The Development of Lingualized Occlusion.

This article is a historical review of the development of the lingualized occlusion concept over the past century. It focuses on the pioneers of lingualized occlusion and their designs rather than on techniques for achieving a lingualized complete denture occlusion.

The Development of Nonanatomic Denture Occlusion - Part I.

Part I of this two-part article concentrates on the early 20th century origin of the nonanatomic concept of complete denture occlusion. It focuses on Dr. Victor Sears, who in 1922 made a courageous departure from convention when he introduced the design for his "Chewing Members." Development of these teeth marked the birth of the School of Nonanatomic Denture Occlusion. Dr. Sears' 35-year journey of research and development is traced here through his mid-1950s association with Dr. Simon Myerson. Their Myerson-Sears design set the standard for flat-planed, nonanatomic denture teeth for the next half century.

The Development of Nonanatomic Denture Occlusion: Part III.

Part III of this four-part series about nonanatomic denture tooth development traces the evolution of this movement from the mid-1930s through the World War II era up to the early 1950s. By this time, the general preference for posterior denture occlusion had shifted from anatomic to nonanatomic teeth, and all the major denture tooth manufacturing companies listed at least one nonanatomic design in their inventories.

The Development of Nonanatomic Denture Occlusion: Part IV.

This fourth and final part of a four-part series concerned with the development of nonanatomic denture occlusion follows nonanatomic tooth design from the time of Victor Sears' first nonanatomic tooth patent through the end of the 20th century. Part IV concentrates on nonanatomic teeth developed during the last five decades of the 20th century. Many of the designs featured in this series exhibited genius, while others are pure nonsense. Sears claimed that a new nonanatomic tooth design appeared every 9 months on average during the first 30 years of nonanatomic tooth production. Many current nonanatomic tooth patents are further refinements of those earlier designs.

The Development of Nonanatomic Denture Occlusion: Part II.

This second part of a four-part series concerned with the development of nonanatomic denture occlusion follows nonanatomic tooth design from the time of Victor Sears' first nonanatomic tooth patent through the mid-1930s. Many of the designs featured in this series exhibit genius, while others are pure nonsense. Sears claimed that a new nonanatomic tooth design appeared every 9 months on average during the first 30 years of nonanatomic tooth production. Many current nonanatomic tooth patents are further refinements of those earlier designs. Part II reviews pioneering designs that appeared during the first dozen or so years of this paradigm shift in denture occlusion philosophy.

A comparison of crown preparation grading via PrepCheck versus grading by dental school instructors.

Recent reports in the literature demonstrate the influence that digital dentistry is having on the preclinical training of dental students. However, none of these articles have discussed the use of PrepCheck (Sirona Dental Systems) in the evaluation of preparation taper in a preclinical environment. The present study compared the subjective grading of student tooth preparations by experienced, well-calibrated faculty with objective digital grading of the same preparations by means of the PrepCheck software. Sixty-nine sophomore dental student preparations were first subjectively graded by their dental instructors, and then the preparations were evaluated by the PrepCheck software. Neither the students nor the instructors were aware that the second PrepCheck evaluation was going to occur. The statistically significant results of this study conclude that the subjective instructor grades were inflated compared with the digital PrepCheck grades. The inflated grading by the instructors may give students a sense that their progress is better than it actually is. The objective, exact nature of the PrepCheck evaluation gives students immediate feedback regarding their preclinical preparations. Although taper was the only parameter examined in this study, PrepCheck allows the operator to examine many other features of a student's preparation. Also made evident in this study is the fact that the present standard for preparation taper is unattainable in a preclinical environment and needs to be readjusted to a wider, attainable range.

The Contributions of Dr. Alfred Gysi.

This article is a historical overview of Dr. Alfred Gysi's contributions to the profession in the areas of denture tooth and articulator design. His understanding of occlusion and mandibular movement resulted in denture tooth designs and occlusal concepts still in widespread use.

Marginal Fit Comparison of CAD/CAM Crowns Milled from Two Different Materials.

