Relationship between the face and the tooth form.

The aim of this study was to re-examine Leon Williams geometric theory and to find the degree of correspondence between the face and the tooth form in the population of Zenica, Bosnia and Herzegovina. Two thousand individuals with intact frontal teeth, in age between 17 and 24 years, were measured for 3 horizontal distances on the face: temporal width (Ft-Ft), zygomatic width (Zyg-Zyg) and gonial width (Go-Go) and for 3 horizontal distances on the both upper incisors: cervical width (CW), contact point width (CPW) and incisal width (IW). The length of the face (Tr-Gn) as well as the length of the central maxillary incisors were also measured. The results revealed: 1. Men had significantly larger dimensions for all facial and tooth dimensions (p < 0.05) than women, except for the cervical tooth width (p > 0.05); the left and the right central incisors were of identical dimensions and forms (p > 0.05). 2. The width of upper central incisors were smaller approximately 1.5 mm than in west Europeans. 3. Upon the relation between the 3 horizontal dimensions measured on the face and upper maxillary incisor, 11 facial forms and 10 upper central tooth forms could be recognised in the study population, but 98% of the population had only 3 tooth and face forms. Face shapes: oval face--83.3%, square-tapered face--9.2% and tapered face--7%; tooth forms: tapered-square incisor--53%, oval incisor--30%, tapered incisor--16%. 4. Reversed and enlarged tooth form was in line associated with the facial form in only 30%, while the most common combination was of the oval face form and the tapered-square central incisor (45%). 5. These results disapprove William's theory and may be helpful for the choice of artificial teeth in complete denture construction and the dental industry.

The effect of tooth loss on the TM-joint articular eminence inclination.

The inclination between the posterior wall of the articular eminence and the referential plane (Frankfurt line) was measured on 137 dry skull specimens (78 with complete dental arches and 59 edentulous). Both left and right joints were measured using direct craniometric method. The results were compared with respect to the loss of teeth, side and sex. A large range of measured values of the eminence inclination shows great individual differences, so that the mean values can have only orientational significance. The mean value of eminence inclination for all measured specimens was 61.9 angular degree. The difference between the two groups established upon dental status is very small and without any statistical significance (P > 0.05). The right joint shows a slightly steeper eminence inclination compared to the left one, but without any statistical significance (P > 0.05). Asymmetry between the right and left joint appears almost as a rule, while maximum measured differences reach up to 33 degrees, with mean absolute difference of 6.9 degrees. The group of edentulous specimens shows a greater symmetry and less differences between the left and right joint, which indicates that different bimechanical conditions in the joint, due to tooth loss might lead to remodellation of the articular eminence. The eminence inclination was significantly steeper in male specimens in all subgroups (P < 0.001), which confirms sexual dimorphism.

Measurement of magnetic field in dentistry.

The principal objective was to measure the magnetic fields occurring in dental surgeries at simultaneous subtraction of direct ground component of the magnetic field. A specifically designed instrument with the Hall probe was used for the measurement. It consisted of two amplifiers and a low frequency filter. Its task was to measure mean square values of the field (RMS) dependent on the position in space. Qualitative and quantitative analyses of the investigated variables enabled making conclusions about the magnetic fields in dental surgeries. A number of studies have shown that many dental instruments produce radiation with magnetic field higher than 40 G, at a significant decrease in power of the magnetic field with increasing distance from the source. It has also been reported that instruments of older generations produce stronger magnetic fields than do the new ones.

Three dimensional model of the human mandible.

A new biomechanical three-dimensional (3D) model for the human mandible is proposed. A simple two-dimensional model cannot explain the biomechanics of the human mandible, where muscular forces through occlusion and condylar surfaces are in a state of dynamical 3D equilibrium. All forces are resolved into components according to a selected coordinate system. The muscular forces, which during clenching act on the jaw, along with the necessary force level for chewing, also act as some kind of stabilizers of the mandibular condyles preventing dislocation and loading of nonarticular tissues.

Terminal hinge axis--Hobo point--Frankfurt horizontal relations.

