The lateral leeway in the habitual intercuspation: experimental studies and literature review

Distribution patterns of occlusal contact areas on natural posterior teeth - Evaluations of a cross-sectional population-based study with the Greifswald Digital Analyzing System (GEDAS)

AIM

The aim of our investigations is to optimize the anatomical basis for the design of a sufficient occlusal relationship, especially in view of the innovative technologies by analyzing the occlusal contact point patterns at cusp structures according to A-, B-, C- localization tooth by tooth on the individual occlusal surfaces in the posterior region in static habitual occlusal position.

MATERIALS AND METHODS

In 3300 subjects of the population-based Study of Health in Pomerania (SHIP 1) the interocclusal registration in habitual intercuspation using silicone registration was used and analyzed by using the special evaluation software Greifswald Digital Analyzing System (GEDAS II). Chi square test was used to investigate whether the distribution of contact areas differed in the group of premolars or molars - each considered separately for maxilla and mandible - on the basis of the probability of error p < 0.05.

RESULTS

In 709 subjects (446 male with a mean age of 48.9 ± 13.04 years; 283 female with a mean age of 52.4 ± 14.23 years) the antagonistic situation was specifically considered on natural posterior teeth without conservative or restorative-prosthetic interventions, i.e. without caries, fillings, crowns or other restorations. On the basis of these subjects, the silicone registrations were analyzed using GEDAS II. For the first and second upper molars, the ABC contact distribution was the most frequent: 20.4 % for the first and 15.3 % for the second molar. The second most frequent contact area for maxillary molars was area 0. The upper molars had contact areas only at the maxillary palatal cusp (B-/C-contacts). This contact relationship was most frequent in the maxillary premolar (18.1-18.6 %). In mandibular premolars, with the buccal cusps areas A and B were frequently involved (15.4-16.7 %). Mandibular molars showed a frequent contact pattern involving all A-, B-, C- and 0- contact areas (13.3-24.2 %). To capture the possible influence of the antagonistic dentition situation, the antagonistic situation was specifically considered and except for the mandibular premolars (p < 0.05) the contact distribution did not differ for molars and maxillary premolars regarding the dental status of the antagonistic teeth. Natural posterior teeth without occlusal contacts were observed from 20.0 % in the second lower molars to 9.7 % in the first upper molars.

CONCLUSION

Our results suggest a clinically relevant due to the fact, that this study is the first population-based epidemiological study to analyze the occlusal contact point patterns at cusp structures according to A-, B-, C- localization tooth by tooth on the individual occlusal surfaces in the posterior region in static habitual occlusal position in order to optimize the anatomical basis for the design of a sufficient occlusal relationship.

Smile Design: Mechanical Considerations

Smile designing refers to the cosmetic and esthetic dental reconstruction that is visible during smiling. The use of modern digital tools requires adequate knowledge about the tooth shape and shade principles. Mechanical, biological, and psychological factors should be understood and tailor an individualized treatment accordingly to achieve pleasing esthetic outcomes. Dental therapy is becoming more appearance-driven, and thus, both patients and dental clinicians mainly emphasize on cosmetic dental and facial aspects of treatments.

Class II correction by maxillary en masse distalization using a completely customized lingual appliance and a novel mini-screw anchorage concept - preliminary results

Background

The aim of the study was to evaluate the efficacy of a novel en masse distalization method in the maxillary arch in combination with a completely customized lingual appliance (CCLA; WIN, DW Lingual Systems, Germany). Therefore, we tested the null-hypothesis of a significant deviation from an Angle-Class I canine relationship and a normal overjet defined by an individual target set-up after dentoalveolar compensation in Angle Class II subjects.

Methods

This retrospective study included 23 patients, (m/f 3/20, mean age 29.6 years (min/max, 13.6/50.9 years)), with inclusion criteria of an Angle Class II occlusion of more than half a cusp prior to en masse distalization and treatment completed consecutively with a CCLA in combination with a mini-screw (MS) anchorage for uni- or bilateral maxillary distalization (12 bilateral situations, totalling 35). Plaster casts taken prior to (T0) and following CCLA treatment (T3) were compared with the treatment plan / set-up (TxP, with a Class I canine relationship and a normal overjet as the treatment objective). MSs were placed following levelling and aligning (T1) and removed at the end of en masse distalization at T2. Statistical analysis was carried out using Schuirmann’s TOST [two one-sided tests] equivalence test, based on a one-sample t-test with α = 0.025 on each side (total α = 0.05).

Results

Ninety-seven percent of planned correction of the canine relationship was achieved (mean 3.6 of 3.7 mm) and also 97 % of the planned overjet correction (mean 3.1 of 3.2 mm), with a statistically significant equivalence (p < 0.0001) for canine relationship and overjet between the individual treatment plan (set-up) and the final outcome. Adverse effects were limited to the loss of n = 2 of 35 mini-screws. However, in each instance, the treatment was completed, as scheduled, without replacing them. Accordingly, the null-hypothesis was rejected.

Conclusions

The technique presented allows for a predictable correction of an Angle-Class II malocclusion via dentoalveolar compensation with maxillary en masse distalization.

