Predictors of postretention stability of mandibular dental arch dimensions in patients treated with a lip bumper during mixed dentition followed by fixed appliances

OBJECTIVE

To identify which dental and/or cephalometric variables were predictors of postretention mandibular dental arch stability in patients who underwent treatment with transpalatal arch and lip bumper during mixed dentition followed by full fixed appliances in the permanent dentition.

MATERIALS AND METHODS

Thirty-one patients were divided into stable and relapse groups based on the postretention presence or absence of relapse. Intercuspid, interpremolar, and intermolar widths; arch length and perimeter; crowding; and lower incisor proclination were evaluated before treatment (T0), after lip bumper treatment (T1), after fixed appliance treatment (T2), and a minimum of 3 years after removal of the full fixed appliance (T3). Logistic regression analyses were performed to evaluate the effect of changes between T0 and T1, as predictive variables, on the occurrence of relapse at T3.

RESULTS

The model explained 53.5 % of the variance in treatment stability and correctly classified 80.6 % of the sample. Of the seven prediction variables, intermolar and interpremolar changes between T0 and T1 (P = .024 and P = .034, respectively) were statistically significant. For every millimeter of increase in intermolar and interpremolar widths there was a 1.52 and 2.70 times increase, respectively, in the odds of having stability. There was also weak evidence for the effect of sex (P = .047).

CONCLUSIONS

The best predictors of an average 4-year postretention mandibular dental arch stability after treatment with a lip bumper followed by full fixed appliances were intermolar and interpremolar width increases during lip bumper therapy. The amount of relapse in this crowding could be considered clinically irrelevant.

Comparison of dental arch dimensions in models of preschool children with cleft lip/palate repaired by means of surgery alone versus controls

BACKGROUND

Cleft lip and palate (CLP) anomaly is one of the most prevalent congenital defects causing disturbances of dental arch dimensions. This study aimed at investigating differences in these dimensions between preschool children with cleft lip/palate and a matched control group representing healthy individuals with normal occlusion (NO).

MATERIALS AND METHODS

The sample of this cross-sectional analytical study consisted of 108 plaster models of children aged from 4 to 5.5 years. They were divided into five groups: the cleft lip group, the cleft palate (CP) group, the unilateral cleft lip and palate group, the bilateral cleft lip and palate group, and the NO group. The NO group was used as a control group. All cleft-affected children were treated only with surgery. Dental arch length and widths were measured.

RESULTS

The dental arch dimensions of the cleft lip group were nearly similar to those in the controls. Moreover, the mandibular transverse widths of the CP group were close to those in the controls. However, the mandibular arch length and all maxillary dimensions of the CP group were smaller than those in the controls. In the unilateral cleft lip and palate group, the arch lengths in both jaws and the maxillary transverse widths were smaller than those in the controls, whereas the mandibular transverse widths were similar to those in the controls. In the bilateral cleft lip and palate group, the arch lengths in both jaws were close to those in the controls, but both arches were narrower than those in the controls.

CONCLUSION AND RECOMMENDATIONS

The various types of CLP were found to be associated with differences in most maxillary and some mandibular arch dimensions. These data can be used for cleft patient counseling and treatment planning.

Archform comparisons between skeletal class II and III malocclusions

The purpose of this cross-sectional research was to explore the relationship of the mandibular dental and basal bone archforms between severe Skeletal Class II (SC2) and Skeletal Class III (SC3) malocclusions. We also compared intercanine and intermolar widths in these two malocclusion types. Thirty-three virtual pretreatment mandibular models (Skeletal Class III group) and Thirty-five Skeletal Class II group pretreatment models were created with a laser scanning system. FA (the midpoint of the facial axis of the clinical crown)and WALA points (the most prominent point on the soft-tissue ridge)were employed to produce dental and basal bone archforms, respectively. Gained scatter diagrams of the samples were processed by nonlinear regression analysis via SPSS 17.0. The mandibular dental and basal bone intercanine and intermolar widths were significantly greater in the Skeletal Class III group compared to the Skeletal Class II group. In both groups, a moderate correlation existed between dental and basal bone arch widths in the canine region, and a high correlation existed between dental and basal bone arch widths in the molar region. The coefficient of correlation of the Skeletal Class III group was greater than the Skeletal Class II group. Fourth degree, even order power functions were used as best-fit functions to fit the scatter plots. The radius of curvature was larger in Skeletal Class III malocclusions compared to Skeletal Class II malocclusions (r_WALA3>r_WALA2>r_FA3>r_FA2). In conclusion, mandibular dental and basal intercanine and intermolar widths were significantly different between the two groups. Compared with Skeletal Class II subjects, the mandibular archform was more flat for Skeletal Class III subjects.

Biomechanical aspects of the optimal number of implants to carry a cross-arch full restoration

A proper definition of the 'optimal' number of implants to support a full arch prosthesis should go beyond solely a listing of the number of implants used in a treatment plan; it should be based upon a biomechanical analysis that takes into account several factors: the locations of the implants in the jaw; the quality and quantity of bone into which they are placed; the loads (forces and moments) that develop on the implants; the magnitudes of stress and strain that develop in the interfacial bone as well as in the implants and prosthesis; and the relationship of the stresses and strains to limits for the materials involved. Overall, determining an 'optimal' number of implants to use in a patient is a biomechanical design problem. This paper discusses some of the approaches that are already available to aid biomechanically focused clinical treatment planning. A number of examples are presented to illustrate how relatively simple biomechanical analyses - e.g. the Skalak model - as well as more complex analyses (e.g. finite element modelling) can be used to assess the pros and cons of various arrangements of implants to support fullarch prostheses. Some of the examples considered include the use of 4 rather than 6 implants to span the same arc-length in a jaw, and the pros and cons of using tilted implants as in the 'all-on-4' approach. In evaluating the accuracy of the various biomechanical analyses, it is clear that our current prediction methods are not always perfectly accurate in vivo, although they can provide a reasonably approximate analysis of a treatment plan in many situations. In the current era of cone beam computerised tomography (CT) scans of patients in the dental office, there is significant promise for finite element analyses (FEA) based on anatomically-accurate input data. However, at the same time it has to be recognised that effective use of FEA software requires a reasonable engineering background, especially insofar as interpretations of the clinical significance of stresses and strains in bone and prosthetic materials.

Influence of thickness and area of reline on the stress distribution in peri-implant bone during the healing period: a three-dimensional finite element analysis

The current study used finite element analysis to evaluate how the thickness of reline material and the area of its placement in conventional complete dentures affected the stress distribution in peri-implant bone during function in the healing period. For this study, three-dimensional models were created to simulate a severely resorbed mandible with two implants placed recently in the anterior region. Two of these models received a layer of soft liner material that covered the entire length of the denture base (1.5 mm or 3.0 mm); for the other sample models, soft liner material was placed (in thicknesses of 1.5 mm or 3.0 mm) in the implant region only. The models were exported to mechanical simulation software; two simulations were performed by placing a load in the mandibular right canine (35 N) and the mandibular right first molar (50 N). Data were quantitatively and qualitatively evaluated by means of maximum principal stress. In all cases, models that received 3.0 mm of soft liner material showed lower values of stress concentration than those receiving 1.5 mm of soft liner material. Likewise, localized application of soft liner in the implant region showed lower stress concentration compared with models in which the entire denture base was relined. These results indicate that the thickness and area of reline in conventional complete dentures has a direct effect on stress distribution in the peri-implant bone tissue during the healing period.

