Influence of mandibular residual ridge resorption on objective masticatory measures of lingualized and fully bilateral balanced denture articulation

PurposeTo assess the influence of mandibular residual ridge resorption (RRR) on objective masticatory measures of two occlusal schemes: lingualized occlusion (LO) and fully bilateral balanced articulation (FBBA).MethodsThe enrolled patients (n = 22) were randomly allocated one set of complete dentures with either LO or FBBA. Maximum occlusal force, masticatory performance (by the MPI), and mandibular movements were measured at 3- and 6-month follow-ups. Mandibular RRR was assessed as the sum of the mandibular bone height at the midline, first premolar region, and least vertical height region, and from the mental foramen to the alveolar crest, measured on panoramic radiographs; the treatment groups were subclassified into severe or moderate RRR subgroups by the value of the sum of individual measurements.ResultsSignificant differences were observed in the between-subgroup comparisons (Kruskal–Wallis test) of the MPI (3 months, p = 0.01; 6 months, p = 0.04) and linear deviation from intercuspal position (anterior–posterior: 6 months, p = 0.01; inferior–superior: 3 months, p = 0.008; 6 months, p = 0.02). The patients with severe RRR in the FBBA group showed a significant decrease in the MPI and increase in linear inferior deviation from intercuspal position at 3 months (post hoc comparison) as well as a significant increase in the linear posterior and inferior deviation from intercuspal position at 6 months.ConclusionsLO is the preferable occlusal scheme for patients with severe RRR. (This trial has been registered at http://clinicaltrials.gov/ct2/show/NCT00959530.)     

Occlusal tooth wear in Chinese adults with shortened dental arches

To assess associations between occlusal tooth wear and shortened dental arches (SDA) in Chinese 40 years and older subjects. From a sample of 1462 urban and rural adults, those presenting with SDA (n = 150) were compared with a control group of 65 randomly selected subjects with complete dentitions (CDA). Occlusal wear was assessed using a modified Smith and Knight index – the occlusal tooth wear index (OWTI) – and analysed using multivariate (logistic) regression. There was no significant effect from SDA on severe occlusal wear (OTWI score 3 or 4: OR = 2·016; 95% CI = 0·960–4·231; P = 0·064). Higher age was associated with severe occlusal wear (P values ≤0·007) and with higher mean OTWI scores; urban had less often severe occlusal wear than rural residents (OR = 0·519; P = 0·008). Higher mean OTWI scores were associated with rural residents, except for anterior teeth. Females had lower mean OTWI score for anterior teeth (effect = ?0·153; P = 0·030). Premolars in SDA had higher mean OTWI scores compared with those in CDA (effect = +0·213; P = 0·006). In SDA, more posterior occluding pairs (POPs) were associated with lower mean OTWI sores for anterior teeth (effect: ?0·158; P = 0·008) and higher scores for molars (effect: +0·249, P = 0·003). Subjects with SDA or CDA presented comparable occlusal wear, but premolars in SDA tend to have higher probability for having occlusal wear. Fewer numbers of POPs were associated with more wear in anterior teeth.     

The influence of resilient liner and clip attachments for bar‐implant‐retained mandibular overdentures on opposing maxillary ridge. A 5‐year randomised clinical trial

This study aimed to compare the influence of resilient liner and clip attachments for bar‐implant‐retained mandibular overdentures on opposing maxillary ridge after 5 years of denture wearing. Thirty edentulous male patients (mean age 62·5 years) received two implants in the anterior mandible after being allocated into two equal groups using balanced randomisation. After 3 months, implants were connected with resilient bars. New maxillary complete dentures were then constructed, and mandibular overdentures were retained to the bars with either clips (group I, GI) or silicone resilient liners (group II, GII). The prosthetic and soft tissue complications of the maxillary dentures were recorded 6 months (T_6 m), 1 year (T1), 3 years (T3) and 5 years (T5) after overdenture insertion. Traced rotational tomograms were used for measurements of maxillary alveolar bone loss. The proportional value between bone areas and areas of reference not subject to resorption was expressed as a ratio (R). Change in R immediately before (T0) and after 5 years (T5) of overdenture insertion was calculated. Maxillary denture relining times and frequency of flabby anterior maxillary ridge occurred significantly more often in GI compared with GII. The change of R in anterior part of maxilla was significantly higher than change of R in posterior part in both groups. GI showed significant resorption of anterior residual ridge compared with GII. Relining times and frequencies of flabby ridge were significantly correlated with change in R. Within the limitations of this study, resilient liner attachments for bar‐implant‐retained mandibular overdentures are associated with decreased resorption and flabbiness of maxillary anterior residual ridge and fewer maxillary denture relining times when compared with clip attachments.     

