Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Tooth Preparation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,099 records · Page 61Linked to original sources
PubMedDate not supplied

Retention, marginal leakage, and cement solubility of provisional crowns cemented with temporary cement containing stannous fluoride.

PURPOSE: This in vitro study investigated the (1) retention and microleakage of provisional crowns cemented with temporary cements to which stannous fluoride (SnF2) was added, and (2) solubility of these cements. MATERIALS AND METHODS: Provisional crowns were constructed of acrylic resin with shoulder preparations for 12 molars. The crowns were luted with Tempbond, Tempbond NE, and Freegenol temporary cements, and also with SnF2 added to these cements. Specimens were thermocycled 100 times, stored for 6 days, and immersed in 0.5% basic fuschin. Seven days after cementation, crown removal (retention) tests were conducted. Marginal leakage was assessed using a five-level scale to score dye penetration. Solubility in water of the cements with and without SnF2 was assessed using cement disks. RESULTS: Freegenol was more retentive than the other cements. The incorporation of SnF2 significantly increased the retention capacity of Freegenol and Tempbond NE but had no effect on Tempbond. Tempbond showed significantly higher dye penetration than Freegenol. The addition of SnF2 did not alter the dye penetration of the cements. There were no significant differences in the solubility of the cements. However, the incorporation of SnF2 increased the solubility of Freegenol and Tempbond NE (P < .001) and Tempbond (P < .01). CONCLUSION: The addition of SnF2 increased the retention of temporary crowns cemented with Tempbond NE and Freegenol but did not affect the retention of those cemented with Tempbond. The marginal leakage of crowns cemented with the tested temporary cements with and without the incorporation of SnF2 was similar. However, the addition of SnF2 increased the solubility of the cements.

Acrylic Resins↗
PubMed2004

Vertical marginal discrepancy of ceramic copings with different ceramic materials, finish lines, and luting agents: an in vitro evaluation.

STATEMENT OF PROBLEM: Prosthetic restorations that fit poorly may affect periodontal health and occlusion. Studies that have evaluated the accuracy of fit of ceramic restorations before and after cementation assessed primarily intracoronal restorations. PURPOSE: This in vitro study evaluated the effect of different finish lines, ceramic manufacturing techniques, and luting agents on the vertical discrepancy of ceramic copings. MATERIAL AND METHODS: Two stainless steel molars were prepared for complete crowns with 2 different finish lines (heavy chamfer and rounded shoulder); each molar was duplicated to fabricate 90 copings. A total of 180 copings generated 18 groups (n=10 for each finish line-coping material-luting agent combination). Luting agents tested included zinc phosphate, resin-modified glass ionomer (Fuji Plus), and resin composite cements (Panavia F). A metal frame was developed on which to screw the stainless steel model and a ceramic coping; the distance (microm) between 2 predetermined points was measured before and after cementation by a profile projector under a torquing force. A 4-way ANOVA with repeated measurements was performed to assess the influence of each factor in the vertical marginal discrepancy: 3 between-coping factors (finish line-coping material-luting agent) and 1 within-coping factor (before and after cementation) (alpha=.05). RESULTS: Procera copings presented the lowest mean values ( P <.05) of vertical marginal discrepancy before and after cementation (25/44 microm) when compared to Empress 2 (68/110 microm) and InCeram Alumina copings (57/117 microm), regardless of any combinations among all finish lines and luting agents tested. CONCLUSION: Considering each factor separately, the ceramic manufacturing technique appeared to be the most important factor tested for the definitive vertical discrepancy of all-ceramic copings, with lower mean values for Procera copings.

Aluminum Oxide↗
PubMed1999

Retention of provisional crowns fabricated from two materials with the use of four temporary cements.

