Argon laser initiated resin photopolymerization for the filling of root canals in human teeth.

This work was undertaken to determine if 488 nm light is transmitted through dentin in quantities adequate to polmerize resin located several milimeters from the light source (an optical fiber). The spread of polymerization in a camphorquinone activated resin due to 488 nm light emanating from an opaque plastic canal was compared with light emanating from a canal of the same diameter in tooth dentin. Results indicated that irradiation of a resin-filled chamber via an opaque canal generated a series of ellipsoidal forms, while irradiation via a root canal generated bullet-shaped forms of much larger volume and weight. The base of these bullet-shaped forms was flat against the dentin-resin interface and surrounded the canal. These results indicated that 488 nm argon laser light was transmitted through dentin and could act to polymerize resin at a distance of several millimeters from the canal. Further experiments verified that resin in lateral canals of tooth roots was readily polymerized by 488 nm light applied at low power levels (50 mW). These experiments demonstrate the effectiveness of the argon laser in polymerizing light activated dental resins located within or adjacent to tooth dentin at distances up to several milimeters from the fiberoptic terminus. The flexibility and control that these procedures make possible in the obturation of root canals may lead to substantial improvements in endodontic therapy.

A model for dentinal caries progression by digital subtraction radiography.

Extracted teeth with preexisting carious lesions were incubated in vitro at 37 degrees C in an artificial saliva buffer. Four teeth were exposed to buffer alone, four to buffer containing 5% glucose, and four to buffer containing 5% sucrose. Time-lapse radiographs were made of the carious lesions using an orienting device that fixed the position of the tooth, x-ray film, and x-ray tube collimator. The radiographs were analyzed over a period of 8 weeks using digital subtraction radiography. The subtracted images revealed that three of the four teeth incubated in saliva alone showed an increase in radiodensity (remineralization) at the depths of the lesion; one tooth showed no detectable change. Three of the four teeth incubated in the presence of 5% glucose showed increased radiolucency (demineralization); one showed no detectable change. The four teeth incubated in the presence of 5% sucrose exhibited results similar to those teeth incubated in 5% glucose.

Laser photopolymerization of dental materials with potential endodontic applications.

Photopolymerizing resins were exposed to three different wavelengths of light emanating from the argon laser. It was determined that the most efficient wavelengths for photopolymerization of camphorquinone-activated resins were at 477 and 488 nm. The 514.5-nm wavelength was relatively ineffective in activating polymerization. Four camphorquinone-activated resins were placed in the root canals of teeth and tested for polymerization depth using a 488-nm wavelength laser beam coupled to an optical fiber 200 microns in diameter. In regard to polymerization depth, these materials ranked as follows: Genesis greater than Prisma-Fil greater than Prisma Microfine greater than Prisma VLC Dycal. Alterations in the positions of the optical fiber and the surface of the resin in the canal made only minor differences in polymerization depth of the samples. The results indicate that an argon laser coupled to an optical fiber could become a useful modality in endodontic therapy.

DNA homologies shared among E. corrodens isolates and other corroding bacilli from the oral cavity.

In a previous microbiological study of Eikenella corrodens, we noted the presence of E. corrodens strains with variability in colony morphology, as well as other corroding bacilli phenotypically similar to E. corrodens but which were unidentifiable on the basis of biochemical reactions. This raised questions as to whether E. corrodens constitutes a genetically heterogeneous group of organisms, and whether the unidentified corroding bacilli represent atypical E. corrodens or genetically unrelated organisms. In the present study, the genetic relationship among 14 E. corrodens isolates and 6 unidentified corroding bacilli was examined. DNA base compositions were determined from the melting temperatures of DNA samples. DNA homologies among E. corrodens and corroding bacilli were determined by DNA hybridization in solution using S1 nuclease. The % G + C content of E. corrodens strains varied from 56 to 58%, and from 56 to 60% for unidentified corroding bacilli. The DNA homologies among 12 E. corrodens isolates and 2 reference strains varied from 57 to 97%. Although these E. corrodens isolates exhibited variabilities in colony morphology and biochemical profile, no subspecies was identified. The unidentified corroding bacilli shared less than 33% homology with either of the E. corrodens reference strains. These corroding bacilli were further divided into 3 species on the basis of DNA hybridization studies using radiolabeled DNA from 2 representative corroding bacilli. One of the unidentified corroding bacilli appears to be a component of the normal flora in the human oral cavity. Our results indicate that E. corrodens is a genetically homogeneous species containing no recognizable subspecies.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships among isolates of oral haemophili as determined by DNA-DNA hybridization.

