Labial Margin Research Articles

Stresses within porcelain veneers and the composite lute using different preparation designs

The purpose of this study was to investigate compressive and tensile stresses in porcelain and composite at the labial marginal region of porcelain veneer restorations using chamfer, shoulder, or knife-edge labial margin designs with labial window or incisal overlap incisal preparation designs. Porcelain veneer models were constructed and loaded with (1) a 200-N, 45 degrees palatal load to simulate functional loading, and (2) a horizontal labial loading of 200 N to mimic trauma. Maximum tensile and compressive stresses were recorded within the labial marginal region of both porcelain and composite lute. Under the 45 degrees palatal load, stresses within the palatal marginal porcelain were chiefly compressive, and stresses for the knife-edge designs as much as 42% less than for shoulder designs. Incisal overlap preparations were generally associated with less compressive stress within both porcelain and composite than the window preparation. When a labial load was applied, tensile stresses were as much as 25 times greater for the chamfer and shoulder designs compared with the knife-edge design. Labial loading also resulted in an increase in tensile stresses within the composite lute, and stresses were again lowest within the knife-edge margin design. Under the limitations of this study, using the incisal overlap preparation, porcelain veneers with knife-edge labial margins could better sustain occlusal loading without fracture. J Prosthodont 2001;10:16-21.

Ultrastructure, Number, Distribution and Innervation of Electroreceptors and Mechanoreceptors in the Bill Skin of the Platypus, <i>Ornithorhynchus anatinus</i> (Part 2 of 2)

The platypus is presently the only mammal demonstrated to use electroreception to obtain food. The electroreceptive system of the platypus is far more complex than that of its close relative the echidna. This paper presents an anatomical study of the basis of electroreception in the platypus. The innervation of the bill by the trigeminal nerve is described, as are three sensory structures, associated with food gathering, within the bill skin. There are 40,000 mucous gland electroreceptors found in the bill skin of the platypus. The papillary portion of each of these sensory mucous glands is modified to accommodate electrosensory nerve terminals. In contrast to fish electroreceptors, the electrosensory terminals of the platypus are not associated with a sensory cell. These mucous gland electroreceptors are arranged in a series of parasagittal stripes on the bill. This array suggests a basis for the ability of the platypus to quickly and accurately locate the origin of an electrical stimulus. A push-rod mechanoreceptor, similar in morphology to Eimer's organ of the mole, and bill-tip organs in birds, was also found in the bill skin. The slightly differing morphology of these mechanoreceptors when compared to their avian and talpid counterparts suggests that this is another example of convergent evolution, with the common need to provide a solution to increasing tactile sensitivity on bare rhinarial skin. These push-rods are found to be most dense around the labial margins of the bill, with a marked decrease in density towards the middle and caudal portions of the bill. The distribution of the push-rods is similar to the distribution of the third sensory structure found on the bill, the sensory serous gland. Although less numerous than the mechanoreceptors (46,500 mechanoreceptors compared with 13,500 sensory serous glands), these sensory serous glands have a similar distribution and similar changes in density. These concurrent distributions argue for some functional correlation of these two sensory structures. The papillary region of the serous gland is modified in a manner similar to that of the mucous gland electroreceptor to accommodate sensory input. The sensory terminals of the serous glands are very similar to those of the mucous gland electroreceptors, and so it is presumed that these sensory serous glands are a type of electroreceptor that might be involved in detection of electrical signals at close quarters where the mechanorecemors are also engaged.

Ultrastructure, number, distribution and innervation of electroreceptors and mechanoreceptors in the bill skin of the platypus, Ornithorhynchus anatinus.

The platypus is presently the only mammal demonstrated to use electroreception to obtain food. The electroreceptive system of the platypus is far more complex than that of its close relative the echidna. This paper presents an anatomical study of the basis of electroreception in the platypus. The innervation of the bill by the trigeminal nerve is described, as are three sensory structures, associated with food gathering, within the bill skin. There are 40,000 mucous gland electroreceptors found in the bill skin of the platypus. The papillary portion of each of these sensory mucous glands is modified to accommodate electrosensory nerve terminals. In contrast to fish electroreceptors, the electrosensory terminals of the platypus are not associated with a sensory cell. These mucous gland electroreceptors are arranged in a series of parasagittal stripes on the bill. This array suggests a basis for the ability of the platypus to quickly and accurately locate the origin of an electrical stimulus. A push-rod mechanoreceptor, similar in morphology to Eimer's organ of the mole, and bill-tip organs in birds, was also found in the bill skin. The slightly differing morphology of these mechanoreceptors when compared to their avian and talpid counterparts suggests that this is another example of convergent evolution, with the common need to provide a solution to increasing tactile sensitivity on bare rhinarial skin. These push-rods are found to be most dense around the labial margins of the bill, with a marked decrease in density towards the middle and caudal portions of the bill. The distribution of the push-rods is similar to the distribution of the third sensory structure found on the bill, the sensory serous gland. Although less numerous than the mechanoreceptors (46,500 mechanoreceptors compared with 13,500 sensory serous glands), these sensory serous glands have a similar distribution and similar changes in density. These concurrent distributions argue for some functional correlation of these two sensory structures. The papillary region of the serous gland is modified in a manner similar to that of the mucous gland electroreceptor to accommodate sensory input. The sensory terminals of the serous glands are very similar to those of the mucous gland electroreceptors, and so it is presumed that these sensory serous glands are a type of electroreceptor that might be involved in detection of electrical signals at close quarters where the mechanoreceptors are also engaged.