STATEMENT OF PROBLEM: Practitioners often choose resin materials and temporary cements with little understanding about their effect on provisional crown retention. PURPOSE: This study evaluated the retention of provisional restorations made with 2 materials and cemented with 4 temporary cements. METHODS AND MATERIAL: Recently extracted molars were prepared with a flat occlusal surface, 4-mm axial length and 20-degree angle of convergence. Specimens were distributed into equivalent groups. Provisional crowns were constructed for each preparation with polymethyl methacrylate (Temporary Bridge Resin) or bis-acrylic composite (Protemp Garant) and later cemented with Temp-Bond, Temp-Bond NE, Temrex, and an experimental calcium hydroxide temporary cement. A second group with Temrex was evaluated using half the recommended liquid. A cementing force of 2.5 kg for 5 minutes was used. After initial bench set followed by 24 hours in room temperature water, the crowns were removed with an Instron mechanical testing machine at 0.5 mm/min. A 2-factor ANOVA was used with alpha=.05 (n = 10). Mode of debonding was analyzed with a nonparametric chi-square test of association. RESULTS: Mean dislodgment stresses ranged from 670 to 1072 kPa for polymethyl methacrylate crowns and 554 to 884 kPa for those made of composite. Differences were nearly significant for the type of provisional material (P =.061) and the cross-product interaction (P =.376) was not significant, whereas there were significant differences among the cements (P =.002) and the mode of debonding (P =.0034). CONCLUSIONS: Excluding Temp-Bond to eliminate a cross-product interaction demonstrated that the polymethyl methacrylate crowns were 19.3% more retentive than the composite crowns (P =.015). There was no statistically significant difference among the 4 temporary cements when the manufacturer's mixing instructions were followed (P =.186). However, the thicker consistency Temrex was more retentive than the recommended Temrex mix and Temp-Bond.

Analysis of Variance↗
PubMed2002

In vitro evaluation of the retention of composite fiber and stainless steel posts.

PURPOSE: This study compared the tensile retentive strength of composite fiber-reinforced dowels luted with a resin cement to stainless steel dowels luted with zinc phosphate cement. MATERIALS AND METHODS: The crowns of 40 extracted human mandibular premolars were removed with a separating disc 1-mm coronal to the cementoenamel junction. The teeth were randomly divided into 4 groups (n = 10). A post space was prepared in each specimen to a depth of 9 mm, using the drill supplied by the respective manufacturer. For the stainless steel post group, 1.25-mm-diameter posts were cemented with zinc phosphate cement. For the composite fiber reinforced groups, posts with diameters of 1.00, 1.25, and 1.50 mm were luted with a Bisphenol A-Glycidyl Methacrylate (BIS-GMA) resin bonding system (Jeneric/Pentron, Wallingford, CT) according to manufacturer specifications. The specimens were stored in a sealed container with a moist environment for 24 hours, placed in a fixture in an 801 Materials Test Systems (MTS) machine (MTS Systems Corp, Minneapolis, MN), and loaded in tension at a rate of 5.0 mm/min until failure. Differences among the 4 groups were determined using a one-way analysis of variance and Tukey-B post-hoc tests (alpha = 0.05). RESULTS: The mean loads to failure ranged from 43.9 +/- 10.4 kg for the stainless steel dowel group to 19.9 +/- 5.7 kg for the composite fiber-reinforced 1.00-mm-diameter group. The stainless steel post luted with zinc phosphate cement provided significantly greater tensile resistance than all composite fiber dowel groups. The retention of the 1.00-mm composite fiber-reinforced post was significantly less than the remaining groups. CONCLUSIONS: Under the conditions of this study, the stainless steel dowel luted with zinc phosphate cement provided significantly greater retention.

Analysis of Variance↗
PubMed2005

Microleakage of various cementing agents for full cast crowns.

