Intercuspal Distance Research Articles

Molar intercuspal dimensions: genetic input to phenotypic variation.

Molecular studies indicate that epigenetic events are important in determining how the internal enamel epithelium folds during odontogenesis. Since this process of folding leads to the subsequent arrangement of cusps on molar teeth, we hypothesized that intercuspal distances of human molar teeth would display greater phenotypic variation but lower heritabilities than overall crown diameters. Intercuspal distances and maximum crown diameters were recorded from digitized images of dental casts in 100 monozygotic and 74 dizygotic twin pairs. Intercuspal distances displayed less sexual dimorphism in mean values but greater relative variability and fluctuating asymmetry than overall crown measures. Correlations between intercuspal distances and overall crown measures were low. Models incorporating only environmental effects accounted for observed variation in several intercuspal measures. For those intercuspal variables displaying significant additive genetic variance, estimates of heritability ranged from 43 to 79%, whereas those for overall crown size were higher generally, ranging from 60 to 82%. Our finding of high phenotypic variation in intercuspal distances with only moderate genetic contribution is consistent with substantial epigenetic influence on the progressive folding of the internal enamel epithelium, following formation of the primary and secondary enamel knots.

Administration of osteocalcin accelerates orthodontic tooth movement induced by a closed coil spring in rats.

The effect of local administration of osteocalcin (OC) on experimental tooth movement was examined in the rat. The maxillary first molar was first moved mesially with an initial tipping force of 30 g with a closed-coil spring anchored to the incisor for 10 days (n = 48). Three experimental groups (n = 8) were injected with purified rat OC at doses of 0.1, 1, and 10 micrograms, respectively. The injection into the palatal bifurcation site of the first molar was repeated daily. The control groups (n = 8) were injected with rat serum albumin (10 micrograms), phosphate buffered saline (PBS), or were not injected. Tooth movement was evaluated daily by measuring the inter-cuspal distance between the first and the second molars on a precise plaster model. The cumulative tooth movement (mm) in the 1-microgram OC-injected groups was significantly more than that in all of the control groups on day 9. The rate of tooth movement (mm/day) showed periodical elevation, with high values on days 1, 4, 7, and 9. Acceleration of tooth movement by OC was significant in the early experimental period. Subsequently, acceleration of early tooth movement by OC was histologically evaluated (n = 40). Each of four animals from the control (PBS, n = 20) and the experimental (1 microgram OC, n = 20) groups was killed daily up to 5 days. A significantly larger number of osteoclasts accumulated on the mesial alveolar bone surface in the 1-microgram OC-injected group on day 3 than that observed in control group. These results suggest that administration of OC accelerates orthodontic tooth movement due to enhancement of osteoclastogenesis on the pressure side, primarily in the early experimental period.

Modified cuspal relationships of mandibular molar teeth in children with Down's syndrome.

A total of 50 permanent mandibular 1st molars of 26 children with Down's syndrome (DS) were examined from dental casts and 59 permanent mandibular 1st molars of normal children were examined from 33 individuals. The following measurements were performed on both right and left molars (teeth 46 and 36 respectively): (a) the intercusp distances (mb-db, mb-d, mb-dl, db-ml, db-d, db-dl, db-ml, d-dl, d-ml, dl-ml); (b) the db-mb-ml, mb-db-ml, mb-ml-db, d-mb-dl, mb-d-dl, mb-dl-d angles; (c) the area of the pentagon formed by connecting the cusp tips. All intercusp distances were significantly smaller in the DS group. Stepwise logistic regression, applied to all the intercusp distances, was used to design a multivariate probability model for DS and normals. A model based on 2 distances only, mb-dl and mb-db, proved sufficient to discriminate between the teeth of DS and the normal population. The model for tooth 36 for example was as follows: p(DS) = (e(30.6-5.6(mb-dl)+25(mb-db)))/(1 + e(30.6 5.6(mb-dl)+25(mb db))). A similar model for tooth 46 was also created, as well as a model which incorporated both teeth. With respect to the angles, significant differences between DS and normals were found in 3 out of the 6 angles which were measured: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was higher, and the mb-dl-d angle was smaller. The dl cusp was located closer to the centre of the tooth. The change in size occurs at an early stage, while the change in shape occurs in a later stage of tooth formation in the DS population.

Biomechanical behaviour of modern human molars: implications for interpreting the fossil record.

