Effect of Core Material and Restoration Design on Strength of Endodontically Treated Bovine Teeth: A Laboratory Study

Purpose: The purpose of this study was to evaluate the fracture resistance of bovine teeth restored with one-piece cast core/crowns and no ferrule, compared to teeth restored with amalgam cores and full coverage crowns, with and without a dentine ferrule.
Materials and Method: Thirty bovine incisors were selected and modified to ensure all teeth had axial dentine walls of similar size. The teeth were then randomly allocated to one of the three groups: control group restored with amalgam core and cast crown without ferrule; ferrule group restored with amalgam core and cast crown with a 2-mm dentine ferrule; one-piece group restored with one-piece cast core/crown without ferrule. Each tooth was loaded to the point of fracture.
Results: The mean load resisted by the control group, the ferrule group, and the one-piece group were 1092.5, 1843.5, and 1463.1 N, respectively. The mean load resisted by the ferrule group was significantly greater than the control group ( p < 0.001) and the one-piece cast core/crown group ( p = 0.04). The mean load resisted by the one-piece cast core/crown group was significantly greater than the control group ( p = 0.04).
Conclusions: The maximum load resistance was significantly enhanced by a 2-mm ferrule compared with teeth with no ferrule and teeth restored with one-piece cast core/crowns. Teeth restored with one-piece cast core/crowns were significantly more resistant to loading than teeth restored with amalgam cores and crowns without a ferrule.     

Traction--a surgical/orthodontic procedure.

Maxillary crowding may cause failure of eruption of the canine. The teeth so displaced are directed buccally or palatally. In both cases, surgical intervention is indicated after space has been made in the arch. Palatally displaced canines are treated by surgical excision of palatal mucosa to promote eruption. Wide excision is indicated to prevent the healing process from covering the exposed tooth crown. Because of the anatomy of the buccal mucosa, however, surgical excision of the crowns of buccally displaced canine frequently results in periodontal problems. An alternative technique is therefore presented; this involves the surgical exposure of the crowns of buccally displaced teeth to allow the attachment of a wire traction hook. The crown is then recovered. The traction hook provides a point of attachment, so that orthodontic forces may be applied to the unerupted tooth to guide its eruption. The preservation of the mucosal flap ensures a normal epithelial attachment develops on the buccal surface of the tooth, and the normal gingival anatomy of the buccal mucosa is maintained. The procedure may also be used in cases where upper incisors have been prevented from erupting because of the presence of supernumerary teeth. Even after surgical removal of the supernumerary teeth, the permanent incisors often fail to erupt. In such cases, the placement of traction hooks will enable the orthodontist to bring the unerupted teeth into their correct positions in the arch.     

Changes of anterior clinical crown height in patients provided with single-implant restorations after more than 15 years of follow-up

PURPOSE: To measure the long-term changes of clinical crown height in patients treated with single-implant crowns and compare them to those of an adult population with normal dentition. MATERIALS AND METHODS: The test group comprised 23 patients, consecutively restored with a total of 48 single-implant crowns in the anterior maxilla. Mean age was 26.1+/-11.4 years at inclusion. Original master casts were stored after treatment, and patients were recalled for new study casts an average of 15.8+/-0.74 years later. The control group comprised 141 dental students with a mean age of 22.9 +/-1.20 years at inclusion. Study casts were made at inclusion and after 10 (n = 141) and 20 years (n = 60). Clinical crown height was measured for maxillary anterior teeth, and data were pooled and compared regarding clinical crown height and changes in height. RESULTS: Implant clinical crowns were an average of 0.6+/-1.04 mm longer than the contralateral teeth (P < .05). Central and lateral incisors showed mucosal recession at an average of 0.4+/-0.53 mm (P < .05) and 0.6+/-0.58 mm (P < .01), respectively. In the control group, only minor insignificant changes (+/-0.1 mm) in mean clinical crown height could be observed during the follow-up period. However, obvious individual variations of changes could be found in the control group, and were more pronounced for women. Altogether, 15% and 9% of measured teeth showed > or = 1.0 mm increase or decrease of clinical crown height during 20 years, respectively. Initially, shorter teeth presented a trend (P < .05 to .001) of more mucosal recession than longer teeth. CONCLUSION: Mean values of clinical crown height disguise significant individual variations of changes. To perform a risk evaluation for potential future mucosal recession, it could be suggested that greater changes in clinical crown height may occur in patients provided with implant-supported crowns than in untreated control subjects, possibly more for women than men, and more for initially shorter teeth than for longer adjacent teeth.     