OBJECTIVES: To evaluate microleakage and marginal gaps in full cast crown restorations bonded with six different types of cementing agents. METHODS: Sixty non-carious human premolars and molars were prepared in a standardized manner for full cast crown restorations. The mesial and distal margins were located in dentin, while the vestibular and palatal/lingual margins were located in enamel. Crowns were made from a high-gold alloy using a standardized technique. The specimens were randomized to six groups of cementing agents: one zinc-phosphate cement (Harvard cement), one conventional glass-ionomer cement (Fuji I), one resin-modified glass-ionomer cement (Fuji Plus), two standard resin cements (RelyX ARC, Panavia F), and one self-adhesive universal resin cement (RelyX Unicem). After 4 weeks of storage in distilled water at 37 degrees C, the specimens were subjected to 5000 thermocycles ranging from 5 to 55 degrees C. Then, they were placed in a silver nitrate solution, embedded in resin blocks, and vertically cut in buccolingual and mesiodistal direction. Subsequently, the objects were evaluated for microleakage and marginal gap using a high-resolution digital microscope camera. RESULTS: A number of inter-group differences were statistically significant. RelyX Unicem showed the smallest degree of microleakage both in enamel and in dentin. Panavia F und RelyX Unicem were associated with significantly larger marginal gaps than all other cementing agents. No association was observed between microleakage and marginal gap other than a weak direct correlation when using Harvard cement on enamel. SIGNIFICANCE: The cementing agents investigated revealed different sealing abilities. These differences were not associated with specific types of materials.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Longevity and failure load of ceramic veneers with different preparation designs after exposure to masticatory simulation.

STATEMENT OF PROBLEM: Laminate veneers are widely used in the management of unesthetic anterior teeth. However, limited information is available regarding the influence of preparation design on longevity of ceramic veneers. PURPOSE: This study evaluated the influence of preparation design on longevity and failure load of ceramic veneers bonded to human maxillary central incisors after cyclic loading and thermal cycling in a dual-axis masticatory simulator. MATERIAL AND METHODS: Sixty-four caries-free maxillary central incisors were divided into 4 groups (n = 16). The control group remained unprepared (NP). For Group WP, a window preparation was made. Specimens in Group IOP were prepared with an incisal overlap of 2 mm without palatal chamfer. For Group CVP, specimens were prepared with a complete-veneer design of 3-mm incisal reduction and 2-mm palatal extension. Forty-eight IPS Empress 1 ceramic veneers were bonded adhesively with dual-polymerizing composite (Variolink II). All specimens were subjected to cyclic mechanical loading (1.2 million cycles, cycle frequency 1.3 Hz, invariable palatal load 49 N) and thermal cycling (5 degrees C-55 degrees C, dwell time 60 seconds, 5500 cycles) in a masticatory simulator. Failure was defined by bulk fracture of a specimen. Subcritical crack patterns were observed. Surviving specimens were loaded in a universal testing machine until fracture. The failure-load values (N) (1.5 mm/min crosshead speed) were automatically recorded by controlling software. Statistical analysis of data was performed by Kruskal-Wallis analysis of variance (alpha = .05) and pairwise Wilcoxon rank sum tests (alpha = .05). RESULTS: Three specimens from group NP, 1 specimen each from the WP and CVP groups, and 2 specimens from group IOP fractured during fatigue. After 1.2 million cycles, the highest crack rates were observed for complete veneers and originated in the palatal concavity extending to the facial surface. The median (interquartile range = x .25 - x .75 ) failure loads (N) were as follows: NP 713.3 (404.4-777.1), WP 549.5 (477.5-597.7), IOP 695.3 (400.0-804.6), and CVP 519.2 (406.1-732.9). No significant differences in longevity and failure load were demonstrated between natural teeth and teeth restored with ceramic veneers ( P = .555). CONCLUSION: Maxillary teeth restored with the 3 types of IPS Empress 1 veneers showed fracture resistance similar to that of unprepared incisors ( P = .555).

Aluminum Silicates↗
PubMed2005

The significance of marginal gap and overextension measurement in the evaluation of the fit of complete crowns.