Kinematic analysis of jaw protrusion in orectolobiform sharks: A new mechanism for jaw protrusion in elasmobranchs.

Jaw protrusion is an important component of prey capture in fishes, although the mechanics of protrusion have thus far been studied largely in teleosts. Elasmobranchs are also able to protrude their jaws (Tricas and McCosker [1984] Proc. Cal. Acad. Sci. 43: 221-238; Tricas [1985] Mem. S. Calif. Acad. Sci. 8:81-91.; Frazzetta and Prange [1987] Copeia 4:979-993). Several related features of the feeding apparatus contribute to jaw protrusion in sharks. Labial cartilages form an extendible series attached dorsally to the anterolateral face of the palatoquadrate and ventrally to the anteroventral surface of Meckel's cartilage. The labial cartilage chain swings anterolaterally as the lower jaw is depressed, thrusting the labial margins forward to form a circular oral opening and displacing the jaw apparatus towards the food; this pattern is analogous to halecomorph and primitive actinopterygian fishes in which the maxilla swings forward (Lauder [1979] J. Zool. Lond. 187:543-578). The palatoquadrate and Meckel's cartilage also project anteriorly and represent the major contribution to protrusion. These movements occur simultaneously with enlargement of the oral cavity to generate suction. The wobbegong sharks (Orectolobidae) are specialized for jaw protrusion. The spotted wobbegong protrudes its jaw by 33% of its chondrocranial length using two different mechanical systems. In the first mechanism of jaw protrusion, the intermandibularis and interhyoideus muscles medially compress the lower jaw and hyomandibulae. Compression of the lower jaw results in a more acute symphyseal angle so that the anteroposterior alignment of the lower jaw increases due to the rotation of each lower jaw towards a saggital orientation. Distal compression of the hyomandibulae at their attachments to the jaws swings the jaws forward. The second mechanism involves rotation of the ceratohyal around a posterior process of the lower jaw, pushing the hyomandibulae anteroventrally, thereby pushing the jaw articulation ventrally and anteriorly to protrude the jaws. © 1994 Wiley-Liss, Inc.

Effect of ultrasonic cleaning and air polishing on porcelain labial margin restorations

This study examined porcelain labial margins after ultrasonic scaling and air polishing. Thirty metal coupons were covered with 1.5 mm thick shoulder porcelain and cemented to acrylic resin blocks. A reference mark divided each specimen into a “treated” and an “untreated” side. The specimens were treated as three groups with: (1) an air polisher; (2) an ultrasonic scaler, and (3) the ultrasonic scaler and the air polisher. Surface roughness was determined and selected specimens were observed under scanning electron microscope. Surface roughness ranged from 0.37 μm to 1.06 μm for the untreated sides and from 0.86 μm to 2.80 μm for the treated sides. Increases in roughness were 69% for the ultrasonic scaler/air-polisher; 127% for the air polisher, and 162% for the ultrasonic scaler. ANOVA indicated a significant difference between the treatments. Specimens treated with the air polisher or the ultrasonic scaler and air polisher combination were less distorted than those treated with the ultrasonic scaler alone. The data suggested that careless use of an ultrasonic scaler or air polisher could substantially alter porcelain facial margins.

Effects of labial margin design on stress distribution of a porcelain-fused-to-metal crown.

This study compared the stress distribution of three porcelain-fused-to-metal labial margins on a central incisor under simulated occlusal force. The margin designs were rounded-shoulder, rounded-shoulder with a bevel, and a chamfer. Evaluation of mean equivalent Mises tensile stress did not show any difference at the cement-dentin and metal-cement interfaces of the three margins. The mean equivalent Mises tensile stress at the porcelain-metal interface was found to be significantly higher for rounded-shoulder when compared with the chamfer. There was no significant difference in the axial stresses along the three interfaces among the three margin designs. Statistically significant differences in radial stresses at some interfaces of the three margin designs were found. The change of cement thickness of the chamfer margin is significantly greater than that of either the rounded-shoulder or the bevelled-shoulder margin.

All-porcelain labial margin for ceramometal crowns.

The elimination of the labiogingival metal collar of a porcelain-fused-to-metal (PFM) restoration is an attempt to achieve an improved esthetic result. In their expectation of a more cosmetic tooth restoration, patients may influence dentists to use the all-porcelain labial margin to avoid metal showing in the final restoration. Success of this type of restoration depends upon proper tooth preparation. The all-porcelain margin requires a 1.2-mm wide labiogingival shoulder of approximately 70 or 90 degrees wrapping into the interproximal area. Much of the effectiveness of the restoration depends upon the design of the metal substructure. The following change is made in the design of this substructure for this modified PFM crown: the labiogingival portion of the metal is finished back to the gingival-pulpal line angle with the metal against the axial wall being from 0.3 mm to 0.5 mm thick. This allows for 0.2 to 0.3 mm of opaque and 0.7 to 1.0 mm of shoulder porcelain. The direct lift-off technique is a useful method of achieving clinically acceptable all-porcelain margins. Such restorations may give excellent results.

