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The holographic storage of study models
Volume 87 Number 4
Reviews and abstracts 349
Despite the modest price of the book, paper quality is satisfactory and most illustrations are clear and understandable. Unfortunately, some of the tissue views are less than desirable and would have been improved significantly by color. Let us hope that the next edition will include a few color plates; these would greatly enhance the appeal. T. M. Graber
Behandslungsziel Beim Deckbiss (Management of Deep Bite Problems) Rolf Diernberger Fortschr.
Kieferorthop.
45: 297,
I984
This article is directed primarily to Class II, Division 2 malocclusions. Malocclusions of this type are characterized by a very deep overbite and by the lingual inclination of the maxillary incisors with the actual labial position of the apices of the teeth. The author discusses the genetic predisposition of these cases and the periodontal and gnathologic implications. He then describes the therapy that he believes to be most effective, considering the predominance of morphogenetic pattern and the strong relapse tendencies usually encountered. The conventional method of tipping the crowns labially and creating a Class II, Division 1 malocclusion is questioned. This method tends to perpetuate the labial apical position of the maxillary anterior teeth. It is important instead to torque the lingually inclined incisors in their original position, so as not to alter the muscle balance. Depressive forces are needed while lingual torque is being applied. Early assault on the torque problem is more likely to be successful. To maintain facial and muscle balance, selected extractions of maxillary premolars are often necessary. T. M. Graber
The Holographic Storage of Study Models P. J. Keatlng, FL A. Parker, D. Keane, and L. Wright Br. J. Orthod.
II:
19-25,
1984
As most orthodontists know from sad experience, the storage of plaster study models poses major logistic problems. As in Dukat’s “Sorcerer’s Apprentice,” the models keep coming and soon fill all available space. Pulling out models for each case, restoring them, lengthy preparation, breakage, and shipping on transfer
are just a few of the concerns. Legally, the orthodontist is required to keep the records for a minimum of 10 years (7 years in Britain), so disposal when the case is completed is out of the question. The use of holographic films to record three-dimensional, measurable images of study models may well provide a viable substitute. Based on holography (the wavefront reconstruction process invented by the Nobel prize laureate Gabor), the actual roots of the process go as far back as Grimaldi in 1660. The development of the laser beam made holography practical. The authors describe the principles of holography and then explain how to record a holograph by the single-beam reflection method developed by Soviet scientist Yuri Denisyuk in 1962. The system described is in operation in the Medicai Physics Department of the Royal County Hospital in Brighton, England, designed by two of the authors. A helium-neon laser beam of 25 mW power irradiates a holographic film of high resolution for about 2 seconds. The film is held between two optical-quality glass plates of 2.5 mm thickness, which keeps the film flat and firm. The orthodontic study models are placed beneath these glass plates, as close as possible without touching. No vibrations are allowed. This is so critical that the glass plates are allowed to set for up to 3 minutes after placement of the film prior to exposure. After processing, as described by the authors, image reconstruction is analyzed. Because the holograms are of the white-light reflection type, it is not necessary to use a laser beam for reconstruction. The advantages from a cost point of view are obvious. A pinpoint white halogen light is utilized that provides images sharp enough for clinical purposes. The virtual image obtained by reconstruction of the transmission’ hologram (that is, the image that appears where the model was) can be measured accurately in three dimensions. Conditions needed to achieve this are described. A preliminary investigation has been conducted to determine the accuracy of the virtual images. Twelve different dimensions, representing most of the normal requirements, were measured ten times each on the model and the hologram; half the measurements were made a month later. Statistical analysis shows that the random errors were clinically insignificant. They were only slightly greater than 0.33 mm at maximum. Only two dimensions differed by more than. this amount-intercanine width (0.39 mm) and model depth from the left canine cusp to the model base (0.64 mm). It is possible that the intercanine error occurred not only in the measurement but also in the definition of the
350 Reviews and abstracts
Am. J. Orthod. April 1985
