Radiographic Appearance of Interocclusal Record Materials for Cone Beam Computed Tomography-Guided Implant Surgeries

PURPOSE

To select an ideal interocclusal record material for cone beam computed tomography (CBCT)-guided implant surgery based on the material's radiodensity on the scan.

MATERIALS AND METHODS

Twelve commonly used interocclusal record materials were used for this investigation: two were waxes, one was polyether, and nine were polyvinyl-siloxane-type materials. A scan template was fabricated by duplicating existing dentures in Ortho-Jet acrylic resin mixed with 30% barium powder for the teeth and 10% barium powder for the denture base between the teeth and the tissue. An interocclusal record was fabricated with each material, and the same template was used to obtain a CBCT scan with an ICAT machine (Imaging Sciences International) at 0.3 voxel and 14-bit depth settings. Twelve CBCT scans were obtained and analyzed. The radiopacity of the barium teeth was used as a control and was compared with the opacity of the 12 materials using a paired t test. A post hoc analysis of variance (ANOVA) test was used to compare the densities of the various materials with each other.

RESULTS

There was a statistically significant difference between the radiopacity of barium teeth (gray value: 1,959.475) and that of Modelling Wax (gray value: 750; P = .0026), Aluwax (gray value: 795.22; P = .0022), Blu-Bite CT (gray value: 1,105; P = .005), Ramitec (gray value: 1,105.3; P = .08), Memosil 2 (gray value: 1,202; P = .01) followed by Reprosil (gray value: 1,407.73; P = .01). Compared with the barium teeth, there was no statistically significant difference between the densities of Futar D (gray value: 1,866.5; P = .51), Jet Bite (gray value: 1,660.04; P = .08), Lab-Putty (gray value: 1,402.14; P = .19), and Memoreg 2 (gray value: 1,754.72; P = .1). The highest radiodensity was seen with Blu-Mousse (gray value: 2,949; P = .007) and Take 1 (gray value: 2,229.85; P = .025), which were also significantly different from the density of the barium teeth but in the opposite direction, making them more opaque.

CONCLUSION

Within the limitations of this in vitro study, the most radiolucent appearance of Modelling Wax, Aluwax, Memosil 2, Blu-Bite CT, and Ramitec made them the suitable materials of choice of those tested, as the interocclusal registration record during CBCT scanning allowed clear visualization of barium teeth.

Application of three-dimensional digital models for the morphometric analysis of predentition plasters: accuracy and precision

AIM

This study aimed to test the accuracy and precision of measurements of three-dimensional (3D) digital models from the pre-dentition period using a noncontact 3D measurement system (3D scanner) versus the gold standard method of direct measurements using a digital caliper on plaster models.

MATERIALS AND METHODS

Ten pairs of plaster models were obtained from children during the predentition period. Linear measurements were performed using both methods. Three operators were trained in the use of both methods for this study. Measurements were performed with a minimum 2-week interval between measurements in a randomly chosen order.

RESULTS

The mean difference between the measured values using the two methods was <0.2 mm for each measurement. There was no linearity in the measurements using pre-dentition digital models. An ANOVA Gage R&R analysis revealed that there was no significant operator difference (P < 0.307). The rate of variation of the 3D scanner over the total variation was 2.8%. The ICC was 0.982 (P< 0.001), suggesting excellent interoperator agreement.

CONCLUSION

The results suggest that measurements of digital 3D pre-dentition models are highly accurate and precise, and also comparable to measurements using the gold standard method.

Evaluation of the use of digital study models in postgraduate orthodontic programs in the United States and Canada

OBJECTIVE

To investigate the extent, experience, and trends associated with digital model use, as well as the advantages of using a particular study model type (digital or plaster) in postgraduate orthodontic programs in the United States and Canada.

MATERIALS AND METHODS

An electronic survey consisting of 14 questions was sent to 72 program directors or chairpersons of accredited orthodontic postgraduate programs in the United States and Canada.

RESULTS

Fifty-one responded for a 71% response rate. Sixty-five percent of the schools use plaster study models compared with 35% that use digital models. The most common advantages of plaster models were a three-dimensional feel and the ability for them to be mounted on an articulator. The most common advantages of digital models were the ease of storage and retrieval, and the residents' exposure to new technology. About one third of the plaster model users reported that they wanted to switch to digital models in the future, with 12% planning to do so within 1 year.

