Vertical preparation for fixed prosthesis rehabilitation in the anterior sector.

This clinical report describes a biologically oriented preparation technique (BOPT) for teeth and an implant for the esthetic rehabilitation of the maxillary anterior sector. The technique was designed to create an anatomic crown with a prosthetic emergence profile that simulated the shape of the natural tooth.

Effects of repeated firing on the marginal accuracy of Co-Cr copings fabricated by selective laser melting.

STATEMENT OF PROBLEM: Selective laser melting (SLM) is a technique used to fabricate Co-Cr dental restorations; however, because marginal accuracy is important for the long-term success of restorations, the marginal accuracy of SLM after repeated firings must be considered. PURPOSE: The purpose of this study was to evaluate the marginal accuracy of dental Co-Cr alloy copings fabricated by SLM and to investigate the effects of repeated firing on the marginal fit of these copings. MATERIAL AND METHODS: SLM-fabricated and cast Co-Cr alloy copings (n=15) were prepared for a zirconia die. The marginal gap widths of each group were evaluated with a silicone replica technique after the first, third, fifth, and seventh firing cycle. The thickness of the reference point was measured with a stereomicroscope with ×100 magnification. Analysis of variance was used to evaluate the effect of repeated firing on the marginal accuracy of the 2 alloys. The Student t test was used to compare the marginal gap widths of the SLM-fabricated and cast Co-Cr alloy copings after repeated firing (α=.05). RESULTS: The marginal gap width values between the 2 groups at all firing periods were statistically significant (P<.05). The mean marginal gap width values for SLM-fabricated copings were 36 µm, 37 µm, 38 µm, and 38 µm after the first, third, fifth, and seventh firing, while the mean marginal gap width values for cast copings were 67 µm, 71 µm, 72 µm, and 73 µm at the same number of firings. The marginal gap width values within the 2 groups were not statistically different from each other with additional firing (P>.05). CONCLUSIONS: The SLM copings demonstrated superior marginal accuracy at all firings. Repeated firing had no significant influence on the marginal accuracy of both copings, and the marginal fit of both copings after repeated firing was within a clinically acceptable range.

Die spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study.

STATEMENT OF PROBLEM: The inability to control die spacer thickness has been reported. However, little information is available on the congruency between the computer-aided design parameters for die spacer thickness and the actual printout. PURPOSE: The purpose of this study was to evaluate the accuracy and precision of the die spacer thickness achieved by combining computer-aided design and 3-dimensional printing technology. MATERIAL AND METHODS: An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone models were produced from Type IV dental stone. The dies were randomly divided into 5 groups with assigned die spacer thicknesses of 25 µm, 45 µm, 65 µm, 85 µm, and 105 µm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D Systems), were cemented onto their respective die-stone models with self-adhesive resin cement and stored at room temperature until sectioning into halves in a buccolingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die. Images of the printed resin coping/die-stone model internal gap dimensions were obtained with an inverted bright field metallurgical microscope at ×100 magnification. The acquired digital image was calibrated, and measurements were made using image analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery rate at 5% was used to adjust for multiple testing. Coefficient of variation was used to determine the precision for each group and was evaluated statistically with the Wald test (α=.05). RESULTS: The accuracy, expressed in terms of the mean differences between the prescribed die spacer thickness and the measured internal gap (standard deviation), was 50 µm (11) for the 25 µm group simulated die spacer thickness, 30 µm (10) for the 45 µm group, 15 µm (14) for the 65 µm group, 3 µm (23) for the 85 µm group, and -10 µm (32) for the 105 µm group. The precision mean of the measurements, expressed as a coefficient of variation, ranged between 14% and 33% for the 5 groups. CONCLUSIONS: For the accuracy evaluation, statistically significant differences were found for all the groups, except the group of 85 µm. For the precision assessment, the coefficient of variation was above 10% for all groups, showing the printer's inability to reproduce the uniform internal gap within the same group.

In vitro evaluation of accuracy and precision of automated robotic tooth preparation system for porcelain laminate veneers.

