Larry L. Laster

Biochemical mediators of the effects of mechanical forces and electric currents on mineralized tissues

SummaryCyclic nucleotides (cAMP and cGMP) and prostaglandin E (PGE) have been implicated as possible mediators of the effects of external stimuli on bone cells. The objective of this study was to determine changes in relative levels of these substances in mineralized tissue cells in response to mechanical and electrical stimuli, by the use of a combined immunohistochemical-microphotometric procedure. Canine teeth of eight 10–12 month-old female cats were tipped distally with 80 g force for either 1 h or 14 days. After 1 h, a slight elevation of staining intensity in alveolar bone osteoblasts and periodontal ligament (PDL) cells was observed at sites of tension and compression. After 14 days of treatment, this effect was markedly increased. Fifteen female cats, 10–12 months old, received electric stimulation (20 µ amperes d.c.) to the gingiva of 1 maxillary canine for 1, 5, 15, 30, or 60 min. At the cathode, significant increases of staining intensity in periosteal osteoblasts for cAMP, cGMP, and PGE were found at 15 and 60 min. At the anode, a significant rise in the staining intensity of these cells for PGE was seen at 15 min; at 60 min, cGMP and PGE, but not cAMP, were elevated. These results demonstrate the usefulness of the immunohistochemical technique in detecting relative changes in mineralized tissue cell content of cyclic nucleotides and prostaglandins in response to local application of physical stimuli of short and long duration.

Cephalometric superimposition on the cranial base: A review and a comparison of four methods

Spatial change in the jaws of growing persons is often evaluated by superimposing cephalometric tracings made at different points in time. Methods of superimposition vary according to structures used as references within the skull. This study compares four different superimposition methods. The sample consisted of 26 patients (13 boys, 13 girls) treated for Class II, Division 1 malocclusions with extraction of the four first premolars. Tracings of pretreatment (average age for boys, 12.5 years; for girls, 12.2 years) and posttreatment (average age for boys, 15.4 years; for girls, 14.9 years) cephalograms were superimposed according to the following methods: (1) best fit of anterior cranial base anatomy, (2) superimposition on SN line, registered at S, (3) superimposition on registration point R with Bolton-nasion planes parallel, and (4) superimposition on basion-nasion (Ricketts), registered at point CC (4) and point N (4a). Differences in amount of change among the superimposition methods were assessed independently for each of the following landmarks: PNS, ANS, A, B, Pog, Gon. On each patient and for each landmark, ten distances--the paired differences of five posttreatment positions obtained by methods 1, 2, 3, 4, and 4a--were evaluated. Two methods were compared at a time. A t test examined the average difference for each comparison. Because all differences between all paired methods were significant (P less than 0.01), t tests were then viewed under the hypothesis that a difference less than or equal to 1 mm was insignificant clinically. Clinically-statistically significant differences were found only for boys and for the total sample between methods 4a and each of methods 1, 2, and 3. As method 4a is advocated to assess changes of point A (Ricketts), this method gives, for the same person, an interpretation of anterior maxillary change in position different from the other methods. Conclusions about facial changes may be made only in reference to the superimposition method.

Histopathologic and dietary prognostic factors for canine mammary carcinoma

SummaryHistologic and dietary prognostic factors for survival following naturally occurring breast cancer were studied for 145 pet dogs. Information was collected from the dogs owner and veterinarian regarding medical and reproductive history, nutritional status, treatment, tumor recurrence, and length of survival. The usual intake of all dog and table foods consumed 1 year prior to diagnosis was obtained using a validated quantitative food frequency questionnaire. A histologic malignancy score was derived based on 7 histopathologic criteria. The mean age of the dogs was 10.4 ± 2.5 years; 37% had been ovariohysterectomized prior to diagnosis. Product-limit estimates of survival indicated that 6 factors, namely body conformation 1 year prior to diagnosis (p = 0.03), histologic tumor type (p = 0.004), histologic malignancy score (p = 0.02), histologic invasion (p = 0.002), tumor recurrence (p<0.0001), and completeness of surgery (p = 0.01) were of prognostic significance. In addition, when dogs were characterized by the percent of total calories they derived from fat and protein, the median survival time for dogs in the low fat group (<39%) with protein >27%, 23–27%, and <23% was 3 years, 1.2 years, and 6 months, respectively (p = 0.008). For dogs in the high fat group (≥39%), there was no difference in survival for the different intake levels of dietary protein (p = 0.84). When these data were fitted to a proportional hazards model, recurrence, histologic score, tumor type, percent of calories derived from protein, fat group, and a protein-fat group interaction term were statistically significant. Predicted 1 year survival for dogs on a low fat diet with 15%, 25%, and 35% of total calories derived from protein was 17%, 69%, and 93%, respectively.