Biomechanical behavior of restored and unrestored mandible with shortened dental arch under vertical loading condition

The aim of this in vitro study was to investigate the strain distribution of the compressed mandible bone under the applied restoration- removable partial denture and to compare with the same but unrestored mandible under vertical (occlusal) load and to find out whether removable partial denture-restored or unrestored mandible causes greater strain effect on supporting tissue. Four mandible models were tested during loading for the purpose of strain measuring. Digital image correlation system (GOM - German Optical Measuring, Braunschweig, Germany), used for measuring strain consists of two digital cameras and software ARAMIS (6.2.0, Braunschweig, Germany). Remaining teeth suffer from greater strain in the mandible model without removable partial denture (7.5-10%). On the contrary, mandible with removable partial denture shows the maximum strain below the denture saddle (3.5%). However, it can be noticed that the marginal bone of the second lower praemolar in both experimental models is deformed whether the mandible model has (2.8%) or has not (10%) replacement. Within the limitations of this study the higher strain is observed in mandible model without replacement and the strain is limited locally, in the bone region that surrounds remaining teeth and mental foramen.

[Effect of adverse oral habits on the development of the dentomaxillary system]

Main features of the dentomaxillary system (breathing, chewing, swallowing) are provided by the rhythmic movements of the mandible, tongue, lips, mimic muscles, learned during ontogenesis and coordinated neuromusculary and largely automated.

AIM

The aim of our study was to prove the role of oral habits in the development of dentomaxillary anomalies. We made experimental investigations--model studies, fotostatic test for face and side face, radiological examinations, clinical general and ENT exam for accurately assess of the factors which contribute to the emergence and development of dentomaxillary anomalies.

MATERIAL AND METHODS

The study group consisted of 175 children (94 girls and 81 boys) aged between 7 and 14 years. We made individual sheets for recording neuromuscular and oropharyngeal balance starting from a patient's overall clinical appearance.

RESULTS

The diagnosis of most teenagers was first Angle's class of malocclusion with tongue thrusting and mouth breathing. Oral habits disrupt the muscular balance and bone growth producing changes in the dental arch and ocllusal characteristics. The high prevalence of dentomaxillary anomalies (52.57%) and obvious interrelationship with functional imbalances of the dentomaxillary system (62.82% of subjects examined) supports the implication of functional factors in those etiology.

CONCLUSIONS

Suppression of vicious habits by methods of awareness, myogymnastic and functional reducing exercises are the first steps of early functional treatment for dentomaxillary anomalies.

Bone stress analysis of various angulations of mesiodistal implants with splinted crowns in the posterior mandible: a three-dimensional finite element study

PURPOSE

Ideally, implants for dental prostheses should be placed parallel to each other. However, anatomic limitations sometimes make nonparallel implants necessary. The purpose of this study was to determine the bone stresses on implants tilted at various angles and to determine what arrangements might carry a higher risk of failure.

MATERIALS AND METHODS

Three-dimensional finite element models were constructed using the mean values measured for the Asian mandible in the first and second molar areas. Eight implants were divided into three tilting types: parallel implants (P1(PP), P2(MM), and P3(DD)), convergent implant apices (C1(PD) and C2(MP)), and divergent implant apices (D1(DP), D2(DM), and D3(PM)). A biting load of 200 N was applied vertically and obliquely on the occlusal central fossa of the splinted crowns. The main effects of each level of the three investigated factors (loading type, relationship of implant apices, and distal tilting of one or both implants) in terms of the stress values were computed for all models.

RESULTS

The loading type was the main factor affecting the stress in bone when comparing implant apices and distal tilting of the implant body. When loading was combined with distal tilting, the stress values were significantly increased, especially in models P3(DD) and C1(PD).

CONCLUSION

The loading type is the main factor affecting the stress distribution for different implantation arrangement. Moreover, placement of the implants with distal tilting should be avoided in the posterior mandible.

Morphologic and bony structural changes in the mandible after a unilateral injection of botulinum neurotoxin in adult rats

PURPOSE

Previous animal experiments showed how reduced masticatory function plays an important role in the craniofacial and mandibular regions in the growing period. However, articles focusing on the effects of reduced masticatory function in adult animals are quite scarce. The purpose of this study was to evaluate the effects of reduced masticatory muscle activity on the jaw bones of adult rats.

MATERIALS AND METHODS

Botulinum neurotoxin type A (BTX-A) was injected into the left masseter muscle to reduce masticatory muscle function, and sequential changes in the jaw bones were investigated. Ten male 60-day-old Sprague-Dawley rats with a mean body weight of about 300 g were used. The following procedures were performed on each sample: 25 U/mL (0.3 mL) of BTX-A was injected into the left masseter muscle, whereas the right masseter muscle received an equal amount of sterilized saline solution. Ninety days after the procedure, the rats were sacrificed, and the weights of the masseter muscles were recorded. Meanwhile, direct anthropometric measurements were taken, and the cortical thickness, trabecular thickness, and bone mineral content of the skull and mandible were measured. All measurements were evaluated with statistical software.

RESULTS

There were significant differences in all measurements on the BTX-A side compared with those on the control side. The differences included a decreased ramus height, increased gonial angle, and increased crown height of the posterior teeth on the injection side. Significant decreases in the muscle weight, bone mineral content, cortical thickness, and trabecular thickness were also seen on the paralyzed side compared with the non-injection side.

CONCLUSIONS

We found that reduced masticatory function in adult rats affected the weight of the masseter muscle and the bony structure and dentition.

Implant-supported crowns for a shortened dental arch: a case report

AIM

The aim of this report is to highlight the efficiency of implant restoration of a shortened dental arch (SDA) for a partially edentulous patient.

BACKGROUND

The SDA refers to a dentition with loss of posterior teeth. The goal of dental care is the maintenance of a natural dentition with regard to esthetics, speech, chewing, and oral comfort. In order to achieve this goal several issues were examined in a SDA clinical scenario including masticatory ability, occlusal factors, the effect of removable partial dentures, oral comfort, and periodontal support.

REPORT

A 62-year-old female with a SDA presented for treatment with concern about her compromised periodontal and restorative status. Following professional scaling and root planing and oral hygiene motivation, the bite was opened. Restorative treatment was rendered up to the second premolars with the issues associated with a SDA in mind.

SUMMARY

A body of evidence in literature showed an arch extending to the second premolars is adequate for normal functional demands, oral hygiene, oral comfort, and possibly reduced costs on a dentition subjected to modern diet. The reported clinical outcomes of using implant supported crowns till the second premolar area using the concept of restoring only an existing SDA were highly satisfactory for the well-oriented patient.

Effects of tongue volume reduction on craniofacial growth: A longitudinal study on orofacial skeletons and dental arches

The interaction between tongue size/volume and craniofacial skeletal growth is essential for understanding the mechanism of specific types of malocclusion and objectively measuring outcomes of various surgical and/or orthodontic treatments. Currently available information on this interaction is limited. This study was designed to examine how tongue body volume reduction affects craniofacial skeleton and dental arch formation during the rapid growth period in five 12-week-old Yucatan minipig sibling pairs. One of each pair received a standardized reduction glossectomy to reduce tongue volume by 15-17% (reduction group), and the other had the reduction glossectomy incisions without tissue removal (sham group). Before surgery, five stainless steel screws were implanted into standardized craniofacial skeletal locations. A series of cephalograms, lateral and axial, were obtained longitudinally at 1 week preoperative, and 2 and 4 weeks postoperative. These images were traced using superimposition, and linear and angular variables were measured digitally. Upon euthanasia, direct osteometric measurements were obtained from harvested skulls. Five en-bloc bone pieces were further cut for bone mineral examination by dual photon/energy X-ray absorptiometry (DEXA). The results indicate that: (1) while daily food consumption and weekly body weight were not significantly affected, tongue volume reduction showed an overall negative effect on the linear expansion of craniofacial skeletons; (2) premaxilla and mandibular symphysis lengths, and anterior dental arch width were significantly less in reduction than sham animals at 2 and/or 4 weeks after the surgery; (3) both premaxilla/maxilla and mandible bone mineral density and content were lower in reduction than sham animals, significantly lower in anterior mandible; (4) craniofacial skeletal and dental arch size were significantly smaller in reduction than sham animals, being most significant in the mandibular anterior length and ramus height, the anterior dental arch and midface width. These results suggest that reducing tongue body volume in young animals slows craniofacial skeletal growth and anterior dental arch expansion during rapid growth. The mandible, in particular its symphysis portion, and the anterior dental arch width are most affected. These effects may in part contribute to the decrease of functional loads in the anterior mouth by a volume-reduced tongue.

