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.

Influência da técnica de preparo sobre o contorno cervical dos laminados cerâmicos: relato de caso / Influence of the preparation technique on the cervical contour of ceramic laminates: a case report / Influencia de la técnica de preparación en el contorno cervical de los laminados cerámicos: reporte del caso

Introdução: Devido à crescente demanda estética, a odontologia restauradora se renova na intenção de alcançar melhores resultados na harmonia do sorriso. Entretanto, a atenção deve voltar-se também aos tecidos periodontais, visto que há uma integração entre material restaurador e os tecidos. Objetivo:Descrever e discutir as etapas clínicas para a confecção de laminados cerâmicos, atentando-se a preparos minimamente invasivos, contorno cervical e fatores que podem intervir na longevidade do procedimento.Relato de caso:Paciente do sexo masculino, 28 anos de idade, compareceu a Associação Brasileira de Odontologia, seção de Alagoas, relatando insatisfação em relação ao tamanho dos seus dentes. Os arcos superior e inferior foram moldados para a obtenção dos modelos de estudo e enceramento diagnóstico. Ao início do tratamento foi orientado ao paciente clareamento dental pela técnica combinada. O preparo dos dentes foi guiado por uma matriz de silicone, sendo estes uniformes e conservadores, seguido de moldagem, fase laboratorial e cimentação final. Finalizado o caso foi realizado o ajuste oclusal solicitando ao paciente que realizasse movimentos de lateralidade e protrusão. Conclusões:A técnica do preparo influência na longevidade dos laminados cerâmicos, por relacioanar-se à adesão e a saúde periodontal. O preparo deve ser mínino e limitado ao esmalte dental sempre que possível, determinando assim um maior e melhor prognóstico (AU).

Introduction:Due to the growing aesthetic demand, restorative dentistry is renewed to achieve better results in smile harmony. However, attention should also be turned to periodontal tissues since there is an integration between restorative material and tissues. Objective:To describe and discuss the clinical steps for the manufacture of laminate veneers, paying attention to minimally invasive preparations, cervical contour, and factors that can intervene in the procedure's longevity. Case report:A 28-year-old male patient attended the Brazilian Dental Association, the Alagoas section, reporting dissatisfaction with his teeth' size. The upper and lower arches were molded to obtain the study and diagnostic waxing models. At the beginning of treatment, the patient was instructed by the combined technique. After the case, the occlusal adjustment was performed, asking the patient to perform laterality and protrusion movements. Conclusions:The preparation technique influences the longevity of laminate veneers due to adherence and periodontal health. The preparation should be minimal and limited to dental enamel whenever possible, thus determining a higher and better prognosis (AU).

Introducción: Debido a la creciente demanda estética, la odontología restauradora se renueva para lograr mejores resultados en la armonía de la sonrisa. Sin embargo, también se debe prestar atención a los tejidos periodontales ya que existe una integraciónentre el material restaurador y los tejidos.Objetivo: Describir y discutir los pasos clínicos para la confección de carillas laminares, prestando atención a las preparaciones mínimamente invasivas, al contorno cervical y a los factores que pueden intervenir en la longevidad del procedimiento.Reporte del caso: Un paciente masculino de 28 años asistió a la Asociación Dental Brasileña, sección de Alagoas, reportando insatisfacción con el tamaño de sus dientes. Los arcos superior e inferior fueron moldeados para obtener los modelos de depilación de estudio y diagnóstico. Al comienzo del tratamiento, el paciente fue instruido por la técnica combinada. La preparación de los dientes fue guiada por una matriz de silicona, siendo estas uniformes y conservadoras, seguidas de moldeo, fase de laboratorio y cementación final. Después del caso, se realizó el ajuste oclusal, pidiendo al paciente que realizara movimientos de lateralidad y protuberancia. Conclusiones: La técnica de preparación influye en la longevidad de los laminados cerámicos, debido a la adherencia y la salud periodontal. La preparación debe ser mínima y limitada al esmalte dental siempre que sea posible, determinando así un pronóstico más alto y mejor (AU).

Evaluation of the use of a guided bur during preclinical teaching of tooth preparation: A pilot study.

