[Non-retentive adhesive restorations]. / Niet-retentieve adhesieve restauraties.

With the advent of adhesive dentistry, tooth preparation can be minimally invasive. An optimal adhesion to the dental tissues is a requirement. Rubberdam isolation, using a gold standard adhesive and bonding to freshly prepared dentin are all factors that improve the adhesion to tooth tissue. For non-retentive restorations, indirect composite and glass-ceramic materials are suitable. To date, several studies have shown a high survival rate of indirect adhesive restorations. The adage "if you can isolate the tooth, you can preserve it" may guide the choice of starting an adhesive procedure.

Effect of magnifying loupes on tooth preparation of complete coverage crown: A quantitative assessment using a digital approach.

OBJECTIVE: The purpose of this study was to evaluate the use of magnifying loupes (×2.5) on the quality of tooth preparation for complete coverage crowns; performed by predoctoral students using an objective and quantitative digital method. MATERIALS AND METHODS: Forty-two predoctoral students were randomly assigned into 2 groups to perform tooth preparation for a complete coverage crown on a mandibular first molar in a manikin, with and without the use of magnifying loupes. All preparations were digitally evaluated by PrepCheck 3.0 (Dentsply Sirona). Parameters including tooth reduction, total occlusal convergence (TOC), undercut, margin quality and surface quality were assessed. Continuous data were analysed using Paired t-tests or Wilcoxon Signed Ranks tests. Ordinal data were analysed by McNemer's tests. To further detect the majority pattern ( > 50%) in each group (with and without loupes), one-sample t-test or one-sample Wilcoxon Signed Rank test was performed. The level of significance was set at p = .001 after Bonferroni adjustments for multiple testing. RESULTS: No significant differences in the measured outcomes were found between the groups with or without the use of magnifying loupes (p > .002). The majority (>50%) of both groups had no undercuts (99.3% and 99.4% both p < .001) and the preparation type was within tolerance (81.6% and 85.3%, both p < .001) with acceptable margin (86.4% and 86.3%, both p < .001) and acceptable surface quality (99.0% and 99.1%, both p < .001). However, the majority of both groups underprepared occlusally (96.0% and 95.4%, both p < .001) and axially (65.3% and 67%, both p < .001). Only 30.0%-42.1% of the participants achieved the TOC within 0-20°. CONCLUSIONS: Within the limitations of this study, the use of magnification loupes does not appear to significantly improve the quality of tooth preparation for complete coverage crown. The TOC was also found to be overprepared and occlusally underprepared.

How sandblasting on lingual surfaces can be carried out with minimum enamel damage: An in vitro study on human teeth.

OBJECTIVE: The aim was to assess the extent of enamel damage sandblasting might cause and to identify a combination of sandblasting durations and MicroEtcher nozzle-tooth surface distance (NTD) resulting in the least enamel damage. MATERIALS AND METHODS: Lingual surfaces of 30 human teeth were sandblasted with 2 different distances: 1, 2mm and 3 different durations: 1, 2, 3s and photographed using a light microscope. The cavity depth and diameter of the sandblasted teeth were measured on the light microscope's pictures. A pilot study was performed to minimize possible combinations of sandblasting durations and distances. To validate the measurement method, sandblasted teeth were ground cut for comparison. Inter-examiner reliability was assessed with Bland-Altman analysis. Mann-Whitney U-test was used to detect cavity and diameter changes for every sandblasting duration and NTD combination. RESULTS: From the pilot study sandblasting durations 1,2 and 3s and NTD<2mm were chosen. The cavity diameter of the sandblasted area did not change with increased sandblasting duration nor NTD (P>0.05). The cavity depth of the sandblasted area increased statistically with an increased sandblasting duration (P<0.05) but did not increase with an increase NTD (P>0.05). The 95% limits of inter-examiner agreement were narrow. CONCLUSION: All distance and duration combinations tested caused enamel damage. Sandblasting duration had greater impact on the cavity depth than the NTD. The blasting duration should, therefore, not exceed 2s and the NTD should be held at maximum 2mm to minimize the risk of unintentional spread.