CONCLUSIONS

Based on our study, 35% of accredited orthodontic postgraduate programs in the United States and Canada are using digital study models in most cases treated in their programs, and the trend is for increased digital model use in the future.

Prevalence of dental anomalies in Saudi orthodontic patients

AIM

This study aimed to investigate the prevalence of dental anomalies and study the association of these anomalies with different types of malocclusion in a random sample of Saudi orthodontic patients.

MATERIALS AND METHODS

Six hundred and two randomly selected pretreatment records including orthopantomographs (OPG), and study models were evaluated. The molar relationship was determined using pretreatment study models, and OPG were examined to investigate the prevalence of dental anomalies among the sample.

RESULTS

The most common types of the investigated anomalies were: impaction followed by hypodontia, microdontia, macrodontia, ectopic eruption and supernumerary. No statistical significant correlations were observed between sex and dental anomalies. Dental anomalies were more commonly found in class I followed by asymmetric molar relation, then class II and finally class III molar relation. No malocclusion group had a statistically significant relation with any individual dental anomaly.

CONCLUSION

The prevalence of dental anomalies among Saudi orthodontic patients was higher than the general population.

CLINICAL SIGNIFICANCE

Although, orthodontic patients have been reported to have high rates of dental anomalies, orthodontists often fail to consider this. If not detected, dental anomalies can complicate dental and orthodontic treatment; therefore, their presence should be carefully investigated during orthodontic diagnosis and considered during treatment planning.

[Quantitative evaluation for the accuracy of dental model three-dimensional scanner]

OBJECTIVE

To establish a method to evaluate dental model three-dimensional scanner quantitatively, and to evaluate the accuracy which is a core indicator of 3Shape D700 scanner.

METHODS

A standard geometric model similar to the dental arch was designed by three-dimensional reverse software and processed by high precision CNC (computer numerical control) processing technology. Core indicators of dental model three-dimensional scanner including single scanning accuracy, space consistency and rescan accuracy were evaluated.

RESULTS

The result of single scanning accuracy of 3Shape D700 scanner was (15.00±10.84) μm, and there was no statistics difference between the accuracy given by manufacturer's instructions which is 20 μm (P=0.053), and same as the results of space consistency (compare the accuracy in vertical direction and horizontal direction, P=0.524) and rescan accuracy (compare the rescan accuracy in vertical direction, P=0.633, and in horizontal direction P=0.221).

CONCLUSION

It is feasible to evaluate accuracy of dental model three-dimensional scanner by this method, which can avoid observer error caused by selecting points manually.

Prevalence and distribution of hypodontia in a Turkish orthodontic patient population: results from a large academic cohort

AIM

Purpose of this study is to investigate the prevalence and distribution of congenitally missing permanent teeth (CMT) in a Turkish orthodontic patient population.

MATERIALS AND METHODS

Panoramic radiographs, intraoral photographs and dental casts of 2761 patients (females 1677, males 1084) aged from 9 to 46 who underwent orthodontic treatment at Selcuk University Department of Orthodontics from 1990 to 2005 were retrospectively reviewed for CMT. A comprehensive chart review was conducted in all subjects. Patient and treatment-related data were registered in a computer database for comparative analysis.

RESULTS

When missing third molar data were included, prevalence of CMT in the overall population was 30.64% with no significant differences between male and female patients (p=0.546). On the other hand, prevalence of CMT excluding third molars was 6.77% with a significantly higher prevalence in females compared to male patients (7.63% vs. 5.44%, p=0.030). The most commonly congenitally missing tooth types in decreasing order were the third molars followed by maxillary lateral incisors and mandibular second premolars. The majority of missing third molars were located in the maxilla (55.7%) with no significant gender differences (p=0.334). 58.4% of CMT excluding third molars in females were located in the maxilla compared to only 40.8% in males (p=0.001). In both gender groups, majority of CMT excluding third molars were located in the anterior segment (55.6% and 58.4% in male and female patients respectively, p=0.713).