Objectives: An innovative calibrated bur, aiming to improve precision during reduction of the incisal edge, was recently proposed to guide practitioners during tooth preparation. However, limited information is available concerning its usefulness in dental preclinical education. The aim of this study was to evaluate whether using this innovative guided bur improves learning experience quality and the performance of students during tooth preparation. Material and methods: After having provided written consent, 60 second-year students were divided into two groups. One group used a 1-mm rounded bur to perform depth grooves, whereas the second group used the innovative guided bur, consisting in a 2-mm-depth marker with a stopping surface. Once the grooves were obtained, they were then connected using the same wheel bur in both groups. The aim was to obtain a final 2-mm reduction of the incisal edge. Quality of the learning experience (stress level, motivation to restart, self-evaluation of the preparation, and difficulty) was quantified using a visual analog scale. Duration of the procedure was also measured in both groups. 3D measurements for each tooth were performed using an STL comparison software. Results: There were no significant differences between groups in terms of stress and self-evaluation of the preparation. Students in the guided bur group reported significantly lower perception of exercise difficulty (p < .001) and significantly higher motivation to restart the procedure (p < .001). The guided bur group performed the procedure in 16.4% less time than the rounded bur group. The use of the guided bur led to a 23% over-reduction, whereas the use of the rounded bur led to a 10% under-reduction. Conclusions: Overall, the present study shows that the guided bur provides significant improvement in the student's learning experience with increased motivation and decreased perception of difficulty. It shortens the duration of procedure performance, but it also induces a reduction in preparation accuracy.

Axial wall angulation for rotational resistance in a theoretical-maxillary premolar model.

Objectives: The aim of this study was to determine the influence of short base lengths and supplemental grooves on surface area and rotational resistance in a simulated-maxillary premolar. Materials and Methods: Trigonometric calculations were done to determine the total surface area with and without supplemental grooves. Additional computations were done to determine the maximum wall angle needed to resist rotation displacement in a premolar-sized model. Wall heights of 3.0, 4.0, and 5.0 mm were used in the surface area and rotational axis computations. The rotational axis was located on the lingual restoration margin to produce a buccal-to-lingual rotational displacement. Results: Total surface area decreased with increasing four-wall taper levels from 2° to 18° and decreasing preparation heights from 5 to 3 mm. Significant surface area improvements were found with the supplemental use of mesial and distal axial grooves compared with the same condition without grooves in all taper levels and preparation height categories. Resistance to rotational displacement was determined to occur at only at very low levels of opposing wall taper angles. The use of supplemental grooves on mesial and distal axial walls significantly improved both total surface area and rotational resistance. Conclusions: The vertical wall taper angles, preparation heights, and supplemental grooves play a role in resistance form and restoration stability.

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.

Remaining coronal dentin and risk of fiber-reinforced composite post-core restoration failure: a meta-analysis.

PURPOSE: The amount of coronal residual structure has been recognized as critical to the survival probability of pulpless teeth. The aim of this study was to analyze whether and how coronal dentin loss would affect the failure rate of fiber-reinforced composite (FRC) post-core restorations. MATERIALS AND METHODS: Eligible studies were searched in PubMed, Cochrane Library, Embase, and China National Knowledge Infrastructure databases from their inception through April 2014. The risk ratio with 95% confidence interval (CI) was estimated using the Mantel and Haenszel method. RESULTS: Five studies were included in this meta-analysis. The risk ratio for coronal wall absence was 2.73 (95% CI: 1.48-5.03). The risk ratio for ferrule absence was 1.94 (95% CI: 0.57-6.54). CONCLUSIONS: This meta-analysis of the limited studies available suggested that coronal wall absence might increase the risk of FRC post-core restoration failure, while the role of ferrule effect is still not entirely understood.

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.

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.

Evaluation of occlusal rest seats with 3D technology in dental education.

The preparation of rest seats must comply with specific sizes and shapes. Various technological systems such as Kavo PrepAssistant have been used as an auxiliary method to evaluate preclinical preparations more objectively. The aims of this study were to establish an alternative system for evaluating occlusal rest seats and to compare different types of assessment. Seventy-six undergraduate students at Oporto University Faculty of Dental Medicine in Portugal were selected as a convenience sample to prepare two occlusal rest seats in Kavo teeth #45 and #46 (FDI World Dental Federation ISO-3950) and were randomly assigned to two groups. Bearing in mind the ideal characteristics of rest seats, the investigators defined ten assessment parameters, and their evaluation weights were independently estimated by three evaluators. Four of these parameters were measured in Kavo PrepAssistant. The results of the different evaluation methods and evaluators varied considerably. The classical evaluation presented final results worse than those of the evaluations using parameters. In this study, carrying out the assessment with Kavo PrepAssistant helped to achieve a more objective and less evaluator-dependent final evaluation.