Finite-element models of 29 intact molars were created and subjected to cleavage-type loads in order to assess differences in the biomechanical behaviour of molars. A simulated food particle, which was one-third the size of the intercuspal distance and had the properties of a Mezzettia seed, was pushed onto the occlusal basin of these models at various angles, resulting in either both or one particular cusp being preferentially loaded. In all cases, the maximum tensile stresses occurred in enamel at the intercuspal fissure. With regard to first maxillary molars, supporting (functional) and guiding (nonfunctional) cusps apparently dissipate loads equally well, whereas, in second and third maxillary molars, the guiding cusps are better designed to resist loads. Overall, lingual cusps of maxillary posterior molars dissipate loads poorly. Conversely, loads exerted toward supporting cusps of mandibular molars are consistently well dissipated, regardless of position along the tooth row. Because the directions of loads to which these teeth are best adapted change along the tooth row, it seems reasonable to suggest that these may correlate with the well-documented structural and functional orofacial complex. This study indicates that the biomechanical behaviour of molars and the orofacial skeleton are likely to have undergone complementary directional changes during evolution. Consequently, caution must be exercised in making inferences about dietary adaptations of extinct species on the basis of isolated teeth or fragmentary gnathic remains without proper regard of the orofacial skeleton as a whole.

Morphometric analysis of developing crowns of maxillary primary second molars and permanent first molars in humans

The purpose of this study was firstly to characterize the changes occurring in size and form of the mineralizing maxillary second primary molar and first permanent molar crowns, and secondly to determine if similar changes in size and form characterize enamel apposition in the crowns of these teeth. Twenty-five primary second molars and 20 maxillary permanent first molars at various stages of development, found in archaeological excavations in Israel, were examined for a number of measured variables using image analyser software. Teeth were divided into two groups according to their stage of development: stage 1 included all teeth at an early stage of development in which mesiobuccal-cusp height was less than 5 mm for the primary molar and 5.9 mm for the permanent molar; stage 2 included all teeth in later stages of development where mesiobuccal-cusp height was greater than these values. In the primary molar, a significant increase was found between the two stages in almost all variables. Significant correlations were also found between all intercusp distances and the external variables. Strong correlations between height of the mesiobuccal cusp and all external and internal variables were noted in stage 1, but fewer in stage 2. In the permanent tooth, no increase was observed in intercusp distances and very few correlations were found between and among the variables. The results suggest that a change in the shape of the maxillary primary second molar occurs during formation, with the lingual cusp tips moving lingually and distally, and the distobuccal cusp tips moving distally. No change occurs in the shape of the maxillary permanent first molar during crown formation. Growth of the maxillary primary second and permanent first molar crowns occurs in ‘bursts’ of development.

Cusp reinforcement by bonding of amalgam restorations

The purpose of the present study was to assess the effectiveness of several adhesives in bonding amalgam in order to recover tooth stiffness. A non-destructive experimental methodology was adopted, using strain gauges bonded to the midbuccal surfaces of 40 teeth, with sequential evaluation of loaded intact, prepared and restored stages of the same tooth. Continuous strain measurement as a function of the applied load was acquired by A/D equipment and a data acquisition programme. The strain-force behaviour of the sound teeth under non-axial force up to 97.5 N served as the baseline. The five experimental groups (8 × 5) consisted of control (no adhesive) and four different adhesives. One-way analysis of variance with repeated measures was calculated for the deformation ratio, relative stiffness and recovery values. Reductions in tooth structure by cutting a mesio-occlusal-distal preparation, width one-third intercuspal distance, resulted in 39–52% loss of buccal cusp stiffness. Non-bonded amalgam produced negligible increase (5%) in the stiffness recovery values of the buccal cusps. The adhesives splinted the cusps together, thereby decreasing cuspal flexure and increasing relative stiffness values. Recovery values obtained ranged from 39% to 61%. Assuming that cusp fracture occurs as a result of brittle tooth structure fatigue, amalgam adhesives may contribute to the strengthening of weakened cusps.