STATEMENT OF PROBLEM: Controlling tooth reduction for porcelain laminate veneers (PLVs) in fractions of millimeters is challenging. PURPOSE: The purpose of this study was to assess an automated robotic tooth preparation system for PLVs for accuracy and precision compared with conventional freehand tooth preparation. MATERIAL AND METHODS: Twenty maxillary central incisor tooth models were divided into 2 groups. Ten were assigned to a veneer preparation with a robotic arm according to preoperative preparation design-specific guidelines (experimental group). Ten were assigned to conventional tooth preparation by a clinician (control group). Initially, all tooth models were scanned with a 3- dimensional (3D) laser scanner, and a tooth preparation for PLVs was designed on a 3D image. Each tooth model was attached to a typodont. For the experimental group, an electric high-speed handpiece with a 0.9-mm-diameter round diamond rotary cutting instrument was mounted on the robotic arm. The teeth were prepared automatically according to the designed image. For the control group, several diamond rotary cutting instruments were used to prepare the tooth models according to preoperative preparation design guidelines. All prepared tooth models were scanned. The preoperative preparation design image and scanned postoperative preparation images were superimposed. The dimensional difference between those 2 images was measured on the facial aspect, finish line, and incisal edge. Differences between the experimental and the control groups from the 3D design image were computed. Accuracy and precision were compared for all sites and separately for each tooth surface (facial, finish line, incisal). Statistical analyses were conducted with a permutation test for accuracy and with a modified robust Brown-Forsythe Levene-type test for precision (α=.05). RESULTS: For accuracy for all sites, the mean absolute deviation was 0.112 mm in the control group and 0.133 mm in the experimental group. No significant difference was found between the 2 (P=.15). For precision of all sites, the standard deviation was 0.141 mm in the control group and 0.185 mm in the experimental group. The standard deviation in the control group was significantly lower (P=.030). In terms of accuracy for the finish line, the control group was significantly less accurate (P=.038). For precision, the standard deviation in the control group was significantly higher at the finish line (P=.034). CONCLUSIONS: For the data from all sites, the experimental procedure was able to prepare the tooth model as accurately as the control, and the control procedure was able to prepare the tooth model with better precision. The experimental group showed better accuracy and precision at the finish line.

Effect of ferrule location on the fracture resistance of crowned mandibular premolars: An in vitro study.

STATEMENT OF PROBLEM: How the location of a ferrule affects the fracture resistance of endodontically treated mandibular premolars is unclear. PURPOSE: The purpose of this in vitro study was to compare the effect of ferrule location on the fracture resistance of endodontically treated mandibular premolars. MATERIAL AND METHODS: Seventy-two extracted human mandibular premolars were selected and divided into 6 test groups (n = 12) according to ferrule location: control group, GHT; endodontically treated teeth without endodontic posts and crowns, GCF; teeth with a 2 mm circumferential ferrule, GBF; teeth with a 2 mm buccal ferrule; GLF, teeth with a 2 mm lingual ferrule; GBLF, teeth with a 2 mm buccal and lingual ferrule; and teeth without ferrule, GWF. After glass fiber posts were cemented with a self-adhesive resin cement and foundation restorations were placed, NiCr crowns were luted to each prepared tooth. All specimens were quasistatically loaded at 30 degrees in a universal testing machine until fractured. Data were then analyzed with 1-way ANOVA, followed by multiple comparisons using the Tukey honestly significant difference test (α=.05). RESULTS: Mean ± SD failure loads for groups ranged from 791.1 ± 177.5 N to 1086.1 ± 181.1 N. One-way ANOVA revealed a statistically significant difference between the groups (P ≤ .05). However, no statistically significant differences were observed among groups (P > .05), except between GHT (control group) and groups GBLF and GWF (P = .025, P = .022). CONCLUSIONS: Within the limitations of this study, the location of the ferrule had no significant effect on the fracture resistance of endodontically treated mandibular premolars.

Dental preparation with sonic vs high-speed finishing: analysis of microleakage in bonded veneer restorations.

