Roberto Martina

Effect of Occlusal Interference on Habitual Activity of Human Masseter

It has been suggested that occlusal interference may increase habitual activity in the jaw muscles and may lead to temporomandibular disorders (TMD). We tested these hypotheses by means of a double-blind randomized crossover experiment carried out on 11 young healthy females. Strips of gold foil were glued either on a selected occlusal contact area (active interference) or on the vestibular surface of the same tooth (dummy interference) and left for 8 days each. Electromyographic masseter activity was recorded in the natural environment by portable recorders under interference-free, dummy-interference, and active-interference conditions. The active occlusal interference caused a significant reduction in the number of activity periods per hour and in their mean amplitude. The EMG activity did not change significantly during the dummy-interference condition. None of the subjects developed signs and/or symptoms of TMD throughout the whole study, and most of them adapted fairly well to the occlusal disturbance.

Mandibular rest position and electrical activity of the masticatory muscles.

STATEMENT OF PROBLEM The determination of a correct vertical dimension of occlusion is a critical procedure in clinical dentistry. PURPOSE The objectives of this study were to analyze the relation between mandibular rest position and electrical activity of masticatory muscles and to compare clinical and electromyographic rest position in subjects with different vertical facial morphologic features. MATERIAL AND METHODS Clinical rest position and electromyographic rest position were investigated in 40 subjects. Electromyographic rest position ranged from 0.4 to 12.7 mm (average 7.7 +/- 2.7 mm). Clinical rest position ranged from 0.1 to 4.4 mm (average 1.4 +/- 1.1 mm). The average difference between electromyographic rest position and clinical rest position was 6.3 +/- 2.5 mm (range 0.3 to 10.3 mm). Sixteen subjects were selected according to the Frankfort mandibular plane angle and separated in two groups having a mandibular plane angle > or = 28 degrees. RESULTS Rest position was significantly greater (p < 0.05) in the low-angle group (2 +/- 1.3 mm) than in the high angle group (0.8 +/- 0.8 mm). Electromyographic rest position did not differ between subjects with different facial morphologic features (8.1 +/- 1.7 mm low-angle group; 7.6 +/- 4.1 mm high angle group). By varying the vertical dimension millimeter by millimeter, masseter and anterior temporal electromyographic activity demonstrated a considerable decrease over an interocclusal distance of 3 to 4 mm. Further mandibular opening up to 18 mm corresponded to small changes in postural activity. CONCLUSION This study suggests that a jaw posture with a few millimeters of interocclusal distance involves a great reduction of masticatory muscle activity.

Postural stability and unilateral posterior crossbite : Is there a relationship?

The aim of this study was to test the hypothesis that unilateral posterior crossbite influences postural stability of the whole body. Twenty-six subjects (14 males and 12 females) affected with unilateral posterior crossbite were selected and compared with 52 controls matched for age and gender. Postural stability was assessed using a stabilometric platform. The following stabilometric measurements were assessed: weight distribution on foot area and speed of body sway. Tests were performed under two occlusal conditions: teeth in intercuspal position (ICP) and while keeping two cotton rolls between teeth without clenching. The weight distribution on foot area and the speed of body sway were not significantly influenced from crossbite (with and without lateral mandibular slide), occlusal conditions (ICP, cotton rolls), and gender. Therefore, the treatment of this malocclusion in order to prevent or to treat postural disorders is not justified.

Evaluation of surface roughness of orthodontic wires by means of atomic force microscopy

OBJECTIVE To compare the surface roughness of different orthodontic archwires. MATERIALS AND METHODS Four nickel-titanium wires (Sentalloy(®), Sentalloy(®) High Aesthetic, Titanium Memory ThermaTi Lite(®), and Titanium Memory Esthetic(®)), three β-titanium wires (TMA(®), Colored TMA(®), and Beta Titanium(®)), and one stainless-steel wire (Stainless Steel(®)) were considered for this study. Three samples for each wire were analyzed by atomic force microscopy (AFM). Three-dimensional images were processed using Gwiddion software, and the roughness average (Ra), the root mean square (Rms), and the maximum height (Mh) values of the scanned surface profile were recorded. Statistical analysis was performed by one-way analysis of variance (ANOVA) followed by Tukeys post hoc test (P < .05). RESULTS The Ra, Rms, and Mh values were expressed as the mean ± standard deviation. Among as-received archwires, the Stainless Steel (Ra  =  36.6 ± 5.8; Rms  =  48 ± 7.7; Mh  =  328.1 ± 64) archwire was less rough than the others (ANOVA, P < .05). The Sentalloy High Aesthetic was the roughest (Ra  =  133.5 ± 10.8; Rms  =  165.8 ± 9.8; Mh  =  949.6 ± 192.1) of the archwires. CONCLUSIONS The surface quality of the wires investigated differed significantly. Ion implantation effectively reduced the roughness of TMA. Moreover, Teflon(®)-coated Titanium Memory Esthetic was less rough than was ion-implanted Sentalloy High Aesthetic.