Anatomic crown width/length ratios of unworn and worn maxillary teeth in white subjects

STATEMENT OF PROBLEM: Dimensions of teeth have been available for a century. Some significant and clinically relevant aspects of dental esthetics, however, such as the crown width/length ratios, have not been presented in tooth morphology sources until recently. PURPOSE: The purpose of this study was to analyze the anatomic crowns of 4 tooth groups (central incisors, lateral incisors, canines, and first premolars) of the maxillary dentition with respect to width, length and width/length ratios and determine how these parameters are influenced by the incisal edge wear. MATERIAL AND METHODS: Standardized digital images of 146 extracted human maxillary anterior teeth from white subjects (44 central incisors, 41 lateral incisors, 38 canines, 23 first premolars) were used to measure the widest mesiodistal portion "W" (in millimeters) and the longest inciso-cervical/occluso-cervical distance "L" (in millimeters). The width/length ratio "R" (%) was calculated for each tooth. A 1-way analysis of variance was used to compare the mean values of W, L, and R for the different groups ("unworn" and "worn" subgroups, except for premolars). Multiple least significant difference range tests (confidence level 95%) were then applied to determine which means differed statistically from others. RESULTS: There was no influence of the incisal wear on the average value of W (width) within the same tooth group. The widest crowns were those of central incisors (9.10 to 9.24 mm) > canines (7.90 to 8.06 mm) > lateral incisors (7.07 to 7.38 mm). Premolars (7.84 mm) had similar width as canines and worn lateral incisors. The L-value was logically influenced by incisal wear (worn teeth were shorter than unworn teeth) except for lateral incisors. The longest crowns were those of unworn central incisors (11.69 mm) > unworn canines (10.83 mm) and worn central incisors (10.67 mm) > worn canines (9.90), worn and unworn lateral incisors (9.34 to 9.55 mm), and premolars (9.33 mm). Width/length ratios also showed significant differences. The highest values were found for worn central incisors (87%) and premolars (84%). The latter were also similar to worn canines (81%), which constituted a homogeneous group with worn lateral incisors (79%) and unworn central incisors (78%). The lowest ratios were found for unworn canines and unworn lateral incisors (both showing 73%). CONCLUSIONS: Along with other specific and objective parameters related to dental esthetics, average values for W (mesiodistal crown dimension), L (inciso-cervical crown dimension), and R (width/length ratio) given in this study for white subjects may serve as guidelines for treatment planning in restorative dentistry and periodontal surgery.     

Dental morphology and crowding. A multivariate approach

The objective of this study was to compare, combined and individually, the mesiodistal (MD) and buccolingual (BL) tooth sizes as well as their respective crown proportions in the permanent dentition in dental arches with moderate, mild, and no crowding. Dental casts from two-hundred 12 to 16-year-old school children from a typical high school from Lima, Peru, were used. The MD and BL tooth sizes of all permanent teeth except second and third molars were measured, and their crown proportion (MD/BL ratio) was estimated. Each dental arch was classified as presenting moderate (-5.1 mm or more of discrepancy), mild (-0.1 and -5 mm of discrepancy), and no crowding (zero or a positive discrepancy). Combined and tooth-specific comparisons among the crowding groups for the tooth sizes as well as crown proportions were performed with a multivariate analysis of variance (MANOVA, using Wilks lambda). Combined MD tooth sizes and crown proportions differed among crowding groups. Subsequent individual comparisons indicated differences for MD tooth size of all upper teeth and for lower premolars and central incisors. Differences were also detected for crown proportions of the upper second premolar, canine, and both incisors; as well as for the lower first premolar, canine, and central incisor. No differences were found for the BL tooth sizes among crowding groups. MD tooth sizes and crown proportions from specific teeth are significantly different between dental arches with moderate, mild, and noncrowded arches. This study helps to understand the odontometric component of the dental crowding multifactorial origin.     