CONCLUSION

The most commonly congenitally missing tooth type is third molars followed by maxillary lateral incisors and mandibular second premolars in our population. Although there were no gender differences in prevalence and anatomical distribution of missing third molars, CMT excluding third molars was significantly more prevalent in females with predominantly maxillary distribution in our population.

An audit of study casts used to monitor tooth wear in general practice

OBJECTIVE

To assess the outcome of compliance of advice sent to patients and dentists about monitoring tooth wear in general practice.

METHOD

Postal questionnaires were sent to 70 patients and their dentists requesting information on the outcome of letters of advice sent to general dental practitioners regarding monitoring tooth wear with study casts. They also requested information about the reasons for the patients' referral, the outcome of treatment and whether study models had been taken.

RESULTS

Replies were received from 60 dentists (87%) and 53 patients (75%). Of these, 16 patients and 16 dentists had moved from their recorded address. Study casts were reported as having been taken by 23 dentists (38%) and reported by 18 patients (34%). The most common reason for referral was advice about monitoring the wear and the appearance of their teeth.

CONCLUSIONS

The compliance of the patients and dentists in monitoring tooth wear by using study casts in general practice was not successful. It raises issues regarding the value of consultant advice letters to this common clinical problem.

Comparison of peer assessment rating (PAR) index scores of plaster and computer-based digital models

INTRODUCTION

The peer assessment rating (PAR) index is a valid and reliable tool for measuring malocclusion on plaster models, but it has not been shown to be valid and reliable when used to score computer-based digital models. The purpose of this study was to determine whether the PAR index is a valid and reliable measure on digital models.

METHODS

The study sample consisted of 48 pairs of plaster and digital pretreatment models. One examiner, calibrated in the PAR index, scored the digital and plaster models. The overall PAR scores were examined for reliability and validity by using analysis of variance and the intraclass correlation coefficient (ICC). Reliability of the components of the PAR score was compared with values originally presented by Richmond et al (1992).

RESULTS

No significant differences were found between overall PAR scores of plaster and digital models (P = .82), and scores were highly correlated (ICC = 0.95; lower confidence boundary (LCB) = 0.92; upper confidence boundary (UCB) = 0.97). Intraexaminer reliability was excellent for both plaster models (ICC = 0.98; LCB = 0.97; UCB = 0.99) and digital models (ICC = 0.96; LCB = 0.94; UCB = 0.98). Reliability of all components of the PAR score generated on digital models except for buccal occlusion was similar to those of Richmond et al.

CONCLUSION

PAR scores derived from digital models are valid and reliable measures of occlusion.

Clinical use of the ABO-Scoring Index: reliability and subtraction frequency

This study tested the reliability and subtraction frequency of the study model-scoring system of the American Board of Orthodontists (ABO). We used a sample of 36 posttreatment study models that were selected randomly from six different orthodontic offices. Intrajudge and interjudge reliability was calculated using nonparametric statistics (Spearman rank coefficient, Wilcoxon, Kruskal-Wallis, and Mann-Whitney tests). We found differences ranging from 3 to 6 subtraction points (total score) for intrajudge scoring between two sessions. For overall total ABO score, the average correlation was .77. Intrajudge correlation was greatest for occlusal relationships and least for interproximal contacts. Interjudge correlation for ABO score averaged r = .85. Correlation was greatest for buccolingual inclination and least for overjet. The data show that some judges, on average, were much more lenient than others and that this resulted in a range of total scores between 19.7 and 27.5. Most of the deductions were found in the buccal segments and most were related to the second molars. We present these findings in the context of clinicians preparing for the ABO phase III examination and for orthodontists in their ongoing evaluation of clinical results.