Efficacy of the Sander bite-jumping appliance in growing patients with mandibular retrusion: a randomized controlled trial

OBJECTIVES The efficacy of functional appliances remains highly debated. This randomized controlled trial investigated the skeletal and dentoalveolar effects determined by the Sander bite-jumping appliance (BJA). The null hypothesis to be tested was that the appliance would not induce supplementary mandibular growth compared to untreated controls. SETTING AND SAMPLE POPULATION This study was carried out at the Section of Orthodontics, University of Naples Federico II, Italy. Forty-six patients receiving a clinical diagnosis of skeletal and dental class II due to mandibular retrusion were either allocated to a treatment (23 patients;15 boys, 8 girls; mean age ± SD: 10.9 ± 1.3 years) or to an untreated control group (23 patients;11 boys, 12 girls; mean age ± SD: 10.5 ± 1.2 years), by using a balanced block randomization. METHODS Lateral cephalograms were taken before and after treatment and used for comparisons. Measurements were analyzed by descriptive statistics, univariate and multivariate statistical tests. RESULTS Treated individuals had a significant increase in mandibular length (6.4 ± 2.3 vs. 3.5 ± 2.5 mm; p < 0.001), overjet reduction (-5.0 ± 2.9 vs. 0.3 ± 1.2 mm; p < 0.001) and molar relationship improvement (-5.3 ± 2.4 vs. 0.1 ± 1.1 mm; p < 0.001) compared to controls. The use of the appliance did not significantly affect jaw divergence. Proclination of lower incisors was slightly greater (3.0°, p = 0.023) in treated patients than in controls. The increase in mandibular length was not significantly influenced by cervical stage (p = 0.40). CONCLUSION The BJA can effectively correct class II malocclusions by a combination of dentoalveolar and skeletal effects. The long-term stability of the correction needs to be evaluated.

Unilateral Posterior Crossbite is Not Associated with TMJ Clicking in Young Adolescents

Unilateral posterior crossbite has been considered as a risk factor for temporomandibular joint clicking, with conflicting findings. The aim of this study was to investigate a possible association between unilateral posterior crossbite and temporomandibular disk displacement with reduction, by means of a survey carried out in young adolescents recruited from three schools. The sample included 1291 participants (708 males and 583 females) with a mean age of 12.3 yrs (range, 10.1–16.1 yrs), who underwent an orthodontic and functional examination performed by two independent examiners. Unilateral posterior crossbite was found in 157 participants (12.2%). Fifty-three participants (4.1%) were diagnosed as having disk displacement with reduction. Logistic regression analysis failed to reveal a significant association between unilateral posterior crossbite and disk displacement with reduction (odds ratio = 1.3; confidence limits = 0.6–2.9). Posterior unilateral crossbite does not appear to be a risk factor for temporomandibular joint clicking, at least in young adolescents.

Transverse changes determined by rapid and slow maxillary expansion – a low-dose CT-based randomized controlled trial

OBJECTIVES To compare transverse skeletal changes produced by rapid (RME) and slow (SME) maxillary expansion using low-dose computed tomography. The null hypothesis was that SME and RME are equally effective in producing skeletal maxillary expansion in patients with posterior crossbite. SETTING AND SAMPLE POPULATION This study was carried out at the Department of Oral Sciences, University of Naples Federico II, Italy. Twelve patients (seven males, five females, mean age ± SD: 10.3 ± 2.5 years) were allocated to the SME group and 14 patients (six males, eight females, mean age ± SD: 9.7 ± 1.5 years) to the RME group. MATERIALS AND METHODS All patients received a two-band palatal expander and were randomly allocated to either RME or SME. Low-dose computed tomography was used to identify skeletal and dental landmarks and to measure transverse maxillary changes with treatment. RESULTS A significant increase in skeletal transverse diameters was found in both SME and RME groups (anterior expansion = 2.2 ± 1.4 mm, posterior expansion = 2.2 ± 0.9 mm, pterygoid expansion = 0.9 ± 0.8 mm). No significant differences were found between groups at anterior (SME = 1.9 ± 1.3 mm; RME = 2.5 ± 1.5 mm) or posterior (SME = 1.9 ± 1.0 mm; RME = 2.4 ± 0.9 mm) locations, while a statistically significant difference was measured at the pterygoid processes (SME = 0.6 ± 0.6 mm; RME = 1.2 ± 0.9 mm, p = 0.04), which was not clinically relevant. CONCLUSION Rapid maxillary expansion is not more effective than SME in expanding the maxilla in patients with posterior crossbite.