Effects of preventing intercuspation on the precision of jaw movements

BACKGROUND

Closing movements are among the jaw's basic physiological motor actions. During functional movements, the jaw changes position continually, which requires appropriate proprioception. However, the significance of the various proprioceptive receptors involved and how they interact is not yet fully clear.

OBJECTIVES

This study's main objective was to test whether preventing intercuspation (IC) for 1 week would affect the precision of jaw-closing movements into IC and the functional space of habitual chewing movements (HCM). A secondary objective was to compare precision of jaw-closing movements into IC with the precision of movements into a target position (TP) far from IC.

METHODS

Fourteen participants' HCM and jaw-closing movements into IC were recorded on two sessions (T1 and T2) 1 week apart. Between sessions, participants wore posterior bite plates to prevent IC. They also received a 10-minute training session at T1 to guide their jaw-closing movements into TP. The precision of the closing movements into IC and TP was analysed. For HCM, the vertical amplitude, lateral width and area of chewing cycles were evaluated.

RESULTS

The precision of jaw movements into IC increased as the jaw gap decreased, but precision did not differ significantly between T1 and T2. For HCM, the vertical amplitude and area of chewing cycles increased significantly between T1 and T2. The precision of the closing trajectory into TP increased significantly during the training session.

CONCLUSION

Our results confirm the excellent adaptability of the craniomandibular system, controlled by stringent motor programmes that are supported by continuous peripheral sensory input.

Accuracy of Buccal Scan Procedures for the Registration of Habitual Intercuspation

Clinical Relevance:

Accurate reproduction of the jaw relationship is important in many fields of dentistry. Maximum intercuspation can be registered with digital buccal scan procedures implemented in the workflow of many intraoral scanning systems.

Objective:

The aim of this study was to investigate the accuracy of buccal scan procedures with intraoral scanning devices for the registration of habitual intercuspation in vivo. The hypothesis was that there is no statistically significant difference for buccal scan procedures compared to registration methods with poured model casts.

Methods and Materials:

Ten individuals (full dentition, no dental rehabilitations) were subjects for five different habitual intercuspation registration methods: (CI) poured model casts, manual hand registration, buccal scan with inEOS X5; (BC) intraoral scan, buccal scan with CEREC Bluecam; (OC4.2) intraoral scan, buccal scan with CEREC Omnicam software version 4.2; (OC4.5β) intraoral scan, buccal scan with CEREC Omnicam version 4.5β; and (TR) intraoral scan, buccal scan with Trios 3. Buccal scan was repeated three times. Analysis of rotation (Rot) and translation (Trans) parameters was performed with difference analysis software (OraCheck). Statistical analysis was performed with one-way analysis of variance and the post hoc Scheffé test (p&lt;0.05).

Results:

Statistical analysis showed no significant (p&gt;0.05) differences in terms of translation between groups CI_Trans (98.74±112.01 μm), BC_Trans (84.12±64.95 μm), OC4.2_Trans (60.70±35.08 μm), OC4.5β_Trans (68.36±36.67 μm), and TR_Trans (66.60±64.39 μm). For rotation, there were no significant differences (p&gt;0.05) for groups CI_Rot (0.23±0.25°), BC_Rot (0.73±0.52°), OC4.2_Rot (0.45±0.31°), OC4.5β_Rot (0.50±0.36°), and TR_Rot (0.47±0.65°).

Conclusions:

Intraoral scanning devices allow the reproduction of the static relationship of the maxillary and mandibular teeth with the same accuracy as registration methods with poured model casts.

Conservative interdisciplinary treatment of a case with multiple facial and condyle fractures

The purpose of this case report is to describe an interdisciplinary approach for a 51-year-old male who underwent multiple facial fractures including bilateral condyle fractures. The patient underwent emergency surgery, which included open reduction of the maxilla and mandibular symphysis and closed reduction of the bilateral condyle fractures. Although the patient recovered a comfortable range of mouth opening and alleviation of the temporomandibular joint (TMJ) symptoms after surgery, he suffered from a large anterior-posterior discrepancy due to less stability on the condyle-fossa relationships and from open bite with contacts only on both second molars and right second premolars. In this case, first, to increase the occlusal contact, comprehensive orthodontic treatment was completed. Second, occlusal equilibration was selectively performed to relieve the interferences and establish a stable range of mandibular movement without any changes in the vertical dimension. Third, both the upper central incisors and left lateral incisor were minimally restored with splinted and single zirconia crowns, which had modified lingual contours to provide adequate anterior guidance permitting the anterior-posterior discrepancy of the posterior teeth during protrusion. This conservative interdisciplinary treatment, including open and closed reduction, orthodontic treatment, occlusal adjustment, and minimal prosthetic restorations, resulted in a stable mandibular position and recovery of mastication function.

Intraoperative condyle positioning by sonographic monitoring in orthognathic surgery verified by MRI

OBJECTIVE

Repositioning of the jaw in orthognathic surgery must produce precise and stable long-term results; an effective and practical method of intraoperative condyle positioning is required to achieve this. Most traditional methods, such as manual positioning or positioning plates do not permit intraoperative monitoring of the temporomandibular joint (TMJ) position. This study evaluates the results of intraoperative, sonographically-monitored joint positioning, comparing preoperative and postoperative MRI scans.