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.

Study of surface topography, roughness, and microleakage after dental preparation with different instrumentation.

PURPOSE: The purpose of this study was to compare the differences in surface characteristics and roughness of teeth finished for porcelain veneer laminates using different instrumentation and to assess their influence on microleakage. MATERIALS AND METHODS: Fifty-six extracted human maxillary central incisors were divided randomly into two groups: Group HsR teeth were finished with a high-speed handpiece with diamond burs; group SO teeth were finished with a sonic oscillating diamond instrument. Porcelain veneers were bonded to 24 teeth in each group. Microleakage was measured in the cervical area. Four remaining teeth in each group were examined using confocal laser-scanning microscopy and scanning electron microscopy. RESULTS: Oscillating instruments produced a rougher dentinal surface (Ra values; P = .029) than those finished with high-speed rotary technology. CONCLUSIONS: There is less microleakage when bonded restoration edges are situated over dentin that has been finished with sonic oscillating instrumentation (P = .006).

The effect of ferrule height on stress distribution within a tooth restored with fibre posts and ceramic crown: a finite element analysis.

OBJECTIVES: To evaluate via finite element analysis the effect of different ferrule heights on stress distribution within each part of a maxillary first premolar (MFP) restored with adhesively luted glass fiber-reinforced resin (GFRR) posts and a ceramic crown. METHODS: The solid models consisted of MFP, periodontal ligament and the corresponding alveolar bone process. Four models were created representing different degrees of coronal tissue loss (0mm, 1mm, 2mm and 3mm of ferrule height). First set of computing runs was performed for in vivo FE-model validation purposes. In the second part, a 200-N force was applied on the buccal cusp directed at 45° to the longitudinal axis of the tooth. Principal stresses values and distribution were recorded within root, abutment, posts, crown and related adhesive interfaces. RESULTS: All FE-models showed similar stress distribution within roots, with highest stress present in the chamfer area. In composite abutments higher stress was observed when no ferrule was present compared to ferruled FE-models. Stress distribution within crown and GFRR posts did not differ among the models. Stress values at the adhesive interfaces decreased with increasing ferrule height. SIGNIFICANCE: The stress state at abutment-crown and post-root interfaces was very close to their strength, when ferrule was not present. Similarly, higher ferrule produced more favorable stress distribution at post-abutment and abutment-root interfaces. Endodontically treated teeth with higher ferrule exhibit lower stress at adhesive interfaces that may be expected to lower the probability of clinical failure.

Clinical determination of angle convergence in a tooth preparation for a complete crown.

The relationship of the convergence angle (CA) to the height of the axial walls is the most important factor for providing retention and resistance in tooth preparation for a complete crown. Several studies have shown that the ideal CA is difficult to achieve in clinical practice. The technique described in this article allows for the determination of the CA during the tooth preparation procedure, based on an instrument developed and created by the authors.

Hall versus conventional stainless steel crown techniques: in vitro investigation of marginal fit and microleakage using three different luting agents.

PURPOSE: This study's purpose was to investigate microleakage and marginal discrepancies in stainless steel crowns (SSCs) placed using conventional and Hall techniques and cemented with three different luting agents. METHODS: Seventy-eight human primary maxillary second molars were randomly assigned to two groups (N=39), and SSCs were applied either with the Hall or conventional technique. These two groups were further subgrouped according to the material used for crown cementation (N=13 per group). Two specimens in each group were processed for scanning electron microscopy investigation. The extent of microleakage and marginal fit was quantified in millimeters on digitally photographed sections using image analysis software. The data were compared with a two-way independent and a two-way mixed analysis of variance (P=.05). RESULTS: The scores in the Hall group were significantly worse than those in the conventional technique group (P<.05). In both groups, resin cement displayed the lowest extent of microleakage, followed by glass ionomer and polycarboxylate cements (P<.05). CONCLUSIONS: Stainless steel crowns applied using the Hall technique displayed higher microleakage scores than those applied using the conventional technique, regardless of the cementation material. When the interaction of the material and technique was assessed, resin cement presented as the best choice for minimizing microleakage in both techniques.

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.

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.

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.