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Biomedical subjects

J O Andreasen

Publications and source records attributed to J O Andreasen.

15 recordsLinked to original sources
PubMed1992

In vitro solubility of human pulp tissue in calcium hydroxide and sodium hypochlorite.

The tissue solvent capacity of a 2% stabilized sodium hypochlorite solution (Milton) and a commercial calcium hydroxide solution (Calasept) was examined under in vitro conditions where autolyzed human pulp fragments weighing approximately 0.0065 g were immersed in these solutions at 37 degrees C for periods of up to 10 days. It appeared that sodium hypochlorite was able to dissolve half the volume of pulp tissue within 1 h and the remaining tissue after 2-2 1/2 h. Calcium hydroxide dissolved half the pulp volume within 2 h, whereas it took 1 week for the remaining tissue to dissolve. These findings support the use of sodium hypochlorite as an irrigation solution during canal preparation and calcium hydroxide as a canal dressing for the purpose of creating a canal free of pulp remnants before root filling.

Calcium Hydroxide↗
PubMed1992

Rigidity of various fixation methods used as dental splints.

Horizontal and vertical rigidity of teeth fixed with seven types of dental splints were evaluated by two tooth mobility measuring devices. Altogether 21 dissected sheep mandibles including soft tissues were used for the experiments in which Fermit, flexible wire-composite, Kevlar, Fiber, Protemp, rigid wire-composite and Triad Gel splints were applied to four incisors. The mean rigidity of the central incisors within the splint was measured by means of Mühlemann periodontometer (horizontal mobility) and Periotest (horizontal and vertical mobilities). Mobility values of teeth before splinting were used as covariants and the values with the splints were illustrated as adjusted mobility. Statistical significance between the rigidity of various splints was analyzed by an unpaired t-test. It was shown that the most rigid splints both in horizontal and vertical directions were Triad Gel, rigid wire-composite and Fermit splints. Kevlar and Fiber splint allowed more horizontal movement than other splints. Protemp and flexible wire-composite splints proved to produce adequate lateral support for the fixed teeth and allowed vertical flexibility which is experimentally known to improve periodontal healing of luxated teeth.

Acrylic Resins↗
PubMed1992

Root resorption following traumatic dental injuries.

Permanent teeth are usually not attacked by osteoclasts despite their situation in a site where active bone resorption constantly takes place as a result of local and systemic osteoclast activating factors. This fact points to antiresorption factors residing in both the periodontal ligament (PDL) and the pulp. Concerning the PDL homeostasis factor (i.e. permanency of a separation between the alveolar socket and the root surface and protection of the root surface against osteoclastic activity), recent studies have shown that this factor, at least with respect to trauma and wound healing, is linked to, and probably resides in, the cementoblast layer and/or the cells next to this layer. If there is loss of this tissue integrity, root resorption may occur; especially if non-PDL derived cells gain access to the site. With respect to the pulp, no systematic research has been performed regarding the homeostasis of this structure (i.e. permanency of the pulpal organ with its specific anatomy and functional stability). In evaluating the events where resorption does occur, it appears that the loss of tissue components within the pulp (including odontoblasts) implies a risk of root canal resorption if nonpulpally derived cells gain access to the site. Root resorption following traumatic dental injuries, whether located along the root surface or within the root canal appears to be a sequel to wound healing events, where a significant amount of the PDL or pulp has been lost due to the effect of acute trauma. The goal of these processes is removal of injured tissue from zones of trauma, space creation for neovascularization or control of infection. Irrespective of the goal, these processes have a potential for root resorption. The type of tissue repair, i.e. repair originating from the dental pulp, the PDL or bone or a combination, seems to be of importance in determining the risk of root resorption during the healing process.

Dental Pulp↗
PubMed1979

Cultivation of fibroblasts on human teeth. Ultrastructural observations of cells cultivated in multilayers.

The periodontal ligament in a traumatically lost tooth is often destroyed due to drying. In attempts to restore the periodontal ligament, a technique has been worked out for using gingival biopsies as an alternative cell source. A biopsy from the attached gingiva was set up for tissue cultivation. After the establishment of a pure fibroblast culture, cells were repeatedly added to the root surfaces of 12 human teeth from which the cells and the original periodontal ligament had been removed. The teeth were examined in the transmission electron microscope. The root surface of specimens from all 12 teeth was covered with a pelliclelike material arranged in a layered pattern. The cells frequently appeared in multilayers on top of the pellicle. The cells were flattened and appeared elongated in sections. Areas of close proximity between cells and the pellicular material were seen and were interpreted as adherence junctions. The possibility that these multicellular arrangements can replace the periodontal ligament in transplantation has to be further investigated.

Cell Membrane↗
PubMed1978

Periodontal and pulpal healing of monkey incisors preserved in tissue culture before replantation.