No correlation between primary mandibular anterior crowding and vertical craniofacial configuration or lower incisor inclination

The aim of the present study was to evaluate the correlation between primary mandibular anterior crowding and vertical craniofacial configuration or sagittal lower incisor inclination. The collective comprised 100 consecutive patients (50 males, 50 females) subject to 4 selection criteria: mandibular anterior crowding > or = 1.0 mm, no previous orthodontic therapy, completely preserved deciduous canines and molars, and lateral cephalograms of good diagnostic quality before initiation of orthodontic treatment. Study casts of all patients were used to measure the mesiodistal width of the incisors and deciduous canines as well as the anterior arch circumference. The difference between the 2 represented the amount of crowding. On all cephalograms 16 parameters of vertical craniofacial configuration and 9 parameters of lower incisor inclination were measured. For error evaluation all measurements were repeated independently on 10 randomly selected study casts and cephalograms. This error amounted for the combined tooth width to 0.51% +/- 0.81, for arch circumference to 0.03% +/- 0.68, and for all cephalometric parameters to 0.38% +/- 4.81. For all parameters, arithmetic means, standard deviations and ranges were calculated. Further, correlation coefficients were calculated between anterior crowding and all 25 cephalometric parameters. The arithmetic mean of crowding was m = 2.0 +/- 1.3 mm with a range of 1.0 to 6.6 mm. The values of all cephalometric parameters were close to well accepted norms in the literature. The correlation coefficients between crowding and all cephalometric parameters varied from r = 0.0 to 0.3. According to this study there is no correlation between primary mandibular anterior crowding and vertical craniofacial configuration or sagittal lower incisor inclination.

Investigations on the palatal rugae pattern in cleft patients. Part I: A morphological analysis

The characteristics of the palatal rugae zone (number of rugae, relief type, posterior limitation) were investigated on the maxillary casts of 44 patients with unilateral cleft lip and palate and 28 patients with bilateral clefts by means of reflex microscopy, a three-dimensional, computer-assisted, touch-free measuring system for the metrical registration and analysis of the parameters directly on the maxillary casts for the segments of the 2 cleft groups. The features "number of palatal rugae" and "relief type" (primary rugae) were determined both before and after surgical repair of the cleft palate. Both segments in unilateral cleft lip and palate and both lateral segments in bilateral clefts most commonly had 4 to 5 palatal rugae. The number of rugae in cleft patients is thus in a range that other authors have reported for non-cleft individuals. Following palatal cleft repair, the rugae counts per segment decreased significantly in patients with unilateral and bilateral cleft lip and palate but the 3rd rugae was never lost after surgery. The relief type identified in unilateral and bilateral cleft lip and palate was the same as in isolated cleft palates and did not differ from that in non-cleft subjects. The posterior limitation of the palatal rugae zone was determined both in a tooth-defined manner and as an absolute linear distance (at all time points). The most frequent tooth-defined posterior limitation of the rugae zone in unilateral and bilateral clefts was the second deciduous molar, which is also the position identified for non-cleft individuals. The linear distance from the tuberosity line to the rugae zone increased in all segments of unilateral and bilateral clefts during the interval up to palatal cleft repair, indicating sagittal maxillary development in the posterior area of the palate. Surgical repair of the cleft palate resulted in a significant shortening of the distance in both segments of the unilateral cleft, most likely due to the displacement of mucosa and periosteum required to cover the palatal cleft.

Condylar repositioning in mandibular retrusion

STATEMENT OF PROBLEM

There has been debate about which anteroposterior maxillomandibular relationship should be used in fixed and removable prosthodontics for patients without a definite maximal intercuspation. The choice has important implications for complete denture fabrication in which any guidance to the previous dentulous maximal intercuspal position is missing.

PURPOSE

This study was designed to estimate the posterior displacement that takes place at the mandibular condyles and occlusal surfaces when the mandible is moved from maximal intercuspal position to the most retruded mandibular position.

MATERIAL AND METHODS

Articulated occlusal models of 18 subjects with a natural dentition and well-defined maximal intercuspation were studied. Models were rearticulated in retruded contact position, and the original vertical dimension of occlusion was restored by eliminating all interfering occlusal contacts on the retruded path of closure. Measurement of change in condylar position was estimated using a SAM2 articulator with condylar position indicator. Posterior displacement at the occlusal surfaces was measured with a traveling microscope.