Orbicularis Oris Muscle

The release of abnormal insertions of orbicularis oris muscle from the columella and ala base, and from their inferior attachments along the labial margin, provides muscle flaps for a double-breasted suture in cleft lip repair. Using the muscle flaps for double-breasted sutures realigns the orbicularis oris muscle fibers to achieve an anatomical and functional repair that is characterized by a symmetrical lip length, nostrils, philtral column, and philtral dimple. Double-breasted sutures also increase muscle thickness surrounding the lip and consequently provides better symmetry for the nostril floor.

The dimensionsal accuracy of improved dental stone, silverplated, and epoxy resin die materials

1 mproved dental stone is the predominant material in dentistry for making dies used in the lost-wax process. Although improved dental stones have served the profession well, the main disadvantages of their use as dies are (1) susceptibility to dimensional change due to abrasion, (2) limited reproduction of fine detail,’ and (3) lack of strength. The lack of strength can result in breakage of dies, especially those duplicating long, narrow preparations. In the fabrication of all-porcelain labial margins or some of the new generation cast porcelain restorations, dies that exhibit greater strength and abrasion resistance than gypsum dies are desirable. Alternate die materials that may yield dimensionally accurate dies, are more resistant to abrasion, and are stronger than the improved dental stone dies presently in use are available. The literature concerning dimensional accuracy of various die materials is somewhat equivocal. Gypsum die materials generally exhibit an average setting expansion of O.l%.* Such minimal expansion is thought to be beneficial in terms of aiding compensation for metal shrinkage, wax pattern dimensional change, and other unavoida.ble inaccuracies in the casting process. Electroplated dies have been found to be less accurate dimensionally than improved stone dies when formed with polysulfide rubber or condensation-reaction silicone impression m.aterials.3 One study demonstrated that silver-plated dies tend to be undersized by as much as 0.2%; whereas another found that they tend to be oversized.5 It has been shown that vinyl polysiloxane impression ma.terials are the most accurate for making silver-plated dies.+ Castings made on silver-plated dies have been shown to have smaller marginal openings than those made on improved stone dies.6 Epoxy resin dies have been found to be generally undersized, pri.marily because of polymerization shrinkage.’ The manufacturer of the new generation epoxy resin die systern claims to have controlled this shrinkage and that dimensional accuracy can be precisely con-

A metal-ceramic restoration with a porcelain labial margin: A modified direct lift method

A metal-ceramic restoration with a porcelain labial margin: A modified direct lift method

The esthetic metal-ceramic margin: A comparison of techniques

Metal-ceramic crowns with all-porcelain labial margins may have esthetic and biologic advantages. Several techniques for making these restorations have been described in the prosthodontic literature. The authors used all the techniques and compared the results in terms of quality and degree of difficulty in construction. Clinically acceptable results can be achieved with all described techniques. The advantages and disadvantages of each method are summarized in Table I.

Preparation design and margin distortion in porcelain-fused-to-metal restorations

The relationship between preparation finish line configurations and marginal stability of porcelain-fused-to-metal restorations during the firing cycle was studied. Four labial finish lines presently in use were examined. The shoulder finish lines, with and without a bevel, were found to produce significantly less distortion in labial margins of porcelain-fused-to-metal restorations than do chamfer finish lines with and without a bevel.

On the muscles of expression in the geladaTheropithecus gelada (R�ppell) (primates, Cercopithecidae)

Musculature innervated by the N. facialis inTheropithecus gelada (Ruppell) is patterned on broad lines in agreement with related genera of catarrhine monkeys, but presents some specializations and divergences in detail. Noteworthy is the extension to the labial margins superficially of the combined levator labii superioris and zygomaticus in the upper and the pars mandibularis of trachelo-platysma in the lower lip. A specialization of the medial fibres of levator labii superioris forms a sling-like structure within the upper lip and serves to implement the “lip-flip” gesture characteristic of the genus. Its antagonist is the orbicularis oris. Special features of all other facialis muscles are considered.

Acute Lobar Pneumonia

Upon admission Reginald's face was flushed-more markedly on the right cheek; his left pupil was dilated more than the right. There was marked play of the alae nasi and herpetic eruption (fever blister) of right labial margin. Lips were semicyanotic; tongue dry, coated, and furrowed. His temperature was 1034 F. (rectally); pulse 120, full and bounding; respirations 36, shallow. Phys cal examination disclosed: slight li itation of movement of right chest; heart tones forceful, of good quality, no murmurs; abdomen slightly distended; bladder full. A catheterized specimen of urine (was unable to void) was sent to the laboratory on which the report was: Acid reaction; specific gravity 1.028 (denotes concentration); cloudy; slight amount of albumen. Due to the toxic reaction on the urinary system there was retention of urine and the patient had to be catheterized. External heat was applied over the bladder region and hot lemonade was given, but he was unable to void until the