Microcirculation changes in gingival tissue after ultrasonic tooth preparation in beagle dogs.

OBJECTIVE: Ultrasonic wave technology is widely used during dental treatments. We previously demonstrated that this method protects the gingival tissue. However, the physiological change on the gingival microvasculature caused by this method remains unclear. The aim of this study was to investigate the relationship between the morphological and physiological effects on gingival microcirculation when preparing teeth, using the conventional dental turbine or ultrasonic method. METHODOLOGY: The lower premolar teeth of beagle dogs were prepared along the gingival margin by using a dental turbine or ultrasonic wave instrument. Gingival vasculature changes were investigated using scanning electron microscopy for corrosion resin casts. Gingival blood flow at the preparation site was determined simultaneously by laser Doppler flowmetry. These assessments were performed immediately (Day 0), at 7 days and 30 days after tooth preparation. RESULTS: At day 0, in the turbine group, blood vessels were destroyed and some resin leaked. Furthermore, gingival blood flow at the site was significantly increased. In contrast, the ultrasonic group demonstrated nearly normal vasculature and gingival blood flow similar to the non-prepared group for 30 days after preparation. No significant alterations occurred in gingival circulation 30 days after either preparation; however, the turbine group revealed obvious morphological changes. CONCLUSIONS: Based on multiple approach analyses, this study demonstrated that ultrasonic waves are useful for microvascular protection in tooth preparation. Compared with a dental turbine, ultrasonic wave instruments caused minimal damage to gingival microcirculation. Tooth preparation using ultrasonic wave instruments could be valuable for protecting periodontal tissue.

Microcirculation changes in gingival tissue after ultrasonic tooth preparation in beagle dogs

Abstract Ultrasonic wave technology is widely used during dental treatments. We previously demonstrated that this method protects the gingival tissue. However, the physiological change on the gingival microvasculature caused by this method remains unclear. Objective The aim of this study was to investigate the relationship between the morphological and physiological effects on gingival microcirculation when preparing teeth, using the conventional dental turbine or ultrasonic method. Methodology The lower premolar teeth of beagle dogs were prepared along the gingival margin by using a dental turbine or ultrasonic wave instrument. Gingival vasculature changes were investigated using scanning electron microscopy for corrosion resin casts. Gingival blood flow at the preparation site was determined simultaneously by laser Doppler flowmetry. These assessments were performed immediately (Day 0), at 7 days and 30 days after tooth preparation. Results At day 0, in the turbine group, blood vessels were destroyed and some resin leaked. Furthermore, gingival blood flow at the site was significantly increased. In contrast, the ultrasonic group demonstrated nearly normal vasculature and gingival blood flow similar to the non-prepared group for 30 days after preparation. No significant alterations occurred in gingival circulation 30 days after either preparation; however, the turbine group revealed obvious morphological changes. Conclusions Based on multiple approach analyses, this study demonstrated that ultrasonic waves are useful for microvascular protection in tooth preparation. Compared with a dental turbine, ultrasonic wave instruments caused minimal damage to gingival microcirculation. Tooth preparation using ultrasonic wave instruments could be valuable for protecting periodontal tissue.

Evolution of Indirect Restorations for Fixed Prosthodontics: Planning, Preparation and Cementation.

The provision of indirect restorations utilising contemporary materials for single or multiple abutment units in primary health care is an essential requirement for all general dental practitioners to ensure predictable patient outcomes. This paper highlights the important considerations for comprehensive planning and adept treatment execution and delivery that can enhance the patient's dental experience and outcome. A selection of clinical cases highlighting established and novel restorative materials utilising conventional and adhesive clinical techniques is presented and discussed.

The extraction method of tooth preparation margin line based on S-Octree CNN.

