REVIEWS AND ABSTRACTS

Book reviews and article abstractsAlex Jacobson, DMD, MS, PhDBirmingham, Ala

THESIS ABSTRACTS

Studying an in-vitro model todetermine the feasibility of usingliposomes for sustained antibioticreleaseB. EvansDepartment of Orthodontics, University of the Pacific, SanFrancisco, Calif

The purpose of this project was to determine if liposomescan be used to store and slowly release antibiotics that are usefulagainst periodontal pathogens. Liposomes are bacteria-sizedspheres of phospholipids that can sequester both hydrophobicand hydrophilic drugs and release them slowly over severalweeks. Our laboratory showed that certain liposomes bind tomolecules and cells in the periodontal pocket to provide enoughantibiotic to protect the area for at least a week. These arenegatively charged liposomes that contain a polyethylene glycol,which has been shown to greatly prolong the in-vitro perfusionsystem to mimic the environment of the periodontal pocket,including a constant flushing of crevicular fluid. We tested theability of these liposomes to retain 1 of the following antibiotics:tetracycline, metronidazole, or doxycycline. The rate of loss ofthe antibiotic was followed for 6 hours. The kinetic analysis ofthis loss showed that the rate of release from the liposomes wastoo quick to be useful. I concluded that these antibiotics are toohydrophobic to be retained by liposomes to make a usefulliposome-based drug delivery system for periodontal diseases.

0889-5406/2002/$35.00 � 0 8/8/122489doi:10.1067/mod.2002.122489

Development of a liposome-based carriersystem for stimulants of bone growthJ. FellerDepartment of Orthodontics, University of the Pacific, SanFrancisco, Calif

The goal of our laboratory was to develop tools to controlthe regeneration of oral tissues. We are currently developinga liposome-sequestered cytokine system that will control theactivity of fibroblasts. The purposes of the current studieswere to determine (1) which liposomes are more stable, (2) howmuch protein activity will be destroyed during the loadingprocess, and (3) whether lyophilization loading would be moreefficient in loading proteins than passive loading, and whether

lyophilization would degrade the activity of the protein. Severaltypes of liposomes were loaded with calcein and tested forretention in an in-vitro mode of a perfused interstitium. Wefound that artificially derivatized forms of phospholipids weremuch more stable. Unfortunately, these phospholipids require amuch higher annealing temperature that may destroy the loadedenzymes’ activity. To elucidate how destructive the loadingprocess is, we measured alkaline phosphatase (ALP) activityafter 2 extreme aspects of the loading process—sonication andheat exposure. We tested ALP loading efficiency for 2 loadingmethods—lyophilization and passive. Our results indicate thatsynthetic, anionic liposomes constructed with cholesterol are thebest choice for protein loading. We showed that enzyme activityis not significantly damaged at the annealing temperature for thesynthetic liposomes or with sonication. We also demonstratedthat the lyophilization loading method is 14 to 17 times as efficientas the passive loading method. The results of these studies go along way in developing a prototype to control tissue regeneration.

0889-5406/2002/$35.00 � 0 8/8/122490doi:10.1067/mod.2002.122490

Assessment of the accuracy of theCRIL Stereo X-ray and 3DMetricssystems in linear measurementN. SallapudiDepartment of Orthodontics, University of the Pacific, San

Francisco, Calif

This study was undertaken to assess the accuracy of theCRIL Stereo X-ray and 3DMetrics systems in linear measure-ment. Several metal tie points and landmark identifiers wereplaced on a dry skull. Multiple measurements were then madebetween the tie points and also between landmarks. Threedifferent methods of measurement—direct caliper measurement,the CRIL Stereo X-ray system, and the 3DMetrics system—were used. The direct caliper measurement was considered thegold standard, with which the other 2 systems were compared.The results of the experiment showed that the CRIL StereoX-ray system was accurate at measuring tie point measurementsbut inaccurate at landmark measurement. The 3DMetrics systemwas inaccurate in landmark measurements and even less accu-rate for tie point measurements. Future development of the CRILStereo X-ray system should focus on landmark location.

0889-5406/2002/$35.00 � 0 8/8/122491doi:10.1067/mod.2002.122491

328 American Journal of Orthodontics and Dentofacial Orthopedics/March 2002