An improved method to analyse tooth and restoration contour using image analysis: application in the maxillary anterior teeth in Chinese population

OBJECTIVES: The aim of this study was to develop a method to analyse tooth and restoration contour, and apply it to investigate the differences in coronal contour of maxillary anterior teeth in Chinese population. METHODS: One hundred and sixteen Chinese volunteers participated in this study. An upper cast was fabricated with self-cure acrylic resin for each participant. The images of serial slices obtained from the resin teeth were analysed to produce a data set (x, y) representing the coronal contour. The data were used to find appropriate equations to describe the shape of the contours. The values of the equation parameter and the reliability of the technique were analysed using SPSS statistical software. RESULTS: A high level of repeatability was found suggesting that the method is reliable. In this study the facial and lingual contour were best represented by two equations: y=a+bx(0.5) and ln(y)=a+bx(2), respectively. The b values generated from this analysis provided a measure of tooth contour. In this group of Chinese population, the facial surfaces had a straighter coronal contour in male and the surfaces became gradually straighter from the canine to the central incisor with the greatest convexity being found in the mesial third of each tooth. On the lingual surfaces the greatest concavity was found in the middle third of each tooth, this being greatest in the canine. CONCLUSIONS: This method was suitable for analysis of tooth contour, revealing statistically significant differences in contour between genders, tooth types and parts of tooth in a dentally healthy adult Chinese population. The method should also be suitable for analysis of contour in restored teeth.     

Objective assessment of occlusal and coronal characteristics of untreated normals: a measurement study.

To determine whether tooth shape and position are constant within tooth types, dental casts of 68 Indians (age range, 10-32 years; mean, 18.72 years) were analyzed. The casts were selected from a larger sample and met the following criteria: Class I molar and canine relationships; overjet and overbite within normal limits; well-related vertical, transverse, and anteroposterior relationships with pleasing profiles and well-aligned arches; and no supernumerary teeth or large restorations. None of the subjects had received orthodontic treatment, and all were in good health and exhibited normal growth. Crown angulation, inclination, offset of maxillary molar, curve of Spee, crown facial prominence, horizontal crown contour, and vertical crown contour were assessed. Means, standard deviations, and standard errors were calculated. The measurements were compared with Andrews's data on 120 nonorthodontic normal occlusion casts. The Student t test was used to determine the significance of differences between the 2 sets of data. It was found that teeth of the same tooth type have similar values of horizontal and vertical crown contours. Values for inclination, angulation, and relative prominence were also similar. Hence, we concluded that tooth shape and position are constant for each tooth type. The data from this study were comparable with Andrews's findings. However, from this study, it would be safe to presume that all teeth except the maxillary second molars require alterations in the bracket base inclination value, and that the maxillary lateral incisor, canine, second premolar, and second molar, and the mandibular canine, require alterations in angulation values.     

The role of coronal contour in gingival health.

1. Total clinical crown contour is related to gingival health. 2. The subgingival convexity of a tooth or a restoration should extend facially or lingually no more than one half of the thickness of the gingiva. This protects the gingival crevice and promotes a knifelike free gingival margin, important in plaque control. 3. The facial and lingual surface contours should have gradual curvatures in all directions to facilitate the rubbing and cleaning function of the lips, cheeks, and tongue. 4. The interproximal contour of adjacent teeth, of the tooth contact areas, and of the teeth in relation to the gingival papilla must be such that moving tissues can rub or the patient can perform oral hygiene easily. The requirements may vary depending on the degree of gingival recession and cosmetic needs. 5. Undercontour is better than overcontour where clinical judgment is vague.     

Impression pressures against teeth in a partially edentulous model with a mobile tooth: influence of impression tray design

The purpose of the present study was to examine the effect of custom tray designs on local pressures against teeth during the impression procedure. In a previous study, a partially edentulous simulation model with a mobile tooth was used, and the effect of custom tray designs on the displacement of the mobile tooth was examined during the impression procedure. Based on that study's results, we have assumed that the differences in impression pressures between the labial and the lingual sides of a mobile tooth could either cause or affect displacement. The present study was undertaken to determine the local impression pressures against each side of three anterior teeth, including one mobile tooth, using the same simulation model and the same custom trays as in the previous study. It was found that the local pressures exerted against teeth during the impression procedure were affected by the custom tray designs and varied according to the coronal shape, axis inclination and location of the teeth.     