What dentition assures oral function?

OBJECTIVE

To evaluate the relationship between dentition and oral function.

MATERIAL AND METHODS

A search of the English literature was undertaken using PubMed and appropriate keywords. Citations were identified and hand sorted to confirm their validity against our inclusion criteria. Four specific areas of oral function were addressed; (I) masticatory function, (II) aesthetics, satisfaction and psychosocial ability, (III) occlusal support and stability and (IV) other functionality including tactile perception, phonetics and taste.

RESULTS

From an initial pool of 1460 citations, 83 articles met the inclusion criteria. These were summarized and relevant data extracted for incorporation into the review. Masticatory efficiency (assessed as comminution efficiency) and masticatory ability (self-reported) are both linked to the number of teeth. A minimum of 20 teeth with nine to 10 pairs of contacting units (including anterior teeth) is associated with adequate efficiency and ability. Tooth numbers below that level yield impaired masticatory efficiency and are likely to result in reduction in reported masticatory ability. Aesthetics and satisfaction are markedly impaired with loss of anterior teeth. Satisfaction is most likely to be achieved in people who also retain a premolar dentition. Further, there is little increase in satisfaction seen in subjects who retained molar teeth. However, there are marked variations in subjective measures of aesthetics and psychosocial comfort between age groups, social classes, cultures, regions and countries. For most people, occlusal support and stability are obtained with three to four functional posterior units with a symmetrical pattern of tooth loss or five to six units with an asymmetrical pattern. There was no relationship between occlusal factors and symptoms of temporomandibular dysfunction. Phonetics may be maintained even with large anterior restorations. Patients generally attribute a low significance to phonetics, tactile perception and taste compared with mastication and appearance.

CONCLUSIONS

The World Health Organization goal for the year 2000, namely to maintain a natural dentition of not less than 20 teeth throughout life, is substantiated by the current literature review as this proposed dentition will assure an acceptable level of oral function.

Differences between high- and low-angle subjects in arch form and anterior crowding from 23 to 33 years of age

The aim of this study was to compare changes in arch width and length in high- and low-angle subjects. The material comprised the cephalograms and study models of 17 males and 15 females with a high-angle and 12 males and 16 low-angle females. The age of the subjects at the first examination (T1) was 22 years 10 months and 22 years 8 months in the high-angle groups, 22 years 5 months and 22 years 8 months in the low-angle subjects, respectively, for males and females. The second assessment (T2) was 10 years and 9 years 10 months later in the high-angle and, 10 years 3 months and 9 years 10 months in the low-angle groups, respectively. Statistical analysis of changes for each group during the observation period T1-T2 was undertaken using a paired t-test, and the differences between the groups with two-sample t-tests. The findings showed a general reduction in upper and lower arch length, an increase of intermolar width, and a decrease of intercanine width in both genders. Anterior perimeter and anterior space in both angles decreased in both males and females. The mean changes were small, but with large individual differences. There were no significant differences between the genders or the high- and low-angle groups in the changes, except that the female high-angle group had a statistically significant (P = 0.05) greater decrease in mandibular arch length than the low-angle female group.

Biomechanical effects of rapid palatal expansion on the craniofacial skeleton with cleft palate: a three-dimensional finite element analysis

OBJECTIVE

To explore the biomechanical effects of rapid palatal expansion (RPE) on the craniofacial skeleton with cleft palate.

DESIGN

A finite element model of a patient's skull with cleft lip and palate (CLP) was generated using data from spiral computed tomographic (CT) scans. Finite elemental analysis (FEA) was performed to depict the physiological changes and stress distribution in craniofacial structures loaded with orthopedic forces that created 5 mm of displacement on the region of the maxillary first premolar and first molar crown.

PATIENTS, PARTICIPANTS

A 14-year-old girl with left complete unilateral CLP was included in this study.

INTERVENTIONS

Spiral CT was carried out prior to any treatment.

MAIN OUTCOME MEASURE(S)

Three-dimensional (3D) features of displacement and stress distribution were analyzed following application of transverse orthopedic force.

RESULTS

Marked amount of displacement and deformation occurred in the dental region. Asymmetric displacement and deformation of UCLP under RPE were evident. The stress generated by RPE was dispersed around the cleft palate and nasal cavity, and was distributed at the buttress of the maxilla-inferior border of the nasal cavity, outboard of the orbit, and central frontal bone near the nasion.

CONCLUSIONS

Application of RPE to UCLP patients induces a pyramid-like displacement of the nasomaxillary complex along with fan-like expansion of the upper dental arch. The uniqueness of RPE with UCLP, however, lies in the asymmetric expansion and dispersed stress distribution around the lateral maxilla buttress and outboard of orbit.

Unilateral posterior crossbite and mastication

OBJECTIVE

This study was designed to characterize masticatory-cycle morphology, and distance of the contact glide in the closing masticatory stroke, in adult subjects with uncorrected unilateral posterior crossbite (UPXB), comparing the results obtained with those obtained in a parallel group of normal subjects.

STUDY DESIGN

Mandibular movements (masticatory movements and laterality movements with dental contact) were registered using a gnathograph (MK-6I Diagnostic System) during unilateral chewing of a piece of gum. Traces were recorded on the crossbite and non-crossbite sides in the crossbite group, and likewise on both sides in the non-crossbite group.

RESULTS

Mean contact glide distance on the crossbite side in the UPXB group was significantly lower than in the control group (p<0.001), and mean contact glide distance on the non-crossbite side in the UPXB group was significantly lower than in the control group (p=0.042). Cycle morphology was abnormal during chewing on the crossbite side, with the frequency distribution of cycle types differing significantly from that for the noncrossbite side and that for the control group (p<0.001).

CONCLUSIONS

Patients with crossbite showed alterations in both contact glide distances and masticatory cycle morphology. These alterations are probably adaptive responses allowing maintenance of adequate masticatory function despite the crossbite.

Craniofacial growth and functional change in oligodontia with ectodermal dysplasia: a case report

A case of ectodermal dysplasia in a Japanese boy is presented in this report. After prosthetic treatment was performed with partial dentures in both jaws, mandibular movement, dental casts, and lateral and frontal cephalograms were taken at an initial visit (age 7 years 8 months), and at follow-up 1 year and 8 months later (age 9 years 3 months) to evaluate the developmental changes in masticatory movement, dental arch width, and craniofacial morphology. Stability of the jaw movements improved during the follow-up period both with and without dentures. The facial skeleton grew between the initial visit and follow-up. Mandibular length remained long compared with the average value for Japanese children. A possible genetic marker for mandibular growth (growth hormone receptor), which is considered to be an important factor in mandibular growth and development, was analysed for the gene variant and the result supported the characteristic mandibular growth in the reported case. These results indicate the characteristic craniofacial growth in this disease and emphasize the potential ability of functional development of jaw movements with oligodontia.