The tooth preparation margin line has a significant impact on the marginal fitness for dental restoration. Among the previous methods, the extraction of margin line mainly relies on manual interaction, which is complicated and inefficient. Therefore, we propose a method to extract the margin line with the convolutional neural network based on sparse octree (S-Octree) structure. First, the dental preparations are rotated to augment the dataset. Second, the preparation models are treated as the sparse point cloud with labels through the spatial partition method of the S-Octree. Then, based on the feature line, the dental preparation point cloud is automatically divided into two regions by the convolutional neural network (CNN). Third, in order to obtain the margin line, we adopt some methods such as the dense condition random field (dense CRF), point cloud reconstruction, and back projection to the original dental preparation model. Finally, based on the measurement indicators of accuracy, sensitivity, and specificity, the average accuracy of the label predicted by the network model can reach 97.43%. The experimental results show that our method can automatically accomplish the extraction of the tooth preparation margin line.

The influence of restorative material and glass fiber posts on fracture strength of endodontically treated premolars after extensive structure loss.

OBJECTIVE: The aim of this in vitro study was to investigate the fracture strength and cuspal deflection of endodontically treated premolars restored using different composite resins along with or without fiber post application. MATERIALS AND METHOD: Eighty intact premolars were randomly divided into eight groups (n = 10); CO group: intact teeth (control), OPR group: mesio-occlusal-distal-palatal (MODP) preparation (OPR) + endodontic treatment (ET), TC group: MODP preparation + ET + Tetric N-Ceram, TB group: MODP preparation + ET + Tetric EvoCeram Bulk Fill, SO group: MODP preparation + ET + SonicFill 2, TC-P group: MODP preparation + ET + Hahnenkratt glass fiber post + Tetric N-Ceram, TB-P group: MODP preparation + ET + Hahnenkratt glass fiber + Tetric EvoCeram Bulk Fill, and SO-P Group: MODP preparation + ET + Hahnenkratt glass fiber post + SonicFill 2. After thermocycling, specimens were subjected to a compressive load until fracture. Data were analyzed using analysis of variance and Tukey tests (P < 0.05). RESULTS: The mean fracture strength of groups which received post treatment showed similar fracture strength values [TC-P (931.6 ± 97.9), TB-P (882.0 ± 59.7), SO-P (862.0 ± 143.0) (P > 0.05)] and was significantly higher than OPR (530.6 ± 41.7), TC (841.2 ± 93.1), TB (774.5 ± 101.8), and SO (735.0 ± 178.01) groups (P < 0.05). No significant difference was detected among groups considering cuspal deflection (P > 0.05). The fiber post insertion resulted in more unfavorable fractures. CONCLUSION: Endodontically treated teeth restored with fiber post and bulk-fill or conventional composite resins demonstrated fracture strength values similar to intact teeth.

Impression of Subgingival Dental Preparation Can Be Taken with Ultrasound.

Because of its ability to capture hard structures behind soft tissue, ultrasound-based micro-scanning may be a promising alternative for taking digital impressions of teeth, especially in the case of subgingival margin preparations. The aim of this study was to assess the accuracy of ultrasound impressions taken of subgingivally prepared teeth compared with digital optical impressions. Ten extracted human teeth (7 pre-molars, 3 molars) were prepared for crowns with chamfer finish line and then digitized using two different intra-oral scanners (Cara Trios, 3 Shape, Heraeus Kulzer, Hanau, Germany; and Lava COS; 3M ESPE, Seefeld, Germany) and one extra-oral scanner (Cares CS2, Straumann, Basel, Switzerland). Afterward, the preparation margin was covered with porcine gingiva (thickness ranged between 0.3 and 0.9 mm), and every sample was scanned with a high-frequency ultrasound scanner under experimental subgingival conditions. Optical scanning processes were performed without gingiva. The data sets were superimposed on each other for pairwise comparisons, and deviations between different scans were determined using a 3-D evaluation software (CloudCompare). Kruskal-Wallis and post hoc tests (Dunn-Bonferroni) were applied to detect significant differences at p ≤ 0.05. The ultrasound scanner was able to detect subgingival preparation margins. Mean deviations for all comparisons ranged from 12.34 to 46.38 µm. There were no statistically significant differences between superimpositions of intra-oral and extra-oral scans (Trios-Lava, Lava-CS2, Trios-CS2), whereas in comparisons between intra-/extra-oral scans and ultrasound scans, mean deviations were statistically significantly higher. There were no significant differences with respect to type of tooth (pre-molar and molar). However, gingiva thickness was significantly correlated with the quality of the ultrasound scan; thin layers had better image quality than thicker layers. Ultrasound was able to scan tooth preparation margins covered with gingiva, although with less accuracy than achieved by conventional optical scanners (non-covered margins). Gingiva thickness may play an important role in ultrasound scan accuracy.

