The right upper first molars of 25 twelve-week-old male Wistar anaesthetized rats were loaded with forces in order to be moved mesially. Constant forces for 4 hours of 0.25 and 0.5 N were applied in five animals each. Furthermore, constant forces for 2 hours of 0.1 N were applied in 10 animals and afterwards, the first and second molars were permanently separated with composite. In these animals, the antagonists were sliced and five rats were killed after 1 day and five after 2 days. As a last experiment, intermittent forces of 0.1 N and 0.25 Hz were applied in five different animals for 4 hours. The untreated contralateral sides served as the control. Paraffin-embedded sections were analysed by immunohistochemistry for proliferating cell nuclear antigen (PCNA), runt-related transcription factor 2 (Runx2/Cbfa1), and phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2). Statistical analysis to determine differences between the groups was carried out using a Student's t-test.

In selected areas under tension, the proportion of pERK1/2-positive cells was increased compared with those in control teeth under all types of loading, whereas these proportions in selected areas under pressure were increased only after the application of intermittent forces. In representative areas, both under tension and pressure, the proportion of Runx2-positive cells decreased after the application of constant forces. After the application of constant forces for 4 hours in representative areas, both under tension and pressure, the proportion of PCNA-positive cells was lower than those in control teeth.

The involvement of pERK1/2, Runx2/cbfa-1, and PCNA in the reaction of PDL cells to different load regimens was verified.

A nickel-titanium (Ni-Ti) closed coil spring delivering a force of 10 g was inserted between the upper anterior alveolar bone and the first molar in 8-week-old male C57BL/6 mice. Bisphosphonate (2 µg/20 µl) was injected daily into a local site adjacent to the upper molar. After 12 days, the distance the tooth had moved was measured. The number of tartrate-resistant acid phosphatase (TRAP)-positive cells was counted as osteoclasts in histological sections. Root resorption was assessed by scanning electron microscopy. The data were analysed with a Student's t-test.

The orthodontic appliance increased the number of osteoclasts on the pressure side and mesial movement of the first molar. Bisphosphonates reduced the amount of tooth movement and the number of osteoclasts. In addition, they also reduced root resorption on the pressure side.

Bisphosphonates inhibit orthodontic tooth movement and prevent root resorption during orthodontic tooth movement in mice. These results suggest that bisphosphonates might have an inhibiting effect on root resorption during orthodontic tooth movement in humans and that they may interrupt tooth movement in orthodontic patients undergoing treatment, thus altering the outcome of treatment.

The dental casts and lateral cephalometric radiographs of 301 Croatian subjects (127 males and 174 females, mean age 16.86 ± 2.93 years) were selected from a larger sample of records of the archives of the Orthodontic Department, School of Dental Medicine, University of Zagreb, Croatia. The subjects were from malocclusion groups according to Angle classification, with the corresponding skeletal characteristics. The MD dimensions of all teeth from first molar to first molar were measured on the dental casts using digital callipers. Statistical analysis was undertaken using Kolmogorov–Smirnov, t, and Scheffé's tests and one-way analysis of variance.

A statistically significant gender difference was found in anterior ratio (P = 0.017). A significant difference in the overall and posterior ratio was observed between Class II and Class III subjects. There was a tendency for mandibular tooth size excess in subjects with an Angle Class III malocclusion and for maxillary tooth size excess in those with an Angle Class II malocclusion. The percentage of subjects more than 2 standard deviations from Bolton's means for anterior and overall ratios was 16.28 and 4.32, respectively.

The lingually inclined, crowded lateral incisor presented an extrusive and buccal movement and showed the lowest force in the vertical direction, whereas the self-ligating group of brackets generated the highest force in the buccolingual direction. The moments applied by the three bracket systems followed the general trend shown for forces; in the vertical axis, the self-ligating brackets exerted lower forces than their conventional counterpart. This was modified in the buccolingual direction where, in most instances, the self-ligating appliances applied higher moments compared with the conventional bracket. In most cases, the magnitude of forces and moments ranged between 30–70 cN and 2–6 N mm, respectively. However, maximum forces and moments developed at the lateral incisor were almost four times higher than the average.

This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions.

Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.

Anterior coronoid marginal depth correlated negatively (r = 0.71) with gonial angle, SNA, and overjet. The coronoid angle also correlated negatively (r = 0.86) with both the vertical and horizontal lengths from sella to the coronoid tip as well as with the horizontal length from sella to the posterior ramus margin. Furthermore, the coronoid length correlated positively (r = 0.61) with the coronoid angle and the anterior coronoid marginal depth. The coronoid width was also positively (r = 0.69) correlated with overbite.

Coronoid process morphology is related not only to mandibular morphology and position but also to maxillary position and the dental relationship in the anterior region. It therefore seems clear that coronoid process morphology might be related to temporal muscle functioning and its associated craniofacial morphological measurements.

The experimental connector is easily constructed, inexpensive, and small enough for use as an intraoral MAS. To evaluate durability, the axial and diagonal tensile breaking strengths of the MAS, using high- or low-density polyethylene (HDPE or LDPE) lateral toothed belts, were compared with those of a conventional mobile MAS (Silensor). The values were compared by factorial analysis of variances and post hoc Scheffe's S multiple comparison intervals, with the value of statistical significance set at alpha = 0.05. In addition, the experimental LDPE connectors were clinically tested in 30 patients (23 males and 7 females aged 19–71 years) and evaluated.

Compared with the Silensor, the experimental MAS exhibited sufficient breaking strength, especially when a diagonal tensile load was applied to mimic mandibular lateral translation. When examining the clinical evaluation between 3 and 4 months after insertion, no damage or failure was observed.

The experimental connecting system may have clinical applications. To make the connector stronger for clinical use, HDPE should be used.

