An Electromyographic Analysis of Orbicularis Oris and Buccinator Muscle Activity in Patients With Complete Dentures Fabricated Using Two Neutral Zone Technique

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  An Electromyographic Analysis of Orbicularis Oris andBuccinator Muscle Activity in Patients with CompleteDentures Fabricated Using Two Neutral ZoneTechniques—A Pilot Study Komal G. Ladha, BDS, MDS, 1 Shubhra Gill, BDS, MDS, 2 Rekha Gupta, BDS, MDS, DNB, 2 Mahesh Verma, BDS, MDS, MBA, 2 & Meena Gupta, MBBS, MD, DM 3 1 Department of Prosthodontics, ESIC Dental College and Hospital, New Delhi, India 2 Department of Prosthodontics, Maulana Azad Institute of Dental Sciences, New Delhi, India 3 Department of Neurology, G.B. Pant Hospital, New Delhi, India Keywords Electromyography; orbicularis oris;buccinator; neutral zone. Correspondence Komal G. Ladha, Department ofProsthodontics, ESIC Dental College andHospital, New Delhi, India and Flat no. 416,Gaur Heights, Sector-4, Vaishali, Ghaziabad,India. E-mail: komalladha@yahoo.co.in The authors deny any conflicts of interest. Accepted January 23, 2013doi: 10.1111/jopr.12055 Abstract Purpose:  Several studies have evaluated electromyographic (EMG) activity of pe-rioral muscles in patients using unsatisfactory old complete dentures and after theinsertion of new clinically acceptable dentures; however, studies evaluating EMGactivity of orbicularis oris (OO) and buccinator (BUC) muscles in patients wear-ing complete dentures fabricated using swallowing (SNZ) and phonetic neutral zone(PNZ) techniques are lacking in the literature. The purpose of this study was to eval-uate differences in muscle activity of the superior orbicularis oris (SOO), inferiororbicularis oris (IOO) and BUC muscle during the use of unsatisfactory old completedentures,incomparisonwiththesatisfactorydenturesfabricatedusingthetwoneutralzone techniques. Materials and Methods:  Ten completely edentulous participants dissatisfied withtheir existing mandibular complete dentures participated in the study. Each patientreceived two sets of new dentures fabricated using the SNZ and PNZ techniques.Surface EMG activity of the OO and BUC muscles was recorded using a 4-channelMedelecpremierpluselectromyographymachinewhilethepatientsstillusedtheirolddentures (group A) and with the SNZ (group B) and PNZ (group C) dentures. On thebasis of participation in the study, five participants first received the SNZ dentures andfivethePNZtype.Afterhavingworntheprosthesisforaminimumof2months,EMGrecordingswererepeatedforthefirstsetofdentures.Theprostheseswerethenchangedandtheproceduresrepeated.TheactivityofOOandBUCmuscleswasrecordedatrest,while pursing and laughing, and during pronunciation of various syllables. Resultsare expressed as mean ± SD and as absolute numbers and percentage. ANOVA withappropriate correction (Bonferroni or Tamhane) and Student’s  t  -test were used forstatistical analysis. A  p -value < 0.05 was taken to indicate a significant difference. Results:  There was no statistically significant difference in the mean EMG activityof SOO, IOO, and BUC muscles at rest, or during pursing or laughing among thethree groups. No significant difference was observed in the mean EMG activity of SOO and BUC muscle among the groups for all the syllables pronounced. For IOO,a statistically significant difference was observed among the groups for the words“baby” and “cheese.” Within-group comparisons of the mean EMG activities of SOOandIOOduringpronunciationandpursingshowednosignificantdifference;however,at rest a statistically significant difference was observed in group B. Conclusion:  OO and BUC muscle activities did not significantly differ, irrespectiveof the technique used for fabrication of complete dentures. 566  Journal of Prosthodontics  22  (2013) 566–574  C  2013 by the American College of Prosthodontists  Ladha  et al   EMG Analysis of Orbicularis Oris and Buccinator Muscles Oralfunctionsinvolvetheuniqueinterplayoftheoralstructuresand muscles. All oral functions, such as speech, mastication,swallowing, smiling, and laughing, involve the synergistic ac-tions of tongue, lips, cheeks, and the floor of the mouth, all of which are very complex and highly individual. The oral cav-ity constitutes a complex morpho-functional system in whichthe peri-oral muscles, mainly the orbicularis oris (OO) and thebuccinator(BUC),exertinwardforcesbalancedbytheoutwardforces exerted by the tongue. 1-5 When all natural teeth are lost, a void, which is the potentialdenture space, exists in the oral cavity. The complete denturethat will occupy this space must be molded by muscle functionto be in harmony with its surrounding structures.The neutral zone (NZ) is the area in the potential denturespacewheretheforcesofthetonguepressingoutwardsareneu-tralized by the forces of the cheeks and lips pressing inwards.The actions of the lips, cheeks, and tongue during various oralfunctions help determine the tooth position and shape of thepolished surfaces, thereby enhancing the stability and retentionof complete dentures. 6 Swallowing is used as the principle modeling function in thetraditional “modeling compound-swallowing impression tech-nique,” for obtaining the NZ. 7 The term “swallowing neutralzone technique” (SNZ) has been used in the present study forthe same. Speech is another important part of routine oral ac-tivities. It is used as the principle modeling function in a tech-nique called piezography. Piezography records the mandibu-lar denture space by means of pressure developed during oralfunctions, primarily speech. 