same points on the model and on the hologram. The model depth dimension probably suffered from the same conditions. It was concluded that, while the angle of perspective and the depth of field are partially limited, no other method (excluding study models) gives the three-dimensionality available with this method. From a clinical point of view, one holographic film containing 5 views (maxillary and mandibular occlusal and frontal, left, and right three-quarter face views in occlusion) will suffice. The listing of the eight most obvious advantages of holography makes it abundantly clear that, in the matter of storage, this is a viable alternative to the time-honored study casts. T. M. Graber
Research abstract Tissue Reactions FolIoyAng Different Orthodontic For-s in Rat and in Man Eva Lilia Karolinsko Institute, Stockholm, 1983
This doctoral dissertation describes the reactions leading to invasion of phagocytes in the pressure zone. The five aims of the study were as follows: 1. To develop a method for experimental tooth movement in the rat that allows application of welldefined orthodontic forces, as well as analysis of tooth movement and tissue reactions with minimal postexperimental changes 2. To use the method to correlate the magnitude of orthodontic force to the compression of the periodontal membrane (PDM) and to some aspects of tissue injury 3. To compare findings in rat and man regarding the development of the hyaline zone and the phagocytic activity on the pressure zone 4. To study some plasma proteins as indicators of vascular injuries in the pressure zone of man 5. To study the phagocytic activity around the hyaline zone with special reference to the degradation of necrotic tissue after treatment times of up to 1 month in man
The experimental material consisted of the upper jaws from young adult female Sprague-Dawley rats. The human material was made up of premolar material of girls and boys aged 12 to 17 years with Class II malocclusion and crowding. Conventional fixed orthodontic appliances were used. Morphometric, morphologic, enzymatic, and hematologic parameters were examined by techniques such as morphometry, scanning electron microscopy, enzyme histochemistry, and immunohistochemistry. Summarizing the results, the developed methods characterized the position of orthodontically treated teeth within their alveoli. The compression of the PDM followed a logarithmic function when plotted against the magnitude of force. Two force ranges, designated high and low, were defined, based on the morphometric study. High forces were shown to cause hyalinization of the pressure zones, although this was not seen following low forces. Both forces seemed to provoke invasion of phagocytes into the PDM. Tissue reactions were then studied with special reference to vascular reactions and to me origin and activity of the invading phagocytes. High orthodontic forces produced extravasation of IgG and fibrinogen and the formation of a coagulum. Plasma proteins probably contributed to the hyaline appearance of the pressure zones. The impaired blood flow most likely led to ischemia, resulting in necrotic areas devoid of enzyme activity. The lack of lysosomal enzymes may be one reason for degradation of the hyaline zone from the periphery. The phagocytes that degraded the hyaline zone differed morphologically and with respect to some hydrolytic enzymes from phagocytes degrading alveolar bone. On the basis of these differences, it was concluded that cells from the monoc yte-macrophage line degraded the hyaline zone. The cells penetrating the hyaline zone in man were associated with an intense activity of prostaglandin synthetase, the result of which probably stimulated and maintained the phagocytic activity in the area. T. M. Graber
Reviews and abstracts 349
Despite the modest price of the book, paper quality is satisfactory and most illustrations are clear and understandable. Unfortunately, some of the tissue views are less than desirable and would have been improved significantly by color. Let us hope that the next edition will include a few color plates; these would greatly enhance the appeal. T. M. Graber
Behandslungsziel Beim Deckbiss (Management of Deep Bite Problems) Rolf Diernberger Fortschr.
Kieferorthop.
45: 297,
I984
This article is directed primarily to Class II, Division 2 malocclusions. Malocclusions of this type are characterized by a very deep overbite and by the lingual inclination of the maxillary incisors with the actual labial position of the apices of the teeth. The author discusses the genetic predisposition of these cases and the periodontal and gnathologic implications. He then describes the therapy that he believes to be most effective, considering the predominance of morphogenetic pattern and the strong relapse tendencies usually encountered. The conventional method of tipping the crowns labially and creating a Class II, Division 1 malocclusion is questioned. This method tends to perpetuate the labial apical position of the maxillary anterior teeth. It is important instead to torque the lingually inclined incisors in their original position, so as not to alter the muscle balance. Depressive forces are needed while lingual torque is being applied. Early assault on the torque problem is more likely to be successful. To maintain facial and muscle balance, selected extractions of maxillary premolars are often necessary. T. M. Graber
The Holographic Storage of Study Models P. J. Keatlng, FL A. Parker, D. Keane, and L. Wright Br. J. Orthod.