The effect of delayed replantation and tissue culture as a prevention against root resorption was examined in green Vervet monkeys (Cercopithecus aethiops). Extracted incisors were kept in tissue culture medium (Eagle's medium) for 5--14 days before replantation. The extra-alveolar dry period before tissue culture ranged from to 0 to 60 min. Incisors not subjected to tissue culture served as controls. The animals were sacrificed 8 weeks after replantation. The following histologic parameters were registered for each tooth: surface resorption, inflammatory resorption, replacement resorption (ankylosis), downgrowth of pocket epithelium, and periapical inflammatory changes. The evaluation of the pulp included the extent, recorded in mm, of pulp survival. Histometric evaluation showed that teeth immediately placed in tissue culture medium for 5--14 days showed improved periodontal healing, exhibiting significantly less inflammatory resorption than control teeth immediately replanted. Also the extent of pulp survival was significantly increased in teeth replanted after tissue culture. Teeth bench-dried for 60 min and thereafter placed in tissue culture medium also showed a significant reduction in the amount of inflammatory resorption and increased amount of pulp survival compared with control teeth replanted after the 60-min dry extra-alveolar period. Replacement resorption (ankylosis) was found in all teeth in both groups.

Animals↗
PubMed1977

Cultivation of periodontal ligament fibroblasts on extracted monkey incisor. A histologic study of three culturing methods.

Forty-two permanent incisors were extracted from green vervet monkeys and cultivated in Eagle's medium at 37 degrees C using the following culture methods: 1. teeth placed at the bottom of the culture flask; 2. teeth placed in an upright position in the culture flask and supported by an open glass cylinder; 3. teeth placed in an upright position in the culture flask and supported by a semisolid tissue culture medium. The teeth were cultured from 1 to 21 days and then examined histologically and periodontal changes registered histometrically. After 2 days, most of the periodontal membrane showed signs of extensive cell necrosis. After 3 days the first signs of proliferation of cells were seen either as clusters around existing vessels or as a surface layer on the periodontal membrane. After 7 days an almost complete over of connective tissue cells had formed on the root surface. This layer had formed on periodontal ligament with cell necrosis as well as on areas with preserved vitality of the periodontal cells. Areas on the root surface without periodontal ligaments were also covered with a cell layer. No significant change took place within the periodontal membrane with extended culture periods (2 and 3 weeks). Better results were achieved using liquid medium as compared with semisolid medium.

Animals↗
PubMed1977

The influence of traumatic intrusion of primary teeth on their permanent successors in monkeys. A macroscopic, polarized light and scanning electron microscopic study.

Primary maxillary and mandibular central incisors were experimentally intruded on 13 monkeys, in order to examine changes of the enamel in the permanent successors. To study the effect of removal of the displaced tooth, the left primary incisor was extracted 1 h after the trauma, whereas that on the right was left in the jaw. Six weeks later the animals were sacrificed. Macroscopically, circumscribed areas of opacities on labial enamel were noted. The SEM examination showed that non-affected parts of enamel had reached anatomical form, whereas inhibition studies and microradiographs demonstrated that the maturation process was far from complete. Arrest of enamel maturation was noted as corresponding to the extent of the surface opacity. In the SEM small areas displaying rupture of the surface enamel were seen. No differences were observed either macroscopically or histologically in relation to immediate removal or preservation of the intruded primary incisor.

Animals↗
PubMed1977

Effect of drying on viability of periodontal membrane.

The influence of a dry extra-alveolar period on the viability of cells in the periodontal membrane of human and monkey teeth was examined in vitro. Extracted mature teeth were allowed to dry for 0, 30, 60, 90, and 120 min. Cell viability was examined with the following methods: 1) Culturing the teeth with subsequent typsination and counting of viable cells. 2) Culturing the teeth with subsequent vital staining of the root surface with neutral red and estimation of the vital stained periodontal membrane area in percentage of the total root surface. Both methods revealed that the number of viable cells in the period declines very rapidly with an increase in drying time. After 2 h it was not possible to demonstrate cell viability using tissue cultrue technique.

Animals↗
PubMed1976

The influence of traumatic intrusion of primary teeth on their permanent successors. A radiographic and histologic study in monkeys.

Intrusion of maxillary central primary incisors was performed in 18 green vervet monkeys (Cercopithecus aethiops) with the purpose of studying early and late histologic changes in odontogenesis of permanent tooth germs and the effect of treatment of primary tooth injury. Immediate changes were studied in five monkeys where both maxillary central primary incisors were intruded. The monkeys were sacrificed 10-15 min after intrusion. The immediate changes in the permanent tooth germ consisted of contusion and displacement of the reduced enamel epithelium and slight displacement of the hard dental tissue in relation to the cervical loop, or Hertwig's epithelial root sheath. Late changes and effect of treatment were studied in 13 monkeys where both maxillary central incisors were intruded. One central primary incisor was removed 1 hour after intrusion while the other incisor was allowed to remain in the jaw. The monkeys were sacrificed 6 weeks after injury and the anterior portion of the maxilla was examined histometrically. The late changes consisted of metaplasia of the reduced enamel epithelium into a stratified squamous epithelium and, in most cases, changes in morphology of the dentin and enamel matrices. On the side where the injured tooth was preserved, significantly larger areas of epithelial metaplasia of the reduced enamel epithelium were present compared with the extraction side. Changes in morphology of the enamel matrix and dentin were found with the same frequency in the two groups, but tended to be less severe in the extraction group. It is concluded that more studies are needed on the effect of metaplasia of the reduced enamel epithelium on complete mineralization of the enamel before an optimal treatment of intruded primary incisors can be determined.

