Growth and development: hereditary and mechanical modulations

Growth and development is the net result of environmental modulation of genetic inheritance. Mesenchymal cells differentiate into chondrogenic, osteogenic, and fibrogenic cells: the first 2 are chiefly responsible for endochondral ossification, and the last 2 for sutural growth. Cells are influenced by genes and environmental cues to migrate, proliferate, differentiate, and synthesize extracellular matrix in specific directions and magnitudes, ultimately resulting in macroscopic shapes such as the nose and the chin. Mechanical forces, the most studied environmental cues, readily modulate bone and cartilage growth. Recent experimental evidence demonstrates that cyclic forces evoke greater anabolic responses of not only craniofacial sutures, but also cranial base cartilage. Mechanical forces are transmitted as tissue-borne and cell-borne mechanical strain that in turn regulates gene expression, cell proliferation, differentiation, maturation, and matrix synthesis, the totality of which is growth and development. Thus, hereditary and mechanical modulations of growth and development share a common pathway via genes. Combined approaches using genetics, bioengineering, and quantitative biology are expected to bring new insight into growth and development, and might lead to innovative therapies for craniofacial skeletal dysplasia including malocclusion, dentofacial deformities, and craniofacial anomalies such as cleft palate and craniosynostosis, as well as disorders associated with the temporomandibular joint.     

Statistical Methodologies Useful for the Analysis of Data from Risk-assessment Studies

In dentistry, the vast majority of studies attempting to predict who is at high risk for getting a disease or condition, or attempting to identify risk factors for a specific disease or condition, have focused either on only one risk factor at a time, or have measured multiple potential risk factors, but analyzed their effects in isolation. Since researchers tend to agree that most dental conditions have a multiple etiology, it is necessary to develop models that consider simultaneously the effect of a number of potential risk factors on the disease or condition of interest if we are to have any understanding of the relative impact of potential risk factors. Many existing statistical techniques will aid dental researchers in identifying risk factors. However, the selection of an appropriate analytic technique depends on a number of conditions. The strategy for this paper is to discuss a wide range of possible statistical techniques that may be applied to the problem of deriving a model for identification of multiple risk factors for dental diseases and conditions. We have approached this task by presenting a number of dental research problems needing an appropriate analytic technique. Next, basic issues that must be considered in choosing an appropriate analytic strategy are discussed. These issues include features of the study design, the data structure of the variables being measured, and the types of assumptions that are applicable to provide valid inferences about the target population of interest. A matrix of possible analytic techniques is presented for various combinations of study-design and data-structure features. After a discussion of each of the techniques, the appropriate statistical techniques for each of the dental examples are described. The issues and examples presented in this paper should be of use to dental researchers who wish to investigate multiple risk factors for a disease or condition of interest.     

Measuring Beliefs about Orthodontic Treatment: A Questionnaire Approach

Objectives : Few studies have examined what parents and orthodontists expect from and value about orthodontic treatment. In this study, we designed and tested a questionnaire to outline what drives consumer demand for children's orthodontic care. Further, we present data from the questionnaire to illustrate how expectations and values pertaining to orthodontic treatment relate to sociodemographic variables. Methods : Subjects were 220 Pennsylvania orthodontists and 220 parents at a university orthodontic clinic who were administered a questionnaire designed to assess what parents and orthodontists value about and expect from orthodontic treatment. Items for the questionnaire were developed via a qualitative, telephone interview process. Data were analyzed using factor analysis and reliability analysis for scale development, and analysis of variance for preliminary validity assessment. Results : Through factor analysis, the questionnaire was reduced from 84 to 52 items, and eight scales were examined: expected treatment benefits, expected treatment risks (short- and long-term), expected treatment inconveniences, value of treatment benefits, value of risks (short- and long-term), and value of treatment inconveniences. For parents, the reliability for all scales was in the acceptable range. For orthodontists, only the “short-term risks” scale failed to attain an acceptable reliability. Preliminary validity was assessed through examining relationships between demographic variables and subscale scores. For parents, income, father's education level, and sex of respondent were related to treatment expectations and values. For orthodontists, age, sex, and patient volume were related to treatment values. Conclusions : The questionnaire developed in the present study was found to be practical and reliable for use with providers and consumers of orthodontic care and can be used to explore factors affecting the demand for orthodontic care. Implications of possible unrealistic treatment expectations on the part of orthodontists and parents also are discussed.     

