Larry L Laster | University of Pennsylvania (original) (raw)

Papers by Larry L Laster

Statistics in Medicine, 2006

The 'at least as good as' criterion, introduced by Laster and Johnson for a continuous response v... more The 'at least as good as' criterion, introduced by Laster and Johnson for a continuous response variate, is developed here for applications with dichotomous data. This approach is adaptive in nature, as the margin of non-inferiority is not taken as a ÿxed di erence; it varies as a function of the positive control response. When the non-inferiority margin is referenced as a high fraction of the positive control response, the procedure is seen to be uniformly more e cient than the ÿxed margin approach, yielding smaller sample sizes when sizing non-inferiority trials under identically speciÿed conditions. Extending this method to proportions is straightforward, but highlights special considerations in the design of non-inferiority trials versus superiority trials, including potential trade-o s in statistical e ciency and interpretability. Copyright ? 2005 John Wiley & Sons, Ltd.

Journal of Veterinary Dentistry, 1996

In 1350 client-owned dogs in North America, the association of calculus, gingival inflammation an... more In 1350 client-owned dogs in North America, the association of calculus, gingival inflammation and periodontal bone loss with diet (dry food only, or other than dry food only), and with access to other chewing materials was analyzed. There were few apparent differences seen in dogs fed dry food only compared with those fed other than dry food only. There was progressively less accumulation of calculus, less gingival inflammation and less periodontal bone loss in dogs that were given access to more types of chewing materials (rawhides, bones, biscuits, chew toys) compared with dogs given access to fewer or no chewing materials. When the effects of individual chewing materials were analyzed, access to rawhides overall had the greatest apparent periodontal protective effect, and this effect was more apparent in dogs fed dry food only compared with those fed other than dry food only.

Journal of Veterinary Dentistry, 1994

Thirteen hundred and fifty dogs were examined under anesthesia at veterinary hospitals in the USA... more Thirteen hundred and fifty dogs were examined under anesthesia at veterinary hospitals in the USA and Canada. Periodontal health was recorded in detail. Teeth were frequently absent (particularly lower third molar, upper and lower first premolars, and incisor teeth). Calculus was most extensive on the upper fourth premolar and molar teeth. Missing teeth, mobility of remaining teeth, extent of calculus and gingival inflammation, and furcation exposure and attachment loss all were more common in small dogs compared with larger dogs, and in older dogs compared with younger dogs.

American journal of veterinary research, 1990

Serum IgA, IgG, and IgM concentrations were determined for Beagle sires and dams of 717 matings t... more Serum IgA, IgG, and IgM concentrations were determined for Beagle sires and dams of 717 matings to assess the relationship of parental immunoglobulins with the morbidity and mortality of their pups. A significant relationship was not found between parental immunoglobulins and pup mortality. Pups born to dams with low serum IgA (P less than 0.001) and IgM (P less than 0.02) concentrations, however, were found to have an increased incidence of sneezing, coughing, nasal discharge, and conjunctivitis. Thirty-eight percent of pups born to dams with IgA less than or equal to 40 mg/dl developed these same conditions during the first 18 weeks of life, compared with 32% of pups of dams with IgA of 41 to 65 mg/dl and 27% of pups of dams with IgA greater than 65 mg/dl. Similarly, 41% of pups born to dams with low IgM (less than or equal to 135 mg/dl) developed abnormal respiratory tract signs, compared with 34% and 30% of pups born to dams with medium (136 to 175 mg/dl) and high (greater than ...

American journal of veterinary research, 1999

To characterize the variation in plasma lactate concentration among samples from commonly used bl... more To characterize the variation in plasma lactate concentration among samples from commonly used blood sampling sites in conscious, healthy dogs. 60 healthy dogs. Cross-sectional study using a replicated Latin square design. Each dog was assigned to 1 of 6 groups (n = 10) representing all possible orders for 3 sites (cephalic vein, jugular vein, and femoral artery) used to obtain blood. Samples were analyzed immediately, by use of direct amperometry for pH, PO2, Pco2, glucose, and lactate concentration. Significant differences in plasma lactate concentrations were detected among blood samples from the cephalic vein (highest), femoral artery, and jugular vein (lowest). Mean plasma lactate concentration in the first sample obtained, irrespective of sampling site, was lower than in subsequent samples. Covariation was identified among plasma lactate concentration, pH, and PCO2, but correlation coefficients were low. Plasma lactate concentrations differed among blood samples from various s...

American journal of veterinary research, 1988

Concentrations of serum IgA, IgG, and IgM were determined for 829 adult Beagles from a commercial... more Concentrations of serum IgA, IgG, and IgM were determined for 829 adult Beagles from a commercial kennel in which several IgA-deficient dogs had been identified previously (index kennel). These values were compared with measurements of 100 adult dogs from another Beagle kennel (control kennel). After adjustment for differences in the ages and gender of the dogs, dogs from the index kennel had significantly (P less than 0.0001) lower IgA concentrations (mean, 46 mg/dl) than dogs from the control kennel (mean, 68 mg/dl). Regardless of kennel, males had significantly (P less than 0.01) higher IgA concentrations than did females. Dogs in the control kennel had significantly (P less than 0.04) higher IgG concentrations (mean, 2,649 mg/dl) than did dogs in the index kennel (mean, 2,478 mg/dl), and female dogs in the control kennel had significantly (P less than 0.05) higher IgM concentrations (mean, 189 mg/dl) than dogs of either sex in the index kennel (mean, 162 mg/dl) or male dogs in t...

