PULPAL BLOOD FLOW CHANGES IN ABUTMENT TEETH OF REMOVABLE PARTIAL DENTURES

Th e purpose of this study was to investigate the eff ect of tooth supported (TSD) and toothtissue supported (TTSD) removable partial denture wearing on pulpal blood fl ow (PBF) of the abutment teeth by using Laser Doppler Flowmeter (LDF). Measurements were carried out on  teeth of  patients ( teeth and  patients of TTSD group,  teeth and  patients of TSD group) who had not worn any type of removable partial dentures before, had no systemic problems and were non smokers. PBF values were recorded by LDF before insertion (day ) and after insertion of dentures at day , day  and day . Statistical analysis was performed by student t test and covariance analyses of repeated measure-


Introduction
Th ere are two basic types of partial dentures for partially edentulous arch; a) tooth supported removable partial dentures (TSD) and b) tooth tissue supported removable partial dentures (TTSD).Th e TSDs are self-explanatory in that the forces in function are borne primarily by the remaining natural teeth, which in turn transmit these forces to the periodontal ligament and to the bone structure for support.Cast circumferential clasps are ideally suited for TSD because of the potential for excellent retention and reciprocation.However, circumferential clasps are not usually indicated for TTSD because the retentive tip lies forward of the axis of rotation and has the potential for applying torquing forces to the abutment.In TTSD functional forces applied to the denture base causes its movement towards the tissue.Th is movement is the result of a rotation movement of the RPD bases around an axis connecting the most distal abutment teeth (-).Th e rotation can also cause torquing forces to act on the clasped abutment teeth.Stress-releasing clasp designs overcome these effects.RPI, RPA, RPL clasp systems are available systems in TTSD.Th e RPI is one of these designs ().Th e major attributes of infrabulge retainers are their potential for disengaging during functional movements of TTSD.
Understanding any changes, which may occur in the abutment teeth through the wear of TSD and TTSD, is an important process.Since the abutment teeth are exposed to functional forces, one of the measurements to catch change in the abutment teeth is the investigation of pulpal blood fl ow changes (PBF).Th e laser Doppler fl owmeter (LDF) evaluates dynamic changes in blood fl ow through noninvasive measurement methods (,) by detecting blood cell movement in a small volume of tissue (approximately  mm).Th e fl ow in individual microvessels, the number of vessels with active flow, and the vessel diameter cannot be analyzed (), but total fl ow can be monitored throughout the tissue.Its use in human teeth was fi rst described by Gazelius et al ().Distal extension situations, in which no posterior abutments remain, require an entirely diff erent partial denture design than does one in which total abutment support is available.In these situations the greater torque and tipping leverages that the distal extension partial denture will impose on the abutment teeth must be taken into consideration ().Sufficient differences exist between the TSD and TTSD to justify a distinction between them.While in TSD functional forces are received by teeth, periodontal ligament and the bone structure in TTSD functional forces are received also by the mucosa that covers the bone.So there may be different force distribution in TSD's and TTSD's abutment teeth.This situation may affect the PBF of abutment teeth.However, to date, no study has evaluated the PBF changes in abutment teeth of removable partial dentures.In this prospective clinical study, the purpose is to investigate the eff ect of TSD and TTSD wearing on the PBF of the abutment teeth by using LDF.