Marginal Fit of Metal-Ceramic Copings: Effect of Luting Cements and Tooth Preparation Design.

PURPOSE: To evaluate the effect of the triad finish line design, axial wall convergence angle, and luting cement on the marginal fit of metal copings used in metal-ceramic crowns. MATERIALS AND METHODS: Schematic dies and their respective copings were cast in NiCr alloy. The dies exhibited the following finish line/convergence angle combinations: sloping shoulder/6°, sloping shoulder/20°, shoulder/6°, shoulder/20°. Marginal fit was evaluated under a stereomicroscope, before and after cementation. Copings were air-abraded with 50 µm Al2 O3 particles and cemented with Cimento de Zinco, RelyX U100, or Panavia F cements (n = 10/group). Data were square-root transformed and analyzed by 3-way factorial random effect model and Tukey's post hoc test (α = 0.05). RESULTS: Statistical analysis showed significance for the interactions finish line and convergence angle (p < 0.05), convergence angle and time (p < 0.001), and luting cement and time (p < 0.001). Sloping shoulder/20° provided the highest marginal discrepancy when compared to the other finish line/convergence angle combinations, which were statistically similar among each other. For both convergence angles and for all luting cements, the marginal discrepancy was significantly higher after cementation. Before and after cementation, 6° provided better marginal fit than 20°. After cementation, Panavia F provided higher marginal discrepancy than Cimento de Zinco. CONCLUSION: Lower convergence angle combined with shoulder and a low-consistency luting cement is preferable to cement metal copings.

Replacement of maxillary incisor crowns over discolored substrates in a single visit with a CAD-CAM system and lithium silicate ceramic.

Discolored substrates constitute a challenge to the esthetics of the definitive restoration. Because of technique sensitivity, the generally prolonged treatment time is a drawback to both the patient and the dentist. The technique described presents the replacement of ceramic maxillary incisors crowns over discolored substrates in a single visit by using a milling machine. Translucent blocks of a lithium silicate ceramic reinforced with zirconium dioxide particles were used. Intraoral scans of the trial restorations and of the tooth preparations were performed. The crown parameters were defined in the software. Ceramic blocks were milled in the presintered phase and characterized. The crowns were cemented at the end of the appointment with excellent esthetics.

Influência de diferentes agentes isolantes aplicados sobre o selamento dentário imediato na resistência à tração de restaurações provisórias / nfluence of different insulating agents applied on immediate dental sealing on the tensile strength of temporary restorations

Constatação do problema: A possível ineficácia dos agentes isolantes utilizados na proteção da camada de dentina hibridizada na técnica do selamento dentinário imediato contra aderência das restaurações à base de polimetilmetacrilato pode impactar negativamente na resistência de união das futuras restaurações definitivas e comprometer o sucesso da técnica. Objetivos: O objetivo deste estudo foi avaliar a capacidade de diferentes agentes isolantes em impedir a adesão entre as restaurações provisórias à base de polimetilmetacrilato e as superfícies de dentina hibridizadas pela técnica do selamento dentinário imediato. Materiais e Métodos: Quarenta dentes humanos extraídos receberam preparos para laminados oclusais ultrafinos, selamento dentinário imediato (OptiBond FL; Kerr) e proteção com diferentes agentes isolantes antes da provisionalização. Os dentes foram divididos em 3 grupos experimentais, de acordo com o agente isolante: vaselina pastosa, gel de glicerina hidrossolúvel (KY; Johnson & Johnson) e agente isolante hidrossolúvel (Pro-V Coat; Bisco). Restaurações provisórias diretas de resina acrílica foram fabricadas sobre os dentes preparados. Após 2 semanas, foi realizado o teste de tração das restaurações provisórias para análise de resistência à tração. A análise do padrão de falha das superfícies dentinárias foram realizadas por microscopia confocal a laser 3D e microscopia eletrônica de varredura. Os dados foram analisados com o teste de variância de um fator e teste post hoc de Tukey (α=0,05). Resultados: O uso do Pro-V Coat apresentou valores de resistência à tração (30,39 ± 10,01 N) significantemente menores em comparação aos outros agentes isolantes (p<0,05). O padrão de falha mostrou-se do tipo misto em todos os grupos avaliados. Conclusão: Pro-V Coat apresentou a maior capacidade de isolamento da superfície dentinária hibridizada pela técnica do selamento dentinário im