Progress in clinical and biological research, 1985

Journal of Periodontology, 1996

The primary etiologic factor in Periodontitis is bacterial plaque, which results in an inflammato... more The primary etiologic factor in Periodontitis is bacterial plaque, which results in an inflammatory lesion in the adjacent tissue leading to progressive destruction of the supporting periodontal tissues.1-7 An essential goal of current periodontal therapy is to control the inflammatory lesion in such a way that progressive destruction of the periodontium is arrested. Toward this end, a number of

Journal of Periodontology, 1972

Journal of Periodontology, 1976

The validity of using a periodontal probe for the transgingival sounding of the alveolar crest le... more The validity of using a periodontal probe for the transgingival sounding of the alveolar crest level has been demonstrated for buccal surfaces of the jaw. The measurements from the occlusal surfaces of the teeth to the estimated level of the alveolar crest using this technique accurately reflected the actual distances measured after surgical exposure of the alveolar crest at these sites.

Journal of Periodontology, 1974

Medicine. ** Basement membrane is used to describe the PAS-positive boundary layer visible by lig... more Medicine. ** Basement membrane is used to describe the PAS-positive boundary layer visible by light microscopy surrounding the periphery of vascular channels. Basal or basement lamina re fers to the limiting layer of blood vessels visible by electron microscopy only, which consists of a lamina lucida and a lamina densa.

Journal of Periodontology, 1975

Journal of Clinical Periodontology, 1985

69 adults ranging in age from 20 to 73 (mean age: 37) were randomly assigned to a control (C) and... more 69 adults ranging in age from 20 to 73 (mean age: 37) were randomly assigned to a control (C) and a test (T) group. Of these, 61 completed the 3-year longitudinal study. All subjects had varying degrees of gingivitis at the start, but no overt periodontitis. Following a base line examination for PII, GI, probing depth (PD) and recession, a differential darkfield microscopic (DDFM) count of subgingival bacterial morphotypes was carried out on a pooled sample originating from one tooth surface in each sextant with the greatest probing depth. Examinations were repeated every 5 months for 3 years. The C group received regular prophylaxes every 6 months. The Tstibjects received prophylaxes according to a previously described schedule, and on the basis of the DDFM test outcome. Recall intervals at the end of the study for the T group ranged from 1 to 24 months (mean: 15.7 months). Of 30 subjects in the T group at the end of the study, one half had not had their teeth cleaned for periods of 18 to 36 months without any detectable deterioration in their periodonta! status by comparison with the other T subjects or the patients in the C group. Both C and T subjects exhibited increased mean PII and GI scores as compared to base line during the first half of the study. However, mean PD measurements remained unchanged. Increases in PD from base line of 3 mm or more were observed only in approximately I out of a 1000 individual tooth surface comparisons, a frequency comparable to that expected to occur by chance alone. This observation indicates that in this population, little if any pocket formation occurred during the study period. GI score increases of 2 units or more occurred in relatively few subjects. 2 of 31 C patients accounted for 42"!!? of the affected dental units, while 5 out of 30 T subjects accounted for 40.8 % of the affected dental units in that group. These observations suggest that despite the relatively high prevalence and incidence of gingivitis, the subjects were relatively resistant to periodontitis. Neither preventive schedule was effective in eliminating gingivitis. The lack of significant destructive disease in this population prevented any meaningful comparison of the relative effectiveness of the two preventive maintenance regimens in preventing recurrences of periodontitis. Studies have been carried out by ourselves and iti adult periodontitis toward those seen in others which have demostrated sigtiificatit dif

Calcified Tissue International, 1984

Cyclic nucleotides (cAMP and cGMP) and prostaglandin E (PGE) have been implicated as possible med... more Cyclic 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 micron 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.

American Journal of Orthodontics and Dentofacial Orthopedics, 1998

American Journal of Orthodontics and Dentofacial Orthopedics, 1994

Changes in arch width during the early correction of Class II, Division 1 malocclusions with eith... more 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)

American Journal of Orthodontics and Dentofacial Orthopedics, 1987

Spatial change in the jaws of growing persons is often evaluated by superimposing cephalometric t... more 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.

American Journal of Orthodontics and Dentofacial Orthopedics, 2005

The aims of this study were (1) to evaluate cephalometric changes in subjects with Class II Divis... more The aims of this study were (1) to evaluate cephalometric changes in subjects with Class II Division 1 malocclusion who were treated with headgear (HG) or Fränkel function regulator (FR) and (2) to compare findings from regional superpositions of cephalometric structures with those from conventional cephalometric measurements. Methods: Cephalographs were taken at baseline, after 1 year, and after 2 years of 65 children enrolled in a prospective randomized clinical trial. The spatial location of the landmarks derived from regional superpositions was evaluated in a coordinate system oriented on natural head position. The superpositions included the best anatomic fit of the anterior cranial base, maxillary base, and mandibular structures. Results: Both the HG and the FR were effective in correcting the distoclusion, and they generated enhanced differential growth between the jaws. Differences between cranial and maxillary superpositions regarding mandibular displacement (Point B, pogonion, gnathion, menton) were noted: the HG had a more horizontal vector on maxillary superposition that was also greater (.0001 Ͻ P Ͻ .05) than the horizontal displacement observed with the FR. This discrepancy appeared to be related to (1) the clockwise (backward) rotation of the palatal and mandibular planes observed with the HG; the palatal plane's rotation, which was transferred through the occlusion to the mandibular plane, was factored out on maxillary superposition; and (2) the interaction between the inclination of the maxillary incisors and the forward movement of the mandible during growth. Conclusions: Findings from superpositions agreed with conventional angular and linear measurements regarding the basic conclusions for the primary effects of HG and FR. However, the results suggest that inferences of mandibular displacement are more reliable from maxillary than cranial superposition when evaluating occlusal changes during treatment.