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.     

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.     

Lingual orthodontics (Part 2): Archwire fabrication

One essential component of a successful lingual treatment concept is the precise calculation and manufacture of individual lingual arch wires. As in several parts of daily life, the use of modern CAD/CAM technology leads in lingual orthodontic treatment to a rationalisation of working processes with maximized precision. The lingual module developed by the author is a new scanner-independent procedure for calculation and manufacture of individual lingual arch wires with the Orthomate/Orthotherm system (OrthoTel, Berlin/Dallas, Tx). Especially the precise individualization of superelastic, shape-memory materials reduces the archwire sequence and simplifies lingual treatment considerably. Individual second and third order overcorrections (incisal torque, reverse curve of Spee) can be programmed into the first archwire, with further three-dimensional corrections being added for each single tooth during finishing. Embedded in a systematic treatment concept, the use of modern CAD/CAM technology for individual lingual archwire production with the Orthomate/Orthotherm system is an important aid to successful integration of lingual orthodontic treatment into routine practice.     

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.     

Occlusion splint therapy in patients with craniomandibular disorders (CMD)

The etiology of craniomandibular disorders (CMD) is multi-factorial and the treatment should be selected with recognition of the different factors. The aim of the study was to investigate the influence of occlusion splint therapy (Michigan splint), physical exercises and transcutaneous nerve stimulation (TENS) on CMD symptomatology. At the Clinic of Maxillofacial Surgery in Belgrade, in the period from May, 2001-December, 2003, 168 patients were examined by the CMD working group. This group, comprised of different specialties (maxillofacial surgeon, prosthodontist, orthodontist, neurologist, psychiatrist and physiatrician), enabled multidisciplinary treatment of CMD patients according to the guidelines given by American Academy for Craniomandibular Dysfunctions. In all, a total of 30 patients with prevalent muscular tensions among other CMD symptoms were included in this study. The examination form according to Fricton and Shiffman for Craniomandibular Index (CMI) was used in order to evaluate the function of Craniomandibular system before and after therapy.A statistically significant difference (t = 8,735; P < 0,001) between the average values for CMI of patients before (0,2297 +/- 0,0827) and after therapy (0,1002 +/- 0,0479) was observed.Performed treatment resulted in complete response (pain relief and absence of CMD symptoms and signs) in over than 80% of patients and could be considered as a method of choice in reversible occlusal therapy.     

Investigation of Pd-Ag alloy for porcelain fusing. (Part 2) Thermal expansion (author's transl)]

Thermal expansion coefficient and thermal expansion hysteresis (residual expansion after thermal cycles) were measured using nine Pd-Ag alloys (In and/or Sn added) prepared in Part 1. The following results were obtained. (1) The thermal expansion coefficients were ranged 13 approximately 15 x 10(-6)/ degrees C in the temperature range of 400 to 200 degrees C. (2) The effects of the addition of indium and tin to the thermal expansion coefficient depended on the concentration of palladium and silver. (3) The thermal expansion hysteresis was ranged from 0.21 to -0.02% third thermal cycle. It was very small in comparison with that of precious alloys. (4) The thermal expansion hysteresis decreased with increase of addition of indium and tin. (5) The thermal expansion coefficient had no correlation with the bonding strength.     

Studies on Ni-Ta alloys. (Part 2) Age-hardening and metal-to-ceramic bonding (author's transl)]

Age-hardening and metal-to-ceramic bonding were studied on Ni-Ta alloy for dental application. In the first experiment, it was shown the precipitation-hardening was recognized in Ni-33 wt% Ta, Ni-34 wt% Ta except for Ni-30 wt% Ta. The precipitates were of a Widmamst?tten type structure and appeared to be a intermetallic compound, namely Ni3Ta, from the results of X-ray diffraction (debyesherrer) despite of the close proximity of the diffraction patterns of Ni and Ni2Ta. In the second experiment, it was shown that the bonding strength was 176 kg/cm2 for Ni-30 wt% Ta-ceramic system, compared with that of 222 kg/cm2 of Wiron S-ceramic system. The oxide layer was as wide as 3 approximately 5 micron at the Ni-30 wt% Ta-ceramic interface, in which high concentrations of Ni, Ta, and low concentrations of Al, Si were observed. The coefficient of thermal expansion, which was larger than that of porcelain, was 17.4 x 10(-6)/degrees C for Ni-30 wt% Ta.     

Studies of calcium phosphate glass-ceramics--development of dental materials. (Part 2) Acid resistance--(author's transl)]

It is well known that minerals of bone or tooth are essentially of CaO-P2O5 system. Glass and the crystallized product, i.e., so-called "glass-ceramics" of which chemical composition is 55 CaO . 45 P2O5 (in mole %) and have been developed for biomaterials were subjected to chemical durability test. Human enamel was also tested for the comparison of the data with them. All the specimens were ground to powders in size from 74 to 140 micrometer. A hundred milligram of the powders were immersed into 100 ml. of N/10 acetate buffer (1 mol acetic acid) solution (pH 4.1) at a constant temperature of 37 degrees C. Amount of Ca2+ and P5+ dissolved were determined by an atomic absorption method and Fiske-Subbarow method, respectively. The order of dissolution is human enamel greater than glass greater than glass-ceramics: the amount of Ca2+ (SCa) and P5+ (Sp) with soaking time (t) was expressed by the following equations, :formula: (see book). The glass and the glass-ceramics show good resistance against a weak acid.