INTRODUCTION: An important criterion for the success of a crown is marginal fit. However, in the patient's mouth fit can only be evaluated by subjective methods. This study describes the correlation between objective marginal fit and its subjective evaluation by dentists and dental technicians. MATERIALS AND METHODS: Thirty human premolars and molars were randomly divided into six groups and prepared with a shoulder. For each of the six groups, complete crowns were made of different alloys and technologies (casting: AuAgCu, AuPdPt, PdAgAu, CoCrMo, and Ti; milling: Ti). The crowns were cemented with provisional cement. Ten dentists and 10 technicians were asked to evaluate the fit of the crowns with a new dental explorer. The crowns were then cleaned and cemented with a zinc-oxide-phosphate-cement. The marginal gap and a possible overextended margin of the crowns were examined under a special 4x light microscope with a magnification level of 560 X. The means of the gaps and the overextended margins were calculated for each group. Significances were detected by analysis of variance (ANOVA) and the post-hoc-test (Bonferroni, p<0.05). Correlations between objective measuring and subjective evaluation were evaluated using the Pearson test. The influence of the measured values on the subjective evaluation was determined by regression analyses. RESULTS: Crowns made from different alloys and technologies showed partly significantly (p<0.05) different marginal gaps (mean ranging from 35 microm to 92 microm) and significantly (p<0.05) different overextended margins (mean ranging from 40 microm to 149 microm). There were significant correlations (p<0.05) between subjective findings and objective data. Significant correlations (p<0.01) were also found between the subjective findings of dentists and technicians. Compared to the marginal gap, only the overextended margin had a significant influence (p=0.00) on the subjective evaluations of the clinicians. CONCLUSION: Crowns from different alloys and technologies showed differences in marginal fit. Marginal gap and the overextension of the crowns significantly correlated with the subjective evaluation of their fit by dentists and dental technicians. For the decision of the clinicians, whether a crown is acceptable, overextension was more important than marginal gap.

Analysis of Variance↗
PubMedDate not supplied

Influence of posts and cores on light transmission through different all-ceramic crowns: spectrophotometric and clinical evaluation.

PURPOSE: The influence of different types of posts and cores on light transmission through all-ceramic crowns was assessed by spectrophotometric analysis and clinical evaluation. MATERIALS AND METHODS: Three extracted natural teeth were replicated in acrylic resin, with roots prepared to receive standardized posts and cores. Using a silicone impression material as a template, various prosthodontic reconstructions were obtained by combining four types of posts and cores (polished and matte-finished gold alloy, all-ceramic, and ceramized metal alloy) and three types of all-ceramic crowns (IPS-Empress 2 surface-colored, IPS-Empress 2 stratified, and In-Ceram). The spectrophotometric analysis was performed in the dark at 25 degrees C. The teeth were backlit with an incandescent lamp at the color temperature of A illuminant and shielded to avoid spurious light entering the spectrophotometer. The transmitted light was analyzed in terms of luminance at four points of the sample surface (cervical, middle, incisal, and proximal). Twelve measurements were performed for the natural teeth, and 144 were performed for the artificial teeth. RESULTS: Natural teeth had the highest luminance. Among all-ceramic crowns, surface-colored IPS-Empress 2 had the highest luminance, and stratified IPS-Empress 2 had the lowest. Regarding posts and cores, the luminance was highest with the all ceramic, lower with the ceramized and the polished gold alloy (which had very similar luminance), and lowest with the matte-finished gold alloy. No significant difference among prosthodontic combinations was detected under clinical observation. CONCLUSION: The surface-colored glass ceramic (IPS-Empress 2) was the most translucent crown. At the standard crown thickness used, there were small, significant spectrophotometric, but not clinical, differences among the combinations tested. These findings show no esthetic contraindications for the use of polished gold alloy posts and cores with all-ceramic crowns.

Acrylic Resins↗
PubMed2005

Clinical acceptability of crown margins versus marginal gaps as determined by pre-doctoral students and prosthodontists.