PURPOSE: To evaluate the marginal fit of CAD/CAM copings milled from hybrid ceramic (Vita Enamic) blocks and lithium disilicate (IPS e.max CAD) blocks, and to evaluate the effect of crystallization firing on the marginal fit of lithium disilicate copings. MATERIALS AND METHODS: A standardized metal die with a 1-mm-wide shoulder finish line was imaged using the CEREC AC Bluecam. The coping was designed using CEREC 3 software. The design was used to fabricate 15 lithium disilicate and 15 hybrid ceramic copings. Design and milling were accomplished by one operator. The copings were seated on the metal die using a pressure clamp with a uniform pressure of 5.5 lbs. A Macroview Microscope (14×) was used for direct viewing of the marginal gap. Four areas were imaged on each coping (buccal, distal, lingual, mesial). Image analysis software was used to measure the marginal gaps in µm at 15 randomly selected points on each of the four surfaces. A total of 60 measurements were made per specimen. For lithium disilicate copings the measurements for marginal gap were made before and after crystallization firing. Data were analyzed using paired t-test and Kruskal-Wallis test. RESULTS: The overall mean difference in marginal gap between the hybrid ceramic and crystallized lithium disilicate copings was statistically significant (p < 0.01). Greater mean marginal gaps were measured for crystallized lithium disilicate copings. The overall mean difference in marginal gap before and after firing (precrystallized and crystallized lithium disilicate copings) showed an average of 62 µm increase in marginal gap after firing. This difference was also significant (p < 0.01). CONCLUSIONS: A significant difference exists in the marginal gap discrepancy when comparing hybrid ceramic and lithium disilicate CAD/CAM crowns. Also crystallization firing can result in a significant increase in the marginal gap of lithium disilicate CAD/CAM crowns.

The History of Articulators: The Contributions of Rudolph L. Hanau and His Company-Part II.

This article is an historical overview of the Hanau Engineering Company from the time of Rudolph Hanau's death in 1930 to the present. It explores the development of many articulators intended both for removable and fixed prosthodontic restorations. The article is divided into the eras of the company's corporate history, and it reviews articulator designs and major improvements made during each of those periods.

Canine guidance via Biogeneric Copy: a clinical report.

The advent of computer-aided design/computer-aided manufacturing (CAD/CAM) technology in dentistry has enabled a wide range of applications. The Cerec Acquisition Center (Cerec AC, Sirona Dental Systems Inc., Charlotte, NC) allows for the construction of all-porcelain restorations, either in-office or through a remote dental laboratory. One feature of the Cerec AC is its ability to duplicate the dental morphology of an existing tooth onto a new CAD/CAM ceramic restoration designed for that tooth. This design mode capability of the Cerec AC is termed Biogeneric Copy. This function has been discussed in the literature where it has been utilized to fabricate a CAD/CAM ceramic crown to fit an existing removable partial denture (RPD).1-3 There are occasions in dentistry where the exact anatomy and position of an existing tooth, not associated with an RPD, should ideally be replicated in a definitive restoration. This case report describes such an occasion.

The History of Articulators: The Wonderful World of "Grinders," Part III.

This is the third article in a three-part series on the history of denture occlusal grinders. The first article reviewed the earliest attempts to "grind in" denture occlusion by hand manipulating simple articulators with special features to those more complex devices powered by hand cranks. The second article explored devices that were motor driven, either those with cast holders to grind the occlusion of processed dentures or those designed to utilize an articulator's condylar or incisal controls for that purpose. This article examines those articulators that have a rotary occlusal grinder as an essential feature. Additionally, this article reviews those grinding devices produced as attachments for popular contemporary articulators.

Retention of CAD/CAM all-ceramic crowns on prefabricated implant abutments: an in vitro comparative study of luting agents and abutment surface area.