RESULTS

Condylar analog retrusion in the horizontal plane at the initial retruded contact position varied from 0.6 to 2.4 mm (mean 1.0 +/- 0.4 mm); however, after occlusal adjustment to restore the original vertical dimension of occlusion, retrusion was reduced to a range of 0 to 0.4 mm (mean 0.2 +/- 0.1 mm). Retrusion at the occlusal surfaces was found to vary from 0.4 to 1.5 mm (mean 0.7 +/- 0.3 mm) at retruded contact position; however, after occlusal adjustment, retrusion was reduced to a range of 0 to 0.5 mm (mean 0.2 +/- 0.1 mm).

CONCLUSION

Posterior displacement at both the occlusal surfaces and the condyles was small when interfering occlusal contacts on the retruded path of closure were removed.

The effect of tooth size discrepancy on occlusion: An experimental study

The purposes of this experimental study are the following: (1) to compare the anterior and overall tooth size ratios reported by Bolton to values reported in epidemiologic studies, (2) to assess the accuracy of tooth size discrepancy measurements, (3) to investigate to what extent generalized tooth size discrepancy affects occlusion, (4) to investigate the effect of leveling the curve of Spee, and (5) to evaluate the effect of extraction therapy of 4 premolars on occlusion. For the first part of the study, Bolton's mean anterior and overall tooth size ratio (as well as the extraction values) were compared with calculations derived from 4 publications reporting mean mesiodistal tooth width by using the t test (P </=.05). The second part of the study was carried out on a setup made from 1 dental cast of a male patient judged to have an ideal occlusion at the end of a nonextraction treatment. Our data reveal (1) no significant difference between the overall tooth size ratios of the Bolton values compared to 4 studies, but the anterior ratios were significantly different, (2) high reproducibility (99%) of tooth size discrepancy measurements, (3) that severe tooth size discrepancy affects the occlusion only a little, (4) that an excessive (6 mm) curve of Spee creates the poorest setup result, and (5) that extraction therapy only slightly affected the final occlusion. The effect of generalized tooth size discrepancy appears to be limited.

Compressibility of two polyvinyl siloxane interocclusal record materials and its effect on mounted cast relationships

STATEMENT OF PROBLEM

Addition silicones (polyvinyl siloxanes) are universally accepted as accurate and stable impression materials. They have also gained popularity as interocclusal record materials. However, it has not been defined if it is possible to work with polyvinyl siloxanes without changing the recorded maxillomandibular relations.

PURPOSE

This study examined the compressibility of 2 addition silicones as interocclusal record materials, analyzing the changes of maxillomandibular relations at the condyle region when different compressive forces are used to stabilize articulated casts.

MATERIAL AND METHODS

Sixteen interocclusal records, obtained from the same patient (8 of each polyvinyl siloxane, Blu-Mousse, Fast Set), were interposed between the patient casts in a new measuring system obtaining 48 curves of load versus maxillomandibular positional changes in 3 axes (x, y, z). These curves were compared with curves obtained with the casts in maximum intercuspation without interocclusal records (reference curves). Analysis of variance was used to compare maxillomandibular positional changes among the 3 groups (n = 48 each): Blu-Mousse, Fast Set, and control group or maximum intercuspation without interocclusal record.

RESULTS

There was no significant change in maxillomandibular relations when forces up to 1 kgf were applied to stabilize the casts related by means of Blu-Mousse and Fast Set addition silicone interocclusal records.

CONCLUSION

It is possible to use these polyvinyl siloxanes as interocclusal record materials without changing the recorded maxillomandibular relations.

Three-dimensional virtual imaging of facial skeleton and dental morphologic condition for treatment planning in orthognathic surgery

The improvement of esthetics and function, including the occlusal relationship, needs to be carefully considered in treatment planning for the success of orthognathic surgery. Conventional lateral cephalograms and dental study casts have been used usually for the assessment of skeletal morphologic condition and occlusion, respectively, in planning procedures. However, these traditional techniques do not allow for simultaneous evaluation of the skeletal morphologic condition and the occlusal harmony. A new technique has been developed that combines the conventional clinical diagnostic materials, cephalograms, and dental study casts to produce a 3-dimensional virtual image for routine practice. A 3-dimensional graphic image of dental study casts was generated with a laser surface scanner. A 3-dimensional skeletal image was constructed based on the coordinates of anatomic landmarks registered on frontal and lateral cephalograms. The image of the study cast was then set up with the 3-dimensional skeletal image to create a 3-dimensional dataset of the virtual image. The 3-dimensional virtual image, combining the cephalometric and the dental study cast information, permits simultaneous display of skeletal morphologic condition and occlusal relationship. This 3-dimensional virtual imaging can be helpful in planning orthodontic-surgical treatment and in providing graphic information to the patient. This article describes the technique and outline. A clinical application with this imaging technique is also demonstrated.