Morphometric variables of developing primary maxillary first molar crowns in humans

The following morphometric variables were examined in 18 primary maxillary first molars at various stages of development, collected from archaeological excavation sites in Israel: perimeters and areas from the occlusal view; buccolingual and mesiodistal dimensions and intercusp distances; the angle between the line joining the distobuccal, mesiobuccal and lingual cusps; and the height of the mesiobuccal cusp. An image-analysing technique comprising a photographic camera, a monitor, a computer with appropriate software and a digital caliper was used. Significant correlations were demonstrated between most variables. Teeth were divided into two groups according to their stage of development: stage one included all teeth at an early stage of development in which mesiobuccal cusp height was less than 5 mm; stage two included all teeth in later stages of development where mesiobuccal cusp height was greater than 5 mm. All external variables showed an increase in size between the two stages (while, among the internal ones, only the angle between the cusps showed a very small increase). The small sample is a limitation but the results suggest the following: (1) growth of the primary maxillary molar crown occurs with ‘bursts’ of development ; and (2) a change in the shape of the crown occurs during its formation where the mesiobuccal cusp moves buccally and distally, and the lingual cusp moves mesially.

Influence of different metal restorations bonded with resin on fracture resistance of endodontically treated maxillary premolars

Statement of problem. Fracture of endodontically treated teeth has been of great interest because it is a common clinical occurrence. Purpose of study. This research evaluated the fracture resistance of endodontically treated first maxillary premolars restored with different metal restorations and bonded with Panavia Ex resin. Material and methods. Fifty teeth were randomly divided into five groups with MOD tooth preparation: (1) inlay with an isthmus width of one third the intercuspal distance for a silver amalgam restoration (negative control), (2) inlay with an isthmus width equal to that in group 1, (3) inlay with an isthmus width of half the intercuspal distance, (4) equal to group 3 with lingual and proximal preparation, and (5) onlay (positive control). The cast restorations of groups 2, 3, and 4 were bonded with Panavia Ex resin and those from group 5 cemented with zinc phosphate cement. Samples were restored and subjected to thermocycling, and the teeth were submitted to an axial compressive force. Results. The cast inlay restorations that bonded with Panavia Ex resin significantly elevated the fracture resistance of endodontically treated maxillary premolars compared with the silver amalgam restorations. However, teeth restored with cast onlay restorations cemented with zinc phosphate cements recorded the best results. Conclusion. The increase of fracture resistance by MOD inlay cast restoration bonded with Panavia Ex resin suggested valid clinical application within the conditions of this study. (J Prosthet Dent 1997;77:365-9.)

The teaching of all-ceramic restorations in North American dental schools: curricular requirements and indications.

A survey was conducted to examine the manner in which North American dental school curricula provide instruction to pre-doctoral students in the applications of all-ceramic restorative materials. A questionnaire was sent to all 64 dental schools and the response rate was 80%. All dental schools offered didactic instruction, and 96% also provided some clinical experience. Most of the time, two departments are involved in teaching this clinical subject, with fixed prosthodontics being the department most frequently cited. Veneers were the most commonly taught all-ceramic restoration. Crowns were most frequently used on anterior teeth and premolars, especially in the maxillary arch. Inlays were almost exclusively performed for class I and class II lesions, whereas onlays were considered when the isthmus width of an inlay preparation exceeded one half of the intercuspal distance. Contraindications for the use of these materials were listed, with occlusal dysfunction such as bruxism being the most commonly cited reason for not using all-ceramic materials. The primary reasons for not teaching these procedures included insufficient longitudinal research and the lack of in-house laboratory support. Most schools indicated that the relative importance of all-ceramic restorations as a component of their curriculum was increasing.

Does an Incremental Filling Technique Reduce Polymerization Shrinkage Stresses?

It is widely accepted that volumetric contraction and solidification during the polymerization process of restorative composites in combination with bonding to the hard tissue result in stress transfer and inward deformation of the cavity walls of the restored tooth. Deformation of the walls decreases the size of the cavity during the filling process. This fact has a profound influence on the assumption--raised and discussed in this paper--that an incremental filling technique reduces the stress effect of composite shrinkage on the tooth. Developing stress fields for different incremental filling techniques are simulated in a numerical analysis. The analysis shows that, in a restoration with a well-established bond to the tooth--as is generally desired--incremental filling techniques increase the deformation of the restored tooth. The increase is caused by the incremental deformation of the preparation, which effectively decreases the total amount of composite needed to fill the cavity. This leads to a higher-stressed tooth-composite structure. The study also shows that the assessment of intercuspal distance measurements as well as simplifications based on generalization of the shrinkage stress state cannot be sufficient to characterize the effect of polymerization shrinkage in a tooth-restoration complex. Incremental filling methods may need to be retained for reasons such as densification, adaptation, thoroughness of cure, and bond formation. However, it is very difficult to prove that incrementalization needs to be retained because of the abatement of shrinkage effects.