PURPOSE: Previous studies considering retention of cast metal restorations to implant abutments incorporated some degree of frictional fit due to internal surface nodules and roughness of the restoration. In comparison, CAD/CAM restorations have minimal surface irregularities, possibly impacting retention. There is insufficient knowledge of retentive force of CAD/CAM restorations to titanium abutments, and therefore the topic warrants further investigation. This in vitro study investigated the retention of all-ceramic CAD/CAM restorations to three different prefabricated implant abutments using five different cements. MATERIALS AND METHODS: A total of 150 Astra Tech dental implant abutments were used, with each group of 50 being subdivided into five groups of 10. An optical impression of each size of abutment was made with the CEREC 3D intraoral camera. A full-coverage restoration was designed and milled with an enlarged, conical-shaped occlusal surface, which served to secure the restoration into a brass jig used with a universal testing machine. Five different cements were used with three different-sized abutments. Following cementation, the implant/abutment/restoration assemblies were stored for 24 hours at 37°C in 100% humidity. A pull-out test using a universal testing machine, set at a 0.5 mm/min crosshead speed, was used to evaluate retention of the individual restorations. The load required to remove each all-ceramic restoration was recorded. Retention values were analyzed using ANOVA and Fisher's PLSD multiple comparisons test at the 0.05 level of significance. RESULTS: Peak loads for two provisional cements and a resin-modified glass ionomer cement ranged from 56 N to 127 N. Peak loads for two resin cements ranged from 184 N to 318 N. Two-way ANOVA showed significant effects upon retentive forces for both the cement and abutment design. Post hoc Fisher's PLSD multiple comparisons test found significant differences in retention for 7 of the 10 pairings of cements at a 0.05 level of significance. In addition, Fisher's PLSD multiple comparisons test found significant differences between Astra Tech Direct Abutments 4 and Astra Tech Direct Abutments 5 as well as Astra Tech Direct Abutments 4 and Astra Tech Direct Abutments 6 at a 0.05 level of significance. No significant difference was found between Astra Tech Direct Abutments 5 and Astra Tech Direct Abutments 6. CONCLUSIONS: Of the five cements tested, the most retrievable CAD/CAM restorations were luted with Temp Bond NE and Improv Temporary Cement. Resin-modified glass ionomer retentive forces were closer to those of the "temporary cements" than those of the permanent adhesive-resin cements. The abutment surface area became less important when using adhesive-resin cements. Retention of CAD/CAM all-ceramic restorations to prefabricated abutments has not been reported in the literature. This in vitro study demonstrated clinically significant variation among the selected cements used to retain all-ceramic CAD/CAM restorations to implant abutments. In addition, abutment size influenced the retention of all-ceramic CAD/CAM restorations.

The history of articulators: the wonderful world of "grinders," Part 2.

This is the second article in a three-part series on the history of denture grinding devices. The first article reviewed the earliest attempts to mechanically grind the occlusion of artificial teeth from the manipulation of simple articulators to very elaborate and complex machines powered by hand cranks. This article explores motor-driven grinders, most driven by way of a belt-driven pulley powered by an external source. A few were self-contained; that is, the motor was mounted on the grinder base. There were basically two types of grinders: those with cast holders for mounting processed dentures and those with provisions for using articulators for that purpose.

Lingualized occlusion revisited.

Lingualized occlusion represents an established method for the development of functional and esthetic complete denture articulation. Since its introduction, the lingualized technique has undergone many changes. This article provides an overview of the history and development of lingualized occlusion, and addresses common misconceptions associated with the lingualized technique. In addition, a practical method for the development of lingualized denture occlusion is presented.

The history of articulators: the Contributions of Rudolph L. Hanau and his company--part I.

This article is a historical review of the last decade of Rudolph Hanau's life. It covers his introduction to dentistry and explores his prolific articulator designs and contributions to the prosthodontic literature.

The history of articulators: the "Articulator Wars" phenomenon with some circumstances leading up to it.

At the dawn of the 20th century, all was not well with the practice of "plate prostheses." Removable prosthodontics had been degrading for several decades and was now generally in low esteem, even though there had been many significant advances. W. E. Walker had introduced adjustable condylar guides, George Snow, the facebow, and Carl Christensen, a method for clinically measuring the condylar inclines. Nevertheless, the average practicing dentist was still using simple hinge articulators and was apathetic to the deplorable state of the artificial teeth available; however, this was all going to change dramatically when two dentists, Alfred Gysi and J. Leon Williams, working together between 1910 and 1914, presented to the profession the "Trubyte Artificial Tooth System" that embodied both a typal system for selecting anterior teeth and new posterior occlusal carvings that made possible, for the first time, the articulation of artificial teeth. This incited many of prosthetic dentistry's elite to introduce their own theories of mandibular movement and the articulators that they designed to reflect those theories. The intense debates that ensued, both in the meeting halls and in the literature, were numerous and lasted for decades. At the time, the "Articulator Wars" had both positive and negative consequences. Today, with many of the "Articulator Wars" issues remaining as part of the practice of dentistry, the "Articulator Wars" can be considered a phenomenon of enlightenment.