PURPOSE: To compare marginal microleakage in porcelain veneer restorations following dental finishing using two types of instruments to test the hypothesis that microleakage will be less when teeth are prepared with sonic oscillating burs than when prepared with high-speed rotating burs. MATERIALS AND METHODS: Fifty-six extracted human maxillary central incisors were selected and divided randomly into two groups. Group 1 samples underwent dental finishing using high-speed rotating diamond burs, while group 2 used sonic oscillating diamond burs. Buccal chamfer preparation was carried out for both groups. Forty eight of the samples (24 per group) were restored using IPS Empress ceramic veneers. 2% methylene blue was used to evaluate microleakage at the tooth/composite veneer interface. Teeth were sectioned lengthwise into three parts and microleakage was measured at two points - cervical and incisal - on each section. Before bonding, four teeth per group underwent SEM examination. RESULTS: Evaluation of microleakage at the cervical dentin margin showed a value of 10.5% in group 1 and 6.6% in group 2, which was statistically significantly different (p < 0.05). Incisal microleakage was 1.3% for group 1 and 1.2% for group 2, which was not significantly different. SEM revealed different patterns of surface texture in both areas according to the instrument used. Group 1 exhibited parallel horizontal abrasion grooves with a milled effect and thick smear layers; group 2 showed abrasive erosion, discontinuous perpendicular depressions, and thin smear layers. CONCLUSION: Tooth preparations finished with sonic burs produced significantly less microleakage in the cervical dentin area of bonded veneer restorations. No differences were found in the incisal enamel area.

Ultrasonic versus drills implant site preparation: a histologic analysis in bovine ribs.

PURPOSE: Ultrasonic surgery is a recently developed system for cutting bone with microvibrations. The aim of the current study was a histologic comparison between conventional drills versus ultrasonic surgery devices in implant bed preparation. METHODS: Ten bovine ribs were used, and a total of 100 perforations were randomly performed: half (n = 50) (group A) of the perforations were done through conventional drills using a single cylindrical bur (Bone System, Milan, Italy), 13 mm in height and 2 mm in width at a speed of 400 rpm, and the other half (n = 50) (group B) using an ultrasonic device (Surgysonic; Esacrom, Imola Italy), mounted with a diamond-coated cylindrical tip. After implant sites' preparation, the ribs were immediately stored in 10% buffered formalin and processed to obtain thin ground sections. RESULTS: At higher magnification, microcracks at the interface were detected. In group A, they were numerous and showed a thickness and depth ranging from 20 to 120 µm and from 500 to 1000 µm, respectively. In group B, very few or no microcracks were present. Statistically significant differences were found in the microcracks density in the cortical bone but not in the cancellous bone. CONCLUSIONS: The findings from this study suggest that ultrasonic implant site preparation showed a higher performance in terms of accuracy and uniformity of the osteotomy cut, compared with conventional rotary instruments. Further studies should be conducted to understand whether a smooth, congruent implant bed able to retain fine bone structures may affect the early phases of bone healing and therefore improve osseointegration.

Influence of oscillating and rotary cutting instruments with electric and turbine handpieces on tooth preparation surfaces.

STATEMENT OF THE PROBLEM: Rotary and nonrotary cutting instruments are used to produce specific characteristics on the axial and marginal surfaces of teeth being prepared for fixed restorations. Oscillating instruments have been suggested for tooth preparation, but no comparative surface roughness data are available. PURPOSE: To compare the surface roughness of simulated tooth preparations produced by oscillating instruments versus rotary cutting instruments with turbine and electric handpieces. MATERIAL AND METHODS: Different grit rotary cutting instruments were used to prepare Macor specimens (n=36) with 2 handpieces. The surface roughness obtained with rotary cutting instruments was compared with that produced by oscillating cutting instruments. The instruments used were as follows: coarse, then fine-grit rotary cutting instruments with a turbine (group CFT) or an electric handpiece (group CFE); coarse, then medium-grit rotary cutting instruments with a turbine (group CMT) or an electric handpiece (group CME); coarse-grit rotary cutting instruments with a turbine handpiece and oscillating instruments at a low-power (group CSL) or high-power setting (group CSH). A custom testing apparatus was used to test all instruments. The average roughness was measured for each specimen with a 3-dimensional optical surface profiler and compared with 1-way ANOVA and the Tukey honestly significant difference post hoc test for multiple comparisons (α=.05). RESULTS: Oscillating cutting instruments produced surface roughness values similar to those produced by similar grit rotary cutting instruments with a turbine handpiece. The electric handpiece produced smoother surfaces than the turbine regardless of rotary cutting instrument grit. CONCLUSION: Rotary cutting instruments with electric handpieces produced the smoothest surface, whereas the same instruments used with a turbine and oscillating instruments achieved similar surface roughness.