Effect of prosthetic restoration on oral health‐related quality of life in patients with shortened dental arches: a multicentre study

The aim of this multicentre prospective study was to investigate the effect of prosthetic restoration for missing posterior teeth in patients with shortened dental arches (SDAs). SDA patients with 2–12 missing occlusal units (a pair of occluding premolars corresponds to one unit, and a pair of occluding molars corresponds to two units) were consecutively recruited from seven university‐based dental hospitals in Japan. Patients chose no replacement of missing teeth or prosthetic treatment with removable partial dentures (RPDs) or implant‐supported fixed partial dentures (IFPDs). Oral health‐related quality of life (OHRQoL) was measured using the oral health impact profile (Japanese version – OHIP‐J) at baseline and follow‐up/post‐treatment evaluation. Of the 169 subjects who completed baseline evaluation, 125 subjects (mean age; 63·0 years) received follow‐up/post‐treatment evaluation. No‐treatment was chosen by 42% (53/125) of the subjects, and 58% (72/125) chose treatment with a RPD (n = 53) or an IFPD (n = 19). In the no‐treatment (NT) group, the mean OHIP summary score at baseline was similar to that at follow‐up evaluation (P = 0·69). In the treatment (TRT) group, the mean OHIP summary score decreased significantly after the RPD treatment (P = 0·002), and it tended to decrease, though not statistically significant (P = 0·18), after the IFPD treatment. The restoration of one occlusal unit was associated with a 1·2‐point decrease in OHIP summary score (P = 0·034). These results suggest that the replacement of missing posterior teeth with RPDs or IFPDs improved OHRQoL. Prosthetic restoration for SDAs may benefit OHRQoL in patients needing replacement of missing posterior teeth.     

Assessment of occlusion after placement of stainless steel crowns in children – a pilot study

Many stainless steel crowns (SSCs) disrupt the occlusion in children, but stabilisation appears to occur within a short period post‐placement. The extent and mechanism of these short‐term occlusal changes in children are unknown. This study sought to determine whether placement of a SSC changes the maximum intercuspation position (MIP) in children, whether the MIP returns to normal within 4 weeks and whether local anaesthesia had an effect on the child's ability to achieve MIP. The T‐Scan^® III was used for the measurement of occlusal contacts. Reliability and reproducibility of the system was determined using a calibration exercise where MIP recordings were taken of eleven children not undergoing any dental treatment. For the main study, the percentage of total occlusal force on each tooth was recorded in 20 children preoperatively, after local anaesthesia, after SSC placement and 4 weeks postoperatively. There was no significant difference in MIP (P = 0·435) preoperatively and post‐administration of local anaesthesia. There was a significant difference between the preoperative force on a tooth and the reading after crown placement (P = 0·0013, Wilcoxon test). By 4 weeks, there was no significant difference overall between post‐SSC placement and the preoperative value for the tooth (P = 0·3). Administration of local anaesthesia did not affect the ability of a child to attain MIP. Maximum intercuspation position was disturbed by the placement of a SSC in seven of 20 cases. When MIP was disturbed, in most cases, it returned to preoperative status within 4 weeks of crown placement.     

