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Biomedical subjects

K K Lew

Publications and source records attributed to K K Lew.

At least 37 records · Page 2Linked to original sources
PubMed1992

The reliability of computerized cephalometric soft tissue prediction following bimaxillary anterior subapical osteotomy.

The accuracy of predicting the results of orthodontic-surgical treatment following bimaxillary anterior subapical setback osteotomy was analyzed retrospectively. Comparisons of pretreatment prediction tracings of the lateral cephalograms with the 6-month postsurgical cephalograms of 38 patients showed that there was no statistically significant difference between the actual and predicted dentoalveolar setback in both arches. The computer-generated soft tissue predictions were generally accurate, with the exception of the horizontal position of the lower lip, which was underestimated, and, to a lesser extent, the vertical position of the upper lip, which was also underestimated. Computerized cephalometric prediction following bimaxillary anterior subapical osteotomy is sufficiently accurate to be of value to be used routinely in treatment planning for the horizontal upper lip prediction, but some modifications are advisable to obtain a more accurate horizontal lower lip prediction.

Adult↗
PubMed1992

Assessment of orthodontic treatment needs by teenagers in an Asian community in Singapore.

The purpose of this study was to determine (1) the preference of dental occlusion types among teenagers, and (2) their assessment of the necessity for orthodontic treatment. A total of 1189 teenagers (mean age 15.3 +/- 3.2 years) were asked to rank a series of colour photographs of seven occlusion types. Their ranking, in descending order of attractiveness, were as follows: Class I occlusion, anterior open bite, Class III occlusion, Class II occlusion, anterior spacing, anterior crowding and deep bite occlusion. The perceived need for treatment was found to be inversely correlated with the rank order of attractiveness. There appeared to be no statistical difference (P less than 0.05) in the perception for treatment among different racial and income groups. However, with the exception of anterior open bite and deep overbite occlusions, a statistically significant (P less than 0.05) greater number of females than males perceived a need for treatment. Assessment of occlusal disharmonies among teenagers could provide clinicians and health care personnel with an indication of the relative attractiveness among occlusion types and hence the establishment of treatment priorities.

Adolescent↗
PubMed1991

A comparison of profile changes between ramus and anterior mandibular subapical osteotomies in class III Chinese patients.

The purpose of this study was to compare cephalometrically the differences in soft-tissue profile changes produced by intraoral ramus and anterior subapical osteotomies for the treatment of Chinese patients with class III malocclusion. Thirty-seven Chinese adults whose class III malocclusion was treated either with an intraoral ramus (group A) or an anterior subapical (group B) osteotomy were selected for the study. Serial lateral cephalograms taken presurgically (T1) and at least 6 months postrentention (T2), showed marked improvement in the soft-tissue profile in both groups. Although the percentage response of soft- to hard-tissue movement was similar at lebrale inferius, the response at soft-tissue point B was found to be statistically less in group B than in group A (P less than .05). Although the correlation between the upper lip response to mandibular ramus setback in group A was weak (r = 0.11), there appeared to be a relatively strong correlation between posterior movement of the upper lip and the magnitude of the lower segmental setback (r = 0.65). The differences in soft- to hard-tissue response with the two osteotomy procedures appear to vary with those reported in whites. This study emphasizes the need for different prediction ratios of soft- to hard-tissue movement in different racial types.

Adult↗
PubMed1991

A comparison of shear bond strengths between new and recycled ceramic brackets.

The recycling of 'used' ceramic brackets in the orthodontic surgery has been previously described. The present study investigated the shear bond strength of both recycled and new ceramic brackets. The mean shear bond strengths of the new and recycled ceramic brackets were 259.7 +/- 88.2 N and 187.2 +/- 60.8 N, respectively. Although significantly lower (P less than 0.01), the bond strength of recycled ceramic brackets appeared to be clinically adequate. There appeared to be little difference in the variation in bond strength between the new and recycled ceramic bracket group. Our results showed that the site of bond failure depended on the magnitude of bond strength. Scanning electron micrograph examination of the failure sites showed enamel fracture in one sample where the bond strength was extremely high.