The influence of coronal restoration type on the survival of endodontically treated teeth

The aim of this study is to investigate the association between coronal restoration type and survival of endodontically treated teeth. A review was performed of treatment records of patients who had endodontic treatment performed in the Department of Restorative Dentistry, University Dental School & Hospital, Cork, Ireland during the period 1993-96. Demographic and dental factors such as age, gender, tooth type, coronal restoration type, and tooth status recorded at a review appointment were recorded. Tooth status at review was defined as 'tooth present' or 'tooth absent' based on the presence or absence of the endodontically treated tooth recorded in the treatment records at a review appointment held a minimum of one year following obturation of the root canal system. Of 176 teeth (166 patients) treated, survival of endodontically treated teeth was significantly more likely where restored with cast restorations (91.7%), amalgam restorations (86.5%), or composite restorations (83.0%), than teeth restored with temporary restorations (34.5%) (p<0.0001) (mean follow-up time 38 months, range 12-60 months). Survival of endodontically treated teeth was found to be associated with permanent coronal restorations. Loss of endodontically treated teeth occurred more often with those restored with temporary restorations (34.5%) than other restoration types (p<0.05).     

Tooth structure removal associated with various preparation designs for anterior teeth

STATEMENT OF PROBLEM: The conservation of sound tooth structure helps preserve tooth vitality and reduce postoperative sensitivity. Innovative preparation designs, like those for porcelain laminate veneers, are much less invasive than conventional complete-coverage crown preparations. However, no study has quantified the amount of tooth structure removed during these preparations. PURPOSE: The purpose of this study was to quantify and compare the amount of tooth structure removed when various innovative and conventional tooth preparation designs were completed on different teeth. MATERIAL AND METHOD:. A new comprehensive tooth preparation design classification system was introduced. Typodont resin teeth representing the maxillary left central incisor, maxillary left canine, and mandibular left central incisor were prepared with the following designs: partial (V1), traditional (V2), extended (V3), and complete (V4) porcelain laminate veneer preparations; resin-bonded retainer preparation with grooves (A1) and with wing/grooves (A2); all-ceramic crown preparation with 0.8 mm axial reduction and tapering chamfer finish line (F1), all-ceramic crown preparation with 1.0 mm axial reduction and rounded shoulder finish line (F2), and metal-ceramic crown with 1.4 mm axial reduction and facial shoulder finish line (F3). After tooth preparations (10 per group), the crown was separated from the root at the CEJ. The removed coronal tooth structure was measured with gravimetric analysis. Means and standard deviations for tooth structure removal with different preparation designs were calculated and analyzed with analysis of variance at a significance level of P<.05. RESULTS: Significant differences in the amount of tooth structure removal were noted between preparation designs. Ceramic veneers and resin-bonded prosthesis retainers were the least invasive preparation designs, removing approximately 3% to 30% of the coronal tooth structure by weight. Approximately 63% to 72% of the coronal tooth structure was removed when teeth were prepared for all-ceramic and metal-ceramic crowns. For a single crown restoration, the tooth structure removal required for an F3 preparation (metal-ceramic crown) was 4.3 times greater than for a V2 preparation (porcelain laminate veneer, facial surface only) and 2.4 times greater than for a V4 preparation (more extensive porcelain laminate veneer). CONCLUSION: Within the limitations of this study, tooth preparations for porcelain laminate veneers and resin-bonded prostheses required approximately one-quarter to one-half the amount of tooth reduction of conventional complete-coverage crowns.     

The use of extracted teeth to evaluate clinical measurements of periodontal disease.

Clinical indicators of periodontal disease, Gingivitis Index, Gingival crevicular fluid and pocket depth measurements were obtained from the gingiva surfaces of 30 teeth. The gingival margins were marked on the surfaces of the teeth prior to extraction. The extracted teeth were stained with hematoxylin and air dried, and the distances from the groove to the base of the calculus, plaque, and connective tissue attachment were obtained. The plaque-free zone was also measured. Comparisons were made between clinical and tooth surface measurements. A high correlation was found between clinical pocket depth measurements and tooth surface parameters. The correlations between all tooth surface parameters and GCF were statistically significant. The G.I. was significantly correlated only with the penetration of calculus into the pocket. The clinical pocket depth was statistically the same as the distance from the gingival groove to the coronal connective tissue attachment. The plaque-free zone appeared to represent the junctional epithelium.     