Intraarch and interarch relationships of the anterior teeth and periodontal conditions

This study was undertaken to investigate the association between orthodontic anomalies and periodontal conditions. Three parameters of the intraarch relationship on both dental arches (displacement of contact point, crowding, and spacing) and four parameters of interarch relationship (overjet, open bite, crossbite, and overbite) assessed with either Index of Orthodontic Treatment Need or Index of Complexity, Outcome and Need were correlated with parameters of periodontal condition, ie, hygiene (Plaque Index and Retention Index), inflammation (gingival inflammation and Gingival Bleeding Index), and periodontal disease severity (pocket depth, clinical attachment loss, and gingival recession). In the main, weak but significant correlations were found between certain parameters of intraarch and interarch relationship and some indices of periodontal conditions. Within the limitations of this study, it was concluded that providing orthodontic treatment on the ground of deleterious effect of malocclusion and malpositioned teeth on periodontal condition is justified.

A review of the shortened dental arch concept focusing on the work by the Käyser/Nijmegen group

The aims of this paper were to review the literature on shortened dental arches with special focus on publications of the Käyser/Nijmegen group, and to evaluate the discussions on the shortened dental arch concept found in the literature. A MEDLINE (PubMed) search was conducted for articles in English published in the dental literature from 1966 to November 2005. The search revealed epidemiological, cross-sectional and longitudinal clinical studies as well as opinion papers, the majority of which were published by the Dutch group. The studies found in general no clinically significant differences between subjects with shortened dental arches of three to five occlusal units and complete dental arches regarding variables such as masticatory ability, signs and symptoms of temporomandibular disorders, migration of remaining teeth, periodontal support, and oral comfort. The findings from cross-sectional studies were corroborated longitudinally. No systematic clinical study with conflicting results was found. The shortened dental arch concept was accepted by a great majority of dentists but not widely practised. The studies reviewed showed that shortened dental arches comprising anterior and premolar teeth in general fulfil the requirements of a functional dentition. It may therefore be concluded that the concept deserves serious consideration in treatment planning for partially edentulous patients. However, with ongoing changes, e.g. in dental health and economy, the concept requires continuing research, evaluation and discussion. Patients' needs and demands vary much and should be individually assessed but the shortened dental arch concept deserves to be included in all treatment planning for partially edentulous patients.

Treatment outcome in unilateral cleft lip and palate evaluated with the GOSLON yardstick: a meta-analysis of 1236 patients

BACKGROUND

The goal of this study was to assess determinants for treatment outcome in unilateral cleft lip and palate, evaluated according to the Great Ormond Street London and Oslo (GOSLON) Yardstick and 5-year-index ratings by means of a meta-analysis.

METHODS

Multiple databases were searched for publications in which patient groups were evaluated by GOSLON ranking or the GOSLON-like 5-year index. From the 15 selected publications, the following background variables could be extracted and were evaluated as determinants for treatment outcome in unilateral cleft lip and palate: year of birth, average age of the patient at the time of GOSLON classification, racial background, presence of Simonart's band, infant orthopedics, palatal closure before the age of 3 versus palatal closure at a later age, bone graft, and number of surgeons.

RESULTS

The total number of patients included in the meta-analysis was 1236. Patients whose soft and hard palate were closed before the age of 3 presented significantly poorer (p = 0.003) GOSLON scores (mean score, 2.9; SD 0.4) than patients whose palate was closed at a later age (mean GOSLON score, 2.3; SD 0.2).

CONCLUSIONS

Delayed palatal closure generally results in better dental arch relationships than early palatal closure. Well-designed, randomized clinical trials are required for further investigation of the optimal timing for palatal closure.

Factors Associated with Masticatory Performance in Unilateral Distal Extension Removable Partial Denture Patients

PURPOSE

Masticatory performance of denture patients is an outcome of the intricate inter-relationship between patient characteristics and denture construction. This study aimed to identify both patient- and denture-related factors associated with masticatory performance in unilateral distal extension removable partial denture patients (RPDs).

MATERIALS AND METHODS

Seventy-two patients (25 male and 47 female, mean age 63.4 +/- 6.7 years) with unilateral distal extension RPDs were included in the study. The Mixing Ability Index (MAI) obtained from a chewing test using standard two-colored wax cubes, determined masticatory performance. The effect of each evaluated factor on masticatory performance was first determined by an independent t-test or one-way analysis of variance. The statistically significant factors were entered in a model of multivariate linear regression analysis to estimate the independent effect on MAI.

RESULTS

The MAI ranged from -3.06 to 0.80 (Mean -0.71 +/- 0.86). Univariate analyses identified male gender, high maximum bite force, more functional tooth units, and natural dentition opposing RPDs as patient factors increasing the MAI. Multivariate analysis (adjusted R(2)= 0.346) revealed that gender (p < 0.001), maximum bite force (p= 0.02), and number of functional tooth units (p= 0.03) were independent predictors for masticatory performance. None of the denture-related factors had a significant influence on MAI.

CONCLUSION

Gender, maximum bite force, and number of functional tooth units were the main factors influencing masticatory performance of unilateral distal extension RPD patients.

Evaluation of tongue pressure on the inferior dental arch in patients with mandibular prognathism

The aim of the present study was to find out whether there is a difference between the force exerted by the tongue (pressure) in patients with mandibular prognathism and healthy controls and to determine the difference in tongue pressure on the inferior dental arch in patients with mandibular prognathism before and after mandibular setback.

MATERIAL AND METHODS

Patients with mandibular prognathism were compared with healthy controls and data on tongue pressure were collected.

RESULTS

Tongue pressure on the inferior dental arch in patients with mandibular prognathism ranged from 1.98 N to 12.26 N (mean 5.356 N). Tongue pressure in the control group ranged from 2.36 N to 16.9 N (mean 6.56 N), with most of the values ranging from 4.02 N to 7.84 N.

CONCLUSIONS

Tongue pressure on the inferior dental arch is reduced in patients with mandibular prognathism. 1. Surgical treatment for mandibular prognathism using vertical ramus osteotomy does not affect tongue pressure, contradicting the view that the tongue is the main cause of skeletal relapse after mandibular setback. 2. There is no need for routine tongue size reduction prior to orthognathic surgery for mandibular prognathism.

[Comparison of shortened dental arches with complete dental arches by clinical examinations]

PURPOSE

Recently, there have been reports in favor of avoiding prosthodontic intervention as Shortened Dental Arch (SDA) in Northern Europe. However, many of these reports were conducted through interviews and questionnaires, and so the evaluation of the results lacked objectivity. Thus, this research analyzed the clinical status of SDA.

METHODS

For the selection of subjects, seven patients (average age: 59.3+/-13.2 years old) who had had the free-end missing on both sides of the lower dental arches for over five years were chosen as the SDA group. As the complete dental arch (CDA) group, seven patients (average age: 61.3+/-9.6 years old) who had no clinical defects in their masticatory function, and who had no missing teeth other than the third molar, were selected. Measurement items in this study were occlusal contact areas for the mandible premolar, center of force, occlusion time, and interdentium. The Mann-Whitney U test was used for statistical analysis and the significance level was assumed to be 5%.

RESULTS

The results were as follows: 1) The occlusal contact area of the mandible premolar of SDA was significantly large. 2) The center of force of SDA was significantly forward. 3) The occlusion time of SDA had a tendency of prolongation. 4) Interdentium of 3 2 | 2 3, 4 3 | 3 4 and 5 4 | 4 5 of SDA were significantly wide.

CONCLUSIONS

There were differences of clinical parameters between SDA and CDA in this study.

The relation between the point of force application and flaring of the anterior segment

The purpose of this study was to determine whether application of an intrusive force by an intrusion arch at the distal wings of the lateral incisor brackets causes a change in the axial inclination of the anterior segment. Maxillary incisor intrusion was performed, and records were taken from 40 adolescent patients at the beginning and end of intrusion. Intrusion of the maxillary anterior segment caused a statistically significant mean increase in axial inclination of the central incisor of 8.74 degrees. The following correlations were investigated and found not statistically significant. The correlation between the (1) distance from the point of force application to the center of resistance at the start of intrusion and the change in axial inclination of the incisor, (2) distance from the point of force application to the center of resistance at the start of intrusion and the change in distance from the incisal edge to the distal side of the first molar, (3) distance from the point of intrusive force application to the center of resistance at the start of intrusion and at the end of intrusion, (4) distance from the point of intrusive force application to the center of resistance at the start of intrusion and the change in this distance between start and end of intrusion, and (5) amount of intrusion and the change in axial inclination.