Effect of Dynamic Loading Methods on Cement Film Thickness In Vitro

Purpose Reduced cement film thicknesses can improve crown seating and decrease marginal discrepancies. Improved marginal adaptation has the potential to reduce plaque accumulation, periodontal disease, and cement dissolution. Studies have indicated that dynamic seating methods can reduce seating discrepancies associated with zinc phosphate and resin cements. However, other types of cements and other dynamic techniques have not yet been studied or compared, nor has the mechanism for improved seating been fully explained. Therefore, the purpose of this study was to investigate the effect of a variety of loading methods on the film thicknesses of current types of crown and fixed partial denture cements compressed between glass plates. Materials and Methods This study investigated the effect of three dynamic loading methods on film thickness of six representative fixed prosthodontic cements. These included zinc phosphate, resin-modified glass ionomer, encapsulated glass ionomer, adhesive composite resin, composite resin, and polycarboxylate. The method was derived from American Dental Association specifications for cement film thickness. In control groups, the cements were placed between two glass plates and statically loaded with a 15-kg weight. The test groups were initially similarly loaded, and then for 30 seconds further subjected to simulated repeated patient opening and closing, vibrations from an electromallet, or an ultrasonic device. Results Mean film thicknesses ranged from 7.4 μm for polycarboxylate/ultrasound up to 40.3 μm for composite resin/static. Two-way analysis of variance revealed that the effects of material type and cementation method and their interaction all significantly affected film thickness (P < .0001). Multiple range analysis showed that dynamic methods were generally superior to static loading and that the ultrasonic method was the best overall. Conclusions The different dynamic loading methods all significantly decreased cement film thicknesses between glass plates. The ultrasonic method was the most effective. The type of cement used also influenced film thickness. Composite resins were more affected than other materials.     

Transverse molar movements during growth

The purpose of this study was to evaluate changes in molar crown torque and intermolar arch width from the time of permanent first molar eruption to early adulthood. Molar crown torque and intermolar arch width were measured in 36 untreated subjects with Class I occlusion from the Iowa Facial Growth Study at approximate ages 7.5, 10.3, 12.9, 16.5, and 26.4 years. On average, the mandibular first and second molars uprighted buccally by 5.0 degrees and 7.5 degrees, respectively. Mandibular first and second molar intermolar width increased by 2.2 and 0.78 mm, respectively. On average, maxillary first and second molars uprighted lingually by 3.3 degrees and 5.9 degrees, respectively. Maxillary first and second intermolar width increased by 2.8 and 2.0 mm, respectively. Results of statistical analysis by the Wilcoxon signed rank test indicate that (1) maxillary molars erupt with buccal crown torque and upright with age, whereas mandibular molars erupt with lingual crown torque and upright with age (P <.01), and (2) molar crown torque changes are accompanied by concurrent increases in maxillary and mandibular intermolar width (P <.01).     

The Role of Abutment-Attachment Selection in Resolving Inadequate Interarch Distance: A Clinical Report

A critical factor that needs to be evaluated during the diagnosis and treatment planning phase for patients seeking an implant-tissue-supported overdenture or metal-resin implant fixed denture is the presence of adequate interarch distance. The amount of interarch distance is critical to the selection of appropriate implant abutments and attachments for both implant-tissue-supported overdentures and metal-resin implant fixed complete dentures. This clinical report describes a patient with complications related to the failure to diagnose inadequate interarch distance, and the methods used to resolve the patient's chief complaint. A guide for abutment-attachment selection using one commercially available implant system is given.