On the relationship between crown form and clinical features of the gingiva in adolescents

Abstract The purpose of the present study was to examine the relationship between the form of the crowns in the maxillary front tooth segment and (1) a group of morphological characteristics and (2) the thickness of the gingiva. 108 subjects devoid of symptoms of destructive periodontal disease were examined regarding, e.g., probing depth, thickness of the free gingiva, width of the keratinized gingiva and the contour of the marginal gingiva. From clinical photographs of the maxillary front tooth region, the width (at the apical third – CW) and the length (CL) of the crowns of the 6 front teeth were determined. A CW/ CL-ratio was calculated for each tooth and averaged for each tooth region. The individual mean CW/CL-ratio values for the central incisors were ranked. After correction for incisal attrition, the 10 subjects ranked highest and the 10 ranked lowest were selected as having either a long-narrow (group N) or a short-wide (group W) form of the crown of the tooth. The data for each of the examined parameters were averaged for each tooth region in each subject and mean values for subjects in groups W and N were compared using the Student t-test. Stepwise multiple regression analysis, including data from the whole sample, was performed for each tooth region with the thickness of the free gingiva as the dependent variable. The results from the analyses demonstrated that individuals with a long-narrow form of the central incisors displayed, compared to individuals with a short-wide crown, form (i) a narrow zone of keratinized gingiva, (ii) shallow probing depth, and (hi) a pronounced “scalloped” contour of the gingival margin. There was no significant difference between groups N and W with respect to the thickness of the free gingiva. The CW/CL-ratio data revealed that a certain form of the crowns in the central incisors was accompanied by a similar form in the lateral incisor and canine tooth region. The regression analyses demonstrated that the thickness of the free gingiva in central incisors was significantly related to (i) the width of the keratinized gingiva, (ii) the buccolingual width of the crown and (iii) the presence of an interproximal gingival groove. In lateral incisors, the thickness of the free gingiva was associated with the probing depth at the buccal surface. No single variable was significantly related to the thickness of the gingiva in canines.     

Impact fracture characteristics of intact and crowned human central incisors

Dynamic fracture energies and patterns of fracture in extracted human central incisors were determined for groups of intact controls, groups with Vita Dur N® crowns, Vita Hi Ceram® crowns, Dicor® crowns and porcelain veneers. Teeth were struck on their middle labial surfaces by a pendulum impact device.
The mean fracture energy for teeth with Dicor crowns was significantly lower than for all other groups ( P <0.05). Control tooth crowns fractured obliquely in an apicaldirection. Vita Dur N® and Dicor® crowns, shattered, the underlying tooth usually fracturing in the plane of the impact force. Vita Hi Ceram® crowns chipped at the site of impact and some fractures were located in the roots. Gold crowns remained cemented and fracture occurred at the crown/root junction, or in the root. Porcelain veneers fractured at the site of impact but remained cemented. Dicor® crowns were less fracture resistant than other restoration types tested. Porcelain veneers and full gold crowns stiffened teeth which led to more root fractures than the porcelain crowns.     

Fracture strength of intact and fragment-bonded teeth at various velocities of the applied force

Bonding of a tooth fragment to the remaining tooth substance can restore crown fracture of an anterior tooth. In this study, sheep central incisors were used. The crowns were fractured transversely and the crown fragment was bonded to the remaining tooth structure. This technique involves acid etching, use of an experimental adhesive (Gluma+) and a BisGMA/TEGDMA resin. The mean fracture strength of the restored teeth was not significantly different from that of intact teeth when tested at a rather low crosshead speed (0.5 mm/min) but different and about 30% lower when tested at a higher crosshead speed (500 mm/min). In studies aiming to test resistance to forces which might cause trauma, it might be appropriate to use a high crosshead speed.     

