a narrow alveolar bone ridge can cause inappropriate location or direction of dental implant placement . these can affect following prosthetic rehabilitation . more than 1 mm width of alveolar bone is needed around the installed dental implant . when the alveolar ridge width is insufficient for the planned implant diameter , horizontal ridge augmentation techniques such as onlay bone grafting , guided bone regeneration ( gbr ) , and alveolar ridge splitting are used for proper implant placement the ridge split technique for horizontal bone augmentation was introduced by simion et al .   in 1992 . a non - absorbable membrane covered the gap between buccal and lingual cortical bone with no application of bone graft material . the primary stability of a dental implant comes from the apical 3 to 4 mm intact bone . with this technique , about 1.0 to 1.5 mm expansion of alveolar bone can be obtained in the mandible and 3 to 4 mm in the maxilla . in 1994 , scipioni et al .   also reported immediate implant placement after a ridge split of maxillary alveolar bone . in this study , membranes and bone graft materials were not applied to reduce the risk of postoperative infection . in earlier studies , ridge split techniques were performed mainly in the maxillary alveolar bone . in the ridge split technique , lateral movement of buccal cortical bone plate was more difficult in the mandible than in the maxilla due to dense cortical bones and external oblique ridge . thus , the available width of ridge expansion in the mandible is commonly smaller than that of the maxilla . holtzclaw et al .   introduced a piezoelectric hinge - assisted ridge split ( phars ) technique in the atrophic posterior mandible . use of a piezoelectric device , ridge expansion by hinge movement , simultaneous bone graft , and delayed implantation were the main procedures in the phars technique . this study achieved successful dental implant treatment with the phars technique in the horizontally atrophic posterior mandible . a healthy 67-year - old woman visited the dental clinic with mastication difficulties . both sides of the posterior mandible needed prosthetic rehabilitation . the right side of the posterior mandible had adequate vertical and horizontal width of alveolar bone for the dental implants placement . however , the left side of the posterior mandible had a narrow alveolar ridge ( fig.1a , 2a ) . delayed placement of dental implants was planned after horizontal ridge augmentation with the phars technique . after local anesthesia , a full - thickness periosteal flap was made to expose the alveolar bone . alveolar bone width was observed to be about 4 to 5 mm at the alveolar crest ( fig . an initial bone cut was made at the alveolar bone crest , considering the implant position . after crestal osteotomy , lateral vertical osteotomies were performed with a length of around 10 mm , and apical horizontal osteotomy was performed for the hinge movement of the buccal cortical plate . a piezoelectric surgery device ( piezosurgery ; mectron , carasco , italy ) was used for the bone osteotomy . guide pins in the crestal osteotomy line were angulated lingually to the axis of premolar teeth ( fig . a periapical film was placed parallel with the guide pins , and a periapical radiograph was taken to evaluate the position of inferior alveolar canal and mental foramen . lateral vertical osteotomies were deepened in the lingual direction through the cancellous bone until the cutting tip reached the lingual bone plate . after that , the apical horizontal osteotomy was retraced carefully to avoid complete separation of the buccal bone plate ( fig . after 3 to 4 mm lateral movement of buccal bone plate , xenogenic bone ( biocera ; oscotec , seongnam , korea ) was grafted into the gap between buccal and lingual bone plates . a resorbable collagen membrane ( bio - gide ; geistlich , wolhusen , switzerland ) four months after the operation , implant placement surgery was performed on the horizontally expanded alveolar bone ( fig . two implants ( implantium ; dentium , suwon , korea ) of 4.5 mm diameter were inserted into the bone grafted region ( fig . 