Accurate extraction of outermost biological characteristic curves in tooth preparations with fuzzy regions.

BACKGROUND: The accuracy of extraction of biological characteristic curves in tooth preparations directly determines whether the tooth restorations and preparations are closely matched to allow appropriate adhesion. Ultimately, these will affect the success of the dental restoration surgery. In the process to obtain the tooth preparation, the dentist is required to grind the tooth manually and fuzzy regions may thus exist. Multiple feature curves with locally increased curvatures exist in these fuzzy regions, but only the outermost is preferred. The characteristic curve consists of points, some with and some without extreme curvature values. This study aims to extract an accurate biological characteristic curve. METHOD: This challenging problem is mapped to the search of the minimum cost path for a graph, and is solved using the well-known A* algorithm. To identify the mapped graph, the outward direction coefficient is first introduced followed by the extremality coefficient node. Both of these coefficients ensure that the biological characteristic curve can be accurately extracted. RESULTS: The conducted experiment demonstrated that the proposed algorithm can rapidly, accurately, and automatically obtain the outermost feature curve which passes through the fuzzy region of the tooth preparation. Additionally, the part of the biological characteristic curve related to the non-fuzzy region can also be accurately extracted. CONCLUSIONS: The proposed algorithm significantly improves the accuracy of the extraction curve and the quality of the restoration design.

Preparo dental com pontas ultrassônicas e cimentação com resina termomodificada / Clinical sequence of ceramic laminates ­ dental preparation with ultrasonic tips and thermically modified resin cementation

Paciente apresentava dentes 12 e 22 com formatos conoides e restaurações insatisfatórias, os demais dentes eram hígidos e apresentavam formato natural. Assim, o tratamento adotado foi a remoção das restaurações insatisfatórias associada a preparos minimamente invasivo e laminados confeccionados com cerâmica feldspática nos dentes 12 e 22. As restaurações em resina composta apresentavam proporções e anatomias adequadas, adotando-as como guia para os preparos dentais. Inicialmente, foram utilizadas brocas diamantadas em alta rotação para o preparo inicial e, em seguida, pontas ultrassônicas para remoção da resina composta e finalização dos preparos. Realizou-se a moldagem com silicone de adição e os laminados cerâmicos foram confeccionados pela técnica da aplicação sobre troquel refratário. Clinicamente, realizou-se a prova das cerâmicas e a cimentação após aprovação da paciente. A fase da cimentação seguiu o seguinte protocolo: isolamento absoluto, profilaxia dos preparos dentais, condicionamento ácido e aplicação de sistema adesivo. As superfícies internas dos laminados foram condicionadas e então aplicados silano e sistema adesivo. A resina composta foi aquecida e inserida na superfície dos laminados, que foram posicionados sobre os preparos dentais com o auxílio do instrumento ultrassônico até a sua posição final. Após a remoção dos excessos, realizou-se a fotopolimerização do conjunto, polimento da interface adesiva, ajustes oclusais e polimentos finais. O caso foi realizado com acompanhamento clínico e radiográfico de 12 meses, e favorável prognóstico. (AU)

