Three-dimensional positional changes of teeth adjacent to posterior edentulous spaces in relation to age at time of tooth loss and elapsed time

The purpose of this study was to study the stability of teeth adjacent to posterior edentulous spaces and correlate it with patient age and time lapse since tooth loss. Dental casts, panoramic radiographs, and questionnaires of patients treated in a University setting were employed. Teeth adjacent and opposing posterior edentulous spaces were examined for the following parameters: Supraeruption, rotation, space closure, and axial inclination. One hundred twenty three patients with 229 edentulous spaces were analyzed. Statistical analysis showed that the effects of "jaw", "gender", and "age group at the time of tooth loss" were not significant for any of the variables tested. The effect of time lapse since tooth loss was significant regarding the "amount of distal tooth inclination" (P<0.001), the "amount of distal tooth rotation" (P=0.004), and "space closure" (P=0.038). Post-hoc analysis of the "amount of distal tooth inclination" revealed a marked increase in inclination 5 years after tooth loss. Within the limitations of this study, it was concluded that in the group of patients studied, minor positional changes in teeth opposing or adjacent to posterior edentulous spaces had occurred. The greatest changes in position were recorded for mandibular teeth distal to edentulous spaces

Compensation of a ball end tool trajectory in complex surface milling

This work is consecrated to the minimising of machining errors based on a method for the compensation of the trajectory to be machined in hemispherical milling. This compensation is found to be necessary because of the tool deflection due to the cutting forces. In order to remedy to the machining errors, caused by this deflection, a compensation method has been proposed. The latter is inspired from the mirror method, since the compensated position is going to be determined as being the trajectory reflection, deviated onto the mirror. The advantage of this proposed method is that it takes into account the three deflections dx, dy and dz, respectively to the directions X, Y and Z. After that, two-parallel machinings, separated by a groove and achieved absolutely in the same conditions and with the same tool, are carried out, on the same complex part. The first machining is with compensation, but the second is without compensation. The coordinates of the two obtained surfaces are recorded by a 3D measuring machine. The comparison of the two-surfaces shows the presence of an important correction of the tool trajectory, and reveals a similarity between the part obtained by simulation and the one conceived in CAM

Evaluation of Die Trim Morphology Made by CAD-CAM Technology

Statement of problem The die contour can affect the emergence profile of prosthetic restorations. However, little information is available regarding the congruency between a stereolithographic (SLA) die and its corresponding natural tooth. Purpose The purpose of this vitro study was to evaluate the shapes of SLA die in comparison with the subgingival contour of a prepared tooth to be restored with a ceramic crown. Material and methods Twenty extracted human teeth, 10 incisors, and 10 molars, were disinfected and mounted in a typodont model. The teeth were prepared for a ceramic restoration. Definitive impressions were made using an intraoral scanner from which 20 SLA casts with removable dies were fabricated. The removable dies and corresponding human teeth were digitized using a 3-dimensional desktop scanner and evaluated with computer-aided design software. The subgingival morphology with regard to angle, length, and volume at the buccolingual and mesiodistal surfaces and at zones A, B, C, and D were compared. Data were first analyzed with repeated measures analysis of variance (ANOVA), using locations (buccolingual and mesiodistal), zones (A, B, C, and D), and model type (SLA and Natural) as within-subject factors and tooth type (molar and incisor) as the between-subject factor. Post hoc analyses were performed to investigate the difference between natural teeth and corresponding SLA models, depending upon the interaction effect from the repeated measures ANOVA (α=.05). Results For angle analysis, the incisor group demonstrated a significant difference between the natural tooth and SLA die on the buccolingual surfaces (PPPPPP Conclusions For the comparison of angles, SLA dies did not replicate the subgingival contour of natural teeth on the buccolingual surfaces of the incisal groups. For the comparison of length and volume, SLA dies were more concave and did not replicate the subgingival contour of natural teeth in the incisal and molar groups

Retrospective analysis of the correlation between the facial biotype and the inclination of the upper canine cusp axis to the occlusal plane