Crown formation times of human permanent anterior teeth

One gap in knowledge of human dental-growth standards is the age at which crown fractions of anterior permanent teeth are attained. The aim of this study was to document stages of crown formation for permanent incisors and canines from a small skeletal collection of known age. The source was C18th and C19th coffin-buried skeletal material from Spitalfields in London; developing teeth from 50 individuals with recorded age-at-death (range 0-5.40 years) and 56 unaged individuals were assessed. Teeth were dissected and crown height measured directly. Each developing crown was assigned to the nearest average fraction (C14, C12, C34, Cc). These fractions were calculated from the total crown height of unworn completed teeth from this sample. Median age for C12 of the permanent upper central incisor was 1.34 years (n=16) and for the canine was 2.52 years (n=16). Data on crown formation are also presented in relation to permanent lower first molar stages C12, C34 and Cc. When M(1) was at stage C34 the modal stage for I(1) was C34 and for other incisors and canines was C12. Although the sample is small, these results fill an important gap in tooth chronology and add to knowledge of growth variation in early childhood.     

Load fatigue of compromised teeth: a comparison of 3 luting cements

PURPOSE: This study compared the number of cycles to failure of central incisors restored with full cast crowns and then cemented with 3 different luting cements. MATERIALS AND METHODS: Fifteen human maxillary central incisors received cast post-and-core restorations. These were cemented with zinc phosphate. The teeth were then divided into 3 groups of 5 samples each. Each tooth had a ferrule length of 1.0 mm and was prepared for a full crown. A waxing jig was used to standardize the load application point on all waxed crowns. Complete cast crowns were cemented to the compromised teeth using 3 different luting cements: a zinc phosphate cement (control group), a resin-modified glass-ionomer cement, and a resin cement with a dentin bonding agent. A fatigue load of 1.5 kg was applied at a rate of 72 cycles per minute until failure of the cement layer occurred between the crown and the tooth (preliminary failure). The independent variable was the number of load cycles required to create preliminary failure. An electrical resistance strain gauge was used to provide evidence of preliminary failure. RESULTS AND CONCLUSION: The resin cement samples had a significantly higher number of load cycles to preliminary failure than both the zinc phosphate and the resin-modified glass ionomer (P < or = 0.05). There was no significant difference between the zinc phosphate and the resin-modified glass-ionomer cements.     

Does the canine dental follicle cause resorption of permanent incisor roots? A computed tomographic study of erupting maxillary canines

We performed computed tomography (CT) on 107 children and adolescents aged 9-15 years with 176 unerupted maxillary canines (152 erupting ectopically and 24 erupting normally) to determine whether there is an association between widened dental follicles of the maxillary canines and resorption of the adjacent incisors during eruption. Contiguous axial (transverse) CT scans were obtained through the maxilla in the region of the canines. The width and shape of the dental follicles were recorded, as were any contacts between the follicles and the crowns of the maxillary canines and neighboring incisors. Fifty-eight lateral incisors (38%) and 14 central incisors (9%) had some type of root resorption. The position of the maxillary canine in relation to the root of the lateral incisor varied greatly, as did the width and shape of the canine dental follicle. Follicle width ranged from 0.5 mm to 7.0 mm. The mean +/- SD width of dental follicles was, on average, larger for the ectopically positioned canines (2.9 +/- 0.8 mm) than for the normally erupting canines (2.5 +/- 0.8 mm) (P < or = .01). We found that during eruption, the follicle of the erupting maxillary canine frequently resorbed the periodontal contours of adjacent permanent teeth but not the hard tissues of the roots. We concluded that the dental follicle did not cause root resorption of permanent teeth. Resorption of neighboring permanent teeth during maxillary canine eruption was most probably an effect of the physical contacts between the erupting canine and the adjacent tooth, active pressure during eruption, and cellular activities in the tissues at the contact points, all of which are part of the eruptive mechanism. The findings also confirm an association between root resorption of deciduous canines and the dental follicles of erupting permanent canines.     