PURPOSE: Marginal integrity is a very important element in evaluating a restoration; however, there is no agreement in definition of a clinically acceptable margin. The purpose of this investigation was to examine margin acceptability using an explorer versus the actual marginal gap widths at four locations on uncemented crowns on three extracted teeth using both predoctoral students and prosthodontists as evaluators. MATERIALS AND METHODS: The crown margin evaluation used 16 surfaces of four crowns fitting to three extracted caries-free teeth fitted into a dentiform. The teeth (nos. 14, 20, and 29) were prepared for a full cast (gold) crown using a chamfer finish line configuration, with some margins supragingival and others subgingival. After final impressions and working casts were made, die spacer was applied to the marginal area of the die before waxing to vary the marginal opening. The dentiform was placed in a mannequin in a supine position. Predoctoral students (N = 10) and prosthodontists (N = 9) evaluated each axial surface of each crown in the zone along the margin with an explorer and rated each surface as either "clinically acceptable" or "unacceptable." After casting, the axial marginal openings were measured with Image Pro Software using a digital microscopic image of the surface. Each participant repeated the margin evaluations 6 months later. RESULTS: Upon casting, marginal gaps ranged from 40 microm to 615 microm. The proportions of prosthodontists and of predoctoral students rating a given surface as "clinically unacceptable" were highly correlated (Spearman rank correlation = 0.81, p= 0.0001). The prosthodontists did not provide more or fewer ratings of clinical acceptability than the students, although kappa results indicated that the prosthodontists might be more consistent among themselves than the student raters. Upon re-evaluation, both groups rated between one and six of the surfaces differently than they had previously: the median number of inconsistencies was 1 for prosthodontists and 3 for predoctoral students. The prosthodontists tended to have fewer inconsistencies than the predoctoral students (0.05 < p < 0.10 Wilcoxon rank sum test), but this was not statistically significant. CONCLUSION: The data provided evidence that those surfaces associated with greater margin gaps tended to have a greater proportion of ratings of "clinically unacceptable." The proportion of prosthodontists and predoctoral students rating a margin "clinically unacceptable" were highly correlated. Prosthodontists tended to have fewer inconsistencies than predoctoral students, but that difference was not statistically significant.

Crowns↗
PubMed1998

Precision of fit: the Procera AllCeram crown.

STATEMENT OF PROBLEM: Strength, color stability, and precision of fit are requirements for all-ceramic restorations. The Procera AllCeram crown system, composed of a densely sintered high-purity alumina core combined with a low fusing surface porcelain, appears to satisfy most of these requirements. However, evaluation of marginal fit has not been reported. PURPOSE: This study measured the precision of fit of the Procera AllCeram crown fabricated with Procera CAD/CAM technology for the premolar and molar teeth fit to a die. MATERIAL AND METHODS: Five ivorine maxillary first premolars and first molars were prepared for full-coverage crowns. Preparations were standardized with a convergence angle of 10 degrees, chamfer margins of 1.3 to 1.5 mm circumferentially, and occlusal reduction of 2.0 mm. AllCeram crowns were fabricated for the dies, and the fit of the crown to the die was determined by using a standardized procedure with a silicone impression material that served a dual role: (1) as a retrievable luting agent, and (2) to replicate the internal aspects of the crown. Laser videography was used to measure the gap dimension between the crowns and the dies at the marginal opening, the axial wall, the cusp tip, and the occlusal adaptation measurement locations. Mean gap dimensions and standard deviations (SDs) were calculated for marginal opening, internal adaptation, and precision of fit. RESULTS: Mean gap dimensions and standard deviations at the marginal opening for the premolar and molar crowns were 56.0 microns SD +/- 21 and 63.0 microns SD +/- 13 microns, respectively. The mean gap dimensions and SDs of the internal adaptation were 69.0 microns SD +/- 17 microns for axial wall, 48.0 microns SD +/- 12 microns for cusp tip, and 36.0 microns SD +/- 7 microns for occlusal adaptation for the premolar crowns; and 49.0 microns SD +/- 3 microns axial wall, 67.0 microns SD +/- 21 microns cusp tip, and 74.0 microns SD +/- 29 microns occlusal adaptation for molar crowns. Precision of fit and SDs for premolar and molar crowns were 52.0 microns SD +/- 19 microns and 63.0 microns SD +/- 20 microns, respectively. Mean marginal openings and precision of fit gap dimensions for the crown groups were not significantly different at the .05 level. However, gap dimensions that defined the internal adaptation at the measurement locations were different (P < or = .05). CONCLUSION: Mean gap dimensions for marginal openings, internal adaptation, and precision of fit for the crown groups were below 70 microns. These findings show that the crowns studied can be prescribed with confidence knowing that the precision of fit will consistently be less than 70 microns.

