[How to become a dentist in Sweden during the 19th century]. / Hur blev man tandlakare i Sverige under 1800-talet?

Two hundred years ago, in 1797, a decree from the Government stated that 50 so called "operators" within dentistry must undergo examination by the Royal Medical Board. It was only non-Swedish dentists who underwent examination until 1833, when the first Swedish citizen was approved as a dentist. He had been educated in France and in Germany. After 1840, the dental curriculum was based on private courses, such as lectures in anatomy, physiology and clinical training at a private dental practice. The result of the studies was dependent on the student's own initiative. When the Swedish Dental Association was founded in 1860, an organized and systematical work started in order to establish a Dental School run by the Government in Sweden. In 1898 this goal was reached.

Preoperative radiographic evaluation of implant sites by computed tomography. Radiation dose profiles.

The purpose of the present study was to compare radiation dose profiles for one and two mm slice thicknesses typically used for preoperative computed tomographic examination of potential implant sites. A Siemens Somatom DRH CT-system was used. A single two mm slice absorbed only 29% of the integral dose and a single one mm slice, absorbed only 17% of the integral dose. This is because the radiation beam was unchanged between the two different examinations. The integral dose is therefore identical for a single one mm slice and for a single two mm slice. When 10 consecutively two mm thick slices were exposed, approximately 50% of the integral dose was absorbed within the examined region. When 20 one mm thick slices were exposed, slightly less of the integral dose was absorbed within the examined region. This difference may be explained by uncertaines in the measuring instruments. The integral dose is, with the 10 two mm thick slices, half the integral dose compared to a serie of 20 one mm slices. In spite of a well restricted beam, more than half of the integral dose is absorbed outside the examined part. Consequently, during examination the thyroid gland, the eyes lens and the pituitary gland will be exposed to some irradiation.

Comparison between panoramic and periapical radiography in the diagnosis of periapical bone lesions.

The diagnostic accuracy of panoramic and periapical radiography was compared by five oral radiologists who assessed the periapical status of 117 teeth evenly distributed throughout the jaws with a 50% probability that either an osteolytic or sclerotic lesion was present. Receiver operating characteristic (ROC) analysis demonstrated no overall significant difference between panoramic and periapical radiography. However, for sclerotic lesions and for all lesions on maxillary premolars and mandibular molars periapical radiography was significantly superior (P less than 0.001); it was also superior for osteolytic lesions in the maxilla as well as for the lesions on mandibular premolars but with a smaller significant difference (P less than 0.05).

Absorbed doses and energy imparted from radiographic examination of velopharyngeal function during speech.

Absorbed doses of radiation were measured by thermoluminescent dosimeters (TLDs) using a skull phantom during simulated cinefluorographic and videofluorographic examination of velopharyngeal function in frontal and lateral projections. Dosages to the thyroid gland, the parotid gland, the pituitary gland, and ocular lens were measured. Radiation dosage was found to be approximately 10 times less for videofluoroscopy when compared with that of cinefluoroscopy. In addition, precautionary measures were found to reduce further the exposure of radiation-sensitive tissues. Head fixation and shielding resulted in dose reduction for both video- and cinefluoroscopy. Pulsing exposure for cinefluoroscopy also reduced the dosage.

In vitro root caries progression measured by 125I absorptiometry: comparison with chemical analysis.

Radiation from a 125I source and a non-image-forming detector was used for non-destructive measurements of root caries progression. Blocks were cut parallel to the cementum surface of unexposed human roots. These blocks were then individually demineralized in under-saturated calcium phosphate solutions over an 84-hour period. In order for the in vitro root surface demineralization to be followed, the changes in transmission (delta T) through the blocks were measured, by 125I absorptiometry, eight times during the course of the experiment. Chemical analyses of the calcium output (delta Ca) from the blocks into the demineralizing solutions were also performed, and the rate of demineralization (Vdem) was calculated from these values. The precision of 125I absorptiometry was calculated from 176 duplicate transmission measurements, and the coefficient of variation was found to be 0.20%. The correlation coefficient between delta T and total delta Ca for each of 22 cementum/dentin blocks ranged between r = 0.934 and r = 0.998. The progression of root hard-tissue lesions observed by these two methods and by the calculated Vdem was found to be proportional to the square and cubic roots of time. The study shows that 125I absorptiometry can be used for continuous non-destructive measurements of root hard-tissue demineralization in vitro.

Detectability of artificial marginal bone lesions as a function of lesion depth. A comparison between subtraction radiography and conventional radiographic technique.

Subtraction of serially obtained standardized radiographs of the marginal periodontal bone offers possibilities for an increased detectability of small bony changes compared to conventional radiography. In this study, the depth of artificially induced bone lesions in the alveolar crest was assessed by means of 125I absorptiometry. The results served as reference values when a series of radiographs containing lesions of various depths was interpreted by 10 examiners. Both conventional radiographs and subtraction images made from the conventional radiographs after digitization were interpreted. The ROC-curve technique was used to evaluate the two techniques. A close to perfect accuracy was found at a lesion depth corresponding to 0.49 mm of compact bone using the subtraction technique. A similar degree of accuracy was not reached for the conventional technique until the lesions were approximately 3 times deeper.