Calorimetric and Thermomechanical Properties of Titanium-Based Orthodontic Wires: DSC–DMA Relationship to Predict the Elastic Modulus

Orthodontic treatment is strongly dependent on the loads developed by metal wires, and the choice of an orthodontic archwire should be based on its mechanical performance. The desire of both orthodontists and engineers would be to predict the mechanical behavior of archwires. To this aim, Gum Metal (Toyota Central R&L Labs., Inc.), TMA (ORMCO), 35°C Copper NiTi (SDS ORMCO), Thermalloy Plus (Rocky Mountain), Nitinol SE (3M Unitek), and NiTi (SDS ORMCO) were tested according to dynamic mechanical analysis and differential scanning calorimetry. A model was also developed to predict the elastic modulus of superelastic wires. Results from experimental tests have highlighted that superelastic wires are very sensitive to temperature variations occurring in the oral environment, while the proposed model seems to be reliable to predict the Young’s modulus allowing to correlate calorimetric and mechanical data. Furthermore, Gum Metal wire behaves as an elastic material with a very low Young’s modulus, and it can be particularly useful for the initial stage of orthodontic treatments.

Effects of orthopedic maxillary expansion on nasal cavity size in growing subjects: A low dose computer tomography clinical trial

OBJECTIVE The aim of this retrospective clinical trial was to evaluate the effects of rapid maxillary expansion on skeletal nasal cavity size in growing subjects by use of low dose computer tomography. METHODS Eight Caucasian children (three male; five female) with a mean age of 9.7 years (SD±1.41) were the final sample of this research that underwent palatal expansion as a first phase of orthodontic treatment. The maxillary expander was banded to the upper first molars and was activated according a rapid maxillary expansion protocol. Low-dose computer tomography examinations of maxilla and of the low portion of nasal cavity were performed before inserting the maxillary expander (T0) and at the end of retention (T1), 7 months later. A low-dose computer tomography protocol was applied during the exams. Image processing was achieved in 3 steps: reslicing; dental and skeletal measurements; skeletal nasal volume computing. A set of reproducible skeletal and dental landmarks were located in the coronal passing through the first upper right molar furcation. Using the landmarks, a set of transverse linear measurements were identified to estimate maximum nasal width and nasal floor width. To compute the nasal volume the lower portion of the nasal cavity was set as region of interest. Nasal volume was calculated using a set of coronal slices. In each coronal slice, the cortical bone of the nasal cavity was identified and selected with a segmentation technique. Dependent t-tests were used to evaluate changes due to expansion. For all tests, a significance level of P<0.05 was used. RESULTS Rapid maxillary expansion produced significant increases of linear transverse skeletal measurements, these increments were bigger in the lower portion of the nasal cavities: nasal floor width (+3.15 mm; SD ± 0.99), maximum nasal width (+2.47 mm; SD ± 0.99). Rapid maxillary expansion produced significant increment of the total nasal volume (+1.27 cm(3) ± SD 0.65). The anterior volume increase was 0.58 cm(3) while the posterior one was 0.69 cm(3). CONCLUSION In growing subjects RME is able to significantly enlarge the dimension of nasal cavity. The increment is bigger in the lower part of the nose and equally distributed between the anterior e the posterior part of the nasal cavity.

The relationship between molar dentoalveolar and craniofacial heights

Excessive vertical growth of the posterior dentoalveolar region has been implicated in the etiology of the so-called long-face syndrome. In this study, we tested the hypothesis that molar dentoalveolar heights are positively related to vertical craniofacial features. Cephalometric measurements obtained from 82 adult subjects were entered as independent variables in a multiple regression model. Maxillary and mandibular molar dentoalveolar heights were entered as dependent variables. Approximately 70% of the total variance was explained by anterior lower facial height (ANS-Me) and the mandibular palatal plane angle (PP-MP). Increases of ANS-Me and PP-MP had opposite effects on the amount of molar dentoalveolar heights. The lowest values of molar dentoalveolar heights were found in subjects with a small ANS-Me distance but with a wide PP-MP angle. The findings suggest that individuals with a marked divergence of the jaws may also have a reduced molar dentoalveolar vertical development.