Estimation of the rate of tooth wear in permanent incisors: a cross‐sectional digital radiographic study

This study used conventional digital radiography to estimate the rate of tooth wear (TW) of maxillary and mandibular central incisors based on a cross‐sectional study design. The crown length of 1239 permanent maxillary and mandibular central incisors from 346 persons (age groups: 10, 25, 40, 55 and 70 years ±3) were measured by three calibrated dentists. Study teeth were intact incisally, had clearly visible incisal edges and cementoenamel junctions and had natural tooth antagonists. Measures were based on digital radiographic images (N = 666) archived in MiPACS within the electronic health record (axiUm^®) from the College of Dentistry patient database. Incisor crown length decreased at a linear rate in both arches over the 60 years represented by the age groups. The average crown length for maxillary incisors in the youngest age group was 11·94 mm, which decreased by an average of 1·01 mm by median age 70. For mandibular incisors, the average crown length in the youngest age group was 9·58 mm, which decreased by an average of 1·46 mm in the oldest age group. Males and females showed similar rates of TW. Regardless of age, females demonstrated smaller mean crown height for maxillary incisors than males (P < 0·0001). Measures by the examiners demonstrated good agreement, with an interclass correlation coefficient of 0·869 and an average intra‐examiner correlation of 99·5%, based on repeated measurements (n = 100). TW was estimated to average 1·01 mm for maxillary central incisors and 1·46 mm for mandibular central incisors by age 70 years.     

Management of shortened dental arches and periodontal health: 5‐year results of a randomised trial

In a multicentre randomised trial (German Research Association, grants DFG WA 831/2‐1 to 2‐6, WO 677/2‐1.1 to 2‐2.1.; controlled‐trials.com ISRCTN97265367), patients with complete molar loss in one jaw received either a partial removable dental prosthesis (PRDP) with precision attachments or treatment according to the SDA concept aiming at pre‐molar occlusion. The objective of this current analysis was to evaluate the influence of different treatments on periodontal health. Linear mixed regression models were fitted to quantify the differences between the treatment groups. The assessment at 5 years encompassed 59 patients (PRDP group) and 46 patients (SDA group). For the distal measuring sites of the posterior‐most teeth of the study jaw, significant differences were found for the plaque index according to Silness and Löe, vertical clinical attachment loss (CAL‐V), probing pocket depth (PPD) and bleeding on probing. These differences were small and showed a slightly more unfavourable course in the PRDP group. With CAL‐V and PPD, significant differences were also found for the study jaw as a whole. For CAL‐V, the estimated group differences over 5 years amounted to 0·27 mm (95% CI 0·05; 0·48; P = 0·016) for the study jaw and 0·25 mm (95% CI 0·05; 0·45; P = 0·014) for the distal sites of the posterior‐most teeth. The respective values for PPD were 0·22 mm (95% CI 0·03; 0·41; P = 0·023) and 0·32 mm (95% CI 0·13; 0·5; P = 0·001). It can be concluded that even in a well‐maintained patient group statistically significant although minor detrimental effects of PRDPs on periodontal health are measurable.     

Influence of different narrative instructions to record the occlusal contact with silicone registration materials

This study examined the influence of narrative instructions on the occlusal contact area, occlusal contact point and masticatory muscle activities in normal subjects. Twelve healthy men and 12 healthy women with no more than one missing tooth per quadrant participated. Surface EMG was recorded from the masseter and temporal muscle. As a control measurement, intercuspal position was maintained to produce a habitual clenching record (NCR) while the occlusal contact area and occlusal contact point was recorded by means of silicone material. Subsequently, the occlusal contact area was recorded with the narrative instruction for minimum clenching record (MCR), light clenching record (LCR) and strong clenching record (HCR). While the EMG activity (%MVC) increased modestly from MCR to LCR (from 9·3 ± 2·0% to 11·5 ± 1·5%), the occlusal contact area increased rapidly (from 17·2 ± 11·3 mm² to 26·8 ± 15·6 mm²) (P < 0·05). Both EMG activity and occlusal contact area increased gradually from LCR to NCR (to 17·7 ± 2·0% and to 31·4 ± 14·2 mm², respectively). Finally, EMG activity still increased from NCR to HCR (to 44·5 ± 3·7%) (P < 0·05), but the occlusal contact area remained stable (to 36·8 ± 16·6 mm²). Occlusal contact points at left posterior, right posterior, anterior and total area were not significantly different between each task. This study showed that narrative instructions while recording the bite can result in largely stable occlusal contact area. An adequate narrative instruction may therefore contribute to taking a stable occlusal recording in natural dentition.     