Biochemical aspects of orthodontic tooth movement I. Cyclic nucleotide and prostaglandin concentrations in tissues surrounding orthodontically treated teeth in vivo

The objective of this study was to extract and assay cyclic nucleotides and prostaglandins from tissues surrounding orthodontically treated canines in cats. Seven groups of three to five female cats were treated by 80 g tipping force to one maxillary canine for 0 to 28 days. Tissue samples were removed from sites of compression and tension around treated teeth, and from the corresponding control sites. Cyclic nucleotides and prostaglandins were simultaneously extracted by a solvent system at 0 to -5 degrees C. A portion of the aqueous fraction was used for cAMP assay by a binding protein method; cGMP was purified by column chromatography and measured by radioimmunoassay. The solvent fraction was dried, reconstituted with assay buffer, and each of the prostaglandins measured by radioimmunoassay. Analysis of variance showed no significant differences between summary control and treated sites at each of the time periods studied. However, when interactions at secondary and tertiary levels were considered (such as tension and compression, position [apical-gingival sites] of tissue sample, and jaws), significant differences were found in PGE, cAMP, and PGF2 alpha values. These results demonstrate that alterations in the levels of each of these substances in tissues surrounding teeth may be brought about by long-term applications of orthodontic force in vivo. The method of tissue sampling, however, does not permit measurement of the levels of these substances in target cells alone, thus diluting the acute response that may have occurred in these cells.

The effects of acids, alkalies, and chelating agents on dentine permeability.

Abstract The ability of eight different solutions to increase or decrease dentine permeability was evaluated in extracted human two-rooted maxillary premolars. Thirteen teeth were used in each group, making a total of 104 teeth. The Dentine Permeability Index18 was used to calculate the depth of penetration of a 2 per cent methylene blue dye into the dentinal tubules. For statistical analysis and subsequent comparisons, only ten teeth were used from each group (a total of eighty teeth). It was found that R-C Prep alternating with 5 per cent sodium hypochlorite increased dentine permeability in the apical and middle thirds of the root more than any other solution. Concentrated sulfuric acid almost eliminated dentine permeability.

Changes of arch width in the early treatment of Class II, division 1 malocclusions.

Changes in arch width during the early correction of Class II, Division 1 malocclusions with either the Fränkel functional appliance or headgear are compared in an ongoing prospective randomized clinical trial. The data were collected from 43 children, ages 7.5 to 12.85 years, who met strict dental and cephalometric criteria for inclusion in the study. They were assigned at random to treatment with either a headgear (n = 21) or a Fränkel appliance (n = 22). Occlusal measurements included the maxillary and mandibular intermolar distances (buccal and palatal/lingual) and intercanine distances. Measurements (millimeters) were performed on casts taken every 2 months, with digital calipers accurate to 0.01 mm. Four months after the initiation of treatment, the mean maxillary intermolar distance was larger in the Fränkel group (palatal: 1.58, SE: 0.22; buccal: 1.58, SE: 0.20) than the headgear group (palatal: -0.39, SE: 0.21; buccal: 0.26, SE: 0.23), and the difference was statistically significant (palatal: p < 0.0001 and buccal: p = 0.0001). The mean maxillary intercanine distance increased more with the headgear (1.62, SE: 0.19) than the Fränkel appliance (0.62, SE: 0.23) p = 0.003. As treatment progressed, the average intermolar distance in the headgear group increased, but was still higher in the Fränkel group by more than 1 mm. The intercanine distance remained larger in the headgear group. The mandibular intermolar and intercanine distances were higher after Fränkel therapy than with headgear.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring growth during orthodontic treatment