Force needed to separate acrylic resin from primed and unprimed frameworks of different designs.

PURPOSE: Poor mechanical and chemical bondings at the interface between a framework and denture base resin have been responsible for many removable partial denture failures. This study tested the force necessary to separate acrylic resin bases from test frameworks using different acrylic retention designs (smooth metal plate, metal plate with bead retention, lattice retention, and mesh retention). The force needed to separate acrylic resin from primed test frameworks was also measured. MATERIALS AND METHODS: Eighty chromium-cobalt test frameworks were fabricated using preformed wax patterns and cast according to manufacturer's instructions. Half the specimens were primed prior to acrylic processing. The same base acrylic was used for all specimens. Separation forces that fractured acrylic resin from test frameworks were generated by a universal testing machine at a crosshead speed of 25 mm/min. Loads at failure and types of failure were recorded. Data were analyzed using ANOVA. RESULTS: The mean separation force of acrylic resin from unprimed retention designs was highest for the metal plate with beads (3.1 kN), followed by mesh (2.8 kN) and lattice (2.1 kN), and lowest (0.1 kN) for the smooth metal plate. The mean separation force for primed acrylic retention designs was highest for the metal plate with beads (4.2 kN), followed by mesh (3.4 kN) and smooth metal plate (3.0 kN), and lowest for lattice retention (2.6 kN). Bond failure occurred both adhesively at the interface between metal and acrylic resin and cohesively within the acrylic resin. Cohesive bond failure increased when specimens were primed. The rate of cohesive bond failure remained the same for primed mesh retention specimens. CONCLUSIONS: Significantly increased force was necessary to separate the acrylic from each design of primed test specimens compared with unprimed specimens of the same design. The primed metal plate with beads exhibited significantly greater separation force than the other three designs. Primed mesh had significantly greater separation force values than primed lattice and smooth metal plate. Primed lattice was significantly less retentive than the other three primed designs. Except for the retentive mesh specimens, there was higher occurrence of cohesive failures in the acrylic resin when the frameworks were primed.

In vitro tensile bond strength of denture repair acrylic resins to primed base metal alloys using two different processing techniques.

PURPOSE: Approximately 38% of removable partial denture (RPD) failures involve fracture at the alloy/acrylic interface. Autopolymerizing resin is commonly used to repair RPDs. Poor chemical bonding of repair acrylic to base metal alloys can lead to microleakage and failure of the bond. Therefore, ideal repair techniques should provide a strong, adhesive bond. This investigation compared the tensile bond strength between cobalt-chromium (Super Cast, Pentron Laboratory Technologies, Llc., Wallingford, CT) and nickel-chromium (Rexalloy, Pentron Laboratory Technologies, Llc.) alloys and autopolymerized acrylic resin (Dentsply Repair Material, Dentsply Int, Inc, York, Pa) using three primers containing different functional monomers [UBar (UB), Sun Medical Co., Ltd., Shiga, Japan: Alloy Primer (AP) Kuraray Medical Inc., Okayama, Japan; and MR Bond (MRB) Tokyuyama Dental Corp., Tokyo, Japan] and two processing techniques (bench cure and pressure-pot cure). MATERIAL AND METHODS: One hundred and twenty eight base metal alloy ingots were polished, air abraded, and ultrasonically cleaned. The control group was not primed. Specimens in the test groups were primed with one of the three metal primers. Autopolymerized acrylic resin material was bonded to the metal surfaces. Half the specimens were bench cured, and the other half were cured in a pressure pot. All specimens were stored in distilled water for 24 hours at 37 degrees C. The specimens were debonded under tension at a crosshead speed of 0.05 cm/min. The forces at which the bond failed were noted. Data were analyzed using ANOVA. Fisher's PLSD post hoc test was used to determine significant differences (p < 0.05). Failure modes of each specimen were evaluated under a dissecting microscope. RESULTS: Significant differences in bond strength were observed between combinations of primers, curing methods, and alloys. Primed sandblasted specimens that were pressure-pot-cured had significantly higher bond strengths than primed sandblasted bench-cured specimens. The pressure-pot-curing method had a significant effect on bond strength of all specimens except Co-Cr alloy primed with UB. The highest bond strength was observed for both Co-Cr and Ni-Cr alloys that were sandblasted, primed with MRB, and pressure-pot cured. Co-Cr alloys primed with UB had the lowest bond strength whether bench cured or pressure-pot cured. Primed specimens generally experienced cohesive bond failures within the primer or acrylic resin. Nonprimed specimens generally experienced adhesive bond failures at the resin/metal interface. CONCLUSIONS: Within the limitations of this study, MRB provided the highest bond strength to both Ni-Cr and Co-Cr alloys. Generally, bond strength improved significantly when specimens were primed. Pressure-pot curing, in most cases, resulted in higher bond strength than bench curing. The results of this in vitro study suggest that MRB metal primer can be used to increase bond strength of autopolymerized repair acrylic resin to base metal alloys. Curing autopolymerized acrylic under pressure potentially increases bond strength.