The marginal fit of selective laser melting-fabricated metal crowns: an in vitro study.

STATEMENT OF PROBLEM: The selective laser melting technique is attracting interest in prosthetic dentistry. The marginal fit is a key criterion for fixed restorations. PURPOSE: The purpose of the study was to evaluate the marginal fit of cast cobalt-chromium alloy crowns versus the fit of selective laser melting-fabricated crowns. MATERIAL AND METHODS: The marginal gap widths of 36 single crowns (18 selective laser melting-fabricated cobalt-chromium metal crowns and 18 cobalt-chromium cast crowns) were determined with a silicone replica technique. Each crown specimen was cut into 4 sections, and the marginal gap width of each cross section was evaluated by stereomicroscopy (× 100). The Student t test was used to evaluate whether significant differences occurred in the marginal gap widths between the selective laser melting-fabricated and cast cobalt-chromium metal crowns (α=.05). RESULTS: The mean marginal gap width of the cast crowns (170.19 µm) was significantly wider than that of the selective laser melting-fabricated crowns (102.86 µm). CONCLUSIONS: Selective laser melting-fabricate cobalt-chromium dental crowns found improved marginal gap widths compared with traditional cast crowns.

Influence of occlusal contact and cusp inclination on the biomechanical character of a maxillary premolar: a finite element analysis.

STATEMENT OF PROBLEM: Restoring teeth with large amounts of dentin loss is challenging, especially for posterior teeth with high cusps. However, strategies for reducing the lateral forces are based on clinical experience instead of than scientific evidence. PURPOSE: The purpose of this study was to analyze the biomechanical characteristics of maxillary premolars with different ferrule configurations and to investigate the influence of occlusal contact and cusp inclination on stress distribution with the finite element method. MATERIAL AND METHODS: Five numerical casts of a maxillary premolar were generated; each adopted 1 of the 5 coronal dentin configurations: i (access cavity with 4-mm dentin height) and ii to v (2-mm complete ferrule, 2-mm facial ferrule, 2-mm palatal ferrule, 2-mm proximal ferrule, and restored with a post and core, respectively). Both gold-alloy and glass-fiber posts were modeled. An oblique load of 200 N was applied to the top, middle, and bottom of the 45-degree facial cusps. The cusp inclination was remodeled to 60 degrees, followed by the application of a 200-N load to the top. The values of the maximum principal stress and von Mises stress were calculated to assess overload risk. RESULTS: When the top of 45-degree facial cusps was loaded, the maximum local stress concentration on dentin was found in teeth with a facial ferrule and restored with a gold-alloy post. When the middle of 45-degree facial cusps were loaded, the principal stresses of teeth with a complete ferrule, palatal ferrule, and proximal ferrule were similar to those of the access cavity teeth. In contrast, the principal stress of a tooth with a facial ferrule was close to that of the access cavity tooth after remodeling the facial inclination to 60 degrees. CONCLUSIONS: Maxillary premolars with only facial dentin remaining show higher local stress on root dentin. Altering the loading position and reducing the facial cusp inclination can reduce local stresses.

The effect of occlusal surface relief of dies on marginal adaptation of metal-ceramic casting copings.