Effect of mandibular ridge height on masticatory performance with mandibular conventional and implant-assisted overdentures

Purpose

This study assessed the impact of mandibular bone height on masticatory performance following treatment with a mandibular conventional denture (CD) or implant-retained overdenture (IOD).

Materials and Methods

Evaluation of masticatory performance in 63 participants was made with original CDs and 6 months after treatment completion with new dentures; 25 patients received a mandibular CD and 38 received a mandibular IOD. Anterior ridge height at the mandibular symphysis was determined on lateral cephalograms to provide subgroups of low (< or = 21 mm), moderate (> 21 mm, < 28 mm), and high (< or = 28 mm) ridge height for both CDs and IODs. Masticatory performance tests on the preferred chewing side (PS) and swallowing threshold tests were made with peanuts and carrots.

Results

Analysis of variance was used for comparisons of mean change in performance after treatment with study dentures for the 3 bone height groups; this indicated significant differences between the CD and IOD for PS masticatory performance with peanuts (P=.05) and carrots (P=.03). Post hoc tests found significant mean differences between the CDs and IODs with peanuts (P=.008) and carrots (P=.01) only in the low bone height group. Although no significant differences were found in swallowing threshold performance, the mean change scores for subjects with low bone height were greater with the IODs than those with CD for swallowing threshold performance, strokes, and time.

Discussion

It is suggested that only in patients with advanced ridge resorption is the mandibular IOD more likely than a CD to result in improvements in masticatory performance.

Conclusion

The study indicated that treatment with a mandibular IOD may improve masticatory performance only in persons with a less than adequate mandibular ridge.     

Relapse of skeletal class III with anterior open bite after bimaxillary orthognathic surgery depending on maxillary posterior impaction and mandibular counterclockwise rotation

The goal of this study is to evaluate relapse after orthognathic surgery of skeletal class III with anterior open bite depending on the posterior impaction and mandibular counterclockwise rotation. Patients (n = 29) were divided into two groups according to the change of mandibular occlusal plane angle (MnOP): Group A had a clockwise change of MnOP > 0° (n = 11) and Group B had a counterclockwise change of MnOP < −2° (n = 18). Lateral cephalograms were analyzed preoperatively, and at immediate stage, six weeks, six months, and one year after surgery. One year after surgery, the stability of the maxilla was good in both groups. Upward movement of the mandible was observed six weeks after surgery due to mandibular autorotation. The amount of mean relapse was small, although a significant difference was observed horizontally between groups. Group B demonstrated more forward movement of B point, pogonion, and menton than Group A (p < 0.05). SNB angle increased in both groups (p < 0.05). At one year follow up, good occlusal stability was observed in both groups with positive overbite. Our study suggested that bimaxillary procedures with clockwise and counterclockwise rotation of mandibular occlusal planes for correction of mandibular prognathism with anterior open bite appeared to be relatively stable procedures.     

Long‐term use of occlusal appliance has impact on sleep structure

Acrylic occlusal appliances (OAs) have been used for temporomandibular disorders and sleep bruxism, but the effects of the treatment are still insufficiently evaluated. Two all‐night polysomnographic recordings were made in a sleep laboratory on 14 bruxists (9 females and 5 males with mean age of 27·5 years). The measurement included basic polysomnography with additional masseter muscle electromyogram and movement recording (static charge‐sensitive bed method) using randomisation. The base night recording was followed by the second study night after 8 weeks regular use of OA. The OA was made on the occlusal surface of the teeth of the upper jaw, and it was used at night time during the study period. With the OA, rapid eye movement sleep changed from 23·3% to 19·6% (P = 0·078), and slow wave sleep increased significantly from 10·2% to 14·7% (P = 0·039). Masseter contraction (MC) episodes occurred with similar frequency (9·7 vs. 10·5 episodes per hour, P = 0·272). The intensity of the rhythmic MC bursts within an episode decreased from 5·5 to 4·4 (P = 0·027). The groups were post hoc divided into responders and non‐responders using a 20% change in MC episode per hour as a cut‐off point. The results indicated that 43% of bruxists increased activity (negative responders), while 36% decreased (positive responders), and in 21%, there was no change in the level. It is concluded that OA does not have significant feedback inhibition on masseter muscle motor activity during sleep. However, OA may increase slow wave sleep.     

