Krister G. Svensson

Clinical advantages of computer‐guided implant placement: a systematic review

OBJECTIVES To systematically scrutinize the current scientific literature regarding the clinical advantages of computer guidance of implant placement. MATERIALS AND METHODS Four electronic databases were searched using specified indexing terms. The reference lists of publications were also searched manually. For inclusion, publications had to meet pre-established criteria. RESULTS The searches yielded 1028 titles and abstracts. After data extraction and interpretation, 28 publications and 2 systematic reviews remained for inclusion. Fifteen studies were prospective observational and four were retrospective observational. Nine studies included a control group (controlled clinical trials) of which seven were prospective and two retrospective. Only three of the prospective studies were randomized (RCTs). A total of 852 patients were treated with 4032 implants using computer-guided implant surgery. The number of patients included in each study ranged from 6 to 206. The age ranged from 16 to 92 years and the follow-up period varied between 1 and 49 months. CONCLUSIONS The limited scientific evidence available suggests that guided placement has at least as good implant survival as conventional protocols. However, several unexpected procedure-linked adverse events during guided implant placement indicate that the clinical demands on the surgeon were no less than those during conventional placement. A clinical advantage with flapless guided surgery is that the technique is likely to decrease pain and discomfort in the immediate postoperative period.

Impaired force control during food holding and biting in subjects with tooth- or implant-supported fixed prostheses.

AIM Our goal here was to assess the ability of subjects with their natural teeth (natural), bimaxillary tooth-supported bridges (bridge) and bimaxillary implant-supported bridges (implant) to control the low contact and high biting forces associated with holding and splitting food between the teeth. MATERIALS AND METHODS Ten subjects in each of these groups performed a task involving holding and splitting morsels of food with different degrees of hardness (biscuits and peanuts) between a pair of opposing central incisors. RESULTS The hold force employed by the implant group was significantly higher and more variable than the corresponding force exerted by the bridge group, whereas the natural group used lowest and least variable force. For all three groups, the split force was higher and the split phase duration longer with peanuts than for biscuits. In the case of the natural group, a significantly higher rate of force increase (peak force rate) was observed when splitting peanuts when compared with biscuits, whereas no such difference could be seen for the other two groups. CONCLUSION These findings demonstrate that individuals with bimaxillary tooth- or implant-supported bridges (in whom sensory information provided by the periodontal mechanoreceptors is impaired or missing) are unable to apply low-hold forces at the levels of individuals with natural teeth or to adapt the rate of the split force to the hardness of the food. We thus conclude that adequate sensory information from periodontal mechanoreceptors is essential for normal control of both low contact and high biting forces.

Regulation of bite force increase during splitting of food

The purpose of the study was to analyze how increases in the bite force, during the splitting of food morsels of different hardness, are modulated, and to evaluate the role of periodontal mechanoreceptors in this control. Fifteen subjects were instructed to hold and split food morsels of different hardness (peanuts and biscuits) between a pair of opposing central incisors before and during anesthesia of the teeth. The split occurred at an average bite force of 9 N for biscuits and at an average bite force of 18 N for peanuts. The duration of the split phase was longer, and the split force rate higher, for peanuts compared with biscuits. Furthermore, a steeper force trajectory was observed for the peanut. During anesthesia of the teeth, the duration of the split phase increased and the mean split force rate decreased for peanuts. Force trajectories for peanuts and biscuits were indistinguishable during anesthesia. The present results show that when higher bite forces are needed to split a morsel, both the duration and the rate of the bite force produced is increased. Furthermore, adaptation of the bite force rate to the hardness of the food is dependent on information from periodontal mechanoreceptors.

Alterations in intraoral manipulation and splitting of food by subjects with tooth‐ or implant‐supported fixed prostheses

OBJECTIVES Sensory information provided by the periodontal mechanoreceptors (PMRs) is used by the nervous system to optimize the positioning of food, force levels, and force vectors involved in biting. The aim of this study was to describe motor performance during a novel manipulation-and-split task and to assess the extent to which control of this performance involves information from the PMRs. MATERIALS AND METHODS A total of 10 subjects with natural teeth, 10 with bimaxillary tooth-supported fixed prostheses (TSP) and 10 with bimaxillary implant-supported fixed prostheses (ISP) (61-83 [mean 69] years of age) were asked to perform an intraoral manipulation-and-split task that involved positioning a spherical chocolate dragée between the front teeth and then splitting it into two parts of equal size. The vertical jaw movement, sound of food cracking and masseter muscle activity were monitored during this task and the accuracy of the split was evaluated. RESULTS The group with natural teeth was significantly better than the other groups at splitting the candy with high precision. The jaw movements were similar between groups, but the contact phase prior to the split was significantly longer for those with natural dentition. CONCLUSIONS The present findings support the conclusion that the nervous system collects rich information about contact between the teeth and food from the PMRs prior to powerful jaw action. Impairment (TSP) or absence (ISP) of this information alters motor behavior and impairs performance during the natural biting task employed here.