PURPOSE: The purpose of this study was to evaluate the impact of occlusal relief of dies on internal adaptation of metal-ceramic casting copings. MATERIALS AND METHODS: Standardized preparations were made on 80 extracted third molar teeth. Impressions were made with poly(vinyl siloxane), and stone dies were prepared. Dies were covered with four layers of die spacer, covering the entire preparation together with the occlusal surface excluding the apical 0.5 mm of the preparation in group 1 (40 specimens), and covering the same area excluding the occlusal surface in group 2 (40 specimens). Copings were cast using nickel-chromium-based metal ceramic alloy and cemented using zinc phosphate cement. The specimens were sectioned along the long axis. Internal discrepancies were recorded with a 0.001-mm resolution stereoscope at 6 points: the middle of the occlusal surface (MO), middle of the lingual wall (ML), middle of the buccal wall (MB), middle of the buccal shoulder finish line (MSH), middle of the lingual chamfer finish line (MCH), and middle of the buccal bevel finish line (MBL). Student's t-test was used for statistical analysis. Significance level was set at p < 0.05. RESULTS: The marginal discrepancies of group 1 were higher than those of group 2. Significant differences in discrepancies were found on MO (p < 0.0001), MSH (p = 0.012), and MBL (p = 0.035). The bevel margin showed the least marginal discrepancy following occlusal surface of the die with no relief. CONCLUSION: Leaving the occlusal part of the die uncovered with the die spacer improved the crown seating considerably in the occlusal surface as well as shoulder and bevel margins.

Ultrasonic margin preparation for fixed prosthodontics: a pilot study.

PURPOSE: Atraumatic, oscillating ultrasonic instruments have recently been developed for prosthodontic margin finishing. This in vitro observational pilot study aimed to compare the condition of crown preparation margins finished using new ultrasonic instruments with margins finished with conventional rotary instruments. METHODS: Two extracted human canine teeth were prepared for crowns. A split-tooth model was used to refine the margins: half of the margin was finished with conventional rotary instruments, the other with ultrasonic instruments. The profiles of the margins were observed using scanning electron microscopy, and a quantitative comparison of surface roughness was obtained using surface roughness analysis software. RESULTS: The margins finished with the ultrasonic instruments exhibited a better-defined axial wall/margin angle and a smoother marginal surface. Rotary instruments produced a sharper and more continuous external line angle. Two-dimensional surface roughness analysis showed that the margins produced with the ultrasonic instruments were approximately half as rough as the margins prepared with the conventional rotary instruments. CONCLUSION: The ultrasonic instruments produce margins in better condition than the current standard and appear to have some practical advantages. CLINICAL SIGNIFICANCE: Preparations for fixed prosthodontics finished with these ultrasonic instruments created better-defined margins, which could result in more successful prostheses.

The effect of ultrasonic instruments on the quality of preparation margins and bonding to dentin.

STATEMENT OF THE PROBLEM: Ultrasonic instruments have recently been developed for finishing crown preparations. They are successful in accessing difficult areas on the preparation margin, but their effects on the dentin surface and on bond strength are contradictory. PURPOSE: The aim was to evaluate the condition of crown preparation margins finished using new ultrasonic instruments and to assess their effects on dentin bond strength. METHODS: Characteristics of tooth surfaces prepared using two different ultrasonic protocols were compared; Perfect Margin Shoulder (PMS) (PMS 3, Satelec, Merignac, France) 1, 2, and 3 (complete finishing) versus PMS 1 and 2 (partial finishing). They were assessed using scanning electron microscopy (SEM) and surface roughness analysis. Bonding of composite resin to dentin surfaces prepared with the complete PMS kit was compared with dentin surfaces prepared with finishing diamond burs, using micro-tensile testing. RESULTS: SEM images revealed a clear difference between the two preparation sequences (PMS 1, 2 versus PMS 1, 2, and 3). Surfaces finished using the PMS tips 1, 2, and 3 appeared continuous, even, and smooth compared with PMS tips 1 and 2 only. The additional use of the PMS 3 uncoated tip enhanced smear layer removal. There was no significant difference when comparing the surface roughness obtained with the PMS 1, 2, and 3 protocol with the PMS 1 and 2 only (p > 0.05). Micro-tensile bond strength was not significantly different between the surfaces prepared with the ultrasonic instruments and the surfaces prepared with the diamond burs (p > 0.05). CONCLUSION: The use of the complete PMS finishing kit (PMS 1, 2, and 3) produced better quality finishing lines than PMS 1 and 2. The use of ultrasonic instruments to prepare dentin resulted in comparable bond strengths to the use of diamond burs. CLINICAL SIGNIFICANCE: The extremely precise preparation margin possible with ultrasonic instruments improves the quality and accuracy of crown preparations, which may lead to better impressions and closer adaptation of restorations. The complete set of three Perfect Margin Shoulder instruments is recommended, which can produce comparable bond strengths to preparations with rotary instruments.