This patient had conoid teeth at the 12 and 22 positions with unsatisfactory restorations. The remaining teeth were healthy. Thus, the treatment adopted was the removal of the restorations associated with minimally invasive preparations and feldspathic ceramics on tooth numbers 12 and 22. The restorations in composite resin had adequate proportions and anatomy, adopting them as a guide for dental preparations. Initially, diamond burs were used in high-rotation speed for the initial preparation, and then ultrasonic tips for removal of the composite resin and finalization. An impression was carried out with addition silicone and the ceramic laminates made using the refractory die technique. Clinically, the ceramics were tried-in and cemented after patient approval. The cementation phase was made as the following: rubber dam isolation, prophylaxis, acid etching and adhesive application. The inner laminate surfaces were conditioned, silanated, and received the adhesive system. The composite resin was heated and inserted into the laminates, which were placed on the dental preparations with the the ultrasonic instrument to their final position. After excess removal, photactivation was made and the adhesive interface was polished, followed by occlusal adjustments and fi nal polishing. After clinical and radiographic follow-up of 12 months, a favorable prognosis was observed. (AU)

Effect of silver diamine fluoride on adhesion and microleakage of a pit and fissure sealant to tooth enamel: in vitro trial.

AIM: To identify the effect of silver diamine fluoride in adhesion and microleakage of a pit and fissure sealant to tooth enamel. METHODS: An in vitro study including 120 human molars without caries, and caries grade 1 was performed. Molars were randomly divided into four groups. Occlusal surfaces of groups 2 and 4 were sealed. In groups 1 and 3 silver diamine fluoride (SDF) was placed in the occlusal surface and then molars were sealed according to manufacturer's instructions. Afterwards, all groups were submitted to the adhesion test. Groups 1 and 2 were placed in a forming cylinder and their roots were submerged in polymethyl methacrylate after that they were stored in deionised water (37 °C ± 1). Subsequently, they were tested by applying a tractional load (Instron machine, speed cross of 1 mm/min). Sealant adhesion was evaluated through: Resistance to the detachment (MPa), residues of sealant area (mm2) and adhesive remaining index (ARI) (0-3 interval). Microleakage test: Groups 3 and 4 were placed in a plastic container and subjected to 2000 cycles at different temperatures one at 6 °C ± 1 and the other at 60 °C ± 1. Later the occlusal surface was immersed for 24 h in 1% toluidine blue. Microleakage was observed by optical microscopy (10×) and was interpreted in micrometres. RESULTS: Of the samples without SDF 18.1 and 23.0% of the sealant remaining and of the samples with SDF present 100% of sealant remaining on enamel. Samples with SDF obtained an average in the test of detachment of 6.89 ± 3.09 MPa, whereas in the group without SDF the average obtained was 6.42 ± 3.35 MPa. Differences were not statistically significant (p = 0.579). Most of the samples not treated with SDF (81.6%) showed microleakage than those treated with SDF in which 47% presented microleakage. CONCLUSIONS: There is an improvement in the retention properties of a fissure sealant applied after treatment with silver diamine fluoride. The application of fissure sealant to improve the aesthetics of teeth treated with SDF is recommended.

Dentinal tubule occluding capability of nano-hydroxyapatite; The in-vitro evaluation.

In this in-vitro study, the effectiveness of experimental pure nano-hydroxyapatite (nHAP) and 1%, 2%, and 3% F¯ doped nano-HAp on dentine tubule occlusion was investigated. And also, the cytotoxicity of materials used in the experiment was evaluated. Nano-HAp types were synthesized by the precipitation method. Forty dentin specimens were randomly divided into five groups of; 1-no treatment (control), 2-specimens treated with 10% pure nano-HAp and 3, 4, 5 specimens treated with 1%, 2%, and 3% F- doped 10% nano-HAp, respectively. To evaluate the effectiveness of the materials used; pH, FTIR, and scanning electron microscopy evaluations were performed before and after degredation in simulated body fluid. To determine cytotoxicity of the materials, MTT assay was performed. Statistical evaluations were performed with F and t tests. All of the nano-HAp materials used in this study built up an effective covering layer on the dentin surfaces even with plugs in tubules. It was found that this layer had also a resistance to degradation. None of the evaluated nano-HAp types were have toxicity. Fluoride doping showed a positive effect on physical and chemical stability until a critical value of 1% F- . The all evaluated nano-HAp types may be effectively used in dentin hypersensitivity treatment. The formed nano-HAp layers were seem to resistant to hydrolic deletion. The pure and 1% F- doped nano-HAp showed the highest biocompatibility thus it was assessed that pure and 1% F- doped materials may be used as an active ingredient in dentin hypersensitivity agents.