Animals↗
PubMed1976

Influence of maturation status and tooth type of permanent teeth upon electrometric and thermal pulp testing.

The threshold values of developing teeth were determined for two commonly used electrometric pulp testers (Siemens Sirotest and Bofors Pulp Tester) and a new thermal test based on carbon dioxide snow (Odontotest). The teeth examined were divided into 7 stages according to maturation status. This study showed that teeth in Stages 3-5, i.e. until completion of root formation, show an increased electrometric threshold value. The Siemens tester appeared to be equal to the Bofors tester with regard to reliability. The Odontotest was the most reliable method examined, giving a consistent positive response in all examined teeth.

Adolescent↗
PubMed1976

Influence of splints and temporary crowns upon electric and thermal pulp-testing procedures.

The influence of different splints and temporary crowns upon the reliability of electric and thermal pulp-testing procedures was examined in 10 patients with vital maxillary central incisors and 10 patients with vital maxillary central incisors and 10 patients with unilateral pulp necrosis of a central incisor. The pulp-testing procedures were: (1) Bofors Pulp Tester, (2) Siemens Sirotest, (3) heated guttapercha, (4) ice, and (5) carbon dioxide snow (Odontotest). The splints or temporary crowns were: (1) silver cap splint, (2) acrylic cap splint, (3) Hawley orthodontic plate, (4) Saur's arch bar, (5) orthodontic bands, (6) stainless steel crown, and (7) stainless steel crown with labial surface removed. A reliable electrometric pulp response could only be elicited if the pulp tester was applied directly upon enamel and preferably upon the incisal edge. In this instance metal splints or partial steel crowns applied to the tooth had no effect on the pain threshold. A false positive reaction in case of pulp necrosis was only elicited when the electrode was placed directly upon metal which contacted neighboring vital teeth. The use of ice and heated guttapercha appeared to be of limited value, due to inconsistent pulp responses. Carbon dioxide snow gave a reliable response, unless applied on the incisal edge.

Adult↗
PubMed1976

Histometric study of healing of periodontal tissues in rats after surgical injury. I. Design of a standardized surgical procedure.

A standardized surgical procedure in rats is described which allowed a histometric registration of the repair of cementum, periondontal ligaments and bone, and which eliminated the possibility of interference of pocket epithelium during the healing process. Using an extraoral incision, the lateral surface of the mandible was exposed, and a cavity was cut through the vestibular bone plate, the periodontal ligaments and into the root surface, using a specially designed handpiece and bur. This procedure was performed in 20 male Wistar rats, 9 weeks old. The observation period was 12 weeks. The systematic error, precision and interanimal variation were examined for histometric registrations of the repair of cementum, periodontal ligaments and bone. The precision of the histometric procedures was in this study found to be 5% or less for most of the different structures measured, and the estimated combined systematic errors probably less than 5% for cementum repair. The coefficient of variation in cementum repair among different rats was 24%. This variance has two components, the combined influence of systematic errors and precision of histologic and histometric procedures and the other the biological variance due to inter-animal differences. The precision and systematic errors probably do not account for more than one third of this variance, the remaining two thirds being inter-animal differences. These differences could not be completely controlled in this study in spite of the use of a controlled genetic strain of rats bred in litters of the same size under SPF conditions.

Alveolar Process↗
PubMed1976

Histometric study of healing of periodontal tissues in rats after surgical injury. II. Healing events of alveolar bone, periodontal ligaments and cementum.

A standardized surgical periodontal injury was performed in 67 male Wistar rats 9 weeks of age. An osteotomy was made with a burr through the vestibular bone plate and the periodontal ligaments and into the superficial part of the root surface of the mandibular first molar. The rats were sacrificed with observation periods ranging from 1 day to 2 years postoperatively. A histometric registration was made of the repair of alveolar bone, periodontal ligaments and cementum. Bone repair was found after 7 days and included a bony alkalosis. On the period from 7 to 14 days after surgery this ankylosis was removed by resorption process. Argyrophilic reticulin fibers were present 3 to 5 days after surgery. Precollagen fibers were found after 4 days, whereas mature collagen fibers inserting in new formed cementum, was seen after 14 days. The number of collagen fibers increased substantially until 28 days after surgery. Initial cementum repair was found after 14 days and increased substantially with increasing observation periods tending to reach the thickness of the contralateral control tooth. Based on these findings a new concept of healing of the surgically injured periodontium in rats is presented. According to this the healing occurs in three successive phases. 1. Bone repair with formation of an ankylosis. 2. Repair of the periodontal ligament including removal of the established ankylosis. 3. Repair of Cementum.

Alveolar Process↗