The effects of fixed and removable implant-stabilised prostheses on posterior mandibular residual ridge resorption

Abstract: This study investigated the change over time in the area of the posterior mandibular residual ridge in patients wearing either i) mandibular overdentures stabilised by two implants (Brånemark System; Nobel Biocare, Göteborg, Sweden) connected by a bar, or ii) mandibular fixed cantilever prostheses stabilised on five or six implants. Proportional measurements were made in order to compare the area of the residual ridge with an area of bone uninfluenced by resorption. Measurements were made by digitising tracings of panoramic radiographs that were taken shortly after implant insertion and up to seven years later. With the use of overdentures, the posterior bone area index reduced by a mean of 1.1% per annum, while a mean bone area index increase of 1.6% per annum was demonstrated in association with fixed prostheses. A multiple linear regression model was fitted to predict the change in posterior area from type of prosthesis, gender, age, years of edentulism and initial height of the mandible. The model was only significant for initial height of mandible (P = 0.04) and type of prosthesis (P = 0.0001). In conclusion, patients rehabilitated with implant‐stabilised mandibular overdentures demonstrated low rates of posterior mandibular residual ridge resorption, while patients rehabilitated with implant‐stabilised mandibular fixed cantilever prostheses demonstrated bone apposition in the same area.     

The effects of salivas on occlusal forces

Contacting surfaces of opposing teeth produce friction that, when altered, changes the contact force direction and/or magnitude. As friction can be influenced by several factors, including lubrication and the contacting materials, the aim of this study was to measure the occlusal load alterations experienced by teeth with the introduction of different salivas and dental restorative materials. Pairs of molar teeth were set into occlusion with a weighted maxillary tooth mounted onto a vertical sliding assembly and the mandibular tooth supported by a load cell. The load components on the mandibular tooth were measured with three opposing pairs of dental restorative materials (plastic denture, all‐ceramic and stainless steel), four (human and three artificial) salivas and 16 occlusal configurations. All lateral force component measurements were significantly different (P < 0·0001) from the dry (control) surface regardless of the crown material or occlusal configuration, while the effects of the artificial salivas compared to each other and to human saliva depended on the crown material.     

Posterior scissors‐bite: masticatory jaw movement and muscle activity

Scissors‐bite is a malocclusion characterised by buccal inclination or buccoversion of the maxillary posterior tooth and/or linguoclination or linguoversion of the mandibular posterior tooth. This type of malocclusion causes reduced contact of the occlusal surfaces and can cause excessive vertical overlapping of the posterior teeth. This case–control study is the first to evaluate both masticatory jaw movement and masseter and temporalis muscle activity in patients with unilateral posterior scissors‐bite. Jaw movement variables and surface electromyography data were recorded in 30 adult patients with unilateral posterior scissors‐bite malocclusion and 18 subjects with normal occlusion in a case–control study. The chewing pattern on the scissors‐bite side significantly differed from that of the non‐scissors‐bite side in the patients and of the right side in the normal subjects. These differences included a narrower chewing pattern (closing angle, P < 0·01; cycle width, P < 0·01), a longer closing duration (P < 0·05), a slower closing velocity (P < 0·01) and lower activities of both the temporalis (P < 0·05) and the masseter (P < 0·05) muscles on the working side. In 96% of the patients with unilateral posterior scissors‐bite, the preferred chewing side was the non‐scissors‐bite side (P = 0·005). These findings suggest that scissors‐bite malocclusion is associated with the masticatory chewing pattern and muscle activity, involving the choice of the preferred chewing side in patients with unilateral posterior scissors‐bite.     