Delayed eruption of mandibular primary central incisors in a child with severe lingual inclination and their spontaneous movement to appropriate positions

We previously reported a quite uncommon case of delayed eruption of primary mandibular bilateral incisors with severe lingual inclination identified in a Japanese girl aged 2 years 8 months. An intraoral examination demonstrated the tooth crown morphology of the primary mandibular incisors in the lingual submucosal area, while radiographic examinations of the affected teeth revealed what appeared to be a standard root morphology and the permanent successors located close to the affected teeth. We decided to perform periodical examinations at least until the roots of the permanent successors were sufficiently formed and here report recent findings in this case. At 2Y10M, the edge of the tooth crown of the primary mandibular left central incisor had emerged into the oral cavity and one-third of the tooth crown was identified at 2Y11M. Thereafter, the tooth crown of the primary mandibular right central incisor was identified under the mucosa at 3Y1M. A periapical radiograph taken at 3Y7M demonstrated formation of the permanent successors under development. At 3Y10M, nearly the entire part of the tooth crowns of both affected teeth had emerged and then they started to move gradually in a labial direction. At 4Y2M, the crowns of the affected were nearly within the dental arch, while periapical radiograph images showed straight roots for the affected teeth and the developing permanent successors. We intend to continue to perform periodical examinations to follow the development of the permanent successors until eruption.     

Occlusal wear of metal-free ceramic-filled polymer crowns after 2 years in service

PURPOSE: Improvements in the physical properties of modern composites have led to continuous expansion of their field of application to include extensive, occlusion-bearing posterior restorations and even metal-free polymer crowns. The objective of this clinical study was to investigate the influence of gender, arch, and crown location on the occlusal wear of metal-free ceramic-filled polymer crowns and to compare their wear with the mean annual occlusal wear of enamel (15 to 38 microm). MATERIALS AND METHODS: One hundred fourteen ceramic-filled polymer crowns made of Artglass (Heraeus Kulzer) were placed in 74 patients. After 1 year, 93 crowns were available for wear measurement. After 2 years, 76 crowns were available. Wear was determined by use of replicas. A 3-dimensional optical profilometer (Laserscan 3D, Willytec) was used to digitize and superimpose the occlusal surfaces of the baseline and recall replicas (occlusal matching). RESULTS: After 1 year, median wear of the entire occlusal surface was 19 microm for anterior and canine teeth, 19 microm for premolars, and 21 microm for molars. After 2 years, median wear was 36 pm for anterior and canine teeth, 44 microm for premolars, and 84 microm for molars. The wear of the occlusal contact areas was significantly higher. Significant effects of crown location (premolar or molar) on the extent of wear of the occlusal contact areas were found. CONCLUSIONS: Ceramic-filled polymer crowns are subject to measurable occlusal wear that exceeds that of natural enamel.     

Evaluation and comparison of strip crowns and primary anterior zirconia crowns in 3–5 years old children at one year

BackgroundPreservation of the decayed primary anterior teeth is important until their natural exfoliation time as it acts as natural space maintainer. Two most common anterior aesthetic full coronal restorations, the strip crowns and the preformed zirconia crowns, are available options.ObjectiveTo evaluate and compare the clinical outcomes (gingival health, plaque accumulation, teeth wear of opposing dentition, color match and restoration failure) of strip crowns and preformed primary anterior zirconia crowns at one year follow up in 3-5 years old children.Material and methodsForty maxillary primary incisors were restored by either strip crown or zirconia crown. Permuted block randomisation method was used for allocation of participants. Gingival health, plaque accumulation, teeth wear of the opposing dentition, color match and restoration failure for crowns were assessed at one-year follow-up. Data was analysed using McNemar- Bowker test and Chi-Square test.ResultsAt one-year follow-up, gingival inflammation, plaque accumulation, restoration failure were significantly higher for the strip crowns (level of significance = 0.012, 0.013 and 0.0001, respectively) and, no statistically significant difference was found between the strip crowns and zirconia crowns for teeth wear of opposing dentition and color match evaluation (level of significance = 0.435 and 0.168, respectively).ConclusionOverall, zirconia crowns were found more successful than strip crowns for the rehabilitation of caries affected primary incisors.     