In order to assess the relationships among strains of the genera Actinobacillus and Haemophilus, DNAs from 50 strains of these genera were isolated and purified. The guanine plus cytosine (G + C) content of DNAs from strains of Haemophilus segnis and Haemophilus parainfluenzae were determined by thermal denaturation. DNA-DNA homologies were measured using labelled probes from one strain representing Haemophilus segnis (strain ATCC 10977), and two strains representing Haemophilus parainfluenzae (strains ATCC 9796 and ATCC 7901). Strains isolated as H. segnis had a G + C content of 39.0 to 42.9% and were 49-92% homologous with the ATCC 10977 DNA probe. All of the strains freshly isolated as H. parainfluenzae were 70-81% homologous with the ATCC 9796 DNA probe and had a G + C content of 34.9 to 38.3%. Strain ATCC 7901 was 11% homologous with the ATCC 9796 DNA probe, had a G + C content of 42.4%, and was 65-78% homologous to DNA from strains identified as Haemophilus aphrophilus and Haemophilus paraphrophilus. From these results we conclude that strain ATCC 7901 is a mislabelled strain of H. paraphrophilus. The results of multiple DNA-DNA hybridizations indicated that separate species designations were appropriate for H. segnis, H. parainfluenzae, Actinobacillus actinomycetemcomitans ("Haemophilus actinomycetemcomitans"), and H. aphrophilus. H. aphrophilus and H. paraphrophilus were closely related organisms and did not fulfill the generally accepted criteria for designation as separate species.

The movement of radioactive molecules across dentine in vivo in the dog.

Using a technique for measuring the movement of circulating molecules across the odontoblast-dentinal complex, the movement of water and alpha-aminoisobutyric acid through dentine and into a flow cell prepared on the tooth is described. The movement of water depended on dentine thickness, and varied from 0.40 microliter/min per cm2 in a flow cell overlying an average thickness of 0.74 mm of dentine, to 1.23 microliter/min per cm2 in a flow cell with a dentinal floor of 0.40 mm average thickness. The data suggest that alpha-aminoisobutyric-acid concentrations were lower in dentinal fluid than in blood plasma.

Fusobacterium periodonticum, a new species from the human oral cavity.

Isolates of Fusobacterium that differ from type strains of various fusobacterial species with respect to DNA sequence, cellular fatty acid composition, and biochemical activity, were obtained from periodontitis lesions in a patient with insulin-dependent diabetes mellitus. These isolates have the following distinguishing characteristics: 28% guanine + cytosine content; 40% or less DNA homology with type strains of representative fusobacterial species; cell size, 0.5 - 1 X 4 -100 microns; absence of motility; ability to ferment glucose, fructose, and galactose, but not 25 other carbohydrates; ability to produce indole; ability to hydrolyze hippurate but not esculin; sensitivity to bile; ability to produce little or no gas; ability to utilize threonine but not lactate. We propose that the organisms be classified as a distinct species of Fusobacterium to be named Fusobacterium periodonticum. The type strain of this new species has been deposited with the American Type Culture Collection under the designation ATCC 33693.

Relationships among the oral fusobacteria assessed by DNA-DNA hybridization.

DNA was purified from 16 strains of Fusobacterium nucleatum and from five strains representing other Fusobacterium species. The relationships among fusobacteria were examined by DNA-DNA hybridization and by determining the guanine plus cytosine content of the DNA. F. nucleatum was found to comprise a heterogenous group of organisms related to Fusobacterium periodonticum and Fusobacterium simiae, but unrelated to any of the other species of Fusobacterium tested.

Recombination in bacteriophage T1 in the presence of host restriction.

When unmodified phage T1 infects restricting host cells at high multiplicities of infection, there is an increase in recombination frequency in all regions of the T1 map compared to the level of recombination in standard crosses when short distances are examined. The enhancement of recombination frequency is not uniform for all regions but is greatest for markers near the center of the map and not so great for markers near the ends. Crosses between markers at the extremities of the map show that there is no increase in recombination frequency under restriction conditions. An examination of phage T1 heterozygotes suggests that an increase of ends created by the process of P1 restriction increases recombination. When T1 crosses are done in the absence of host restriction, recombination defects in the host have no effect on phage recombination and we conclude that phage T1 codes for its own recombination genes. Host recombination functions are also dispensable for the recombination occurring during infection of restricting host cells by unmodified phage at high multiplicities of infection.

Physiological study of cooperative infection by restricted bacteriophage T1.

The ability of certain phages to successfully infect a restricting host at a high multiplicity of infection is known as cooperative infection or cooperation. We have examined the ability of unmodified T1 (T1.0) to participate in cooperative infection in cells possessing the P1 restriction system. We have found that cooperation is dependent upon protein synthesis during the first few minutes after phage infection. However, we have been unable to attribute the necessary protein to a known T1 cistron. Degradation of the restricted T1 genome is approximately equally extensive whether cooperative infection occurs or whether it is blocked by chloramphenicol. It is postulated that an inducible host repair mechanism may be responsible for the phenomenon of cooperative infection.