Effects of interocclusal distance on bite force and masseter EMG in healthy participants

The aim of this study was to investigate effects of interocclusal distance (IOD) on bite force and masseter electromyographic (EMG) activity during different isometric contraction tasks. Thirty‐one healthy participants (14 women and 17 men, 21·2 ± 1·8 years) were recruited. Maximal Voluntary Occlusal Bite Force (MVOBF) between the first molars and masseter EMG activity during all the isometric‐biting tasks were measured. The participants were asked to bite at submaximal levels of 20%, 40%, 60% and 80% MVOBF with the use of visual feedback. The thickness of the force transducer was set at 8, 12, 16 and 20 mm (= IOD), and sides were tested in random sequence. MVOBF was significantly higher at 8 mm compared with all other IODs (P < 0·001). Only in women, IOD always had significant influence on the corresponding root‐mean‐square (RMS) value of EMG (P < 0·011). When biting was performed on the ipsilateral side to the dominant hand, the working side consistently showed higher masseter EMG activity compared with the balancing side (P < 0·020). On the contralateral side, there was no difference between the masseter EMG at any IODs. The results replicated the finding that higher occlusal forces can be generated between the first molars at shorter IODs. The new finding in this study was that an effect of hand dominance could be found on masseter muscle activity during isometric biting. This may suggest that there can be a general dominant side effect on human jaw muscles possibly reflecting differences in motor unit recruitment strategies.     

Maxillary anterior and mandibular posterior residual ridge resorption in patients wearing a mandibular implant-retained overdenture

The mandibular implant-retained overdenture could improve masticatory function compared to the conventional complete denture. However, increased forces exerted by the overdenture could increase residual ridge resorption of the maxillary anterior and mandibular posterior areas. The aim of this study was to compare the effect of the mandibular implant-retained overdenture using two or four dental implants, or the conventional complete denture on resorption of the residual ridge of the maxillary anterior and mandibular posterior areas over a period of 10 years. In total, 120 patients, 30 patients treated with an overdenture on two implants (two-implant group), 30 patients with an overdenture on four implants (four-implant group) and 60 patients treated with a conventional full denture (conventional group), participated in this study. On panoramic radiographs, made before and 10 years after treatment, proportional area measurements were applied to determine changes in bone height. After 10 years, a statistically significant amount of bone resorption had occurred in the anterior maxilla in the two-implant group and in the four-implant group. A significant amount of bone resorption had occurred in the posterior mandible in all three groups. There were no statistically significant differences between the groups in both areas. Patients presented large individual differences. It is concluded that patients rehabilitated with implant-retained mandibular overdentures are not subjected to more residual ridge resorption in the anterior maxilla when compared to patients wearing a conventional full denture. Regarding the mandibular posterior residual ridge, resorption was irrespective of wearing an implant-retained mandibular overdenture or a conventional mandibular denture.     

Assessment of masticatory function in patients with non‐sagittal occlusal discrepancies

Non‐sagittal occlusal discrepancies such as posterior cross‐bite and anterior openbite are common types of malocclusion, but studies on masticatory function related to those malocclusions have been scarce. The aim of this study was to quantify the masticatory performance in patients with non‐sagittal discrepancies compared to those with normal occlusion, using both objective and subjective measures. Maximum bite force and contact area using Dental Prescale^® system as a static objective assessment, Mixing Ability Index (MAI) as a dynamic objective evaluation and food intake ability (FIA) as a subjective assessment were analysed from 21 people in normal occlusion (Group N) and 64 patients with posterior cross‐bite (Group C), anterior openbite (Group O) or both (Group B). The differences of the maximum bite force, the contact area, the MAI and the FIA were compared, and their correlations were figured out. The non‐sagittal malocclusion groups showed lower values in the maximum bite force, the contact area, the MAI and the FIA compared to those in the normal group (P < 0·0001). Compared to Group N, Groups C, O and B showed 61·5%, 42·1% and 40·1% of the maximum bite force, and 84%, 84% and 76% of hard food FIA, respectively. However, there were no significant differences among Groups C, O and B. The MAI showed higher correlation with the FIA (r = 0·38, P < 0·01), than with the maximum bite force and the contact area (both r = 0·24, P < 0·5). These results revealed that masticatory function in patients with non‐sagittal discrepancies is significantly reduced both objectively and subjectively.     