Permanent maxillary canines are the second most frequently impacted teeth and the prevalence of this clinical condition is estimated to be 1-2% in the general population. The diagnosis of maxillary canine impaction should be based on both clinical and radiographic examinations. The aim of this study was to evaluate the presence of a correlation between the facial biotype and the inclination of the upper cusp axis. A correlation between the total radicular length of the lateral incisors was also evaluated, by comparing the side of impaction with the healthy side. Twenty three patients with a diagnosis of unilateral upper cusp impaction were recruited. For each patient, dental casts and radiographic material (panoramic radiographs and lateral cephalograms) were examined. Statistical analyses were done with Spearman's rank correlation coefficient or Spearman's rho (V). X-ray examinations demonstrated that canine impaction was associated to other dental anomalies (32% of the sample). The mean S angle measurements were 22.9° ± 4.1°, and mean values of the T angle were 34.7°± 4.0°. The mean distance “d” value was 14.6 mm ± 1.2 mm. The mean values of the angle between the upper cusp axis and the perpendicular-to-Fh plane were 20.8 °± 2.6°. Among the 23 subjects recruited, 5 showed values included in the range 25°-45° and 1 an inclination > 45°. The results obtained in the present study demonstrate a significant inverse correlation between the MM angle and the inclination of the upper cusp axis to the perpendicular-to-Fh plan

Mechanics and Mathematical Modeling of Class III Treatment with Orthodontic Appliances with a Movable Ramp

Treatment of class III is a current problem in orthodontics that requires constant improvement of its methods, development of new or modifications of known methods and techniques. We have developed and studied the modification of removable functionally-directing orthodontic appliances for treatment of Class III, which consists of a plastic base, vestibular arc, retaining clasps, ramp, which is connected with the base by means of two torsion springs. Its usage ensures a prolonged contact of ramp with the teeth. We studied two types of club-shaped springs (torsion springs): one spring, which create an amortization effect during the action of the ramp, but do not change its inclination angle and second one – spring that seek to increase the angle of the ramp inclination due to the disclosure of its curl

Moving an incisor across the midline: A treatment alternative in an adolescent patient

A 13-year-old sought treatment for a severely compromised maxillary left central incisor and an impacted fully developed left canine. Extraction of both teeth became necessary. As the key component of the revised comprehensive treatment plan, the right maxillary central incisor was moved into the position of the left central incisor. All other maxillary teeth were moved mesially to close any gaps. Active orthodontic treatment was completed after 34 months. Frenectomy, minor periodontal surgeries, and bonded lingual retainers were used to improve aesthetics and stabilize the tooth positions. The patient was pleased with the treatment outcome. Cone-beam computed tomography provided evidence that the tooth movement was accompanied by a deviation of the most anterior portion of the median palatine suture. This observation may make relapse more likely if long-term retention cannot be ensured. Root resorption was not observed as a consequence of the major tooth movement. (Am J Orthod Dentofacial Orthop 2011;139:533-43

Into Mesh Lubrication of Spur Gears with Arbitrary Offset Oil Jet. I: For Jet Velocity Less than or Equal to Gear Velocity

An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or less than pitch line velocity. The analysis includes the case for the oil jet offset from the pitch point in the direction of the pinion and where the oil jet is inclined to intersect the common pitch point. Equations were developed for the minimum oil jet velocity required to impinge on the pinion or gear and the optimum oil jet velocity to obtain the maximum impingement depth

New image analysis of large food particles can discriminate experimentally suppressed mastication

Objective parameters that could provide a basis for food texture selection for elderly or dysphagic patients have not been established. We, therefore, aimed to develop a precise method of measuring large particles (>2 mm in diameter) in a bolus and an analytical method to provide a scientific rationale for food selection under masticatory dysfunction conditions. We developed a new illumination system to evaluate the ability of twenty female participants (mean age, 23·4 ± 4·3 years) to masticate carrots, peanuts and beef with full, half and one quarter of the number of masticatory strokes. We also evaluated mastication under suppressed force, regulated by 20% electromyographic of the masseter muscle. The intercept and inclination of the regression line for the distribution of large particles were adopted as coefficients for the discrimination of masticatory efficiency. Single set of coefficient thresholds of 0·10 for the intercept and 1·62 for the inclination showed excellent discrimination of masticatory conditions for all three test foods with high specificity and sensitivity. These results suggested that our method of analysing the distribution of particles >2 mm in diameter might provide the basis for the appropriate selection of food texture for masticatory dysfunction patients from the standpoint of comminution