Supplementing retention through crown/preparation modification: an in vitro study.

STATEMENT OF PROBLEM: The best treatment for a crown that has come loose but has appropriate marginal fit and form is not clear. PURPOSE: This study was designed to determine whether the retention of such crowns can be increased without remaking the crown or by extensively modifying the tooth preparation. MATERIAL AND METHODS: Ninety cast metal complete crowns, divided into 9 groups of 10, were fabricated to be slightly loose in their internal adaptation to metal dies with an optimal tooth preparation. Horizontal grooves were formed around the circumference of the internal crown surface and the external surface of the metal die, the control being the unaltered crown and die. The crowns were cemented with resin-modified glass ionomer cement and then subjected to a tensile force until they were dislodged. The data were subjected to a 2-way ANOVA to determine the significance of the differences between crowns and dies, and 2 t tests were then used to compare each crown/die combination to the control (α=.05). RESULTS: The mean retention was significantly higher when 1 horizontal groove was placed inside the crowns (P<.001) and was even higher when 2 grooves were placed inside the crowns (P<.001). Placing 1 or 2 grooves in the metal die or in both the crown and die was not significantly more retentive than placing grooves only in the crown. CONCLUSIONS: Placing 1 or 2 horizontal circumferential grooves into the internal surface increased the retention of metal complete crowns made for optimal tooth preparations. Grooves placed into the crown were as effective as or more effective than grooves placed into the tooth / die.

Preparation time and surface roughness of core foundation resins and dentin.

STATEMENT OF PROBLEM: It is unclear if the preparation of core foundation resins is similar to that of dentin. PURPOSE: The purpose of this in vitro study was to compare the preparation time and resulting roughness of 5 core foundation resins and dentin. MATERIAL AND METHODS: Standardized preparations (10 mm length, 5 mm height) were made of 5 specimens of 5 core materials with a device-mounted dental handpiece (150 000 rpm, water-cooling) with weight-controlled contact pressure (50 g). To assess the cutting time of 100 µm grit cylindrical diamond rotary cutting instruments, 2 mm and 4 mm depths were cut 3 times (n=15). Afterwards surface roughness Ra and Rz were measured. Blocks of dentin were used as a control. Both preparation time and surface roughness data were statistically analyzed (1-way ANOVA, Scheffé correction, α=.05). RESULTS: The average preparation times for dentin were 7 seconds for a 2 mm preparation depth and 22 seconds for a 4 mm depth with an average Ra of 5.4 µm or Rz of 30 µm. For a 4 mm depth, preparation times for Build-It, Rebilda LC, and Ti-Core ranged from 24 to 27 seconds. The preparation times of these 3 core foundation materials did not differ significantly from dentin for a 4 mm depth. The results of Core Paste and Luxacore were significantly lower (10 and 11 seconds, P<.001). For a 2 mm cutting depth, Core Paste and Luxacore showed similar preparation times compared to dentin (7 seconds, P>.05). Build-It (12 seconds) and Rebilda LC (10 seconds) showed greater preparation times compared to dentin, whereas Ti-Core preparation (5 seconds) was less. ANOVA revealed significantly lower Ra (5.0 µm) and Rz values (23-26 µm) after preparation of Core Paste, Luxacore, and Ti-Core than those of dentin (P<.05). CONCLUSIONS: The preparation times of only some core foundation materials were comparable to dentin. Regarding the cutting depths, different materials provided a dentin-like preparation ability. The surface roughness values of core resins were comparable with or significantly lower than those of dentin.

