completed for all bonding systems after dry storage, and microscopic examination (optical and SEM) was performed for all specimens. RESULTS AND CONCLUSIONS: This study indicated that certain systems can provide stable bonding of resin to metal substructures despite prolonged wet storage and intensive thermocycling. These systems can also be used clinically without retentive configurations on metal frameworks, resulting in better esthetics. Some bonding systems revealed progressive weakening of bond strengths, so research is needed to verify their clinical efficacy.

[Surface morphology of alloys treated with the Rocatec system]. / Zur Oberflächenmorphologie von mit dem Rocatec-System behandelten Legierungen.

The new Rocatec-System is propagated for improving the resin metal bond. With a tribotechnical blasting procedure a silicate layer is applied to the alloy surface. The resin is bonded to this layer with a silane coupling agent. This study investigates the alloy surface morphology alterations caused by the blasting procedures. The volume loss increases with blasting time, high gold alloys showing higher volume loss. Thin edges are deformed due to the high blasting pressure.

[Properties of the polycarboxylate and glass-ionomer cements]. / Idiotetes ton konion tou polyakrylikou oxeos.

This paper is a review article on the properties of the polycarboxylate and glass-ionomer cements. Much research has been done during the past years on the strength, solubility and adhesion of these cements with the dental tissues and the conclusions on these topics are discussed in this paper.

Biotransformation studies of di-acid angiotensin converting enzyme inhibitors.

The biotransformation of di-acid inhibitors of angiotensin converting enzyme was studied in the urine of rats using gas chromatography/mass spectrometry. It was found that after oral administration (10 mg/kg) of enalapril significant amounts (9.2%) of a hydrolytic metabolite of enalaprilat were excreted in urine which was identified as 2-N-alanyl-4-phenylbutanoic acid. This metabolite was present only in trace concentrations in urine after intravenous administration. This pathway was not present, however, with either ramipril or perindopril suggesting that the amide bond in these newer inhibitors is more resistant to hydrolysis than for enalapril. Glucuronidase hydrolysis of urine obtained from rats dosed with either enalapril, ramipril or perindopril indicated the absence of glucuronidate conjugates of these inhibitors in rat urine.

Biotransformation studies of di-acid angiotensin converting enzyme inhibitors.

The biotransformation of di-acid angiotensin converting enzyme inhibitors (I) to cyclized lactam metabolites was studied in the urine of rats using gas chromatography-mass spectrometry. Chemical synthesis of the corresponding piperazine-dione metabolite (III) was achieved by reaction of enalapril, perindopril or ramipril with acetic acid anhydride followed by hydrolysis of the ester group by sodium in ethanol or by acid hydrolysis. Electron impact and chemical ionization mass spectra confirmed the structure of these potential novel metabolites. Selected ion monitoring of urinary extracts demonstrated small amounts (less than 5%) of these lactams for all three inhibitors, however, it was shown that the majority of these lactams were formed as a result of sample treatment rather than due to biotransformation.