Identity of 1:2:1 and 2:4:2 subgingival spirochetes by DNA hybridization

A group of 1:2:1 and 2:4:2 subgingival spirochetes, well characterized by transmission electron microscopy, biochemical tests, cellular fatty acid and carbohydrate analyses, and ribotyping, was recently suggested to represent new treponemal species. The present study used DNA hybridization to examine this possibility. When DNA of a representative strain (no. 16) of the 8 1:2:1 spirochetes examined was labeled by iodination, it showed, after SI nuclease treatment, from 58 to 104% (average 76%) homology with DNA from the 1:2:1 spirochetes. 94% homology with DNA from the type strain of Treponema socranskii and of T. socranskii subsp. socranskii , i.e., ATCC 35536T, and 62% homology with DNA from T. socranskii subsp. buccale , strain ATCC 35534^T. Similarly treated DNA from a representative strain (no. 3) of 8 2:4:2 spirochetes exhibited from 90 to 105% (average 97%) homology with DNA from the 2:4:2 spirochetes, and 85% and 87% homology, respectively, with DNA from Treponema denticola strains ATCC 33520 and FDC T1. There was a negligible degree of homology between the 1:2:1 and 2:4:2 spirochetes. Thus, all the 2:4:2 spirochetes belonged to T. denticola . 1:2:1 strains with DNA homology levels >70% (5 strains) belonged to T. socranskii or T. socranskii subsp. socranskii , while those with homology levels from 58 to 63% (3 strains) most likely belonged to other subspecies of T. socranskii .     

Fluoride: a review--Part II: Topical fluorides

Fluoride therapy continues to be the best defense in the battle against dental caries. The decision to utilize topical fluorides is no longer age dependent. Changing disease patterns require dentists to critically evaluate the caries risk of each patient and develop a fluoride treatment plan based upon the needs of the individual patient. A variety of professional and self-applied fluoride products are available and new fluoride delivery systems have recently entered the market. A critical review of literature, combined with an understanding of the advantages and disadvantages of each topical fluoride system will assist the dentist in selecting the product best suited for each patient.     

Craniofacial distraction osteogenesis: a review of the literature: Part 1: clinical studies

A review of the literature dealing with distraction osteogenesis (DO) of the craniofacial skeleton, provided by a PUBMED search (National Library of Medicine, NCBI; revised 3 April 2000) from 1966 to December 1999 was conducted. Key words used in the search were distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, craniofacial and maxillofacial. This search revealed 285 articles. One hundred and nine articles were clinically orientated and were analysed in detail in this study. The type of distraction, indications, age, type of surgery, distraction rates and rhythms, latency and contention periods, amount of lengthening, follow-up period, relapse, complications and the nature of the distraction device were analysed. This review revealed that 828 patients underwent DO of the craniofacial skeleton; 579 underwent mandibular DO, 129 maxillary DO, 24 simultaneous mandibular and maxillary DO and 96 midfacial and/or cranial DO. Craniofacial DO has proven to be a major advance for the treatment of numerous congenital and acquired craniofacial deformities. Treatment protocols and success criteria for craniofacial DO are suggested on the basis of these results. There is still, however, a lack of sufficient data, especially on follow-up and relapse, so that treatment strategies have to be validated by long-term studies in the future.     

Sinusoidal voltammetry:: a frequency based electrochemical detection technique

Sinusoidal voltammetry is an electrochemical technique, which uses a large amplitude sinusoid as the potential waveform and performs data analysis in the frequency domain. When the amplitude of the applied potential waveform is large (i.e. >50 mV) the current–potential behavior of the electrochemical interface is extremely non-linear. As a result the faradaic response exhibits signal intensity at higher order harmonics of the fundamental excitation frequency. In contrast, the major source of noise, due to the capacitive charging current, is primarily linear and the vast majority of its intensity remains at the fundamental frequency. The dramatic difference in the frequency response between these signals can be exploited in many ways to enhance both the signal-to-noise ratio and selectivity of an electrochemical measurement. The extent of faradaic signal distribution to the harmonics of the fundamental excitation frequency is dependant on many standard voltammetric parameters. In addition to enhanced sensitivity at the higher harmonics, redox species with different electrochemical properties (e.g. E°, number of electrons, electron transfer rate constant, etc.) can be detected selectively based on their unique ‘fingerprint’ frequency response. The experimental parameters (e.g. E_switch, scan rate, excitation potential window amplitude, etc.) can be optimized, as well as the frequency and phase angle to achieve the best selectivity for the analyte of interest.