A new intraoral device to facilitate preparation of the guide plane for removable dental prostheses.

This article presents a prototype of an intraoral device that facilitates preparation of parallel guide planes with accuracy and minimal occlusal divergence. The design of this device facilitates transfer of the desired path of insertion from the diagnostic cast to the mouth quickly and efficiently.

Dentists' Perception and Clinical Use of Preformed Metal Crowns to Restore Primary Molar Defects in Chengdu City, China: A Cross-Sectional Study.

BACKGROUND: Preformed metal crowns (PMCs), as an effective technique recommended for the enduring restoration of primary molar defects, have not been widely implemented in China as well as that in Western countries. This study is aimed at assessing the knowledge on the clinical use of the PMC technique and its effective factors among dentists in Chengdu, China. Thus, the present study is aimed at providing the best available evidence on clinical decision-making to manage dental caries in children and the overall benefits. METHODS: The self-designed questionnaire in this study consisted of two main sections, including the sociodemographic characteristics of the respondents and their perception and use of PMCs. The anonymous questionnaire was distributed among 1000 dentists practicing in Chengdu via SO JUMP. RESULTS: The response rate was 45%. Most respondents (69.6%) did not use PMCs. Academic qualification, working specialty, and professional experience were associated with dentists' use of PMCs. The lack of knowledge about the PMC technique was the main obstacle to the dental practitioners' use of PMCs (41.7%). The lack of understanding of the rationale behind PMCs was the main reason for parents' acceptance of PMC restorations (43.6%). Attending continuing education programs was the main approach to learning the PMC restorative technique (59.1%). CONCLUSIONS: The clinical use of PMCs was not very popular in Chengdu city. To promote this restorative technique, knowledge and practical training should be incorporated into routine courses of undergraduate dental education.

The clinical microscope and direct composite veneer.

This paper presents the advantages and limitations related to the use of a clinical microscope in restorative dentistry, and it demonstrates the aid of magnification during preparation and restoration of a direct composite veneer. Good illumination and visibility is important to adequately viewing the adjacent dental tissues so that the resin composite buildup can mimic natural teeth. The reproduction of details results in a naturally esthetic direct veneer.

Esthetic 7/8 crown--the Tucker technique.

As restorative dentists, one of the largest challenges we face is to restore proper form and function while considering the impact on the esthetic outcome. One must consider the clinical strengths and weaknesses of various materials and their applicability in different situations. For each clinical situation, there is always a most favorable choice coordinating material and design for optimum physiological, functional and esthetic results. The cast gold 7/8 crown with esthetic buccal margin, as designed and advocated by Dr Richard V Tucker, is an extremely valuable procedure, providing a very long-lasting, esthetically pleasing restoration for extensive involvement of maxillary bicuspid or first molar teeth--particularly in cases where there has been some degree of recession of the buccal or mesial-buccal cusp, while that cusp remains strong and of good stock in the gingival third of the tooth. Under the right circumstances, these teeth can be extensively restored without showing the gold, while leaving the natural color and contours of the buccal cusp and avoiding insult to the gingival tissues from the restoration margin. All of these benefits contribute to esthetics that are superior to porcelain-to-metal or all-ceramic restorations, with less loss of tooth structure and trauma to the pulp.

Ultrasonic sulcus penetration: a new approach for full crown preparations.

Newly developed ultrasonic diamond-coated tips (UDT) have been created for sulcus penetration and intracrevicular finish line preparation and polishing. One hundred forty-two freshly extracted premolars and molars were employed for a cutting efficiency test. Dentin surface roughness was analyzed with an optical profilometer and a scanning electron microscope. Within a reasonable cutting time, the UDTs possessed sufficient dentin-cutting capacity. The surface roughness of dentin prepared with the UDT can be improved by using a smaller grit size UDT or a smooth tip set at lower power, and the roughness approaches that of dentin prepared with a referenced red diamond bur. A clinical protocol of ultrasonic sulcus penetration with these developed UDTs is proposed.