Five identical appliances were manufactured from three different materials all with a thickness of 1.0 mm (Ideal Clear®, Erkodur®, and Biolon®). For measuring the forces, an isolated measuring tooth, as part of a standardized resin model incorporated in a newly developed measuring device, was tipped in nine arc minute ( degree) steps, from 0 to degrees in the vestibular and palatal directions around a rotational axis through the virtual apex, after positioning an appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of ±0.151 mm from the incisor edge were determined. Means and standard deviations (SDs) were calculated. The Kruskal–Wallis test for overall effects and the Wilcoxon two-sample test for individual group pairings were used (P < 0.05 significance level).

The mean Fx forces ranged from –2.82 N (SD 0.62) to 5.42 N (SD 0.56). The mean Fz forces were between –0.14 N (SD 0.52) and –2.3 N (SD 0.43). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the Biolon® appliance were found to be much greater (P < 0.01) than those of the other materials.

The forces delivered by the materials investigated were mostly higher than those stated in the literature.

Single or multiple hypodontia was diagnosed in 137 patients (6.5 per cent), 62 males and 75 females. One or more supernumerary teeth were found in 42 patients (2 per cent), 22 males and 20 females. CHH was diagnosed in seven subjects (0.33 per cent), four males and three females. In the CHH subpopulation, the total number of absent and supernumerary teeth was nine and eight, respectively. Hypodontia always occurred in the permanent dentition and was more frequent in the mandible than in the maxilla (four versus three teeth). Supernumerary teeth were more frequent in the permanent than in the primary dentition (six versus two teeth). Five supernumeraries were located in the maxilla and three in the mandible.

Bleeding on probing (BOP), plaque index (PI), and pocket probing depth (PPD) were measured in 10 adults (8 females and 2 males, aged 29.0 ± 4.7 years) who received treatment with custom-made lingual appliances (Incognito/iBraces) before (T₀) and 3 months after beginning of treatment (T₁). No supportive dental prophylaxis was undertaken. In addition, a 16S rRNA-based polymerase chain reaction (PCR) method was used to detect Aggregatibacter actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) in the crevicular fluid. A Wilcoxon test was used to compare clinical parameters at the buccal (control) and lingual sites between T₀ and T₁.

At T₀, BOP was 12.4 ± 8.2 per cent, PPD 2.1 ± 0.3 mm, and PI 0.1 ± 0.2 at the buccal sites and at T₁ 14.3 ± 8.1 per cent, 2.1 ± 0.2 mm and 0.1 ± 0.2, respectively. At the lingual sites, BOP was 22.2 ± 19.0 per cent, PPD 2.3 ± 0.3 mm, and PI 0.1 ± 0.2 at T₀ and at T₁ 56.2 ± 31.6 per cent, 2.9 ± 0.3 mm, and 1.2 ± 1.1, respectively. Differences between T₀ and T₁ were significant for clinical parameters only at the lingual sites. Aa was found in five patients at baseline and in four at T₁, whereas Pg was found in one patient at T₀ and in two at T₁.

Insertion of fixed lingual appliances without supportive dental prophylaxis induced a worsening of clinical parameters restricted to the lingual sites, whereas the relative prevalence of Aa and Pg remained unchanged.

One-way analysis of variance showed a significant effect of ligation mode on the frictional properties of the three-bracket set-ups (P < 0.001). Post hoc pairwise comparison showed that the frictional forces arising from passive self-ligation were significantly lower (P < 0.01) than those resulting from elastic ligation. The same result was achieved when comparing self-ligation and metallic ligation (P < 0.01). No significant difference was found when comparing elastic and metallic ligation.

Little or no microleakage was observed between the composite–enamel interfaces for the three investigated composites, and any difference was not statistically significant. However, statistically significant differences were found between microleakage at the composite–wire interface for both the conventional and flowable composite groups (P < 0.001). Flowable composite showed the highest leakage (mean: 4.8 ± 0.8 mm), while Transbond XT (mean: 0.5 ± 0.3 mm) and Transbond LR (mean: 1.1 ± 1.2 mm) showed significantly lower and comparable results. The amount of microleakage at the wire–composite interface was significantly greater than that at the enamel–composite interface of flexible spiral wire retainers (FSWRs). The null hypothesis is therefore rejected. Flowable composites may not be appropriate for bonding FSWRs.

Little or no microleakage was observed between the composite–enamel interface for any of the three groups, and any difference was not statistically significant. The amount of microleakage at the wire–composite interface was higher than that at the enamel–composite interface. Multiple comparison testing showed statistically significant differences in microleakage between Transbond LR and the ACP-containing adhesive used with primer at the composite–enamel and composite–wire interfaces (P < 0.001). ACP-containing adhesive used with primer showed the highest microleakage scores at the composite–enamel (mean: 0.39 ± 0.42 mm) and composite–wire (mean: 1.66 ± 0.47 mm) interfaces. The hypothesis is rejected. The ACP-containing composite used with or without primer showed significantly higher leakage at the composite–wire interface, while conventional lingual retainer composite showed lower microleakage scores.

Statistical analysis showed that the bond strengths of the control (Transbond LR, mean: 24.77 ± 9.25 MPa) and Clearfil Protect Bond with etching, (mean: 20.24 ± 8.5 MPa) were significantly higher than Clearfil Protect Bond without etching, (mean: 12.56 ± 6.93 MPa). In general, a greater percentage of the fractures were adhesive, at the tooth–composite interface (60–65 per cent). No statistically significant difference was found among the groups. The hypothesis is thus rejected. Within the limits of this in vitro model, antibacterial monomer-containing self-etch adhesive with acid etching did not significantly affect shear bond strength when compared with the control. However, the same adhesive used without acid etching resulted in a significant decrease in bond strength.