Kenneth Lew - Academia.edu (original) (raw)
Papers by Kenneth Lew
American Journal of Orthodontics and Dentofacial Orthopedics, 1989
Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used... more Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used for transmission electron microscopic quantification of their effects on the periodontal ligament vessels. In this study, a continuous extrusive load of 1.0 N, applied to the rat maxillary first molar for 30 minutes, produced statistically significant changes in the microvascular bed of the tensioned apical periodontal ligament. The mean vascular volume, as a percentage of apical periodontal ligament volume, increased (p less than 0.01) in postcapillary-sized venules, venous capillaries, arterial capillaries, and terminal arterioles from 16.6% to 22.3%, 2.0% to 2.7%, 0.4% to 1.0%, and 1.0% to 2.5%, respectively. Mean endothelial surface area per cubic millimeter of apical periodontal ligament tissue increased (p less than 0.01) in postcapillary-sized venules from 16.8 to 25.7 x 10(6) microns 2/mm3, in venous capillaries from 3.0 to 4.8 x 10(6) microns 2/mm3, and in arterial capillaries from 0.7 to 1.5 x 10(6) microns 2/mm3. The number of fenestrae per square micron of endothelium in postcapillary-sized venules, venous capillaries, and arterial capillaries showed a mean increase from 0.02 to 0.07, 0.11 to 0.31, and 0.02 to 0.21 fenestrae/microns 2, respectively (p less than 0.01). Fenestrae per cubic millimeter of periodontal ligament tissue also demonstrated a statistically significant increase with extrusion (p less than 0.01) in postcapillary-sized venules from 0.37 to 1.55 x 10(6) fenestrae/mm3, in venous capillaries from 0.27 to 1.34 x 10(6) fenestrae/mm3, and in arterial capillaries from 0.02 to 0.22 x 10(6) fenestrae/mm3. Fenestrae in control vessels had a mean diameter of 54.2 +/- 0.56 nm (SE) compared with 61.1 +/- 0.7 nm in tensioned vessels (p less than 0.01). This investigation demonstrates multiple ultrastructural changes in the periodontal ligament microvascular bed after tooth extrusion.
British journal of orthodontics, 1989
The tooth positioner is a one-piece, resilient appliance which may be used for finishing orthodon... more 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.
European journal of orthodontics, 1989
Thirty-two adult oriental patients aged 18-26 years who sought treatment for their bimaxillary pr... more Thirty-two adult oriental patients aged 18-26 years who sought treatment for their bimaxillary protrusion were treated with the Begg appliance following extraction of four first premolars. A cephalometric study was undertaken to determine the soft tissue changes in lip profile following treatment. Results show that the upper incisors were retracted by 5.6 mm +/- 0.8 mm and the lower incisors by 4.4 +/- 0.8 mm on the average. The nasolabial angle became more obtuse increasing from 80.7 degrees to 90.7 degrees. The upper lip and lower lip lengthened by 1.9 mm and 1.2 mm, respectively. The lower lip to 'E' line reduced from 7.5 mm to 3.7 mm. All the previous changes were statistically significant (p less than 0.01). The upper lip to upper incisor retraction was 1:2.2 while the lower lip to lower incisor retraction was 1:1.4. The correlation coefficients (r) were 0.72 (p less than 0.01) and 0.80 (p less than 0.01), respectively. The changes in the cants of mandibular and occlusa...
Clinical Materials, 1993
In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond str... more In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond strengths with resin-bonded bridges) is compared to a conventional no-mix orthodontic Bis-GMA bracket adhesive. Results showed that there was no statistically significant difference in the shear bond strengths between the two resins when used as adhesives for bonding orthodontic brackets. Coupled with the fact that Panavia requires an anaerobic environment for comDlete polvmerization. its routine use as a bracket adhesive in direct bonding of o&hod&c brackets is not indicated.
The Journal of Nihon University School of Dentistry, 1989
A review of the literature pertaining to the histological and ultrastructural changes related to ... more 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 < 0.01). The results of this study suggest that the postcapillary venules are the most vulnerable segment in the PDL microvascular system.