PATIENTS AND METHODS

Of the 97 patients who were originally assessed (53 female, average age 29 ± 10.93; and 44 male, average age 28 ± 9.25), 21 had incomplete data sets and were excluded, leaving 76 evaluable patients. MRIs were performed preoperatively between 2 days and 100 weeks (median 30.5 days), and postoperatively between 12 and 96 weeks (median 150 days). Condyle positioning, intercondylar distance, and disc degeneration and dislocation were compared in preoperative and postoperative MRIs, and differentiated by Angle class on horizontal, axial and sagittal scans. Condyle to fossa distances were measured on parasagittal images from 0° (the vertical sagittal plane), 45° anteriorly and 45° posteriorly. The intercondylar distances between the condylar head midpoints were measured on axial sections. Two-sided t-tests (α < 0.05) were used for comparisons within classes; the interclass correlation was performed using univariate ANOVA and linear correlation for paired sample correlation settings.

RESULTS

In 27 Angle class II cases, the anterior distance of both condyles increased on average 0.3 ± 1.0 mm, the posterior position decreased 0.1 ± 1.2 mm, and the vertical position decreased 0.2 ± 1.1 mm postoperatively. In 47 Angle class III cases the anterior distance of both condyles increased on average 0.3 ± 0.8 mm, the posterior 0.1 ± 0.8 mm and the vertical distance 0.1 ± 0.8 mm postoperatively. All alterations of the condyle-fossa relation were non-significant except for the anterior distance in Angle class ІІІ (p = 0.02). Alterations of the disc position and disc degeneration were non-significant in class II. In class ІІІ, the disc degeneration deteriorated slightly on the left side (p = 0.02). Intercondylar distance increased 1 ± 5.5 mm in class ІІ and decreased by 1 ± 5.5 mm in class ІІІ postoperatively, alterations were non-significant.

CONCLUSION

Sonography is a non-invasive, comfortable, fast, economical and effective intraoperative method of condyle positioning. The results of the present study support this statement because the degree of disc degeneration and luxation remained unaltered and the condyle position did not change significantly. Prospective randomized comparison to manual positioning is in preparation and will be conducted in the near future.

Reproducibility of habitual intercuspation in vivo

OBJECTIVES

The aim of this in vivo study was to investigate how reproducible individuals find their habitual intercuspation.

METHODS

A new type of highly accurate measuring procedure was involved using an intraoral optical scanning device (Cerec Bluecam). First, a pilot test investigated the accuracy of the procedure within a standardized setting. With regard to the in vivo study, fifteen participants with full dentition were selected. For each of these individuals, eight scans were taken both in the morning and in the afternoon. Furthermore, during each session, scans were taken both in horizontal and upright position. In order to compare this to ubiquitous used processes, plaster replicas of five individuals were investigated as well. The scans were analysed, and the differences in the position of the lower jaw were calculated by a specialized superimposition program (n=570 comparisons/OraCheck).

RESULTS

The results showed that there was no significant difference between the time of day and the position of the patient. The overall mean ± SD value for locating the habitual intercuspation was 42 ± 34 μm, however ranging from 22 ± 9 μm to 77 ± 58 μm for single individuals. On the other hand, the differences in positioning plaster replicas reached a mean of 135 ± 77 μm.

CONCLUSIONS

The reproducibility of the habitual intercuspation can be obtained under in vivo conditions by a newly developed and highly accurate measuring procedure. Individuals with full dentition show values in average of 42 μm.

CLINICAL SIGNIFICANCE

Determining the occlusal jaw relation is an important precondition in restorative dentistry and many methods are proposed for a proper occlusal registration. Although much is known about in vitro accuracy of these techniques, little is known how reproducible the habitual occlusal position itself is found between individuals.

Reproducibility of condyle position and influence of splint therapy on different registration techniques in asymptomatic volunteers

The current study aims to analyze and quantify the effects of different registration techniques on the reproducibility of condyle position and the influence of stabilization splint therapy on the technique's reproducibility. Three-dimensional electronic-condylar-position analysis (EPA) with an ultrasound-based jaw-tracking system was recorded during intermaxillary registration of manually guided centric relation (CR), maximal intercuspation (MI), and clenching-force-dependent Gothic arch tracing guided centric relation (DIR method) before (T0) and after (T1) splint therapy. Patients were supplied with a stabilization splint for three months on the basis of the DIR registration. Participants were 26 asymptomatic volunteers with a mean age of 30.6 +/- 9.5 years. The registration technique was found to have a significant (p = 0.001) effect on condylar displacement in all axes before, and in X- and Y-axes after splint therapy. Condyles during DIR were found to be in a more anterior-inferior position compared with CR and MI, with the condyles in the latter position being likewise more anterior than in CR. There were significant (p < 0.03) differences in reproducibility of the condyle position dependent on the technique, both at T0 and T1. The DIR method showed the highest reproducibility, followed by MI and CR. There was no significant effect of time of investigation on the technique's reproducibility.