8,9 This technique customizes thecontours of the lingual surface and precludes over-extension.The term “phonetic neutral zone technique” (PNZ) has beenused in the present study for the same. 10 Any complete denture that interferes with the actions of thesurrounding muscles will therefore lack stability. 6 In such sit-uations, it can be assumed that the muscle activity will differin patients when wearing unsatisfactory conventional completedentures replaced with satisfactory dentures fabricated usingthe neutral zone techniques.Electromyography(EMG)isapractical andefficientmethodfor the study of muscle function and activity, thus serving as avaluable tool in dental research. EMG is the study of musclefunction through the analysis of the electrical signals emanatedduring muscular contractions. 11,12 Surface electromyographyis used to measure the muscular activity noninvasively usingsurface electrodes placed on the skin overlying the muscle. 13,14 Peri-oral muscles have received considerable attentionin the literature. Numerous EMG studies of the OO andBUC have been conducted relating to facial expression, 15-19 pronunciation, 17,20 swallowing, 17,21 sucking, 16,17,21 blow-ing, 17,21 mandibular movements, 17,21 and mastication. 20-23 The actions that activate OO and BUC muscles, such aspursing, 15 laughing, 15,16,18 and speaking, 17,20 are used to recordtheNZ.Areviewoftheliteraturerevealsalackofdataregardingevaluation of the EMG activity of BUC and OO muscles inedentulouspatientswearingcompletedenturesfabricatedusingneutral zone techniques.Therefore, the present study aimed at disclosing differencesin the activity of OO and BUC during the use of subjectivelyand clinically unsatisfactory dentures, in comparison with Table 1  Inclusion/exclusion criteriaInclusion criteria Exclusion criteria1. 60–80 years of age2. Conventional complete denturewearers using dentures for aminimum of 1 year anddissatisfied with their existingmandibular denture3. Advanced mandibular ridgeresorption (Atwood’s class Vand VI)1. Acute/chronic symptoms ofTMD2. Uncontrolled systemicdiseases3. Psychological conditions thatcould influence the patients’reaction to the treatment4. Pendulous residual ridges5. Smokers and tobacco users the satisfactory dentures fabricated using the swallowing(SNZ) and the phonetic (PNZ) neutral zone techniques. Thehypothesis of the present study is that the activity of thesemuscles will decrease when the dentures are constructed usingthe neutral zone technique, which harmonizes with the actionsof surrounding muscles. Materials and methods Participants Ten completely edentulous patients (male = 9, female = 1) be-tween the ages of 60 and 80 years were selected from the OPDof the Department of Prosthodontics, Maulana Azad Instituteof Dental Sciences, New Delhi, India for participation in thepresent study. The patients were selected based on the inclu-sion and exclusion criteria given in Table 1. All the patientshad ill-fitting and unsatisfactory old dentures. Each patient re-ceived two sets of new dentures fabricated using the SNZ andPNZ techniques. Five patients first received the SNZ denturesand five the PNZ type. Written informed consent was obtainedfrom all the patients after receiving a full explanation of thepurpose and method of the study. The study protocol was ap-provedbytheInstitutionalEthicalCommitteeofMaulanaAzadInstitute of Dental Sciences, New Delhi. Electromyographictests were carried out at the Neuroelectrophysiology Labora-tory of the Department of Neurology, G. B. Pant Hospital,New Delhi. Denture fabrication method Twoneutralzonetechniques(PNZ,SNZ)wereusedtofabricatedentures. After primary and final impressions were made forcompletedenturefabrication,NZrecordbaseswereconstructedon the master casts. An acrylic keel of 2 to 3 mm width wasconstructed over the record base, having two posterior and oneanterior segment. Tissue conditioner was used as a recordingmaterial in both techniques. The phonetic technique  In this technique, the tissue conditioning material was loadedand molded segmentally. 24 The right posterior segment wasmolded first, followed by the left, and, finally the anteriorsegment was molded. Tissue-conditioning material was mixedin the ratio recommended by the manufacturer (Viscogel,Dentsply International, Surrey, UK). After loading, the patient Journal of Prosthodontics  22  (2013) 566–574  C  2013 by the American College of Prosthodontists  567  EMG Analysis of Orbicularis Oris and Buccinator Muscles  Ladha  et al  Figure 1  Schematic drawing showing the three landmarks, points A,B, and C for external location of the buccinator muscle (landmarks andangle as labeled by Tavares da Silva et al 25 ). was asked to pronounce a series of words in Hindi and English:“Papa Ne Shor Machete Baby Ko Cheese Khilakar KhushKiya, Aur, Kavita Se Kaha Sadak Par Mat Chal, Jakar ShisheKe Thermos Main Coffee La,” which included bilabial (m, p,b), labiodental (f, v), alveolar (s, sh), and dental (th) sounds.To induce sufficient muscle contraction, all the sounds hadto be pronounced clearly, loudly, and vigorously. The patientrepeated