Acid Etching, Dental↗
PubMed1991

A ten-year follow-up case report following surgical correction of anterior open bite.

A case is reported whereby an anterior open-bite was treated with the Köle osteotomy in an adult Chinese girl. This study documents cephalometrically the post-treatment changes occurring in the dento-alveolar complex over a ten year follow-up period and describes the possible mechanisms contributing to the remarkable stability of the open-bite correction.

Adolescent↗
PubMed1991

Orthodontic considerations in the treatment of bimaxillary protrusion with anterior subapical osteotomy.

Severe bimaxillary dentoalveolar protrusion, a dentofacial deformity prevalent among Asians, can be easily addressed with the use of anterior subapical osteotomies in conjunction with extraction of a tooth in each quadrant. Presurgical orthodontic preparation for anterior subapical osteotomy includes intra-arch (leveling, alignment, and derotations) and interarch (sagittal, vertical, and transverse) objectives. The procedure requires careful attention to the use of segmental orthodontic mechanics and surgical arch wires, in conjunction with surgical splints and rigid osteosynthesis. The controlled use of training box and vertical elastics postsurgically and the proper choice of retainers have greatly facilitated the achievement of a good and stable end result.

Adult↗
PubMed1991

Lower incisor angulation differences in Class II division 1 malocclusions with and without full 'lip trap'.

A cephalometric study was designed to investigate whether a difference in lower incisor angulation exists in Class II division 1 malocclusion subjects with and without the presence of a lower lip trap. Chinese subjects (N = 40) with Class II division 1 malocclusions who demonstrated a complete lower lip trap were compared to an equal number of subjects with a partial lip trap. Intergroup comparisons of several cephalometric parameters indicated the presence of statistically significant differences in both the degree of lowe incisor proclination/retroclination (p < 0.01) and the magnitude of the overjet (p < 0.05). In the complete lip trap group, the lower incisor was more retroclined and the overjets were also statistically larger than the partial lip trap group.

Adult↗
PubMed1991

Anterior crown dimensions and relationship in an ethnic Chinese population with normal occlusions.

Odontometric measurements of anterior tooth crown sizes in a Chinese sample of 85 Class I occlusions were similar to those published in the white population except for larger upper lateral incisors and smaller upper central incisors in Chinese. Sex differences in tooth sizes were seen only in the maxillary and mandibular canines while differences between antimeres were not significant. The Bolton ratios of our Chinese sample revealed a Bolton ratio of 77.89 +/- 1.62 for the combined mesio-distal widths of the six mandibular anterior teeth as compared to the combined mesio-distal widths of the six maxillary anterior teeth. Surprisingly, the Bolton ratio in our sample compared favourably with those originally published by Bolton although the interfacial angles, overbite and overjet relationships were statistically different.

Adolescent↗
PubMed1990

Temporary pontics in aesthetic orthodontics--a new design.

A new and simple technique for aesthetic tooth replacement during orthodontic treatment, with a pontic using orthodontic wire mesh, is described and appears in the author's clinical practise to be superior to the other techniques reported previously. These pontics may be used in maxillary first bicuspid extraction cases, and with adaptation where anterior teeth have to be replaced because of agenesis, extractions, or traumatic loss. This technique thus also provides the clinician with an aesthetic and dependable space maintainer for anterior teeth whilst orthodontic treatment is being completed.

Adult↗
PubMed1990

Evaluation of soft tissue profile following intraoral ramus osteotomy in Chinese adults with mandibular prognathism.

Twenty-five Chinese adults with mandibular prognathism were treated with either the intraoral vertical subcondylar osteotomy or the bilateral sagittal split ramus osteotomy. The patients were kept in maxillomandibular fixation for 6 to 8 weeks while osteosynthesis was achieved with the use of intraosseous wiring. Serial lateral cephalograms were taken presurgery and between 12 and 26 months postsurgery, and specific soft and hard tissue points were digitized on a computer. The mean mandibular setback postsurgically was 8.4 +/- 3.2 mm, with a 5.2-degree reduction in point A-nasion-point B angle. Posterior movement of pogonion, point B and the mandibular incisal edge was accompanied by posterior movement of 95% at soft tissue pogonion (r = .96), 89% at soft tissue point B (r = .83), and 67% at labrale inferius (r = .81), respectively. The correlation between changes in the labrale superius and mandibular setback appeared to be dependent on both the amount of mandibular setback and the degree of mandibular rotation during the setback surgery. The presently reported ratios of the soft tissue response to hard tissue movement vary from those reported in white patients by other researchers, which confirms the need for different ratios for different racial types.