II:
19-25,
1984
As most orthodontists know from sad experience, the storage of plaster study models poses major logistic problems. As in Dukat’s “Sorcerer’s Apprentice,” the models keep coming and soon fill all available space. Pulling out models for each case, restoring them, lengthy preparation, breakage, and shipping on transfer
are just a few of the concerns. Legally, the orthodontist is required to keep the records for a minimum of 10 years (7 years in Britain), so disposal when the case is completed is out of the question. The use of holographic films to record three-dimensional, measurable images of study models may well provide a viable substitute. Based on holography (the wavefront reconstruction process invented by the Nobel prize laureate Gabor), the actual roots of the process go as far back as Grimaldi in 1660. The development of the laser beam made holography practical. The authors describe the principles of holography and then explain how to record a holograph by the single-beam reflection method developed by Soviet scientist Yuri Denisyuk in 1962. The system described is in operation in the Medicai Physics Department of the Royal County Hospital in Brighton, England, designed by two of the authors. A helium-neon laser beam of 25 mW power irradiates a holographic film of high resolution for about 2 seconds. The film is held between two optical-quality glass plates of 2.5 mm thickness, which keeps the film flat and firm. The orthodontic study models are placed beneath these glass plates, as close as possible without touching. No vibrations are allowed. This is so critical that the glass plates are allowed to set for up to 3 minutes after placement of the film prior to exposure. After processing, as described by the authors, image reconstruction is analyzed. Because the holograms are of the white-light reflection type, it is not necessary to use a laser beam for reconstruction. The advantages from a cost point of view are obvious. A pinpoint white halogen light is utilized that provides images sharp enough for clinical purposes. The virtual image obtained by reconstruction of the transmission’ hologram (that is, the image that appears where the model was) can be measured accurately in three dimensions. Conditions needed to achieve this are described. A preliminary investigation has been conducted to determine the accuracy of the virtual images. Twelve different dimensions, representing most of the normal requirements, were measured ten times each on the model and the hologram; half the measurements were made a month later. Statistical analysis shows that the random errors were clinically insignificant. They were only slightly greater than 0.33 mm at maximum. Only two dimensions differed by more than. this amount-intercanine width (0.39 mm) and model depth from the left canine cusp to the model base (0.64 mm). It is possible that the intercanine error occurred not only in the measurement but also in the definition of the
350 Reviews and abstracts
Am. J. Orthod. April 1985
same points on the model and on the hologram. The model depth dimension probably suffered from the same conditions. It was concluded that, while the angle of perspective and the depth of field are partially limited, no other method (excluding study models) gives the three-dimensionality available with this method. From a clinical point of view, one holographic film containing 5 views (maxillary and mandibular occlusal and frontal, left, and right three-quarter face views in occlusion) will suffice. The listing of the eight most obvious advantages of holography makes it abundantly clear that, in the matter of storage, this is a viable alternative to the time-honored study casts. T. M. Graber
Research abstract Tissue Reactions FolIoyAng Different Orthodontic For-s in Rat and in Man Eva Lilia Karolinsko Institute, Stockholm, 1983
This doctoral dissertation describes the reactions leading to invasion of phagocytes in the pressure zone. The five aims of the study were as follows: 1. To develop a method for experimental tooth movement in the rat that allows application of welldefined orthodontic forces, as well as analysis of tooth movement and tissue reactions with minimal postexperimental changes 2. To use the method to correlate the magnitude of orthodontic force to the compression of the periodontal membrane (PDM) and to some aspects of tissue injury 3. To compare findings in rat and man regarding the development of the hyaline zone and the phagocytic activity on the pressure zone 4. To study some plasma proteins as indicators of vascular injuries in the pressure zone of man 5. To study the phagocytic activity around the hyaline zone with special reference to the degradation of necrotic tissue after treatment times of up to 1 month in man
The experimental material consisted of the upper jaws from young adult female Sprague-Dawley rats. The human material was made up of premolar material of girls and boys aged 12 to 17 years with Class II malocclusion and crowding. Conventional fixed orthodontic appliances were used. Morphometric, morphologic, enzymatic, and hematologic parameters were examined by techniques such as morphometry, scanning electron microscopy, enzyme histochemistry, and immunohistochemistry. Summarizing the results, the developed methods characterized the position of orthodontically treated teeth within their alveoli. The compression of the PDM followed a logarithmic function when plotted against the magnitude of force. Two force ranges, designated high and low, were defined, based on the morphometric study. High forces were shown to cause hyalinization of the pressure zones, although this was not seen following low forces. Both forces seemed to provoke invasion of phagocytes into the PDM. Tissue reactions were then studied with special reference to vascular reactions and to me origin and activity of the invading phagocytes. High orthodontic forces produced extravasation of IgG and fibrinogen and the formation of a coagulum. Plasma proteins probably contributed to the hyaline appearance of the pressure zones. The impaired blood flow most likely led to ischemia, resulting in necrotic areas devoid of enzyme activity. The lack of lysosomal enzymes may be one reason for degradation of the hyaline zone from the periphery. The phagocytes that degraded the hyaline zone differed morphologically and with respect to some hydrolytic enzymes from phagocytes degrading alveolar bone. On the basis of these differences, it was concluded that cells from the monoc yte-macrophage line degraded the hyaline zone. The cells penetrating the hyaline zone in man were associated with an intense activity of prostaglandin synthetase, the result of which probably stimulated and maintained the phagocytic activity in the area. T. M. Graber