Aim of this investigation was to determine the spatial relations of the terminal hinge axis of the temporomandibular joints toward Frankfurt horizontal. The sample consisted of 50 examinees. Terminal hinge axis was located, using Lauritzen's technique, on the left side of face for each examinee. Arbitrary point, as proposed by Sumiya Hobo, was measured and point Orbital was defined by palpation. On designated points steel pellets 0.25 mm in diameter were stocked. Lathero--latheral cephalogram was obtained for each examinee. Cephalograms were traced down on a transparent foil and points Orbital, THA--terminal hinge axis, Hobo and Porion--as the uppermost point of the metal ear rod of the cephalostat, were designated. Connecting points Orbital and Porion, Frankfurt horizontal was defined, and shortest distance toward points THA and Hobo, as well as between them were measured. Lines parallel and perpendicular to Frankfurt horizontal were drawn through point THA. In a co-ordinate system defined in such a way, upper left quadrant was first, upper right second, lower right third, and lower left was fourth. Observation was made in which quadrant Hobo point was located. Measured values were statistically evaluated. Results revealed that Hobo point is located in first quadrant in 5 cases, in second in 7, third quadrant in 18, and in fourth in 20 cases. That means that Hobo point is located lower to the THA point in majority of our population. Points THA and Hobo were not identical in any case. Mean values of variables showed that investigated points were inferior to the FH. Measures of variability revealed great variability of both points toward FH, as well as for their mutual distance. It could be pointed out that THA point should be defined kinematically during prosthodontic procedures, and that orientation in articulator's space should not be according to the FH.

Comparative review of gnathometric characteristics in total dentures and eugnathic subjects.

The problem of determining the position and lining of the teeth in total dentures is presented by a comparative examination of gnathometric variables in eugnathic subjects and in those wearing total dentures. The material consisted of 51 plaster casts of eugnathic subjects and 49 subjects wearing total dentures. The following were examined: upper total number of incisors (T1), anterior width (AW), posterior width (PW), anterior length (AL) and posterior length (PL) of models. Analysis of the investigated variables was carried out by means of sliding calipers MECANIC Type 6901 (IVOCLAR, Lichtenstein) with a scale of 0-130 mm, and reading accuracy 97.5%. A three-dimensional pair of compasses according to Korhaus (Dentaurum, Germany) was used to measure the anterior and posterior lengths of models, with a scale 10-60 mm and reading accuracy 95%. No significant difference was observed between the eugnathic subjects and subjects wearing total dentures (p > 0.05). The results of this comparative gnathometric analysis of examined variables (Tl, AW, PW, AL and PL) are a contribution to the rules when lining anterior and posterior teeth in total dentures.

Radiographic cephalometry of the facial profile.

Radiographic cephalometry is a biomorphological measuring method used in the prosthodontics as well, and for the facial profile analysis of persons with complete dentures. The purpose of this examination was to objectivize the facial esthetics in patients with complete dentures. The measurements were taken from LL X-ray radiographs obtained by the apparatus "Ortoceph 10" (Siemens, Bensheim, Germany). On the sample of 80 subjects a convexity angle of facial bone structures (N-A: A-Pg) and profile angle of soft facial tissue (ft-unt: lnt-ct) have been examined. The subjects were divided into a group with upper and lower complete dentures (20 males and 20 females) and a group with natural teeth of eugnatic characteristics (20 male and 20 female). The measurements were taken by standard protractor at 0.5% precision. The statistical analysis within and among groups has been made by F-test and t-test respectively. The results showed that the bone structure convexity angle span a range between 0 degree and 5.5 degrees (X = 2.5 degrees), and the facial profile angle between 139.5 degrees and 155 degrees (X = 149 degrees) in persons with complete dentures. In persons with natural teeth the values of bone structure convexity angles span a range between -0.5 degree and 4.8 degrees (X = 2 degrees), and the facial profile angle between 136 degrees and 155.5 degrees (X = 151 degrees). The results of tests proved that there were no statistically significant differences in examined variables between persons with natural teeth and those with complete dentures (p > 0.05). The conclusion is that clinical methods of determining the vertical and horizontal intermaxilliary relations used in the designing procedures of complete dentures were reliable enough in reconstruction of examined angles of soft and hard facial profile structures.