[Individualized clinical evaluation of tooth movement. Treatment of Class II: molar splints and structural effects]

The presentation of a synoptic chart allowing a dental arch analysis and Class II correction strategy is presented and followed by a study on 30 patients in mixed dentition and 37 growing patients in permanent dentition. These patients presenting a Class II malocclusion have been treated by Class II mechanics and lower molar individualised splint enhancing the vertical lower face height and skeletal Class II correction. This study shows a good vertical stabilization of the facial planes during the treatment, a significant growth of the lower face but it is noticed a posterior rotation of the occlusal plane in the mixed dentition sample.

A three-dimensional computer model of the human mandible in two simulated standard trauma situations

PURPOSE

A three-dimensional finite element model of the human mandible was developed to simulate and analyse biomechanical behaviour in two standard trauma situations. This computer-based study was made to assess the stress patterns within human mandibles generated by impact forces.

MATERIAL AND METHODS

The mandibular model was generated using 7.073 nodes and 30.119 tetrahedra. A commercial finite element solver was then applied to this mesh to compute stresses generated in standard trauma situations (a blow in the symphysis region and another one to the body of the mandible).

RESULTS

The results indicate that following a blow to the symphysis region, maximum stress areas were located at the symphysis, retromolar and condylar regions. In the case of a blow to the mandibular body, the maximum stress areas were located at the contralateral angle, the ipsilateral body and the ipsilateral condylar neck regions.

CONCLUSION

The main application of this study was the prediction of fractures as a consequence of known forces.

The shortened dental arch: A review of the literature

The functional demands of patients are highly variable and individual, requiring dental treatment to be tailored to the individual's needs and adaptive capability. The World Health Organization indicates that a functional, esthetic, natural dentition has at least 20 teeth, while the literature indicates that dental arches comprising the anterior and premolar regions meet the requirements of a functional dentition. The English-language peer-reviewed literature pertaining to the short dental arch (SDA) was identified through the Medline search engine covering the period between 1966 and the present and critically reviewed. This treatment option for the partially dentate patient may provide oral functionality, improved oral hygiene, comfort, and, possibly, reduced costs.

Nonsurgical correction of skeletal deep overbite and class II division 2 malocclusion in an adult patient

Treatment modalities for Class II Division 2 malocclusion include growth modification, dental compensation, and surgical-orthodontic therapy; which treatment is chosen depends on the patient's age and growth potential. Deep overbite can be corrected by intrusion of anterior teeth, extrusion of posterior teeth, or a combination of both. Treatment considerations include the patient's facial profile, skeletal pattern, growth potential, and severity of dental malocclusion. Here, we present the nonsurgical orthodontic treatment of an adult patient with deep overbite and underlying skeletal Class II discrepancy. He had a hypodivergent facial pattern, Class II Division 2 malocclusion, and traumatic deep overbite due to supereruption of the mandibular anterior teeth. He refused orthognathic surgery but would accept orthodontic treatment alone, with the understanding that the treatment results could be compromised. We corrected the deep overbite by proclining the mandibular incisors; this helped to level the exaggerated curve of Spee. The posttreatment occlusion was significantly improved, both functionally and esthetically, with stable interincisal contacts. However, the improvement in occlusion and esthetics was achieved at the expense of reduced periodontal support for the mandibular anterior teeth.

Biomechanics of the dental arch and incisal crowding

During horizontal contact, the dental arch represents a link chain in which two convex articular surfaces are in contact and are tensioned by the dentogingival and dentoalveolar fibrous tissue. Joints composed of convex-convex surfaces are equivalent to stretched dimeric link chains whose links are in a mechanically unstable position under compression. Experiments on plaster models show that the dimensional stability of an articulated (dental) arch is considerably increased when a concave and a convex articular surface are in contact, as these joints are equivalent to an overlapping dimeric link chain whose links are in a mechanically stable position when under compression. In the abraded denture of Stone Age man, horizontal interdental contacts of transversally concave-convex dental surfaces may be found extending even into the incisal region. Increased stability of the dental arch and reduced problems of incisal crowding are to be expected if an overlapping dimeric chain is produced morphologically in each horizontal contact by means of slight interproximal enamel reduction.

How should postoperative palatal contraction be inhibited following palatoplasty? Dental arch development due to artificial antimolding action and natural molding action: clinical trial

Push back palatoplasty induces postoperative contraction and collapse of the dental arch. To inhibit collapse, 2 kinds of intersegment fixation plate, segment yoking plates, were applied. In one method, the segments were fixed with a resin plate onto the mucoperiosteal flap by 2 screws to fix palatal bone for 6 months (PB resin group, number of patients = 11). In the other method, the segments were fixed with a titanium plate by 2 screws onto the palatal bone under the mucoperiosteal flap until 4 years of age (PB titanium group, n = 10). Operation by conventional push back palatoplasty (PB Group, n = 25) was used as a control. Consecutive plaster models were measured by 3-dimensional laser scanner from at palatoplasty up to 4 years of age. In the PB resin group, the anticontraction effect worked only at the early postoperative stage. At 4 years of age, the narrowest intercanine width due to segment rotation caused by medial shift of the cleft side canine point and lateral shift of the cleft side tuberosity point was observed. As a result, a V-shaped dental arch developed. In the PB titanium group, the widest intercanine width due to a rigid anticontraction effect was observed at 4 years of age. Three push back methods demonstrated different arch morphologies due to each rigidity of the plate.

Chewing ability of subjects with shortened dental arches

OBJECTIVES

The objective was to study chewing ability in subjects with shortened dental arches in Tanzania.

METHODS

A sample of 725 adults with shortened dental arches comprising intact anterior regions and 0-8 occluding pairs of posterior teeth and 125 adults with complete dental arches were recruited. Subjects were classified into nine categories according to arch length and symmetry. Chewing ability was investigated by interview on chewing complaints and on perceived difficulty of chewing 20 common Tanzanian foods, 12 soft, and 8 hard.

RESULTS

Categories with extreme shortened arches (0-2 pairs of occluding premolars) reported most frequent (95-98%) and most severe complaints ('cannot chew all foods' or 'have to use special or specially prepared food'). Categories with intact premolar regions and at least one occluding pair of molars had nearly no complaints (95-97%). The other arch categories had an intermediate volume of complaints (33-54%). Perceived difficulty of chewing deteriorated with a decrease of occluding pairs of teeth. Subjects with 0-2 pairs of occluding premolars had major difficulties with chewing. Subjects with 3-4 pairs of occluding premolars or asymmetric arches comprising a short side with none or one pair of premolars and a long side including at least one occluding pair of molars had more difficulties with chewing compared to subjects with more complete dental arches. As a whole, they perceived for hard foods, 'minor problems, not adapted'.

CONCLUSIONS

Shortened dental arches with intact premolar regions and at least one occluding pair of molars provide sufficient chewing ability. Shortened arches with 3-4 pairs of occluding premolars and asymmetric arches with a long side result in impairment of chewing ability, especially for hard foods. In extremely shortened arches comprising 0-2 occluding premolars, chewing ability is severely impaired.

Rehabilitation of occlusal support by removable partial dentures with free-end saddles

This study aimed to assess the level of restored occlusal support by removable partial dentures with free-end saddles. The maximal clenching force of 61 subjects was measured using pressure sensitive film with and without their dentures. The restored level of occlusal support was estimated from the shift of the occlusal load centre. In comparison with previous results of experimental occlusions using splints for eight normal dentate subjects, the restored level using dentures ranged from 40-60% of that of natural teeth. The analysis of the shift of the occlusal load centre could reasonably evaluate the prostheses from the standpoint of occlusal support.