Effect of prosthetic restoration on masticatory function in patients with shortened dental arches: a multicentre study

The aim of this multicentre study was to investigate the effect of prosthetic restoration for missing posterior teeth on mastication in patients with shortened dental arches (SDAs). Partially dentate patients who had an intact teeth in anterior region and missed distal molar(s) (2–12 missing occlusal units) classified as Kennedy Class I or Class II were recruited from seven university‐based dental hospitals in Japan. Of the 125 subjects who underwent baseline (pre‐treatment) and follow‐up/post‐treatment evaluation, 53 chose no replacement of missing teeth and 72 chose treatment with removable partial dentures (n = 53) or implant‐supported fixed partial dentures (n = 19). Objective masticatory performance (MP) was evaluated using a gummy jelly test. Perception of chewing ability (CA) was rated using a food intake questionnaire. In the no‐treatment group, mean MP and CA scores at baseline were similar to those at follow‐up evaluation (P > 0·05). In the treatment group, mean MP after treatment was significantly greater than the pre‐treatment mean MP (P < 0·05). However, the mean perceived CA in the treatment groups was similar at pre‐ and post‐treatment (P > 0·05). In a subgroup analysis of subjects in the treatment group, subjects with lower pre‐treatment CA showed a significant CA increase after treatment (P = 0·004), but those with higher pre‐treatment CA showed a significant decrease in CA (P = 0·001). These results suggest that prosthetic restoration for SDAs may benefit objective masticatory performance in patients needing replacement of missing posterior teeth, but the benefit in subjective chewing ability seems to be limited in subjects with perceived impairment in chewing ability before treatment.     

Smoothness of chewing jaw movements in adults with mandibular prognathism

Summary Indices such as smoothness, movement time, peak velocity, and symmetry of the velocity profile have been shown to be effective in explaining the degree of skilfulness of human saccadic eye, limb, and jaw motions. We investigated whether adult subjects with mandibular prognathism show impaired smoothness of the masticatory jaw movements. Forty‐nine adults with skeletal Class III malocclusions and 52 healthy adults with acceptably good occlusions were selected respectively as Test and Control subjects. Subjects of the Test Group were subdivided into two groups: Class III_closed showed full occlusal contact between the upper and lower teeth at the habitual intercuspal position, whereas Class III_open showed inability of occlusal contact between the upper and lower anterior teeth. Each subject was asked to chew a piece of chewing gum. The normalised jerk‐cost (NJC), movement duration, and tangential velocity profile during jaw‐closing movements were compared between groups. Test Groups showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than the Control Group did. Class III_closed showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than Class III_open did. Results show that the mandibular movements made by the Test Groups exhibit lower skilfulness than those made by the Control Group. The jaw movement skilfulness of the prognathic patients decreases most drastically with existence of malocclusal contact between upper and lower anterior teeth.     

The effect of mucosal cuff shrinkage around dental implants during healing abutment replacement

Soft tissue shrinkage during the course of restoring dental implants may result in biological and prosthodontic difficulties. This study was conducted to measure the continuous shrinkage of the mucosal cuff around dental implants following the removal of the healing abutment up to 60 s. Individuals treated with implant‐supported fixed partial dentures were included. Implant data – location, type, length, diameter and healing abutments' dimensions – were recorded. Mucosal cuff shrinkage, following removal of the healing abutments, was measured in bucco‐lingual direction at four time points – immediately after 20, 40 and 60 s. anova was used to for statistical analysis. Eighty‐seven patients (49 women and 38 men) with a total of 311 implants were evaluated (120 maxilla; 191 mandible; 291 posterior segments; 20 anterior segments). Two‐hundred and five (66%) implants displayed thick and 106 (34%) thin gingival biotype. Time was the sole statistically significant parameter affecting mucosal cuff shrinkage around dental implants (P < 0·001). From time 0 to 20, 40 and 60 s, the mean diameter changed from 4·1 to 4·07, 3·4 and 2·81 mm, respectively. The shrinkage was 1%, 17% and 31%, respectively. The gingival biotype had no statistically significant influence on mucosal cuff shrinkage (P = 0·672). Time required replacing a healing abutment with a prosthetic element should be minimised (up to 20/40 s), to avoid pain, discomfort and misfit.