Factors influencing changes in maxillary arch dimensions in unilateral cleft lip and palate patients until six months of age

OBJECTIVE

The objectives of the present study were (1) to investigate whether growth increments until 6 months of age are influenced by particular factors, (2) to analyze whether anterior cleft reduction is dependent on the extent of the cleft width at birth, and (3) to examine the correlation between maxillary measurements at birth and the anterior cleft width at 6 months of age.

DESIGN

The study design was prospective and longitudinal.

SETTING

Heidelberg University Hospital Interdisciplinary Cleft/Craniofacial Center.

PATIENTS AND METHOD

The longitudinal records of 34 patients (24 male and 10 female) with complete unilateral cleft lip, alveolar ridge, and hard and soft palate were included in this study. All patients were treated with the same protocol. All participants were assessed at 0 and 6 months of age. Maxillary plaster casts of the patients were analyzed using a computer-controlled three-dimensional digitizing system.

MAIN OUTCOME MEASURE

Maxillary models were measured and compared to putative factors influencing growth.

RESULTS

No statistically significant differences were found between maxillary growth changes and increases in weight and length. Similarly, there was no significant interaction between the extent of the alveolar cleft width at birth and its reduction prior to lip closure. In contrast, significant differences of maxillary growth increments could be found between male and female patients. Stepwise regression analysis demonstrated a correlation between maxillary measurements at birth and growth increments.

CONCLUSION

The results of the study indicate that gender plays a certain role in growth changes within the first 6 months of age.

[The intergroup variability and sex dimorphism in the size of the human dental arches in personal identification]

The morphology of dental arch has been studied in representatives of 11 contrast (by anthropological characteristics) ethnic groups from regions of their compact residence. The sampling from each ethnic group consisted of 200 subjects (100 male and 100 female) aged 13-20 years. A total of 4,500 plaster models of dental arches were examined. The results were statistically processed using factor, canonical, discriminant analyses, and multidimensional scanning. The data on the variability and sex dimorphism in the size and shape of dental arches in subjects belonging to different ethnic groups may be practically significant in forensic medical personality identification.

Three-dimensional acquisition and visualization of dental arch features from optically digitized models

A method for the acquisition and evaluation of 3D coordinates from anatomically oriented plaster casts is presented, which is based on optical phase shifting profilometry (a fringe projection technique). With the computer-controlled setup, measurements from different views can be combined to obtain a complete three dimensional reconstruction of the model surface. To allow faster evaluation, the result is converted into a range image. From this digital data set the characteristic features like cusp tips can be identified and located semi-automatically. Based on these marks, quantitative values for differences between situation models like local displacements, e.g. during orthodontic treatment, can be determined. The results are visualized as interactively controllable 3D computer graphics, which helps to make spatial relations clearer.

Comparison of the accuracy of working casts made by the direct and transfer coping procedures

STATEMENT OF PROBLEM

A working cast with dies that accurately record the prepared abutments, surrounding soft tissues, and adjacent and opposing teeth is necessary.

PURPOSE

This study compared the accuracy of the direct and transfer coping methods in recording the vertical and horizontal dimensional relationship of a pair of removable dies in a working cast before and after separation from the stone base. Among the procedures used for making impressions of abutments for fixed partial dentures, the transfer coping procedure has specific advantages. In particular, where there are multiple abutments, this procedure, in which individual impressions are made of the abutments, transfer copings are made, and a transfer impression of the copings is used for seating the dies and fabrication of a dental stone base, is useful.

METHODS

Two groups of working casts were fabricated from a stone master cast containing 2 ivorine teeth to simulate abutments. The first group of working casts was fabricated directly from the elastomeric impression of the abutments using a 2-pour procedure. The second group of working casts was made using the transfer coping procedure.