Morphometric variables of developing primary mandibular second molars

Morphometric variables of second primary molar crowns from birth to completion were examined and measured. An image analysing technique comprising a photographic camera, a monitor, a computer with appropriate software and a digital caliper was used. Strong correlations were found between the ‘external’ aspect of the crown (mesiobuccal cusp height, mesiodistal and buccolingual dimensions and perimeter), and between all the ‘occlusal’ measurements of the crown, i.e. all the intercusp distances. However, poor correlations were found between the external and internal measurements of the crown such as the mesiobuccal cusp height and mesiobuccal-mesiolingual cusp-tip distance. It was also found that the mesiobuccal cusp serves as the apex of two triangles, the one formed by mesial cusps, and one formed by the distal cusps. The cusps on the mesial portion of the crown (ML, DB) are on a similar radius from the MB cusp, and the cusps on the distal portion are on a similar radius from the MB cusp. The small sample is a limitation but the results suggest a separate and independent pattern and rate of development of the external and the occlusal morphological variables of the tooth crown. Further research is needed on larger samples.

Cuspal ridges of deciduous upper second molars in Japanese subjects.

The occlusal surfaces of deciduous upper second molars were photographed by moire contourography using the standard trigonal plane. The ridges of a cusp, omprising a central ridge and the mesial and distal accessory ridges, were identified by the patterns of the moire fringes. The central ridge was present on all cusps except for the hypocone in both sexes. Frequencies of the two accessory ridges on trigonal cusps exceeded 60% except for the distal accessory ridge on the etacone. The mesial accessory ridge on the metacone was significantly more common in females than in males, but the running pattern of the cuspal ridges showed little difference between sexes. The oblique ridge of the deciduous molar was well developed compared with that of the permanent first molar. This ridge was observed in all subjects, but its height and structural components varied remarkably. A small tubercle on the oblique ridge was sometimes observed, usually located on the metacone side. This tubercle was similar to the metaconule in its position and morphology. Intercuspal distances showed larger mean values in the molars with a metaconule than those without. This implied that the overall crown size was affected by the degree of development of some crown components, such as the ridges and tubercles.

The dimensions of everyday class-II cavity preparations for amalgam.

Six hundred and ten epoxy plastic models, made from impressions of permanent teeth in which class-II cavity preparations for amalgam restorations had been prepared by eight Scandinavian dentists, were examined. The outlines of the cavity preparations were relatively large, with mean buccolingual extensions occlusally of 50% of the intercuspal distance and proximally of 40% of the length of the circumference of the proximal surface. There was a gradual increase in the size of the cavities towards the distal part of the dental arch, measured both in millimeters and in relation to the anatomic structures. The amount of hard tissue being removed varied among the operators and was possibly influenced by the dentist's ability to handle the cutting instruments. The large cavity preparations may be the result of using procedures for cavity preparation which are not adjusted to the tremendous cutting potential of modern dental instruments to produce stereotyped 'ideally designed' cavities.

Three-dimensional measurement of the occlusal surface the upper first molar in South African samples.

Three-dimensional measurement of the occlusal table of the upper first maxillary molar in three racial populations in South Africa was carried out with the use of moire contourography. Three populations were San Bushman, Central Sotho Bantu (Negroid) and Asiatic Indian (Caucasian). Their dental casts had been collected in 1968-1969 in Botswana and Lenasia by Nuffield Foundation and are now housed in Arizona State University. A moire photograph of the occlusal table in which contour lines were projected was obtained from each molar, and the height of cuspal tips and the intercuspal distance were measured. Cusps were highest in Asiatic Indian, intermediate in Bantu and lowest in Bushman. However, Bantu showed larger intercuspal distances than Indian, while Bushman had the smallest value of the distance. The results were compared with those of other racial populations previously investigated, then it was found that arrangement of four cusps in these samples were different from Mongoloid samples and that the proportion between cusp height and intercuspal distance in Asiatic Indian was close to another Caucasian, European white.

Three dimensional measurement of the occlusal surface of the deciduous upper second molar in Japanese population.

The occlusal surfaces of deciduous upper second molars in the Japanese population were measured with the aid of moire contourography. The mean values of the cusp heights and intercuspal distances were larger in females than in males, although these differences were insignificant except for the distance between the paracone and metacone. When the results obtained were compared with those permanent first molars, the crown size was smaller in deciduous than in permanent molars, especially. the height of the hypocone and the intercuspal distances in the buccolingual direction. Low correlations between the cusp heights and the intercusal distances in the permanent molara were also found in deciduous molars, suggesting that the cusp height of the human deciduous molar is independent from the transverse size of the crown.

