Relationship between dental anomalies and orthodontic root resorption of upper incisors.

The aim of this study was to examine the potential relationship between the occurrence of orthodontic root resorption and presence of dental anomalies such as tooth agenesis and pipette-shaped roots. Dental anomalies and root resorption were assessed on dental panoramic tomographs (DPT) of 88 subjects, 27 males and 61 females, mean age 28.4 (SD = 11.3 years), selected from orthodontic patients on the basis of the following exclusion criteria: previous fixed appliance treatment, bad quality of the DPTs and no visibility of the periodontal ligament of every tooth, and younger than 15 years of age at the onset of treatment with fixed edgewise appliance lasting at least 18 months. A pipette-shaped root was identified as defined by a drawing. Tooth agenesis was assessed on DPTs and from subjects' dental history. Root resorption was calculated as the difference between the root length before and after treatment, with and without a correction factor (crown length post-treatment/crown length pre-treatment). If one of the four upper incisors showed root resorption of ≥2.3 mm with both formulas, the patient was scored as having root resorption. Chi-square tests indicated that there was no relationship between orthodontic root resorption and agenesis (P = 0.885) nor between orthodontic root resorption and pipette-shaped roots (P = 0.800). There was no relationship between having one of the anomalies and root resorption either (P = 0.750). In the present study, it was not possible to confirm on DPTs a relationship between orthodontic root resorption and dental anomalies, such as agenesis and pipette-shaped roots.

Assessment of dental anomalies on panoramic radiographs: inter- and intraexaminer agreement.

The presence of dental anomalies has been rated radiographically in a number of studies. However, since the reliability of the assessment of these anomalies has rarely been investigated, the aim of this study was to examine inter- and intraexaminer agreement in identifying morphological dental anomalies, such as tooth agenesis, dilacerated, pipette-shaped, blunt, pointed, and short roots. Pre-treatment panoramic radiographs of 40 patients (13 males and 27 females; mean age 27.7 ± 10.8 years) treated between 1983 and 2008 were selected. Four examiners independently assessed the radiographs twice. For a dilacerated root and agenesis, a definition was given. For pipette-shaped, blunt, or pointed roots, a drawing was shown, and for a short root, a ratio was used to identify the anomaly. Intraexaminer agreement of the assessments of the dental anomalies was presented by Cohen's Kappa and varied between -0.01 for short roots and 1.00 for agenesis. With respect to short roots, three of the examiners did not rate them to be present on at least one measurement occasion. This implies that intraexaminer agreement could not be calculated for these three examiners. Interexaminer agreement for dilacerated roots varied between 0.14 and 0.50, for pipette-shaped roots between -0.01 and 0.33, for blunt roots between 0.05 and 0.32, and for pointed roots between 0.17 and 0.37. All values for agenesis were 1.00. It can be concluded that assessing agenesis on panoramic radiographs is reliable. Rating the presence of dilacerated, pipette-shaped, blunt, pointed, and short roots on panoramic radiographs, however, does not result in a reliable assessment.

The adaptive response of jaw muscles to varying functional demands.

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties. This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions. Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.

Pulpal cellular reactions to experimental tooth movement in rats.

OBJECTIVE: The objective was to study the early cellular reactions of the dental pulp during experimental tooth movement. STUDY DESIGN: A total number of 98 male rats were used. Tooth movement was induced for 1 to 168 hours by inserting elastic bands between maxillary first and second molars of animals, which were labeled with tritiated thymidine. Pathologic signs, macrophage content, and proliferation of fibroblasts and endothelial cells were assessed histologically on autoradiographs of second molar pulps. Data were analyzed using ANOVA with Tukey's test as post hoc pairwise comparison. RESULTS: Pathologic signs and macrophage content generally increased with time after the induction of tooth movement. The proliferation of pulpal connective tissue progenitor cells and endothelial cells increased as a reaction to the force application. CONCLUSIONS: Force-induced tooth movement may lead to extensive, however temporary, trauma of the pulpal tissues, which react with early wound-healing events, such as macrophage invasion, cell proliferation, and angiogenesis.

Dentoalveolar compensation in subjects with vertical skeletal dysplasia.

INTRODUCTION: The purpose of this cephalometric study was to investigate vertical dentoalveolar compensation in untreated adults with excessive (long-face) and deficient (short-face) lower anterior face heights. METHODS: Vertical and sagittal base relationships, vertical dentoalveolar dimension in the anterior region of the jaws, incisor inclination, overbite, and overjet were assessed in 112 short-face and 95 long-face subjects. The contribution of skeletal and dentoalveolar components to achieve a normal overbite was assessed by means of regression analysis. For the 2 most important independent variables of the regression equation, the values were calculated that would render an overbite of 2 mm. It was subsequently investigated whether the calculated value fell within the range of the sample. RESULTS: In long-face subjects, overbite was mainly related to lower anterior face height; in short-face subjects, it was mainly related to mandibular anterior alveolar and basal heights. Dentoalveolar compensation occurred in both groups mainly by adaptations in mandibular incisor alveolar and basal heights. Molar height was unrelated to overbite. Cutoff values for achieving a positive overbite were calculated for lower face height and mandibular incisor alveolar and basal heights. CONCLUSIONS: The lower face height mainly determines the overbite in long-face subjects, while in short-face subjects, lower dentoalveolar morphology influences overbite. Lower dentoalveolar compensation can maintain a normal overbite in long-face subjects to a limited extent.

Cell kinetics of mechanically stimulated rat oral epithelia.

OBJECTIVE: To study cell kinetics of rat gingival (GE), sulcular (SE) and junctional (JE) epithelia in the steady-state and after application of mechanical pressure. DESIGN: Elastic bands were inserted between first and second maxillary molars of 8-week-old male rats, which were labelled with H(3) TdR and killed in groups of six to seven animals together with equal-sized groups of labelled control animals at intervals between 1 and 168 h. Autoradiographs were used to determine epithelial cell proliferation on the pressure side of M1 by calculating the percentage of (3)H TdR-labelled cells (PLC) in the basal (BL) and suprabasal (SL) layers of GE, SE and JE and to estimate median cell cycle (MCC) duration of BL cells by plotting mean and median grain counts against time. RESULTS: (3)H TdR-labelled cells were present in SL of SE and JE 1-12h after isotope injection suggesting that the BL might be not the only source of progenitor cells for JE as they might also be derived through migration from adjacent SE. Application of pressure significantly (ANOVA, P<0.05) reduced PLC in BL of GE, SE and JE indicating a decrease of cell proliferation after 1-12h in response to pressure. In steady-state, the MCC durations of BL cells of GE, SE and JE were 39, 14 and 9h, respectively. After application of pressure, they increased significantly (chi(2)-test, P<0.05) to 48, 44 and 34 h, respectively. CONCLUSIONS: Sustained pressure may lead to reduction of proliferative activity of these epithelia inducing slower progression of progenitor cells through the cell cycle.