4 ) . a trephine bur ( internal diameter 2.3 mm / external diameter 3.0 mm ) was used to obtain bone tissues at the planned implant sites . splitting is often done with a bone chisel , diamond disk , or microsaw . with the use of bone chisel , it is difficult to make precise cuts in the dense cortical bone of the posterior mandible . the piezoelectric surgery device used in this study can produce a precise osteotomy , without trauma to the soft tissue , and has a wide range approach in the operative sites , so that the accurate apical horizontal osteotomy can be performed successfully and mal - fracture of dense cortical buccal plate avoided . a few studies   reported ridge split technique in the posterior mandible when cleaving the buccal cortical plate and installing dental implant immediately . the split crestal bone was adjusted back to its previous position and fixed with a bone screw . in these cases , buccal plate cleavage might be inevitable because a piezoelectric surgery device could not be used . the ridge split technique can be classified by immediate or delayed ridge splitting in terms of split timing . the immediate ridge split procedure with simultaneous implant placement offers favorable bone healing and implant success rates [ 1012 ] . the main procedures of this technique were rectangular corticotomy followed by reposition of mucoperiosteal flap with no lateral movement of buccal bone plate . after mucoperiosteal flap healing , fracture and lateral movement of the buccal bone plate with implant placement were performed . in 2010 , sohn et al .   reported a clinical study comparing immediate and delayed lateral ridge expansion techniques in the posterior mandible . uneventful lateral movement and predictable alveolar bone augmentation were observed in the delayed lateral ridge expansion , whereas unwanted fracture of buccal cortical plate occurred in five patients among the 23 patients who underwent immediate lateral ridge expansion . the short treatment period was the primary advantage of immediate lateral ridge expansion , although lack of implant stability , unwanted bone fracture , and compromised direction of dental implants were disadvantages . immediate ridge splitting was used in this study , although differently from the original techniques in that a minimal depth of apical horizontal osteotomy was used only to guide lateralization . after the ridge split procedure , implant installation was delayed so that pressure during placement of implant or drilling could be avoided . jensen et al .   reported the amounts of marginal bone loss after lateral ridge expansion procedures . a bone split of below 3 mm width of the alveolar ridge tends to cause more marginal bone loss than one above 4 mm width . they also demonstrated that elevation of full thickness periosteal flap leads to more marginal bone loss than a partial thickness periosteal flap . in this case , slight crestal bone resorption was observed on the postoperative three months radiographic images , in spite of using the barrier membrane ( fig . this might be related to the elevation of a full thickness mucoperiosteal flap to expose alveolar bone . the osteotomy line was still visible on the three month post - surgical radiographic image . however , bone healing of the osteotomy line was evident at four months after the operation ( fig . this radiographic finding of bone healing was similar to basa s study . during the ridge split procedure the distance to vital structures such as the inferior alveolar canal and the mental foramen in the posterior mandible could be directly measured through the periapical radiograph using guide pins . there was no need to preserve at least 3 to 4 mm intact apical bone for primary stability of dental implant because immediate implant installation was not planned in this case . it was possible to make a 3 to 4 mm lateral expansion of stiff cortical plate in the posterior mandible and install the implant fixture 4.5 mm in diameter in a direction favorable for prostheses . a bone biopsy was performed to evaluate the bone formation at the grafted area during implant placement surgery . the histologic result showed the new bones around the graft materials and no inflammatory reactions ( fig . although the bone formation was incomplete four months after the bone graft , the bone grafted site was considered appropriate for implant placement . the stable level of crestal bone around implants on the panoramic radiograph at six months in function indicated that the bone graft was successful ( fig . the phars procedure is a delayed implant installation method with immediate ridge splitting . with this method , the effects of resorption of alveolar crest after ridge splitting are avoidable , and sufficient horizontal augmentation can be achieved predictably in atrophic posterior mandible . further long - term clinical study is necessary to confirm the success of the augmented sites .
onlay bone grafting , guided bone regeneration , and alveolar ridge split technique are considered reliable bone augmentation methods on the horizontally atrophic alveolar ridge . among these techniques , 
 alveolar ridge split procedures are technique - sensitive and difficult to perform in the posterior mandible . 
 this case report describes successful implant placement with the use of piezoelectric hinge - assisted ridge split technique in an atrophic posterior mandible .