RESULTS

When the interdie dimensions in each group were compared with that of the master cast, after separation and replacement of the dies in the stone base, the differences were less than 100 microm and similar for both the direct and transfer coping techniques.

CONCLUSIONS

These findings show that either procedure is equally effective in positioning the dies in the working casts.

Occlusal stability after extraction orthodontic therapy in adult and adolescent patients

In this study we compared the posttreatment stability of occlusion in adults and adolescents treated for crowding or maxillary protrusion with four-premolar extractions and edgewise mechanics at an average of more than 4 years out of treatment. The adolescent sample showed a significantly greater posttreatment increase in mandibular anterior crowding than the adult sample. Posttreatment overjet and overbite remained more stable in the adolescents. We noted a correlation between in-treatment expansion and posttreatment narrowing of mandibular intercanine width in the adults. Differences in postorthodontic occlusal changes were noted between the adult and adolescent samples.

An accuracy evaluation of four removable die systems

STATEMENT OF PROBLEM

The advent of implant dentistry has redefined the need for accuracy of working cast models. Die stone expansion and errors introduced by removable die casts may exceed the accuracy required for the passive fit of implant prostheses.

PURPOSE

Several removable die systems claim improved accuracy because of their design and/or technical advancements. This study evaluated the 3-dimensional accuracy of 4 removable die systems. All 4 systems tested use either 1 or 2 pins as the repositioning device.

MATERIAL AND METHODS

Four removable die systems were evaluated (Belle de St. Claire, Pindex, DVA, and conventional brass dowel system). Master model impressions were made with polyvinyl siloxane material and were later cast with type IV die stone material. Comparative dimensional analysis between the master model and the solid and sectioned casts was made by placing the cast in a standardized position and fabricating an individual custom base for each cast. Landmarks were measured with a traveling microscope, and by mathematically rotating the casts. Discrepancies beyond that of stone expansion or residual stress release at the time of die separation were due to the inability to precisely reposition the removable die of the sectioned cast. Data were analyzed with multivariate analysis of variance and paired t tests at alpha = .05 (n = 10).

RESULTS

Significant differences were found among die systems tested (P = .005). When sectioned dies were compared with the master model, the accuracy of all 4 die systems was within 0.055 mm of the master model. Once sectioned, the Pindex system had the least linear expansion in the y dimension, and the brass dowel system demonstrated the least reseating discrepancy in the z (occlusogingival) dimension.

CONCLUSIONS

All 4 die systems provided a similar degree of dimensional accuracy, although Pindex showed the least horizontal movement and the brass dowel system produced the least occlusogingival reseating discrepancy.

A three-dimensional analysis of mandibular arch changes following curve of Spee leveling in nonextraction orthodontic treatment

The present study was conducted to determine the effects of curve of Spee leveling on three-dimensional arch length and specific components of arch form. The mandibular pretreatment and posttreatment dental casts of 33 patients treated orthodontically without the extraction of teeth were digitized with a three-dimensional positioning transducer integrated with a graphics calculator. Statistical analysis was carried out with general linear models and the calculation of Pearson correlation coefficients of the relationships between the dependent variable of the curve of Spee leveling and the independent variables of arch length, arch depth, and three arch widths. The regression and correlation analyses essentially showed no relationship between the independent variables (arch length, arch depth, and the three arch widths) and the dependent variable (curve of Spee leveling). Although the three-dimensional arch length was increased after leveling of the curve of Spee in 24 of the 33 dental casts evaluated, the results from the statistical analyses indicated that this increased arch length was not necessarily the result of the curve of Spee leveling but may have been caused by other variables.