Adult↗
PubMed1990

The use of psychometric tests in the evaluation of patients presenting for orthognathic surgery--a preliminary report.

Psychological evaluation in some orthognathic patients may be necessary as the psychosocial stress of the deformity may lead to psychiatric morbidity such as depression or paranoid disorders. It is also possible for patients with underlying psychosis to present first to the dental surgeon for jaw correction. The use of several psychological tests appropriate for patients presenting with dentofacial deformities is discussed. Nine patients with skeletal malocclusions who were referred for psychiatric assessment are reported here. Three case vignettes are included to give an impression of the type of clinical situations where such an assessment may be helpful.

Adolescent↗
PubMed1990

Soft tissue profile changes following orthodontic treatment of Chinese adults with Class III malocclusion.

Thirty-eight adult Chinese patients (mean age 24.3 +/- 3.2 years) exhibiting true Class III dental and skeletal malocclusions were treated orthodontically with the edgewise appliance and extractions of mandibular first premolars together with simultaneous anterior expansion of the maxillary arch. A retrospective cephalometric study was undertaken to determine the soft tissue profile changes at least 6 months postretention. Significant cephalometric changes included decrease in the mandibular incisor protrusiveness by 6.4 mm (P less than .001) and accompanying lower lip protrusiveness by 4.4 mm (P less than .01), together with a slight forward movement of the maxillary incisors by 1.7 mm (P less than .05) and, consequently, a slight increase in upper lip protrusiveness by 1.2 mm (P less than .05) and decrease in nasolabial angle (P less than .05). The overall improvement in lip profile provided by this mandibular arch contraction/maxillary arch expansion orthodontic approach appears to be a viable alternative in mild-to-moderate Class III patients who decline orthognathic surgery.

Adult↗
PubMed1989

Extremes in second molar eruption in two oriental patients.

Two cases are presented where the maxillary second molars were just erupting. The first was a Chinese boy of 8 years 2 months and the other, a Chinese boy of 17 years 4 months. These extremes in eruption time are unusual and do not appear to have been reported in the literature.

Adolescent↗
PubMed1989

The orthodontic tooth positioner--an appraisal.

The tooth positioner is a one-piece, resilient appliance which may be used for finishing orthodontic cases. The appliance fills the free-way space, and covers the clinical crowns of all the teeth and about 3-mm of the buccal and lingual gingival mucosa. The positioner is constructed over a predetermined 'set-up' and fabricated from either rubber or plastic. This article reviews the literature and describes the author's method of manufacture and usage.

Equipment Design↗
PubMed1989

Orthodontically induced microvascular injuries in the tension zone of the periodontal ligament.

A review of the literature pertaining to the histological and ultrastructural changes related to orthodontic tooth movement reveals that much attention has been devoted to the fibrillar and cellular components of the periodontal ligament (PDL). Although the vascular response to experimental tooth movement has been investigated, specific morphological and morphometric data on changes in the tension zone of the PDL microvascular system are lacking. The present investigation was conducted to study the ultrastructural vascular response in the tension zone of the PDL following a short-term extrusive force. Six 12-week-old male Porton rats were anesthetized and cannulated via the aorta after applying a 1-N extrusive force for 30 min to the right maxillary first molar. The contralateral molar served as a control in all animals. The apical portion of both the control and experimental PDL was prepared for TEM examination. In the experimental PDL, degenerative changes in the endothelial cell wall and incipient nuclear shrinkage were observed in about 30% of the postcapillary venules and 18% of the capillaries, whereas the arterial components were generally spared. Compared to the control PDL, these degenerative changes were significantly marked in the experimental PDL (p less than 0.01). The results of this study suggest that the postcapillary venules are the most vulnerable segment in the PDL microvascular system.

Animals↗