Journal of Esthetic and Restorative Dentistry, 1992
Arch bars are well-known dental appliances for the management of fractures and orthognathic surge... more Arch bars are well-known dental appliances for the management of fractures and orthognathic surgery. Traditionally both the commercially available, prefabricated arch bars as well as the custom-made arch bars are made of metal so as to provide good rigidity. Each of these types of arch bars has its own advantages as well as drawbacks. This article looks at a type of custom-made arch bar that is easy to construct and use. At the same time, it provides good rigidity, fit, and esthetics.
Journal of Esthetic and Restorative Dentistry, 1992
With the advent of acid etching techniques and the elimination of unesthetic band materials, dire... more With the advent of acid etching techniques and the elimination of unesthetic band materials, direct bonding of orthodontic attachments kindled a desire for cosmetic appliances such as labial ceramic brackets and lingual orthodontics. Owing to the esthetic nature of our combination upper-lingual lower-ceramic orthodontic approach, adults who would have normally avoided orthodontic treatment are now seeking treatment. This study evaluated the cephalometric changes in the soft tissue lip profile following treatment of Class II Division 1 malocclusion with upper first bicuspid extractions with our esthetic orthodontic appliance approach. Serial lateral cephalograms (pretreatment and posttreatment) of 16 adult patients with a mean age of 22.1 +/- 3.2 years were studied. The mean upper incisor retraction, upper lip retraction, upper lip lengthening, and lower lip retraction were 5.75 +/- 1.91 mm, 2.8 +/- 1.4 mm, 1.5 +/- 0.6 mm, and 1.4 +/- 0.6 mm, respectively. All these changes were statistically significant (p < 0.01). The nasolabial angle increase of 10.8 +/- 3.0 degrees was also statistically significant (p < 0.01). The upper lip retraction to upper incisor retraction was 1:2.1, while the upper lip lengthening to upper incisor retraction was 1:3.8. The correlation coefficients (r) were 0.91 (p < 0.01) and 0.57 (p < 0.01), respectively. This study shows that significant esthetic changes in lip profile are possible with this cosmetic orthodontic appliance approach. The treatment results in this study appear comparable to those published with labial metal brackets. With very few exceptions, patients were able to adapt within 2 weeks, with almost no trauma to the tongue.
Journal of Esthetic and Restorative Dentistry, 1992
The purpose of this study was to determine the facial profile preferences in a sample of 1,189 As... more The purpose of this study was to determine the facial profile preferences in a sample of 1,189 Asian teenagers (aged 15.3 +/- 3.2 years). Five facial profile types were computer-generated by trained personnel (orthodontists and oral maxillofacial surgeons) to represent distinct facial types. Subjects were asked to rank the profiles in descending order of attractiveness. The ranking was as follows: orthognathic profile, bimaxillary retrusive profile, bimaxillary protrusive profile, mandibular retrognathic profile, and mandibular prognathic profile. The differences in rank scores between all the profile types were statistically significant (p < 0.05). Assessment of profile types among lay personnel could provide clinicians an indication into the relative attractiveness among profile types and health care workers in treatment prioritization among dysmorphic facial types.
British Dental Journal, 1989
Two cases are presented where the maxillary second molars were just erupting. The first was a Chi... more 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.
Australian Dental Journal, 1993
Population norms derived from one ethnic group may not necessarily be valid and accurate for othe... more Population norms derived from one ethnic group may not necessarily be valid and accurate for other ethnic groups. With the increasing number of ethnic Chinese immigrants in Australia, Europe, and America, it would be useful for dental practitioners to be informed about malocclusion prevalence among Chinese. This study was carried out on 1050 Chinese school children (aged 12-14 years) to assess both qualitatively and quantitatively certain occlusal features. The population was found to have a high incidence of Class Ill malocclusions compared with Caucasians. However, the incidence of Class II malocclusions was quite similar to those reported in Caucasians. Normal occlusions occurred in about 7 per cent of this population. Although this percentage was much lower than those reported in blacks, it was similar to those reported in caucasians. Crowding occurred in about 50 per cent of cases, which was slightly less than for those reported for Caucasians. Increased overbites were also less common in this Chinese population compared with Caucasians. Compared with Caucasians, crossbites were also less frequent in this Chinese population.