Occlusal and TMJ loads in subjects with experimentally shortened dental arches

To determine whether shortened dental arches (SDAs) cause functional overloading of the teeth and the temporomandibular joints, which has been implicated in periodontal diseases and temporomandibular disorders, we investigated the influences of SDA on occlusal and joint loads. Bite force and masticatory muscle electromyograms were recorded in five dentate subjects who clenched maximally on intra-oral appliances, creating symmetrical SDAs experimentally. Muscular forces estimated from the recorded electromyograms were fed into a finite element jaw model for calculating bite forces and joint loads. Comparison between the measured and the calculated bite forces ensured that the joint loads were representative. The bite force on each tooth increased with missing molar occlusions, while joint loads decreased. The bite force per root surface area was always greatest on the most posterior tooth, and these values were most constant. The findings provide no evidence that SDA causes overloading of the joints and the teeth, which suggests that neuromuscular regulatory systems are controlling maximum clenching strength under various occlusal conditions.

A study on occlusal stability in shortened dental arches

PURPOSE

The aim of this study was to verify the hypothesis that shortened dental arches constitute a risk to occlusal stability.

MATERIALS AND METHODS

Using cluster samples, 725 subjects with shortened dental arches comprising intact anterior regions and zero to eight occluding pairs of posterior teeth and 125 subjects with complete dental arches were selected. Subjects with shortened dental arches were classified into eight categories according to arch length and symmetry. Parameters for occlusal stability were interdental spacing, occlusal tooth wear, occlusal contact of incisors in intercuspal position, and vertical and horizontal overlap. Additionally, tooth mobility and overeruption of unopposed teeth were assessed. Influence of independent variables (dental arch category, age, gender, and residence) on the parameters for occlusal stability was assessed by one-way ANOVA and Tukey's multiple range tests.

RESULTS

Extreme shortened dental arches (zero to two pairs of occluding premolars) had significantly more interdental spacing, occlusal contact of incisors, and vertical overlap compared to complete dental arches. Occlusal wear and prevalence of mobile teeth were highest in these categories. The category with three to four occluding premolars had significantly more interdental spacing and, for the older age group, more anterior teeth in occlusal contact compared to complete dental arches. Age was consistently associated with increased changes in occlusal integrity.

CONCLUSION

Signs of increased risk to occlusal stability seemed to occur in extreme shortened dental arches, whereas no such evidence was found for intermediate categories of shortened dental arches.

The effects of overjet on dentoalveolar compensation

The purpose of this study was to investigate the relationship between overjet and dentoalveolar compensation in different overjet patterns. The lateral cephalometric head films of 80 untreated subjects (40 males and 40 females) aged 13-15 years were divided into four groups based on a normal, edge-to-edge, negative, or positive overjet. Seven linear and eight angular cephalometric measurements were used to assess dentoalveolar compensation in the different overjet patterns, and the differences between the groups and between genders were assessed by means of analysis of variance and the least significant difference (LSD) test. In addition, correlation coefficients between overjet and other variables were calculated. The results showed that there were statistically significant differences in measurements of MxAABH (mm), MxPABH (mm), and angles 1-NA, 1-1, 1-SN, 1-SN, 1-MP, and SN-AB among the overjet groups. In addition, significant correlation coefficients were found between overjet and MxAABH (mm), 1-NA (mm), and angles 1-1, 1-SN, 1-SN, 1-MP, and SN-AB. The evaluation of dentoalveolar compensation in different overjet patterns may be useful in treatment planning and treatment success.

Risk factors for poor dental arch relationships in young children born with unilateral cleft lip and palate

To identify risk factors for poor dental arch relationships in children with unilateral cleft lip and palate in the United Kingdom, the authors performed a cross-sectional outcome study with retrospective data capture of treatment histories in children under the care of 44 cleft teams in the United Kingdom. The study sample comprised 238 children born with nonsyndromic complete unilateral cleft lip and palate between April 1, 1989, and March 31, 1991, who were between 5.0 and 7.7 years of age (mean age, 6.5 years) at the time of data collection. The Five-Year-Old Index was used to rank dental arch relationships from dental study models. Velopharyngeal insufficiency was assessed with the use of the Cleft Audit Protocol for Speech. An independent panel recorded surgical treatment histories from the clinical notes. There was no association between the technique and the timing of primary repair, the experience of the surgeon, or presurgical orthopedics and dental arch relationships. Secondary velopharyngeal surgery was independently associated with poor outcome (OR, 4.14; 95 percent CI, 1.6 to 10.7; p = 0.003). Primary nasal repair was protective (OR, 0.47; 95 percent CI, 0.23 to 0.93; p = 0.031) against poor dental arch relationships. Secondary velopharyngeal surgery and primary nasal repair were found to be independently associated with dental arch relationship outcomes in young children with unilateral cleft lip and palate in the United Kingdom.

[Treatment of crossbite with the quadhelix appliance and lower lingual arch to maintain constant lower intermolar width]

The quadhelix appliance is often recommended for the treatment of children with crossbite. It is characterized by high effectiveness, low cost and short treatment time. Its modification with asymmetric arms enables asymmetric expansion of the upper arch. However, no clinical studies confirming such action are known. During maxillary expansion the lower arch tends to follow the maxillary teeth by tipping laterally. This phenomenon hinders crossbite treatment. The aim of the present study was to evaluate the effect of asymmetric arms of the quadhelix appliance during treatment of crossbite and to assess the effectiveness of the lower lingual arch in maintaining lower intermolar width. The study group included 20 children with crossbite. The treatment procedure comprised slow maxillary expansion with the quadhelix appliance. A lower lingual arch activated 1 mm inwards was simultaneously used in order to prevent increase in the lower intermolar width through occlusal contacts. The maxillary intermolar widths were measured between the central fossae of the right and left first permanent upper molars. Mandibular intermolar widths were measured between medial buccal cusps. The mean increase in upper intermolar width was 4.1 mm. The mean change in the lower intermolar width was -0.1 mm and was statistically insignificant. Posterior crossbite was eliminated in 16 children (80%). In 20% of children an improvement (e.g. reduction of the number of teeth in crossbite) was noted. The subtraction sum of the upper and lower intermolar widths was -5.7 mm before treatment and -1.4 mm after treatment. The upper dental arch before treatment had an asymmetric shape in all subjects. The width of the more deficient side was 19.65 mm and the wider side measured 22.3 mm. This difference was statistically highly significant (p < 0.0001). After treatment, the width of the side where the shorter arm was used was 22 mm. The width of the opposite side was 23.7 mm. The difference was statistically significant (p < 0.003). The width of the palate increased on the average by 3.5 mm. The change in overbite was statistically insignificant, enabling safe application of this method in patients with crossbite and open vertical skeletal configuration. The length of the upper arch increased by 0.2 mm (p < 0.01). The average treatment time was 17 weeks, depending on the number of teeth in crossbite before treatment (Rs = 0.58; p < 0.007). Longer treatment times (6-7 months) were reported in other studies describing patients of the same age. The quadhelix with asymmetric lateral arms is recommended for the treatment of crossbite with an asymmetric upper dental arch. The simultaneous application of lower lingual arch prevents lower intermolar expansion, thus shortening the time of treatment.