Optimization of jaw muscle activity and fine motor control during repeated biting tasks

OBJECTIVE To investigate if repeated holding and splitting of food morsel change the variability of force and jaw muscle activity in participants with natural dentition. METHODS Twenty healthy volunteers (mean age=26.2±3.9 years) participated in a single session divided into six series. Each series consisted of ten trials of a standardized behavioural task (total 60 trials) involving holding and splitting a flat-faced tablet (8mm, 180mg) placed on a bite force transducer with the anterior teeth. The hold and split forces along with the electromyographic (EMG) activity of the left and right masseter (MAL and MAR), left anterior temporalis (TAL) and digastric (DIG) muscles were recorded. A series (ten trials) of natural biting tasks was also performed before and after the six series of the behavioural task. RESULTS The mean hold force (P<0.001) but not the mean split force (P=0.590) showed significant effect of number of series. No significant effect of series was seen on the variability of hold and split force and the EMG activity except for the variability of EMG activity for MAL during the hold phase (P=0.021) and DIG during the split phase (P<0.001). The behavioural task had no effect on the EMG activity of the natural biting task. CONCLUSION There was no evident optimization of jaw motor function in terms of reduction in the variability of bite force values and muscle activity, when this simple task was repeated up to sixty times in participants with normal intact periodontium.

Effects of short-term training on behavioral learning and skill acquisition during intraoral fine motor task.

Sensory information from the orofacial mechanoreceptors are used by the nervous system to optimize the positioning of food, determine the force levels, and force vectors involved in biting of food morsels. Moreover, practice resulting from repetition could be a key to learning and acquiring a motor skill. Hence, the aim of the experiment was to test the hypothesis that repeated splitting of a food morsel during a short-term training with an oral fine motor task would result in increased performance and optimization of jaw movements, in terms of reduction in duration of various phases of the jaw movements. Thirty healthy volunteers were asked to intraorally manipulate and split a chocolate candy, into two equal halves. The participants performed three series (with 10 trials) of the task before and after a short-term (approximately 30 min) training. The accuracy of the split and vertical jaw movement during the task were recorded. The precision of task performance improved significantly after training (22% mean deviation from ideal split after vs. 31% before; P<0.001). There was a significant decrease in the total duration of jaw movements during the task after the training (1.21 s total duration after vs. 1.56 s before; P<0.001). Further, when the jaw movements were divided into different phases, the jaw opening phase and contact phase were significantly shorter after training than before training (P=0.001, P=0.002). The results indicate that short-term training of an oral fine motor task induces behavior learning, skill acquisition and optimization of jaw movements in terms of better performance and reduction in the duration of jaw movements, during the task. The finding of the present study provides insights into how humans learn oral motor behaviors or the kind of adaptation that takes place after a successful prosthetic rehabilitation.

Motor behavior during the first chewing cycle in subjects with fixed tooth‐ or implant‐supported prostheses

OBJECTIVES Appropriate sensory information from periodontal mechanoreceptors (PMRs) is important for optimizing the positioning of food and adjustment of force vectors during precision biting. This study was designed to describe motor behavior during the first cycle of a natural chewing task and to evaluate the role of such sensory input in this behavior. MATERIAL AND METHODS While 10 subjects with natural dentition, 11 with bimaxillary fixed tooth-supported prostheses (TSP) and 10 with bimaxillary fixed implant-supported prostheses (ISP) (mean age 69 [range 61-83]) chewed a total of five hazelnuts, their vertical and lateral jaw movements were recorded. Data obtained during the first chewing cycle of each hazelnut were analyzed. RESULTS The amplitude of vertical and lateral mandibular movement and duration of jaw opening did not differ between the groups, indicating similar behavior during this part of the chewing cycle. However, only 30% of the subjects in the natural dentate group, but 82% of those in the TSP and 70% in the ISP group exhibited slippage of the hazelnut during jaw closure in at least one of five trials. The TSP and ISP groups also exhibited more irregular and narrower patterns of motion (total lateral/vertical movement = 0.15 and 0.19, respectively, compared to 0.27 for the natural group). CONCLUSIONS Subjects with fixed tooth- or implant-supported prostheses in both jaws show altered behavior, including inadequate control of the hazelnut, during the first chewing cycle. We propose that these differences are due to impairment or absence of sensory signaling from PMRs in these individuals.