Wear testing of composite, gold, porcelain, and enamel opposing a removable cobalt-chromium partial denture alloy.

PURPOSE: Eighty percent of all removable partial denture (RPD) frameworks are fabricated from cobalt-chromium (Co-Cr) alloys. The advantages of this material include low density and high modulus of elasticity, hardness, and strength. Hardness is of particular concern when related to excessive wear of natural teeth or restorative materials. The purpose of this study was to compare the differences in localized wear among enamel, composite, gold, and porcelain by a Co-Cr alloy RPD. MATERIALS AND METHODS: Thirty-two polished specimens were prepared and positioned in an acrylic-filled custom fixture for testing. Upon optical examination, the highly polished surfaces of the specimens were scratch-free. They were mounted into a water bath fixture and subjected to 250,000 cycles in a wear simulator equipped with a conical Co-Cr stylus specially fabricated to produce localized wear. A posttest was generated, and the profiles were fitted and evaluated using software. The total volume loss and depth of the wear facet on each specimen were analyzed using ANOVA and Fisher's PLSD test. RESULTS: Volume loss (mm3) was as follows: composite, 0.110; gold, 0.021; enamel, 0.008; porcelain, 0.006. The maximum depths (microm) were: composite, 92; gold, 22; enamel, 13; porcelain, 17. Resin composite had significantly higher values (p < 0.0001) of volumetric loss and maximum depth than the other materials. No significant differences were detected among volumetric loss and maximum depth values for gold, enamel, and porcelain. CONCLUSIONS: Significant differences for mean wear volume loss and maximum depth were found between composite and gold, enamel, and porcelain. Enamel proved to be wear resistant to the Co-Cr alloy. CLINICAL IMPLICATIONS: porcelain and gold appear to be good options for occlusal surfaces opposing a Co-Cr alloy; however, the test composite was not found to be a recommended option.

Restoration of the severely compromised maxilla using the multi-cup denture.

Among the millions of edentulous Americans, a persistent minority have not been able to tolerate wearing dentures. Complicating factors may have precluded surgical intervention with grafts or dental implants to improve the physical and anatomic limitations of these unfortunate patients. A heat-cured polymer liner containing multiple small suction cups has been used for decades to successfully restore many such debilitated individuals. Two middle-aged female patients with edentulous maxillae and near fully dentate mandibles had both reached a point where they could no longer retain a maxillary complete denture, or function with it. Both had experienced multiple failed surgical attempts to improve their situations. They were both successfully restored with maxillary complete dentures containing heat-cured silicone liners with multiple small suction cups. Two young female maxillectomy patients had significant difficulties wearing maxillary obturators due to defect size and absence of defect undercuts. One had an edentulous maxilla, while the other had no axial undercuts on her few remaining maxillary teeth. Without an obturator, both suffered considerable air and fluid leaks, unintelligible speech, and swallowing problems. They too were successfully restored with obturators containing a heat-cured, multi-cup, silicone liner. The multi-cup, silicone denture liner has offered an economic, noninvasive alternative for patients unable or unwilling to undergo surgical intervention to facilitate prosthesis retention.