[Biomechanical fundamentals of the dentofacial anomalies treatment]

The results of biomechanical investigations of the central incisor having the formed root by mathematical modeling methods are presented. The centre of resistance of a tooth, the optimal horizontal forces of action and reaction were determined. The advantage of discontinuous forces due to amortization influence of periodontal ligament fluid was biomechanically proven. The recommendations which were given after experiments and mathematical modelling were used during orthodontic treatment of 30 patients (12-18 years) with anomalies of dental arches and occlusions by mechanically acting appliances and combined ones. At the end of the treatment 90.0% of the patients had physiological teeth angulation, 93.3% had the physiological torque. However using the removable single-jaw mechanically acted appliances had not lead to improvement of the first Angle-Endruce's key in 50.0% of the patients and to elimination of gaps between teeth in 23.4% of the patients.

Maximum clenching force of patients with moderate loss of posterior tooth support: a pilot study

STATEMENT OF PROBLEM

Patients who have lost moderate posterior tooth support may also lose clenching force as a result of sensitivity to increased loading to the remaining teeth and possibly a loss of muscle strength, because clenching forces are limited to avoid stress to the remaining teeth. Few studies have correlated moderate posterior tooth loss with maximum clenching force.

PURPOSE

The purpose of this pilot study was to test the hypothesis that moderate loss of posterior tooth support will have a significant effect on maximum clenching force.

MATERIAL AND METHODS

The maximum clenching force of 44 adults, ages 28 to 76 (mean 46), with posterior tooth loss was compared with the maximum clenching force of a control group of 20 healthy full dentition adults, ages 18 to 55 (mean 30), by use of a bilateral strain-gauged transducer. The transducer consisted of 2 stainless steel plates separated by a steel sphere that balanced occlusal forces between right and left sides. Acrylic resin pads were fabricated for each patient to protect the cusps of the teeth. The overall accuracy was found to be within 2.3% of full scale over a range of 0 to 4000 N (0 to 900 lbs). The calibration reliability of the system was checked frequently by use of a dead weight of 222 N (50 lbs). Clenching forces were supported by first and second molars and second premolars when possible. The instrumentation, methods, and operator were the same for both groups. A 2-tailed Student t test (alpha=0.01) and a pooled estimate of the mean were used to determine possible statistical significance. To test for possible correlations between clenching force and lost tooth support and between clenching force and age, a linear regression correlation coefficient R was calculated.

RESULTS

For the 44 subjects with posterior tooth loss, the mean clenching force was 462 N (104 lbs), with a range of 98 to 1031 N (22 to 232 lbs). This compares with a mean of 720 N (162 lbs) with a range of 244 to 1243 N (55 to 280 lbs) for the full-dentition subjects. A 2-tailed t test showed that the average difference of 258 N (58 lbs) between the 2 groups was significant (P< or =.01). There was only a moderate negative association between clenching strength and loss of mandibular tooth support (R = -0.35). Clenching force was not well correlated with age as indicated by low R values (R = 0.21, missing tooth group and R = -0.03, full dentition group).

CONCLUSION

Within the limitations of this study the maximum clenching force was less (P< or =.01), by 258 N (58 lbs) on average, in subjects with moderate loss of posterior tooth support. Loss of maximum clenching force was associated with a modest negative correlation to the number of missing teeth in the mandibular arch (R = -0.35). The range of clenching force was surprisingly large for both the missing tooth (98 to 1031 N) and full dentition (244 to 1243 N) groups.

Effect of varying the force direction on maxillary orthopedic protraction

The aim of this study was to examine the effect of varying the force direction on maxillary protraction. A total of 20 patients with class III maxillary retrognathism were randomly divided into two groups. Group 1 was comprised of nine patients with a mean age of 8.58 years, and group 2 was composed of 11 patients with a mean age of 8.51 years. Both groups received a cap splint-type rapid palatal expander and the screw was activated twice a day for 10 days. After the expansion procedure the face mask protraction procedure was initiated. In group 1, we applied the force intraorally from the canine region with a forward and downward direction at a 30 degrees angle to the occlusal plane. In group 2, the force was applied extraorally 20 mm above the maxillary occlusal plane. In both groups a unilateral 500 g force was applied and the patients were instructed to wear the face mask for 16 h/d for the first three months and 12 h/d for the next three months. The Wilcoxon sign rank test was used to evaluate the effect of the two different face masks, and a Mann-Whitney U-test was carried out to evaluate the differences between the two groups. The results showed that both force systems were equally effective to protract the maxilla; however, in group I we observed that the maxilla advanced forward with a counter-clockwise rotation. In group 2 we observed an anterior translation of maxilla without rotation. The dental effects of both methods were also different. The maxillary occlusal plane did not rotate in group 1, in contrast to the clockwise rotation in group 2. The maxillary incisors were proclined slightly in group 1, but in contrast they were retroclined and extruded in group 2. In conclusion, the force application from near the center of resistance of the maxilla was an effective method to prevent the unwanted side effects, such as counter-clockwise rotation of the maxilla, in group 1. The group 2 results suggest that this method can be used effectively on patients who present as class III combined with an anterior open bite.

Dental arches and occlusion in bilateral cleft lip and palate patients after two different routines for palatal surgery

BACKGROUND

Delayed hard palate repair (DHPR) is believed by many researchers to improve maxillary growth and facial appearance in patients born with cleft lip and palate. However, only few studies dealing with the midfacial growth outcome after this type of surgery in bilateral cleft patients have been published.

PATIENTS AND METHOD

The purpose of this retrospective study was to compare long-term results of maxillary morphology, dental arches and occlusion in two groups of patients with bilateral cleft lip and palate. The palatal surgery differed between the two groups, particularly with respect to the timing of hard palate repair. The DHPR group (n = 16) underwent soft palate closure at 12 months and hard palate repair at around 8 years, whereas the early palatal repair group (EPR) (n = 12) had completed two-stage palatal closure during the first year of life. These latter subjects had undergone more traditional palatal surgery with vomer flaps for repair of the anterior part and push-back closure for the posterior part of the cleft. Surgery was performed in both groups by the same surgical team at Sahlgrenska University Hospital, Göteborg, Sweden. Dental casts were used to analyze the pre- and postoperative maxillary morphology, dental arch dimensions, and occlusion of both samples, which were followed longitudinally from infancy to early adulthood.

RESULTS

Differences recorded in both maxillary growth and occlusion were generally in favor of the DHPR group. However, major intragroup variations and relatively small sample sizes precluded statistical verification of the differences, except for development during the early stages.

Constriction of the maxillary dental arch by mucoperiosteal denudation of the palate

OBJECTIVE

This study examined the influence of two factors in the constriction of the maxillary dental arch by mucoperiosteal denudation of the palate: (1) inhibition of lateral growth and (2) medial inclination of teeth.

METHOD

Thirty-five male 20-day-old Wistar rats were divided into experimental and control groups. The experimental group had bilateral mucoperiosteum excised in the lateral one third of the palate. Methyl methacrylate resin-embedded frontal sections were prepared from both groups after alternate weekly injections of tetracycline and calcein in the dorsal subcutaneous area. The sections were observed and photographed under either a confocal laser scanning microscope, a fluorescence microscope, or both. Chronological changes in lateral palatal growth, maxillary dental arch width, and inclination of the upper first molars were examined up to 8 weeks after the operation. Paraffin-embedded frontal sections were also made and stained with Elastica van Gieson stain.

RESULTS

The scar tissue formed on the rat palate by the mucoperiosteal denudation was tightly connected to the palatal bone and teeth. The intervals between the labeling lines of the experimental group were less definite during the first 2 weeks after the operation. Increments of palatal and maxillary dental arch widths were smaller in the experimental group than in the control group. The upper first molars in the control group gradually inclined laterally, whereas those in the experimental group inclined medially with age.

CONCLUSION

Medial inclination of teeth is a stronger influence than inhibition of lateral growth on constriction of the rat maxillary dental arch.

