Richard K. K. Ow

Relationship Between Jaw Movement and Food Breakdown in Human Mastication

Different quantities and sizes of peanuts were offered to six human subjects for mastication at two or three experimental sessions during which jaw movements and chewing cycle duration were measured. The amplitude of vertical movement and cycle duration depended on the position of a chew in a sequence of chews (masticatory sequence). Cycle duration also depended on the position of a given masticatory sequence during the first experimental session, the earlier sequences tending to be longer. Lateral jaw movements fluctuated about a reasonably constant value during a sequence and were unaffected by different food inputs. The amplitude of vertical movements increased markedly with an increase in food weight but was unaffected by change in the initial food particle size. These results were analyzed in the light of previous reports on the comminution of peanuts. It is hypothesized that observed jaw movements were unrelated to food particle size but that the amplitude of each vertical movement depended on the volume of food that was broken by the teeth during the next closing stroke. This food volume was provided and selected by bulk movements of the tongue during the preceding jaw opening.

Ocular prosthetics: Use of a tissue conditioner material to modify a stock ocular prosthesis

The custom-made ocular prosthesis contributes to enhanced tissue health of the anophthalmic socket. For this purpose, an acrylic resin ocular prosthesis may be modified, by using an appropriate dental impression material and being adapted closely to the anophthalmic socket. The modeling impression material is subsequently replaced by acrylic resin. This article describes the application of a viscoelastic tissue conditioner material, as an impression medium for prosthetic modification of an ocular prosthesis. The tissue conditioner material exhibits favorable tissue compatibility, adhesion to acrylic resin, and detailed surface registration. These advantages facilitate the clinical procedure and evaluation of modifications made to the ocular prosthesis.

Assessment of Colour Differences in Silicone Hand and Digit Prostheses: Perceptible and Acceptable Thresholds for Fair and Dark Skin Shades

This study addresses the dilemma of initial clinical and social acceptance of a newly fabricated silicone prosthesis in relation to its colour match to the natural skin. This was achieved by derivation of specific colour difference thresholds defining perceptible and acceptable levels of colour sensitivity. Two separate sets of 10 fair and dark shade digit prosthesis samples were each fabricated with a stepped increase in colour difference (ΔE) against the baseline hand prosthesis. Ninety individuals with normal colour vision scores were selected as colour assessors. The colour difference of each prosthesis in the two series was evaluated visually against the baseline by the assessors, using defined scores. The thresholds for perceptible and acceptable colour difference determined in this study were ΔE = 0.8 and ΔE = 1.8 for the fair series and ΔE = 1.3 and ΔE = 2.6 for the dark series, respectively. The acceptable threshold values differed from the perceptible threshold values by ΔE = 1.0 for the fair-shade samples and ΔE = 1.3 for the dark-shade samples. This study demonstrated that subjective visual assessment is positively correlated with ΔE values computed from colorimetric measurements for both fair and dark-shade silicone samples (p<0.001). This results shows that human subjects with normal colour vision are capable of accurately assessing colour differences. These observations emphasize the importance of subjective feedback on colour by the patient, provided the latter has perfect colour-tested vision. The study also showed that human subjects were less sensitive to perceived colour differences in darker-shade than fairer-shade samples (p<0.001). This finding seems relevant in a clinical setting involving a multi-ethnic patient population.

Biting Forces in Patients with Craniomandibular Disorders

Treatment for 10 female patients having craniomandibular disorders of neuromuscular origin showed a reduction in dysfunctional symptoms and improvement in their condition. In response to treatment, a standardized recording method was used to measure alterations to bite force values. In about 60 percent of categories representing various positions in the dental arch from which maximal and submaximal biting forces were measured, there was significant variation between replicate registrations. This persisted after treatment, indicating some loss of sensory acuity for fine bite-force adjustments in these patients. Discriminatory ability for large force adjustments was not, however, observed to be affected. Bite force values showed considerable fluctuation both before and after treatment. The lack of substantial increase in force values after a reduction in muscular dysfunction with treatment appears to suggest that an inhibitory mechanism controlling jaw-closing activity and pressure persists as a protective reflex for these patients.

The effect of food texture on the replication of jaw movements in mastication

Abstract The effect of different food textures on the replication of jaw movements has been generally ignored. In this study, the jaw movements of 28 young male subjects were measured while they chewed two samples of three foods—pork luncheon meat, dried apple and roasted salted peanuts. Several parameters, that characterized each chewing cycle when viewed from a frontal projection, were measured, and the average value for each variable was calculated. Values for dried apple and pork luncheon meat did not differ significantly between trials. However, for the second trial with peanuts, the chewing cycle duration was shorter (the duration of the closing phase being less and the closing velocity greater). These changes may have been due to exercizing caution during the chewing of a hard food while gaining familiarity with its texture.

A method of studying the effect of adhesives on denture retention

lhe physical forces that hold a denture in situ include those acting on the fitting surfaces of the denture base and the supporting mucosal surface. Different authors have reviewed the influence of adhesive and cohesive forces, surface tension, atmospheric pressure, the viscosity and volume of saliva, and gravity on denture retention.‘” Clinical procedures during impression making are designed to obtain a maximum area of coverage, an intimate tissue/denture contact, and an effective border seal. There are occasional situations in which it is not possible to obtain the desirable optimal retention. In these instances patients frequently resort to the use of denture adhesives. The objective of this article is an evaluation of the effect on retention of two such adhesives under controlled conditions in vivo by means of a hydraulic sensor.

Masticatory function in patients with congenital and acquired maxillofacial defects

Ninety-eight patients who received prosthodontic treatment for maxillofacial defects were examined clinically and by means of questionnaires and registration of chewing efficiency and occlusal force. Although 30% of the patients stated that they could chew soft food, and one third could not chew the test food (almonds), only 14% said they had a poor chewing ability. The mean occlusal force was small (80 N) but the individual variation was great (median 49 N, maximum 327 N). Despite major defects and poor functional test results, most patients were remarkably well-adapted to their situation and to maxillofacial prosthodontic rehabilitation. Severe signs and symptoms of temporomandibular disorders were rare.

The relationships of upper facial proportions and the plane of occlusion to anatomic reference planes

A study was made of 28 dentulous Chinese (Singaporean) adults by using lateral skull radiographs. The dimensions of the maxillae and various craniofacial reference lines related to prosthodontic use were analyzed. The craniofacial reference angles that reflect the vertical height and horizontal depth of the maxillae in Chinese adults differed significantly from the norms obtained in a white North American adult population. By comparison, Chinese adults have a vertically high and horizontally receded upper face that could cause planes such as the Frankfort horizontal plane or an arbitrary axis-orbitale plane to assume a steeper anterior inclination, thus modifying the mechanical inclination of the maxillary cast and occlusal plane on the articulator.

Orientation of the plane of occlusion

A study was made of 28 dentulous Chinese Singaporean adults, using lateral skull radiographs. Various craniofacial reference lines and their relations to the maxillary occlusal line were analyzed. The orientation of the natural occlusal line in Chinese adults differed significantly from Swedish white adults. The Frankfort horizontal line in particular was considered disadvantageous as a clinical reference plane largely because of the acknowledged variation of its inclination between Chinese Singaporean and Swedish white adults. The shallow anatomic cant of the maxillary occlusal line in the Chinese patient could be misrepresented by a steep mechanical inclination on the articulator.