Minimally Invasive Ceramic Restorations: A Step-by-Step Clinical Approach.

Minimally invasive treatments are a dominant trend in dentistry. Due to the evolution of adhesive materials and ceramics, minimalistic ceramic restorations have been proposed as alternative treatment options to avoid unnecessary tooth reduction. The aim of this article is to show a clinical protocol for the correct diagnosis, treatment planning, and execution of minimally invasive ceramic veneers. Requiring only slight tooth preparation, this conservative technique is well-suited for restoration of teeth that need color and shape modification. The present clinical case demonstrates immediate success in restoring patient esthetics, function, and, in turn, self-esteem. After 2.5 years all veneers were still in exceptional condition and periodontal tissue was healthy. Minimally invasive ceramic restoration is shown to be an excellent option for conservative restorative treatment.

Effect of Magnification on the Precision of Tooth Preparation in Dentistry.

OBJECTIVES: To evaluate the impact of magnification aids on the precision of tooth preparation under simulated clinical conditions. METHODS AND MATERIALS: Two plastic blocks marked with a geometric shape were fixed in a dental phantom head: a circle as the distal surface of tooth 16 (UNS 3) and a y-shaped figure as the occlusal surface of tooth 36 (UNS 19). Sixteen dentists (mean age: 39 years; range: 26-67 years) prepared the geometric shapes from the inside to the boundary line with a cylindrical bur and water-cooling. The boundary line had to be touched but not erased. Chair-side assistance was provided to simulate the clinical situation. Tooth 16 was prepared under indirect vision via a dental mirror. Tooth 36 was prepared under direct vision A) without magnification aids, B) with Galilean loupes, 2.5× and light-emitting diode light, and C) with a microscope, 6.4× and coaxial light. The preparation procedure was performed three times in different sequences of the magnification devices and with a break of at least 1 week between each procedure. The correctly prepared contour and the incorrectly prepared areas were evaluated in relation to the whole circumference of the geometric shapes. RESULTS: For both values the precision was significantly higher when a microscope was used, followed by preparation using loupes; precision was lowest without magnification aids ( p<0.0001). This was true for both indirect and direct vision ( p<0.05). CONCLUSIONS: Magnification devices improved the precision of tooth preparation under simulated clinical conditions.

FDPS finish line design and tooth preparation technique.

The purpose of this research is to perform and verify the “modified 50° preparation” suggested by the authors. This procedure was performed with a scrupulous standardization of the tooth’s preparation and then of the laboratory techniques to produce a metal-ceramic crown, and the same for the crown cementation technique of on the preparation of the original sample. After the esthetic evaluations, the obtained sample was included in EPON resin and sectioned in the lingual-vestibular sense. The sections were then observed with an optical microscope in different magnifications for the final evaluations. The geometric design proposed presents the advantages of two great preparation techniques: 50° preparation and circumferential shoulder. The 50° bevel designed in first phase of preparation and the second phase of the circumferential 27° shoulder, together allowed to satisfy the following requirements: aesthetic, marginal accuracy, periodontal compliance, conservation and stability. However, this type of prosthetic preparation is not the only one, but it is one of the marginal designs in prosthetic dentistry.

[Research status of tooth preparation quantitative guide technique].

Tooth preparation is a basic operation in prosthodontics treatment and the quality of preparation influences the effect of treatment directly. How to achieve a precise and quantitative tooth preparation is always one of the main aims of dental prosthodontics. The known types of tooth preparation guide technique can be divided into visual guidance, passive constraint guidance and active constraint guidance (automated tooth preparation), respectively represented by silicon rubber index, tooth preparation guide plate and computerized numerical control cutting system (CNC cutting system). Studies in advanced manufacturing technologies such as robot systems and numerical control ultra-short pulse laser (USPL) have also been reported recently. This review comprehensively introduced tooth preparation quantitative guide techniques and partially summarized the application effects and limitations to provide reference for relative researches and clinical application.