Collective dose to the Swedish population from intraoral radiography.

In 1984 the Swedish National Institute of Radiation Protection (SSI) undertook an investigation (KAST) of 400 randomly selected dental offices to check the extent to which the new rules and recommendations concerning radiation protection (SSI 1978, 1980) were applied. Data for calculation of the energy imparted per bitewing examination of an adult were available. The information obtained was utilized for estimating the collective dose in Sweden from intraoral radiography. The mean value of the energy imparted from an ordinary bitewing examination was 0.48 mJ. The quotient between the sum of all imparted energy during 1984, 5,519 J, and the number of inhabitants in that year was 0.66 mJ. This corresponds to 1.5 ordinary bitewing examinations per individual in Sweden. The collective effective dose equivalent is 79 manSv after transformation from the total energy imparted. The average energy imparted from the annual natural irradiation in Sweden is 100 mJ, with variations between 35 and 350 mJ, giving totally to the population 830,000 J. The dose contribution from intraoral radiography is thus considered of minor importance when taking into account the variations of the natural irradiation as well as the benefit of the diagnostic gain in dentistry and the enhancement of public dental health.

Effective dose equivalent from intraoral radiography.

By means of available data of mean organ doses from intraoral radiography the effective dose equivalent from dental radiography was calculated. The dose values used correspond to 65 kVp, 0.2 m FSD and 20 exposures with film in speed group D. The effective dose equivalent was calculated for circular (55 mm diameter) as well as rectangular collimator (35 mm X 44 mm) and amounted to 0.23 and 0.14 mSv, respectively. In comparison with the annual natural radiation the corresponding time would be 6 and 3 weeks, respectively. Following the definition of the effective dose equivalent by ICRP (1977) it was found that the most radiosensitive organs contributed 20-25 per cent of the total effective dose equivalent. The organs with the highest weighting factors thus received very small or negligible dose equivalents. The calculation necessitates a detailed knowledge of the absorbed doses and the weighting factors, which made the application for dental radiography somewhat uncertain. The concept of energy imparted might be a more direct measure to compare the risk from different examinations in dental radiography.

Proximal alveolar bone loss in a longitudinal radiographic investigation. IV. Smoking and some other factors influencing the progress in individuals with at least 20 remaining teeth.

In Sweden people in all age groups now have more remaining teeth than previously. An investigation has been made to identify some predictors of alveolar bone loss in a 10-year period in subjects with at least 20 remaining teeth. The material consisted of 349 individuals, examined radiographically, clinically, and by interview in 1970 and in 1980. These subjects, born in 1904-1952, constituted a subgroup, with regard to remaining teeth, of an unselected sample of the population of the old county of Stockholm. In the unselected sample statistically significant predictors of alveolar bone loss found in a stepwise multiple regression analysis were alveolar bone loss in 1970, age, number of lost teeth, and Russell's Periodontal Index (PI). In the subgroup the predictors were in the order Russell's PI and smoking. The prediction values (R2) of further variables were marginal. The analyses showed that there was an interaction between PI and smoking, implying that the effect of smoking on alveolar bone loss was increased in individuals with high PI values. Furthermore, a tendency was found for a dose-response effect of tobacco consumption. This tendency almost disappeared when controlling for PI.

Proximal alveolar bone loss in a longitudinal radiographic investigation. III. Some predictors with a possible influence on the progress in an unselected material.

The difference in proximal alveolar bone height between 1970 and 1980, the 'ABD index', has been measured longitudinally in radiographs from an unselected material. The group constitutes 406 individuals born in 1904-1952 in the county of Stockholm. Thirteen of 18 predictors determined in 1970 were significantly related to the ABD index in the simple correlation analyses. The predictor 'the alveolar bone loss 1970' ('ABL index 1970') had the strongest correlation to the ABD index. In the stepwise multiple regression analysis the predictor ABL index 1970 and three other predictors reached significant levels. These were age, number of lost teeth, and Russell's Periodontal Index.

Maxillary expansion of unilateral cross-bite in preschool children.

The influence of a low force appliance on the maxilla in correction of unilateral cross-bite was studied clinically and radiographically in 29 preschool children following a standardized treatment schedule. Four weeks' expansion was followed by a 4-wk retention and a 12-wk postretention period. Inter- and intraobserver evaluations of the reliability of the measurements on radiographs were performed. In all children but one the cross-bites were corrected after 4 wk of expansion. The mean maxillary expansion was 3.3 mm in the second molar and 1.3 mm in the canine region, but decreased to 1.5 mm and 1.0 mm, respectively, at the end of the postretention period without relapse of the corrected malocclusion. No significant remaining orthopedic effects could be registered on radiographs by this low force appliance used. The modified quad helix appliance was found to be suitable for correction of unilateral cross-bite in the primary dentition and was well tolerated by the children.