Predictive variables for the outcome of early functional treatment of Class III malocclusion

The aim of this study was to select a model of cephalometric and occlusal predictive variables for the results of early treatment of Class III malocclusion, due to mandibular protrusion in the deciduous dentition. Lateral cephalograms and dental casts of 45 subjects (22 boys and 23 girls) with Class III malocclusion in the deciduous dentition were analyzed at the start of treatment (mean age 5.57 +/- 0.85 years). The patients were treated with a functional appliance (removable mandibular retractor). All subjects were reevaluated after a mean period of 9.54 +/- 2.28 years comprising active treatment plus retention. At this time, the sample was divided into two groups according to occlusal criteria: successful group (23 subjects) and unsuccessful group (22 subjects). Stepwise variable selection on the measurements at the time of first observation identified three predictive variables; the inclination of the condylar axis in relation to the stable basicranial line (CondAx-SBL), the inclination of the nasal line to the mandibular line (NL-ML), and the transverse width of the mandibular arch measured at the first deciduous molars. Discriminant analysis assigned a classificative power of 95.55% to the predictive model. On the basis of the equation generated by the multivariate statistical method, outcome of early treatment for each new case with Class III malocclusion in the deciduous dentition can be accordingly predicted. The important role of both vertical and transverse relationships in Class III prognosis was emphasized.

[Sex determination with a discriminant function analysis of deciduous teeth size in plaster models]

Plaster models of the teeth of 3-year-old Japanese children (96 males, 98 females) were used to record the crown length, crown width and crown thickness of 5 maxillary and 5 mandibular deciduous teeth (30 measurement values). These measurements were used to devise a number of sex determination formulae. A sex-determination formula using all 30 values was calculated. Furthermore, a number of practical formulae were derived from only the crown width and crown thickness values because the deciduous teeth wear in 4 years and older children rapidly progress, making the crown length measurement unreliable. These formulae were calculated for the maxillary teeth alone and mandibular teeth alone. The formulae based on only the crown width or thickness were also calculated for both maxillary and the mandibular teeth. A step-wise discriminant analysis was then used to ascertain the most reliable measurements and a practical formula subsequently devised. The results obtained were as follows: 1. The mean value for each measurement was greater in males than in females. 2. Significant differences in the values recorded were seen in 28 out of the 30 measurements taken. The measurement items not exhibiting these significant differences were the crown width of the maxillary lateral incisor and the crown thickness of the mandibular second molar. 3. The accuracy rates for the sex-determination analysis and the step-wise sex determination analysis calculated using all 30 values were 78.6% and 75.7%, respectively. 4. The accuracy ranges for the modified sex-determination formulae and the associated step-wise sex determination analyses were 70.6-78.4% and 67.0-76.8%, respectively.

[The accuracy of holograms compared to other model measurements]

Because holograms are easy to deal with, and because their information content is especially high, they will potentially play a much larger role in the future. In this study plaster casts were placed in a measuring device fabricated in our department, measured by means of a laser beam, and then the accuracy of these measurements was compared to hologram measurements taken by means of a sliding caliper. The result was that the computer-guided hologram measurements evidenced no significant differences with the measurements with a laser beam. The hologram measurements, which are regarded as having an accuracy of 0.182 mm, should therefore be significantly superior to sliding caliper measurements. When measuring the mesiodistal width of teeth, the caliper yields a pseudo-accuracy which doesn't correspond to the factual conditions. When defining the Z-coordinates, the sliding caliper's measuring deficiencies are easily circumvented, but this does not automatically imply a higher degree of accuracy.

Accuracy of models for indirect posterior restorations

Effects of materials and techniques on the accuracy of models used to make indirect restorations was measured using a 4-unit posterior model containing a MOD and full crown preparation. Improved stone and fast setting epoxy dies backed with either improved stone or a thermoplastic hot melt stone were made from single-viscosity addition silicone impressions. Technique variations included heating or not heating the impression, cooling and pouring dies and placement of the hot melt stone on set or unset epoxy. The dimensions of the MOD (L, W, H) and of the crown (W, H) dies were measured at 1 and 24 h. No clinically significant changes occurred between 1 and 24 h. The stone control reproduced the dimensions of the master die best, and models made by pouring epoxy into the impression followed by immediate pouring of the hot melt stone gave the poorest reproduction. Other variations in technique using epoxy for the anatomical portion gave no practical differences in accuracy. Of the epoxy dies, those prepared from a previously heated impression with hot melt poured after the epoxy set had the best values; however, epoxy dies were smaller than stone dies. The fast set epoxy was noteworthy for rapid processing and sharp detail, however, negative changes for W and H of the crown and H and L of the MOD showed that a die spacer would be essential in the preparation of indirect restorations.