Movement of teeth adjacent to posterior bounded edentulous spaces

Bounded edentulous spaces (BES)-a missing posterior tooth with intact adjacent teeth-are thought to lead to arch collapse resulting from the movement of adjacent teeth. To determine the rate of change in distance between teeth adjacent to a BES, we examined three successive measurable radiographs of 116 untreated posterior BES cases. The distance between the teeth (DBT) adjacent to the space was measured, and change in DBT (delta DBT) between pre-extraction and follow-up radiographs was calculated. We used linear spline regression to construct models for tooth movement and to identify factors associated with delta DBT. The mean delta DBT was < 1 mm during the first year post-extraction, and the DBT continued to decrease at a successively slower rate each following year. Overall and for each tooth type, the greatest rates of decrease in DBT were seen in the zero to two-year period. In a multivariable model, time since extraction and tooth type were significantly associated with delta DBT. These findings suggest that movement of teeth adjacent to a posterior BES after the first two years is usually gradual and minor within the time frame of this study.

Modal analysis of the maxillary dentition in cleft lip and palate patients before and after bone grafting

The aim of this study was to analyze the vibratory characteristics in the maxillary dentition of 4 cleft lip and palate (CLP) patients before and after bone grafting. First, the central incisor on the noncleft side was impacted with an impact hammer, and the responses were received using an acceleration sensor from the teeth between the upper first molars on both sides. The transfer functions were then obtained from each measurement point using a fast Fourier transform analyzer. Finally, a computer analysis and simulation were performed based on the measured transfer functions to obtain the natural frequency, modal shape, decay rate (DR) and maximum displacement (MDP). Before bone grafting, distinct phase differences between the major and minor dental arches (MDA and mDA) were observed in the modal shapes. After surgery, however, both the MDA and mDA vibrated in phase. These results were identical in all subjects. The MDPs of the central incisors conspicuously decreased after bone grafting in 3 subjects. From the standpoint of vibratory characteristics, this study indicated that bone grafting had a favorable effect on prosthodontic treatment using a fixed prosthesis across the cleft in CLP patients.

Severe dental open bite malocclusion with tongue reduction after orthodontic treatment

We treated a 21-year-old woman with a severe open bite and macroglossia with a standard edgewise appliance and without partial glossectomy. This was followed by retention using a Begg-type plate retainer for the upper dental arch and a fixed canine-to-canine for the lower arch. A crib was added to the upper plate retainer for suppression of a tongue thrust. The lower arch relapsed during the retention period, with a widening of the intermolar distance, flaring of the anterior teeth, and increased mobility of the teeth. We chose tongue reduction to resolve these problems and one-third of the middle dorsal part of the tongue was excised. After the tongue reduction, the patient experienced no functional problem in mastication, swallowing, and gustation, but she complained of mild speech difficulty and slight pain on the dorsal portion of her tongue. These symptoms disappeared 6 months after surgery. At this time, the mandibular dental arch was markedly improved. The flared lower dental arch had returned to an upright position and the tooth mobility reduced to normal. No appliance was used after surgery. Most of the recovery changes occurred within 4 months. This case highlights the importance of the teeth tending to move toward a balance between the tongue pressure from the inside and labio-buccal pressure from the outside.

A computer study of biodegradable plates for internal fixation of mandibular angle fractures

PURPOSE

This computer-based study was performed to determine the suitability of small biodegradable plate systems for mandibular angle fractures.

MATERIALS AND METHODS

In a 3-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. The angle fracture was fixed with 2 polylactide (PLA) midiplates or with 2 PLA maxiplates. The first plate was positioned buccally on the external oblique ridge. Two positions of the second plate were studied: halfway up the height of the mandible or on the lower border. Maximum fracture mobility was set at a limit of 150 microm to enable undisturbed fracture healing. Maximum plate strain was set at the yield strain of PLA.

RESULTS

Fixation with the PLA maxiplates, with the second plate positioned halfway up the height of the mandible, resulted in fracture mobility below the set limit for all bite points. For the other PLA fixation strategies, fracture mobility exceeded the set limit. Fixation with the second plate positioned halfway up the height of the mandible generally resulted in less fracture mobility than with the plate positioned on the lower border. The yield strain of PLA was not exceeded in any of the fixation strategies.

CONCLUSIONS

Based on the computer model, 2 PLA maxiplates are suitable for fixation of mandibular angle fractures. One plate should be positioned buccally on the external oblique ridge, and the other should be positioned halfway up the height of the mandible.

Characteristic forms of the upper part of the oral cavity in newborns with isolated cleft palate

OBJECTIVE

To determine the functional and morphological compensation of the lack of integrity in the upper part of the oral cavity in newborns with isolated cleft palate. Integrity of the upper part of the oral cavity is required for the effective pumping of amniotic fluid, the essential mode of nutrition in intrauterine life. The adaptation could be seen immediately after birth.

MATERIALS

Plaster casts of the upper part of the oral cavity in 60 newborns with isolated cleft palate of various extent and plaster casts of the upper part of the oral cavity in 27 newborns without cleft were used. A number of surface points were identified and used for a trigonometric morphological analysis.

RESULTS

The parameters of the upper part of the oral cavity in four groups of newborns with various extent of isolated cleft palate were compared with newborns without cleft palate. The results indicate a shift of the functional oral cavity into the nasal cavity and the pharynx, depending on the extent of the cleft.

CONCLUSION

The pumping activity of the tongue forms the upper part of the oral cavity and consequently the tongue moves into the nasal cavity and pharynx, depending on the extent of the cleft. In this way, effective pumping of amniotic fluid is possible despite the cleft. This is of vital importance for the fetus during intrauterine life. A poorly passable or even unpassable respiratory way is only of secondary importance during that time.

Occlusal stability in shortened dental arches

Shortened dental arches consisting of anterior and premolar teeth have been shown to meet oral functional demands. However, the occlusal stability may be at risk as a result of tooth migration. The aim of this nine-year study was to investigate occlusal stability in shortened dental arches as a function over time. Occlusal stability indicators were: 'interdental spacing', 'occlusal contacts of anterior teeth in Intercuspal Position', 'overbite', 'occlusal tooth wear', and 'alveolar bone support'. Subjects with shortened dental arches (n = 74) were compared with subjects with complete dental arches (controls, n = 72). Repeated-measurement regression analyses were applied to assess age-dependent variables in the controls and to relate the occlusal changes to the period of time since the treatment that led to the shortened dental arches. Compared with complete dental arches, shortened dental arches had similar overbite and occlusal tooth wear. They showed more interdental spacing in the premolar regions, more anterior teeth in occlusal contact, and lower alveolar bone scores. Since the differences remained constant over time, we conclude that shortened dental arches can provide long-term occlusal stability. Occlusal changes were self-limiting, indicating a new occlusal equilibrium.

The consequences of not replacing a missing posterior tooth

BACKGROUND

Failure to replace a missing posterior tooth is assumed to result in host of adverse consequences, which include shifting of teeth and loss of alveolar bone support.

METHODS

A retrospective longitudinal study (median follow-up period 6.9 years), using the radiographs of 111 patients who had an untreated bounded edentulous space, or BES, was conducted to determine the extent to which these adverse outcomes occurred.

RESULTS

The majority of patients lost 1 millimeter or less of the distance between teeth adjacent to the space, extrusion of the opposing tooth was < or = 1 mm in 99 percent of the cases, and the amount of alveolar bone loss next to the adjacent teeth was < or = 1 mm in 83 percent of the cases.

CONCLUSIONS

Within the follow-up time in this study, this group of patients did not exhibit the expected adverse consequences with either the frequency or severity generally assumed to be associated with nonreplacement of a single posterior tooth.

CLINICAL IMPLICATIONS

These findings suggest that for the large majority of patients who experience a single-tooth posterior BES, immediate treatment may not be critical to the maintenance of arch stability. Instead, regular follow-up assessments to monitor change in stability and periodontal health may be warranted.