Proximal alveolar bone loss in a longitudinal radiographic investigation. II. A 10-year follow-up study of an epidemiologic material.

Four hundred and six individuals from an unselected sample from the County of Stockholm aged 18-65 years in 1970 were examined radiographically in 1970 and 1980. The differences in proximal alveolar bone height were recorded, attention being paid to the divergences in projection between the two investigations. The mean of the alveolar bone difference was 5.5% of the mean root length, which corresponds to an average annual bone loss of 0.09 mm. Ninety per cent of the individuals had a difference in alveolar bone height of less than 10% of the root length--that is, an average bone loss of 1.6 mm or less during 10 years. By linear regression analysis it was shown that the difference in alveolar bone height is a function of the initial bone loss; that is, the greater the initial bone loss, the greater the alveolar bone loss during the 10-year period. The result of the regression analysis may facilitate predictions of alveolar bone loss.

Proximal alveolar bone loss in a longitudinal radiographic investigation. I. Methods of measurement and partial recording.

A longitudinal radiographic investigation was made of the progression of the proximal alveolar bone loss over a 10-year period (1970-1980). The material was unselected and consisted of 669 individuals in the county of Stockholm. Sixty-one individuals were randomly selected for evaluation of a recording system using alternative methods of measurement, and 90% of the measurement sites could then be assessed. The correlations between some of the methods were high, such as between measurement of alveolar bone height and root length and between alveolar bone height and tooth length. To reduce the number of measurements, a partial recording was made, giving a high correlation coefficient between the partial recording and total recording. When five measurement sites (12 m, 11 m, 33 d, 31 d, 41 m) were were used, the correlation coefficient was 0.96, and a slight increase of the coefficient was obtained when using additional sites.

Energy imparted from intraoral radiography.

During the recent decade the equipment for dental radiography in Sweden has been standardized by the Swedish National Institute for Radiation Protection. The aim of this study was to experimentally determine the energy imparted to a phantom from a full survey with 20 intraoral films as well as from a single bitewing projection, using this standardized technique. Thermoluminescence dosimeters in predetermined volume elements of an anatomically formed tissue equivalent Alderson-phantom were irradiated (65 k Vp) using both a rectangular and a circular collimator of 0.2 m FSD. Exposure times fitted to film in speed group D were used. The energy imparted was determined from the integrated absorbed doses in the volume elements as well as calculated using published depth dose data. The energy imparted was found to be 9.6 mJ (circular collimator) and 5.9 mJ (rectangular collimator) for the full survey. For the single bitewing exposure the energy imparted was 0.42 mJ (circular collimator) and 0.29 mJ (rectangular collimator). With the rectangular collimator and film in speed group D the energy imparted from a full survey will correspond approximately to two weeks of environmental irradiation. With more sensitive film in speed group E the energy imparted would further be reduced by 40 per cent with retained diagnostic information.

Absorbed doses from intraoral radiography with special emphasis on collimator dimensions.

Thermoluminescence dosimeters were used in a phantom head and on patients to measure the absorbed dose to organs of special interest from full surveys with intraoral films (20 exposures) and single bitewing exposures. Two x-ray machines were used, operating at 65 kVp. The apertures of the circular tube collimators had diameters of 55 mm and 48 mm. Rectangular (35 mm X 44 mm) tube collimators were also used. The distance from the x-ray focus to the open end of the collimators (FSD) was 0.20 and 0.35 m. Exposure values for Kodak Ultra-Speed film (speed group D) were used. The maximum skin dose measured from the full surveys decreased by 25 per cent on changing from the circular to the rectangular apertures. Using 0.35 m FSD and rectangular collimator the maximum skin dose was 13 mGy. The absorbed doses to the salivary glands and the thyroid gland were significantly reduced on changing from circular to rectangular apertures. The doses in the central part of the parotid and the thyroid glands were then 0.5 and 0.12 mGy, respectively, from a full survey with 20 intraoral films. With a leaded shield the thyroid dose was reduced to 0.05 mGy. All dose values could be further reduced by 40 per cent by using Kodak Ektaspeed film (speed group E).

Alveolar bone mass using 125I absorptiometry.

Small changes in alveolar bone mass are very difficult to detect using radiograms. A method is described for registering minute changes in bone mass in restricted parts of the jaw. The method is based on the use of collimated monenergetic radiation from 125I and replacement of the roentgen film by a non-image forming detector. As the apparatus also can be used for measuring the object thickness, the attenuation formula can be used for calculating the alveolar bone mass. The radiation dose can be kept an extremely low level and the reproducibility of the measurements is high. The technique therefore may be used for long-term studies of changes in alveolar bone mass. The alveolar bone mass responds rapidly to changes in the neighboring tissues. The reaction following gingivectomy or dental trauma is characterized by a significant loss of alveolar bone mass initially. After 4 weeks an increase in the alveolar bone mass is noted and found to continue during the subsequent months.