Influence of overdenture abutment tooth contour on the periodontium: a preliminary report

The effect of overdenture abutment tooth contour on plaque retention and periodontal health was evaluated in four patients over a 1-year period. Each patient had mandibular canines with similar periodontal support; however, one abutment was dome shaped while the other had 2 mm of natural peripheral root contour coronal to the ginvival margin. Eight parameters of periodontal health were measured, and no significant differences between different contours were observed after 1 year. Furthermore, irrespective of overdenture abutment contour, no deterioration in periodontal status occurred. Two subjects had significant wear of the overdenture abutments after 1 year. Further evaluation of more subjects over a longer period of time is indicated.     

Comparative data from young men and women on masseter muscle fibres, function and facial morphology.

The primary aim was to relate information about masseter muscle fibres and function to aspects of facial morphology in a group of healthy young men. The secondary aim was to investigate possible sex differences using data previously obtained from a comparable group of age-matched, healthy women. Dental status and facial morphology were recorded in 13 male students aged 20-26 years. Functional examinations included bite-force measurements and electromyographic recordings of masseter activity. A biopsy was removed from the masseter of each participant during surgical extraction of a wisdom tooth, and the tissue examined for myosin ATPase activity. Further, the cross-sectional areas of the different fibre types were measured. In spite of using age-matched healthy men and women with a full complement of teeth, statistically significant sex differences were found among measures related to muscle function and some measures of facial morphology. Thus data from men and women should not be pooled uncritically. The greater bite force in men than women corresponded with the greater diameter and cross-sectional area of type II fibres. Further, the males had more anteriorly inclined mandibles and shorter anterior facial height, suggesting a relation between the greater muscle force and the shape of the face. However, linear regression analysis failed to demonstrate any significant association between bite force and facial morphology among men and women. Thus, craniofacial morphology could be a result of far more contributing factors than previously believed.     

Study of the morpho-dimensional relationship between the maxillary central incisors and the face

The aim of this study was to evaluate the frequency of agreement between the shape of the maxillary central incisor (MCI) and that of the face; verify which is the most pleasing MCI shape for the two genders; whether there is coincidence in the preference for tooth shape; and measure the most pleasant proportion of tooth and facial width for the esthetics of the smile. One hundred patients were selected from among front view photographs of the face and smile. The photographs were evaluated to determine the shape of the face and the type of dental contour, the pleasant appearance of the set consisting of the teeth and facial features. The widths of the MCIs and the face were measured and the proportional values were associated with the evaluators' opinions with regard to the pleasant appearance of the set of facial features. There was a significant association between the shape of the face and the MCI (Bowker's test, p = 0.0015). There is a relationship between the shape of the MCI and the shape of the face, with a greater prevalence of the oval shape of the teeth and face; it was not possible to associate the pleasant appearance of the shape of teeth with gender; there was no agreement on the pleasant appearance of the shape of teeth in the photographs of the patient smiling and in the images of the smile; and there was no relationship between the pleasant appearance of the face and the dentofacial proportion and bizygomatic width.     

Acid-etch patterns on the buccal surface of human permanent teeth

Since the introduction of acid etching to aid adhesion to enamel, there has been much research into dental materials to improve bond strength, but little into the surface topography of etched enamel, particularly regarding possible variations between tooth types. This study was a systematic investigation into the quality and quantity of etch patterns found on the buccal surfaces of different human permanent teeth. Twenty-nine orthodontic patients had high-resolution silicone impressions taken of the buccal surface of incisor, canine, premolar and molar, upper and lower teeth, following etching for 30s with 37% phosphoric acid. Impressions (n=266) were replicated in epoxy resin and examined under high magnification in a scanning electron microscope. A modification of the classification of Galil and Wright was used, with histometric techniques, to quantify the quality of etch patterns on enamel surfaces where orthodontic brackets are typically bonded. There was no difference between right and left or between upper and lower teeth of the same type (P>0.05). There was a general trend toward the increasing occurrence of no etch (type D) from anterior to posterior teeth, and a trend toward fewer good-quality etches (types A and B) in the same direction. Etch types A and B were found to occupy the smallest area on the etched buccal surface enamel. The greatest amount of type A etch 'ideal' was found on the lower incisors, yet it occupied less than 5% of the etched buccal surface enamel. The greatest area of etched enamel surface was occupied by type C (etched, but enamel prisms not evident). It was concluded that there is a significant difference in the acid-etch patterns achieved on different tooth types, which suggests that bond-strength studies should be performed with a single tooth type or that an equal number of different tooth types be included.     