Horizontal impaction of primary mandibular bilateral central incisors identified in 2-year-8-month-old girl

A girl aged 2 years and 8 months came to our clinic for consultation with regard to unerupted primary mandibular bilateral central incisors. An intraoral examination revealed that the teeth had not emerged into the oral cavity and showed a tooth crown morphology similar to that of the primary mandibular incisors, which appeared in the lingual submucosal area outside of the mandibular dental arch. Periapical radiographs demonstrated that the tooth crowns of both affected teeth were severely displaced to the lingual side. Computed tomography examinations were performed to clarify the three-dimensional positions of the affected teeth and their permanent successors, which revealed that the affected teeth were located in their estimated positions and had a standard root morphology. In addition, the permanent successors, which had not initiated root formation, were located close to the affected teeth. We decided to postpone extraction of the affected teeth and perform periodical examinations until the roots of the permanent successors are sufficiently formed. At the age of 2 years and 10 months, the edge of the tooth crown of the primary mandibular left central incisor was found emerged into the oral cavity. According to her parents, the patient did not complain of the emerging edge and no abnormal conditions were observed around the tooth.     

In vitro fracture resistance of endodontically treated central incisors with varying ferrule heights and configurations

STATEMENT OF PROBLEM: The in vitro effectiveness of a uniform circumferential ferrule has been established in the literature; however, the effect of a nonuniform circumferential ferrule height on fracture resistance is unknown. PURPOSE: This in vitro study investigated the resistance to static loading of endodontically treated teeth with uniform and nonuniform ferrule configurations. MATERIAL AND METHODS: Fifty extracted intact maxillary human central incisors were randomly assigned to 1 of 5 groups: CRN, no root canal treatment (RCT), restored with a crown; RCT/CRN, no dowel/core, restored with a crown; 2 FRL, 2-mm ferrule, cast dowel/core and crown; 0.5/2 FRL, nonuniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast dowel/core and crown; and 0 FRL, no ferrule, cast dowel/core and crown. The teeth were prepared to standardized specifications and stored for 72 hours in 100% humidity prior to testing. Testing was conducted with a universal testing machine with the application of a static load, and the load (N) at failure was recorded. Statistical analysis was performed with a 1-way analysis of variance and the Tukey Honestly Significant Difference test (alpha=.05). The mode of fracture was noted by visual inspection for all specimens. RESULTS: There was strong evidence of group differences in mean fracture strength ( P <.0001). Following adjustment for all pairwise group comparisons, it was found that the lack of a ferrule resulted in a significantly lower mean fracture strength (0 FRL: 264.93 +/- 78.33 N) relative to all other groups. The presence of a nonuniform (0.5 to 2-mm vertical height) ferrule (0.5/2 FRL: 426.64 +/- 88.33 N) resulted in a significant decrease ( P =.0001) in mean fracture strength when compared with the uniform 2-mm vertical ferrule (2 FRL: 587.23 +/- 110.25 N), the group without RCT (CRN: 583.67 +/- 86.09 N), and the RCT-treated tooth with a crown alone (CRN/RCT: 571.04 +/- 154.86 N). The predominant mode of failure was an oblique fracture extending from the lingual margin to the facial surface just below the insertion of the tooth into the acrylic resin. CONCLUSION: The results demonstrated that central incisors restored with cast dowel/core and crowns with a 2-mm uniform ferrule were more fracture resistant compared to central incisors with nonuniform (0.5 to 2 mm) ferrule heights. Both the 2-mm ferrule and nonuniform ferrule groups were more fracture resistant than the group that lacked a ferrule.     

Changes in Gingival Recession Related to Orthodontic Treatment of Traumatic Deep Bites in Adults

INTRODUCTION: It was the aim of this investigation to establish whether orthodontic treatment of traumatic deep bites can restore trauma-related gingival recessions in adults. SUBJECTS AND METHODS: Forty-one incisor sites with trauma-related recession (group Tr) and 54 trauma-free sites (group NonTr) were diagnosed in the upper palatal or lower buccal regions in twelve adult patients (mean age 38.3 +/- 8.1 years). The 48 antagonistic sites on the buccal aspects of the upper incisors (Ubuc) and 47 sites on the lingual aspects of the lower incisors (L-ling) were also evaluated. Changes in clinical crown lengths achieved during treatment were measured on dental casts, and length changes in recessions were measured on screen projections of magnified intraoral photographs. RESULTS: The clinical crown lengths (mean: -1.13 +/- 0.97 mm) and recession depths (mean: -2.05 +/- 0.93 mm) decreased significantly (p < 0.001) in the trauma group (Tr). We also observed significant shortening (p < 0.05) of clinical crown lengths in the buccal sites of upper incisors (U-buc) (mean: -0.16 +/- 0.46 mm). All other changes were insignificant. CONCLUSIONS: Orthodontic treatment of traumatic deep bites involving removal of gingival trauma and intrusion of incisor teeth shows great potential in reducing the length of clinical crowns and depth of gingival recessions. In trauma-free buccal sites of upper incisors, intrusion therapy may also improve the gingival marginal contour.     