Aluminum Oxide↗
PubMed2004

The in vitro effect of pulpal pressure and luting agent on tensile bond strength of complete cast crowns.

STATEMENT OF PROBLEM: The degree to which pulpal pressure may affect bond strength of complete cast crowns is unknown. PURPOSE: The aim of this in vitro study was to evaluate the effect of simulated pulpal pressure on the tensile bond strength of complete cast crowns luted with 2 different cements. MATERIAL AND METHODS: Forty-eight human mandibular canine teeth were cleaned and stored in saline solution. The crowns were prepared by 1 investigator, and standardization of the preparation was accomplished by fixing a dental handpiece in a parallelometer. Uniform grooves, 0.5 mm in depth, were prepared with burs with depth guides. The complete crowns were prepared with a 0.5-mm shoulder margin. Teeth were randomly divided into 2 groups of 24 teeth each (Group I and Group II). In Group I, bonding and tensile test procedures of the teeth were carried out under simulated pulpal pressure (15 cm of saline solution). In Group II, simulated pulpal pressure was not used. The roots were removed 1 mm below the cementoenamel junction to create direct communication with the pulp chamber. The remaining pulpal tissues were carefully removed, and crowns were embedded in acrylic resin. The acrylic resin was then penetrated by a stainless steel tube that connected the pulp chamber and the barrel of a disposable plastic 5-ml syringe. The pulp chambers were filled with physiological saline solution under elevated pressure to locate the area of greatest permeability on the dentinal surface. Crowns were cast (Co-Cr alloy) with a 20-mm bar to allow testing of the bond strength. Each of the 2 groups were further divided into 2 luting cement groups of 12 each (Group I, A and B, and Group II, A and B). Group IA/IIA and Group IB/IIB specimens were luted with a polycarboxylate luting cement (Poly-F Plus) and an adhesive luting cement (Superbond C&B), respectively. After storage in distilled water for 24 hours, all specimens were subjected to a tensile bond test in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The maximum load at fracture (Newton) was recorded. The results were then evaluated with 2-way analysis of variance and Tukey's honestly significant difference tests (alpha=.05). RESULTS: Simulated pulpal pressure increased the bond strength of cast complete crowns cemented with an adhesive luting agent (P=.01). No significant difference was found in the bond strength of complete cast crowns cemented with polycarboxylate cement with or without pulpal pressure. Superbond C&B adhesive luting agent showed significantly higher bond strength values for Group I (388.9+/-32.7) and Group II (300.9+/-66.8), when compared with polycarboxylate cement for Group I (221.3+/-17.3) and Group II (186.8+/-38.5) (P=.001). CONCLUSION: Simulated pulpal pressure had a positive effect on the retention of complete cast crowns when cemented with Superbond C&B adhesive luting agent. Superbond C&B significantly increased the retention of crowns in either the presence or absence of pulpal pressure.

Analysis of Variance↗
PubMed2001

Evaluation of effect of 3D video glasses on perceived pain and unpleasantness induced by restorative dental treatment.