Community Dentistry and Oral Epidemiology, 1993
A retrospective survey of 358 local Chinese adult orthodontic patients was undertaken to determin... more A retrospective survey of 358 local Chinese adult orthodontic patients was undertaken to determine the motivating faetors behind orthodontic treatment and the discomfort caused by fixed orthodontic appliances. Frotn the completed questionnaires of 203 patients, the principal conclusions were that the itnprovetnent in dento-facial aesthetics following orthodontic treatment enhanced their self-confidence and self-esteem in a majority of patients; discomfort in oral soft tissues and teeth were transient and did not exceed 7 days; transient pain frotn teeth was experienced by 91% of patients and in 39% of these patients the discomfort to teeth was experienced with each new arehwire or elastic force application. These results may be useful in relating discomfort levels to prospective orthodontie patients. It was also evident in the study that several cross-cultural differences existed in the attitudes of our patients compai'ed to those I'eported in Caucasians.
Journal of oral and maxillofacial …, 1992
Using a double selection process comprised of professional and lay judges, the cephalometric trac... more Using a double selection process comprised of professional and lay judges, the cephalometric tracings on a final sample of 48 Chinese adults with esthetically pleasing profiles were analyzed. The soft-tissue cephalometric norms and standard deviations of two widely accepted soft-tissue analyses, the Legan and Burstone analysis and the Holdaway analysis, were determined. In comparison with white norms, the Chinese nose was less prominent (P < .Ol), the nasolabial angle was less obtuse (P < .Ol), both the upper and lower lips were more protrusive (P < .05), the upper lip curvature was greater (P < .Ol), and the soft-tissue chin thickness was less (P < .05). This variance between racial types emphasizes the need to recognize that soft-tissue lateral cephalometric norms are specific for the racial group and cannot always be applied across different racial types.
American Journal of Orthodontics and Dentofacial Orthopedics, 1989
Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used... more Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used for transmission electron microscopic quantification of their effects on the periodontal ligament vessels. In this study, a continuous extrusive load of 1.0 N, applied to the rat maxillary first molar for 30 minutes, produced statistically significant changes in the microvascular bed of the tensioned apical periodontal ligament. The mean vascular volume, as a percentage of apical periodontal ligament volume, increased (p less than 0.01) in postcapillary-sized venules, venous capillaries, arterial capillaries, and terminal arterioles from 16.6% to 22.3%, 2.0% to 2.7%, 0.4% to 1.0%, and 1.0% to 2.5%, respectively. Mean endothelial surface area per cubic millimeter of apical periodontal ligament tissue increased (p less than 0.01) in postcapillary-sized venules from 16.8 to 25.7 x 10(6) microns 2/mm3, in venous capillaries from 3.0 to 4.8 x 10(6) microns 2/mm3, and in arterial capillaries from 0.7 to 1.5 x 10(6) microns 2/mm3. The number of fenestrae per square micron of endothelium in postcapillary-sized venules, venous capillaries, and arterial capillaries showed a mean increase from 0.02 to 0.07, 0.11 to 0.31, and 0.02 to 0.21 fenestrae/microns 2, respectively (p less than 0.01). Fenestrae per cubic millimeter of periodontal ligament tissue also demonstrated a statistically significant increase with extrusion (p less than 0.01) in postcapillary-sized venules from 0.37 to 1.55 x 10(6) fenestrae/mm3, in venous capillaries from 0.27 to 1.34 x 10(6) fenestrae/mm3, and in arterial capillaries from 0.02 to 0.22 x 10(6) fenestrae/mm3. Fenestrae in control vessels had a mean diameter of 54.2 +/- 0.56 nm (SE) compared with 61.1 +/- 0.7 nm in tensioned vessels (p less than 0.01). This investigation demonstrates multiple ultrastructural changes in the periodontal ligament microvascular bed after tooth extrusion.