A comparative study of effectiveness in plaque removal by Super Floss® and waxed dental floss

The effectiveness of Super Floss and waxed dental floss as proximal surface cleansing agents was compared in 34 subjects. Each subject used 1 agent twice daily for 2 weeks followed by the other agent used with the same frequency and for the same period. The order in which the agents were used was selected at random. Plaque was stained by erythrosin, and a plaque index of Wolffe used. Super Floss was found to be superior to waxed dental floss in removing proximal plaque, but neither was 100% effective. Some plaque was present in 49.9% of the proximal surfaces when Super Floss had been used and on 54.7% when the waxed dental floss had been used. Both agents cleaned distal surfaces better than mesial surfaces, proximal surfaces of anterior teeth more effectively than those of posterior teeth, the coronal half of the proximal surfaces better than the apical half and the facial half more efficiently than the lingual half. No differences were found between maxillary teeth and mandibular teeth. Subjects used more lengths of Super Floss than of waxed dental floss, indicating its relative 'brittleness'. However, the majority of subjects preferred Super Floss, mainly because it was thicker and felt more abrasive.     

Impact resistance of crowned endodontically treated central incisors with internal composite cores

Abstract The impact fracture resistance of crowned endodontically treated teeth with composite cores but without posts, that had either no coronal dentin remaining or a 1mm dentin collar was compared to that of unrestored, caries free teeth. The teeth were struck mid-labially to simulate a common trauma situation using a pendulum device and fracture1 resistance determined by calculation of absorbed energies. No significant difference was found between the intact teeth and the-crowned root treated teeth with composite core and a 1mm dentin collar. Crowned loot treated teeth with a composite core but no coronal dentin had significantly reduced fracture resistance (p < 0.05). Teeth with the dentin collar mainly fractured obliquely from the bueeal crown margin to a point coincident with the simulated alveolus, representing a clinical situation which would allow retention rather than extraction of the tooth.     

How accurate is Invisalign in nonextraction cases? Are predicted tooth positions achieved?

Objective:To evaluate the accuracy of Invisalign technology in achieving predicted tooth positions with respect to tooth type and direction of tooth movement.Materials and Methods:The posttreatment models of 30 patients who had nonextraction Invisalign treatment were digitally superimposed on their corresponding virtual treatment plan models using best-fit surface-based registration. The differences between actual treatment outcome and predicted outcome were computed and tested for statistical significance for each tooth type in mesial-distal, facial-lingual, and occlusal-gingival directions, as well as for tip, torque, and rotation. Differences larger than 0.5 mm for linear measurements and 2° for angular measurements were considered clinically relevant.Results:Statistically significant differences (P < .05) between predicted and achieved tooth positions were found for all teeth except maxillary lateral incisors, canines, and first premolars. In general, anterior teeth were positioned more occlusally than predicted, rotation of rounded teeth was incomplete, and movement of posterior teeth in all dimensions was not fully achieved. However, except for excess posttreatment facial crown torque of maxillary second molars, these differences were not large enough to be clinically relevant.Conclusions:Although Invisalign is generally able to achieve predicted tooth positions with high accuracy in nonextraction cases, some of the actual outcomes may differ from the predicted outcomes. Knowledge of dimensions in which the final tooth position is less consistent with the predicted position enables clinicians to build necessary compensations into the virtual treatment plan.     