In vitro study investigating the mass of tooth structure removed following endodontic and restorative procedures

STATEMENT OF PROBLEM: There is limited scientific evidence which quantifies the amount of tissue removed during endodontic and restorative procedures. PURPOSE: The purpose of this study was to measure and compare the mass of tissue structure removed from incisor and canine teeth following successive preparations. MATERIAL AND METHODS: Twenty-two intact, disease- and restoration-free teeth (n=11/group) were collected from consenting patients undergoing dental extractions at Eastman Dental Hospital. The teeth were stored in 4% formaldehyde saline and successively prepared for an access opening (AC), endodontic instrumentation (EI), porcelain laminate veneer (PC), metal-ceramic (MC) crown, and post-and-core (PC) preparations. The baseline mass for each tooth was measured and recorded, in grams, at baseline and after each preparation, on a digital analytical balance. A standard protocol was applied to ensure accurate mass measurements. Repeated measures analysis of variance (ANOVA) was used to make comparisons between the incisor and canine groups (alpha =.05) for actual mass of tooth in milligrams, percentage of tooth mass remaining compared to baseline, and percentage decrease in mass compared to the preceding procedure. RESULTS: The estimated marginal percentage mass lost was significantly greater (P<.001) in the incisor group compared to the canine group, as an overall trend, with the incisors losing proportionally more mass for each procedure (P<.001). CONCLUSIONS: Mean percentage of removed tooth tissue increased successively from EI, AC, PC, and PV preparation, with greatest change from the previous procedure occurring for MC crown preparation.     

Interrelation of tooth crown diameters

The purpose of this study was to clarify the interrelation of the tooth crown diameters using statistical methods. The material consisted of 414 dental casts from orthodontic patients in the Japanese female. The mesiodistal diameters of all permanent teeth on the left side were measured, excluding the third molars. These values were examined by correlation coefficient matrix and multivariate analyses such as multiple regression, principal component and canonical correlation, etc. The results were as follows: 1) The tooth crown diameters showed a strong intercorrelation within each jaw and between both jaws. 2) When the incisors and the canine were large in size, the premolars and the molars tended to be small. 3) When the incisors and the molars were large in size, the canine and the premolars tended to be small. 4) When the incisors and the premolars were large in size, the canine and the molars tended to be small. 5) All of the teeth except the upper lateral incisor were classified according to size into the four groups of incisors, canines, premolars and molars. 6) The dentition with small teeth tended to show a spaced arch.     

Restoring primary anterior teeth

A variety of esthetic restorative materials are available for restoring primary incisors. Knowledge of the specific strengths, weakness, and properties of each material will enhance the clinician's ability to make the best choice of selection for each individual situation. Intracoronal restorations of primary teeth may utilize resin composites, glass ionomer cements, resin-modified ionomers, or polyacid-modified resins. Each has distinct advantages and disadvantages and the clinical conditions of placement may be a strong determining factor as to which material is utilized. Full coronal restoration of primary incisors may be indicated for a number of reasons. Crowns available for restoration of primary incisors include those that are directly bonded onto the tooth, which generally are a resin material, and those crowns that are luted onto the tooth and are some type of stainless steel crown. However, due to lack of supporting clinical data, none of the crowns can be said to be superior to the others under all circumstances. Though caries in the mandibular region is rare, restorative solutions for mandibular incisors are needed. Neither stainless steel crowns nor celluloid crown forms are made specifically for mandibular incisors. Many options exist to repair carious primary incisors, but there is insufficient controlled, clinical data to suggest that one type of restoration is superior to another. This does not discount the fact that dentists have been using many of these crowns for years with much success. Operator preferences, esthetic demands by parents, the child's behavior, and moisture and hemorrhage control are all variables which affect the decision and ultimate outcome of whatever restorative treatment is chosen.