The relationship between somatic growth and orthodontic treatment has been limited to the evaluation of body height and skeletal age relative to craniofacial development. The aim of this study was to evaluate the correlation of anthropometric and biochemical measures of general growth with facial and occlusal changes during the early treatment of Class II Division 1 malocclusion. Findings are reported from 46 children, ages 7.20 to 12.85 years (skeletal ages, 5.75 to 12.75 years), who are enrolled in a prospective clinical trial. Body and knee heights were measured monthly, with a Holtain stadiometer and a Knee Height Measuring Device, respectively. Every three months, serum levels were measured of the hormone dehydroepiandrosterone sulfate (DHEAS), an androgen associated with growth in midchildhood, and osteocalcin, an indicator of bone turnover. Significant correlations existed between knee height and various occlusal measurements, but mandibular length was not significantly correlated with knee height and DHEAS levels. Knee height correlated significantly (P < .05) with DHEAS and osteocalcin only in 46% and 37% of the children, respectively. The results indicate that the evaluated biochemical measures, at the time intervals considered, may not increase the accuracy of growth depiction by physical measures alone (height and skeletal maturation).

Scoring the full extent of periodontal disease in the dog: development of a total mouth periodontal score (TMPS) system.

The development of a total mouth periodontal scoring system is described. This system uses methods to score the full extent of gingivitis and periodontitis of all tooth surfaces, weighted by size of teeth, and adjusted by size of dog.

Identification of condylar anatomy affects the evaluation of mandibular growth: Guidelines for accurate reporting and research

Mandibular length is measured on cephalographs to depict changes during growth and after orthodontic treatment, and is often defined between condylion (Co, most posterior superior point on the condylar outline) and pogonion (Pog, most anterior point on the chin). The aim of this study was to assess the accuracy of identifying condylar anatomy, thus the validity of using Co-Pog to evaluate mandibular growth. The sample included 34 children from a prospective study on the early treatment of distoclusions. Two lateral head films were taken of each child, the first with the mouth closed (MC), the second with the mouth open (MO). Three examiners, two orthodontists (U.H. and K.H.) and a dental radiologist (R.B.), rated the condyle as identifiable, nonidentifiable, and interpreted. The rating was applied to the left (L) and right (R) condyles, or to only one outline (O) when the R and L structures appeared superimposed and were not distinguished separately. Besides Co-Pog, the orthodontists traced sella-nasion (SN) and incisor tip-menton (I-Me) to evaluate variability in measurements that do not include Co. One operator (J.G.) measured all distances. Agreement among the three examiners was best in rating the MO radiographs (50%): 4.1% identifiable, 5.9% nonidentifiable or interpreted; in the MC films, they agreed in 32.3% of the cases, but only one of the ratings was identifiable (2.9%). The highest agreement was in identifying the left condyle on the MO film (35.3%). Intraclass correlation coefficients for CO-Pog ranged from r = 0.73 (L side) to r = 0.92 (O) for one orthodontist, and for the other from r = 0.76 (O) to r = 0.85 (L). Both orthodontists had high correlations for SN and I-Me between MC and MO (0.94 < r < 0.98). The variability between examiners in recognizing condylar anatomy, particularly on radiographs taken with the mouth closed, suggests that the identification of condylar anatomy must be rated in studies of mandibular growth. Researchers measuring mandibular length in investigations of mandibular growth after orthodontic therapy should differentiate between cases where the condyle is readily identified, and those where condylar anatomy is interpreted.

Validation of use of subsets of teeth when applying the total mouth periodontal score (TMPS) system in dogs.

A total mouth periodontal score (TMPS) system in dogs has been described previously. Use of buccal and palatal/lingual surfaces of all teeth requires observation and recording of 120 gingivitis scores and 120 periodontitis scores. Although the result is a reliable, repeatable assessment of the extent of periodontal disease in the mouth, observing and recording 240 data points is time-consuming. Using data from a previously reported study of periodontal disease in dogs, correlation analysis was used to determine whether use of any of seven different subsets of teeth can generate TMPS subset gingivitis and periodontitis scores that are highly correlated with TMPS all-site, all-teeth scores. Overall, gingivitis scores were less highly correlated than periodontitis scores. The minimal tooth set with a significant intra-class correlation (≥ 0.9 of means of right and left sides) for both gingivitis scores and attachment loss measurements consisted of the buccal surface of the maxillary third incisor, canine, third premolar, fourth premolar, and first molar teeth; and, the mandibular canine, third premolar, fourth premolar, and first molar teeth on one side (9 teeth, 15 root sites). Use of this subset of teeth, which reduces the number of data points per dog from 240 to 30 for gingivitis and periodontitis at each scoring episode, is recommended when calculating the gingivitis and periodontitis scores using the TMPS system.