British journal of orthodontics, 1989
The tooth positioner is a one-piece, resilient appliance which may be used for finishing orthodon... more 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.
European journal of orthodontics, 1989
Thirty-two adult oriental patients aged 18-26 years who sought treatment for their bimaxillary pr... more Thirty-two adult oriental patients aged 18-26 years who sought treatment for their bimaxillary protrusion were treated with the Begg appliance following extraction of four first premolars. A cephalometric study was undertaken to determine the soft tissue changes in lip profile following treatment. Results show that the upper incisors were retracted by 5.6 mm +/- 0.8 mm and the lower incisors by 4.4 +/- 0.8 mm on the average. The nasolabial angle became more obtuse increasing from 80.7 degrees to 90.7 degrees. The upper lip and lower lip lengthened by 1.9 mm and 1.2 mm, respectively. The lower lip to 'E' line reduced from 7.5 mm to 3.7 mm. All the previous changes were statistically significant (p less than 0.01). The upper lip to upper incisor retraction was 1:2.2 while the lower lip to lower incisor retraction was 1:1.4. The correlation coefficients (r) were 0.72 (p less than 0.01) and 0.80 (p less than 0.01), respectively. The changes in the cants of mandibular and occlusa...
Clinical Materials, 1993
In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond str... more In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond strengths with resin-bonded bridges) is compared to a conventional no-mix orthodontic Bis-GMA bracket adhesive. Results showed that there was no statistically significant difference in the shear bond strengths between the two resins when used as adhesives for bonding orthodontic brackets. Coupled with the fact that Panavia requires an anaerobic environment for comDlete polvmerization. its routine use as a bracket adhesive in direct bonding of o&hod&c brackets is not indicated.
The Journal of Nihon University School of Dentistry, 1989
A review of the literature pertaining to the histological and ultrastructural changes related to ... more 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 < 0.01). The results of this study suggest that the postcapillary venules are the most vulnerable segment in the PDL microvascular system.
Journal of Esthetic and Restorative Dentistry, 1992
Arch bars are well-known dental appliances for the management of fractures and orthognathic surge... more Arch bars are well-known dental appliances for the management of fractures and orthognathic surgery. Traditionally both the commercially available, prefabricated arch bars as well as the custom-made arch bars are made of metal so as to provide good rigidity. Each of these types of arch bars has its own advantages as well as drawbacks. This article looks at a type of custom-made arch bar that is easy to construct and use. At the same time, it provides good rigidity, fit, and esthetics.
Journal of Esthetic and Restorative Dentistry, 1992
With the advent of acid etching techniques and the elimination of unesthetic band materials, dire... more With the advent of acid etching techniques and the elimination of unesthetic band materials, direct bonding of orthodontic attachments kindled a desire for cosmetic appliances such as labial ceramic brackets and lingual orthodontics. Owing to the esthetic nature of our combination upper-lingual lower-ceramic orthodontic approach, adults who would have normally avoided orthodontic treatment are now seeking treatment. This study evaluated the cephalometric changes in the soft tissue lip profile following treatment of Class II Division 1 malocclusion with upper first bicuspid extractions with our esthetic orthodontic appliance approach. Serial lateral cephalograms (pretreatment and posttreatment) of 16 adult patients with a mean age of 22.1 +/- 3.2 years were studied. The mean upper incisor retraction, upper lip retraction, upper lip lengthening, and lower lip retraction were 5.75 +/- 1.91 mm, 2.8 +/- 1.4 mm, 1.5 +/- 0.6 mm, and 1.4 +/- 0.6 mm, respectively. All these changes were statistically significant (p < 0.01). The nasolabial angle increase of 10.8 +/- 3.0 degrees was also statistically significant (p < 0.01). The upper lip retraction to upper incisor retraction was 1:2.1, while the upper lip lengthening to upper incisor retraction was 1:3.8. The correlation coefficients (r) were 0.91 (p < 0.01) and 0.57 (p < 0.01), respectively. This study shows that significant esthetic changes in lip profile are possible with this cosmetic orthodontic appliance approach. The treatment results in this study appear comparable to those published with labial metal brackets. With very few exceptions, patients were able to adapt within 2 weeks, with almost no trauma to the tongue.