Materials and Methods
Th is study was performed on  healthy abutment teeth (maxiller incisors, canines, premolars) in  patients who had not worn any type of removable partial dentures previously.Patients had no systemic problems and were non smokers.Th e patients were chosen, whose teeth did not need recontouring and preparation for guide surfaces and minor connectors, in order not to affect the PBF of the abutment teeth.Radiographic and clinical (percussion, palpation and mobility tests) examination and electrical pulp stimulation confi rmed that the abutment teeth were vital and healthy.Prior to measurement, the purpose and method of the measurement was explained to each participant and written informed consent was obtained.Eighteen patients were planned to be TTSD ( teeth) (group TTSD) and  patients to be TSD ( teeth) (group TSD) wearers.Measurements were made only on maxiller incisors, canines and premolars.Th e removable partial dentures in all the patients were planned by the same dentist and the same techniques were used to obtain optimum conditions on abutment teeth (functional impressions, maximum mucosal surface coverage, rigid major connectors, reduction in occlusal surfaces of denture teeth, balanced occlusion, etc.).I bar clasp in TTSDs as an infrabulge retainer and circumferential clasp in TSDs as a suprabulge retainer was used.To minimize the eff ect of extrapulpal factors on LDF measurements, the teeth were examined by the same investigator under standardized environmental conditions.Blood fl ow recordings were made from the teeth with a LDF monitor (Perifl ux  LDFM Unit; Perimed AB, Järfälla, Sweden) which uses infrared light.Th e instrument's dental probe was  mm in length and , mm in diameter.Th e probe was fi xed to each tooth with a clipon splint that covered the crown of the abutment teeth.Th e splint was constructed from self curing acrylic resin (Orthocryl E Q, Dentaurum, Germany) on a plaster model of the teeth.Th e probe tip was inserted into a stainless-steel tube that was incorporated into the splint over the central long axis of the crown of the tooth, perpendicular to the enamel surface and with its centre  mm from the gingival margin.The alignment of the probe around its long axis was kept constant between trials by aligning marks on the probe and the tube.Th is precaution was necessary to ensure that reproducible results were obtained under each of the experimental conditions.Before the measurements an opaque, black rubber dam (Four D Rubber Co. Ltd., Heanor, England) is applied to the teeth and removed at each step.At each stage, the blood fl ow signal was allowed to stabilize for several minutes before the measurements were made, then the effect on the signal of covering the gingival and surrounding soft tissue with opaque rubber dam was determined.At each measurement, blood-fl ow data were collected for  seconds at each tooth.Changes of PBF of the abutment teeth were recorded before insertion of dentures and ,  and  days after insertion.Th e means of the perfusion units (PU) are installed to a software (Perisoft version ., Gastrosoft Inc, Perimed AB, Järfälla, Sweden) and calculated.Th e statistical analyses were performed using Student t test and covariance analysis with Bonferroni correction within the SPSS (. for Windows) program.Th e results were accepted to be significant when p< ,.

Results
The mean ages of the group TTSD was ,±, (min., max.), and the mean ages of the group TSD was ,±, (min., max.).There were no statistically significant difference between the mean ages of two groups (p>,).Th ere were no statistically signifi cant diff erence between PBF mean values before the insertion of TTSD and TSD groups (p>,).However, there was statistically signifi cant diff erence between PBF mean values at st day (p<,),  th day (p<,) and  th day (p<,) of the two groups.It was seen that the statistical signifi cant difference between PBF mean values of the two groups began at day  and reached to maximum at day  and continued at about this level until day  (Table ,  In comparing the repeated measurements by covariance analysis, PBF mean values in the group TTSD decreased statistically signifi cantly at day  when compared with PBF values before insertion (p<,).Th ere was no statistically signifi cant diff erence between the PBF mean values at ,  and  days.However, in the group TSD, there were no statistically signifi cant diff erence among PBF mean values before insertion and at ,  and  days.On the other words, PBF mean values in the group TSD continued without changing statistically signifi cant at day , day  and day  (Table , Figure ).Before the insertion of the dentures, the mean values of the PBF were not statistically diff erent between the groups TTSD and TSD (p>,).However after the insertion of the dentures the difference of the mean values of the PBF between the two groups was seen to increase more and more in the measurements at day  (p<,),  (p<,) and  (p<,).