Previous studies on modulation of anxiety, pain and unpleasantness have documented a positive effect of video glasses (I-Glasses, Virtual i-O, Seattle, USA) on the perceived pain and unpleasantness under different laboratory and clinical conditions. The aim of this study was to evaluate whether distraction induced by video glasses also had an effect on the perceived intensity of pain and unpleasantness during dental treatment. Pain and unpleasantness was evoked by the preparation (drilling) of a minor dental cavity (class I). Twenty-three patients (17 female and six male, age range 20-49 years) with a need for an occlusal dental restoration in two homologous teeth participated in the study. In this split-mouth design, the patient received the dental treatment wearing 3D video glasses and without video glasses (control situation) in a randomized order. The tooth cavities were prepared in accordance with conventional techniques after mounting the video glasses. The patient rated the intensity of pain and unpleasantness on 100 mm visual analogue scales (VASs) after preparation of the first cavity; immediately after, the opposite tooth was prepared and again the volunteer rated the intensity of pain and unpleasantness. The cavities were then filled using a routine composite technique. Eventually, the patient indicated whether she would prefer video glasses or not if she were to have another filling and what the expectations of the effect had been. Differences in VAS ratings in the video and control situation were tested by Student's t-test. There was no statistically significant effect on the perceived pain (p=0.90) or unpleasantness (p=0.39), but the majority (74%) of the patients would still prefer to wear video glasses if they were to have another dental filling, and 73% had expected a positive effect of the video glasses. These findings suggest that perceived intensity of dental pain is resistant to a simple distraction technique.

Adult↗
PubMed1977

Construction of a crown to fit a removable partial denture clasp.

This technique allows an accurate cast to be made of a prepared abutment tooth with the removable partial denture in place in the mouth. The partial denture is carefully removed from the cast, the crown waxed up, and the removable partial denture re-placed as many times as necessary during wax-up to obtain a crown that accurately fits the clasp.

Crowns↗
PubMed1986

Photoelastic analysis of stresses in resin-bonded cingulum rest seats.

Two-dimensional photoelastic analysis of resin-bonded cingulum rest seats demonstrated improvement in stress distribution when the lingual surface of the tooth was prepared with a cingulum groove. This preparation is more important for teeth that are more vertically or lingually oriented and have flatter lingual surfaces, such as mandibular canines.

Cuspid↗
PubMed1983

Lysosomes and removal of the basal lamina of ameloblasts in early stages of odontogenesis.

Differentiation of ameloblasts is characterised by the development of cytoplasmic organelles and changes in the distal cytoplasm and surface adjacent to the basal lamina. Examination of rat tooth germs prepared for thin section electron microscopy and for freeze fracture, and also stained for acid phosphatase, reveals that three concomitant events occur in this region. The distal surface membrane becomes progressively more undulated, there is an increase in acid phosphatase-containing membrane-bound vesicles (lysosomes) and the basal lamina becomes less apparent and finally disappears. Since the progressive disappearance of the basal lamina is accompanied by an increase in lysosomes, it is possible that lysosomal enzymes are involved in the breakdown of the basal lamina or, alternatively, that the basal lamina is broken down by enzymes derived from odontoblasts, and that its remnants are taken up by the many coated pits and invaginations of the distal surface membrane to be further degraded iun the lysosomal system.

Ameloblasts↗
PubMed2006

Orthodontic materials research and applications: part 1. Current status and projected future developments in bonding and adhesives.

The purpose of this opinion article, to be presented in 2 parts, is to project immediate future developments expected in orthodontic materials research and applications. Analysis of the material is structured around 2axes: presentation of evidence summarizing the current status in various fields, and formulation of a hypothesis for short-term future developments. This first part of the article deals with advances and developments in bonding to enamel. Projected adhesive developments include greater use of high-energy lamps for polymerization in light-cured systems, universal application of molar tube bonding, widespread use of self-etching primers, broader acceptance of glass ionomers in their conventional and modified modes, and elimination of 2-phase adhesives in favor of no-mix and light-cured adhesives. Long-term future adhesive applications might also include biomimetic approaches, adopting mechanisms used by living organisms to adhere to surfaces.

Biomimetic Materials↗