the sentence until the material polymerized. Thewhole sequence had to be completed quickly to ensure purephonetics and no swallowing. The segment was remoldedif the patient accidentally swallowed during pronunciation.Excess tissue conditioning material anterior to the premolararea was removed. The same procedure was repeated to moldthe left posterior and the anterior segment. The swallowing technique  The SNZ was also developed segmentally in a manner similarto the phonetic technique. While each segment was molding,thepatientwasinstructedtoperformaseriesofactionsuntilthematerialwasset:smiling,pursingthelips,sucking,swallowing,and wetting the lips with the tongue. To facilitate swallowing,each patient was provided with a cup of warm water that he/shecould sip. The base was removed once the material was set,and any excess material that had flowed in the other segmentwas removed. Upon completion, the record was inspected foraccuracy. Denture fabrication  Putty indices were made around the recorded NZ, and waxrims were prepared corresponding to the indices. Teeth were Figure 2  EMG activity of SOO muscle at rest and during pursing foreach denture. arranged in the NZ, and wax try-in was done. Balanced occlu-sion was achieved on the articulator. Try-in and recording of polished surface  After the wax try-in was found satisfactory, polished surfacesofthetrialdentureswererecordedusingZOEimpressionpaste.During recording, the patient either performed the respectivephysiologic movements used for SNZ recording or pronouncedthe sentence used for PNZ recording. Completion of dentures  Thetrialdentureswereinvested,processed,finished,andlightlypolished to prevent alteration of contours. The dentures wereinserted, carefully evaluated, and checked for occlusal errors.The patient was made to use dentures fabricated by each tech-nique for a period of 2 months, and EMG activity was recordedwith both. Experimental procedure for EMG All tests were conducted with surface electrodes. The elec-trodes were placed at the exact points corresponding to theexternal location of the muscles whose electrical activity wasto be measured. Activities of superior and IOO muscles andleft buccinator muscle were recorded, with the patients’ old 568  Journal of Prosthodontics  22  (2013) 566–574  C  2013 by the American College of Prosthodontists  Ladha  et al   EMG Analysis of Orbicularis Oris and Buccinator Muscles Figure3  EMGactivityofIOOmuscleatrestandduringpursingforeachdenture. dentures and the two sets of NZ dentures. Recordings withthe new dentures were made after 2 months of adaptation.Measurements of muscle activities with each denture wereperformed at rest, while pursing (OO) and laughing (BUC)and during pronunciation of syllables. EMG recording A 4-channel Medelec Premier Plus Electromyography ma-chine (Oxford Instruments, Oxfordshire, UK) was used. Dis-posable silver-silver chloride surface electrodes of 10 mm di-ameter were used. Each patient’s skin was cleaned with al-cohol, and Ten20 neurodiagnostic electrode paste (Weaverand Co., Aurora, CO) was applied on the electrodes prior toplacement.During the measurements, individuals remained seated com-fortably on a chair, in an upright position, with their feet onthe floor and their arms leaning on their legs. Their headswere positioned with the Frankfort horizontal plane parallelto the floor. A silent and partially illuminated environmentwas maintained, and patients were asked to remain relaxed toavoid any involuntary contractions that could affect muscularactivity. Figure 4  EMG activity of BUC muscle at rest and during laughing foreach denture. Positioning of electrodes The electrodes for OO were placed in the midline superiorlyand inferiorly to the vermilion border of the lips. 22 Electrodesfor recording the activity of BUC were placed as suggested byTavares Da Silva et al. 25 A vertical plane was dropped straightfrom the external angle of the eye (point A) perpendicular tothe floor. A horizontal plane, parallel to the floor, starting fromthe labial angle (point B) intersected with the vertical planeat a point corresponding to the central point of the buccinator(point C). The surface electrode was placed at this point, andthe angle formed between the planes was nearly 90 ◦ (Fig 1). 25 EMG recordings were made in the following order for eachdenture:1. Superior orbicularis oris (SOO)—activity at rest, cali-bration 100 µ V/div; during pursing the lips, calibration500 µ V/div(Fig2).Sweepspeedwassetat1second.Thereference electrode was placed at the inferior orbicularisoris (IOO).2. Inferior orbicularis oris (IOO)—activity was recorded atrest and during pursing at similar calibrations as withSOO (Fig 3). The reference electrode was placed atSOO.3. BUC—activity at rest, calibration 100  µ V/div; duringlaughing, calibration 500  µ V/div (Fig 4). Sweep speedwas set at 1 second. The reference electrode was securedat the masseter region.4. SOO,IOO,andBUC—activitywasrecordedduringpro-nunciation of various words (Papa, Shor, Baby, Cheese,Khush, Kavita, Sadak, Chal, Shishe, Thermos, Coffee);calibration 200  µ V/div. Sweep speed was set at 5 sec-onds. The reference electrode was secured at the nape Journal of Prosthodontics  22  (2013) 566–574  C  2013 by the American College of Prosthodontists  569
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