Principal component analysis of intercusp distances on the lower first molars of three human populations

The distances between the five main cusps of lower first molars were measured on moiré photographs of casts obtained from Japanese, Dutch and Australian Aboriginal children. Principal component analysis of the intercusp distances, log transformed and standardized so that average tooth size was held constant, revealed three sources of shape variation in cusp topography. All populations were similar for scores on component 1 which was concerned with variations in the position of the hypoconulid. The Dutch had lowest scores on component 2 indicating small buccolingual distances compared with mesiodistal, whereas the Australian Aboriginals had the lowest mean score on component 3, expressing the distances between metaconid, entoconid and hypoconulid.

Three-dimensional measurement of the morphological relationship between molar occlusal surface and enamel-dentin junction.

The occlusal surfaces of lower molars and their enamel-dentin junction (EDJ) were photographed by means of moire contourography. Three-dimensional measurements were obtained from these photographs to show the differences in the intercuspal distances and the heights between the enamel surface and the EDJ. The average ratio of the heights of cusps on the EDJ relative to those on enamel surface was 87.5 % in M1, 81.5 % in M2 and 88.5 % in M3, respectively. The average ratio of total length of the four distances between cusps on the EDJ relative to those on the enamel surface was 88.0 % in M1, 88.3 % in M2 and 93.8 % in M3. The results indicated that the volume of enamel in M3 was smallest among the three lower molars. The differences in the thickness of the enamel between the region of the cuspal tip and the groove were shown to be related to the differences in the heights of the cusps between the EDJ and the enamel surface. Quantitative aspects of enamel formation were discussed.

Fractures of posterior teeth in adults

Examined in this study were 191 patients with 206 complete or incomplete fractures of posterior teeth. The patients ranged in age from 14 to 76 years, with 66.5% younger than 40 years. The number of fractures occurring in each arch was almost equal. The mandibular first molar was the most frequently fractured posterior tooth. The lingual cusps of mandibular molars fractured more often than did the buccal cusps of mandibular molars by a ratio of 2 to 1. In maxillary molars, buccal and lingual cusps fractured with almost equal frequency, but, in maxillary premolars, the lingual cusps fractured slightly more often than buccal cusps. Data gathered on the widths of the isthmuses of restorations in 109 teeth showed that fewer fractures occurred in teeth with more conservative restorations, with widths of isthmuses a quarter of the inter-cusp distance, and intact marginal ridges.

Intercuspal distances of maxillary pre-molar teeth in Australian Aboriginals.

Intercuspal distances and mesiodistal and buccolingual crown diameters of maxillary pre-molars were recorded from dental casts of 262 Australian Aboriginals. Although mesiodistal and buccolingual dimensions showed sexual dimorphism, no significant differences were noted between the sexes for intercuspal distances. Intercuspal dimensions showed greater variability and fluctuating asymmetry than did either of the traditional measures. No significant differences in heritability were noted among the three dimensions. Correlations between mesiodistal and buccolingual dimensions were higher than those between buccolingual and intercuspal measures. It appears that the sex differences, which are observed in overall crown dimensions, are established after the cusp tips are localized. Intercuspal distances appear to have a strong genetic component of variability, although they show high phenotypic variability and fluctuating asymmetry. Total tooth size may be subject to more intense selective pressures than the sites of initial calcification.

Maxillary arch dimensions in Saudi and Egyptian population sample

Observations relating to maxillary arch dimensions were obtained from 243 randomly selected subjects. The group consisted of 146 Saudi subjects with an average age of 24 years and 97 Egyptian subjects with an average age of 27 years. The measurement distances from canine to canine (C-C), molar to molar (M-M), molar to canine (M-C), and molar to incisor (M-I) were based on Mack4 criteria. There was a highly significant-difference by sex for Saudi and Egyptian samples, and the mean value of C-C, M-M, and M-I intercusp distances was significantly higher for Egyptians than for the Saudi sample. No significant difference was found in the M-C measurement. The results of this study demonstrate the median location of maxillary arch dimensions of Saudi and Egyptian groups combined as a sample Middle Eastern population when compared with Nigerian and British samples. Furthermore, this work can be used as a basis for future studies by anthropologists in all countries of the Middle East to define the possible changes that occur in the maxillary arch dimensions and the expected changes in the future.