Changes in the soft tissue chin after orthodontic treatment

The study envisages changes in the contour of the soft tissue chin immediately and 5 years after orthodontic treatment in a group of 31 male and 29 female patients. The group was classified according to facial types and whether treatment involved extraction of first premolar teeth. The average age before treatment was 10 years 7 months, immediately after treatment it was 14 years 6 months, and 5 years after treatment was 21 years 6 months. The chin contour was studied from cephalometric x-ray tracings. The facial types--mesofacial, brachyfacial, and dolichofacial--were identified on the basis of cephalometric analysis. The chin thickness was registered at six different locations around the symphysis, from the point on the soft tissue chin corresponding to B point to the chin point corresponding to menton. Statistical means and standard deviations for all of the six chin thicknesses were calculated. It was found that the overall soft tissue chin thickness increased after orthodontic treatment. The females had less increase at all levels than the males. The dolichofacial group showed a greater increase in the soft tissue chin thickness after treatment. The mesofacial and brachyfacial groups of females showed no statistically significant increases. Regression tests of independent variables, including age, sex, facial type, and such other cephalometric measurements as 1 - A Pog, 1 to A Pog, mandibular plane, mandibular arc, facial axis, lower face height, and classification of malocclusion, indicated that age, sex, and facial type were the only variables that influenced the soft tissue chin thickness.     

釉质发育不全磨牙的微观磨损性能研究

目的对比研究釉质发育不全磨牙的微观摩擦磨损性能。方法分别采用原子力显微镜（AFM）、能量色散X线光谱仪（EDX）对釉质发育不全牙及正常牙进行微观形貌观察和物质成分分析;通过纳米划痕技术并结合扫描电镜（SEM）对比分析其微观摩擦磨损性能上的差异。结果AFM图显示釉质发育不全牙釉质比正常牙釉质连接疏松且可见有孔状结构,粗糙度大。EDX检测发现釉质发育不全牙釉质Ca、P含量较正常牙低,C含量较正常牙高。釉质发育不全牙釉质在同等载荷下较正常牙的摩擦系数大,破坏严重。结论釉质发育不全牙与正常牙在微观结构、物质组成和微观摩擦磨损上均有较大差异。在临床上对釉质发育不全牙做修复时,应充分考虑这一因素。     

Influence of remaining coronal tooth structure location on the fracture resistance of restored endodontically treated anterior teeth

STATEMENT OF PROBLEM: A restored endodontically treated tooth is less likely to fracture when there is axial tooth structure between the core base and preparation finish line. However, an accurate prognosis requires knowing whether fracture resistance depends on a complete circumferential distribution of tooth structure or tooth structure in a specific location related to the applied force. PURPOSE: This in vitro study investigated the fracture resistance of restored endodontically treated teeth when residual axial tooth structure was limited to one half the circumference of the crown preparation. MATERIAL AND METHODS: Fifty extracted maxillary anterior teeth were sectioned 18 mm from their apices, endodontically treated, and divided into 5 groups of 10 teeth each. Four groups were prepared with full shoulder crown preparations having axial wall heights of 2 mm around the preparation circumferences. In 3 of the groups with axial tooth structure, one half of the axial tooth structure was removed, palatally, labially, or proximally, and groups were identified according to the site of retained coronal tooth structure. For the fifth group, all axial tooth structure was removed to the level of the preparation shoulder. Thus, in 1 group the axial walls were circumferential, 360 degrees around the preparations (Complete group), in 3 groups the axial walls were continuous for 180 degrees (Palatal, Labial, and Proximal groups), and the last group had no retained coronal tooth structure incisal to the finish line (Level group). All 50 prepared teeth were then restored with quartz fiber posts (Bisco), composite resin (Bisco) cores, and metal crowns. A universal testing machine compressively loaded the tooth specimens from the palatal at a crosshead speed of 0.5 cm/min at an angle of 135 degrees to the long axis of teeth until failure occurred. A survival analysis was conducted using a log-rank test followed by Holm-Sidak pairwise tests (alpha=.05) to detect significant differences in median failure load between groups. The mode of failure was determined by visual inspection of all specimens. RESULTS: The median failure load (P<.001) was 607 N, 782 N, 358 N, 375 N, and 172 N for the Complete, Palatal, Labial, Proximal, and Level groups, respectively. The predominant mode of failure was an oblique palatal to facial root fracture for the groups with remaining coronal tooth structure. In the Level group, post debonding was the predominant mode of failure. CONCLUSION: For restored endodontically treated teeth that do not have complete circumferential tooth structure between the core and preparation finish line, the location of the remaining coronal tooth structure may affect their fracture resistance.     