Discussion
There are no literature investigating the PBF of the abutment teeth of TSDs and TTSDs by using LDF.LDF measurements can be aff ected from extrapulpal factors such as room temperature, recent stimulants/drugs (tea, beta-blokers, etc.), posture (seated, semisupine, supine) or age (,) ().The data reported in the present study was obtained from old persons aged - and there was no statistically signifi cant diff erence between the mean ages of the two study groups (p>,).
LDFs are used extensively to monitor changes in blood fl ow in the skin and other organs.Th eir advantages are that they are non-invasive, simple to apply, and provide a continuous or near continuous record.Th eir principal disadvantage is that it is impossible to calibrate them in absolute units and their output may not be linearly related to blood fl ow ().Although the measurement depth of LDF is mm, the PBF of a permanent teeth with enamel and dentin of -, mm thickness can be measured ().According to Yanpiset et al. (), LDF is an improved method for the detection of revascularization of reimplanted teeth in dog.In their study, PBF measurements were made from dog incisors and premolars.
In the present study, the measurements were made in human maxillary incisors, canines and premolars by LDF because of its validity.When using LDF (), the tip of the probe must be in contact or very close to the tissue surface.If not, the refl ected light from the surface of the refl ection area will be received also by the optical fi ber, and enlarge the fraction of no frequency changing scattered light.The results of the studies (-) show that the signal recorded from a tooth is reduced by up to  when gingival and surrounding tissues are covered with black rubber dam.Th is reduction can be accounted for by two eff ects of the dam; screening of light from periodontal, gingival and other surrounding tissues, and a reduction in gingival blood fl ow due to compression of the gingival tissue.Both will have reduced the amount of light picked up by the probe that had been scattered by blood fl owing in non pulpal tissues ().In the present study, we used also black rubber dam.Th e wavelength of the light will also aff ect the extent to which the signal is aff ected by tissues outside the tooth.Th is is because the light of long wavelength, such as infrared, penetrates into the tissues to a greater depth than the shorter wavelengths, such as red, and particularly green ().In the present study infrared light was used because of the advantages of long wavelength.Akazawa et al. () investigated the influence of the continuous compression assumed as a result of light clenching on the blood fl ow of the denture underlying mucosa in TSD and TTSD wearers by using LDF.Th ey reported that even if it is light, a continuous clenching results in ischemia and delays the recovery of blood fl ow in the mucosa underlying the denture after release of compression.Also Atasever et al () investigated the effect of wearing complete dentures on human palatal mucosal blood flow by Xe (xenon) clearance.They reported that wearing complete dentures hindered the blood supply of the palatal mucosa area.
In the present study, the measurements were made at similar intervals with Atasever's () study; that is, before the insertion of the dentures on delivery day as control, and ,  and  days after insertion.Atasever et al () evaluated the effect of wearing complete dentures on human palatal mucosal blood flow in four sessions; before the insertion of complete dentures,  and  days after the insertion of dentures and  h after the removal of dentures.
In TTSD, the abutment tooth is more at risk than that with TSD.TTSDs, in which no posterior abutments remain, require an entirely different partial denture design than does one in which total abutment support is available ().While in TSD functional forces are being shared by the teeth which are placed at the anterior and posterior sides of the edentulous ridge, in TTSD, these forces are being shared by the mucosa lying on the edentulous ridge and also by the abutment teeth at the anterior of this edentulous ridge.Th e diff erence in compression of the periodontal membrane of the abutment tooth and the mucosa under the base means that all loads, even vertical ones, on the base are transmitted to the abutment tooth as torque ().Th is compression diff erence may increase torquing forces as confi rmed by the results of the present study.In this study it was found that the PBF of the abutment teeth in TTSDs reduced statistically significantly on the st day after insertion in respect to the initial values.Th is decrease continued on the  th and  th days but not statistically significantly different when compared to the st day measurements.Th is study shows that wearing of TT-SDs continuously hindered the PBF.Th e hindrance of blood fl ow is not an irreversible condition however after  and  days the decrease of PBF values were not statistically significant (Table  , Figure ).This situation can be explained by removing the dentures from the mouth during night to allow the tissues and abutment teeth to rest and to allow the recovery of blood flow to the abutment teeth ().Permanent effects of the lowering of PBF might, however, result from the wearing of dentures for long periods of time.On the other hand, wearing TSDs did not affect the PBF of the abutment teeth.This situation confirms that in TTSDs, mastication causes torquing forces on abutment teeth and these torquing forces may have a traumatic eff ect on the periapical tissues causing ischemia.
Figure ).PBF -Pulpal blood fl ow TTSD -Tooth tissue supported denture TSD -Tooth supported denture Based on estimated marginal means (a) Adjustment for multiple comparisons: Bonferroni, (NS) Not signifi cant

TABLE 1
. Because the pulps of human teeth decrease in size with age, blood fl ow records from young human teeth should include a larger pulpal component than those from teeth of . Comparison of PBF mean values before insertion and at day 1 , at day 7 and at day 30 between the groups TTSD and TSD

TABLE 2 .
Comparison of the changes in the PBF values of diff erent times in the study groups GÖKNIL ERGÜN KUNT ET AL.: PULPAL BLOOD FLOW CHANGES IN ABUTMENT TEETH OF REMOVABLE PARTIAL DENTURES older individuals GÖKNIL ERGÜN KUNT ET AL.: PULPAL BLOOD FLOW CHANGES IN ABUTMENT TEETH OF REMOVABLE PARTIAL DENTURES