Robert L. Engelmeier

Complications of head and neck radiation therapy and their management

Patients who receive radiation therapy to the head and neck suffer potential complications and undesirable side-effects of this therapy. The extent of undesirable responses is dependent on the source of irradiation, the fields of irradiation, and the dose. The radiotherapist determines these factors by the extent, location, and radiosensitivity of the tumor. The potential undesirable side-effects are xerostomia, mucositis, fibrosis, trismus, dermatitis, photosensitivity, radiation caries, soft tissue necrosis, and osteoradionecrosis. Each of these clinical entities and their proposed management have been discussed.

Moldable tissue equivalent bolus for high‐energy photon and electron therapy

In radiation therapy, there is often a need to treat irregular surfaces with electron and photon beams. These surfaces require smoothing to achieve uniform doses at depth and proper buildup of dose at the surface. The surface smoothing and dose buildup is achieved by applying bolus. To deliver a known dose, produce a known central axis depth dose, and beam flatness for successful treatment, it is necessary that water or tissue equivalent bolus material is used. This material must also be able to fill extremely irregular voids. Several moldable materials, currently or formerly used in dental clinics, were evaluated for adequacy as tissue equivalent bolus. Availability was also considered during evaluation. Polyflex, a hydrocolloid, was found to be near water equivalent for electron and photon beams. It was also inexpensive, readily available, and held up well over time.

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 Fishers 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.

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 manufacturers 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. Fishers 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.

Autoclavable custom-made metal impression trays to improve infection control.

P e d i a t r i c impressions, particularly impressions on infants with cleft palates, are always a challenge. Part of the problem is that most commercially available, disposable impression trays are bulky. Tray thickness becomes even more of a problem if impressions must be made with the patient under general anesthesia and when an oral-tracheal tube is in place. A solution to this problem is to make various sizes of infant impression trays from a nonpreeious removable partial denture alloy (Ticonium, Tieonium Co., Albany, N.Y.). The trays can be made thin yet sufficiently strong to permit use in situations where bulky trays cannot be used, and they can be sterilized in an autoclave.

Fabricating denture teeth with custom anatomic and nonanatomic metal occlusal surfaces

Abstract A simple, step-by-step technique has been given for prefabricating anatomic and nonanatomic denture teeth with metal occlusal surfaces.

The History of Articulators: The Wonderful World of “Grinders,” Part 2: 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.

The Development of Nonanatomic Denture Occlusion: Part III: Development of Nonanatomic Denture Occlusion

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.

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

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.