Sexual dimorphism of canine teeth of small dogs.

Sex-associated morphological characteristics were shown in the permanent canine teeth of dogs. Crowns and roots were respectively about 23 per cent and 40 per cent longer, and about 26 per cent and 50 per cent wider in males. The smaller crown: root ratio in males together with the greater root width indicate a dimorphism in the tooth anchorage mechanism. Ratios of widths of various regions of the teeth showed that the canine teeth of male dogs were not only larger but, because of their expanded midroot width, were of different contour to those of females. The differences in tooth size and contour far exceeded the general statural difference of about 6 per cent expected between the sexes. Evidence from other sources suggests that these differences may be due to a direct effect of circulating sex hormones on tooth development.     

The use of Periograf in periodontal defects. Histologic findings

Hydroxylapatite (Periograf) was placed into periodontal defects around five teeth scheduled for extraction in two young adult females with excellent plaque control. On the facial surface for one tooth the material was placed in a supracrestal position. Twelve months later the teeth were extracted in block section and were examined microscopically. Hydroxylapatite crystals were seen in the histologic sections with evidence of new bone formation in juxtaposition. The hydroxylapatite was tolerated relatively well by the surrounding tissue. A "cap' of bone was present coronal and facial to those crystals placed in the supracrestal position. In some areas bone was seen attached to the root via a periodontal ligament coronal to the Durapatite crystals. The question of accidental implantation of the material into the adjacent bone versus the actual regeneration of a true new attachment was discussed.     

Width/length ratios of normal clinical crowns of the maxillary anterior dentition in man

The purpose of this investigation was to analyze the clinical crown of the 3 tooth groups of the maxillary anterior sextant of the permanent dentition of normal subjects with respect to (i) width, length and the width/length ratios and (ii) determine if there is a correlation between tooth dimensions or tooth group ratios and subject height. Subjects (> or = 20 y.o.) were recruited for this study if (i) the free gingival margin on the facial surface of teeth in the maxillary sextant was positioned apical to the cervical bulge, (ii) there was no evidence of attachment loss; as determined by lack of a detectable CEJ and (iii) the marginal tissue was knife edged in form, firm in consistency and coral pink in color. Teeth were excluded if (i) there was evidence of gingival alteration, i.e., gingival overgrowth/hyperplasia, inflammation, altered passive eruption, attachment loss, gingival recession or history of periodontal surgery, or (ii) there was evidence or history of incisal edge/proximal tooth alteration as in, i.e., restorative intervention, traumatic injury or occlusal wear into dentin. At least 1 suitable tooth from each tooth group of the maxillary anterior dentition had to be present. A maxillary impression was taken and poured in yellow die stone. The widest mesial-distal portion and the longest apical-coronal portion of the test teeth were measured. Gender, ethnicity and subject height (SH) were recorded for each participant. Due to a limited ethnic diversity only data from the Caucasian group were analyzed. The mean coronal tooth width (mm) of males versus females was CI: 8.59 versus 8.06, LI: 6.59 versus 6.13 and CA: 7.64 versus 07.15. The mean coronal tooth length (mm) of males versus females was CI: 10.19 versus 9.39, LI: 8.70 versus 7.79 and CA: 10.06 versus 8.89. All width and length measures were significantly greater for males than for females. The mean coronal tooth width/length ratios for males versus females was CI: 0.85 versus 0.86, LI: 0.76 versus 0.79 and CA: 0.77 versus 0.81. A comparison between genders of the width/length ratios of the CI and LI were found not to differ, however the CA ratio for females was significantly greater than for males. A statistically significant difference was found to exist between the mean (cm) SH for males versus females: 181.2 versus 164.0. A positive correlation (p < or = 0.0001 to 0.0691) was found to exist between tooth group width/height ratios within genders. No significant correlation was found between any of the tooth dimensions or tooth group ratios and SH. The results of this study indicate that within male and female Caucasians, the mean width/length ratio of the maxillary 3 anterior tooth groups is 0.81. As well, within both genders there is a positive correlation between tooth group width/length ratios. The significance of these findings with respect to periodontal mucogingival plastic surgical procedures is discussed.