Journal of Esthetic and Restorative Dentistry, 1992
The purpose of this study was to determine the facial profile preferences in a sample of 1,189 As... more The purpose of this study was to determine the facial profile preferences in a sample of 1,189 Asian teenagers (aged 15.3 +/- 3.2 years). Five facial profile types were computer-generated by trained personnel (orthodontists and oral maxillofacial surgeons) to represent distinct facial types. Subjects were asked to rank the profiles in descending order of attractiveness. The ranking was as follows: orthognathic profile, bimaxillary retrusive profile, bimaxillary protrusive profile, mandibular retrognathic profile, and mandibular prognathic profile. The differences in rank scores between all the profile types were statistically significant (p < 0.05). Assessment of profile types among lay personnel could provide clinicians an indication into the relative attractiveness among profile types and health care workers in treatment prioritization among dysmorphic facial types.
British Dental Journal, 1989
Two cases are presented where the maxillary second molars were just erupting. The first was a Chi... more 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.
Australian Dental Journal, 1993
Population norms derived from one ethnic group may not necessarily be valid and accurate for othe... more Population norms derived from one ethnic group may not necessarily be valid and accurate for other ethnic groups. With the increasing number of ethnic Chinese immigrants in Australia, Europe, and America, it would be useful for dental practitioners to be informed about malocclusion prevalence among Chinese. This study was carried out on 1050 Chinese school children (aged 12-14 years) to assess both qualitatively and quantitatively certain occlusal features. The population was found to have a high incidence of Class Ill malocclusions compared with Caucasians. However, the incidence of Class II malocclusions was quite similar to those reported in Caucasians. Normal occlusions occurred in about 7 per cent of this population. Although this percentage was much lower than those reported in blacks, it was similar to those reported in caucasians. Crowding occurred in about 50 per cent of cases, which was slightly less than for those reported for Caucasians. Increased overbites were also less common in this Chinese population compared with Caucasians. Compared with Caucasians, crossbites were also less frequent in this Chinese population.
Community Dentistry and Oral Epidemiology, 1993
A retrospective survey of 358 local Chinese adult orthodontic patients was undertaken to determin... more A retrospective survey of 358 local Chinese adult orthodontic patients was undertaken to determine the motivating faetors behind orthodontic treatment and the discomfort caused by fixed orthodontic appliances. Frotn the completed questionnaires of 203 patients, the principal conclusions were that the itnprovetnent in dento-facial aesthetics following orthodontic treatment enhanced their self-confidence and self-esteem in a majority of patients; discomfort in oral soft tissues and teeth were transient and did not exceed 7 days; transient pain frotn teeth was experienced by 91% of patients and in 39% of these patients the discomfort to teeth was experienced with each new arehwire or elastic force application. These results may be useful in relating discomfort levels to prospective orthodontie patients. It was also evident in the study that several cross-cultural differences existed in the attitudes of our patients compai'ed to those I'eported in Caucasians.
Journal of oral and maxillofacial …, 1992
Using a double selection process comprised of professional and lay judges, the cephalometric trac... more Using a double selection process comprised of professional and lay judges, the cephalometric tracings on a final sample of 48 Chinese adults with esthetically pleasing profiles were analyzed. The soft-tissue cephalometric norms and standard deviations of two widely accepted soft-tissue analyses, the Legan and Burstone analysis and the Holdaway analysis, were determined. In comparison with white norms, the Chinese nose was less prominent (P < .Ol), the nasolabial angle was less obtuse (P < .Ol), both the upper and lower lips were more protrusive (P < .05), the upper lip curvature was greater (P < .Ol), and the soft-tissue chin thickness was less (P < .05). This variance between racial types emphasizes the need to recognize that soft-tissue lateral cephalometric norms are specific for the racial group and cannot always be applied across different racial types.