Perturbed oral motor control due to anesthesia during intraoral manipulation of food

Sensory information from periodontal mechanoreceptors (PMRs) surrounding the roots of natural teeth is important for optimizing the positioning of food and adjustment of force vectors during precision biting. The present experiment was designed to test the hypothesis; that reduction of afferent inputs from the PMRs, by anesthesia, perturbs the oral fine motor control and related jaw movements during intraoral manipulation of morsels of food. Thirty healthy volunteers with a natural dentition were equally divided into experimental and control groups. The participants in both groups were asked to manipulate and split a spherical candy into two equal halves with the front teeth. An intervention was made by anesthetizing the upper and lower incisors of the experimental group while the control group performed the task without intervention. Performance of the split was evaluated and the jaw movement recorded. The experimental group demonstrated a significant decrease in measures of performance following local anesthesia. However, there was no significant changes in the duration or position of the jaw during movements in the experimental and control group. In conclusion, transient deprivation of sensory information from PMRs perturbs oral fine motor control during intraoral manipulation of food, however, no significant alterations in duration or positions of the jaw during movements can be observed.

Effect of short-term training on fine motor control in trigeminally innervated versus spinally innervated muscles

We hypothesized that the trigeminally innervated jaw muscles and spinally innervated hand muscles would differ in the force control and muscle activity when similar fine motor training tasks are performed. Sixteen healthy volunteers performed six series (with ten trials each) of an oral fine motor task (OFMT) and a hand fine motor task (HFMT), in random order. The task was to hold-and-break a test material (5 cm spaghetti pasta) placed on the force transducer between either their anterior teeth (OFMT) or the thumb and the index finger (HFMT). The hold and the break forces along with the electromyographic (EMG) activity of the left and right masseter (MAL and MAR), left anterior temporalis (TAL) and digastric (DIG) muscles during OFMT, and first dorsal interosseous (FDI) and abductor pollicis brevis (APB) during HFMT, were recorded. There was no significant difference in the relative change of holding force during the six subsequent series, neither for the OFMT (P = 0.39) nor for the HFMT (P = 0.10). The relative change of EMG activity of MAL (P = 0.01) and MAR (P = 0.02) during the hold phase decreased significantly during the six series of OFMT. Also the relative change of break force (P = 0.001) and the relative change of EMG activity of APB during the hold (P = 0.003) and break phases (P = 0.002) decreased significantly during the six series of HFMT. The results indicate functional differences between the jaw and hand muscles during a similar hold-and-break task, with the most pronounced changes for the spinally innervated hand muscles. Overall, these findings indicate that training-related neuroplasticity cannot be extrapolated directly from the spinal to the trigeminal system and vice versa.

Physiological Considerations of Oral Implant Function

Synopsis Normal regulation of oral functions, such as biting and chewing, is dependent on information provided by several sensory organs, including the periodontal mechanoreceptors (PMRs) surrounding natural teeth. The detailed information on the magnitude and spatial aspects of the forces involved in tooth-food contact provided by the PMRs is processed by the central nervous system in a feedback manner (moment-to-moment control) to regulate the level and direction of bite forces. In addition, information provided by these same receptors is used in a feedforward manner to adjust the rate of increase in force to the intrinsic properties (e.g., hardness) of the food, as well as to optimize the direction of the bite force vector. Absence of information from the PMRs (e.g., as a result of anesthesia or the presence of bimaxillary implant-supported prostheses) disturbs such regulation. Furthermore, the presence of PMRs around teeth connected in a fixed prosthesis does not appear to be beneficial to spatial control during positioning of the food or adaptation to its hardness during mastication. Thus jaw function with a full-arch dental implant prosthesis will be similar to that with a full-arch tooth-supported one. In addition, in the case of the partly edentulous jaw, implants in between free-standing natural teeth may allow preservation of at least some of the rich sensory information provided by the PMRs.